kinematics of rock flow in a crustal scale shear zone implication for the orogenic evolution of the southwestern hellenides combined shear sense criteria finite strain data and vorticity analyses were used to study the deformation path in a curved crustal scale shear zone phyllite quartzite series of the southwestern hellenides the results are combined with data on the structural evolution of a cover nappe pindos thrust belt to provide new insights into the orogenic evolution of this region ductile deformation within the phyllite quartzite series was associated with a top to the west southwest shearing and was partitioned into two structural domains a root zone and a frontal domain the root zone is characterized by vertical coaxial stretching high strain and upward movement of the material while the frontal domain comprises simple shear deformation at the base and pure shear at the top this pattern suggests superposition of pure shear on simple shear deformation and implies tectonic extrusion of the material from the root zone the initiation of brittle deformation in the pindos thrust belt was associated with westward translation above the sub horizontal pindos thrust later as the mountain range elevated normal faulting at high altitudes and migration of thrusting to the west occurred while east directed folding and thrusting in the belt started to the east according to the proposed model crustal thickening was taking place throughout the oligocene and early miocene including the subduction of the apulian beneath the pelagonian microcontinent and the intracontinental subduction of the phyllite quartzite series during the lower miocene vertical buoyancy forces led to the successive steepening of the shear zone and the simultaneous duplexing of its basement facilitating tectonic extrusion of the material from its root zone finally an indentation process caused vertical expulsion of the orogenic wedge and gravity collapse in the brittle crust

the limitations of three dimensional kinematic vorticity analysis abstract the kinematic vorticity number wk can be calculated for three dimensional as well as two dimensional geologic deformations for steady state deformations wk can be correlated to and analyzed in terms of finite strains the analysis shows that assumptions commonly made for two dimensional deformations are not applicable to three dimensional deformations a single wk describes an infinite number of three dimensional deformations further even knowledge of flow apophyses orientation instantaneous stretching axes orientation and or wk are not sufficient to describe deformation three dimensional deformations also require knowledge of the deformation type or boundary conditions of deformation e g transpression hence in addition to being difficult to estimate the value of knowing wk for three dimensional deformations is greatly reduced compared with plane strain the most useful methods of determining wk from naturally deformed rocks are presented

thermodynamics of the amphiboles ca mg fe2 quadrilateral a thermodynamic model has been developed and calibrated for monoclinic and orthorhombic amphiboles compositionally contained within the ca mg fe 2 amphibole quadrilateral the model incorporates the energetic consequences of cation ordering of fe 2 and mg over nonequivalent sites in the crystal structure and accounts for the temperature pressure and compositional dependence of the orthorhombic monoclinic phase transition calibration is based on previously published work on the thermodynamic properties of fe 2 mg amphiboles and tremolite and experimental cation ordering data along with solvus width and tieline orientations of natural coexisting amphiboles in the quadrilateral among derived parameters is the enthalpy of formation of end member ferroactinolite 10534 966 kj mol a calculated femg 1 isopotential solvus at mid composition in the quadrangle agrees well with a revised calibration of experimental data from cameron 1975 the solvus is not strongly asymmetric and narrows with increasing fe mg ratio and temperature phase relations along the mg and fe sides of the quadrilateral are compared and contrasted cummingtonite anthophyllite phase relations are shown in the t x f e plane with and without coexisting calcic amphibole the breakdown reactions of quadrilateral amphiboles to assemblages of two pyroxenes olivine quartz and h 2 o are depicted as functions of temperature pressure composition h 2 o activity and oxygen fugacity some highlights of their relevance to metamorphic and igneous systems are discussed

strain models within spreading nappes abstract internal strain within nappes and thrust sheets is especially important in the understanding of emplacement mechanisms in this paper strain patterns within spreading nappes are investigated theoretically and experimentally three types of spreading nappe are distinguished using various boundary conditions spreading gliding spreading and extruding spreading nappes each type is placed in its proper natural environment strain components and strain gradients are summarized from the use of scale models performed with analogue materials mathematical computations from experimental modelling allow the calculation of 1 1 the schistosity trajectories in vertical flow planes 2 2 the relationship between stretch and transport direction and 3 3 the spatial distribution of different types of strain ellipsoid these provide some tests which make it possible to demonstrate in the field whether nappes are or are not gravity induced finally some field examples from the central alps and the pyrenees are briefly discussed they provide good support to the strain models presented in the present paper

