uranium and boron distributions related to metamorphic microstructure evidence for metamorphic fluid activity the distribution of uranium and boron in polymetamorphosed granulite facies schists and gneisses has been studied using particle track methods the concentration and distribution of these elements when examined in relation to mineralogy and microstructure provide an insight into 1 the behaviour of u and b in metamorphism 2 the activity of a fluid phase in the metamorphic processes and 3 the nature of chemical processes during schistosity development a low concentration of primary u occurs in micro inclusions of apatite and zircon many are metamict in the granulite facies m1 assemblage this assemblage which lacks b except for zoned sillimanite has undergone a localized retrograde metamorphism rm1 characterised by hydrous alteration products containing abundant u and b the rm1 metamorphism is attributed to fluids generated during granulite facies dehydration reactions a schistosity s2 defined by m2 fibrolite aggregates overprints the m1 events it is associated with 1 intragranular u concentrated in m2 apatite and titanium bearing minerals and 2 abundant intergranular u within the fibrolite aggregates high b contents also occur with the fibrolite the s2 schistosity appears to develop in a metamorphic environment containing a fluid enriched in u and b

the effect of microstructural and rheological heterogeneity on porphyroblast kinematics and bulk strength in porphyroblastic schists abstract the kinematic record and bulk viscous strength of polyphase rocks depend in part upon the relative strengths and distributions of rheologically distinct fabric elements here we explore the effects of microstructural and rheological heterogeneity in porphyroblastic schists electron backscatter diffraction and petrographic analyses reveal asymmetric microboudinage of staurolite indicating relative rotation of staurolite porphyroblasts synchronous with bulk non coaxial strain boudinage and relative rotation both require porphyroblast matrix shear coupling based on 2d optical observations the extent of the coupling appears related to the initial and boudinaged staurolite grain shape and orientation as well as the geometry of heterogeneities such as mica domains or shear bands we designed 2d finite element numerical models to assess the role of microstructural variation and rheological heterogeneity on the degree of porphyroblast matrix shear coupling and bulk viscous strength model results indicate that the bulk strength of a three phase system comprising inclusion weak domain and matrix is sensitive to the relative proximity of weak and strong domains particularly at high viscosity contrasts i e matrix weak 10 the threshold for bulk weakening below the matrix strength occurs over a narrow range of weak domain viscosities matrix weak 2 6 5 5 regardless of the relative abundance and spatial distribution of weak domains kinematic decoupling of porphyroblasts occurs at low viscosity contrasts when weak domains are proximal matrix weak 2 5 but for all other spatial distributions and modal abundances investigated kinematic decoupling occurs at viscosity contrasts of matrix weak 15 20 these data indicate that bulk weakening due to rheological heterogeneity is not necessarily coincident with kinematic decoupling

spectral signatures of submicron scale light absorbing impurities in snow and ice using hyperspectral microscopy light absorbing impurities lai can darken snow and ice surfaces reduce snow ice albedo and accelerate melt efforts to allocate the relative contribution of different lai to snow ice albedo reductions have been limited by uncertainties in the optical properties of lai we developed a new method to measure lai spectral reflectance at the submicron scale by modifying a hyperspectral imaging microscope spectrometer hims we present the instrument s internal calibration and the overall small influence of a particle s orientation on its measured reflectance spectrum we validated this new method through the comparison with a field spectroradiometer by measuring different standard materials measurements with hims at the submicron scale and the bulk measurements of the same standard materials with the field spectroradiometer are in good agreement with an average deviation between the spectra of 3 2 for the 400 1000 nm wavelength range the new method was used 1 to identify bc black carbon mineral dust including hematite and the humic substances present in an environmental sample from plaine morte glacier and 2 to collect the individual reflectance spectra of each of these types of impurity the results indicate that this method is applicable to heterogeneous samples such as the lai found in snow and ice

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

x ray computed micro tomography of spiral garnets a new test of how they form abstract garnet porphyroblasts with spiral shaped inclusion trails of two micaschist samples have been investigated with x ray computed tomography for each garnet crystal the orientation of its internal foliation intersection inflexion axes fia was measured its volume and shape orientation the latter via calculation of best fit ellipsoids additionally image analysis of inclusion trails was performed in slices passing through garnet centres oriented normal to fia our data demonstrate subvertical and subhorizontal preferred orientations of the inclusion trails and of the porphyroblast crystals themselves in both samples this supports a genetic model in which garnets periodically overgrew a succession of vertical and horizontal foliations during alternating crustal shortening and gravitational collapse without significantly rotating the fact that both samples come from areas previously identified as regional shear zones supports the idea that porphyroblasts are able to maintain stable positions even in such environments our study exemplifies the strength of x ray computed micro tomography compared to previous techniques based on serial thin sections for distinguishing multiple fia sets present in single samples

lattice preferred orientation of quartz inclusions within garnet porphyroblasts from the imjingang belt south korea abstract quartz inclusions within intertectonic garnet porphyroblasts of metapelites from the southern imjingang belt have a lattice preferred orientation c axis fabrics of the quartz inclusions tend to show a single girdle pattern at a high angle to an earlier foliation together with a submaximum subparallel to an earlier lineation this lattice preferred orientation of the quartz inclusions might result from intracrystalline deformation together with solution creep prior to the garnet growth or from selective entrapment of quartz grains with a specific lattice orientation during the garnet growth

the p t deformation path for a mid proterozoic low pressure terrane the reynolds range central australia the proterozoic low pressure high temperature lpht terrane of the reynolds range occurs in a 130 km long nw trending belt in the central part of the arunta block central australia the reynolds range has been affected by two mid proterozoic tectonic cycles di and dii associated with two metamorphic events mi and mii di mi effects are restricted to the older of two sedimentary successions the lander rock beds which are separated from the younger reynolds range group by an angular unconformity the dominant structural metamorphic features formed during dii mii affected both sedimentary successions and the various granites that intruded them and reworked most di mi effects the dii deformation history can be subdivided into one prograde two peak and one retrograde stage average p t calculations in the southeastern half of the range indicate a peak metamorphic pressure of 4 1 0 3 kbar because the calculated values are derived from the same stratigraphic level corresponding to the base of the reynolds range group which is exposed throughout the area it is likely that pressures were similar in the entire range in fact however the peak metamorphic temperature shows a dramatic increase from greenschist facies c 400 c in the northwest to granulite facies 740 60 c in the southeast indicating that mii was associated with anomalously high heat flows the p t path is anticlockwise with isobaric cooling from the metamorphic peak indicated by corona textures however the evidence of a prograde increase in pressure is indirect and based on the compressional nature of the structures peak metamorphic mineral assemblages and retrograde mineral assemblages in amphibolite facies shear zones show the same metamorphic zonation suggesting they formed in response to the same thermal event if this is true the implication is that a thermal perturbation external to the crust was maintained for a considerable period of time 110 ma based on zircon dating as it is not clear whether proterozoic asthenosphere active thermal perturbations operated for this long the alternative interpretation must be considered namely that the peak metamorphic events are separate from the shear zone event associated with reheating of the area

causes of variability in light absorption by particles in snow at sites in idaho and utah this file accompanies namer2014snowbc dohertyetal v1 xlsx which contains data on black carbon bc and other light absorbing particles in snow in utah and idaho for samples collected january march 2014 in jan feb 2013 and 2014 in utah data are available as an excel file with headers or as a comma separated data file with no headers there is one entry per layer of snow sampled all entries other than column titles in the xlsx are numeric detailed information on our measurements can be found in a series of publications as given below description of the instrument and method used to make the measurements grenfell t c s j doherty a d clarke and s g warren spectrophotometric determination of absorptive impurities in snow appl opt 50 14 pp 2037 2048 2011 summary and discussion of dataset namer2014snowbc dohertyetal xlsx including maps of sample locations doherty s j d a hegg p k quinn j e johnson j p schwarz c dang and s g warren causes of variability in light absorption by particles in snow at sites in idaho and utah j geophys res atmos 121 doi 10 1002 2015jd024375 2016 note that the measurement and analysis techniques used to produce these data were also used in a broad arctic survey 2006 2010 of bc and other light absorbing particles snow as reported here doherty s j s g warren t c grenfell a d clarke and r e brandt light absorbing impurities in arctic snow atmos chem phys 10 11647 11680 doi 10 5194 acp 10 11647 2010 2010 http www atmos chem phys net 10 11647 2010 acp 10 11647 2010 html

interpretation of porphyroblast inclusion trails limitations imposed by growth kinetics and strain rates porphyroblast inclusion trails provide important information about the tectonometamorphic evolution of a metamorphic rock however there remains considerable controversy over whether porphyroblasts rotate during bulk non coaxial deformation with reference to an area of the scandinavian caledonides and utilizing existing data from theoretical and experimental modelling this study demonstrates that both straight and s shaped inclusion trails are consistent with an interpretation in terms of syndeformational porphyroblast growth in a regime approximating to newtonian simple shear at crustal strain rates of 10 14 s 1 and porphyroblast growth times of 0 1 1 0 ma it is shown that a maximum of 5d 9d angular rotation would occur during growth at faster strain rates of 10 12 s 1 e g those in a shear zone porphyroblast angular rotations of 90d are shown to occur in 0 1 0 25 ma i e times comparable with or faster than porphyroblastesis in view of this s shaped inclusion trails are to be expected in porphyroblasts growing in active shear zones or other situations of high shear strain whereas straight inclusion trails can be interpreted as static overgrowth of an existing fabric or as syndeformational porphyroblastesis at low strain rates

