detection and classification of surface roughness in an arctic marginal sea ice zone sea ice dynamic and thermodynamic processes are important and highly variable elements of the marginal ice zone miz this study examines the detection and classification of statistically separable sea ice classes in the miz through a range of temporal and spatial scales a helicopter based laser system was used to obtain large scale and a ship based laser profiler to identify small scale roughness types respectively the analysis of variance of surface height data from helicopter and ship based laser systems active microwave amw c band backscattering data and passive microwave pmw 37 and 89 ghz brightness temperature data reveal different classes that statistically differ from one another we found significant statistical difference in variances in amw data with six classes that differ in vv polarization three classes in vh polarization and five classes in hh polarization in the miz e g snow covered first year ice ice rubble pancake ice frost flowers melt pond flooded ice and ice edge of southeastern beaufort sea the pmw emission was not as effective at discrimination yielding only one statistically separable class the results can potentially be extended to satellite based investigations of the miz at regional scales copyright 2012 john wiley sons ltd

modelling plastic deformation of peridotite with the self consistent theory theories for deformation of polycrystals have been substantially refined enabling us to model deformation of metals and minerals with considerable sophistication so far most modelling has been confined to single phase aggregates such as quartzite and limestone we present the first results for a polyphase aggregate peridotite consisting of 70 olivine and 30 enstatite the problem is approached with a viscoplastic self consistent theory satisfying stress equilibrium and strain compatibility for the average polycrystal and taking account of anisotropic neighbor interactions it is assumed that olivine deforms by 010 100 001 100 and 010 001 slip and enstatite deforms by 100 001 slip simulated textures for olivine and enstatite in peridotite resemble simulated textures in the pure phases indicating that for this system and for these volume fractions there is little influence of the different phases upon each other in our model the harder mineral enstatite deforms at a slower rate than olivine interaction between neighboring grains appears to be minimal which may be due to model assumptions predicted pole figures with olivine 010 axes and enstatite 100 axes aligning with the direction of shortening are in good agreement with preferred orientations in naturally and experimentally deformed peridotites

microstructures and c axis fabrics indicative of quartz dissolution in sheared quartzites and phyllonites abstract quartzites sheared in low metamorphic grade shear zones that extend along the contact with migmatitic gneissic complexes in the quadrilatere ferifero region southeastern brazil show quartz microstructures indicating deformation by dissolution dissolution occurred adjacent to the foliation planes preferentially in quartz porphyroclasts oriented with their 0001 planes parallel to the foliation dissolution worked as an efficient mechanism to remove porphyroclast edges smoothing foliations and enabling strain accommodation both dissolution and crystal plasticity were competitive crystallographically controlled processes operating in different domains of the evolving microstructure dissolution occurred along the foliation planes while isovolume crystal plasticity and accompanying recrystallization operated essentially in the quartzose domains between folia phyllonites formed in the most strained domains of the shear zones fine grained quartz grains in phyllonites show uncommon c axis fabrics c axis oriented at low angles to the stretching lineation which were interpreted to form either by direct reprecipitation or by residual concentration of grains unfavourably orientated to undergo dissolution domainal c axis fabrics reflect a deformation partitioning path with increasing participation of solution transfer strengthening c axis maxima at low angles with the stretching lineation at the expense of crystal plastic processes during progressive phyllonitization

fabric transitions in the saxony granulite terrain abstract quartz fabric transitions reported from the saxony granulite terrain and from the nearby ore mountains are interesting because of the changes in the pattern types and the variation in the opening angles of the fabric skeletons a short summary is presented of salient features in research documented in the east german literature between 1961 and 1978 the changes in fabric skeleton with decreasing metamorphic grade are proposed as mainly consequent to the deactivation of prism c glide systems as temperature decreases fabrics indicative of the appearance of the c burgers vector might be diagnostic for deformation in regimes of comparatively high temperatures or low strainrates or for deformation under conditions such that there is a relatively high kinetically effective hydroxyl content in the quartz structure

pure shear and simple shear calcite textures comparison of experimental theoretical and natural data abstract the pattern of lattice preferred orientation texture in deformed rocks is an expression of the strain path and the acting deformation mechanisms a first indication about the strain path is given by the symmetry of pole figures coaxial deformation produces orthorhombic pole figures while non coaxial deformation yields monoclinic or triclinic pole figures more quantitative information about the strain history can be obtained by comparing natural textures with experimental ones and with theoretical models for this comparison a representation in the sensitive three dimensional orientation distribution space is extremely important and efforts are made to explain this concept we have been investigating differences between pure shear and simple shear deformation incarbonate rocks and have found considerable agreement between textures produced in plane strain experiments and predictions based on the taylor model we were able to simulate the observed changes with strain history coaxial vs non coaxial and the profound texture transition which occurs with increasing temperature two natural calcite textures were then selected which we interpreted by comparing them with the experimental and theoretical results a marble from the santa rosa mylonite zone in southern california displays orthorhombic pole figures with patterns consistent with low temperature deformation in pure shear a limestone from the tanque verde detachment fault in arizona has a monoclinic fabric from which we can interpret that 60 of the deformation occurred by simple shear

