deformation enhanced fluid distribution in feldspar aggregates and implications for ductile shear zones experiments at 900 c and 1 4 gpa show that the distribution of aqueous fluid in fine grained feldspar aggregates changes from isolated pores under hydrostatic conditions to mostly wetted grain boundaries during deformation the isolated pore distribution is rapidly regained during annealing following deformation the deformation enhanced fluid distribution causes a switch from dislocation creep to diffusion creep accompanied by a significant decrease in strength it also increases the bulk transport rate through the aggregate by more than an order of magnitude a change in fluid distribution is not observed in fine grained quartz aggregates deformed at similar conditions if deformation enhanced fluid distribution occurs in naturally deformed feldspathic rocks it could help to explain the localization of strain and enhancement of bulk transport in ductile shear zones

fluid flow and volume loss during mylonitization an origin for phyllonite in an overthrust setting north carolina u s a abstract in the western blue ridge province of the southern appalachians north carolina granite gneisses are converted to phyllitic mylonites phyllonites along the base of the rector branch thrust sheet the mylonites show evidence for fluid infiltration and large volume losses with decreasing distance from the thrust and local shear zones feldspars undergo grain size reduction by cracking followed by chemical breakdown to muscovite sericite and zoisite the following reaction was important during mylonitization 3 k feldspar 2 h muscovite 2 k 6 sio 2 quartz displays evidence for dynamic recrystallization whereas feldspar deforms brittely which together with the secondary mineral assemblages suggest that deformation occurred at temperatures of between 300 c and 500 c in the presence of a fluid the mylonites are enriched by a factor of at least 2 5 in elements such as tio 2 p 2 o 5 zr y v la ce and depleted in sio 2 in comparison to their protolith gneisses the immobile element enrichments are attributed to enrichment in residual phases such as ilmenite zircon apatite and epidote in the mylonites and are interpreted as due to minimum volume losses of 60 mass balance calculations based on major element chemistry indicate the mylonites lost large amounts of sio 2 and smaller amounts of alkalies and were infiltrated by fluid rock weight ratios of between 10 2 and 10 3 phyllonitization as a process involves several deformation mechanisms including cataclasis and solution of feldspar as well as dislocation creep of quartz and micas reaction enhanced softening was apparently important in strain localization

dynamic recrystallization and solution transfer in mylonitic rocks of the tetagouche group northern new brunswick canada a steeply dipping shear zone is present in augen schists and green phyllites of the ordovician tetagouche group a multiply deformed volcanic sedimentary complex in the canadian appalachians the shear zone developed early in the tectonic history and constituent rocks are marked by foliation transposition strong extension and mylonitic or phyllonitic microstructures dynamic recrystallization was an important deformation process but the l s tectonites also contain various generations of veins the deformation of these veins in combination with relict crack seal vein microstructures vein controlled alteration and the differentiation of the tectonic layering illustrates pervasive solution transfer during shear zone evolution various stages of brittle ductile deformation can be recognized in veins of different ages this reflects a microstructural competition between solute mass transfer and crystal plastic processes which is discussed in terms of wet versus dry mylonitization

transpression and extensional collapse steep belts and flat belts in the appalachian central mobile belt northern new brunswick canada models of the appalachian caledonian orogen infer oblique collision and an enigmatic reversal from sinistral silurian to dextral devonian transpression the miramichi highlands in canada are relevant to such models because 1 they are a subductional thrust complex in which the inferred reversal coincided with recumbent folding and 2 its kinematic indicators include rotated thrust structures and conjugate sets of coeval structures both are easily mistaken as evidence for sinistral and dextral transpression the thrust complex is part of the appalachian central mobile belt and is partitioned into steep belts and flat belts according to the attitude of the schistosity we argue that the steep belts are coeval with late silurian plutonism and low pressure metamorphism representing transpressional zones d 2 in which the extension lineation of d 1 thrusting was tilted twice first from gentle to steep then back to a gentle plunge the transpression was synchronous with exhumation as well as sedimentation flat belts represent a later flattening d 3 that probably resulted from extensional collapse and preceded early devonian dextral transpression d 4 along the central mobile belt our model for the flat belts differs principally from models proposed for equivalent flat belts in newfoundland

prograde and retrograde metamorphism of hematitebearing basic schists in the sanbagawa belt in central shikoku the mineral assemblages of hematite bearing basic schists in intermediate high pressure metamorphism are temperature dependent for assemblages with excess hematite albite muscovite and quartz the paragenetic relations can be dealt with in terms of a four component system without omitting or grouping major components in the sanbagawa belt in central shikoku the dominant amphibole in the hematite bearing basic schists changes from winchite via crossite and barroisite to hornblende the stability of amphibole is described chemographically within a pseudoternary system with another excess phase epidote many amphiboles are chemically heterogeneous owing to retrograde reactions which produced low t p amphibole around the prograde amphibole the examination of amphibole zoning makes it possible to draw a retrograde p t trajectory which passes on the lower pressure side of the prograde one

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

tectonics and hydrogeology of accretionary prisms role of the decollement zone abstract at convergent margins the decollement zone comprises the plate boundary and is marked by profound structural disharmony by changes in stress orientation and by a discontinuity in plate velocity the decollement zone initiates in a weak sediment layer typically a low permeability hemipelagic mud lying below a more rapidly deposited stronger more permeable trench turbidite sequence at the deformation front trench turbidites tend to be offscraped whereas the finer grained hemipelagic and pelagic sediments are more likely to be underthrust offscraped materials may undergo only limited burial whereas underthrust deposits can be deeply buried undergo high pressure metamorphism and are more likely to be preserved in the stratigraphic record burial rates associated with underthrusting are high exceeding 20 km my with high rates of underthrusting sediment descending below the decollement zone is probably buried faster than it can dewater resulting in emplacement of relatively high porosity deposits at depth fluids flowing from modern decollement zones have migrated substantial distances laterally and tapped deep sources the episodicity of flow suggests pumping of fluid by cycles of dilation and flow to the decollement zone followed by failure and fluid expansion along the decollement zone possible pressure gradients below the decollement zone allow flow upward into it while maintaining minimum effective stress along it the thickness of sediment underthrust beneath the decollement zone determines whether these deposits are emplaced by diffusive underplating with stratal disruption and efficient dewatering or by coherent underplating with the formation of macroscopic duplexes and transfer of fluid to the base of the accretionary prism deformation mechanisms affecting accreted sediment depend on depth of entrainment into the decollement zone and duration of residence

tracing fluid pathways in fossil hydrothermal systems with near infrared spectroscopy we present a new method to detect and reconstruct fluid pathways in fossil hydrothermal systems that is based on systematic study of white micas in hydrothermally altered rock using near infrared spectroscopy this method developed in an early archean volcanic sequence in the panorama district in western australia uses new near infrared spectroscopic data and published geological and geochemical data of fossil submarine hydrothermal systems in the area analysis of new near infrared spectroscopic data revealed that the abundance of white mica and its al content in altered volcanic rock vary systematically along fossil fluid pathways from zones of low temperature recharge to zones of high temperature discharge as a function of hydrothermal fluid chemistry temperature of alteration coexisting minerals and composition of volcanic host rock the abundance of white mica relative to that of chlorite and the al content of white micas can be used to discriminate among the hydrothermal alteration facies along these fluid pathways which permits detection and reconstruction of fossil fluid pathways

