fluid inclusions and hydrothermal alteration on the dixie valley fault nevada footwall rocks of the 1954 rupture segment of the dixie valley fault show extensive hydrothermal alteration related to fluids that were present on the fault during tectonic events hydrothermal alteration of granitic host rocks consists of temporally and spatially overlapping mineral assemblages an early biotite feldspar assemblage is followed by later fe chlorite and epidote both chlorite and epidote are replaced by hydrothermal sericite and cross cut by calcite hematite and quartz calcite veins biotite is partially replaced by prehnite the latest hydrothermal minerals are stilbite laumontite kaolinite alunite smectite illite and pervasive replacement of rock units with fine grained quartz chalcedony and opal secondary fluid inclusions trapped in healed microfractures in igneous quartz include type i inclusions that contain a moderate salinity aqueous liquid and vapor type ii inclusions that contain a moderate salinity aqueous liquid and co2 type iii inclusions that show eutectic melting temperatures below the nacl h2o eutectic and contain substantial cacl2 and type iv inclusions containing halite and other daughter minerals microthermometric measurements on these inclusions yield variable compositions and homogenization temperatures salinities of type i inclusions vary from 0 1 to 12 9 wt nacl with the mode in the interval 0 to 1 salinities of type ii co2 bearing inclusions range from 0 62 to 6 81 wt nacl relative to h2o and salinities of type iii inclusions with low eutectic melting temperatures are 12 9 to 25 3 nacl equivalent wt salinities of halite bearing inclusions are 30 1 to 39 2 wt nacl homogenization temperatures span the range 120 to 400 c the processes of isochemical cooling with upward displacement of the footwall mixing of cool low salinity water with hotter components and mixing of cool evaporite brine with hotter components could be responsible for variable fluid inclusion compositions homogenization temperatures and densities the p t path of the fault fluids is established by mineral equilibria and fluid inclusion characteristics the path includes a lithostatic fluid pressure at 305 c and 1570 bars along with cooling and escape of co2 from fluids the fluid p t path probably approaches hydrostatic pressure conditions at lower temperatures hydrothermal alteration product minerals fluid temperatures pressures and compositions in the footwall of the dixie valley fault constrain minimum fault age to 20 to 25 ma displacement to 6 km with about 3 km of pre 10 to 13 ma and 3 km of post 10 ma uplift fluid compositions and p t data suggest the following mechanism for rupture initiation and arrest ruptures may be initiated as a result of high fluid pressures then opening of dilatant fractures causes drastic decrease in fluid pressure separation of steam and co2 the drastic reduction in fluid bulk modulus that accompanies volatile phase separation permits propagation of the ruptures even though fluid pressure is reduced in areas where fluid pressure reduction is not accompanied by phase separation fractures are arrested by dilatant hardening

chemical and isotopic effects of retrogression in metamorphic fluid inclusions fluid inclusions may provide compositional and isotopic information about fluids from which the host mineral precipitated as long as the host mineral does not react with the fluid our transmission electron microscope tem investigation of grain boundaries and of fluid inclusions in zoisite and quartz of high pressure metamorphic rocks from dabie shan eastern china demonstrates daughter minerals such as margarite muscovite calcite and anhydrite their precipitation changes 1 the composition of the fluid by selective and mineral specific removal of co2 carbonates h2o sheet silicates hydration of the walls or s gypsum anhydrite sulfides 2 the concentrations and proportions of ions dissolved in the fluid and 3 the isotopic composition of the fluid because of isotopic fractionation between mineral precipitate and fluid and between unmixed fluids fluid leakage from overpressurized fluid inclusions with daughter minerals changes the overall chemical and isotopic composition of the inclusion irreversibly even when the daughter crystals later redissolve such fluid loss yields a wide range of compositionally and isotopically different fluids from a single starting fluid depending on the relation between mineral reactions in and fluid loss from the inclusion the fluid remaining in the inclusion and the fluid lost from the inclusion may appear entirely unrelated

deformation of the caledonide lithosphere of northwest scotland abstract an interpretation of the moist seismic reflection profile along the north coast of scotland has shown the pattern of deep crustal structure across the margin of the caledonian orogen with the hebridean cratonic foreland to the northwest it is proposed that the lower crust of the orogen is characterised by a suite of easterly dipping thrusts that divide it into flakes that were imbricated during lateral compression of the lithosphere the effects of concomitant and subsequent uplift and erosion led to the removal of the major part of the upper crust within the orogen so that the present crust and moho are largely the relics of the caledonian lower crust as time progressed the thrust front encroached further into the foreland and cut down to a basal decollement at successively deeper levels this behaviour is explained as a consequence of the response of the brittle ductile transition to changing the temperature regime rock composition and strain rate as the orogeny proceeded palinspastic reconstructions of the whole lithosphere illustrate the process following the compressional phase of the orogeny uplift led to initiation of extension and the reactivation of the thrusts as normal listric faults rotation of basement blocks gave rise to wedge shaped sedimentary basins

ductile and brittle deformations in the northern snake range nevada abstract the northern snake range east central nevada is one of the metamorphic core complexes of the sevier hinterland within the range a major decollement separates an upper plate composed of brittlely deformed paleozoic sedimentary rocks mostly carbonates from a lower plate composed of metamorphic upper precambrian lower cambrian rocks intruded by gneissic granites a study of the geometry and kinematics of structures and fabrics at outcrop scale and in thin sections indicates that the northern snake range decollement has been a zone of intense non coaxial e vergent shear and transport in a n115 e direction outstanding asymmetric boudinage within the marble sheet capping the lower plate testifies for late ductile shear strains of at least 20 the interface between brittlely and ductilely deformed rocks seems too sharp to represent a regional rheological transition but might result from two distinct phases of deformation ductile deformation in and below the decollement could have occurred before brittle deformation in the upper plate brittle faulting in the upper plate related to basin and range extension reactivated the upper surface of the ductile shear zone high topographic relief on the normal faults bounding the range triggered the slide of olistolites from the upper plate into the adjacent oligo miocene basins

mineral assemblages and oxygen and sulphur fugacities in natural water rock interaction processes abstract several mineral assemblages capable of buffering oxygen and sulphur fugacity and theoretical calculations were used to determine the fugacities of these two gas species over a temperature range between 150 and 350 c computed values were compared with those calculated from the composition of the geothermal fluids of larderello travale bagnore and piancastagnaio italy the geysers usa and cerro prieto mexico the possible hydrothermal mineral assemblages that best fit the field data are those containing minerals frequently found in many geothermal fields epidote chlorite k feldspar quartz and pyrite these assemblages can be used in place of the classical buffers based on iron oxides and sulphides

collision tectonics in the nw himalayas west himalayan tectonics involve the collision of microplates between the indian and asian plates the kohistan complex consists largely of tightly folded basic volcanics and sediments generated as late jurassic to late cretaceous island arcs these were intruded by post folding mid cretaceous eocene plutonics produced from continued subduction of the indian plate after closure of a suture between kohistan and the karakorum the himalayan structures show major thrust sheets and the kohistan arc is essentially a crustal pop up with southward upright and northward verging structures developed above a thick ductile decoupling zone the indus suture which can be traced for 100 km beneath kohistan on large reentrants this pop up formed by a two stage process closure of the northern suture followed by closure of the southern indus suture granitic rocks of the kohis tan ladakh batholith dated at 100 40 ma post date most of the structures related to the northern suture but were deformed and carried southwards on shear structures related to the indus suture postcollisional deformation carried this kohistan complex on deep decoupling zones over the indian plate on a series of imbricated gneiss sheets the thrusts climbing up section in the movement direction so that in the far s some override their own molasse debris folds above these deep decoupling zones deformed their overlying thrust sheets into large antiforms i e the nanga parbat and hazara syntaxes the nanga parbat syntaxis probably formed due to a shear couple near a branch line where one of the main himalayan thrusts joined the indus suture beneath kohistan crustal delamination to produce the imbricated gneiss sheets could not account for all the displacement of india into asia suggested by palaeomagnetic data there must also have been lateral displacement as demonstrated by the large oblique slip shear zone in the hunza valley n of kohistan

the pumpellyite actinolite and contiguous facies in part of the phyllite quartzite series central northern peloponnesus greece variations in assemblage and composition of the constituent minerals in basic and intermediate metavolcanics encountered in the zarouchla group of the phyllite quartzite series are consistent with a progressive sequence corresponding to temperature conditions estimated at 290 380 c minimum values under a total pressure greater than 3 5kbar and possibly as high as 5 kbar in the absence of more critical evidence the parageneses recorded in the metavolcanic rocks are interpreted as belonging to a prograde facies series from the lawsonite albitechlorite facies through the pumpellyite actinolite facies to the greenschist facies the present distribution of mineral assemblages does not show a simple increase of metamorphic grade in a given direction but is apparently related to the tectonic evolution of the metamorphic sequence

structural evolution and asymmetric uplift of the nanga parbat syntaxis pakistan himalya the nanga parbat syntaxis in the nw himalaya is a still growing crustal scale north trending antiformal structure in the core of which indian plate gneisses have been uplifted from beneath the overthrust rocks of the kohistan island arc isotopic and fission track geochronology show that uplift rates within the syntaxis have increased to present day rates of 6 mm yr uplift has been accommodated by a combination of initial northwest verging thrusting on the western margin of the syntaxis followed by crustal scale folding within the syntaxis and latterly by dextral reverse faulting on the western margin this thrusting folding and faulting is the effect of deformation at the north western lateral tips of the main himalayan thrusts where they interfere with the south southeast verging thrusts of the northwest himalaya

thrust tectonics thin skinned or thick skinned and the continuation of thrusts to deep in the crust abstract the paper analyses the geometry of thin skinned thrust zones where the thrusts shallow out at depth and of thicker skinned fault zones where much of the crust is involved and where the thrusts are frequently observed to become steeper downwards in the interiors of many orogenic belts the steep dip of faults is not original but due to the folding above lower decoupling zones the energy involved in the internal deformation of hanging wall rocks may prohibit many faults becoming more shallow upwards such shallowing upwards faults may occur in more ductile rocks to maintain compatibility between zones which have experienced different deformation intensities but displacements on the faults are unlikely to be large another mechanism for producing faults which steepen downwards is proposed for the major thrusts which form the southern margin to the himalayas these carry large thicknesses 30 to 100 km of crustal and upper mantle rocks to the south causing flexuring and isostatic depression of the indian plate the steeply dipping thrusts are not footwall ramps these may be some distance behind the steepened zone this thrust induced isostatic bending of the crust has important implications when considering regional seismic interpretations as well as thrust mechanics and kinematics

