aftsolve a program for multi kinetic modeling of apatite fission track data aftsolve is a computer program for deriving thermal history information from apatite fission track data it implements a new fission track annealing model that takes into account the known kinetic variability among different apatite species to fully utilize this model a fission track worker must obtain data that can be used to infer the kinetic characteristics of each apatite grain from which a measurement was taken such data can consist of etch figure lengths or chemical composition the benefit of this overall approach is that it allows useful information to be derived from previously unusable analyses extends the practical range of geological temperatures constrained by fission track analyses and increases overall confidence in model predictions aftsolve also incorporates the effects of fission track orientation relative to the apatite crystallographic c axis variation in initial track length and the biasing effect of 2 5 2 cf irradiation for enhancing confined horizontal track length detection aftsolve is written for windows operating systems and has a graphical interface that allows interactive input of thermal histories and real time generation of estimates for fission track length distributions and ages for up to six simultaneously modeled kinetic populations it also includes procedures for estimating the range of time temperature histories that are statistically consistent with a data set and constraints entered by the user

alteration zoning and primary geochemical dispersion at the bronzewing lode gold deposit western australia the late archaean bronzewing lode gold deposit is in the yandal greenstone belt western australia it is located in a 500 m wide n s trending structural corridor consisting of an anastomosing set of brittle ductile shear zones and is chiefly hosted by tholeiitic basalts which are metamorphosed at mid to upper greenschist facies syn peak metamorphic alteration surround all ore bodies and alteration extends laterally for 80 m from individual mineralised structures individual alteration haloes partially overlap and form a 1 5 km long and 300 m wide domain the alteration sequence studied here at 140 m below the present undisturbed surface comprises distal calcite chlorite albite quartz intermediate calcite dolomite chlorite muscovite albite quartz and proximal ankerite dolomite muscovite albite quartz pyrite zones mass transfer calculations indicate that chemical changes during alteration include enrichment of ag au ba bi co2 k rb s sb te and w and depletion of na sr and y the elements al ca cr cu fe mg mn ni p ti v zn and zr are immobile the degree of chemical change increases with proximity to gold ore zones in addition abundant quartz veins indicate substantial silica mobility during the hydrothermal event although there is no large relative silica loss or gain in the host rock the broadest anomaly surrounding the bronzewing gold deposit is defined by tellurium 10 ppb which if it is a hydrothermal anomaly extends beyond the 400 600 m study area anomalous values for co2 k rb and sb also define wider zones than does anomalous gold 4 ppb although even the lithogeochemical gold anomaly extends across strike for as much as 80 m away from ore and 600 m along the n s strike of the shear zone corridor also carbonation and sericitisation indices outline large exploration targets at the bronzewing deposit sericitisation indices define anomalies that extend for tens of metres beyond visible potassic alteration whereas the anomalies defined by the carbonation indices do not extend beyond visible carbonation none of the individual alteration indices or pathfinder elements are able to define consistent gradients towards ore however the respective dimensions of individual geochemical anomalies can be used as an extensive although stepwise vector towards ore this sequence is from species with broadest dispersion first as follows te co2 ca sb 3k al rb ti au w y ti depletion ag bronzewing ore

palinspastic reconstruction and topographic evolution of the eastern alps during late tertiary tectonic extrusion this paper presents a new palinspastic restoration of the eastern alps for neogene time and an attempt to reconstruct the neogene palaeogeology palaeotopography and palaeohydrography in connection with the structural evolution the eastern alps underwent radical horizontal displacement during the neogene due to large strike slip systems and formation of structural windows our palinspastic reconstruction considers a the rearrangement of tectonic units dismembered during tectonic extrusion b the tectonic denudation driven by displacement of the crystalline blocks c geochronological arguments and d the sedimentary record of the syn extrusion basins the rearrangement of tectonic blocks results in a remarkably good fit of highly dismembered zones both in crystalline and sedimentary areas and shows the pre miocene unstretched pattern of the eastern alps reduced to 65 of its present day e w elongation using this structural frame and considering the sedimentary record a set of palaeogeologic and palaeotopographic sketch maps with the palaeo river systems is presented for three time slices pre syn and post extension situation in late oligocene and early miocene times the western eastern alps were already mountainous whereas the eastern part of the orogen formed lowlands or hilly areas enhanced block movement in the course of the extrusion process around the early middle miocene boundary led to the formation of intramontane sedimentary basins and a fault induced reorientation of the drainage pattern which forms the basis of the modern river system in the area east of the tauern window this region where pre miocene land surfaces are preserved probably became a mountainous area not before late miocene time and never reached the elevations of the areas further west

two billion years of evolution enclosed in hydrothermal rutile recycling of the sao francisco craton crust and constraints on gold remobilisation processes abstract the quadrilatero ferrifero in the sao francisco craton brazil is known for its world class gold deposits hosted by the rio das velhas greenstone belt rdv as in other greenstone belts gold is also concentrated in late archean early paleoproterozoic supracrustal units in this case within the moeda formation this unit has been compared to the witwatersrand basin where there has been a long term debate over the nature of the gold and whether it is detrital placer hydrothermal or hybrid modified placer presently links between gold in the moeda formation and rdv are tenuous to enlighten this area of ambiguity a new approach using chemical isotopic and mineral inclusion data from detrital rutile found in the gold bearing horizons of the moeda formation is presented grain textures and mineral inclusions have contributed to establishing a primary hydrothermal origin for the rutile related to as fe cu sb pb w rich mineralising fluids fe nb and v indicate that the likely source of the gold related rutiles is the archean banded iron formations within the rdv where most of the lode gold occurs average nb ta values of these rutiles are lower than average continental crust ratios which suggests fractionation driven by fluid precipitation and or competing mineral phases u pb data yield primary crystallization ages older than deposition ages 2 58 ga supporting the detrital nature of these rutiles rutiles record either resetting or new growth at 2 1 ga and at ca 500 ma during which gold was remobilised hence this study supports a modified placer model for the gold bearing horizons of the moeda formation these fluid assisted gold remobilisation events can be found in other correlated paleoproterozoic gold bearing horizon units that represent intracratonic basins related to the rifting of the kenorland supercontinent this study reinforces the suitability of rutile and mineral inclusions as a powerful tool to elucidate processes and provenance

kinematics of the inntal shear zone sub tauern ramp fault system and the interpretation of the transalp seismic section eastern alps austria abstract a new interpretation of the inntal tauern sector of the transalp seismic section is presented one of the most prominent contrasts in reflectivity in the transalp seismic section is the contact between the bajuvaric unit in the footwall and the overlying tirolic unit and its basement across a moderately south dipping interface we trace this contact from the surface at the southern margin of the inn valley to a depth of 5 km there the contact is deformed or cut by the tauern window northern margin we define the contact between bajuvaric and tirolic units as brixlegg thrust which is older than miocene tauern window exhumation and has a paleogene age the sub tauern ramp connects with the inntal fault system at the surface and roots below the tauern window oblique thrust movements across this fault system in the miocene caused exhumation of the hanging wall where the fault has a ramp geometry which is in the area of the transalp cross section and west of it east of the transalp cross section the fault system merges with alpine basal thrust which is a flat no miocene exhumation occurred above the flat

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

nucleation and growth of myrmekite during ductile shear deformation in metagranites myrmekite is extensively developed along strain gradients of continuous lower amphibolite facies shear zones in metagranites of the gran paradiso unit western alps to evaluate the role of stress strain energy and fluid phase in the formation of myrmekite we studied a sample suite consisting of weakly deformed porphyric granites wdgs foliated granites fgs representative of intermediate strains and mylonitic granites mgs in the protolith most k feldspar is microcline with different sets of perthite lamellae and fractures in the wdgs abundant quartz oligoclase myrmekite developed inside k feldspar only along preexisting perthite lamellae and fractures oriented at a high angle to the incremental shortening direction in the wdgs stress played a direct role in the nucleation of myrmekites along interfaces already characterized by high stored elastic strain because of lattice mismatch between k feldspar and albite in the fgs and mgs k feldspar was progressively dismembered along the growing network of microshear zones exploiting the fine grained recrystallized myrmekite and perthite aggregates this was accompanied by a more pervasive fluid influx into the reaction surfaces and myrmekite occurs more or less pervasively along all the differently oriented internal perthites and fractures independently of the kinematic framework of the shear zone in the mgs myrmekite forms complete rims along the outer boundary of the small k feldspar porphyroclasts which are almost completely free of internal reaction interfaces therefore we infer that the role of fluid in the nucleation of myrmekite became increasingly important as deformation progressed and outweighed that of stress mass balance calculations indicate that in al si conservative conditions myrmekite growth was associated with a volume loss of 8 5 this resulted in microporosity within myrmekite that enhanced the diffusion of chemical components to the reaction sites and hence the further development of myrmekite

