the structural state of the former lower continental crust in calabria s italy in the northern serre s italy a continuous section through a former lower continental crust is exposed schenk 1984 1985 these granulite facies rocks have not been penetratively deformed during their uplift to higher crustal levels therefore they allow to study the structural state of the lower continental crust most rockforming minerals among them ortho and clinopyroxene and cordierite show recrystallization structures quarz basal subgrain boundaries are developed in lower levels of the lower crust and disappear toward higher levels in addition to dimensional orientations of the rockforming minerals the preferred crystallographic orientations of plagioclases cordierite amphibole pyroxenes and rarely quartz reflect the strain orientation of the prograde high t deformation during this deformation the stretching direction was constant nne ssw throughout the exposed lower crustal section shear indicators are rare this points to the fact that deformation has been homogeneous and coaxial flattening there is only a small variation in orientation and strength of textures throughout the exposed lower crust therefore neighbouring layers of different composition rather than different deformation might serve as seismic reflectors in the former lower crust

quartz recrystallization regimes c axis texture transitions and fluid inclusion reequilibration in a prograde greenschist to amphibolite facies mylonite zone ribeira shear zone se brazil abstract the crystal plastic behavior of quartz mylonites from the ribeira shear zone se brazil a major strike slip structure that was active during a prograde metamorphic phase related to the neoproterozoic brasiliano pan african orogeny was investigated using a multi method approach geothermobarometry results indicate deformational conditions ranging from 300 to 630 c and 500 700 mpa a strong correlation between mapped metamorphic zones and a dominance of different dynamic recrystallization mechanisms of quartz occurs within the mylonite zone bulging recrystallization blg dominates within the chlorite zone between 300 and 410 c subgrain rotation recrystallization sgr operates within the biotite zone from 410 to 520 c and grain boundary migration recrystallization gbm dominates in the garnet zone above 520 c the development of quartz c axis textures is mainly governed by temperature and dynamic recrystallization mechanisms textures from blg zone mylonites are characterized by maxima around z sgr zone mylonites display single girdles or asymmetric type i crossed girdles and gbm zone mylonites comprise maxima around y and intermediate between x and z the scarcity or absence of water bearing fluid inclusions in quartz mylonites from the sgr and gbm zones which are dominated by carbonic inclusions suggests water deficient conditions whereas blg zone mylonites are dominated by water bearing inclusions this evidence indicates that water was available in the protoliths but has been eliminated with increasing deformation and deformation temperature no effect of the water content variation on the quartz microstructural and recrystallized grain size evolution was detected and little influence on c axis texture development was observed most of the fluid inclusion densities were reequilibrated during the shear zone exhumation history recording a decompression in the range of 300 500 mpa while microstructural reequilibration effects related to the prograde metamorphism are largely preserved fluid inclusion microstructures and densities from two sgr zone samples preserved evidence for a near isothermal compression within the interior of the ribeira shear zone during the prograde metamorphism

syndeformational fluid trapping in quartz determining the pressure temperature conditions of deformation from fluid inclusions and the formation of pure co2fluid inclusions during grain boundary migration observations and microthermometric data on fluid inclusions from a terrane that underwent deformation following peak metamorphic conditions show that grain boundary migration recrystallization favours the entrapment of carbonic inclusions whereas microfracturing during brittle deformation favours the infiltration and eventual entrapment of aqueous fluids our results imply that pure co2 fluid inclusions in metamorphic rocks are likely to be the residue of deformation recrystallization process rather than representing a primary metamorphic fluid where the temperature of deformation can be deduced by other means the densities of fluid inclusions trapped during recrystallization which we call recrystallization primary fluid inclusions can be used to constrain the ambient pressure during deformation using these constraints the data imply that the post metamorphic hercynian exhumation in sardinia brought rocks at 300 c to within 3km of the surface this conclusion is similar to that described for the rapidly uplifted southern alps in new zealand

the p t d development at the basement cover boundary in the north eastern tauern window eastern alps alpine continental collision at the basement cover boundary of the north eastern tauern window eastern alps the following alpine p t d development has been reconstructed on the basis of macro and micro structures as well as preferred crystallographic orientations mineral parageneses and compositions during increasing p t conditions in the greenschist facies a first period of deformation produced imbrication of the basement gneisses and cover sediments and then monoclinal folds up to the kilometre scale tectonic transport was continuously top to the ene a second period of deformation began at about peak p t conditions of 9 kbar and c 540 560 c in the south and about 7 9 kbar and 490 500 c in the north this continued locally to lower temperature during the second period transport was continuously top to the se crystallographic orientations of white mica and plagioclase give particularly useful information on the kinematic framework in addition data on the ductile behaviour of dolomite and plagioclase can be inferred at c 7 9 kbar dolomite recrystallization starts at 450 480 c and the beginning of plagioclase recrystallization coincides with the oligoclase boundary in general the alpine geodynamic history of the basement cover boundary may be related to continental collision processes between a northerly plate european or brianconnais and a southerly adriatic one the first deformation period possibly reflects subduction of the gneiss sediment boundary toward the wsw to a depth of 31 32 km the second period may be a result of obduction toward the nw followed by late stage uplift most of the basement domes of the eastern tauern window appear as a result of the final stage of the first deformation formed prior to the peak of metamorphism possibly partly influenced by the final collision between the northern and the southern continents

short lived polyphase deformation during crustal thickening and exhumation of a collisional orogen ribeira belt brazil abstract the ribeira belt brazil is a neoproterozoic collisional related feature that was located in a south central position in west gondwana we present quantitative data on finite strain flow vorticity and deformation temperatures for the curitiba terrane a major segment of the southern ribeira belt six deformation phases d 1 d 6 related with crustal thickening and exhumation were recognized d 1 and d 2 related microstructures are preserved exclusively within porphyroblasts in part grown during stages of high pressure 9 12 kbar isobaric heating after crustal thickening d 3 phase was active from peak metamorphism attained in contrasting crustal levels 810 400 c to the early stage of exhumation 500 400 c as indicated by petrological microstructural and quartz c axis fabric evidence kinematic vorticity results indicate that the sl 3 mylonitic fabric resulted from a simple shear dominated deformation related with westward thrusting north verging overturned d 4 folds with e w trending subhorizontal axes derived from a pure shear dominated deformation regional d 5 open folds with subvertical axes and nne ssw trending traces were produced by indentation tectonics d 6 phase comprises retrograde orogen parallel transcurrent shear zones related with scape tectonics geochronological data indicate that d 3 d 6 phases occurred between 584 and 580 ma suggesting a fast exhumation rate of 8 mm year for the deepest rocks from the southern ribeira belt

regional variation in exhumation and strain rate of the high pressure sambagawa metamorphic rocks in central shikoku south west japan regional variation in the p t path of the sambagawa metamorphic rocks central shikoku japan has been inferred from compositional zoning of metamorphic amphibole rocks constituting the northern part saruta river area exhibit a hairpin type p t path where winchite actinolite grew at the prograde stage the peak metamorphism was recorded by the growth of barroisite to hornblende and sodic amphibole to winchite actinolite grew at the retrograde stage in the southern part asemi river area rocks exhibit a clockwise type p t path where barroisite to hornblende core is rimmed by winchite to actinolite the difference in p t path could suggest a faster exhumation rate i e more rapid decompression in the southern than in the northern part on the other hand physical conditions of deformation during the exhumation stage have been independently inferred from microstructures in deformed quartz recrystallized quartz grains in rocks from the low grade chlorite and garnet zones are much more stretched in the southern part aspect ratio 4 0 than in the northern part aspect ratio 4 0 indicating a higher strain rate in the former than in the latter these facts may indicate that the exhumation and strain rates are correlated i e the exhumation rate increases with increasing the strain rate the difference in the exhumation rate inferred from amphibole zoning between the northern and southern parts could be explained by an extensional model involving normal faulting where the lower plate can be exhumed faster than the upper plate due to the displacement along the fault furthermore the model may explain the positive correlation between the exhumation and strain rates because the lower plate tended to support more stress than the upper plate

