microstructural deformation record of an orogen parallel extension in the vepor unit west carpathians abstract deformation microstructures of quartzo feldspathic rocks have been used to analyse the orogen parallel stretching of the vepor unit in the west carpathians during cretaceous convergence this process occurs contemporaneously with the burial of the vepor basement related to the overthrusting palaeozoic volcano sedimentary sequences of the gemer unit the microstructures develop along a metamorphic gradient indicating an increase of pressure and temperature towards the structural footwall the recrystallization of quartz occurs in the field of subgrain rotation recrystallization sgr while the plagioclase and k feldspar disintegrate into a neocrystallized muscovite albite matrix palaeopiezometry of the recrystallized quartz in conjunction with p t estimates yield strain rates of 9 10 12 to 6 10 14 s 1 depending on temperature 380 480 c and choice of piezometer and flow law calibration strain analysis of the recrystallized quartz aggregates and quartz texture analysis indicate an overprint of the variscan magmatic and high grade fabrics by a cretaceous plane strain deformation resulting in vertical shortening and horizontal orogen parallel east west stretching spatial distribution and conflicting sense of shear of the asymmetrical quartz lattice preferred orientation patterns indicate that the large scale pure shear deformation of the vepor unit is locally accommodated by simple shear zones observed metamorphic gradients across the vepor unit are interpreted to result from later large scale folding and heterogeneous exhumation of the orogen parallel deformation fabric

the rigid grain net rgn an alternative method for estimating mean kinematic vorticity number wm the use of porphyroclasts rotating in a flowing matrix to estimate mean kinematic vorticity number wm is important for quantifying the relative contributions of pure and simple shear in penetratively deformed rocks the most common methods broadly grouped into those that use tailed and tailless porphyroclasts have been applied to many different tectonic settings however attempts have not been made to unify the various methods here we propose the rigid grain net rgn as an alternative graphical method for estimating wm the rgn contains hyperbolas that are the mathematical equivalents to the hyperbolic net used for the porphyroclast hyperbolic distribution phd method we use the rgn to unify the most commonly used wm plots by comparing the distribution of theoretical and natural tailless porphyroclasts within a flowing matrix test samples from the south tibetan detachment tibet yield indistinguishable results when the rgn is compared with existing methods because of its ease of use ability for comparing natural data sets to theoretical curves potential to standardize future investigations and ability to limit ambiguity in estimating wm the rgn makes an important new contribution that advances the current methods for quantifying flow in shear zones 2006 elsevier ltd all rights reserved

calcite twin widths and intensities as metamorphic indicators in natural low temperature deformation of limestone abstract twins in naturally deformed coarse grained limestones of the northern subalpine chain france show a direct relationship of twin width and intensity number of twins per mm to the peak metamorphism under diagenetic and anchimetamorphic conditions the transition from dominant thin twinning to dominant thick twinning occurs between a mean vitrinite reflectance ro of 1 60 and 2 60 or temperatures of between 150 and 200 c below the transition temperature increasing strain is apparently accommodated by adding new twins and above the transition temperature increasing strain is accommodated by twin widening similar transitions from thin to thick twinning with increasing metamorphism are also present in the helvetic alps the prealps and the central appalachian valley and ridge province these data for naturally deformed limestones support the interpretation from experimental studies of a temperature effect on twin width and intensity and indicate that the twinning in the northern subalpine chain occurred at or near peak metamorphism

relationships among vitrinite reflectance illite crystallinity and organic geochemistry in carboniferous strata ouachita mountains oklahoma and arkansas the ouachita mountains contain a thick section of carboniferous strata that display an extreme range in thermal maturity as determined by vitrinite reflectance clay mineralogy illite crystallinity and organic geochemistry of shales from those strata are systematically related to thermal maturity shales of the stanley jackfork and atoka formations are predominantly composed of illite and chlorite with minor occurrences of mixed layer clays restricted to samples characterized by mean vitrinite reflectance less than 1 5 and pyrophyllite restricted to samples characterized by mean vitrinite reflectance greater than 2 7 illite crystallinity is significantly related to vitrinite reflectance ro weaver s illite sharpness ratio sr increases with increasing ro log sr 0 28 0 08 ro whereas kubler s illite crystallinity index ci decreases with increasing ro log ci 1 01 0 07 ro plots of bitumen ratio bitumen total organic carbon vs vitrinite reflectance weaver s illite sharpness ratio and kubler s crystallinity index all reveal hydrocarbon generation preservation curves that define submature mature and supermature zones with regard to a liquid hydrocarbon window these results suggest that in the absence of vitrinite illite crystallinity can be used quantitatively to estimate levels of thermal maturity and cautiously to approximate hydrocarbon generation preservation stages of potential source rocks

the expulsinator versus conventional pyrolysis the differences of oil gas generation and expulsion simulation under near natural conditions abstract the expulsinator provides a new technique to simulate generation and expulsion of hydrocarbons under near natural conditions this is realized by application of lithostatic pressure onto an intact source rock disc with undisturbed mineral matrix and kerogen network and by hydrous pyrolysis conducted in open flow through mode conventional pyrolysis methodologies serve well in generation kinetics assessment but are only of limited use for investigation of primary migration and expulsion due to destructive sample preparation inappropriate pressure regimes and pyrolysis in closed mode and or in the absence of water however comparison of results generated with conventional pyrolysis with expulsinator experiments is important to assess the performance of the generation and expulsion simulation carried out with the expulsinator thus the generation and expulsion behaviour of this new methodology has been compared with established pyrolysis methodologies like hypy and closed small vessel pyrolysis csvp and has been assessed by rock eval pyrolysis expulsinator experiments released higher amounts of bitumen than csvp this has been attributed to increased cross linking reactions of bitumen in case of the classic pyrolysis favouring formation of pyrobitumen differences in yields and composition of n alkanes were controlled not by generation kinetics exclusively but also by expulsion effects in particular delayed expulsion caused by geochromatography expulsinator conversion rates of toc exceeded 81 whereas those of hydrous csvp remained at 65 higher expulsinator toc conversion was accompanied by lower gas generation compared to csvp this is attributed to the open setup of the expulsion experiment which by rapid removal of products generated prevents their secondary alteration particularly polymerization to pyrobitumen and oil to gas cracking at higher temperatures hypy of expulsinator pyrolysis residues verified a low generation potential remaining after the expulsion experiment the expulsinator device delivers oil and gas generation data which can be applied in numerical modelling exercises

modeling the impact of marine stratocumulus on boundary layer structure an ensemble average closure model intended for mesoscale studies is applied to a marine stratocumulus capped pbl the intention is to test this model in particular for cases where cloud and subcl

microstructural evolution of the serido belt ne brazil the effect of two tectonic events on development of c axis preferred orientation in quartz the polyphase evolution of the serido belt ne brazil includes d crust formation at 2 3 2 1 ga d 2 thrust tectonics at 1 9 ga and crustal reworking by d 3 strike slip shear zones at 600 ma microstructural investigations within mylonites associated with d 2 and d 3 events were used to constrain the tectono thermal evolution of the belt d 2 shear zones commenced at deeper crustal levels and high amphibolite facies conditions 600 650 degreesc through grain boundary migration subgrain rotation and operation of quartz q prism slip continued shearing and exhumation of the terrain forced the re equilibration of high t fabrics and the switching of slip systems from c prism to positive and negative a rhombs during d 3 enhancement of ductility by dissipation of heat that came from syn d 3 granites developed wide belts of amphibolite facies mylonites continued shearing uplift and cooling of the region induced d 3 shear zones to act in ductile brittle regimes marked by fracturing and development of thinner belts of greenschist facies mylonites during this event switching from a prism to a basal slip indicates a thermal path from 600 to 350 degreesc therefore microstructures and quartz c axis fabrics in polydeformed rocks from the serido belt preserve the record of two major events which includes contrasting deformation mechanisms and thermal paths c 2003 elsevier ltd all rights reserved

simple shear deformation and quartz crystallographic fabrics a possible natural example from the torridon area of nw scotland ln this paper the microstructures and crystallographic fabrics of a 30 cm wide deformed quartz vein from the torridon area of nw scotland are described the vein which lies along a joint separating two blocks of proterozoic gneiss was deformed by crystal plastic processes when the rigid joint blocks moved in opposite directions parallel to the vein margins mylonitic foliation within this quartzose ductile shear zone locally displays the classic orientation variation expected for heterogeneous simple shear deformation in thin section the vein is a mylonite composed of dynamically recrystallized elongate quartz grains aligned oblique to the mylonitic foliation fabrics within the central part of the vein have been examined by optical and x ray texture goniometry methods together with orientation distribution function odf analysis the a axis fabric consists of a dominant single point maximum orientated within the xz plane at 9 to the lineation x this point maximum occupies a pole position to the corresponding single girdle c axis fabric for individual positions on the c axis fabric skeleton the orientations of potential crystallographic slip systems slip plane and direction relative to shear zone co ordinates have been calculated by odf analysis the calculation of relative resolved shear stresses schmidfactors for the potential slip systems assuming a simple shear kinematic framework reveals an elegantly simple relationship between individual grain c axis orientation and correspond ing orientations of potential slip systems these results are readily interpreted in terms of bulk simple shear deformation

grain boundary sliding and development of grain boundary openings in experimentally deformed octachloropropane abstract in situ observations of grain boundary sliding and associated accommodation mechanisms in experimentally pure and simple sheared octachloropropane at 75 85 of its absolute melting temperature and at strain rates of 10 5 10 6 s 1 are discussed discontinuities in the strain rotation and or translation components of deformation across the grain boundary induce grain boundary sliding the influence of crystallographic orientation of grains on grain boundary sliding is so strong that grains unfavorably oriented for basal slip contribute to deformation mainly by grain boundary sliding grain boundary diffusion and intragranular plastic deformation are observed to accommodate grain boundary sliding grain boundary diffusion also causes grain boundary migration types ii and iii that is different from conventional grain boundary migration type i in being non conservative and in the details of boundary movement with respect to material points within grains grain boundary openings filled with fluid octachloropropane vapor are strongly associated with grain boundary sliding openings develop preferentially along grain boundaries at low angles to the shortening direction once openings grow they are closed by thrusting of sliding grains and by diffusion in faster strain rate experiments and entirely by diffusion in slower strain rate experiments an approximately steady openings ratio of 0 5 3 of the sample volume persists without the development of any large scale fracture all grain boundary openings disappear during static readjustment of the microstructure after deformation

