magnetic fabric development in the lower seve thrust from the cosc 1 drilling swedish caledonides abstract the cosc 1 project drilled the several hundred meters thick basal shear zone of the lower seve nappe with mylonites in mica schists amphibole schists and gneisses in zones of high magnetic susceptibility from 1910 to 2450 m we studied magnetic and petrographic fabrics and magnetic mineralogy borehole imaging allowed for geographic reorientation of the samples and offered the opportunity to study anisotropy of magnetic susceptibility ams in relation to tectonic evolution of the seve thrust we measured ams at room temperature added low temperature and field dependent ams for a subset of samples and compared magnetic with petrographic fabrics triaxial and prolate magnetic fabrics with degree of anisotropy p up to 3 2 together with abundant s c fabrics and strain partitioning around porphyroclasts indicate dominant simple shear until 2300 m magnetite and ilmenohematite mimic the rock fabric due to fabric parallel alignment and or magnetic interaction and either contribute to increase or decrease of p depending on the dominating rock fabric elements field dependency of pyrrhotite and magnetite in kmax direction further increases p homogeneous and oblate petrographic and magnetic fabrics in the greenschist grade overprinted rocks below 2300 m with subhorizontal kmax kint girdle distributions indicate dominant flattening ams depicts shear fabrics including magnetite and ilmenohematite and is additionally increased by retrograde magnetite rutile intergrowth in ilmenohematites we interpret that shape and degree of ams are controlled by a tectonic deformation and strain b alteration and magnetic grain interaction and c field dependency of deformed pyrrhotite and or magnetite we observed that all petrographic and magnetic subfabrics are coaxial and lineations are mainly e w to se nw directed confirming the transport direction of the caledonian allochthonous from our microstructural and ams results we suggest that thrusting of the lower seve unit commenced under simple shear conditions at higher metamorphic grades and subsequently switched to more pure shear under greenschist grade conditions

initial tectonothermal evolution within the scandinavian caledonide accretionary prism constraints from40ar 39ar mineral ages within the seve nappe complex sarek mountains sweden in the caledonide orogen of northern sweden the seve nappe complex is dominated by rift facies sedimentary and mafic rocks derived from the late proterozoic baltoscandian miogeocline and offshore continent iapetus transition metamorphic breaks and structural inversions characterize the nappe complex within the sarek mountains the sarektjakka nappe is composed of c 600 ma old dolerites with subordinate screens of sedimentary rocks these lithological elements preserve parageneses which record contact metamorphism at shallow crustal levels the sarektjakka nappe is situated between eclogite bearing nappes mikka and tsakkok nappes which underwent high p metamorphism at c 500 ma during westward subduction of the baltoscandian margin 40ar 39ar mineral ages of c 520 500 ma are recorded by hornblende within variably foliated amphibolite derived from mafic dyke protoliths within the sarektjakka nappe plateau ages of 500 ma are displayed by muscovite within the basal thrust of the nappe and are consistent with metamorphic evidence which indicates that the nappe escaped crustal depression as a result of detachment at an early stage of subduction cooling ages recorded by hornblende from variably retrogressed eclogites in the entire region are in the range of c 510 490 ma and suggest that imbrication of the subducting miogeocline was followed by differential exhumation of the various imbricate sheets hornblende cooling ages of 470 460 ma are recorded from massive dyke protoliths within the sarektjakka nappe these are similar to ages reported from the seve nappe complex in the central scandinavian caledonides probably these date imbrication and uplift related to early ordovician arrival of outboard terranes e g island arc sequences represented by structurally lower horizons of the koli nappes metamorphic contrasts and the distinct grouping of mineral cooling ages suggest that the various seve structural units are themselves internally imbricated and were individually tectonically uplifted through argon closure temperatures during assembly of the seve nappe complex the cooling ages of 520 500 ma recorded within seve terranes and along terrane boundaries of the sarek mountains provide evidence of significant accretionary activity in the northern scandinavian caledonides in the late cambrian early ordovician

geochemical investigation of soils developed in different lithologies in bhutan eastern himalayas within a project studying soil genesis on the southern slopes of the eastern himalayas a comprehensive set of major trace and rare earth element ree contents has been compiled for the first time six saprolites and their associated pedons were sampled on metamorphic migmatitic and leucogranitic parent materials at altitudes ranging from 1520 m to 3770 m metamorphic soils are largely illitic with si decreasing and al and fe increasing with decreasing degree of metamorphism the subsoil of a tourmaline bearing leucogranite is characterised by equally high si but higher contents of k and lower fe mg and ti a migmatitic profile in southern bhutan is dominated by hornblende and is quite distinct from the other lithologies with lower contents of si and k but higher fe mg ca and mn chondrite normalised ree patterns compare with post archaean materials with steep light rare earth lree and flat heavy rare earth hree patterns in comparison to generalised upper crustal composition ucc the bhutanese lithologies show a pronounced eu anomaly whereas the patterns appear rather homogenised in topsoils the influence of the parent materials causes deviations from the general trend with increasing depth the occurrence of marine tethyan sediments is confirmed by a strong positive ce anomaly in the central bhutanese phobjikha valley in the leucogranitic profile ree depletion is attributed to the presence of monazite as corroborated by trace element behaviour because of the hornblende ree patterns of the migmatitic profile are flat and without a eu anomaly chemical indices of alteration cia of between 71 and 92 indicate advanced weathering even at high altitudes correlation analyses show that ree are associated with the silt and clay fraction 63 m at elevations above approximately 3500 m physical weathering causes passive ree enrichment however no differentiation of ree concentrations or patterns within the profile is observed below 3500 m increased chemical weathering and leaching appears to be sufficient to release and translocate rees in this process hree are preferentially translocated whereas ce is more refractory than the other lanthanides this case study confirms that soil weathering and ree behaviour are closely related

soil variability in the area of an archaeological site near sparta greece results are analysed from a late roman site one of 20 studied in the laconia rural sites project the aim was to consider the extent to which effects of human activity at the time the site was inhabited were still evident in the soil and the exent to which these could be distinguished from natural soil variations the site has not been excavated patterns of soil properties of artefacts on the ground surface and of those encountered in the topsoil whilst sampling are analysed for a 5 m interval grid soil samples from 20 cm depth were analysed for total p pb cu zn fe mn ni ca mg k and organic c mass specific and volume magnetic susceptibility secondary crystalline and amorphous fe ph caco3 particle size distribution and colour all variables are mapped and data are further analysed using cluster regression and principal components analyses relatively high values for soil p cu pb ca organic c magnetic susceptibility and clay content and low ph and darker soil colour are associated with areas of the grid where artefact counts were highest the distinctive character of the soil in these areas reinforced by cluster and principal components analyses is attributed to a combination of inherent soil and anthropogenic effects