tectonic evolution of the cenozoic olympic subduction complex washington state as deduced from fission track ages for detrital zircons

exhumation in a convergent orogen the western tauern window unroofing of the western tauern window involved both low angle detachment faulting brenner fault and enhanced footwall erosion contemporaneous with upright antiformal folding this combination reflects orogen parallel e w extension during continued n s alpine convergence new fission track ages establish the relative chronology of folding and faulting and demonstrate that displacement was not always accommodated on the same surface during exhumation some units migrated from the footwall to the hanging wall of the main detachment fault due to the interplay between folding and faulting the region can effectively be divided into 3 distinct domains 1 the penninic units of the western tauern window were always in the footwall to the fault with maximum exhumation in the core of the dome due to folding and erosion 2 the lower austroalpine unit north of the tauern window was first part of the hanging wall to the brenner fault at a later stage this unit was exhumed by a further 4 5 km as part of the footwall to a more discrete through going fault the silltal fault 3 the middle and upper austroalpine units west of the tauern window were always within the hanging wall exhumation of the footwall from an initial depth of 25 km led to a transition in mechanical behaviour the curviplanar folded ductile shear zone marking the boundary to the tauern window was eventually transected by a more planar discrete brittle fault silltal fault with unit 2 now in the footwall along which the pre existing mylonites were passively exhumed to the surface

complex mineral zoning patterns caused by ultra local equilibrium at reaction interfaces chemically zoned minerals are useful records of temporal variations in ambient conditions and bulk chemical composition of the fl uid from which the minerals precipitate in fl buffered systems zoning of mineral compositions is expected to refl ect directly the evolution of fl composition here we show that during rapid fl uid rock reactions ultra local equilibrium can form complex mineral zoning patterns even when the overall system is highly fl uid buffered we reacted cleaved calcite single crystals with aqueous arsenate phosphate solutions with molar ratios of as as p between 0 01 and 0 15 at 250 c and water saturated pressure we fithat complex zoning patterns and solid solution between hydroxylapatiteand arsenate bearing hydroxylapatite that pseudomorphically replaced calcite formed within hours and these zoning patterns were destroyed within days during secondary reactions we propose a two stage reaction process in the formation of the fi nal reaction product 1 on an hour time scale calcite is dissolved and replaced by compositionally heterogeneous apatite the thin reaction interface fllayer becomes extremely enriched in arsenic at an ultra local scale as the reaction removes phosphate faster than the interface fl uid can re equilibrate with the bulk fl uid 2 the heterogeneous apatite is replaced by homogeneous apatite that refl ects the bulk fl uid composition over a longer days time scale through interface coupled dissolution precipitation this paper highlights the complexity that can arise from ultra local fl uid composition variations due to rapid fl uid rock interaction in a short lived fl uid fl ow event for example during a seismic cycle subsequent interpretation of complex zoning patterns as refl ecting the evolution of bulk fl uid would be erroneous

dissolution and replacement creep a significant deformation mechanism in mid crustal rocks abstract zoning patterns and zoning truncations in metamorphic minerals in a granodioritic orthogneiss indicate that strain and s c fabrics in these rocks were produced by dissolution precipitation and replacement processes even at epidote amphibolite facies metamorphic conditions the metamorphic fabric is defined by alternating layers and folia dominated by quartz feldspars and biotite epidote zoning patterns in most metamorphic plagioclase orthoclase epidote and sphene are truncated at boundaries normal to the shortening direction suggesting dissolution interfaces of relict igneous orthoclase phenocrysts that face the shortening direction are embayed and replaced by biotite epidote and myrmekitic intergrowths of plagioclase and quartz metamorphic plagioclase grains are also replaced by epidote we interpret these microstructures to reflect strain enhanced dissolution the cores of many grains show asymmetric overgrowths with at least two generations of beards all oriented on the ends of grains that face the extension direction we interpret these textures to reflect precipitation of components dissolved by deformation enhanced dissolution while biotite and quartz probably deformed by dislocation creep the overall deformation was accommodated by dissolution perpendicular to the shortening direction and precipitation parallel to it these chemical processes must have been activated at lower stresses than the dislocation creep predicted from extrapolations of data from experiments in dry rocks thus wet crust is likely to be weaker than calculated from these experimental studies

the record of periadriatic volcanism in the eastern alpine molasse zone and its palaeogeographic implications precise provenance analysis of andesite and dacite pebbles from conglomerates in the eastern alpine molasse zone using geochemical and geochronological methods provides evidence for a synorogenic volcanic chain in the eastern alps which is completely eroded today this volcanism was related to periadriatic magmatism along the periadriatic lineament and took place in the palaeogene roughly between 40 and 30 ma the occurrence of remnants of these volcanic rocks together with other marker lithologies in the eastern alpine molasse implies an early to middle miocene drainage system which was in some respects similar to the present inn river system but had a considerably larger catchment area reaching farther south the palaeo inn drained the central and eastern sections of the periadriatic magmatic belt to the northern foreland basin

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

questions about myrmekite in deformed rocks abstract several questions about the development of myrmekite in deformed felsic and metapelitic rocks remain unanswered although a general relationship between deformation and myrmekite appears to be well established the fact that myrmekite grows into relatively non deformed k feldspar while being simultaneously deformed and recrystallized at the rear of the growing lobes suggests that strain energy may not be a major contributor to the advance of the growth interface of the myrmekite colony furthermore because myrmekite typically nucleates on existing plagioclase rather than in k feldspar strain energy may not contribute directly to nucleation of myrmekite either at least in many instances however strain energy probably contributes indirectly by facilitating access of fluids to growth sites thereby altering the local chemical environment and so promoting development of myrmekite because myrmekite recrystallizes readily in deformed felsic rocks it is one of the main contributors to the development of folia

post collisional orogen parallel large scale extension in the eastern alps abstract large scale extension affected the eastern alps during post collisional lateral tectonic extrusion in early and middle miocene times the tauern window was mainly tectonically exhumed by the 160 km pullapart of the rigidly behaving austroalpine basement blocks forming the tectonic lid of the penninic contents of the window an evaluation of the syn extrusion fault pattern reveals displacements of several tens of kilometers along the low angle extensional shear zones at the western and eastern margins of the window and along the important strike slip fault zones north and south of the window large scale shear is reflected by discontinuities in mineral cooling patterns across important shear zones the cooling histories of the tectonic blocks show that the window boundaries during exhumation coincide only partly with the classical boundaries of the window defined by thrust units reconstruction of the exhumation history shows an asymmetric evolution of the tauern window we argue that the eastern and western low angle extensional shear zones formed in sequence which is reflected by different evolutions of the fragmentation and uplift history of the austraolpine tectonic blocks to the east and west of the window in the central and eastern alps three structural domes the lepontin dome in the central alps and the tauern and rechnitz domes in the eastern alps were formed by large scale extension in miocene times total e w stretch amounts to more than 300 km and results in 70 extension we propose that the central and eastern alps are part of an extensional province that also includes the pannonian basin and has a counterpart separated by the moesian indenter in the rhodope mountains the aegean sea and the menderes massif in asia minor in these regions a number of mainly tectonically exhumed domes or deep sedimentary basins formed by miocene large scale extension

some garnet microstructures an illustration of the potential of orientation maps and misorientation analysis in microstructural studies the microstructures of two contrasting garnet grains are mapped using automated electron backscatter diffraction in both cases there is a very strong crystallographic preferred orientation with measurements clustered round a single dominant orientation each garnet grain is divided into domains with similar orientations limited by boundaries with misorientations of 2 or more in both samples most of misorientation angles measured across orientation domain boundaries are significantly lower than those measured between random pairs of orientation domains one sample is a deformed garnet that shows considerable distortion within the domains lines of orientation measurements within domains and across domain boundaries show small circle dispersions around rational crystallographic axes the domain boundaries are likely to be subgrain boundaries formed by dislocation creep and recovery the second sample is a porphyroblast in which the domains have no internal distortion and the orientation domain boundaries have random misorientation axes these boundaries probably formed by coalescence of originally separate garnets we suggest that misorientations across these boundaries were reduced by physical relative rotations driven by boundary energy the data illustrate the potential of orientation maps and misorientation analysis in microstructural studies of any crystalline material

