structural traverse across the sierra madre oriental fold thrust belt in east central mexico the exposed structural geometry of the sierra madre oriental foreland fold thrust belt is quantified for an 130 km long strip along the moctezuma river 21 n lat east central mexico the strip extends from the belt s leading edge in the east to its most internal continuous outcrops in the west where the cordilleran structures disappear beneath cenozoic volcanic rocks the style of deformation is controlled mainly by the geometry and lithology of two major cretaceous carbonate banks el doctor and valles san luis potosi the long dimensions of which parallel the cordilleran structural trend the exposed shortening is concentrated on the platform margins 5 km on the eastern edge of the el doctor bank and 10 to 12 km on either edge of the valles san luis potosi platform and is characterized by thrust and fold nappes the thrust faults cut across the platform margin carbonates on 20 inclined tectonic ramps that were partly steepened by imbrication or by subsequent folding but pass in the overlying mechanically weak rocks nearly parallel to bedding the interiors of the platforms appear relatively undeformed whereas the regions between the two platforms zimapan basin and between the eastern edge of the valles san luis potosi platform and the foreland are composed of flexural slip folds resulting from decoupling along several incompetent layers the exposed bulk shortening measures 41 4 km or 25 for the entire traverse retrodeformable sections of the subsurface structure down to basement result in a bulk shortening of 90 1 km or 40 the subsurface deformation model for the western part of the traverse is thin skinned and has geometry similar to that on the surface the model is very speculative in the eastern part where the areal shortening calculated for thin skinned models is much larger than is the exposed linear shortening balance was attained by inferring a blind thrust on an upper detachment in the late cretaceous which has a shortening of 20 to 30 km it could also be attained however by intrabasement decoupling in a depth of 10 to 20 km deformation is brittle in the eastern part of the belt east of the valles san luis potosi platform whereas igneous intrusion controlled higher ductility characterizes the western part of the foreland fold thrust belt

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

equilibrium oxygen hydrogen and carbon isotope fractionation factors applicable to geologic systems as demonstrated by the chapters in this short course stable isotope techniques are an important tool in almost every branch of the earth sciences central to many of these applications is a quantitative understanding of equilibrium isotope partitioning between substances indeed it was harold urey s 1947 thermodynamically based estimate of the temperature dependence of 18o 16o fractionation between calcium carbonate and water and a recognition of how this information might be used to determine the temperatures of ancient oceans that launched the science of stable isotope geochemistry the approach pioneered by urey has since been used to estimate temperatures for a wide range of geological processes e g emiliani 1955 anderson et al 1971 clayton 1986 valley this volume in addition to their geothermometric applications equilibrium fractionation data are also important in the study of fluid rock interactions including those associated with diagenetic hydrothermal and metamorphic processes baumgartner and valley this volume shanks this volume finally a knowledge of equilibrium fractionation is a necessary first step in evaluating isotopic disequilibrium a widespread phenomenon that is increasingly being used to study temporal relationships in geological systems cole and chakraborty this volume in the fifty four years since the publication of urey s paper equilibrium fractionation data have been reported for many minerals and fluids of geological interest these data were derived from 1 theoretical calculations following the methods developed by urey 1947 and bigeleisen and mayer 1947 2 direct laboratory experiments 3 semi empirical bond strength models and 4 measurement of fractionations in natural samples each of these methods has its advantages and disadvantages however the availability of a variety of methods for calibrating fractionation factors has led to a plethora of calibrations not all of which are in agreement in this chapter we evaluate the major methods for determining fractionation factors

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

vein growth mechanisms and fluid sources revealed by oxygen isotope laser microprobe in situ laser microprobe analyses of millimeter wide quartz veins has revealed the largest 18o gradients 9 mm yet documented in terrestrial samples the systematic isotopic variations indicate a crack seal growth mechanism that variably interleaved 18 o enriched quartzite porphyroclasts with newly precipitated 18 o depleted vein quartz the isotopically light quartz requires open system infiltration of meteoric fluids into the quartzite during its incorporation into the ruby gap duplex central australia documentation of the fluid source in these small veins would not be possible without submillimetre isotopic sampling capabilities application of this laser based technology to other geologic problems should result in similar documentation of large isotopic gradients and provide new insight into fluid rock interactions

brittle failure mode plots for compressional and extensional tectonic regimes abstract equations governing different macroscopic modes of brittle rock failure extensional fracturing extensional shear fracturing compressional shear failure and reshear of existing faults can be represented on plots of differential stress vs effective vertical stress for a set of material properties such plots can be constructed for different tectonic regimes and correlated to depth for particular fluid pressure conditions allowing easy evaluation of the physical controls on brittle rock failure and ready comparison of the fields occupied by the three failure modes in different tectonic settings they emphasize the relative ease in terms of differential stress and fluid pressure levels of deforming a rock mass by brittle fracturing and faulting in extensional regimes compared with compressional aside from their relevance to general structural mechanics these generic failure plots have wide ranging application to understanding the initial development and progressive evolution of fault fracture systems both in sedimentary basins and as hosting structures for hydrothermal mineralization in different tectonic settings