development of preferred orientation and microstructure in sheared quartzite comparison of natural data and simulated results abstract c axis fabric and microstructures in a quartzite sample sheared and extensively recrystallized under greenschist facies conditions have been analyzed and compared with theoretical predictions using a viscoplastic self consistent model modified to incorporate the effects of dynamic recrystallization an asymmetric small circle c axis fabric about the finite shortening z axis with a small half opening angle 35 is present in the sample it consists of four orientation components which are represented by host grain c axis orientations referred to as a b c and d a and b are at high angles to the foliation plane displaced against and with the sense of shear respectively c is in an intermediate direction between the y and z axis of finite strain and d forms a subsidiary concentration around the intermediate strain y axis b and c grains are favorably oriented for basal 0001 and pyramid 10 1 1 a slip respectively and strongly deformed while a and d grains are unfavorably oriented for the slip systems and little or moderately deformed some of a grains are even fractured the degree of dynamic recrystallization increases with increasing strain undergone by differently oriented grains in the sequence of a d c and b grains microstructural evidence and theoretical predictions indicate that harder a c and d grains were significantly consumed by the grain boundary migration of the softer recrystallized b component although the consumption of a grains was not really documented in the quartzite sample the conclusion is supported by the fact that the b component is much more dominant in the recrystallized than in the host c axis fabric hence the c axis maximum nearly perpendicular to the shear plane and apparently displaced with the sense of shear commonly found in naturally sheared quartzites correlated with the b component is presumably developed by the growth of soft orientations for basal 0001 slip by grain boundary migration at large strains

improving short term numerical weather prediction in the california coastal zone by dynamic initialization of the marine boundary layer abstract few data are available over the world s oceans to characterize the initial atmospheric state in numerical models objective analysis in these regions is largely based on forecast fields obtained from a global model and used as the background first guess unfortunately global models often do not resolve the marine boundary layer mbl structure which is important for simulating stratus clouds coastal zone circulations and electromagnetic wave propagation furthermore initialization of the mbl in the coastal zone and data sparse oceanic regions poses a challenging mesoscale modeling problem the goal of this study therefore is to improve warm season short term mesoscale numerical prediction of california coastal zone meteorology by improving the model initial conditions in the coastal zone and offshore data void regions initialization strategies tested include standard static and dynamic techniques and a new marine boundary layer initialization scheme that uses a dynamic initialization

deformation conditions in the northern subalpine chain france estimated from deformation modes in coarse grained limestone abstract in low temperature experiments the deformation mode and ductility in a single rock type are most directly controlled by the confining pressure and strain magnitude a graphical technique is developed from published experimental microstructural data that allows for the determination of deformation mode for coarsegrained limestone on the basis of microstructural point count data the deformation mode and strain are used to constrain the confining pressure during thin section scale deformation by comparison with experimental deformation results the technique is applied to coarse grained samples of cretaceous and tertiary limestone from the northern subalpine chain france and reveals that the majority of samples deformed mostly by twinning in the uniform flow mode at minimum depths estimated from deformation mode and strain of between 0 and 6 0 km and maximum depths interpreted from peak metamorphic temperatures and geothermal gradient of about 2 7 9 7 km in the remaining samples brittle failure probably occurred at relatively shallow depths

fabric and anisotropy of slates from classical studies to new results abstract slates are low grade metamorphic argillaceous rocks which have developed an intense tectonic fabric referred to as slaty cleavage due to their unique properties they have long been used as building materials especially tiles for roofs and floors the fabric characterized by strong alignment of platy phyllosilicate crystals produces extreme anisotropy that has been of great interest in structural geology what different fabric types are observed how do they form here we review crystal preferred orientation cpo and add new information to establish a comprehensive base for future studies slates are composed of fine grained phyllosilicates dominantly white mica and chlorite sometimes chloritoid quartz and accessories texture analyses of these polyphase rocks with high energy synchrotron x ray diffraction and high resolution ebsd reveal strong alignment of mica and chlorite in some cases exceeding any previously reported texture strength including metals interestingly the cpo of quartz with highly flattened grains shape preferred orientation or spo is practically random recrystallization microstructures observed by scanning electron microscopy suggest that the phyllosilicate preferred orientation is largely caused by crystal growth under stress and that quartz was subject to pressure solution and reprecipitation producing an anisotropic shape while phyllosilicates preferred orientation in slates is much higher than reports for shale schists and gneiss elastic seismic anisotropy for slates is similar to shales where a significant component is due to aligned porosity

fabric analysis of quartzites with negative magnetic susceptibility does ams provide information of spo or cpo of quartz abstract we ask the question whether petrofabric data from anisotropy of magnetic susceptibility ams analysis of deformed quartzites gives information about shape preferred orientation spo or crystallographic preferred orientation cpo of quartz since quartz is diamagnetic and has a negative magnetic susceptibility 11 samples of nearly pure quartzites with a negative magnetic susceptibility were chosen for this study after performing ams analysis electron backscatter diffraction ebsd analysis was done in thin sections prepared parallel to the k1k3 plane of the ams ellipsoid results show that in all the samples quartz spo is sub parallel to the orientation of the magnetic foliation however in most samples no clear correspondance is observed between quartz cpo and k1 magnetic lineation direction this is contrary to the parallelism observed between k1 direction and orientation of quartz c axis in the case of undeformed single quartz crystal pole figures of quartz indicate that quartz c axis tends to be parallel to k1 direction only in the case where intracrystalline deformation of quartz is accommodated by prism slip it is therefore established that ams investigation of quartz from deformed rocks gives information of spo thus it is concluded that petrofabric information of quartzite obtained from ams is a manifestation of its shape anisotropy and not crystallographic preferred orientation

tectonic evolution of low grade metamorphosed rocks of the cretaceous shimanto accretionary complex central japan abstract we reconstructed the tectono metamorphic evolution of the low grade metamorphosed cretaceous shimanto accretionary complex in the kanto mountains central japan based on radiolarian fossils metamorphic temperatures derived from illite crystallinity analysis and timing of metamorphism based on illite k ar dating the accretionary age of the kobotoke group is turonian to maastrichtian 66 94 ma based on radiolarian fossils illite crystallinity data indicate metamorphic temperatures of approximately 300 c the illite k ar ages constrain the timing of metamorphism to the middle eocene around 40 ma combining our results and previous study we defined two types of low grade metamorphism within cretaceous shimanto accretionary complex of the kanto mountains the early metamorphism in excess of 300 c was related to the uplift of the sambagawa metamorphic rocks in turn associated with the subduction of the kula pacific ridge during the late cretaceous 65 75 ma this metamorphism is recorded in the otaki group within the northernmost part of the complex in the kanto mountains subsequent to the subduction of the kula pacific ridge a later period of metamorphism recorded in the kobotoke group is characterized by the thermal effects of the subduction of the young hot pacific plate during the middle eocene the effect of the early metamorphism occurred synchronously 500 km along the trench from southwest to central japan the later metamorphism occurred at 50 ma in kyushu and shikoku of southwest japan and at 40 ma in the kanto mountains of central japan this difference in the timing of metamorphism between southwest and central japan is explained by the northward migration of the young hot pacific plate

cloudiness and marine boundary layer dynamics in the astex lagrangian experiments part i synoptic setting and vertical structure abstract a goal of the atlantic stratocumulus transition experiment astex southeast of the azores islands in the east central atlantic ocean during june 1992 was to examine the coupled evolution of cloud dynamical and thermodynamical vertical structure in a marine boundary layer mbl air mass as it advected from cold to warm water in the trade winds in two lagrangian observation periods during astex an unprecedentedly complete view of mbl and cloud evolution was achieved by nearly continuous aircraft coverage of such an air mass for 36 48 hours using three boundary layer aircraft supplemented by satellite ship and balloon observations during the first lagrangian period an accelerated stratocumulus to trade cumulus transition occurred in a clean marine air mass in the second lagrangian period a 200 hpa deep decoupled modified continental mbl persisted with almost no change in structure cumulus rising into intermittent stratocumulus were observed throughout the period the two contrasting a

channel flow extrusion model to constrain dynamic viscosity and prandtl number of the higher himalayan shear zone constraining magnitudes of mechanical and thermo mechanical parameters of rocks and shear zones are the important goals in structural geology and tectonics talbot in j struct geol 21 949 957 1999 such parameters aid dynamic scaling of analogue tectonic models ramberg in gravity deformation and the earth s crust in theory experiments and geological applications 2nd edn academic press london 1981 which are useful to unravel tectonics in further details schultz ela and walsh in j struct geol 24 247 275 2002 the channel flow extrusion of the higher himalayan shear zone hhsz higher himalaya can be explained by a top to s sw simple shear i e the d2 deformation in combination with a pressure gradient induced flow against gravity presuming its newtonian incompressible rheology with parallel inclined boundaries the viscosity of this shear zone along a part of the himalayan chain through india nepal and bhutan is estimated to vary widely between 1016 and 1023 pa s and its prandtl number pr within 1021 1028 the estimates utilized ranges of known thickness 6 58 km of the hhsz that of its top subzone of ductile shear of normal shear sense stdsu 0 35 9 4 km total rate of slip of its two boundaries 0 7 131 mm year 1 pressure gradient 0 02 6 kb km 1 density 2 2 3 1 g cm 3 and thermal diffusivity 0 5 10 6 2 1 10 6 m s 2 along the orogenic trend considering most of the parameters specifically for the sutlej section india the calculated viscosity and the prandtl number pr of the hhsz are deduced to be 1017 1023 pa s and pr 1022 1028 the upper limits of the estimated viscosity ranges are broadly in conformity with a strong tibetan mid crust from where a part of the hhsz rocks extruded on the other hand their complete ranges match with those for its constituent main rock types and partly with those for the superstructure and the infrastructure the estimated mechanical and thermo mechanical parameters of the hhsz will help to build dynamically scaled analogue models for the himalayan deformation of the d2 phase

an observational study of the structure of stratiform cloud sheets part i structure results from six flights with an instrumented aircraft in marine stratiform cloud topped boundary layers are presented the flights took place around the u k in a variety of conditions both during the day and at night the data comprise simultaneous high resolution turbulence cloud microphysics and radiation measurements on five of the flights turbulent mixing in the cloud layer was found to be primarily maintained by convection resulting from cloud top radiative cooling in four cases this mixed layer was observed to be decoupled from the surface i e the cloud induced mixing did not extend down to the surface and the cloud formed part of a detached turbulent layer one flight in high surface wind conditions displayed a significantly different structure possible reasons for this are suggested the mean microphysical features of the different cloud layers are compared as are the measured and theoretically calculated radiation fluxes the latter show good general agreement but some systematic differences are apparent again possible causes of these disparities are discussed features of the turbulent velocity field are presented and a number of similarities between data from the convective cases and cloud free boundary layers driven by heating from below are found values of the entrainment velocity are estimated directly from the measured cloud top water fluxes in all but one case together with an estimate of the errors incurred the measured vertical turbulent fluxes are found to be reasonably well predicted by diagnostic mixed layer models using the measured boundary conditions as long as the heights of the mixed layer boundaries are also specified from observations such a model is also used to help explain the main observed features of the mixed layer structure and the differences between the various cases