role of myrmekite and associated deformation fabrics in controlling development of granitic mylonites in the pofadder shear zone of southern namibia myrmekites developed within metagranites of the pofadder shear zone psz in southern namibia were investigated to understand how alkali feldspar deforms under fluid poor mid crustal conditions myrmekites showed two different morphologies 1 wormy myrmekite with a fine grained vermicular structure that occurred closest to the alkali feldspar host and 2 recrystallised myrmekite composed of regularly sized quartz grains that formed 120 boundaries with the plagioclase and occurred along the exterior of alkali feldspar and in contact with the mylonitic matrix these textures were interpreted to represent two generations of myrmekite growth recrystallised myrmekite masses were dismembered and incorporated into the fine grained matrix this suggests that myrmekite formation during psz deformation contributed to the grain size reduction of alkali feldspar and aided in the generation of the fine grained polymineralic matrix which accommodated most of the strain syn kinematic reactions such as myrmekite and muscovite production were internally balanced and t mh2o pseudosections indicated that progressive deformation could have occurred under closed conditions the biotite muscovite plagioclase alkali feldspar quartz equilibrium assemblage was stable with decreasing fluid contents until fluid saturated or slightly fluid undersaturated conditions were reached around 2 mol h2o the variability of the quartz rod spacing and the wide range of results from two feldspar thermometry and phengite barometry on associated muscovite growth indicates that peak metamorphic conditions were around 500 c 0 5 gpa and that myrmekite growth continued as the shear zone was exhumed the myrmekite forming reaction is a deformation induced interface coupled dissolution precipitation reaction with relict magmatic plagioclase supplying the needed cationic inputs these results indicate that deformation within granitic units of the psz was aided by the formation and deformation of myrmekite and could have taken place under closed relatively fluid poor conditions

inversion of long period regional body waves for crustal structure long period regional distance 2 12 body waves are strongly influenced by the waveguide nature of the crust if the seismic source is known it is possible to parameterize the waveforms in terms of gross structural properties of crustal thickness and pn velocity since the regional distance waveforms are a product of interference of multiple reflected and mode converted phases changes in crustal thickness or pn velocity changes the relative timing of the various phases approximate green s function for a suite of crustal structures can be constructed by stretching or squeezing the green s function of an average crustal model which is the basis of an interative least squares inversion procedure for crustal structure the crustal structure of the western u s is inverted as a test of the technique

from source terrains of the eastern alps to the molasse basin detrital record of non steady state exhumation fission track cooling ages of detrital apatite aft in the east alpine molasse basin display age groups corresponding to geodynamic events in the orogen since jurassic times these age groups are typical of certain thermotectonic units which formed a patchwork in the swiss and eastern alps by a combination of petrographic and thermochronologic data progressive erosion of source terrains is monitored in different catchments since the oligocene the aft cooling ages show a decrease in lag time until when rapidly cooled debris derived from tectonically exhumed core complexes became exposed after termination of tectonic exhumation lag times of debris derived from the core complexes increased neither on the scale of the entire eastern alps or on the scale of individual catchments steady state exhumation is observed due to the highly dynamic changes of exhumation rates since late eocene collision d 2005 elsevier b v all rights reserved

two dimensional thermal modelling of normal faulting the simplon fault zone central alps switzerland abstract two dimensional finite difference thermal modelling of the major extensional simplon fault zone in the central alps establishes that the shape of cooling curves for samples from the footwall and hanging wall at various distances from the detachment are very sensitive to the actual displacement history if the displacement had occurred within a very limited time span 18 15 ma samples from the hanging wall close to the detachment should have significantly increased in temperature with a peak around 14 ma this is not discernible in the cooling curves interpreted from the mineral ages if the rate of normal fault displacement had been lower but constant from 18 ma to present the cooling curves for the footwall should show a correspondingly steady decrease in temperature the interpreted cooling curves from mineral ages are steep after 18 ma becoming shallower in more recent times this shape can be reproduced by the thermal modelling for a variable rate of fault displacement initially rapid total relative displacement 10 mm a across the fault zone between 18 and 15 ma but reducing to a more steady 0 4 mm a between 15 ma and 3 ma the corresponding exhumation rate of the footwall was 4 6 mm a from 18 to 15 ma and 0 6 mm a from 15 to 3 ma whereas the hanging wall was exhumed at a constant rate of 0 4 mm a the difference in cooling curves for samples with increasing horizontal distance into the footwall reflects a distributed ductile shear with the sample at 20 km distance initially at 25 km depth at 25 ma whereas that at 70 m distance was only at 19 km depth at the same time samples in the hanging wall were at 10 km depth total relative displacement parallel to the fault plane was around 36 km the thermal modelling demonstrates that during rapid fault displacement the apparent exhumation rate calculated assuming a constant geothermal gradient is too low whereas the apparent rate calculated for the subsequent period of slower displacement is too high

successive hydration and dehydration of high p mafic granofels involving clinopyroxene kyanite symplectites mt daniel fiordland new zealand three texturally distinct symplectites occur in mafic granofels of the arthur river complex at mt daniel fiordland new zealand these include symplectic intergrowths of clinopyroxene and kyanite described here for the first time pods of mafic granofels occur within the contact aureole of the early cretaceous western fiordland orthogneiss batholith the pods have cores formed entirely of garnet and clinopyroxene and rims of pseudomorphous coarse grained symplectic intergrowths of hornblende and clinozoisite that reflect hydration at moderate to high p these hornfelsic rocks are enveloped by a hornblende clinozoisite gneissic foliation s1 narrow garnet reaction zones in which hornblende and clinozoisite are replaced by garnet clinopyroxene assemblages developed adjacent to fractures and veins that cut s1 fine grained symplectic intergrowths of 1 clinopyroxene and kyanite and 2 clinozoisite quartz kyanite and plagioclase form part of the garnet reaction zones and partially replace coarse grained s1 hornblende and clinozoisite the development of the garnet reaction zones and symplectites was promoted by dehydration most probably following cooling of the contact aureole maps of oxide weight percent and cation proportions calculated by performing matrix corrections on maps of x ray intensities are used to study the microstructure of the symplectites

post collisional sediment budget history of the alps tectonic versus climatic control based on the sediment budget of the eastern swiss and western alps since the oligocene the regional tectonic evolution has been identified as the dominant factor it is superimposed on the influence of both regional and global climate change and global sea level change during late pliocene and pleistocene times climate became the dominant factor because of cyclic glaciations the early post collisional history of the alps is characterized by a doubling of sediment discharge rates around the rupelian chattian boundary this increase is attributed to isostatic re adjustment either after large scale thermal reorganization of the lithosphere related to slab break off or to crustal thickening as continental crust became subducted from middle oligocene to late miocene times the overall trend of sediment discharge rates in the entire alps was modified only during relatively short lived phases these are characterized by an increase in aquitanian ca 23 21 ma and late burdigalian times ca 18 16 4 ma and a decrease in early to middle burdigalian 21 19 ma and langhian to serravalian times 16 4 12 ma an important still ongoing period of uplift reflected by rapidly increasing sediment discharge rates started in latest miocene times in the swiss and western alps and affected the eastern alps some 2 million years later the reason for this uplift is not clear but deep seated lithospheric processes appear to be likely

revealing exhumation of the central alps during the early oligocene by detrital zircon u pb age and fission track double dating in the taveyannaz formation

nomenclature of amphiboles additions and revisions to the international mineralogical associations amphibole nomenclature the introduction of a fifth amphibole group the na ca mg fe mn li group defined by 0 50 b mg fe 2 mn 2 li 1 50 and 0 50 b ca na 1 50 apfu atoms per formula unit with members whittakerite and ottoliniite has been required by recent discoveries of b lina amphiboles this and other new discoveries such as sodicpedrizite which is herein slightly but significantly changed from the original idealized formula necessitate amendments to the ima 1997 definitions of the mg fe mn li calcic sodic calcic and sodic groups the discovery of obertiite and the finding of an incompatibility in the ima 1997 subdivision of the sodic group requires further amendments within the sodic group all these changes which have ima approval are summarized

