white mica crystallinity finite strain and cleavage development across a large variscan structure nw spain x ray diffraction analyses were performed on white micas formed under strain and low grade metamorphic conditions from sandstones and siltstones along a transect through the narcea antiform a large structure that separates the external from the internal zones of the variscan belt of nw spain the results indicate a close spatial relationship between the onset of metamorphism and the cleavage front at the cleavage front strain is characterized by oblate ellipsoids that have x y z ratios from 1 to 1 5 the x y z ratio increases westward up to 3 0 as does the grade of metamorphism and is accompanied by an increase in the 9crystallinity9 index of the white mica from very low to low metamorphic grade this increase corresponds qualitatively to an increase in penetrativeness of the axial planar cleavage in the western part of the narcea antiform the major deformation event was the development of kilometre scale reverse shear zones because of polyphase deformation these rocks are not suitable for quantitative strain analysis but qualitatively finite strain can be observed to be prolate and invariably larger in this region than in the eastern sector the metamorphic grade is higher in the western part of the narcea antiform with local maxima occurring next to the base of the shear zones the b 0 cell parameter a semi quantitative geobarometer measured in the white mica is chaotic in the eastern sector showing a clear detrital inheritance in the western sector it is rational due to complete re equilibration during thermal resetting the inverse correlation between finite strain and white mica 9crystallinity9 is close showing that the anchizone epizone limit can be related to the increase of finite strain above values of r s 1 5 the close relation between white mica 9crystallinity9 and strain is suitable for tracking strain variations in extensive fine grained siliciclastic rocks where no appropiate strain markers are found

application of neural networks for the prediction of the unconfined compressive strength ucs from equotip hardness abstract this paper presents the application of a neural network for the prediction of the ucs from hardness tests on rock samples to investigate the suitability of this approach the results of the network are compared to predictions obtained by conventional statistical relations the network was trained to predict the ucs based on the hardness porosity density grain size and rock type information of a rock sample a dataset containing 194 rock sample records ranging from weak sandstones to very strong granodiorites was used to train the network with the levenberg marquardt training algorithm two sets each containing 17 rock samples were used to validate the generalization and prediction capabilities of the network

element mobility during alteration of silicic ash to kaolinite a study of tonstein a laterally persistent kaolinitic mudstone parting tonstein occurring in a wyoming coal bed of eocene age was sampled to estimate the compositional contrast with a probable silicic ash precursor and to determine the compositional influence of leached ash on immediately adjacent coal with the exception of al and possibly ti the tonstein is highly to moderately leached of major elements relative to a range of compositions estimated for silicic ash of the region in agreement with the behaviour of geochemically similar major elements alkali trace elements rb cs are highly leached transition series metals moderately leached and ga is residual additional immobile trace elements are zr and hf but some other trace elements that are considered relatively immobile during low temperature alteration th ta nb ree y were apparently leached by the low eh low ph organic rich pore fluids of the coal forming swamp the migrational range of many of the leached elements is highly limited by the intimate association of tonstein with enclosing organic matter mixtures of coal minor tonstein that occur within 20 mm of contacts are consistently enriched in some elements relative to either tonstein or nearby coal u cu or relative to calculated mixtures of tonstein and coal in their measured proportions th y ree pb ba v ti direct observations by fission track radiography and electron microprobe indicate a preference of u and fe for the organic component of mixtures metal fixation is probably by adsorption on insoluble organic matter humic acids or by precipitation as minor sulphides in these low sulphur coals

flow vorticity in zhangbaling transpressional attachment zone se china abstract plagioclase porphyroclasts with well preserved idiomorphic shapes and zoning and showing limited clast interaction are ubiquitous in the flat lying zhangbaling schist that is exposed east of the tan lu fault in southeast china plagioclase porphyroclasts define rigid particles whose distribution be related to the kinematic vorticity of the schist using the methods of porphyroclast hyperbolic distribution phd and modified rf passchier wallis plot the kinematic vorticity numbers calculated from this approach range from wk 0 72 to 0 82 increasing progressively from south to north along the zhangbaling belt such a wk distribution indicates that the zhangbaling schist was deformed uniformly under simple shear dominated general shear and that the zhangbaling ductile crust experienced relatively even crustal thinning deformation the subhorizontal zhangbaling schist is considered a mid crustal attachment zone that coupled the rigid upper crust to a subvertical wrench shear zone in the lower crust

deformation volume and cleavage development in metasedimentary rocks from the ballarat slate belt psammites from the ballarat slate belt in se australia exhibit well developed differentiated or spaced cleavage defined by alternating phyllosilicate and quartz rich domains termed p and q domains respectively strain estimates derived from independent microstructural and chemical observations suggest that the p q fabrics developed in response to plane strain deformation dominated by solution transfer with the principal finite shortening in the p domains approximately twice that in the adjacent q domains significant finite extensions are indicated by ubiquitous quartz albite chlorite overgrowths in both p and q domains while pressure shadow development around syntectonic pyrite porphyroblasts suggest finite extension of at least 100 this estimate is comparable with the extension predicted for constant volume deformation and consequently there appears to have been no significant bulk material loss or gain on the hand specimen scale these observations are consistent with solute transfer scales as little as a few centimetres via diffusion in a stationary fluid and do not require although do not necessarily preclude large scale advective fluid transport through the slate belt during cleavage formation as suggested in previous studies

estimating the sawability of large diameter circular saws based on classification of natural stone types according to the geological origin abstract different physico mechanical parameters density uniaxial compressive strength brazilian tensile strength cerchar abrasivity index schmidt hammer hardness shore scleroscope hardness and mean grain size were used to find out the sawability of large diameter circular saws in the metamorphic and sedimentary natural stones the simple multiple linear and non linear regression models were developed for estimation of the areal slab production rate of the large diameter circular saws first simple regression analyses were performed to find out the best relationships between the dependent variable areal slab production rate and each independent variable physico mechanical properties in three different groups of natural stones as metamorphic sedimentary and metamorphic sedimentary combined second multiple linear and non linear regression analyses were carried out using selected independent variables then the significances of these models were statistically validated the models developed in this study could be used by planners and natural stone producing companies for cost prognosis and sawing operation schedule in the metamorphic and sedimentary stones

development of slaty cleavage and degree of very low grade metamorphism a review illite crystallinity ic and other indicators of the grade of very low grade metamorphism associated with the appearance of various stages of slaty cleavage in phyllosilicate rich rocks have been compiled from a wide variety of terranes ic values have been converted to a kubler equivalent standard scale but the diverse characterizations of the cleavage fabrics in published descriptions do not always allow an unequivocal identification of equivalent stages of cleavage development nevertheless there exists a distinct relationship between grade and the appearance of various stages of cleavage development 1 indications of incipient slaty cleavage such as s0 s1 pencil structure appearance of primary s1 crenulation cleavage and of closely spaced cleavage without parallel fabric in the microlithons is associated with a wide range of mostly medium and high grade diagenetic ic values 2 the appearance of smooth cleavage with a strong parallel fabric in the microlithons and or quartz mica beards and the chlorite mica stacks shortened at a high angle to 001 and of irregular cleavage in sandy beds is associated with a much narrower range of predominantly low and medium grade anchimetamorphic grades rarely high grade diagenetic the first appearance of these stages of cleavage development with higher grades can often be related to post kinematic magmatic heating polymetamorphism pre cleavage metamorphism or static recrystallization without cleavage formation for example in low strain zones there exists a relationship between finite strain fabric and metamorphic grade in mudstones and slates in coarser clastic rocks the same finite strain fabric relationship occurs at appreciably higher grades a relationship between finite strain in carbonate rocks and ic in the nearby rocks has been reported from the helvetic zone of the swiss alps the earlier stages of cleavage formation are associated with little improvement in ic the narrow range of ic associated with smooth cleavage is concluded to represent recrystallization and grain growth concurrent with cleavage formation

