chlorine cycling during subduction of altered oceanic crust eclogitic rocks that have experienced devolatilization with little or no interaction with external fluid sources can be viewed as analogues of crustal material which may be transferred back into the mantle during subduction thus they can be used to evaluate the extent of the recycling of volatile elements such as chlorine we report new oxygen isotope ratios of omphacite and fluid inclusion data determined from eclogitic metagabbros of the rocciavre massif italian alps the data are compared with those obtained for the monviso cyclades and the franciscan complex high pressure rocks in all localities relics of early dehydration fluids are preserved as primary fluid inclusions in the cores of omphacite megacrysts rocciavre monviso and franciscan complex or garnet cyclades salinity estimates of the inclusion fluids range from 32 to 45 wt nacl in rocciavre 17 to 21 wt nacl in monviso and are similar to seawater in other areas omphacite and bulk rock 18o values of rocciavre 5 1 6 8 and monviso 3 0 5 3 metagabbros are markedly lower than those of cyclades 6 8 14 3 and the franciscan 6 7 13 1 metabasites the fluid salinity 18o systematics of eclogitic rocks is similar to that documented along a typical section of the altered oceanic crust and unmetamorphosed ophiolites this suggests that high pressure metamorphism and associated processes did not modify significantly the variability in chlorine concentrations and oxygen isotope ratios inherited from a stage of sea floor hydrothermal alteration under low basaltic layer and high temperature gabbroic layer conditions respectively extrapolating the estimated h2o and cl contents of eclogitic rocks to a representative section of the subducted oceanic crust indicates that a minimum of 100 to 200 ppm cl could be recycled into the mantle during subduction this yields a cl h2o ratio of 3 6 to 7 5 10 2 for the subducted oceanic crust which is similar to e morb on the basis of available cl isotopic data we infer that a large proportion 70 of the cl stored in the altered crust should be recycled to the mantle to generate an isotopic composition of the subducted crust equivalent to the source of unaltered mid ocean ridge basalt 37cl 4 7

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

evolution of synmetamorphic veins and their wallrocks through a western alps transect no evidence for large scale fluid flow stable isotope major and trace element systematics quartz rich synfolial veins and wallrocks from different areas of a western alps cross section are examined in an attempt to constrain the scale and mechanisms of fluid flow through metamorphic terrains different portions of this cross section underwent distinct p t evolutions as reflected by the mineralogy of veins a in the greenschist external dauphinois domain veins are characterized by quartz and calcite together with an aluminosilicate pyrophyllite na k bearing phyllosilicates and a femg bearing silicate chlorite b in narrow domains of the brianconnais and piemontais zones with a non eclogitic hp lt evolution followed by rapid cooling veins are characterized by quartz calcite ca and fe mg bearing silicates lawsonite and fe mg carpholite respectively and c in the major part of the brianconnais andpiemontais zones where low grade blueschistfacies metamorphism is followed by a greenschist facies evolution veins are characterized by the replacement of earlier lawsonite and carpholite by na and k bearing micas in order to constrain the provenance of fluids involved in vein formation we determined stable isotope c 0 h and major and trace element compositions in minerals and whole rocks for a large set of veins and wallrocks these rocks are compared with some non metamorphic shales from the northern paris basin considered as protoliths of the alpine schists stable isotope compositions of calcites are regionally distinct 6r80 28 0 smow in the northern paris basin 26 0 in the brianconnais zone 22 0 in the piemontais zone and 18 0 in the dauphinois zone within each studied region calcite g o values are quite homogeneous regardless of rock type vein or wallrock this feature is explained as an isotopic homogenization with the most abundant lithology in each zone rock buffered system where the overall ratio of calcite of marine origin to detrital silicate minerals determines the final isotopic composition of the whole rock w r after equilibration during alpine metamorphism g o gd values of analysed hydrated minerals and whole rocks si80 15 to t 25 0 and 6d 60 0 smow lie within the field of alpine cover rocks and of fluids in equilibrium with these rocks interaction with an external o or d depleted fluid such as hydrothermal waters meteoric water or basement fluid can be ruled out major and trace element systematics indicate an enrichment in si ca p sr y ta and locally eu in the veins with respect to the wallrock related to massive crystallization of quartz and carbonates together with phosphate and oxide potential fluid sources chemical composition of the fluid phase and the mechanisms of fluid flow during vein formation are discussed fluid flow takes place within tectonic units at both hectometric and decimetric scale fluid may also have migrated along and across the major tectonic contacts but this process is poorly documented

reconstructing site organization in the eastern aleutian islands alaska using multi element chemical analysis of soils this study presents the results of multi element analysis of weak acid extractions of 953 soil samples collected by coring on and around pre historic village sites on two islands sanak and amaknak in the eastern aleutians concentrations of aluminum al barium ba calcium ca iron fe potassium k magnesium mg manganese mn phosphorus p strontium sr titanium ti and zinc zn were determined using an inductively coupled plasma mass spectrometer icp ms resultant elemental signatures allow the identification of site features and organization in the absence of large scale excavation all the archeological sites showed similar and distinct chemical signatures regardless of the several thousand year date range of the sites or the length of time a site was occupied however intensity of occupation does appear to affect concentrations of elements site features such as houses house berms house floors and middens had distinct anthropogenic signatures and could be distinguished from one another this approach may be used to identify sites that do not have distinct surface features and to target areas for excavation

channelized fluid flow and mass transfer along a rift related detachment fault eastern alps southeast switzerland remnants of a rift related low angle detachment system are spectacularly exposed in the continental err nappe and occur discontinuously in the underlying oceanic platta nappe in southeast switzerland rocks along the detachment fault exhibit systematic changes in mineralogy fabrics and structures that are related to deformation and hydration of granite to form cataclasite and subsequent gouge structural mineralogical and geochemical data indicate a continuous evolution of fluid flow and mass transfer along the detachment fault mass balance calculations together with stable isotope data suggest 1 an altered seawater source and local interaction with mantle rocks 2 limited fluid rock interaction and mass transfer during initial cataclasis at deeper crustal levels and temperatures of 150 to 200 c 3 increased fluid flux and mass transfer at slightly lower temperatures 100 150 c during gouge formation at shallower crustal levels and 4 strongly localized fluid rock interaction at low temperatures 65 80 c near the sea floor at a final stage of detachment faulting we propose a model in which seawater dominated fluids penetrated and locally interacted with mantle rocks before they were caught and channelized along large scale detachment faults flow direction is upward along the detachment from higher to lower temperatures suggesting that the driving force of fluid flow was thermal fluid convection associated with mantle exhumation our study suggests that this large scale detachment fault is a good analog for extensional structures along present day nonvolcanic rifted margins such structures along ocean continent transitions are important in controlling fluid pathways and mass transfer between mantle and continental crust

oxygen and carbon isotope evidence for seawater hydrothermal alteration of the macquarie island ophiolite abstract rocks of the miocene macquarie island ophiolite south of new zealand have oxygen and carbon isotopic compositions comparable to those of seafloor rocks basalt glass and weathered basalts have 18o values at 5 8 6 0 and 7 9 9 5 respectively similar to drilled seafloor rocks including samples from the leg 29 dsdp holes near macquarie island compared to the basalt glass the greenschist to amphibolite facies metaintrusives are depleted in18o 18o 3 2 5 9 similar to dredged seafloor samples whereas the metabasalts are enriched 18o 7 1 9 7 although the gabbros are only slightly altered in thin section they have exchanged oxygen with a hydrothermal fluid to a depth of at least 4 5 km there is an approximate balance between18o depletion and enrichment in the exposed ophiolite section the carbon isotopic composition of calcite in the weathered basalts 13c 1 0 2 0 is similar to those of drilled basalts but the metamorphosed rocks have low 13c values 14 6 to 0 9 these data are compatible with two seawater circulation regimes in the upper regime basalts were weathered by cold seawater in a circulation system with high water rock ratios 1 0 based on calcite compositions weathering temperatures were less than 20 c and the carbon was derived from a predominantly inorganic marine source as previously suggested for the samail ophiolite it is postulated that the lower hydrothermal regime consisted of two coupled parts at the deeper levels seawater circulating at low water rock ratios 0 2 0 3 and high temperatures 300 600 c gave rise to18o depleted gabbro and sheeted dikes via open system exchange reactions during reaction the seawater underwent a shift in oxygen isotopic composition 18o 1 0 5 0 and subsequently caused18o enrichment of the overlying metabasalts in the shallower part of the hydrothermal regime the metabasalts were altered at relatively high water rock ratios 1 0 10 0 and temperatures in the range 200 300 c the relatively low water rock ratios in the hydrothermal regime are supported by the low 13c values of calcite interpreted as evidence of juvenile carbon in contrast to the inorganic marine carbon found in the weathered basalts