misorientation analysis and the formation and orientation of subgrain and grain boundaries in contrast to the behaviour of individual grains both inter and intra granular boundaries within rocks have received much less attention however many geological processes particularly during deformation e g yielding dislocation creep recrystallisation superplasticity and various fracture mechanisms and petrophysical properties depend to some extent on the nature of boundaries present in a rock in this contribution we consider the role of intergranular and intragranular crystal boundaries a precise characterisation of such boundaries depends on defining the crystallographic and dimensional orientations of the boundary and the misorientation between the adjacent regions i e grains subgrains etc separated by the boundary although several theoretical descriptions of boundary configuration are available practical precision is lacking and approximations are necessary we describe two specific approximations for boundary formation and orientation obtained using the sem electron channelling technique the first is a geometrical interpretation of electron channelling patterns ecp in terms of the likely formation and orientation of the intervening boundary the second considers the misorientation between adjacent regions across a boundary this involves a model which assumes a simple geometrical relationship between crystal slip systems responsible for the rotation and misorientation between adjacent regions and the formation and orientation of the resulting boundary these approximations are capable of a identifying trends in the dispersion of crystallographic directions during deformation b identifying active slip systems c calculating the relative schmid factors for each crystal slip system and therefore the most likely system to be activated d modelling synthetic misorientations and predicting the crystal slip systems and boundary configurations to be expected and e comparing real data with synthetic models our analyses are illustrated via natural examples of dynamic recrystallisation in quartzite and a theoretical simulation of the behaviour of an individual quartz grain during deformation

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

discriminatory petrofabric analysis of quartz rocks using sem electron channelling abstract this paper describes the first use of sem electron channelling in quartz petrofabric analysis the technique is discriminatory in that the complete crystallographic orientation of an individual grain is measured via electron channelling pattern ecp and orientation contrast images ecp s are unique for a particular crystal orientation and are indexed by comparison with spherical ecp maps which extend over the full stereographic projection required by crystal symmetry the ecp map recognizes the true trigonal nature of quartz symmetry and therefore extends over one third of a hemisphere we show how both inverse pole figure and pole figure diagrams can be constructed from ecp data using as an example a quartzite from northwest scotland

effect of water on the rheology of experimentally deformed quartzite empirical flow laws have been determined for simpson quartzite samples deformed to mechanical steady state in the quartz stability field using griggs blacic solid medium deformation apparatus experiments were conducted on samples both as received dry and with water added via the dehydration of a talc confining medium wet best fits of the power law type yield a stress exponent of 2 72 0 19 an activation enthalpy of 134 32 kj mol 1 and a preexponential constant of 1 16 1 15 0 58 10 7 mpa 2 72 s 1 for the dry quartzite law and are 2 61 0 15 145 17 kj mol 1 and 5 05 5 00 10 6 mpa 2 61 s 1 for the wet quartzite the enhanced hydrolytic weakening of the wet experiments appears to affect the flow laws mostly in the preexponential constants possibly as a defect concentration term that is higher in the wet than in the dry law over the range of experimental conditions 750 900 c 10 7 to 10 4 s 1 and 1 0 1 25 gpa confining pressure dry specimens are 1 5 2 5 times stronger than wet samples deformed at the same conditions the microstructures produced are analogous to those observed in many natural quartz tectonites recrystallization is well developed in the wet but not the dry specimens at flow stresses below 500 mpa microstructures indicative of recovery are well developed a comparison of our creep activation enthalpies with those determined from diffusion experiments are consistent with deformation of wet simpson quartzite that is limited by oxygen self diffusion inconsistencies between the present study and previous studies are probably the result of differences in sample material sample treatment and sample assemblies chemical environment

boundary layer upper ocean and ice observations in the greenland sea marginal ice zone during the 1984 marginal ice zone experiment a coordinated ocean boundary layer and mixed layer experiment was carried out in concert with a complete heat and mass balance study in the summer marginal ice zone miz of the greenland sea the measurements were made at two drifting ice stations and included observations of ocean boundary layer turbulence profiles of water temperature salinity and velocity ice ablation ice concentration solar radiation and spectral albedos ocean conditions were found to be extremely variable the ice and water velocities were heavily influenced by tidal and inertial motions with amplitudes from 6 to 12 cm s 1 in the course of the drift a 30 km eddy was crossed wherein ice and water velocities exceeded 15 cm s 1 the northern extension of the east greenland polar front was encountered and a northward flow of atlantic water into the arctic basin was observed below the eastern edge of the front but the drift station never moved quite far enough west to be caught in the southward transport of arctic surface water heat from the ocean was a major factor in ice melt and when the ice was over atlantic water it was the dominant factor the events that had the greatest impact on the ice were two outbreaks during which off ice winds blew the ice across warm ice edge ocean fronts once south of these fronts and over surface water as warm as 1 c the ice bottom melted at rates up to 100 kg m 2 d 1 the rapid changes in stratification associated with the outbreaks had a dramatic impact on the drag and heat transfer coefficients the drag coefficient relative to the square of the relative water velocity at 30 m ranged from 0 002 to 0 02 and averaged 0 006 the heat transfer coefficient relative to the friction velocity u and the mixed layer temperature elevation above freezing ranged from 0 0025 to 0 009 and averaged 0 0038 in agreement with the idea that stratification inhibits turbulent exchange the heat transfer coefficient decreased when stratification increased in fact the observed melt rates can be simulated well if molecular heat and salt transfer through a thin near surface laminar boundary layer are accounted for as well as transfer through the turbulent outer boundary layer also in agreement with turbulent boundary layer theory the drag coefficient decreased when stratification increased slightly above neutral however for the large increases in surface stratification the drag coefficient increased this was due to the generation of internal gravity waves by ice bottom roughness because the surface exchange coefficients are so sensitive to surface stratification which is in turn highly variable in the miz accurate simulations of ice motion and ice melt will require realistic estimates of stratification and a good understanding of the relation between the ice ocean interactions and upper ocean conditions