multi proxy records of holocene palaeoenvironmental changes in the varna lake area western black sea coast high resolution spore pollen analysis of laminated sediments of newly taken core 3 870 cm long from varna lake northeastern bulgaria is combined with multiproxy micropalaeontological analyses of dinoflagellate cysts acritarchs and other non pollen palynomorphs npp including fossil algal and fungal remains the location of the core is close to several submerged praehistorical sites and the varna chalcolithic necropolis and permits more precise palaeoecological correlations of obtained results with available archaeological and geochronological data the established age vs depth model shows that the formation of the lake started after 7870 cal bp due to a rise of the black sea level also known as the first phase of the vityazevyan black sea transgression after ca 94 y the second phase of the vityazevyan black sea transgression is registered by a major change in the sedimentation and formation of molluscan shell hash layer of mytilus galloprovincialis that covers the interval 7776 to 6183 cal bp mixed oak and hornbeam forests dominated the vegetation cover during the atlantic subboreal and subatlantic chronozones of the holocene an important change in the forest composition occurs at ca 5518 cal bp when carpinus betulus reached its maximum spread due to a climate change the high resolution geoarchaeological reconstruction of palaeovegetation also reveals the extent of anthropogenic influence in the varna lake area with deforestation and agricultural practice two periods of significant presence of pollen from cultivated cereals and secondary anthropogenic indicators weeds and ruderals were identified according to the available ams radiocarbon data these periods correspond to the late eneolithic and early bronze age the transitional period without human activities between these two archaeological periods lasted ca 319 y and coincides with a rise of the black sea level reflected by the increase of euryhaline marine dinoflagelate cysts lingulodinium machaerophorum and spiniferites belerius and acritarchs cymatiosphaera globulosa and micrhystridium cf ariakense during the first phase of the kalamitian black sea transgression the increased values of corylus coincidently with decrease of quercus and ulmus suggest clearance of forests and enlargement of arable areas during the late eneolithic the npp record of spores of coprophyllous fungi cercophora sordaria podospora and chaetomium indicates the presence of domestic animals during the early bronze age the maximum of alnus ulmus fraxinus excelsior type and fagus pollen at 717 cal bp suggests an increase of humidity and cooling of climate during the subatlantic

first high resolution marinopalynological stratigraphy of late quaternary sediments from the central part of the bulgarian black sea area abstract spores pollen and dinoflagellate cysts of late pleistocene and holocene sediments were analyzed from giant gravity core 18 from the black sea continental slope recovered from a water depth of 971 m the investigated length of the core is 203 5 cm it includes 3 lithological units light grey clay sapropels and coccolith bearing ooze the core was sampled at 5 10 cm intervals sampling of the interval 141 5 126 cm was carried out at every cm ams radiocarbon dating of bulk organic carbon was performed on 18 selected sediment layers this chronological data allowed the first high resolution pollen stratigraphy of late quaternary sediments from the western black sea area to be presented the percentage spore pollen diagram is divided into 6 local pollen assemblage zones the trends in the vegetation dynamics and climate changes and the early history of migration of the majority of the arboreal taxa that nowadays occur in the eastern balkan range were traced out the palynological record suggests that open oak forests were spread in the eastern balkan range at the beginning of the holocene and shows early migration of the major temperate arboreal species such as quercus ulmus tilia and carpinus betulus this vegetation palaeosuccession continues with the spreading of mixed oak forests from 8950 until 2620 cal bp 8650 40 until 3120 35 14c bp followed by destructive changes due to human impact and climate deterioration a cooling of holocene climate that is well known in the north atlantic region as the 8200 yrs cold event is identified for the first time in marine records from the bulgarian black sea area the assemblages of dinoflagellate cysts and acritarchs were investigated to provide a reconstruction of surface seawater salinity and surface seawater temperature changes two main dinoflagellate cyst assemblages one dominated by fresh to brackish water species such as spiniferites cruciformis and pyxidinopsis psilata and a subsequent one that is characterized by euryhaline marine mediterranean species such as lingulodinium machaerophorum spiniferites belerius spiniferites bentorii operculodinium centrocarpum and acritarchs cymatiosphaera globulosa testified a change in sss from low salinity

deformation mechanisms in the southeastern ramp region of the pine mountain block tennessee a field and petrofabric study of the southwestern part of the pine mountain thrust sheet shows that most deformation features may be attributed to one of two processes the first layer parallel compression is responsible for a a layer parallel maximum shortening direction in the mechanically twinned fabric of the limestone and dolomite country rock b transport parallel extension fractures and joints c transport normal stylolite surfaces and d some small thrusts the second bending at thrust ramp hinges is responsible for a non bedding parallel maximum shortening directions in mechanically twinned calcite from fracture fillings b transport normal extension fractures and joints and c small normal faults possible explanations for the failure of calcite in the country rock to twin in response to bending at the ramp include both 1 an early imposed pre thrusting calcite twin strain hardening and 2 deformation of the country rock by competing mechanisms such as pressure solution small normal faults are parallel to the strike of the thrust sheet and seem to have evolved from strike parallel extension fractures in response to continued extension both small thrusts and stylolite surfaces are rare in outcrop there seems to be no major change in deformation of rocks which have traveled through different fractions of the total ramp length so long as the rocks have passed onto the ramp