shear zone vs folding origin for spiral inclusion trails in the canton schist the three dimensional geometry of spiral inclusion trails from the canton schist were measured to determine whether the spirals were a product of porphyroblast rotation within a shear zone or porphyroblast growth during a series of overprinting fold events the spiral inclusion trails are composed of three separate sub planar inclusion trail surfaces occupying texturally distinct parts of the porphyroblasts these surfaces are correlated across a 10 km2 area using textural criteria and relative timing measured patterns of inclusion trail orientation and asymmetry suggest they did not form by porphyroblast rotation within a non coaxial shear zone rather the porphyroblasts grew during three successive overprinting fold events f2 f4 and the spiral inclusion trails represent the accumulated curvature associated with folding of successive axial plane foliations the data show that spiral garnets are not peculiar to shear zones and can form by overprinting crenulations and folds this is consistent with the common occurrence of spiral garnets in multiply deformed regionally metamorphosed fold belts

mineral dust impact on snow radiative properties in the european alps combining ground uav and satellite observations in this paper we evaluate the impact of mineral dust md on snow radiative properties in the european alps at ground aerial and satellite scale a field survey was conducted to acquire snow spectral reflectance measurements with an analytical spectral device asd field spec pro spectroradiometer surface snow samples were analyzed to determine the concentration and size distribution of md in each sample an overflight of a four rotor unmanned aerial vehicle uav equipped with an rgb digital camera sensor was carried out during the field operations finally landsat 8 operational land imager oli data covering the central european alps were analyzed observed reflectance evidenced that md strongly reduced the spectral reflectance of snow in particular from 350 to 600 nm reflectance was compared with that simulated by parameterizing the snow ice and aerosol radiation radiative transfer model we defined a novel spectral index the snow darkening index sdi that combines different wavelengths showing nonlinear correlation with measured md concentrations r2 0 87 root mean square error 0 037 we also estimated a positive instantaneous radiative forcing that reaches values up to 153 w m2 for the most concentrated sampling area sdi maps at local scale were produced using the uav data while regional sdi maps were generated with oli data these maps show the spatial distribution of md in snow after a natural deposition from the saharan desert such postdepositional experimental data are fundamental for validating radiative transfer models and global climate models that simulate the impact of md on snow radiative properties

permo triassic changes in bulk crustal shortening direction during deformation and metamorphism of the taebaeksan basin south korea using foliation intersection inflection axes implications for tectonic movement at the eastern margin of eurasia during the songrim indosinian orogeny abstract the permo triassic songrim indosinian orogeny in south korea was a major tectonic event involving complicated continental collisions at the eastern margin of eurasia previous studies have examined the structural and metamorphic features of the songrim orogeny in each of the paleozoic terranes of the orogenic belt i e the taebaeksan basin the okcheon basin and the imjingang belt but correlations of these features among the terranes remain uncertain the aim of this paper is to reveal deformation history including bulk crustal shortening directions in the taebaeksan basin and to correlate the tectono metamorphic evolution of the taebaeksan basin with other phanerozoic mobile belts in eastern asia based on a combined analysis of foliation intersection inflection axes fia trends and metamorphic p t and t t time paths the orientations and relative timing of fia preserved as inclusion trails within porphyroblasts of andalusite chloritoid garnet and staurolite reveal two age groups of inclusion trails in the pyeongan supergroup at the northeastern margin of the taebaeksan basin these microstructures indicate the development of early nnw nne trending structures and fabrics followed by later e w trending ones these observations suggest a change in the orientation of bulk crustal shortening from e w to n s during the songrim orogeny based on the similar microstructures and temperature time paths of the three paleozoic terranes we interpret that the e w bulk crustal shortening influenced the eastern part of the korean peninsula during the early stages of the songrim orogeny presumably related to amalgamation between the proto japan terrane and the eastern margin of eurasia whereas the n s bulk crustal shortening was stronger in the western part of the peninsula during the later stages of the orogeny related to collision between the south and north china blocks

the origin and microstructures of metamorphic felsic dykes emplaced during brittle ductile extension southeast sinai structural petrographic and chemical analyses of a set of northeast trending quartzofeld spathic dykes in wadi kid area southeastern sinai show that they are the product of anatexis of pelitic rocks metamorphic p t data indicate that anatexis could have occurred only 2 km below the present erosion level the partial melts intruded into overlying rocks during regional metamorphism along a set of northeast oriented extensional fractures thereby recrystallizing and in some cases obtaining tectonite fabrics the fractures were formed perpendicular to the regional mineral lineation and show that the area was within the deeper parts of the brittle ductile transition zone the original depth of the presently exposed crustal level corresponds well with the theoretical and experimentally derived depths of the brittle ductile transition zone in high heat flow regimes the emplacement of a granitoid pluton or gneiss dome possibly of dioritic composition could be responsible for both melting and tensile fracturing of the overlying rocks

fold mechanisms in the canton schist constraints on the contribution of flexural flow abstract fold mechanisms operating in the canton schist have been resolved using the geometric relationship between folds and spiral inclusion trail geometries of the four end member fold mechanisms tangential longitudinal strain folding and slip folding are unable to produce the observed inclusion trail and fold geometries but a combination of flexural flow and pure shear folding is consistent with the geometric constraints the maximum flexural flow component during each fold event was determined from the geometric data during f 3 and f 4 flexural flow produced 27 and 37 of measured limb rotation respectively which corresponds to a maximum of 24 limb rotation by flexural flow in each fold event to satisfy the geometric constraints the remainder of limb rotation must be a product of pure shear folding the maximum possible component of flexural flow folding during f 3 and f 4 increases with increased variation in vorticity between layers in the rock mass in the flexural flow pure shear model a maximum of 28 of inclusion trail curvature is produced by rotation of porphyroblasts relative to irrotational fold limbs with a minimum 72 curvature due to rotation of fold limbs relative to irrotational porphyroblasts all model solutions produce less than 8 syn folding porphyroblast rotation relative to geographic coordinates

rotated staurolite porphyroblasts in the littleton schist at bolton connecticut usa staurolite porphyroblasts 1 5 8cm in length and 0 3 2cm in width in the littleton schist at bolton connecticut contain curved quartz inclusion trails which document synkinematic rotations of at least 135 the orientations of long axes of these staurolite crystals define a weak preferred orientation in a plane approximately parallel to the external foliation serial sections of four differently orientated crystals and u stage measurements of the orientations of their inclusion trails demonstrate that the inflection hinge line and the statistical symmetry axis characterizing the foliation within a porphyroblast are unrelated to the orientations of external crenulations and are in all cases parallel to the long axis of the porphyroblast the cumulative rotation reflected in the curvature of the inclusion trails is a maximum in a c axis section through the initial core of a crystal the amount of rotation about the c axis decreases linearly along the length of the crystal away from the nucleation site the sense and amount of rotation recorded by a porphyroblast is related to its orientation a tightly constrained transition from clockwise to anticlockwise rotation defines a slip direction that coincides with the preferred orientation of the staurolite c axes the total rotation reflected by the inclusion trails increases as a function of the angle between the c axes of the staurolite crystals and the slip direction initially random staurolite porphyroblasts rotated during growth as a consequence of laminar shear in the surrounding viscous matrix this interpretation is quantitatively consistent with the staurolite preferred orientation its coincidence with the apparent slip direction the correlation between both the sense and the amount of rotation and the orientation of the long axis of the porphyroblast and the twisted conical shape of the family of surfaces defined by the inclusion trails

the interrelationship between deformation and metamorphismpapers presented at an international meeting held in granada spain 23 26 may 2011 celebrating the career contribution of t h bell the interrelationship between deformation and metamorphism is a topic of active research connecting such disciplines as structural geology metamorphic petrology geochronology material science and economic geology this special issue is dedicated to a notable scientist who is also our friend mentor and colleague prof tim h bell james cook university of north queensland australia the eight papers in this issue were presented at a conference last year in granada spain at the occasion of tim s retirement an additional set of 15 papers will appear in tectonophysics as fruit of the same conference