alteration and mass transfer in cataclasites and mylonites in 6 6 km of granitic crust at the siljan impact structure central sweden granitic rocks deformed by cataclasis and mylonitization on macro a few meters and micro thin section scales are found at depths down to 6 6km in the siljan impact structure in central sweden granites near fault planes exhibit 1 fracturing kinking fragmentation and recrystallization of feldspars into pure k and na endmember varieties 2 fragmentation polygonization and development of undulose extinction in quartz and 3 kinking appearance of wavy extinction and alteration of biotite chlorite amphibole and alteration of ilmenite and magnetite whole rock chemical analyses of deformed and undeformed rocks show that deformed rocks are enriched in sio2 by about 5 wt and depleted in other oxides by variable percentages apart from rb and co the concentrations of other trace elements including ba sr zn zr pb cd cu cr ni v u th la and li are lower in deformed relative to undeformed rocks mass balance calculations for a 1000 cm3 model granite which were based on modal mineralogy whole rock chemistry and mineral analyses suggest that the break down of primary biotite chlorite and amphibole in deformed zones released elements to circulating fluids these calculations also indicate liberation of water and a doubling of porosity from 1 to 2 during the deformation episodes later precipitation of minerals in shear and tension fractures reduced this porosity within the upper 2000 m of the gravberg 1 well the formation of fracture filling minerals smectite calcite hematite chlorite and albite is impact related and was favored by active circulation of meteoric water fracture filling minerals in the upper 2000 m of the borehole formed at temperatures of 70 to 200 c between depths of 2000 and 3500 m fracture filling mineral assemblages dominated by fe mg chlorite sphene and epidote suggest formation temperatures in the range of 150 to 300 c occurrence of pumpellyite and prehnite in some altered biotite and chlorite of the deformed zones between 3500 and 5500 m suggest preimpact metamorphism and formation temperature above 150 c below 5500 m the mineral assemblages in the fractures are dominated by quartz sphene epidote and some muscovite and chlorite indicating a temperature range between 300 and 450 c one of the possible origins for the ch4 and h2 gases detected in the gravberg 1 well is a combination of hydrogen ions released by decomposition of hydrated silicates biotite chlorite hornblende with carbon the presence of iron in the deformed granitic rocks prevented the resulting ch4 from being oxidized

rbsr dating of the kohistan arc batholith in the trans himalaya of north pakistan and tectonic implications the kohistan arc batholith in northern pakistan is situated between the indus suture and the northern suture it belongs to the trans himalayan belt which continues eastwards as the ladakh arc batholith in northwest india and the kangdese batholith in southern tibet in kohistan the island arc consists upward sequence of the chilas stratiform complex of norites noritic gabbros and chromite layered dunites which formed in the sub arc magma chamber plutons of tonalite and diorite one of which has a rbsr isochron age of 102 12 ma the chalt volcanics of basaltic tholeiites succeeded by andesites to rhyolites and the yasin group sediments which formed in overlying intra arc basins and which contain albian aptian faunas all these rocks were deformed by major fold structures which are correlated with the formation of the northern suture ne sw trending basic jutal nomal dykes north of gilgit cross cut all the above structures and have a39ar 40ar hornblende age of 75 ma thus the northern suture must have formed in the period 102 12 to 75 ma with the island arc attached to the eurasian plate further northward subduction of the tethyan plate gave rise to an andean type batholith two plutons of which have rbsr isochron ages of 54 4 ma and 40 6 ma the dir utror group of calc alkaline lavas and sediments with eocene fossils are remnants of the volcanic cover of the andean type batholith we suggest that late cretaceous blueschists formed during subduction under the active continental margin and that continental collision and formation of the indus suture was in the eocene the batholith was intruded by layered aplite pegmatite sheets at 34 14 ma and 29 8 ma rbsr ages in post collisional times the87sr 86sr initial ratios of all the dated rocks range between 0 7039 and 0 7052

use of reaction path modeling to identify the processes governing the generation of neutral na cl and acidic na cl so4 deep geothermal liquids at miravalles geothermal system costa rica abstract the eq3 6 software package was used to investigate the irreversible water rock mass exchanges governing the production of neutral na cl and acidic na cl so 4 geothermal liquids circulating at depth into the miravalles geothermal system first we reconstructed the in situ reservoir composition including ph we evaluated the boundary conditions p co 2 p h 2 s and or p o 2 which are necessary for the implementation of reaction path modeling we estimated the thermodynamic affinity of the reservoir liquids with respect to relevant hydrothermal solid phases and we identified possible compositions of the initially acidic meteoric magmatic liquids then we modeled both the interaction between meteoric magmatic fluids and calc alkaline volcanic rocks and the interaction between neutral na cl waters and highly altered volcanic rocks reaction path modeling was performed through a purely stoichiometric approach without considering the kinetics of irreversible mass exchanges results of reaction path modeling suggest that the neutral na cl liquids hosted in the miravalles geothermal reservoirs are produced through interaction between initially acidic magmatic meteoric aqueous solutions and volcanic rocks and represent the final product of this process however the deep acid na cl so 4 liquids of miravalles are not intermediate products in this process they are instead generated through interaction of neutral na cl waters with volcanic rocks affected by advanced argillic alteration representing old solfataras buried by later volcanics as suggested by robert o fournier about 10 years ago

preliminary conclusions of the royal society and academia sinica 1985 geotraverse of tibet the 1985 chinese british expedition to the tibetan plateau attempted to solve the question of the origin of the very thick crustal rocks in this region continuing northwards movement of the indian plate over the past 38 myr has given rise to severe folding and thrust faulting causing crustal thickening by internal deformation previous collisions of microplate terranes derived from gondwanaland occurred during mesozoic times but the kun lun terrane of northern tibet was already part of laurasia by the carboniferous

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

geochemistry of late metamorphic hydrothermal alteration and graphitisation of host rock macraes gold mine otago schist new zealand abstract the macraes gold deposit in the otago schist new zealand formed during late metamorphic fluid flow through a lower greenschist facies shear zone mineralisation occurred near to the brittle ductile transition at about 300 c large volumes of host rock in a shear zone up to 120 m thick have been hydrothermally altered by this fluid activity most alteration is not structurally controlled apart from proximity to the shear zone ductile and brittle microshears traverse the most mineralised rocks and some structural control of fluid flow occurred as well fluid flow was slow similar to that in metamorphic rocks mm year and diffusion through interconnected fluid was a significant chemical process localised extensional hydrofractures m scale are filled with mineralised quartz most alteration of the host rocks was isochemical with respect to the lithophile elements and mineralised rocks have been variably enriched in as au sb w mo and bi but not co or cd addition of sulphur has occurred to both host rocks and mineralised rocks up to 1 wt above a background of 0 1 wt host rock sulphur is mainly pyritic and is not structurally controlled mineralised rocks have pyrite and arsenopyrite along microshears pyrite chalcopyrite sphalerite and galena have formed from sulphidation of silicates with no addition of metals graphite has been added to mineralised rocks along microshears up to 3 wt locally above a background of 0 1 wt noncarbonate carbon graphite deposition may have occurred as a result of mixing of two fluids water methane and water carbon dioxide graphitisation and sulphidation reactions released low d water which accumulated in the slow moving mineralising fluid distinction between this low d reaction water and meteoric water incursion is difficult

evolution of the latera geothermal system ii metamorphic hydrothermal mineral assemblages and fluid chemistry abstract the latera field vulsini volcanic complex latium italy is one of the geothermal areas of the peri tyrrhenian belt along which a regional high thermal anomaly has been detected so far nine deep wells have been drilled within the latera caldera and four of them have been productive the geothermal reservoir is located within the fractured carbonatic rocks of the tuscan nappe the overlying volcanic units sealed by hydrothermal minerals mainly calcite and anhydrite act as an impervious cover the fluid produced by the wells comes from a deep aquifer about 1000 1500 m depth which at present is not connected with the shallow aquifer in the volcanoclastic units fluid temperatures range between 200 and 230 c in hole temperatures as high as 343 c at 2775 m depth have been measured in dry wells the study of the newly formed mineral assemblages from both volcanic and sedimentary units as sampled from the geothermal wells can be used to reconstruct the thermal evolution of the geothermal field the intrusion of a syenitic melt up to a depth of about 2000 m dated 0 86 ma represents the major thermal event for the units in the area and is assumed to represent the first step in the geothermal evolution of the latera system the above mentioned newly formed mineral assemblages can be divided into three groups a contact metasomatic calcite anhydrite diopsidic pyroxene grossularitic garnet phlogopite wollastonite or monticellite b high temperature hydrothermal calcite anhydrite k feldspar vesuvianite melanitic garnet tourmaline amphibole epidote sulphides c low temperature hydrothermal calcite anhydrite k feldspar clay minerals sulphides group a minerals are now relics part of b and all of c group are still in equilibrium with the existing conditions in different parts of the geothermal system thermodynamic calculations on the observed mineral assemblages permitted estimates of the p t conditions and gas fugacities

biotite and apatite as tools for tracking pathways of oxidized fluids in the archean east repulse gold deposit australia fluid pathways in hydrothermal ore deposits can potentially be traced through alteration zoning patterns and the chemistry of mineral phases i e major trace elements and isotopic composition which provide insight into the physico chemical gradients within and adjacent to pathways world class neoarchean gold deposits of the eastern yilgarn can be zoned with respect to alteration assemblages but in many cases fluid pathways are poorly understood which makes it difficult to identify the nature and source of fluids this study conducted detailed core logging sem mineral mapping of alteration assemblages and microprobe analysis of biotite and apatite in order to identify chemical gradients across the east repulse gold deposit of the st ives gold camp eastern yilgarn western australia results show that the east repulse deposit is vertically zoned with relatively oxidized sulfate rich alteration in the footwall of the deposit anhydrite celestine and or barite sulfide rich alteration in the core of the deposit pyrite magnetite with minor barite and celestine and relatively reduced sulfide only assemblages pyrite pyrrhotite with minor pentlandite millerite and cobaltite in the hanging wall of the deposit gold was identified as inclusions in pyrite and associated biotite implying a link between biotite pyrite alteration and gold mineralization the abundance of f in biotite and apatite progressively decreases from the footwall of the deposit into the mineralized core this trend of decreasing f in biotite and apatite with decreasing depth is consistent with an hypothesis that oxidized f and k bearing fluids were focused along subvertical pathways beneath the deposit within or subjacent to granitoid dikes the biotite apatite geothermometer shows that these fluids were relatively hot 480 60 c at the time of alteration these relatively high temperature oxidized f and k bearing fluids may have been derived from a proximal magmatic source

