the origin and age of the metamorphic sole from the rogozna mts western vardar belt new evidence for the one ocean model for the balkan ophiolites abstract this study brings new geochronological and petrochemical data from the metamorphic sole beneath the rogozna mts western vardar ophiolite belt the rogozna metamorphic sole is located at the base of a serpentinite nappe and consists of amphibolites and talc chlorite schists the rogozna amphibolites are medium to fine grained rocks with nematoblastic texture and pronounced foliation they consist of green amphibole 70 vol with variable silica contents 6 4 to 7 8 si apfu as well as mg molmg mg fe tot 0 53 to 0 77 and variably albitized plagioclase 30 vol ab 24 ab 98 amphibolites are overprinted by a retrograde assemblage containing actinolite epidote clinoclore sericite chlorite and magnetite the amphibolites formed due to metamorphism of two basaltic suites subalkaline tholeiitic and alkaline subalkaline tholeiitic amphibolites possess low zr nb y th hf tio 2 and p 2 o 5 values and a lree depleted pattern typical for the n morb normal mid ocean ridge basalt to bab back arc basalt origin alkaline amphibolites show elevated concentrations of zr nb y th hf tio 2 and p 2 o 5 with a lree enriched pattern typically displayed by oib ocean island basalt amphibolites were crystallized during intra oceanic thrusting at temperatures between 685 c and 765 c and at a depth of 12 17 km 40 ar 39 ar cooling ages of amphibole ranging from 165 to 170 ma slightly postdate the sole formation talc chlorite schists are related to retrograde greenschist facies metamorphism they consist of fe rich talc and cr rich chlorite peninite diabantite pseudomorphs after amphibole and morb type cr al spinel surrounded by al and mg poor ferrit chromite the occurrence of ferrit chromite is related to earlier amphibolite facies metamorphism chlorite pseudomorphs after amphibole were formed at 300 410 c this study suggests that there is no essential difference in the emplacement age of the dinaric and west vardar ophiolite belts supporting the interpretation involving a single mesozoic ocean in the balkan sector

palinspastic reconstruction versus cross section balancing how complete is the central taurides fold thrust belt turkey in many fold thrust belts cross section derived shortening estimates are significantly lower than predicted based on plate convergence this has led to controversial hypotheses that shortening may be largely underestimated due to wholesale underthrusting convergence without shortening below far traveled continent or ocean derived nappes the late cretaceous eocene taurides fold thrust belt southern turkey may contain a highly incomplete shortening record of convergence likely caused by wholesale underthrusting to estimate this underthrusting we calculate convergence across the belt using a map view palinspastic reconstruction that takes into account major rotations of tectonic units during their accretion we use paleomagnetic and fault kinematic analysis timing of accretion and africa eurasia convergence to constrain our reconstruction our paleomagnetic results confirm an 40 clockwise vertical axis rotation of the geyikdagi nappe that forms the core of the belt which we interpret is accommodated by a lateral gradient in underthrusting on faults structurally above and below the geyikdagi nappe we reconstruct 400 450 km of convergence across the taurides during their accretion we compare this predicted convergence to shortening calculated from balanced cross sections in which we reconstruct a minimum of 154 km shortening 57 km within far traveled nappes 70 km thrusting of far traveled nappes over the geyikdagi nappe and 27 km shortening within the geyikdagi nappe shortening in the taurides created a significant nappe stack but the majority of convergence was accommodated by wholesale underthrusting with barely a trace at the surface including 160 km of convergence by rotation of the belt and 90 130 km related to missing africa eurasia convergence

neoproterozoic adakitic plutons in the northern margin of the yangtze block china partial melting of a thickened lower crust and implications for secular crustal evolution abstract numerous neoproterozoic felsic and mafic ultramafic intrusions occur in the hannan region at the northern margin of the yangtze block among these the wudumen and erliba plutons consist of granodiorites and have shrimp zircon u pb ages of 735 ma the rocks have high k 2 o 0 8 3 6 wt and na 2 o 4 4 6 4 wt and low mgo 0 4 1 7 wt they also have high sr y 32 209 and la yb n ratios 4 4 38 6 their e nd values range from 0 41 to 0 92 and zircon initial 176 hf 177 hf ratios from 0 282353 to 0 282581 these geochemical features are similar to those of adakitic rocks produced by partial melting of a thickened lower crust our new analytical results combined with the occurrence of voluminous arc related mafic ultramafic intrusions emplaced before 740 ma lead us to propose that the crustal evolution in the northern margin of the yangtze block during neoproterozoic involved 1 rapid crustal growth and thickening by underplating of mafic magmas from the mantle which was modified by materials coming from the subducting oceanic slab from 1 0 to 0 74 ga and 2 partial melting of the thickened lower crust due to a thermal anomaly induced by upwelling of asthenosphere through an oceanic slab window producing the 735 ma adakitic wudumen and erliba plutons our model suggests that the crustal thickness was more than 50 km at the northern margin of the yangtze block at 735 ma and rule out the possibility of a mantle plume impact causing the 735 ma magmatism in the region

paleozoic mesozoic tectono sedimentary evolution and magmatism of the egersund basin area norwegian central north sea abstract this study focuses on the tectonic evolution of the greater egersund basin in the norwegian central north sea with special emphasis on late paleozoic extensional tectonics following caledonian collapse and the variscan orogeny and the impact of the basement structural grain on this evolution the caledonian collapse likely resulted in development rejuvenation of the deepest e w trending structures depocenters by late devonian time thus a late devonian early carboniferous age can be assigned to the initial extension which was associated with the development of an e w striking basin system to be overprinted by n s extensional structures of similar age a phase of regional magmatism at the carboniferous permian transition 300 ma may be associated with a large igneous province centred on the skagerrak area faulting during late carboniferous early permian was minor within the study area as reflected by uniform sedimentary thicknesses of the uppermost carboniferous and lower permian sequences major normal faults mainly trending n s were active during a late permian early triassic rift phase affecting large parts of the central and northern north sea area a later phase of extension was initiated in late middle jurassic time and the egersund basin proper formed during the late jurassic early cretaceous the depocenters that developed during this phase was influenced by the deep late paleozoic sub salt structural grain including strike slip movements along the sorgenfrei tornquist zone later events include mild inversion along the northern flank of the egersund basin possibly as a late cretaceous response to far field alpine compression and cenozoic regional tilting