preservation of a magnetization carried by magnetite inclusions during amphibolite grade metamorphic conditions an example from the sarek dykeswarm northern swedish caledonides an outcrop consisting of a 608 myr old sheeted dyke complex and dyke intruded metasediments has been investigated palaeomagnetically it is located in the interior of a nappe the basal and upper parts of which suffered penetrative deformation and amphibolite grade metamorphism during the caledonian orogeny the only trace from the orogeny at the outcrop is a widely spaced network of brittle and ductile shear zones crosscutting dyke contacts foliated amphibolite consisting of hornblende quartz plagioclase garnet and sphene occur locally within them the opaque mineralogy of the dykes differs from that commonly found in continental dykes with ilmenite and pyrrhotite being the major visible opaque phases and there are indications that magnetite inclusions exsolved from silicates carry a primary remanence even though ar 39 40 ar mica ages were reset at ca 430 myr during the orogeny a secondary component carried by pyrrhotite is less prominent but falls on the baltican apw path at 430 myr the inferred primary component has a large directional uncertainty but indicates low palaeolatitudes for the baltscandian margin during rifting less

an empirical failure criterion for rocks and jointed rock masses abstract a new triaxial strength equation is proposed as fitting the available laboratory triaxial test data it is shown how the five triaxial parameters unconfined compressive tensile and shear strengths coefficient of friction and exponent in the triaxial equation can be inter related by three equations a relation between intact rock strength rock mass strength ratio and barton s rock quality 1974 is next developed based on geomechanical data for four longwall panels and in situ coal strength data this relation and the coefficient of internal friction from barton s classification are used in the three inter relations to evaluate the rest of the triaxial parameters for rock masses performance of the failure criterion is studied using practical cases of rock structures in coal and coal measure strata viz five longwall caving panels and four coal pillars

detrital muscovite 40ar 39ar ages from carboniferous sandstones of the british isles provenance and implications for the uplift history of orogenic belts major progradations of clastic sediments are recorded in the sedimentary record of the famennian and the visean namurian of the united kingdom and surrounding waters we have determined 40ar 39ar ages of 162 detrital muscovites from 11 coarse sandstones which were deposited between 370 and 465 ma spanning both progradations detrital mica ages are dominated by a peak at 415 ma with minor peaks at 440 ma and 390 ma the 415 ma muscovites are derived from the unroofing of the scandian nappes during the compressional phase of the caledonian orogeny in scandinavia the 440 ma muscovites record pre scandian orogenic activity which is rarely preserved in the orogenic record thermochronological evidence suggests that episodic postorogenic uplift and exhumation events kept the scandian orogen a major topographic feature and likely a sediment source for over 100 million years after nappe emplacement and implicates tectonic rather than climatic control on the clastic sediment progradations the near total absence of detrital muscovites with ages 415 ma suggests that the scandian nappes had not been entirely eroded despite repeated uplift during the postorogenic extension the river s which supplied the sediments probably ran parallel to the strike of the major scandian thrusts along the length of the caledonian orogen in a manner analogous to the major river systems of contemporary orogenic highlands

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

exhumation of the high pressure tsakkok lens swedish caledonides insights from the structural and white mica 40ar 39ar geochronological record

mantle fragments in the scandinavian caledonides abstract mantle fragments of ultramafic composition are widespread in the scandinavian caledonides sc lenses and boudins of alpine type peridotites in the scandinavian caledonides represent parts of dismembered ophiolite sequences and fragments of sub continental upper mantle metaperidotites of nappes in internal positions are generally isofacial with the metamorphic envelope usually caledonian metasediments but in places also precambrian metagranitoids forming the basement cores of the nappes caledonian metamorphism strongly modified the texture and mineralogy of the peridotites and resulted in a systematic metamorphic pattern which is consistent with the pattern observed in the envelope metaperidotites of the external massifs display at least a two stage metamorphic history an early caledonian high pressure high temperature phase related to early crustal stacking and a late caledonian regional metamorphic overprint which produced a regular barrovian type metamorphic pattern of in situ metamorphism metaperidotites from nappes in intermediate positions iapetus ocean ophiolites and ultramafic rocks from island arc environments show strongly diverging histories metaperidotites from internal ophiolites oceanic ophiolites koli lack any evidence of subduction metamorphism are serpentinized to various degrees show abundant primary mantle relic mineralogies and the caledonian metamorphic overprint is low metaperidotites from external island arc ophiolites and other associations seve often show relic high pressure metamorphism related to the finnmarkian phase of the caledonian orogeny the seve metaperidotites are occasionally associated with eclogites and show a weak overprint of late caledonian regional metamorphism alpine type peridotites are absent in the foreland of the baltic shield and in the innermost nappes lofoten the metamorphic characteristics and evolution recorded by the metaperidotites in the scandinavian caledonides allow a general reconstruction of the dynamics of collision belt formation

40ar 39ar geochronological evidence for multiple postmetamorphic hydrothermal events focused along faults in the southern abitibi greenstone belt thermal histories in the abitibi and pontiac subprovinces vary for three general domains 1 zones of impermeable rock with cooling rates of 8 c ma 2 zones of impermeable rock that are spatially associated with monzogranite plutons with apparent cooling rates of 1 2 cima and 3 permeable high strain zones with apparent cooling rates of 2594 ma from the volcanogenic massive sulphide related sericite alteration with the coarser mica yielding the younger date based on radiometric dating impermeable rocks were affected weakly by postmetamorphic hydrothermal events minerals in zones of higher permeability were reset during the intrusion of monzogranite plutons highly permeable zones such as the larder lake cadillac and porcupine destor faults were overprinted repeatedly this produces a drawn out series of dates from minerals with varying closure temperatures radiometric ages from fault zones or ore deposits cannot be used to interpret the cooling history and evolution of the abitibi belt as a whole

extensional deformation along the late precambrian cambrian baltoscandian passive margin the sarektjakka nappe swedish caledonides the structural evolution of a part of the late precambrian baltoscandian passive margin just before the inception of seafloor spreading is described recording the change from deformation by faulting to dominantly magmatic extension of the crust the allochthon of the scandinavian caledonides contains the imbricated passive margin of continental baltica overlain by various exotic terranes the sarektjakka nappe in the seve nappe complex which contains the outer parts of baltica s passive margin consists of sedimentary rocks occurring as screens between vendian 573 74 ma diabase dykes these dykes constitute 70 80 of the nappe and locally form sheeted dyke complexes the sarektjakka nappe largely escaped penetrative caledonian deformation and preserves igneous metamorphic and structural elements that are linked to the evolution of a pre caledonian rift to a passive continental margin extensional deformation before dyke emplacement is recorded by normal faults pull apart structures and folds unconformities dykes affected by brittle deformation and fluidization of sediments during dyke emplacement indicate close relations between the deposition of sediments extensional deformation and dyke emplacement the sarektjakka nappe is compared with other parts of the baltica s passive margin and its tectonic evolution is discussed

geomechanical characterisation of cataclastic rocks experience from the cleuson dixence project abstract the mechanical behaviour of cataclastic rocks is hard to characterise because of many difficulties arising in getting undisturbed samples during field investigations in specimen preparation and in performing appropriate laboratory testing to acquire a better understanding of such kind of very poor rocks the epfl s rock mechanics laboratory has carried out an extensive laboratory testing programme on cataclastic rocks from the cleuson dixence project switzerland after some reflections on the quantification of the intensity of tectonic degradation process by means of the geological strength index the paper describes briefly the sampling and testing techniques then it focuses on the failure criterion and the stress strain relationship of two types of cataclastic rocks quartzitic sandstones and phyllitic schists a new failure criterion is suggested it consists in an extension of the hoek and brown failure criterion that takes into account the progressive damage undergone by cataclastic rocks during the tectonic degradation process its parameters are bounded by an upper limit corresponding to the original rock and a lower limit corresponding to a soil like extremely tectonised material finally the stress strain behaviour of the tested cataclastic rocks is found to depend on the confining stress and the tectonisation degree and is adequately approached by the hyperbolic law of duncan and chang