fluid inclusion evidence for progressive folding during decompression in metasediments of the voltri group western alps italy abstract quartz veins syntectonic to distinct folding events in metasediments from the voltri group ligurian alps were studied in order to compare fluid and structural evolution studied veins vs1 vs2 vs3 pertain to three distinct generations of folds f 1 f 2 f 3 that formed during the retrograde metamorphic evolution two types of fluids characterize the different generations of veins and are represented essentially by aqueo carbonic mixtures of moderate salinity with decreasing densities 1 01 0 41 g cm 3 the chemical evolution is characterised by a progressive decrease of h 2 o from early fluids associated with opening of vs1 and vs2 xco 2 0 08 to fluids related to vs3 formation xco 2 0 3 the close match between the fluids in vs1 and vs2 suggests that the development of two superimposed systems of folds f 1 and f 2 folds occurs under very similar p t conditions during a progressive and continuous deformational event at glaucophanic and or barroisitic metamorphic grade a different evolution is outlined for the formation of vs3 during low greenschist grade successive isochores allow us to define a retrograde decompression path for the voltri group present results indicate that fluid inclusions are powerful markers to constrain the p t t conditions of different folding events

aquatic palynomorphs from modern marine sediments in a reconnaissance transect across the northwest passage baffin bay region abstract surface sediments from 18 boxcores across the canadian arctic provide the first assessment of modern non pollen non dinocyst palynomorph regional distribution patterns palynomorphs are abundant and well preserved 400 21 900 ind g average 5730 ind g comprising acritarchs zoomorphs invertebrate eggs egg capsules mouthparts foraminiferal linings tintinnid loricae ciliate cysts and freshwater algae acritarch p and halodinium minor were the most abundant and widely distributed acritarchs avg 410 and 340 ind g respectively invertebrate eggs avg 570 ind g and foraminiferal linings avg 1600 ind g were prominent six tintinnid forms were identified cf parafavella parumdentata avg 40 ind g 10 stations showing the widest distribution ciliate cysts included strombidium cyst a a spherical flask shaped cell with short spines and a rounded base avg 120 ind g 16 stations pediastrum sp avg 140 ind g and botryococcus sp avg 1040 ind g were especially abundant in the west likely delivered via rivers out of 14 environmental parameters only sedimentary biogenic silica si opal was significant in explaining palynomorph variation at group level tinitinnids showed the strongest positive correlation to si opal individually the tintinnid acanthostomella sp 1 ciliate cyst fusopsis cyst a and the acritarch palaeostomocystis fritilla were almost solely and positively explained by si opal this suggests that si opal strongly determines palynomorph variability particularly for microzooplankton implying that siliceous organisms diatoms play an important role in shaping palynomorph content in the sedimentary record our data suggest that palynomorphs represent a valuable addition to organic walled microfossils dinocysts routinely used in this region offering a unique multiproxy glimpse into the ecosystem

plumbing accretionary prisms effects of permeability variations fault zones focus fluid expulsion in the muddy northern barbados ridge accretionary prism with fault parallel permeabilities about 1000 times greater than intergranular permeabilities in the adjacent sediment in the oregon prism the low bedding perpendicular permeability due to mudstones inhibits intergranular dewatering however intergranular flow is concentrated where submarine erosion breaches high permeability sandy layers even so faults can capture fluid flow from these exposed sandy layers suggesting the faults have a still higher permeability such observations coupled with laboratory measurements permeabilities suggest that faults off oregon may have fault parallel permeabilities at least 10 10000 times greater than the adjacent sediments results from barbados and oregon suggest fluid flow is concentrated along the most active faults at the toe of prisms the fault zones are being progressively loaded by the thickening wedge and are undergoing compaction preliminary experiments show that permeability decreases relative to the surrounding wall rocks along faults within this compactive deformation regime we believe that these faults must undergo dilation perhaps linked to transient increases in pore pressure if they are to be preferential fluid conduits farther upslope erosion exposes rocks that are more consolidated commonly more cemented and generally of lower intergranular permeability than rocks of equivalent burial further seaward because of their lithification and overconsolidation these rocks dilate during faulting locally enhancing fracture permeability in such dilative regimes faults become evermore focused zones of fluid expulsion relative to occluded intergranular pathways