epidote group minerals in low medium pressure metamorphic terranes epidote group minerals are common in metamorphosed mafic to intermediate igneous rocks quartzofeldspathic sediments and calc alumina silicate marl rocks of higher grade zeolite to medium grade amphibolite facies of low medium pressure contact and regional metamorphic terranes i e pressure and temperature conditions below the calcite to aragonite transition within any one rock epidote composition in terms of fe3 fe3 al can be variable but in general is limited by whole rock composition such that epidote group minerals in metabasite lithologies are more fe rich than those in marls that tend to be more al rich and typically include zoisite because of their wide range of p t stability epidote group minerals of variable composition may form in a single rock during several stages of metamorphic re equilibration slow rates of intra crystalline fe3 al exchange especially at low temperatures preserve complex zonation patterns in individual grains that can serve as a tape recorder providing evidence for continuous or discontinuous prograde and retrograde reactions and the p t fluid redox conditions of metamorphism thus relic lower grade epidote typically fe rich often form cores over which new typically less fe rich higher grade epidote rims form in such a case the boundary between the two generations of epidote may be sharp or gradational depending on the temperature history of the rock and fe3 al diffusivity often compositional differences are blurred across the boundary in addition to zoning is the spread of individual epidote grain compositions within a rock even on a thin section scale this is related to variation in the composition of coexisting phases or reactants e g quartz ca al silicates such as plagioclase margarite lawsonite mafic silicates such as chlorite pumpellyite amphiboles other ca fe3 silicates such as prehnite andraditic garnet carbonates fe oxides relict volcanic glass which serve as compositional micro domains in which epidote may form

occurrence and origin of marialitic scapolite in the humboldt lopolith n w nevada the occurrence and origin of marialitic scapolite in the humboldt lopolith was investigated in the field and in the laboratory using petrographic and experimental techniques scapolite occurs in three modes as a pervasive replacement of plagioclase and other minerals in gabbro diorite and extrusive rocks as a poikiloblastic mineral in scapolitite dikes and as a fracture filling mineral with analcime albite and sphene in scapolite veins additional secondary minerals associated with scapolite include epidote prehnite hornblende and diopside salite clinopyroxene relations with these minerals suggest that most marialitic scapolite grew at temperatures around 400 c scapolite composition varies from eqan12 to eqan37 containing from 72 to 96 atomic cl in the r position experiments on systems of similar compositions indicate that nacl h2o fluid having more than 40 mol nacl is needed to stabilize the scapolite

multistage hydrothermal alteration of gabbroic rocks from the failed mathematician ridge oxygen isotopic mineralogical and fluid inclusion data are presented for fresh and hydrothermally altered gabbroic rocks from the failed mathematician ridge the mathematician ridge though initially a fast spreading ridge presently has a deep central rift valley more typical of slow spreading rifts the inner rift walls expose rare plutonic rocks uncomplicated by proximity to deep large offset fracture zones undeformed mathematician ridge gabbros preserve most of the original texture and phase compositions and have been only slightly mineralogically or isotopically modified by post crystallization hydrothermal alteration metagabbros have been subjected to a pervasive ductile deformation and recrystallization to foliated rocks composed of aluminous amphibole low calcium plagioclase and ilmenite oxygen isotope and phase chemical data suggest this event began at temperatures of up to 700 c water rock ratios of less than one and produced modified seawater fluids with isotopic compositions of 3 5 6 0 the amphibolites are cross cut by multiple generation quartz epidote veins forming a network replacement of the amphibole grade mineralogies by greenschist grade mineralogies fluid oxygen isotopic compositions of 2 4 and a two phase separation in the fluid captured in conjugate vapor fluid inclusions are all associated with the formation of this network fluid inclusion data for the quartz indicate initial temperatures of over 500 c these samples may represent rocks from the 1 2 km deep plumbing system of black smoker type venting

mafic sheets from indian plate gneisses in the nanga parbat syntaxis their significance in dating crustal growth and metamorphic and deformation events

anatomy of a continental subduction zone the main mantle thrust in northern pakistan the himalayas form an ideal natural laboratory to study the deformation processes of continental crust during collision orogeny new information is presented concerning the structural evolution of the main mantle thrust zone in the himalayas of n pakistan in the region around nanga parbat the hanging wall lies at relatively high levels within the kohistan arc terrane which has been emplaced onto indian continental rocks this thrust probably originated as a breakback structure in the hanging wall to the pre collisional oceanic subduction zone the present hanging wall contains a shear zone of about 1 km width developed under amphibolite facies conditions simple shear dominant strains have developed new fabrics parallel to the main thrust zone however these structures are redeformed by discrete extensional and compressional shears within about 100 m of the thrust contact again developed under amphibolite facies conditions the footwall consists of an old basement complex the nanga parbat gneisses overlain by a distinct suite of metasediments now at amphibolite facies this cover assemblage of psammites pelites and marbles with local metabasites consistently lies directly against rocks derived from the kohistan arc along the mmt the absence of structures suggestive of consistent rheological contrasts within the cover assemblages suggests that the vast majority of the deformation features they contain were developed only once they experienced substantial tectonic overburdens prior to this the indian cover rocks will have been passively subducted beneath the kohistan arc until into amphibolite facies we discuss these inferences in terms of evolving shear zone width with time and comment on the implications for predicting the character of mid deep crustal shear zones particularly from seismic reflection profiles

tectonic evolution of the himalayan syntaxes the view from nanga parbat acknowledgements i was introduced to the himalayas by mike coward in the mid 1980s and remain indebted to him for inspiring a career studying orogenic tectonics i also thank the numerous colleagues both from the uk and from peshawar university who were companions on many field campaigns especially around nanga parbat this contribution has been greatly improved by incisive reviews by tom argles and phaedra upton although of course the author takes full responsibility for the views presented here finally i thank peter treloar for inviting this review and for his patience while i put it together funding over the years this research has been variously supported by the uk s natural environment research council and the royal society published in himalayan tectonics a modern synthesis

chemical variations in assemblages including epidote and or chlorite in the fossil hydrothermal system of saint martin lesser antilles abstract epidote and or chlorite are common minerals in the roots of the fossil geothermal system of saint martin lesser antilles they appear in four distinct assemblages 1 epidote actinolite quartz magnetite near the contact between the tuffaceous host rocks andesitic modal composition and the quartz diorite intrusion of philipsburg 2 epidote chlorite quartz in host rocks as far as a lateral distance of about 3 km from the intrusion 3 epidote chlorite haematite quartz locally in iron and manganese rich host rocks 4 chlorite phengite magnetite appearing as late sealing of porosity in fracture controlled quartz veins with strongly phengitized wall rocks all these assemblages constitute a large alteration grading from propylitic alteration to thermal metamorphism actinolite bearing assemblage detailed microprobe studies of epidotes replacing plagioclases and of chlorites replacing glass and mafic minerals reveal notable compositional variations which have been studied with respect to temperature paleogradients estimated from fluid inclusions study distance from the thermal source and fo2 conditions the mean ps pm 100 fe3 mn3 al3 fe3 mn3 of epidotes vary from 21 in the presence of magnetite near the intrusion to 32 in haematite bearing iron and or manganese volcanic and sedimentary formations the intra grain chemical scattering of epidotes increases with increasing distance of the pluton and decreasing temperature of crystallization all the chlorites coexisting with epidote are mg rich xfe

al fe super 3 and ca sr super 2 epidotes in metagreywacke quartzofeldspathic schist southern alps new zealand al fe super 3 or and sr super 2 or bearing epidotes are a common constituent in chlorite and biotite albite zone metagreywacke quartzofeldspathic schist in the southern alps of new zealand on the basis of electron microprobe backscattered electron scanning of complexly zoned grains five generations of epidote growth are recognized first generation epidotes ps sub 29 25 are typically fractured as a result of cataclasis during d1 deformation and presumably represent relics of prehnite pumpellyite and or pumpellyiteactinolite facies conditions of metamorphism second generation epidote ps sub 25 20 rims first generation epidote and replaces fragmented grains third generation epidote involved sr replacement up to 8 5 wt sro of earlier grains along fracture planes and grain margins single grains exhibit a range of sr ca replacement that can vary by up to 4 wt sro fourth generation post d 1 epidote ps sub 20 9 occurs as overgrowths on earlier generation epidotes and as continuously zoned grains within the lowest grade part of the biotite albite oligoclase zone fourth generation epidote cores ps sub 10 13 are overgrown by slightly more fe rich fifth generation rims ps sub 16 14 suggesting involvement of the epidote ca 2 al 3 si 3 o 12 oh component in an oligoclase producing reaction in quartzofeldspathic lithologies epidote disappears at higher grades than the appearance of oligoclase epidote compositions plot within the miscibility gap defined and a discontinuity between compositions of ps 20 and ps 16 in chlorite zone rocks is attributed to the persistence of relic cores due to incomplete fe super 3 al diffusional exchange at low temperature and textural grade with increasing grade there is a decrease in the range of zoning in individual epidote grains resulting in a more homogeneous population of epidote compositions with the most al rich epidotes becoming fe super 3 or rich and the most fe super 3 or rich epidotes becoming more al rich the formation of sr epidote appears to be related to the release of sr into the fluid phase from the breakdown of detrital plagioclase over the pumpellyite clinozoisite isograd during d1 deformation early formed oligoclase in the biotite albite oligoclase zone resulting from the disappearance of epidote contains up to 0 4 sro mobility of sr and ca is indicated by veins containing sr bearing epidote and calcite the complex zoning of epidotes is a function of bulk composition time variation in fluid composition temperature pressure and deformation of the rocks

fault zone reactivation kinematics and mechanisms the kinematics and mechanisms of fault zone reactivation are reviewed reactivation is dependent upon fault zone orientation and the existence of weak mylonites along these zones the recognition of reactivation within mylonite zones and the softening processes that first concentrate deformation into these and secondly provide a weak medium for reactivation are discussed attention is given to the darling mobile zone western australia and the redbank zone see obee white this symposium as examples of reactivated zones

isotopic constraints on the cooling history of the nanga parbat haramosh massif and kohistan arc western himalaya nineteen 40ar 39ar and 22 rb sr mineral ages are presented for metamorphic rocks and granites collected from the northern part of the nanga parbat haramosh massif nphm and adjacent parts of the kohistan arc western himalaya the majority of these ages are interpreted as exhumation related cooling ages and they therefore place important constraints on the exhumation history of the region the 40ar 39ar and rb sr mica cooling ages for areas of the nphm to the north of the indus river lie in the range 2 8 ma and are similar to previously published ages from the indus gorge itself cooling histories for these areas show little systematic variation from east to west suggesting that the basement may have been exhumed as a relatively rigid block after the main stages of folding mica ages increase dramatically from the nphm westward into the kohistan arc where ages lie in the range 13 30 ma the contrast in both cooling ages and the age differential between mineral pairs between the two terranes indicates rapid cooling of the nphm in the last 10 m y compared with the kohistan arc the relationship between rates of cooling and exhumation is poorly constrained in regions of rapid uplift where the characteristics of the evolving geotherm are not well understood however the results are consistent with an anomalously rapid exhumation history of the nphm during the last 10 m y compared with the adjacent kohistan arc the interpretation of some of the ages documented in this study is problematical two biotite samples from contrasting lithologies within the nphm have yielded higher 87sr 86sr ratios than the corresponding whole rocks but the cause of this isotopic disequilibrium remains unclear other biotite samples from the region have consistently yielded younger rb sr ages than 40ar 39ar ages which may be a reflection of either preferential leaching of 87sr during fluid infiltration on a regional scale or the presence of excess argon alternatively the relative ages indicate slightly lower closure temperature for strontium diffusion in biotite than for argon diffusion in biotite where samples have undergone rapid cooling

hypersaline fluids generated by high grade metamorphism of evaporites fluid inclusion study of uranium occurrences in the western zambian copperbelt in the pan african lufilian belt western zambian copperbelt uranium mineralizations preferentially scattered in kyanite talc micaschists metamorphosed evaporitic sediments or concentrated along transposed quartz veins provide an opportunity to 1 understand the time space relationship between the ore minerals and the deformation of the host rocks 2 identify the different fluid events associated with specific stages of quartz deformation and 3 characterize the ore fluid geochemistry in terms of fluid origin and fluid rock interactions in the u occurrences studied in lolwa and mitukuluku domes region western zambian copperbelt two mineralizing stages are described the first generation of ore fluids 53 59 wt cacl2 13 15 wt nacl n2 h2 in the gas phase of fluid inclusions circulated during the high temperature quartz recrystallization at 500 700 c this temperature is in agreement with the p t conditions recorded during the crustal thickening related to continental collision at ca 530 ma la icpms analyses show the presence of uranium within this fluid with a concentration mode around 20 ppm the second generation of ore fluid 21 32 wt nacl 19 21 wt cacl2 co2 co in the gas phase of fluid inclusions percolated at lower temperature conditions at the brittle ductile transition between 200 and 300 c this temperature could be related to the exhumation of the high grade metamorphic rocks at ca 500 ma the formation of h2 and co is interpreted as the result of radiolysis in the presence of dissolved uranium in the aqueous phase of these fluid inclusions finally a late fluid 14 16 wt naclequiv circulated in the brittle domain but seems unrelated to u re mobilization event