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

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

phosphate fractionation and spatial patterning in ancient ruins a case study from yucatan abstract as time passes phosphorus p in soils tends to become more tightly bound with minerals phosphate fractionation enables the measurement of loosely versus tightly bound p archaeologists have used p fractionation as a chronometric technique older soils should have greater proportions of p tightly bound with minerals research at chunchucmil a large maya ruin in yucatan mexico has used extractable p concentrations and other lines of evidence to investigate ancient uses of space because contemporary maya villagers use the land among the chunchucmil ruins in a number of ways and because the ancient land surfaces are neither sealed nor deeply buried we used p fractionation to determine whether geochemical signatures of activities such as gardening resulted from ancient or modern inhabitants the fractionation results at chunchucmil are unusual in comparison to studies from other sites furthermore there are strong correlations between the sum of p fractions and carbonate we discuss potential explanations for these patterns in p fractionation data these explanations consider local pedology differential length of ancient occupation and localized dumping of the byproducts of maize processing to examine the chemical signatures of maize processing specifically soaking maize in lime water contemporary samples of sediments and residues from this activity were analyzed our results suggest that dumping water from maize soaking provides a potential explanation for the ancient p patterns

permeability generation and resetting of tracers during metamorphic fluid flow implications for advection dispersion models advection dispersion fluid flow models implicitly assume that the infiltrating fluid flows through an already fluid saturated medium however whether rocks contain a fluid depends on their reaction history and whether any initial fluid escapes the behaviour of different rocks may be illustrated using hypothetical marble compositions marbles with diverse chemistries e g calcite dolomite quartz are relatively reactive and will generally produce a fluid during heating by contrast marbles with more restricted chemistries e g calcite quartz or calcite only may not if the rock is not fluid bearing when fluid infiltration commences mineralogical reactions may produce a reaction enhanced permeability in calcite dolomite quartz or calcite quartz but not in calcite only marbles the permeability production controls the pattern of mineralogical isotopic and geochemical resetting during fluid flow tracers retarded behind the mineralogical fronts will probably be reset as predicted by the advection dispersion models however tracers that are expected to be reset ahead of the mineralogical fronts cannot progress beyond the permeability generating reaction in the case of very unreactive lithologies e g pure calcite marbles cherts and quartzites the first reaction to affect the rocks may be a metasomatic one ahead of which there is little pervasive resetting of any tracer centimetre scale layering may lead to the formation of self perpetuating fluid channels in rocks that are not fluid saturated due to the juxtaposition of reactants such layered rocks may show patterns of mineralogical resetting that are not predicted by advection dispersion models patterns of mineralogical and isotopic resetting in marbles from a number of terrains for example chillagoe marulan south reynolds range australia adirondack mountains old woman mountains notch peak usa and stephen cross quarry canada vary as predicted by these models

ancient settlement activities as important sources of nutrients p k s zn and cu in eastern mediterranean ecosystems the case of biblical tel burna israel abstract human settlement activities are connected with the accumulation of nutrients in archaeological soils we address the question of whether the large scale mapping of the elemental composition of the topsoil in contemporary rangeland can be used for the detection of ancient settlement activities using portable x ray fluorescence pxrf we mapped the elemental composition of contemporary soils over an area of 67 ha in and around the bronze and iron age settlement of tel burna identified as probably corresponding with biblical libnah ancient settlement activities substantially increased concentrations of nutrients p k s zn and cu in the contemporary topsoil owing to the deposition of biomass ashes and organic wastes increased concentrations of elements were detected 2500 years after the site was abandoned and we can therefore suppose that changes in the elemental composition of the soil caused by ancient settlement activities are irreversible on a timescale in which human societies operate ancient settlement activities increased concentrations of nutrients in contemporary soil to the same level as recent intensive fertiliser application on an adjacent arable field used for vegetable production concentrations of nutrients higher than those on the tell summit were recorded only in recent cattle resting areas with intensive deposition of cattle faeces changes in the elemental composition of the soil caused by ancient settlement activities consequently result in differential nutrient availability for contemporary vegetation affecting ecosystem functions for thousands of years using pxrf large scale mapping of the elemental composition of the topsoil layer at archaeological sites can help to identify the extent and provide basic information on the character of past human activities in the affected landscape units

aspects of the three dimensional structure of the alberta foothills and front ranges ever more detailed subsurface images of the alberta foothills and front ranges obtained from improving seismic techniques coupled with an ever expanding base of information from deep wells and improved structural analysis techniques have produced an understanding of fold thrust deformation that is probably applicable to other fold thrust belts comprehensive subsurface data obtained by the petroleum industry are used to outline and analyze the three dimensional configuration of fold thrust deformation of paleozoic carbonate strata these data indicate that displacement changes smoothly along individual thrusts but displacement changes along strike may be large marked by considerable horizontal rotation 20 30 or more of hanging wall stratigraphic cutoffs relative to the footwalls stacking of thrusts with varying displacements has produced summed horizontal rotations of hanging wall cutoffs of as much as 45 50 the three dimensional trajectories of the thrusts through the stratigraphy are smooth for large distances interrupted by abrupt offsets at lateral and oblique ramps these are more common than previously realized the intersections of these ramps with other thrusts produce complex three dimensional links between thrusts with concomitant abrupt displacement changes some simple examples of these linkages are examined with a three dimensional geometric analysis the predictions of the analysis are consistent with structural geometries observed in two case studies of subsurface structures the links at lateral ramps imply simultaneous displacement on parts of the thrusts connected by the ramps since the ramps extend downdip 20 km or more displacement occurred simultaneously on structures occupying relatively interior and exterior positions in the thrust belt the smooth and long radius of curvature folding of many upper detachments indicated by reflection seismic data also is consistent with simultaneous or overlapping periods of motion on groups of thrusts distributed along regional dip most major alberta foothills thrust sheets terminate southward at lateral ramps at the paleozoic level the abrupt southwest northeast offsets at these features are most clearly apparent on a palinspastic reconstruction these offsets cause the paleozoic deformation front to step out east and northeast around the southern and eastern margins of the main arc of the foothills in contrast northward thrust terminations at the paleozoic level commonly occur at both tip lines and lateral ramps subsurface data reveal that there have been some misconceptions regarding large scale structural relationships for example the mcconnell and livingstone sheets are actually portions of the same thrust sheet as are the bighorn and nikanassin sheets when corrected for these misconceptions the data from the alberta foothills suggest that maximum displacement has a nonlinear relationship to thrust length although a linear relationship cannot be ruled out

asbestos fibre identification vs evaluation of asbestos hazard in ophiolitic rock melanges a case study from the ligurian alps italy in recent years the high incidence of harmful health effects through inhalation of airborne asbestos from amphibole bearing rock melanges has been thoroughly documented here we present a field based multi scale geological approach aimed at illustrating the occurrence of amphibole fibrous mineralisation in an ophiolitic suite from the ligurian alps italy and discussing the implication on in situ determination of the asbestos hazard the rock melange is composed of plurimetre sized blocks of different lithotypes metagabbro serpentinite chloritoschist juxtaposed by the meaning of tectonic structures the geological structural survey revealed that the fibrous mineralisation is localised in specific structural sites of the rock volume including veins and schistosity both micro chemical and crystal structure analyses on selected fibrous samples revealed that actinolite fibres grow in veins within the metagabbro and in chloritoschists while fibrous tremolite occurs in serpentinite schistosity the morphological features of these amphibole fibres have been analysed in tem images and used for classifying them as asbestiform or non asbestiform the results show that the asbestos hazard determination is not unequivocally identified when different procedures for asbestos fibre identification and classification are applied this may have impact on normatives and regulations in defining environmental hazards due to asbestos occurrence

oxygen isotope geothermometers for metamorphic rocks the chicago mineral carbonate oxygen isotope fractionation curves have been combined with mineral water fractionation data for jadeite zoisite and rutile and new data for grossular water to provide a set of self consistent mineral pair calibrations the a coefficients in the equation 1000 in a 106t 2 of the new mineral pair fractionations are jadeite zoisite grossular rutile quartz 1 69 2 00 3 03 5 02 jadeite 0 31 1 34 3 33 zoisite 1 03 3 02 grossular 1 99 the isotopic fractionation properties of natural pyralspite garnet ca fe mg mn 3al2si3o12 can be approximated by those of the grossular end member appropriate substitutions also yield coefficients for the solid solution minerals sodic pyroxene and epidote e g aquartz sodic pyroxene 2 75 1 06xjd aquartz epidote 2 00 0 75xps where xjd and xps are the mole fractions of the jadeite and pistacite components respectively the new data set is particularly suitable for the geothermometry of metamorphic rocks 18o data from minerals of the high pressure metamorphic rocks of the sesia zone of italy and cyclades complex of greece yield well constrained mean temperatures of 572 and 478d c respectively type iii blueschist metabasalts of the franciscan formation of california give mean quartz garnet temperatures of 354d c

the ancient agricultural landscape of the satellite settlement of ramonal near tikal guatemala abstract soil science methodologies often enrich archaeological reconstructions in the maya lowlands of mesoamerica stable carbon c isotope ratio 13c analysis of soil organic matter som from profiles near ancient archaeological sites has been used to interpret the vegetative histories related to ancient maize agriculture due to distinct photosynthetic processes the decomposed organic matter from the cultivation of maize can be distinguished from som derived from native forest detritus the recalcitrant nature of humic substances allows for this distinction to be preserved through time this study evaluates som 13c from 98 soil profiles near tikal guatemala to identify areas of ancient maya agriculture and the staple crops used ancillary physical and chemical properties of the soil profiles were examined to facilitate and to supplement the interpretation of the isotope data most of the soils analyzed in this study are shallow haprendolls with limited c isotopic evidence of prehistoric vegetation changes the deeper well developed argiudolls and hapludolls contained strong evidence of vegetation changes associated with ancient maize agriculture areas with strong 13c signatures of ancient c4 vegetation corresponded with foot and toeslope locations high clay content and low phosphorus p levels the shallow backslope soils lacked significant evidence of ancient agriculture the connections between profile location settlement isotope data and p levels enable the identification of both agriculture production zones and enhanced understanding of stable c isotope dynamics in soils within the unique physiographic and archaeological surroundings of the maya lowlands