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

the role of fluids in syntectonic mass transport and the localization of metamorphic vein type ore deposists abstract in low to medium grade metamorphic environments the mobilization of species is closely associated with the operation of solution precipitation creep processes during foliation development such deformation processes involve dissolution of material from source sites which are usually discrete dissolution surfaces having orientations controlled by the applied stress and displacement fields mass transfer occurs via solute diffusion in an essentially static fluid network or by transport of dissolved species in a migrating fluid precipitation of material removed from dissolution sites occurs in a variety of sink sites including pore surfaces grain scale microcracks and veins sink sites may be close to or distantly removed from source sites the transport of material during deformation involving solution precipitation creep is largely controlled by the mobility of metamorphic fluids in regions of high fluid mobility significant mass transfer may occur over large distances fluid flow mass transfer paths and the development of sink sites in such cases are constrained by the structurally controlled development of high fluid pressure domains and the consequent mechanical enhancement of permeability by hydraulic fracture processes and the development of grain scale dilatancy these processes may result in focussed fluid flow and precipitation of mobilized species in restricted regions a proportion of syntectonically mobilized material is precipitated to form vein type deposits in hydraulic fracture arrays which develop in high fluid pressure environments the microstructures developed in minerals deposited in these sites reflect the interaction of a range of nucleation and growth processes which usually involve multiple generations of fracture growth and mineral crystallization the formation of syntectonic gold quartz vein deposits in central victoria australia illustrates the importance of structural controls on both the large scale migration of metamorphic fluids and the development of sites suitable for the precipitation of metamorphically mobilized species

stress sensitivity of stylolite morphology abstract stylolites are rough surfaces that form by localized stress induced dissolution using a set of limestone rock samples collected at different depths from a vertical section in cirque de navacelles france we study the influence of the lithostatic stress on the stylolites morphology on the basis of a recent morphogenesis model we measured the roughness of a series of bedding parallel stylolites and show that their morphology exhibits a scaling invariance with two self affine scaling regimes separated by a crossover length l at the millimeter scale consistent with previous studies the importance of the present contribution is to estimate the stylolite formation stress from the sample position in the stratigraphic series and compare it to the crossover length l using the expected relationship l 2 we obtained a successful prediction of the crossover behavior and reasonable absolute stress magnitude estimates using relevant parameters depth of stylolite formation between 300 to 600 m with corresponding normal stress in the range of 10 18 mpa accordingly the stylolite morphology contains a signature of the stress field during formation and we thus suggest that stylolites could be used as paleo stress gauges of deformation processes in the upper crust

insights into fluid flow and water rock interaction during deformation of carbonate sequences in the mexican fold thrust belt analysis of mesoscopic structures and related veins allows the history of deformation and role of fluids to be established for part of the central mexican fold thrust belt mftb the mftb developed in mostly carbonate rocks with prominent lateral facies changes associated with two platforms and two basins fluids played a key role in the deformation both physically and chemically by reducing strength and inducing extensional fracturing through raised pore pressure and by providing the medium for solution transfer on the grain scale veins preserve portions of water related to deformation as fluid inclusions lithology and lithological variations strongly control deformation styles with thrusts dominant in the platforms and folds dominant in the basins and also influence fluid behavior by controlling both porosity and permeability structural observations allow distinguishing veins dominantly calcite of several generations emplaced early during and late after deformation v1 v3 respectively 13c and 18o analyses in calcite from veins and host rock show that the veins confined within thrust slices are isotopically buffered by the host rock and differ in isotopic composition from veins emplaced along major thrusts or crosscutting thrust slices d analyses in fluid inclusions and clay minerals strongly suggest rock interaction with meteoric fluids in the west hinterland and with fluids close to smow in the less deformed eastern foreland side of the cross section by focusing on a single stratigraphic interval exposed across the width of the fold thrust belt we propose a conceptual model that explains the differences in vein rock isotopic composition the differences of in isotopic composition of aqueous fluids active during deformation and the progression of clay dehydration reactions as being related to variations in temperature and intensity of deformation in a growing tectonic wedge

warm fluid migration along tectonic melanges in the kodiak accretionary complex alaska analyses of methane water fluid inclusions from syntectonic quartz veins in melange boudins of the kodiak accretionary complex alaska indicate fluid temperatures ranging from 215 to 290 c at depths between 10 and 14 km these fluid temperatures are significantly higher than those predicted by conductive heat flow models of subduction zones given the available geological constraints this discrepancy is interpreted as the result of migration of warm fluids from deeper structural levels along active fault zones during subduction related underthrusting of these units this interpretation requires more careful consideration of how migrating fluids affect the general thermal structure of subduction zones