rate and mechanism in prograde metamorphism for a given rate of heat input into a prograde metamorphic sequence the extent of overstep of reaction temperature disequilibrium depends on the slowest of three sequential steps a surface detachment of reactant minerals b transport of material to the site of mineral growth and c nucleation and growth of the product mineral we have developed analytical expressions which enable determination of the rates of mineral dissolution and growth and of advective and diffusive mass transport during metamorphism the dissolution and growth steps are linear functions of the driving force g of the overall reaction while diffusion may take place either through a grain boundary fluid film or through the disorganized grain boundary itself

finite strain analysis of the zhangbaling metamorphic belt se china crustal thinning in transpression abstract finite strain analysis of pebbles in the metatillite and phyllite shows that the deformation of the metatillite phyllite zone is flattening to plane strain dominated results of spo analysis of the rigid plagioclase porphyroclasts in three perpendicular planes indicate monoclinic strain symmetry of the zhangbaling schist and oblate geometry of the clast forward strain modeling of rigid clasts is performed based on the shape fabric of the clast population integrated results of finite strain modeling and finite strain analysis indicate that this midcrustal section experienced at least 18 36 thinning in the oblique convergence between north and south china blocks

early palaeozoic foreland thrusting and basin reactivation at the palaeo pacific margin of the southeastern australian precambrian craton a reappraisal of the structural evolution of the southern adelaide fold thrust belt abstract regional and detailed structural mapping kinematic analysis and balancing and restoration of cross sections has lead to a re interpretation of the adelaide fold belt in south australia in this belt sedimentary rocks of the late proterozoic adelaidean and early cambrian normanville and kanmantoo sequences were deposited during at least two episodes of subsidence related to major crustal attenuation contraction and crustal thickening accompanied by granitoid intrusions are related to the cambro ordovician delamerian orogeny during this event both basins were reactivated inverted and the sedimentary rocks are now incorporated in a wnw verging foreland fold and thrust belt at the margin of the proterozoic southeast australian craton maximal shortening of the orogen was around 55 within the adelaidean basin shortening is dominantly accommodated by major mylonitic shear zones and reverse faults in the cambrian kanmantoo basin several thrusts are demonstrably reactivated growth faults across which thickness changes of cambrian sedimentary rocks are revealed by balancing and restoration of cross sections owing to the steep easterly dips of these faults in the western part of the kanmantoo basin lateral shortening of up to 58 is largely accommodated by intense folding and fold axial planar flattening strain further east strain magnitudes wane and the overall shortening of around 30 is accommodated by both discrete thrust zones and regional folds the basin reactivation along the australian part of gondwana s palaeo pacific craton margin reflects the rapid transition from passive to active tectonism which possibly is a consequence of the disintegration of the formerly conjugate margins of gondwana and laurentia

the role of pressure solution and intermicrolithon slip in the development of disjunctive cleavage domains a study from helvick head in the irish variscides the offset of sedimentary laminae bedding surfaces veins and other passive markers across disjunctive cleavage domains has commonly been attributed solely to pressure solution a detailed study of disjunctive cleavage within siltstones and sandstones from helvick head co waterford on the eastern margin of the irish variscides indicates that the cleavage domains were initially formed by pressure solution processes however the study also revealed features which cannot be explained by pressure solution alone the cleavage domains represent planes of weakness within otherwise relatively homogeneous rock during fold tightening they were rotated out of parallelism with the principal xy plane of the finite strain ellipsoid thus enabling shear movement between the microlithons it is considered that this intermicrolithon slip caused a rotation of the elongate quartz grains within the cleavage domains resulting in an asymmetry of their long axes with respect to the cleavage domain margin grain microfracturing and occasionally slickensides on cleavage surfaces intermicrolithon slip is unlikely to be a localized phenomenon but is probably widespread throughout the irish variscides and other orogenic belts

rock buffered fluid rock interaction in deformed quartz rich turbidite sequences eastern australia quartz vein 18o 16o ratios across a 500 km transect through the lachlan fold belt of southeastern australia are remarkably uniform 1 1 5 permil at both local centimeter to meter and regional over 104 km2 scales they define isotopic zones that correlate with the tectonic divisions of the cambrian through devonian dominantly ordovician quartz rich turbidites determined by regional mapping from west to east these divisions are 1 stawell 18o 14 7 1 1 47 samples 2 bendigo ballarat 18o 17 5 1 3 204 samples 3 melbourne 18o 19 0 1 6 80 samples 4 tabberabbera 18o 16 3 1 9 12 samples and 5 omeo 18o 14 4 1 0 26 samples isotope profiles across zone boundaries and intrazone fault zones particularly within the bendigo ballarat zone show steps indicating abrupt changes across faults with little or no evidence of fluid mixing within the fault zones 18o values of veins are insensitive to relative age type of vein and immediate host rock lithologies the 18o values of coexisting vein and host rocks show nonequilibrium relationships which can be explained in terms of rock buffering under conditions of low fluid rock ratios water rock 1 limited d h determinations on fluid inclusions fall mainly in the range 70 and 100 with one value as low as 140 these low deuterium values when considered in the context of paleolatitude may have been inherited from deutrium depleted detrital minerals and do not necessarily require the direct penetration of meteoric fluids to midcrustal depths the work suggests that vein formation is possible in regions where the integrated water rock w r ratio is very low w r 1 as long as a pervasive fluid phase is present this fluid appears to achieve a steady state isotopic composition on scales of hundreds of meters and once a quasi steady state has been reached the isotopic compositions of the resultant quartz veins are rather insensitive to the diachronous and nonisothermal conditions under which vein growth occurs advective cycling of the fluid on this scale is by episodic dilatancy pumping in fracture networks associated with localized faulting

cleavage development within a foreland fold and thrust belt southern pyrenees spain abstract in the southern pyrenees lithologically distinct cleavage fronts are each parallel to bedding and dip 20 towards the foreland pressure solution was the dominant mechanism of cleavage development the mudstone cleavage front is coincident with the 195 c paleoisotherm and is associated with a pressure solution strain of 5 a mechanical twin strain of 4 and a deviatoric stress magnitude of 65 mpa illite crystallinity measurements define a geothermal gradient of 15 c km 1 and indicate that the paleoisotherms are bedding parallel deviatoric stress magnitudes from calcite twins were regionally constant at 65 mpa and principal stress axes were perpendicular to cleavage temperature was the primary control on deformation micromechanisms and the position and orientation of the cleavage front within the foreland thrust wedge deformation below the cleavage front occurs predominantly by pressure solution which in conjunction with mechanical twinning and microfracturing produces a quasi plastic rheology stress magnitudes determined from mechanical twinning of carbonate grains and long term 10 6 10 76 y strain rates determined for regional folds and faults suggest an apparent macroscopic viscosity of 9 8 10 18 to 7 2 10 19 pa s for the lower thrust wedge above the cleavage front temperature pressure solution strain total strain and mesoscale deformation diminish the region of the thrust wedge above the 100 c paleoisotherm is characterized by large brittle faults with cataclastic fault zones and negligible grain scale deformation indicating an elastico frictional rheology