systematics of chlorite alteration at the phelps dodge massive sulfide deposit matagami quebec hydrothermal alteration at the phelps dodge archcan volcanogenic massive sulfide deposit has converted rhyodacite and rhyolite footwall rocks into the following mineral assemblages quartz chlorite albite epidote or sericite quartz chlorite or sericite chlorite or sericite and chlorite talc or stilpnomelane alteration at constant al was initiated by hydration addition of fe mg silicification and leaching of ca na which produced al saturated chlorites with a wide range of fe fe mg ratios within the assemblage quartz chlorite albite epidote or sericite with continued addition of fe and less mg combined with extensive leaching of quartz the chlorite became al undersaturated quartz chlorite talc assemblage and ultimately formed a rock composed essentially of chlorite the chlorite talc or stilpnomelane assemblage is stable in late crosscutting veinlets and in the ore zone chlorites in the si al mg fe system form a rectangular solid solution plane with limited substitution of al for si and extensive substitution of fe for mg in si al space the solid solution plane is outlined by al saturation presence of other al rich mineral and al undersaturation presence of al poor or al free mineral boundaries al iv substitution for si in the chlorites increases from 2 3 to 3 01 formula units based on 8 si al iv with fe fe mg whereas al iv occupancy decreases from 2 88 to 2 65 the valence charge balance is compensated by octahedral site vacancies or by the conversion of fe super 2 to fe super 3 the al iv content of chlorite also increases with temperature chlorites on the al saturated boundary of the solid solution field form a potentially useful geothermometer t degrees c 106 al iv 18 al iv is corrected for changes with the fe fe mg ratio as al iv corrected al iv 0 7 fe fe mg the fe fe mg ratios of bulk rock and contained chlorite correlate well birefringence colors of the chlorite change from green to brown violet and berlin blue as fe fe mg changes from 0 18 to 0 64 the fe fe mg variation apparently depends largely on the proportions of mg rich seawater and fe rich hydrothermal fluid in the altering brine

tectonic setting of the tetagouche group in northern new brunswick implications for plate tectonic models of the northern appalachians a regional compilation and reinterpretation of geochemical analyses of mafic igneous rocks from the ordovician tetagouche group in northern new brunswick indicates the presence of at least three mafic assemblages two groups of basalts and gabbros and one group of gabbros only the three groups can be separated on the basis of tio2 and trace element content group a basalts generally have mid ocean ridge basalt morb like compositions whereas group b basalts indicate a within plate setting wpb group c gabbros intrude into silicic volcanics that underlie the basalts but are rare or absent in the areas underlain by group a and b basalts the group c gabbros probably represent the earliest stages of mafic igneous activity and have morb like compositions or represent a transition between morb and arc basalts the association of group a and b basalts with abundant marine sediments such as thinly bedded turbidites and black and red shales and the fact that they erupted locally on top of continental crus

brunswick subduction complex in the canadian appalachians record of the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick subduction complex in the new brunswick part of the canadian appalachians records the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick complex is anomalously well preserved compared with equivalent rocks and structures elsewhere owing to its unique position in the deepest part of the quebec reentrant of the laurentian margin this part of the margin experienced less underthrusting and exhumation and overprinting by orogen parallel faulting than the adjacent promontories where collision started earlier the early southeast to east vergent thrust related structures represent a progressive d1 deformation that formed in response to northwestward subduction of the previously extended gander margin and subsequent tectonic unroofing of the subduction complex the original shallow northwestward dipping envelope to s1 was deformed in the late silurian by d2 upright folds and associated shear zones into a steep belt during terminal collision the d2 structures probably formed in response to sinistral transpression together d1 and d2 indicate that convergence was oblique and sinistral most rocks incorporated in the subduction complex formed in the tetagouche back arc basin that evolved from rifting of an arenig magmatic arc built on the gander margin into a wide marginal basin subduction was initiated in the late ordovician 455 ma in the back arc basin following collision of the middle ordovician popelogan arc with laurentia in the caradoc shortly after its opening in the late arenig 473 ma the closure history of the iapetus ocean involved more than one subduction zone and arc continent collision and rivals the southwestern pacific ocean in its complexities

fluid infiltration and volume change during mid crustal mylonitization of proterozoic granite king island tasmania the development of 10 30 m wide mylonite zones at mid crustal depths in late proterozoic granitoids on king island tasmania was associated with pervasive infiltration of low 18o fluids 5 to 7 on the scale of the shear zones syndeformational fluid rock interaction produced substantial differences in mineral composition and bulk rock chemistry among several adjacent shear zones which are hosted by the same granite in a shear zone at cape wickham with a normal slip component changes in whole rock chemistry between granite and mylonites indicate a gain of ca and losses of k and na during deformation which was nearly isovolumetric notable losses of k rb and si occurred during partial retrograde alteration of mylonites near the western margin of this shear zone the alteration suggests a component of up temperature fluid flow in contrast 3 km to the south east in a strike slip shear zone at disappointment bay complete albitization of plagioclase was associated with na gain and ca loss deformation also involved losses of mg and fe up to 60 volume gain occurred during the formation of closely spaced mesoscopic to microscopic quartz veins during mylonitization the substantial silica gain in this as well as in two mylonite zones further south east is interpreted to have been associated with upward flow of aqueous fluids along these shear zones on the basis of a gradient reaction model minimum time integrated fluid fluxes of 106 m3 m2 are estimated for the disappointment bay west shear zone

discussion taconian orogenesis sedimentation and magmatism in the southern quebec northern vermont appalachians stratigraphic and detrital mineral record of iapetan suturing

fluid history during deep burial and exhumation of oil bearing volcanics hercynian belt of southern brittany france in southern brittany france the porphyroid nappe a variscan tectonic unit made of volcanic pyroclastic deposits that was involved in a low temperature high pressure prograde metamorphic path followed by exhumation and extension displays evidence for very large and distributed strains achieved through dissolution crystallization processes such distributed strains at low temperature are rather unusual in felsic lithologies recent studies have documented that these rocks deformed within a system closed to fluids this paper presents results of detailed analyses of fluid inclusions and stable isotopes within the deformed metavolcanics and their undeformed counterparts in order to document the fluid history of the tectonic unit results show that its initial thermal evolution likely occurring in a context of basin inversion involved important open system alteration with k metasomatism adularization oil impregnation and hydration during the subsequent tectonic evolution the fluids maintained a constant composition in the c h o n system within the porphyroid nappe and its para autochthon being water rich and containing hydrocarbon components likely related to oil pyrolysis oxidation atoll like fluid inclusion morphology and rare undisturbed fluid inclusions with steep isochore slopes are consistent 750 mpa with pressures estimated for the peak of metamorphism using mineral solid solution thermodynamics fluid inclusions indicate a sub isothermal retrograde path between 420 and 300 c followed by a high thermal gradient at the end of the retrograde path within the underlying para autochthonous unit only the late high temperature gradient is recorded by fluid inclusions the sub isothermal low grade path suggests fast exhumation of the unit without thermal relaxation the high geotherm observed at the end of the p t path is consistent with the post thickening extensional collapse and associated intrusion of granites documented in the area hydration and heterogeneous oil water distribution achieved in the early metasomatic evolution of the porous pyroclastic deposits are responsible for subsequent fluid confining in the porphyroid nappe and for its strongly distributed strain pattern

