40ar 39ar and oxygen isotope studies of polymetamorphism from tinos island cycladic blueschist belt greece petrological oxygen isotope and 40ar 39ar studies were used to constrain the tertiary metamorphic evolution of the lower tectonic unit of the cyclades on tinos polyphase high pressure metamorphism reached pressures in excess of 15 kbar based on measurements of the si content in potassic white mica temperatures of 450 500 c at the thermal peak of high pressure metamorphism were estimated from critical metamorphic assemblages the validity of which is confirmed by a quartz magnetite oxygen isotope temperature of 470 c some 40ar 39ar spectra of white mica give plateau ages of 44 40 ma that are considered to represent dynamic recrystallization under peak or slightly post peak high pressure metamorphic conditions early stages in the prograde high pressure evolution may be documented by older apparent ages in the high temperature steps of some spectra eclogite to epidote blueschist facies mineralogies were partially or totally replaced by retrograde greenschist facies assemblages during exhumation oxygen isotope thermometry of four quartz magnetite pairs from greenschist samples gives temperatures of 440 470 c which cannot be distinguished from those deduced for the high pressure event the exhumation and overprint is documented by decreasing ages of 32 28 ma in some greenschists and late stage blueschist rocks and ages of 30 20 ma in the lower temperature steps of the ar release patterns of blueschist micas almost flat parts of ar ar release spectra of some greenschist micas gave ages of 23 21 ma which are assumed to represent incomplete resetting caused by a renewed prograde phase of greenschist metamorphism oxygen isotope compositions of blueschist and greenschist facies minerals show no evidence for the infiltration of a 18o enriched fluid rather the compositions indicate that fluid to rock ratios were very low the isotopic compositions being primarily controlled by those of the protolith rocks we assume that the fundamental control catalysing the transformation of blueschists into greenschists and the associated resetting of their isotopic systems was the selective infiltration of metamorphic fluid a quartz magnetite sample from a contact metamorphic skarn taken near the miocene monzogranite of tinos gave an oxygen isotope temperature of 555 c and calculated water composition of 9 1 the value of 18o obtained from this water is consistent with a primary magmatic fluid but is lower than that of fluids associated with the greenschist overprint which indicates that the latter event cannot be directly related to the monozogranite intrusion

eclogite blueschist relationships as evidenced by mineral equilibria in the high pressure metabasic rocks of sifnos cycladic islands greece

tectono metamorphic evolution of a nappe stack a case study of the swiss alps fold and thrust belts are prominent structures that occur at the front of compressional orogens to unravel the tectonic and metamorphic evolution of such complexes kinematic investigations quantitative microstructural analysis and geothermometry calcite graphite calcite dolomite were performed on carbonate mylonites from thrust faults of the helvetic nappe stack in central switzerland paleo isotherms of peak temperature conditions and cooling stages fission track of the nappe pile were reconstructed in a vertical section and linked with the microstructural and kinematic evolution mylonitic microstructures suggest that under metamorphic conditions close to peak temperature strain was highly localized within thrust faults where deformation temperatures spatially continuously increased in both directions from n to s within each nappe and from top down in the nappe stack covering a temperature range of 180 380 c due to the higher metamorphic conditions thrusting of the lowermost nappe the doldenhorn nappe was accompanied by a much more pronounced nappe internal ductile deformation of carbonaceous rock types than was the case for the overlying wildhorn and gellihorn nappes ongoing thrusting brought the doldenhorn nappe closer to the surface the associated cooling resulted in a freezing in of the paleo isotherms of peak metamorphic conditions contemporaneous shearing localized in the basal thrust initially still in the ductile deformation regime and finally as brittle faulting and cataclasis inducing ultimately an inverse metamorphic zonation with ongoing exhumation and the formation of the helvetic antiformal nappe stack a bending of large scale tectonic structures thrusts folds peak temperature isotherms and cooling isotherms occurred while this local bending can directly be attributed to active deformation underneath the section investigated up to times of 2 3 ma a more homogeneous uplift of the entire region is suggested for the very late and still active exhumation stage

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

the stable isotope signature of kilometre scale fracturedominated metamorphic fluid pathways mary kathleen australia abstract large calcite veins and pods in the proterozoic corella formation of the mount isa inlier provide evidence for kilometre scale fluid transport during amphibolite facies metamorphism these 10 to 100 m scale podiform veins and their surrounding alteration zones have similar oxygen and carbon isotopic ratios throughout the 200 10 km mary kathleen fold belt despite the isotopic heterogeneity of the surrounding wallrocks the fluids that formed the pods and veins were not in isotopic equilibrium with the immediately adjacent rocks the pods have 13ccalcite values of 2 to 7 and 18ocalcite values of 10 5 to 12 5 away from the pods metadolerite wallrocks have 18owhole rock values of 3 5 to 7 and unaltered banded calc silicate and marble wallrocks have 13ccalcite of 1 6 to 0 6 and 18ocalcite of 18 to 21 in the alteration zones adjacent to the pods the 18o values of both metadolerite and calc silicate rocks approach those of the pods large calcite pods hosted entirely in calc silicates show little difference in isotopic composition from pods hosted entirely in metadolerite thus 100 to 500 m scale isotopic exchange with the surrounding metadolerites and calc silicates does not explain the observation that the 18o values of the pods are intermediate between these two rock types pods hosted in felsic metavolcanics and metasiltstones are also isotopically indistinguishable from those hosted in the dominant metadolerites and calc silicates these data suggest the veins are the product of infiltration of isotopically homogeneous fluids that were not derived from within the corella formation at the presently exposed crustal level although some of the spread in the data may be due to a relatively small contribution from devolatilization reactions in the calc silicates or thermal fluctuations attending deformation and metamorphism the overall l shaped trend of the data on plots of 13c vs 18o is most consistent with mixing of large volumes of externally derived fluids with small volumes of locally derived fluid produced by devolatilization of calc silicate rocks localization of the vein systems in dilatant sites around metadolerite calc silicate boundaries indicates a strong structural control on fluid flow and the stable isotope data suggest fluid migration must have occurred at scales greater than at least 1 km the ultimate source for the external fluid is uncertain but is probably fluid released from crystallizing melts derived from the lower crust or upper mantle intrusion of magmas below the exposed crustal level would also explain the high geothermal gradient calculated for the regional metamorphism

modelling an infiltration driven geochemical front modelling of geochemical alteration profiles e g in 18o or 87sr 86sr resulting from fluid infiltration has provided important constraints on the volumes of fluid that move through the crust during metamorphism these models consider that alteration results from a combination of advection with diffusion and or kinetically limited solid fluid exchange models incorporating advection and one of the two broadening mechanisms have analytical solutions whilst the three parameter solution does not given a particular alteration profile it is therefore important from a computational point of view to determine whether use of the more comples three parameter model places tighter limits on the characteristics of the fluid infiltration event in this paper we address this problem through modelling of a measured oxygen isotope alteration profile from naxos greece for each end member model we calculate a set of best fit parameters emphasising which features of the data control the fit of each of the models we then consider numerical solutions which allow all three processes to operate and conduct a grid search in parameter space to map out the structure of the variance between the model and data while it is not possible to distinguish a single combination of the three processes that produces a strong global minimum in variance we can distinguish a family of solutions which are equally valid and we use this minimum variance family to place bounds on the time scales fluid velocity and porosity characteristic of the fluid alteration event

stream analysis of small drainage basins in an ancient landform korean peninsula abstract much of the topography of korea is ancient but many quaternary fault outcrops and marine terraces have been observed in the southeastern part of the korean peninsula sufficient evidence of a quaternary fault is lacking in the geological features of the commercially developed jukbyun and uljin areas knickpoints that develop on streams can be formed by tectonic activity such as faulting and folding or can result simply from the differential erosion rates of bedrock in this study we investigated the relationship between stream steepness and faults in the jukbyun area stream profile analyses of the bugu and namdae basins were performed using a digital elevation model to estimate quaternary tectonic movements stream parameters obtained from analysis of the longitudinal stream profiles of the bugu and namdae drainage basins in the northeastern part of the korean peninsula indicated neotectonic movement thirty of the thirty nine knickpoints that developed in the downstream areas of the fluvial channels corresponded to fault zones it is thought that fault activity results in knickpoints in river systems the normalized relative slope k sn value 54 9 of the bs1 stream in the bugu drainage basin was higher than that 28 8 36 3 of the other streams in both basins despite a similar lithology to ns1 and ns2 therefore we concluded that stream steepness might be a result of tectonic forcing rather than a product of rock strength in the study area and that stream parameters could provide indirect evidence of quaternary tectonics in ancient landforms

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

structure and kinematics of upper cenozoic extensional detachment on naxos and paros cyclades islands greece this paper presents a study of the ductile and brittle deformation on naxos and paros islands cyclades greece previous maps and studies of the two islands have shown that a major low angle fault zone separates surface rocks above the contact from an initially deep seated unit below showing a metamorphic evolution from high to low pressures structural analysis as well as available stratigraphical metamorphic and geochronological data taken together demonstrate that this fault zone is a major normal sense detachment zone dipping to the north rapid denudation of footwall rocks subsequent to high temperature metamorphism at an estimated rate of 1 8 9 5 mm yr attests for tectonic unroofing during regional scale top to the north ductile shearing the change from ductile to brittle behavior of the footwall rocks together with a progressive localization of high strain intensity deformations just below the hangingwall is explained by the progressive cooling of the uprisen footwall of the detachment mio pliocene clastic sediments in the hangingwall represent the infilling of half grabens opened in between major normal faults that are synthetic to the underlying ductile shear zone these sediments are as old as aquitanian 25 ma or younger than the earliest recognized evidence of ductile extension in the footwall this provides a minimum age for the onset of extension in the cyclades which appears significantly older than maximum ages reported up to now 13 5 ma structural data strongly suggest that the detachment fault was initially rather low dipping 35 an evolutionary model is proposed in which migmatite domes in the footwall correspond to the uprise of the lower ductile crust between two separating upper crustal blocks during a process of asymmetric boudinage of the crust this detachment model applies to a previously thickened continental lithosphere which then suffers thermal relaxation and weakening allowing extensional deformation to reach a climax during and subsequent to high temperature metamorphism in the cyclades crustal scale extension started after early cenozoic thrusting while the crust was still thick or less likely before late underthrusting below the present surface

cooling induced strain localization in carbonate mylonites within a large scale shear zone glarus thrust switzerland abstract the glarus thrust switzerland offers a great field example of strain localization under retrograde conditions along the thrust mylonitic microfabrics are characterized by a temperature stress controlled balance of grain size reducing mechanisms and grain growth consequently mean grain sizes decrease along the thrust with decreasing metamorphic conditions and towards the thrust contact in an opposite manner calcite twin densities increase towards the contact cpos are strongest between 0 5 and 15 m away from the thrust but become generally weaker in the last centimeters where also cataclasites occur the cpo weakening and grain size reduction towards the shear zone point to a change from predominant dislocation creep to granular flow finally ending in cataclastic deformation the microfabric changes correlate with a decrease in 13c and 18o towards the thrust contact indicating the presence of fluids during cycles of brittle and plastic deformation based on the microfabric changes variations in stable isotopes and cross cut relationships a subdivision into a low and high temperature shear zone can be made the microfabric modifications resulted from changes in deformation conditions due to ongoing thrusting and exhumation induced cooling promoting further strain localization of an existing high strain shear zone

