introduction summer marginal ice zone experiments during 1983 and 1984 in fram strait and the greenland sea sphere is complicated by numerous land masses which largely confine it during the winter to the sea of okhotsk and to the bering labrador and greenland norwegian seas during the spring and summer the miz retreats from the peripheral seas generally the total extent of the northern miz is less than one half that of the southern numerous studies have demonstrated the sensitivity of weather and climate to the state of the polar ice cover and it is of fundamental importance to understand how annual and interannual variations in ice extent are related to large scale and mesoscale circulations in the atmosphere and ocean successful modeling and parameterization of processes which govern the location and state of the miz are important not only for predicting the impact of sea ice on global climate but also for furthering man s activities in the miz regions e g offshore oil exploration seaborne transport of arctic resources development of the rich fisheries close to the ice margin and naval operations in recent years realization of the scientific and economic significance of the miz has focused attention on the need for coordinated multidisciplinary studies of conditions and processes near ice open ocean boundaries and has led to the development of the marginal ice zone experiment mizex although of substantial interest the remoteness of the vast antarctic miz poses serious logistic difficulties and mizex efforts to date have concentrated on the more accessible northern miz considerable work has been carried out in the

variations of mesoscale and large scale sea ice morphology in the 1984 marginal ice zone experiment as observed by microwave remote sensing during the summer 1984 marginal ice zone experiment in the fram strait and greenland sea mizex 84 passive and active microwave sensors on five aircraft and the nimbus 7 scanning multichannel microwave radiometer smmr acquired synoptic sequential observations which when combined give a comprehensive sequential description of the mesoscale and large scale ice morphology variations during the period june 9 through july 16 1984 the high resolution ice concentration distributions in these images agree well with the low resolution smmr distributions for diffuse ice edges the 30 smmr ice concentration isopleth corresponds to the ice edge while for compact conditions the ice edge falls within the 40 to 50 smmr isopleths throughout the experiment ice edge meanders and eddies repeatedly formed moved and disappeared but the ice edge remained within a 100 km wide zone the ice pack behind this alternately diffuse and compact edge underwent rapid and pronounced variations in ice concentration over a 200 km wide zone the aircraft microwave images show the complex structures and ephemeral nature of the mesoscale sea ice morphology the difference in oceanographic forcing between the eastern and western sectors of the experiment area generated pronounced ice morphology differences on the yermak plateau from 3 e to 10 e the weak ocean circulation allowed the wind to be the dominant force in determining the ice morphology to the southwest of this region over the molloy deep and the greenland continental shelf break from 3 e to 8 w the ice morphology was dominated by the energetic east greenland current with its associated eddies and meanders

sea surface height determination in the arctic ocean from ers altimetry 1 accurate sea surface height measurements have been extracted from ers altimeter data in sea ice covered regions for the first time the data have been used to construct a mean sea surface of the arctic ocean between the latitudes of 60 degreesn and 81 5 degreesn based on 4 years of ers 2 data an rms value for the crossover differences of mean sea surface profiles of 4 2 cm was observed in the ice covered canada basin compared with 3 8 cm in the ice free greenland iceland norwegian seas comparisons are made with an existing global mean sea surface osumss95 highlighting significant differences between the two surfaces in permanently ice covered seas in addition we present the first altimeter derived sea surface height variability map of the arctic ocean comparisons with a high resolution coupled ocean sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability quantitatively we found that the observed variability was on average a factor of 3 4 greater than model predictions

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

natural deformation fabrics of plagioclase implications for slip systems and seismic anisotropy abstract the optical and tem microstructures and fabrics of twelve naturally deformed plagioclase containing rocks of compositions from an0 an80 have been studied with a view to determining the deformation mechanisms the optical indicatrix fabrics have been recorded in all samples with respect to the foliation and lineation in general and form a girdle in the foliation plane with a high concentration of normal to the foliation in some cases the orientation of 010 and 001 cleavages or albite and pericline twins has allowed the construction of pole figures in all cases 010 has been shown to be the dominant slip plane with either 001 or 100 the dominant slip direction tem shows that the dominant slip system is 010 001 with secondary 010 100 the seismic p wave anisotropy has been calculated for the first time from the lpo data of plagioclase the anisotropy coefficient is high at around 15 the minimum p velocity is normal to the lineation in the foliation plane and the maximum is sub parallel to the foliation normal the combined information on deformation kinematics and seismic anisotropy is valuable for interpretations of deep crustal seismic sections

quartz microstructures and c axis preferred orientations in high grade gneisses and mylonites around the morin anorthosite grenville province quartz in deformed rocks from two large high grade shear zones around the morin anorthosite morin terrane grenville province displays distinctive microstructures as well as c axis preferred orientations in the west dipping morin shear zone east of the morin anorthosite four distinct quartz microstructures types 1 4 are identified based on deformation features and grain size the c axis orientations are characterized by a single maximum near the stretching lineation and two maxima in type 1 microstructure and by an asymmetrical single girdle in type 2 microstructure quartz c axes show crossed girdle pattern in type 3 microstructure both quartz microstructures and c axis preferred orientations suggest that crystal plastic slip and dynamic recrystallization are the dominant deformation mechanisms the asymmetry of c axis orientations with respect to the mylonitic foliation as well as the substructures developed in quartz indicates a dextral sense of shear in the morin shear zone type 4 micr

deformation and recrystallization mechanisms in naturally deformed omphacites from the sesia lanzo zone geophysical consequences buatier m van r rmund h l m drury m r and lardeaux j m 1991 deformation and recrystallization mechanisms in naturally deformed omphacites from the sesia lanzo zone geophysical consequences teetonophysrc c 195 11 27 naturally deformed omphacites clinopyroxenes from the sesia lanzo zone western italian alps have been studied using light and transmission electron microscopy techniques deformation and recrystallization of omphacite took place at 5 50 600 c and minimum pressures of 14 16 kbar tem reveals isolated free dislocations loops nodal points tiltwalls complex dislocation networks minor twins stacking faults and antiphase domain boundaries the activated slip systems are l z llo llo l llo and al assisted by climb in nodal points and complex dislocation networks dislocations with burgers vector l 2 112 are present in low strain domains most of the subgrain transitional and new grain boundaries subparallel to wl develop from 110 tiltwalls which accommodate lattice bending produced by the l 2 110 110 slip system a component of the misorientation across such newly formed sub grain boundaries is however also formed by sub rain boundary migration grain rotations in the intermediate and high strain domains are more complex but can be explained by the activated slip systems the omphacite microstructures indicate that initial strain induct rec stallisation occurred by a rotation mechanism where single crystals become polycrystals by the development of numerous high angle grain boundaries at a subsequent more advanced stage migration recrystallization is also activated and a different kind of recrystallization mechanism occurs which involves the discontinuous development of new strain free grains these grains are derived from the extremum of the orientations produced by heterogeneous strain and slip system activity the evident ductility of omphacite during low to intermediate eclogite metamorphism is inferred to be facilitated by hydrolitic weakening effects as such the plastic behaviour of omphacite should be incorporated in geophysical flow models dealing with subducted oceanic and or lithosperic plate margins

sea surface height and dynamic topography of the ice covered oceans from cryosat 2 2011 2014 we examine 4 years 2011 2014 of sea surface heights ssh from cryosat 2 cs 2 over the ice covered arctic and southern oceans results are from a procedure that identifies and determines the heights of sea surface returns along 25 km segments of satellite ground tracks variability in the retrieved sshs is between 2 and 3 cm standard deviation in the arctic and is slightly higher 3 cm in the summer and the southern ocean average sea surface tilts along these 25 km segments are 0 01 3 8 cm 10 km in the arctic and slightly lower 0 01 2 0 cm 10 km in the southern ocean intra seasonal variability of cs 2 dynamic ocean topography dot in the ice covered arctic is nearly twice as high as that of the southern ocean in the arctic we find a correlation of 0 92 between 3 years of dot and dynamic heights dh from hydrographic stations further correlation of 4 years of area averaged cs 2 dot near the north pole with time variable ocean bottom pressure from a pressure gauge and from grace yields coefficients of 0 83 and 0 77 with corresponding differences of 3 cm rms these comparisons contrast the length scale of baroclinic and barotropic features and reveal the smaller amplitude barotropic signals in the arctic ocean broadly the mean dot from cs 2 for both poles compares well with those from the icesat campaigns and the dot2008a and dtu13mdt fields short length scale topographic variations due to oceanographic signals and geoid residuals are especially prominent in the arctic basin but less so in the southern ocean