orogenic gold common or evolving fluid and metal sources through time abstract orogenic gold deposits of all ages from paleoarchean to tertiary show consistency in chemical composition they are the products of aqueous carbonic fluids with typically 5 20 mol co 2 although unmixing during extreme pressure fluctuation can lead to entrapment of much more co 2 rich fluid inclusions in some cases ore fluids are typically characterized by significant concentrations of ch 4 and or n 2 common estimates of 0 01 0 36 mol h 2 s a near neutral ph of 5 5 and salinities of 3 7 wt nacl equiv with na k ca mg this fluid composition consistency favors an ore fluid produced from a single source area and rules out mixing of fluids from multiple sources as significant in orogenic gold formation nevertheless there are broad ranges in more robust fluid inclusion trapping temperatures and pressures between deposits that support a model where this specific fluid may deposit ore over a broad window of upper to middle crustal depths much of the reported isotopic and noble gas data is inconsistent between deposits leading to the common equivocal interpretations from studies that have attempted to define fluid and metal source areas for various orogenic gold provinces fluid stable isotope values are commonly characterized by the following ranges 1 18 o for precambrian ores of 6 to 11 and for phanerozoic ores of 7 to 13 2 d and 34 s values that are extremely variable 3 13 c values that range from 11 to 2 and 4 15 n of 10 to 24 for the neoarchean 6 5 to 12 for the paleoproterozoic and 1 5 to 10 for the phanerozoic secular variations in large scale earth processes appear to best explain some of the broad ranges in the o s and n data fluid rock interaction particularly in ore trap areas may cause important local shifts in the o s and c ratios the extreme variations in d mainly reflect measurements of hydrogen isotopes by bulk extraction of waters from numerous fluid inclusion generations many which are not related to ore formation radiogenic isotopes such as those of pb sr nd sm and os measured on hydrothermal minerals are even more difficult to interpret for defining metal source particularly as the low salinity ore fluids transport limited amounts of these elements and significant amounts of these may be locally added to the minerals during alteration reactions at the sites of gold deposition noble gas and halogen data are equally equivocal fluid exsolution from granitoids emplaced into the upper and middle crust metamorphism of the crust or fluids entering trans crustal fault zones from below the crust all remain as permissive scenarios associated with orogenic gold formation as the abundant geochemical data are equivocal however geological and geochronological data weigh heavily against a magmatic hydrothermal model in the upper to middle crust there is no universal temporal association between orogenic gold and magmatism and where there is an overlap in age there is no specific type of magmatism consistently associated with gold formation nor element zonation around any specific pluton a crustal metamorphic model for fluid and metal sources is very consistent with geological geochronological and geochemical data although metamorphism on a regional scale that releases these components into major fault zones can be associated with many processes along active continental margins these can include crustal thickening and radiogenic heating slab rollback and heating during crustal extension or subduction of a spreading ridge heating the base of an accretionary prism in rare examples where phanerozoic orogenic gold deposits are hosted in precambrian high grade metamorphic terranes fluids and metals must however enter a transcrustal fault system from a sub crustal source this could either be a devolatilized subducted relatively flat perhaps stalled slab and its overlying sediment or the corner of the fertilized mantle wedge that releases a fluid during a thermal event

salt influenced normal fault growth and forced folding the stavanger fault system north sea abstract displacement ratio d r is the ratio between salt thickness t v and sub salt normal fault displacement d d r t v d and it is typically used to predict the degree of geometric and kinematic linkage between sub and supra salt fault populations and the overall structural style in salt influenced extensional settings however we currently lack natural examples of how d r and the underlying geological controls vary and how these may control the three dimensional geometry and evolution of salt influenced normal fault systems furthermore it is currently unknown if kinematic coherence in salt influenced extensional settings can be maintained over relatively long length scales 10 1 10 3 m and for relatively long timeframes and how this may impact the growth and geometry of large throw 500 m salt influenced normal fault systems in this paper we use a 3600 km 2 high quality 3d seismic reflection dataset and borehole data from the stavanger fault system sfs egersund basin eastern north sea basin to investigate i how pre rift salt thickness t v and sub salt fault throw t control the structural style and evolution of a basin bounding salt influenced normal fault system and ii the role salt plays in maintaining kinematic coherence in normal fault systems we demonstrate that i pre rift salt distribution t v specifically its presence in the proto footwall i e when t v 0 is the primary control on partitioning of faulting and forced folding along the fault system and the style of linkage i e hard or soft linkage between sub and supra salt fault populations and ii sub and supra salt fault populations represent brittle elements of a single geometrically and kinematically coherent structure the geometry and evolution of which is related to the ductile translation of strain on a scale up to 8 km and duration c 65 myr that believe is significantly greater and longer than previously documented

gold in the oceans through time during sedimentation and diagenesis of carbonaceous shales in marine continental margin settings au is adsorbed from seawater and organic matter and becomes incorporated into sedimentary pyrite la icpms analysis of over 4000 sedimentary pyrite grains in 308 samples from 33 locations around the world grouped over 123 determined ages has enabled us to track in a first order sense the au content of the ocean over the last 3 5 billion years gold was enriched in the meso and neoarchean oceans several times above present values then dropped by an order of magnitude from the first great oxidation event goe1 through the paleoproterozoic to reach a minimum value around 1600 ma gold content of the oceans then rose with perturbations through the meso and neoproterozoic showing a steady rise at the end of the proterozoic 800 to 520 ma which most likely represents the effects of the second great oxidation event goe2 gold in the oceans was at a maximum at 520 ma when oxygen in the oceans rose to match current maximum values in the archean and proterozoic the au content of seawater correlates with the time distribution of high mg greenstone belts black shales and banded iron formations suggesting that increases in atmospheric oxygen and marine bio productivity combined with the higher background of au in komatiitic and mg rich basalts were the first order causes of the pattern of au enrichment in seawater we suggest the lack of major au deposits from 1800 to 800 ma is explained by the low levels of au in the oceans during this period

tectonics and magmatism in turkey and the surrounding area this volume contains 23 papers from a range of international contributors describing recent research into the tectonics and magmatism of turkey and its surroundings this region is sited at the collision zone between eurasia and afro arabia and as such provides an extraordinarily complete and well exposed record of the staged tectonic evolution of this sector of the alpine himalayan orogen the geological history of this area involves separation of continental fragments from the margin of gondwana their migration across the tethyan oceans the subsequent closure of these oceans and finally the development of the neotectonic regime which continues to evolve to the present day such a comprehensive record is relevant to the understanding of collisional zones worldwide the volume is divided into five sections tethyan evolution neotethyan ophiolites post tethyan basin evolution neotectonics and igneous activity the first two sections deal with tethyan oceans whose growth and subsequent closure dominated the geodynamic framework in the mesozoic and cenozoic the subsequent sections deal with more recent geological developments from the balkan peninsula in the west to the transcaucasus in the east that followed consumption of the tethyan oceans there is a broad mix of papers throughout the volume wide ranging review papers on ocean development and extensional tectonics are followed by detailed descriptions of petrology and geochemistry and geographically focused studies on basin evolution specific aspects of extensional and strike slip tectonics and discussions of the relationship of magmatic activity to the tectonic development of the area tectonics and magmatism in turkey and the surrounding area presents up to date results and ideas from a large number of international contributors on a wide range of current research activity in this region it is essential reading for all geoscientists with an interest in both academic and applied aspects of eastern mediterranean geology

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

sequence stratigraphy of carbonate evaporite basins models and application to the upper permian zechstein of northeast england and adjoining north sea the successions of carbonate evaporite basins which are periodically cut off from the world ocean are considered in terms of their sequence stratigraphy two basin types are distinguished those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation it is argued that following relative sea level falls sequences begin with the evaporites precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin centre halite fills in the second the evaporites pass up into carbonate sediments which are mainly deposited on shallow water platforms around the basin during transgressive and highstand systems tracts the concepts and models developed are applied to the zechstein upper permian strata of northeast england and adjoining north sea seven sequences are proposed with some containing thin parasequences the sequence approach to carbonate evaporite basins which considers both basin margin and basin centre facies gives a more encompassing perspective of sedimentation than the traditional cycle concept with its emphasis on the basin centre

metamorphic and structural setting of archaean amphibolitehosted gold deposits near southern cross southern cross province yilgarn block western australia abstract the southern cross archaean greenstone belt comprises dominantly low to mid amphibolite facies high strain domains which show evidence of a complex deformational and metamorphic history aeromagnetic field and petrographic data suggest that this complex structural metamorphic history was related to a single progressive deformation event which was broadly synchronous with granitoid emplacement between 2 68 and 2 62 ga lode gold deposits at corinthia hopes hill fraser s and polaris south occur in sequence from north to south along the fraser s corinthia shear zone in the southern cross greenstone belt corinthia and hopes hill are situated along a sheared granitoid greenstone contact whereas fraser s and polaris south occur within the greenstones about 200 m west of the contact gold mineralisation along the fraser s corinthia shear zone is associated predominantly with variably deformed quartz pyrrhotite pyrite plagioclase and or pyroxene calcite quartz plagioclase apatite veins with zoned alteration haloes of quartz plagioclase pyroxene calcite apatite and amphibole biotite chlorite there are accessory amounts of scheelite chalcopyrite arsenopyrite and galena with the fe sulphides bismuth and gold a variety of evidence including structural timing p t conditions deduced from critical metamorphic 550 c 2 5 3 7 kbars and metasomatic alteration assemblages 520 c 3 4 kbars the high thermodynamic variance of the metasomatic mineral assemblages and the zoning of individual alteration minerals indicates that gold related wallrock alteration occurred during or immediately after peak metamorphism there is some evidence for a sympathetic decline in metamorphic grade and the temperature of gold related alteration from south polaris south to north corinthia along the mineralised shear zone the shear zone acted as a major conduit for ore fluids at a depth of about 12 14 km 3 3 5 kbars lithostatic pressure in the crust gold mineralisation along the shear zone is related to large and small scale extensional crenulation cleavages the gold deposits might thus represent a relatively deep section of the crustal continuum of lode gold deposits proposed for the yilgarn block