rare earth and trace element mobility in mid crustal shear zones insights from the mont blanc massif western alps the behaviour of rare earth elements ree during fluid rock interaction in mid crustal shear zones has received little attention despite their potential for mass balance calculation and isotopic tracing during deformation in this study several cases of large ree mobility during alpine fluid driven shear zone development in the pre alpine granitic basement of the mont blanc massif are considered on a regional scale the undeformed granite compositions range within 5 wt sio2 70 5 75 3 wt and magmatic chemical variations are of the order of 10 20 ascribed to minor effects of crystal fractionation major and trace element mobility observed in shear zones largely exceeds these initial variations shear zones developed a range of mineral assemblages as a result of shearing at mid crustal depths at not vert similar0 5 gpa 400 c five main shear zone assemblages involve muscovite chlorite epidote actinolite and calcite respectively as major phases in most cases selective enrichments of light or heavy ree and y ta hf are observed ree mobility is unrelated to deformation style cataclastic mylonitic the intensity of strain and to the shear zone s major metamorphic mineral assemblages instead the changes in ree concentrations are ascribed to the alteration of pre existing magmatic ree bearing minerals during deformation related fluid rock interaction and to the syntectonic precipitation of metamorphic ree bearing minerals mainly monazite bastnasite aeschynite and tombarthite minor proportions 2 of these accessory phases with grain sizes mostly 20 m account for enrichments of up to 5 1 compared to the initial granite whole rock ree budget the stability of the ree phases appears to be largely dependent on the altering fluid composition ree mobility is ascribed to changes in ph and to the availability of co32 po42 and so42 ligands in the fluid such processes are likely to influence the mobility of ree y hf and ta in shear zones

the seismic source parameters of the 1991 costa rica aftershock sequence evidence for a transcurrent plate boundary the april 22 1991 valle de la estrella costa rica earthquake ms 7 6 was a back arc thrusting event associated with the underthrusting of the caribbean plate beneath central america a network of three passcal type portable instruments was deployed to monitor the aftershock activity in southern costa rica 2 to 6 weeks after the main shock the waveforms recorded on three component midperiod seismometers were used to recover source information for 15 small aftershocks magnitudes between 3 2 and 4 4 with a linear moment tensor inversion method we conducted several tests to investigate the effects of unknown structure and event mislocation on source parameter recovery the longer period waveforms in general are less sensitive to the effects of the structural details so that the essential source information can be successfully extracted from the waveform data the earlier part of the seismic wave forms has proven to be the most important carrier of the source information a gross crustal model can be used to describe the structure for the source study the small changes in the waveform character resulting from the mislocation of the events or inexact green s functions generated from the oversimplified crustal model do not prohibit us from the recovery of the source orientation at local distances in contrast the determination of the focal depth is subject to uncertainty because of the lack of detailed structural information our focal mechanisms are generally in good agreement with p wave first motion fault plane solutions determined from a local short period network the aftershocks show a clear spatial segmentation based on focal mechanism type most aftershocks near or southeast of the main shock were thrusting events with focal mechanisms similar to the main shock in contrast a cluster of aftershocks northwest of the main shock showed dominantly left lateral strike slip motion on a northeasterly striking nodal plane this suggests that a diffuse deformation zone exists in central costa rica and is characterized by left lateral strike slip motion this diffuse transcurrent deformation zone coincides with several geologic and geophysical features and perhaps is a result of the slower subduction rate of the buoyant cocos ridge than its adjacent segments along the middle america trench mat the diffuse transcurrent boundary may intersect with the north panama deformed belt npdb near limon costa rica and is very likely a plate boundary for the proposed panama block

exhumation of the rechnitz window at the border of the eastern alps and pannonian basin during neogene extension abstract the rechnitz window is the easternmost penninic window of the alps and the only one that is partly covered by neogene sediments zircon and apatite fission track ages have been measured on the penninic metasediments of the rechnitz series to better understand the exhumation of the window at the alpine pannonian border the zircon ft ages range from 21 9 to 13 4 ma similar to the white mica k ar ages 19 and 23 ma the exhumation rate during the early miocene extension was high 40 c ma apatite samples display ft ages of 7 3 and 9 7 ma thus the cooling rate was significantly less 7 11 c ma during the post rift uplift uplift in late miocene pliocene than in the early miocene escape period zircon ft ages decrease eastward due to the gradual southeastward slide of the austroalpine cover along low angle normal faults the exhumation of the rechnitz metamorphic core complex is younger than the unroofing of the eastern tauern window morphology of detrital zircon crystals of the penninic metasediments was used for the differentiation of tectonic subunits and to trace the internal structure of the window one population was probably derived from undifferentiated calc alkaline granitoids and tholeiitic granitoid sources while the other derived from evolved calc alkaline granitoids and alkaline granitoids of anorogenic complexes the areal distribution of zircon populations is in harmony with the eastward shift of zircon cooling ages these data indicate the exhumation of deep levels of penninic metasediments in the centre of the window

ordinary mesostasis and not so ordinary symplectites late stage assemblages in howardites abstract two categories of symplectites have been observed in howardites three phase composed of vermicular intergrowths of ferroan augite fayalitic olivine and silica and two phase composed of vermicular intergrowths of orthopyroxene and troilite three phase symplectites have been previously shown to represent the breakdown products of metastable pyroxene in howardites they appear to be genetically related to gabbroic eucrites in some cases and under yet to be specified conditions ferroan clinopyroxene in gabbroic eucrites may undergo only localized decomposition resulting in oriented exsolution like features breakdown phases in those cases are fayalitic olivine silica and depending on the mgo content of the system orthopyroxene as opposed to three phase symplectites two phase symplectites are most likely of diogenitic origin they probably formed via impact induced localized melting of diogenitic orthopyroxene in the presence of troilite grain boundary melting three phase symplectites in howardites occasionally contain accessory amounts of ilmenite troilite and or kamacite and are exclusively associated with medium grained feo rich pyroxene silica and plagioclase all minerals involved are late stage crystallites or mesostasis phases in general highly evolved eucritic lithologies constitute only a minor fraction of howardites however considering that three phase symplectites are generated in a low pressure i e near surface environment feo and cao rich eucritic rocks may be exposed locally on vesta s surface this in turn is highly relevant to the ongoing dawn mission

geometry amount and sequence of thrusting in the subalpine molasse of western austria and southern germany european alps in this paper we review the structure of the most external thrust belt of the alps between the rhein valley and salzburg based on a new tectonic map and the re interpretation of seismic sections specifically we address the correlation between deformation in the subalpine molasse and the alpine thrust belt in general and focus on the control of sedimentary facies on the structural style a dramatic change in architecture from a ramp flat structure to buckle folding is related to a change from coarse grained fans to fine grained deposits within the subalpine molasse additionally the interaction of escape tectonics with postcollisional shortening controls the decrease of late early miocene and younger shortening within the subalpine molasse from 50 km near the rhine valley to almost zero near salzburg transfer of shortening into the hinterland which is the zone of lateral escape ended foreland propagation of the alpine thrusts and initiated a general break back sequence of thrusting throughout this time the thrusts remained active in such a scenario tectonic units on top of the subalpine molasse are expected to undergo clockwise rotation around vertical axes as thrusting in the subalpine molasse is closely related to contemporaneous transport and shortening within the tectonically higher helvetic thrust sheets amounts of miocene differential shortening and related clockwise vertical axis rotation are minimum amounts true clockwise vertical axis rotation is probably larger than the 12 deduced from the subalpine molasse thrust belt

redistribution of high pressure fluids during retrograde metamorphism of eclogite facies rocks voltri massif italian western alps abstract high pressure clinopyroxenes in metasomatic mafic rocks rodingites and metagabbros containing titanoclinohumite and eclogites from the voltri massif ligurian western alps retain primary two phase aqueous inclusions h 2 o nacl kcl in the metasomatized rocks the inclusions align with the c axes and the cleavage planes of diopside the eclogites display mylonitic textures primary fluid inclusions are hosted in early porphyroclasts of omphacite omphacite i and are absent in later fine grained omphacite omphacite ii that forms the mylonitic foliation omphacite i has been frequently replaced by retrograde symplectites clinopyroxene plagioclase amphibole in such cases the fluid inclusions are either absent or occur in much lower number the textural observations suggest that formation of the symplectites has been controlled by availability of the fluid inclusions inside omphacite i the symplectites have been in turn overgrown by glaucophanic and winchitic amphiboles indicating that breakdown of the omphacite i to symplectites still occurred at relatively high pressure post entrapment changes have caused a large range of densities in the analyzed inclusions although the textural evidence constrains the entrapment of fluid inclusions to high pressure conditions the highest density isochores in the eclogites indicate pressure temperature conditions 8 kbar and 550 c lower than those attained during the high pressure stage such p t estimates approach those of symplectite formation after omphacite i thus the fluid inclusions preserved in omphacite were formed by low pressure re equilibration of a fluid presumably trapped at eclogite facies conditions the inclusions kinetically triggered the retrograde breakdown of the eclogitic clinopyroxenes the compositional overlap between the analyzed inclusions and those related to the latest greenschist evolutionary stage suggests further redistribution of the high pressure fluids and close system behaviour of these rocks during their overall exhumation path