response of the ganges dispersal system to climate change a source to sink view since the last interstade the forcing of sediment dispersal systems by climate is widely accepted but there remains disagreement on the general responses to climate change such as how resulting signals propagate downstream and ultimately how they are preserved in the stratigraphic record towards a better understanding of these issues this paper presents a comprehensive overview of ganges dispersal system behavior since the last interstade which reveals major coeval responses to changes in the south asian monsoon at 3000 km from its mountain headwaters to deep sea fan the ganges dispersal system is immense and yet shows tight coupling between source area catchment basin and coastal and marine depocenters furthermore system wide responses and downstream transfer of the signal appear to occur at least as fast as current temporal resolution of 1 2 ky this tight linkage of source to sink components is considered a function of the southwest summer monsoon s overwhelming control on regional hydrology about 80 of the ganges discharge and 95 of its sediment load are delivered to the margin during only 4 months making the system extremely sensitive to this seasonal forcing in addition the regional scale and distribution of the monsoon weather system means that changes in atmospheric circulation affect the entire drainage basin rather than local subcomponents finally despite its present intensity strength of the summer monsoon has varied significantly over the past 150 ky under orbitally driven changes in insolation and global glacial boundary conditions the resulting changes in precipitation both well above and below modern values have forced system wide responses ranging from glacier advance retreat to sediment fluxes to the margin and deep sea fan the overall conclusions are 1 that this immense dispersal system responds to multimillennial scale 104 years climate change in a system wide and largely contemporaneous manner and 2 that major sedimentary signals can be transferred rapidly from source to sink with little apparent attenuation furthermore these acute responses to climate change have produced sedimentary stratigraphic features that diverge from traditional sequence models in their nature and timing

strontium carbon and oxygen isotope compositions of marbles from the cycladic blueschist belt greece the cycladic blueschist belt greece is mostly submerged below sea level and regional correlations are difficult to establish marbles are widespread within the belt and locally used as marker horizons to subdivide monotonous schist sequences however owing to the lack of distinctive petrographic characteristics the marbles have not been used for island to island correlations this study aims to investigate the potential of sr c and o isotope compositions of marbles as a tool for unravelling the litho and or tectonostratigraphic relationships across the cycladic islands and as a proxy for the time of sediment formation for this purpose we have studied metamorphic carbonate rocks from the islands of tinos andros syros sifnos and naxos identical 87sr 86sr values for certain marble horizons occurring on tinos andros and sifnos are interpreted to document coeval regional carbonate precipitation the 87sr 86sr values of the apparently least altered samples intersect the seawater curve multiple times within the most likely time interval of original carbonate precipitation 240 ma as indicated by previously published ion probe u pb zircon data and thus an unequivocal age assignment is not possible very broad temporal correlations are possible but more subtle distinctions are not feasible on andros the overlapping sr isotope values of marbles representing the lowest and highest parts of the metamorphic succession are in accordance with a model suggesting isoclinal folding or thrusting of a single horizon or very fast sedimentation in contrast distinct 87sr 86sr values for samples from tinos representing different levels of the metamorphic succession suggest that these rocks represent a temporal succession and not the tectonic repetition of a single horizon based on sr o and c isotope characteristics alone the time equivalence of marbles occurring on different islands could not be documented unambiguously however by using various combinations of these parameters some occurrences can be discriminated from the overall sample population the new data further accentuate the general potential of coupled sr c and o isotope characteristics for identification of archaeological provenance and complement existing datasets for aegean marbles

channel profiles around himalayan river anticlines constraints on their formation from digital elevation model analysis 1 we present a comparison between measured and numerically modeled channel profiles of rivers in two important drainage basins of central nepal the kali gandaki and the arun drainage basins modeled channel profiles are based on a simple stream power approach using best fit exponents defining the nonlinearities in the relative contributions of local channel gradient and water flux to erosion rate our analysis of the stream power in the whole river network confirms the work of other authors that a 50 to 80 km wide zone roughly corresponding to the high himalayan topography is subjected to rapid rock uplift we suggest a model where the uplift of this zone is driven by erosion and isostatic response so that centers of maximum uplift are located within the main channels of the north south draining rivers we also suggest that the rate of uplift slows down with increasing distance to the main channels such a spatial distribution of the uplift leads ultimately to the formation of river anticlines as observed along all major himalayan rivers we propose that the formation of river anticlines along south draining himalayan rivers was accelerated by a sudden increase of the drainage area and discharge when the rivers captured orogen parallel drainages on the north side of the range this may follow successive headward cutting into the tibetan plateau the model is confirmed by differences between main channels and east west running tributaries time dependent numerical models predict that capture events cause strongly elevated erosion rates in the main channel

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

resetting of oxybarometers and oxygen isotope ratios in granulite facies orthogneisses during cooling and shearing adirondack mountains new york the petrography petrology and oxygenisotope geochemistry of granulite facies granitic and syenitic orthogneisses of the diana and stark complexes adirondack mountains new york show that the extent and nature of resetting of isotopic and mineralogic systems is highly variable there is a strong correlation between retrogression and shearing and the rocks may be divided texturally into 1 unsheared lithologies that preserve little retrogressed pyroxene or hornblendebearing peak metamorphic mineralogies and 2 sheared rocks that underwent retrogression marked by the growth of late biotite in centimetre to metre wide shear zones after the peak of metamorphism oxygen fugacities in the unsheared lithologies were estimated for reintegrated mineral compositions from magnetiteilmenite mt ilm and ferrosilite magnetic quartz fs mt qtz equilibria mt ilm yields logfo2mt ilm values of 15 9 to 17 6 0 6 to 1 3 log units below the fayalite magnetite quartz buffer fmq and temperatures of 670 745 c that agree with those from other geothermometry and phase equilibria studies these data suggest that aside from oxyexsolution of ilmenite from magnetite the fe ti system underwent only minor resetting during cooling and the fe ti oxides yield good estimates of peak metamorphic temperatures and fo2 in unsheared ilmenite magnetite orthopyroxene quartz assemblages values of logfo2mt ilm are lower than logfo2fs mt qtz by an average of 0 6 when the orthopyroxene activity model of sack and ghiorso is used minor resetting of the fe ti oxides analytical errors and errors in the placement of end member reactions probably account for this relatively small difference in fo2 values whole rock 18o values of unsheared diana and stark lithologies range from 4 0 to 10 3 reflecting pre regional metamorphic oxygen isotope ratios peak metamorphic minerals preserve high temperature oxygen isotope fractionations and in many samples the effective diffusion of oxygen in minerals ceased at higher temperatures than predicted from wet experimental diffusion data these data suggest that the rocks did not contain an aqueous fluid phase during cooling the combination of petrologic isotopic and textural data also permits a detailed study of shearing and retrogression ilmenites in the sheared lithologies underwent greater degrees of hematite loss than in the unsheared rocks resulting in logfo2mt ilm values as low as 24 1 3 1 log units below fmq and mt ilm temperatures that are up to 175 c below regional estimates sheared rocks also have higher 18o values up to 13 3 during shearing 18o values of biotite k feldspar and magnetite reset readily while the degree of isotopic resetting of quartz correlates with the intensity for recrystallization

the stable isotopic evolution of a metamorphic complex naxos greece a detailed study of the stable isotope composition of pelites amphibolites and marbles from the m2 metamorphic complex on naxos is presented the low grade rocks of this metamorphic complex have isotopic compositions typical of metasedimentary rocks whilst those at high grades have values typical of igneous rocks the isotopic compositions of rocks at intermediate grades vary smoothly between these two end members this variation is shown to result from the superimposition of at least two fluid flow events on a pre existing isotopic gradient the contrast between the observed seemingly simple mixing trend and the complexity of the isotopic history of these rocks has important implications for quantitative studies of fluidrock interactions

mechanisms of oxygen isotopic exchange and isotopic evolution of 18 o 16 o depleted periclase zone marbles in the alta aureole utah insights from ion microprobe analysis of calcite oxygen isotope ratios have been measured by ion microprobe and millimeter scale dental drill along detailed sampling traverses across the boundary between periclase bearing 18o 11 8 and periclase free 18o 17 2 marble layers in the periclase per zone of the alta stock aureole utah these data define a steep coherent gradient in 18o that is displaced a short distance 4 cm into the periclase free cal fo layer sem and ion microprobe analyses show two isotopically and texturally distinct types of calcite at the grain scale clear well polished calcite grains are isotopically homogeneous within analytical uncertainty 0 27 2sd more poorly polished pitted texturally retrograde turbid looking calcite has lower and more variable 18o values and replaces clear calcite along fractures cleavage traces or grain boundaries despite significant lowering of the 18o values in calcite throughout both layers during prograde metamorphism ion microprobe analyses indicate that individual clear calcite grains are now isotopically homogeneous across the entire gradient in 18o diffusion calculations indicate that conservative time scales required for isotopic homogenization of calcite grains by volume diffusion 30 000 62 000 years at 575 600 c exceed significantly the timescale 1 250 years estimated for the prograde development of the 18o gradient at the boundary between these two marble layers the ion microprobe data and these diffusion calculations suggest instead that surface reaction mechanisms accompanying recrystallization are responsible for the observed oxygen isotope homogeneity of these calcite grains thus the ion microprobe data are consistent with the formation of calcite in oxygen isotope exchange equilibrium with infiltrating fluid during prograde reaction and recrystallization

deep fluid circulation in fault zones massive fluid circulation in retrogressive ductile shear zones is a well established but poorly understood phenomenon in some cases surface derived fluids which must initially have been at hydrostatic pressures can be shown to have entered shear zones in which fluids would normally be expected to be at lithostatic pressure in these circumstances thermal convection is an unlikely driving force for fluid movement underthrusting of a surficial fluid reservoir beneath shear zones is a viable mechanism in some cases but not for metasomatic shear zones in the pyrenees where insufficient underthrusting has occurred seismic pumping provides an alternative mechanism to explain the paradox of fluid access into ductile shear zones a kinematic analysis of a hypothetical fault zone shows that stress and dilatancy cycles will be out of phase above and below the frictional quasiplastic transition if this effect is sufficiently large hydraulic gradients may force fluid downward across the transition immediately after earthquake rupture through highly permeable microcrack networks between earthquake cycles plastic creep in mylonites will overprint microcrack networks increase fluid pressure and promote slow upward movement of fluid at low permeability for smaller shear zones such as those in the pyrenees seismic pumping could occur down a shallow decollement with subsequent upward fluid flow through shear zones in the hanging wall of the decollement