preferred orientation and anisotropy of seismic and magnetic properties in gabbronorites from the bushveld layered intrusion abstract the preferred orientation of plagioclase and pyroxene in gabbronorites from the bushveld layered igneous intrusion south africa was investigated using electron backscatter diffraction in two localities 200 km apart belfast and rustenburg strong preferred orientation was observed with the principal fabric features aligned in the subhorizontal foliation plane defined by 010 planes of plagioclase and 100 planes of pyroxene the pattern appears to result from the orientation of tabular crystals during the dynamic intrusion events that formed the layered structure primary magmatic oxides are also influenced by the preferred orientation of plagioclase generating an oblate magnetic susceptibility fabric parallel to the foliation plane plagioclase preferred orientation gives rise to other directionally dependent geophysical properties including a large seismic anisotropy with p waves traveling 4 8 faster in the vertical than in the horizontal direction

u pb zircon dates of morin anorthosite suite rocks grenville province quebec u pb zircon ages of samples of anorthosite pyroxene monzodiorite jotunite and pyroxene quartz monzonite quartz mangerite of the morin anorthosite complex grenville province quebec are 1155 plus minus 3 1146 plus minus 4 and 1135 plus minus 3 ma respectively these dates are very similar to available dates for equivalent units of the lac st jean and adirondack anorthosite suite occurrences and slightly predate estimates of 1075 1100 ma for peak metamorphic conditions during the grenville orogeny in this region sup 87 sr sup 86 sr initial ratios of 0 7048 0 7051 for the three morin units sampled permit a comagmatic origin if the different emplacement or cooling times can be reconciled the mangerite sampled cannot have been formed by fusion of the upper crust but may have been derived from a relatively juvenile crust at depth all three units have interacted with continental crust given the likely depleted nature of the mantle in this region

shear wave velocities anisotropy and splitting in high grade mylonites shear wave velocities have been measured for 10 high grade granulite and upper amphibolite facies mylonites from the snowbird tectonic zone canada at various pressures up to 600 mpa in order to explore the kinematic significance of shear wave splitting in the lower crust at 600 mpa vs anisotropy ranges from 11 in amphibolitic mylonites to 2 in granulite facies pyroxene bearing and tonalitic mylonites hornblende bearing granitic mylonites display intermediate vs anisotropy 6 7 vs anisotropy is lower than vp anisotropy in hornblende rich mylonites whereas vs anisotropy is higher than vp anisotropy in feldspar rich mafic tonalitic granitic and diatexitic mylonites shear wave splitting is pronounced in rocks displaying strong s wave anisotropy in most of the high grade mylonites studied the polarization direction of the first arrival vs1 corresponds to the extension lineation x when propagation is parallel to y perpendicular to lineation and parallel to foliation or to the y direction when propagation is parallel to x for all other propagation directions the polarization direction of vs1 is oblique to the x y and z directions therefore it may be difficult to infer the structural implications of shear wave splitting in lower continental crustal shear zones if one does not know 1 the orientation of the propagation and fast vibration directions with respect to in situ lineation and foliation and 2 the lattice preferred orientation of in situ rock forming minerals

the dislocation substructures of naturally deformed omphacites abstract a transmission electron microscopy study of naturally deformed omphacite has revealed twins antiphase boundaries and a variety of dislocation substructures consisting of curved free dislocations loops isolated nodal points and networks both free dislocations and dislocation boundaries contain nodes that involve dislocations with the following burgers vectors 001 1 2 110 and 1 2 112 this implies a reaction of the type 001 1 2 110 1 2 112 by analogy with quartz and olivine the dislocation substructures in the omphacites are considered to be indicative of dislocation creep mechanisms and responsible for most of the optical defect structures using microstructural and geochemical data the metamorphic conditions during the creep deformation are estimated to be minimum 8 kbar 550 c maximum 15 kbar 625 c

dynamic recrystallization processes in plagioclase porphyroclasts abstract recrystallization processes in plagioclase porpyroclasts were studied in samples from an anorthositic gabbro of the jotun complex south norwegian caledonides the deformation took place at a temperature of approximately 700 c and at pressures below 900 mpa two populations of plagioclase porphyroclasts can be distinguished based on microstructural observations the crystallographic orientation and grain shapes for the two populations are interpreted as soft and hard orientations of the dominant slip system 010 001 with respect to the kinematic reference system the orientations of porphyroclasts and recrystallized grains were measured with a u stage microscope analysis of misorientations between porphyroclasts and adjacent recrystallized grains yields different results for the two types of porphyroclasts in type 1 porphyroclasts soft orientation the misorientation is inferred to be caused by subgrain rotation due to the activation of the 010 001 slip system resulting in a host control orientation relationship whereas in type 2 porphyroclasts hard orientation no dominant misorientation relationship could be identified the slip systems of the dislocations inferred from transmission electron microscopy tem analysis correspond well with the results of the u stage misorientation analysis in type 2 porphyroclasts hard orientation micro fracturing was observed in the tem whereas microfractures are absent in type 1 porphyroclasts soft orientation micro fracturing is likely to be the mechanism for nucleation of new grains in type 2 porphyroclasts resulting in a no host control orientation relationship between porphyroclasts and recrystallized grains

pyroxene orientation within the upper mantle petrofabric analyses of orthopyroxene and olivine for a suite of rocks from the bay of islands ophiolite newfoundland show systematic relationships between the minerals9 fabrics the plane of the mohorovicic discontinuity determined from the contact of the gabbro and ultramafic sections and the spreading direction inferred from the attitude of the sheeted dikes the orthopyroxene c crystallographic axes maxima which are aligned subparallel to the spreading direction coincide with olivine a axes maxima the orthopyroxene b axes and olivine c axes also lie approximately within the plane of the mohorovicic discontinuity but parallel the ridge whereas the orthopyroxene a axes maxima and olivine b axes maxima are approximately perpendicular to the mohorovicic discontinuity using olivine and orthopyroxene elastic constants and their pressure derivatives velocities have been calculated from composite petrofabric data and contoured for varying proportions of olivine and pyroxene the results of these calculations show that within a vertical direction compressional wave velocities change only slightly with increasing pyroxene content whereas parallel to the mohorovicic discontinuity velocities decrease with increasing pyroxene content anisotropy decreases from 4 for a rock with 100 olivine to 2 6 for a rock with 50 olivine and 50 orthopyroxene also within the plane of mohorovicic discontinuity the maximum and minumum velocities occur at approximately the same azimuth for differing percentages of orthopyroxene a comparison of the calculated anisotropy and the observed seismic anisotropy off the coast of california shows a striking agreement from this comparison it is estimated that the percentage of orthopyroxene within the upper mantle of this region varies between 0 and 30

creep and strain dependent microstructures of synthetic anorthite diopside aggregates abstract we investigated plastic deformation of fine grained synthetic diopside and two phase anorthite diopside aggregates in triaxial compression and torsion up to 5 temperature confining pressure and stress ranged between 950 1180 c 200 400 mpa and 5 500 mpa respectively water content of samples ranged between 0 005 0 002 and 0 075 0 025 wt h 2 o all samples deformed in linear viscous creep with a stress exponent of 1 0 0 2 the activation energy ranged between 571 53 and 290 28 kj mol depending on mineralogy and water content sample strength depended on water fugacity with an exponent of 1 55 0 25 samples deformed in torsion and coaxial compression gave similar flow laws in spite of significant differences in the corresponding microstructures scanning and transmission electron microscopy of two phase samples deformed in torsion showed phase mixing cavitation and dislocation processes we suggest that linear viscous creep of fine grained two phase aggregates involved grain boundary sliding accommodated by grain boundary diffusion and significant dislocation accommodation at high strains we also observed that cavity coalescence and microcracking led to sample failure hence dynamic instabilities may exist in high strain shear zones accommodating viscous deformation in the lower continental crust