comments on the interpretation of deformation textures in rocks abstract in rocks that undergo ductile deformation preferred orientation develops as a result of intracrystalline slip and mechanical twinning the orientation distribution is a consequence of the microscopic mechanisms and of the strain path it can be used to get some insight into the deformation history however it is never unique the interpretation relies largely on polycrystal plasticity theory the concepts of stress equilibrium and strain compatibility which are two extreme assumptions made to model deformation are discussed new approaches such as the viscoplastic self consistent theory are a compromise and may be applicable to mineral systems which display a high degree of plastic anisotropy important extensions allow for heterogeneous deformation in the polycrystal from grain to grain and even within grains in correspondence with microstructural observations all these theories defy the popular notion which is becoming entrenched in the geological literature that the microscopic slip plane normal aligns with the axis of maximum principal compressive stress and that in simple shear the crystallographic slip plane rotates into the macroscopic shear plane and the slip direction into the macroscopic shear direction an orientation referred to by geologists as easy glide it is emphasized that future work on texture development of rocks should be based on rigorous physics rather than ingenious intuition in accordance with an old recommendation of walter schmidt

a comparison of quartz c axis preferred orientations in experimentally deformed aplites and quartzites the effect of feldspar on the development of quartz c axis preferred orientations was investigated by experimentally deforming aplite 30 quartz and pure quartzite under equivalent conditions and comparing the quartz c axis patterns axial compression experiments were performed at temperatures of 800 and 900 c strain rates of 10 6 and 10 5s 1 and a confining pressure of 1500 mpa under these conditions both quartz and feldspar deform by dislocation creep with only minor syntectonic recrystallization the quartz c axis preferred orientations produced in the two rock types at equivalent deformation conditions and quartz grain strains were found to be essentially identical in pattern and strength these results indicate that the presence of feldspar has little or no effect on the operative slip systems in adjacent quartz grains in quartzo feldspathic rocks and that quartz c axis preferred orientation analyses can be performed on a wide range of crustal rock types

investigation of the strength contrast at the moho a case study from the oman ophiolite we investigate the viscosity contrast between the crust and mantle by analysis of deformed gabbronorite dikes in the mantle section of the oman ophiolite our study provides a rare opportunity to directly constrain the rheological contrast between a plagioclase rich lithology typical of the lower crust and an olivine dominated harzburgite we constrain deformation conditions using field relationships geothermometry grain size piezometry and electron backscatter diffraction the viscosity of gabbronorite was at least two orders of magnitude lower than the viscosity of the harzburgite consistent with the rheological contrast between plagioclase and olivine calculated via experimental flow laws these flow laws predict that a significant viscosity contrast exists at the crust mantle boundary where the crustal lithology is dominated by plagioclase or where deformation localizes within plagioclase rich layers

bottom ablation and heat transfer coefficients from the 1983 marginal ice zone experiments bottom ablation in the marginal ice zone miz is a fundamental process that controls the ice edge position in both the winter and the summer during the east and west marginal ice zone experiments mizex west and mizex east in 1983 periodic sonic distance measurements between the overlying ice and transducers fixed on masts below ice floes determined the bottom ablation the melt rates for floes within 15 km of the ice edge ranged from near zero when the ice was in water at the freezing point to 0 5 m d 1 when the ice entered warm water greater than 3 k to the south simultaneous velocity and temperature measurements at 2 m below the ice in mizex west and at 2 m and 10 m below the ice in mizex east show the response of the melt rate to changing oceanographic conditions for the first time the combined oceanographic and ablation measurements allow the direct calculation of the bulk heat transfer coefficient ch between the ice and the ocean at 2 m and 10 m below the ice for the bering sea experiment ch was 8 10 4 while for the fram strait experiment ch varied from 2 10 4 to 4 10 4 within each set of experiments ch remained nearly constant over a wide range of melt rates relative ice water speeds and seawater temperatures