strain path partitioning within thrust sheets microstructural and petrofabric evidence from the moine thrust zone at loch eriboll northwest scotland abstract quartz c axis fabrics and microstructures have been investigated within a suite of quartzites collected from the loch eriboll area of the moine thrust zone and are used to interpret the detailed processes involved in fabric evolution the intensity of quartz c axis fabrics is directly proportional to the calculated strain magnitude a correlation is also established between the pattern of c axis fabrics and the calculated strain symmetry two kinematic domains are recognized within one of the studied thrust sheets which outcrops immediately beneath the moine thrust within the upper and central levels of the thrust sheet coaxial deformation is indicated by conjugate mutually interfering shear bands globular low strain detrital quartz grains whose c axes are aligned sub parallel to the principal finite shortening direction z and quartz c axis fabrics which are symmetric both in terms of skeletal outline and intensity distribution with respect to mylonitic foliation and lineation non coaxial deformation is indicated within the more intensely deformed and recrystallized quartzites located near the base of the thrust sheet by single sets of shear bands and c axis fabrics which are asymmetric with respect to foliation and lineation tectonic models offering possible explanations for the presence of kinematic strain path domains within thrust sheets are considered

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

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

characteristics of mesospheric gravity waves over antarctica observed by antarctic gravity wave instrument network imagers using 3 d spectral analyses we have obtained horizontal phase velocity distributions of the gravity waves around 90 km from four antarctic airglow imagers which belong to an international airglow imager instrument network known as angwin antarctic gravity wave instrument network results from the airglow imagers at syowa 69 s 40 e halley 76 s 27 w davis 69 s 78 e and mcmurdo 78 s 167 e were compared using a new statistical analysis method based on 3 d fourier transform matsuda et al 2014 for the observation period between 7 april and 21 may 2013 significant day to day and site to site differences were found the averaged phase velocity spectrum during the observation period showed preferential westward direction at syowa mcmurdo and halley but no preferential direction at davis gravity wave energy estimated by i i was 5 times larger at davis and syowa than at mcmurdo and halley we also compared the phase velocity spectrum at syowa and davis with the background wind field and found that the directionality only over syowa could be explained by critical level filtering of the waves this suggests that the eastward propagating gravity waves over davis could have been generated above the polar night jet comparison of nighttime variations of the phase velocity spectra with background wind measurements suggested that the effect of critical level filtering could not explain the temporal variation of gravity wave directionality well and other reasons such as variation of wave sources should be taken into account directionality was determined to be dependent on the gravity wave periods

orogenic evolution of the hellenides new aspects this progress report is based on investigations of the tectonometamorphic development of crystalline complexes and is restricted to a few key problems of the hellenides these results reveal the mechanisms of intracratonic tectonics remobilization of continental crust and intracrustal detachment throughout the evolution of the hellenides

proto polymorphs of jimthompsonite and chesterite in contact metamorphosed serpentinites from japan proto polymorphs of jimthompsonite and chesterite occur in metamorphosed serpentinites from two japanese ultramafic complexes the lattice constants of the proto triple chain silicate measured by x ray diffraction are a 0 93605 208 b 2 72560 588 and c 0 53160 89 nm whereas those of the mixed double and triple chain silicate are a 0 94202 78 b 4 54402 392 c 0 53440 45 nm and 90 026 18 the lattice constants and systematic extinctions revealed by selected area diffraction patterns are consistent with proto triple chain silicate pbcn and mixed double and triple chain silicate a 2 m am but not with the ortho and clino polymorphs high resolution transmission electron microscopy 016 images of the triple chain silicate and 0 1 15 images of the mixed chain silicate indicate they have a x configuration proto forms of wide chain pyriboles might be geologically widespread