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

temperature and strain gradients through lesser himalayan rocks and across the main central thrust south central bhutan implications for transport parallel stretching and inverted metamorphism in order to understand mass and heat transfer processes that operated during himalayan orogenesis we collected temperature finite and incremental strain and kinematic vorticity data through a 5 km thickness of lesser and greater himalayan rocks in southern bhutan this transect crosses two major shear zones the main central thrust mct and shumar thrust st raman spectroscopy on carbonaceous material and garnet biotite thermometry are integrated with deformation temperatures from quartz petrofabrics these data define inverted field gradients that correspond in structural position with the mct and st which are separated by sections in which temperatures remain essentially constant temperatures increase from 400 500 c to 700 750 c between 675 m below and 200 m above the mct this defines a 269 44 c km inverted gradient interpreted to have formed via high magnitude 100 250 km shearing on a discrete mct zone delineated by the limits of inverted metamorphism temperatures increase from 300 400 c to 400 530 c across the st which is attributed to differences in maximum burial depth of hanging wall and footwall rocks strain and vorticity data indicate that lesser and greater himalayan rocks were deformed by layer normal flattening transport parallel lengthening and foliation normal shortening increase from 38 71 and 36 49 respectively between 2 3 1 0 km below the mct the mct acted as a stretching fault with translation on the order of 100 s of km accompanied by transport parallel stretching of footwall and hanging wall rocks on the order of 10 s of km this demonstrates that stretching accommodated between major shear zones can make a significant contribution to cumulative mass transfer

bryozoans as carbonate sediment producers on the cool water lacepede shelf southern australia abstract modern sediments on the lacepede shelf and adjacent slope are typical mid latitude cool water palimpsest deposits dominated by bryozoan mollusc and quartz particles bryozoan bioclasts form autochthonous and to a lesser extent allochthonous accumulations across the grain size spectrum from mud to boulder size the bryozoan skeletons are grouped on the basis of architecture and style of disarticulation fragmentation into nine morphotypes erect rigid forms comprise 1 fenestrate 2 foliose 3 flat robust branching and 4 delicate branching morphotypes large adeona sp skeletons are recognised as a separate type of fenestrate form because of their distinctive shape mineralogy and restricted environment erect flexible forms are either 5 articulated branching or 6 articulated zooidal other important morphotypes are 7 encrusting 8 nodular arborescent and 9 vagrant differences in skeletal architecture result in distinct particle types encrusting morphotypes on soft organic substrates and the wide variety of erect rigid forms are broken into fragments erect flexible forms disintegrate upon death into definitive sand and silt size grains encrusting morphotypes on hard substrates nodular arborescent and vagrant forms remain whole and when large accumulate in place morphotypes are mineralogically distinct and so bryozoan sediment composition is environmentally controlled shallow water

geochronology and calibration of global milankovitch cyclicity at the cenomanian turonian boundary new 40 ar 39 ar geochronology and global cyclostratigraphic calibration provide high resolution insights into the timing of geochemical fluctuations across oceanic anoxic event ii oae ii five new 40 ar 39 ar data from a single section in western canada suggest an age of 96 4 1 ma for the cenomanian turonian c t boundary this is 3 m y older than previously dated time series analysis e g wavelet transform reveals that oae ii was synchronously deposited worldwide over a period of 320 k y the preservation and stationarity of milankovitch cyclicity in sections across the atlantic indicates that no major fluctuations in sedimentation rate occur across the oae ii except for a minor short term decrease in the rate just before the c t boundary a 13 c org increase of 2 took place at the beginning of oae ii over a period of 110 k y and likely represents a period of worldwide excessive organic carbon burial during transgression leading to a 12 c depletion of seawater and sedimentation this interval was followed by a three step decrease to pre oae ii 13 c values

laminated bioturbated cycles in maastrichtian chalk of the north sea oxygenation fluctuations within the milankovitch frequency band the maastrichtian chalk of the southern central graben danish north sea is a homogeneous pure white coccolithic chalk mudstone deposited in a deep epeiric shelf sea which covered large parts of northern europe the sediment displays a pronounced cyclicity marked by decimetre thick bioturbated beds alternating with slightly thinner non bioturbated mainly laminated beds the laminated half cycles consist of alternating millimetre thick graded high porosity laminae and non graded low porosity laminae the cyclicity has been interpreted previously as caused by periods of slow background sedimentation and bioturbation interrupted by periods of rapid deposition of laminated beds with the latter reflecting random and local resedimentation processes based on textural and structural analysis the millimetre scale non graded laminae are interpreted as having been deposited directly from pelagic rain of pelleted coccoliths representing the primary production the graded laminae were deposited from small volume low density turbidity currents and suspension clouds the sedimentation rates of the cyclical chalk are similar to those known elsewhere and the lamination is interpreted as having been preserved from destruction through bioturbation by anoxic conditions at the seafloor bioturbated laminated cycles are thus formed by slow sedimentation during alternating seafloor redox conditions probably on a milankovitch scale a direct implication of this interpretation is that the cycles are areally widespread probably extending throughout the southern central graben area and may be useful for correlation and high resolution cyclostratigraphy in the chalk fields of the danish north sea if the laminated half cycles represent a few rapid resedimentation events with a high sedimentation rate as suggested by most workers then the sediment would not be truly cyclic but would represent event sedimentation within a pelagic background represented by the bioturbated beds in this case the cycles would have very limited potential for correlation

petrofabrics of high pressure rocks exhumed at the slab mantle interface from the point of no return in a subduction zone sivrihisar turkey the highest pressure recorded by metamorphic rocks exhumed from oceanic subduction zones is 2 5 gpa corresponding to the maximum decoupling depth mdd 80 10 km identified in active subduction zones beyond the mdd the point of no return exhumation is unlikely the sivrihisar massif turkey is a coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record p t fluid deformation conditions during exhumation from 80 to 45 km crystallographic fabrics and other features of high pressure metasedimentary and metabasaltic rocks record transitions during exhumation in quartzite microstructures and crystallographic fabrics record deformation in the dislocation creep regime including dynamic recrystallization during decompression and a transition from prism slip to activation of rhomb and basal slip that may be related to a decrease in water fugacity during decompression 2 5 to 1 5 gpa phengite lawsonite and omphacite or glaucophane in quartzite and metabasalt remained stable during deformation and omphacite developed an l type crystallographic fabric in marble aragonite developed columnar textures with strong crystallographic fabrics that persisted during partial to complete dynamic recrystallization that was likely achieved in the stability field of aragonite p 1 2 gpa results of kinematic vorticity analysis based on lawsonite shape fabrics are consistent with shear criteria in quartzite and metabasalt and indicate a large component of coaxial deformation in the exhuming channel beneath a simple shear dominated interface this large coaxial component may have multiplied the exhuming power of the subduction channel and forced deeply subducted rocks to flow back from the point of no return

heterogeneous sub simple deformation in the gol e gohar shear zone zagros sw iran insights from microstructural and crystal fabric analyses petrofabrics and microstructural characteristics of the quartz rich mylonites were investigated in the nw se trending gol e gohar shear zone with length of ca 25 km within the zagros transpression zone sw iran the semi quantitative vorticity analysis using quartz c axis fabric rxz method and rigid porphyroclast geometry rigid grain net method reveals that mean kinematic vorticity number wm increases towards the baghat thrust fault displaying the occurrence of spatial and temporal variations of flow during progressive deformation the wm values show pure shear dominated flow progressively was changed to a simple shear dominated flow toward to the late stages of ductile deformation implying that the accelerating flow path was accompanied with progressive cooling and strain localization at the lower parts of the zone the measured vertical thinning dip parallel elongation suggests that thrust emplacement and metamorphic rock extrusion likely occurred by a combination of simple shear with a pure shear component of deformation i e general shear the estimated deformation temperatures based on the quartz c axis fabric patterns and their opening angles highlight greenschist to amphibolite facies conditions

a new empirical calibration of the quartz c axis fabric opening angle deformation thermometer abstract the opening angle of quartz c axis fabrics oa is strongly temperature dependent and has proven to be a powerful deformation thermometer for natural metamorphic rocks previous considerations of empirical data have identified a linear correlation between oa and temperature between 250 and 650 c and no correlation above 650 c however possible effects of pressure have not been investigated we expanded the data set of oa versus temperature including data from rocks deformed over 300 1050 c and 2 5 15 kbar disregarding possible effects of pressure the oa temperature relationship can be described by two linear correlations for the intervals 250 650 c and 650 1050 c t c 6 9 o a degrees 48 250 c t 650 c and o a 87 t c 4 6 o a degrees 258 650 c t 1050 c and o a 87 the change on the curve slope of the oa temperature relationship correlates approximately to the low to high quartz transition and to changes in the dynamic recrystallization mechanism from subgrain rotation to grain boundary migration the available data suggest that pressure has a secondary effect accompanying the major temperature dependence of oa which is particularly important for temperatures above 650 c where the correlation between oa and temperature is less pronounced for fixed pressures the oa has logarithmic relationships with temperature over the range 250 1050 c the following thermometer equation is formulated from a multiple regression t c 410 44 ln oa degrees 14 22 p kbar 1272 an uncertainty of 50 c is inherited from the petrological temperature estimates of the natural samples the data suggest the gradual increasing importance of prism c slip relative to slip in quartz with rising temperature under conditions of average geological strain rate and water weakening prism c slip dominates for deformation above 700 c