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

isograds and mineral assemblages in the eastern axial zone montagne noire france implications for temperature gradients and p t history detailed petrography across a metapelitic sequence in the eastern axial zone of the montagne noire france is the basis for a sequence of isograds marking the first appearance of biotite cordierite staurolite andalusite and sillimanite the juxtaposition of low grade biotite free rocks against medium grade rocks at the gently dipping biotite cordierite isograd is attributed to tectonic telescoping of the metamorphic sequence study of mineral assemblages with respect to an afm reaction sequence indicates the staurolite isograd is related to changes in rock composition and complex assemblages in the sillimanite zone may be the result of unstable persistence of minerals formed when metamorphic grade was lower these assemblages are interpreted to contain a record of part of the p t history during which pressure decreased as temperature increased p t profiles show that temperature gradients of 200 300 c km suggested by previous workers are not required to explain the isograd pattern gradients of 37

correlating deformation in variscan nw iberia using porphyroblasts implications for the ibero armorican arc abstract 3 d microstructural analysis of 30 porphyroblastic samples from the variscan orogen in nw iberia has revealed four sets of inclusion trails with distinctive geographic trends and relative timing the chronological and orientational consistency of these microstructures provides a reference frame for the correlation of macroscopic structural successions the two younger inclusion trail sets correlate with the main map scale structures of middle to upper carboniferous age whereas the two older sets correspond to mesoscopic structures preserved locally in low strain pods and dating back as far as 365 ma upper devonian inclusion trail orientations appear uninfluenced by a major orocline in the study area ibero armorican arc outlined by late stage folds and thrusts with variable trends it is proposed that the orocline developed by wnw ese trending transpression superposed on originally n s to ne sw trending structures during a late stage of the orogeny upper carboniferous domains of low or zero strain e g porphyroblasts are inferred to have maintained relatively constant orientations in the zone of transpression presumably due to deformation partitioning effects consequently they preserve a succession of pre orocline structural trends the collected microstructural data also indicate moderate preferred vertical and horizontal orientations of inclusion trails in the analysed samples as reported earlier in other variscan regions this probably witnesses a dynamic equilibrium between tectonic forces and gravity during four periods of differently oriented crustal shortening that generated the four recognised sets of inclusion trails

geochemical evidence for sources of surface dust deposited on the laohugou glacier qilian mountains abstract atmospheric dust deposited on glacier surfaces can decrease snow albedo by enhancing lighting absorption and by forming cryoconites via microbial activity which accelerates glacier melt using snow and cryoconite sampled from the laohugou glacier no 12 in the qilian mountains during spring 2012 and summer 2014 this work investigates the sr nd isotopic and rare earth element ree geochemistry of dust and its environmental significance results demonstrate that dust rees possess lower eu eu and l hree and higher gd yb n values compared with that of the mu us and hobq deserts but yield higher la yb n l hree la sm n and la yb n ratios than that of the taklimakan desert the ree composition of glacier surface dust is similar to the material from nearby arid regions such as the qaidam basin and the tengger and badain jaran deserts surrounding the eastern tibetan plateau the e nd 0 values of glacial dust resemble the isotopic ratios of the qaidam badain jaran tengger deserts and local dust e nd 0 value of 13 6 but differ from that of the taklimakan desert which has higher 87 sr 86 sr ratios analysis of air mass trajectory also indicates a potential dust input from the surrounding areas to the alpine glaciers in the qilian mountains these results strongly indicate that the dust source from the arid northern tibetan plateau region was the dominant contributor to atmospheric dust deposition on the glacier surface rather than dust originating from the long range transport of taklimakan desert material

foliation development and refraction in metamorphic rocks reactivation of earlier foliations and decrenulation due to shifting patterns of deformation partitioning reactivation of early foliations accounts for much of the progressive strain at more advanced stages of deformation its role has generally been insufficiently emphasized because evidence is best preserved where por phyroblasts which contain inclusion trails are present reactivation occurs when progressive shearing operating in a synthetic anastomosing fashion parallel to the axial planes of folds changes to a combination of coarse and fine scale zones of progressive shearing some of which operate antithetically relative to the bulk shear on a fold limb reactivation of earlier foliations occurs in these latter zones reactivation decrenulates pre existing or just formed crenulations generating shearing along the decrenulated or rotated pre existing foliation planes partitioning of deformation within these foliation planes such that phyl losilicates and or graphite take up progressive shearing strain and other minerals accom modate progressive shortening strain causes dissolution of these other minerals this results in concentration of the phyllosilicates in a simi lar but more penetrative manner to the for mation of a differentiated crenulation cleavage except that the foliation can form or intensify on a fold limb at a considerable angle to the axial plane of synchronous macroscopic folds reactivation can generate bedding parallel schistosity in multideformed and meta morphosed terrains without associated folds heterogeneous reactivation of bedding gen erates rootless intrafolial folds with sigmoidal axial planes from formerly through going struc tures reactivation causes rotation or refrac tion of axial plane foliations forming in the same deformation event causing reactivation in those beds or zones in which an earlier foli ation has been reactivated and results in destruction of the originally axial plane foli ation at high strains reactivation also provides a simple explanation for the apparently wrong sense but normally observed rotation of gar net porphyroblasts whereby the external foli ation has undergone rotation due to antithetic shear on the reactivated foliation alter natively the rotation of the external foliation can be due to its reactivation in a subsequent deformation event porphyroblasts with inclusion trails com monly preserve evidence of reactivation of earl ier foliations and therefore can be used to ident ify the presence of a deformation that has not been recognized by normal geometric methods because of penetrative reactivation reac tivation often reverses the asymmetry between pre existing foliations and bedding on one limb of a later fold leading to problems in the geo metric analysis of an area when the location of early fold hinges is essential the stretching lineation in a reactivated foliation can be rad ically reoriented potentially causing major errors in determining movement directions in mylonitic schistosities in folded thrusts geometric relationships which result from reactivation of foliations around porphyroblasts can be used to aid determination of the timing of the growth of porphyroblasts relative to deformation events other aspects of reac tivation however can lead to complications in timing of porphyroblast growth if the presence of this phenomenon is not recognized for example d grown porphyroblasts may be dis solved against reactivated s and hence appear to have grown syn d

the direct derivation of sillimanite from a kaolinitic precursor evidence from the geco mine manitouwadge ontario three substances occur in some of the geco gneisses a colorless to pale brown translucent material occurring in biotite dark brown to black clots associated with sillimanite in quartz dominated matrices and massive felted brown material forming a constituent of fibrolite patches electron microprobe analysis reveals a range of hydrous alumino silicates containing variable small amounts of impurities the compounds range from kaolinite or halloysite through sillimanite in some instances the precursor developed from earlier partial kaolinization of biotite thus accounting for the common intergrowth of sillimanite and biotite in metamorphic rocks modified journal abstract

deformation history of the otago schists new zealand from progressively developed porphyroblast matrix microstructures uplift collapse orogenesis and its implications abstract foliation overprinting relationships preserved in porphyroblasts and the surrounding matrix in the otago schists indicate development of up to six penetrative foliations during the late paleozoic mesozoic rangitata orogeny s1 s3 and s5 formed with steep dips and s2 s4 and s6 formed with gentle dips s1 and s2 are preserved only as inclusion trails in porphyroblasts because of matrix foliation reworking during progressive deformation s3 s6 are preserved in the matrix as well as in porphyroblasts and are generally correlatable from one to the other inclusion trail asymmetries define the location of the orogenic uplift core during the rangitata orogeny when the porphyroblasts grew the location of this core is consistent with macroscale geological and structural observations alternating steep and gently dipping foliations are inferred to indicate alternating horizontal compression and extension predictions made by an orogenic model compatible with continually alternating horizontal compression and extension compare favorably with geometries observed in the schists reconstruction of the gross geometry of the otago schists during the rangitata orogeny based on the three dimensional geometry of porphyroblast inclusion trails is similar to reconstructions based on regional geological considerations and plate tectonic calculations

from adria to africa driven orogenesis evidence from porphyroblasts in the betic cordillera spain abstract in order to unravel the kinematic evolution of the betic rif orogen we investigated the geometry of porphyroblast inclusion trails in the nevado filabride complex a high pressure unit situated at the base of the betic nappe stack a large number of quantitative orientation data for these microstructures and their mutual overprinting relationships reveal two age groups of inclusion trails in the study area with distinctive geographic trends coupled to a comprehensive compilation of field data in the study area these microstructures are shown to coherently witness the development of early ne sw trending structures and fabrics followed by younger nw se trending ones whereby the former experienced clockwise reorientations a major change in the direction of bulk crustal shortening from nw se to ne sw is inferred from these data and tentatively linked to the plate tectonic history of the mediterranean region paleomagnetic data indicate that prior to about 35 ma nw se convergence between adria eurasia and iberia produced orogenesis along a belt bordering greater iberia including sardinian and corsica and probably continuous in the alps brianconnais domain the roughly ne sw trend of this precursor appears to be preserved within porphyroblasts that grew during this period presumably due to the partitioning of deformation around them africa iberia relative motion had been mainly transcurrent until 35 ma azores transform but then rapidly changed to head on nne ssw convergence this gave rise to a second set of nw se trending structures which accompanied deformation of the precursor orogen into several oroclines western alps gibraltar and calabria arcs orogenic collapse and crustal extension initiated shortly after this transition in tectonic regime suggesting a causal relationship we propose that the waning of compressive stresses transmitted by adria and their substitution by a near perpendicular maximum stress direction resulting from africa eurasia convergence could have enhanced the sinking of a thick lithospheric root or roll back of a subducted slab which in turn would have provoked crustal extension and basin formation

porphyroblast inclusion trails the key to orogenesis detailed microstructural analysis of inclusion trails in hundreds of garnet porphyroblasts from rocks where spiral shaped inclusion trails are common indicates that spiral shaped trails did not form by rotation of the growing porphyroblasts relative to geographic coordinates they formed instead by progressive growth by porphyroblasts over several sets of near orthogonal foliations that successively overprint one another the orientations of these near orthogonal foliations are alternately near vertical and near horizontal in all porphyroblasts examined this provides very strong evidence for lack of porphyroblast rotation the deformation path recorded by these porphyroblasts indicates that the process of orogenesis involves a multiply repeated two stage cycle of 1 crustal shortening and thickening with the development of a near vertical foliation with a steep stretching lineation followed by 2 gravitational instability and collapse of this uplifted pile with the development of a near horizontal foliation gravitational spreading near coaxial vertical shortening and consequent thrusting on the orogen margins correlation of inclusion trail overprinting relationships and asymmetry in porphyroblasts with foliation overprinting relationships observed in the field allows determination of where the rocks studied lie and have moved within an orogen this information combined with information about chemical zoning in porphyroblasts provides details about the structural metamorphic p t t paths the rocks have followed the ductile deformation environment in which a porphyroblast can rotate relative to geographic coordinates during orogenesis is spatially restricted in continental crust to vertical ductile tear transcurrent faults across which there is no component of bulk shortening or transpression