precise 40ar 39ar ages from the metamorphic sole of the mersin ophiolite southern turkey abstract the mersin ophiolite is located on the southern flank of the e w trending central tauride belt in turkey it is one of the late cretaceous neotethyan oceanic lithospheric remnants the mersin ophiolite formed in a suprasubduction zone tectonic setting in southern turkey at the beginning of the late cretaceous the mersin ophiolite is one of the best examples in turkey in order to study reconstruction of ophiolite emplacement along the alpine himalayan orogenic belt 40ar 39ar incremental heating measurements were performed on seven obduction related subophiolitic metamorphic rocks hornblende separates yielded isochron ages ranging from 96 0 0 7 ma to 91 6 0 3 ma all errors 1 five of the seven hornblende age determinations are indistinguishable at the 95 confidence level and have a weighted mean age of 92 6 0 2 2 ma we interpret these ages as the date of cooling below 500 c intraoceanic thrusting occurred 4 ma soon after formation of oceanic crust the sole was crosscut by microgabbro diabase dikes less than 3 m y later the final obduction onto the tauride platform occurred during the late cretaceous early paleocene our new high precision ages constrain intraoceanic thrusting for a single ophiolite mersin in the tauride belt

formation of gold deposits a metamorphic devolatilization model a metamorphic devolatilization model can explain the enrichment segregation timing distribution and character of many goldfields such as those found in archean greenstone belts slate belts and other gold only provinces in this genetic model hydrated and carbonated greenschist facies rocks particularly metabasic rocks are devolatilized primarily across the greenschist amphibolite facies boundary in an orogenic setting devolatilization operates on the scale of individual mineral grains extracting not just h2o and co2 but also s and in turn au elevated gold in solution is achieved by complexing with reduced s and by h2co3 weak acid buffering near the optimal fluid ph for gold solubility the buffering is more important than being at the point of maximum gold solubility low salinity ensures low base metal concentrations in the auriferous metamorphic fluid migration of this fluid upwards is via shear zones and or into hydraulic fracture zones in rocks of low tensile strength the geometry of the shear zones dictates the kilometre scale fluid migration paths and the degree of fluid focusing into small enough volumes to form economic accumulations of gold deposition of gold from solution necessitates breakdown of the gold thiosulphide complex and is especially facilitated by fluid reduction in contact with reduced carbon bearing host rocks and or by sulphidation of wallrocks to generate iron bearing sulphide and precipitated gold as such black slate carbon seams banded iron formation tholeiitic basalt magnetite bearing diorite and differentiated tholeiitic dolerite sills are some of the important hosts to major goldfields gold deposition is accompanied by carbonation sulphidation and muscovite biotite alteration where the host rock is of suitable bulk composition the correlation of major gold deposits with rock type even when the gold is primarily in veins argues for rock dominated depositional systems not fluid dominated ones as a consequence a general role in gold deposition for fluid mixing temperature decrease and or fluid pressure decrease and boiling is unlikely although such effects may be involved locally several geological features that are recorded at gold only deposits today reflect subsequent modifications superimposed upon the products of this generic metamorphic devolatilization process overprinting by higher grade metamorphism and deformation and or palaeo weathering may provide many of the most obvious features of goldfields including their mineralogy geochemistry geometry small scale timing features geophysical response and even mesoscopic gold distribution

k ar dating of some infra ophiolitic metamorphic soles from the eastern mediterranean new evidence for oceanic thrustings before obduction abstract k ar dating on separated minerals from the infra peridotitic metamorphic soles outcropping beneath various eastern mediterranean ophiolite complexes pindos nappe in greece lycian antalya beysehir hoyran mersin and pozanti karsanti nappes in the taurides belt turkey baer bassit nappe in syria shows that the main metamorphic recrystallization of those rocks occurred 25 30 m y prior to the tectonic emplacement of the ophiolite complexes onto a continental platform these data support the hypothesis of an early slicing of the oceanic crust before its obduction advocated recently by several authors

a holistic model for the origin of orogenic gold deposits and its implications for exploration the term orogenic gold deposits has been widely accepted but there has been continuing debate on their genesis early syn sedimentary or syn volcanic models and hydrothermal meteoric fluid models are now invalid magmatic hydrothermal models fail because of the lack of consistent spatially associated granitic intrusions and inconsistent temporal relationships the most plausible models involve metamorphic fluids but the source of these fluids is equivocal intra basin sources within deeper segments of the hosting supracrustal successions the underlying continental crust subducted oceanic lithosphere with its overlying sediment wedge and metasomatized lithosphere are all potential sources several features of precambrian orogenic gold deposits are inconsistent with derivation from a continental metamorphic fluid source these include the presence of hypozonal deposits in amphibolite facies domains their anomalous multiple sulfur isotopic compositions and problems of derivation of gold related elements from devolatilization of dominant basalts in the sequences the phanerozoic deposits are largely described as hosted in greenschist facies domains consistent with supracrustal devolatilization models a notable exception is the jiaodong gold deposits of china where ca 120 ma gold deposits are hosted in precambrian crust that was metamorphosed over 2000 million years prior to gold mineralization other deposits in china are comparable to those in the massif central and elsewhere in france in that they are hosted in amphibolite facies domains or clearly post date regional metamorphic events imposed on hosting supracrustal sequences if all orogenic gold deposits have a common genesis the only realistic source of fluid and gold is from devolatilization of a subducted oceanic slab with its overlying gold bearing sulfide rich sedimentary package or the associated metasomatized mantle wedge with co2 released during decarbonation and s and ore related elements released from transformation of pyrite to pyrrhotite at about 500 c although this model satisfies all geological geochronological isotopic and geochemical constraints and is consistent with limited computer based modeling of fluid release from subduction zones the precise mechanisms of fluid flux are model driven and remain uncertain from an exploration viewpoint the model re emphasizes the ubiquitous occurrence of orogenic gold deposits in subduction related orogenic belts and importance of continental scale lithosphere tapping fault and shear zones to focus large volumes of auriferous fluid it confirms the importance of the consistent spacing between world class deposits broadly equivalent to the depth of the moho as derived from empirical observations