calcite precipitation in synthetic veins implications for the time and fluid volume necessary for vein filling although calcite is a common vein filling mineral in rocks there has been little understanding of the kinetics of vein filling that gives a quantitative estimation of the fluid volume and time needed for calcite vein formation in subsurface fracture systems a new experimental system capable of simulating calcite precipitation in veins was used to determine the influences of flow velocity and initial solution saturation state on the quantitative precipitation pattern of calcite in synthetic veins results are in relatively good agreement with the model predictions use of a mn2 tracer indicated that even at low concentrations manganese can have a substantial effect on the morphology of the calcite precipitate our model predicts that an extremely large volume of fluid is required to produce calcite veins in nature typically 105 to 106 for a fluid calcite volume ratio for formation of thin short veins the model also predicts the time necessary for vein filling is thousands to millions of years and is highly variable depending on factors such as fluid saturation state flow velocity vein dimension and the precipitation kinetics that can differ under subsurface conditions

fluids in metamorphic rocks abstract basic principles for the study of fluid inclusions in metamorphic rocks are reviewed and illustrated a major problem relates to the number of inclusions possibly formed on a wide range of p t conditions having also suffered in most cases extensive changes after initial trapping the interpretation of fluid inclusion data can only be done by comparison with independent p t estimates derived from coexisting minerals but this requires a precise knowledge of the chronology of inclusion formation in respect to their mineral host the three essential steps in any fluid inclusion investigation are described observation measurements and interpretation observation with a conventional petrographic microscope leads to the identification and relative chronology of a limited number of fluid types same overall composition eventually changes in fluid density for the chronology the notion of gis group of synchronous inclusions is introduced it should serve as a systematic basis for the rest of the study microthermometry measurements completed by nondestructive analyses mostly micro raman specify the composition and density of the different fluid types the major problem of density variability can be significantly reduced by simple considerations of the shape of density histograms allowing elimination of a great number of inclusions having suffered late perturbations finally the interpretation is based on the comparison between few isochores representative of the whole inclusion population and p t mineral data essential is a clear perception of the relative chronology between the different isochores when this is possible as illustrated by the complicated case of the granulites from central kola peninsula a good interpretation of the fluid inclusion data can be done if not fluid inclusions will not tell much about the metamorphic evolution of the rocks in which they occur

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

the character and distribution of mineralized fractures in the kodiak formation alaska implications for fluid flow in an underthrust sequence the kodiak formation an accreted slate belt in southwest alaska experienced two major episodes of fracturing and mineralization in the late cretaceous early tertiary the earlier of these episodes is related to underthrusting of sediments below a major decollement d1 whereas a later episode is marked by development of fold and thrust structures and a regionally pervasive slaty cleavage within the accretionary wedge d2 d1 veins are restricted to sand layers and are concentrated at the highest structural level of the kodiak formation the most pervasive d1 fractures occur within a melange zone where the kodiak formation is thrust beneath the older uyak complex microstructures in the melange suggest that these veins formed during the later stages of a deformation that involved layer parallel shear in conjunction with progressive lithification d2 veins cut sand and shale layers and are concentrated at the lowest structural levels of the kodiak formation microstructures within these veins indicate that d2 veins are hydrofractures that were either 1 intermittentiy sealed along the length of the crack e g in the smallest veins 0 5 cm width fracturing coincided with development of a slaty cleavage in a regime of progressive simple shear from highest to lowest structural levels there is a gradual increase in measured finite strain the abrupt appearance of pervasive d2 veins and a greater noncoaxiality of strain related to southeast directed thrusting these observations suggest that d2 veins formed above a decollement that was active at the base of a late cretaceous early tertiary accreted package in total the d1 and d2 veins suggest substantial fluid flow within an ancient subduction complex with development of hydrofractures first in the footwall and then in the hanging wall of a basal decollement that stepped from shallow to deeper structural levels

the holocene history of the ne black sea and surrounding areas an integrated record of marine and terrestrial palaeoenvironmental change here we present an almost complete and integrated holocene record of marine and terrestrial palaeoenvironmental change from the ne shelf of the black sea a dinoflagellate cyst record used to recon

application of prestack orthotropic avaz inversion for fracture characterization of a deep carbonate reservoir in northern kuwait prestack anisotropic orthotropic symmetry avaz inversion of full azimuth 3d seismic data for fracture characterization of the upper najmah formation in northern kuwait was conducted this formation comprises a thin tight naturally fractured carbonate overlying a kerogen rich shale source rock the inversion methodology uses an orthotropic system of symmetry that is appropriate for analysis of vertical transverse isotropic vti anisotropic rock layers containing swarms of aligned vertical fractures measured seismic amplitudes show good agreement with synthetic models created at different well locations indicating reliable representation of fractures in amplitude data inversion results show good agreement with well and drilling data rock physics modeling shows a relationship between elastic properties and seismic anisotropy and between elastic properties and reservoir properties such as porosity and fracture density