thin ice impacts on surface salt flux and ice strength inferences from advanced very high resolution radiometer temperatures and albedos derived from satellite imagery are combined with a thermodynamic ice model to estimate thin ice thickness distributions over the beaufort and the northern greenland seas the study shows that thin ice thinner than 1 m occupied over half the area in the seasonal ice zones in november and december of 1990 but dropped significantly in april 1991 the beaufort shelf showed the largest seasonal change the aggregate properties of surface salt flux and compressive ice strength both strongly dependent on the thin end of the ice thickness distribution were estimated with data from advanced very high resolution radiometer to reveal the spatial and temporal variations over a large scale the salt flux from growing thin ice was 1 2 orders of magnitude larger on the beaufort and greenland shelves than in the deep basins on the shelves flux from thin ice accounted for over 90 of the total surface salt budget these satellite derived estimates provided detailed spatial information on salt flux which can be of great use in studies of surface patterns of salinity forcing and shelf basin interaction also revealed by the satellite data was the wide range in values of compressive strength which affects how freely the ice cover can deform strengths were low in early winter and in seasonal ice zones and nearly doubled in spring both thin ice fraction and compressive ice strength estimated from satellite imagery were in good agreement with those simulated by a coupled ice ocean model monitoring the seasonal and interannual behavior of sea ice properties with noaa satellites is both an opportunity and a challenge the opportunity arises from twice daily overpasses which provide excellent coverage of the polar ocean the challenge lies with the surface being sampled sea ice appears radiometrically similar in the imagery of advanced very high resolution radiometer avhrr making it difficult to monitor for example the mass of the sea ice cover compromises in which useful ice properties match what satellites can distinguish must be made one useful property is the surface area and thickness of thin ice defined here as ice with thickness 1 m in winter thin ice has a warmer surface and appears darker than the surrounding thicker ice these thermal contrasts form the basis for the approach followed in this paper an example of a clear sky avhrr image over the southern canada basin shows the leads as linear dark red and orange features that are 10o 20oc warmer than the thick floes plate 1 since thin ice in leads responds rapidly to changes in wind and temperature and is generally covered with no or little snow the thickness of thin ice not just its presence can be inferred directly from the radiative surface temperature detected by the satellite fortuitously several aggregate properties are sensitive to thin ice and can be largely or completely determined by thin strength of the ice cover figure 1 shows an annual cycle of salt flux from both thin and thick ice while the thick ice continues melting negative salt flux in september thin ice grows vigorously as the air cools the growing thin ice dominates the total salt budget until january when thicker ice reaches the peak of its growth cycle in the annual mean brine rejection from thin ice is about 8 times larger than that from thicker ice profoundly affecting the density structure of underlying water thin ice also controls the compressive strength p and thus the mechanical behavior of sea ice high percentages of thin ice reduce the stresses transmitted among ice floes and make pressure ridges more likely to form the compressive ice strength can be related explicitly to the thin end of the ice thickness distribution e g rothrock 1975

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

multiyear sea ice thermal regimes and oceanic heat flux derived from an ice mass balance buoy in the arctic ocean the conductive and oceanic heat fluxes and the mass balance of sea ice were investigated utilizing an ice mass balance buoy imb deployed in the arctic ocean after imb deployment the ice thinned from 1 95 m in late august to 1 46 m by mid october 2008 from then on ice growth until mid june 2009 increased the ice thickness to 3 12 m the ice temperature and consequently the conductive heat flux at the ice surface exhibited persistent high frequency variations due to diurnal and synoptic scale atmospheric forcing these signals propagated downward with damped magnitude and temporal lag the competition of oceanic and conductive heat flux dominated the low frequency variations of ice growth however high frequency variations in ice growth were controlled largely by the oceanic heat flux from mid november 2008 to mid june 2009 the average oceanic heat flux along a track from 86 2 n 115 2 w to 84 6 n 33 9 w was 7 1 w m2 this was in agreement with that derived from an imb deployed in 2005 about 1 5 to the north of our buoy we attributed the relatively high oceanic heat flux 10 15 w m2 observed during autumn and early winter to summer warming of the surface ocean upward mixing of warm deep water as observed when our buoy drifted over the shallow region of the lomonosov ridge 85 4 85 9 n 52 2 66 4 w demonstrated the impact of bathymetry on the oceanic heat flux under ice cover and consequently on the basal ice mass balance 2013 american geophysical union all rights reserved

a theory for plastic deformation and textural evolution of olivine polycrystals seismic anisotropy in the upper mantle is due primarily to preferred orientation of olivine crystals induced by progressive deformation in order to understand better the origin of seismic anisotropy we present a simple theory for plastic deformation and textural evolution of olivine polycrystals each crystal in the aggregate is assumed to deform by intracrystalline slip on three major slip systems whose hardnesses and stress exponents are known from experiments the evolving grain orientation distribution in the aggregate is calculated by minimizing the difference between the local crystal deformation and the global aggregate deformation subject to the constraint of global strain compatibility the axial compression texture predicted by our model agrees well to first order with that determined experimentally by nicolas et al 1973 although there are significant discrepancies in the details our results suggest that the orientation texture developed during progressive plane strain deformation is a nearly unique function of the finite strain such that the crystallographic axes 100 010 and 001 are concentrated around the finite strain axes a c and b respectively a b c this result may allow the state of finite strain at depth to be estimated from observations of seismic anisotropy

winter mixed layer entrainment of weddell deep water observations from the somov during the us ussr weddell polynya expedition show that the mixed layer below the sea ice just prior to the austral spring retreat in the 60 s greenwich meridian region has an oxygen content of 7 4 ml 1 this is 86 of full oxygen saturation representing an oxygen deficit relative to full saturation of 1 1 ml 1 the source of this deficit is believed to be a consequence of oxygen poor 4 5 ml 1 weddell deep water wdw entrainment by the winter mixed layer assuming effective cutoff of ocean atmosphere oxygen exchange by the nearly complete snow and sea ice cover with no net impact of oxygen content as a result of biological factors a mixing ratio of 1 3 for wdw to beginning of winter surface water is required to explain the end of winter mixed layer oxygen content accompanying the wdw transfer into the mixed layer is heat transfer of approximately 7 103 cal cm2 2 9 108 j m2 during the five winter months of sea ice coverage as well as salt transfer which requires 34 cm of fresh water to produce typical mixed layer salinity during the seven ice free months when entrainment is expected to be minor diffusive heat and salt flux continues a mean annual heat flux of 12 w m2 is suggested with an annual demand for freshwater of 46 cm yr consideration of the winter period salinity budget indicates net sea ice melting of 20 cm which can be attributed to regional convergence of sea ice the remaining freshwater is derived from excess precipitation and possibly iceberg melt oxygen undersaturation of the winter surface water suggests slightly less potential for abyssal water ventilation than might be expected from a fully saturated condition