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

diffusional isotopic exchange across an interlayered marble schist sequence with an application to tinos cyclades greece marble schist contacts are frequently characterized by fine scale interlayering which prevents the application of semi infinite layer width assumptions to advection diffusion models of isotope profiles using a finite layer width boundary condition we show that the minimum width w of a layer required in order that diffusional exchange at both boundaries will not mutually interfere is given by the relation w k dt 1 2 where d is the effective diffusion coefficient t is the duration of the diffusion and k is a constant determined by the initial compositional step and the noise i e natural homogeneity and or analytical accuracy when this condition is not satisfied a solution of the diffusion equation for a multilayer transition zone containing several schist and marble layers of different finite widths is applicable application of this refinement of the diffusion model to an oxygen isotope profile from tinos cyclades greece gives 10 4 dt 10 2 m2 this dt range and a dt value of 10 1 m2 previously determined for sifnos indicates that rocks undergoing the oligocene miocene greenschist facies overprint of eocene high pressure metamorphic rocks in the cyclades were characterized by extremely low porosities permeability perpendicular to marble schist contacts was sufficiently low to prevent advection into the marbles correspondingly it is suggested that the layer parallel schistosity permitted infiltration of the fluids required for the hydration reactions of the metamorphic overprint

evolution of the blueschist and greenschist facies rocks of sifnos cyclades greece the metamorphism on the island of sifnos is characterized by the eocene development of a coherent highpressure blueschist terrane and an early miocene greenschist facies overprint this study documents the metamorphic evolution of the blueschist assemblages still preserved in the northern parts of the island and their subsequent transformation into greenschists in the central and southern parts the oxygen isotope geothermometry is based on calibrations for quartz pyroxenes and magnetite matthews et al 1983a augmented by revised calibrations for the minerals muscovite qz mu 1 55 106 t 2 epidote qz ep 1 56 1 92 ps 106 t 2 and rutile qz ru 4 54 106 t 2 oxygen isotope analyses of minerals from the blueschist unit of northern sifnos give consistent fractionations which are independent of rock type an average temperature of 455 c was obtained although the scatter in temperatures deduced from the various geothermometers suggests that equilibration occurs under slightly changing physicochemical conditions analyses of minerals and whole rocks shows that pervasive equilibration in the presence of a common metamorphic fluid has not occurred the minerals and whole rocks of the greenschists of central sifnos are systematically enriched in 18o relative to the blueschist assemblages chemical data indicate that the greenschist overprint was accompanied by a metasomatic enrichment of ca2 and co2 the petrologic isotopic and chemical evidence favour a metamorphism governed by the infiltration of 18o co2 enriched aqueous solutions it is reasonable to assume that this is connected with the miocene magmatic activity observed throughout the cyclades the marbles separating the blueschist from the greenschist unit probably acted as barriers to fluid infiltration into the blueschists and were responsible for their preservation the pressure of the blueschist metamorphism is estimated at 14 2 kbar corresponding to a depth of ca 50 km the structural style and stratigraphy of sifnos are suggestive of the subduction of a continental margin sequence it is clear that the considerable tectonic depression may be associated with continental collision and underthrusting

thermal and kinematic modeling of bedrock and detrital cooling ages in the central himalaya 1 we introduce a new method that convolves detrital mineral cooling ages with digital elevation models to test numerical models of erosion in collisional orogens along a trans himalayan transect in central nepal we develop a kinematic and thermal model to predict variations in bedrock cooling ages in modern himalayan topography the model assumes a thermal steady state and utilizes a simple ramp and flat style decollement representing the main himalayan thrust the model also assumes a topographic steady state such that overthrusting is balanced by erosion to maintain a constant topographic profile erosion rates display strong spatial variations as a function of the angle between the slope of the topographic surface and the trajectories of rock particles approaching the surface to predict the detrital cooling age signal we combine the distribution of bedrock cooling ages within a catchment with the rate of erosion and distribution of muscovite predicted cooling age distributions are compared with detrital 40ar 39ar muscovite data to assess varying tectonic and erosion scenarios such cooling age distributions are very sensitive to how much of the total plate convergence is expressed as erosion of the overthrusting plate the best fit model assigns 4 6 km myr 1 of overthrusting equivalent to as much as 1 5 2 km myr 1 of vertical erosion to the asian plate although a trade off exists between ramp geometry along the decollement and the best fit rate only a narrow range of ramp dips decollement depths and erosionally compensated overthrusting rates are compatible with the observed detrital ages

petrology of marble and peridotite in the seiad ultramafic complex northern california usa peridotite and infolded marble of the seiad ultramafic complex were recrystallized in the upper amphibolite facies as part of the regional progressive metamorphism of the rattlesnake creek terrane field relations including the occurrence of metarodingites and metasomatic zones between dissimilar rock types demonstrate that the metasediments and serpentinized ultramafic rocks were juxtaposed prior to regional barrovian metamorphism temperatures are estimated to have reached 760 800 c at pressures of 7 8 kbar during the peak of metamorphism four low variance parageneses have been identified within a small 3 km2 area of the complex which may reasonably be assumed to have formed under the same p and t conditions isobaric t xco2 diagrams of appropriate equilibria are presented for three different internally consistent sets of thermodynamic data despite the seemingly small numerical differences between the standard state thermodynamic properties of the data sets only one diagram allows the four observed assemblages to coexist within a reasonable temperature range all three phase diagrams require differences in fluid composition on the scale of a thin section strong evidence for effective control of pore fluid composition by local mineral reactions during metamorphism

tectonic footprints and landscape evaluation along kulur river valley kumaun lesser himalaya india abstract tectonic reactivation along the major boundary thrusts and subsidiary thrust faults in the himalaya during the quaternary period has resulted in the rejuvenation of the landforms considering the role of neotectonic activity in the hazardous kumaun region we aim to study the neotectonically formed landscape along the kulur river valley a non glacier fed tributary of the saryu river in the zone of the berinag thrust bt the field evidences encompassing a variety of geomorphic indicators e g unpaired fluvial terraces palaeo river channels alluvial fans active and stabilized landslides lineaments waterfalls alignment of springs deeply dissected hills straight meandering course of rivers streams v shaped valleys triangular fault facets and water logged river ponding along with integrated values of eight morphometric parameters and stream steepness index ks indices characterize the modification of landscape in the kulur river valley the computed morphometric parameters in the kulur river drainage and its tributaries show that the basin has been tilted and uplifted forming v shaped valleys along with deformed and disequilibrium longitudinal profile thereof suggesting it to be controlled by lithology and tectonics based on the response of active tectonics in form of geomorphic features and quantitative measurements of river channels the entire basin has been divided into three segments in which the northern and southern segments are active compared to the middle sector a possible nne ssw trending lineament fault running parallel to the kulur river has been observed in the upper catchment and is characterized by fluvial terraces river ponding and deflection and offsetting of drainage with rectangular pattern etc this may have given rise to the widening and straightening of river courses which provide the favorable room for river ponding resulting in deposition of about 2 m thick lacustrine mud deposit

isotopic and petrological evidence for the infiltration of water rich fluids during the miocene m2 metamorphism on naxos greece abstract a detailed carbon and oxygen isotopic study in conjunction with petrological work has been carried out across calcite dolomite marble layers in the high grade metamorphic sequence on the island of naxos greece the purpose of this study is to examine fluid flow during the miocene barrovian metamorphic event individual marble bands show two dominant styles of isotopic alteration from core values of 22 to 29 in 18o and 1 to 3 in 13c firstly contacts between the marble bands and surrounding pelitic rocks have altered isotopic ratios across a metre wide boundary layer the isotopic values of the marble along the contacts drop to 15 to 17 in 18o and 1 to 5 in 13c secondly there is a drop in the isotopic composition of the marbles along vein networks associated with the development of calc silicates the isotopic compositions in these veins drop to 14 to 16 in 18o and 3 to 4 in 13c cross cutting relationships observed between these two alterations allow the relative timing of infiltration to be determined the development of boundary layers is shown to result from the infiltration of fluids with isotopic signatures of 12 to 16 in 18o and 3 to 12 in 13c and an xco2 less than 0 3 these fluids are derived from dehydration of graphite bearing pelites during the prograde metamorphism these conclusions are at odds with those of previous workers who suggested that the prograde metamorphism was a result of the pervasive influx of mantle derived fluids with xco2 greater than 0 5 the alteration associated with vein networks results from peak to post peak infiltration of fluids which drive decarbonation reactions at least some of these fluids have an xco2 less than 0 05 but this is obscured by the production of co2 during the decarbonation reactions these fluids were most probably produced from the crystallising partial melts formed during the prograde metamorphism these infiltrating fluids are thought to have 18 o 10 and 13c of 5 to 7

textural and isotopic development of marble assemblages during the barrovian style m2 metamorphic event naxos greece a detailed petrological analysis of the marble assemblages observed within the m2 metamorphic complex on naxos is presented two distinct periods of mineral growth are documented the first is associated with prograde m2 metamorphism and the second with retrograde m2 metamorphism occurring during ductile extensional thinning of the complex the textural and miner alogical characteristics and the carbon and oxygen isotope compositions of each generation are described and the p t xco2 conditions at which these two mineral generations were stable and the compositions of the fluids present during metamorphism are characterised whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution the retrograde mineral generation is shown to have grown as a result of the infiltration of a water rich fluid phase that transported silica al2o3 na2o and feo into the host rocks this observation together with the stable isotope compositions of the retrograde calcite and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas t 600 c of the metamorphic complex suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures the existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on naxos because many of the unusually low 18o compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde m2 fluids rather than with prograde fluids

low angle faults above and below a blueschist belt tinos island cyclades greece new observations from the island of tinos greece allow a better definition of the structural position of the alpine eocene blueschist belt exposed in the islands of the aegean sea these blueschists over a significant part of the aegean sea are delimited from below by a low angle thrust fault while from above they are delimited by a low angle normal type fault which omits a substantial crustal interval both underlying and overlying rocks were not affected by the high metamorphism the rapid uplift and exhumation of the high rocks was therefore mainly the result of fault movements rather than erosion and whole crust uplifting the low angle normal fault apparently had a major role in the uplift of the blueschists

high integrated fluid rock ratios during metamorphism at naxos evidence from carbon isotopes of calcite in schists and fluid inclusions calcite in schists of the metamorphic complex at naxos is depleted both in 13c and in 18o with respect to massive marbles this effect is attributed to isotope exchange with circulating co2 rich fluids which had an x text co text 2 0 5 according to fluid inclusions the carbon isotopic composition of the calcites is close to equilibrium with fluid inclusion co2 at metamorphic temperatures mass balance calculations assuming initial 13c values of 0 for calcite and 5 for the fluid give integrated fluid rock volume ratios between 0 1 and 2 0 such high fluid rock ratios are supported by observations on the distribution of co2 h2o ratios of fluid inclusions carbon isotopic compositions of fluid inclusion co2 and oxygen isotope systematics of silicates