de bugging the millipede porphyroblast microstructure a serial thin section study and 3 d computer animation abstract seventy five spatially orientated serial thin sections cut from a single rock containing millipede porphy roblast microstructure from the robertson river metamorphics australia reveal thc three dimensional 3 dj geometry of oppositely concave microfolds ocms that define the microstructurc electronic animations showing progressive scrial sections of thc 3 d microstructurc arc made available via the world wide web the ocm amplitudes decrease regularly from a maximum in near central sections to a minimum in near marginal scctions whereas the ocm interlimb angles increase regularly from a minimum in near ccntral sections to a maximum in near marginal sections these observations illustrate that the ocms are noncylindrical surfaces with culminations located in near central scctions because the porphyroblast cores appear to have been present before significant development of the syn ocm foliation all of the ocms were formed by heterogcncous cxtension around thcse cores the overall gcometry of the ocms described hcre reflects the strain state and cannot be used to constrain defor mation paths

albedo of dirty snow during conditions of melt the evolution of spectrally averaged albedo wavelengths between 0 28 m and 2 8 m of snow surfaces treated with known initial concentrations of particles of submicron sized soot and air fall volcanic ash was investigated during conditions of natural melt depending on the particle type and concentration the initial applications reduced the surface albedo to values ranging from 0 18 to 0 41 which were substantially lower than the albedo of the untreated natural snow about 0 61 many of the soot particles flushed through the snowpack with the meltwater and surface concentrations of soot greater than about 5 10 7 kg kg did not persist for more than a few days the migration of particles to depth caused the snow to brighten after the initial application thus limiting the amount of albedo reduction and the consequent effects on melting nevertheless the soot remaining near the surface had a substantial long term effect the residual concentration of 5 10 7 kg kg persisted for several weeks and compared to the untreated surface reduced the albedo by about 30 and increased melting by 50 particles of volcanic ash with diameters larger than about 5 m remained at or near the snow surface although many of the smaller particles flushed through the snow with the meltwater the surface albedo was not changed significantly by their removal the different behaviors of the ash and soot are probably related to the difference in their particle size distributions in relation to the thickness of water films that form the transport paths under conditions of partial saturation that are characteristic of melting snow

microfabric reconstruction via quantitative digital petrographic image analysis for weakly foliated gneisses abstract detection and documentation of petro structural features such as alignment features of minerals grains and extraction of such spatial property data are two fundamental steps for structural geology such tasks were mostly carried out manually however manual analysis is laborious and potentially biased these drawbacks are less obvious when the foliation is well developed and the amount of platy mineral is higher for samples with weakly developed foliation and low platy mineral content automatic method is required for subjective interpretation a semi automatic computerized method of 3d foliation orientation reconstruction via two dimensional petrographic shape fabric analysis from serial oriented digital microphotograph has been developed and demonstrated in this study the foliation is reconstructed by fitting a best fitting plane to the maximum modal peaks of micro textural parameters spo for different mineral groups of platy and granular minerals from each thin section on a stereonet for four coarse grained biotite gneiss samples collected along the jialie fault se tibet china regardless of platy or granular mineral aggregates the reconstructed foliations showed similar orientation within 10 angular variation to the field measurement the 10 angular variation can be maintained if the foliations are reconstructed by consecutive thin section groupings 50 angular intervals and a horizontal thin section the angular spread increased to 30 for thin section groupings with 50 to 100 angular intervals with a horizontal thin section major advantages of the computerized photometric methods demonstrated by this study are the reduction of human prejudice and obtaining quantified and repeatable data sets

contact spectroscopy for determination of stratigraphy of snow optical grain size we present a technique for in situ measurement of the vertical and spatial stratigraphic distribution of snow optical grain size with a coupled contact illumination probe and field spectroradiometer accurate measurements of optical equivalent grain size are critical for modeling radiative properties of snow such as spectral albedo and microwave emission measurements of the spectral reflectance of the snow pit surface are made at 2 cm intervals in the vertical plane under constant illumination and view geometries we invert the integral of the continuum normalization of the ice absorption feature with maximum at 1 03 mm wavelength for optical equivalent grain size using the validated model of nolin and dozier 2000 that has accuracy of 10 50 mm across the grain size range 50 900 mm results are presented for an alpine site in southwest colorado usa across the ablation season and for a greenland ice sheet site at the onset of snowmelt these results suggest that traditional measurements of grain size using a hand lens are nearly accurate only for rounded grains r 2 0 41 rmse 160 mm for polycrystals and faceted grains the hand lens approach is very inaccurate r 2 0 03 and 0 24 rmse 1206 and 1010 mm respectively we demonstrate an order of magnitude improvement in modeling of shortwave spectral albedo and net shortwave flux with contact spectroscopy measurements of grain size stratigraphy over those from a hand lens

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

non rotation of garnet porphyroblasts and 3 d inclusion trail data an example from the imjingang belt south korea abstract we describe non rotation of garnet porphyroblasts in non coaxially deformed metapelites of the imjingang orogenic belt in the middle korean peninsula the three dimensional geometry of inclusion trails within 1 2 mm garnet porphyroblasts was analyzed by serial polishing and reflected light microscopy most of the garnet porphyroblasts have straight inclusion trails of quartz and some plagioclase s i oblique to an external foliation s e serial polishing of two samples normal to mineral elongation lineation a plane and normal to s e and parallel to the lineation b plane with twenty intervals of about 0 1 mm reveals that the straight s i is a planar structure measurement of the angles between s i and s e on both planes from samples of sixteen outcrops shows that s i orientation of individual garnets is fairly constant in each sample the attitude of s i in geographic space determined by using its pitch angles on the a and b planes is more or less constant throughout the area over 6 5 km traversing normal to the strike of regional foliation the sense of asymmetry of strain shadows at the margin of garnet porphyroblasts and the s i s e relationship indicate rotation of s e rather than garnet porphyroblasts with respect to the geographic reference frame rotation of s e is also supported by a sense of shear inferred from other shear criteria all indicating a top up to the south shearing

growth and concentration of fibrous sillimanite related to heterogeneous deformation in k feldspar sillimanite metapelites in foliated k feldspar sillimanite metapelites fibrous sillimanite is commonly concentrated in folia that anastomose between lenticular pods of coarser grained aggregates rich in quartz feldspar and biotite with or without garnet cordierite and residual andalusite many of the folia appear to be limbs of crenulation microfolds the sillimanite concentrations may be due largely to the ability of fibrous sillimanite aggregates to undergo strong non coaxial deformation by grain boundary sliding fibre sliding without appreciable build up of dislocations whereas other minerals are unstable in these zones and so concentrate in lower strain interfolial zones initiation and especially concentration of the sillimanite in folia may be assisted by fluid flow and local base cation leaching whereby minerals unstable in zones of strong non coaxial strain are dissolved and removed from these zones

cryoconite on a glacier on the north eastern tibetan plateau light absorbing impurities albedo and enhanced melting cryoconite is a dark coloured granular sediment that contains biological and mineralogical components and it plays a pivotal role in geochemistry carbon cycling and glacier mass balance in this work we collected cryoconite samples from laohugou glacier no 12 lhg on the north eastern tibetan plateau during the summer of 2015 and measured the spectral albedo to explore the impacts of this sediment on surface ablation the ice melting differences between the cryoconite free removed ice and the intact layers were compared the results showed that the mean concentrations of black carbon bc organic carbon oc and total iron fe in the lhg cryoconite were 1 28 11 18 and 39 94 mg g 1 respectively bc was found to play a stronger role in solar light adsorption than oc and free fe in addition ice covered by cryoconite exhibited the lowest mean reflectance i e 1 and free fe bc and oc were estimated to contribute 1 01 0 99 and 0 76 cm d 1 respectively this study provides important insights for understanding the role of cryoconite in the glacier mass balance of the northern tibetan plateau

possible eastward extension of chinese collision belt in south korea the imjingang belt structural petrological and geochronological data from the middle korean peninsula indicate that the qinling dabie sulu collisional belt of east central china crosses the yellow sea and extends into the imjingang belt the yeoncheon complex first identified as the western imjingang belt comprises primarily north dipping metamorphic sequences 1 the northern jingok unit consisting of barrovian type metapelites and 2 the southern samgot unit consisting of calc silicate and amphibolitic rocks south vergent structures with reverse sense shearing are dominant in the jingok unit whereas late normal sense shearing is pervasive in the samgot unit and the deformed granitoid to the south these structural patterns are interpreted to correspond to extensional deformation associated with uplift following compression in a collisional belt pressure temperature p t estimates from the amphibolites suggest a high p amphibolite facies metamorphism 8 13 kbar and 630 790 c possibly evolving from eclogite facies conditions along a clockwise p t path sm nd and rb sr geochronological data suggest that the amphibolites emplaced in late proterozoic time were metamorphosed during permian triassic time