a microstructural and microchemical study of cleavage lamellae in a slate abstract the results of a detailed microstructural and microchemical study of a slate from the chewton area victoria australia are reported in which it was found that cleavage developed from microcrenulations phyllosilicates in p domains differed in their chemistry from those in q domains and were concentrated in the p domains by localized metamorphic reactions which were aided by mechanical rotation and solution processes wide dark cleavage lamellae often taken as evidence for the passive concentration of insoluble minerals appear to have had a similar origin the p domains exhibited two types of microstructure one which was consistent with annealing and the other with deformation within the domain cataclasites had formed along some p domains suggesting that they had become preferential sites for late phase brittle deformation

oblique cleavage folds a critical discussion with examples from the canadian appalachians abstract examples of transected folds from three localities in notre dame bay north central newfoundland are described and analyzed the oblique relationship of cleavage and folds is the result of overprinting of the folds by the cleavage in two of the three localities and the result of overprinting of the cleavage by the folds in the third locality thus it is argued that transected folds need not form synchronously with the oblique cleavage an axial plane cleavage associated with the folds may be completely obliterated by the oblique cleavage or may never have existed the term oblique cleavage folds is introduced as a geometric term to describe folds with a cleavage oblique to their hinges transected fold models are generally based on the orientation of cleavage and folds with respect to the strain ellipsoids on the scale of the deforming zones or on the scale of layers of variable competence here we follow a different approach transected fold models and the geometry of oblique cleavage folds are discussed in terms of the progressive development of the folds and cleavage we assume no special relationships to strain oblique cleavage folds are most commonly reported from shear zones where the strain path is non coaxial and the deformation is progressive such zones produce overprinting relationships even where only one deformation event is involved and commonly have a long history of reactivation we suggest that the significance of this correlation is that transected folds are generally and perhaps always a product of overprinting the age of folds and cleavage however may be very similar and both may be a product of the same protracted deformation event thus in studying oblique cleavage folds the possibility that the cleavage is pre syn or post folding should be considered even where there is only one recognisable generation of both folds and cleavage

wall rock petrology and geochemistry in alteration halos associated with mesothermal gold mineralization central victoria australia integrated petrological and geochemical examination of metasedimentary assemblages associated with mesothermal lode gold mineralization in five major centers of past and present production ballarat percydale tarnagulla maldon fosterville in central victoria australia reveal that hydrothermal alteration in the hosting cambro ordovician turbidites is much more pronounced and extensive than has previously been recognized characteristically the auriferous reef structures are surrounded by bleached zones up to several tens of meters wide sericitization carbonatization and carbonate spotting and pyrite and arsenopyrite porphyroblasts within and beyond zones of visible bleaching are the most obvious features of alteration quantitative xrd analysis illustrates that these marked bleached halos are due to the replacement of albitized plagioclase clasts by white mica and the breakdown of metamorphic chlorite to form secondary carbonates and to a lesser extent kaolin the negative correlation between metamorphic chlorite and hydrothermal carbonate phases provides a reliable mineralogical alteration index useful to exploration geochemical reconnaissance profiles also indicate the development of systematic trends in response to hydrothermal alteration involving mainly sio2 k2o na2o co2 as au and s at constant bulk rock volume calculation of a geochemical alteration index given by the ratio k2o co2 k2o co2 na2o al2o3 suggests that this can be a reliable indicator of alteration in particular where concentrations of individual invariable oxides such as al2o3 vary too much in response to lithological variations saturation indices that are based on ratios of 3k al and co2 mg fe ca are less reliable because muscovite and carbonate are not always the dominant alteration mineral species of relevance the alteration assemblages as well as mineralogical and geochemical trends at the five ore systems investigated herein are common to many slate belt hosted gold deposits the results of this investigation show that although the detection of such systematic spatial variations relative to mineralization can be complicated for example by postore modification of the wall rocks due to contact metamorphism e g at maldon or where mineralization is not associated with massive to laminated quartz veins e g at fosterville recognition of extensive though not always conspicuous alteration halos around mesothermal lode gold mineralization represents a potentially powerful tool for exploration in slate belts

kinematic and metamorphic aspects of cleavage formation in very low grade metamorphic slates abstract fabric studies on first cleavages in very low grade metamorphic slates from the rheinisches schiefergebirge and other very low grade metamorphic fold belts reveal two types of slaty cleavage 1 1 cleavage without syntectonic phyllosilicate recrystallization these are generally crenulation cleavages 2 2 cleavage with syntectonic phyllosilicate recrystallization with increasing syntectonic metamorphism the crenulation fabric is modified by solution of grains along cleavage planes and precipitation of material within the cleavage lamellae with further increase of metamorphism the crenulation fabric is gradually obliterated the finite fabric results from progressive solution crystallization and recrystallization superimposed with bending kinking and internal rotation achieved by slip parallel to the basal planes of phyllosilicates

finite strain heterogeneity and volume loss in slates of the taconic allochthon vermont u s a abstract slates of the taconic allochthon have ellipsoidal reduction spots which have been used to determine the finite state of strain at seven sites the strain is highly heterogeneous at all scales ranging from several centimeters to many kilometers variations in x y ratios is small but variations in y z ratios is large and this pattern is seen at all scales the heterogeneity can be used to determine a strain path which is nearly horizontal on a flinn diagram we propose that uniaxial flattening associated with late stage cleavage development was accommodated by volume loss and that the most highly strained sites have experienced an average 55 volume loss at a minimum explaining our results without volume loss requires a subhorizontal extension and creates strain compatibility problems consideration of the strain history of these rocks suggests that folding related strains have been modified by later cleavage related events the last of which was uniaxial flattening accommodated by volume loss the finite strains are reflective almost exclusively of the latest cleavage producing strains

relations between stages of diagenetic and metamorphic evolution and the development of a primary cleavage in the northwestern moroccan meseta abstract the metamorphic evolution of the studied region is determined by the illite crystallinity index and by the evolution of the other phyllosilicates essentially chlorite and mixed layer minerals several zones are described at a regional scale characterized respectively by a diagenetic anchimetamorphic and epimetamorphic evolution the estimation of total strain is approached by the type of the cleavage in greywackes mapping of all these parameters reveals at the scale considered a close relationship between metamorphism and strain which is briefly discussed