the mechanism of veining and retrograde alteration of alpine eclogites the introduction of externally derived fluids into rocks of the zermatt saas zone of the swiss alps gave rise to the simultaneous formation of shear and hydraulic fractures these fractures are now filled with albite rich assemblages and surrounded by alteration halos up to c 2 m wide the alteration assemblages are zoned and an examination of reactions in p t ah2o space implies that the parageneses developed by the hydration of fluid absent eclogites a mechanical analysis of the veins after sibson 1981 shows that pfluid pload must have been at least 0 96 fluid migration into the country rocks must have been driven by excess hydraulic head either derived from the vertical extent of the veins or due to their connection to a deeper external reservoir possibly tapped along thrust surface s diffusive and capillary transport were insignificant the fluids may have been derived from underlying metasediments that were dehydrating during the quasi isothermal uplift of this part of the alps or they may have originated during the prograde mesoalpine metamorphism documented in the area

geochemical and stable isotope resetting in shear zones from taschalp constraints on fluid flow during exhumation in the western alps fluid flow at greenschist facies conditions during exhumation of the western alps occurred in several penecontemporaneous systems including shear zones at lithological contacts deformed contacts between serpentinite bodies and metabasalts albite veins within metabasalts and calcite quartz veins within calcareous schists fluid flow in shear zones that juxtapose metasediments and ophiolitic rocks within the piemonte unit reset o and h isotope ratios 18o values are buffered by the wall rocks however calculated fluid 2h values are similar within all the shear zones suggesting that they formed an interconnected network the similarity of 2h values of the sheared rocks and those of unsheared calcareous schists suggests that the fluids were derived from or had equilibrated with the schists that envelop the ophiolite rocks time integrated fluid fluxes at the sheared contacts estimated from changes in si in metabasalts were up to 105 m3 m 2 with the fluid flowing up temperature driven either by topography or seismic pumping individual shear zones were active for c 2 3 myr implying average fluid fluxes of up to 10 9 m3 m 2 s 1 rocks in shear zones within the ophiolite away from contacts with the metasediments show much less marked isotopic and geochemical changes implying that fluid volumes decreased into the ophiolite unit consistent with the source of fluids being the metasediments fluids were generated by dehydration reactions that were intersected during exhumation and while many rocks show the affects of fluid rock interaction large scale fluid flow between major units was not common

stable isotope geochemistry of alpine ophiolites a window to ocean floor hydrothermal alteration and constraints on fluid rock interaction during high pressure metamorphism the subduction of hydrated oceanic lithosphere potentially transports large volumes of water into the upper mantle however despite its potential importance fluid rock interaction during high pressure metamorphism is relatively poorly understood the stable isotope and major element geochemistry of pennine ophiolite rocks from italy and switzerland that were metamorphosed at high pressures are similar to that of unmetamorphosed ophiolites suggesting that they interacted with little pervasive fluid during high pressure metamorphism cover sediments also have oxygen isotope ratios within the expected range of their protoliths in the rocks that escaped late greenschist facies retrogression different styles of sub ocean floor alteration may be identified using oxygen isotopes petrology and major or trace element geochemistry within the basalts zones that have undergone high and low temperature sub ocean floor alteration as well as relatively unaltered rocks can be distinguished serpentinites have 18o and 2h values that suggest that they were formed by hydration on or below the ocean floor the development of high pressure metamorphic mineralogies in metagabbros occurred preferentially in zones that underwent sub ocean floor alteration and which contained hydrated fine grained reactive assemblages given that the transformation of blueschist facies metabasic rocks to eclogite facies assemblages involves the breakdown of hydrous minerals e g lawsonite zoisite and glaucophane and will thus liberate considerable volumes of fluids metamorphic fluid flow must have been strongly channelled high pressure quartz calcite omphacite glaucophane titanoclinohumite veins that cut the ophiolite rocks represent one possible channel however stable isotope and major element data suggest that they were not formed from large volumes of exotic fluids fluids were more likely channelled along faults and shear zones that were active during high pressure metamorphism such strong fluid channelling may cause fluids to migrate toward the accretionary wedge especially along the slab mantle interface which is probably a major shear zone this may preclude all but a small fraction of the fluids entering the mantle wedge to flux melting additionally because fluids probably interact with relatively small volumes of rock in the channels they cannot scavenge elements from the subducting slab efficiently

the flow of surface derived fluids through alice springs age middle crustal ductile shear zones reynolds range central australia the south east reynolds range central australia is cut by steep north west trending alice springs age c 334 ma shear zones that are up to hundreds of metres wide and several kilometres long with reverse senses of movement amphibolite facies 550 600 c 500 600 mpa shear zones cut metapelites while greenschist facies shear zones 420 535 c 400 650 mpa cut metagranites the sheared rocks commonly underwent metasomatism implying that the shear zones were the pathways of significant fluid flow altered granites within greenschist facies shear zones have gained si and k but lost ca and na relative to their unsheared counterparts suggesting that the fluid flowed down temperature and hence probably upward through the shear zones time integrated fluid fluxes calculated from silica addition are up to 2 1 1010 mol m 2 c 4 2 105 m3 m 2 similar time integrated fluid fluxes are also estimated from changes in k and na the sheared granitic rocks locally have 18o values as low as 0 which is much lower than the 18o values of the adjacent unsheared granites 7 to 9 implying that the fluid which flowed through these shear zones was derived from the surface for the estimated time integrated fluid fluxes the fluids would be able to retain their isotopic signature for many tens to hundreds of kilometres the flow of surface derived fluids into the ductile middle crust with subsequent expulsion upwards through the shear zones may have been driven by seismic activity accompanying the alice springs deformation

stable isotope and ar ar evidence of prolonged multiscale fluid flow during exhumation of orogenic crust example from the mont blanc and aar massifs nw alps the spatial and temporal scales and the geometry of fluid pathways in a collisional orogen are investigated using stable isotope analysis o c and h and 40ar 39ar dating of vein minerals formed at circa 11 16 ma in the mont blanc and the aar external crystalline massifs in both massifs 40ar 39ar dating of veins adularia provides evidence for progressive crystallization from 16 to 9 ma and mainly at 11 12 ma following veins opening during shear zone activity the fluid flow duration thus ranges from 4 to 5 ma in the two massifs the 18o values of vein quartz and calcite are similar to those of undeformed crystalline and sedimentary host rocks suggesting rock buffering while carbon isotope ratios of vein calcites fall into three compositional groups a type veins have 13c values that are buffered by the helvetic metasediments which suggests that these veins formed in a closed system from a locally derived co2 rich fluid the fluid in equilibrium with c type veins has depleted 13c values similar to mantle co2 while the intermediate 13c values of b type veins suggest mixing between the a type and c type fluids these results are in agreement with crustal to lithosphere scale upward vertical fluid flow along vertical shear zones related to the strike slip system bounding the adriatic block since 16 20 ma connecting a deep seated fluid to some downward flow in the sedimentary cover of external crystalline massifs

horizontal contraction or horizontal extension heterogeneous late eocene and early oligocene general shearing during blueschist and greenschist facies metamorphism at the pennine austroalpine boundary zone in the western alps mylonitic structures related to two orogenic events are described from the upper and lower contacts of the combin zone and the immediately overlying upper austroalpine dent blanche nappe mont mary klippe and the directly underlying lower austroalpine etirol levaz slice the first event late eocene in age commenced during blueschist facies p t conditions but pre dated the peak of subsequent greenschist facies overprint the second event early oligocene in age took place during retrograde greenschist facies conditions most sense of shear indicators associated with the retrograde mylonites indicate top se shearing but subordinate top nw displacing shear sense indicators have also been mapped mylonitic top se shearing appears to be restricted to the combin zone and its upper and lower contacts within the dent blanche nappe and mont mary klippe and at the base of the etirol levaz slice structures were observed which developed during blueschist greenschist facies conditions and are in conjunction with the p t t history of these rocks inferred to be older associated kinematic data indicate a top nw shear sense comparable blueschist greenschist facies shear sense indicators have not been observed in the combin zone nonetheless the foliation in the combin zone shows a progressive evolution from blueschist facies to greenschist facies to retrograde greenschist facies conditions this indicates that the combin zone and the immediately over and underlying austroalpine units shared a common tectono metamorphic evolution since the late eocene finite strain data reveal oblate strain fabrics which are thought to result from a true flattening strain geometry flow path modelling reveals a general non coaxial deformation regime and corroborates significant departures from a simple shear deformation in the study area mylonitic top se shearing in the combin zone is attributed to early oligocene backfolding and backthrusting of the mischabel phase temperature time curves suggest slight reheating in the monte rosa nappe underneath and cooling in the dent blanche nappe above the combin zone hence confirming a thrust interpretation for this event the top nw displacing structures are thought to result from late eocene emplacement of the dent blanche nappe and the combin zone onto the middle pennine barrhorn series along the combin fault as related structures initiated during mildly blueschist facies conditions in the dent blanche nappe and the underlying combin zone and both were emplaced together onto the greenschist facial barrhorn series it is concluded that the structures developed as the nappes moved upward relative to the earth s surface thus the combin fault is regarded as a thrust the geometry of this structure indicates that the combin fault is an out of sequence thrust that locally cut down section hence top nw out of sequence thrusting caused local thinning of the metamorphic structural section in association with horizontal shortening out of sequence thrusts cutting down section and back thrusts offer the possibility of explaining the pronounced break in the grade of metamorphism across the combin fault i e the contact between the eclogite facial zermatt saas zone and the overlying lower grade combin zone by contractional deformation