quartz preferred orientation in naturally deformed mylonitic rocks montalto shear zone italy a comparison of results by different techniques their advantages and limitations in the geologic record the quartz c axis patterns are widely adopted in the investigation of crystallographic preferred orientations cpo of naturally deformed rocks to this aim in the present work four different methods for measuring quartz c axis orientations in naturally sheared rocks were applied and compared the classical universal stage technique the computer integrated polarization microscopy method cip the time of flight tof neutron diffraction analysis and the electron backscatter diffraction ebsd microstructural analysis and cpo patterns of quartz together with the ones obtained for feldspars and micas in mylonitic granitoid rocks have been then considered to solve structural and geological questions related to the montalto crustal scale shear zone calabria southern italy results obtained by applying the different techniques are discussed and the advantages as well as limitations of each method are highlighted importantly our findings suggest that patterns obtained by means of different techniques are quite similar in particular for such mylonites a subsimple shear 40 simple shear vs 60 pure shear by shape analysis of porphyroclasts was inferred a general tendency of an asymmetric c maximum near to the z direction normal to foliation suggesting dominant basal slip consistent with fabric patterns related to dynamically recrystallization under greenschist facies is recognized rhombohedral slip was likely active as documented by pole figures of positive and negative rhombs tof which reveal also potential mechanical dauphine twinning results showed that the most complete cpo characterization on deformed rocks is given by the tof from which also other quartz crystallographic axes can be obtained as well as various mineral phases may be investigated however this use is restricted by the fact that a there are very few tof facilities around the world and b there is loss of any domainal reference since tof is a bulk type analysis ebsd is a widely used technique which allows an excellent microstructural control of the user covering a good amount of investigated grains cip and us are not expensive techniques with respect the other kind of investigations and even if they might be considered obsolete and or time consuming they have the advantage to provide a fine and grain by grain first round inspection on the investigated rock fabric

diagenetic overprinting of the sphaerosiderite palaeoclimate proxy are records of pedogenic groundwater delta18o values preserved meteoric sphaerosiderite lines msls defined by invariant d 18 o and variable d 13 c values are obtained from ancient wetland palaeosol sphaerosiderites millimetre scale feco3 nodules and are a stable isotope proxy record of terrestrial meteoric isotopic compositions the palaeoclimatic utility of sphaerosiderite has been well tested however diagenetically altered horizons that do not yield simple msls have been encountered well preserved sphaerosiderites typically exhibit smooth exteriors spherulitic crystalline microstructures and relatively pure 95 mol feco3 compositions diagenetically altered sphaerosiderites typically exhibit corroded margins replacement textures and increased crystal lattice substitution of ca 2 m g 2 and mn 2 for fe 2 examples of diagenetically altered cretaceous sphaerosideritebearing palaeosols from the dakota formation kansas the swan river formation saskatchewan and the success s2 formation saskatchewan were examined in this study to determine the extent to which original early diagenetic d 18 o and d 13 c values are preserved all three units contain poikilotopic calcite cements with significantly different d 18 o and d 13 c values from the co occurring sphaerosiderites the complete isolation of all carbonate phases is necessary to ensure that inadvertent physical mixing does not affect the isotopic analyses the dakota and swan river samples ultimately yield distinct msls for the sphaerosiderites and mcls meteoric calcite lines for the calcite cements the success s2 sample yields a covariant d 18 o vs d 13 c trend resulting from precipitation in pore fluids that were mixtures between meteoric and modified marine phreatic waters the calcite cements in the success s2 formation yield meteoric d 18 o and d 13 c values a stable isotope mass balance model was used to produce hyperbolic fluid mixing trends between meteoric and modified marine end member compositions modelled hyperbolic fluid mixing curves for the success s2 formation suggest precipitation from fluids that were 25 sea water

the structure of gradually transforming marine stratocumulus during the astex first lagrangian experiment summary an analysis of the mean and turbulent structure of the planetary boundary layer is presented using aircraft data obtained during the atlantic stratocumulus transition experiment e rst lagrangian experiment the analysis of the mean vertical structure relies mostly on slant proe le data however part of the analysis also uses socalled porpoise runs in the vicinity of the cloud top the analysis of the turbulence structure utilizes all of the data horizontal eight legs as well as slant proe les and presents both scaled turbulence statistics and a spectral analysis the purpose is to investigate details in the temporal development of the e rst lagrangian experiment and to study the turbulent structure in order to e nd scale relations that can be utilized in improved modelling of the stratocumulus capped boundary layer the hypothesis is that so called cloud decoupling has a signie cant impact on the turbulence scaling the measured cloud water is corrected to become consistent between the two participating aircraft the corrected maximum cloud water is more constant in time than in previous studies of the erst lagrangian it is suggested that previously analysed temporal variability may be an artefact of using two different instruments to measure cloud water the cloud top jump in equivalent potential temperature is positive in the erst three eights sufe ciently large for a stable cloud top but decreases and becomes negative for the last two eights in line with the breaking up of the cloud eeld the upper part of the boundary layer warms and dries more rapidly than the lower suggesting entrainment to be a dominant factor in the development of the cloud the analysis of the porpoise e ight legs illustrates how sharp features at the cloud top inversion are smoothed out while analysing several proe les eight legs or even entire eights rather than normalizing each proe le with the height to the local cloud top scaling of the turbulent e uxes and the velocity variances shows that the cloud layer is decoupled throughout almost the entire erst lagrangian it is also shown that while surface layer scaling is appropriate for the marine atmospheric boundary layer mabl the cloud layer turbulence scales with convective scaling the lowfrequency spectrum has no spectral gap with the exception of the vertical velocity and continues to increase with decreasing frequency with only a change in slope this indicates the presence of mesoscale motions the cospectra of the turbulent euxes are very noisy throughout when averaging several spectra into height intervals the scales of the turbulence as indicated by the peak in the averaged spectra appear to vary with height above the surface in the mabl but to be height independent in the cloud layer an attempt to calculate a dissipation length scale shows scatter but is consistent with a dissipation length scale increasing linearly with height in the mabl but being roughly constant or possibly parabolic with height in the cloud layer

aircraft measurements of turbulence spectra in the marine stratocumulus topped boundary layer abstract mixed layer scaling was successfully applied to the velocity temperature and moisture spectra of the marine stratocumulus topped mixed layers observed during the first isccp regional experiment fire these turbulence spectra provide considerable insight into the physical phenomena that affect this kind of boundary layer at least four of these phenomena contribute to the turbulence spectra eddies that result directly from shear and buoyant production of turbulent kinetic energy the microscale energy production subrange smaller eddies that result from the inertial cascade of energy the inertial subrange quasi two dimensional mesoscale variations and gravity waves the velocity temperature and moisture spectra are affected differently by each of these phenomena the turbulence spectra highlight the differences between the cold current marine stratocumulus topped boundary layer and the overland convective boundary layer

mechanical twinning in quartz shock experiments impact pseudotachylites and fault breccias abstract increasing use of diffraction methods to study preferred orientation of minerals has established that quartz in deformed rocks not only displays characteristic c axis orientation patterns but that there is also generally a distinct difference in the orientation of positive and negative rhombs in the trigonal quartz crystal structure positive and negative rhombs are structurally different and particularly negative rhombs e g 01 1 1 are much stiffer than positive rhombs e g 10 1 1 here we focus on the role of mechanical dauphine twinning under stress as a cause of this difference and illustrate with ebsd measurements ubiquitous twinning in quartz bearing rocks subjected to high stresses characteristic twinning is observed in experimentally shocked sandstones and stishovite bearing quartzites from the vredefort meteorite impact site in south africa similar twinning is documented for quartz associated with pseudotachylites from the santa rosa mylonite zone in southern california whereas quartz in underlying ductile mylonites are more or less twin free it suggests that twinning was produced by local seismic stresses that caused fracture and frictional melting on fault surfaces quartz bearing breccias from the safod san andreas fault observatory at depth drilling project also show evidence of twinning and suggest high seismic stresses in the currently creeping segment of the san andreas fault at parkfield from these observations it appears that dauphine twin microstructures can be diagnostic of high local and transient stresses

vitrinite reflectance illite crystallinity and tectonics results from the northern apennines italy abstract vitrinite reflectance measurements were used in the ligurian apennines to identify 14 tectonic units nappes these are arranged in 5 tectonic supergroups with different degrees of coalification relative dating of 2 orogenetic processes and heating events in the eocene and late miocene was possible maximum paleotemperatures around 300 c and burial depths of up to 5 km are estimated enormous masses are thought to have accumulated and to have been removed within a very short time span the development of the sedimentary organic matter from diagenetic very low grade up to initial low grade metamorphic stages is investigated the joint occurrence of vitrinite and transitional matter between vitrinite and graphite is significant of the initial graphitization process diessel et al 1978 and occurs between 4 and 7 r max vitrinite reflectance r m and illite crystallinity are closely correlated in a similar way as in other areas of a similar tectonic history the relationship between the quantity of mixed layer minerals and vitrinite reflectance suggests a connection with the degree of diagenesis