the role of pore water circulation during the deformation of foreland fold and thrust belts volume loss strain accompanying pressure solution of calcite occurred within both the umbria marches apennines of italy and the appalachian mountains of western new york data from strain markers show that volume loss strain was greater within the shallow portions of the apennines than within the appalachians within the deeper portions of both fold and thrust belts strain was nearly volume constant calcite solubility data suggest that downward circulation of meteoric water is necessary for the 35 volume loss strain of the limestones within the apennines strain at a depth of about 1 km was volume constant and is interpretated as indicative of restricted pore fluid circulation in the appalachians calcite comprises less than 1 of the clastic rocks and a 10 volume loss of this calcite may occur during circulation of connate or dehydration water derived from dewatering of the shales but in an environment that restricts the circulation of meteoric water here the volume of calcite removed 0 1 of the total rock is so small that circulation of meteoric water is not necessary for strain by pressure solution

fracture controlled paleohydrology in a map scale detachment fold insights from the analysis of fluid inclusions in calcite and quartz veins abstract this study uses fluid inclusions in quartz and calcite veins to characterize the fracture controlled paleohydrology of a map scale evaporite cored detachment fold in the sierra madre oriental of northeastern mexico field observations indicate that the veins are tectonic in origin and that they formed in a general sequence that corresponds to four broad stages of progressive folding we collected samples from each vein stage in various structural and stratigraphic positions across the fold after determining the mineral paragenesis and origin of inclusions in each sample we used standard microthermometric techniques to measure the homogenization temperatures t h salinities and eutectic temperatures of the available two and three phase aqueous inclusions neither t h salinity nor eutectic temperature varied systematically with inclusion origin or mineral type the data are also not significantly correlated with structural position or vein type but are strongly partitioned by stratigraphy suggesting that the area was a vertically stratified hydrologic system consisting of three regional paleohydrostratigraphic units an upper unit comprised the indidura formation through difunta group and is characterized by t h near 150 c and salinity t h near 150 c and salinities near 12 or 22 wt nacl equivalent the lower unit comprised the zuloaga and la casita formations and is characterized by an average t h near 225 c and salinities in three groups near 12 22 or 36 wt nacl equivalent the preservation of multiple distinct fluid types in many veins suggests that fracture development during folding and uplift created a second paleohydrologic system that overprinted the vertically stratified system fracture controlled fluid migration in this second system occurred in periodic repeated and spatially variable pulses

the importance of diffusion advection and host rock lithology on vein formation a stable isotope study from the paleozoic ouachita orogenic belt arkansas and oklahoma more than 600 stable isotope analyses from veins and their metasedimentary host rocks from the ouachita orogenic belt of arkansas and oklahoma provide an opportunity to study fluid rock interaction processes associated with vein formation during deformation and low grade regional metamorphism the 18o values of vein quartz vary from 16 0 to 26 4 whereas coexisting host rocks have a greater range from 12 9 to 27 4 the oxygen isotopic compositions of quartz vein versus those of the coexisting host rocks follow an array described by 18ovein quartz 18owhole rock e where e 8 0 3 18owhole rock this relationship emphasizes the dependence of 18o values of vein quartz on host rock oxygen isotopic composition the e term empirically monitors the difference between the quartz water fractionation factor and the compositional dependence of the bulk rock water fractionation factor vein quartz host rock 18o fractionations are 0 in chert novaculite quartzite and siliceous shale and typically between 1 and 4 in sandstones and shales in quartzite and sandstone units that are bounded by shales and associated with significant quartz crystal deposits vein quartz host rock fractionations are often unusually large near 7 quartz calcite oxygen isotope geothermometry indicates that veins from the ouachita mountains formed over a temperature interval of 100 c consistent with fluid inclusion temperatures previously obtained from quartz crystals individual quartz veins are homogeneous with 0 4 variation for all vein orientations at all scales even though vein formation occurred over a temperature interval in which quartz water fractionation varies by 5 this homogeneity highlights the insensitivity of vein quartz 18o values to temperature when veins form under rock buffered conditions the similarity between vein and host rock 18o values in quartz rich lithologies and between vein and host rock 13c values in calcite bearing rocks indicates that diffusion was an important mass transport mechanism the variability in 18o values between calcite bearing veins and host rocks and large vein quartz whole rock fractionations in some sandstones and quartzites indicates that advection also played a major role in mass transport associated with vein formation this inference leads to the interpretation that veins from the ouachita mountains formed by a combined diffusion advection process whereby 18o and 13c from the host rock was transported into the veins with the assistance of a rock buffered fluid on outcrop scales of 10 100 m

the use of fluid inclusions to constrain fault zone pressure temperature and kinematic history an example from the alpi apuane italy the alpi apuane is a tectonic window that exposes ductilely deformed greenschist facies metaigneous and metasedimentary rocks beneath relatively unmetamorphosed brittlely deformed sedimentary rocks of the tuscan nappe the brecciated fault zone the window fault separating the two tectonic units was originally described as a simple thrust fault but has recently been interpreted to have been reactivated as a later extensional detachment although evidence for extensional faulting is seen above and below the window fault the amount of extensional displacement along this fault is unclear fluid inclusions from veins cementing the fault breccia were used to estimate the pressures and temperatures during the last fault movement minimum pressure estimates obtained from these inclusions range from 105 to 240 mpa pressure corrected trapping temperatures for these fluids range from about 300 to 345 c these pressures and temperatures indicate that the fault was last active at a depth of about 10 km assuming a geothermal gradient at the time of 31 c km 1 this rules out complete extensional unroofing of the alpi apuane by movement along the window fault fluid salinities increase abruptly from the footwall into the fault zone this pattern suggests that fluids rose from the footwall entered the fault zone and were channeled within it leaching salt from the overlying evaporite the lack of quartz veins above the fault zone indicates that these fluids did not circulate into the overlying tuscan nappe