structural style and early stage growth of inversion structures 3d seismic insights from the egersund basin offshore norway abstract high quality three dimensional 3d seismic reflection and borehole data from the egersund basin offshore norway are used to characterise the structural style and determine the timing of growth of inversion related anticlines adjacent to a segmented normal fault system two thick skinned normal faults which offset permian clastics and evaporites delineate the north eastern margin of the basin these faults strike nnw sse have up to 1900 m of displacement and are separated by an ese dipping c 10 km wide relay ramp both of these faults display exclusively normal separation at all structural levels and tip out upwards into the upper part of the lower cretaceous succession at relatively shallow structural levels in the hangingwalls of these faults a series of open low amplitude fault parallel anticlines are developed these anticlines which are asymmetric and verge towards the footwalls of the adjacent faults are interpreted to have formed in response to mild inversion of the egersund basin the amplitude of and apparent shortening associated with the anticlines vary along strike and these variations mimic the along strike variations in throw observed on the adjacent fault segments we suggest that this relationship can be explained by along strike changes in the propensity of the normal faults to reactivate during shortening wider damage zones and lower angles of internal friction coupled with higher pore fluids pressures at the fault centre mean that reactivation is easier at this location than at the fault tips or in the undeformed country rock seismic stratigraphic analysis of growth strata indicate that the folds initiated in the latest turonian to earliest coniacian c 88 6 ma and santonian c 82 6 ma the control on this c 6 myr diachroneity in the initiation of fold growth is not clear but it may be related to strain partitioning during the early stages of shortening anticline growth ceased in the maastrichtian and the inversion event is therefore interpreted to have lasted at least c 20 myr this study indicates that 3d seismic reflection data is a key tool to investigate the role that normal fault segmentation can play in controlling the structural style and timing of inversion in sedimentary basins furthermore our results highlight the impact that this structural style variability may have on the development of structural and stratigraphic hydrocarbon traps in weakly inverted rifts

progressive metamorphism of mafic rocks from greenschist to granulite facies in the dharwar craton of south india in the archean dharwar craton of southern india n s trending belts of metabasic rocks are exposed which underwent regional metamorphism at about 2 5 ga ago the progressive changes in the assemblages and mineral chemistry of metabasites was studied in a n s traverse covering the chitradurga and nagaman gala belts the sargur area and the nilgiri hills towards the south with increasing metamorphic grade greenschists chl act ab ep pm carb qtz give way to amphibolites hbl plag pm qtz gar cumm and mafic granulites pyx plag gar pm hbl qtz the amphibole composition changes from actinolite in the greenschist zone to tschermakitic hornblende in the amphibolite zone and pargasitic hastingsitic hornblende in the granulite zone the ti content of the amphiboles systematically increases in this direction the plagioclase composition changes from albite in the greenschist zone to oligoclase andesine in the amphibolite zone and andesine labradorite in the granulite zone almandin

supra salt normal fault growth during the rise and fall of a diapir perspectives from 3d seismic reflection data norwegian north sea abstract normal faulting and the deep subsurface flow of salt are key processes controlling the structural development of many salt bearing sedimentary basins however our detailed understanding of the spatial and temporal relationship between normal faulting and salt movement is poor due to a lack of natural examples constraining their geometric and kinematic relationship in three dimensions to improve our understanding of these processes we here use 3d seismic reflection and borehole data from the egersund basin offshore norway to determine the structure and growth of a normal fault array formed during the birth growth and decay of an array of salt structures we show that the fault array and salt structures developed in response to i late triassic to middle jurassic extension which involved thick skinned sub salt and thin skinned supra salt faulting with the latter driving reactive diapirism ii early cretaceous extensional collapse of the walls and iii jurassic to neogene active and passive diapirism which was at least partly coeval with and occurred along strike from areas of reactive diapirism and wall collapse our study supports physical model predictions showcasing a three dimensional example of how protracted multiphase salt diapirism can influence the structure and growth of normal fault arrays

subduction complex of pre jurassic age northern anatolia turkey in northern anatolia a zone of pre liassic orogenic deformation is located mainly between the internal anatolian massifs and the north anatolian fault this belt consists of metamorphic rocks in blueschist greenschist and amphibolite facies and an ophiolitic dynamometa morphic melange the metamorphic rocks represent deformed and metamorphosed oceanic crust and upper mantle whereas the melange rocks originated in diverse environments in abyssal plain trench arc trench gap and forearc environments the evolution of these assemblages is interpreted as a product of subduction probably associated with the closure of the tethys subduction related deformation and meta morphism terminated diachronously from pre late triassic in the west to pre late liassic in the east probably as a result of the diachronous closure of the tethys

pervasive exsolution within the calcic amphibole series tem evidence for a miscibility gap between actinolite and hornblende in natural samples

origin and evolution of ore fluid and gold deposition processes at the giant taishang gold deposit jiaodong peninsula eastern china abstract the early cretaceous taishang gold deposit is the largest deposit in the linglong goldfield jiaodong peninsula with a pre mining endowment of 326 t of gold it is hosted in the 165 150 ma linglong biotite granite and controlled by the nee to ne trending potouqing fault near the northern end of the regional zhaoping fault system hydrothermal alteration is well developed in the footwall of the potouqing fault and is characterized by a narrow zone of sericitization followed by a wider zone of silicification and an even wider zone of potassic alteration the main orebodies no i orebody comprise disseminated and stockwork veinlet systems although about 5 of the resources are in larger quartz veins no ii orebody four stages have been identified for both styles of mineralization on the basis of cross cutting relationships and mineralogical and textural characteristics pyrite quartz sericite stage 1 quartz pyrite stage 2 quartz pyrite base metal sulfide stage 3 and quartz carbonate stage 4 gold was mainly deposited in stages 2 and 3 with minor amounts in stage 1 petrographical microthermometric and laser raman spectroscopic studies on fluid inclusion assemblages in quartz and calcite from the four stages reveal three types of primary fluid inclusions type 1 h 2 o rich aqueous carbonic type 2 co 2 rich aqueous carbonic and rare type 3 carbonic inclusions stage 1 quartz primary inclusions are only type 1 inclusions with an estimated composition of 88 h 2 o 10 co 2 4 5 wt nacl equiv and 0 5 ch 4 with trapping at 336 c and 1 7 kbars the gold rich stages 2 and 3 from both orebodies typically contain primary fluid inclusion assemblages with both type 1 and 2 inclusions which show similar phase transition temperatures and were trapped between 246 and 294 c the stage 4 quartz and calcite contain only primary type 1 inclusions which are estimated to have a composition of 93 h 2 o 6 0 co 2 3 6 wt nacl equiv and trace amount of ch 4 and were trapped at temperatures of 236 c the 34 s values of hydrothermal pyrite from the four stages have a narrow range from 4 5 to 8 0 and are within the ranges for whole rock sulfides from the archean jiaodong group and magmatic pyrite from mesozoic granitoid and intermediate basic dikes the 18 o values of hydrothermal quartz range mainly from 10 9 to 12 5 and remain constant for all four stages calculated fluid 18 o values are 1 3 10 0 the d water values calculated from hydrothermal sericite range from 60 to 45 considering the fluid inclusion compositions 18 o and d compositions of ore forming fluids and regional geological events the most likely ultimate potential fluid and metal reservoirs would be the paleo pacific oceanic slab and its overlying sediments which were thrust below the high grade metamorphic rocks of the jiaodong peninsula the initial ore forming fluids were medium high temperature co 2 rich and low salinity h 2 o co 2 nacl ch 4 homogeneous fluids over the duration of the hydrothermal system the fluid remained fairly consistent in p t x although becoming slightly more water rich during final post ore activity fluid immiscibility occurred during stages 2 and 3 ore deposition at pressures that fluctuated strongly from 1700 to 580 bars during hydrofracturing the hs 2 ion was the most probable gold transporting complex at taishang wall rock sulfidation and episodic pressure drops with associated fluid unmixing and other chemical changes were the two main mechanisms of ore deposition