interactions between serpentinite devolatilization metasomatism and strike slip strain localization during deep crustal shearing in the eastern alps the greiner shear zone in the tauern window eastern alps changes from a zone of distributed dominantly sinistral shear in supracrustal rocks to a series of narrow gully forming dextral splays where it enters basement gneisses within these splays granodiorite is transformed into quartz poor biotite and or chlorite schists reflecting hydration removal of si ca and na and concentration of fe mg and al stable isotope analyses show a prominent increase in d and a decrease in 18o from granodiorite into the shear zones these changes indicate significant channelized flow of an externally derived low 18o high d fluid through the shear zones the shear zone schists are chemically similar to blackwall zones developed around serpentinite bodies elsewhere in the greiner zone and the stable isotope data support alteration via serpentinite derived fluid monazite in schist from one shear zone yields spot dates of 29 20 ma indicating that the fluid influx and switch from sinistral to dextral shear occurred at or shortly after the thermal peak of the alpine orogeny c 30 ma we suggest that alpine metamorphism of serpentinites released large amounts of high d low 18o si undersaturated fe mg saturated fluids that became channelized along prior zones of weakness in the granodiorite infiltration of this fluid facilitated growth of chlorite and biotite which in turn localized later dextral strain in the narrow splays via cleavage parallel slip this dextral strain event can be linked to other structures that accommodated tectonic escape of major crustal blocks during dextral transpression in the eastern alps this study shows that serpentinite devolatilization can play an important role in modifying both the chemistry and rheology of surrounding rocks during orogenesis

dillon cutoff basement involved tectonic link between the disturbed belt of west central montana and the overthrust belt of extreme southwestern montana the front of the cordilleran fold and thrust belt in western montana follows the disturbed belt in the north merges with the southwest montana transverse zone in the west central part of the region and in southwestern montana is marked by a broad zone characterized by complex interaction between thrust belt structures and basement uplifts the front margin of the thrust belt in montana reflects mainly thin skinned tectonic features in the north an east trending lateral ramp that curves southwest in the central part into the dillon cutoff an oblique slip thick skinned displacement transfer zone that cuts through basement rocks of the lima recess and a zone of overlap between thin and thick skinned thrusts in extreme southwestern montana the transverse ramp and basement involved thrust faults are controlled by proterozoic structures

impact of microtopography on the geochemistry of soils within archaeological sites in se poland the geochemical record of human impact within three archaeological sites in se poland was analysed the total levels of cd cu pb zn and p were defined the content of the studied elements was found to be higher than the determined geochemical background in all cases significantly higher concentrations 2 3 times of trace metals were found in sediments filling small depressions and foot slope locations these concentrations were often higher than in the profiles within the archaeological objects the vertical distributions of elements were also different from soil profiles located on flat surfaces the study thus confirms that microtopography and soil erosion may impact diversify the initial horizontal and vertical variation of geochemistry of soils within archaeological sites caused by human activity this should be taken into account when using geochemical prospecting in archaeological studies in areas with varied topography

a supervised machine learning approach towards geochemical predictive modelling in archaeology abstract in this work data fusion of multi element xrf results from archaeological feature soils and regional background soils was applied to assess the complementary value of geochemistry and machine learning on predictive modelling in archaeology our principal aim was to integrate multiple data sources train learning models for classification of archaeological soils and background soils and compare model predictions for three validation areas with current archaeological interpretation and established predictive models this was done using three supervised machine learning algorithms k nearest neighbors support vector machines and artificial neural networks which were trained cross validated and tested the validation areas included a high archaeological potential area n 247 samples the dutch province of zeeland n 261 samples and an excavated imprint of an ancient farmhouse n 38 samples the predictive models showed good overall performance and correctly classified about 95 of all test instances according to the learning models the first validation site has a top soil horizon that shows limited parallels with archaeological horizons used in model training whereas features of high archaeological probability become more apparent below this horizon this is in good correspondence with geochemical depth profiles and current archaeological interpretation as for the second validation site the models highlighted several archaeological hotspots that to some extend spatially coincide with areas of high archaeological potential as indicated by established predictive modelling reversely the classifiers attributed high archaeological potential status to the most southern region of zeeland thereby complementing established modelling results for the third validation site none of the instances were correctly classified and these results clearly show the limitations of geochemical predictive modelling of significantly different soil types fine to coarse sands compared to the training set clayey sands present proof of concept study shows that modelling of multiple source geochemical soil data using machine learning algorithms can be successfully accomplished and that model predictions nicely complement current interpretation and or established archeological predictive modelling of areas of archaeological interest limitations of our approach were found to reside in lithological differences between sites used for model training and prediction sites

identification of activity areas by multi element characterization of sediments from modern and archaeological house floors using inductively coupled plasma atomic emission spectroscopy abstract a pilot study on the chemical analysis of earthen house floors using both modern and archaeological localities was undertaken to determine the degree to which activities leave detectable chemical residues and whether these residues are preserved in archaeological contexts the goals were to develop techniques for the identification and interpretation of activity areas in archaeological structures and to determine which elements serve to distinguish activities one modern structure from oaxaca mexico and two archaeological house floors from british columbia canada and oaxaca mexico were studied soil samples were collected from floors at all three sites and analysed by inductively coupled plasma atomic emission spectroscopy icp aes for al ba ca fe k mg mn na p sr ti and zn preliminary results show that activity areas in the modern house compound can readily be distinguished on the basis of chemical residues in soils that archaeological features are chemically distinct from natural soils and that features such as floors and hearths can be distinguished from each other and from the natural prehistoric ground surface multi element characterization by icp aes offers an advantage over traditional single element analysis by yielding more useful data for less effort expense and time

multi element soil prospection aiding geophysical and archaeological survey on an archaeological site in suburban sagalassos sw turkey in order to take full advantage of the archaeological information contained within buried archaeological sites it is important to apply an integrative approach combining complementary prospection methods in this study geochemical prospection data are combined with archaeological and geophysical survey results on an unexcavated site in suburban sagalassos sw turkey with the aim of obtaining better insights into the structural shapes and past functionalities of the area spatial and multivariate statistical analyses of the chemical data reveal anomalies of k p and zn on a location where archaeological and geophysical results suggest the presence of ceramic producing kilns these elemental enrichments are thought to result from burning wood or dung as fuel for the detected kilns in addition local anomalies of co cr fe mg mn and ni were found to reflect the working and storage of ophiolitic clays employed as a raw material for ceramic production radiocarbon dating of charcoal in a 2 5 m deep drill core in this zone provides ages between ad 120 and 350 at depths of 50 and 60 cm al as ba ca na sr ti and pb are considered geogenic elements in this study the present study supports the theory that geochemical prospection holds potential as a surveying technique as it was found that chemical data facilitate the interpretation of structures detected by geophysical and archaeological methods thereby creating an extra dimension to the interpretation of survey data the results further argue in favour of using strong acid extractions and the consideration of a large suite of elements when applying chemical soil survey as an archaeological prospection technique and highlight the importance of considering site lithology multivariate statistics proved to be invaluable in distinguishing anthropogenic from lithological soil patterns

the gabbro eclogite transformation an oxygen isotope and petrographic study of west alpine ophiolites both magmatic and eclogitic parageneses are preserved in the gabbros of western alpine ophiolites samples with relic magmatic mineralogies display partial transformation to eclogitic assemblages along cracks and grain boundaries gabbros with eclogitic mineralogies contain zoned pseudomorphs after olivine comprising talc rich cores with kyanite mg chloritoid and omphacite in outer cores and garnet rims the compositional zonation of these olivine pseudomorphs closely parallels that shown by olivines in hydrothermally altered ocean floor gabbros the eclogitic gabbros are hydrous containing paragonite zoisite and other water bearing minerals and it has been suggested that water was introduced during high pressure metamorphism however the similarity of olivine alteration patterns to those of ocean floor gabbros suggests that hydration and local metasomatism leading to the stability of aluminous minerals in olivine sites occurred during hydrothermal alteration prior to subduction oxygen isotope systematics are consistent with this proposal alpine gabbros with magmatic relics have a mean 18o value of 5 7 0 7 similar to that of unaltered oceanic crust whereas eclogitic gabbros have a mean 18o value of 4 8 0 9 this statistically significant difference is consistent with the eclogitic samples having undergone high temperature ocean floor alteration the preservation of magmatic and hydrothermal 18o values in ocean floor gabbros that have been metamorphosed at 2 2 5 gpa 60 75 km implies that the deeper levels of ocean crust have not experienced pervasive fluid flow during subduction or subsequent exhumation magmatic assemblages were preserved despite an overstep of eclogitization reactions by at least 0 6 1 1 gpa implying that equilibrium was not attained in undeformed parts of the system because of slow diffusion in water deficient rock volumes