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

a field chemical and stable isotope study of subseafloor metamorphism of the josephine ophiolite california oregon the josephine ophiolite is a large complete ophiolite generated in a late jurassic back arc basin along western north america the ophiolite underwent subseafloor metamorphism under a steep thermal gradient as indicated by downward changes in mineralogy and 18o values characteristic mineral zonation includes mica orthoclase and hematite in the lower extrusives greenschist facies assemblages in the upper sheeted dikes and amphibolite facies assemblages in the lower sheeted dikes and high level gabbro cumulate gabbros are only incipiently altered but are depleted in 18o indicating high temperature alteration with fluids that evolved at low water w rock r ratios a second off axis circulation system is recorded by metalliferous sediments that occur 8 21 m above the ophiolite alteration in the upper sheeted dike complex and especially the extrusive sequence is heterogeneous at outcrop scale as indicated by large variations in mineralogy chemistry and 18o values within individual pillows and dikes the heterogenity is due to 1 variations in w r ratio and starting material during alteration by downwelling seawater e g pillow cores versus glassy rims and 2 localized discharge mineralization mostly epidosites superimposed on the background recharge alteration epidosites occur largely as dike parallel stringers irregular replacement of pillow and massive lava and replacement of interpillow and pillow breccia matrices the chemistry of most extrusives and sheeted dikes is characterized by loss of ca and gain in na and mg consistent with alteration by downwelling fluids in addition the sheeted dikes are depleted in k2o and the lower sheeted dikes and high level gabbros are depleted in zn and cu the 18o and d values for most samples from the extrusive sequence indicate alteration by seawater at 50 rotation of the entire crustal sequence at the spreading axis suggests that the ophiolite formed at a slow spreading center where magma chambers were episodic

chemical and thermal constraints on focussed fluid flow in the lower oceanic crust the mechanism of heat extraction from the lower oceanic crust near the ridge axis is poorly constrained despite its importance for understanding both the process of accretion of the plutonic complex and the mass fluxes associated with ridge hydrothermal systems we have investigated the role of zones of focussed fluid flow in the plutonic complex of the oman ophiolite in the near axis cooling of the oceanic crust lineaments identified on aerial photographs that occur at 1 km spacing show evidence for extensive hydrothermal fluid flow through regions 10 to 50 m wide fluid flow is initiated in these regions at 800 c and continues at least into the lower greenschist facies strontium isotope analyses indicate that the fluid flux through these zones is sufficient to transport a metasomatic front from the base of the sheeted dike complex to close to the moho computed minimum fluid fluxes to transport a metasomatic front through the focussed fluid flow zones are 1x108 kgm2 modeling of diffusive exchange of calcium from olivine to clinopyroxene indicates enhanced cooling rates adjacent to the focussed fluid flow zones heat fluxes estimated from the enhanced cooling rates are broadly consistent with the fluid fluxes determined from modeling the sr isotopic composition of samples from the focussed fluid flow zones the combination of independent estimates of the fluid and heat fluxes such as these can provide more rigorous constraints on the thermal history than either approach used in isolation our results show that focussed fluid flow could play a major role in the cooling in the lower oceanic crust significant focussed fluid flow in the lower oceanic crust has important implications for predicting the total mass flux associated with hydrothermal circulation at mid ocean ridges this is because fluids flowing through channels become chemically rock buffered at smaller fluid fluxes than those flowing pervasively through a rock mass thus if focussed fluid flow is an important mechanism of heat loss from the lower oceanic crust the chemical fluxes from ridge hydrothermal systems into the oceans may be smaller than currently thought

the northern samail ophiolite an oxygen isotope microprobe and field study geological petrological and oxygen isotopic data are presented for 228 whole rock and mineral samples collected from a 100 20 km area of the northern samail ophiolite in oman most of these samples are from three detailed profiles through the pillow lavas sheeted dikes and layered gabbros of this laterally heterogeneous fragment of cretaceous oceanic crust down to and across the petrologic moho the profiles encompass a range of petrologic and tectonic styles and each profile exhibits distinctive 18 16 o variations compared to one another and to mid ocean ridge basalts as a result of pervasive seawater hydrothermal interaction that varied in intensity along strike in the ophiolite in general 18 o depletions are observed in the layered gabbros and 18 o enrichments in most of the sheeted dikes and pillow lavas similar to results previously observed in the southern part of the ophiolite ibra area where 18 o depletions within the gabbroic section are quantitatively balanced by 18 o enrichments in the shallower parts of the oceanic crust the wadi hilti profile selected as an example of relatively intact crust differs from ibra in having more uniform and slightly higher 18 o in the gabbros 5 4 to 6 3 as well as in containing more hydrous alteration minerals amphibole epidote chlorite and prehnite the profiles in the wadi kanut shafan and wadi rajmi sections are much more complex and reveal the impact of off axis intrusions and deep crustal shearing plagiogranite wehrlite intrusions in the shafan kanut area superimposed a local hydrothermal aureole on the ophiolite evident in dikes highly depleted in 18 o quartz sulfide veins abundant epidote thullite and chlorite in shallower rocks and low temperature hydrous alteration of deeper gabbroic rocks the latter produced an overall increase in whole rock 18 o 6 2 to 6 9 such late stage intrusions are found throughout the northern half of the samail ophiolite the wadi rajmi area which is a possible fossil transform or propagating rift represents the most complex of the three profiles it also contains the most abundant highly deformed and hydrothermally altered rocks together with the deepest and largest zone of 18 o depletion yet found in any ophiolite locally 18 o 2 0 conduits for large volumes of high temperature hydrothermal fluids were provided by fractures now occupied by low 18 o gabbro pegmatites and low 18 o dikes material balance estimates for the regional samples and from the various transects through the ophiolite give crustal bulk 18 o averages 5 9 to 6 3 that are within sampling error almost identical to the average morb basalt value of about 5 8 if both vertical and lateral crustal heterogeneities are integrated into a three dimensional model this supports and amplifies the conclusion of earlier workers that the 18 o of seawater is buffered and controlled by hydrothermal interaction with oceanic crust as long as the cumulative effects both spatial and temporal of all seafloor magmatic hydrothermal processes are considered the very slight out of balance enrichment of the integrated crustal average 18 o compared to morb may be explained by the ubiquitous mineralogical and isotopic evidence for a late low temperature alteration event in the basal gabbros these effects are prominent in the vicinity of the petrologic moho and may indicate exchange with low temperature aqueous fluids during or after detachment of the obducted slab

plagioclase and epidote buffering of cation ratios in mid ocean ridge hydrothermal fluids experimental results in and near the supercritical region abstract experiments have been performed with na ca k cl fluids of seawater chlorinity and diabase basalt and plagioclase bearing mineral mixtures at 350 425 c and 250 400 bars to help constrain hydrothermal alteration processes at mid ocean ridges dissolved ca na and ph for all experiments responded systematically to differences in dissolved sio2 concentrations and the compositions of plagioclase reactants diabase alteration at low fluid rock mass ratios 0 5 to 1 produces fluids undersaturated with respect to quartz during hydration of primary olivine and orthopyroxene whereas basalt alteration under similar conditions yields fluids slightly supersaturated with respect to quartz during breakdown of glass to smectite and amphibole fluid chemistry in all experiments appears to approach a partial equilibrium state with the albite and anorthite components in plagioclase and approaches a ph consistent with plagioclase alteration to epidote trace element data from vent fluids specifically b and sr together with major element chemistry ca na sio2 ph provides evidence that the reaction zone for black smoker fluids at mid ocean ridges is composed of only slightly altered diabase and is characterized by small amounts of epidote nearly fresh plagioclase and clinopyroxene and partially to completely hydrated olivine and orthopyroxene fluids reacting with this rock may be undersaturated with respect to quartz so pressure estimates based on the quartz geobarometer should be regarded as minimums using equilibrium between plagioclase the dominant reactant and epidote the dominant reaction product in experiments we estimate that temperatures in reaction zones are in excess of 375 c for most vent systems these temperatures are higher than measured vent temperatures suggesting that hotspring fluids commonly loose heat during ascent to the seafloor

deep crustal break back stacking and slow exhumation of the continental footwall beneath a thrusted marginal basin grenville orogen canada abstract granulite to upper amphibolite facies ductile thrusting in the central gneiss belt grenville orogen ontario represents the tectonic shortening of a continental scale footwall beneath the thrust emplaced central metasedimentary belt during the closure of a postulated back arc basin ca 1 19 1 18 ga break back stacking in the footwall occurred at mid to deep crustal depths ca 35 km within tectonically thickened ca 70 km continental crust and culminated with renewed thrusting at the base of the overlying central metasedimentary belt ca 1 08 1 05 ga the individual mylonite belts which constitute the ductile thrust zones and the scale of penetrative deformation of the intervening crystalline thrust sheets are comparable with the largest known examples of high grade thrust belts elsewhere they reflect the large scale thermal and theological boundary conditions of the deformation flow within individual thrust zones may reflect local boundary conditions such as the rheological behaviour of older thrust sheets and the geometry of interfaces within the thrust stack restoration of the thickness of erosionally removed crustal overburden by break back thrusting may retard the rates of exhumation and cooling of a mid to deep crustal thrust stack