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

metamorphic constraints on the tectonic evolution of the allochthonous monocyclic belt of the grenville province western quebec the tectono metamorphic evolution of grenvillian monocyclic terranes in western quebec has been constrained along a northwest southeast transect from reservoir cabonga to the morin anorthosite by t

sea ice detection using u k tds 1 gnss r data a sea ice detection algorithm developed using the u k techdemosat 1 u k tds 1 global navigation satellite systems gnsss reflectometry data over the arctic and antarctic regions is presented it is based on measuring the similarity of the received gnss reflected waveform or delay doppler map ddm to the coherent reflection model waveform over the open ocean the scattered signal has a diffusive incoherent nature it is described by the rough surface scattering model based on the geometric optics and the gaussian statistics for the ocean surface slopes over sea ice and in particular newly formed sea ice the scattered signal acquires a coherence which is characteristic for a surface with large flat areas in order to measure the similarity of the received waveform or ddm to the coherent reflection model three different estimators are presented the normalized ddm average the trailing edge slope tes and the matched filter approach here a probabilistic study is presented based on a bayesian approach using two different and independent ground truth data sets this approach allows one to thoroughly assess the performance of the estimators the best results are achieved for both the tes and the matched filter approach with a probability of detection of 98 5 a probability of false alarm of 3 6 and a probability of error of 2 5 however the matched filter approach is preferred due to its simplicity data from amsr2 processed using the arctic radiation and turbulence interaction study sea ice algorithm and from an special sensor microwave imager sounder radiometer processed by ocean and sea ice saf have been used as ground truth a pixel has been classified as a sea ice pixel if the sea ice concentration sic in it was larger than 15 the measurement of the sic is also assessed in this paper but the nature of the u k tds 1 data lack of calibrated data does not allow to make any specific conclusions about the sic

evolution of microwave sea ice signatures during early summer and midsummer in the marginal ice zone emissivities at frequencies from 5 to 94 ghz and backscatter at frequencies from 1 to 17 ghz were measured from sea ice in fram strait during the marginal ice zone experiment in june and july of 1983 and 1984 the ice observed was primarily multiyear the remainder first year ice was often deformed results from this active and passive microwave study include the description of the evolution of the sea ice during early summer and midsummer the absorption properties of summer snow the interrelationship between ice thickness and the state and thickness of snow and the modulation of the microwave signature especially at the highest frequencies by the freezing of the upper few centimeters of the ice

strain softening and microstructural evolution of anorthite aggregates and quartz anorthite layered composites deformed in torsion torsion experiments of anorthite an aggregates and layered composites with equal volume fractions of quartz qtz and an were performed in a gas medium apparatus at a confining pressure of 400 mpa temperatures from 1373 to 1473 k and twist rates from 1 0 x 10 4 to 3 0 x 10 4 rad s dense specimens were fabricated from an glass and qtz crystalline powder using hot isostatic pressing hip techniques both an aggregates and qtz an layered composites show a continuous strain weakening from a peak stress at gamma 0 2 0 3 to gamma 3 2 and steady state flow has not reached under the experimental conditions the weakening is even more pronounced in the layered composites than the monolithic aggregates suggesting channeling or localization of flow into the weak material between strong layers the sheared an specimens developed pervasively c s c structures which are similar to those observed in natural ductile shear zones tem and electron backscattering diffraction ebsd fabric analyses suggest that grain boundary migration recrystallization accommodated dislocation creep with 010 100 as the dominant slip system was operating in the an the strain softening may be due to the development of crystallographic preferred orientation cpo the operation of dynamic recrystallization and the formation of extremely fine grained recrystallized material in the narrow c shear bands c 2004 elsevier b v all rights reserved

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

geochronological constraints on the last stages of terrane assembly in the central part of the grenville province abstract new u pb zircon and monazite ages for syn and post kinematic pegmatites that cut major shear zones within the western quebec portion of the grenville province constrain the timing of deformation and final terrane assembly within this region from the grenville front se along the present section the grenville province consists of a reworked archean promontory partly covered by proterozoic allochthons and two proterozoic metasedimentary and metaigneous terranes which are probably allochthonous the age of the grenville front is still poorly constrained in this area as pegmatites intersecting high grade rocks exhumed some 30 km south of the front have upper intercept u pb ages of 2642 6 5 ma field and geochronological data in this paper however lend support to the possibility of late archean exhumation of high grade terranes along the front south of the front two types of ductile shear zone are responsible for the geometry of terranes in this part of the grenville province the first type corresponds to the boundary of allochthons transported onto the archean parautochthon the corresponding structures are not directly dated but reheating of the parautochthon at about 1020 ma u pb ages on monazite sets a minimum age for thrusting in this area late movement along an east dipping shear zone located within the parautochthon the cabonga thrust ct 998 9 5 ma is rather unique in that it involves rocks of the parautochthon and is characterized by a westerly directed transport the shear zones of the second type are subvertical ne trending generally sinistral and intersect the parautochthon the allochthon or both from the front towards the se these shear zones are the cadgecrib shear zone 998 16 6 ma intersecting the parautochthon the renzy shear zone 1003 4 5 ma involving allochthonous metasediments the baskatong shear zone 1020 2 1 ma which marks the nw limit of proterozoic rocks of the mont laurier terrane the labelle shear zone 1078 6 ma separating the mont laurier and the morin terrane and the taureau shear zone 1074 4 ma bounding the morin terrane to the east all the above timing constraints are from u pb ages on syn to post kinematic pegmatites emplaced within the respective shear zones this age distribution suggests a propagation of transcurrent deformation towards the nw which is responsible for the final configuration of terranes

plagioclase preferred orientation by tof neutron diffraction and sem ebsd abstract the lattice preferred orientation lpo of an anorthosite composed of andesine sampled from a highly deformed anorthositic mylonite grenville province quebec was measured by tof neutron diffraction and sem ebsd the quantitative texture analysis of neutron data was accomplished by using the rietveld texture analysis with the wimv algorithm implemented in the program package materials analysis using diffraction maud the texture calculations of the ebsd data were performed by using the program beartex analyses from neutron and electron diffraction data gave similar results if ebsd data are smoothed to account for grain statistics the principal pole figures show 010 roughly parallel to the rock foliation 001 poles exhibiting a low angle 25 to the pole to foliation and 100 poles close to the y direction perpendicular to the lineation and foliation pole the 100 crystallographic direction shows a maximum in the lineation direction 010 directions concentrate near the foliation pole the geological deformation conditions and the constructed pole figure patterns indicate that the preferred orientation could be attributed to intracrystalline slip dominantly on 010 with 100 as slip direction elastic properties calculated by averaging document weak anisotropy that has implications for the seismic structure of the lower crust

satellite microwave and in situ observations of the weddell sea ice cover and its marginal ice zone the radiative and physical characteristics of the weddell sea ice cover and its marginal ice zone are studied using multichannel satellite passive microwave data in conjunction with in situ observations during the 1983 antarctic marine ecosystem research at the ice edge zone experiment time series studies from winter through spring using every other day observations from the nimbus 7 scanning multichannel microwave radiometer reveal significant spatial variability of the brightness temperatures of consolidated ice in winter and a recurring temporal and oftentimes larger spatial variability in spring the recurring effect in spring was found to be strongly correlated with observed surface air temperatures and is apparently associated with the cyclic changes in wetness of the snow cover of the ice while experiencing the freeze thaw cycle analysis of scatter plots of observed brightness temperatures from selected study regions using two or three frequencies and or polarizations shows that to effectively discriminate ice from open water within the ice pack a minimum of two channels at different frequencies preferably 18 ghz and 37 ghz is required serious problems associated with using only one frequency even at two polarizations i e 37 ghz and perhaps higher frequencies have been observed ice concentrations derived from the sensor are compared with helicopter and ship observations and results show consistency but a relatively low correlation coefficient partly due to the quasi qualitative nature of the in situ observations and uncertainties in ice emissivity in spring the character and the northernmost extent of the ice margin are quantified using radial plots of ice concentration across the ice pack and into ice free ocean temporal changes in the ice margin structure are compared with ship data of physical temperature ice characteristics wind and weather studies of the mass balance of fresh water and of biological features of the marginal ice zone are shown to benefit from time series information concerning the position of the ice edge as derived from satellite remote sensing