microstructures and late stage magmatic processes in layered mafic intrusions symplectites from the sept iles intrusion quebec canada replacive symplectites vermicular intergrowths of two or more minerals are an important feature of layered igneous intrusions recording evidence of late stage reactions between interstitial liquid and crystals they are common throughout the layered series of the 564 ma sept iles layered intrusion in quebec canada and fall into three types oxy symplectites type i symplectites and type ii symplectites oxy symplectites are comprised of magnetite and orthopyroxene nucleate on olivine primocrysts and form via the reaction olivine o2 orthopyroxene magnetite type i symplectites of which there are 3 distinct categories are comprised of anorthitic plagioclase with pyroxene amphibole or olivine vermicules grow from primocryst oxide grains and replace primary plagioclase and type ii symplectites of which there are 2 distinct categories are comprised of anorthitic plagioclase with orthopyroxene amphibole vermicules grow from primocryst olivine

paleogene early miocene igneous rocks and geodynamics of the alpine carpathian pannonian dinaric region an integrated approach a review of paleogene early miocene igneous rocks of the alpine carpathianpannonian dinaric region is presented in this paper we attempt to reveal the geodynamic link between paleogene early miocene igneous rocks of the mid hungarian zone and those of the alps and dinarides our summary suggests that paleogene early miocene igneous rocks of all these areas were formed along a single subduction related magmatic arc the study also highlights orthopyroxene rich websterite mantle xenoliths from west hungary and east serbia that were formed in the vicinity of a subducted slab we discuss the location and polarity of all potential subduction zones of the area that may account for the igneous rocks and orthopyroxene rich mantle rocks however results of seismic tomography on subducted slabs beneath the studied area combined with geological data demonstrate that igneous rocks and mantle rocks cannot be explained by the same subduction process we propose that the paleogene early miocene arc was mainly generated by the budva pindos subduction zone subordinately by penninic subduction whereas mantle rocks were possibly formed in the vicinity of the older vardar subduction zone continental blocks possibly moved together with their mantle lithosphere the present diverging shape of the proposed arc has been achieved by considerable shear and rotations of those lithospheric blocks

estimation of crustal structure in central and west japan from waveform modeling of regional pl waves an inverse method of modeling the regionalpl waveform with the predominant period of about 20 s was developed to estimate the averages velocity structure of the upper crust applicability of the waveform modeling was confirmed by the results of the numerical experiments thepl waveform is most sensitive to thes velocity in the upper crust whereas it is not affected significantly by errors involved in the focal mechanism solution and focal depth determination when thepl wave is well developed the method was applied to the observed seismograms recorded in central japan from the earthquakes with epicentral distances 300 500 km as a result distinct regional differences were found in the upper crustals velocity in particular between the southern shikoku district west japan and the southern chubu district central japan and between the mountainous and the coastal areas in the southern chubu district these differences are in agreement with the general features ofp velocity structures obtained by explosion experiments and by analyses of natural earthquakes our method is effective to the extent that the crustal structure along the propagation path can be assumed a horizontally layered structure it is not applicable when the sensitivity of thepl waveform to the error in the focal mechanism solution is exceptionally high

exhumation of the central alps evidence from 40ar 39ar laserprobe dating of detrital white micas from the swiss molasse basin 40ar 39ar single grain laserprobe dating of detrital white micas from early oligocene to middle miocene 31 14 ma sedimentary rocks of the central swiss molasse basin reveals three distinct clusters of cooling ages for the hinterland two palaeozoic age clusters reflect cooling after the variscan orogeny with only limited reheating during the alpine orogeny the third tertiary age cluster reflecting late alpine cooling is restricted to sediments younger than 20 myr old micas with cooling ages 30 myr are interpreted to originate from the footwall of the simplon detachment fault thus representing formerly exposed upper levels of the present day lepontine metamorphic dome erosion of these levels is reflected by an increase of low grade metamorphic lithic grains in the sandstones this interpretation puts constraints on the timing of exhumation as well as on the evolution of the drainage pattern of the central alps

intragranular dynamic recrystallization in naturally deformed calcite marble diffusion accommodated grain boundary sliding as a result of subgrain rotation recrystallization abstract intragranular microshear zones within a greenschist facies calcite marble were studied to try to constrain better the processes of dynamic recrystallization as well as the deformation processes that occur within newly recrystallized grains intragranular recrystallized grains within large twinned calcite porphyroclasts can be related to the host from which they have recrystallized and are the focus of an electron backscatter diffraction study lattice distortions low angle boundaries and some high angle boundaries 15 in the microshears within a porphyroclast have the same misorientation axes suggesting that deformation occurred by climb accommodated dislocation creep involving subgrain rotation recrystallization changes in the ratio of host and twin domain as the deformation zone is entered show that twin boundary migration also occurred recrystallized grains have similar sizes 10 60 m to subgrains suggesting that they formed by subgrain rotation however within the intragranular microshear zones the misorientations between recrystallized grains and porphyroclasts are considerably larger than 15 and misorientation axes are randomly oriented moreover recrystallized grain orientations average around the porphyroclast orientation we suggest that the recrystallized grains once formed are able to deform partly by diffusion accommodated grain boundary sliding which is consistent with predictions made from lab flow laws

geochemistry and geochronology of gneiss pebbles from foreland molasse conglomerates geodynamic and paleogeographic implications for the oligo miocene evolution of the eastern alps abstract gneiss pebbles deposited in foreland fans during the miocene epoch were studied with geochemical and thermochronological methods to reconstruct the paleodrainage evolution of the eastern alps and the geodynamic behavior of the source areas clear discrimination between upper plate austroalpine and lower plate penninic gneiss pebbles was achieved by single pebble paleocooling paths austroalpine gneisses showed highly variable and regionally distinctive paleocooling paths which record variscan to cretaceous rb sr and k ar cooling ages penninic gneisses showed paleogene to lower miocene high temperature rb sr k ar and miocene low temperature zircon and apatite fission track cooling ages cooling rates of penninic gneisses indicate maximum exhumation rates at 17 ma during the climax of lateral tectonic extrusion recording dominance of tectonic unroofing the paleodrainage evolution was characterized by a relatively stable catchment configuration in the western part of the eastern alps wh

time calibration of a pt path from the western tauern window eastern alps the problem of closure temperatures new hornblende k ar and 39ar 40ar and mica rb sr and k ar ages are used to place specific timemarks on a well constrained pressure temperature path for the late alpine metamorphism in the western tauern window after identification of excess 40ar the closure behavior of ar in hornblende is compared with that of sr and ar in phengite and biotite samples were collected in three locations whose maximum temperatures were 570 c zemmgrund 550 c pfitscher joch and 500 540 c landshuter hutte

variability of apatite fission track annealing kinetics ii crystallographic orientation effects a method is presented that permits the length of any horizontal confined fission track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis the model is based on the results of annealing experiments for six selected apatites five calcian fluorapatites and durango apatite representing a subset of the 15 total apatite specimens studied an iterative process of calculation is required to project fission track lengths onto the c axis and computer source code implementing the solution to this problem is presented this method of projecting apatite fission track lengths onto the crystallographic c axis is shown to remove effectively fission track length variation within single fission track populations due to anisotropic track length reduction for all 15 apatites studied in addition a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission track density etched fission tracks per unit area of apatite surface and the arithmetic mean fission track length finally it is shown that natural fission track populations exhibit fission track length anisotropy similar to that of fission track populations created and annealed in the laboratory this observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment

alkali diffusion in plagioclase feldspar tracer diffusion kinetics at 1 atm pressure under dry conditions using 6li 41k and 87rb in four plagioclase feldspars have been determined diffusion profiles were measured using an ion microprobe sims the arrhenius parameters and 2 uncertainties for li k and rb respectively in albite are pre exponential factor log do 3 8 1 0 3 4 1 4 and 5 8 3 8 in m2 s and activation energies 146 14 296 30 and 283 85 kj mol the diffusion rate of k in albite at 700 c and 100 mpa water pressure equals that at 1 atm dry suggesting that diffusion of k is not dependent on water fugacity between 0 004 and 100 mpa the k diffusion rate depends on plagioclase anorthite content and is approximately 20 times slower in labradorite than albite li diffusion rates in albite and anorthite are identical a linear relation between log d for the alkalis measured and their ionic radius squared permits an estimate of cs diffusion kinetics diffusion rates are isotropic or nearly so in albite