characterization and p t evolution of melt bearing ultrahigh temperature granulites an example from the anapolis itaucu complex of the brasilia fold belt brazil between garnet orthopyroxene and sillimanite and coronae or sapphirine quartz ultrahigh temperature metamorphism symplectites involving corundum sapphirine spinel cordierite plagioclase sillimanite orthopyroxene biotite and ilmenite the retrograde segment of the p t path was further constrained by biotite producing reactions a composite p t path was constructed

deformation temperatures and flow vorticities near the base of the greater himalayan series sutlej valley and shimla klippe nw india abstract we report new deformation temperature and flow vorticity data from the base of the greater himalayan series ghs exposed in the sutlej valley and shimla klippe of nw india we focus on three groups of transects across the hanging wall of the main central thrust mct in order of relative foreland hinterland positions they are the shimla klippe western and eastern sutlej transects deformation temperatures indicated by quartz c axis fabric opening angles increase both from foreland to hinterland at a given structural distance above the mct and up structural section from the mct within individual transects deformation temperatures in the immediate hanging wall to the mct are estimated at 510 535 535 550 and 610 c on the shimla western sutlej and eastern sutlej transects respectively the steepest inferred field gradients in deformation temperatures are recorded adjacent to the mct and progressively decrease up structural section following a power law relationship comparison with temperature estimates based on multi mineral phase equilibria data suggests that penetrative shearing occurred at close to peak metamorphic conditions vorticity analyses indicate that shearing along the base of the ghs occurred under sub simple shear conditions wm values of 0 9 1 0 with a minor component of pure shear

biological response to milankovitch forcing during the late albian kirchrode i borehole northwestern germany abstract we studied the biological response to orbital forcing in marine upper albian sediments recovered from the 245 m long kirchrode i borehole in the lower saxony basin in northwestern germany results from quantitative analysis of planktonic and benthic foraminifera of calcareous nannofossils and radiolaria were used for this study spectral analysis in the depth domain indicates for the high sedimentation rate part of the upper albian dominant periods with wavelengths of 10 13 m 5 6 m and 2 3 m which we interpret to represent the biological response to orbital forcing in the milankovitch frequency bands eccentricity obliquity and precession respectively in addition a low amplitude 40 50 m cycle was found which would represent the long term eccentricity variation of roughly 400 ka microfossil cyclicity does not change significantly within the whole core indicating sedimentation rates of 11 12 cm ka on an average with variations between 3 5 and 13 ka microfossils show greater variability in their abundance changes than the physical and chemical parameters and also greater power in the higher frequency bands obliquity and precession while most of the planktonic foraminifer species studied are dominated by variations in the obliquity most benthic foraminifer species show an additional strong influence of precession these differences in the cyclicity of the abundance changes are interpreted as reflecting a stronger influence of low latitude water in the deep waters of the late albian lower saxony basin than in the shallow waters this basin was part of a wide boreal epicontinental sea which was connected to the tethys to the south via the polish strait and via the paris basin and which was connected with the north atlantic and arctic to the north in analogy to results from analysis of data from the late neogene strong effects of precession interpreted as being more characteristic for changes influences triggered in the low latitudes and those of obliquity to be more characteristic for influences from the high latitudes the presence of a relatively strong eccentricity cycle not only in the compound parameters but also in the abundance changes of single species during the late albian means that there must have been a non linear response to orbital forcing and internal feedbacks

orbital forcing of palynofacies in the jurassic of france and the united kingdom palynofacies analysis of marine jurassic sedimentary successions in france and the united kingdom demonstrates the pervasiveness of regular cycles in qualitative and quantitative aspects of the microscopic particulate organic content of the rocks especially that part which is ignored during routine palynology the cycles are attributed to precession obliquity and eccentricity forcing most of the palynofacies cycles are independent of lithology whether it be cyclic irregular or uniform terrestrially derived organic particles record the effects of orbital cyclicity on land which may be controlled by orbital cycles different from those controlling marine sediment deposition the majority of studies on orbital cyclicity in the sedimentary record concentrate on cyclicity in lithology this study demonstrates that sections lacking regular lithological cycles may still record evidence of orbital forcing of both the depositional environment and sediment source and transport

c slip in quartz from subsolidus deformed granite abstract the slip behaviour of quartz from a granite and granitic veins during subsolidus high temperature conditions 700 800 c of deformation is studied by lattice preferred orientation lpo and microstructural techniques lpos with a point maximum of c axes parallel to the shear direction which is close to the stretching lineation are presented and interpreted with the aid of light and electron microscopy in terms of c as the dominant slip direction during plastic deformation microscopy of such samples reveals the presence of 0001 tilt boundaries and free 0001 burgers vector dislocations in edge orientations a change in lpo in a decreasing temperature environment from c axes parallel to the shear direction to c axes normal to the shear direction documents a fabric transition from the rare c slip to the more common a slip fabric it is concluded that conditions of high temperature and partial pressure of water are required to initiate dominant c slip during deformation at geological strain rates

prism c slip in the quartzites of the oakhurst mylonite belt california abstract quartz c axis fabrics from 21 amphibolite facies quartzites of the oakhurst mylonite belt california suggest that prism c prism a and basal a slip systems were activated during deformation qualitative two dimensional kinematic models consistent with meso and microscopic shear criteria are constructed based on a regime of combined pure and simple shear in this kinematic framework most of the observed c axis fabric patterns of the oakhurst mylonite belt can be explained if prism c slip was dominant during the early increments of deformation until a transition to dominant basal a slip occurred an apparent relationship between grain size and type of crystallographic fabric is interpreted as resulting from some quartz syntectonic vein quartz having recorded only the latest increments of deformation comparison with the metamorphic evolution of fault zones of similar tectonic origin in california suggests that prism c slip was enhanced by the circulation of hot fluids which hydrolytically weakened quartz and allowed prism c slip to occur at relatively low temperature

intracrystalline vorticity record of flow kinematics during shear zone reactivation abstract the vorticity axis of deformation of a shear zone is a rotational axis controlled by the relative movement of its boundaries when characterized it is a reliable tool to determine the ductile flow geometry monoclinic general monoclinic transpressive or triclinic and an asset to identify the kinematics of complex oblique collisions advancements in analysis of electron backscattered diffraction ebsd maps now permit inference of vorticity axes known as crystallographic vorticity axes cvas from the intragranular lattice orientation dispersion of strain bearing minerals however natural shear zones may preserve a record of multiple shear events with contrasting kinematics and it is not understood to which extent the quartz lattice may preserve a kinematic record through multiple deformation events herein we characterize the finite flow kinematic record produced during reactivation of the eastern highlands shear zone ehsz in an oblique collision within the canadian appalachians we integrate field and thin section observations quartz lattice preferred orientations ebsd maps and grain classification leading to a new method to determine and compare cva within relict and recrystallized quartz grains using this method we were able to conclude that the ehsz was reactivated in an heterogenous monoclinic flow environment

kinematics nature of deformation and tectonic setting of the taxaquara shear zone a major transpressional zone of the ribeira belt se brazil abstract in this paper we have investigated the taxaquara shear zone tsz a major strike slip structure within the ribeira belt rb se brazil in order to assess its kinematics the nature of deformation of rocks affected by the tsz and its tectonic setting the tsz presents a vertical ne trending mylonitic foliation and ene to wsw stretching lineation with variable plunge granitic rocks are intensely deformed giving rise to mylonites with newformed matrix assemblage quartz oligoclase k feldspar biotite muscovite rutile magnetite this assemblage within a pseudosection couple with muscovite biotite thermometer helps to constrain a metamorphic condition during deformation which spans 513 525 c and 3 9 4 4 kbar with mean peak at 520 c and 4 0 kbar quartz accommodates deformation through dislocation creep achieving subgrain rotation with minor contribution of grain boundary migration at a mean strain rate of 10 13 10 12 s 1 feldspar porphyroclasts record brittle deformation microfaults and evidences of dislocation creep e g kink twinning the cpos for monomineralic quartz ribbons display monoclinic pattern and activation of basal rhomb slip systems during deformation however the cpos for quartz and feldspar from fine grained polyphase matrix show a switch in deformation mechanism from dislocation creep to diffusion creep the vorticity and three dimensional finite strain data results suggest that the tsz was developed under a moderate to high strain conditions and a transpressional sub simple shear environment with predominance of simple over pure shear regional correlation with other structures from the ribeira belt and african belts based on finite strain quantification support that a major transpressional system was mainly responsible for the shear zones development during late stages of braziliano pan african orogeny

thermometry and microstructural analysis imply protracted extensional exhumation of the tso morari uhp nappe northwestern himalaya implications for models of uhp exhumation