kinematics of the central taurides during neotethys closure and collision the nappes in the sultan mountains turkey in the central taurides the sultan mountains comprise in ascending order the cimendere unit and the aksehir doganhisar cay nappes composed of metasedimentary sequences deposited from cambrian to tertiary the overthrust of the cay nappe on the lutetian celeptas formation representing the uppermost stratigraphic position in the cimendere unit indicates that the latest nappe emplacement occurred during the middle eocene the oligocene and miocene rocks are in post tectonic facies in the west central taurides the kinematic data from these nappes related to closure of the neotethys reveal a top ne shear sense in the northwest part and a top se shear sense in the southeast part of the sultan mountains the sultan mountains are located in the north part of the isparta angle which was tectonically assembled by the lycian hoyran beysehir hadim and antalya allochthons on the bey daglari and anamas akseki autochthons from the latest cretaceous to the late pliocene the previous paleomagnetic data showed that the west and east subsections of the isparta angle were subjected to post eocene 30 40 anticlockwise and clockwise rotations respectively in consideration of these paleomagnetic data the kinematic data measured in the sultan mountains might be restored into approximately e w trending linear fabric associated with a top e shear sense these new kinematic data from the nappes in the sultan mountains disagree with the existing tectonic models that suggest n s nappe translation over the central taurides during the latest cretaceous middle eocene the alternative tectonic model for the antalya nappes in the core of the isparta angle related to east west compression suggests westward and eastward nappe emplacements on the surrounding autochthons however the new kinematic data presented here point consistently to a top e shear sense in all tectonostratigraphic units in the sultan mountains currently located in the north part of the anamas akseki autochthon

the geochemistry of postkinematic mafic dike swarms and subophiolitic metabasites pozanti karsanti ophiolite turkey evidence for ridge subduction doleritic and gabbroic dike swarms cut the pozanti karsanti ophiolite and basal metamorphic sole but do not extend into the underlying melange or platform carbonates dike emplacement therefore postdated formation of the ophiolite and metamorphic sole but predated final obduction onto the tauride anatolide platform the dikes are compositionally similar to island arc basalts and basaltic andesites and were affected by retrograde static hydrothermal metamorphism over temperatures ranging from 900 c to below 450 c geochemical modeling of trace elements including rees show that the dikes are possibly fractionated products of multiple compositionally variable parental magmas the range of parental magmas is interpreted to represent variably mixed melt increments generated through polybaric fractional or continuous melting within a column of rising mantle material melt increments extracted from shallower parts of the melting column at lower pressures are more refractory and apparently pooled less efficiently than melt fractions generated from deeper sources and higher pressures amphibolite and greenschist facies metabasalt from the subophiolitic sole represent metamorphosed alkalic basalt and morb like basalt respectively the pozanti karsanti ophiolite probably constituted part of the fore arc mantle wedge directly above an intra oceanic subduction zone whereas the metamorphic sole represents material progressively transferred and accreted to the base of the ophiolite from the downgoing oceanic plate during subduction since late stage pre obduction dike swarms transect the metamorphic sole a probable subduction plane melt generation must have occurred below the wadati benioff zone and not in the overlying mantle wedge a probable source of parental liquids for the dikes may therefore be a subducting neo tethyan spreading center

fluid assisted granulite metamorphism a continental journey abstract lower crustal granulites which constitute the base of all continents belong to two series high pressure granulites generated by crustal thickening subduction and ultra high temperature granulites associated with crustal extension fluid inclusions and metasomatic features indicate that the latter were metamorphosed in the presence of low water activity fluids high density co2 and brines which have invaded the lower crust at peak metamorphic conditions fluid assisted granulite metamorphism high pressure and ultra high temperature granulites commonly occur along elongated paired belts they were formed from the early proterozoic onwards during a small number of active periods lasting a few hundreds of m y these periods were separated from each other by longer periods of stability each period ended with the formation of a supercontinent whose amalgamation coincided with low to medium pressure ultra high temperature granulite metamorphism immediately before continental break up it is proposed that large quantities of mantle derived co2 stored in the lower crust at the final stage of supercontinent amalgamation are released into the hydro and atmosphere during breakup of the supercontinent fluid assisted granulite metamorphism therefore appears to be an important mechanism for transferring deep mantle fluids towards the earth s surface possible consequences were for example the sudden end of proterozoic glaciations as well as the post cambrian explosion of life

reactivation of intrabasement structures during rifting a case study from offshore southern norway abstract pre existing structures within crystalline basement may exert a significant influence over the evolution of rifts however the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood using borehole constrained 2d and 3d seismic reflection data from offshore southern norway we identify and constrain the three dimensional geometry of a series of enigmatic intrabasement reflections through 1d waveform modelling and 3d mapping of these reflection packages we correlate them to the onshore caledonian thrust belt and devonian shear zones based on the seismic stratigraphic architecture of the post basement succession we identify several phases of reactivation of the intrabasement structures associated with multiple tectonic events reactivation preferentially occurs along relatively thick c 1 km relatively steeply dipping c 30 structures with three main styles of interactions observed between them and overlying faults i faults exploiting intrabasement weaknesses represented by intra shear zone mylonites ii faults that initiate within the hangingwall of the shear zones inheriting their orientation and merging with said structure at depth or iii faults that initiate independently from and cross cut intrabasement structures we demonstrate that large scale discrete shear zones act as a long lived structural template for fault initiation during multiple phases of rifting

origin of an anhydrite sheath encircling a salt diapir and implications for the seismic imaging of steep sided salt structures egersund basin northern north sea the ingress of meteoric fluids into the crests of salt structures typically results in the formation of anhydrite dominated caprock the migration of connate fluids up the margins of salt structures has also been documented although the products related to this are rarely sampled in the deep subsurface we use 3d seismic reflection and borehole data to document the geometry and lithology of a salt diapir seismic data suggest that a weld is developed along the diapir stem although borehole data indicate that the stem consists of an inner c 1500 m thick halite dominated zone and an outer c 250 m thick anhydrite dominated sheath the anhydrite may have formed early in the basin history as a depositional anhydrite or crestal caprock an alternative interpretation is that the anhydrite represents lateral caprock which formed late in the basin history in response to the migration of nacl poor fluid up the margins of the diapir and dissolution of halite the possibility that lateral caprock may form adjacent to salt structures has implications for understanding the patterns and vigour of groundwater flow in sedimentary basins furthermore our study shows the margins of steep sided salt structures may be misidentified by several hundred metres if time migrated seismic reflection data are used

cascadia subducting plate fluids channelled to fore arc mantle corner ets and silica deposition in this study we first summarize the constraints that on the cascadia subduction thrust there is a 70 km gap downdip between the megathrust seismogenic zone and the episodic tremor and slip ets that lies further landward there is not a continuous transition from unstable to conditionally stable sliding seismic rupture occurs mainly offshore for this hot subduction zone ets lies onshore we then suggest what does control the downdip position of ets we conclude that fluids from dehydration of the downgoing plate focused to rise above the fore arc mantle corner are responsible for ets there is a remarkable correspondence between the position of ets and this corner along the whole margin hydrated mineral assemblages in the subducting oceanic crust and uppermost mantle are dehydrated with downdip increasing temperature and seismic tomography data indicate that these fluids have strongly serpentinized the overlying fore arc mantle laboratory data show that such fore arc mantle serpentinite has low permeability and likely blocks vertical expulsion and restricts flow updip within the underlying permeable oceanic crust and subduction shear zone at the fore arc mantle corner these fluids are released upward into the more permeable overlying fore arc crust an indication of this fluid flux comes from low poisson s ratios and vp vs found above the corner that may be explained by a concentration of quartz which has exceptionally low poisson s ratio the rising fluids should be silica saturated and precipitate quartz with decreasing temperature and pressure as they rise above the corner

flow of mantle fluids through the ductile lower crust helium isotope trends heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust minimum 3he 4he ratios in surface fluids from the northern basin and range province western north america increase systematically from low crustal values in the east to high mantle values in the west a regional trend that correlates with the rates of active crustal deformation the highest ratios occur where the extension and shear strain rates are greatest the correspondence of helium isotope ratios and active transtensional deformation indicates a deformation enhanced permeability and that mantle fluids can penetrate the ductile lithosphere even in regions where there is no substantial magmatism superimposed on the regional trend are local high 3he 4he anomalies indicating hidden magmatic activity and or deep fluid production with locally enhanced permeability identifying zones with high resource potential particularly for geothermal energy development