porphyroblast rotation during crenulation cleavage development an example from the aureole of the mooselookmeguntic pluton maine usa in the low pressure high temperature metamorphic rocks of western maine usa staurolite porphyroblasts grew at c 400 ma very late during the regional orogenesis these porphyroblasts which preserve straight inclusion trails with small thin section scale variation in pitch were subsequently involved in the strain and metamorphic aureole of the c 370 ma mooselookmeguntic pluton the aureole shows a progressive fabric intensity gradient from effectively zero emplacement related deformation at the outer edge of the aureole 2900 m map distance from the pluton margin to the development of a pervasive emplacement related foliation adjacent to the pluton the development of this pervasive foliation spanned all stages of crenulation cleavage development which are preserved at different distances from the pluton the spread of inclusion trail pitches in the staurolite porphyroblasts as measured in two dimensional 2 d thin sections increases nonlinearly from 16 to 75 with increasing strain in the aureole these data provide clear evidence for rotation of the staurolite porphyroblasts relative to one another and to the developing crenulation cleavage the data spread is qualitatively modelled for both pure and simple shear and both solutions match the data reasonably well the spread of inclusion trail orientations 40 75 in the moderately to highly strained rocks is similar to the spread reported in several previous studies we consider it likely that the sample scale spread in these previous studies is also the result of porphyroblast rotation relative to one another however the average inclusion trail orientation for a single sample may in at least some instances reflect the original orientation of the overgrown foliation

porphyroblast non rotation during crustal extension in the variscan lys caillaouas massif pyrenees abstract the dominant foliation s 2 in the variscan lys caillaouas massif central pyrenees france spain formed in a subvertical orientation during crustal thickening d 2 subsequent non coaxial crustal extension produced a subhorizontal crenulation cleavage s 3 whereby s 2 was folded and rotated andalusite staurolite cordierite and biotite porphyroblasts grew very early during this extension d 3 and included s 2 as straight curved and weakly crenulated inclusion trails these inclusion trails exhibit a strong subvertical preferred orientation which is independent of the local magnitude of d 3 strain the dip angle of the external main foliation s 2 or the aspect ratio and shape orientation of porphyroblasts this indicates that porphyroblasts did not rotate in the d 3 deformation field and hence preserve the orientation of s 2 at the time it was trapped in the porphyroblast relative to the bulk d 3 flow plane porphyroblasts could maintain a stable orientation in the d 3 flow due to complete accommodation of the bulk flow vorticity by heterogeneous shear strain the lack of vorticity of local volumes of zero shear strain such as porphyroblasts was balanced by concentration of shear strain in planar zones anastomosing around them it is likely that s 2 maintained a subhorizontal orientation throughout the d 3 crustal extension which would imply that porphyroblasts also remained stationary relative to the earth s surface during d 3 whereas s 2 in the deforming matrix experienced shear induced rotation a late brittle ductile folding event d 4 involving differential rigid block rotations dispersed the orientation of inclusion trails to some degree these late rotations could be corrected for by artificial unfolding of the f 4 folds

on the significance of foliation patterns preserved around folds by mineral overgrowth abstract simple inclusion trail geometries in porphyroblasts that vary symmetrically around folds suggest the porphyroblasts have rotated during folding however they do not provide proof that the porphyroblasts have rotated as such geometries may also form by overgrowth during folding this uncertainty results from the difficulty in establishing the relative ages of the fold and the porphyroblasts when the latter contain simple trails simple inclusion trail geometries in porphyroblasts that do not change around a fold remaining orthogonal to the axial plane from limb to limb suggest that the porphyroblasts have not rotated during folding however they can be rationalized as having rotated by arguing that synthetic rotation due to buckling has been exactly counterbalanced by antithetic rotation due to flexural flow if the folds vary in tightness from open to isoclinal and the trails still remain perpendicular to the axial plane this can still be rationalized by arguing for rotation during buckling balancing that due to flexural flow followed by coaxial deformation with no subsequent rotation tests of porphyroblast behaviour are only useful if they conclusively demonstrate that inclusion trail geometries around a fold are incompatible with rotation or alternatively non rotation of the porphyroblasts simple inclusion trail geometries in porphyroblasts that uniquely indicate a fold mechanism involving no rotation are those which remain parallel from limb to limb but lie oblique to the axial plane independent of limb angle particularly powerful indicators of folding mechanisms involving no porphyroblast rotation are folds containing two different porphyroblastic phases that preserve contrasting geometries for example rocks containing porphyroblasts preserving parallel trails from limb to limb in the earlier phase and symmetrically varying trails for the later phase such folds demonstrate that simple trails that vary symmetrically around a fold cannot be used as proof of porphyroblast rotation where the rotation axes of such simple inclusion trail geometries lie at a high angle to the axial plane and vary around the fold proof of porphyroblast rotation may be possible however such proof can be more readily provided using complex inclusion trails with an orthogonal and or truncational character that vary in orientation from limb to limb

distribution of pre folding linear indicators of movement direction around the spring hill synform vermont significance for mechanism of folding in this portion of the appalachians abstract three distinctly oriented sets of pre folding and one set of syn folding axes of curved inclusion trails are preserved in garnet porphyroblasts in 50 samples around the doubly plunging spring hill synform in southeast vermont over one third of the samples contain consistent changes in the trend of these axes from the core to rim since the core grew before the rim this enabled the relative timing of each set of axes to be determined from the oldest to the youngest as ne sw e w nnw sse and nne ssw the youngest trend is parallel to the axial plane of the regional folds only those samples with the latter trend have their inclusion trails connected continuously to the matrix foliation the three pre folding sets of axes have the same orientation on both limbs this consistency in orientation has significant implications for the processes operating during folding and three mechanisms are presented that could potentially explain it these involve the classic card deck model of shear folding de sitter s model of clay bricks shortening as they shear past one another and the progressive bulk inhomogeneous shortening model the relative merits of each of these models are discussed

the kinematic interpretation of obliquely transected porphyroblasts an example from the trois seigneurs massif france abstract obliquely transected porphyroblasts otps contain a straight inclusion pattern that is continuous with the external foliation but oblique in orientation otps are interpreted to form by porphyroblast growth between two phases of deformation the obliqueness of the inclusion pattern and external foliation is due to the second deformation phase and has been variously explained by porphyroblast rotation in the kinematic reference frame of bulk flow or by foliation rotation around a stationary porphyroblast the two models imply opposite sense of vorticity also loosely referred to as sense of shear to produce the same geometry and their relevance should be known if otps are to be used as sense of vorticity indicators andalusite otps in the trois seigneurs massif french pyrenees have a spool shape in three dimensions that is interpreted to result from passive overgrowth of andalusite on a spaced s 2 cleavage subsequent non coaxial d 3 flow led to development of an s 3 crenulation cleavage and the otp geometry although the porphyroblasts rotated rotation of the foliation in the kinematic reference frame of bulk flow was mainly responsible for the otp geometry this example shows that otps can indeed develop by foliation rotation in non coaxial flow similar looking otps can apparently develop in flows with opposite sense of vorticity depending on whether foliation or porphyroblast rotation is dominant the dominance of either development mechanism depends on the importance of flow partitioning and solution transfer during progressive deformation

conjugate shear folding a model for the relationships between foliations folds and shear zones abstract microstructural mapping of whole thin sections cut from two samples of micaschist containing cm scale folds plus garnet porphyroblasts has provided new insight in the relationships between folding shearing and foliation development the garnets exhibit coherent inclusion trail patterns that place important constraints on the kinematic development of both samples which are shown to be representative of coaxial versus non coaxial deformation in rocks containing a pre existing schistosity a comparison of crenulations cleavages geometries in both samples and a review of the geometry of natural and experimental multilayer folds leads to the conclusion that folding involves conjugate shearing at different scales at microscopic scales crenulation cleavages nucleate as conjugate kink or shear instabilities and develop further as a function of the macroscopic partitioning of deformation in fold hinge domains bulk coaxial deformation results in equal development of conjugate crenulations that progressively coalescence into symmetrical crenulation patterns so that macroscopically parallelism is achieved between foliation fold axial planes and long axes of strain ellipses fold limb domains represent a system of conjugate shear zones where single sets of crenulation instabilities with synthetic shearing component preferentially develop producing oblique relationships between the aforementioned elements cleavage fanning is inferred as a direct consequence of this conjugate shear origin of folds the model implies that crenulation cleavages and s c fabrics in shear zones form by analogous processes in both cases involving a component of shearing along foliation planes the development of conjugate sets of foliation planes surrounding porphyroblasts during early relatively coaxial stages of deformation explains continued gyrostatic behaviour during more advanced non coaxial stages as indicated by consistently oriented inclusion trails in the studied samples

accelerated glacier melt on snow dome mount olympus washington usa due to deposition of black carbon and mineral dust from wildfire assessing the potential for black carbon bc and dust deposition to reduce albedo and accelerate glacier melt is of interest in washington because snow and glacier melt are an important source of water resources and glaciers are retreating in august 2012 on snow dome mount olympus washington we measured snow surface spectral albedo and collected surface snow samples and a 7 m ice core the snow and ice samples were analyzed for iron fe used as a dust proxy via inductively coupled plasma sector field mass spectrometry total impurity content gravimetrically bc using a single particle soot photometer sp2 and charcoal through microscopy in the 2012 summer surface snow bc 54 50 g l fe 367 236 g l and gravimetric impurity 35 18 mg l concentrations were spatially variable and measured broadband albedo varied between 0 67 0 74 bc and dust concentrations in the ice core 2011 summer horizon were a magnitude higher bc 3120 g l fe 22000 g l and gravimetric impurity 1870 mg l corresponding to a modeled broadband albedo of 0 45 based on the measured bc and gravimetric impurity concentrations the big hump forest fire is the likely source for the higher concentrations modeling constrained by measurements indicates that the all sky 12 h daily mean radiative forcings in summer 2012 and 2011 range between 37 53 w m 2 and 112 149 w m 2 respectively with the greater forcings in 2011 corresponding to a 29 38 mm d enhancement in snowmelt the timing of the forest fire impurity deposition is coincident with an increase in observed discharge in the hoh river highlighting the potential for bc and dust deposition on glaciers from forest fires to accelerate melt