seismic reflectivity of a finely layered granulite facies ductile shear zone in the southern grenville province quebec abstract lithoprobe reflection profile 54 across the granulite facies morin shear zone msz in the grenville tectonic province quebec canada reveals a west dipping zone of strong reflections the origin of these reflections has been investigated by detailed field mapping laboratory measurements of p wave velocities and densities of representative rock samples from the main lithological units and forward synthetic modeling petrofabric and microstructural analyses were performed in order to interpret the measured seismic properties synthetic seismograms generated from the velocity and density data demonstrate that reflections originate from lithologic thin layers and thin layer clusters likely resulted from intensive tectonic transposition and metamorphic differentiation lattice preferred orientation lpo induced anisotropy of granulite facies mylonites except for those containing abundant sillimanite biotite or amphibole is very low and hence unlikely to be the primary cause for reflections confining pressure does not significantly affect the reflectivity of the shear zone because the reflection coefficients are not sensitive to pressure up to at least 600 mpa since composite reflections of thin layer clusters can cause high reflectivity the strong reflectivity from some deep crustal sections with low refraction velocities may be interpreted to be due to the presence of thin layer mafic clusters within dominantly felsic rocks

ab initio calculations of elastic constants of plagioclase feldspars 2014 by walter de gruyter berlin boston plagioclase feldspars comprise a large portion of the earth s crust and are very anisotropic making accurate knowledge of their elastic properties important for understanding the crust s anisotropic seismic signature however except for albite existing elastic constants for plagioclase feldspars are derived from measurements that cannot resolve the triclinic symmetry we calculate elastic constants for plagioclase end members albite naalsi3o8 and anorthite caal2si2o8 and intermediate andesine labradorite nacaal3si5o16 using density functional theory to compare with and improve existing elastic constants and to study trends in elasticity with changing composition we obtain elastic constants similar to measured elastic constants and find that anisotropy decreases with anorthite content

satellite observations of polar ice fields this paper outlines the research needed to advance the knowledge of polar ice masses that could be or has been provided by satellite techniques inland ice sheets ice shelves and pack ice on polar oceans are discussed in separate sections because a satellite radar altimeter can cover wide areas of polar ice economically and rapidly the interpretation of altimeter results is discussed in detail theoretical considerations are used to explain various characteristics of pulse shapes recorded over antarctica by seasat over inland ice surface undulations cause the pulse shape to change rapidly with location and the leading edge to migrate rapidly altimetry over ice shelves should be accurate to better than 1 m and provide new methods for studying their mass balance nearly all sea ice returns that have been studied show a characteristic glistening quite distinct from returns from the open ocean inland ice or ice shelves reasons for glistening are presented and the need for ground truth stressed because pulse shapes should provide an additional source of data to define pack ice characteristics from satellite observations ice sheets in greenland and antarctica constitute 10 of the surface land area of the earth their accumulated 36 x 106 km3 of ice comprises 90 of global freshwater reserves sea ice covers a maximum global surface area of 24 x 106 km2 during the northern summer ca 7 of the world ocean surface these ice masses are coupled closely with other aspects of the natural environment through complex exchanges of energy and mass radok 1978 sergin i979 an understanding of their dynamics and thermodynamics is fundamental to realistic global modelling of climatic oceanographic and lithospheric processes the investigation of ice masses principally in polar areas is hampered by extreme cold long periods of darkness and persistent cloud cover in some areas remote sensing has and will play a critical role in the gathering of data and their routine surveillance this paper briefly reviews the most important research needs for the study of polar ice and points out where research can benefit from satellite techniques table 1 lists these needs for ice sheets and ice shelves and the contributions that have been made by satellite missions or those being planned table of gudmandsen this symposium lists similar requirements for the study of sea ice these cover two types of data sets one acquired within a time domain to study timedependent changes such as sea ice distribution and glacier dimensions the other within a spatial domain where very detailed geographic coverage is required because of their importance to both types of study techniques of radio altimetry from satellites are discussed in some detail

new tectonic divisions of the grenville province southeast canadian shield on the basis of geological geophysical and geochronological data the grenville province has been divided into three first order longitudinal belts the parautochthonous belt pb allochthonous polycyclic belt apb and allochthonous monocyclic belt amb these are set apart by three first order tectonic boundaries the grenville front gf allochthon boundary thrust abt and monocyclic belt boundary zone mbbz the belts are subdivided into terranes based on internal lithological character the gf separates the archean to proterozoic foreland northwest of the orogen from reworked equivalents to the southeast continuous at the scale of the orogen its main characteristic is that of a crustal scale contraction fault the pb although less clearly identified along the length of the orogen in most places represents upgraded and tectonically reworked rocks of the adjacent foreland the boundary between the pb and the apb to the southeast the abt is most clearly delineated in the eastern half of the province it is the locus of major crustal delamination along which high grade mostly middle proterozoic polycyclic terranes were tectonically transported northwest toward and onto the pb the amb comprises two separate areas underlain by the wakeham supergroup and what is currently known as the grenville supergroup respectively its basal contact the mbbz is a decollement zone of variable kinematic significance between older polycyclic rocks and tectonically overlying monocyclic rocks this first order zonation implies a tectonic polarity to the grenville province superimposed on which are second order features evident from contrasting tectonic styles and radiometric ages these characteristics are consistent with a diachronous or oblique collisional model for the grenville orogen

rheology of synthetic anorthite diopside aggregates implications for ductile shear zones 1 we investigated the high temperature creep strength of fine grained anorthite diopside rocks at temperatures ranging from 1323 k to 1523 k and at 300 mpa confining pressure in a paterson type gas medium deformation apparatus flow stress varied between 20 and 450 mpa resulting in strain rates between 6 1 10 7 s 1 and 7 5 10 4 s 1 pure diopside and anorthite samples were hot pressed from crushed natural single crystals and glass powders respectively two phase samples were produced by hot isostatic pressing of mechanically mixed powders of anorthite glass with 25 50 and 75 vol diopside particles arithmetic mean grain size of the anorthite matrix is dan 3 5 m three different ranges of diopside particle size were used ddi 25 m 35 m and 45 m water content of as is samples was about 0 05 0 02 wt h2o and predried samples contain about 0 004 0 001 wt h2o at experimental conditions as is samples are assumed to be water saturated water content of predried samples is about 3 times less than that of starting diopside single crystals the specimens contain about 1 vol glass located at fluid inclusions and some multiple grain junctions two grain boundaries examined by high resolution transmission electron microscopy did not show amorphous layers to a resolution of 1 nm at experimental conditions pure diopside aggregates are about 2 3 orders of magnitude stronger than pure anorthite samples for as is and predried specimens respectively in general strength of the two phase aggregates increases with increasing diopside content but remains between isostress and isostrain rate bounds aggregate strengths predicted from continuum mechanics models are in good agreement with the experimental data for dilute diopside particle mixtures and high volume fractions when diopside particles form a load bearing framework at low stresses 100 200 mpa the stress exponent is n 1 suggesting diffusion controlled creep at higher stresses mechanical data and microstructures suggest that samples deformed in the transition region between diffusion controlled creep and dislocation creep for pure anorthite and diopside aggregates deforming in dislocation creep we estimated stress exponents of n 3 and n 5 5 respectively for the two phase aggregates n is between n 3 and n 5 depending on diopside content at low stresses deformation microstructures indicate load transfer from a weak anorthite matrix to stronger diopside particles creep activation energies for pure diopside and anorthite mixtures range from 286 kj mol 1 for wet anorthite deformed at low stresses to 691 kj mol 1 for dry diopside deformed at high stresses activation energies of two phase mixtures are between or close to those of the end members as is samples have significantly lower activation energies than predried samples