ion probe and fluid inclusion evidence for co seismic fluid infiltration in a crustal detachment we have investigated the geochemical pattern of fluid infiltration in the extensional detachment of tinos island cyclades greece ion microprobe o isotope analyses and fluid inclusion studies have been conducted in strain fringes developing around pyrite blasts in the mylonite of the shear zone micro scale traverses in quartz and calcite fibres show that 18o increases from 17 18 to 20 21 in 1 mm towards the blast drops of 3 in 200 m then rises again in the direction of growth 18o variations are interpreted as transient influxes of exotic fluids into the shear zone between periods of closed system buffering by the host rock fluid inclusions trapped in the fibres show fluctuating salinities 0 4 wt nacl eq and densities that reflect drops of the pore pressure from lithostatic 1 to hydrostatic 0 4 values during fringe growth isotopic and microthermometric data are consistent with models of seismic pumping developed for compressive shear zones we therefore suggest that co seismic pore pressure variations developed suction forces sufficient to drive large scale fluid migration in the tinos detachment as in convergent tectonic settings

relation between the intensity of deformation and retrogression in blueschist metapelites of tinos island greece evidenced by chlorite mica local equilibria the late greenschist deformation of the cycladic blueschists unit on tinos island evolves along a ne sw gradient of non coaxial strain across a major extensional shear zone deformation is more intense and the greenschist overprint is also more severe close to the shear zone that separates the cycladic blueschists from the upper ophiolitic unit in the ne of the island the compositional variability of chlorite and k white mica kwm in metapelites sampled along a ne sw cross section is characteristic of their p t conditions of crystallization and is mainly characterized by variations of their si al fe and mg contents due to the tschermak substitution siiv fe mg vi alvialiv multi equilibrium p t estimates based on the assumption of local equilibrium indicate that each sample recorded a part of the p t history which depends on the distance to the contact to the main shear zone i e the intensity and the pattern of deformation the combination of p t estimates obtained from all the samples collected along the transect provides a continuous p t path which is composed of two parts it provides insights on the syn and post orogenic exhumation for some of the cycladic blueschists in particular we could distinguish two stages in the exhumation process a first stage in the blueschist facies occurred along a cold p t path during the construction of the hellenides the second exhumation stage occurred along a warmer p t path during the formation of the aegean sea between the two stages of exhumation there is a thermal reequilibration of the crust and a partial thermal overprint of the blueschist parageneses

the late alpine evolution of an extensional shear zone naxos greece the mid miocene structural evolution of the metamorphic complex on naxos involved deformation in a kilometre scale low angle ductile shear zone the structures described are consistent with exhumation of the metamorphic complex during crustal extension after and possibly during localized high temperature barrovian style metamorphism non coaxial fabrics developed throughout the structural history indicate that upper levels were transported to the north during ductile extension this shear sense is opposite that inferred previously for the development cordilleran style metamophic core complexes in the cvclades ductile deformation was accompanied during its later stages by e w directed compression

single grain argon laser probe dating of phengites from the blueschist to greenschist transition on sifnos cyclades greece measurements of 40ar 39ar age spectra on single white mica crystals of tertiary age is a new means of obtaining detailed geochronological information of alpine blueschists internal consistency of the data set as well as excellent agreement with previous conventional k ar results demonstrates that this new technique can be used with confidence to obtain information on the thermal evolution of young metamorphic belts

strain dependent variation of microstructure and texture in naturally deformed carrara marble this study investigates the microstructure and texture variations across a mm scale shear zone in carrara marble of the alpi apuane italy the microstructures have been investigated for grain size texture and shape fabrics textures have been measured with computer integrated polarization microscopy cip and electron back scattered diffraction ebsd separating porphyroclast and recrystallized grains the deformation which post dates an earlier deformation phase and subsequent annealing is strongly localized the microstructures and textures change across the shear strain gradient and are interpreted to preserve a time sequence of progressive stages of deformation the bulk shear strain rate is estimated to be about 10 11 sec 1 at deformation temperatures of approximately 325 c 30 c the protomylonite is characterized by a core mantle structure with a bimodal grain size distribution which changes gradually to a completely dynamically recrystallized microstructure with a unimodal grain size distribution in the mylonitic center of the shear zone core mantlestructures are produced by dominant rotation recrystallization accompanied by some grain boundary migration the microstructural transition from protomylonite to mylonite coincides with a change in texture with increasing strain the single c axis maximum of an earlier inherited texture in the protomylonite is replaced by a similar texture in a different orientation maximum normal to the shear plane which is consistent with dominant basal hai and r h 2201i slip the microstructural and textural variations depend on the proportion of recrystallized grains as dynamic recrystallization progresses with finite strain the texture development is finite strain dependent the comparison of the microstructures and textures to other natural and to experimental examples explains the progressive change of the texture and demonstrates the texture evolution produced by dynamic recrystallization 2006 elsevier ltd all rights reserved

fission track evidence for quaternary uplift of the nanga parbat region pakistan the north striking nanga parbat haramosh massif protrudes into the northwestern himalaya along the axis of a great syntaxis1 2 fig 1 where the hindu kush karakorum and himalayan ranges converge as the indus suture zone3 enters this region from the east it bifurcates into two branches encircling what may be a docked island arc terrane4 the southern branch the main mantle thrust crops out on both flanks of the nanga parbat massif forming a tight structural loop5 this massif and the adjacent terrane contain some of the highest peaks in the himalaya nanga parbat and the indus river located just 20km away define the world s greatest continental relief 6 930 m we report here the discovery of unexpectedly young sphene zircon and apatite fission track dates from the nanga parbat haramosh massif these dates as low as 1 3 myr for zircon and 0 4 myr for apatite imply that during the pleistocene the nanga parbat region was uplifted and eroded at nearly 1 cm yr 1

petrology of upper amphibolite facies marbles from the east humboldt range nevada usa evidence for high temperature retrograde hydrous volatile fluxes at mid crustal levels

fluids and thrusting abstract recent studies of the structure of the continental crust by cocorp and birps have shown that major thrust structures in the lower crust are ubiquitous plate tectonic processes of continental crust destruction or construction at sites where subduction or collision occurs the himalayas or the andes involve thrusting of continental materials or ocean crust beneath continents and local overthrusting may accompany transcurrent motion in all such cases massive fluid flow must occur as first stressed by m k hubbert and w w rubey thrusting mechanisms require that fluid pressures are close to or greater than lithostatic pressures when thrusting occurs compaction of the underplate must occur rapidly expelling pore water crustal thickening leads to gradual heating of the underplate with prograde metamorphism near the top and even melting at the base if the overthrust plate is thick and hot at the base retrograde metamorphism will occur at the base of the overthrust plate and rising fluids will encounter inverted thermal gradients in such a region veins need not occur but leaching phenomena may dominate if an underthrust plate is hydrated and or contains sedimentary aquifers large fluid volumes are expelled through shear zones into the overthrust plate the scale of fluid release processes can be large thus in thin skinned tectonics where the overthrust plate is 10 15 km thick induced fluid release can easily reach 4 109 g m 2 of thrust surface the flow of such fluids will be controlled by the thrust surface and lithology both of which will influence hydraulic fracture mechanisms and spacing of fractures the chemistry of thrust derived fluids may be highly variable depending on lithology and the time constants of thrusting vertical thermal and redox environments will be similarly dependent in the subduction process impressive quantities of fluids must pass back up the thrust surface and such fluids have recently been directly observed during drilling dewatering of spilites serpentinites and sediment layers of the underthrust oceanic lithosphere must produce massive fluid flow back to the surface but some of these fluids may form hydrated minerals in the overlying mantle and at great depth flux mantle melting extreme metasomatism in blueschist belts must result from such fluids a case of particular interest involves the cessation of subduction when a high level slab reaches thermal equilibrium in general flow regimes in the thrust and fault zones associated with collisions follow a sequence from conditions of high t p with locally derived fluids at low water rock ratios during initiation of the structures to high fluxes of reduced metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs later in the tectonic evolution and at shallower crustal levels there may be incursion of oxidizing near surface fluid reservoirs into the faults these fluids may have extremely low 18o values where mountain ranges form on rebound faults and high altitude depleted fluids penetrate down the rebound structure extensive mineralization may be associated with such thrust derived fluids examples which will be discussed include the mother lode au deposits of california u s a and the large u deposits of lagoa real brazil

the effect of water on recrystallization behavior and grain boundary morphology in calcite observations of natural marble mylonites fluids are inferred to play a major role in the deformation and recrystallization of many minerals e g quartz olivine halite feldspar in this study we sought to identify the effect of fluids on grain boundary morphology and recrystallization processes in marble mylonites during shear zone evolution we compared the chemistry microstructure and mesostructure of calcite marble mylonites from the schneeberg complex southern tyrole italy to that from the naxos metamorphic core complex greece these two areas were selected for comparison because they have similar lithology and resemble each other in chemical composition in addition calcite dolomite geothermometry indicates similar temperatures for shear zone formation 279g25 8c schneeberg complex and 271g15 8c naxos high grade core however the two settings are different in the nature of the fluids present during the shear zone evolution in the schneeberg mylonites both the alteration of minerals during retrograde metamorphism in the neighboring micaschists and the existence of veins suggest that aqueous fluids were present during mylonitization the absence of these features in the naxos samples indicates that aqueous fluids were not as prevalent during deformation this conclusion is also supported by the stable isotope signature observations of broken and planar surfaces using optical and scanning electron microscopes did not indicate major differences between the two mylonites grain boundaries in both settings display pores with shapes controlled by crystallography and have pore morphologies that are similar to observations from crack and grain boundary healing experiments grain size reduction was predominantly the result of subgrain rotation recrystallization however the coarse grains inside the wet protomylonites schneeberg are characterized by intracrystalline shear zones q 2005 elsevier ltd all rights reserved

stable and sr isotope evidence for fluid advection during thrusting of the glarus nappe swiss alps at the glarus thrust in the swiss helvetic alps permian verrucano siltstones are allochthonously superimposed over tertiary flysch with an intermediate about 1 metre thin layer of intensively deformed calcmylonite of probable mesozoic provenance the h o c and sr isotope compositions of minerals from the calc mylonite and strongly mylonitized verrucano siltstones were determined in order to assess 1 equilibrium disequilibrium relationships 2 isotopic composition of the fluid phase its provenance and water rock ratios 3 sources of sr in the calc mylonite 4 deformation temperatures the isotopic composition of cale mylonite micro samples from five sites along the thrust varies from 22 to 12 and 2 to 10 for 18o and 13c respectively all samples are 18o depleted by up to 14 relative to the presumed marine helvetic carbonate protoliths 18o 25 4 2 a pronounced geographic trend of 18o depletion from 22 in the north to 12 in the south is observed in calc mylonites 87sr 86sr ratios range from typical mesozoic marine carbonate protolith signatures 0 708 0 005 to more radiogenic values as high as 0 722 a variable contribution of radiogenic 87sr to the calc mylonite is though to reflect interaction with fluids that aquired their sr from the hercynian granitic basement chlorites and muscovites from the calc mylonite and verrucano have uniform 18o values but display d values from 40 to 147 the d enriched values correspond to the primary metamorphic or formational fluids expelled during thrusting whereas the d depleted samples reflect selective h isotope exchange with meteoric fluids during uplift of the alpine belt the isotopic composition of the calc mylonites requires exchange with 18o depleted 87sr enriched fluids at very high water rock ratios possible sources for these are dewatering of the underlying flysch and or metamorphic fluids or formation brines expelled along the thrust from greater depth these could be derived from compaction and dewatering of the flysch in the northern part of the thrust in the south however where verrucano is thrust over 18o rich mesozoic carbonates the extreme 18o depletion of the calc mylonite has to be explained either by fluid advection within the verrucano hanging wall and thrust zone or alternatively by exchange with metamorphic fluids from greater depth expelled along the thrust microstructural evidence abundant veins stylolites breccias suggests that fluids played an important role in deformation and strain localization excepting albite all major components quartz chlorite muscovite calcite are both dynamically recrystallized and crystallized as secondary minerals in pressure shadows and syn mylonitic veins indicating that these minerals were potentially open to oxygen isotopic exchange during alpine metamorphism and thrust deformation within the mylonitized verrucano silstones isolated quartz chlorite and quartz calcite fractionations yield temperatures of around 320 c close to values obtained from calcite dolomite thermometry 355 c 30 and in agreement with the regional lower greenschist facies metamorphism quartz calcite and quartz albite fractionations indicate slightly lower temperatures around 250 c owing to selective lower temperature re equilibration of the calcite and albite during post peak metamorphism