sea salt corrections and interpretation of constituent ratios in marine precipitation differentiation of sea salt and non sea salt or excess components is essential for many studies of marine aerosol and precipitation chemistry uncertainties in such calculations arise from 1 uncertainties in the composition of seawater 2 analytical uncertainties 3 the amount of dry deposited sea salt in samples 4 the validity of assuming a purely marine source for the sea salt reference species and 5 the validity of assuming no fractionation during or after production of sea salt aerosols we assessed these uncertainties and using the reduced major axis regression technique evaluated these assumptions by analyzing the composition of precipitation at amsterdam island 38 s 78 e and at bermuda 32 n 65 w precipitation on amsterdam island contained significant excess concentrations of na 2 and cl 5 relative to mg2 indirect evidence indicates that these departures from seawater ratios are probably not due to the influence of terrestrial material the excess cl was sufficient to account for approximately 20 of free acidity suggesting that scavenging of vapor phase hcl may affect the acid base chemistry of precipitation at the site volume weighted excess so42 based on na and mg2 differed by 11 a nonnegligible source of bias in estimating the wet deposition of non sea salt sulfur precipitation on bermuda contained significant concentrations of locally derived alkali and alkaline earth metals the influence of continental and non sea salt marine sources on concentrations of excess so42 was also evident these observations suggest that assumptions involved in sea salt corrections are not always satisfied and that it is therefore necessary to evaluate individual data sets using objective criteria to select the appropriate reference species

contrasts in sillimanite deformation in felsic tectonites from anhydrous granulite and hydrous amphibolite facies shear zones western canadian shield abstract the deformation behavior of crustal materials in variably hydrated metamorphic environments can significantly influence the rheological and seismic properties of continental crust optical observations and electron backscatter diffraction ebsd analyses are used to characterize sillimanite deformation behavior in felsic tectonites from two deformation settings in the athabasca granulite terrane western canadian shield under estimated conditions of 0 8 1 0 gpa 725 850 c in the cora lake shear zone the data suggest that sillimanite deformed by dislocation creep with slip in the 001 direction accompanied by subgrain rotation recrystallization where sillimanite locally remained undeformed strain was concentrated in surrounding weaker phases under hydrated conditions of 0 4 0 6 gpa 550 650 c in the grease river shear zone textures and cathodoluminescence imaging point to dissolution precipitation creep as the major deformation mechanism for sillimanite resulting in synkinematic growth of foliation parallel euhedral sillimanite in a preferred orientation with 001 parallel to the lineation the results suggest that temperature fluid content and modal mineralogy of the surrounding phases may all have significant influence on sillimanite deformation but that preferential alignment of sillimanite 001 parallel to the lineation persists regardless of contrasts in the conditions or mechanisms of deformation

metamorphism of the pelitic rocks of the snyder group in the contact aureole of the kiglapait layered intrusion labrador effects of buffering partial pressures of water the petrography and mineral chemistries of the aphebian snyder group pelitic rocks in the contact aureole of the kiglapait layered intrusion labrador reveal a rapid increase in metamorphic grade o

optical characteristics of cryoconite surface dust on glaciers the relationship between light absorbency and the property of organic matter contained in the cryoconite

microstructural relationships of sillimanite and fibrolite at broken hill australia microstructural criteria are used to distinguish prograde sillimanite formed during lower granulite facies metamorphism m 1 from late amphibolite facies m 2 fibrolite in some metapelitic schists and gneisses at broken hill australia evidence that fibrolite nucleation was after the formation of the m 1 coarse grained paragenesis is 1 replacement of perthite biotite sillimanite plagioclase garnet and cordierite by fibrolite 2 concentration of fibrolite in perthite perthite grain boundaries 3 fibrolite transecting the lamellar twins in plagioclase 4 fibrolite cutting across polygonal grain boundaries in quartz aggregates and 5 kinked prismatic sillimanite out by undeformed grains of fibrolite particle track data suggests that s 2 fibrolite zones and associated minerals are uranium bearing and that fibrolite has a higher boron content than other silicate minerals the association of highly mobile u and b with fibrolite and the microstructural data suggests that the formation of fibrolite took place under the influence of a fluid phase enriched in h 2 o uranium and boron and hydrogen metasomatism appears to be a likely mechanism in the fibrolitization of pre existing minerals

unravelling the spirals a serial thin section study and three dimensional computer aided reconstruction of spiral shaped inclusion trails in garnet porphyroblasts seventy seven spatially orientated serial thin sections cut from a single rock reveal changes in the geometry of spiral shaped inclusion trails sslts in garnet porphyroblasts the observed sits are doubly curved non cylindrical surfaces with total inclusion trail curvature decreasing systematically from the cores to the rims of porphyroblasts the three dimensional geometry of the ssits reconstructed with the aid of computer graphics shows that the orientations of spiral axes defined by the ssits are not related in any expected nor predictable way to the main foliation in the matrix this suggests continued deformation after or during the latest stages of porphyroblast growth which has important implications for the use of ssits as shear sense indicators whether the formation of ssits involves significant porphyroblast rotation with respect to a geographically fixed reference frame cannot be determined from the available data key wocds computer graphics garnet porphyroblasts serial thin sections spiral shaped inclusion trails three dimensional reconstruction

the timing and p t conditions of regional metamorphisni in the central highlands scotland the central highlands of the scottish caledonides are dominated by a sequence of poly deformed metasedimentary rocks largely belonging to the grampian and appin groups of the dalradian supergroup in the northern part of the area these are separated from a suite of variably gneissose to locally migmatitic rocks by a number of prominent mid crustal shear zones the early evolution of the central highlands is interpreted in terms of regional d1 d2 folding and n to nw directed thrusting accompanied by kyanite grade metamorphism p 7 0 8 0 kbar t 500 600 c the later stages of this event were characterized by continued ductile shearing along the pre existing shear zones under sillimanite grade metamorphic conditions p 4 7 5 9 kbar t 585 695 c the exact age of this progressive tectonothermal event remains uncertain however available geochronological data can be interpreted as indicating an entirely precambrian age c 840 800 ma this questions previously held views of an entirely caledonian age for deformation throughout the highlands

mode of formation of ablation hollows controlled by dirt content of snow on observe que des figures de fonte de neige sont importantes en presence d impuretes non solubles mais qu elles sont moins importantes pour une forte concentration d impuretes qui migrent dans les crevasses la reduction de l albedo a un faible effet sur l ablation

light absorbing impurities in snow cover across northern xinjiang china light absorbing impurities lais e g black carbon bc organic carbon oc mineral dust md deposited on snow cover reduce albedo and accelerate its melting northern xinjiang nx is an arid and semi arid inland region where snowmelt leads to frequent floods that have been a serious threat to local ecological security there is still a lack of quantitative assessments of the effects of lais on snowmelt in the region this study investigates spatial variations of lais in snow and its effect on snow albedo radiative forcing rf and snowmelt across nx results showed that concentrations of bc oc only water insoluble oc md ranged from 32 to 8841 ng g 1 77 to 8568 ng g 1 and 0 46 to 236 g g 1 respectively weather research and forecasting chemistry model suggested that residential emission was the largest source of bc snow ice and aerosol radiative modelling showed that the average contribution of bc and md to snow albedo reduction was 17 and 3 respectively rf caused by bc significantly exceeded rf caused by md in different scenarios changes in snow cover duration scd caused by bc and md decreased by 1 36 0 61 to 6 12 3 38 d compared with md bc was the main dominant factor in reducing snow albedo and scd across nx

the accumulation regime of blue glacier u s a 1914 96 precipitation at 2050m on blue glacier was measured daily from august 1957 through july 1958 its correlation with a nearby lowland station with a good long term 1914 1996 record is used to estimate precip itation on the glacier over that entire period average annual precipitation on blue glacier is 4500 mm water equivalent snowfall depends on the joint distribution of precipitation and temperature over the period 1948 96 when twice daily radiosonde observations are available temperature at any eleva tion on the glacier is interpolated in the radiosonde profile to partition the precipitation as either rain or snow daily partitioning is prefered especially during spring and autumn storms when averaging over longer periods may substantially under or over estimate snowfall on the glacier prior to 1948 snowfall is estimated from the mean over 1948 96 in a particular month and elevation of the fraction of the precipitation falling as snow the standard error in the october may snowfall at 2100m is estimated to be 250 mm water equivalent during the radiosonde era 1948 96 and 350 mm prior to then for the first ten or so years after mass balance measurements began at blue glacier 1957 precipitation increased and winter temperature at 850mb about 1450 m decreased but since then the trends have reversed the combined eect increasing snowfall until 1965 and decreasing since closely parallels measured mass changes of blue glacier when the average vertical profile of total annual snowfall is subjected to a hypothetical 1 k warming the resulting reduction in snowfall is greatest at the glacier terminus and decreases upglacier the average over the entire glacier is 300 mm water equivalent