structural and isotopic constraints on fluid flow regimes and fluid pathways during upper crustal deformation an example from the taemas area of the lachlan orogen se australia 1 structural and stable isotope studies of calcite veins and host rocks in a 1000 m thick devonian limestone sequence in the taemas area of the lachlan orogen in se australia indicate that externally derived fluids migrated through the sequence over a protracted interval during folding and associated reverse faulting at temperatures of 200 c the evolution of fluid pathways was governed by growth of fold related and fault related fracture networks at transiently supralithostatic fluid pressures the internal structures of veins indicate growth during repeated cycles of permeability enhancement and sealing systematic increase in 18o of vein calcite upward through the limestone sequence and the presence of an o isotope alteration front in the vein system is related to buffering of fluid compositions by fluid rock reaction during upward migration of overpressured low 18o fluids repeated switching of fractures between high permeability and low permeability states promoted episodic flow and changes in flow paths during progressive deformation a lack of significant migration of the isotopic front during the flow history is consistent with fluid rock interaction being associated with numerous separate pulses of fluid ascending through the percolation network irregular variations in fluid 18o with time during vein growth are interpreted to be driven by repeated changes in reactive path lengths reaction rates and flow rates in a discontinuous flow regime systematic upward changes in vein 18o over an area of 20 km2 requires that on a time averaged basis most of the vein system was hydraulically well connected to the external fluid reservoir and that growth of the fracture network occurred by fluid driven invasion percolation processes repeated failure and sealing events in the fracture system are interpreted to have been driven by episodic migration of fluid pressure waves up through the fracture network possibly in response to deeper level fault rupture events repeatedly breaching an overpressured fluid reservoir

oxygen and hydrogen isotope geochemistry of cretaceous bentonites and shales from the disturbed belt montana the mineralogy o18 and d of the 0 1 m fraction of 22 cretaceous bentonites and the mineralogy and o18 of the 0 1 m fraction of 14 adjacent shales collected from outcrops in the sweetgrass arch and disturbed belt montana have been determined mixed layer illite smectite i s is the dominant mineral in the bulk bentonite and usually the only mineral in the 0 1 m fraction i s is also the major clay mineral in the shales the diagenetic grade in bentonite is qualitatively given by the percentage of illite layers in i s which varies from 2 to 25 sweetgrass arch to as high as 95 disturbed belt o18 of 0 1 m bentonite generally decreases from about 20 to about 13 with increasing diagenetic grade on a plot of d versus o18 data for the 0 1 m bentonite define a field that generally parallels but falls on the meteoric water line side of the smectite water line savin and epstein 1970 o18 of bulk bentonite is 1 to 3 more negative than the o18 of the 0 1 m fraction due to the presence of volcanic quartz and feldspar o18 of several size fractions of clay sized quartz separated from the bentonite varies from 11 to 24 and in a given bentonite generally increases with decreasing grain size among the different bentonites the o18 range of the different grain sizes decreases as the percentage of illite layers in the coexisting i s increases the o18 of 0 1 0 5 m shale quartz is generally 1 to 4 more positive than clay sized quartz from an adjacent bentonite and the o18 of 0 1 m i s concentrate of shales is generally 1 to 4 more negative than the 0 1 m i s from an adjacent bentonite isotopic temperatures interpreted to be maximum burial temperatures range between about 160 c shale to about 250 c bentonite the isotopic data can be interpreted using the stages 1 1 deposition of volcanic glassy ash containing some quartz and feldspar 2 2 devitrification into mostly 100 expandable smectite with a o18 of about 20 and d of 60 to 80 3 3 tectonic burial beneath thrust sheets in the disturbed belt region which induced elevated temperatures that allowed oxygen and hydrogen isotope reequilibration as the percentage of illite layers in i s increased and diagenetic quartz formed and 4 4 exhumation of the strata with preservation of o18o16 and d h attained during burial

palaeoecological setting of the western black sea area during the last 15000 years analysis of pollen dinoflagellate cysts and lithology was carried out on ten cores from the western deep black sea and combined with radiocarbon dating to reconstruct the vegetation climate and palaeoecological conditions all the cores record a consistent sequence of lateglacial and early holocene steppe vegetation which persisted until about 7100 7500 yr bp when quercus corylus tilia and other temperate trees expanded at about the same time as the influx of mediterranean waters that resulted in sapropel deposition in the deep black sea the sequence implies dry climatic conditions and a low level of the black sea during the early holocene