plastic anisotropy and geometrical hardening in quartzites abstract lattice rotation in crystals which creates a characteristic preferred orientation in deformed tectonites takes place whenever slip dislocation glide is involved in the deformation process the crystal lattice either rotates to an orientation favorable for further slip or to one that is unfavorable resulting in an overall hardening or softening of the polycrystal during deformation this effect of plastic anisotropy which arises due to changes in the crystal orientation distribution is analyzed quantitatively for quartz polycrystals using the taylor model the results indicate that in easy basal a slip region low temperature quartzites become softer in flattening with increasing strain whereas in easy prism a slip region high temperature quartzites become softer in elongation with increasing strain accordingly deformation is facilitated by flattening at low temperature and by elongation at high temperature if it can be heterogeneous to a certain degree this is borne out by geological observations which indicate that at low metamorphic grade flattening to plane strain is the most frequently observed strain mode e g moine thrust whereas at high metamorphic grade constriction is favored e g sambagawa belt the strain distribution in a large geological body may depend on internal anisotropic plastic properties such as preferred slip systems as well as imposed external boundary conditions heterogeneities are also observed on the hand specimen scale grains in orientations where easier slip systems are difficult to activate remain relatively undeformed in a ductile matrix consisting of grains in which strain is accommodated mostly by easier slip systems some aspects of the taylor model for creep rate sensitivity are discussed

a 3 d kinematic model of fabric development in polycrystalline aggregates comparisons with experimental and natural examples abstract a 3 d generalization of the approach previously developed by etchecopar for the simulation of fabrics in polycrystalline aggregates is presented the model is based on a geometric minimization of gaps overlaps and boundary displacements between deformed neighbouring cells each cell may deform using a small number

simulation of fabric development in recrystallizing aggregates i description of the model abstract a new computer simulation of the development of grain shape and crystallographic preferred orientations in dynamically recrystallizing aggregates is presented this model is based on a uniform array of points each of which represents a small area of crystal this model combines homogeneous strains simplified versions of the lattice rotations predicted by taylor bishop hill theory mobile grain boundaries and the nucleation of subgrains it allows the progressive development of the fabrics and microstructures to be followed the limitations of the simplifying assumptions used in this model are discussed

the relationship of strain and preferred orientation of phyllosilicate grains in rocks a review abstract the calculation of strain from the preferred orientation of platy phyllosilicate grains taking strain to be homogeneous is surprisingly often successful from a pragmatic point of view although numerous theoretical objections to this procedure can be and have been raised for the calculation to succeed the original distribution of mica or clay mineral grains must be known or assumed the usual assumption that the starting distribution was random and therefore nearly uniform implies that the strain history of pelitic sediments is taken to start when the watery sediment was last stirred by waves or bioturbation or if it was laid down in still anoxic waters from the moment of first deposition it therefore includes compaction as part of the strain history which is usually neglected by structural geologists originally random distribution of clay flake orientations has been observed in recently deposited sediments in many instances and has been theoretically explained in various ways exceptions probably exist but their frequency has not been estimated biologically disturbed sediments may be brought nearer to a state of random orientation of clay flakes than they were at deposition with the exception of whole beds or concretions in which pores are early filled with cement mudrocks are almost always compacted by the weight of later deposits the strain so induced is axially symmetric about the vertical and thus about the pole of the bedding planes compaction acts on soft unconsolidated rocks but may continue with increasing overburden on rocks strengthened by cementation and by increasing interlocking of grains tectonic deformation may start early before the rock is fully compacted or it may begin only much later and the mechanisms of deformation increase in complexity with the increasing temperature and hydrostatic stress of deeper burial up to a certain level of mild metamorphism however phyllosilicate grains seem to be rather permanent if not as mineral species then at least by preservation of their constituent sheets of silica tetrahedra given this permanence the mechanisms of rock deformation whether intergranular slip cataclasis or dissolution and reprecipitation and various intragranular processes in the non phyllosilicate matrix hardly matter as far as the recording of strain is concerned even a certain amount of stress solution at especially heavily loaded points of the phyllosilicate grains themselves does not destroy their value as strain markers as long as the dissolved material is disposed of mainly by crystallographically continuous overgrowth on existing grains the same holds for local dissolution of phyllosilicates in portions of old grains that have become thermodynamically unstable by bending widespread irregular or random nucleation and growth of newly nucleated phyllosilicate grains at intermediate or high grades of metamorphism can reduce the reliability of the strain record and so can domainal structure of the deformed rock if both the volume fraction of phyllosilicate grains and the intensity of total strain differ sharply from one domain to another if distinct domains are not equant and have themselves a strong preferred orientation of shape nevertheless rocks containing an anastomosing network of zones rich in phyllosilicate grains as slates and other deformed mudrocks commonly do have in many cases been found to have average preferred orientations of mica or chlorite which if used to estimate the strain give results similar to those obtained from independent strain markers in the same rocks thus the most significant verification of the usefulness of strain estimates by measurement of preferred orientation is the mutual confirmation with independently determined strain the limit to such verification is the rarity of strain markers so that the coexistence of two independent ones is exceptionally rare for this reason however it is important to make full use of the orientation of phyllosilicate grains where they are available the alternative to have no strain measurements at all causes structural geologists to miss potential information