porphyroblast microstructures a review of current and future trends many recent papers show how porphyroblast microstructures play an important role in a wide range of structural and metamorphic studies this paper reviews ten current applications of these microstructures 1 porphyroblast growth timing criteria 2 tracking progressive foliation development relative to changing metamorphic conditions 3 timing of pluton emplacement relative to deformation and metamorphism 4 finite longitudinal strain determinations 5 kinematics and porphyroblast rotation 6 use of linear fabrics preserved in porphyroblasts 7 porphyroblasts and folding mechanisms 8 inclusion trail orientations and orogenic processes 9 inferring shear strain rates from porphyroblast growth rates and 10 in situ age determinations although there is still no concensus on the interpretation of some porphyroblast microstructures a bright future lies ahead as traditional and newly developed techniques of microstructural analysis are combined with modern chemical and microprobe techniques to provide an increased understanding of the relationships between deformation and metamorphism in a wide range of metamorphic settings

porphyroblast inclusion trail orientation data eppure non son girate extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non coaxial ductile deformation of the matrix subsequent to their growth this has been demonstrated for all tectonic environments so far investigated the work also has provided new insights and data on metamorphic structural and tectonic processes including 1 the intimate control of deformation partitioning on metamorphic reactions 2 solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones and relative plate motion and 3 a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens

parageneses and th u distributions among allanite monazite and xenotime in barrovian type metapelites imjingang belt central korea the paragenetic relationships and th u distributions among allanite monazite and xenotime were investigated in a progressive sequence of garnet to kyanite zone metapelites of the imjingang belt korea allanite is predominant in the garnet and staurolite zones whereas monazite and xenotime predominate in the kyanite zone epidote grains in the lower garnet zone are commonly zoned from allanite core to relatively y rich rare earth element ree epidote to clinozoisite rim although both ree epidote and clinozoisite disappear in higher grade metapelites moreover allanite and ree epidote often contain minute inclusions of thorium silicate the isogradic distributions and similarity of ree patterns between allanite and monazite suggest that the latter has grown at the expense of the former in addition the discontinuous th zoning in monazite is apparently inherited from heterogeneous th distribution and thorium silicate inclusions in allanite thus thorium silicate possibly provided the additional th and u necessary for the monazite formation paragenetic relationships of allanite and monazite inclusions within various index minerals suggest that at amphibolite facies conditions allanite is stable at higher pressures than monazite xenotime grains in the staurolite zone are rarely produced by the breakdown of clinozoisite and ree epidote whereas those in the kyanite zone are grown primarily at the expense of garnet incorporation of th and u into monazite and xenotime is governed mainly by the brabantite and thorite substitutions respectively taken together our results suggest that the allanite to monazite transformation is primarily responsible for the distributions of rees th and u among metapelitic phases and that the xenotime formation was facilitated by the contribution from major silicates particularly garnet

preferred orientation of planar microstructures determined via statistical best fit of measured intersection lines the fitpitch computer program the fitpitch computer program allows characterisation of preferred orientation of planar microstructures in a rock from the orientations of their intersection lines on different sections measured pitch or strike angles of such intersection lines are fitted to the theoretical intersection lines of a single model plane or a combination of two or three model planes the degree of fit is quantified in terms of the deviation between natural and theoretical intersection lines normalised by uniform data a first application is described concerning porphyroblast inclusion trails whose orientation in 28 samples from the variscan iberian massif was measured analysis of these data illustrates how the method can be used to quantify preferred orientation of relict foliations contained in a group of porphyroblasts and how this complements existing techniques for determining foliation intersection axes fia in porphyroblasts a second described application deals with previously published orientation data for microfracture trace lines in quartz grains of a variscan granite in the rhine graben qualitatively established best fit planes derived originally from this data are compared with the numerically established planes using the fitpitch program and discussed in terms of the advantages and potential limitations of the method q 2002 published by elsevier science ltd

the ardara pluton ireland deflating an expanded intrusion abstract the ardara pluton north western ireland is a circular monzodiorite granodiorite intrusion with a tail it has been regarded as a typical example of a pluton emplaced entirely by expansion balloning after initial intrusion most of the foliation in the pluton is magmatic with weak superimposed solid state features apart from a thin rind of strong solid state deformation the solid state deformation in the pluton appears to be largely if not entirely of post intrusive tectonic origin flattened microgranitoid enclaves a concentric magmatic flow foliation and compositional zoning in the pluton are consistent with some expansion of magma prior to crystallization however strains in the wall rocks indicate that only a small amount 25 38 of the volume of the pluton can be ascribed to ballooning this relatively small amount of expansion could account for a observed structural concordance and strong syn metamorphic deformation in the aureole b flattening of microgranitoid enclaves magma globules in the pluton and possibly c a small amount of solid state deformation in the pluton during lock up of magmatic flow evidence of solid state deformation superimposed on a strong magmatic flow foliation in the tail of the pluton implies that a fault was active during emplacement and may have assisted the intrusion further space for the pluton may have been made by a complex interaction of processes many of which cannot be constrained from a two dimensional cross section through the area these possibilities highlight the limitations of attempting to constrain emplacement mechanisms on the sole basis of structures adjacent to plutons

temporal and spatial variations in spectral reflectance and characteristics of surface dust on gulkana glacier alaska range spectral reflectances in the visible to near infrared wavelength range 350 1050 nm were measured on the surface of gulkana glacier alaska range alaska usa at six different elevations from may to september 2001 the measurements showed variable spectral reflectances on the glacier surface and the spectra changed over time and elevation the spectra in may were those of a typical wet snow surface the reflectance ranged approximately from 0 4 to 0 8 and generally decreased as the wavelength increased as snowmelt proceeded the reflectance gradually fell and specific absorptions appeared in the spectrum at wavelength ranges of 400 600 and 670 680 nm corresponding to a red snow surface due to snow algal bloom as the ice surface was exposed the spectrum finally shifted to a lower 0 1 0 4 and flat reflectance curve typical of an ice surface contaminated with dust analyses of the dust on the glacier surface showed that its quantity and characteristics changed spatially and seasonally and were correlated with spectral albedo the results showed that the temporal and spatial variations in spectral reflectance on this glacier are due not only to physical properties of the glacier surface but also to biogenic materials on the surface e g red colored snow algal cells and cryoconite

porphyroblast rotation eppur si muove in a number of recent papers the theory has been postulated that porphyroblasts as a rule do not rotate with respect to geographical coordinates and can be used to determine the original orientation of older foliations complex inclusion patterns in spiral garnets have even been used to advocate a new model of orogenesis involving several alternating phases of horizontal shortening and extension critical assessment of the assumptions and data used to support the theory of irrotational porphyroblasts reveals numerous flaws millipede structures used as proof for flow partitioning can also form by other flow geometries evidence quoted to support irrotational behaviour of porphyroblasts is unsound porphyrobl asts do occur in sets with a preferred orientation of the internal foliation trace but these cannot be shown to represent original orientations microstructures which resemble truncation planes in spiral garnets are used as evidence that these structures developed by several phases of deformation and as proof for periodic extension and horizontal shortening in orogenesis they can however also be explained by intermittent growth of a rotating porphyroblast during a single phase of deformation finally porphyroblast sets in which orientation is a function of aspect ratio indicate that porphyroblast rotation with respect to kinematic axes does occur in at least some situations

polymetamorphism and ductile deformation of staurolite cordierite schist of the bossost dome indication for variscan extension in the axial zone of the central pyrenees the bossost dome is an e w trending elongated structural and metamorphic dome developed in cambro ordovician metasedimentary rocks in the variscan axial zone of the central pyrenees a steep fault separates a northern half dome cored by massif granite from an e w trending doubly plunging antiform with granitic sills and dykes in the core to the south the main foliation is a flat lying s 1 2 schistosity that grades into a steeper dipping slaty cleavage at the dome margins three major deformational and two metamorphic phases can be differentiated s 1 2 schistosity is an axial planar cleavage to w vergent recumbent folding that probably occurred in mid westphalian time peak regional metamorphism m 1 is characterized by static growth of staurolite and garnet following thermal relaxation of the previously thickened crust strong non coaxial deformation recording uniform top to the se extension during d 2 a is preserved in staurolite garnet schists in a 1 5 km thick shallowly se dipping zone in the southeastern dome a 500 m thick contact aureole m 2 was imprinted on the regionally metamorphosed rocks following the intrusion the bossost granite during d 2 b more coaxial deformation prevailed during synkinematic growth of m 2 phases in the inner part of the contact aureole around the northern part of the dome where it obliterated d 2 a fabrics progressive non coaxial deformation continued in the southeastern antiform and is recorded by late synkinematic growth of cordierite successive overprinting of the m 1 staurolite garnet assemblage by andalusite and cordierite of m 2 is preserved in the southern part the assemblage muscovite cordierite staurolite biotite is considered metastable given the low mn and zn contents of staurolite and cordierite and interpreted as the result of prograde metamorphism during decompression p t conditions during m 2 were approximately 3 kbar and 600 c pervasive crenulations and mesoscopic to regional southerly verging folds are the result of d 3 nne ssw compression post dating ductile deformation and contact metamorphism polymetamorphic assemblages of the bossost dome preserve a regionally confined zone of ese directed extensional shearing within an overall n s compressional setting exact timing of extensional shearing is not known but can be constrained by recumbent folding during the mid westphalian and granitic intrusions which confine it to late carboniferous time c 305 ma crustal scale flat lying extensional shear zones with similar orientation and time frame are observed in the hospitalet massif of the eastern axial zone this suggests that crustal extension though probably restricted by regional strain partitioning over orthogneiss or intruding granitic bodies within an overall compressive setting was not uncommon in late carboniferous time in the axial zone of the pyrenees