catastrophic rock slope failures and late quaternary developments in the nanga parbat haramosh massif upper indus basin northern pakistan abstract the nanga parbat haramosh massif has some of the greatest relief on earth and highest measured rates of uplift denudation and river incision in bedrock many studies have sought to understand how its morphology relates to geotectonic evolution and glaciations however few catastrophic rock slope failures had been recognised and many of their impacts had been attributed to other processes recently more than 150 of these landslides have been found within a 100 km radius of nanga parbat 8125 m new discoveries are reported east north and west of nanga parbat along the indus streams most generated long run out rock avalanches that dammed the indus or its tributaries some impounding large lakes they initiated episodes of intermontane sedimentation followed by trenching and removal of sediment valley floor features record a complex interplay of impoundment and sedimentation episodes superimposition of streams in pre landslide valley floors and exhumation of buried features these findings depart from existing reconstructions of quaternary events a number of the rock avalanche deposits were previously misinterpreted as tills or moraine and their associated lacustrine deposits attributed to glacial lakes features up to 1000 m above the indus formerly seen as tectonically raised terraces are depositional features emplaced by landslides or erosion terraces recording the trenching of valley fill in landslide interrupted river reaches unquestionably tectonics and glaciation have been important but decisive and misread formative events of the holocene involve a post glacial landslide fragmented fluvial system the latter has kept valley developments in a chronic state of disequilibrium with respect to climatic and geotectonic controls accepted glacial chronologies are put in doubt particularly the extent and timing of the last major glaciation the pace and role processes in the holocene have been seriously underestimated

tectonic juxtaposition of blueschists and greenschists in sifnos island aegean sea implications for the structure of the cycladic blueschist belt abstract in the cyclades kilometre thick high pressure rock sequences displaying blueschist and eclogite facies mineral assemblages overlie a rock sequence which was thoroughly overprinted in the greenschist and amphibolite facies during its exhumation both rock sequences subducted and metamorphosed at high pressures in eocene times have been considered by previous workers to have been exhumed as a coherent rock unit in contrast it is suggested here that the preserved high pressure rock sequences were exhumed more rapidly and prior to the underlying greenschists significant metamorphic structural and geochronological discontinuities exist across the blueschist greenschist contact and field evidence suggests that the high pressure metamorphic rocks in sifnos are tectonically juxtaposed above the greenschists these two rock sequences were juxtaposed by a low angle fault subsequent to the oligocene miocene greenschist facies overprint published geochronological data and petrological criteria are used to show that the high pressure sequence cooled below 350 c when the rocks now immediately underlying it suffered a greenschist facies overprint at temperatures of ca 450 c the section inferred to absorb this temperature difference is now missing and it is suggested that it has been cut out by the low angle fault

the tectono metamorphic evolution of a dismembered ophiolite tinos cyclades greece the six exposures of the upper tectonic unit of the cycladic massif occurring on the island of tinos are shown to comprise a metamorphosed dismembered ophiolite complex the common stratigraphic section consisting of tens of metres thick tectonic slices of mafic phyllites overlain by serpentinites and gabbros is considered to have been derived by a combination of thrusting during obduction and subsequent attenuation by low angle normal faults all rock types show evidence of a phase of regional greenschist facies metamorphism which in the case of the phyllites is accompanied by penetrative deformation the greenschist facies metamorphism in gabbros is preceded by high temperature sea floor amphibolite facies alteration whereas in the serpentinites the antigorite forsterite greenschist facies assemblage overprinted an earlier low temperature lizardite serpentinite trace element patterns of the mafic phyllites and a harzbur gitic origin of meta serpentinites suggest a supra subduction zone ssz affinity for the ophiolitic suite 5 o values of phyllites gabbros and serpentinites range from 6 to 15 o model calculations indicate that such values are consistent with low temperature 50 200 c alteration of parent rocks by sea water at varying water rock ratios this would agree with the early low temperature mineralogy of the serpentinites but the early high temperature alteration of the gabbros would require the presence of o enriched sea water the following overall history is suggested for tinos ophiolitic slices 1 oceanic crust was generated at a supra subduction zone spreading centre with high temperature alteration of gabbros 2 tectonic distur bance its early hot stages recorded in an amphibolitic shear zone at the base of serpentinites brought the already cooled ultramafics into direct contact with sea water and caused low 7 serpentinization 3 tectonism after cooling involved thrusting which caused repetition and inversion of the original order of the oceanic suite 4 regional metamorphism of all the ophiolite components at greenschist facies conditions 450 c overprinted the early alteration mineralogy it was probably induced by continued thrusting and piling up of nappes the tinos ophiolite dated as late cretaceous and genetically related to other low pres sure rock units of the same age in the aegean differs in age and degree of dismemberment and metamor phism from ophiolites in mainland greece

impact of tectonics on drainage network evolution of suru basin kargil n w himalaya jammu and kashmir india the main objective of this paper is to work out quantitative measurement of various geomorphic parameters as well as analysis of geomorphic landforms to study the tectonic character of suru basin morphometric analysis being widely used to assess the drainage characteristics of the river basins has also been found to be a useful tool to delineate tectonically active zones a number of parameters including the mountain front sinuosity asymmetry factor transverse topography symmetry hypsometry longitudinal profile and the shape parameters have been used the low mountain front sinuosity values 1 4 indicate that the tectonic forces dominate over erosive activity also the asymmetry factor 66 98 suggests that the right side of the basin has experienced uplift with the development of unpaired river terraces hypsometric integral 0 96 convex up hypsometric curve and the gps data of year 2011 2013 indicate that the relief of the basin is high relative to mean is in youthful stage and actively uplifting at the rate of 2 18 0 99 mm year the shape parameters further suggest that the suru river basin having lower elongation ratio is indicative of elongate shape of basin with tectonic forces outpacing the erosion power area altitude analysis of the suru river basin indicates that about 72 of the area of the basin is steeply to very steeply sloping and 28 area is moderately to gently sloping the area altitude indicates 72 area of basin could slide when there is slight shift in terms of tectonic disturbance in addition to the geomorphic indices the field investigations reveal tectonically unstable character exhibit a complex topography and varied quaternary sedimentation the major geomorphic landforms viz alluvial terraces alluvial fans debris cone scree and talus cone at the foothills are present throughout the valley with tectonic structures like micro folds back tilted beds deeply incised valleys faults and tectonic deposits ophiolites indicating that the tectonic activity has affected the basin the synergized results of geomorphometry field investigations and gps data indicate that the suru basin is tectonically active and uplifting

model investigation of the influence of the crustal magnetic field on the oxygen ion distribution in the near martian tail 1 to investigate the influence of the martian crustal magnetic field on the acceleration and escape of the planetary ions in the near tail region the distributions of planetary oxygen ions are studied by means of test particle simulation in an electromagnetic environment created by a recent multispecies magnetohydrodynamics mhd simulation of the solar wind interaction with mars with crustal field included or excluded results under different crustal field conditions are compared to determine the effects of crustal field it is found that when crustal field is present draped magnetic field lines are replaced by closed field lines in the near tail region and the electric field is also intensified because of the hall effect as a result the oxygen ion distribution reveals distinct stream structures in the tail region when crustal field is included with one hot stream at the central tail and two cold streams at the flank of the tail some energetic ions inside the hot stream are accelerated toward the planet instead of escaping downstream

evolution of hydrothermal regime along a crustal shear zone tinos island greece 1 structural cathodoluminescence and sims 18o analyses of quartz calcite veins are combined to constrain the evolution in space and time of fluid infiltration in an exhuming detachment shear zone tinos island cyclades greece careful description of vein arrays shows that the plumbing system evolved into an interconnected network just beneath the ductile to brittle transition microtextures of quartz and calcite infilling veins display deformed relics and newly precipitated grains high resolution 18o mapping in relics yields a steady quartz calcite fractionation of 2 at 400 c whereas fractionation increases in neograins from 2 to 5 in 190 m toward the fault or a 150 c temperature fall cooling is associated with a shift of fluid stable isotope signature from 15 to 0 beneath the detachment results are interpreted as advective removal of heat by massive infiltration of surface derived fluids over depths of 10 15 km fluid penetration was promoted by the coalescence of late ductile early brittle veins as the exhuming footwall crossed the ductile brittle transition only small amounts of fluids penetrated the ductile crust beneath the transitional rheology

regional analysis of bedrock stream long profiles evaluation of hack s sl form and formulation and assessment of an alternative the ds form the equilibrium form of the fluvial long profile has been used to elucidate a wide range of aspects of landscape history including tectonic activity in tectonic collision zones and in continental margin and other intraplate settings as well as other base level changes such as due to sealevel fluctuations the hack sl form of the long profile which describes a straight line on a log normal plot of elevation normal versus distance logarithmic is the equilibrium long profile form that has been most widely used in such studies slope area analysis has also been used in recent years we show that the sl form is a special case of a more general form of the equilibrium long profile here called the ds form that can be derived from the power relationship between stream discharge and downstream distance and the dependence of stream incision on stream power the ds form provides a better fit than the sl form to river long profiles in an intraplate setting in southeastern australia experiencing low rates of denudation and mild surface uplift we conclude that if an a priori form of the long profile is to be used for investigations of regional landscape history the ds form is preferable in particular the ds form in principle enables equilibrium steepening due to an increase in channel substrate lithological resistance parallel shift in the ds plot to be distinguished from disequilibrium steepening due to long profile rejuvenation disordered outliers on the ds plot slope area analysis and the slope distance ds approach outlined here are complementary approaches reflecting the close relationship between downstream distance and downstream catchment area copyright 2006 john wiley sons ltd