textural and mechanical evolution with progressive strain in experimentally deformed aplite determining meaningful flow laws for the polyphase aggregates that characterize the crust is difficult because the strength of such aggregates depends on the strengths volume proportions and geometrical arrangement of their constituent phases and all of those factors may change with progressive strain in order to investigate some of these factors we have performed a series of axial compression experiments on a fine grained granite aplite over a range of shortening strains 20 85 and temperatures 700 900 c at 1 5 10 6 s 1 and 1400 mpa we have also done comparison experiments on pure quartz and feldspar aggregates the aplite is composed of 1 3 quartz and 2 3 oligoclase and microcline with minor biotite and magnetite the quartz grains are dispersed in a continuous matrix of feldspar optical and tem scale microstructures indicate that the deformation mechanisms of the quartz and feldspar grains in the aplites are similar to those of pure quartz and feldspar aggregates deformed at the same conditions the feldspars deform by semi brittle flow at 700 and 800 c and by recrystallization accommodated dislocation creep at 900 c while quartz deforms by recrystallization accommodated dislocation creep at 700 c and by climb accommodated dislocation creep at 800 and 900 c pure albite aggregates are stronger than quartz aggregates over this range of conditions however in the aplite an apparent strength reversal is inferred from grain strain measurements and changes in phase distribution with increasing temperature at 700 c the dispersed quartz grains in the aplite remain less deformed than the feldspar grains because the scarcity of quartz quartz grain boundaries limits recovery by grain boundary migration recrystallization causing the quartz strength to rise above that of feldspar however the aplite is weaker than a pure feldspar aggregate because cracking is enhanced by stress concentrations at the quartz grains at 800 c the two phases undergo approximately equal strain because easy dislocation climb in quartz allows individual grains to strain homogeneously the aplite strength is close to that of a pure feldspar aggregate at 900 c the initially continuous feldspar grains deform inhomogeneously and undergo microboudinage while the quartz grains deform homogeneously and gradually become more interconnected and undergo higher strain than the feldspars the aplite strength is initially closer to that of a feldspar aggregate but with increasing strain it becomes closer to that of a quartz aggregate the aplite undergoes strain softening over the whole range of conditions at 700 and 800 c the weakening is due to grain boundary migration recrystallization of feldspar in the fine grained crush products along grain scale faults at 900 c the weakening is due to a combination of grain boundary migration recrystallization of the feldspars plus increasing interconnection of the weaker quartz grains these results demonstrate that the textural evolution of a polyphase aggregate with increasing strain is determined by both the phase distribution and the deformation mechanism of each phase and that very high strains may be required to approach microstructural and mechanical steady state therefore measuring or calculating a flow law appropriate for granite at mid crustal conditions is not simple

orientation analysis of localized shear deformation in quartz fibres at the brittle ductile transition abstract the crystallographic preferred orientation of fibrous quartz veins deformed under subgreenschist facies conditions along a temperature gradient from 270 to 370 c has been investigated to explore the active mechanism during deformation of the quartz fibres the complete crystallographic orientation of individual recrystallized grains and subgrains was determined by using a combination of cip computer integrated polarization microscopy ebsd electron back scatter diffraction and additional specially developed image analysis techniques it was found that the quartz fibres deformed along crystallographically controlled shear bands from inverse pole figures of normals to the shear band boundaries it is evident that these bands occur along the positive and negative rhomb planes of quartz it is suggested that they are initiated as fractures along these planes inside the shear bands small grains broken off from the host grain show passive rotation of the lattice consistent with the shear sense of the shear bands continued deformation and increasing temperature lead to different recrystallization microstructures inside and outside the shear bands and to a partial obliteration of the sharp orientation relationships

quartz microstructures and crystallographic preferred orientation which shear sense do they indicate abstract crystallographic preferred orientation cpo and shape fabrics of dynamically recrystallized quartz are currently used as shear sense indicators we show that the cpo and shape fabric in a polyphase rock do not necessarily indicate the shear sense at the global scale of the shear zone but rather at the local scale of the deforming and recrystallizing quartz aggregates in lower amphibolite facies shear zones in the gran paradiso metagranodiorite magmatic quartz grains have recrystallized dynamically by subgrain rotation and grain boundary migration and deform inside a very fine grained feldspar mica matrix the quartz cpo has a peripheral c axis maximum inclined synthetically with the local shear sense the orientation of the surface fabric is related to the orientation of the c axis maximum and the microscopic shear sense in the quartz aggregate the geometry of the surface fabric ranges from monoclinic to symmetric depending on the relative contribution of grain boundary migration it is inferred that flow partitioning between the quartz aggregates and the matrix controls the local kinematics cpos are only reliable shear sense indicators in polyphase rocks if the most highly strained parts are analyzed where spin of the aggregates with respect to the shear zone boundary has ceased

the geometrical relationship between the stretching lineation and the movement direction of shear zones abstract the geometrical relationship between foliations and lineations in shear zones is considered quantitatively assuming that the internal structures of shear zones have monoclinic symmetry the common practice of directly correlating the pitch or plunge of the stretching lineation with the obliquity of the shear direction is challenged it is the orthogonal projection of the stretching lineation on the shear zone boundary that is parallel to the shear direction a shear zone is parallel to a plane containing both the pole to the symmetry plane and the strike of the shear zone and the shear direction is parallel to the intersection of the symmetry plane and the shear zone boundary the symmetry plane is determined by the stretching lineation and the poles to the s foliation the implications of this study for the interpretation of shear zones are discussed with reference to an actual example

the augen gneisses of the peloritani mountains ne sicily granitoid magma production during rapid evolution of the northern gondwana margin at the end of the precambrian abstract the medium to high grade polymetamorphic basement rocks of the peloritani mountains northern sicily include large volumes of augen gneiss of controversial age and origin by means of a geochemical and shrimp zircon study of representative samples the emplacement age of the original granitoid protoliths of the augen gneisses and the most likely processes and sources involved in that granitoid magmatism have been determined u pb dating of three samples from widely spaced localities in the peloritani mountains yielded igneous protolith ages of 565 5 545 4 and 545 4 ma respectively these late ediacaran early cambrian ages are much older than was previously assumed on geological grounds and are typical of the peri gondwanan terranes involved in the geodynamic evolution of the northern gondwana margin at the end of the avalonian cadomian orogeny major and trace element compositions and sr nd isotopic data in combination with zircon inheritance age patterns suggest that the granitoid protoliths of the sicilian and coeval calabrian augen gneisses were generated by different degrees of mixing between sediment and mantle derived magmas the magmas forming the ca 545 ma inheritance rich granitoids appear to have had a significant contribution from partial melting of paragneiss that is the dominant rock type in the medium to high grade peloritanian basement the closeness of the inferred deposition age of the greywacke protoliths of the paragneisses with the intrusion age of the granitoids indicates rapid latest precambrian crustal recycling involving erosion burial metamorphism to partial melting conditions and extensive granitoid magmatism in less than ca 10 ma

the vertical turbulence structure of the coastal marine atmospheric boundary layer the vertical turbulence structure in the marine atmosphere along a shoreline has been investigated using data from tower and aircraft measurements performed along the baltic coast in the southeast of sweden two properties make the baltic sea particularly interesting it is surrounded by land in all directions within moderate advection distances and it features a significant annual lag in sea surface temperature as compared with inland surface temperature the present data were collected mostly during spring or early summer when the water is cool i e with a stably or neutrally stratified marine boundary layer usually capped by an inversion substantial daytime heating over the land area results in a considerable horizontal thermal contrast measurements were made on a small island on a tower with a good sea fetch and with an airborne instrument package the profile data from the aircraft is from 25 slant soundings performed in connection to low level boundary layer flights the results from the profiles are extracted through filtering techniques on individual time space series individual profiles applying different normalization and finally averaging over all or over groups of profiles the land based data are from a low tower situated on the shoreline of a small islandmore with a wide sector of unobstructed sea fetch several factors are found that add to the apparent complexity of the coastal marine environment the state of the sea appears to have a major impact on the turbulence structure of the surface layer jet shaped wind speed profiles were very common at the top of the boundary layer in about 50 of the cases and distinct layers with increased turbulence were frequently found well above the boundary layer in about 80 of the cases the present paper will concentrate on a description of the experiment the analysis methods and a general description of the boundary layer turbulence structure over the baltic sea 40 refs 16 figs 2 tabs less

illite polytype distribution as an inorganic indicator of thermal maturity in the smackover formation of the manila embayment southwest alabama abstract illite polytype distribution is compared to pyrolysis tmax values in the smackover formation in the manila embayment southwest alabama to determine its potential as an indicator of thermal maturity the percent 2m illite polytype 2m 1m 2m increases from 20 to 80 over the formation temperature interval 100 165 c and as tmax values increase from 432 to 461 c illite polytype distribution is considered a good qualitative indicator of thermal maturity in the smackover formation of the study area the correlation between the percentage of 2m illite and temperature and thermal maturity in the smackover formation is believed to be primarily the result of the diagenetic transition from the 1m to the 2m polytype depositional effects are manifested in four samples as anomalously high 2m polytype percentages this variation is interpreted to be the result of locally high concentrations of detrital 2m muscovite because original sediment composition and illite chemistry may vary significantly both locally and regionally illite polytype distribution is a useful thermal maturity indicator only within a particular basin and when calibrated with other thermal maturity indicators

nature of accretion related to paleo tethys subduction recorded in northern thailand constraints from melange kinematics and illite crystallinity abstract we reconstructed the accretion process related to paleo tethys subduction recorded in northern thailand based on melange and thrust structures and metamorphic temperatures derived from illite crystallinity data melange formation was characterized by hydrofracturing and cataclastic deformation with mud injection under semi lithified conditions followed by shear deformation and pressure solution illite crystallinity data suggest metamorphic temperatures below 250 c during melange formation the combined structural and metamorphic data indicate that during melange formation the accretionary complex related to paleo tethys subduction developed at shallow levels within an accretionary prism asymmetric shear fabrics in melange indicate top to south shear after correction for rotation associated with collision between the indian and eurasian continents the trend of the paleo tethys subduction zone is estimated to have been n80 e we conclude that the paleo tethys was subducted northward beneath the indochina block from the permian to triassic

deformation thermometry based on quartz c axis fabrics and recrystallization microstructures a review abstract for quartz rich tectonites two types of deformation thermometer are currently commonly employed 1 the quartz c axis fabric opening angle thermometer that provides an estimate of deformation temperatures when fabrics were locked in during dislocation creep and dynamic recrystallization 2 the quartz recrystallization thermometer that indicates a range of likely deformation temperatures based on observed microstructures and inferred mechanisms of dynamic recrystallization a critically important caveat in applying both thermometers is the assumption that deformation temperature is the primary controlling factor in recrystallization mechanisms and fabric development however fabric opening angles and recrystallization mechanisms are also sensitive to other variables such as strain rate and water weakening in this paper the development of these thermometers is reviewed and their potential sensitivities to competing factors such as temperature strain rate water weakening and in the case of opening angles 3d strain type are discussed examples of the application of these potential thermometers to naturally deformed quartz rich rocks are given and case studies of correlations between deformation temperatures estimated by these thermometers and temperatures of synkinematic metamorphism determined by petrology based thermobarometers are highlighted in the review attention is focused on problems associated with applying these thermometers to natural deformation and examples of such problems are discussed