the assemblage stilpnomelane chlorite phengitic mica a geothermobarometer for blueschist and associated greenschist terranes two anhydrous equilibria can be written among the components of stilpnomelane chlorite white mica and quartz namely 89 daphnite 131 fe celadonite 190 quartz 96 stilpnomelane 71 muscovite and amesite mg celadonite muscovite clinochlore we assume that the free energy change of reaction g go rt lnaij is approximated by g a bt c p 1 rt lnaij where go is the free energy change of the end member components at temperature t and pressure p ai is the activity of component i whose coefficient in the equilibrium is j and a b and c are constants to be determined values of c can be approximated by the change in volume on reaction namely c 406 517 j bar for the first reaction and c 0 613 j bar for the second reaction constants a and b were determined by using six occurrences of the assemblage stilpnomelane chlorite white mica for which p t have been otherwise estimated using solution models from the literature linear regression gives for the first equation a 6118 269 kj b 4584 09 j k and for the second equation a 19 397 kj b 66 72 j k these values predict p t within 0 5 kbar and 25 k for all occurrences and appear reasonably robust relative to probable analytical errors p t are determined by intersection of the curves generated by given compositions in p t space fine grained and or zoned chlorite and white mica make application of the geothermobarometer difficult in some instances but our work in the bathurst region of new brunswick suggests that with patience and care useful analyses can be obtained and the database for the geothermobarometer greatly expanded

compositional variations of syntectonic white mica in low grade ignimbritic mylonite the silla del gobernador shear zone sgsz coastal range of central chile 328s is a low grade mylonite generated from a triassic acidic ignimbritic protolith different microstructures e g quarter mats and pressure shadow structures associated with pressure solution and solution transfer processes and well preserved porphyroclasts can be observed white mica generation appears to be favoured by reaction softening from dissolved quartz and feldspar porphyroclasts according to the mylonite fabrics three different types of white mica can be established a b and c representing mylonites with evidences of relatively low intermediate and high strain conditions deformation mechanisms suggest low grade 350 400 8c conditions for mylonitic deformation in the presence of fluids consistent with the temperature estimations based on chlorite chemistry the geological setting of the sgsz also suggests low pressure 3 kbar conditions no major element mobility with respect to protolith composition was observed in low strained mylonites whereas for the highly strained mylonites a marked k2o secondary input and higher fo2 conditions during deformation are suggested the chemical composition of the neoformed white mica correlates with strain intensity the high strained mylonites contain phengitic celadonitic micas whereas lowstrained mylonites have paragonitic and muscovitic micas white mica geobarometry in highly deformed rocks yields pressure values with no geological significance because the metasomatic k input favour their high k content independent of the confining pressure thus the white mica composition in the mylonites of the sgsz is controlled by the whole rock geochemistry and is related to strain conditions

large scale duplexes within the new britain accretionary wedge a possible example of accreted ophiolitic slivers a multichannel seismic line acquired in the western solomon sea images reflectors within the new britain accretionary wedge which we interpret as accreted duplexes of the downgoing oceanic plate the seaward edge of the largest duplex is located just 6 km from the toe of the accretionary wedge suggesting recent incorporation into the wedge these data therefore provide an excellent opportunity to determine the dynamics of oceanic basement accretion the oceanic basement is represented by a high amplitude low frequency reflector that can be traced up to 40 km arcward of the toe of the accretionary wedge on several seismic lines in this survey another prominent reflector similar in character to the basement reflector lies approximately one second higher in at least one seismic section this reflector is likely to be the top of a basement duplex structures imaged above the basement duplex define a preduplex accretionary wedge whereas those at the toe indicate a new episode of postduplex accretion we have tested this interpretation using both magnetic modeling and interval velocity analysis magnetic models of the wedge that include basement duplexes provide a good match to the observed magnetic data and provide limits on the size and interval velocities of the slivers interval velocities between the two strong reflectors calculated using stacking velocities and constrained through magnetic modeling exceed 5000 m s and are consistent with our interpretation of ophiolitic slivers within the accretionary wedge

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

13c constraints on ocean carbon cycle models 1 the sensitivity of oceanic 13c fields to overturning and gas exchange is investigated in a suite of ocean general circulation models the deep and oceanic mean 13c in the models was sensitive to the balance between deep waters forming in the north atlantic and the southern ocean increasing the southern ocean deep water formation rate to improve deep sea 14c and aou fields was detrimental to model data 13c fidelity a concurrent increase in north atlantic deep water would be needed to match the observed 14c and 13c constraining both the rate and schematics of model deep water formation respectively and improving sensitivity to future perturbations inter basin trends in 13c were sensitive to the rate of overturning in the models with high mixing model configurations matching the observations best models anthropogenic 13c changes used as a diagnostic of model co2 uptake were in agreement with the observations except at high southern latitudes 50 s where the model 13c changes were greater than observed there were predictive relationships among models uptake of anthropogenic co2 and depth integrated 13c changes model relationships between model anthropogenic co2 uptake and the air sea 13c disequilibrium and the sea surface 13c depend on preindustrial riverine fluxes of terrestrial organic carbon and on the wind field used to drive the model circulation respectively among the models tested the relations among anthropogenic co2 uptake and 13c changes in the ocean are biased by the ocmip practice of driving model momentum with one wind field and gas exchange rates with another

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

near infrared spectra of muscovite tschermak substitution and metamorphic reaction progress implications for remote sensing near infrared nir spectra of precambrian metagraywacke in the black hills south dakota demonstrate that reflectance spectroscopy can be used to monitor progressive changes in mineral chemistry as a function of metamorphic grade the wavelength of a combination al o h absorption band in muscovite measured using both laboratory and field portable nir spectrometers shifts from 2217 nm in the biotite zone to 2199 nm in the sillimanite k feldspar zone the band shift corresponds to an increase in the al vi content of muscovite determined by electron microprobe and is thus a monitor of al 2 si 1 fe mg 1 tschermak exchange spectroscopic measurements such as these are useful in the case of aluminum deficient rocks which lack metamorphic index minerals or appropriate assemblages for thermobarometric studies and in low grade rocks subgarnet zone which lack quantitative indicators of metamorphic grade and are too fine grained for petrographic or microprobe studies more important spectroscopic detection of mineral chemical variations in metamorphic rocks provides petrologists with a tool to recover information on metamorphic reaction histories from high spectral resolution aircraft or satellite remote sensing data

processes governing the supply of iron to phytoplankton in stratified seas 1 the impact of iron speciation on phytoplankton dynamics in the marine environment is currently not well understood in this study we modified the existing ciao model of the ross sea to include major aspects of iron chemistry and examined the processes governing the supply of iron to phytoplankton we suggest that the melting of sea ice and ensuing stratification dictates the speciation and bioavailability of iron photoreduction is the key process governing the supply of bioavailable fe to the resident phytoplankton of the ross sea access to organically complexed iron is of greater significance in strongly stratified waters dominated by diatoms than in weakly stratified waters dominated by phaeocystis antarctica light may control phytoplankton taxonomic composition in the ross sea by impacting both photosynthetic performance and iron speciation the efficiency with which iron fuels phytoplankton carbon incorporation is greater in seasonal ice zones than in permanently ice free waters therefore changes in the physical structure of the southern ocean could impact iron bioavailability independent of any change in iron supply