conditions of vein formation in the southern appalachian foreland constraints from vein geometries and fluid inclusions abstract the nolichucky shale in the whiteoak mountain thrust sheet of the southern appalachian foreland contains four coeval bed normal calcite vein sets that trended 015 055 090 and 320 before thrusting the pretectonic veins were displaced by syn tectonic bed parallel slickensided calcite veins during local alleghanian thrusting fluid inclusion thermometry indicates precipitation of both bed normal and bed parallel veins from nacl cacl2 brines 27 wt nacl equiv salinity at 80 110 c for bed normal veins and 110 c for bed parallel veins these temperatures correspond to burial depths of 2 4 3 6 km which were attained after the middle mississippian these pressure corrected homogenization temperatures are comparable to time temperature indicators such as cai and illite crystallinity and indicate that inclusions were trapped near maximum burial conditions and were not deformed after trapping this conclusion is supported by the absence of petrographic evidence for inclusion failure and a worst case mechanical analysis that indicates a lack of brittle deformation to inclusions after trapping the four coeval bed normal vein sets could not be formed by one simple stress field nor by the development of a single structure but required the interaction of at least two stress components or structures it is proposed that the interaction of the alleghanian and ouachita orogenic stress components beyond the limits of thrusting produced the sets as coeval alleghanian orthogonal 055 320 and ouchita sub orthogonal 015 090 mode i fractures

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

hydrogen isotope fractionation factor for mixed layer illite smectite at 60 to 150 c new data from the northeast texas gulf coast abstract the d values of water and clay collected from 0 6 to 5 5 km deep wells in 9 oil and gas fields within the houston salt basin located in the northeast texas gulf coast were used to reevaluate the temperature dependence of hydrogen isotope fractionation between mixed layer illite smectite i s and water and the equations of yeh 1980 geochim cosmochim acta 42 140 143 and capuano 1992 geochim cosmochim acta 56 2547 2554 for the calculation of i s water both of which are commonly cited in the literature d values of water and clay in the normally pressured and geopressured sections are different in the normally pressured section

regional stratigraphy and distribution of epigenetic stratabound celestine fluorite barite and pb zn deposits in the mvt province of northeastern mexico northeastern mexico hosts numerous epigenetic stratabound carbonate hosted low temperature hydrothermal deposits of celestine fluorite barite and zinc lead which formed by replacement of mesozoic evaporites or carbonate rocks such deposits can be permissively catalogued as mississippi valley type mvt deposits the deposits studied in the state of coahuila are associated with granitic and metasedimentary basement highs horsts marginal or central to the mesozoic sabinas basin these horsts controlled the stratigraphy of the mesozoic basins and subsequently influenced the laramide structural pattern the sabinas basin consists of 6 000 m thick jurassic to cretaceous siliciclastic carbonate and evaporitic series the mvt deposits are mostly in barremian and in aptian albian to cenomanian formations and likely formed from basinal brines that were mobilized during the laramide orogeny although earlier diagenetic replacement of evaporite layers barite and celestine deposits and lining of paleokarstic cavities in reef carbonates zn pb deposits is observed fluid inclusion microthermometry and isotopic studies suggest ore formation due to mixing of basinal brines and meteoric water homogenization temperatures of fluid inclusions range from 45 c to 210 c salinities range from 0 to 26 wt nacl equiv and some inclusions contain hydrocarbons or bitumen sulfur isotope data suggest that most of the sulfur in barite and celestine is derived from barremian to cenomanian evaporites regional geology and a compilation of metallogenic features define the new mvt province of northeastern mexico which comprises most of the state of coahuila and portions of the neighboring states of nuevo leon durango and perhaps extends into zacatecas and southern texas this province exhibits a regional metal zonation with celestine deposits to the south fluorite deposits to the north and barite and zn pb deposits mostly in the central part

calibration of the anchizone a critical comparison of illite crystallinity scales used for definition instrumental settings for determination of illite muscovite crystallinity half height width of the 10 a x ray diffraction peak and the limits of the anchimetamorphic zone adopted by various authors fall into several groups the variation in the limiting peak widths between the authors that have adopted kubler s neuch tel boundary values of 0 42 and 0 25 2 can be interpreted in terms of variation in the instrumental settings the choice of time constants higher than those given by the formula causes peak broadening this effect is particularly marked at high scan rates the peak broadening is by constant increments that are virtually independent of the absolute peak width the differences between the kubler neuch tel derived limiting values and some other scales are appreciably greater than can be accounted for by these differences in instrumental settings many of these scales are not equivalent in particular the limits adopted by dunoyer de segonzac 1969 and subsequent workers at strasbourg are too broad their anchizone represents a range of grades of metamorphism lower than that of kubler widely overlapping the latter s diagenetic zone those adopted by some other mainly french authors are too narrow the limits of the anchizone should be calibrated by inter laboratory standards and the instrumental settings should be specified in full