assessing the geochemical and tectonic impacts of fluid rock interaction in mid crustal shear zones a case study from the intracontinental alice springs orogen central australia the reynolds anmatjira ranges central australia form part of a high grade basement terrane dissected by intensely metasomatized transpressional shear zones active during the ordovician carboniferous alice springs orogeny unlike typical retrograde structures associated with discrete fluid flow the mid crustal setting and intracontinental nature of these shear systems present significant problems for the source and ingress mechanism of the fluid involved in their rehydration to address these issues we describe two detailed traverses across deformed and metasomatized basement rocks in this region and interrogate their record of fluid rock interaction from various perspectives both traverses combine structural and petrological observations with zr in rutile and ti in quartz thermobarometry oxygen and hydrogen stable isotope analysis and major trace and rare earth element mobility trends each technique is critically evaluated for its utility in this study and its more widespread applicability to alternative field areas providing a strategic framework for the general investigation of fluid affected shear zones ultimately the integrated data sets specify pressure temperature conditions of 530 c and 4 5 kbar implying average apparent thermal gradients of 29 36 c km 1 and depths of 14 18 km other characteristic features to emerge include strongly variable element mobilities and pronounced isotopic depletion fronts consistent with the alteration effects of an externally derived non equilibrium fluid this is confirmed by calculated fluid compositions indicative of contributions from a fluid of meteoric origin with estimated 18o and d values as low as 2 3 and 59 8 respectively we propose that these surficial fluid signatures are imposed on the mid crust by the prograde burial and dehydration of hydrothermally altered fault panels produced during pre orogenic basin formation progressive fluid release with continued subsidence then leads to the accumulation of increasing fluid volumes in the vicinity of the brittle ductile transition promoting extensive hydration metasomatism and reaction softening at the locus of stress transmission from plate boundary sources the sustained injection of externally derived fluids into refractory crustal material may thus stimulate a critical reduction in the long term strength of the lithosphere providing strong impetus for the initiation and advancement of intracontinental orogenesis

geostatistical modelling of chemical residues on archaeological floors in the presence of barriers maps representing the distribution of chemical residues over anthropogenic floors are the main diagnostic tools used by archaeologists for addressing the identification of geochemical signatures of past actions geostatistics allows producing these maps from a sample of locations by modelling the spatial autocorrelation structure of these kind of phenomena however the homogeneity of the prediction regions is a strong assumption in the model the presence of barriers such as the inner walls of domestic units introduces discontinuities in prediction areas in this paper we investigate how to incorporate information of a geographical nature into the process of geostatistical prediction we propose the use of cost based distances to quantify the correlation between locations a solution which has proved to be a practical alternative approach for archaeological intrasite analysis the cost based approach produces more reliable results avoiding the unrealistic assumption of the homogeneity of the study area as a working example a case study of the distribution of two specific chemical signatures in domestic floors is presented within a controlled ethnographical context in northern gujarat india on a broad disciplinary scale the benefits of using our approach include improved estimates in regions with complex geometry and lower uncertainty in the kriging predictions

the story in the floors chemical signatures of ancient and modern maya activities at aguateca guatemala abstract soil chemical analysis has been one of the most active and promising areas among the recent innovations in household archaeology ancient inhabitants unintentionally left chemical imprints of daily activities providing important clues as to past practices and space use which are difficult to judge from artifactual data alone soil chemical testing in the maya region is particularly promising given the highly calcareous nature of the soils derived from the carbonate geology of the region as calcium ions and soil alkalinity render phosphorous iron and other metallic ions insoluble this paper reports the results of soil chemical analysis of modern and ancient residential structures at the archaeological park of aguateca guatemala an ethnoarchaeological study of the guards living quarters and archaeological data from rapidly abandoned classic period residences provided opportunities to refine an understanding of the relationship between human activities and soil chemical signatures both cases exhibited good correlations of high phosphorous concentrations in soils with food processing consumption and disposal high levels of heavy metals in the modern structures probably derived from the filing of machetes and the disposal of flashlight batteries whereas the use of mineral pigments and craft activities appear to have contributed to the concentrations of these elements in archaeological contexts

a pedological investigation of an archaeological site in ontario canada ii use of chemical data to discriminate features of the benson site abstract soil samples from the benson site a former huron indian village 1600 s were collected on a 1 m grid at a depth of 15 cm over a portion of the village the benson site is located about 90 km northeast of toronto canada discriminant analysis statistically distinguishes between groups of cases by the employment of descriminating variables this mathematical technique made it possible to rank the chemical attributes of soil materials as to their usefulness in discriminating between huron settlement features such as middens pits longhouses hearths posts and former pathways two discriminant analyses were performed in this study one utilized all the features of the village and the other analysis did not include the chemical data from soils in the midden or pits the midden and some pits were exceedingly rich in most elements which overshadowed the amounts found in other features this tended to complicate the analysis of the data by statistical methods it was found however that soils of the former paths can be separated from those of pits posts and longhouses on exchangeable magnesium levels in addition organic and inorganic phosphorus levels between the soils of the paths pits and houses were statistically distinct dolomite exchangeable calcium and potassium levels are statistically different enough to distinguish the soils in paths or walking trails from those of posts exchangeable magnesium was the most useful chemical constituent of the soil material analyzed at the benson site in terms of the number of settlement features that could be distinguished by this information alone exchangeable magnesium is followed by organic phosphorus dolomite inorganic phosphorus and calcite exchangeable calcium potassium and ph and organic carbon in its usefulness in separating huron settlement features on the basis of chemical attributes of the soils

an evaluation of the site specificity of soil elemental signatures for identifying and interpreting former functional areas abstract soil multi element analysis is now a routine technique employed to help answer questions about space use and function in and around archaeological sites the pattern of enhancement of certain elements including p pb ca zn and cu has been shown by numerous studies to correlate closely with the archaeological and historical record interpretation of these soil signatures however has generally been more problematic one approach to the problem has been the use of ethnographic or known sites to guide interpretation but how confidently can results from one site be extrapolated to another this study of abandoned farms tests the site specificity of soil multi element signatures of past space use through the use of discriminant models data analysis suggests that one to one comparisons of similar sites are much less accurate 38 accuracy than comparisons based on a wider range of sites 59 3 accuracy even when the latter have contrasting geology the results highlight the importance of individual anthropogenic practices during occupation and abandonment in the development of diagnostic soil geochemical signatures

active hydrothermal systems during the recent uplift of nanga parbat pakistan himalaya during the last 10 m y the nanga parbat haramosh massif in the northwestern himalaya has been intruded by granitic magmas has undergone high grade metamorphism and anatexis and has been rapidly uplifted and denuded as part of an ongoing project to understand the relationship between tectonism and petrologic processes we have undertaken an isotopic study of the massif to determine the importance of hydrothermal activity during this recent metamorphism our studies show that both meteoric and magmatic hydrothermal systems have been active over the last 10 m y we suggest that the rapid uplift of the massif created a dual hydrothermal system consisting of a near surface flow system dominated by meteoric water and a flow regime at deeper levels dominated by magmatic metamorphic volatiles meteoric fluids derived from glaciers near the summit of nanga parbat were driven deep into the massif along the transpressional faults causing 18 o and d depletions in the gneisses and marked oxygen isotopic disequilibriuui between mineral pairs from the fault zones the discharge of these meteoric fluids occurs in active hot springs that are found along the steep faults that border the massif at deeper levels within the massif infiltration of low 18 o magmatic fluids caused 18 o depletions in the gneisses within the migmatite zone these low 18 o fluids were derived from the young 4 ma relatively low 18 o granites 8 that are found within the core of the massif geochronological evidence in the form of fission track and 40 39 ar cooling ages and u pb ages on accessory minerals from the granites and gneisses provide a constraint on the timing of fluid flow in the surface outcrops we examined fluid infiltration in the migmatite zone rocks located along the tato traverse was coeval with metamorphism granite emplacement and rapid denudation in the interval 0 8 3 3 ma finally we infer from the presence of active hot springs that significant flow systems continue to be active at depth within the central portion of the nanga parbat haramosh massif

sequence and style of major post nappe structures simplon pennine alps abstract in the upper pennine nappe complex of the simplon pennine alps switzerland and italy at least three phases of major post nappe folding in places associated with thrusting can be distinguished these are superimposed on an earlier formed partly chaotic complex of tectonic units including the bernhard and monte rosa continental flakes and the zermatt saas and antrona ophiolite complexes the earliest post nappe folds were essentially isoclinal throughout the whole region and were accompanied by a strong schistosity which is the main foliation in most areas later two successive phases of back folding led to the present overall structure both phases typically show rapid variations in style from open folds lacking axial planar schistosity to very tight structures with complete foliation transposition this has been demonstrated by systematically mapping the major axial traces over the whole region successively removing the major structures in reverse order shows that the ophiolite complexes were originally part of a continuous unit marking an important suture between the bernhard and monte rosa nappes

fluid flow and metasomatic fault weakening in the moresby seamount detachment woodlark basin offshore papua new guinea low angle normal faults play a prominent role in discussions about fault strength as they require significant weakening to remain active at low angles the submerged moresby seamount detachment msd is arguably the best exposed active low angle detachment worldwide we analyzed dredged msd protoliths cataclasites and mylonites to investigate deformation mechanisms and fault weakening processes deformation is accompanied by important syntectonic fluid induced mass transfer controlling the rheological behavior of the msd while the mafic protolith behaves brittlely at the onset of deformation the metasomatic mineralogical and chemical changes cause a transition to plastic flow as the rock is progressively exhumed immobile elements provide a reference frame for total material gains and losses si ca and k are syntectonically enriched while fe ti mg and al are depleted mass increase is about 10 in the cataclasites and about 48 in the mylonites main mechanism is syntectonic veining causing enrichment in calcite and quartz thus making the mylonites capable to flow plastically minimum time integrated fluid flux is calculated as 3 105 m3 m 2 indicating that the msd is an important fluid conduit the fluids have a deep crustal source a bottom water temperature and turbidity anomaly suggests that the hydrothermal system is still active syntectonic veining in fault rocks and recent seismic activity both suggest that the msd is intermittently brittle implying a brittle plastic transition at unusually high temperature and low differential stress we conclude that fault zone metasomatism is crucial in forming weak detachments at passive margins and may be a prerequisite for successful crustal breakup