climate change and forest fires synergistically drive widespread melt events of the greenland ice sheet in july 2012 over 97 of the greenland ice sheet experienced surface melt the first widespread melt during the era of satellite remote sensing analysis of six greenland shallow firn cores from the dry snow region confirms that the most recent prior widespread melt occurred in 1889 a firn core from the center of the ice sheet demonstrated that exceptionally warm temperatures combined with black carbon sediments from northern hemisphere forest fires reduced albedo below a critical threshold in the dry snow region and caused the melting events in both 1889 and 2012 we use these data to project the frequency of widespread melt into the year 2100 since arctic temperatures and the frequency of forest fires are both expected to rise with climate change our results suggest that widespread melt events on the greenland ice sheet may begin to occur almost annually by the end of century these events are likely to alter the surface mass balance of the ice sheet leaving the surface susceptible to further melting

sequential porphyroblast growth and crenulation cleavage development during progressive deformation abstract six stages of crenulation cleavage development during a single deformation event d2 can be recognised in both matrix and porphyroblast inclusion trails in the robertson river formation n e australia these stages progress from undeformed to crenulation and differentiated crenulation of s1 through development of differentiated crenulation cleavage s2 and differentiated schistosity s2 to homogeneous foliation s2 these rocks underwent prograde metamorphism during d2 and chloritoid garnet staurolite andalusite and sillimanite isograds have been mapped most rocks are rich in porphyroblasts which commonly contain well defined inclusion trails the geometry of these trails varies from one mineral type to the next depending on the timing of porphyroblast growth relative to the stage of crenulation cleavage development in the schistose matrix the deformation history involved progressive bulk inhomogeneous shortening and the strain is very heterogeneous on all scales partly as a consequence of this hence each of the six stages of crenulation cleavage development formed locally at various times during d2 therefore if a porphyroblast grew late in the deformation it could overgrow all stages of crenulation cleavage development including the very early ones the temperature increased during metamorphism in any one locality and consequently some porphyroblasts overgrew others that were unstable in the new conditions preserving them from destruction hence the precise timing of mineralogical reactions deduced from isograds and mineral chemistry relative to the stages in schistosity development can also be determined in the andalusite zone the sequence of porphyroblasts in decreasing order of age is biotite garnet biotite staurolite andalusite dissolution of garnet occurred during growth of staurolite and especially andalusite and dissolution of staurolite accompanied andalusite growth

on the internal geometry of mylonite zones mylonite zones are generally characterized by abrupt and very large strain transitions which commonly result in excessively anastomosing schistosities on a wide range of scales when compared with nonmylonitic foliations this geometry is very susceptible to remodification during progressive mylonitization resulting in unusual and complex fold lineation and foliation geometries and interrelationships open folds of the mylonitic foliation with axes parallel to the stretching lineation in the surrounding mylonite cannot have formed by the rotation of fold axes through a large angle within their axial planes as has been usually proposed for isoclinal and sheath folds in mylonitic zones open folds initiate with axes parallel or close to the stretching lineation due to the geometric effects of folding a mylonitic foliation which anastomoses around an ellipsoidal pod of less deformed material this initial geometry also allows the generation of fold axes curved within their axial plane through 1800 about the stretching lineation at the time of nucleation successive mylonitic foliations develop during this folding and refolding process with boundaries that truncate and isolate earlier fold hinges and portions of fold limbs as a consequence stretching and intersection lineations can vary from plane to plane through the mylonite zone although careful examination often reveals a weak overprinting stretching lineation parallel to the bulk movement direction for the whole zone fold asymmetry in mylonite zones is a potential indicator of shear sense across a zone if the fold axes lie at an angle to the bulk stretching lineation direction in such circumstances however a single asymmetry projected onto a plane perpendicular to the mylonitic foliation and containing the bulk stretching lineation can indicate either sense of shear depending on a variety of factors these include whether the foliation folded is primary or mylonitic and in the latter case whether the mylonite zone formed with a steep dip and horizontal stretching lineation or in some other orientation the most satisfactory sense of shear indicator is the asymmetry of s and c planes

the internal inclusion trail geometries preserved within a first phase of porphyroblast growth the inclusion trail geometry within a first phase of porphyroblast growth can differ significantly from that preserved by further enlargement because the porphyroblast forms a rigid mass up against which the rock preferentially strains during ensuing events the geometry of the first overgrown inclusion trails is affected by their primary orientation including any pre existing curvature combined with any heterogeneous rotation of this foliation about the developing stretching lineation this can impact the apparent timing of foliation intersection inflection axes preserved within porphyroblasts fias that nucleated during the development of a sub horizontal foliation but is readily resolved 3 d computer analysis of sigmoidal inclusion trails reveals that the asymmetry method for fia determinations is unaffected by the cut location relative to the porphyroblast core significantly perfect spiral inclusion trail geometries can be produced from a sigmoidal shape in cuts up 30 away from the fia therefore since fias in most porphyroblasts bear no relation to matrix structures there is a 17 chance that thin sections cut relative to the foliation lie within 30 of a fia and could contain such an apparent spiral fias maintain consistent trends for the first phase of porphyroblast growth accompanying horizontal bulk shortening but may vary in plunge fias have sub horizontal plunges for porphyroblasts nucleating during gravitational collapse but may vary in trend for all periods of porphyroblast regrowth the data available indicates that fias remain consistently trending and sub horizontal until the relative direction of plate motion causing orogenesis changes

partitioning of deformation along an orogen and its effects on porphyroblast growth during orogenesis an identical succession of foliation inflection intersection axis trends in porphyroblasts fias is present in three separate areas affected by acadian deformation and metamorphism along 130 kms of the appalachians from east central vermont to north central massachusetts the fias trend successively nw se sw ne w e nnw sse and ssw nne and appear to have formed during the same succession of deformations which have been dated in se vermont as follows not yet dated pre 425 ma 425 to 404 ma 404 to 385 ma and 385 to 360 ma respectively the two areas that are furthest apart in east central vermont and north central massachusetts have strikingly similar total distributions of fias in garnet porphyroblasts that show a somewhat inverse relationship to those observed in the chester athens dome area of se vermont that separates them that is the number of samples containing the first formed fia set is greatest for the two regions lying furthest apart and decreases in younger sets whereas the number of samples containing the first fia set is the least in the central region and increases for more recently developed sets partitioning of deformation into zones of progressive shearing and shortening has been demonstrated to control the sites of development of differentiated crenulation cleavage versus porphyroblast growth and sites of porphyroblast growth on one limb of a regional fold versus the other we argue that partitioning of the deformation around competent feldspathic gneiss bodies at an orogen scale produced the variation in the number of samples containing the various fia sets between the central and outer areas described above porphyroblasts most commonly grew during sw ne directed shortening to the north and south of the chester athens dome region of the appalachians but only rarely grew in the latter region this suggests that deformation at this time partitioned around an outlier of competent basement feldspathic gneiss that underlies the chester athens dome region and this protected the rocks above and in the strain shadow to the nw and se from the effects of the great bulk of the deformation that occurred over the period of time during which nw se trending fias formed we attribute the increase in the number of samples containing progressively younger fias in the chester athens dome area during subsequent periods of nw se n s wsw ene and wnw ese directed shortening to the rise in temperature and pressure recorded in the rocks above the chester athens dome with peak conditions occurring during the development of the nnw sse oriented fia set between 404 and 385 ma as the temperature and pressure increased the gneiss below would have become less competent allowing the deformation associated with the succession of fia sets to partition more pervasively through the dome core this provided more sites for porphyroblast nucleation and growth and hence the number of samples recording these fia sets increased the concomitant decrease in the number of samples in which porphyroblasts grew in the rock within the areas to the north and south with successive fias possibly resulted from a progressive increase in competency of these rocks as the number of porphyroblasts increased

lack of porphyroblast rotation in noncoaxially deformed schists from petrel cove south australia and its implications abstract inclusion trails representing an s 1 cleavage demonstrate the lack of porphyroblast rotation during subsequent highly non coaxial deformations the pelitic schists of the kanmantoo group at petrel cove south australia contain two generations of porphyroblasts the first one consists of cordierite porphyroblasts that formed early in d2 and contain straight to slightly sigmoidal inclusion trails of s 1 the second generation consists of andalusite porphyroblasts that overgrew crenulated s 2 late during d3 several hundred inclusion trail traces from cordierites measured from oriented specimens taken throughout a strongly folded area show a horizontal great circle distribution when plotted and contoured on a stereographic projection hence s 1 was planar and horizontal prior to d2 s 1 measurements on limbs and hinges of a mesoscale d2 foldpair show that folding had little effect on porphyroblast orientation as the s 1 orientation remained constant and subhorizontal around the fold hence porphyroblasts have not rotated during any of the non coaxial deformations accompanying and following their growth this is interpreted as a result of the partitioning of the deformation around them s 1 in the matrix has been totally destroyed by the formation of s 2 as a fully differentiated crenulation cleavage what has previously been regarded as inconsistent senses of shear recorded by porphyroblasts around folds is resolved by the fact that the matrix foliation rotated rather than the porphyroblasts due to the effects of deformation partitioning the presence of a subhorizontal s 1 foliation suggests horizontal movements e g thrusting or detachment faulting during the earliest phase of the adelaidian orogeny