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

chemistry of springs across the mariana forearc shows progressive devolatilization of the subducting plate abstract cold springs upwelling through large serpentinite mud volcanoes in the outer half of the mariana forearc provide a unique window into processes of devolatilization of the subducting pacific plate we have sampled upwelling pore waters with lower chlorinity than seawater from six sites on five serpentinite mud volcanoes by conventional gravity and piston coring by push coring from the rov jason by drilling on odp legs 125 and 195 and by manned submersible the sites range from 13 47 n to 19 33 n and 52 to 90 km from the mariana trench axis corresponding to approximate depths to the top of the downgoing plate of 16 to 29 km the composition of the springs varies systematically over this distance nearer the trench the upwelling waters have much higher ca and sr than seawater and much lower carbonate alkalinity sulfate na cl k rb and b farther from the trench the waters show the opposite trends relative to seawater chlorinity is consistently lower than in seawater and shows large variations that are not systematic with distance from the trench cs is consistently higher than in seawater and increases with distance from the trench all of the waters have high ph and are heavily depleted in mg si li f and 87sr 86sr relative to seawater they tend to be enriched in o18 o16 except for odp drilling none of the cores was long enough to produce an asymptotic compositional trend with depth we have inferred the end member compositions of the upwelling waters by extrapolation against mg at two sites we were able to compare data from gravity cores with data from drill cores or push cores collected at springs to estimate the effects of reactions that occur at shallow depth below the seafloor on mixing of the upwelling waters with seawater these effects are different for sites high in dissolved ca nearer the trench vs those high in alkalinity farther from the trench common to both are large losses from solution of 1 ca as caco3 and in exchange for na 2 mg in exchange for na or ca and as brucite 3 sulfate probably reduced by microbes or possibly precipitated as gypsum 4 sr ba si and f na is consistently leached from the solids into solution whereas k and o18 o16 are relatively unreactive we infer that the upwelling waters are uniformly saturated with caco3 and that the excess h2o and the trends in ca sr alkalinity and sulfate with distance from the trench result from introduction of h2o and dissolved carbonate and sulfate from an external source the sediment and altered basalt at the top of the subducting plate the concurrent trends in na cl b cs and especially k and rb indicate that these species originate from the top of the subducting plate in response to increasing temperature these systematic variations across the outer forearc imply that the solutions ascend more or less vertically from the source region and do not travel long distances laterally along the decollement before ascending based on leaching of k the 150 c isotherm is crossed approximately beneath big blue seamount at a depth of 22 km below the seafloor 70 km behind the trench by this point it appears that carbonate dissolution has joined dehydration as a significant process at the top of the subducting plate

the collision tectonics of the southern greek neotethys continental collision in the aegean area has produced a collage of micro continental blocks which were accreted to the active margin of eurasia in early tertiary times studies undertaken in the argolis peninsula of southern greece located at the southern end of the pelagonian continental terrane confirm that this block was rifted from gondwana in mid triassic times by mid jurassic times at the latest actively spreading oceanic basins had opened in both the pindos and vardar zones on either side of this block identification of late cretaceous oceanic basalts within an accretionary complex in the eastern argolis peninsula extends the history of the neotethys beyond late jurassic ophiolite emplacement previously believed to be the result of continental collision the cretaceous ocean basins were relict jurassic features as no rifting event is known which can account for their formation following ophiolite obduction after a phase of late cretaceous oceanic spreading in the eastern vardar oceanic basin early tertiary collision occurred as a result of northeast dipping subduction along the eastern margins of both pindos and vardar branches of the neotethys two distinct nappe emplacement vectors are identified in the argolis peninsula after accounting for neotectonic rotations these are interpreted to reflect sw directed orthogonal collision in the west and nw directed emplacement in the east resulting from tranpressional collision along the southern end of the pelagonian block

intracontinental wedging and post orogenic collapse in the mesohellenic trough the mesohellenic trough is a 130 km long and about 30 km wide subsiding area which contains a thick sequence of well exposed late cenozoic post orogenic sediments this intermontane basin located at the contact between the apulian and pelagonian collided margins provides a good example of the characteristics needed to study the chronology of late orogenic intracontinental structures