origin of the jiaodong type xinli gold deposit jiaodong peninsula china constraints from fluid inclusion and c d o s sr isotope compositions abstract the xinli gold deposit within the sanshandao cangshang gold belt in the jiaodong gold province is a typical jiaojia type ore deposit with high grade quartz sulfide vein veinlet stockworks that cut mesozoic granodiorite four ore stages are distinguished in the following sequences i quartz k feldspar sericite pyrite ii quartz pyrite iii quartz polymetallic sulfide and iv quartz calcite pyrite fluid inclusions in quartz and calcite in the ores contain c o h fluids dominantly of six types with varied liquid vapor ratio ore fluid in the main ore stage is characterized by medium low temperature low salinity reducing condition and nacl h 2 o co 2 ch 4 in composition the 18 o water smow of quartz in ore stages ii and iii range from 2 82 to 5 34 and the d smow are between 69 6 and 88 3 both suggest that the ore fluid was dominantly magmatic water the 13 c pdb of the calcite are from 6 4 to 2 4 indicating mantle contribution to the ore fluid the pyrite 34 s cdt from four ore stages are basically similar varying from 9 42 to 11 62 which implies significant involvement of crustal materials the initial 87 sr 86 sr ratios in the calcite ranging from 0 710657 to 0 711542 also denote a crustal contribution the fluid composition and systematic h o c s sr isotopic data are explained by a model of slab subduction induced gold mineralization in the model the ore fluid and metals were considered to associate with the dehydration and desulfidation of the subducting paleo pacific slab and the subsequent devolatilization of enriched mantle wedge the h 2 o in the fluid might have been released from the devolatilization of enriched mantle wedge the co 2 could be from mantle wedge or subcontinental lithospheric mantle and the sulfur and strontium would be initially released from the subducted seafloor sediments this process was further supported by the geochemical features of intermediate basic dykes contemporaneous to the gold ore deposits the deposit features and ore forming process of the xinli gold deposit hardly concur those of the orogenic gold deposit and the pluton related gold deposit the study supports the argument of that the gold deposits in the jiaodong belong to a unique gold type related to a complex slab subduction related process the geodynamic engine of the jiaodong type gold deposit is specific i e the slab subduction coupling with the consequent lithospheric thinning and structure adjustment

geochemistry and tectonic significance of metamorphic sole rocks beneath the beysehir hoyran ophiolite sw turkey abstract the beysehir hoyran ophiolite is situated in the western part of the tauride belt sw turkey and crops out at two localities north of the lake beysehir it mainly comprises harzburgitic peridotites that were tectonically emplaced to their present position during the late eocene the ophiolites themselves are tectonically overlain by either slope basin deposits with lava blocks egirler formation or massive triassic limestone blocks deliktas formation high grade sub ophiolitic metamorphic rocks i e epidote amphibolite amphibolite and pyroxene amphibolite together with minor quartzite and calcschist are observed at the base of the ophiolite sequence where they occur as thin tectonic slices with an inverted metamorphic gradient average p t conditions of 630 770 c and c 6 1 5 kbar are calculated for the metamorphism of the amphibolites by conventional geothermobarometry corresponding to a burial depth of 18 20 km both the sub ophiolitic metamorphic rocks and the overlying mantle tectonites were intruded by isolated tholeiitic nb y 0 041 0 108 diabase dikes which do not transect the tectonic contact between the two units geochemical investigations of the amphibolites of the sub ophiolitic rock suite show two different geochemical affinities with the first group being alkaline in character nb y 1 3 86 and the second one being tholeiitic nb y 0 064 0 13 ree patterns trace element plots and tectonomagmatic discrimination diagrams indicate that the most probable protoliths for alkaline amphibolites are within plate type alkali basalts whereas those of the tholeiitic group resemble tholeiitic island arc basalts similarities between the geochemical characteristics of the amphibolites and those of the volcanic rocks of the egirler formation strongly suggest that the latter are the protoliths of the amphibolites

the influence of structural inheritance and multiphase extension on rift development the northern north sea the northern north sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement the geometry and evolution of syn rift depocentres during this multiphase evolution and the mechanisms and extent to which they were influenced by pre existing structural heterogeneities remain elusive particularly at the regional scale using an extensive database of borehole constrained 2d seismic reflection data we examine how the physiography of the northern north sea rift evolved throughout late permian early triassic rp1 and late jurassic early cretaceous rp2 rift phases and assess the influence of basement structures related to the caledonian orogeny and subsequent devonian extension during rp1 the location of major depocentres the stord and east shetland basins was controlled by favorably oriented devonian shear zones rp2 shows a diminished influence from structural heterogeneities activity localises along the viking sogn graben system and the east shetland basin with negligible activity in the stord basin and horda platform the utsira high and the devonian lomre shear zone form the eastern barrier to rift activity during rp2 towards the end of rp2 rift activity migrated northwards as extension related to opening of the proto north atlantic becomes the dominant regional stress as rift activity in the northern north sea decreases through documenting the evolving syn rift depocentres of the northern north sea rift we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics controlling the segmentation of depocentres as well as the locations styles and magnitude of fault activity and reactivation during subsequent events

processes of late cretaceous to late miocene episodic thrust sheet translation in the lycian taurides sw turkey the lycian taurides of sw turkey consist of an allochthonous mesozoic passive margin succession that was episodically detached from its autochthon and translated southeastwards between latest cretaceous to late miocene times a combination of structural analysis sedimentology palaeontology and geochemistry allows subdivision of this orogenic event into 1 latest cretaceous trench passive margin collision causing ophiolite obduction and detachment of the koycegyiz thrust sheet 2 mid late eocene continent continent collision renewing southeastwards thrusting and causing detachment of the teke dere thrust sheet and yavus thrust sheets 3 miocene extensional collapse of the orogen with southeastwards translation of the allochthon coeval with rift basin formation in the hinterland

the beysehir hoyran hadim nappes genesis and emplacement of mesozoic marginal and oceanic units of the northern neotethys in southern turkey the beysehir hoyran hadim nappes crop out over 700 km from nw to se above a regionally autochthonous tauride carbonate platform the beysehir hoyran nappes begin with a thrust sheet c 400 m of mainly redeposited carbonates quartzose sandstones and mudstones of mid late triassic age interpreted as a proximal slope base of slope succession above is a thrust sheet c 1 km of middle upper triassic intermediate acidic extrusive rocks volcaniclastic rocks and minor pelagic carbonates interpreted as a continental rift thin

high pressure metasediments in central turkey constraints on the neotethyan closure history 1 the distribution of oceanic domains and continental blocks in central anatolia remains a challenge in understanding the alpine geodynamic evolution of the tethys realm the consumption of a neotethys oceanic branch at the mesozoic cenozoic boundary welded the central anatolian crystalline complex in central turkey and the anatolide tauride block in western turkey with the northerly eurasian margin whether those two regions constituted a single or two distinct continental masses is still matter of debate high pressure metamorphism has been locally evidenced in the afyon zone which was however defined as a greenschist facies metamorphic zone of the anatolide tauride block since the afyon zone composes a metamorphic equivalent of a continental margin exposed far south of the izmir ankara suture zone this encouraged us to reevaluate its metamorphic evolution in order to better understand the relation between western and central turkey our investigations reveal that the high pressure minerals fe mg carpholite and glaucophane are present in the entire afyon zone which we reconsider as a blueschist facies zone we additionally present a tectonic reconstruction stripping off the postcollisional tectonics it reveals that today s bending of the high pressure belt is consistent with an eocene collision of the anatolide tauride block around the southern edge of the central anatolian crystalline complex we argue that the central anatolian crystalline complex and the anatolide tauride block were two distinct continental masses separated by a neotethyan oceanic stripe the closure of which engendered subduction related metamorphism in the latter and arc volcanism and high grade metamorphism in the former by late cretaceous to early cenozoic