symplectite formation in the presence of a reactive fluid insights from hydrothermal experiments this study describes the microstructural and chemical development of symplectites obtained in fluid mediated mineral replacement experiments during the experiments polymineralic feldspar rich samples were exposed to aqueous na sio2 solution at 600 c and 2 kbar confining pressures for durations of 12 hr to 20 days the resulting reaction rims display high mineralogical and structural complexity and contain two varieties of symplectites represented by nanometre scale intergrowths of gehlenite zeolite and grossular zeolite grains the experimental fluid was enriched in 18o isotope in order to trace oxygen redistribution during the reaction the elevated 18o concentration in the reaction products and the heterogeneity in its distribution suggest that symplectite formation was controlled by dissolution precipitation mechanisms rather than volume diffusion processes microstructural and chemical observations suggest that symplectite formation occurred in multiple stages in response to spatially heterogeneous and temporarily evolving fluid composition at the reaction interfaces hence our results shed light on the fundamental processes involved in symplectite formation improving our ability to interpret symplectite microstructures this article is protected by copyright all rights reserved

quantifying tectonic versus erosive denudation by the sediment budget the miocene core complexes of the alps abstract the denudation budget of the alps is quantified for the main period of lateral extrusion between 22 and 12 ma the relative importance of tectonic denudation increases from w to e from 70 in the lepontine window in the swiss alps to 80 in the tauern window and to more than 95 in the rechnitz window the driving mechanism of tectonic denudation was eastward extrusion due to an unconstrained orogenic margin in the pannonian basin tectonic denudation in the alps was responsible for about 30 of the total exhumation between 22 and 12 ma

the initiation of strain localisation in plagioclase rich rocks insights from detailed microstructural analyses abstract in order to shed light on the cause for onset of strain localisation in plagioclase rich rocks we have performed detailed microstructural analyses on a sheared anorthosite leucogabbro using optical microscopy electron backscatter diffraction ebsd and chemical analyses the analysed sample is from an archaean unit sw greenland deformed at lower to mid crustal conditions t 675 700 c and moderate pressure the initial deformation occurred dominantly by dislocation creep and the grain size was reduced primarily by subgrain rotation recrystallisation recrystallised plagioclase grains average size 80 m are dominantly found in i clusters ii lenses and iii continuous bands subparallel to shear zone boundaries recrystallised grains in clusters and lenses display inherited crystallographic orientations their bulk crystallographic preferred orientation cpo is random however crystallographic characteristics show that parent and daughter grains have the same misorientation axes and possibly the same active slip systems recrystallised grains in continuous bands show a cpo with a single dominant active slip system 001 aligned with the structural xyz framework for these parent and daughter grains misorientation axes are random and the dominant slip system is different grain rotations of recrystallised grains are traceable back to the orientation of the adjacent porphyroclast we infer that the cause for strain localisation is recrystallisation and development of a cpo in continuous recrystallised bands microstructures in combination with misorientation and slip system analyses indicate a possible change from dislocation creep in clusters and lenses to dislocation accommodated grain boundary sliding disgbs in continuous bands this inferred shift in dominant deformation mechanism would lower the strength of the shear zone

deciphering high pressure metamorphism in collisional context using microprobe mapping methods application to the stak eclogitic massif northwest himalaya the stak massif northern pakistan is a newly recognized occurrence of eclogite formed by the subduction of the northern margin of the indian continent in the northwest himalaya although this unit was extensively retrogressed during the himalayan collision records of the high pressure hp event as well as a continuous pressure temperature p t path were assessed from a single thin section using a new multiequilibrium method this method uses microprobe x ray compositional maps of garnet and omphacitic pyroxene followed by calculations of 200 000 p t estimates using appropriate thermobarometers the stak eclogite underwent prograde metamorphism increasing from 650 c and 2 4 gpa to the peak conditions of 750 c and 2 5 gpa then retrogressed to 700 650 c and 1 6 0 9 gpa under amphibolite facies conditions the estimated peak metamorphic conditions and p t path are similar to those of the kaghan and tso morari high to ultrahigh pressure hp uhp massifs we propose that these three massifs define a large hp to uhp province in the northwest himalaya comparable to the dabie sulu province in china and the western gneiss region in norway

interaction of chemical and physical processes during deformation at fluid present conditions a case study from an anorthosite leucogabbro deformed at amphibolite facies conditions we present microstructural and chemical analyses of chemically zoned and recrystallized plagioclase grains in variably strained samples of a naturally deformed anorthosite leucogabbro southern west greenland the recorded microstructures formed in the presence of fluids at mid crustal conditions 620 640 c 7 4 8 6 kbar recrystallized plagioclase grains average grain size 342 m with a random crystallographic orientation are volumetrically dominant in high strain areas they are characterized by asymmetric chemical zoning an80 cores and an64 rims that are directly associated with areas exhibiting high amphibole content and phase mixing analyses of zoning indicate anisotropic behaviour of bytownite plagioclase with a preferred replacement in the left langle 0 10 right rangle direction and along the 001 plane in areas of high finite strain recrystallization of plagioclase dominantly occurred by bulging recrystallization and is intimately linked to the chemical zoning the lack of cpo as well as the developed asymmetric zoning can be explained by the activity of grain boundary sliding accommodated by dissolution and precipitation creep dpc in low strain domains grain size is on average larger and the rim distribution is not related to the inferred stress axes indicating chemically induced grain replacement instead of stress related dpc we suggest that during deformation in high strain areas pre existing phase mixture and stress induced dpc caused grain rotations that allowed a deformation enhanced heterogeneous fluid influx this resulted in local plagioclase replacement through interface coupled dissolution and precipitation and chemically induced grain boundary migration accompanied by bulging recrystallization along with neocrystallization of other phases this study illustrates a strong interaction and feedback between physical and chemical processes where the amount of stress and fluids dictates the dominant active process the interaction is a cause of deformation and external fluid infiltration with a result of strain localization and chemical re equilibration at amphibolite facies conditions

a combined tof sims and emp sem study of a three phase symplectite in the los angeles basaltic shergottite a rare three phase symplectite consisting of ca rich pyroxene fe rich olivine and a silica phase is frequently found rimming pyroxene in the martian meteorite los angeles this assemblage is usually interpreted as the breakdown product of metastable pyroxferroite a very rare pyroxenoid mineral itself however its origin is not entirely understood mainly because the extremely small average size of the constituent phases represents a challenge for precise high resolution analysis in addition to electron microbeam methods the present study uses time of flight secondary ion mass spectrometry tof sims to overcome the limits of spatial resolution and to comprehensively study this mineral assemblage the prevailing breakdown hypothesis is supported by the following results 1 the three symplectite phases are very homogenous in composition from 100 m down to the micrometer scale 2 the silica phase could be shown to be almost pure sio2 3 the symplectite bulk composition is consistent with pyroxferroite sub micrometer sized ti oxide grains are found within the symplectite but not within the ca rich pyroxene and probably represent a minor breakdown phase in addition to the three main phases

textural evolution of plagioclase feldspar across a shear zone implications for deformation mechanism and rock strength caledonian amphibolite facies shear zones developed in granulitefacies anorthosites and anorthositic gabbros of the bergen arcs western norway allow a detailed study of the relationships between fluid infiltration mineral reactions the evolution of microstructure and deformation mechanisms a sequence of rocks from the relatively pristine granulites into a shear zone has been studied by optical microscopy electron microprobe microanalysis empa scanning electron microscopy sem electron backscatter diffraction ebsd and transmission electron microscopy tem focusing on the progressive development of microstructure in the plagioclase feldspars leading up to their deformation in the shear zone at the outcrop scale fluid infiltration into the granulites is marked by a distinct colour change in the plagioclase from lilac brown to white this is associated with the breakdown of the intermediate composition plagioclase an50 in the granulite to a complex intergrowth of na rich and ca rich domains ebsd analysis shows that this intergrowth retains the crystallographic orientation of the parent feldspar but that the ca rich domains contain low angle grain boundaries within the shear zone this complex intergrowth coarsens by grain boundary migration annihilating these grain boundaries but retaining the na rich and ca rich zoning pattern analysis of nearestneighbour misorientations of feldspar grains in the shear zone demonstrates that local crystallographic preferred orientation cpo is inherited from the parent granulite grain orientations random pair misorientation angle distributions show that there is no cpo in the shear zone as a whole nor is there significant shape preferred orientation spo in single grains these observations are interpreted in terms of fluid induced weakening and deformation by dissolution precipitation pressure solution creep