the geology and gold deposits of the victorian gold province abstract the palaeozoic succession of victoria represents a major world gold province with a total production of 2500 t of gold i e 78 million oz on a global scale central victoria represents one of the most gold mineralized areas outside the witwatersrand of south africa and remains the prime example of a slate belt gold province also known as turbidite hosted or shale greywacke gold province production came from quartz veins 1000 t modern placers 1200 t and palaeoplacers 300 t up to 7000 mines produced gold from quartz veins however the 168 mines of this type which produced over 1 t au contributed 68 of the primary gold production twelve goldfields have each produced 30 t au approximately one million ounces from all sources with bendigo 697 t ballarat 408 t and castlemaine 173 t being the largest these twelve goldfields have contributed 71 of the combined primary and secondary production gold mining commenced in 1851 declined dramatically around 1914 and has not increased significantly since the palaeozoic succession of victoria is part of an extensive fold belt along much of eastern australia i e the tasman orogenic belt in victoria the succession is dominated by cambrian to early devonian clastic metasedimentary rocks that have undergone major upright deformation and low grade metamorphism culminating in the middle devonian tabberabberan orogeny north south inliers of cambrian metavolcanic and metasedimentary rocks associated with regional fault zones divide the province into several geologically distinct zones in central victoria there are particularly well developed acid volcanic complexes of late devonian age and synchronous peraluminous granites which represent high temperature crustal melting tertiary to quaternary basalts have covered some of the palaeozoic gold deposits and have also covered several rich gold placer deposits of cainozoic age larger goldfields including bendigo and ballarat occur in ordovician slate and greywacke sequences but a wide range of metamorphosed sedimentary and igneous rock types are host to goldfields most if not all primary deposits demonstrate structural control although the controlling structural features differ between deposits wallrock alteration is strongly influenced by host rock in metasedimentary rocks it is limited and subtle but it is more pervasive in mafic and felsic igneous rocks carbonates muscovite and pyrite are the most widespread alteration minerals in these rocks representing co 2 k and s addition enrichment of as within gold deposits is common with sb important in some small deposits whereas base metals are only abundant locally and bi w mo and te show strong spatial association with granites and are rarely associated with economic gold deposits granites are an important component of the palaeozoic succession in victoria no large deposits are within granites but a few goldfields including maldon 65 t au are within contact aureoles of either s or i type granites of differing degrees of fractionation and silica content a single stage but protracted and possibly diachronous period of gold introduction near the time of the middle devonian tabberabberan deformation can explain geological relationships at many gold deposits the possibility that this event was slightly older i e silurian or early devonian in the west of the state cannot be precluded from the available evidence the mineralizing event appears linked to the same thermal event as diorite lamprophyre dykes and graite intrusions acidic and basaltic volcanism deformation and regional metamorphism the limited amount of fluid chemistry data from victorian gold deposits suggests low salinity fluids which contained co 2 and variable methane with homogenization temperatures from 150 to 300 c the sulphur isotopic compositions of pyrite are mostly 1 to 5 with some values slightly above 10 mineralizing temperatures are inferred to be near 300 c and pressure around 1 2 kbar sulphide rich gold deposits in the east of victoria many of which contain significant base metals contrast with the rest of the province which contains mostly gold deposits with lower sulphide content and this eastern area should possibly be viewed as separate from the victorian gold province per se the benefits to victorian gold mining coming from the 1980 s global gold boom have been insignificant compared to the historical importance of the victorian gold province there seems little justification for assuming that all the large deposits have been discovered and there is reason to believe new deposit styles may emerge to complement the limited current exploration activity which is focussed on the search for extensions and repeats of known deposit types a major advance in scientific understanding of these oft neglected deposits could kindle a major exploration and production revival

vertical and fold axis parallel extension within a slate belt in a transpressive setting northern appalachians abstract an incremental and finite strain study of a mid paleozoic slate belt in a transpressive setting in gaspe canadian appalachians has been undertaken using syntectonic fibers from pyrite type pressure shadows regionally strain estimates are quite consistent and reflect only slightly higher strain in the central part of the anticlinorial structure defining the slate belt extensions of up to 160 vertically and 110 parallel to the fold axis were recorded in the slate belt combined with an estimated overall regional shortening of 80 the fibers first rotated toward the final position of the cleavage within a vertical section normal to the cleavage and then rotated from a vertical to a horizontal orientation this change in fiber orientation observed in cleavage parallel sections indicates an abrupt change in the incremental stretching direction from sub vertical to sub horizontal fold axis parallel the vertical extension is related to folding and cleavage development during coaxial flattening the horizontal extension reflects the strain imposed on the rocks during regional simple shear which produced strike slip faulting and further tightening of the folds folding cleavage development fold axis parallel extension and faulting are all related to oblique convergence during the middle devonian acadian orogeny in this part of the canadian appalachians and clearly indicate an overall transition from a pure shortening deformation to a simple shear dominant deformation in an overall transpressive setting

evidence from mossbauer spectroscopy for intense localization of metamorphic fluid flow during the formation of spaced cleavage arenites in the low grade metasedimentary rocks of the stirling barren group western australia contain discrete spaced cleavages these in part are pure white mica but up to 30 of the cleavage zones consists of fine grained quartz resulting from crystal plastic deformation a modified gresens analysis shows that the cleavage domains formed by a 50 volume loss associated primarily with sio2 and mgo concentration decreases of 58 and 37 respectively and a 12 decrease in fe2o3 mossbauer spectroscopy shows that the fe2 fe3 ratio from lithon to cleavage changed from 50 so to 15 85 this substantial difference cannot be accounted for by loss of iron the data are best explained by the focusing of a highly oxidizing fluid through the cleavage domains where volumetric fluid rock ratios around 150 to 1 are indicated in this example advectic processes appear to be important in low grade regional metamorphism

the problem of shearing along axial plane foliations abstract the structural significance of axial plane foliations cannot be understood unless we make a distinction between rotation of the material plane foliation and rotation of the geometrically defined x y plane of the strain ellipsoid if the foliation rotates as a material plane at any stage of deformation then its final orientation will be different from that of the x y plane it is suggested that reorientation of foliation takes place by some combination of the formation of foliation e g recrystallization along the x y plane and passive rotation of the material plane foliation in the same continuous deformation the deviation between the foliation and the x y plane is then much less than 5 degrees however because of this deviation a considerable amount of shear strain may develop along the foliation the analysis thus explains how a foliation can be approximately parallel to the x y plane and yet be a plane of shearing

deformed graptolites finite strain and volume loss during cleavage formation in rocks of the taconic slate belt new york and vermont u s a abstract an analysis of graptolites in the taconic slate belt of eastern new york and western vermont u s a shows that they are nearly ideal strain markers for the three species used in this study orthograptus whitfieldii orthograptus calcaratus and climacograptus bicornis the spacing of thecae is constant except for the first five or so thecae in the proximal part of the fossil rhabdosome further the thecal apertures are perpendicular to the long axis of the stipe observations of the thecal spacing in deformed rocks leads to a determination of extension e l f l 0 l 0 and a measure of the angle between thecal aperture and stipe axis yields a direct determination of angular shear strain in practice we find it is most straightforward to use length changes to determine the magnitude of principal strains in taconic slates e 1 ranges from 1 0 to 0 24 e 2 ranges from 0 23 to 0 43 and e 3 ranges from 0 56 to 0 74 thus we find that the absolute finite strain in these slates is constrictional at three sites plane strain at another and a true flattening at only one site an examination of volume changes based on strain results in determinations of between 81 volume loss and 7 volume gain with volume losses between 28 and 81 in 9 out of 10 calculations these conclusions are in accord with previous determinations of volume loss based on reduction spot analyses and are consistent with the observation that pressure dissolution was a common grain scale deformation process in cleavage formation but that these slates lack abundant veins fibrous overgrowths or other identifiable sites of reprecipitation

relationship of concretions and chlorite muscovite porphyroblasts to the development of domainal cleavage in low grade metamorphic deformed rocks from north central wales great britain abstract spaced or domainal cleavage is widespread in deformed rocks of low metamorphic grade this study presents evidence on the origin of spaced cleavage in deformed pelites from silurian turbidite sequences in north central wales the variable development of cleavage folia is related to the presence of concretions which served to concentrate strain effects of well developed cleavage folia in the matrix in some zones and to produce strain shadows few or no cleavage folia in others compositional differences between matrix narrow transition zones and concretions also influenced the development of cleavage folia chlorite muscovite porphyroblast growth was initiated before cleavage formation but its further growth and development took place during cleavage formation the relationship of cleavage to the concretions and to the chlorite muscovite porphyroblasts indicates that cleavage developed in a matrix that must have been in an advanced state of lithification anchimetamorphic to lowermost greenschist facies of metamorphism and not during soft sediment deformation