crustal scale geometry and kinematics of late orogenic extension in the central aegean cyclades and ewia island abstract the aegean continental domain is known to be the site of widespread back arc extension since at least the middle miocene overprinting structures related to the mesozoic cenozoic hellenic orogeny features attributed to early thrusting include the overall ductile deformation within two broad belts that have suffered hp lt metamorphism across the aegean this study summarizes the results of a structural study in the central aegean area cyclades and evvia island examining in particular the relationship between ductile and brittle deformation on a regional scale extension appears to be responsible for most of the ductile deformation within hp rock units that have experienced penetrative greenschist facies and higher grade metamorphic overprinting on each island studied progressive extensional deformation has occurred through the development of a major normal sense detachment zone down to depths of about 18 25 km the geometry of the extensional system on the scale of the central aegean is described taking into account the characteristic features of the regional scale ductile strain field at least two probably three subparallel major north dipping detachment zones are identified trending nw se in the northwestern cyclades and e w in the southeastern cyclades both with initial dips estimated at around 30 45 the present geometry of the extensional system implies that these detachment zones and related metamorphic core complexes interfere with each other two main evolutionary models are considered which can account for such a kinematic link between parallel detachment zones structural data favour the sequential development of synthetic major detachments zones in a direction opposite to the sense of dip of the detachments early oligocene lower miocene detachment type extension in the area studied is related to a late orogenic post thickening back arc setting

the interpretation of inverted metamorphic isograds using simple physical calculations several zones of major thrust faulting exhibit a juxtaposition of rocks of higher metamorphic grade over rocks of lower grade this configuration may indicate but does not require that temperature gradients were temporarily inverted near the fault we examine the physical conditions under which such a temperature inversion could occur the overthrusting of hotter rock on colder rock can cause a temporarily inverted gradient both above and below the fault only if the time taken to underthrust rock from the land surface to a given depth z on the fault is less than times the characteristic time for diffusion of heat through the block above the fault where is thermal diffusivity an inverted gradient cannot form without heat generation in the fault zone unless v z sin 100 where v is the rate of underthrusting in millimeters per year z is in kilometers and is the dip of the fault this simple criterion is sufficient to demonstrate that several examples of inverted metamorphic gradients cannot be explained simply by the thrusting of hot on cold rock without heat sources in the fault zone dissipative heating accompanying deformation can cause an inverted temperature gradient within and beneath the thrust zone but whereas the overthrusting of hot upon cold rocks cools the fault zone dissipation heats it thus the overthrusting of hot on cold rock and dissipative heating affect the temperature gradient and the maximum temperatures differently we show that the magnitudes of the inverted temperature gradient and of the maximum temperature above the inverted gradient yield independent estimates of the rate of dissipative heating discrepancy between these estimates implies that some additional process must have occurred such as the post thrusting disruption of the isograds if there is such a discrepancy the maximum temperature probably provides the more reliable estimate of the rate of heating at the fault we illustrate this analysis by applying it to reported inverted metamorphic zonation in the pelona schist the st anthony complex the mt everest region of the main central thrust and the olympos thrust petrological inferences of maximum temperatures depths of metamorphism and magnitudes of apparent inverted gradients imply that shear stresses of about 100 mpa accompanied thrust faulting in some of these regions and that some zones of inverted metamorphism have been tectonically thinned after the metamorphism occured

fluid rock interaction and thermal evolution during thrusting of an alpine metamorphic complex tinos island greece this study examines the fluid rock interaction and thermal evolution along a thrust that juxtaposes calcite rich marbles of high p t metamorphic unit of the attic cycladic massif greece on top of a lower grade dolomite marble unit the tertiary thrust represents a major phase of tectonic movement related to the decompression of the alpine orogen in the hellenides the stable isotope signatures of the thrust plane and adjacent sections of the footwall and hanging wall rocks are characterized by significant carbon and oxygen isotope depletions the depletion is most pronounced in calcite but is almost entirely missing in coexisting dolomite the isotopic patterns in the thrust zone can be explained by the infiltration of an externally derived water rich h2o co2 ch4 fluid x c x co 2 x ch 4 0 05 at water rock ratios on the order of 0 1 to 0 5 by weight the fluid induced calcite recrystallization is viewed as an important rheological control during thrusting the temperature evolution of the footwall hanging wall and mylonitic tectonic contact was determined by calcite dolomite solvus thermometry histograms of calcite dolomite temperatures are interpreted as indicating a heating of the footwall dolomite marble during the thrusting of the hotter upper plate conversely the hanging wall marble unit was cooled during the thrusting the calcite dolomite thermometry of the thrust plane gives temperatures intermediate between the initial temperatures of the lower and upper marble units and this leads to the conclusion that conductive heat transfer rather than fluid infiltration controlled the thermal evolution during thrusting

high si phengite records the time of greenschist facies overprinting implications for models suggesting mega detachments in the aegean sea in the lower main unit of the attic cycladic crystalline belt greece white mica geochronology rb sr k ar 40 ar 39 ar has established the timing of at least two metamorphic events well preserved high pressure low temperature hp lt rocks yielded eocene ages c 53 40 ma and their greenschist facies counterparts provided oligocene miocene dates c 25 18 ma marbles from tinos island contain high si phengite with rb sr phengite calcite and 40 ar 39 ar white mica ages between 41 and 24 ma all ar age spectra are disturbed and 40 ar 39 ar total fusion ages generally are 3 6 ma older than corresponding rb sr ages due to the polymetamorphic history we consider inheritance from the hp stage as the most likely cause for the complex ar age spectra and the older 40 ar 39 ar dates this concept also suggests that the rb sr system is more sensitive to modification during overprinting than the ar isotope system because resetting of the sr isotope system can be accomplished more quickly by sr exchange with other ca rich phases whereas lack of pervasive deformation and or restricted availability of synmetamorphic fluids has favoured partial inheritance of the ar isotope system on tinos the lowermost part of the metamorphic succession has experienced a pervasive greenschist facies overprint si rich phengite from marbles representing this lithostratigraphic level yielded rb sr ages of c 24ma if the earlier metamorphic history is not taken into account such data sets may lead to the erroneous conclusion of miocene hp metamorphism this study indicates that this phengite experienced pervasive rejuvenation of the rb sr isotope system during overprinting without significant changes in si content due to bulk compositional constraints this leads to the conclusion that in the absence of critical mineral assemblages the si value of phengite is not a reliable indicator for metamorphic pressures in impure marbles recent studies have reported large displacements 100 km for detachment faults in the aegean sea a critical parameter for such models is the age of hp metamorphism as deduced from white mica dating in the basal units of the cyclades we question the underlying idea of miocene hp metamorphism and suggest instead that this age constrains the timing of the greenschist facies overprint and that the existence of mega detachments in the study area requires further investigation

oceanic and orogenic fluid rock interaction in 18o 16o enriched metagabbros of an ophiolite tinos cyclades abstract two spatial scales of fluid rock interaction in an ophiolite suite are revealed by oxygen isotope and hydrogen isotope studies of metagabbros on the island of tinos cyclades greece sequentially formed mineral generations in the metagabbros include relict igneous augite hornblende of sub seafloor hydrothermal origin and actinolite and albite formed by regional greenschist facies metamorphism during orogenesis with the exception of augite 18 o 4 4 5 6 the metagabbros are characterized by unusually high 18 o values hornblende 5 8 7 4 actinolite 6 5 10 2 feldspar 14 6 14 9 and whole rocks 7 0 10 5 hornblende d values range from 57 to 66 the high 18 o values and the d range of the hornblendes are compatible with interaction of oceanic gabbro with seawater that had previously been enriched in 18 o 16 o 18 o 6 5 8 by isotopic exchange at moderate to high temperatures the high degree of oceanic alteration in the layered gabbros mass balance calculations of isotopic exchange and field evidence for early oceanic thrusting suggest that seawater could have penetrated deeply into the ocean crust becoming 18 o 16 o enriched through isotopic exchange with gabbros at progressively increasing temperature upward down temperature flow of the high 18 o water would be very effective in elevating the 18 o values of gabbros the regional greenschist metamorphic overprint of the ophiolite possibly the result of continued thrusting and piling up of nappes during obduction is characterized by localized fluid rock exchange actinolite in massive gabbroic layers has 18 o values 6 5 7 2 close to those of the hornblende whereas in deformed meter sized gabbroic blocks the amphiboles have significantly higher values 8 4 10 2 likewise albite in the gabbroic blocks has high 18 o values of ca 15 that are ascribed to meter scale exchange with 18 o rich fluids derived from dehydration reactions in low temperature hydrothermally altered basaltic host rock enclosing the blocks deformation enhanced permeability facilitated fluid infiltration in gabbroic blocks whereas the relatively undeformed and therefore less permeable massive gabbros experienced minor interaction with fluids the orogenic fluid rock interaction thus represents local scale redistribution of hydrous mineral components introduced during seafloor hydrothermal exchange

grain scale stable isotope disequilibrium during fluid rock interaction 2 an example from the penninic austroalpine tectonic contact in eastern switzerland at the tectonic contact between the penninic platta nappe and the lower austroalpine err unit in eastern switzerland carbon and oxygen isotope fronts are preserved at the interface of serpentinites and low grade regional metamorphic metacarbonates the carbon and oxygen isotope compositions of calcite are delta 13 c 2 3 per mil pdb and delta 18 o 21 0 per mil smow in the unaltered metacarbonates at a distance of about 20 m from the lithologic contact and they are delta 13 c 0 0 per mil and delta 18 o 14 0 per mil at the metacarbonate serpentinite interface the concomitant shift in the oxygen isotope composition of quartz is from 24 0 to 17 0 per mil a peculiarity of the isotope pattern is the systematic variation of the quartz calcite oxygen isotope fractionations across the isotopic front quartz calcite fractionations are relatively small nearly equal 3 0 per mil in the unaltered metacarbonate and at the metacarbonate serpentinite interface and they increase in the transitional zone in between with a maximum of 7 1 per mil at a distance of about 2 m from the contact this pattern is interpreted as a result of advective dispersive material transport across the lithologic contact and coupled first order kinetic mineral fluid exchange the oxygen isotope systematics indicate that calcite fluid isotope exchange was fast and local calcite fluid equilibrium prevailed during fluid rock interaction in contrast quartz fluid exchange was relatively sluggish and the quartz calcite oxygen isotope fractionations deviated significantly from their equilibrium values front geometries suggest that dispersive processes contributed substantially to material transport across the metacarbonate serpentinite contact cross layer advective flow was minor with a maximum time integrated volumetric flux of 21 m 3 m 2 from the influence of quartz fluid exchange kinetics on the intermineral fractionations quantitative relations among transport velocities the rates of mineral fluid exchange and the duration of fluid rock interaction are derived these relations are then combined with geologic and experimental data to identify feasible scenarios of fluid rock interaction

evolution of a calcite marble shear zone complex on thassos island greece microstructural and textural fabrics and their kinematic significance abstract the deformation history of a monophase calcite marble shear zone complex on thassos island northern greece is reconstructed by detailed geometric studies of the textural and microstructural patterns relative to a fixed reference system shear zone boundary szb strain localization within the massive marble complex is linked to decreasing p t conditions during the exhumation process of the metamorphic core complex solvus thermometry indicates that temperatures of 300 350 c prevailed during part of the shear zone deformation history the coarse grained marble protolith outside the shear zone is characterized by symmetrically oriented twin sets due to early coaxial deformation a component of heterogeneous non coaxial deformation is first recorded within the adjacent protomylonite enhanced strain weakening by dynamic recrystallization promoted strong localization of plastic deformation in the ultramylonite of the calcite shear zone where high strain was accommodated by non coaxial flow this study demonstrates that both a pure shear and a simple shear strain path can result in similar crystallographic preferred orientations single c axis maximum perpendicular to the szb by different dominant deformation mechanisms separated a axis pole figures a and a axis show different density distributions with orthorhombic texture symmetry in the protolith marble and monoclinic symmetry in the ultramylonite marble consistently with the observed grain fabric symmetry