fabric development in a middle devonian intraoceanic subduction regime the careon ophiolite northwest spain abstract a middle devonian suprasubduction zone ophiolite the careon unit northwest spain displays amphibolite facies ductile deformation fabrics related to the onset of the rheic ocean closure two different fabrics an early high t foliation and a subsequent lower t foliation each of which characterized by distinct deformation mechanisms have been identified in two distinct crustal scale shear zones of the same ophiolitic thrust sheet combined quantitative texture analysis by electron backscattered diffraction and time of flight neutron diffraction were carried out on the shear zones and correlated with micro and macrostructural data the results indicate that the regional lineation and shear zone kinematics east west top to the east represent fabrics developed essentially during the intraoceanic subduction of the rheic ocean and their orientation may be considered a reference vector for convergence models in this part of the variscan belt

sense of shear in high temperature movement zones from the fabric asymmetry of plagioclase feldspars abstract a new method for determining the sense of shear in plagioclase bearing tectonites from the 010 orientation of plagioclase feldspar is presented the method is based on the asymmetry of the 010 plane with respect to the structural frame foliation and lineation and the dominant activity of the 010 slip plane in the high temperature plasticity of plagioclase feldspar using examples from the zabargad gneisses red sea the method is applied to plagioclases of an25 an45 and compared with other methods of shear sense determination quartz c axis fabrics and microstructural criteria

texture and elastic anisotropy of a mylonitic anorthosite from the morin shear zone quebec canada a sample of anorthosite from the granulite facies morin shear zone quebec canada was investigated for crystal preferred orientation and elastic anisotropy time of flight neutron diffraction data obtained with the hippo diffractometer at lansce were analyzed with the rietveld method to obtain orientation distribution functions of the principal phases plagioclase clinopyroxene and orthopyroxene texture and microstructures are compatible with the plastic deformation of the aggregate under high t conditions all mineral phases depict a significant preferred orientation that could be related to the general top to the north shearing history of the morin shear zone texture patterns suggest that 010 001 in plagioclase and 110 001 in clinopyroxene are likely dominant slip systems using preferred orientation data p and s waves velocities and elastic anisotropy were calculated and compared with previous studies to explore elastic properties of rocks with different pyroxene plagioclase mixtures p wave velocity s wave splitting and anisotropy increase with clinopyroxene content seismic anisotropy is linked to the texture symmetry which can lead to large deviations between actual anisotropy and that measured along cartesian xyz sample directions lineation foliation reference frame this is significant for the prediction and interpretation of seismic data particularly for monoclinic or triclinic texture symmetries

variability of arctic sea ice thickness and volume from cryosat 2 we present our estimates of the thickness and volume of the arctic ocean ice cover from cryosat 2 data acquired between october 2010 and may 2014 average ice thickness and draft differences are within 0 16 m of measurements from other sources moorings submarine electromagnetic sensors icebridge the choice of parameters that affect the conversion of ice freeboard to thickness is discussed estimates between 2011 and 2013 suggest moderate decreases in volume followed by a notable increase of more than 2500 km 3 or 0 34 m of thickness over the basin in 2014 which could be attributed to not only a cooler summer in 2013 but also to large scale ice convergence just west of the canadian arctic archipelago due to wind driven onshore drift variability of volume and thickness in the multiyear ice zone underscores the importance of dynamics in maintaining the thickness of the arctic ice cover volume estimates are compared with those from icesat as well as the trends in ice thickness derived from submarine ice draft between 1980 and 2004 the combined icesat and cryosat 2 record yields reduced trends in volume loss compared with the 5 year icesat record which was weighted by the record setting ice extent after the summer of 2007

estimation of sea ice type and concentration by linear unmixing of geosat altimeter waveforms the geosat geodetic satellite altimeter transmits a radar pulse toward earth then measures earth reflected energy in a number of time gates the signal amplitudes in successive gates create a waveform the shape of which is determined by the reflectance characteristics of the earth s surface this study shows that over the polar ice cap the type and concentration of sea ice can be related to geosat return waveform shapes because it is known that an altimeter waveform may be a mixture of returns from two or more ice types within the footprint linear unmixing theory is chosen as the framework for analysis of waveform data the mixing model assumes that data samples are linear combinations of a limited number of end members unmixing analysis therefore consists of identifying the number and nature of the end members followed by an interpretation of the data set in terms of combinations of these end members estimates of ice type and concentration obtained by linear unmixing of waveforms are compared with ground truth derived from visual interpretation of passive microwave imagery and aerial photography which were collected coincident with geosat overpasses during the 1987 marginal ice zone experiment generally good agreement is observed between waveform based ice information and the corresponding imagery ground truth this analysis has revealed some deficiencies in a current parameterization of waveform shape called the geosat ice index a new ice index formulation is proposed

development of an envisat altimetry processor providing sea level continuity between open ocean and arctic leads over the arctic regions current conventional altimetry products suffer from a lack of coverage or from degraded performance due to the inadequacy of the standard processing applied in the ground segments this paper presents a set of dedicated algorithms able to process consistently returns from open ocean and from sea ice leads in the arctic ocean detection of water surfaces and derivation of water levels using returns from these surfaces this processing extends the area over which a precise sea level can be computed in the frame of the european space agency sea level climate change initiative http cci esa int we have first developed a new surface identification method combining two complementary solutions one using a multiple criteria approach in particular the backscattering coefficient and the peakiness coefficient of the waveforms and one based on a supervised neural network approach then a new physical model has been developed modified from the brown model to include anisotropy in the scattering from calm protected water surfaces and has been implemented in a maximum likelihood estimation retracker this allows us to process both sea ice lead waveforms characterized by their peaky shapes and ocean waveforms more diffuse returns guaranteeing by construction continuity between open ocean and ice covered regions this new processing has been used to produce maps of arctic sea level anomaly from 18 hz environment satellite ra 2 data

plastic deformation and development of clinopyroxene lattice preferred orientations in eclogites abstract we use an anisotropic viscoplastic self consistent vpsc model to simulate the development of omphacite lattice preferred orientations lpos in response to deformation by dislocation glide in these simulations we consider slip systems identified either in naturally deformed omphacite or in experimentally deformed diopside simulated lpos reproduce very well the characteristic omphacite lpo pattern in naturally deformed eclogites a strong concentration of 001 axes sub parallel to the lineation and of 010 poles sub perpendicular to the foliation these models reconcile the interpretation of omphacite lpos in eclogites and tem observations of naturally deformed omphacite since they show that omphacite lpos in naturally deformed eclogites may develop by dislocation glide on 1 2 110 110 001 110 and 001 100 we also investigate the effect of the strain regime on the omphacite lpo development the simulations show that changes in deformation regime lead to second order variations in omphacite lpo patterns similar to those observed in eclogites such as an asymmetry of the lpo relative to the structural frame a stronger concentration of the 001 axes relative to the 010 pole concentration or a dispersion of 001 axes in the foliation plane this suggests that omphacite lpo patterns may carry information on the deformation regime simple shear transtension active during the high pressure events

seismic and tectono metamorphic characters of the lower continental crust in phanerozoic areas a consequence of post thickening extension deep seismic profiles of phanerozoic continental crust commonly show a highly reflective lower crust rheological considerations suggest that the seismic fabric of the lower crust can be attributed to the tectonic transposition of various petrological heterogeneities in the main flow plane the variscan provinces of western europe have been affected during phanerozoic times by several extensional and compressional events the geometrical relationships between seismic and geological structures indicate that the layering of the lower crust was acquired during the late carboniferous to permian when the thickened variscan crust was affected by gravitational collapse petrological and geochronological analyses of deep crustal rocks xenoliths and exposed sections indicate that the lower crust has recorded a major high t medium p granulite facies metamorphism during the late variscan extension whereas on the surface upper carboniferous to permian basins were being deposited a similar scenario characterizes other phanerozoic orogenic belts in the caledonian provinces of the british islands the lower crust is seismically reflective it has undergone medium p granulitic metamorphism during the deposition of devonian sedimentary basins at the end of the caledonian orogeny in the same way collapse of the mesozoic belt in the western part of north america is responsible during the cenozoic for pervasive crustal extension whose consequence is a seismic layering of the lower crust accompanied by a low p granulite grade metamorphic event while in the mid and upper crusts low angle ductile normal faults give rise to the basin and range province therefore it is proposed that there is a genetic relationship between 1 post thickening crustal extension 2 low to medium p granulite facies metamorphism of the lower crust and 3 seismic layering of the lower crust