metamorphic sole rocks and their mafic dykes in the eastern tauride belt ophiolites southern turkey implications for oib type magma generation following slab break off the metamorphic sole rocks observed between the pozanti karsanti ophiolite and the melange unit are located on the eastern part of the tauride carbonate platform they consist of ortho amphibolites at the top and metasedimentary lithologies at the base amphibolites from the metamorphic sole rocks are represented by oib morb and iat based on their major trace and ree compositions the isolated dolerite dykes intrude both the metamorphic sole rocks and the ophiolitic unit at different structural levels the dolerite dykes cutting the metamorphic sole rocks are enriched in lile and depleted in hfse enrichment in lile such as th relative to hfse is indicative of the presence of a subduction component flat lying ree patterns of the dolerite dykes also confirm an iat source pyroxenite and albitite dykes also cut the metamorphic sole rocks ree patterns of pyroxenite dykes show prominent lree enrichment similar to that observed in within plate alkaline basalts the alkaline isolated pyroxenite dykes were probably the result of late stage magmatism fed by melts that originated from an oib source shortly before the emplacement of the pozanti karsanti ophiolite onto the tauride carbonate platform a hydrothermal alteration stage is characterized by albitite formation in the joints of the metamorphic sole rocks and by secondary mineralization along the contact zones of dolerite dykes mineral parageneses in the metamorphic sole rocks exhibit amphibolite and greenschist facies assemblages geothermobarometric studies based on a newly recognized mineral assemblage e g kyanite and chemical compositions of minerals in the metamorphic sole rocks indicate that the metamorphic temperature during the metamorphism was 570 580 c and the pressure was around 5 6 kbar

u pb and sm nd geochronology of the kizildag hatay turkey ophiolite implications for the timing and duration of suprasubduction zone type oceanic crust formation in the southern neotethys the kizildag hatay ophiolite in turkey represents remnants of the southern neotethyan ocean and is characterized by a complete ocean lithospheric section it formed in a fore arc setting above a n dipping intraoceanic subduction zone and represents the undeformed more northerly part of the same thrust sheet that also forms the baer bassit ophiolite to the south the ophiolite was emplaced southwards from the southerly neotethyan ocean in maastrichtian time u pb and sm nd dates are used to constrain the crystallization age and duration of magmatic activity of the kizildag ophiolite u pb dating yielded ages of 91 7 1 9 ma for a plagiogranite and 91 6 3 8 ma for a cumulate gabbro the cumulate gabbro also yielded a sm nd isochron age of 95 3 6 9 ma the measured ages suggest that the oceanic crust of the kizildag ophiolite formed in a maximum time period of 6 ma and that the plagiogranite may have formed later than the gabbroic section the u pb zircon ages from the kizildag ophiolite and the cooling age of a metamorphic sole beneath the baer bassit ophiolite are indistinguishable within the analytical uncertainties this indicates the presence of young and hot oceanic lithosphere at the time of intraoceanic subduction thrusting in the southern neotethys the u pb zircon ages from the kizildag the troodos and the semail ophiolites overlap within analytical uncertainties suggesting that these ophiolites are contemporaneous and genetically and tectonically related within the same late cretaceous southern neotethyan ocean

physiography of the ne margin of the permian salt basin new insights from 3d seismic reflection data three dimensional seismic reflection data from the egersund basin offshore norway image geomorphological features that record mid permian footwall degradation of basin bounding fault systems this ancient landscape was subsequently flooded during the pan european late permian transgression of the north permian salt basin and was fossilized beneath zechstein supergroup evaporites we provide the first conclusive evidence for pre zechstein normal faulting in the egersund basin indicating that extensional strain was shared between permian and late jurassic early cretaceous rift events supplementary materials uninterpreted versions of the seismic sections shown in figure 2 are available are available at www geolsoc org uk sup18678

geochemical and petrological aspects of dike intrusions in the lycian ophiolites sw turkey a case study for the dike emplacement along the tauride belt ophiolites lycian ophiolites located in the western taurides are cut at all structural levels by dolerite and gabbro dikes the dolerite dikes from this area are both pristine and metamorphosed the non metamorphosed dikes are observed both in the peridotites and in the metamorphic sole rocks accordingly the non metamorphosed dikes cutting the metamorphic sole were generated after cooling of the metamorphic sole rocks the metamorphosed dolerite dikes are only observed in the peridotites the physical conditions and timing of the metamorphism for the metamorphosed dolerite dikes are similar to those of the metamorphic sole rocks of the lycian ophiolites suggesting that the metamorphosed dolerite dikes were metamorphosed together with the metamorphic sole rocks therefore the dike injections in the western part of the tauride belt ophiolites occurred before and after the generation of the metamorphic sole rocks all metamorphosed and non metamorphosed dikes are considered to have the same origin and all of them are subduction related as inferred from whole rock geochemistry and lead isotopes lead isotope compositions of whole rocks of both dike groups cluster in a narrow field in conventional pb isotope diagrams 206pb 204pb 18 40 18 64 207pb 204pb 15 56 15 58 208pb 204pb 38 23 38 56 indicating a derivation from an isotopically homogeneous source on the 207pb 204pb versus 206pb 204pb diagram isotope compositions of the dikes plot slightly below the orogen curve suggesting contributions from mantle reservoir enriched by subducted oceanic lithosphere such a signature is typical of island arc magmatic rocks and supports the formation of the investigated rocks in a subduction related environment

precise 40ar 39ar ages from the metamorphic sole rocks of the tauride belt ophiolites southern turkey implications for the rapid cooling history the tauride belt ophiolites in southern turkey are located on both sides of the e w trending mesozoic tauride carbonate platform they comprise the lycian antalya beysehir mersin alihoca and pozanti karsanti ophiolites from west to east each ophiolite has a metamorphic rock unit either at the base of the peridotites or in the melange units the metamorphic sole rocks generally consist of amphibolite at the top and near the contact with the overlying tectonized harzburgite of the ophiolites and mica schists mostly at the base near the tectonic contact with the underlying ophiolitic melange 40 ar 39 ar measurements from the metamorphic sole rocks of the lycian antalya and beysehir ophiolites are the first precise ages dating intra oceanic thrusting and the cooling age history during the closure of the neotethyan ocean amphiboles and white micas from the metamorphic sole rocks of the ophiolites yielded 40 ar 39 ar ages between 90 7 0 5 ma and 93 8 1 7 ma and between 91 2 2 3 ma and 93 6 0 8 ma respectively hornblende plateau ages from the amphibolites of the lycian ophiolites near koyce iz agree with those of antalya indicating that they were metamorphosed simultaneously in the neotethyan ocean the white micas display plateau ages concordant with the amphiboles from the same units in koyce iz and yesilova lycian ophiolites and from the pozanti karsanti ophiolite suggesting that the metamorphic sole rocks were rapidly cooled after their generation