differentiated layering in metamorphic rocks abstract metamorphic or differentiated layering is best developed in low prograde metamorphic rocks such as slates and metaturbidites and is most easily recognised where it cuts a demonstrably earlier layering such as bedding it commonly occurs as an axial plane foliation and typically comprises layers rich in phyllosilicates and opaque minerals alternating with layers rich in quartz or carbonate minerals the phyllosilicate layers generally have the geometry of small shear zones offsetting the earlier foliation and are mostly thinner than the adjacent quartz or carbonate rich layers both layers can vary in thickness from centimetres to microns and the structure is manifest in various forms including outcrop scale layering and thin section scale differentiated crenulation or slaty cleavage in a given sequence of rocks there is generally a strong correlation between the coarseness of the layering and the coarseness of the rock such layering may develop by local redistribution of minerals or by localised addition or removal of some components to or from the rock either way transport is believed to take place in solution and various models for the domainal localisation of the solution processes are discussed possible sources of the transporting fluid are considered and it is concluded that the most likely source in general is connate water subducted below the deforming differentiating rock body

structural evolution of sulphide tectonites and their host rocks stratmat mine new brunswick the sulphide orebodies at the stratmat mine in new brunswick are treated as tectonites because their primary characteristics have been so modified by deformation recrystallization and vein injection that most of their original features have been obscured pb zn cu sulphide orebodies at the stratmat mine consist of sulphide and sulphide silicate tectonites gneisses schists phyllites and slates produced by the mixing of two sulphide precursors and silicate host rocks by polyphase deformation much of which relates to progressive non coaxial deformation quartz vein injection during and after this period of deformation and the intermixing of nonsulphide lithotypes led to dilution of the initial ore composition both the deformation of the orebodies and fluid migration manifested by vein injection reflect processes that were operative in a major shear zone no indisputable primary characteristics of the orebodies are preserved although a number of tectonic and or tectonically modified features m

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

predeformational origin of massive sulfide mineralization and associated footwall alteration at the brunswick 12 pb zn cu deposit bathurst new brunswick evidence from the porphyry dike

post taconic blueschist suture in the northern appalachians of northern new brunswick canada a narrow belt of late ordovician early silurian blueschist at least 70 km long separates an allochthonous fragment of back arc oceanic crust of the middle ordovician fournier group from underlying rift related volcanic rocks of the middle ordovician tetagouche group in northern new brunswick canada the basalts on both sides of the blueschist belt are predominantly metamorphosed to greenschist facies conditions the blueschist belt is interpreted to be an out of sequence thrust zone that accommodated tectonic transport of higher pressure rocks on top of lower pressure rocks during post peak blueschist facies metamorphism the blueschists have higher fe sub 2 o sub 3 feo ratios and total iron contents in comparison to otherwise chemically equivalent basalts of the fournier and tetagouche groups that have been metamorphosed into greenschists the blueschist belt was probably the site of channelized flow of oxidizing fluids during active deformation ina subduction complex formed during the closure of a wide taconic back arac basin in late ordovician silurian time

geochemical variations in middle ordovician volcanic rocks of the northern miramichi highlands and their tectonic significance a detailed geochemical study of middle ordovician volcanic rocks undertaken in the northern miramichi highlands of new brunswick shows that 10 basaltic suites can be distinguished these suites are assigned to the tetagouche and fournier groups the contact between these two groups is a major thrust zone marked for over 70 km by a prominent blueschist zone all the tetagouche group volcanic rocks have chemistries consistent with extrusion in a continental rift but most fournier group basalts in the miramichi highlands have chemistries suggestive of an oceanic back arc setting the chemical signatures stratigraphic variations and structural data indicate that the northern miramichi highlands preserve a section across a telescoped middle ordovician back arc basin that initially opened as a result of asthenospheric injection near the rear part of a lower ordovician ensialic arc

optical microstructure of partly recrystallized calcite in some naturally deformed marbles abstract deformed marbles from the mt lofty ranges south australia have microstructures characterized by deformed relics of calcite interspersed with much finer grained recrystallized calcite and with minor quartz and diopside the deformed calcite relics contain numerous subgrains and show abundant evidence of strain induced migration of twin and grain boundaries new calcite grains have nucleated and grown preferentially along twins especially at twin intersections at grain and kink like boundaries and apparently randomly inside deformed relics optical microstructural evidence suggests that dynamic syntectonic recrystallization has taken place along with some static recrystallization probable mechanisms for the initiation of recrystallization include bulge nucleation and subgrain nucleation

taxon specific differences in c p and n p drawdown for phytoplankton in the ross sea antarctica 1 data from 11 cruises to the ross sea antarctica show that non redfield n p and c p drawdown ratios for diatoms and phaeocystis antarctica were a consistent feature of the phytoplankton communities between 1990 and 1998 ratios of n p drawdown for waters dominated by p antarctica ranged from 17 2 19 5 consistently exceeding the redfield ratio of 16 similarly the c p drawdown ratio for p antarctica dominated waters ranged from 120 154 13 45 greater than the redfield ratio of 106 waters dominated by diatoms exhibited much lower ratios than redfield for n p mean 11 9 and c p mean 76 2 drawdown there was no seasonal trend to the drawdown ratios by either taxa sediment trap data exhibited c p ratios for p antarctica dominated samples that were twice that for diatoms suggesting that the large taxonomic difference in c p drawdown ratio is expressed as a difference in particulate c p ratio which is subsequently exported to depth

the nature and importance of phyllonite development in crustal scale fault cores an example from the median tectonic line japan abstract like many large crustal scale faults the median tectonic line mtl in sw japan has a long history of movement having been active predominantly as a strike slip fault since the mid cretaceous fault rock exposures in the core of the mtl preserve a history of deformation at a range of mid to shallow crustal depths ryoke mylonites 1 4 km north of the main contact record deeper level cretaceous top to the south sinistral movements the remainder of the fault zone core is surprisingly narrow exhibiting a wide variety of fault rocks that illustrate both the interaction and effects of syn tectonic fluid influx over a range of deformation conditions exposures within 50 m of the central slip zone display a progressive sequence in fault rock evolution from ultramylonite cataclasite foliated cataclasite phyllonite breccia gouge this sequence occurs because cataclasis in the vicinity of the fault core creates permeable pathways for the ingress of chemically active fluids into the fault zone this leads to the replacement of load bearing phases such as feldspar by fine grained foliated aggregates of intrinsically weaker phyllosilicates such as white mica and chlorite the grain size reduction associated with both cataclasis and mineral alteration creates conditions ideal for the operation of fluid assisted stress induced diffusive mass transfer mechanisms comparison with the findings of recent experimental studies suggest that the fault zone processes observed in the core of the mtl will lead to long term weakening provided the network of phyllosilicate rich fault rocks are able to form an interconnected thin layer of weak material on kilometre to tens of kilometre length scales