preferred lattice orientations of plagioclase from amphibolite and greenschist facies rocks near the insubric line western alps abstract preferred lattice orientations of plagioclase measured by the universal stage from deformed amphibolite and greenschist facies rocks near the insubric line western alps reflect the type and orientation of the strain system either 001 or 010 are oriented parallel or subparallel to the schistosity and form more or less complete girdles around the stretching direction by the preferred orientation patterns dominant 010 001 slip is indicated and additionally slip on 001 parallel to the a direction possibly at somewhat higher temperatures and or at a higher an content of the plagioclase it is suggested that obliquities of the symmetry planes of the orientation patterns against the principle axes of strain are related to the sense of shearing

plagioclase preferred orientation in layered mylonites evaluation of flow laws for the lower crust thesis s m joint program in marine geology and geophysics massachusetts institute of technology dept of earth atmospheric and planetary sciences and the woods hole oceanographic institution 2008

evaluation of cryosat 2 derived sea ice freeboard over fast ice in mcmurdo sound antarctica using in situ data from 2011 and 2013 we evaluate the ability of cryosat 2 cs 2 to retrieve sea ice freeboard over fast ice in mcmurdo sound this provides the first systematic validation of cs 2 in the coastal antarctic and offers insight into the assumptions currently used to process cs 2 data european space agency level 2 esal2 data are compared with results of a waveform fitting wff procedure and a threshold first maximum retracker algorithm employed at 40 tfmra40 a supervised freeboard retrieval procedure is used to reduce errors associated with sea surface height identification and radar velocity in snow we find esal2 freeboards located between the ice and snow freeboard rather than the frequently assumed snow ice interface wff is within 0 04m of the ice freeboard but is influenced by variable snow conditions causing increased radar backscatter from the air snow interface given such snow conditions and additional uncertainties in sea surface height identification a positive bias of 0 14m away from the ice freeboard is observed tfmra40 freeboards are within 0 03m of the snow freeboard the separation of freeboard estimates is primarily driven by the different assumptions of each retracker although waveform alteration by variations in snow properties and surface roughness is evident techniques are amended where necessary and automatic freeboard retrieval procedures for esal2 wff and tfmra40 are presented cs 2 detects annual fastice freeboard trends using all three automatic procedures that are in line with known sea ice growth rates in the region

k u band airborne radar altimeter observations of marginal sea ice during the 1984 marginal ice zone experiment pulse limited airborne radar data taken in june and july 1984 with a 13 8 ghz altimeter over the fram strait marginal ice zone are analyzed with the aid of large format aerial photography airborne synthetic aperture radar data and surface observations variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the marginal ice zone experiment results indicate that the wide beam altimeter is a flexible instrument capable of identifying the ice edge with a high degree of accuracy calculating the ice concentration and discriminating a number of different ice classes this suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited when fused with ssm i avhrr and ers 1 synthetic aperture radar imagery future ers 1 altimeter data are expected to provide some missing pieces to the sea ice geophysics puzzle

using the interferometric capabilities of the esa cryosat 2 mission to improve the accuracy of sea ice freeboard retrievals a significant source of error in the retrieval of sea ice freeboard from pulse limited radar altimeters arises when scattering from off nadir leads dominates the power echo causing the onboard tracker to snag and overestimate the two way travel time this range overestimate translates into an ocean elevation underestimate relative to the ice surface and an overestimate of the sea ice freeboard we demonstrate using interferometric cryosat 2 data that it is possible to infer the across track angle of return to off nadir leads and their location in the cryosat 2 footprint and hence correct for the associated range error for the first time it is found that specular scattering from leads can dominate the radar echo some 1530 m off nadir over the region studied the mean ocean elevation bias is closely associated with the pulse peakiness pp parameter used for identifying specular waveforms considering only the most specular waveforms the elevation bias was measured to be 1 21 0 93 cm however lowering the pp threshold includes lower power waveforms originating from higher off nadir angles and the elevation bias becomes 4 06 1 66 cm unaccounted for these biases represent an 10 40 cm overestimate in ice thickness despite the relatively large error on the mean bias correcting for off nadir ranging contributes only a small amount to the elevation uncertainty when combined with range and orbit determination uncertainties we found that making use of cryosat 2 s interferometric mode over sea ice ultimately decreases the uncertainty on the area averaged ocean elevation by allowing the inclusion of more waveforms in the analysis

ebsd measured lattice preferred orientations and seismic properties of eclogites we investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities alps norway mali and eastern china through the analysis of their microstructures and lattice preferred orientations lpo these samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions omphacite and garnet lpo were determined from electron backscatter diffraction ebsd technique garnet appears to be almost randomly oriented whereas omphacite develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 010 poles concentrated sub perpendicular to the foliation in order to analyze the deformation mechanisms that produced such omphacite lpo we compare our observations to lpo simulated by viscoplastic self consistent numerical models a good fit to the measured lpo is obtained for models in which the dominant slip systems are 1 2h110i 11 0 001 110 and 001 100 dominant activation of these slip systems is in agreement with tem studies of naturally deformed omphacite seismic properties of eclogite are calculated by combining the measured lpo and the single crystal elastic constants of omphacite and garnet although eclogite seismic anisotropies are very weak less than 3 for both p and s wave they are generally characterized by a maximum p wave velocity sub parallel to the lineation and by a minimum velocity approximately normal to foliation the mean p and s wave velocities are high respectively 8 6 and 4 9 km s the s wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation calculated reflection coefficients show that an eclogite crust interface is generally a good reflector rc 0 1 whereas an eclogite body embedded in the upper mantle would be hardly detectable

effects of sea maturity on satellite altimeter measurements for equilibrium arid near equilibrium sea states the wave slope variance is a function of wind speed u and of the sea maturity the influence of both factors on the altimeter measurements of wind speed wave height and radar cross section 0 is studied experimentally the necessary theoretical background both on wave statistics and on the near nadir radar backscatter is outlined it is based on a recently proposed view that the effective fractal dimension for a surface patch corresponding to the equilibrium range of wave spectra increases as the wave field matures the experimental part is based on 1 year s worth of geosat altimeter observations colocated with in situ wind and wave measurements by 20 noaa buoys errors and biases in altimeter wind speed and wave height measurements are investigated a geophysically significant error trend correlated with the sea maturity i e with c0 u where c0 is the phase velocity of waves corresponding to the spectral peak and u is the mean wind speed well above the surface is found in wind speed measurements this trend is explained by examining the effect of the generalized wind fetch x gh1 32 u2 on the curves of the observed dependence 0 f u x we conclude in particular that unambiguous measurements of wind speed by altimeter in a wide range of sea states are impossible without accounting for the actual degree of wave development an approach to a more accurate retrieval of wind speeds is suggested as based on accounting for the actual degree of wave development which can be achieved through processing the total radar cross section simultaneously with the significant wave height information contained in altimeter waveforms the potential capability of a satellite altimeter to estimate wave age and similar measures of wind wave coupling is discussed this capability expands the use of satellite altimeters for air sea interaction studies

cation ordering in omphacite and effect on deformation mechanism and lattice preferred orientation lpo we present microstructural data and lattice preferred orientations lpos of omphacites from a suite of eclogites from the adula cima lunga nappe central alps our work shows a surprisingly strong correlation between the measured lpo and the ordering state of cations in omphacite estimates of deformation temperature from metamorphic petrology together with measured omphacite compositions and lpos determine the field ordering state on the omphacite phase diagram into which each sample falls lpos dominated by l type and s type signatures are developed in samples that fall in the p2 n field ordered structure and c2 c field disordered structure respectively dislocations with b 1 2 110 or b 001 are observed in the transmission electron microscope tem in all samples the former change from a perfect dislocation in the c2 c structure to a partial in p2 n any movement of a partial dislocation requires the formation or growth of a stacking fault furthermore in order to pass an obstacle a partial dislocation has to constrict to a unit dislocation the energy to form a constriction is high in omphacite due to the large separation width thus the activity of the b 1 2 110 dislocation is hindered in the p2 n structure relative to the c2 c structure which change the balance between the two and might give rise to the different lpos