microlithon alteration associated with development of solution cleavage in argillaceous limestone textural trace elemental and stable isotopic observations abstract comparison of microlithons the rock between adjacent cleavage domains in strongly cleaved argillaceous limestone with samples of uncleaved limestone from the same stratigraphic horizon lower devonian kalkberg formation hudson valley of eastern new york indicates that the process of cleavage formation results in significant changes in microlithon fabric and in the chemistry of microlithon calcite petrographic observation indicates that at least 50 of the calcite in microlithons is recrystallized as calcite fibers whose long axes are subparallel to cleavage domains the fibrous calcite occurs as overgrowths on larger grains in thin bed parallel veins and in diffuse extension zones areas of the microlithons in which inequant crystals of microcrystalline calcite are aligned parallel to cleavage domains chemical analyses show that calcite in microlithons of strongly cleaved limestone is enriched in mn and sr relative to calcite in uncleaved limestone 18 o and possibly 13 c values for calcite in strongly cleaved rock are significantly smaller than values for calcite in uncleaved rock these results indicate that microlithon calcite is completely recrystallized i e much more calcite is recrystallized than is visible in thin section and that it underwent exchange with a fluid external to the local rock system calculation of the water rock ratio suggests that 0 1 2 6 volumes of water may have exchanged with the calcite during cleavage formation comparison of the minimum integrated and the inferred instantaneous water rock ratios suggests that bulk fluid flow occurred during microlithon recrystallization comparison of the amount of shortening across cleavage domains with the amount of extension in microlithons and of the volume of calcite dissolved in domains with the amount of fibrous presumably added calcite in microlithons suggests that microlithons are a major sink for the calcite dissolved in domains during cleavage formation and that at this locality development of disjunctive solution cleavage in the kalkberg formation resulted in volume constant plane strain

the interaction of deformation and metamorphism in slates abstract the distribution microchemistry and internal structure of phases present in a slate are reported and used as a basis for a discussion of the interaction between deformation and metamorphism in slates the study reveals details of the interactions between mechanical and chemical processes involved in slaty cleavage evolution evidence for the involvement of mechanical rotation solution and crystallisation recrystallisation and metamorphic reactions is presented and amalgamated into a model of cleavage development the model involves a synchronous variation in the type location and rate of cleavage evolution processes and a change in the importance of particular processes during the total history the early stages of cleavage development are dominated by mechanical rotation associated with crenulation and possibly accompanied by grain boundary sliding and solution processes later stages of cleavage evolution are more heterogeneous and occur by a complex interaction of deformation and metamorphic growth processes which are concentrated at the interfaces between domains generated earlier in the strain history the variations in grain chemistry and orientation together with changes in the strain rate or stress level are suggested to control the different deformation behaviour of different grains along these strain accommodation zones and to dictate whether grains bend kink dissolve recrystallise or react and undergo growth evidence for the involvement of reactions ranging from ionic exchange to crystallisation from solution and solid state reordering is presented and the influence of deformation on the location and rates of these reactions discussed approximately ten potential reactions are involved in the cleavage evolution of the slate studied the model presented incorporates these reactions into the deformation processes and accounts for the concentration of phengite and iron poor chlorites in to one microstructural domain and paragonite quartz and fe rich chlorites into the other domain two transformations appear to be fundamental in the slate studied 1 1 the transformation of illite to phengite 2 2 the transformation of fe rich chlorite to fe poor chlorites and both can be related to particular responses of grains to the reorientation processes at domain interfaces

crenulation cleavage formation evolving diffusion deformation and equilibration mechanisms with increasing metamorphic grade abstract an integrated microstructural and chemical study of crenulation cleavages developed in chlorite to garnet zone schists from the wenchuan maowen shear zone central china has resulted in the recognition of the deformation and equilibration mechanisms operating during their formation at a range of temperatures deformation during crenulation cleavage formation at chlorite to biotite zone temperatures 520 c is essentially a solution deposition process in which transport occurred by a combination of localized advection and grain boundary diffusion recrystallization and hence equilibration of muscovite in discrete cleavages is recognized by distinct compositional differences between muscovite from different domains crenulation cleavages developed in garnet zone schist are characterized by homogeneous muscovite compositions across domains and microstructures related to intracrystalline deformation indicating an increasing importance of volume diffusion and diffusive equilibration of mica at temperatures greater than 520 c

mesoscale to submesoscale transition in the california current system part ii frontal processes this is the second of three papers investigating the regime transition that occurs in numerical simulations for an idealized equilibrium subtropical eastern boundary upwelling current system similar to the california current the emergent upper ocean submesoscale fronts are analyzed from phenomenological and dynamical perspectives using a combination of composite averaging and separation of distinctive subregions of the flow the initiating dynamical process for the transition is near surface frontogenesis the frontal behavior is similar to both observed meteorological surface fronts and solutions of the approximate dynamical model called surface dynamics i e uniform interior potential vorticity q and diagnostic force balance in the intensification of surface density gradients and secondary circulations in response to a mesoscale strain field however there are significant behavioral differences compared to the surface dynamics model wind stress acts on fronts through nonlinear ekman transport and creation and destruction of potential vorticity the strain induced frontogenesis is disrupted by vigorous submesoscale frontal instabilities that in turn lead to secondary frontogenesis events submesoscale vortices and excitation of even smaller scale flows intermittent submesoscale breakdown of geostrophic and gradient wind force balance occurs during the intense frontogenesis and frontal instability events

primary structure influence on compositional banding in psammites examples from the puncoviscana formation north central argentina abstract we investigate the influence of sedimentary structures in development of foliations in banded psammites and pelites in the meta turbiditic pampean belt eastern sierras pampeanas northwest argentina these anchizone to upper greenschist facies rocks were exhumed from near surface to mid crustal levels and preserve sedimentary structures and gradual changes in tectonic fabrics and microstructures primary variations in clay content affected the degree of development of a compaction related pressure solution cleavage s p resulting in enhancement of the original sedimentary banding the resulting compositional banding was overprinted by a tectonic cleavage s 1 related to mid cambrian chevron folding in banded sandstones pressure solution and mica growth that define s p and s 1 foliations are increasingly better developed in phyllosilicate rich domains with increasing structural depth and metamorphic grade clay rich laminae in the protolith acted as the locus for mica nucleation and growth favoring dissolution of quartz up to 42 causing passive concentration of mica pressure solution thus produced banded sandstones with a spaced bedding parallel s p cleavage in shallower sections and compositionally banded psammites and schists at depth these observations demonstrate that formation of compositional banding does not require tectonic transposition of an older planar fabric similar processes may produce compositional banding in a wide range of meta sedimentary rocks

riedel shear a mechanism for crenulation cleavage drag folds 1 from the microfaulting of inclined markers distinguish crenulation cleavage from other cleavage types cleavage as riedel r shears nucleates obliquely to planar anisotropy of foliated rocks and at various angles related to to the shear zone boundaries folds 2 with axes parallel to the instantaneous 1 at high angle and partway with r shears are formed in the xz plane of strain ellipsoid the angle between folds and cleavage is changed in the progressive deformation the largest antithetic counterclockwise r shears rotation and largest opening of initial angle between folds and fractures up to 170 is achieved in the progressive transtension 1 this is not geometrically possible in the simple shear and transpression but forward rotation of the r shears of excess length is prevented by the constant or diminishing thickness of the shear zone the crenulation folds 3 amplify the drag folds of the inclined faulted marker and nucleate with axial planes parallel to the cleavage at higher strains the cleavage propagates further as p shears parallel to flanks of tightened crenulation folds the r shears are in higher order folds 4 reoriented into the axial planar position by pure shear in the yz plane of the first incremental deformational ellipsoid and by the shear induced by flexural slip along the layer boundaries the stretching of the fold limbs and the non coaxial ductile deformation of microlithons in their slip perpendicular to fold axis deform former drag and crenulation folds to a characteristic pattern striation and or faint lineation preserved in the cleavage plane trace the shear directions the shear sense is indicated by the cleavage folds transection and by the asymmetrical structures in the plane cut perpendicularly to clevage and parallel to striations

structural characteristics of granitic plutons emplaced during weak regional deformation examples from late carboniferous plutons morocco abstract strain patterns have been investigated around shallow crustal granitic plutons emplaced during weak regional deformation in the western moroccan hercynian belt the plutons are distributed along reactivated deep faults and display elliptical shapes which are consistently oriented with respect to the regional strain field pluton age orientation and ellipticity can be correlated with strain history ductile deformation and contact metamorphism are mainly located in the thermally softened aureoles finite strain gradients towards plutons are accompanied by the development of superimposed microstructures finite strain trajectories and variations of strain ellipsoid shapes exhibit perturbations of the regional strain field around plutons structures internal to the plutons are continuous with regional structures foliation development in granitoids records a decrease in temperature during syntectonic pluton cooling geometry and kinematics of deformation reflect the influence of both regional deformation and pluton intrusion