physical forcing of phytoplankton dynamics in the southwestern ross sea coastal zone color scanner czcs imagery of phytoplankton pigments and passive microwave imagery of sea ice distributions in the southwestern ross sea are presented for three different seasons 1978 1989 1979 1980 and 1981 1982 and were analyzed in conjunction with meteorological data obtained from a series of automatic weather stations aws dynamics of the phytoplankton bloom in terra nova bay differed from those in the ross sea owing to spatial differences in katabatic wind fields which determine when the surface waters stratify interannual variation in the timing of formation of the ross sea polynya appears to be controlled by winter temperatures which determine sea ice thickness and integrity rather than variability or intensity in wind stress together czcs aws and passive microwave data suggest that when the ross sea polynya forms early stronger and more frequent katabatic winds result in increased advective losses of phytoplankton in surface waters and a delay in the phytoplankton bloom if polynya formation is delayed until after the winds diminish in frequency the phytoplankton bloom will develop earlier the observation that diatoms dominate both the marginal ice zone and terra nova bay which are hydrographically similar while phaeocystis antarctica is found in unstable waters north of the ross ice shelf suggests that stratification plays an important role in determining species composition in the ross sea

deformation of granitoids at low metamorphic grade ii granular flow in albite rich mylonites abstract the high strain deformation at low metamorphic grades of three investigated granitoids is dominated by the granular flow of albite rich polyphase aggregates these aggregates formed by retrograde breakdown reactions from intermediate plagioclase and k feldspar the predominant deformation mechanism changes in granitoids as the grain size is reduced coarse grained low strain examples are deformed by a combination of intracrystalline plasticity quartz and fracturing feldspar in the mylonites intracrystalline plasticity of quartz plays only a minor role and the dominant deformation mechanism is a non cataclastic granular flow of polyphase aggregates consisting largely of albite and quartz deformation appears to be stable probably because grain growth in albite quartz mixtures is inhibited these fine grained aggregates are mechanically weaker than pure quartz aggregates thus the change in deformation mechanism mainly due to feldspar breakdown reactions appears to be important for the localization of high shear strain deformation at low metamorphic grades in granitoids and other lithologies modally dominated by feldspar the rheological behaviour of albite dominated mineral aggregates may have two consequences for middle to upper crustal deformation of modally feldspar dominated lithologies 1 feldspar in the presence of aqueous fluids can be an important mineral controlling the rheology at low metamorphic grades that is below amphibolite facies p t conditions 2 the occurrence of granular flow of fine grained polyphase aggregates in low grade granitoids is probably common and calls for great care in the modelling of middle to upper crustal rheology based on flow laws for intracrystalline plasticity of single minerals such as quartz

spectral properties of foliose and crustose lichens based on laboratory experiments reflectance spectra of rock encrusting lichens were acquired to determine the influence that this vegetation type may have on the reflectance properties of rock exposures located in high latitude and subarctic environments the samples investigated consist of crustose and foliose lichen species collected from exposures of the gog quartzite formation in alberta canada lichen transmittance was estimated to be 3 throughout the 350 2500 nm spectral region using spectra measured from the foliose lichen umbilicaria torrefacta as a representative sample of a broader class of lichens these findings suggest that lichen prevents the transmission of light to the underlying rock substrate therefore the subpixel influence of lichen and rock within a scene can be considered linearly weighted discrimination of lichen species is made possible using ratios of reflectance at 400 685 and 773 685 nm an index using the band ratios 2132 2198 and 2232 2198 nm shows the similarity of lichen spectra in the infrared and a distinguishing feature between rocks with oh bearing minerals and lichen thus spectral unmixing of rock and crustose foliose lichens may be successfully accomplished using a single lichen end member for this spectral range

hydrothermal alteration in the baca geothermal system redondo dome valles caldera new mexico thermal fluids circulating in the active hydrothermal system of the resurgent redondo dome of the valles caldera have interacted with their diverse host rocks to produce well zoned alteration assemblages which not only help locate permeable fluid channels but also provide insight into the system s thermal history the alteration shows that fluid flow has been confined principally to steeply dipping normal faults and subsidiary fractures as well as thin stratigraphic aquifers permeability along many of these channels has been reduced or locally eliminated by hydrothermal self sealing alteration from the surface through the base of the miocene paliza canyon formation is of three distinctive types argillic propylitic and phyllic argillic alteration forms a blanket above the deep water table in formerly permeable nonwelded tuffs beneath the argillic zone pervasive propylitic alteration is weakly developed in felsic host rocks but locally intense in deep intermediate composition volcanics strong phyllic alteration is commonly but not invariably associated with major active thermal fluid channels phyllic zones yielding no fluid were clearly once permeable but now are hydrothermally sealed high temperature alteration phases at baca are presently found at much lower temperatures we suggest either that isotherms have collapsed due to gradual cooling of the system that they have retreated without overall heat loss due to uplift of the redondo dome that the system has shifted laterally or that it has contracted due to a drop in the water table the deepest well b 12 3423 m in the dome may have penetrated through the base of the active hydrothermal system below a depth of 2440 m in this well hydrothermal veining largely disappears and the rocks resemble those developed by isochemical thermal metamorphism the transition is reflected by temperature logs which show a conductive thermal gradient below 2440 m this depth may mark the dome s neutral plane which separates an upper permeable zone of extensional fracturing from a lower less permeable compressional regime the baca hydrothermal system is similar to those which have formed ore deposits in other calderas particularly creede colorado type epithermal silver base metal veins and stockworks recent scientific drilling has also intersected a deep zone of strong phyllic alteration and molybdenum mineralization in the valles caldera s ring fracture system a setting which localized a large stockwork molybdenite orebody in the nearby questa caldera

diffusion creep in feldspar aggregates experimental evidence a combination of mechanical and microstructural results for experimentally deformed albite aggregates of 2 10 m grain size indicates a regime of grain boundary diffusion creep that depends upon the presence of water temperature and strain rate at 900 c and 10 5 s 1 deformation occurs dominantly by recrystallization accommodated dislocation creep when the aggregates contain 0 2 wt water but by grain boundary diffusion creep when the aggregates contain 0 9 wt water experiments at other temperatures and strain rates indicate that fine grained aggregates with added water may go directly from cataclastic flow to grain boundary diffusion creep with increasing temperature or decreasing strain rate bypassing the field of dislocation creep microstructural evidence for grain boundary diffusion creep in the wet fine grained aggregates includes the development of rectangular grains rather than polygonal grains grain growth a very low average dislocation density open grain boundaries including pores and channels and the presence of overgrowths of a different composition on grains in a two plagioclase an1 and an79 aggregate additional evidence for diffusion creep in the wet fine grained aggregates is indicated by their similar microstructures and strengths when deformed at 600 and 1500 mpa in contrast dry feldspar aggregates deforming by dislocation creep show an increase in strength and a transition to semi brittle behavior at lower confining pressures grain boundary diffusion creep of feldspars may be common in naturally deformed rocks due to the ease of grain size reduction by both cataclasis and dynamic recrystallization

fluid channelling during ductile shearing transformation of granodiorite into aluminous schist in the tauern window eastern alps ductile shearing in the core of the tauern window austria transformed metagranodiorite into si undersaturated garnet chlorite staurolite schist at a depth of c 35 40 km during the alpine orogeny four distinct zones have been recognized extending from the wallrock into the centre of the shear zone zone i unaltered metagranodiorite with subordinate amphibolite zone ii biotite white mica garnet schist zone iii biotite phengite schist zone iv quartz absent garnet chlorite staurolite schist with garnets up to 10 cm across whole rock analyses show a dramatic decrease in sio2 from 65 wt in zone i to 35 wt in zone iv ca na and sr also decrease across the shear zone whereas al ti fe mg p cr ni zn and rb all increase towards zone iv mass balance calculations indicate that shearing was accompanied by up to 60 volume loss near the centre of the shear zone comparison of the tauern window samples with other shear zones in granitic hosts indicates that silica loss accompanied by gains in mg fe and ti is typical for volume loss shear zones but is distinctly different from the element behaviour exhibited in shear zones that are thought to represent approximately isovolumetric behaviour in the samples studied here volume loss appears to have resulted from channellized fluid flow during shearing producing time integrated fluid fluxes of 108 cm3 cm 2 in zone iv this large volume of fluid may have originated in part from dehydration of flysch carried beneath the metagranodiorites during eocene movement on the north penninic subduction zone development of an inverted thermal gradient during subduction would have allowed the fluid to scavenge large amounts of silica from the shear zone during ascent and heating