multi phased uplift of the southern margin of the central anatolian plateau turkey a record of tectonic and upper mantle processes abstract uplifted neogene marine sediments and quaternary fluvial terraces in the mut basin southern turkey reveal a detailed history of surface uplift along the southern margin of the central anatolian plateau from the late miocene to the present new surface exposure ages 10be 26al and 21ne of gravels capping fluvial strath terraces located between 28 and 135 m above the goksu river in the mut basin yield ages ranging from ca 25 to 130 ka corresponding to an average incision rate of 0 52 to 0 67 mm yr published biostratigraphic data combined with new interpretations of the fossil assemblages from uplifted marine sediments reveal average uplift rates of 0 25 to 0 37 mm yr since late miocene time starting between 8 and 5 45 ma and 0 72 to 0 74 mm yr after 1 66 to 1 62 ma together with the terrace abandonment ages the data imply 0 6 to 0 7 mm yr uplift rates from 1 6 ma to the present the different post late miocene and post 1 6 ma uplift rates can imply increasing uplift rates through time or multi phased uplift with slow uplift or subsidence in between longitudinal profiles of rivers in the upper catchment of the mut and ermenek basins show no apparent lithologic or fault control on some knickpoints that occur at 1 2 to 1 5 km elevation implying a transient response to a change in uplift rates projections of graded upper relict channel segments to the modern outlet together with constraints from uplifted marine sediments show that a slower incision uplift rate of 0 1 to 0 2 mm yr preceded the 0 7 mm yr uplift rate the river morphology and profile projections therefore reflect multi phased uplift of the plateau margin rather than steadily increasing uplift rates multi phased uplift can be explained by lithospheric slab break off and possibly also the arrival of the eratosthenes seamount at the collision zone south of cyprus

microfabrics in carbonate mylonites along a large scale shear zone helvetic alps abstract carbonate mylonites with varying proportions of second phase minerals were collected at positions of increasing metamorphic grade along the basal thrust of the morcles nappe helvetic nappes switzerland variations of temperature stress and strain rate changes in chemistry of solid and fluid phases and differing degrees of strain localization and annealing were tracked by measuring the shapes mean sizes and size distributions of both matrix and second phase grains as well as crystal preferred orientation cpo of the matrix field structures suggest that strain rate was constant along the fault the mean and distribution of the calcite grain sizes were affected most profoundly by temperature increased temperature presumably accompanied by decreased stress correlated with larger mean sizes and wider size distributions at a given location the matrix grains in mylonites with more second phase particles are on average smaller have narrower size distributions and have more elongate shapes for example mylonites with 50 vol of second phases have matrix grain sizes half that of pure mylonites changes in calcite chemistry and the presence of synkinematic fluids seemed to influence microfabric only weakly temporal variations in conditions such as exhumation induced cooling apparently provoke changes in temperature stress and strain rate along the nappe these changes result in further strain localization during retrograde conditions and cause the grain size to be reduced by an additional 50 the matrix cpo strengthens with increasing temperature or strain but weakens and rotates with increasing second phase content these fabric changes suggest differing rates of grain growth grain size reduction and development of cpo owing to variations in the deformation conditions and perhaps mechanisms to interpret natural mylonite structures or to extrapolate mechanical data to natural situations requires careful characterization of the microfabric and in particular second phase minerals

uplift and exhumation of high pressure metamorphic terrains the example of the cycladic blueschist belt aegean sea the cycladic blueschists emerged from a depth of more than 50 km during the tertiary these rocks are now covered only by a thin fraction of the synmetamorphic overburden upper plate remnants of the upper plate include low p crystalline rocks and sediments which have been juxtaposed onto the lower plate blueschists in several stages since the early miocene the low angle contacts operated as normal faults which removed the overburden from above the cycladic blueschists detailed investigations on tinos island indicate that the fractured blocks of the upper plate lying above a low angle normal fault did not rotate this shows that the faults initiated as rather gently dipping fractures similar structures were also reported from other blueschist terrains kinematic analysis of such flat lying faults implies that the synmetamorphic overburden should be mostly located several hundred kilometers away from the present exposure of the blueschists considering that the cycladic blueschist belt exposes successively shallower units in the west and that rocks of the upper plate have an anatolian nature we suggest that these blueschists were dragged from beneath turkey we recognize that the blueschist unit has undergone further thrusting in the final stage of the exhumation as have its counterparts elsewhere in the hellenides the emergence of the blueschists in the tertiary was concomitant with continental collision and thrusting in the hellenides the operation of low angle normal faults with large extensional displacements occurred within this context of collision tectonics this extension occurred parallel to the strike of the convergent orogen

c o h s fluid composition and oxygen fugacity in graphitic metapelites c 0 h fluid produced by the equilibration of hzo and excess graphite must maintain the atomic h o ratio of water 2 1 this constraint implies that all thermodynamic properties of the fluid are uniquely determined at isobaric isothermal conditions the o h20 and co fugacities j fhto and fc of such fluids have been estimated from equations of state and fit as a function of pressure and temperature these fugacities can be taken as characteristic for graphitic metamorphic systems in which the dominant fluid source is dehydration e g pelitic lithologies because there are no compositional degrees of freedom for graphite saturated fluids produced entirely by dehydration the variance of the dehydration process is not increased in comparison with that in non graphitic systems thus compositional buffering of c 0 h fluids by dehydration equilibria a common petrological model requires that redox reactions decarbonation reactions or external h o 2 fluid sources perturb the evolution of the metamorphic system such perturbations are not likely to be significant in metapelitic environments but their tendency will be to increase the fo of the fluid phase at high metamorphic grades pyrite desulphidation reactions may cause a substantial reduction of fhz0 and slight increases info and fcs relative to sulphur free fluid at low metamorphic grade sulphur solubility in h o s 2 fluids is so low that pyrite decomposition must occur by sulphurconserving reactions that cause iron depletion in silicates a common feature of sulphidic pelites with increasing temperature and sulphur solubility pyrite desulphidation may be driven by dehydration reactions or infiltration of h o rich fluids the absence of magnetite and the assemblages carbonate aluminosilicate or pyrite pyrrhotite ilmenite from most graphitic metapelites is consistent with an h o 2 model for gcoh s fluid for graphitic rocks in which such a model is inapplicable a phase diagram variable that defines the h o ratio of gcoh s fluid is more useful than the conventional

deep fluid circulation in alpine shear zones pyrenees france field and oxygen isotope studies a combined field stable isotope and whole rock chemical study was made on late cretaceous to tertiary metasomatic shear zones cutting hercynian gneisses in the aston massif pyrenees france mylonitisation occurred during the early stages of alpine compression under retrograde conditions at 400 450 c and about 10 km depth whole rock 18o values of 11 to 12 in the gneisses was lowered to 5 to 9 in the shear zones with the quartz muscovite 18o 16o fractionations of about 2 to 4 essentially unchanged these 18o 16o systematics together with d muscovite 40 to 50 indicate that large volumes of formation waters or d rich meteoric waters passed through the shear zones during deformation the same fluids also redistributed major elements as shown by the correlation of 18o shift with muscovitisation and albitisation reactions in granitic wall rocks however even though 18o was universally lowered within the shear zones the 18o 16o ratios were not homogenised nor do they correlate in detail with the presence or absence of muscovitisation suggesting that fluid flow was probably fracture controlled and episodic field mapping shows that along the length of a particular shear zone muscovitisation of granite gneiss dies out 150m above the contact with underlying sillimanite gneiss thus muscovitisation and albitisation of granite gneiss in shear zones and their wall rocks probably occurred during re equilibration of acidic chloride rich aqueous fluids that had previously moved upward within the shear zones through underlying sillimanite gneiss extremely high material balance fluid rock ratios 103 are required to explain the extent of muscovitisation along this shear zone implying integrated fluid mass fluxes of about 108 kg m2 this is probably close to the maximum value for other shear zones in the network similar volumes of a more chemically evolved fluid must have passed through the unmuscovitised mylonites showing that the absence of alteration cannot necessarily be used to infer low values of fluid flux for reasonable pressure gradients and time scales of fluid movement effective permeabilities of 10 15 to 10 17 m2 are required such values can be accounted for by short lived widely spaced cracks produced during seismic activity a model is presented in which formation waters were seismically pumped down an underlying shallow southward dipping decollement and then upward through the steeply dipping shear zone network

the geodynamic evolution of the alpine orogen in the cyclades aegean sea greece insights from diverse origins and modes of emplacement of ultramafic rocks

plio plistocene in sequence thrust propagation along the main central thrust zone kumaon garhwal himalaya india new thermochronological data abstract the kumaon and garhwal himalayas nw india have similar geologic tectonic topographic and precipitation pattern however low temperature thermochronological age pattern varies significantly along the strike as well as across the strike of major faults here we interpret the new set of thermochronological age data across the strike of major faults namely vaikrita thrust vt munsiari thrust mt berinag thrust bt and the baijnath nappe along pindari valley in the kumaon garhwal himalaya in the present work 18 new apatite fission track aft ages of samples collected along a north south transect have been reported ages in the hanging wall of vt which range from 2 1 0 2 to 4 2 0 7 ma have been found to be becoming younger linearly with distance from north to the vt this trend crosses the vt with significant jump in ages in the south of the vt ages are lying between 0 3 0 1 and 3 9 0 8 ma and show linear variation with distance from the vt to bt no significant jump in ages across the mt is observed and the linear trend of younging southward is continuing till the bt the break and displacement in age pattern with youngest ages close to thrusts possibly indicate progressive late thrust movement it reflects sequential uplift and cooling towards the south from the vt to bt which is consistent with an in sequence style of thrust propagation we compare our new data to the published thermochronological data from its adjacent traverses along the goriganga and dhauliganga valleys 25 km away from the present traverse towards east and west respectively in the kumaon garhwal himalaya in order to understand potential along strike variations in the kinematics our observations indicate a dynamic coupling between tectonic and surface processes in the garhwal kumaon himalaya and support that the geometry of crustal scale faults and their associated kinematics control exhumation pathways of rocks

structural aspects of fluid rock interactions in detachment zones metamorphic core complexes and associated detachment faults of the north american cordillera represent gently dipping normal displacement shear zones detachment zones along which hot deeper levels of the crust were transported upward and outward from underneath a brittlely distended upper plate structures that formed during the ductile to brittle evolution of detachment zones can be used to reconstruct the relative magnitudes of fluid pressure and deviatoric stress at different levels within the shear zones mylonitization which occurred along deeper segments of detachment zones below the brittle ductile transition was locally accompanied by tensile failure indicative of low deviatoric stress and high fluid pressure this condition persisted into the earliest phases of brittle deformation after which shear fractures formed due to both a reduction in fluid pressure and an increase in deviatoric stress brittle deformation of upper plate rocks occurred largely under conditions of low fluid pressure structural and geochemical data suggest that normal displacement on detachment zones results in establishment of two fluid systems 1 an upper plate system driven by convection and dominated by meteoric and connate fluids at near hydrostatic pressures and 2 a system within deeper levels of the shear zone where fluids are largely derived from igneous sources and fluid migration is aided by dilatancy pumping the late phases of normal displacement on detachment zones structurally juxtaposed rocks affected by the two fluid systems and locally caused the shear zone rocks to be overprinted by mineralization related to the upper plate fluid system