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part i meso and macro scopic scale there is considerable variability in the thickness structure and macroscopic deformation style within shale prone major thrust zones which also impacts the structural style in the overlying and sometimes the underlying section the properties and percentages of clay minerals and percentages of organic material quartz and calcite affect fault zone weakness and behaviour the distribution of competent units within a shale prone zone can also significantly affect fault zone architecture even over short strike distance of 10s to 100s of metres other influences include high pore fluid pressures and associated veins deformation of the fault zone may disrupt the original principal displacement zones and force them to relocate including switching lithologies calcite veins can become concentrated locally in the fault zone and become a focus of fault zone weakness we still need many more descriptions of shale prone fault zones to understand the potential variations in thrust sheet structural style caused by differences in shale detachment characteristics the variations in structural style in the hanging walls of shale detachments are broad and range between the sledge runner style in many appalachian examples and the extensive closely spaced imbricate style of the osen roa detachment southern norway such contrasts are related to several factors including thrust sheet mechanical stratigraphy thickness of the overburden lateral continuity of the detachment detachment mechanical properties composition pore fluid pressures presence absence of higher level detachments and strain rate in many structural locations and at many scales shale prone sequences will pile up to produce over thickened masses cleavage duplexes s c fabrics duplexes imbricates pseudo duplexes and vein formation can all contribute to the thickening at nested scales a mixture of brittle and solution diffusion processes overall cause the affected unit to exhibit flow like characteristics while the broad principles are now well established considerable work remains to be done understanding the full range of structural geometries associated with shale detachments what factors regarding the nature of the detachments affect overlying structural styles rates of deformation and the controls on deformation mechanisms within the thrust zones

bedding parallel veins and their relationship to folding abstract laminated bedding parallel veins hosted in turbiditic sandstone shale sequences from central victoria australia consist of stacked millimetre thick sub parallel sheets of quartz separated by micaceous layers wall rock slivers and pressure solution seams they have very high length to thickness ratios are laterally continuous over tens to hundreds of metres and have relatively uniform thickness compared to other vein types they are intimately associated with and folded by chevron folds and the quartz grain shape elongation lineation is commonly orthogonal to mesoscopic and macroscopic fold hinge lines the bedding parallel veins have two morphological forms type i are thin commonly 5 10 cm laminated veins which have complex microstructures dominated by phyllosilicate inclusion surfaces related to oblique opening along bedding with varying rates of deposition opening relative to shear displacement slip along the bedding surfaces more common are type ii thicker generally

structure and origin of the fleurieu and nackara arcs in the adelaide fold thrust belt south australia salient and recess development in the delamerian orogen abstract the regional map pattern of structural trends in the early paleozoic adelaide fold thrust belt of south australia resembles an upright letter s in general structures in the fold thrust belt verge toward the gawler craton to the west so the northern curve nackara arc of the s is a salient whereas the southern curve fleurieu arc is a recess the map view axial trace of the nackara arc coincides with the thickest portion of the adelaidean late proterozoic basin and the map view axial trace of the fleurieu arc coincides with the intersection between the adelaidean and kanmantoo cambrian basins our structural analysis of the adelaide fold thrust belt demonstrates that the cross sectional structural geometry of the nackara arc contrasts markedly with that of the fleurieu arc in the nackara arc the belt consists of open detachment folds that probably formed above an evaporite hosted decollement whereas in the fleurieu arc the belt consists of an imbricate fan of basement involved thrusts further the foreland edge of the nackara arc coincides with a blind ramp whose strike parallels fold axes of the arc whereas the foreland edge of the fleurieu arc coincides with emergent thrusts that cut obliquely across earlier formed folds of the arc in the transition region between the two arcs the fold thrust belt consists of an intensely sheared basal duplex overlain by open folds structural contrasts between the nackara and fleurieu arcs indicate that the two curves did not form in the same way we present a model for development of these curves based on a comparison of their structural features to those of curves in other fold thrust belts and based on previous studies of curve formation using sandbox analogs we suggest that curvature of the nackara arc reflects the control of basin stratigraphy on the width of a fold thrust belt while curvature of the fleurieu arc reflects oroclinal bending of the fold thrust belt when it impinged on the southeastern corner of the gawler craton our model explains the structural contrast between the two arcs and illustrates correlations between fold thrust belt curve formation and pre deformational basin geometry

thrust related strain gradients and thrusting mechanisms in a chevron folded sequence southeastern australia an e directed imbricate fan thrust system within a chevron folded monotonous quartz rich turbidite succession shows marked gradients in strain from the upper to lower parts of individual thrust sheets upper parts of thrust sheets show low to moderate strains xz strains 30 1 tight inclined chevron folds ila 30 with predominantly w dipping axial surfaces intense phyllitic cleavage with a strong down dip mineral stretching lineation and long curved tapering quartz pressure shadows on pyrite such differences in fold geometry the intensity of the cleavage and the geometry of quartz fibres in pressure shadows require thrust sheet emplacement to be synchronous with the internal deformation of sheets thrust sheets show a change from an approximately constant volume plane strain coaxial deformation in their upper parts to non coaxial high strain deformation with incremental i between those expected for pure shear and simple shear i e 0 i 5 45 in their basal parts observed geometries and intensities reflect partitioning of strain and deformation mechanisms within individual thrust sheet volumes both during the initiation and propagation of subsurface detachment faults and with their emplacement to shallower crustal levels strain softening related to chevron folding and more intense cleavage development within a 500 m basal zone has controlled the emplacement of these turbidite dominated thrust sheets transport and internal deformation of the thrust sheets did not involve gravitationally induced spreading but required either a push from the rear or some form of underthrusting

high resolution compositional mapping of matrix phases implications for mass transfer during crenulation cleavage development in the moretown formation western massachusetts abstract high resolution compositional maps provide a new tool for investigating mass transfer during cleavage formation the moretown formation of western massachusetts contains a well developed crenulation cleavage with alternating mica rich crenulation limbs and mica poor crenulation hinges compositional mapping shows two generations of plagioclase the second of which was synchronous with the crenulation cleavage a significant amount of the syn crenulation plagioclase 10 20 modally grew in hinge domains a small amount of syn crenulation plagioclase 1 and a large amount of phengitic muscovite grew in limb domains the maps also show that uncrenulated domains experienced mass transfer and reactivation of older cleavages and thus cannot be used as undeformed reference domains for comparison with crenulated regions compositional mapping facilitates a new degree of integration between petrologic and structural analysis knowledge of the structural context of compositional domains allows better selection of phases and compositions for interpreting metamorphic reactions and linking metamorphism to deformational stages knowledge of syntectonic reactions provides new insights into mass transfer and volume change during deformation in the moretown formation plagioclase and phengite producing reactions play a large role in controlling the nature and magnitude of mass transfer but microstructures control the location of reactants and products within the evolving fabric