tectonic history of subduction zones inferred from retrograde blueschist p t paths many phanerozoic convergent plate junctions are marked by discontinuous blueschist belts reflecting relatively high pressure p prograde trajectories common blueschist paragneisses such as those of the western alps exhibit widespread overprinting by greenschist and or epidote amphibolite facies assemblages for this type of high p belt retrograde metamorphism involved fairly rapid nearly isothermal decompression some terranes underwent continued heating during early stages of pressure release uplift probably occurred as a consequence of the entrance of an island arc oceanic plateau or segment of continental crust into the subduction zone collision resulting in marked deceleration or cessation of underflow and buoyant approximately adiabatic rise of the stranded recrystallized subduction complex other high p belts such as the franciscan of western california preserve metamorphic aragonite and lack a low p overprint retrogression approximately retraced the prograde p t temperature path or for early formed high grade blocks occurred at even higher p t ratios parts of this type of metamorphic belt evidently migrated slowly back up the subduction zone in response to isostatic forces during continued plate descent and refrigeration upward motion took place as tectonically imbricated slices as laminar return flow in melange zones and perhaps partly a lateral spreading extension of the underplated accretionary prism retrograde p t trajectories of high pmore belts therefore provide important constraints on the tectonic evolution of convergent plate junctions less

structure origin and concentration of the brunswick 12 and 6 orebodies the origin structure and history of the brunswick iron formation and massive sulfides of the brunswick 6 and 12 mines are reviewed new evidence concerning structure stratigraphy and alteration of the orebodies is presented five generations of folds are described of which the earliest three have an important influence on the large scale structure of the mine areas the earliest folds f 1 are large and overturned to the north and are related to coeval thrusting these folds have not been recognized previously the main orebody folds are upright isoclinal locally downward facing structures of the f 2 generation the mineralization is interpreted as syngenetic but evidence is presented to show that previously interpreted feeder pipes do not exist in a presently recognizable form and that previously interpreted syngenetic alteration is in fact a later diagenetic or postdiagenetic feature remobilization of the sulfide mineralization continued until after the f 3 deformation and concentration of the sulfides may be a relatively late feature but the possibility of the main concentration being syngenetic cannot be ruled out the evidence is obscured by later deformation and alteration the present form of the orebodies is largely a function of deformation and the sulfide layers are thickened locally by folding the orebodies are located in tight structural basins formed by interference of f 1 and f 2

short wavelength infrared spectral characteristics of the hw horizon implications for exploration in the myra falls volcanic hosted massive sulfide camp vancouver island british columbia canada short wavelength infrared swir spectrometry has been used to identify previously unmapped hydrothermal alteration zones around volcanic hosted massive sulfide vhms orebodies at myra falls vancouver island british columbia hydrothermal alteration assemblages are uniformly dominated by fine grained white mica with poor development of mineralogical zonation swir spectrometry is an ideal exploration tool for characterizing this fine grained hydrothermal alteration at myra falls swir spectrometry has identified subtle shifts in the wavelengths of the aloh absorption feature of white mica corresponding to compositional changes in altered rhyolite distal and proximal to ore aloh absorption occurs at shorter wavelengths 2 198 nm and corresponds to lower fe fe mg and si al and higher na na k in strongly altered samples proximal to ore slightly sodic muscovites aloh absorption occurs at longer wavelengths 2 206 nm and corresponds to higher fe fe mg and si al and lower na na k in samples distal to ore nonsodic slightly phengitic muscovites white mica in siltstone within a meter of vhms ore has higher zn v fe and mg contents than white mica distal to these altered samples chlorite compositions identified by swir also show systematic changes with intensity of alteration and distance from ore the average wavelength of the feoh absorption feature for chlorite in rhyolitic samples proximal to ore is 2 241 nm intermediate mg chlorite whereas wavelengths in background samples average 2 247 nm intermediate fe chlorite similar changes are observed in footwall and hanging wall andesites with samples near the battle mine containing muscovite to phengitic muscovite average wavelength of the aloh absorption feature of 2 200 nm and mg rich chlorite average wavelength of the feoh absorption feature of 2 245 nm to regional andesite samples with phengitic muscovite average wavelengths of the aloh absorption feature of 2 209 nm and fe rich chlorite average wavelength of the feoh absorption feature of 2 249 nm in weakly altered rocks white mica compositions also vary with host lithology the aloh absorption feature occurs at longer wavelengths in white mica in dacite and andesite compared to adjacent rhyolitic rocks suggesting that higher fe and mg in the host lithology affects the composition of white mica two zones of intense hydrothermal alteration above the battle and hw orebodies have distinctive swir spectral characteristics with the aloh and feoh features occurring at shorter wavelengths 2 197 and 2 240 nm respectively small anomalous zones of alteration were also identified in the thelwood valley area where minor mineralized zones are present as broad zones of fine grained white mica sericite alteration are ubiquitous throughout the myra falls property alteration proximal to ore cannot be identified simply by visual logging of drill core alteration zonation may be determined by subtle shifts in white mica spectral characteristics this study indicates that swir analysis may be an effective field based exploration tool for quantifying the intensity of alteration associated with vhms orebodies and that trends in mineral compositions even in very fine grained rocks can be used as mine scale vectors to ore

the age of salinic deformation constrained by 40ar 39ar dating of multiple cleavage domains bathurst supergroup new brunswick appalachians in the new brunswick appalachians polydeformed felsic volcanic rocks of the bathurst supergroup record four cleavage forming tectonic events of which d1 and d2 record subduction related underplating of buoyant elements of the tetagouche backarc basin and subsequent collision between composite laurentia and the gander margin respectively during the salinic orogenic cycle here we present an integrated approach to dating multiple cleavage domains in which we performed step heat 40ar 39ar analyses microstructural observations and mineral chemistry analysis on a suite of samples as well as in situ40ar 39ar analysis on two samples from the suite with clear s1 and s2 cleavage relationships we use this dataset to characterize the complex relationships between s1 and s2 white mica between samples at different structural settings across the supergroup we refine the timing of s1 white mica growth and hence m1 d1 of the salinic cycle in the bathurst supergroup to ca 452 to 437 ma and s2 white mica growth also d2 to ca 427 to 418 ma new and published data indicate local thermal resetting of white mica at ca 411 ma which we interpret to indicate a buried intrusion likely a component of the central plutonic belt delineation of the two white mica age components particularly within a single sample was informed by both spatially controlled analysis in situ40ar 39ar and the higher age precision of step heat 40ar 39ar analyses