an anthropic soil transformation fingerprinted by rey patterns abstract this focus article deals intentionally with modern soil disturbance in situ this is of interest to archaeologists as after disturbances both short and long term pedogenesis re starts obliterating previous signs soil modifications induced by human activity may be linked to pedogenetic evidence for disturbance with archaeological evidence for the cultural activities we contrasted two 750 m 3 soil pedons an anthrosol and a kastanozem from which the anthrosol is derived using 77 descriptors of soil properties which have been utilized in archaeological studies pedo morphological routine laboratory biochemical metals and rare earth elements plus yttrium rey with the aim of identifying a group of descriptors able to sort the occurrence of human interventions but which one is more promising our findings indicate that by the use of rare earth spatial patterns it is possible to classify the occurrence of human interventions in the case of emplacement of new parent material in respect to bulk soil disturbance in situ

argon composition of metamorphic fluids implications for 40ar 39ar geochronology the concentration and isotopic composition of argon trapped in fluid inclusions within a mylonitic amphibolite were determined by combining electron microprobe sup 40 ar sup 39 ar laser microprobe and fluid inclusion analyses on the same samples in our study fluid in inclusions formed during ductile deformation was probably derived locally from the paleozoic caledonian sequences whereas brines emplaced in cross cutting fractures were derived from proterozoic footwall rocks several kilometers from the mylonite by utilizing sup 38 ar sub cl to correct for open quotes excess sup 40 ar close quotes we estimate a 370 ma closure age for the amphibole which is distinctly younger than the 440 480 ma plateau ages indicated by step heating spectra the open quotes excess sup 40 ar close quotes responsible for the anomalous plateaus probably resulted from diffusive re equilibration of the amphibole with the fluids present during ductile deformation of the mylonite the significantly younger cooling age determined by our method is concordant with ages determined from more recent geochronological studies in the region these ages indicate that the western gneiss terrain in our study area records deformation and cooling associated with siluro devonian tectonothermal metamorphism rather than an earlier caledonian tectonism as proposed in previous sup 40 ar sup 39 ar investigators 46 refs 8 figs

thermal history of thrust sheets in an orogenic wedge 40ar 39ar data from the polymetamorphic seve nappe complex northern swedish caledonides the seve nappe complex in the scandinavian caledonides contains the fragmented late precambrian continent ocean transition between baltica and the iapetus ocean this passive margin was fragmented and thrust eastwards over the baltic shield during caledonian orogenesis the individual thrust sheets in the seve nappe complex went through different p t t evolutions resulting in dramatic metamorphic contrasts eclogite bearing nappes are juxtaposed with nappes showing no evidence of caledonian deformation or metamorphism in their interiors strain localization to the marginal parts of the thrust sheets left records of both pre orogenic rift and early orogenic subduction and subsequent uplift processes in the thrust sheets of the seve nappe complex even though it has been transported several hundred kilometres only the margins of the eastern part of the sarektjakka nappe are affected by penetrative caledonian deformation this part of the sarektjakka nappe is dominated by pristine tholeiitic dykes and cross bedded sandstones the dykes are 608 1 ma old and make up 70 80 of the nappe widely spaced thin shear zones of the ruopsok fault system represent the only caledonian penetrative deformation in the interior of the nappe previously published ar ar dates indicate cooling below the closure temperature of hornblende at c 470 ma but numerous ages have been recorded ar dating of biotite and muscovite from a cross laminated metapsammite in the sarektjakka nappe gave well defined ages of 428 5 3 6 and 432 4 3 8 ma respectively muscovite from a shear zone in the ruopsok fault system gave 428 2 4 0 ma whereas hornblende from the same locality did not yield interpretable data the results indicate that these rocks were completely degassed at some unknown time presumably at the emplacement of the dyke swarm no subsequent excess argon contamination can be detected a likely candidate for the degassing event is the emplacement of the dykes at 608 ma the interior of the nappe and thus the entire nappe complex cooled below 350 c at around 430 ma cooling from more than 500 c at c 470 ma to 350 c at c 430 ma suggests an average cooling rate of 4 c ma a prolonged period of slow cooling exhumation following the initial rapid uplift of the eclogite bearing nappes and early ordovician construction of the seve nappe complex is suggested

the caledonian heilhornet pluton north central norway geological setting radiometric age and implications for the scandinavian caledonides the heilhornet pluton is a medium sized c 50 km 2 sub circular discordant intrusion which penetrates the thrust zone separating the helgeland nappe complex from paragneisses in the vestranden region north central norway the intrusion consists of biotite hornblende granite and ranges in composition from 61 5 to 72 5 wt si0 2 the initial sr ratio c 0 7070 shows that crustal sources have been involved in the petrogenesis of the granite a u pb zircon age of 444 11 ma for the pluton indicates that juxtaposition of the nappe complex with metasedimentary rocks in vestranden took place prior to or during the late ordovician a consequence of this is that the general correlation of the metasedimentary rocks in vestranden with the seve nappes must be revised final eastward thrusting of the complex together with a yet unknown part of the vestranden supracrustal sequence probably took place during the middle silurian to early devonian scandian orogenic event

defining fault avoidance zones and associated geotechnical properties using masw a case study on the springfield fault new zealand abstract the springfield thrust fault at dalethorpe west canterbury new zealand provides a test case to explore the correlation between shear wave velocities at a range of scales and direct field observations of distributed deformation and outcrop properties the springfield fault ruptures to the surface through hard torlesse greywacke overlain on a flight of late quaternary glacio fluvial terraces by 5 m of gravel fault slip has displaced all but the lowest terraces revealing the geometry and location of faulting we used multi channel analysis of surface waves and meter scale cross hole measurements to map shear wave velocities below the lowest apparently undisplaced terrace we correlated these surveys with geotechnical parameters measured at outcrops and investigated relationships in the laboratory both field and laboratory results indicate that the shear wave velocity of torlesse greywacke declines sharply with increasing fracture density field surveys further indicate that relatively unweathered high velocity greywacke is being exhumed in a bivergent wedge between two opposite facing thrusts the fracturing and low shear wave velocities are focused in a wide low velocity damage zone that has developed in the hanging wall of the main thrust and a smaller but similar feature in the hanging wall of the backthrust this is consistent with the geomorphology of the site our correlations of geomorphic indicators of deformation with fault zone velocity structure provide a useful method with which to characterize the distribution of cumulative strain this type of analysis has utility for land use planning on or close to active faults especially where they are obscured by fluvial deposits