seismic and magnetic susceptibility anisotropy of middle lower continental crust insights for their potential relationship from a study of intrusive rocks from the serre massif calabria southern italy abstract we investigated the relationships between fabric seismic and magnetic anisotropy on lithotypes representative of a continental crust exposed in the serre massif southern italy in particular from five granitoids and one metagabbro cubes were cut according to the fabric elements and seismic properties up to 400 mpa confining pressure were measured with a triaxial multi anvil apparatus we also calculated the elastic properties based on the mineral content and composition in granitoids measured average compressional wave velocity vp of the fracture free aggregate at 400 mpa is 6 2 km s whereas average shear wave velocity vs is 3 6 km s with poisson s ratio ranging from 0 240 to 0 257 related to the modal proportions of quartz in metagabbro average vp and vs at 400 mpa are 6 9 km s and 3 7 km s respectively results showed that intrinsic velocity distribution after microcracks closure depends on progressive alignment of anisotropic minerals such as biotite amphibole and pyroxene with maxima velocities localized within the foliation plane mean magnetic susceptibility k m of the granitic rocks is 6 si units indicating that paramagnetic minerals such as biotite and amphibole control the intensity of magnetic anisotropy comparison of seismic and magnetic anisotropies highlighted the different role of constituting minerals over the petrophysical properties moreover a positive correlation between seismic and magnetic anisotropy has been recognized indicating that biotite and amphibole contribute to the petrophysical and textural anisotropy in the middle crust conversely in metagabbro the anisotropy of magnetic susceptibility ams is controlled by magnetite and pyrrhotite although these form

marine stratocumulus layers part 1 mean conditions abstract the mean radiational dynamical and thermodynamical structure of the marine stratocumulus topped mixed layers of the california coast is described for two days in june 1976 using data from the ncar electra aircraft we suggest that the synoptic conditions found may be typical of about half of the shallow stratocumulus topped boundary layers that occur in this region during summer the inversion was low near the coast and increased in height to the west consistent with the average westward increase in sea surface temperature north south inversion height change was largely due to entrainment and mean mesoscale vertical motions below the inversion strong winds 12 20 m s 1 from the north and horizontal inhomogeneities resulted in large advection terms in mean field equations the sloping inversion often produced large vertical shears of the actual and geostrophic wind velocities across the inversion because of low liquid water contents 0 1 g kg 1 temperature and water vapor could be measure

beyond whole rock geochemistry of shales the importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the ouachita mountain flysch deposits the origin of the ouachita mountains has been the focus of significant debate for decades considerable confusion also exists concerning the provenance of the carboniferous flysch of the ouachitas trace element geochemistry of shales from the stanley group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during mississippian time th sc and cr th ratios indicate a cratonic source for the majority of the stanley group sedimentary rocks however in several samples low th sc ratios and high cr th ratios suggest a contribution from a mafic source using element ratio diagrams all of the samples plot along a curve consistent with a two component mixing model consisting of a dominant felsic and a subordinate mafic source the heavy mineral fraction of these shales sequester many of the trace elements used in whole rock studies monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock the occurrence of monazite almost exclusively in sialic igneous rocks implies that sm nd isotopic signatures are not sensitive to sediment input from more mafic sources in some stanley shale samples chromite and mn oxides were identified and positively identify an oceanic crustal component as a source of stanley group sediment the results of this study emphasize the importance of determining the mineralogic sites of trace elements and realization of specific mineralogic contributions from mafic or sialic tectonic provenances

relationships among vitrinite reflectance illite crystallinity and organic geochemistry in carboniferous strata ouachita mountains oklahoma and arkansas discussion guthrie et al 1986 derived statistically significant regression equations relating weaver s illite sharpness ratio sr and vitrinite reflectance r and kubler s illite crystallinity index ci and r they combined data from the stanley jackfork and atoka formations data from the atoka formation did not provide statistically significant regressions in either equation which they attributed to a more restricted range m thermal maturity however the jackfork data which provided a regression of intermediate significance barely significant at the 5 level for ci against rj covered a wider range of r than the stanley data although there are slightly fewer pairs of data also the stanley data no tabulation is given seemed to provide a statistically significant regression even if restricted to the range of r displayed for the atoka data or if restricted to only 13 pairs of data as with the atoka data it is always questionable whether statistically significant but empirical relationships are of real significance assuming that in this study they are two or more possibilities exist

fabric development in experimentally sheared quartzites abstract a fine grained quartzite was deformed under a combination of simple shear and axial compression to varying amounts of shear strain 1 3 to 2 9 the experiments were conducted at 800 c 1500 mpa and an axial strain rate of 10 6 s in the dislocation creep regime shear zone boundaries were oriented at 45 or 30 to the compressior axis the progressive development of deformation microstructures including planar fabrics and c axis preferred orientations was studied as a function of increasing shear strain elongate original grains define a foliation s which rotates from 45 to 0 to the shear zone boundary with increasing strain producing a sigmoidal foliation in a single shear zone a second foliation invariant in orientation is defined by elongate recrystallized grains which lie at about 30 40 to the shear zone boundaries no c surfaces parallel to the shear zone boundaries were observed however extensional crenulation cleavages c defined by parallel zones of recrystallized grains as well as impurity and melt segregations were observed even at low strain lying at approximately 30 to the shear zone boundaries and these could easily be mistaken for c surfaces c axis preferred orientations of original grains define symmetric type i crossed circle girdles at low strain 2 with the greater concentration of c axes in the direction of shear these features are very similar to those observed in natural ductile shear zones

the near neutral marine atmospheric boundary layer with no surface shearing stress a case study abstract data from a marine coastal experiment over the baltic sea comprising airborne measurements and mast measurements have been used to highlight the turbulence dynamics of a case with most unusual flow characteristics the boundary layer had a depth of about 1200 m the thermal stratification was near neutral with small positive heat flux below 300 m and equally small negative heat flux above the entire situation lasted about 6 hours turbulence levels were unexpectedly high in view of the fact that momentum flux was negligible in fact positive in the layers near the surface and buoyancy flux was also small the turbulence was found to scale with the height of the boundary layer giving rise to velocity spectra having the shape of those characteristic of convectively mixed boundary layers analysis of the turbulence budget for the entire planetary boundary layer pbl revealed that energy was produced from shear instability in the uppermost parts of the pbl and was distributed to the lower par

evidence for regional dauphine twinning in quartz from the santa rosa mylonite zone in southern california a neutron diffraction study preferred orientation in granitic mylonites from the santa rosa mylonite zone in southern california is investigated with time of flight neutron diffraction quartz and biotite display strong preferred orientation whereas feldspar alignment is weak for quartz a c axis maximum in the intermediate fabric direction is consistent with dynamic recrystallization pole figures for positive and negative rhombs such as rz 10 11 and zz 01 11 are distinct over a wide region suggesting that the pattern reflects tectonic deformation and was not

simple shear is not so simple kinematics and shear senses in newtonian viscous simple shear zones this work develops an analytical model of shear senses within an inclined ductile simple shear zone with parallel rigid boundaries and incompressible newtonian viscous rheology taking account of gravity that tends to drive the material downdip and a possible pressure gradient that drives it upward along the shear zone it is shown that i contradictory shear senses develop within two sub zones even as a result of a single simple shear deformation ii the highest velocity and least shear strain develop along the contact between the two sub zones of reverse shear iii for a uniform shear sense of the boundaries a zone of reverse shear may develop within the top of the shear zone if the pressure gradient dominates the gravity component otherwise it forms near the bottom boundary iv a a pivot defined by the intersection between the velocity profile and the initial marker position distinguishes two sub zones of opposite movement directions not shear sense iv b a pivot inside any non horizontal shear zone indicates a part of the zone that extrudes while the other subducts simultaneously v the same shear sense develops v a when under a uniform shear of the boundaries the shear zone remains horizontal and the pressure gradient vanishes or alternatively v b if the shear zone is inclined but the gravity component counterbalances the pressure gradient zones with shear sense reversal need to be reinterpreted since a pro sheared sub zone can retro shear if the flow parameters change their magnitudes even though the same shear sense along the boundaries is maintained

fission track analysis of the crystalline basement rocks of the calabrian arc southern italy evidence of oligo miocene late orogenic extension and erosion abstract fission track analysis is used to provide low temperature and time constraints on the late orogenic cooling and exhumational history of the crystalline basement rocks of the calabrian arc southern italy 65 samples yielded 57 apatite fission track ages 54 zircon fission track ages and 25 apatite confined fission track length distributions interpretation of this data reveals a phase of increased cooling rates related to exhumation between approximately 35 ma mid oligocene and 15 ma middle miocene evidence from the sedimentary record indicates significant oligo miocene erosion related to this period of exhumation new chronological constraints are also applied to localised late orogenic extensional tectonism that has recently been identified within the basement rocks of the calabrian arc this information is used to produce a new model of the oligo miocene tectonic evolution of the calabrian arc it proposes that the crystalline basement rocks were part of a critical orogenic wedge between the mid oligocene and the middle miocene

the structure of radiatively driven convection in stratocumulus data from a series of five research flights in marine stratocumulus are used to investigate the structure of radiatively driven free convective layers conditional sampling methods are used to determine the properties of the primary convective elements negatively buoyant downdraughts the turbulent velocity data are also subjected to spectral analysis and the turbulent kinetic energy tke balance is evaluated for each case results from each case are found to be very similar if scaled using appropriate mixed layer quantities downdraughts are selected using a criterion based on vertical velocity the distributions of their intersected widths at cloud top and the velocity spectra are consistent with downdraughts occupying narrow regions 0 1 0 15 h wide h being the mean mixed layer depth around the periphery of larger regular 0 5 h 0 75 h diameter updraughts as suggested by cellular patterns observed in the cloud tops downdraughts are found to carry over half of the total turbulent fluxes of heat and water substance within cloud and also transport variance down the mean gradients their thermodynamic properties are consistent with their containing a small fraction of air from above cloud top although their negative buoyancy is almost entirely due to the incorporation of radiatively cooled air the properties of the downdraughts near cloud top suggest they are formed primarily as a result of the local horizontal convergence of upwelling motions constrained by the inversion while being cooled radiatively these quasi horizontal motions scour the base of the inversion incorporating some drier air before being forced downwards in relatively narrow zones comparisons with other convective layers over land or sea suggest that convection in stratocumulus proceeds with a greater mass flux and correspondingly reduced differences between convective elements and the environment possibly reflecting the improved ventilation possible at an inversion interface compared with much rougher surfaces the tke balance divides into three main regions and is consistent with the interpretations given above the pressure transport is implied to be the largest source term close to cloud top comparisons with model results reveal some important differences