on the measurement of plagioclase lattice preferred orientations abstract there are two major difficulties in measuring plagioclase lattice preferred orientations lpos by u stage the first which is caused by dependence of the lpo determination on anorthite content cannot be overcome using the u stage method at present the second difficulty which is caused by the dependence on orientation of thin sections can be overcome by measuring all twinned grains in any two orthogonal sections compared with previous methods published in the literature the present method using two rather than three orthogonal sections is more statistically meaningful and time saving in practice this method was used for measuring lpos of plagioclase an 50 from a typical anorthosite mylonite deformed under the granulite facies conditions in the morin ductile shear zone within the canadian grenville tectonic province

first observations of the interaction of ocean swell with sea ice using satellite radar altimeter data the action of ocean waves and swell on sea ice in the marginal ice zone miz controls the size distribution of ice floes and thus affects ice dynamics and the thermodynamics of ice growth and decay an understanding of ice processes is important because of the influence of the sea ice cover on high latitude weather and global climate1 also long term changes in average sea ice extent could provide a sensitive indication of climatic change if the degree of shorter term variability were better understood2 previous observations of the propagation of swell within the ice pack have been limited in spatial and temporal extent3 6 here we present new results from the us seasat satellite which suggest that radar altimetry can provide a powerful means of global synoptic monitoring of the interaction between ocean and ice

a determination of the three dimensional seismic properties of anorthosite comparison between values calculated from the petrofabric and direct laboratory measurements bernard eront and david mainprice zaboratoire de tectonophysique i h iversit montpe lier ii montpe lier france nikolas i christensen department of earth and atmospheric sciences purdue unh ersity west lafayette btdiana we have undertaken a coinparative study of the seisnfic properties of an anorthosite the seisnfic properties have been calculated froin the lattice preferred orientation lpo of plagioclase 90 by volume and olivine 10 by voluine and the elastic constants of these minerals laboratory measurements of vp 24 directions and vs 6 directions have been made on the same sample at room temperature and pressures up to 1 0 gpa the twe techniques agree with 0 1 km s for all orientations studied when the voigt averaging method is used hill and reuss averaging methods give calculated velocities significantly lower than the experimental ones a study of the difference between the velocity values given by the two methods reveals a systematically larger departure in orientations normal to the foliation the orientation dependent difference between the two tedmiques can be explained if there are small errors in the elastic constants for single crystal plagioclase used in the initial calculations the axial lpo symmetry of the plagioclase with all the crystallographic b axes parallel to the specimen symmetry axis allowed us to calculate c22 norinal to 010 directly from the laboratory measurement of vp some constraints can be put on c22 c44 c66 c12 and c23 on average our data require 10 modification of the single crystal constants reported by ryzhova 1964

preferred orientation of anorthite deformed experimentally in newtonian creep abstract synthetic anorthite aggregates were deformed in a paterson gas deformation apparatus at confining pressures up to 400 mpa in torsion and axial compression at temperatures between 950 c and 1200 c samples deformed in torsion under newtonian creep display development of texture or crystallographic preferred orientation as documented with synchrotron x ray diffraction measurements complex diffraction patterns were deconvoluted with the rietveld method to obtain quantitative texture information torsion samples deformed up to shear strains of 4 and samples deformed in compression at higher stresses to total strains of 0 3 develop clear textures texture and shape preferred orientation spo of torsion samples display a monoclinic pattern with an asymmetry inclined against the sense of shear consistent with polycrystal plasticity simulations that assume the deformation is accomplished by dislocation glide these results show that a material deforming in linear viscous creep can develop a strong texture in striking contrast to the paradigm that the presence of a texture precludes low stress newtonian behavior our observations show that the presence or absence of crystallographic preferred orientation is not sufficient to uniquely infer the dominant rheological mechanical regime as sometimes applied for interpretation of seismic anisotropy in the earth

mylonitic deformation of gabbro in the lower crust a case study from the pankenushi gabbro in the hidaka metamorphic belt of central hokkaido japan abstract the mylonitization of the pankenushi gabbro in the hidaka metamorphic belt of central hokkaido japan occurred along its western margin at 600 mpa and 660 700 c through dynamic recrystallization of plagioclase and a retrograde reaction from granulite facies to amphibolite facies orthopyroxene clinopyroxene plagioclase h2o hornblende quartz the reaction produced a fine grained 100 m polymineralic aggregate composed of orthopyroxene clinopyroxene quartz hornblende biotite and ilmenite into which strain is localized the dynamic recrystallization of plagioclase occurred by grain boundary migration and produced a monomineralic aggregate of grains whose crystallographic orientations are mostly unrelated to those of porphyroclasts the monomineralic plagioclase aggregates and the fine grained polymineralic aggregates are interlayered and define the mylonitic foliation while the latter is also mixed into the former by grain boundary sliding to form a rather homogeneous polymineralic matrix in ultramylonites however in both mylonite and ultramylonite plagioclase aggregates form a stress supporting framework and therefore controlled the rock rheology crystal plastic deformation of pyroxenes and plagioclase with dominant 100 001 and 001 1 2 1 1 0 slip systems respectively produced distinct shape and crystallographic preferred orientations of pyroxene porphyroclasts and dynamically recrystallized plagioclase grains in both mylonite and ultramylonite euhedral to subhedral growth of hornblende in pyroxene porphyroclast tails during the reaction and its subsequent rigid rotation in the fine grained polymineralic aggregate or matrix produced clear shape and crystallographic preferred orientations of hornblende grains in both mylonite and ultramylonite in contrast the dominant grain boundary sliding of pyroxene and quartz grains in the fine grained polymineralic aggregate of the mylonite resulted in their very weak shape and crystallographic preferred orientations in the fine grained polymineralic matrix of the ultramylonite however pyroxene and quartz grains became scattered and isolated in the plagioclase aggregate so that they were crystal plastically deformed leading to stronger shape and crystallographic preferred orientations than those seen in the mylonite

physical properties of summer sea ice in the fram strait the physical properties of sea ice in the fram strait region of the greenland sea were examined during june and july 1984 in conjunction with the marginal ice zone experiment field program most of the ice sampled within fram strait during this period was multiyear thicknesses and other properties indicated that none of the multiyear ice was older than 4 to 5 years snow cover on the multiyear ice averaged 29 cm while that on first year ice averaged only 8 cm deep this difference may be related to enhanced sublimation of the snow on the thinner first year ice the salinity profiles of first year ice clearly show the effects of ongoing brine drainage in that profiles from cores drilled later in the experiment are substantially less saline than earlier cores thin section examinations of crystal structure indicate that about 75 of the ice consisted of congelation ice with typically columnar type crystal structure the remaining 25 consisted of granular ice with only a few occurrences of snow ice the granular ice consisted primarily of frazil found in small amounts at the top of floes but mainly observed in multiyear ridges the horizontally oriented crystal c axes showed various degrees of alignment ranging from no alignment to strong alignments in which the alignment direction changed with depth implying a change in floe orientation with respect to the ocean current at the ice water interface during ice growth evidence of crystal retexturing was observed in the upper meter of nearly every multiyear core this retexturing consisting of grain boundary smoothing and nearly complete obliteration of the ice platelet brine layer substructure is attributed to summer warming