earthquake refraction profiles of the root of the sierra nevada we examine the seismic structure of the sierra nevada using records of nine earthquakes and one explosion in and near the sierra recorded on stations in the sierra we first interpret travel times from these paths which are confined to a single tectonic block in terms of one dimensional structures the most nearly reversed pair of earthquakes the 1966 truckee and 1983 durrwood meadows earthquakes share refracted pn arrival times corrected to surface focus along a line t 8 75 0 25 8 0 suggesting that a nearly flat layer of 8 0 km s mantle material lies at depths of 46 48 km first arrivals from these events do not constrain velocities from 30 to 45 km depth secondary arrivals and some first arrivals from other earthquakes suggest that velocities in part of this region range between 6 9 and 7 8 km s the presence of this 7 x km s layer can help to explain previous contradictory observations the 7 x km s layer could be interpreted as either the mafic bottom of a silicic mesozoic magmatic arc or as accreted mafic underplating or rejuvenated mantle related to cenozoic arc volcanism or basin and range spreading arrivals at stations in the foothills and the crest of the sierra cannot be fit with a single longitudinal structure indicating a lateral variation of velocity structure these variations support previously inferred variations of lithospheric structure with higher velocity thinner crust to the west beneath the sierran foothills and slower velocity crust or possibly upper mantle beneath the high mountains in the eastern sierra rapid changes in arrival times between stations separated by short distances in the eastern sierra suggest that a sharp boundary exists between the sierra and the basin and range at moho depths we also present fresh evidence of the asymmetry of the root of the sierra wherein arrivals from earthquakes on the west of the sierra are delayed within the sierra and return to original values in the basin and range while arrivals from earthquakes and explosions from the sierra into the great valley we suggest that if the 7 x km s material occurs in a wedge above the moho then the asymmetry can be explained by arrivals from the west being delayed by the dipping 8 0 km s moho while those from the east may be entering the root along a 7 x km s layer that is near the depth of the basin and range moho

rejuvenation of rbsr mica ages during shearing on the northwestern margin of the nanga parbat haramosh massif abstract the shear zone bordering the western margin of the nanga parbat haramosh massif nphm separates terranes with distinct but well documented cooling histories this study was undertaken in order to examine isotopic behaviour and if possible to date deformation or cooling within the contact zone itself rb sr muscovite and biotite ages and petrographic descriptions are presented for a range of metamorphic lithologies and granite sheets which have been affected to varying degrees by greenschist facies extensional crenulation this deformation has been kinematically linked to the differential uplift of the nphm ages for metamorphic lithologies and granite sheets are similar and are considered together determined muscovite ages mostly lie in the range 9 22 ma whilst the majority of biotite ages lie in the range 2 11 ma mica ages from the shear zone are significantly more variable than ages determined for unsheared lithologies from outside the shear zone even closely spaced samples yield variable mica ages and in some cases there is a significant difference between muscovite and biotite ages determined for the same sample muscovite ages yield a bimodal distribution with groups of ages in the range 17 21 ma and 8 12 ma the older group is thought to reflect the original purely thermostatic cooling of lithologies through the muscovite closure temperature prior to formation of the nphm structure in contrast the younger group of muscovite ages reflects variable degrees of isotopic resetting during shearing at temperatures below the muscovite closure temperature associated with the relative uplift of the nphm the majority of biotite ages also reflect partial to complete resetting during shearing however biotite samples from structurally competent amphibolite horizons preserve older 16 ma ages indicating that there was locally a strong lithological or fluid control on the degree of resetting the flanks of the nphm cooled through the muscovite closure temperature significantly earlier than the deeper structural levels presently exposed within the core of the nphm greenschist grade deformation was occurring within the shear zone at the same time that deeper levels of indian crust were passing through the muscovite closure temperature suggesting that the shearing reflects the relatively passive extensional movement of rocks sliding off the flank of the actively growing nanga parbat structure the results highlight the isotopic complexities of long lived shear zones present in orogenic belts but show that useful radiometric age information may be obtained if the regional tectonic history is well understood and if the samples for dating come from well constrained structural settings

evolution of fluid rock interaction in the reykjanes geothermal system iceland evidence from iceland deep drilling project core rn 17b abstract we describe the lithology and present spatially resolved geochemical analyses of samples from the hydrothermally altered iceland deep drilling project iddp drill core rn 17b the 9 3 m long rn 17b core was collected from the seawater dominated reykjanes geothermal system located on the reykjanes peninsula iceland the nature of fluids and the location of the reykjanes geothermal system make it a useful analog for seafloor hydrothermal processes although there are important differences the recovery of drill core from the reykjanes geothermal system as opposed to drill cuttings has provided the opportunity to investigate evolving geothermal conditions by utilizing in situ geochemical techniques in the context of observed paragenetic and spatial relationships of alteration minerals the rn 17b core was returned from a vertical depth of 2560 m and an in situ temperature of 345 c the primary lithologies are basaltic in composition and include hyaloclastite breccia fine grained volcanic sandstone lithic breccia and crystalline basalt primary igneous phases have been entirely pseudomorphed by calcic plagioclase magnesium hornblende chlorite titanite albitized plagioclase vein epidote and sulfides despite the extensive hydrothermal metasomatism original textures including hyaloclastite glass shards lithic clasts chilled margins and shell fragment molds are superbly preserved multi collector la icp ms strontium isotope ratio 87 sr 86 sr measurements of vein epidote from the core are consistent with seawater as the dominant recharge fluid epidote hosted fluid inclusion homogenization temperature and freezing point depression measurements suggest that the rn 17b core records cooling through the two phase boundary for seawater over time to current in situ measured temperatures electron microprobe analyses of hydrothermal hornblende and hydrothermal plagioclase confirm that while alteration is of amphibolite grade it is in disequilibrium and the extent of alteration is dependent upon protolith type and water rock ratio alteration in the rn 17b core bares many similarities to that of type ii basalts observed in mid atlantic ridge samples

hydrothermal alteration associated with magnetite mineralization in the bafq iron deposits iran abstract bafq mining district bmd is an iron mineralization province that contains more than 2 gt of iron ore located in the early cambrian volcano plutonic arc known as the kashmar kerman zone the host rocks of the fe mineralization are granitic and microgranitic rocks and their extrusive equivalents field observations and petrographic studies showed that both sodic and calcic alteration are related to iron mineralization other alteration styles including silicic chlorite epidote and sericite alteration are less important and post dated the mineralization sodic alteration is associated with the formation of chessboard albite whereas the calcic alteration is featured by a mineral assemblage of actinolite tremolite magnetite apatite available evidence suggests that the involved metasomatic fluids could be mainly of evaporitic sources with a minor contribution from magmatic fluids we suggest that mineralization formed at the end of the precambrian in pull apart basins in a magmatic back arc region associated with subduction of the proto tethys oceanic crust under central iranian plate iron ore mineralization may be related to the interaction of granite derived hydrothermal fluids and brine derived fluids sourced from the latest precambrian rizu and dezu evaporitic sequences

geological constraints structural evolution and deep geology of the northwest scottish caledonides the front of the caledonian orogenic belt in nw scotland is marked by a zone of foreland thrusting which contains imbricates of lewisian basement proterozoic cover and cambrian shelf sediments faults within this moine thrust belt in most localities propagated in a foreland directed sequence therefore the earliest of these thrusts was the moine thrust which carried a basement assemblage of moine and lewisian rocks over the cambrian shelf the development of large duplex and imbricate structures in the footwall postadted movement on this thrust hence a restoration of these imbricates provides a minimum estimate of the eastern extent of the cambrian shelf no synsedimentary or prethrust extensional features are recognised within the cambrian succession which displays a remarkable stratigraphic and thickness consistency this implies a corresponding consistency in crustal structure beneath these cover rocks immediately prior to caledonian thrusting a balanced cross section constructed across the northern part of the moine thrust belt has given a restored width for the cambrian shelf of 54 km geophysical data suggest that the present foreland crustal thickness is 28 km if this is taken to be the crustal thickness beneath the cambrian shelf during caledonian thrusting a minimum cross sectional area of 1512 km of lewisian rocks must remain beneath the present outcrop of the moine thrust sheet this foreland basement wedge may have been imbricated subsequent to the development of the cambrian imbricates caledonian structures within the moine thrust sheet are interpreted as forming an imbricate stack with the moine thrust acting as a floor thrust the ductile imbricate thrusts possibly roofed into the naver slide late open folds which warp foliation slides and metamorphic isograds within the moine sheet may represent culminations in the foreland lewisian imbricates beneath the moine thrust these postulated culminations may have been sufficient to initiate gravity driven structures this may explain late movements on high level faults within the moine thrust belt

fluid inclusions in epidote minerals and fluid development in epidote bearing rocks the widespread occurrence of epidote minerals in metamorphic and igneous rocks as well as in many ore deposit types makes it a promising candidate for fluid inclusion studies apart from high to very high temperature and low to intermediate pressure conditions epidote minerals are stable over a wide range of pressure and temperature in the continental and oceanic crust e g poli and schmidt 1998 yet fluid inclusion studies on epidote minerals are surprisingly scarce even in fluid saturated environments like certain vein type deposits or hydrothermal volcanic vugs and druses for example epidote minerals are not mentioned in the subject index of roedder s 1984 outstanding summary and review of fluid inclusion studies and occurrences which lists more than sixty different host minerals for fluid inclusions nonetheless more recent studies showed fluid inclusions in epidote minerals to be the only direct witness of the physiochemical and compositional fluid evolution during certain geodynamic processes mainly found in fossil geothermal systems ore deposits and high pressure to ultra high pressure rocks the aim of this review is to outline and summarize some aspects and interpretations of geodynamic processes which are based on temperature t pressure p molar volume v and composition x data from fluid inclusions in epidote minerals as well as associated host minerals from various geological environments the review starts with a chapter on some typical mixed volatile solid fluid equilibria involving epidote minerals which are relevant for the here discussed environments this is followed by a short introduction into the basic concepts of fluid inclusion research and the role of epidote minerals the next section covers fluid inclusion studies on epidote minerals from active and fossil geothermal systems as well as low grade metamorphic rocks and constraints on the p t x properties of the fluids present in these systems this is followed by a short introduction

thrust tectonics deep structure and crustal subduction in the alps and himalayas the structural restoration of collision orogenic belts onto crustal templates provides important insights into the tectonic evolution deep structure and amounts of plate convergence after the initial contact between two continental masses balanced cross sections have been constructed parallel to the local displacement directions across the western alps and western himalayas and demonstrate very large amounts of crustal shortening above intra crustal detachments to achieve a balance substantial volumes of lower crust must have been subducted beneath the two tectonic hinterlands a model of eclogite metamorphism is invoked to facilitate this subduction and to explain the varying isostatic responses of the alpine and himalayan hinterlands patterns of eclogite metamorphism are controlled by the geometry of thrust profiles on a lithospheric scale the development of crust mantle detachments being of crucial importance such a profile is proposed for the himalayas suggesting that relatively small volumes of the footwall crust succumbed to eclogite metamorphism in the alps however a steeper thrust profile apparently developed emplacing mantle onto crust causing wholescale eclogite metamorphism in the underlying franco swiss crust the resultant density increase would provide a mechanism of isostatic collapse and flexural subsidence in the po plain region