mesoscale to submesoscale transition in the california current system part i flow structure eddy flux and observational tests in computational simulations of an idealized subtropical eastern boundary upwelling current system similar to the california current a submesoscale transition occurs in the eddy variability as the horizontal grid scale is reduced to o 1 km this first paper in a series of three describes the transition in terms of the emergent flow structure and the associated time averaged eddy fluxes in addition to the mesoscale eddies that arise from a primary instability of the alongshore wind driven currents significant energy is transferred into submesoscale fronts and vortices in the upper ocean the submesoscale arises through surface frontogenesis growing off upwelled cold filaments that are pulled offshore and strained in between the mesoscale eddy centers in turn some submesoscale fronts become unstable and develop submesoscale meanders and fragment into roll up vortices associated with this phenomenon are a large vertical vorticity and rossby number a large vertical velocity relatively flat horizontal spectra contrary to the prevailing view of mesoscale dynamics a large vertical buoyancy flux acting to restratify the upper ocean a submesoscale energy conversion from potential to kinetic a significant spatial and temporal intermittency in the upper ocean and material exchanges between the surface boundary layer and pycnocline comparison with available observations indicates that submesoscale fronts and instabilities occur widely in the upper ocean with characteristics similar to the simulations

rings in the ocean certain robust long lived eddy features in t he world s ocean have come to be k nown as rings the nomenclature stems from fuglister 1 1972 who c oined t he name based on the c ircle or ring of gulf stream waters t hat surrounded a class of eddies formed from t he g ulf stream through the pinch off of meanders here it s uffices to define rings as intense eddies or vortices that represent a wrapped up piece of a major ocean c urrent they t ranslate over space scales of hundreds to thousands of k ilometers and exist for periods lasting from months to years rings move t hrough the ocean carrying anomalies s imilar to the contrasts in physical biological and chemical properties observed across the major ocean c urrents while the term ring is t ied to fuglister t he existence ofthese features was evident at least as early as t he 1930s when iselin 2 1936 1940 encountered strong cold anomalies in the region south of the gulf stream that we would identify as c old corc cyclonic rings today iselin fully rec ognized these features as part of the highly time dependent eddy motion in the ocean later iselin fuglister 1948 were the first to survey what is now k nown as a warm core anticyc lonic ring there are tw o types of rings cold core rings are made up of w aters from the poleward s ide of c urrents like the gulf stream that are introduced to

palinspastic restoration of a post taconian successor basin deformed within a transpressive regime northern appalachians restoration of transpressional orogens requires a three dimensional analysis of the strain state in order to take into account both the pure shear and simple shear components of the deformation and assess their relative contribution throughout the deformation history restoration of the post taconian successor basin the gaspe belt located within the external part of the acadian orogen in the canadian appalachians was performed by using a step by step method based on the successive removal of strain increments the pure shear component contributed 70 of the total strain during the first stages of the deformation whereas the simple shear component contributed 30 of the total strain during the last stages three retrodeformation steps are defined starting with restoration of the last deformation stage and working back to the first deformation stage the first step is to restore slip along acadian strike slip faults the second step is to restore shortening related to the horizontal extension during the acadian regional simple shear event finally the third step is to restore vertical extension related to the pure shear event by removing slip along the reverse faults unfolding and removing internal strain associated with cleavage development retrodeformation of the simple shear component of the transpressive deformation during the first two steps is performed on a horizontal view of the gaspe belt basin which contains the horizontal extension direction and which is perpendicular to the acadian nw se directed compression likewise restoration of the pure shear component is performed in vertical sections which contain the vertical extension and which are perpendicular to the acadian nw se directed compression the palinspastic map presented here is a much more appropriate base map for the basin and allows for a more realistic paleogeographic interpretation of the gaspe belt

volume change accompanying cleavage development in graptolitic shales from gisborne victoria australia studies on shape changes in deformed oncograptus upsilon combined with strain analysis of pressure shadows around framboidal pyrite revealed that a small volume change of the order of 5 percent accompanied the cleavage development in the shales from gisborne victoria starting from the proximal end oncograptus upsilon exhibits progressive increase in the spacing between successive thecae along the stipes a new technique utilizing the distance between a specific number of thecae is used for computing the change in length along stipes of oncograptus upsilon the low volume change accompanying a more than 70 percent shortening deformation indicates that there is a less significant mass loss during cleavage development than has been inferred from some studies on volume change from thecal spacing in deformed graptolites

regional slaty cleavage formation and fold axis rotation by re use and reactivation of pre existing foliations the fiery creek slate belt north queensland abstract a deformation history comprised of six separate deformation events of differing intensity has affected the rocks of the south palmer river region of the the hodgkinson province north queensland within this region a zone of pervasive slaty cleavage herein termed the fiery creek slate belt has developed as a result of the superposition of fabrics formed during several of these events the most important processes in the formation of this composite cleavage were the re use and reactivation of the favourably oriented steep n s trending s2 foliation by the intense fourth deformation event d4 this produced micro meso and macroscopic folds in an originally shallow s3 foliation produced during the intervening d3 deformation with an axial planar s2 s4 foliation the d4 stretching lineation l44 plunges subvertically to steeply north and indicates that shear during d4 was oriented steeply north south in the fiery creek slate belt d2 fold axes are interpreted to have formed in much shallower orientations than their present moderately n s plunging to subvertical orientations we consider this to be a result of d4 shear which caused variable degrees of rotation of d2 fold axes toward the d4 stretching lineation due to subparallelism of the bulk shortening directions of the d2 and d4 events near total destruction of the pre d4 foliations during slaty cleavage formation has produced a misleading impression of a simple deformation history there is no relationship between metamorphic grade and intensity of slaty cleavage development

metamorphism and deformation mechanisms in the sierras australes fold and thrust belt buenos aires province argentina abstract the sierras australes fold and thrust belt is affected by an easternmost anchizonal metamorphism which grades into a western area of greenschist facies metamorphism both areas and their inferred boundary are distinguished on the basis of quartz recrystallization and illite crystallinity data during the first deformation pressure solution and grain boundary diffusion accompanied rigid body rotation and grain boundary gliding processes these mechanisms together with intracrystalline quartz deformation and recrystallization contributed to increasing rock ductility in the area of greenschist facies metamorphism two deformational events expressed by folding cleavage formation and thrusting were followed by static annealing of quartz which affects the southwestern part of the mountain range evidence for fluid and mass transfer also suggests convective fluid driven heat transport as an important mechanism for the final metamorphic overprint under static conditions

quartz pressure solution influence of crystallographic orientation abstract the present contribution examines the relationship between pressure solution and the crystallo graphic orientation of detrital quartz in cleaved sandstones which exhibit a high degree of pressure solution the majority of the detrital grains examined have undergone pressure solution and as a result they have acquired smooth truncated margins along certain cleavage planes the amount of pressure solution varies significantly among the detrital grains this analysis indicates that quartz offers variable resistance to pressure solution along different crystallographic directions quartz grains with a small angle between c axis and the z axis of shortening exhibit the least amount of pressure solution whereas grains with c axes oriented about 50 to z manifest the highest degree of the pressure solution