formation conditions for triple chain silicates since the first report of triple chain silicates in 1977 there has been considerable uncertainty about their formation in nature primarily concerning whether they are stable minerals or an intermediate step in the formation of other chain or sheet silicate minerals the lack of thermochemical data and relevant experimental studies for any triple chain silicate has impeded establishment of their thermodynamic stability relative to other minerals here we combine recently reported thermochemical data for a sodium analog of the triple chain silicate clinojimthompsonite na cjt with existing data for various common minerals i e enstatite talc anthophyllite and chrysotile we also present new experimental data to show that na cjt should form stably at typical metamorphic conditions of 0 2 gpa and 450 c ion activity vs ph diagrams calculated at 100 300 c and 0 1 gpa show that na cjt could form by reaction between primary igneous minerals enstatite forsterite in oceanic harzburgite and seawater at temperatures up to 300 c however formation of na cjt from harzburgite that has been altered to talc and chrysotile is not expected to occur except at the unusually high ph conditions observed for forearc serpentine mounds estimates of the thermochemical properties of the na free end member clinojimthompsonite mg 10 si 12 o 32 oh 4 suggest that it also should form from the primary mineralogy of harzburgite at temperatures and si concentrations typically observed for various oceanic hydrothermal and geothermal systems but probably not from ultramafic rock already hydrated to serpentine

the use of mohr circles to describe non coaxial progressive deformation abstract mohr circles are useful in strain analysis but are also potentially powerful tools to translate geological fabric data into tensors describing the deformation and to reconstruct flow parameters this paper shows how mohr circles can be used to visualize the effects of variable flow parameters such as stretching rate volume change rate and vorticity number on parameters of cumulative deformation as described by the position gradient tensor a mean vorticity number is introduced as a deformation parameter besides finite cumulative strain and volume change

high resolution tem study of jimthompsonite chesterite and chain width disorder in archean ultramafic rocks from isua west greenland jimthompsonite and chesterite occur as intergrowths within anthophyllite up to a few millimeters across in talc magnesite schist from the 3800 ma isua supracrustal belt west greenland pyribole lamellae span the entire intergrowth width and have their own crystal faces the schist is strongly foliated and pyribole intergrowths are aligned with this foliation indicating broad synchronicity among metamorphic deformation recrystallization and pyribole formation chain width errors polytypic disorder zipper terminations displacive planar faults replacement products by sheet silicates polygon shaped cavities cavity filling materials and low angle grain boundaries were revealed by hrtem based on cross cutting relationships the order of the formation of these defects was determined pyribole intergrowths formed prior to displacive planar faults and cavity filling materials fine sheet silicates replaced pyriboles or filled cracks after the pyribole intergrowth formation no obvious reaction or replacement products by talc or chlorite were confirmed at the interface between pyriboles and optically recognizable large sheet silicates suggesting that fine sheet silicates replacing pyriboles formed later than talc and chlorite polysomatic and polytypic lamellae may have grown simultaneously because the lamellae cross cut each other and one does not affect the formation of the other the possible reaction fronts that separate jimthompsonite or chesterite from anthophyllite were not found in 001 hrtem images of our samples instead narrow jimthompsonite and chesterite lamellae that break termination rules were commonly found these textural features can be better understood as a simultaneous growth of jimthompsonite chesterite and anthophyllite and not as a retrograde reaction product of anthophyllite

sense of nappe emplacement from quartz c axis fabrics an example from the betic cordilleras spain preferred crystallographic orientation patterns fabrics in zones of ductile deformation beneath nappes are a potentially useful indicator of the sense of nappe translation quartz c axis fabrics from a shear zone beneath the pile of higher betic nappes in the betic cordilleras spain have distinctly asymmetric topologies revealed by constructing a fabric skeleton these skeletons closely resemble those produced by computer simulations of quartz fabric development basedon taylor bishop hill theory the fabric asymmetry indicates a northerly sense of transport for the nappes consistent with field evidence from the same area analyses of both c and a axis fabrics based on asymmetric intensity distributions within the fabric give equivocal results and may reflect the presence of earlier preferred orientation patterns predating nappe emplacement