thermo kinematic evolution of the annapurna dhaulagiri himalaya central nepal the composite orogenic system the himalayan orogen represents a composite orogenic system in which channel flow wedge extrusion and thrust stacking operate in separate orogenic domains with distinct rheologies and crustal positions we analyze 104 samples from the metamorphic core greater himalayan sequence ghs and bounding units of the annapurna dhaulagiri himalaya central nepal optical microscopy and electron backscatter diffraction ebsd analyses provide a record of deformation microstructures and an indication of active crystal slip systems strain geometries and deformation temperatures these data combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the ghs the profiles define a three stage thermokinematic evolution from midcrustal channel flow stage 1 7008c to 550 6508c to rigid wedge extrusion stage 2 400 6008c and duplexing stage 3 280 4008c these tectonic processes are not mutually exclusive but are confined to separate rheologically distinct orogenic domains that form the modular components of a composite orogenic system these orogenic domains may be active at the same time at different depths positions within the orogen the thermokinematic evolution of the annapurna dhaulagiri himalaya describes the migration of the ghs through these orogenic domains and reflects the spatial and temporal variability in rheological boundary conditions that govern orogenic systems

atypical textures in quartz veins from the simplon fault zone abstract samples of monomineralic quartz veins from the simplon fault zone in southwest switzerland and north italy generally have asymmetric single girdle c axis patterns similar to textures measured from many other regions several samples have characteristically different textures however with a strong single c axis maximum near the intermediate specimen axis y the direction within the foliation perpendicular to the lineation x and a tendency for the other crystal directions to be weakly constrained in their orientation about this dominant c axis maximum this results in streaked pole figure patterns with an axis of rotation parallel to the c axis maximum these atypical samples also have a distinctive optical microstructure with advanced recrystallization and grain growth resulting in a strong shape fabric sb oblique to the dominant regional foliation sa whereas typical samples have a strong sa fabric outlined by very elongate only partially recrystallized ribbon grains the recrystallized grains of the atypical samples are themselves deformed and show strong undulose extinction and a core mantle recrystallization structure the streaked texture is likely to be a direct consequence of lattice bending and kinking during heterogeneous slip on the favoured first order prism 10 1 0 a system the heterogeneity itself being due to problems in maintaining coherence across grain boundaries when insufficient independent easy slip systems are available for homogeneous strain by dislocation glide such bending would be particularly prevalent in very elongate thin ribbon grains resulting in high internal strain energy and promoting recrystallization thus both the texture and the microstructure could be significantly modified by later strain increments affecting quartz grains with an already developed nearly single crystal texture

ultrahigh temperature granulite metamorphism 1050 c 12 kbar and decompression in garnet mg70 orthopyroxene sillimanite gneisses from the rauer group east antarctica highly magnesian and aluminous migmatitic gneisses from mather peninsula in the rauer group eastern antarctica preserve ultrahigh temperature uht metamorphic assemblages that include orthopyroxene sillimanite quartz garnet sillimanite quartz and garnet orthopyroxene sillimanite garnet that ranges up to xmg of 71 5 coexists with aluminous orthopyroxene that shows zoning from cores with 7 5 8 5 wt al2o3 to rims with up to 10 6 wt al2o3 adjacent to garnet peak p t conditions of 1050 c and 12 kbar are retrieved from fe mg al thermobarometry involving garnet and orthopyroxene in very good agreement with independent constraints from petrogenetic grids in feo mgo al2o3 sio2 and related chemical systems sapphirine orthopyroxene and cordierite form extensive symplectites and coronas on the early phases the specific reaction textures and assemblages involving these secondary phases correlate with initial garnet xmg with apparent higher pressure reaction products occurring on the more magnesian garnet and are interpreted to result from an initial phase of ultrahigh temperature near isothermal decompression uht itd from 12 to 8 kbar at temperatures in excess of 950 c later textures that involved biotite formation and then partial breakdown along with garnet relics to symplectites of orthopyroxene cordierite or cordierite spinel may reflect hydration through back reaction with crystallizing melts on cooling below 900 850 c followed by itd from 7 to 8 kbar to c 5 kbar at temperatures of 750 850 c the tectonic significance of this p t history is ambiguous as the rauer group records the effects of archean tectonothermal events as well as high grade events at 1000 and 530 ma late stage biotite formation and subsequent itd can be correlated with the p t history preserved in the proterozoic components of the rauer group and hence with either 1000 or 530 ma collisional orogenesis however whether the preceding uht itd history reflects a temporally unrelated event e g archean or is simply an early stage of either the late proterozoic or pan african tectonism as recently deduced for similar uht rocks from other areas of the east antarctica remains uncertain

benthic faunal response to late maastrichtian chalk marl cyclicity at rordal denmark abstract chalk marl cyclicity is a common and characteristic feature of the upper cretaceous chalk group of nw europe the mainly small sized benthic fauna from an upper maastrichtian cyclic chalk marl succession at rordal denmark is analysed in order to interpret the composition and structure of the benthic fauna and to test if faunal density diversity composition and mode of life substrate were controlled by changes in lithology the material comprises 21 bulk samples weighing 5 kg each collected from all chalk and marl half cycles the samples were washed and sieved and yielded a total of 25 974 specimens these are referred to at least 75 species and 15 bryozoan morphotypes and form the basis for the establishment of 10 guilds the lithological cyclicity is not reflected by the distribution of individual species or by changes in average adult size but there is generally a higher species diversity and density in chalk compared to marl the chalk thus represents times of more favourable living conditions higher environmental stability and probably higher nutrient influx no changes in guilds between marl and chalk are found the variation in substrate character between the two lithologies was thus too small to have exerted any significant influence on the mode of life of the benthic fauna in spite of a difference in clay content averaging 10 two different fossil associations are recognized each covering one to two chalk marl cycles and characterized by a distinct fauna with similar ecological requirements if the chalk marl couplets represent precession cycles within the milankovitch band then the change from one association to the other and back again may represent the 100 000 years eccentricity cycle based on a calculated sedimentation rate of 6 cm ka 1

reconstruction of mid cenomanian orbitally forced palaeoenvironmental changes based on calcareous dinoflagellate cysts abstract mid cenomanian precession controlled 21 ka chalk marl couplets of the cap blanc nez section anglo paris basin have been studied with focus on the effects which milankovitch cycles have had on the palaeoenvironment in this paper we present micropalaeontological and lithological proxies that enable the reconstruction of both the cycle architecture and the transformation of the orbitally forced signal into the sediment a palaeoecological reconstruction based on changes in calcareous dinoflagellate cysts c dinocysts assemblages was carried out in which two characteristic ecological assemblages of c dinocysts were identified gradual changes in absolute and relative abundance of the cyst species in these assemblages over several couplets depict a bundling pattern which is interpreted to reflect the modulation of the intensity of the precession cycle by the eccentricity cycle 100 ka the stacking pattern in the natural gamma ray signal and the carbonate and toc content has the same period and provides lithological support of the bundling a shelf basin circulation model is proposed to explain the relation between orbitally forced climate change its palaeoenvironmental consequences and the resulting sedimentary cyclicity variations in surface water circulation are reflected in the sediment by the chalk marl couplets the most distinctive couplets ocurring at the base and top of the bundles while the chalks reflect well mixed surface water conditions the marls particularly those at the bundle boundaries can be interpreted as the sedimentary expression of stratified water masses during deposition of these marls reduced oceanic mixing due to low seasonality during strong precession maxima at the eccentricity maxima caused periods of water column stratification that in turn led to nutrient depletion and decreased productivity in the surface water masses

al zoning in orthopyroxene in a sapphirine quartzite evidence for 1120 c uht metamorphism in the napier complex antarctica and implications for the entropy of sapphirine a unique sapphirine orthopyroxene quartz granulite from mt riiser larsen in the tula mountains of enderby land east antarctica preserves two generations of coarse and texturally equilibrated orthopyroxene and sapphirine coexisting with quartz initial subhedral orthopyroxene porphyroblasts retain core compositions enriched in al2o3 12 2 0 5 wt compared with their rims and finer orthopyroxene 9 6 0 5 wt al2o3 that forms granoblastic textures with sapphirine sapphirine and quartz also form symplectites on and along cleavage planes within orthopyroxene these compositional and textural features are consistent with the reaction 2mgal2sio6 mg2al4 sio10 sio2 leading to the formation of sapphirine quartz at the expense of aluminous orthopyroxene calculations in the mas and fmas systems and theoretical considerations involving the phases enstatite sapphirine sillimanite quartz and cordierite indicate that the reaction above progresses from left to right with decreasing temperature in the orthopyroxene sapphirine quartz field at pressures of ca 8 10 kbar the temperature difference required to account for the ca 2 5 3 wt decrease in al2o3 in orthopyroxene is at least 60 80 c and implies peak temperatures for the initial assemblage of at least 1120 c if the second granoblastic assemblage equilibrated at 1040 c the p t conditions required by the sapphirine quartz association and other p t sensitive assemblage indicators in the napier complex it is not possible to distinguish whether the two assemblages are simply related by cooling and re equilibration or reflect a polyphase evolution involving the superposition of a second uht event on an earlier even higher temperature uht metamorphism preliminary thermodynamic modelling of the reaction above incorporating the observed range in orthopyroxene al2o3 zoning indicates that present estimates for the entropy of high temperature sapphirine are potentially too high by 15 18 compared with sapphirine entropy estimates that are consistent with mas system experiments the mt riiser larsen sapphirine quartz rocks preserve the first definitive record of regional metamorphic temperatures in excess of 1120 c in the napier complex or indeed any uht granulite terrain worldwide similarly high peak temperatures may be retrieved from detailed studies of sapphirine quartz granulites from other regions further expanding the thermal realm of crustal metamorphism but progress will critically depend on the experimental acquisition of new entropy data for sapphirine