geoarchaeology in an urban context the uses of space in a phoenician monumental building at tel dor israel abstract interpretation of past urban societies in the near east whose settlements are known mostly as tell sites is largely based on macro stratigraphy and on the association of architecture with macroscopic artifacts analyses of sediments common in prehistoric sites are rare in tell sites here we show the results of a detailed geoarchaeological study of the micro stratigraphy of a sedimentary sequence associated with early iron age phoenician monumental architecture the study involves mineralogical micromorphological and phytolith analyses and provides new insights into the stratigraphic sequence and the use of architectural spaces the sedimentary sequence examined comprises alternating layers of gray fill deposits and white floors we show that floors made from local calcareous sandstone in the lower part of the sedimentary sequence were heated and are thus in effect plaster floors a concentration of micro laminated trampled fish remains above the most elaborate of these plaster floors indicates activities related to fish processing fine white layers in the upper part of the sedimentary sequence that were considered as plaster based on macroscopic examination are in fact composed almost entirely of opaline grass phytoliths the phytoliths appear in an undulating micro laminated structure and are associated with dung spherulites and phosphate nodules thus probably reflecting livestock penning the formation of phytolith floors involves extensive volume reduction due to the degradation of the organic material and this may result in floor subsidence a phenomenon that is often observed in archaeological sites most fill deposits include macroscopic and microscopic remains of wood ash bones phytoliths charcoal ceramics plaster and mollusk shells reflecting the debris produced from household activities this study shows how a combination of macro stratigraphy with microscopic and mineralogical analyses of the sediments within architectural spaces can provide information on the varying ways in which the space was used through time and also contributes to solving macro stratigraphic problems

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

deciphering the inorganic chemical record of ancient human activity using icp ms a reconnaissance study of late classic soil floors at cancuen guatemala abstract inorganic chemical analysis of soil floors using inductively coupled plasma mass spectrometry icp ms was undertaken to provide information on the nature and location of past human activity in the ancient maya city of cancuen guatemala the use of icp ms to detect trace and ultra trace elemental enrichment of two excavated soil floors from the late classic period is the first study of its kind in mesoamerican archaeology geochemical background of the site was established by the analysis of palaeosols and nearby undisturbed off site soil profiles robust statistical methods used in the study clearly distinguished the level of anthropogenic enrichment across the former floors many elements measured showed only minor departures 10 20 from the site s background soil chemistry the greatest levels of elemental enrichment were detected in the rare earth elements mercury and gold the latter is of particular interest considering the consensus that gold was absent from the world of the classic period maya comparisons of the spatial pattern of mercury enrichment with lithic and archaeological data show strong linkages to past industrial and ritual activities elevated rare earth element concentrations were recorded broadly across both soil floors and are considered to be related to concentrated human occupation in antiquity

multi element analysis of soils from scottish historical sites interpreting land use history through the physical and geochemical analysis of soil arable farming in the highlands and islands of scotland by the 18th century was characterized by labour intensive techniques of husbandry and the transfer of fertilizing resources from their extensive non arable sector to their arable land such practices had a considerable impact on soil development and characteristics the use of inductively coupled plasma mass spectrometry icp ms in this study has allowed the geoarchaeological significance of a broad range of elements to be investigated on soils collected from a former settlement site on the trotternish peninsula isle of skye the on site geochemical data are expressed as enrichment factors relative to the mean concentration of the control samples of the elements investigated in this study ba la ce pr k cs th and rb were found to be indicative of human settlement at greaulin whilst the spatial enrichment patterns for ca and sr suggest additions of shell sand to the arable land over the central region of the site vanadium co zn pb ni ga sc mg cu and u all showed minimal or no on site enrichment the generally lower on site levels of percentage loss on ignition relative to the control soils are interpreted as reflecting the former use of the fields for cultivation interpretation of the p results in the light of documentary evidence suggest that some of the 19th century croft farmsteads may have reoccupied sites formerly inhabited during pre clachan times hence the clachan at greaulin may not have been as long standing a settlement feature as traditionally envisaged

the geometry and timing of orogenic extension an example from the western italian alps contacts between rocks recording large differences in metamorphic grade are indicative of major tectonic displacements low p upon high p contacts are commonly interpreted as extensional i e material points on either side of the contact moved apart relative to the palaeo horizontal but dating of deformation and metamorphism is essential in testing such models in the western alps the piemonte ophiolite consists of eclogites t 550 600 c and p 18 20 kbar structurally beneath greenschist facies rocks t 400 c and p 9 kbar mapping shows that the latter form a kilometre wide shear zone the gressoney shear zone gsz dominated by top se movement related to crustal extension rb sr data from micas within different gsz fabrics which dynamically recrystallized below their blocking temperature are interpreted as deformation ages ages from different samples within the same fabric are reproducible and are consistent with the relative chronology derived from mapping they show that the gsz had an extensional deformation history over a period of c 9 myr between c 45 36 ma this overlaps in time with the eclogite facies metamorphism the gsz operated over the entire period during which the footwall evolved from eclogite to greenschist facies and was therefore responsible for eclogite exhumation the discrete contact zone between eclogite and greenschist facies rocks is the last active part of the gsz and truncates greenschist facies folds in the footwall these final movements were therefore not a major component of eclogite exhumation pressure estimates associated with old and young fabrics within the gsz are comparable indicating that during extensional deformation there was no significant unroofing of the hangingwall since there are no known extensional structures younger than 36 ma at higher levels in this part of the alps exhumation since the final juxtaposition of the two units at 36 ma seems to have been dominated by erosion key words deformation age eclogite exhumation rb sr dating tectonic

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

interaction of chemical and physical processes during deformation at fluid present conditions a case study from an anorthosite leucogabbro deformed at amphibolite facies conditions we present microstructural and chemical analyses of chemically zoned and recrystallized plagioclase grains in variably strained samples of a naturally deformed anorthosite leucogabbro southern west greenland the recorded microstructures formed in the presence of fluids at mid crustal conditions 620 640 c 7 4 8 6 kbar recrystallized plagioclase grains average grain size 342 m with a random crystallographic orientation are volumetrically dominant in high strain areas they are characterized by asymmetric chemical zoning an80 cores and an64 rims that are directly associated with areas exhibiting high amphibole content and phase mixing analyses of zoning indicate anisotropic behaviour of bytownite plagioclase with a preferred replacement in the left langle 0 10 right rangle direction and along the 001 plane in areas of high finite strain recrystallization of plagioclase dominantly occurred by bulging recrystallization and is intimately linked to the chemical zoning the lack of cpo as well as the developed asymmetric zoning can be explained by the activity of grain boundary sliding accommodated by dissolution and precipitation creep dpc in low strain domains grain size is on average larger and the rim distribution is not related to the inferred stress axes indicating chemically induced grain replacement instead of stress related dpc we suggest that during deformation in high strain areas pre existing phase mixture and stress induced dpc caused grain rotations that allowed a deformation enhanced heterogeneous fluid influx this resulted in local plagioclase replacement through interface coupled dissolution and precipitation and chemically induced grain boundary migration accompanied by bulging recrystallization along with neocrystallization of other phases this study illustrates a strong interaction and feedback between physical and chemical processes where the amount of stress and fluids dictates the dominant active process the interaction is a cause of deformation and external fluid infiltration with a result of strain localization and chemical re equilibration at amphibolite facies conditions

focused fluid flow during subduction oxygen isotope data from high pressure ophiolites of the western alps abstract during subduction hydrothermally altered oceanic crust undergoes extensive dehydration the water released migrates upwards and may escape along the slab mantle interface or continue rising to hydrate the mantle overlying the subducting slab oxygen isotope ratios from eclogitic ophiolites of the western alps correlate closely with lithology samples with little altered basalt as a protolith have 18 o values of 5 1 6 0 material representing low temperature alteration zone rocks have 18 o values of 5 9 6 6 and rocks orginating in high temperature alteration zones have 18 o values of 4 6 5 3 these isotopic values closely approach those of the ocean crust and unmetamorphosed ophiolites these data suggest that the alpine rocks have not experienced significant fluid flow during metamorphism implying that the escape of fluid from subducted ocean crust is highly focused probably along structurally controlled pathways to the top of the slab the fluid may then continue largely along the slab mantle interface although a portion of it rises further to hydrate the overlying mantle

kyanite eclogite to amphibolite fades evolution of hydrous mafic and pelitic rocks adula nappe central alps in the southern adula nappe central alps two stages of regional metamorphism have affected mafic and pelitic rocks earlier eclogite facies with a regional zonation from glaucophane eclogites to kyanite hornblende eclogites was followed by a tertiary overprint which varied from greenschist to high grade amphibolite facies despite a common metamorphic history contrasting equilibration conditions are often recorded by high pressure mafic eclogite and adjacent predominantly lower pressure pelite assemblages this pressure contrast may be explained by different overprinting rates of the two bulk compositions during unloading the rates are controlled by a mechanism in which dehydrating metapelites provide the h2o required for simultaneous overprinting of enclosed mafic eclogites by hydration