oceanic heat flux in the fram strait measured by a drifting buoy as one component of the arctic environmental drifting buoy two thermistor strings were installed through the ice to measure ice temperatures and determine oceanic heat fluxes as the buoy drifted from the arctic basin into the greenland sea ice temperature data between 14 dec 1987 and 2 jan 1988 were retrieved during this period the aedb progressed from approximately 81 n 4 e to 77 n 5 w this constituted the most rapid displacement of the entire drift coinciding with the entry of the floe into the marginal ice zone of fram strait once in the miz water temperatures increased most notably at a depth of 16 m where values changed from 1 8 c to more than 2 c bottom ablation rates of 34 mm day were observed between 21 and 28 dec during this excursion into warmer water the oceanic heat flux increased by a factor of 18 from 7 w m to 128 w m

an illustration of the advantages of a complete texture analysis described by the orientation distribution function odf using quartz pole figure data abstract the preferred orientation of eight crystal directions of quartz was measured with an x ray texture goniometer for selected quartz bearing tectonites with a clear pattern of c axis preferred orientation the advantages of data analysis by means of calculations of the orientation distribution function and other forms of data presentation derived from the odf are demonstrated

heat flux at the ice ocean interface the role of the oceanic heat flux fw in the sea ice energy and mass balance is discussed and a method is described for determining fw from measurements of the temperature and thickness of sea ice results obtained using this method and data collected in the fall of 1988 during a drift in the eastern arctic northeast of fram strait are presented estimates of fw ranged from 0 to 37 w m 2 and varied in both time and space the gradual variation over the course of the drift reflects transformation of the west spitsbergen current into arctic water masses a significant intersite variability on horizontal scales of 10 to 100 m is ascribed to the interaction between under ice topographic features and turbulent energy and mass transfer in the boundary layer in addition there is a variability in the ice growth rate on horizontal scales of 0 1 to 1 m which is ascribed to the instability of the ice ocean phase boundary in the presence of turbulent flow these observations have implications for modeling and future experiments

dynamics and thermodynamics of the ice upper ocean system in the marginal ice zone of the greenland sea measurements were made of the ice upper ocean system in the marginal ice zone of the greenland sea during a 4 day storm in which wind blew the ice south across a frontal region coinciding with the ice edge that had existed when the storm began in response to wind stress of about 0 2 pa a turbulent boundary layer developed under the ice that exhibited marked ekman rotation in both mean velocity average surface speed about 0 17 m s 1 deflection angle about 33 and turbulent stress profiles typical reynolds stress about 0 1 pa ablation of the ice undersurface increased rapidly after crossing the surface temperature front and the observed melt rate corresponded with direct heat flux measurements in the oceanic boundary layer with maximum upward heat flux of about 200 w m 2 we discuss overall momentum and energy balances interpret observed boundary layer measurements with a numerical model and show that molecular effects are important for heat and mass transport at the hydraulically rough ice ocean interface we also develop a simple model for predicting ice melt from interfacial stress and temperature and salinity of the mixed layer

microstructure and micromotion in recrystallization flow of octachloropropane a first look advance of the genetic theory of metamorphic fabric depends in part on improved understanding of dynamic recrystallization processes and the effects of these processes upon various fabric elements this paper describes aspects of the microstructural evolution and associated small scale motion in a dynamically recrystallizing sheet of octachloropropane the material was deformed in progressive pure shear at 2 10 3 sec 1 with interruptions for photography and u stage measurement at 70 of its absolute melting temperature the dominant recrystallization process is migration of grain boundaries with consequent major adjustment of the shapes and sizes of grains but no marked change in the average grain size and no creation of new grains typical grains in the fully deformed material 30 bulk shortening have a composite structure with primitive high strain regions inherited directly from the undeformed state rimmed by successively younger regions of lower strain accreted behind outwardmoving boundaries an array of second phase marker particles permits distinction between grain boundary motion with and through the material and reveals an unexpected ability of grains as a whole to migrate short distances up a bulk strain gradient the markers also show that the only important deformation process is intragranular deformation and that it is proceeding at somewhat different rates in different grains the central problem posed by the observations is to explain the direction and speed of each migrating boundary two hypotheses were tested neither with outstanding success one of these hypotheses is that grain boundary migration is part of a strain accomodation process that operates between grains stretching or shortening at different rates parallel to their mutual boundary

relationships between strain and quartz crystallographic fabrics in the roche maurice quartzites of plougastel western brittany abstract an integrated microstructural and petrofabric study of the plastically deformed and partially recrystallized roche maurice quartzites of plougastel western brittany has revealed a clear correlation between the pattern of c axis fabrics displayed by detrital quartz grains and the symmetry of the calculated strain ellipsoid in specimens with flattening k 0 strains c axes lie on a small circle girdle opening angle 28 42 centred about the principal finite shortening direction z for specimens that exhibit approximate plane strain k 1 cross girdle c axis fabrics consisting of a small circle girdle centred about z and connected through the intermediate principal extension direction y were detected within individual specimens c axis fabrics of syntectonically recrystallized new quartz grains within the matrix are similar to those of detrital quartz grains c axes of new grains located within the relatively undeformed sections of the host detrital grains are commonly orientated at angles between 10 and 40 to the host c axis and are in addition statistically orientated at a higher angle to z than their host c axes these relationships are interpreted as indicating that both host grain control and the local strain and or stress field may have influenced the process of recrystallization the relative influence of these factors is however unknown microstructural and petrofabric studies indicate that the roche maurice quartzites have been subjected to essentially coaxial strain histories the role of syntectonic recrystallization in facilitating continued plastic deformation in quartzites subjected to such strain histories is considered