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

o sr isotopic variations in miocene granitoids from the aegean evidence for an origin by combined assimilation and fractional crystallization sr o and d h isotopic compositions have been analyzed in miocene metaluminous to slightly peraluminous i type granitoids of the central aegean individual plutonic complexes display significant variations in their 18o and initial87sr 86sr compositions d and 18o compositions of minerals and whole rocks are mostly in the magmatic range some samples from naxos and mykonos delos show low d and 18o values characteristic of meteoric water hydrothermal interaction but as a whole the changes in 18o and sr isotopic compositions as a result of hydrothermal alteration were slight even in instances where marked alteration is petrographically observable consequently the bulk rock variations of 18o from 8 1 to 12 0 and of87sr 86sr from 0 70438 to 0 71450 may be regarded as primary and indicative of the conditions of their evolution heterogeneous isotopic compositions observed in the individual plutons of serifos ikaria samos and kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization the granitoids of serifos ikaria and kos display weak correlations between the initial87sr 86sr and 18o and 1 sr the granitoid province shows a positive correlation between87sr 86sr and 18o and a non linear relationship between87sr 86sr and 1 sr whereby 1 sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases it is argued that assimilation of older continental material by mantle derived arc magmas with combined fractionation afc is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock types trend from granodiorites in the south west near the inferred oligocene miocene suture to granites in the center and monzonites in the north east of the province

back arc extension and denudation of mediterranean eclogites eclogite facies rocks exposed in mediterranean back arcs are delimited from above by low angle normal faults and detachments nevertheless our work demonstrates that these extensional structures associated with back arc extension played only a limited role in removing the overburden from above the eclogites extension in mediterranean back arcs began in the late oligocene or early miocene but the pressure temperature time p t t paths of eclogite facies rocks exposed in these areas indicate that a major part of the overburden several tens of kilometers has been removed from above these rocks prior to the oligo miocene we show that the time period bracketed between the peak of eclogite metamorphism eocene in the central aegean probably upper cretaceous in corsica and the betics and the onset of back arc extension in the oligo miocene was characterized by thrust faulting in the central aegean corsica and the betics eclogite bearing units were partly unroofed and then overthrusted lower pressure units we emphasize that with one exception tinos island greece the entire inventory of extensional contacts operated subsequently to the overthrusting of the eclogites above the lower grade sequences thus mediterranean back arc extension lags behind a major part of the denudation process and is superposed on orogenic wedges that contain eclogite facies rocks at relatively shallow structural levels we emphasize that the mode of occurrence of eclogites in mediterranean back arc regions involves a continuum of in situ crustal accretion below the eclogites widespread p t paths that show cooling or isothermal decompression and lower grade rocks at the bottom of the structural pile thus instead of reflecting whole crust back arc extension the tectonic style associated with the denudation of mediterranean eclogites better fits an active accretionary wedge setting this is similar to the mode of occurrence of eclogite facies rocks in mountain belts such as the western alps where decompression was synorogenic and back arc extension played no role

velocities and propagation characteristics of pn and sn beneath the himalayan arc and tibetan plateau possible evidence for underthrusting of indian continental lithosphere beneath tibet new seismological observations on velocities and propagation characteristics of pn and sn waves beneath tibet can be interpreted although not uniquely to indicate the shallow angle underthrusting of the greater indian continental lithosphere beneath the tibetan plateau this is inferred from available geological and geophysical data and is now supported by new seismological observations the most significant observation is that high frequency sn waves shear waves that travel in the mantle lithosphere propagate efficiently in the uppermost mantle beneath the tibetan plateau except beneath the north central part of tibet the chang thang terrane furthermore sn propagates efficiently across the stable block of the tarim basin along the tien shan and himalayan mountains and across the indian shield apparent velocities of pn and sn waves that traverse the uppermost mantle beneath the tibetan plateau are 8 42 and 4 73 km s respectively these velocities are very similar to those beneath the himalayan mountains and the indian shield the efficient propagation and the velocities of pn and sn waves beneath tibet are also similar to those commonly observed beneath shield and stable continental regions these results are consistent with the underthrusting model and do not favor the class of alternative models in which the tibetan plateau is formed by shortening and thickening of hot crustal and uppermost mantle material in response to the convergence of india and asia

the genesis of epithermal au ag te mineralization panormos bay tinos island cyclades greece the panormos bay au ag te vein system tinos island greece which is hosted in mesozoic marbles comprises 30 subparallel steeply dipping quartz veins that extend for at least 500 m in places gold telluride mineralization occurs in hydraulic breccias and alteration halos which are the products of co 2 effervescence of the ore fluid and wall rock interaction respectively seventy ore and gangue minerals have been identified zones of chlorite talc and muscovite albite tourmaline alteration up to 50 cm wide are associated with precious metal bearing milky and clear quartz veins the au ag te mineralization is developed in stage v of eight hydrothermal stages stage v consists of three substages early middle and late that are characterized by ag cu and au bearing tellurides respectively hessite sylvanite altaite native tellurium stutzite cuprian cervelleite and an unnamed cu bearing precious metal sulfotelluride ag au cu 9 te 2 s 3 characterize the early substage whereas melonite rickardite vulcanite weissite and native tellurium are present in the middle substage the late substage contains rickardite kostovite krennerite petzite and calaverite unexploited au ag te mineralization at panormos bay is though to be genetically related to a fluorine and boron bearing per aluminous leucogranite tinos leucogranite a combination of fluid inclusion microthermometry and sylvanite geothermometry suggests that the hydrothermal mineralization was deposited under hydrostatic pressures at a minimum depth of 1 km from moderate temperature 155 320 c low to moderate salinity 0 2 13 2 wt nacl equiv effervescing co 2 bearing fluids that contained appreciable amounts of cacl 2 and mgcl 2 calculated isotope compositions of 18 o 3 3 to 5 1 per mil and d of 73 to 62 per mil for waters in equilibrium with muscovite quartz and talc are consistent with the ore fluids being derived from the tinos leucogranite 18 o 4 2 and d 71 and their subsequent mixing with a more dilute low temperature miocenic meteoric hydrothermal fluid calculated 13 c fluid 2 0 to 0 3 and 34 s h 2 s 10 5 to 0 8 compositions of the ore fluids indicate an igneous source of carbon and sulfur which were highly exchanged with a metasedimentary source physicochemical conditions of the ore fluids were t 300 to 200 c ph 4 6 to 6 5 f s 2 10 10 9 to 10 15 f o 2 10 31 5 to 10 41 f te 2 10 7 7 to 10 10 7 f co 2 10 0 2 to 10 0 8 and f h 2 s 10 1 7 to 10 1 8

late miocene ductile extension and detachment faulting mykonos greece the geometry and style of structural relations at map to microscopic scale on mykonos cyclades aegean sea greece suggests ductile extension and detachment faulting during the late miocene this island is dominated by granitic rocks that have a well developed shallowly dipping mylonitic foliation and a northeast southwest trending mineral elongation lineation kinematic indicators in these rocks exhibit a top to the northeast down dip sense of shear textural relations suggest that conditions during mylonitic deformation were greenschist to amphibolite facies and published k ar geochronology suggests a late miocene age for this deformation event mylonitic rocks lie in the footwall of a low angle fault and fault striae parallel to the elongation lineation suggest kinematic coordination between mylonitic deformation and movement along the fault translation along the fault juxtaposes younger tilted sedimentary rocks of low metamorphic grade upon the once deeper mylonitic rocks the style and geometry of deformational fabrics and map relations on this island are strikingly similar to those observed in metamorphic core complexes of the western united states

chemistry source and behavior of fluids involved in alpine thrusting of the central pyrenees quartz veins occupying extensional fractures that formed relatively late in the alpine thrusting history of the pyrenees contain abundant inclusions of hypersaline brines small amounts of bitumen also occur a range of brine compositions is apparent from the freezing behavior of fluid inclusions from different samples with large variations in na ca ratio but many individual samples contain only one brine composition all brine types display a bimodal distribution of homogenization temperature which is interpreted as the result of fluctuation in fluid pressure from a maximum value equal to lithostatic at 5 7 km depth and around 270 c to a value up to 700 bars lower this is ascribed to dilatancy pumping chemical analyses of brines leached from two samples yields balanced analyses for 14 elements both analyses appear to represent sedimentary formation waters and are closely analogous to oil field brines a basement origin is precluded by the presence of bitumens and the low k ca ratios differences between the analyses probably reflect different source bed mineralogy including the presence or absence of dolomite but triassic red beds are likely to be a major source the occurrence of these brines in the fault planes provides constraints on both the sources and movement of the fluids involved in thrusting significant infiltration of either surface waters or metamorphic water of dehydration can be ruled out because of the high salinities typically 20 25 wt dissolved salts hence although permeability was locally high due to fracturing around the faults fluids were pumped into these fractures from sedimentary formations adjacent to the fault individual fluid pathways were short lived relative to the duration of the deformation event so that different fluids were pumped into the faults at different times in response to local fault propagation

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

morphotectonic analysis of the hazara arc region of the himalayas north pakistan and northwest india abstract in the hazara arc region of northern pakistan some of the active basements structures buried below a thick detached sedimentary layer are inferred from the distribution of lineaments and the drainage patterns as viewed in landsat satellite imagery and from river profiles a prominent set of nw trending lineaments seen on satellite imagery coincides approximately with the southwest or updip side of the indus kohistan seismic zone iksz the most active basement structure of the region even though this structure is buried beneath and decoupled from a 12 km thick sedimentary layer the iksz has been interpreted as an extension of the himalayan basement thrust and is also associated with a prominent topographic step knickpoints on major rivers in the region lie on or north of the iksz all indus river tributaries examined north of the iksz show prominent knickpoints while two tributaries draining south of the iksz have no knickpoints these results suggest ongoing uplift above and north of the iksz and are consistent with the tectonic model obtained from the seismic data another prominent lineament set is detected along the north south section of the indus river this set is probably related to the indus river horst anticline and associated reentrant one of the two highest lineament concentrations occurs at the intersection between the nw trending iksz lineament and the n trending indus river lineament the other is along the west bank of the indus valley 25 km north of tarbela dam a topographic ridge swabi nowshera ridge appears to be forming along the west side of the indus river in the peshawar basin the rising ridge is ponding the kabul river upstream of nowshera where the drainage is braided