high pressure metamorphism of the zermatt saas ophiolite zone switzerland within the zermatt saas ophiolite zone of the western alps a record of polystadial high pressure metamorphism is well preserved early blueschist assemblages retained as inclusions in garnets were succeeded by eclogitic assemblages which in some rocks contained lawsonite kyanite talc and chloritoid these eclogitic assemblages formed by prograde reaction from the early blueschists subsequently reaction of these eclogites with a mixed h 2 o co 2 vapour phase led to the replacement of kyanite by paragonite and the partial replacement of omphacite garnet paragenses by assemblages containing glaucophane paragonite and ankerite high pressure eo alpine metamorphism took place under conditions of 550 600 c and 17 5 20 kbar values of a h 2 o between 0 55 and 1 are high enough to accommodate equilibration with a water rich vapour phase under the highest grade conditions the presence of such a fluid phase is locally indicated by the presence of quartz rich veins containing omphacite and kyanite this vapour phase was absorbed during retrogression later rehydration is limited to areas close to albite veins tectonic contacts and bodies of metasediment the metamorphic conditions determined for the zermatt saas zone are compatible with those suggested for over and under lying units these conditions and the p t path inferred by comparing the reaction histories with a petrogenetic grid for the system na 2 o cao mgo a1 2 o 3 sio 2 h 2 o suggest that metamorphism occurred during subduction to depths of between 60 and 70 km and subsequent exhumation during the alpine orogeny

the geoarchaeological significance and spatial variability of a range of physical and chemical soil properties from a former habitation site isle of skye of the 34 major and trace elements investigated in this study enrichments of k th rb and to a lesser extent cs were associated with former habitation of the area whilst high levels of sr and to a lesser extent ca were associated with the adjacent field area this latter enrichment is thought to represent additions of shell sand and or bone and fish refuse phosphorus is a less reliable indicator of human habitation than k rb and th possibly because p enrichment may be caused by additions of animal manure as well as by human habitation of an area vanadium co zn pb ni ga sc mg cu and u all indicated negligible on site enrichment whilst cr and organic matter content were found to be depleted in the on site soils relative to the control samples consideration of the degree of variability in the soil parameters investigated has implications for the bulk or composite sampling of soils over sites of former habitation

the timing of and nature of greenschist facies deformation and metamorphism in the upper pennine alps the upper pennine nappes in the western alps are cut by structures that locally place european basement rocks over those of the piemonte zone which represent the sutured remains of alpine ocean crust in the taschalp area of switzerland the mischabel backfold and associated se verging shearing carries gneisses of the grand saint bernard nappe over eclogitic material of the zermatt saas zone greenschist facies assemblages are developed locally in the foot wall and hanging wall of the mischabel structure as well as in the sheared rocks of the thrust zone rb sr 40ar 39ar and u pb studies of white micas amphiboles and sphenes show that greenschist assemblages developed at circa 44 ma in the zermatt saas zone of the footwall and at circa 40 ma in the thrust zone rb sr data from the literature document muscovite and biotite ages in strongly foliated grand saint bernard gneisses of the hanging wall of circa 36 and 32 ma respectively these are thought to indicate that deformation on the mischabel structure continued for at least 5 m y rapid cooling inferred for the zermatt saas ophiolites in the mid eocene may document either the tectonic emplacement of the ophiolite over the underlying monte rosa massif or their extensional unroofing it is not possible to determine with certainty whether the mischabel structure is extensional or contractional on a crustal scale the age of cooling and deformation reported here show that it is not possible that the mischabel structure was responsible for the exhumation of the high pressure assemblages in the zermatt saas and monte rosa rocks

ancient maya impacts on the earth s surface an early anthropocene analog abstract the measure of the mayacene a microcosm of the early anthropocene that occurred from c 3000 to 1000 bp comes from multiple late quaternary paleoenvironmental records we synthesized the evidence for maya impacts on climate vegetation hydrology and the lithosphere from studies of soils lakes floodplains wetlands and other ecosystems maya civilization had likely altered local to regional ecosystems and hydrology by the preclassic period 3000 1700 bp but these impacts waned by 1000 bp they altered ecosystems with vast urban and rural infrastructure that included thousands of reservoirs wetland fields and canals terraces field ridges and temples although there is abundant evidence that indicates the maya altered their forests even at the large urban complex of tikal as much as 40 of the forest remained intact through the classic period existing forests are still influenced by ancient maya forest gardening particularly by the large expanses of ancient stone structures terraces and wetland fields that form their substrates a few studies suggest deforestation and other land uses probably also warmed and dried regional climate by the classic period 1700 1100 bp a much larger body of research documents the maya impacts on hydrology in the form of dams reservoirs canals eroded soils and urban design for runoff another metric of the mayacene are paleosols which contain chemical evidence for human occupation revealed by high phosphorus concentrations and carbon isotope ratios of c 4 species like maize in the c 3 dominated tropical forest ecosystem paleosol sequences exhibit maya clays a facies that reflects a glut of rapidly eroded sediments that overlie pre maya paleosols this stratigraphy is conspicuous in many dated soil profiles and marks the large scale maya transformation of the landscape in the preclassic and classic periods some of these also have increased phosphorous and carbon isotope evidence of c 4 species we synthesize and provide new evidence of maya period soil strata that show elevated carbon isotope ratios 13 c indicating the presence of c 4 species in typical agricultural sites this is often the case in ancient maya wetland systems which also have abundant evidence for the presence of several other economic plant species the mayacene of c 3000 to 1000 bp was thus a patchwork of cities villages roads urban heat islands intensive and extensive farmsteads forests and orchards today forests and wetlands cover much of the maya area but like so many places these are now under the onslaught of the deforestation draining and plowing of the present anthropocene

contrasting serpentinization processes in the eastern central alps stable isotope compositions have been determined for serpentinites from between davos arosa platta nappe switzerland and the valmalenco italy d and 18o values 120 to 60 and 6 10 respectively in the arosa platta nappe indicate that serpentinization took place on the continent at relatively low temperatures in the presence of limited amounts of metamorphic fluids that contained a component of meteoric water one sample of chrysotile has a 18o value of 13 providing evidence of high w r ratios and low formation temperature of lizardite chrysotile in this area in contrast relatively high d values 42 to 34 and low 18o values 4 4 7 4 for serpentine in the eastern part of the valmalenco suggest a serpentinization process that took place at moderate temperatures in fluids that were dominated by ocean water the antigorite in the valmalenco is the first reported example of continental antigorite with an ocean water signature an amphibole sample from a metasomatically overprinted contact zone to metasediments d 36 indicates that the metasomatic event also took place in the presence of ocean water lower d values 93 to 60 of serpentines in the western part of the valmalenco suggest a different alteration history possibly influenced by fluids associated with contact metamorphism low water rock ratios during regional metamorphism and metasomatism have to be assumed for both regions

soil chemical identification of ten thousand years of prehistoric human activity areas at the munsungun lake thoroughfare maine abstract soils on a palaeo indian to historic sequence in one maine locale are analysed for chemical enrichment to guide excavation of four discrete sites up to 4000 m 2 samples are collected in grid patterns and analysed for ph mg p and ca concentrations of mg point to probable hearths to define some centres of human activity on each site these correlate well with anomalies determined independently by magnetometric survey excavation of anomalies provides evidence of hearths culturally diagnostic artifacts but also features resulting from tree throw and drainage variation the p and ca results develop definition and delimitation of activity areas thus refining directions for further excavation since p and ca concentrations result from substantial or sustained human occupation they show promise for preexcavation differentiation of habitation sites from limited and specialized activity sites such as lithic chipping stations soil chemical analysis provides both a synchronic and diachronic preview of site perimeters size and activity areas the consistent site definition at the munsungun lake thoroughfare is useful for explaining patterns as well as locating them

identification of the scales of differential element mobility in a ductile fault zone two fundamentally different scales of element mobility have been identified in the upper amphibolite facies hunts brook fault zone of south central connecticut usa field relations mineral chemistry and 80 bulk rock analyses provide overwhelming evidence that the blastomylonitic schists and gneisses of the fault zone were derived from the enclosing granodioritic rope ferry orthogneiss two sample mass balance calculations between the rope ferry gneiss and fault rocks strongly suggest that the rope ferry gneiss was segregated into biotite rich schists and quartz plagioclase rich gneisses through the centimetre scale transfer of si al ca na ba and zr from schists to gneisses three and four sample mass balance calculations provide convincing evidence that al ca na and ba were lost and si and k gained by the entire fault zone both scales of metasomatism have been identified at two localities separated by 20 km implying that the metasomatic processes were pervasive throughout the fault zone from the mass balance calculations an apparent disparity in k mobility arises k appears to be gained by the entire fault zone but is immobile during the centimetre scale segregation this is because mass balance calculations can only detect differential element mobility differential element mobility requires that the mechanism of metasomatism produces chemical potential gradients therefore the identification of differentially mobile elements provides insight into the mechanisms of metasomatism the immobility of k during segregation of schists and gneisses implies that the segregation was not achieved through the extraction of partial melt however the element mobility is reconcilable with deformation driven metamorphic differentiation the gains of si and k and losses of ca na al and ba for the entire fault zone are also inconsistent with the intrusion or extraction of partial melt but may reflect the infiltration of a metasomatizing aqueous fluid

timing and nature of fluid flow and alteration during mesoproterozoic shear zone formation olary domain south australia the development of shear zones at mid crustal levels in the proterozoic willyama supergroup was synchronous with widespread fluid flow resulting in albitization and calcsilicate alteration monazite dating of shear zone fabrics reveal that they formed at 1582 22 ma at the end of the olarian d3 deformational event and immediately prior to the emplacement of regional s type granites two stages of fluid flow are identified in the area first an albitizing event which involved the addition of na and loss of si k and fe and a second phase of calcsilicate alteration with additions of ca fe mg and si and removal of na fluid fluxes calculated for albitization and calcsilicate alteration were 5 56 109 to 1 02 1010 mol m 2 and 2 57 108 5 20 109 mol m 2 respectively these fluxes are consistent with estimates for fluid flow through mid crustal shear zones in other terranes the fluids associated with shearing and alteration are calculated to have 18o and d values ranging between 8 and 11 and 33 and 42 respectively and nd values between 2 24 and 8 11 our results indicate that fluids were derived from metamorphic dehydration of the willyama supergroup metasediments fluid generation occurred during prograde metamorphism of deeper crustal rocks at or near peak pressure conditions shear zones acted as conduits for major crustal fluid flow to shallow levels where peak metamorphic conditions had been attained earlier leading to the apparent retrograde fluid flow event thus the peak metamorphism conditions at upper and lower crustal levels were achieved at differing times prior to regional granite formation during the same orogenic cycle leading to the formation of retrograde mineral assemblages during shearing