kyanite eclogite to amphibolite fades evolution of hydrous mafic and pelitic rocks adula nappe central alps in the southern adula nappe central alps two stages of regional metamorphism have affected mafic and pelitic rocks earlier eclogite facies with a regional zonation from glaucophane eclogites to kyanite hornblende eclogites was followed by a tertiary overprint which varied from greenschist to high grade amphibolite facies despite a common metamorphic history contrasting equilibration conditions are often recorded by high pressure mafic eclogite and adjacent predominantly lower pressure pelite assemblages this pressure contrast may be explained by different overprinting rates of the two bulk compositions during unloading the rates are controlled by a mechanism in which dehydrating metapelites provide the h2o required for simultaneous overprinting of enclosed mafic eclogites by hydration

lithospheric structure of the qiangtang terrane northern tibetan plateau from complete regional waveform modeling evidence for partial melt we report models of p and s wave velocity and attenuation for the the crust and uppermost mantle of the qiangtang terrane northern tibetan plateau inferred by fitting reflectivity synthetic seismograms to observed complete regional waveforms the data are three component broadband seismograms recorded by the 1991 1992 iris passcal incorporated research institutions for seismology program for array seismic studies of the continental lithosphere tibetan plateau experiment and global seismic network stations in the region the qiangtang terrane has thick crust 65 5 km with p and s wave velocities of 6 1 6 3 and 3 34 3 43 km s respectively yielding an anomalously high crustal poisson s ratio of 0 29 0 02 seismic velocities of the upper mantle of the qiangtang terrane are normal for p waves and slow for s waves 8 10 and 4 35 4 41 km s respectively with a high mantle poisson s ratio of 0 29 0 01 attenuation in the crust and upper mantle is high qp 100 200 and qs 44 89 modeling of the broadband p waveforms suggests that a decrease in mantle velocity occurs at about 160 km depth in the mantle however this is not unambiguously supported by the data and modeling the crust and uppermost mantle of the qiangtang terrane probably contains partial melt based on the high poisson s ratio low shear wave velocities and low q the absence of high frequency sn and the presence of volcanism of mantle lithospheric origin support the presence of partial melt crustal and uppermost mantle structure in the qiangtang terrane is different from that for the lhasa terrane immediately to the south based on results of our previous studies the average crustal p and s wave velocities are 4 faster and 2 slower respectively in the qiangtang terrane relative to the lhasa terrane this yields a significant difference in the crustal poisson s ratio with values of 0 29 for the qiangtang terrane and 0 25 for the lhasa terrane differences in the uppermost mantle p and s wave velocities and poisson s ratios of these two adjacent terranes cannot be explained by temperature differences alone using the mantle temperature estimates of mcnamara et al 1997 we suggest that partial melt of an ultramafic composition beneath the qiangtang terrane fits the velocity and poisson s ratio estimates

depositional and structural evolution of a foreland basin margin in a magnetostratigraphic framework the eastern swiss molasse basin this integrated study of the sedimentology magnetostratigraphic chronology and petrography of the mostly continental clastics of the oligocene to miocene swiss molasse basin underpins a reconstruction of facies architecture and delineates relationships between the depositional evolution of a foreland basin margin and exhumation phases and orogenic events in the adjacent orogen a biostratigraphically based high resolution magnetostratigraphy provides a detailed temporal framework and covers nearly the whole stratigraphic record of the molasse basin 31 5 13 ma three transverse alluvial fan systems evolved at the southern basin margin they are characterized by distinct petrographic compositions and document the exhumation and denudation history of the growing eastern swiss alps enhanced northward propagation of the orogenic wedge is interpreted to have occurred between 31 5 and 26 ma during the period 24 19 ma intense in sequence and out of sequence thrusting took place as molasse strata were accreted to the orogenic wedge a third active tectonic phase possibly caused by backthrusting of the plateau molasse probably occurred between ca 15 and 13 ma fan head migration between 31 5 and 13 ma is probably controlled by the structural evolution of the thrust front due to molasse accretion and backthrusting

corona networks as three dimensional records of transport scale and pathways during metamorphism coronal textures in metamorphic rocks are physical evidence that diffusion was the rate limiting process in the local reactions that produced these layered structures mass balance however requires that chemical communication must also take place at length scales significantly greater than those of the corona evidence for the anatomy and scale of pathways along which chemical communication occurred is rarely recorded in metamorphic rocks but orthoamphibole cordierite gneiss from the thor odin dome british columbia canada preserves multi layered coronal reaction textures around garnet and al2sio5 connected by anastomosing networks of cordierite and biotite that represent relict pathways along which mass transport occurred during reaction texture development calculations of component fluxes between reaction textures and surrounding mineral assemblages indicate that relatively long distance centimeter scale diffusional exchange was required for development of 150 500 m thick corona results of electron backscattered diffraction analysis and high resolution x ray computed tomography give new information about the scale and pathways of chemical communication during high grade metamorphism and show that length scales of material transport were two orders of magnitude greater than those of the reaction textures

provenance of rifted continental crust at the nexus of east gondwana breakup the bruce rise a prominent bathymetric feature offshore the bunger hills east antarctica has basement of unknown crustal affinity and age in east gondwana the bruce rise is reconstructed near the naturaliste plateau offshore sw australia and microcontinents now submerged in the eastern indian ocean new zircon u pb hf data from two c 1150 ma granite samples dredged from the eastern escarpment of the bruce rise demonstrate that these rocks are dominated by xenocrystic cargo mesoproterozoic xenocrystic cores show textural evidence of melt mediated coupled dissolution precipitation to form rim domains with apparent ages that skew towards c 1150 ma the zircon u pb hf signatures from the xenocrysts in the bruce rise granites and from c 1230 to 1180 ma felsic intermediate granites and orthogneisses from the conjugate naturaliste plateau basement suggest late mesoproterozoic magmatism occurred at a transition in the regional tectonic architecture between a reworked archean cratonic margin and proterozoic juvenile crust on the basis of plate reconstructions exhumation and thinning of the basement to the bruce rise naturaliste plateau occurred predominantly during rifting of india prior to c 120 ma minor further thinning likely occurred leading up to the onset of seafloor spreading between australia naturaliste plateau and antarctica bruce rise from c 90 to 84 ma

rates and mechanisms of isotopic exchange background the proliferation of stable isotope laboratories in recent years has led to a marked increase in the routine use of stable isotope analyses in geochemical studies this trend is likely to continue because of the development of micro analytical techniques e g laser ablation ion microprobe femtomole carrier gas methods etc for stable isotope analysis and the potential of these techniques to reveal the detailed sequence of thermal and fluid histories preserved in the rock record see mckibben et al 1998 equilibrium isotope fractionation factors and rates of isotopic exchange form the cornerstones for the interpretation of stable isotope data from natural systems indeed determination of the distribution of the stable isotopes of c o h s in gases fluids and minerals has become a standard and extremely powerful approach in elucidating the temperatures material fluxes rock and fluid origins and time scales associated with ancient and active fluid rock interaction processes in the earth s crust see valley et al 1986 although the thermodynamic principles underlying isotopic fractionation behavior were developed more than fifty years ago by urey 1947 the calibration of fractionation factors has proven to be difficult during the last four decades a great deal of progress has been made in determining the equilibrium fractionations of 18o 16o d h 13c 12c and 34s 32s among fluid and mineral components at high temperatures 400 c both from experimental exchange studies theoretical calculations using vibrational spectra semi empirical calculations using bond type considerations and empirical calibrations based on natural assemblages see references in o neil 1986 kyser 1987 criss 1991 1999 chacko et al this volume of these the experimental method is the most direct because it involves the least number of a priori assumptions despite the utility of the equilibrium approach in quantifying the isotopic behavior in select water rock