soil fertility and slope processes in the western cumberland escarpment of kentucky influences on the development of horticulture in the eastern woodlands the archaeological record of dry rockshelters in the red river valley of eastern kentucky contains botanical remains of several weedy annual seed bearing plants that point to the independent development of agriculture during the late archaic and early woodland period the objective of this study is to gather quantitative data through the chemical and physical analysis of soils collected within a valley transect to gain insights into landscape processes and soil fertility that may have played a role in the early development of plant domestication and the location of garden plots in relation to rock shelter sites in the upper cumberland plateau region of eastern kentucky soils on upland benches formed in limestones have soil fertility values that are comparable to fertile floodplain soils upslope outcrops of calcareous bedrock are contributing basic cations to these bench soils additionally in comparison to other landscape positions these upland soils have high levels of organic carbon available p and greater c n ratios soil morphology radiocarbon dates and archaeological evidence indicate that many of the numerous earthflows and debris flows within the region are early to middle holocene in age these slides were likely generated by mid holocene climatic shifts in which the frequency and intensity of summer precipitation increased across the southeastern united states these slope failures may have contributed to the development of plant domestication by creating forest canopy gaps and disturbed soils in which weedy plants thrived

an 40 ar 39 ar investigation of the contact effects of a dyke intrusion kapuskasing structural zone ontario an 40ar 39ar study on biotite and hornblende from baked tonalite gneiss adjacent to a 14 m wide kapuskasing dyke in the chapleau block of the kapuskasing structural zone employed resistance furnace step heating of bulk mineral separates single grain laser step heating and laser spot dating of individual grains in thick section all three methods yielded concordant results for the biotite indicating that it has been uniformly overprinted at ca 2 05 ga this date is probably a close estimate of the age of the dyke intrusion the argon data from the hornblende are more difficult to interpret all three methods suggest that the hornblende was partially overprinted and then affected by a later influx of excess argon from the external environment laser spot dates record an apparent age gradient extending radially outward from 2 25 ga in the grain cores to 2 4 2 7 ga in the grain rims corresponding 37ar 39ar values show no systematic variation across the hornblende although 38ar 39ar ratios display a similar pattern to the age distribution with lower values in the cores than in the rims the bulk separate and single grain step heating spectra mimic a volume diffusion ar loss profile that would appear to be inconsistent with the laser spot dates three possible interpretations to explain this apparent discrepancy may involve either experimental difficulties an effective radius of diffusion which is much smaller than the actual grain radius or an effective radius of diffusion that is of the order of the grain radius it is clear that for the 40ar 39ar dating of samples that have experienced complex geologic histories it is important to utilize both resistance furnace and laser techniques

material sources of the roman brick making industry in the i and ii century a d from regio ix regio xi and alpes cottiae abstract bricks fine pottery ceramic gears and tiles are among the human made objects routinely recovered in archaeological documentation sites associated with early civilizations can provide thousands of samples from a single excavation they come in endless varieties according to economic and social circumstances and as debris can last almost forever provide important clues about the past behaviours in human societies any information about the provenance of ceramics is highly valuable in archaeological analysis in the case of roman brick making the provenance and manufacture of clayey materials are usually interpreted only by studying stamps imprinted on the artefacts when available in this paper the making of bricks tiles and other ceramics for building purposes is investigated in relation to the possible sources of raw materials used for the industry the major questions to be solved relate to the sites from where the romans collected the raw materials the technologies they applied to make bricks and other clayey building materials and how far have they transported raw resources and final products i e mainly bricks and tiles after furnace treatments considering that a crucial point was the nearby availability of timber water and sandy soils without stones some achievements to classify artefacts with identical provenance have been obtained using the structural transformations induced in the material by thermal treatments of pottery comparisons have been made of the trace elements chemical composition in icp ms and some physical properties including magnetic vsm hysteresis loops and mineralogical features with xrd and ir analysis have been identified as proxies to elucidate the possible provenance of rough materials and appreciate the technologies used by the roman brick making industry

influence of tectonic structures on the hope slide british columbia canada abstract the hope slide which occurred on january 9 1965 involved an estimated 47 mm3 of meta volcanics and intrusive rocks previous workers reported the presence of tectonic structures faults and shear zones along the failure surface at the hope slide these tectonic features were investigated in detail to assess their effects on rock mass quality and the related implications for slope stability this paper integrates basic field and laboratory concepts from structural and engineering geology subdividing the failure area into structural domains allowed distinct discontinuity sets to be associated with specific tectonic structures the geological strength index gsi was used to estimate the rock mass damage related to the tectonic structures low gsi values were seen to outline tectonic damage zones point load tests were used to characterise the compressive strength of rocks adjacent to the tectonic structures strength anisotropy tentatively attributed to damage caused by a large shear zone was observed in greenstone samples seepage zones along the failure surface were observed preferentially along shallow discontinuities that dipped downslope and in rock masses of good quality gsi 40 an alternative morphology of the slope failure is proposed by distinguishing between the extent of the surficial damage due to the rock slope failure and the zone of failed material depletion zone for the first time a kinematic mechanism for the hope slide is proposed based on a preliminary 3 dimensional block model a pre 1965 dem was produced from estimates of material lost and gained as reported by previous workers the pre 1965 dem revealed that the tectonic structures recognised during fieldwork bounded the material that failed in the 1965 event

evidence for excess argon during high pressure metamorphism in the dora maira massif western alps italy using an ultra violet laser ablation microprobe 40 ar 39 ar technique ultra high pressure eclogite amphibolite grade metamorphism of the dora maira massif in the western alps is a well established and intensively studied event however the age of peak metamorphism and early cooling remains controversial the 40ar 39 ar step heating and laser spot ages from high pressure phengites yield plateau ages as old as 110 ma which have been interpreted as the time of early cooling after the high pressure event recent u pb and sm nd results challenge this assertion indicating a much younger age for the event around 45 ma and hence a radically different timing for the tectonic evolution of the western alps in a new approach to the problem samples from the undeformed hercynian metagranite brossasco were studied using an ultra violet laser ablation microprobe technique for 40ar 39 ar dating the new technique allowed selective in situ analysis at a spatial resolution of 50 urn of quartz phengite biotite and k feldspar the results demonstrate the frequent occurrence of excess argon with high 40ar 39 ar ratios 1000 10000 and a strong relationship between apparent ages and metamorphic textures the highest excess argon ratios are always associated with high closure temperature minerals or large diffusion domains within single mineral phases the best interpretation of this relationship seems to be that excess argon was incorporated in all phases during the high pressure event then mixed with an atmospheric component during rapid cooling and retrogression producing a wide range of argon concentrations and 40ar 36ar ratios step heating analysis of minerals with this mixture would produce linear arrays on a40ar 36ar versus 40ar 36 ar correlation diagram leading to geologically meaningless plateau ages older than the true closure age in the present case some ages in the range 60 110 ma could be explained by the presence of excess argon incorporated around 40 50 ma ago similar results found in other high pressure terrains in the alps may reconcile the argon geochronometer with other systems such as rb sr u pb or sm nd this study therefore calls for an increasing use of high resolution in situ sampling techniques to clarify the meaning of 40ar 36 ar ages in many high pressure terrains