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

an o isotope profile through the hp lt corsican ophiolite france and its implications for fluid flow during subduction abstract subduction zones are important sites for fluid generation as the downgoing slab undergoes progressive high pressure metamorphism these fluids are thought to play an important role in the generation of arc magmas but their affect on the subducted slab itself is less clear in this study the stable isotope geochemistry of the corsican ophiolite which is variably affected by subduction related metamorphism was investigated to assess the impact of subduction zone fluid flow on the downgoing slab a total of 170 stable isotope analyses oxygen and carbon showed the following features 1 overall the ophiolite preserves the same oxygen isotope profile with depth as unmetamorphosed ophiolites 2 the variation in oxygen isotope values for different areas does not correlate with metamorphic grade 3 oxygen and carbon isotope values for calcite in the ophiolite are not in equilibrium with the ophiolite but are similar to those of the overlying calc schists schistes lustres and 4 hydrogen isotopes indicate that serpentinitisation of ultramafics occurred during sub seafloor hydrothermal alteration and probably also during tectonic emplacement of the ophiolite these features indicate that large scale fluid flow did not affect the corsican ophiolite during subduction zone metamorphism calcite in the ophiolite was probably precipitated from co2 bearing fluids derived from decompression dehydration reactions affecting the overlying schistes lustres during exhumation of the ophiolite bearing schistes lustres nappes given that ocean crust must undergo at least some dehydration during prograde subduction zone metamorphism the evolved fluids must be either highly channelled or exit the slab relatively quickly so as to not interact with it the results of this study indicate that the important fluid pathways on corsica have yet to be identified but are probably the shear zones and fault systems that bound different slices of the high pressure nappe stack

evidence for extension in the western alpine orogen the contact between the oceanic piemonte and overlying continental sesia units abstract in the alps and other orogens major tectonic contacts must have been established during convergence and overthrusting what is less clear is how strongly these contacts were modified as the orogen evolved during alpine collision continental crust of the overriding plate the sesia unit is inferred to have been thrust northwest over oceanic material of the piemonte unit both units preserve in parts eclogite facies metamorphism however all structures along this contact in our study area indicate that final movement was southeast directed with no clear evidence of the kinematics of earlier movement these structures include se verging folds se directed shear bands and larger normal faults downthrowing to the southeast it is inferred that there was a se directed shear regime below the contact which although locally buckling and shortening earlier lithological contacts was dominantly extensional with respect to pre existing tectonic layering the lower limit of this shear regime has not been identified although se directed shear is common throughout the upper greenschist facies part of the piemonte unit we show that this shear passes beneath the sesia zone and does not re emerge it is therefore a shear which was net extensional relative both to the modern surface and to the palaeosurface it may have contributed to the unroofing of eclogite facies rocks in the lower part of the piemonte unit although additional timing data are required to clarify this nearby se directed shears buckle and imbricate earlier layering within the piemonte unit these are normally identified as backthrusts yet they do not appear to breach the base of the sesia unit and might merge with the extensional shear even though these structures shorten layering they too could have been extensional relative to the earth s surface the significance of alpine backthrusts should be reappraised in this context this study indicates that hinterland directed extension could have been an important phenomenon during alpine evolution

elemental prospecting and geoarchaeology in turkey and mexico abstract understanding past human impacts on soils requires many forms of evidence including elemental chemistry human activities leave traces of different elements distinguishing activity sites since the 1990s more scholars have used a full range of analytical techniques including inductively coupled plasma atomic emission spectroscopy icp aes and inductively coupled plasma mass spectroscopy icp ms also since that time the near singular focus on phosphate as a prime indicator of human activity has broadened to include a large suite of elemental indicators aided by the emergence of many tools and techniques such as icp this paper focuses on the elemental chemistry of sediments at two archaeology sites chunchucmil mexico and kinet turkey the purpose of this study is to understand how certain elements correlate with each other and vary by space and time at different archaeology sites and as an important methodological consideration how different solvents affect icp aes analyses in other words does human activity significantly alter the elemental chemistry of a site and if so is this in a systematic way or does it vary geographically and are these chemical signatures of human activity hidden or highlighted by different icp methods we examined soil chemistry by types of geomorphic and archaeological location contexts e g floors natural deposits walls streets and by age of deposit e g hellenistic iron age to detect differences in soil chemistry signatures associated with them and for regional variations in icp methods effectiveness our analyses revealed detectable differences between natural and anthropogenic deposits site types eras and large differences between methods high amounts of lead were correlated with streets and rooms in the medieval and bronze periods in kinet turkey and natural deposits had lower levels of cadmium and mercury icp np treatments revealed higher detection levels of most elements than did icp dt treatments in chunchucmil mexico

integrated geoarchaeological methods for the determination of site activity areas a study of a viking age house in reykjavik iceland for over a decade geoarchaeological methods such as multi element analysis and soil micromorphology have been used to identify and interpret activity areas on archaeological sites however these techniques along with others such as magnetic susceptibility loss on ignition and microrefuse artefact and bone distribution analyses are rarely integrated in the study of a single site even though they provide very different and potentially complementary data this paper presents a comparative study of a wide range of geoarchaeological methods that were applied to the floors sediments of a viking age house at the site of a alstraeti 16 in central reykjavik iceland along with more traditional artefact and bone distribution analyses and a spatial study of floor layer boundaries and features in the building in this study the spatial distributions of artefacts and bones could only be understood in the light of the ph distributions and on their own they provided limited insight into the use of space in the building each of the sediment analyses provided unique and valuable information about possible activity areas with soil micromorphology proving to have the greatest interpretive power on its own however the interpretation potential of the geochemical methods was dramatically enhanced if they were integrated into a multi method dataset

sm nd isotopic evidence on the age of eclogitization in the zermatt saas ophiolite rocks within the zermatt saas ophiolite of the western alps have undergone eclogite facies metamorphism during subduction prior to the alpine collision the metamorphic history of these rocks is well defined with eclogitic assemblages being followed by the limited growth of blueschist assemblages of glaucophane and paragonite subsequent greenschist alteration occurs adjacent to faults veins and metasediments away from such sources of water retrogression is very limited sm nd isotopic analyses of an essentially unretrogressed eclogitic metabasalt suggest that eclogite facies metamorphism occurred at 52 18 ma the large uncertainty is due to the presence of very small amounts of nd rich epidote present as inclusions within garnet as the closure temperature of garnet to sm nd is thought to be 600dc resetting due to post high pressure diffusion is thought to be insignificant given the fine grained protolith to the sample analysed and its extensive deformation under eclogite facies conditions incomplete homogenization of pre metamorphic isotopic variations is also considered unlikely to be responsible for the young age a tertiary age of eclogitization means that models of early alpine evolution based on the cessation of high pressure metamorphism in the cretaceous need to be revised

basement and cover rock deformation during laramide contraction in the northern madison range montana and its influence on cenozoic basin formation two major laramide fault systems converge in the northwestern madison range the northwest striking southwest vergent spanish peaks reverse fault and the north striking east vergent hilgard thrust system analysis of foliation attitudes in basement gneiss north and south of the spanish peaks fault indicates that the basement in thrusted blocks of the hilgard thrust system has been rotated by an amount similar to that of the basement cover contact steeply dipping north striking breccia zones enclosing domains of relatively undeformed basement may have permitted domino style rotation of basement blocks during simple shear between pairs of thrusts in most places along the hilgard thrust system a large basement overhang produced by thrusting of archean blocks above rocks as young as late cretaceous overlies a tight footwall syncline this tight folding is largely concentric and was accommodated by flexural slip resulting in severe crowding in synclinal hinges that resulted in observed or inferred features such as bedding plane slip imbricate and out of syncline thrusting and hinge collapse the north striking madison normal fault system a zone of tertiary and quaternary valley forming normal faults is approximately parallel to the hilgard thrust system in some places normal faults are reactivated thrusts on which large basement overhangs of the hilgard thrust system were dropped back into the madison valley and covered by tertiary basin fill deposits leaving only the rocks of the footwall synclines exposed in other places both the thrusted archean blocks and the near isoclinal footwall synclines are well preserved this paired fault system the madison normal fault system and the hilgard thrust system of the northern madison range is strikingly similar to other paired systems in southwestern montana along and adjacent to the western margins of the ruby range snowcrest range greenhorn range tobacco root mountains and bridger range such systems may be the result of collapse of the crestal zones of large laramide basement uplifts arches during tertiary extension no hydrocarbon discoveries have been made in this unique structural province however petroleum exploration here has focused on basement cored anticlines both surface and subthrust related to the two major laramide fault systems and on the fault bounded blocks of tertiary rocks within the post laramide extensional basins the interplay of the two laramide fault systems during both laramide shortening and tertiary extension has produced a variety of possible structural traps in the madison range that have not yet been thoroughly investigated