a theory of finite strain variation through contrasting layers and its bearing on cleavage refraction abstract a theory of finite strain variation in contrasting viscous layers is presented the theory is applicable to layers which are oblique to two principal strains but parallel to the third and is not restricted to plane strain results may be obtained algebraically or by use of the mohr diagram for strain solutions are given for various examples of layering attitude and viscosity ratio measured with respect to a reference layer it is shown that the finite strain ellipsoid changes in shape and orientation across contrasting layers and in some cases the principal axes may be exchanged low strain is indicated in relatively more viscous layers and high strain with extension at a smaller angle to the layering in less viscous layers the latter may approximate simple shear parallel to layering if the strain is sufficiently high the geological implications of the theory are strong strain variations in layered rock sequences it is suggested that in general strain will be inhomogeneous from layer to layer both in orientation and amount the relationship of strain and cleavage are reviewed in the introduction to establish the validity of predicting cleavage patterns from strain data qualitative comparisons between the theoretical results of strain variation and natural cleavage refraction in layered rocks would appear to justify the assumption that cleavages of varied morphologies are sub parallel to the xy planes of strain with this assumption some three dimensional features of planar and linear fabric refraction in contrasting rocks are predicted

orogenic disseminated gold in phanerozoic fold belts examples from victoria australia and elsewhere abstract orogenic gold mineralisation in the lachlan orogen of southeastern australia and in other phanerozoic fold belts has generally been assumed to be confined entirely to quartz veins however an improved understanding of the tectonic structural and geochronological framework in which these occurrences form and recent advances towards the extent of wallrock alteration around these veins cast doubt on the validity of this deeply entrenched lode gold paradigm ore grade orogenic disseminated gold mineralisation has been recognised in a number of fold belts that are known to host significant orogenic lode gold deposits lachlan orogen australia buller terrane and otago schist new zealand meguma terrane canada tien shan mountains in uzbekistan and kyrgyzstan yana kolyma province baikal verhoyansk and allakh yun fold belts in north central mongolia and far east russia disseminated mineralisation in these collisional belts is invariably hosted by pervasively altered greenschist to subgreenschist facies rocks these occurrences also share a number of characteristics with some carlin type gold deposits in the great basin of western north america e g getchell regarding structural relationships fluid composition mineral paragenesis and a common association of carbonaceous matter with mineralisation features of alteration physico chemical characteristics of the ore bearing fluids and strong structural control in all of the studied occurrences point to a close genetic association with lode gold mineralisation the two styles are considered to represent end members of a crustal continuum of orogenic gold emplacement in phanerozoic fold belts with disseminated mineralisation more likely to develop at shallower levels and within more permeable units during the waning stages of uplift and exhumation these conditions facilitate ground preparation via brittle fracturing and the development of intricate stockwork systems efficient gold segregation from bisulphide complexes is largely controlled by fluid mixing of an evolved metamorphic fluid with either more oxidised ascending fluids or meteoric fluids and accelerated by the presence of carbonaceous matter at the site of deposition

rb sr dating of differentiated cleavage from the upper adelaidean metasediments at hallett cove southern adelaide fold belt abstract upper adelaidean psammites from the foreland part of the late proterozoic adelaide fold belt at hallett cove have suffered one major deformation which produced upright folds that plunge gently south axial to these folds is a well developed differentiation cleavage inferred to have resulted from constant volume plane strain deformation by solution transfer and now defined by alternating p phyllosilicate rich and q quartz rich domains geochemical analyses show that cleavage development resulted in a 2 4 fold fractionation of rb sr between the p and q domains thus the age of deformation is datable and isotopic analyses show the p and q domains form a 531 32 ma isochron this age is statistically older than the pervasive deformation and metamorphism in the more interior parts of the fold belt inferred from intrusive ages to have occurred at 485 6 ma and thus suggests that deformation either propagated across the fold belt from external to interior zones or that it occurred episodically the age data allow but do not demand that cleavage formation predated the deposition of the overlying cambrian kanmantoo group sediments

barotropic instability in the west spitsbergen current 1 barotropic instability in the shoreward branch of the west spitsbergen current is investigated on the basis of data from an array of current meter moorings along 78 83 n across the upper continental slope and shelf break west of svalbard the slowly varying background current profile is modeled as an along slope asymmetric jet anchored to the shelf break numerical linear stability analyses are performed on the idealized current profile and topography revealing the characteristic period wavelength and growth rate of unstable vorticity waves detailed analysis of the ambient current profile in 2007 2008 shows that unstable conditions are present during 40 of the 10 month measurement record depending on the localization width and amplitude of the current jet the resulting vorticity waves are localized at the shelf break and are able to exchange water masses across the oceanic arctic front typical wavelengths and periods are 20 40 km and 40 70 h respectively wavelet coherence and complex demodulation analyses of the current meter data confirm that transient signals of similar periodicity as predicted by the stability analysis exist in the data record prominently during the winter and spring months estimates of the heat loss contribution from isopycnal diffusion reach 1 4 tw during the time intervals when unstable vorticity waves are active at the shelf break implying that the dynamics of the west spitsbergen current play a significant role in the cooling process of the atlantic water on the way to the arctic ocean this cooling corresponds to an along shelf cooling rate of 0 08 c per 100 km

wallrock alteration associated with turbidite hosted gold deposits examples from the palaeozoic lachlan fold belt in central victoria australia abstract the study of wallrock alteration phenomena around slate belt hosted gold deposits can provide valuable information regarding the physico chemical conditions of the ore bearing fluids and the timing relationships between deformation peak metamorphism granitoid emplacement and mineralisation thus studying the processes involved in the interaction of the hydrothermal fluids with the host rock is critical in order to constrain genetic models and ultimately as a tool for exploration largely due to the characteristics of the host rocks turbidite hosted mesothermal gold deposits were historically believed to lack such diagnostic alteration haloes and their study has long been neglected however recent studies in the palaeozoic lachlan fold belt in southeastern australia and in similar tectonic settings elsewhere have demonstrated that alteration around many of these deposits is more widespread and pervasive than previously thought a review of existing information and new data strongly support the viability of studying hydrothermal alteration as a guide to turbidite hosted mineralisation and as an indicator of the character of the solutions associated with ore deposition characteristically the auriferous reef structures are surrounded by broad bleached zones while disseminations of carbonate spots pyrite and arsenopyrite porphyroblasts are the most obvious features of alteration depending on parameters such as fault geometry fluid pressure and reactivity and permeability of the host rocks these disseminations can occur up to a kilometre away from the auriferous structures sericitisation and carbonatisation are commonly discernible within 3 to 10 m wide haloes wallrock alteration chemistry of turbidite hosted gold deposits in the lachlan fold belt shows consistent enrichments of k2o co2 s and as and the anomalous values of these elements also provide the most useful dispersion haloes for turbidite hosted gold exploration due to both their regularity and extent

strain paths during slaty cleavage formation the role of volume loss abstract strain analyses of slates commonly investigate the sequence of shapes that must have been superimposed to produce the observed strained state methods such as rf try to quantify the cleavage forming deformation and see through that component to examine any initial shape an alternative approach is to reverse this process by considering the variation in final shapes derived when plausible cleavage forming strain ellipsoids are superimposed on realistic initial shapes specifically a deformation involving both plane strain and volume loss may be superimposed on an initial shape formed by diagenetic flattening in this case the angle between bedding and the incipient cleavage plane is an important variable in controlling final ellipsoid shapes this approach has been adopted for a data set measured from the ordovician borrowdale volcanics in the english lake district results show that neither successive increments of plane strain without volume loss nor incremental plane strain plus volume loss adequately explain the observed pattern of final shapes one permissible solution is generated if increments of pure volume loss perpendicular to the incipient cleavage plane precedes plane strain distortion initial layer parallel shortening may therefore play an important part during cleavage development in these slates