solid liquid ree fractionation in the lateritic system of goyoum east cameroon the implication for the present dynamics of the soil covers of the humid tropical regions the ree th weathering geochemistry and mineralogy has been investigated in a lateritic soil cover in relation to the close hydrographical system at goyoum east cameroon the stutied area composed of gneissic hills covered by humid tropical forest belongs to the sanaga river basin and corresponds to a transition vegetation zone between rainforest and savannah a representative soil catena was taken as a reference zone close to the sanaga river the gneissic parent rock soil and groundwater samples have been cut off in pits in the lower part of the catena waters were also sampled both in brooks rich in organic matter and in the sanaga river all the waters were sampled seasonally during the rainy and dry periods the water rock interactions and the exportation of ree and th have been discussed as a function of the evolution of specific ratios considering th as the less mobile element during laterization variation of parent rock pr normalized ratios ln th pr vs depth show that the upper ferruginous horizons are depleted in ree while the basal saprolite presents accumulation zones which are differently located for ce and the other lrees the hrees are also depleted the la accumulations are located near the saprolite gneiss weathering front associated with negative ce anomalies ce ce 0 4 the ce accumulations inducing strong positive ce anomalies ce ce 4 are located in the upper saprolite beneath the ferruginous horizons all along the soil catena the secondary lree bearing minerals which reflect lree fractionation during incipient weathering of the gneiss are hydrous phosphates rhabdophane lreepo4 nh2o and cerianite ceo2 whose precipitation depends on the eh ph changes in the soil profiles on the other hand hree depletion is controlled by the dissolution of xenotime the major hree bearer in the parent gneiss in the 0 45 m filtered acidic groundwater ph 5 5 which have flooded the saprolite for a long residence time th contents are extremely low 0 th 10 ppt while lree contents are high 90 la 450 ppt in these filtered waters th seems to be strongly controlled by minerals i e thorianite which lead to its immobilization in the soil while lree remain in the soluble and or colloidal pools moreover the groundwaters show significant negative ce anomalies throughout the year 0 1 ce ce 0 4 the mobilization of lree except redox active ce results from the dissolution and or the mobilization in colloidal form of the secondary phosphates which may present major negative ce anomalies as indicated by the bulk soil analyses at the saprolite gneiss weathering front therefore the groundwaters have the signature of saprolitic materials we propose that the strong positive ce anomalies of the upper saprolite result from ancient weathering processes these processes would have led to much stronger ce iii ce iv dissolution reprecipitation conditions than those occurring at the present time in the saprolite in the 0 45 m filtered brook acidic blackwaters lree and th contents are high 100 th 400 ppt 400 la 1700 ppt in this organic matter rich environment lree and th are highly mobilized the colloial pool controls half of the whole lree th load the geochemical signature of these waters is independent of the gneissic parent rock and soil lree contents there is no ce anomaly this signature is similar to those of other organic rich rivers draining humid tropical ecosystems in the world in the 0 45 m filtered sanaga waters lree and th contents are lower than in the brooks 15 th 40 ppt 40 la 300 ppt these concentrations are dependent on the time and on the colloidal composition however 90 of these elements are mainly controlled by the suspended pool

anthropogenic units fingerprinted by ree in archaeological stratigraphy mas d is spain case abstract on occasions archaeologists have to deal with serious difficulties to differentiate between processes that ultimately are responsible for the formation of stratigraphic units sometimes we face problems related with depositional units in multilayered deposits and other times we ask for the character of some dark surface soils very similar to natural paleosols and usually associated with archaeological findings in both cases the problems we must address concern the relative impact of human activities the imbalance between anthropic and natural processes in the formation of archaeological deposits is crucial for a correct interpretation of the processes involved in the formation of archaeological sites but also of their occupation abandonment dynamics and the understanding of their spatial behaviors and relationship with the environment in this paper we propose a new methodological approach for the identification of anthropogenic fingerprints in stratigraphic units through rare earth elements ree soil analysis the role of ree for the effective identification of sediment provenance due to their coherent behavior during weathering erosion and fluvial transportation and their high resistance to chemical mobilization is well known in other areas of knowledge we try to explore its potentiality in a challenging archaeological context our purpose was to identify human traces in stratigraphic units where archaeological materials are scarce or absent intertwined with others richer in archaeological remains by the determination of multiple elements and statistical studies we believe that rare earth elements ree soil analysis provides unique insights for a better characterization of natural and archaeological sediments but more importantly to recognize different stages of the gradient we expect to discern between natural versus anthropic units and between primary versus secondary deposits redeposition using the case of the neolithic site of mas d is alicante spain as an example the application of the principal component analysis pca remarks differences in ree values those analysis show differences between units of undoubtedly anthropogenic origin and control samples taken from natural sediments including marls bedrock in their vicinity but also we could notice finer nuances like the degree of human contributions to paleosols formation

p t paths in the handl area central scandinavia record of caledonian accretion of outboard rocks to the baltoscandian margin the seve koli nappe complex is widespread in the scandinavian caledonides and is composed of units representing parts of the baltoscandian margin seve nappes now overlain by magmatic sedimentary rocks koli nappes derived from west of this margin the metamorphic evolution of koli and seve units has been studied in the handol area central scandinavian caledonides where a fragmented ophiolite with cover sequence in the lower koli units is thrust over the higher grade seve units thermobarometry constrains metamorphic conditions to 490 570 c 950 600 mpa with a slight downwards increase in grade for the lower koli bunnerviken lens 520 620 c 1000 600 mpa for the upper seve taljstensvalen complex 630 740 c 750 650 mpa for the middle seve snasahogarna nappe and 480 600 c 1150 1000 mpa for the lower seve blahammarfjallet nappe p t paths during garnet growth have been constructed for all units except the highest grade middle seve these paths record heating at the base of the koli and cooling in the underlying seve units pressure increase during garnet growth is indicated for all units leading to anticlockwise p t paths in the seve the results imply thermal convergence with time for all units and spatial convergence in metamorphic grade in the koli it is suggested that the contrasting metamorphic histories on either side of the seve koli boundary resulted from the emplacement of relatively colder koli rocks on top of relatively hotter seve rocks and that emplacement of structurally higher units contributed to the increase in pressure

thermobarometric and40ar 39ar geochronologic constraints on eohimalayan metamorphism in the dinggye area southern tibet mineral assemblages in the dinggye area of southern tibet 28 n 88 e provide new insights regarding the poorly understood eohimalayan metamorphic event in the eastern himalayan orogen major element partitioning thermobarometry of pelitic rocks indicates temperatures of 750 830 k at depths of 14 3 km consistent with the presence of kyanite sillimanite and andalusite schists in the area laser and resistance furnace40ar 39ar analyses of hornblendes from intercalated amphibolites yield closure ages of 25 ma overlap between the probable range of ar closure temperatures for these hornblendes and the metamorphic temperatures estimated through thermobarometry suggests that eohimalayan metamorphism in the dinggye area occurred in late oligocene time no more than about 10 million years before the main or neohimalayan phase of metamorphism in early to middle miocene time muscovite biotite and k feldspar40ar 39ar ages indicate an important episode of rapid cooling between 16 and 13 ma which is interpreted as a signature of tectonic denudation related to movement on n dipping extensional structures of the south tibetan detachment system