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

formation of ishtar terra venus surface and gravity constraints weexaminethegeologyofishtarterra venus asviewedinhigh resolutionmagellan synthetic aperture radar imagery and altimetry in order to interpret regional surface strain patterns we combine constraints imposed by the surface strain with gravity modelingofmagellandegree 75high resolutiongravitydata long wavelength 2500km and short wavelength 500 2500 km features show different apparent depths of isostatic compensation ishtar straddles a long wavelength topographic bulge that is compensated at 130 6 40 km depth whereas the short wavelength features individual mountain belts and tesserae are compensated at varying depths in a range of 25 70 km these two ranges of compensation taken together with surface strain patterns lead us to postulate a new model for the evolution of ishtar terra in the model mantle downflow results in ponding and thickening of partial melt residuum that compensates the long wavelength bulge of ishtar terra thickened lower crust resulting from shear forces associated with structurallydeeperresiduum isostaticallycompensatesshort wavelengthtopography relative displacement of the lower crust beneath the upper crust which deforms in ruglike fashion results in the surface strain patterns

deformation induced clinopyroxene fabrics from eclogites abstract clinopyroxene omphacite microfabric studies in eclogites are useful in characterizing the deformation that has affected deeper parts of subduction zones we present the microfabrics and tem structures of four samples representative of the various deformation types known in eclogites the 001 axis tends to be parallel to the lineation while the 010 plane is close to the foliation but these general features undergo strong variations in relation to the shape fabric in strongly lineated samples 010 tends to be spread out in a great circle normal to the lineation whereas 001 is dispersed in the foliation in the case of strongly foliated samples the slip systems identified by tem are 001 100 001 110 and 1 2 110 110 operation of dislocation creep is testified by the presence of dislocations and dislocation walls but this process alone cannot explain all the observed features particularly some aspects of the crystallographic preferred orientation hence other deformation mechanisms must be involved these may be dynamic migration recrystallization by grain boundary migration as well as mass transfer processes this study illustrates that not every crystallographic mineral preferred orientation can be explained by dislocation glide and or twinning processes alone in addition it also demonstrates that eclogite microfabrics can be used to unravel deformation parameters in subduction and or collision zones

recrystallization and fabric development in plagioclase the microstructures and fabrics of naturally deformed intermediate composition plagioclase feldspars from the amphibolite granulitic gneisses from the lower crust have been studied special interest in the effects of dynamic recrystallization and deformation fabrics has been taken the plagioclase feldspars an40 50 have undergone extensive ductile deformation by intracrystalline slip and twinning they show strong crystallographic preferred orientation which was produced by dominant 010 001 slip dynamic recrystallization is indicated by fine grained new grains neoblasts interspersed with deformed relicts porphyroclasts the neoblasts have formed preferentially along grain boundaries kink band boundaries kbbs intracrystalline shear zones and around solid inclusions such as garnet and pyroxene optical microstructural evidence suggests that dynamic recrystallization occurred primarily by grain boundary migration with subsidiary subgrain rotation which appears to have occurred only at low st

amphibole and lower crustal seismic properties abstract measurements of seismic anisotropy frequently offer insights of the deformation kinematics in situ within the earth in the continental crust seismic anisotropy is commonly ascribed to regionally aligned lattice preferred orientation lpo of mica crystals however determinations of composition suggest that the deep continental crust contains rather little mica in this contribution the role of amphibole a far more plausible constituent especially for deep continental crust of basic composition is assessed a field analogue approach is adopted where the lpo are measured correlated with the strain state of the rocks and used to calculate the seismic properties the seismic properties may be up scaled through the specimen using the modal proportions of the constituent mineral phases to examine the role of composition in controlling the intensity of seismic anisotropy seismic properties are computed using an array of modal compositions so called rock recipes the case history comes from the central block of the lewisian of nw scotland where a regional basic dyke swarm the scourie dykes is locally deformed within amphibolite facies shear zones conditions that are representative of the deep crust shear strain profiles across a 100 m wide shear zone using deflected banding in the host gneisses yield values of 0

seasonal and inter annual variations in antarctic sea ice extent as mapped by radar altimetry previous work has shown that inter annual variations in total sea ice extent may provide a sensitive indicator of global climate change data from passive microwave instruments have allowed mapping of global sea ice extents from 1973 76 and from 1978 up to september 1987 gloerson and campbell 1988 in this paper data from another microwave instrument the geosat radar altimeter have been used to map the antarctic sea ice extent for the period november 1986 to january 1989 comparison with total antarctic sea ice extents derived from the scanning multichannel microwave radiometer smmr show excellent agreement during the freeze up period but show significant differences during the late part of the melt period

how soft is the crust in a series of thermomechanical models of the lithosphere applied to the determination of apparent elastic thickness extension and collision and exhumation burov and coworkers cf e g burov and diament 1995 cloetingh and burov 1996 burov and poliakov 2001 burov et al 2001 model the ductile behaviour of the upper crust sometimes of the whole crust assuming a quartz controlled rheology an extensive comparison of rheological input parameters used in geodynamic modelling fernandez and ranalli 1997 has shown that the dry quartz rheology employed by burov and coworkers results in a crust or upper crust which is about three orders of magnitude softer than in any other model claiming to use the same dry quartz rheology in one case cloetingh and burov 1996 a different set of parameters was included for the purpose of comparison but not used in the calculations the same conclusion is reached by comparing burov and coworkers rheology with the review of lithosphere strength estimates by kohlstedt et al 1995 although experimentally determined rheological parameters show wide scatter this usually results in uncertainties of the order of one order of magnitude or less in estimates of the ductile rheology of the crust of a given composition see ranalli 1995 1997 any larger difference may conceal some problems with the input parameters this would be particularly important in this case as the models by burov and coworkers are at the forefront in the present attempt to understand geodynamic processes and their results are widely used to interpret tectonic features the equation for the strength of a material deforming in power law creep is

crystallographic preferred orientation produced by diffusional creep of harzburgite effects of chemical interactions among phases during plastic flow 1 experimental deformation experiments have been conducted on fine grained two phase aggregates of olivine and orthopyroxene to investigate the role of grain and phase boundary sliding on rheology and fabric development a suite of large strain 1 general shear experiments conducted at t 1200 c and p 1 6 gpa on aggregates ranging from 65 to 0 vol orthopyroxene to characterize the evolution of fabric were complemented by small strain axial compression experiments at t 1200 c and p 0 3 gpa to better constrain the rheology microstructural and rheological data suggest that deformation of these two phase aggregates in the diffusion creep regime occurs via interface reaction controlled diffusion creep that is accompanied by extensive migration of olivine orthopyroxene phase boundaries the resulting rheologies suggest that olivine orthopyroxene composites are weaker than the olivine end member at the conditions tested physically this behavior arises because long range i e grain scale diffusion of si4 is unnecessary in these pseudobinary two phase aggregates we further demonstrate that interface controlled diffusion creep leads to strong crystallographic preferred orientations cpo of the component minerals which develops in the near absence of dislocation activity the cpo formed in these anhydrous low stress experiments has the olivine a axis aligned perpendicular to the flow direction type b fabric argued by some to be the unique result of deformation under conditions of high differential stress and high water fugacity phase boundary dynamics thus are argued as a significant factor in the accumulation of strain in polyphase aggregates

evolution of the southern ocean winter mixed layer and sea ice open ocean deepwater formation and ventilation an analytical model has been developed to describe the nature of the winter ocean sea ice interaction in the southern ocean to determine the principal processes responsible for maintaining stability in this marginally stable region and to predict the response to changes in the external forcing and initial conditions the model accurately describes the sparse winter observations and the general temporal evolution of the ice mixed layer depth and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth a scale analysis and sensitivity study reveal the system parameter dependence this indicates that the magnitude of entrainment is proportional to fst h0 s where fs is the external salt flux h0 the depth of the winter mixed layer and s the salinity gradient through the pycnocline thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads a strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere this limits the amount of ice growth possible and plays the principal role in maintaining the system stability since the ice growth is required for destabilization through haline rejection during the growth process the system is also sensitive to the large ratio of heat to salt in the pycnocline this introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere this moderates the ability to grow ice and drive further entrainment the absolute strength of the salinity gradient on the other hand dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment the effectiveness with which changes in these parameters as well as several other external parameters can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis

resolution enhancement of spaceborne scatterometer data a method for generating enhanced resolution radar images of the earth s surface using spaceborne scatterometry is presented the technique is based on an image reconstruction technique that takes advantage of the spatial overlap in scatterometer measurements made at different times to provide enhanced imaging resolution the reconstruction algorithm is described and the technique is demonstrated using both simulated and actual seasat a scatterometer sass measurements the technique can also be used with ers 1 scatterometer data the sass derived images which have approximately 4 km resolution illustrate the resolution enhancement capability of the technique which permits utilization of both historic and contemporary scatterometer data for medium scale monitoring of vegetation and polar ice the tradeoff between imaging noise and resolution inherent in the technique is discussed