using sea ice to measure vertical heat flux in the ocean results of an experiment performed at drifting ice station fram i in the arctic ocean northwest of spitzbergen during march may 1979 indicate that sensible heat flux from the ocean to the ice cover was less than 2 w m 2 the estimate is based on measurements of temperature gradient growth rate and salinity of young sea ice uncertainty in the magnitude of the heat flux results more from evidence of horizontal inhomogeneity in the growing ice sheet than from measurement errors

calibration of shear wave splitting in the subcontinental upper mantle beneath active orogenic belts using ultramafic xenoliths from the canadian cordillera and alaska abstract despite the abundance of measurements of shear wave splitting around the world some fundamental questions about its geological interpretation have not yet been answered in order to constrain 1 i the orientation and magnitude of s wave anisotropy 2 ii the thickness of the anisotropic layer and 3 iii the possible variation of the anisotropy with depth in the subcontinental upper mantle beneath active orogenic belts we have carried out a systematic investigation on shear wave properties of mantle xenoliths from recent alkaline basalts of the canadian cordillera and alaska it is found that the polarization direction of the fast s wave as well as the time delay t between the two arrivals are strongly dependent on the propagation direction with respect to the structural frame at a single station the variations of measured and t values for sks phases from different events can result from this dependence because the average grain size of olivine in upper mantle samples is commonly larger than 0 5 mm dislocation creep prevails over a thickness of at least 250 km and results in olivine lpo and hence anisotropy and shear wave splitting a single thick anisotropic layer in mountain parallel subvertical shear zones may cause high values of tgd while multiple subhorizontal layers will produce multiple splitting making the measurement and interpretation of s wave splitting difficult our results also suggest that the s wave splitting observed in cold old stable cratons such as the canadian shield is likely dominated by fossil anisotropy whereas that observed in hot active orogenic regions such as the northwest american cordillera and the tibetan plateau may be dominated by modern tectonic deformation in the lithosphere and flow in the asthenosphere

development of shape and lattice preferred orientations application to the seismic anisotropy of the lower crust abstract we review the physical basis of the development of fabrics in plastic and viscous flow and illustrate the typical fabrics formed by these processes in the main rock forming silicates of the lower crust feldspar quartz pyroxene and amphibole the orientation process in plastic deformation where a single slip is dominant is recalled and the role of the constraint of neighbouring grains is emphasized the fabric development of anisometric crystals in viscous flow is discussed as a function of the main controlling parameters shear strain aspect ratio and interference between crystals the same sense of fabric asymmetry is introduced by plastic and viscous flow between the flow plane and the shape preferred orientation and hence coherent kinematic analysis can be undertaken in both modes of flow in order to assess the role of such fabrics in the seismic laminations of the lower continental crust we have calculated the seismic p wave properties of typical fabrics for hypothetical monomineralic and polymineralic rocks the calculations show that the strongest anisotropies develop in monomineralic rock with values between 5 and 16 compared with 5 and 8 for typical rock compositions the strongest anisotropies for layered monomineralic rocks generated by fabrics is only 6 compared to the 14 suggested by model studies of the observed seismic laminations we suggest that other effects such as compositional layering and or constructive interference of seismic waves are responsible for augmenting the apparent anisotropy

simulation of fabric development in recrystallizing aggregates ii example model runs abstract this study investigates the role of the coupling of dynamic recrystallization and lattice rotations in fabric development a new two dimensional computer simulation of polycrystalline deformation is used which combines homogeneous straining internal lattice rotations and dynamic recrystallization processes five example runs of the simulation are described here which compare the progressive development of fabrics resulting from different recrystallization regimes and different straining geometries it is found that these fabrics can evolve significantly with progressive strain from one strong fabric pattern to another the effect of recrystallization is not only to create point maxima concentrations of c axes but also to modify and create girdle distributions correlations are made between the fabrics generated by this model and previously reported quartz and ice fabrics

calcite texture development in experimentally induced ductile shear zones specimens of fine grained micritic limestone were deformed in plane strain geometry in pure shear a combination of simple and pure shear and in simple shear temperatures were 400 c and 500 c confining pressure was 100 mpa in the experiments with a simple shear component strain is concentrated and approximately homogeneous in a 2 3 mm wide shear zone shear displacement is documented by marker lines and circles shear strain varies between 0 84 and 1 56 strain is recorded by flattening of individual grains defining a foliation normal to the axis of principal finite shortening e1 no twinning is observed on a macroscopic scale