key role of organic complexation of iron in sustaining phytoplankton blooms in the pine island and amundsen polynyas southern ocean primary productivity in the amundsen sea southern ocean is among the highest in antarctica the summer phytoplankton bloom in 2009 lasted for 470 days in both the pine island and amundsen polynyas such productive blooms require a large supply of nutrients including the trace metal iron fe the organic complexation of dissolved fe was investigated in the amundsen sea during the spring of 2009 to better understand the potential role of ligands in enhancing the local stock of dissolved fe the main sources of fe and ligands to the amundsen sea are thought to be melting sea ice and the circumpolar deep water cdw which is modified mcdw on the continental shelf and upwells beneath the coastal glaciers and ice shelves upwelling of relatively warm mcdw is also responsible for the rapid melting of the pine island glacier pig and surrounding ice shelves resulting in additional release of fe into surface waters at upwelling stations near ice shelves organic ligands were nearly saturated with fe thus enhancing the stock of fe and its availability to the phytoplankton community however ligands had little capacity to buffer additional fe input from glacial melt in these coastal upwelling regions much of the glacial fe supply is lost due to vertical export of fe via scavenging and precipitation conversely within the phytoplankton bloom in the nearby coastal polynyas the uptake of fe combined with the production of organic matter enhanced the abundance of relatively unsaturated organic ligands capable of stabilizing additional fe supplied from glacial melt these unsaturated dissolved organic ligands combined with the continuous input of fe dissolved and particulate from glacial melt appear to favor the solubilization of fe thus increasing the stock of bioavailable fe and fueling the phytoplankton bloom

spectral reflectance of lichens and their effects on the reflectance of rock substrates rock outcrops in arid and semiarid regions frequently have abundant lichen cover we collected lichens and their granite slate and hornfels substrates in the extremadura region of spain and measured spectral reflectance in the 400 2500 nm region in the laboratory lichen cover as low as 30 percent masks the spectral features of spectrally flat rocks such as slate and hornfels the sharp spectral features of granite are obscured at 60 80 percent lichen cover the strong reflectance peak at 2220 nm in lichens interferes with recognition of the 2200 nm absorption band in hydroxyl bearing minerals that is used to locate hydrothermally altered and potentially mineral rich areas however lichen spectra are characterized by distinctive absorption features that occur in few minerals and can thus be used to identify lichen presence from computer modeling of laboratory spectra we conclude that landsat thematic mapper tm band ratios of 3 4 and 5 2 best minimize lichen effects in tm image analysis

application of airborne laboratory and field hyperspectral methods to mineral exploration in the canadian arctic recognition and characterization of volcanogenic massive sulfide associated hydrothermal alteration in the izok lake deposit area nunavut canada we have investigated the application of ground laboratory and airborne optical remote sensing methods for the detection of hydrothermal alteration zones associated with the izok lake volcanogenic massive sulfide vms deposit in nunavut canada this bimodal felsic zn cu pb ag deposit is located above the tree line in a subarctic environment where lichens are the dominant cryptogamic species coating the rocks the immediate host rhyolitic rocks have been hydrothermally altered and contain biotite chlorite and white micas as dominant alteration minerals these minerals have spectral al oh and fe oh absorption features in the short wave infrared wavelength region that display wavelength shifts which are documented to be due to chemical compositional changes our ground spectrometer measurements indicate that there is a systematic trend in the fe oh absorption feature wavelength position of biotite chlorite with increasing distance from the vms deposit the average fe oh absorption feature wavelength position of the proximal areas 398 3 146 m from mineralization is observed at 2 254 nm and that of the distal areas 5 782 6 812 m at 2 251 nm moreover the proximal areas have an average al oh absorption feature wavelength position at 2 203 nm in contrast with the average wavelength position at 2 201 nm in the distal areas implying a spectral shift of 2 nm these findings indicate that hydrothermal alteration zones can be detected by hyperspectral remote sensing despite the presence of abundant lichen cover however the airborne results discussed in this study required the screening out of more than 99 of the pixels in the area

high resolution biogeochemical investigation of the ross sea antarctica during the aesops u s jgofs program 1 the results of high resolution biogeochemical measurements in the upper 200 m of the ross sea antarctica obtained during the aesops u s jgofs program using the lamont pumping seasoar lps are presented they consist of three west east transects from 170 e to 180 longitude along the aesops study line at 76 5 s and three short north south transects in the ross sea polynya during the initial and maturing stages of phytoplankton blooms in the austral spring and early summer of 1997 the lps carried an in situ instrument array for measurement of temperature salinity fluorescence photosynthetically active radiation par and dissolved oxygen in addition a highpressure pump mounted aboard the lps fish delivered a continuous seawater sample stream to the shipboard laboratory for high speed analysis of its nutrient nitrate plus nitrate phosphate and silicate and total co2 concentrations and co2 partial pressure pco2 vertical resolution of this sampling equaled or exceeded that of hydrostation style conductivity temperature depth ctd casts horizontal resolution nominally equal to a vertical cast every 3 5 km exceeded station resolution by a factor of 10 while not perfectly synoptic the 20 hour duration of these transects is far shorter than the time typically taken to complete the line with conventional sampling methods these surveys clearly identified three distinct deep water masses below about 100 m high salinity shelf water hssw in the western end of the transects modified circumpolar deep water mcdw in the middle of the transects and low salinity shelf water lssw to the east the regions to the west were characterized by high biological productivity with high n p and c p uptake ratios but little si uptake indicating that the production was dominated by phaeocystis to the east biological productivity was lower than in the west and low n p and c p uptake ratios and high si uptake indicated the dominance of diatoms the difference in uptake ratios appears to be entirely due to anomalously high p uptake by diatoms n c uptake ratios are similar in the two regions and very near canonical redfield stoichiometry the area in the center of the transects was characterized by high stratification and low diatom dominated productivity the reason for this low productivity is unclear but is speculated to be due to the short time which this water has been exposed to an ice free surface the presence of strong variability at horizontal length scales of order 10 km is evident in nearly all fields especially in upper 100 m although many of the features are resolved only by two or three lps tracks each separated by only a few kilometers physical bio optical and chemical variability is observed to extend vertically from sea surface to depths as deep as 140 m far below the 1 light level and the mixed layer depth this may be attributed to downwelling of waters associated with eddies and or meandering a simple statistical measure presented to quantify the errors associated with the undersampling of such a highly variable field shows that biogeochemically important parameters like pco2 and oxygen and chlorophyll concentrations are poorly resolved by a commonly used 50 km hydro station spacing longitudinal averages of these parameters however are predicted fairly well at coarser resolutions index terms 4207 oceanography general arctic and antarctic oceanography 4805

formation of low temperature mylonites and phyllonites by alkali metasomatic weakening of felsic volcanic rocks during progressive subduction related deformation abstract dacitic to rhyolitic volcanic rocks of the spruce lake nappe experienced two phases of alkali metasomatism as a result of fluids channelling along shear zones the shear zones formed during a progressive thrust related deformation associated with underplating and incorporation of the volcanic rocks into the brunswick subduction complex of northern new brunswick the fluids mainly represent chemically and isotopically modified seawater released by dewatering of the associated underthrusted shaly sedimentary rocks both phases of metasomatism weakened the felsic rocks leading to strain localisation albitisation of felsic volcanic rocks as a result of na metasomatism during underthrusting facilitated formation of mylonites near peak high pressure metamorphism 330 370 c 600 800 mpa the mylonites are preferentially preserved in the roof thrust shear zone of the spruce lake nappe core mantle structures bulging and crystallographically preferred orientations indicate that albite behaved more ductilely than k feldspar the ductility of albite at these low temperatures is interpreted as a function of abundant intragranular fluids phengite rich phyllonites formed after peak high pressure metamorphism during uplift by out of sequence thrusting these phyllonites are generally characterised by a slight gain in k and loss of na and are best developed in the basal shear zones of the spruce lake nappe