sm nd dating of seve eclogites norrbotten sweden evidence for early caledonian 505 ma subduction the seve nappes consist of long transported thrust sheets belonging to the upper allochthon within the scandinavian caledonides eclogites from two different megalenses within the seve nappe complex in norrbotten northern sweden have been dated with the sm nd method the two eclogite bearing megalenses have been subjected to different pressure and temperature conditions during the high pressure metamorphism garnet omphacite whole rock from ts2 within the tsakkok lens give an age of 505 18 ma 2 i 0 512231 0 000024 mswd 0 10 garnet and whole rock from ts5 and whole rock ts3 also fall on the above isochron the composite isochron gives an age of 503 18 ma 2 these results are interpreted to date the peak of the high pressure metamorphism 500 630 c and 12 15 kbars for the tsakkok lens the eclogites in the vaimok lens at grapesvarre were subjected to higher pressure and temperature conditions and more extensive reequilibration during the early cooling stages retrograde breakdown reactions accompanied by retrograde zoning of relict garnet seems to be associated with disturbance of the sm nd isotopic systems in contrast a sample with unzoned garnet and well preserved high pressure mineralogy from grapesvarre gives a sm nd garnet omphacite age of 503 14 ma 2 i 0 512010 0 000038 2 the ages for the seve eclogites are significantly older than the sm nd eclogite dates from the western gneiss region of norway wgr suggesting the existence of at least two eclogite forming events in the caledonide orogen the younger event has been related to the main continent continent collision stage of the caledonian orogeny while the older event that led to the production of the norrbotten eclogites must have taken place several hundred kilometres to the north and in a different tectonic setting more oceanward to the wgr it appears that the older event ca 505 ma was restricted to the subduction of dyke intruded sedimentary cover rocks which are thought to represent the rifted edge of the baltic continent

polyorogenic 40ar 39ar mineral age record within the kalak nappe complex northern scandinavian caledonides the kalak nappe complex is composed of variably retrogressed middle proterozoic basement and imbricated polydeformed metasedimentary cover successions which at least in part appear to have originated within the late proterozoic early palaeozoic baltoscandian miogeocline mafic alkaline plutons seiland igneous suite occur within uppermost structural units of the nappe complex 40 ar 39 ar incremental release mineral ages suggest local differences in tectonothermal evolution within the kalak nappe complex post metamorphic cooling dates of c 490 ma are locally recorded by hornblende within the structurally highest tectonic unit suggesting significant orogenic activity occurred during and or immediately prior to the arenig a distinctly later metamorphic overprint occurred in the silurian and was of sufficient magnitude to everywhere rejuvenate ar systems in muscovite and nepheline and locally in hornblende this was followed by relatively rapid post metamorphic cooling through hornblende and muscovite ar closure temperatures between c 425 and 415 ma the complex tectonic history suggested for the kalak nappe complex is generally similar to that previously outlined for the central swedish caledonides together 40 ar 39 ar mineral ages from these widely separated areas indicate that significant tectonothermal activity occurred along the baltoscandian margin prior to the silurian this activity appears at least in part to have been associated with formation of a late cambrian early ordovician accretionary wedge over a westward dipping subduction zone during initial closure of the iapetus ocean

rare earth elements in limestone marlstone couplets from the albian cenomanian cismon section venetian region northern italy assessing ree sensitivity to environmental changes abstract we have studied the ree distribution through the albian cenomanian interval of a stratigraphic succession cismon section scaglia variegata formation venetian prealps consisting of rhythmically alternating carbonate rich and carbonate poor strata which are the sedimentary expression of systematic variations of surface fertility and bottom water redox conditions in the depositional basin limestone semicouplets show seawater like shale normalized patterns hree enriched with negative ce anomalies and high er nd ratios indicating a clear dependence on the ree chemistry of surface seawaters marlstones and shales exhibit flatter patterns more moderate ce anomalies and low er nd good correlations between er nd ce ce and mn suggest that superimposed on ree signatures imparted by detrital and biogenic phases the ree composition shows evidence of their sensitivity to palaeoredox conditions resulting in ree fractionation and ce cycling ree data are consistent with results from previous stratigraphic and geochemical major and trace elements investigations in reflecting palaeoenvironmental conditions rhythmically varying from efficiently mixed seawater during the limestone deposition to oxygen depleted bottom waters at the time of marlstone deposition

evaluating the geomechanical properties of misis fault breccia turkey abstract this study investigated the correlations between the uniaxial compressive strength ucs elastic modulus e or the differential stress and density p and s wave velocity volumetric block proportion vbp average block diameter d block average block diameter factor abdf aspect ratio and roundness the results were evaluated by both simple and multiple regression analysis simple regression analysis results show no correlation between ucs e or and the other examined parameters except s wave velocity a correlation was however found between ucs and s wave velocity for 25 and 75 vbp other significant models including density p and s wave velocity and textural properties for the prediction of ucs and were found by multiple regression analysis from these results it is concluded that the strength of the misis fault breccia cannot be defined by a single parameter such as vbp as is the case for some bimrocks it is also concluded that the models developed by multiple regression analysis can be used to predict the ucs and of the misis fault breccia the multiple regression models including two or three independent variables are the most practical equations using these equations to predict the ucs and of the fault breccia is easier faster and cheaper than conducting triaxial or uniaxial compressive strength tests

consolidation settlements above deep tunnels in fractured crystalline rock part 1 investigations above the gotthard highway tunnel surface subsidence associated with tunnelling in fractured crystalline rock masses is rarely considered to be large enough to be a cause for concern recent high precision levelling measurements along the gotthard pass road in central switzerland however have revealed up to 12 cm of subsidence along sections that pass several hundred metres above the gotthard highway tunnel large scale consolidation associated with pore pressure reduction in the rock mass arising from tunnel drainage is believed to be the contributing mechanism although these settlements may appear to be small compared to those associated with groundwater or oil and gas withdrawal from more compliant porous media they are large enough to adversely affect the structural integrity of sensitive concrete structures on the surface e g thin arch concrete dams this is a concern for the 57 km long gotthard base tunnel which is currently under construction as it will pass through similar geological conditions as the gotthard highway tunnel and underneath several important dams the prediction of the expected settlements requires a more complete understanding of the processes underlying the settlements than exist at present this paper part 1 and a companion paper part 2 are a contribution towards this end in part 1 we examine the question of consolidation in fractured crystalline rock introduce the geodetic data and the geological setting of the subsidence associated with the gotthard highway tunnel possible mechanisms for the consolidation are described and estimates obtained for the key hydro mechanical parameters that govern their action such as the normal stiffness of fault zones these data are used to condition analytical scoping calculations of expected subsidence based upon poro elastic theory and to provide input for a series of numerical models used to obtain a more detailed understanding of the data which are presented in part 2 r 2008 elsevier ltd all rights reserved