a new estimate of the conditions for transition from basal a to prism c slip in naturally deformed quartz abstract quartz c axis fabrics of naturally deformed quartz in metacherts from the ryoke metamorphic belt in the yanai district southwestern japan suggest that the prism c prism a and basal a slip systems were activated during the plastic deformation under high temperature metamorphic conditions with increasing temperature quartz c axis fabric patterns change from girdle type through x maximum with a faint crossed girdle to x maximum the dominant orientation of subgrain boundaries in the quartz also changes from prism to basal with increasing temperature closely correlated with the change in quartz c axis fabric the fabric transition is also accompanied by an abrupt increase of recrystallized quartz grain size moreover observations with transmission electron microscopy tem clearly identify the dominant activation of c slip through the presence of basal subgrain boundaries and free dislocations with the 0001 burgers vector in the quartz from the metachert samples exhibiting x maximum c axis fabric based on these observations it is concluded that the mechanism switch from basal a to prism c slip systems occurred with increasing temperature in the metacherts the transition temperature is petrologically estimated to be ca 550 600 c at the natural strain rate

mineral fish their morphological classification usefulness as shear sense indicators and genesis mineral fish are sheared and commonly asymmetric mineral grains or clusters of grains this work reports 11 sub types of mineral fish showing a top to se sense of ductile shearing in the karakoram metamorphic complex kmc the mineral fish are of three broad geometries sigmoid lenticular and parallelogram reliable senses of shear are indicated by the overall asymmetry and inclination of mineral fish on the other hand the true shear sense is not always indicated by either the orientations of their cleavage planes or those of the individual grains in composite mineral fish the ranges of local orientations of single sigmoid mineral fish that include the lower values 23 in the kmc indicate their extensive ductile shearing the studied mineral fish were products of a range of deformation mechanisms including homogeneous deformation simple shear intra granular slip crystal plastic deformation fracturing and synthetic shearing additionally some examples might have undergone duplex slips and a few nucleated and grew either prior to or during the top to se shearing

observations and simulations of a non stationary coastal atmospheric boundary layer this paper studies the turbulent and mesoscale structures of a coastal marine atmospheric boundary layer in the southern baltic sea data from a field experiment are examined for a case during autumn and this case is subsequently modelled with a mesoscale numerical model during this day the marine atmospheric boundary layer develops from a well mixed cloud capped state into a stably stratified sheared boundary layer this development is due to the dissipation of the cloud layer by radiation processes and by synoptic scale subsidence the boundary layer becomes non stationary and spectral analysis shows that the turbulence structure deviates from the ideal steady state homogeneous boundary layer turbulence which forms the basis for most turbulence closures in numerical models it is shown that the subsiding boundary layer top and the increasing stability alter the spatial scale of the turbulent eddies they become vertically distorted and smaller than those expected during steady state conditions in spite of these deviations the turbulence statistics are sufficiently well behaved for simplified higher order closure modelling to be applicable when the mixed layer collapses due to the dissipating clouds the transition triggers an inertial oscillation and a non classical low level jet forms at the same time the changes in depth and stability of the marine boundary layer are perturbed by the mesoscale interaction between the flow and the coastal terrain thus the upstream terrain increasingly blocks the flow so that the inertia jet forms only for the part of the flow that overcomes the terrain obstacle a numerical simulation of the case reveals the primary mechanisms and several sensitivity simulations wherein the terrain and the time evolution of the forcing are manipulated confirm the hypotheses proposed as causing the observed low structure

observations of the interaction between cumulus clouds and warm stratocumulus clouds in the marine boundary layer during astex abstract decoupling of the marine boundary layer beneath stratocumulus clouds and the formation of cumulus clouds at the top of a surface based mixed layer sml have frequently been observed and modeled when such cumulus clouds penetrate the overlying stratocumulus layer the cloud microphysics and hence the radiative properties of the cloud are altered locally observations made during a series of lagrangian experiments in the azores as part of the atlantic stratocumulus transition experiment astex june 1992 have been analyzed to ascertain how the properties of a stratocumulus layer with which cumulus clouds are interacting differ from those of an unaffected cloud layer the results suggest that in regions where cumulus clouds penetrate the cloud layer the stratocumulus is thickened as the cumuli spread out into its base transport of air from the sml into the cloud by convective updrafts is observed and the increase in available moisture within the penetrating cumulus clouds results in increased

geochronological constraints on the timing of granitoid magmatism metamorphism and post metamorphic cooling in the hercynian crustal cross section of calabria exposed cross sections of the continental crust are a unique geological situation for crustal evolution studies providing the possibility of deciphering the time relationships between magmatic and metamor phic events at all levels of the crust in the cross section of southern and northern calabria u pb rb sr and k ar mineral ages of granulite facies metapelitic migmatites peraluminous granites and amphibolite facies upper crustal gneisses provide constraints on the late hercynian peak metamorphism and granitoid magmatism as well as on the post metamorphic cooling monazite from upper crustal amphibolite facies paragneisses from southern calabria yields similar u pb ages 295 293 4 ma to those of granulite facies metamorphism in the lower crust and of intrusions of calcalkaline and metaluminous granitoids in the middle crust 300 10 ma monazite and xenotime from peraluminous granites in the middle to upper crust of the same crustal section provide slightly older intrusion ages of 303 302 0 6 ma zircon from a mafic to intermediate sill in the lower crust yields a lower concordia intercept age of 290 2m a which may be interpreted as the minimum age for metamorphism or intrusion u pb monazite ages from granulite facies migmatites and peraluminous granites of the lower and middle crust from northern calabria sila also point to a near synchronism of peak metamorphism and intrusion at 304 300 0 4 ma at the end of the granulite facies metamorphism the lower crustal rocks were uplifted into mid crustal levels 10 15 km followed by nearly isobaric slow cooling c 3 cm a 1 as indicated by muscovite and biotite k ar and rb sr data between 210 4 and 123 1 ma the thermal history is therefore similar to that of the lower crust of southern calabria in combination with previous petrological studies addressing metamorphic textures and p t conditions of rocks from all crustal levels the new geochronological results are used to suggest that the thermal evolution and heat distribution in the calabrian crust were mainly controlled by advective heat input through magmatic intrusions into all crustal levels during the late hercynian orogeny

microstructural investigation of naturally deformed leucogneiss from an alpine shear zone southern calabria italy in order to reveal any correlation between the preferred orientation of quartz and progressive intensity of strain a suite of deformed leucogneiss collected within a ductile shear zone outcropping in calabria southern italy was investigated based on the microstructural approach and matrix clast relationships the method applied here may be useful for appraising the connection between deformation mechanisms of constituent minerals and bulk textural properties of naturally sheared rocks accordingly quartz c axis orientation patterns were determined by image assisted analysis results revealed a correlation between finite strain and textural features as strain increases the matrix develops at the expense of the clast counterpart which is instead progressively reduced in both size and amount

c axis fabrics and microstructures in quartz schist from the sambagawa metamorphic belt central shikoku japan an integrated study on c axis fabric and microstructure of plastically deformed and dynamically recrystallized quartz in quartz schist from the sambagawa metamorphic belt in central shikoku japan has revealed a correlation between c axis fabrics and three dimensional grain shape recrystallized quartz grains with prolate k 1 oblate 0 2 k 1 and uniaxially oblate k 0 2 shapes exhibit c axis fabric patterns of cleft girdles around the principal finite elongation direction x type i crossed girdles and small circle girdles around the principal finite shortening direction z respectively fabric intensity calculated from the eigenvalues of orientation tensors of the c axis fabrics increases with increasing magnitude of the apparent finite strain inferred from the shape of recrystallized quartz grains these results indicate that the development of recrystallized grain shape as well as c axis fabrics is primarily controlled by finite strain during progressive deformation however the finite strain estimated from three dimensional grain shape is systematically deviated toward the flattening field compared to that estimated from the c axis fabrics we investigated several possible causes for the discrepancy and propose that a scenario of coupled deformation and dynamic recrystallization in the quartz schist is responsible for the formation of these microstructures

simulations of nocturnal drainage flows by a q2l turbulence closure model abstract nocturnal drainage flows observed over a nearly two dimensional ridge called rattlesnake hills near richland washington are simulated by using a simplified turbulence closure model in which only turbulence kinetic energy and turbulence length scale equations are solved prognostically the present model is slightly simpler than a level 2 5 model which has been extensively used in previous simulations of various atmospheric boundary layer phenomena wind and temperature profiles computed by the present model are generally in excellent agreement with observations made by towers erected on the slope of rattlesnake hills strong coupling between the mean and turbulence variables is also demonstrated

syn deformation temperature and fossil fluid pathways along an exhumed detachment zone khao khwang fold thrust belt thailand abstract shale detachment zones their influence on deformational style and their internal mechanisms of deformation are an understudied aspect of fold thrust belts properties such as deformational temperature lithology and mineralogy are often recognized as having a key influence on the rheology and deformational style of detachment zones and overlying fold thrust belts however little work has been conducted on rock properties of known detachment zones a recently described upper level detachment zone in the exhumed khao khwang fold thrust belt of central thailand provides an ideal natural laboratory for investigation of the deformation conditions of the detachment zone and association with its complex deformational style the low grade metamorphic indicator illite crystallinty is used to broadly constrain deformational temperatures while oxygen and carbon stable isotope analysis provides insight into fluid flow history and fluid rock interaction illite crystallinity data indicate deep diagenetic to low anchizonal conditions and temperatures of 160 210 c in the shale detachment interpreted as reflecting peak metamorphic conditions during the triassic indosinian orogeny no trend between the intensity spacing complexity of structures and illite crystallinty is observed however shale shear zones of continuous style deformation and inferred higher finite strain display uniformly higher illite crystallinty than surrounding packages of discontinuously faulted shales we also note a positive association between total organic carbon content in the shales and the spacing and complexity of deformational structures data from limestones and syn tectonic vein fills detail the history of fluid rock interaction during early mesogenesis through to orogenesis the early covariant trend of increasingly negative 13 c and 18 o values is attributed to increasing burial while a divergent orogenic trend of increasingly negative 18 o values is interpreted as the result of a loss of matrix permeability and interruption of fluid rock re equilibration these hottest fluids were concentrated along large thrusts which facilitated fluid movement during orogenesis