the microstructures of microcline from some granitic rocks and pegmatites optical microscopy transmission electron microscopy tem and electron diffraction have been used to study the microstructures in a series of microclines from granitic rocks and pegmatites optical microscopy revealed exsolution of albite in all but one specimen and in general the k phase exhibited cross hatched patterns the tem and optical observations confirm earlier ideas that the cross hatching is associated with intersecting sets of albite and pericline twin lamellae which were formed at the transformation from monoclinic to triclinic symmetry however significant changes subsequently occur which produce microstructures involving essentially albite twinning only although the cross hatched morphology is retained and features associated with the original pericline twins are observed in the tem images and in the associated diffraction patterns the four spot diffraction patterns characteristic of m twinning are observed only from volumes of specimen containing discrete domains of albite twinning and domains of pericline twinning streaking of the diffraction spots is associated with the complex structure of the domain boundaries the influence of exsolution of albite on the initiation of the transformation twinning has also been investigated domains of orthoclase within a matrix of twinned microcline were observed in two specimens but the observations do not appear to provide any direct information about the mechanism of the transformation between these two structures

structure and evolution of the heath steele base metal sulfide orebodies bathurst camp new brunswick canada a structural analysis of the base metal sulfide deposits at the heath steele mines northern new brunswick is presented the structural similarity of the deposits is defined and their relationships to one another discussed the deposits are spatially associated with ordovician sedimentary rocks which are situated in an igneous rock complex comprising felsic and basic volcanics volcaniclastics and intrusives the complex has been subjected to low grade metamorphism and five generations of deformation d 1 d 5 the first two generations of deformation d 1 and d 2 are represented by transposition foliations s 1 and s 2 the present attitude of the s 2 foliation is a result of recumbent folding d 3 and two generations of open folds with vertical axial planar cleavages striking northwest s 4 foliation and northeast s 5 foliation the s 1 foliation is axial planar to conical f 1 folds regionally such folds have been associated with thrusting d 1 along the earliest recognized layering s 0 foliation vein swarms illustrate the local importance of solute mass transfer during this event at the heath steele mines culminating in fracture controlled alteration along a brittle ductile deformation d 1 shear zone near the sulfide deposits and development of metasomatic breccia in the sulfide deposits overall the deposits occur along the s 0 foliation the contact between augen schists and the metasedimentary rocks but massive sulfides are concentrated in f 1 fold closures forming pods and slabs parallel to the s 1 foliation this concentration reflects either mobilization of preexisting sulfides during d 1 or deposit formation by mineralization during d 1 if the contact in s 0 is nontectonic a stratigraphic control on the location of the deposits is indicated and their association with iron formation argues for a syngenetic origin conclusive evidence for these models has been obliterated by the intense deformation and solution transfer

regional stable isotope systematics of hydrothermal alteration and massive sulfide deposition in the west shasta district california the west shasta cu zn district is located in california at the southern end of the klamath mountains and contains numerous pyrite dominant volcanogenic massive sulfide deposits the deposits are hosted in a bimodal suite of intrusive and extrusive basalt to andesite copley greenstone and rhyolite balaklala rhyolite of devonian age regional variations in oxygen hydrogen and sulfur isotope ratios in the copley greenstone balaklala rhyolite and mule mountain trondhjemite record hydrothermal alteration which took place over a large range in temperature from 18 o values vary for the copley greenstone from 3 5 to 11 6 per mil and for the balaklala rhyolite from 7 6 to 13 3 per mil delta d values of the copley range from 71 to 42 per mil and for most samples of the balaklala from 73 to 46 per mil the isotopic variation reflects changing mineralogy in addition to a range of alteration temperatures with progressive chloritization the water content of the copley greenstone increases from 1 51 to 8 34 wt percent h 2 o whereas the delta 18 o values decrease water rock mass ratios calculated from the oxygen isotope data are 1 8 to 2 8 for high temperature alteration regional variations in delta d and delta 18 o values of the copley greenstone indicate higher temperatures of alteration and greater water rock interaction adjacent to the mule mountain stock beneath the area of the iron mountain mine largest of the massive sulfide deposits this suggests that the stock is the heat source responsible for the iron mountain deposit the alteration pattern associated with the stock and the low temperature isotopic alteration of the capping porphyry upper unit of the balaklala indicate that the mule mountain stock was coeval with the middle unit of the balaklala estimates of the oxygen isotope compositions of the balaklala and mule mountain magmas delta 18 o approximately 6 5ppm from analyses of quartz phenocrysts suggest that the two magmas or magma types are consanguineous and were derived from the same source as the copley greenstone sulfur isotope data support this interpretation there is no clear evidence for temporal variations in the isotopic composition of the magmas mass balance considerations and data on the isotopic composition and content of sulfur in the copley greenstone most 95 percent of the sulfur in the ore deposits could have been leached from the copley greenstone during hydrothermal alteration the variation in delta 34 s values of whole rock samples is larger for the copley 4 0 to 22 4ppm most 0 0 to 6 0ppm than for either the balaklala 3 3 to 4 9ppm or the massive sulfide deposits 0 5 to 6 0ppm but most 3 0 to 5 0ppm no correlation is found between the abundance and isotopic composition of sulfur in the copley greenstone isotopic fractionation effects during transport and local reprecipitation of leached sulfur can explain the sulfur isotope variability of the copley greenstone sulfur isotope data also support degassing of the mule mountain or related magmas as a sulfur source

crack seal fibre growth mechanisms and their significance in the development of oriented layer silicate microstructures abstract an analysis of crack seal fibre growth mechanisms has shown two important implications of the crack seal process for the interpretation of microstructures in low grade metamorphic rocks 1 1 the ability of fibre growth to track the incremental separation history of crack walls depends on details of the nucleation and growth mechanisms 2 2 fibrous crystals may develop cristallographic preferred orientations in certain crack seal situations the microstructures of layer silicates and associated phases developed in several examples of syntectonic intragranular microfracture sites and veins indicates that layer silicate 001 and grain shape preferred orientation can develop during crack seal deformation by oriented growth mechanisms during successive crack seal increments preferred orientation may develop in response to an interaction between anisotropic growth kinetics and the displacement history resulting in preferential rejoining by syntaxial overgrowth of pulled apart grains having fast growth directions parallel to the incremental displacement direction across a microcrack preferred orientation may also be developed and enhanced in crack seal growth sites by overgrowth of previously oriented layer silicates in the microcrack walls in this case the crystallographic preferred orientation need not be simply related to the displacement history during crack seal fibre growth since crack seal processes may operate on all scales down to the minimum size of a microfracture in a deforming rock such mechanisms of layer silicate preferred orientation development are expected to be very significant in developing and enhancing foliation during deformation involving microfracture and solution transfer processes

the bathurst mining camp new brunswick data integration geophysical modelling and implications for exploration the bathurst mining camp bmc is one of canada s oldest mining districts for volcanogenic massive sulphide vms deposits most of the 46 known deposits were discovered in the 1950s using a combin