excess 40ar transport scale and mechanism in high pressure phengites a case study from an eclogitized metabasite of the dora maira nappe western alps application of the bulk separate furnace heating laser step heating and in situ laser agemapping 40ar 39ar techniques reveals that high pressure phengites from an alpine eclogite of the dora maira basement nappe western alps were pervasively contaminated with excess 40ar to yield ages 130 ma spot fusion dating of individual grains with the 40ar 39ar laserprobe reveals concentric radial patterns with core ages as high as 320 ma showing that this excess component was trapped at an early stage and subsequently remobilized by volume diffusion during a late greenschist thermal pulse the single grains and population from this hand sample retain major differences in apparent ages indicating that the extent of the excess 40ar contamination varies from grain to grain attempt to model these differences in terms of grain size dependent fractional loss falls short and demonstrates that strong cm scale argon isotopic gradients locally prevailed during syn kinematic high pressure metamorphism on petrostructural grounds a model of internal isotopic buffering is outlined whereby the excess 40ar is argued to have been internally derived from within the eclogite protolith itself low intergranular ar diffusion rates due to reduced water activity buffered below unity by the phengite assemblage resulted in the local segregation and partitioning of the excess 40ar along grain boundaries during ongoing ductile deformation supporting evidence for this model comes from the recent literature on fluid and stable isotope behaviour in alpine eclogites and very high pressure metasediments which shows that volatile recycling during high pressure metamorphism may occur on a very limited scale

timing structural assembly metamorphism and cooling of caledonian nappes in the ofoten efjorden arca north norway tectonic insights from u pb and40ar 39ar geochronology u pb and 40ar 39ar geochronology from part of the northern norwegian caledonides indicates a cooling and unroofing history different from that inferred for the caledonides in southwest norway in the ofoten efjorden area of north norway the narvik nappe complex nnc represents the basal portion of the composite caledonian allochthon and consists of amphibolite facies oceanic affinity metasedimentary rocks intruded by numerous pretectonic felsic dikes two of these dikes yield indistinguishable u pb zircon ages of 437 1 ma providing a maximum age for tectonic assembly metamorphism and deformation at this structural level u pb ages of metamorphic monazite 432 2 ma and zircon 431 7 0 5 ma from pelitic schist and migmatite yield robust estimates of the age of peak metamorphism combined with structural evidence for transport parallel stretching and subvertical attenuation of the rock mass at the time of metamorphism these ages suggest that local and or episodic extensional modification of the

geology of mankind for the past three centuries the effects of humans on the global environment have escalated because of these anthro pogenic emissions of carbon dioxide global climate may depart significantly from natural behaviour for many millennia to come it seems appropriate to assign the term anthropocene to the present in many ways human dominated geological epoch supplementing the holocene the warm period of the past 10 12 millennia

polyorogenic 40 ar 39 ar mineral age record in the seve and koli nappes of the gaddede area northwestern jamtland central scandinavian caledonides in the scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica contrasting tectonothermal histories are recorded in seve and koli nappes exposed in the gad dede area northern jamtland county sweden eclogite bearing seve rocks underwent an initial amphibolite grade regional metamorphism smi with different structural units experiencing contrasting high to intermediate pressure conditions subsequent ductile imbrication sm2 of high and intermediate pressure structural units occurred prior to 460 470 ma cooling through temperatures required for intracrystalline retention of argon in hornblende a later thermal overprint sm3 everywhere rejuvenated seve biotite and muscovite and locally hornblende argon systems at 430 pm 5 ma 40 ar 39 ar plate

pillow lavas as protoliths for eclogites evidence from a late precambrian cambrian continental margin seve nappes scandinavian caledonides pillow lavas containing an eclogitic mineral assemblage locally with glaucophane crossite are described from the tsakkok lens within the seve nappes north central scandinavian caledonides critical primary relationships to the host metasedimentary rocks which are dominated by marble and quartz garnet phengite schist are preserved it is argued that these clastic rocks and the ongoing igneous activity in the tsakkok lens are late precambrian to cambrian in age and that these rocks were deposited emplaced along the outermost part of a continental margin related to the continent baltica

mineral age record of a polyorogenic evolution within the seve and koli nappes trondelag norway abstract in the central scandinavian caledonides eugeoclinal terranes represented in the koli nappes were thrust 500 km onto the baltoscandian platform during the early to middle paleozoic immediately underlying thrust sheets of the seve nappe complex are suspected to have been derived from the outer margin of continent baltica hornblende within amphibolite at one locality within westernmost exposures of seve nappe units in trandelag norway displays an internally discordant 40 ar 39 ar age spectrum which suggests a polyphase thermal evolution including 1 1 initial post metamorphic cooling through argon retention temperatures at c 475 480 ma 2 2 partial rejuvenation during a silurian c 400 425 ma thermal overprint muscovite within the exposure was more extensively rejuvenated during the silurian overprint at twelve other trandelag sample locations hornblende muscovite and biotite within both the seve and koli nappe complexes record post metamorphic cooling ages between 420 and 435 ma and display no direct evidence of a pre silurian thermal record however the widespread occurrence of intracrystalline extraneous argon components and textural complexities clearly point toward a pre silurian tectonothermal history comparison with 40 ar 39 ar mineral ages reported elsewhere in the central scandinavian caledonides suggests a polyorogenic evolution consisting of 1 1 variable high pressure metamorphism of distal baltoscandian miogeoclinal sequences during entrainment in an accretionary wedge which developed in the late cambrian early ordovician over a west dipping subduction zone related arc volcanic activity occurred in more outboard western sectors 2 2 ductile imbrication of high and intermediate pressure sequences within the accretionary wedge diachronous cooling and or chronologically distinct tectonic episodes are indicated throughout the early and middle ordovician 3 3 ultimate accretion of a variety of eugeoclinal terranes along the baltica continental margin 4 4 imbrication and metamorphism of the eugeoclinal terranes and previously deformed portions of the miogeocline during eastward translation onto the baltoscandian platform in the silurian crystalline baltica basement and overlying structural cover units were depressed to significant crustal depths during eastward nappe transport with resultant formation of high temperature eclogues previously reported crystallization ages of c 425 ma suggest that the eclogites formed at approximately the same time as minerals within the superencumbent nappe units cooled through argon closure temperatures following eastward nappe transport the basement experienced rapid uplift and resultant adiabatic decompression this was followed by rapid cooling through argon retention temperatures at 390 400 ma