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

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

rheology of a coaxial shear zone in the virginia blue ridge wet quartzite dislocation creep at 250 280 c abstract cambrian quartzite along the western margin of the blue ridge near front royal virginia records significant penetrative strain under subgreenschist facies conditions strain analyses of the quartzite indicate general flattening and octahedral shear strain values up to 1 25 x z up to 5 7 1 samples with x z as low as 1 5 1 have crystallographic preferred orientations that record a dominance of basal slip and patterns consistent with coaxial flattening in most samples quartz has undergone minor amounts of dynamic recrystallization with mean grain sizes 4 5 m locally the quartzite is brittlely deformed and subgrains and recrystallized bulges are present along fractures and extinction bands fluid inclusion planes and fluid inclusions along deformation lamellae are abundant and quartz ftir analyses yield average h 106si values of 1100 3300 indicating fluid flow and high intragranular water content during deformation higher strain samples generally record lower water contents which may indicate that fluids migrated to grain boundaries during deformation dissolution microstructures are rare in high strain samples and we interpret most strain to have been accommodated by dislocation creep thermal modeling of zircon low temperature thermochronology data coupled with quartz c axis opening angle thermometry suggest deformation temperatures were likely 250 280 c these deformation temperatures are lower than what is typically considered the brittle plastic transition in quartz we attribute localization of this high strain zone and dislocation creep at these temperatures to hydrolytic weakening and a relatively low strain rate estimated to be 10 15 s 1

pure shear dominated transpression and vertical extrusion in a strike slip fault splay from the itapirapua shear zone ribeira belt brazil abstract the itapirapua shear zone is a major ne trending dextral transcurrent zone from the southern ribeira belt brazil which was active during the neoproterozoic brasiliano pan african orogeny related with west gondwana assembly macroscopic sigmoid shaped blocks in its northernmost splay termination present a ne trending subvertical tectonic foliation and subvertical stretching lineation suggesting a transpressional tectonics this paper investigates this splay termination using integration of data from geological mapping thermodynamic modeling microtectonics quartz c axis fabrics kinematic vorticity and finite strain analysis distinct rock assemblages are placed in tectonic contacts along the splay termination including statherian sillimanite biotite paragneiss and granitic orthogneiss apiai mirim complex statherian phyllites bairro dos prestes formation calymmian chlorite epidote actinolite metabasites fazenda velha suite ediacaran phyllites metalimestone and quartzite itaiacoca group and ediacaran granite tres corregos suite isochemical phase diagrams constrain synkinematic metamorphic conditions of 490 510 c and 11 12 5 kbar chlorite biotite phengite phyllite 520 560 c and 9 10 kbar biotite phengite phyllite and 680 690 c and 5 6 kbar sillimanite biotite paragneiss with isothermal decompression paths microstructural evidence suggests that increase in metamorphic temperatures were accompanied by changes in the dominant deformation mechanism in quartz aggregates from subgrain rotation to grain boundary migration recrystallization significant contribution of dissolution precipitation creep indicates water abundant deformational conditions strain ellipsoids are oblate shaped and present ne trending subvertical xy planes and subvertical x axes in agreement with field tectonic fabric quartz c axis fabrics in xz sections of the strain ellipsoid are dominated by symmetrical crossed girdles while the fabrics present dextral asymmetry in horizontal yz sections consistent with macroscopic structural deflection indicating a subvertical vorticity axis vorticity results indicate 48 59 of pure shear contribution the data indicate that strain in the itapirapua shear zone northern termination was accommodated by a pure shear dominated transpression with vertical extrusion at mid crustal conditions which contrasts with a transtensional deformation in the southeastern block

using quartz fabric intensity parameters to delineate strain patterns across the himalayan main central thrust abstract disagreements over how to define shear zones within packages of pervasively recrystallized rock impede our ability to map and correlate these structures here we explore a new approach for delineating the spatial extents of shear zones using quartz petrofabric temperature and kinematic data collected from two transects across the main central thrust mct in western bhutan we calculated cylindricity a fabric intensity parameter that has been previously interpreted as a proxy for finite strain magnitude for each sample cylindricity values measured on a scale from 0 to 1 increase upward from 0 11 to 0 47 between 2 3 and 1 3 km below the mct vary between 0 55 and 0 93 between 700 m below and 200 m above the mct and decrease upward from 0 68 to 0 37 between 2 4 and 11 7 km above the mct fabric intensity increases with proximity to the mct and defines a 900 m thick zone of elevated intensity that overlaps spatially with an interval of inverted metamorphism our results add to a growing number of recent studies that suggest that spatial patterns of fabric intensity when integrated with temperature data and kinematic observations can be used to delineate relative strain patterns across shear zones in the himalaya and elsewhere

simultaneous miocene extension and shortening in the himalayan orogen the south tibetan detachment system separates the high grade metamorphic core of the himalayan orogen from its weakly metamorphosed suprastructure it is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front geochronologic data from the rongbuk valley north of qomolangma mount everest in southern tibet demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago an interval characterized by large scale crustal thickening at lower structural levels these data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of himalayan tectonics in miocene time

effects of chemical environment on dislocation creep of quartzite the water related chemical parameter that affects dislocation creep in quartzite has been determined from variations in sample strength and microstructure with chemical environment in buffered deformation and hydrostatic annealing experiments samples were weld sealed in double capsules and were buffered using solid oxygen buffers agcl or co2 black hills quartzite was deformed at 900 c and 1 5 10 5s 1 two samples were deformed at 1700 mpa confining pressure at constant and with and varying over 8 and 15 orders of magnitude respectively both samples deformed by climb accommodated dislocation creep with flow stresses of 300 mpa two additional samples were deformed at 700 mpa at constant lower than for the 1700 mpa samples with varying over 2 orders of magnitude both samples faulted with a peak strength of 800 mpa these four experiments suggest no dependence of dislocation creep strength on or instead a strong dependence of strength on is inferred previously deformed samples of heavitree quartzite were hydrostatically annealed for 4 days at 800 c and 1200 or 500 mpa confining pressure varying and over 2 5 and 1 order of magnitude respectively the microstructures of these samples show increased rates of dislocation climb and grain boundary migration with increasing but no dependence on these buffered experiments indicate that dislocation creep is affected by alone and suggest that the exponent for the term in the power law creep flow law is 2

deformation within the cycladic subduction exhumation channel new insights from the enigmatic makrotantalo nappe andros aegean new detailed geological structural mapping coupled with microstructural investigations and amphibole chemistry analyses are used to elucidate the enigmatic tectonic evolution of the makrotantalo nappe on northern andros aegean region on the basis of the new geological map we re evaluate the structural position of samples with previously published metamorphic ages to show that the makrotantalo nappe has been affected by the early eocene high pressure hp metamorphism therefore the makrotantalo nappe is an integral part of the cycladic blueschist unit cbu the early main ductile deformation phase recognized in the mapped area is associated with the emplacement of the makrotantalo nappe over the north cyclades nappe at deep subduction levels during early eocene the subsequent deformation phase occurred at the middle eocene oligocene synchronous with the decompression of blueschist rocks from the stability field of glaucophane to that of actinolite during this phase the nappe pile was folded by map scale folds which were locally transposed by ductile shear zones these shear zones were related with ne directed oblique thrusting and locally either restacked the nappe pile or reworked the early nappe contact our results in combination with previous studies in the northern cyclades show that the top to the ne shearing was dominant at a large part of the cbu during exhumation opposite sw directed shearing was restricted at the upper structural levels of the cbu we suggest that the observed spatial variation in shear sense is compatible with ne rather than sw directed ductile extrusion of the cbu