exhumation overrated at nanga parbat northern pakistan abstract new 40 ar 39 ar laserprobe and thermobarometric data from the nanga parbat haramosh massif nphm in northern pakistan provide important constraints on thermal models of the evolving geotherm of the massif simple thermal models indicate that the unusually young cooling ages from this area do not necessarily imply extreme exhumation rates of about 7 mm y because the advection of heat resulting from rapid exhumation leads to a steepened near surface geotherm the most important control on the present day thermal structure of the nphm appears to be the thermal structure resulting from obduction of the kohistan arc some 50 m y ago transient geotherms calculated for the past 10 ma can only be reconciled with published geochronological and thermobarometric studies if exhumation rates lay in the range of 3 to 4 mm y still considerably greater than exhumation rates determined from the main himalayan orogen

the evolution of the waiotapu geothermal system new zealand based on the chemical and isotopic composition of its fluids minerals and rocks abstract the waiotapu geothermal system is hosted by silicic rocks of the taupo volcanic zone new zealand exploration drilling in the late 1950s down to 1100 m provided physical information on the system measured temperatures show a boiling profile to 295 c with shallow inversions particularly in the north total discharge fluid samples were collected the geothermometry and measured temperatures show that fluids derive mainly from a shallow 400 m deep reservoir at about 225 c petrologic study of drillcore samples recovered from seven wells reveals an alteration assemblage of quartz and albite adularia with a variable distribution of chlorite pyrite calcite zeolites epidote pyrrhotite sphene leucoxene apatite and minor base metal sulfides white mica is a late overprint particularly well developed at shallow depths surficial alteration of kaolin cristobalite alunite and smectite clays reflect alteration by acid sulfate steam heated waters the activities of components in minerals determined from microprobe analyses and composition activity relations and fluids speciated to reservoir conditions indicate equilibrium now exists between the fluids and white mica the na k ratio of the fluid is being controlled by dissolution of albite and adularia while its h 2 h 2 s ratio is buffered by pyrite replacing pyrrhotite the fluids are now slightly undersaturated with respect to calcite the present deep fluids boil adiabatically from at least 300 c to 230 c at depths of 500 m this ascending chloride fluid is variably diluted by a steam heated water of zero chloride that lies over and occurs on the margin of the system like a discontinuous umbrella the steam heated water is relatively co2 rich 0 1 m the cooling at shallow levels by this mixing has shifted the alteration from albite adularia stability to white mica stability this shift is enhanced by the co2 rich nature of the diluent dilution of ascending chloride fluids by shallow waters is also supported by the oxygen and hydrogen isotopic composition of the mixture with the deep fluid being enriched in 18o and d from local meteoric by 7 and 10 respectively the patterns in whole rock 18o indicate that they were largely shifted in isotopic composition prior to incursion of steam heated waters possibly induced by a series of hydrothermal eruptions 900 years ago in contrast the 18o composition of late vug calcite indicates its formation is related to the initial incursion of steam heated groundwater and subsequent cooling this is supported by fluid inclusion evidence the d shift from local groundwater composition and the 13c composition of co2 determined from calcite 4 to 6 may be evidence for a magmatic input to the meteoric convection cell the shallow portion of the waiotapu geothermal system has recently evolved both chemically and physically by incursion of fluids from a steam heated carapace continued refluxing of these relatively cool hybrid fluids progressively deeper with their recycled co2 content will hasten hydrolytic leaching in contrast to a single pass of adiabatically cooling deep fluids this action accompanied by argillic alteration may eventually seal the deeper portions of the system hastening its demise there is evidence for similar events occurring in the fossil environment at epithermal depths

mineralogical and geochemical characteristics of hydrothermal alteration of basalt in the kuroko mine area japan implications for the evolution of a back arc basin hydrothermal system abstract basalt in the furutobe district of the kuroko mine area in japan is characterized by abundant chlorite and epidote fluid inclusion studies indicate that chlorite is formed at lower temperatures 230 250 c than epidote 250 280 c the seawater basalt mass ratio for the early chlorite rich alteration was high max 40 but that for the later alteration was low 0 1 1 8 the cao na2o and sio2 of the bulk rock correlate negatively with mgo while feo and fe correlate positively with mgo these changes in the characteristic features of hydrothermal alteration from early to late are generally similar to those for a mid ocean ridge geothermal system accompanying basalt alteration the mgo feo ratios of chlorite and actinolite and the fe2o3 concentration of epidote from the basalt are greater than those of mid ocean ridge basalt probably owing to the differences in the fe2o3 feo and mgo feo ratios of the parent rocks the lower cao concentration and the higher na2o concentration of the bulk rock compared with altered mid ocean ridge basalt can be interpreted in terms of the difference in original bulk rock compositions the furutobe basalt as well as other submarine back arc basalts contains more vesicles filled with hydrothermal minerals epidote calcite quartz chlorite pyrite than do the mid ocean ridge basalts the abundance of vesicles plays an important role in controlling the secondary mineralogy and geochemistry of hydrothermally altered submarine back arc basin basalts

equilibrium and disequilibrium processes across the greenschist amphibolite transition zone in metabasites documentation of textures modes and compositions of minerals in metamorphosed basalts across two greenschist to lower amphibolite facies sequences flin flon manitoba and rossland british columbia was combined with a compilation of the literature data to assess equilibrium and disequilibrium processes across this important transition zone at flin flon and rossland the greenschist amphibolite facies transition occurs over a narrow spatial interval marked by hornblende in oligoclase in and actinolite out isograds the data suggest the existence of stable miscibility gaps separating coexisting actinolite and hornblende and coexisting albite and oligoclase in the lowermost amphibolite facies however actinolite and hornblende show a divergence in compositions going upgrade across the oligoclase in isograd suggestive of disequilibrium between the new progressively more aluminous hornblende and metastably persisting actinolite likewise coexisting albite and oligoclase compositions show no evidence for converging compositions at higher temperatures suggesting they do not remain in equilibrium across a miscibility gap compositional gaps within epidote phases are attributed to disequilibrium preservation of lower grade epidote compositions to higher grade conditions rather than the existence of a miscibility gap at greenschist and amphibolite facies conditions recognition of equilibrium and disequilibrium relations highlights the difficulty of using natural compositional datasets to extract information on miscibility gaps and more generally to extract a x relationships the greenschist to amphibolite facies transition is controlled principally by the consumption of chlorite which primarily occurs upon crossing the oligoclase in isograd concomitant with conversion of actinolite to hornblende and albite to oligoclase the result is a focused pulse of devolatilization over a small spatial and thermal interval

chemical interaction of aqueous solutions with epidote feldspar mineral assemblages in geologic systems ii equilibrium constraints in metamorphic geothermal processes thermodynamic analysis of the system na sub 2 o k sub 2 o cao feo fe sub 2 o sub 3 al sub 2 o sub 3 sio sub 2 h sub 2 o hcl co sub 2 at pressures and temperatures to 5 kb and 600 sup 0 c affords quantitative description and interpretation of phase relations among epidote garnet plagioclase and alkali feldspar solid solutions in hydrothermal systems comparison of computed and observed compositions of these minerals and coexisting fluids suggests that the calculations afford close approximation of equilibrium and mass transfer in metamorphic geothermal processes the standard molal enthalpies of decomposition reactions for plagioclase are of the order of 4 to 50 kcal mole sup 1 which requires the activity of the anorthite component of plagioclase coexisting with epidote solid solutions to increase with increasing temperature at constant pressure in contrast because the standard molal volumes of these reactions are also negative a sub caal sub 2 si sub 2 o sub 8 decreases with increasing pressure at constant temperature either stoichiometric epidote or clinozoisite is compatible with plagioclase quartz calcite and an aqueous phase but only at x sub co sub 2 less than or equal to 0 2 the complex zoning commonly exhibited by both plagioclase and epidote solid solutions in geologic systems can be attributed to minor isothermal isobaric changes in the composition of coexisting aqueous solutions logarithmic activity and fugacitymore diagrams constructed with provision for solid solution permit documentation of such changes and facilitate thermodynamic interpretation of mineral and fluid compositions in metamorphic geothermal systems less

k ar and ar ar geochronology of the himalayan collision in nw pakistan constraints on the timing of suturing deformation metamorphism and uplift mica and hornblende k ar and ar ar data are presented from each of the three crustal components of the himalayan collision zone in north pakistan the asian plate the kohistan island arc and the indian plate together with u pb and rb sr data published elsewhere these new data 1 date the age of suturing along the northern suture which separates kohistan from asia at 102 85 ma 2 establish that the basic magmatism in kohistan which postdates collision along the northern suture predates 60 ma and that the later granite magmatism spanned a range of 60 25 ma 3 show that uplift amounts within kohistan are greater toward the nanga parbat syntaxis than away from it and that rate of uplift near the syntaxis increased over the last 20 ma to a current figure of about 5 5 mm a year 4 show that much of southern kohistan had cooled to below 500 c by 80 ma and that the major deformation which imbricated kohistan probably predated 80 ma and certainly predated 60 ma and was related to the kohistan asia collision rather than the kohistan india one 5 imply that uplift along the hunza shear in the asian plate together with imbrication of the metamorphics in its hanging wall took place at about 10 ma and was associated with breakback thrusting in the hanging wall of the main mantle thrust 6 suggest that the indian plate has a lengthy pre himalayan history with an early metamorphism at about 1900 ma major magmatism at 500 550 ma and early jurassic lithospheric extension or inversion and 7 show that the indian plate rocks were metamorphosed shortly after the collision within kohistan which occurred at circa 50 ma and subsequently cooled back through 500 c at circa 38 ma and 300 c at 30 35 ma with ages of cooling through 200 and 100 c as determined by fission track data locally controlled by nanga parbat related uplift tectonics

epidote bearing veins in the state 2 14 drill hole implications for hydrothermal fluid composition epidote bearing veins in state 2 14 drill core from 900 to 2960 m depth were examined using backscattered electron microscopy and electron probe microanalysis to characterize the mineralogy parageneses texture and composition of vein minerals in order of decreasing abundance minerals in epidote bearing veins are pyrite calcite k feldspar quartz anhydrite hematite chlorite fe cu zn sulfides actinolite titanite and allanite the downhole distribution of minerals in epidote bearing veins pyrite and quartz varies as a function of depth and includes 1 calcite above 2000 m 2 k feldspar between 1700 and 2745 m 3 anhydrite between 2195 and 2745 m 4 hematite sulfides above 2773 m and 5 actinolite below 2890 m where present k feldspar was the first mineral to precipitate in veins followed by epidote in all other veins epidote was the earliest vein mineral to form calcite quartz anhydrite hematite and sulfides were paragenetically later compositional zoning common in most vein epidotes is typically symmetric with al rich cores and fe3 rich rims the minimum mole fraction of ca2fe3si3o12 oh xps in vein epidotes decreases systematically with increasing depth from 0 33 at 906 m to 0 21 at 2900 m and the maximum xps at any given depth is greater than 0 33 thermodynamic analyses of phase relations among vein filling minerals and aqueous solutions at depths near 1867 m and 300 c indicate that the modern reservoir fluid in the salton sea geothermal system is in equilibrium with calcite hematite quartz epidote xps 0 33 anhydrite the predicted fugacity of co2 14 bars for the modern salton sea brine is in close agreement with the calculated value of fco2 for the 1867 m production fluid theoretical phase diagrams in the system cao k2o fe2o3 al2o3 sio2 h2o o2 s2 co2 demonstrate that the mineralogies and mineral parageneses recorded hi epidote bearing veins and the observed variations in al fe3 content of vein epidotes may result from only minor changes in the fugacity of co2 o2 and s2 of the geothermal fluid

tectonic controls on the uplift of the nanga parbat massif pakistan himalayas cenozoic mountain belts like the himalayas contain regions that experienced rapid uplift in comparison with the areas around them1 whether this uplift occurred by buoyant rebound of previously thickened crust2 or during the crustal thickening process itself is uncertain3 4 here we show however that the 7 mm yr 1 recent uplift5 of the nanga parbat massif pakistan himalayas was accomplished during nw directed thrusting located along its western margin this 3 km wide liachar thrust zone operated from amphibolite facies to the present topographic surface and accommodates substantial crustal shortening the adjacent indus river valley itself cut by seismogenic faulting completely transects the massif showing that erosion keeps pace with geologically rapid thrust uplift6