internal wave observations from the arctic environmental drifting buoy a free drifting buoy serving as an ice anchor and flotation sphere for a 125 m instrumented mooring line was deployed in the arctic pack ice by the r v polarstern in august 1987 at the northernmost point achieved by the arktis iv expedition current measurements were made from this arctic environmental drifting buoy aedb using a 150 khz acoustic doppler current profiler adcp attached to the mooring line at a depth of 16 m below the flotation sphere with the transducers facing downward velocity profiles spanning depths between 35 and 327 m with 15 m resolution were collected at half hour intervals over a period of 216 days while the buoy drifted from its starting point near 86 n 22 e to about 70 n 16 w the full experimental record was separated into three sections corresponding to periods of the drift spent in the nansen basin over the yermak plateau and in the greenland sea velocity time series and spectra were computed and results for the three analysis sections were compared spectra in the nansen basin were found to have energy levels significantly less than those typical for mid latitudes roughly one third of the canonical garrett munk gm level and a spectral slope between and 2 5 that was significantly flatter than that expected from the gm model between 83 n and 81 n as the buoy passed over the yermak plateau internal wave energy increased to levels comparable to gm isolated energetic near inertial wave packets with upward group velocity were observed in this portion of the record presumably generated by interaction of the barotropic tide with the bottom topography of the plateau estimates of the upward energy flux from these near inertial packets were comparable to the downward fluxes from typical surface sources interpretation of the greenland sea section was complicated by adcp sampling problems and a lack of argos fixes but the available data showed internal wave spectral levels that were intermediate between those of the nansen basin and yermak plateau and no evidence of upward propagating near inertial energy

an in situ optical investigation of the deformation behaviour of sodium nitrate an analogue for calcite abstract in situ observations have been made under the optical microscope of the deformation of thin polycrystalline specimens of sodium nitrate calcite structure at temperatures between 20 c 0 5 tm and 300 c 0 98 tm at low temperatures or high strain rates deformation twinning is observed between 20 c and 180 c inhomogeneous deformation together with dynamic recrystallisation by subgrain rotation results in a core and mantle microstructure at temperatures above 180 c rapid dynamic recrystallisation by grain boundary migration also occurs producing a coarse grained microstructure the results are interpreted in terms of impurity controlled grain boundary motion as proposed for halite and a strong similarity between the deformation behaviour of sodium nitrate and marble is noted

seven types of subgrain boundaries in octachloropropane abstract subgrain boundaries in thin sheets of octachloropropane deformed at 0 7 0 8 t m on the stage of a microscope are seen to appear in the material in seven different ways type i boundaries show the classical evolution by polygonization of bent crystals type ii are essentially kink boundaries which migrate sideways during deformation to reach their present positions in the crystals type iii develop at the sites of former grain boundaries by reduction of misorientation of adjacent grains type iv and v originate by impingement of migrating grain boundaries or subgrain boundaries respectively type vi propagate in their own planes behind migrating grain boundaries to which they are attached type vii develop statically from optically strain free grains by a process probably otherwise similar to the type i process two thirds of the boundaries are types i or ii in view of the variety of subgrain boundary histories in ocp interpretation of similar features in minerals ought to be undertaken cautiously criteria are needed for telling the different types of subgrain boundaries apart in situations where only a final view of the structure is available as in optical and electron micrographs of rocks

the effect of deformation history on the evolution of olivine cpo abstract olivine crystallographic preferred orientation cpo is the primary cause of seismic anisotropy in the upper mantle in tectonic environments with complex flow patterns for example corner flow near mid ocean ridges or subducting slabs the interpretation of seismic anisotropy may be complicated by evolving thermochemical deformation conditions and the integrated deformation history to understand how deformation history influences cpo evolution deformation experiments were conducted on samples of aheim dunite which has a strong pre existing texture experiments were performed in a triaxial geometry using a griggs apparatus at p 1 gpa t 1473 k up to a maximum strain of 0 7 to simulate different deformation histories samples were deformed in three different configurations with the pre existing foliation perpendicular oblique and parallel to the shortening axis of deformation distinct patterns of cpo development are observed for each experimental configuration likewise texture strength symmetry and orientation evolved differently in each set of experiments these data are interpreted as evidence that cpo did not reach steady state and that achieving steady state texture requires larger strains than previously thought it is concluded that the integrated deformation history plays a significant role in cpo evolution and the consequent interpretation of seismic anisotropy in earth s mantle

spatial and temporal characteristics of the decadal abrupt changes of global atmosphere ocean system in the 1970s 1 using noaa extended reconstruction sst ersst v2 and ncep ncar reanalysis a moving t test technique is employed to detect the decadal abrupt change years dacys in the time series of several atmosphere ocean variables the decadal abrupt changes dacs existed widely in the ocean atmosphere system in 1973 1978 in the ocean the decreased dacs ddacs the variable decreases after the dacy occurred in the north and south pacific and the increased dacs idacs the variable increases after the dacy mainly took place in the eastern pacific southern south pacific and south indian ocean in the atmosphere the idacs happened over the eastern hemispheric tropics and subtropics in the low troposphere and over the global tropics and subtropics in the middle and upper troposphere and stratosphere the higher pressure levels the larger the dac regions and the later the dacys generally the initial oceanic dacs in the 1970s cannot be explained by the dacs of wind stress which happened 2 years a later than the original oceanic dacs in addition the tropical influence through atmosphere and ocean cannot explain the initial ddacs of sst and atmosphere of the north pacific which occurred about 2 a in advance of tropical warming the ddacs in the 1970s of the north pacific cannot interpret that of other oceanic regions because they were not the initial oceanic dacs in the 1970s these findings suggest that the dacs in the 1970s may initially originate from the ocean and a coupled atmosphere ocean decadal interaction mechanism existed in the winter of the north pacific