oceanographic and climatic evolution of the miocene mediterranean deduced from nd sr c and o isotope compositions of marine fossils and sediments isotopic compositions of marine sediments and fossils have been investigated from northern basins of the mediterranean to help constrain local oceanographic and climatic changes adjacent to the uplifting alps stable c and o isotope compositions of benthic and planktonic foraminifera from the umbria marche region umc have an offset characteristic for their habitats and the changes in composition mimic global changes suggesting that the regional conditions of climate and the carbon cycle were controlled by global changes the radiogenic isotope composition of these fossil assemblages allows recognition of three distinct periods in the first period from 25 to 19 ma high nd values and low 87sr 86sr of sediments and fossils support intense tectonism and volcanism related to the opening of the western mediterranean in the second period from 19 to 13 ma the 87sr 86sr ratio of mediterranean umc deviate from the global ocean which is compatible with rapid uplift of the hinterland and intense influx of sr from mesozoic carbonates of the western apennines this local control on the seawater was driven by a humid and warm climate and indicates restricted exchange of water with the global ocean generally the nd values of the fossils are very similar to those of indian ocean water with brief periods of a decrease in the nd values coinciding with volcanic events and maybe sea level variation at 15 2 ma in the third period from 13 to 10 ma the fossils have 87sr 86sr similar to those of miocene seawater while their nd values change considerably with time this indicates fluctuating influence of the atlantic versus the paratethys and or locally evolved seawater in the mediterranean driven by global sea level changes other investigated localities near the alps and from the odp 900 site are compatible with this oceanographic interpretation however in the late early miocene enhanced local control reflecting erosion of old crustal silicate rocks near the alps results in higher 87sr 86sr

the erosion history of the central alps evidence from zircon fission track data of the foreland basin sediments fission track dating on detrital zircons of alpine debris in the swiss molasse basin provides information about the erosion history of the central alps and the thermal evolution of source terrains during oligocene times only sedimentary cover nappes and austroalpine basement units were eroded incision into austroalpine basement units is indicated by increasing importance of cretaceous cooling ages in granite pebbles upsection erosion of penninic basement units started between 25 and 20 ma early oligocene zircon ft ages show that penninic basement units were exposed at 20 ma deeper penninic units of the lepontine dome became exposed first at 14 ma contemporaneously with the opening of the tauern window in the eastern alps a middle miocene cooling rate of 40 c myr 1 is deduced for the lower penninic units of the lepontine dome

the replacement of plagioclase feldspars by albite observations from hydrothermal experiments oligoclase and labradorite crystals have been experimentally replaced by albite in an aqueous sodium silicate solution at 600 c and 2 kbars the replacement is pseudomorphic and is characterised by a sharp chemical interface which progresses through the feldspar while preserving the crystallographic orientation reaction rims of albite up to 50 m thick can be readily achieved within 14 days re equilibration of plagioclase in an 18o enriched sodium and silica bearing solution results in oxygen isotope redistribution within the feldspar framework structure the observed characteristics of the reaction products are similar to naturally albitised plagioclase and are indicative of an interface coupled dissolution reprecipitation mechanism chemical analyses demonstrate that the albitisation is accompanied by the mobilisation of major minor and trace elements also including elements such as al and ti which are commonly regarded as immobile during hydrothermal alteration the results contribute to developing our understanding of the close association between large scale albitisation and secondary ore mineralisation which is common in nature

shear zones and magma ascent a model based on a review of the tertiary magmatism in the alps 1 the alpine oligocene plutons are spatially and temporally associated with the activity of the periadriatic fault system pfs an orogen parallel crustal scale transpressive mylonitic belt excellent three dimensional exposure combined with a wealth of structural seismic petrological geochronological geochemical and paleomagnetic data collected over the last decades help to constrain the relationships between deformation ascent and emplacement of the plutons magmas were channeled from the base of the thickened continental crust into the narrow mylonitic belt of the periadriatic fault system which was used as ascent pathway to cover vertical lengths of 20 to 40 km therefore the linear alignment of the plutons at the surface is not the expression of a linear source region at depth ascent of the melts is controlled by the mylonitic foliation of the pfs which forms the only steep anisotropy continuously traversing the entire alpine crust in contrast the flow direction is not influenced by the specific kinematics of the faults final emplacement of the plutons occurred by extrusion from the periadriatic fault system into the adjacent country rocks the transition from ascent to final emplacement is favored by partitioning of transpressive deformation

the clinopyroxene plagioclase symplectite in retrograde eclogites a potential geothermobarometer the retrograde p t t path of intermediate and high temperature eclogites t 500 50 c is characterized by the transformation of omphacite into a symplectitic intergrowth of clinopyroxene and plagioclase lamellae often this symplectite shows a two stage microstructural evolution i e a coarse lamellar width symplectite s1 followed by a thinner lamellar width symplectite s2 each symplectite may also evolve independently into a final globular microstructure sg

restoring the source to sink relationships in the paleogene foreland basins in the central and southern alps switzerland italy france a detrital zircon study approach late paleogene syn tectonic magmatic products are known from sandstones contained in the north alpine nafb and south alpine safb foreland basins and in the south alpine pelagic trento basin the generally turbiditic and mass flow deposits grade up from marly hemipelagic deeper water series the source and amount of the reworked volcanic materials have been in debate for a long time as a proxy for the magma derived input we use the u pb geochronology and geochemistry 176hf 177hf t and eu eu ratios of detrital zircons and evaluate their temporal and genetic relationships with potential volcanic sources in the periadriatic magmatic systems adamello bergell biella the oldest volcanic sources lutetian priabonian we identify are in the trento basin and glarus nafb during most rupelian bergell and biella volcaniclastics were delivered to the nafb in the glarus alpe de taveyanne and haute savoie bergell and minor adamello magmatic material were supplied to the villa olmo conglomerate in the safb during late rupelian chattian in the entire nafb the influx of paleogene volcanic material faded out at the same time in the safb the como conglomerate shows mixed input from biella and bergell high numbers of old zircons 90 in the nafb document the asymmetry of the early alpine orogenic wedge exposing large basement areas to the north of the periadriatic intrusions the syn sedimentary right lateral movement along the periadriatic fault system is identified as the main driver of magmatic activity uplift and exposure to erosion and transport to the basins on this base the dynamics of the early alpine drainage systems are reconstructed with new accuracy

crustal thickness and upper mantle velocities in the tibetan plateau region from the inversion of regional pnl waveforms evidence for a thick upper mantle lid beneath southern tibet the crustal thickness and upper mantle velocity variation in tibet and surrounding regions was mapped through the inversion of 130 individual long period pnl waveforms the 130 paths crisscross the tibetan plateau hindu kush karakoram southwest china burma and northern india regions we regionalized these areas on the basis of topographic and geologic expression and determined the average upper mantle velocity and crustal thickness value for each block or region through a linear least squares inversion of the 130 parameter values crustal thicknesses in the tibetan plateau karakoram and hindu kush regions range from 63 to 72 km and pn velocities are 0 10 0 20 km s faster beneath these regions than those beneath northern india we observed impulsive first arrivals evidence for positive upper mantle gradients on seismograms recorded at distances between 1000 and 1400 km the paths of these waves crossed portions of tibet the hindu kush and east india regions simple modeling of the long period pn wave form and amplitude requires fairly high upper mantle gradients of 0 18 0 25 km s per 100 km beneath the pamir hindu kush region and requires an upper mantle lid in excess of 100 km thickness the southern half of tibet also requires a lid of about 100 km thickness a thinner upper mantle lid 50 km provided a poor match to the tibetan observations even with a very high gradient of 0 2 km s per 100 km the upper mantle structure of east india appears to be similar to the southern half of tibet 100 km thick positive gradient zone both the increase in pn velocity from india into tibet and the evidence for a thick upper mantle lid beneath tibet are consistent with the model in which indian lithosphere has underthrust southern tibet due to poor path coverage the structure beneath northern tibet cannot be resolved and thus underthrusting beyond central tibet cannot be constrained the rapid increase in upper mantle velocity from northern india into tibet can be explained by the pressure increase alone produced by the double thick crust and indicates that the indian lithosphere which underlies tibet is out of thermal equilibrium

paleogeography and catchment evolution in a mobile orogenic belt the central alps in oligo miocene times abstract in this study we reconstruct the surface evolution of the oligo miocene central alps using geochronological geochemical and petrographical methods on the foreland basin sediments of both flanks of the mountain range our model is illustrated in four sketch maps of different time slices between mid oligocene to middle miocene times for each time slice we try to 1 give a palinspastic reconstruction of the central alps based on the post collisional lateral extrusion model 2 show which tectonic units had become exposed to the surface due to exhumation processes in the central alps 3 describe the thermochronologic evolution of lithological units formerly exposed but completely eroded today 4 differentiate the catchment areas of the paleo river systems which delivered debris to the foreland basins and 5 describe the position of the main drainage divide relative to the exposed tectonic units