87sr 86sr values in groundwaters of the east bull lake pluton superior province ontario canada abstract the east bull lake pluton is a 2 48 ga old layered mafic intrusion located on the southern margin of the superior province precambrian shield in ontario canada the groundwaters have been studied as part of a detailed geological mapping and geochemical study of the pluton for the canadian nuclear fuel waste management program all groundwater samples are dilute the most concentrated na cl type water contains 3 1 g l total dissolved solids present day87sr 86sr values of the rock samples varies from 0 705 to 0 714 and the groundwaters from 0 711 to 0 720 the ca hco3 recharge waters show the greatest range in values in contrast to the deeper na hco3 and deep na cl waters where a narrow range of 0 712 0 713 is found fracture filling laumontite calcite and gypsum have the same isotopic signature as the deep water the ca hco3 water is the youngest component of the groundwater system and its spread in isotopic values reflects local conditions at the surface the na cl water is considered to be the oldest component and its sr isotopic ratio value indicates equilibration with silicate fracture mineral phases the isotopic data suggest that laumontite calcite and gypsum fracture phases have either crystallized from this water or are currently controlling its isotopic composition by dissolution no age can be assigned to the deep waters except that the na cl component may date from the early paleozoic based on geological arguments or more likely be 104 106 years old based on kinetic studies of rock water interaction and other isotopic data if seawater was one component of the na cl water history there is no record of this in the87sr 86sr ratios

sur l origine de la pyrite et des skarns du gisement en contexte evaporitique de niccioleta toscane italie l etude detaillee du gisement de niccioleta revele les reactions metasomatiques ayant transforme l anhydrite en grenatite la dolomie en pyroxenite et les micaschistes en epidotite et celles qui ont entraine la reduction du sulfate en pyrite les solutions ferriferes ont lessive na k co2 et partiellement ca mg et s l inertie de al et ti et les deplacements de ca si s et sr precisent les modalites des transformations dont on a evalue les bilans pour un volume restant constant le comportement de s est complexe lessive lors de la grenatisation il est apporte lors de la cristallisation de la pyrite sans que le bilan global soit equilibre l origine de ce s est discutee en liaison avec le contexte evaporitique et un systeme geothermique regional tertiaire en l absence de preuve d eventuelles preconcentrations sulfurees syn sedimentaires le gisement parait resulter d une metasomatose de l anhydrite dans un systeme geothermique semblable a celui de larderello mais a alimentation marine

thrust tectonics and the deep structure of the pakistan himalaya the systematic restoration of thrust systems provides a powerful constraint on the deep structure of orogenic belts a balanced cross section through the imbricated upper crust of the indian plate in the footwall to the main mantle thrust of the western himalaya restores to a minimum width of 730 km the implicit shortening being in excess of 470 km this requires the himalaya and southern tibetan region to be underlain by a wedge of indian crust however a full appraisal of gross crustal structure awaits deep seismic control

mineralogy 40ar 39ar dating and apatite fission track dating of rocks along the castle mountain fault alaska abstract the castle mountain fault is a 200 km long right lateral fault that forms the northern boundary of the cook inlet basin and matanuska valley alaska fault gouge and fault rock at six localities contain the clay minerals illite smectite chlorite and interstratified illite smectite at one locality gouge contains deformed illite smectite with very little wall rock chlorite contamination fine 36 24 0 08 ma for fine to coarse sizes respectively argon retention ages obtained from 40ar and 39ar retained in the three size fractions of illite at room temperature during neutron irradiation are 37 36 0 15 42 11 0 14 and 47 20 0 10 respectively apatite fission track ages were measured in arkose at a locality on the fault 60 km west of the gouge locality three samples of arkose were dated one within 10 m of the fault core one 170 m from the fault and one 335 m from the fault the sample nearest to the fault yielded an age of 29 3 2 8 ma but it only had four track lengths at 10 13 m two apatite grains from the intermediate sample yielded a pooled age of 34 3 6 1 ma the distant sample 25 grains counted 101 track lengths yielded an age of 32 0 2 9 ma this sample has a broad distribution of track lengths and a broad distribution of individual grain ages ranging from 14 8 5 1 to 67 8 8 8 ma monte carlo modeling of the apatite age and track length data is consistent with hydrothermal mineralization at 37 39 ma followed by rapid uplift and cooling after 10 ma the 40ar 39ar total gas ages k ar are minimum ages and the argon retention ages are maximum ages the thermal model derived from the fission track data and the argon retention age for the finest illite fraction of 37 ma date a hydrothermal mineralization event on the fault

cyclic deformation and chemical transport in the folson lake fault zone east bull lake anorthosite gabbro complex evidence for seismic pumping abstract the east bull lake anorthosite gabbro a late archean 2472 24ma magmatically layered lopolith at the southern margin of the superior province has experienced regional retrograde metamorphism and is transected by the folson lake fault zone a structure of regional extent the fault zone displays repeated episodes of ductile brittle deformation and vein development it has been extensively metasomatized in domains marked by the sequential development of quartz adularia epidote chlorite laumontite calcite and clay fe oxyhydroxide downhole geochemical profiles through the fault zone show coherent patterns for zr hf zr th ta nb and cr co ni which are interpreted to reflect variations in primary igneous compositions by alteration insensitive elements metasomatism is marked by peaks of sio2 k2o or na2o with al2o3 fe mn and mg and ca plus volatiles corresponding to domains of quartz adularia or albite chlorite and laumontite plus calcite respectively the analogue elements th and u are present at uniformly low levels averaging 1 1 and 0 4 ppm respectively thorium covaries with zr such that variations of abundance reflect primary differences whereas th u ratios scatter between 1 5 to 10 indicating minor remobilization of u strontium has been extensively redistributed within the fault zone and cs covaries with k retrograded areas of the pluton have whole rock 18 values ranging between 4 5 and 7 2 per mil both below and above primary values of 5 7 per mil indicating open system behaviour during regional retrograde metamorphism within the fault zone hydrothermal reservoirs involved in later k metasomatism were at temperatures of 150 250 c where 18 o h2o 2 6 to 1 7 per mil likely representing isotopically and chemically evolved deep pore fluids expelled during crustal activity related to tectonic processes in the nearby grenville province calcite and laumontite developed by the advection through the fault zone of ca rich thermal brines at temperatures around 50 200 c where 18oh2o 15 to 0 per mil such fluids were evolved formation brines with a major component of meteoric h2o expelled in the lower paleozoic the multiple deformation metasomatism events are interpreted in terms of episodic seismic pumping on a fault that was intermittently active over a time scale in excess of 1 ga

regional scale hydrothermal alteration in the central blake river group western abitibi subprovince canada implications for vms prospectivity the late archean blake river group is a thick succession of predominantly mafic volcanic rocks within the southern zone of the abitibi greenstone belt it contains a number of silicic volcanic centers of different size including the large noranda volcanic complex which is host to 17 past producing volcanogenic massive sulfide deposits the noranda complex consists of a 7 to 9 km thick succession of bimodal mafic and felsic volcanic rocks erupted during five major cycles of volcanism massive sulfide formation coincided with a period of intense magmatic activity cycle iii and the formation of the noranda cauldron hydrothermal alteration in these rocks is interpreted to reflect large scale hydrothermal fluid flow associated with rapid crustal extension and rifting of the volcanic complex the alteration includes abundant albite chlorite epidote and quartz silicification which exhibit broad stratigraphic and structural control and correlate with previously mapped whole rock oxygen isotope zonation the mine sequence volcanic rocks are characterized by abundant iron rich chlorite fe fe mg 0 5 hydrothermal amphibole ferroactinolite and coarse grained epidote of clinozoisite composition 10 wt fe2o3 lacking the clinozoisite solid solution alteration in the mine sequence volcanic rocks persists along strike well beyond the limits of the main ore deposits as far as several tens of kilometers and can be readily distinguished from greenschist facies metamorphic assemblages at a regional scale the lack of similar alteration in the pre cauldron sequences is consistent with limited 18o depletion and suggests that the early history of the volcanic complex did not support large scale high temperature fluid flow in these rocks comparisons with a much smaller barren volcanic complex in nearby ben nevis township reveal important differences in the alteration mineralogy between volcanoes of different size with implications for area selection during regional scale mineral exploration the ben nevis complex consists of a 3 to 4 km thick succession of mafic intermediate and felsic volcanic rocks centered on a small subvolcanic intrusion alteration of the volcanic rocks comprises mainly low temperature assemblages of prehnite pumpellyite magnesium rich chlorite fe fe mg 10 wt fe2o3 and calcite actinolite magnetite alteration occurs proximal to the intrusive core of the complex but the limited extent of this alteration indicates only local high temperature fluid circulation adjacent to the intrusion a distal zone of carbonate alteration is located 4 6 km from the center of the volcano although iron bearing carbonates are present locally within this zone the absence of siderite argues against a high temperature origin for this alteration these observations do not offer positive encouragement for the existence of a fossil geothermal system of sufficient size or intensity to have produced a large massive sulfide deposit