40 ar 39 ar mineral age record of early caledonian tectonothermal activity in the baltoscandian miogeocline central scandinavia in central portions of the scandinavian caledonides greenschist facies volcanosedimentary successions within the koeli nappe complex have been thrust several hundred kilometers eastward onto the baltoscandian platform these were derived from eugeoclinal terranes situated outboard west of the baltica continent during the early paleozoic the koeli nappe complex is tectonically underlain by higher grade units within the seve nappe complex these are composed of amphibolite and granulite facies rocks and locally contain eclogites the seve nappes tectonically separate koeli units from structurally lower allochthons derived from more inboard environments along the baltoscandian miogeocline previous mineral isotopic age determinations from seve and koeli units have been in the 430 to 390 ma range and have been interpreted to presumably date cooling following scandian middle silurian to early devonian metamorphism however incremental release sup 40 ar sup 39 ar dates recorded by minerals within some of the koeli and seve nappes exposed in jaemtland sweden taennforsen and are districts provide evidence of earlier tectonothermal activity hornblendes from the seve and koeli nappe complexes display variably discordant age spectra as a result of low temperature experimental evolution of loosely bound extraneous argon components however in most analyses plateau ages of 510 to 475 ma koeli and 465 to 455more ma seve are defined in contrast muscovite and biotite from all tectonic units record scandian cooling ages between 245 and 410 ma the older events recorded by hornblende within these seve and koeli units are evidence of early caledonian tectonothermal activity and subsequent diachronous cooling during the early middle ordovician less

an x ray computed tomography based index to characterize the quality of cataclastic carbonate rock samples x ray computed tomography xrct can reconstruct in a nondestructive way and in three dimension the distribution of densities within opaque materials consequently it provides an effective possibility to characterize the inner content of rock core samples and in particular their alteration products sensu lato which generally appear less dense than the intact rock matrix in this paper a new index based on xrct data is tested for evaluating the degree of alteration of highly tectonized carbonate rock samples and is compared with visual based classification systems this xrct based analysis leads to a diagnosis of alteration which appears objective precise and in agreement with the visual observations besides this method takes into account the entire volume of the sample is rapid to carry out and allows an intact rock core to be used for further laboratory testing

argon retentivity and argon excess in amphiboles from the garbenschists of the western tauern window eastern alps 22 hornblende k ar ages and 10 39ar 40ar spectra were obtained for hornblende garbenschists from the western tauern window the post kinematic amphiboles were produced during the late alpine prograde metamorphism 6 10 kb and 500 570 c two nearly potassiumfree cummingtonites rimming hornblende yield k ar ages of 120 ma while the 20 tschermakitic hornblendes scatter between 17 and 37 ma the reason for this scatter is excess ar possibly incorporated into amphiboles during healing of fractures now traceable by trails of fluid inclusions excess ar is semiquantitatively corrected for by combining cogenetic hornblende and cummingtonite with k ar isochrons it can be quantified in 4 out of 10 hornblendes by 39ar 40ar stepwise heating experiments ages of 18 20 ma result for corrected hornblendes the retentivity of 40ar after correction for excess shows no correlation with chemistry within the narrow compositional range observed rather it shows intriguing correlations with irregularities in ca k spectra pointing to a microstructurally controlled mechanism for ar loss this observation leads to a critical evaluation of the closure temperature constant which apparently depends on an incompletely known number of mineralogical and environmental parameters in particular those 39ar 40ar release spectra which yield low temperature steps with younger ages than the plateaus are not interpretable in terms of a synchronous closure this gives evidence that loss of radiogenic isotopes proceeds by a more complex mechanism than simple volume diffusion through isotropic media

anthropogenic processes in the evolution of a soil chronosequence on marly limestone substrata in an italian mediterranean environment abstract due to anthropic pressure many areas of the world are affected by a process of soil entisolization that leads to the formation of anthropogenic soils in order to investigate man s role in soil evolution a survey was carried out in southeastern sicily italy where for years there have been wide farming areas with anthropogenic soils a chronosequence of anthropogenic soils in a vineyard area cultivated for 22 years was investigated the first stage of the chronosequence was made by the original soils which in the study area had been undisturbed till the 1980 s these soils classified as entic haploxerolls under the american soil taxonomy st or calcaric kastanozem according to the world reference base wrb system were used for almond groves and or grazing and showed an a c or a bw c profile in 1982 these soils were subjected to trenching in order to establish a vineyard and resulted in a complete mixing of the original soil horizons and the formation of soils classifiable as haplic xerarents st or aric regosols wrb after 20 years in 2002 the vineyard was removed and the surface of the entisol regosol was covered by a 50 70 cm thick layer of transported parent material composed of soft marly limestone in july 2004 these soils were mixed once again by deep ploughing 100 cm deep to establish a new vineyard these deeply disturbed soils were surveyed again and tentatively classified these newly created soils show a double sequence of artificial horizons at an oblique angle to the soil surface their complex genesis pattern does not allow their classification as arents st or regosols wrb so a tentative classification is proposed following both the st and the wrb rules as miscic geofragmexerants and geomiscic anthrosols respectively

the middle to late devonian hoybakken detachment central norway 40ar 39ar evidence for prolonged late post scandian extension and uplift the regionally significant 0 5 2 km thick hoybakken detachment in central norway bounds the southern margin of the central norway basement window and exhibits a well developed top to the wsw fabric characteristic of late scandian devonian ductile extension 40 ar 39 ar data obtained from hornblende mica and k feldspar mineral separates of rocks collected in a transect through the hoybakken detachment yield well defined plateau and isochron mineral ages early devonian exhumation and cooling of the hoybakken detachment footwall is recorded by hornblende ages of 400 ma and mica ages of 390 ma the mylonitic fabric overlying the footwall records younger middle devonian mica crystallization ages of 384 381 ma that are among the youngest extensional ductile fabrics dated in the caledonides and suggest prolonged extensional activity on the hoybakken detachment after inferred cessation of ductile extension at 381 ma the rate of uplift and cooling was reduced and the footwall records late devonian to early carboniferous k feldspar ages of 371 356 ma prolonged extensional activity at hoybakken is compatible with recent u pb ages of deformed titanite crystals and established rb sr ages of white mica in shear related pegmatites both from the southwestern part of the fosen peninsula and 40 ar 39 ar ages of syn tectonic mica overgrowth from the adjacent hitra snasa fault together these ages suggest the onset of ductile extension soon after 401 ma and with the middle devonian crystallization ages determined here suggest that ductile extension on the hoybakken detachment had a duration of 11 20 ma the youngest age of 320 ma was obtained from a k feldspar in a cataclastic granite of the hoybakken detachment s hangingwall and is considered to date a phase of post scandian brittle deformation that overprinted the mylonitic shear fabric

early ordovician u pb metamorphic ages of the eclogite bearing seve nappes northern scandinavian caledonides eclogite grade metamorphism of the seve nappe complex snc in norrbotten sweden records the attempted subduction of the baltic continental margin during the early palaeozoic evolution of the iapetus ocean metamorphic titanite sampled from several calcsilicate gneisses of the snc in norrbotten occurs as part of a prograde eclogite facies metamorphic mineral assemblage and yields concordant to nearly concordant u pb ages of 500 475 ma later structural disruption of these rocks occurred during the siluro devonian scandian phase of the caledonide orogeny but the u pb systematics show no evidence of a second generation metamorphic or recrystallized of titanite or of post early ordovician disturbance through pb loss hence the u pb ages are believed to record the time of prograde mineral growth during eclogite facies metamorphism of the snc these results support earlier sm nd and 40ar 39ar studies indicating an early ordovician metamorphic age for the eclogitic norrbotten snc and confirm the early ordovician destruction of at least this segment of the palaeozoic passive margin of baltica these results indicate that the snc in the northern scandinavian caledonides was subducted and metamorphosed to high grade some 50 70 myr prior to the high grade metamorphism of the snc in the central scandinavian caledonides this result requires significantly different early palaeozoic tectonic histories for rocks mapped as snc in the northern caledonides and those in the central caledonides despite a seemingly similar tectonostratigraphic position and broadly similar high grade metamorphism