the influence of grain boundary fluids on the microstructure of quartz feldspar mylonites quartz rich domains in pre alpine water deficient amphibolite facies 510 580 c 250 450 mpa pegmatite mylonites from mont mary mm western alps preserve a fine dynamically recrystallized grain size without significant annealing despite the high synkinematic temperatures and subsequent static greenschist facies alpine overprint the microstructure is dramatically different from more typical water rich amphibolite facies mylonites such as from the simplon fault zone in the central alps where the recrystallized grain size is on the millimetre scale the difference reflects the dominant strain induced recrystallization mechanism 1 progressive subgrain rotation and grain boundary bulging for the dry mm examples and 2 fast grain boundary migration for the wet simplon examples the grain boundary microstructure imaged with sem is also very different with most grain boundaries in the dry mm samples lacking porosity whereas grain boundaries in the wet samples are decorated by a multitude of pores quartz grain boundaries from both wet and dry samples are locally coated by thin 100 s of nanometres possibly amorphous silica films despite the differences in microstructure the crystallographic preferred orientations cpos of quartz rich domains from both areas are very similar water deficient conditions hinder grain boundary mobility and thereby modify the dominant recrystallization mechanism s but apparently have little influence on the intracrystalline slip systems as reflected in the cpos strong c axis y maxima in mm mylonites both k feldspar and plagioclase an33 38 dynamically recrystallize consistent with the inferred metamorphic conditions under water deficient conditions mid to lower crustal rocks can deform heterogeneously under transitional ductile brittle conditions at high differential stress for mm ca 300 500 mpa as estimated for dry mohr coulomb failure and preserve this high stress microstructure because of the low mobility of dry grain boundaries

evolution of a passive crustal scale detachment syros aegean region insights from structural and petrofabric analyses in the hanging wall abstract new detailed micro structural investigations quartz petrofabric analyses and geological structural mapping in southeast syros cycladic massif aegean region allow us to place new constraints on the tectonic evolution of the uppermost unit which occupies the immediate hanging wall of the crustal scale vari detachment we show that the eocene oligocene deformation history in the hanging wall of this detachment is associated with sw directed ductile shearing this history includes an early distributed constrictional deformation expressed by transport parallel upright folds l tectonites and cleft girdles quartz c axis fabrics that were formed at temperatures 500 c ductile deformation progressively localized at the bottom of the uppermost unit leading to the formation of a greenschist facies mylonitic zone under plane strain conditions inferred from type i cross girdles quartz c axis fabrics the ongoing mylonitization was also associated with temporally increasing pure shear component of deformation coupled with cooling from 500 c to 400 c we suggest that the vari detachment represents a passive normal sense roof fault resulted from the ne directed ductile extrusion of the blueschist unit footwall at middle eocene oligocene times in the middle miocene the activation of the brittle ssw directed late vari detachment enhanced the brittle exhumation of both the blueschist unit and the vari detachment

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

reversible water weakening of quartz abstract we have performed looped pressure stepping deformation experiments at the same temperature 800 c and strain rate 2 10 6 s 1 on a milky quartz crystal and a quartzite that deform by dislocation creep our results demonstrate that flow strengths at fixed water content depend on f h 2 o and that the dependence is reversible thus rheology of quartzite can be predicted if f h 2 o is known in addition the effect of f h 2 o on strength of quartzite is greater than that of the milky quartz single crystal the differing sensitivities are due to differing effects that water has on deformation and recovery within grain interiors and at or near grain boundaries these results indicate that as temperature increases with depth and the dominant recovery mechanism of dislocation creep changes from recrystallization at grain boundaries to intragranular recovery dependence of quartz creep on f h 2 o may also decrease

enrichment of co2 in fluid inclusions in quartz by removal of h2o during crystal plastic deformation abstract ductile strain induced leakage of h 2 o from mixed co 2 h 2 o fluid inclusions in quartz is proposed as a mechanism for producing occurrences of pure co 2 fluid inclusions in metamorphic rocks the h 2 o needed for hydrolytic weakening of quartz under stress may be provided by the h 2 o in fluid inclusions with dislocation creep as dislocations nucleate on the walls of fluid inclusions or intersect them h 2 o can be transported with the dislocations from the inclusion to the grain boundaries the process should continue so long as there is stress on the host quartz and the inclusion contains h 2 o the h 2 o taken to the grain boundaries would due to its wetting properties be wicked out along the grain boundaries if the h 2 o is totally removed from an inclusion by a flux of dislocations through the quartz during the crystal plastic flow then a residual inclusion bearing components other than water should remain a mixed co 2 h 2 o inclusion would as a consequence of the process become a pure co 2 fluid inclusion during dynamic recrystallization the co 2 would collect at grain boundary triple junctions and following grain boundary migration would become incorporated into the recrystallized quartz as fluid inclusions this mechanism of generating pure co 2 inclusions could result in co 2 fluid inclusions having densities appropriate for the pressure temperature conditions during deformation using estimates of temperature of deformation the total confining pressure during deformation could be determined from the density of the co 2 fluid in these inclusions

tectonic evolution of palaeozoic terranes in west junggar xinjiang nw china nine separate cambrian to carboniferous terranes recognized in west junggar northwest china they were amalgamated as part of the central asian orogenic belt which records accretion of continental island arc and oceanic terranes to archaean proterozoic continental nuclei tangbale kekesayi ebinur and mayila terranes cambrian silurian evolved in intra oceanic settings and docked along a series of north dipping subduction zones on to the laba terrane to their south this southern continent was contiguous with lithosphere of the kulumudi ocean to the north devonian subduction on the northern edge of this ocean resulted in formation of a continental arc toli terrane and accretionary complex kulumudi terrane the karamay terrane formed as an accretionary complex during the carboniferous the ophiolitic sartuohai terrane was emplaced as melange between kulumudi and karamay terranes during the late carboniferous subduction migrated southward continuing beneath these terranes resulting in the intrusion of i type granites into the toli kulumudi sartuohai and karamay terranes these granites are closely associated with epithermal and porphyry style gold mineralization composite terranes either side of the kulumudi ocean collided in the late carboniferous marking the final consolidation of central asia collision was accompanied by anorogenic granite and diabase dyke intrusion followed by widespread latest carboniferous to permian extension and subsequently the formation of the junggar basin west junggar has been further disrupted by cenozoic strike slip faulting along junggar and dalabute faults

the evolution of a late variscan high t low p region the southeastern margin of the bohemian massif a characteristic feature of the moldanubian part of the central european variscides is late orogenic high t low p metamorphism its past history and the possible reasons for this metamorphism are highlighted by the tectonometamorphic development at the south eastern margin of the bohemian massif during the variscan orogeny at ca 340 ma two different crustal segments were juxtaposed by thrusting the drosendorf unit on top of the monotonous unit this probably marks a collisional event that is widespread in the southeastern moldanubian zone the collision was followed by crustal uplift accompanied by strong heating in the lowermost structural unit monotonous unit during the subsequent orogenic collapse the moldanubian nappe pile was thrust over parts of the moravo silesian terrane a late stage of crustal extension under greenschist facies conditions is linked with pluton emplacement in general magmatic underplating as well as delamination of the lithospheric mantle explains the high t low p metamorphism and the large scale plutonism in the southeastern moldanubian zone

composite ichnofabrics and tiering of burrows infaunal communities in marine environments typically are tiered that is different taxa live at different depths within the sediment tiered suites of biogenic structures yield complex biogenic sedimentary fabrics ichnofabrics with the traces of deep burrowing organisms overprinted on those of shallow burrowing organisms careful analysis of crosscutting relationships of burrows in such composite ichnofabrics allows reconstruction of the tiered nature of fossil endobenthic communities it is important to recognize that the best preserved and most prominently displayed trace fossils in most assemblages usually represent the deepest tier thus they were farther removed from the sea floor and therefore less indicative of actual sea floor conditions than the more poorly preserved traces of the shallower tiers on which the deeper traces are juxtaposed

global correlation of cenomanian upper cretaceous sequences evidence for milankovitch control on sea level we have investigated the sequence stratigraphy of two widely separated marine cenomanian successions in southeast india and northwest europe and used high resolution ammonite biostratigraphy to demonstrate that sea level changes are globally synchronous and therefore must be eustatically controlled sequence scale sea level changes in the cenomanian were driven by the long eccentricity cycle 400 k y in the milankovitch band we hypothesize that during pre quaternary time the third order sequences of vail and haq are essentially a sediment response to sea level changes driven by the 400 k y cycle construction of a relative sea level curve for the marginal marine succession in india demonstrates that the short term sea level changes are rapid 10 100 m m y and have a magnitude of 2 20 m glacioeustasy is a possible but unproven driving mechanism