tectonic implication of quantitative micro fabric analyses of quartz c axis development within the tutak gneiss dome zagros hinterland fold and thrust belt quartz c axis fabrics finite strain and kinematic vorticity number analyses were used to investigate deformation characteristics of the tutak gneiss dome located in the eastern edge of the basement involved zagros hinterland fold and thrust belt the opening angle of the quartz c axis fabric patterns was used to estimate deformation temperatures which suggest greenschist to amphibolite facies conditions 430 50 c to 660 50 c the kinematic vorticity number varies from 0 6 to 0 95 mean kinematic vorticity number of 0 81 which indicates that the metamorphic rocks of the tutak gneiss dome experienced a sub simple shear regime by contribution of both pure shear 39 and simple shear 61 deformation components nw se striking foliations have commonly sw and ne dips accompanied by mostly nw se plunging and subordinate ne sw plunging stretching lineations these indicate more extension along the nw se trend to produce a prolate elliptical wedge shape in map view structural and vorticity analysis suggests that the tutak gneiss dome has experienced earlier dome formation followed by thrust stacking rather than the two deformations occurring synchronously and a protracted progressive deformation through a decreasing temperature regime

quartz c axis fabric development associated with shear deformation along an extensional detachment shear zone chapedony metamorphic core complex central east iranian microcontinent abstract lattice preferred orientations lpos of quartz were used to establish differences in deformation geometry finite strain and temperature across an extensional detachment shear zone within the chapedony metamorphic core complex in the central east iranian microcontinent along the northern flank of gondwana quartz c axis data show a continuous evolution across the core complex from asymmetric type i crossed girdles at the southwest margin to broken asymmetric type i crossed girdle and single girdle with a large concentration of axes plotted in the center of the stereoplot at the central parts of the core complex and small circle girdle pattern at the northeast margin these variations in quartz c axis patterns imply change in strain geometry during deformation from plane strain to general flattening and pure flattening integrating analyses of quartz c axis opening angles quartz c axis patterns and recrystalization regimes of quartz and feldspar suggests deformation temperatures range between less than 400 c and 650 c which yield greenschist to amphibolite facies conditions mean kinematic vorticity number wm measured in the mylonite samples ranges between 0 67 and 0 71 which indicates that exhumation of the metamorphic rocks of the cmcc was facilitated by a significant component of pure shear strain within a general shear regime

evolution of a calcite marble shear zone complex on thassos island greece microstructural and textural fabrics and their kinematic significance abstract the deformation history of a monophase calcite marble shear zone complex on thassos island northern greece is reconstructed by detailed geometric studies of the textural and microstructural patterns relative to a fixed reference system shear zone boundary szb strain localization within the massive marble complex is linked to decreasing p t conditions during the exhumation process of the metamorphic core complex solvus thermometry indicates that temperatures of 300 350 c prevailed during part of the shear zone deformation history the coarse grained marble protolith outside the shear zone is characterized by symmetrically oriented twin sets due to early coaxial deformation a component of heterogeneous non coaxial deformation is first recorded within the adjacent protomylonite enhanced strain weakening by dynamic recrystallization promoted strong localization of plastic deformation in the ultramylonite of the calcite shear zone where high strain was accommodated by non coaxial flow this study demonstrates that both a pure shear and a simple shear strain path can result in similar crystallographic preferred orientations single c axis maximum perpendicular to the szb by different dominant deformation mechanisms separated a axis pole figures a and a axis show different density distributions with orthorhombic texture symmetry in the protolith marble and monoclinic symmetry in the ultramylonite marble consistently with the observed grain fabric symmetry

turbulence structure in decoupled marine stratocumulus a case study from the astex field experiment the average and turbulence structure of two marine stratocumulus layers from the atlantic stratocumulus transition experiment are analyzed these layers were in adjacent air masses with different

observed lagrangian transition of stratocumulus into cumulus during astex mean state and turbulence structure aircraft measurements made during the first lagrangian of the atlantic stratocumulus transition experiment astex between 12 and 14 june 1992 are presented during this lagrangian experiment an air mass was followed that was advected southward by the mean wind five aircraft flights were undertaken to observe the transition of a stratocumulus cloud deck to thin and broken stratocumulus clouds penetrated by cumulus from below from the horizontal aircraft legs the boundary layer mean structure microphysics turbulence structure and entrainment were analyzed the vertical profiles of the vertical velocity skewness are shown to illustrate the transition of a cloudy boundary layer predominantly driven by longwave radiative cooling at the cloud top to one driven mainly by convection due to an unstable surface stratification and cumulus clouds during the last flight before the stratocumulus deck was observed to be broken and replaced by cumuli the total water flux the virtual potential temperature flux and the vertical velocity variance in the stratocumulus cloud layer were found significantly larger compared with the previous flights to analyze the cloud top stability the mean jumps of conserved variables across the inversion were determined from porpoising runs through the cloud top these jumps were compared with cloud top entrainment instability criteria discussed in the literature it is suggested that enhanced entrainment of dry air is a key mechanism in the stratocumulus cumulus transition

the stable internal boundary layer over a coastal sea part i airborne measurements of the mean and turbulence structure abstract it has been recognized that progress toward understanding the mesoscale structure of the ocean requires more knowledge of the small scale structure of the marine atmosphere and the processes that couple the air and the sea the coastal ocean is characterized by large variations in sea surface temperature and surface roughness that affect the structure of the atmosphere stable layers are frequent features of the coastal marine atmospheric boundary layer their main effect is the formation of a discontinuity between the sea surface and the upper part of the boundary layer that supports gravity waves wind speed jets and large wind shear the general structure of a stable internal boundary layer ibl that forms over the sea downstream of a warm landmass is discussed aircraft data are presented from the internal boundary layer experiment iblex conducted over the irish sea in 1990 with the airflow from the land to the sea thermodynamic profiles were obtained perpendicular to the coast to inv

evolution of c axis pole figures and grain size during dynamic recrystallization results from experimentally sheared quartzite 1 quartzite samples experimentally sheared at conditions where subgrain rotation and grain boundary migration recrystallization are active show a striking change in the c axis crystallographic preferred orientation cpo with increasing shear strain up to 8 and degree of recrystallization up to 100 we used optical methods to determine the c axis cpo for the bulk samples and for porphyroclasts and recrystallized grains separately and to track the strengths of the cpos in five different orientation domains with increasing the c axis pole figure evolves from a broad peripheral maximum indicative of basal a slip to an inclined single girdle with two maxima indicative of rhomb a slip and finally an elongate single maximum at the girdle center indicative of prism a slip throughout this sequence the fabric skeleton rotates with the sense of shear the bulk preferred c axis orientation results from growth and shrinkage of differently oriented crystallographic domains grain boundary density analysis indicates that the size of prism a recrystallized grains is 1 5 times that of average and 2 times that of rhomb grains indicating that prism a slip is significantly easier at our experimental conditions this inference is supported by autocorrelation function analysis of the various orientation domains and how they evolve with strain similar progressive changes in c axis cpo are observed in quartzites naturally sheared at conditions where grain boundary migration recrystallization operates these results indicate that achievement of microstructural and mechanical steady state requires high strain and complete recrystallization

texture development of recrystallised quartz polycrystals unravelled by orientation and misorientation characteristics abstract the development of microstructures and textures i e crystallographic preferred orientations during recrystallisation of naturally deformed quartz polycrystals has been studied via electron diffraction techniques in the scanning electron microscope in the investigated sample series of quartz rich rocks originating from different deformation regimes the microstructural and textural changes in quartz have been significantly influenced by dynamic recrystallisation based on microstructural observations paired with orientation and misorientation analyses down to the scale of grains and subgrains criteria could be established which characterise the dominant recrystallisation process and its influence on texture development it is shown that the texture development during dynamic recrystallisation is controlled by a differential activation of slip systems in grains of soft and hard orientations the analyses provide further evidence that specific grain orientations are preferred during crystal plastic deformation recrystallisation and grain growth the influence of twinning after the dauphine law was also investigated observations of a progressive reduction in the population of dauphine twin boundaries during recrystallisation and a penetrative deformation in both hosts and twins indicate a generation prior to deformation and recrystallisation a mechanical origin for twinning and possible influence on texture development was therefore discarded

hydrocarbon potential of the silurian and carboniferous shales in the western and central taurus region of turkey abstract organic maturity levels of the silurian and carboniferous shales in the western and central taurus regions are thermally over mature and therefore they can still contain shale gas a total of 43 samples were determined using toc analysis and rock eval pyrolysis to indicate the first basic hydrocarbon source rock characteristics average toc values of silurian samples range from 0 61 to 2 56 in wt however carboniferous samples have low toc values of less than 1 0 present low hydrogen index values between 2 and 14 mg hc g toc and average oil saturation index values ranging from 8 to 17 indicate that there is no hydrocarbon generation x ray diffraction data for the samples show the presence of quartz feldspar calcite dolomite mica and clay minerals the calculated illite crystallinity values of the samples usually fall into the diagenetic zone and wet gas generation zone corresponding to the late catagenesis stage sharpness ratio or weaver index values of the samples except for kayrak formation samples fall into the diagenetic zone on the other hand the calculated sharpness ratios of the kayrak formation samples between 2 35 and 5 15 indicate anchizone these results show that there is a consistency between the ic values sharpness ratios and rock eval pyrolysis data the data obtained in this study would be important during the evaluation of unconventional hydrocarbon resources in the future

the effect of dauphine twinning on plastic strain in quartz we present an electron backscatter diffraction analysis of five quartz porphyroclasts in a greenschist facies t 300 400 c granitoid protomylonite from the arolla unit of the nw alps mechanical dauphine twinning developed pervasively during the incipient stage of deformation within two porphyroclasts oriented with a negative rhomb plane z almost orthogonal to the compression direction z twin orientation twinning was driven by the anisotropy in the elastic compliance of quartz and resulted in the alignment of the poles of the planes of the more compliant positive rhomb r nearly parallel to the compression direction r twin orientation in contrast we report the lack of twinning in two porphyroclasts already oriented with one of the r planes orthogonal to the compression direction one twinned porphyroclast has been investigated with more detail it shows the localization of much of the plastic strain into discrete r twins as a consequence of the higher amount of elastic strain energy stored by r twins in comparison to z twins the presence of dauphine twins induced a switch in the dominant active slip systems during plastic deformation from basal regions without twinning to and pervasively twinned regions dynamic recrystallization is localized along an r twin and occurred dominantly by progressive subgrain rotation with a local component of bulging recrystallization part of the recrystallized grains underwent rigid body rotation approximately about the bulk vorticity axis which accounts for the development of large misorientation angles the recrystallized grain size piezometer for quartz yields differential stress of 100 mpa the comparison of this palaeostress estimate with literature data suggests that mechanical dauphine twinning could have a potential use as palaeopiezometer in quartz bearing rocks