the tectonic history of kohistan and its implications for himalayan structure the tectonic history of kohistan northern pakistan involves two collisional events cleavage and folding developed at 90 100 ma along the northern suture between the kohistan island arc and the asian plate at the same time there was major folding and shearing of the lower part of the kohistan arc approximately 100 km south of the suture this deformation was followed by ocean subduction south of the kohistan arc generating the kohistan calc alkaline batholith with subsequent ocean closure during the eocene and obduction of the kohistan arc together with the adjacent part of the asian plate over the indian continental crust the construction of balanced cross sections through the imbricated upper part of the indian continental crust in the footwall to this southern suture indicates a minimum displacement of 470 km requiring the western himalayan hinterland to be underlain by a large wedge of indian middle to lower crust there is some shortening of the overriding kohistan and asian plates by thrusts and shear zones but it is insufficient to satisfy the palaeomagnetic data there must be major crustal shortening involving thrusts in the hindu kush and pamirs north of kohistan the post eocene thrust direction which for most of pakistan is towards 160 is almost perpendicular to that immediately to the east in the himalayan belt generating complex refolded thrust patterns in the hazara syntaxis and large scale folding and rapid uplift with associated brittle faulting and seismic activity adjacent to the nanga parbat syntaxis these different thrust trends indicate that major thrust movement as well as the folds and deformation fabrics cannot always be related to plate movement vectors but are modified by or develop from complex rotations during place collision or from the gravitational spreading of a thickened crust a regional approach is required to recognize and correctly attribute the various components in thrust displacements

length scales for continental deformation in convergent divergent and strike slip environments analytical and approximate solutions for a thin viscous sheet model the deformation of a thin viscous layer that has a moving boundary is investigated for comparison with zones of deformation in the continental lithosphere exact analytical solutions for the case of a newtonian fluid and approximate solutions for the case of fluid with power law rheology show that when the imposed velocity vector is normal to the boundary congressional or extensional regime the deformation field decays away from the boundary with a characteristic length scale 1 3 to 1 10 the wavelength of the imposed boundary velocity distribution for n between 1 and 10 where n is the stress strain exponent in the rheology in contrast when the imposed velocity vector is parallel to the boundary transcurrent regime the length scale of the deformation field is approximately 4 times smaller in each case these length scales decrease approximately as n the difference in length scales arises even in the absence of any buoyancy forces acting on thickened or thinned crust such forces would modify the ratio of length scales but not sufficiently to affect this result

compositional order disorder and stable isotope characteristics of al fe epidote state 2 14 drill hole salton sea geothermal system epidote ca2fe3si3o12 oh ca2al3si3o12 oh is a common hydrothermal mineral in metasediments and veins at depths 900 m in the state 2 14 drill hole of the salton sea geothermal system the mole fraction of ca2fe3si3o12 oh in epidotes xps from this drill hole ranges from 0 11 to 0 42 and complex compositional zoning of octahedral fe3 and al is typical within single grains with increasing depth there is an overall but irregular decrease in the fe3 content of epidotes in metasandstones in most samples vein epidotes are more fe3 rich and exhibit a wider compositional range than metasandstone epidotes from the same depth octahedral fe3 in the m 1 sites in four epidotes evaluated by 57fe mossbauer spectroscopy ranges from 7 5 1 7 to 11 4 1 5 of the total iron the most ordered epidote formed in veins at 2618 m in the biotite zone this epidote has an ordering parameter 1 2xfe3 m 1 of 0 85 0 03 which corresponds to a calculated state of equilibrium order disorder at 390 60 c in close agreement with the probable downhole temperature of 340 c two epidote samples from the chlorite calcite zone 1420 m 265 c 1867 m 300 c are more disordered corresponding to calculated states of equilibrium order disorder of 450 c these data suggest that the analyzed epidotes from the chlorite calcite zone are in a metastable state of substitutional order disorder the measured value of depidote from 1420 m is 96 which is 5 6 lighter than epidotes from 1867 m depidote 90 2227 m depidote 91 and 2618 m depidote 90 when compared to the reservoir fluid from the december 1985 flow test the derived fractionation of hydrogen isotopes between epidote and the geothermal brine is 19 at 1867 m and 340 c this value is in accord with published experimental hydrogen isotope fractionations between iron rich epidote and aqueous electrolyte solutions therefore considering the complexity of the salton sea brine the isotopic temperature is similar to the inferred downhole temperature

mineralogical and fluid inclusion features of rock alterations in the seigoshi gold silver mining district western part of the izu peninsula japan abstract propylitic and advanced argillic alterations occur in the seigoshi gold silver mining district in the western part of the izu peninsula japan the propylitic alteration has the following zonal arrangement from the deeper portion to the shallower portion an epidote prehnite k feldspar chlorite zone a wairakite laumontite zone and a stilbite heulandite montmorillonite zone lateral and vertical zoning is conspicuous in the advanced argillic alteration the inner zone is silica rich and this grades laterally and vertically through alunite to clay rich zones fluid inclusions from the epidote prehnite k feldspar chlorite zone are liquid dominated and filling temperatures of this zone are in the range of 225 285 c filling temperatures for the zeolite zone are variable being in the range of 240 380 c this wide range suggests that boiling of the fluids was responsible for the zeolite zone filling temperatures of the advanced argillic alteration range widely from 210 to 430 c this wide range and the coexistence of liquid and vapor dominated fluid inclusions in a given sample suggest that liquid vapor separation simultaneously occurred during the advanced argillic alteration process it is deduced that the ranges of gaseous fugacity are quite different for each type of alteration for instance f s 2 and f o 2 of the advanced argillic alteration are estimated to be higher than those of the propylitic alteration based on the alteration mineral assemblage chemical composition and mode of occurrence of alteration minerals fluid inclusions estimated ranges of gaseous fugacities and comparison of these features with those of active geothermal systems it is concluded that the propylitic alteration minerals were probably precipitated due to the loss of gases such as co 2 and that the formation of advanced argillic alteration was caused by subsurface mixing of volcanic gas and or condensed hot water with groundwater these coexisting propylitic and advanced argillic alterations are commonly found in the other au ag mining districts in japan

chemographic and thermodynamic analysis of the paragenesis of the major phases in the vicinity of the 6120 foot 1866 m flow zone california state well 2 14 the major phases found in the vicinity of the 1866m flow zone are k feldspar epidote pyrite hematite and chlorite these are found to exist in primarily four two phase assemblages the dominant being k feldspar pyrite epidote pyrite epidote hematite and chlorite pyrite complete reaction relations among these isobaric isothermal divariant phase assemblages oriented in log fo2 ph space are compatible with stable growth at 300 c sensitivity of reaction relations to total sulfur temperature pressure and thermodynamic values is investigated the aqueous fluid sampled at 1866 m is out of equilibrium with the more reducing phase assemblages lying stratigraphically above and below the flow zone as well as pyrite bearing assemblages in the flow zone and shows aspects of mixing with other hotter flow zones high concentrations of co2 may indicate contribution to the fluid of co2 from hotter portions of the system low total sulfur and high total iron are due to possible gas loss during down hole sampling and reaction of the fluid with well casing and lost circulation materials

crustal structure of the rhenish massif results of deep seismic reflection lines dekorp 2 north and 2 north q the reflection seismic line dekorp 2 n reveals an almost complete cross section through the rhenohercynian zone the most external part of the variscan orogen in europe

geology of the northern part of the nanga parbat massif northern pakistan and its implications for himalayan tectonics the northern outcrop termination of indian continental crust lies at the nanga parbat massif from where this contribution presents new field data the tectonic contact with the structurally overlying kohistan island arc is concordant and ductile is associated with interleaving of nanga parbat and kohistan lithologies and may be correlated with the main mantle thrust found elsewhere in the nw himalayas this ductile shear zone is locally overprinted by cataclastic faults associated with exhumation of the massif but overall the northern outcrop termination of the massif is controlled by erosion through a gently northward plunging antiformal structure this folds both the main mantle thrust and the underlying concordant 9layered unit9 of the nanga parbat basement thus there is no indication that the massif acted as a promontory to the indian continent during collision nor that it is a structure entirely bound by neotectonic faults ductile shear fabrics associated with the 9main mantle thrust9 are cross cut by leucogranite sheets and pegmatites these may represent the stockwork to a significant crustal melt granite body described here in the northern massif this jutial granite shows many geochemical characteristics in common with similar bodies in the high himalayas which are consistent with anatexis of the buried indian continental basement rocks however the granite is enriched in heat producing elements particularly th 22 ppm and shows extremely high 87 sr 86 sr ratios 0 88 the high concentrations of radiogenic sr are also an attribute of a suite of hitherto enigmatic leucogranitic pegmatites that laces the nanga parbat massif suggesting that these may represent a stockwork to a largely buried body of which the jutial granite is a small exposure the enrichment in heat producing elements within the granite may reflect similarly high heat production in the source indian continental crust requiring in turn a fundamental re examination of the thermal evolution of this crust during himalayan metamorphism and exhumation

metamorphism of an obducted island arc example of the kohistan sequence pakistan in the himalayan collided range in northern pakistan the extraordinary 40 km thick kohistan sequence of metamorphosed mafic ultramafic and calc alkaline layered plutonic and volcanic mainly andesitic to rhyodacitic rocks has been recently reinterpreted as the only complete vertical section of an intra oceanic island arc presently exposed anywhere in the world plate scale models have been suggested to explain the origin and the tectonic evolution of this arc in the himalayan collision range despite some noticeable differences in the models there is general agreement that the kohistan sequence represents the crust of an arc obducted onto the northern edge of the indian plate before the oligocene collision of india against asia new data on the tectonometamorphic evolution of the kohistan sequence have led to the conclusion that a first major d 1 event developed with increasing metamorphic grades oriented downward the kohistan pile but also toward ensandwiched basic ultrabasic granulitic rocks rare geochronological data and petrological evidence indicate that the latter granulites pyriclasites and various plagiopyrigarnites pyrigarnites metatroctolites metawebsterites metadunites etc were parts of enormous lower to middle cretaceous layered calc alkaline plutons emplaced during the arc building stages as the d 1 metamorphic event is correlated with the upper cretaceous obduction process of the kohistan onto india it is proposed that the d 1 thermal structure was strongly controlled by remnant magmatic heat source s within the obducted arc this interpretation fits nicely with recent theoretical thermal models since the obduction of the arc was probably shortly after 10 20 ma the emplacement of the former plutonic arc rocks a blueschist tectonic melange underlying the obducted arc was possibly synchronous to the obduction and not clearly linked to the older subductive process the oligocene collision of india against asia was associated with a barrovian overprinting metamorphism in the kohistan arc during this second event the dynamo thermal structure was much more classical and not controlled by the occurrence of the cretaceous metaplutonic rocks a tentative model of the thermal structures during the major events which affected the kohistan arc is proposed

corundum cr muscovite rocks at o briens zimbabwe the conjunction of hydrothermal desilicification and lil element enrichment geochemical and isotopic evidence monomineralic domains of chlorite corundum and cr muscovite coexist over a kilometer scale within ultramafic schists of the harare greenstone belt 2 73 ga this exotic lithological association includes the conjunction of some of the most aluminous al2o3 88 wt and potassic k2o 10 wt rocks known the paragenetic sequence developed from chlorite corundum corundum diaspore cr muscovite variably overprinted both the corundum and chloritite domains terminal stages were marked by sporadic production of andalusite quartz and finally margarite