conditions of contact metamorphism papoose flat pluton eastern california usa implications for cooling and strain histories petrological study of highly strained carbonate and pelitic rocks within the contact aureole surrounding the western part of the papoose flat pluton yields thermal profiles plots of metamorphic temperature versus distance across the aureole that show temperature gradients which are relatively flat and narrow 100m the gradients occur close to the contact and indicate a slight decrease in temperature from 500 550 c at the pluton wall rock contact to 450 500 c at the outer margin of the aureole one thermal profile across low strain metasedimentary rocks located in the southern part of the aureole shows that thermal effects from emplacement extend no further than 600 m from the contact coexistence of andalusite and cordierite in pelitic rocks of the aureole constrain pressures to 4 kbar thermal modelling using an analytical solution of the conductive heat flow equation for a rectangular shaped pluton reproduces the observed thermal maxima and profile shape conductive rather than convective cooling also is supported by isotopic and field evidence for limited fluid flow along the strongly deformed margin of the pluton simple thermal models coupled with observed high temperature deformation features and a measured 90 attenuation of stratigraphic units in the plastically deformed western part of the pluton s aureole indicate that strain rates may have been of the order of 10 12s 1 evidence for episodic heating such as two distinct generations of andalusite growth in pelites from the aureole alternatively may indicate a longer heating event and therefore slower strain rates thermal models also indicate that parts of the pluton still may have been above the solidus during deformation of the pluton margin and aureole

the effect of hydrous mineral content on competitive strain localization mechanisms in felsic granulites abstract this study investigates the grain scale mechanisms that facilitated strain localization in the lower crust within the east athabasca mylonite triangle of northern saskatchewan canada there two distinct lithotectonic units the upper deck and northwestern domain are juxtaposed across a km scale shear zone that has been previously interpreted to record thrust and or normal sense displacement our study reports new quartz c axis opening angle ti in biotite and ti in quartz geothermometry and amphibole plagioclase geothermobarometry within syn kinematic phases indicating that both units were deformed and metamorphosed at upper amphibolite to granulite facies 725 c and 0 8 gpa while sharing similar conditions the dominant mechanisms of deformation across the two units are strongly linked to modal proportion of syn kinematic hydrated mineral phases detailed microstructural and crystallographic preferred orientation cpo analyses reveals that specimens poor in hydrated minerals 10 pressure solution and re precipitation processes enhanced phase mixing and promoted grain boundary sliding resulting in weakly developed or absent quartz cpo these results indicate a strong mineralogical and fluid control on deformation and therefore which strain softening process es may dominate in lower crustal shear zones

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

a milankovitch scale for cenomanian time a detailed cyclostratigraphy is present in the rhythmically bedded cenomanian hemipelagic chalks of the northern anglo paris basin which can be correlated over 100 000 km2 individual decimetre scale couplets probably represent the precession cycle modes at 18 or 23 kyr and can be readily grouped in sets averaging five indicative of the short cycle of eccentricity 100 kyr a composite cyclostratigraphy for the basin is presented here and is used as the basis for a cenomanian time scale 20 and 100 kyr units the total duration of the cenomanian thus obtained 4 4 myr compares well with recent radiometric dates of 4 0 4 5 myr the time scale is used to estimate the length of ammonite inoceramid and planktonic foraminiferal zones the rates of formation of authigenic minerals glauconite sedimentation rates and the duration of transgressions and anoxic events

the role of dynamic recrystallization in the development of lattice preferred orientations in experimentally deformed quartz aggregates abstract experiments on coaxially deformed quartz aggregates show that when dynamic recrystallization involves grain size reduction the lattice preferred orientation lpo of the recrystallized grains depends on the recrystallization mechanism at low temperatures and fast strain rates strain induced grain boundary migration recrystallization favors growth of grains oriented poorly for slip on the basal and prism planes resulting in an lpo of c axes parallel to the 1 direction at higher temperatures or slower strain rates progressive subgrain rotation produces recrystallized grains which inherit the small circle girdle lpo of their deformed host grains and which continue to re orient by slip at even higher temperatures and slower strain rates progressive subgrain rotation is accompanied by rapid grain boundary migration which does not favor grains of any particular orientation thus the lpo is again similar to that of non recrystallized grains in contrast when dynamic recrystallization involves grain growth driven by surface energy reduction a strong lpo of c axes parallel to 1 develops during grain growth but then evolves with increasing strain toward a small circle girdle the correlation of lpos with recrystallization mechanisms has important implications for the assumption of homogeneous strain in theoretical models of lpos and for interpreting natural lpos in recrystallized rocks

variation in vorticity of flow during exhumation of lower crustal rocks neoproterozoic ambaji granulite nw india abstract the exhumation of the neoproterozoic ambaji granulite in the aravalli delhi mobile belt nw india took place along nnw sse trending d2 shear zones the shear zones evolved from a high temperature 700 c thrust slip shearing event in the lower middle crust to a low temperature 450 c retrograde sinistral top to nw shearing event at the brittle ductile transition bdt the vorticity of flow wm along the shear zones is estimated with the rigid grain net and strain ratio orientation techniques the wm estimates of 0 32 0 40 and 0 60 coincide with the high temperature event and suggests pure shear dominated deformation the low temperature phase coincides with wm estimates of 0 64 0 87 and 1 0 implying two flow regimes the shear zone was first affected by general non coaxial deformation and gradually became dominated by simple shearing we interpreted that the high temperature event happened in a compressive tectonic regime which led to horizontal shortening and vertical displacement of the granulite to the bdt the low temperature event occurred in a transpressive tectonic setting that caused the lateral displacement of the granulite body at bdt depth the wm values indicate a non steady strain during exhumation of granulite this tectonic evolution is comparable with that of the himalayas

bryozoan distribution and growth form associations as a tool in environmental interpretation tasmania australia abstract the cool temperate carbonate sediments of eastern and western tasmania and bass strait composed of 29 50 of bryozoan skeletal grains two hundred and eighty three bryozoan bulk sediments around tasmania were studied to determine the relationship between bryozoan zoarial growth form association and their depth zone bryozoans skeletons are grouped into 11 morphotypes according to architecture and style of disarticulation fragmentation encrusting forms erect flexible cellariiform and erect rigid robust branching adeoniform cheilostomes are consistently the most widespread with delicate branching cyclostomes the next most common growth form associations were grouped into four depth related settings strand line shallow shelf middle shelf and deep shelf this study demonstrates that bryozoan morphotype associations occupying different depth zones are valuable for providing fundamental paleo environmental information morphotype associations are related mainly to water depth water energy sedimentation rate and substrate in the strand line setting encrusting unilaminar and erect flexible articulated branching are abundant while in the shallow shelf erect flexible encrusting multilaminar erect rigid robust fenestrate and delicate branching are major growth forms the above associations indicate high to moderate energy levels moderate to high sedimentation rates and flexible to hard substrates in middle shelf areas erect rigid fenestrate robust and delicate branching cheilostomes and cyclostomes are the most common growth forms these associations indicate decreasing water energy lower sedimentation rate and presence of stable hard to soft substrates in the deep shelf setting the dominance of erect rigid robust fenestrate and foliose forms indicate deep quiet water low sedimentation rate and hard substrate

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

a new technique for quantifying symmetry and opening angles in quartz c axis pole figures implications for interpreting the kinematic and thermal properties of rocks abstract variations in flow kinematics influence the type of crystallographic preferred orientations cpos in plastically deformed quartz yet we currently lack a robust means of quantifying the diagnostic symmetries that develop in the c axis 0001 pole figure in this contribution we demonstrate how the symmetry of common c axis topologies may be quantified by analysing the intensity distribution across a line transect of the pole figure margin a symmetry value s measures the relative difference in intensities between marginal girdle maxima in the pole figure and thus the degree to which the pole figure defines orthorhombic or monoclinic end member symmetries this provides a semi quantitative depiction of whether the rocks underwent coaxial or non coaxial flow respectively and may subsequently be used to quantify other topological properties such as the opening angle of girdle maxima the open source matlab toolbox mtex is used to quantify pole figure symmetries in quartzite samples from the main central thrust nw himalaya and the moine thrust nw scotland

strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab everest massif tibet this paper presents quantitative data on strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab the data were collected from the tibetan side of the everest massif where two low angle normal faults bound the upper surface of the greater himalayan slab the earlier and structurally lower lhotse detachment and the later and structurally higher qomolangma detachment greenschist to sillimanite grade quartz rich metasedimentary rocks exposed in the rongbuk to north col region of the everest massif are characterized by cross girdle quartz c axis fabrics indicating approximate plane strain conditions fabric opening angles progressively increase with depth beneath the overlying lhotse detachment and indicate progressively rising deformation temperatures of 525 625 50 c at depths of 300 600 m beneath the detachment deformation temperatures of c 450 c are indicated by fabric opening angles in epidote amphibolite facies mylonites located closer to the overlying detachment a top down to the north normal shear sense is indicated by the asymmetry of microstructures and c axis fabrics but the degree of asymmetry is low at distances greater than 400 m beneath the detachment and sillimanite grains are drawn into adjacent conjugate shear bands but still appear pristine indicating that deformation occurred at close to peak metamorphic temperatures these quenched fabrics and microstructures indicate rapid exhumation in agreement with previous isotopic dating studies mean kinematic vorticity numbers w m were independently calculated by three analytical methods calculated w m values range between 0 67 and 0 98 and indicate that although a simple shear component is generally dominant particularly in greenschist facies mylonites located between the lhotse and overlying qomolangma detachments there is also a major component of pure shear in samples located at 400 600 m beneath the lhotse detachment pure and simple shear make equal contributions at w k 0 71 our integrated strain and vorticity data indicate a shortening of 10 30 perpendicular to the upper surface of the greater himalayan slab and confirm that the upper surface of the slab is a stretching fault with estimated down dip stretches of 10 40 assuming plane strain deformation measured parallel to the flow plane transport direction

ultrafine grained quartz mylonites from high grade shear zones evidence for strong dry middle to lower crust creep strength of the crust depends upon the rheology of the most common mineral usually quartz recrystallized quartz grains in many high grade shear zones from the middle to lower crust are typically large millimeter sized implying active grain boundary migration but equivalents from old polymetamorphic and water deficient basement sheared at similar crustal depths can be very small for the latter strong crystallographic preferred orientation cpo of quartz with c axes aligned close to y progressive misorientation of crystals subgrain and dislocation development and core mantle structures with recrystallized grains of 2 8 m size all point to dislocation glide dominantly on the prism a system with recrystallization by subgrain rotation recrystallized grain size piezometry of such quartz indicates high flow stress in fine grained shear zones while the synkinematic metamorphic mineral assemblage and the cpo are typical of amphibolite facies conditions this is evidence that middle to lower crust is not inevitably weak due to its high temperature water content also has an important influence

textures and c axis orientations of deformed quartz crystals from porphyric dikes of the alpine root zone western alps deformation textures and c axis preferred orientations of quartz phenocrysts from porphyric dikes of the alpine root zone have been formed under conditions of greenschist to low amphibolite facies it is shown that the deformation textures as shear planes and kink bands boudins grain boundary sutures subgrains coarse and fine recrystallized grains deformation lamellae and fractures are developed in a chronological sequence during first increasing and later decreasing temperatures

unusual transition in quartzite dislocation creep regimes and crystal slip systems in the aureole of the eureka valley joshua flat beer creek pluton california a case for anhydrous conditions created by decarbonation reactions abstract microstructures and quartz c axis fabrics were analyzed in five quartzite samples collected across the eastern aureole of the eureka valley joshua flat beer creek composite pluton temperatures of deformation are estimated to be 740 50 c based on a modified c axis opening angle thermometer of kruhl j metamorph geol 16 1998 142 in quartzite layers located closest 140 m to the pluton wall rock contact flattened detrital grains are plastically deformed and partially recrystallized the dominant recrystallization process is subgrain rotation dislocation creep regime 2 of hirth and tullis j struct geol 14 1992 145 although grain boundary migration dislocation creep regime 3 is also evident complete recrystallization occurs in quartzite layers located at a distance of 240 m from the contact and coincides with recrystallization taking place dominantly through grain boundary migration regime 3 within the quartzites strain is calculated to be lowest in the layers closest to the pluton margin based on the aspect ratios of flattened detrital grains the c axis fabrics indicate that a slip operated within the quartzites closest to the pluton wall rock contact and that with distance from the contact the operative slip systems gradually switch to prism c slip the spatial inversion in microstructures and slip systems apparent high temperature deformation and recrystallization further from the pluton contact and apparent low temperature deformation and recrystallization closer to the pluton contact coincides with a change in minor phase mineral content of quartzite samples and also in composition of the surrounding rock units marble and calc silicate assemblages dominate close to the pluton wall rock contact whereas mixed quartzite and pelite assemblages are dominant further from the contact we suggest that a thick marble unit located between the pluton and the quartzite layers acted as a barrier to fluids emanating from the pluton decarbonation reactions in marble layers interbedded with the inner aureole quartzites and calc silicate assemblages in the inner aureole quartzites may have produced high x co 2 water absent fluids during deformation the presence of high x co 2 fluid is inferred from the prograde assemblage of quartz calcite and not wollastonite diopside k feldspar in the inner aureole quartzites we suggest that it was these dry conditions that suppressed prism c slip and regime 3 recrystallization in the inner aureole and resulted in a slip and regime 2 recrystallization which would normally be associated with lower deformation temperatures in contrast the prograde assemblage in the pelite dominated outer part of the aureole is biotite k feldspar these wet pelitic assemblages indicate fluids dominated by water in the outer part of the aureole and promoted prism c slip and regime 3 recrystallization because other variables could also have caused the spatial inversion of c axis fabrics and recrystallization mechanisms we briefly review those variables known to cause a transition in slip systems and dislocation creep regimes in quartz our conclusions are based on a small number of samples and therefore the unusual development of crystal fabrics and microstructures in the aureole to the ejb pluton suggests that further study is needed on the effect of fluid composition on crystal slip system activity and recrystallization mechanisms in naturally deformed rocks

quantifying geometrically necessary dislocations in quartz using hr ebsd application to chessboard subgrain boundaries abstract this study presents the first use of high angular resolution electron backscatter diffraction hr ebsd to quantitatively characterise geometrically necessary dislocations in quartz subgrain structures hr ebsd exploits cross correlation of diffraction patterns to measure intragranular misorientations with precision on the order of 0 01 with well constrained misorientation axes we investigate the dislocation structures of chessboard subgrains in quartz within samples from the greater himalayan sequence nepal our results demonstrate that chessboard subgrains are formed primarily from two sets of subgrain boundaries one set consists primarily of m c edge dislocations the other consists primarily of dislocations with a burgers vectors apparent densities of geometrically necessary dislocations vary from 10 13 m 2 within some subgrain boundaries to 12 m 2 within subgrain interiors the results suggest that at pressures above approximately 10 kbar chessboard subgrains may form within the quartz stability field most importantly this study demonstrates the potential of hr ebsd as an improved method for analysis of intragranular microstructures in quartz that are used as indicators of deformation conditions

dynamic recrystallization of quartz correlation between natural and experimental conditions quartz veins in the eastern tonale mylonite zone italian alps were deformed in strike slip shear due to the synkinematic emplacement of the adamello pluton a temperature gradient between 280 c and 700 c was effected across this fault zone the resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization subgrain rotation recrystallization and grain boundary migration recrystallization the transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships deformation temperatures are obtained from metamorphic reactions in the deformed host rock flow stresses and deformation temperatures are used to determine the strain rate of the tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10 14s 1 to 10 12s 1 the deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of hirth tullis linking the microstructures of the naturally and experimentally deformed quartz rocks a recrystallization mechanism map is presented this map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known

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

refining the structural framework of the khimti khola region east central nepal himalaya using quartz textures and c axis fabrics abstract new quartz texture and c axis fabric data from across the paleoproterozoic ulleri phaplu melung orthogneiss in the khimti khola region of east central nepal provide new constraints on the internal structural framework of the himalaya that help shed light on the convergence accommodation processes active in the upper portion of the crust during orogenesis these data outline a strain history that varies across the unit deformation near the base of the unit occurred at 605 50 c with evidence of significant static recrystallization and recovery preserved in quartz whereas deformation near the top of the unit occurred at 540 50 c with quartz characterized by dynamic recrystallization mechanisms the strength of the quartz c axis fabrics follows a similar spatial pattern with those from near the top of the unit recording stronger fabrics than those measured from lower in the unit together these data are interpreted to indicate strain localization possibly at progressively lower temperature near the top of the ulleri phaplu melung orthogneiss this interpretation is consistent with cooling ages that indicate the upper boundary of the unit coincides with an out of sequence shear zone this study not only provides a structural characterization of the shear zone helping to refine the kinematic framework of this portion of the himalaya but also confirms the utility of fabric strength analysis in deciphering strain localization within pervasively deformed rocks

macro and microstructural analysis of the zhujiafang ductile shear zone hengshan complex tectonic nature and geodynamic implications of the evolution of trans north china orogen