fabric domains in quartz mylonites localized three dimensional analysis of microstructure and texture fabric domains of a quartz vein deformed under greenschist facies conditions arc analysed with domainal x ray texture goniometry optical microscopy computer integrated polarization microscopy cip and shape analysis in two mutually perpendicular sections the analysed domains consist of large non recrystallized deformed clast fragments prolate non recrystallized ribbon grains and prolate recrystallized domains in terms of texture monomaximal and polymaximal domains have been distinguished pronounced partitioning of deformation is observed between these domains this strain partitioning asks for caution when making kinematic inferences for fault zones based on a study of domainal fabrics domains persist as fabric elements up to high strains this emphasizes the often neglected role of a non random initial fabric neighbouring domains with alternating c axis orientations and grain boundary preferred orientations indicating opposing senses of shear occur in both sections the bulk texture is controlled by clast and ribbon domains rather than being strictly deformation induced we infer that prolate elongation of clasts and ribbons is achieved mainly by combined prism and basal slip recrystallized domains are characterized by different textures they are deformed by intracrystalline slip combined with grain boundary migration and sliding inclined preferred grain boundary orientations are continuously maintained by grain boundary migration copyright 0 1996 elsevier science ltd

fabric controls on strain accommodation in naturally deformed mylonites the influence of interconnected micaceous layers abstract we present microstructural analyses demonstrating how the geometrical distribution and interconnectivity of mica influences quartz crystallographic preferred orientation cpo development in naturally deformed rocks we use a polymineralic qtz pl kfs bt ms grt tur mylonite from the zanskar shear zone a section of the south tibetan detachment nw himalaya to demonstrate how quartz cpo intensity decreases from quartz dominated domains to micaceous domains independently of whether or not quartz grains are pinned by mica grains we then use a bimineralic qtz ms mylonite from the main central thrust nw himalaya to show how increasing mica grain connectivity is concomitant with a systematic weakening of quartz cpo our results draw distinctions between cpo weakening due to i second phase drag leading to ineffective recovery in quartz and ii increased transmission and localisation of strain between interconnected mica grains in the latter case well connected micaceous layers take up most of the strain weakening the rock and preventing straining of the stronger quartz matrix our findings suggest that rock weakening in quartz rich crustal rocks is influenced not only by the presence of mica rich layers but also the degree of mica grain connectivity which allows for more effective strain localization through the entire rock mass

microstructural compositional and petrophysical properties of mylonitic granodiorites from an extensional shear zone rhodope core complex greece at the southern boundary of the rhodope massif ne greece the kavala shear zone ksz represents an example of the eastern mediterranean deep seated extensional tectonic setting during miocene time extensional deformation favoured syntectonic emplacement and subsequent exhumation of plutonic bodies this paper deals with the strain related changes in macroscopic geochemical and microstructural properties of the lithotypes collected along the ksz comprising granitoids from the pluton aplitic dykes and host rock gneisses moreover we investigated the evolution of seismic anisotropy on a suite of granitoid mylonites as a result of progressive strain isotropic compressional and shear wave velocities v p v s and densities calculated from modal proportions and single crystal elastic properties at given pressure temperature p t conditions are compared to respective experimental data including the directional dependence anisotropy of wave velocities compared to the calculated isotropic velocities which are similar for all of the investigated mylonites average values v p 5 87 km s 1 v s 3 4 km s 1 v p v s 1 73 and density 2 65 g cm 3 the seismic measurements give evidence for marked p wave velocity anisotropy up to 6 92 at 400 mpa in the most deformed rock due to marked microstructural changes with progressive strain as highlighted by the alignment of mica chlorite minerals and quartz ribbons the highest p and s wave velocities are parallel to the foliation plane and lowest normal to the foliation plane importantly v p remains constant within the foliation with progressive strain but decreases normal to foliation the potential of the observed seismic anisotropy of the ksz mylonites with respect to detectable seismic reflections is briefly discussed

the annual warm to cold phase transition in the eastern equatorial pacific diagnosis of the role of stratus cloud top cooling abstract the forcing of the march to may southerly surface wind tendency along the equatorial south american coast which leads to the annual transition of the eastern tropical pacific basin s climate from its peak warm phase in april is explored through diagnostic modeling modeling experiments with a high resolution 18 levels 2 5 30 zonal waves steady state global linear primitive equation model that produces a striking simulation of most aspects of the march to may change in the lower tropospheric circulation over the eastern tropical pacific including the notable southerly surface wind tendency have provided unique insight into the role of various physical processes the model is forced by the 3d distribution of the residually diagnosed diabatic heating and the submonthly momentum and thermal transients all obtained from the twice daily 2 5 2 5 european centre for medium range weather forecasts uninitialized analyses for 1985 95 the principal findings are the following the initia

tourmaline bearing rocks in the singhbhum shear zone eastern india evidence of boron infiltration during regional metamorphism frozen in reaction textures combined with mineral chemistry of tourmaline bearing metamorphic assemblages provide valuable information about fluid rock interaction during orogenesis tourmaline occurs in four distinct mineralogical associations in the singhbhum shear zone ssz of the precambrian east indian craton the tourmaline bearing rocks are associated intimately with pelitic to psammopelitic and quartzofeldspasthic rocks including meta granite the rocks were affected by two sets of folding f1 and f2 and ductile shearing associated with f1 during ca 1 6 1 8 ga tectonic activity in this belt quantitative geothermobarometry and the stability relations of the metamorphic assemblages developed in the pelitic rocks establish the presence of two episodes of metamorphism a prograde m1 event that culminated at 480 40 c 6 4 0 4 kbar and an m2 event that caused retrogression of the m1 assemblages field and petrographic observations in combination with data on chemical composition of tourmaline indicate three stages of tourmaline growth the earliest stage is represented by pretectonic pre metamorphic greenish yellow tourmaline cores in the tourmalinite from the surda area association a the textural relations demonstrate that in the second stage greenish yellow cores of oscillatory zoned tourmaline in the metagranite albite quartz biotite chlorite muscovite apatite magnetite association c very fine tourmaline grains in muscovite schist muscovite quartz association b and greenish yellow cores of tourmaline in biotite muscovite schist biotite muscovite magnetite chlorite apatite quartz association d crystallized during the f1 m1 events post tectonic greenish blue tourmaline belonging to the third stage replaces the earlier tourmaline grains along their margins and cracks compositionally tourmalines of all four associations fall in the alkali group most of the data fall in the dravite field with a few analyses straddling the boundary between schorl and dravite an abrupt compositional change was noted across the different color zones in the tourmaline grains this change is explained by one or more of the coupled substitutions al nar 1 car naal 1 and mg fe 1 where r mg fe2 mn integrating the field petrographic and phase compositional data it has been demonstrated that tourmaline growth in the second and third stages was induced by infiltration driven b metasomatism during prograde metamorphism of the rocks deep seated magma was the source of the b bearing hydrothermal fluid

structural setting of a transpressive shear zone insights from geological mapping quartz petrofabric and kinematic vorticity analysis in ne sardinia italy

revisiting elastic anisotropy of biotite gneiss from the outokumpu scientific drill hole based on new texture measurements and texture based velocity calculations abstract a sample of biotite gneiss from the outokumpu deep drilling project in finland was investigated by kern et al 2008 for crystal preferred orientation and elastic anisotropy considerable differences between measured acoustic velocities and velocities calculated on the basis of texture patterns were observed measured p wave anisotropy was 15 1 versus a voigt average yielding 7 9 here we investigate the same sample with different methods and using different averaging techniques analyzing time of flight neutron diffraction data from dubna skat and lansce hippo diffractometers with the rietveld technique much stronger preferred orientation for biotite is determined compared to conventional pole figure analysis reported previously the comparison reveals important differences hippo has much better counting statistics but pole figure coverage is poor skat has better angular resolution using the new preferred orientation data and applying a self consistent averaging method that takes grain shapes into account close agreement of calculated and measured p wave velocities is observed 12 6 this is further improved by adding 0 1 vol flat micropores parallel to the biotite platelets in the simulation 14 9

syndeformational magnetization in the ordovician bigfork chert at black knob ridge western ouachita mountains southern oklahoma abstract paleomagnetic and rock magnetic results from unweathered samples of the ordovician bigfork chert at black knob ridge in southern oklahoma indicate the presence of a pervasive magnetization that resides in magnetite the magnetization has a steep southeast direction small and medium scale folds acquired magnetization during or after carboniferous folding the declination in sites along black knob ridge also shows a north to south 28 counter clockwise shift the bigfork chert at black knob ridge was folded and thrusted along the ti valley fault system in the late paleozoic a pervasive late paleozoic magnetization with a shallow inclination occurs in the laterally equivalent viola limestone in front of the thrust and in the arbuckle mountains this direction is used as a reference for comparison with the bigfork chert formation at black knob ridge the steep inclinations in the rocks at black knob ridge are interpreted to be primarily the results of rotation around a horizontal axis as a result of thrusting the declination change along the ridge is also interpreted to be the result of rotational movements during thrusting the pervasive magnetizaion at black knob ridge is interpreted to have been acquired during the deformation the results of fold tests and an incremental test correcting for both strike and dip suggest remanence acquisition during late stage folding and during an early stage of thrusting the low thermal history of the bigfork chert suggests that the pervasive component is a chemical remanent magnetization crm although a strain related mechanism cannot be definitely ruled out the proposed crm may be related to fluid migration through fractures produced during folding and thrusting alternatively an in situ chemical process e g maturation of hydrocrabons may have caused the remagnetization

lattice strain measurements on sandstones under load using neutron diffraction abstract neutron diffraction methods both time of flight and angle dispersive diffraction are applied to intracrystalline strain measurements on geological samples undergoing uniaxial increasing compressional load the experiments were carried out on cretaceous sandstones from the elbezone east germany consisting of 95 quartz which are bedded but without crystallographic preferred orientation of quartz from the stress strain relation the young s modulus for our quartz sample was determined to be 72 2 2 9 gpa using results of the neutron time of flight method the influence of different kinds of bedding in sandstones laminated and convolute bedding could be determined we observed differences of factor 2 convolute bedding and 3 laminated bedding for the elastic stiffness determined with angle dispersive neutron diffraction crystallographic strain and with strain gauges mechanical strain the data indicate which geological conditions may influence the stress strain behaviour of geological materials the influence of bedding on the stress strain behaviour of a laminated bedded sandstone was indicated by direct residual stress measurements using neutron time of flight diffraction the measurements were carried out six days after unloading the sample residual strain was measured for three positions from the centre to the periphery and within two radial directions of the cylinder we observed that residual strain changes from extension to compression in a different manner for two perpendicular directions of the bedding plane