structure and petrology of tauride ophiolites and mafic dike intrusions turkey implications for the neotethyan ocean cretaceous neotethyan ophiolites occur in four east west trending subparallel zones within the tauride tectonic belt in southern turkey the ophiolites of the inner intermediate and outer zones tectonically overlie the mesozoic platform carbonates of the tauride belt and are commonly underlain by a cenomanian ophiolitic melange these ophiolites consist mainly of tectonized mantle rocks mafic ultramafic cumulates and gabbros and commonly lack sheeted dike complexes and extrusive rocks of a complete ophiolite sequence metamorphic soles that are several hundred meters thick occur as thrust faulted slices beneath these ophiolites and show well developed metamorphic field gradients ophiolitic units and the metamorphic soles are intruded by mafic dike swarms that are truncated at the contact with the underlying melange unit dike rocks are made of subalkalic basalt to andesite typical of evolved island arc tholeiites they display large compositional variations with sio 2 content between 50 and 60 wt and mgo between 8 and 4 wt and contain higher ti augite phenocrysts and significantly less calcic plagioclase than their host cumulates the majority of the analyzed dike rocks show a slight depletion in light rare earth elements ree with low la smn ratios and are depleted in both high field strength hfs and heavy rees while enriched in large ion lithophile elements lile relative to normal mid ocean ridge basalt morb these characteristics suggest a mantle source that underwent previous melt extractions and subsequent metasomatism by lile and light ree enriched fluids geochemical modeling of trace elements shows that melting occurred at relatively low pressures under hydrous conditions and that it may have required the existence of an asthenospheric window in which the dike magmas developed through tapping and mixing of melts generated within a rising melting column starting slightly within the garnet stability field or in a transitional zone between the garnet and spinel stability fields at about 60 km depth this asthenospheric window was probably created during subduction of a neotethyan ridge system magmas ascending from the melt column within this window generated dikes that crosscut the metamorphic soles and were injected into the overlying mantle wedge and oceanic lithosphere the new 40 ar 39 ar hornblende dates of 92 90 ma and 90 91 ma from the metamorphic soles and dike swarms respectively show that evolution of these two geologic units was closely related in time and space and that they formed at the same intraoceanic subduction zone within the inner tauride seaway these data suggest that the tauride ophiolites within the three zones to the north originated from the same root zone situated north of the tauride carbonate platform and that they constitute remnants of a single ophiolitic nappe sheet derived from the inner tauride seaway within the neotethyan ocean

the jiaodong type gold deposits characteristics origin and prospecting abstract the jiaodong type comprises a unique class of gold mineralisation which includes the linglong type quartz vein hosted and the jiaojia type fracture disseminated style deposits although the type area is in the jiaodong peninsula in ne china where some of the world s richest gold reserves occur we identify similar occurrences in other parts of china and elsewhere in the world under this category the ore fluids migrated upwards forming quartz vein type of gold ore linglong type wherever the ore controlling fractures are at high angles fluid infiltration into the surrounding wall rocks and generation of the jiaojia type disseminated style deposits resulted where the ore bearing fluids encountered low angle fractures on a regional scale the jiaodong type gold mineralisation occurs along the margins of reactivated cratons within the interior of cratons along paleosuture zones or along the junctions of micro blocks and is distinctly different from the classic orogenic gold in terms of their tectonic setting ore characteristics and genetic history unlike skarn and porphyry type of deposits the jiaodong type gold deposits do not always show close spatial relationship with magmatic intrusives and some of the deposits occur distal to plutons 10 km in this paper we evaluate the salient geological geochronological geochemical and isotopic features of the jiaodong type gold deposits and propose some general guidelines for gold prospecting based on case studies we predict that the gold lodes in the jiaodong type mineralised zones might extent vertically up to 3000 m with only minor mineralogical and geochemical variations

archean gold relation to granulite formation and redox zoning in the crust the archean was the principal period for gold mineralization these rocks compose 12 of the exposed crust but have produced more than half of the world9s gold most major lode deposits formed at 2 7 0 2 ga this corresponds to the principal time of crustal thickening and stabilization an essential part of which was formation of granulite the anhydrous refractory base for the crust upward streaming of mantle co 2 along shear zones in the lower crust is one means for dehydrating amphibolite to form granulite and is accompanied by removal of large ion lithophile lil elements to higher crustal levels archean lode gold deposits were formed along major shear zones at intermediate crustal depths they are enclosed by zones of co 2 metasomatism many of them kilometres in extent 13 c data indicate that the co 2 is juvenile some major archean deposits have been shown to have formed from relatively oxidized hydrothermal fluids co 2 streaming with lil element depletion could only have occurred under relatively oxidized conditions that permitted a free co 2 vapor to exist in the lower crust such conditions would also have favored dissolution of gold and associated sulfide and their transfer to the mid crust in a co 2 h 2 o fluid the h 2 o coming from dehydration of amphibolite

early middle jurassic intra oceanic subduction in the izmir ankara erzincan ocean northern turkey abstract the izmir ankara erzincan suture zone near cankiri comprises an ophiolite related rock suite of amphibolite pyroxene amphibolite and epidote amphibolite the geochemical data reveal that the basaltic protoliths of the cankiri amphibolite suite are derived from different mantle sources amphibolites showing a lree enrichment in chondrite normalized ree pattern relatively high la n yb n 8 5 13 1 sm yb 2 8 3 7 ce sm 8 8 9 8 nb yb 14 4 20 5 th nb 1 1 2 6 originate from an oib like type i amphibolites mantle source those with flat chondrite normalized ree pattern low la n yb n 0 6 sm yb 1 0 ce sm 2 7 nb yb 0 6 suggest derivation from a depleted morb like type ii amphibolites mantle source a third type of amphibolite is characterized by la n yb n 1 54 sm yb 1 1 ce sm 4 5 nb yb 1 1 and th nb 0 3 it is derived from an enriched morb source and shows characteristics similar to island arc basalts amphiboles from these rocks yielded 40 ar 39 ar plateau ages between 177 08 0 96 ma and 166 9 1 1 ma these dates are interpreted as metamorphic ages of the amphibolitic rocks they differ significantly from previous ages of amphibolitic rocks the metamorphic sole rocks related to turkish ophiolites however similar metamorphic ages have been reported for metamorphic sole rocks of the hellenic dinaric ophiolites further west the metamorphic sole rocks have been generated in intra oceanic environments via intra oceanic subduction thrusting events the new age data of the cankiri amphibolite suite suggest that the izmir ankara erzincan ocean was subducted around early middle jurassic times i e roughly coeval with the oceanic basin s generating the hellenic dinaric ophiolites in the early middle jurassic time the tectonic regime in the izmir ankara erzincan ocean was compressional and the ocean was closing at that time the new age data presented here could imply that jurassic granites which cross cut basement rocks of the pontides are related to the northward subduction of the izmir ankara erzincan ocean during jurassic time

quantitative analysis of triassic extension in the northern viking graben it has been recognized for over a decade that large displacement pre jurassic faults are present in the northern viking graben part of the north sea rift these faults define a series of major fault blocks below the more obvious jurassic rift basin we attempt here to quantify the amount of extension associated with this older rift event which is probably of early triassic age quantitative modelling of the triassic rift and the succeeding period of thermal subsidence has been undertaken using a combination of flexural backstripping and flexural cantilever forward modelling these techniques suggest that triassic extension across the horda platform norwegian sector reached c 40 s 1 4 the consequences of this extension were deposition of a thick 3 km triassic upper jurassic syn rift and post rift sequence prior to renewed but minor extension in the late jurassic earliest cretaceous the thickness of the viking group reservoirs in the troll area appears to have been almost entirely controlled by sediment loading during post triassic thermal subsidence jurassic extension on the horda platform was in the uk sector of the viking graben triassic structures are less obvious than those below the horda platform because of jurassic overprinting they are however still present average triassic extension across the east shetland basin was c 15 comparable with the magnitude of jurassic extension in the same area we believe that the tern eider and cormorant fault blocks with proven shallow basement comprised a large eroded horst during the early triassic uplifted in the footwalls of major faults flanking the magnus and statfjord half graben during the triassic the magnus half graben was contiguous with the unst basin now situated in the western footwall of the younger jurassic basin the presence of the unst basin suggests that triassic extension occurred across the area that is now the northern shetland platform continuing into the west shetland area although the more obvious structures in the viking graben are jurassic in age the earlier triassic event was equally as important in controlling the structural and stratigraphic history of the basin

evolution of the nw margin of the north permian basin uk north sea mapping of depositional zones within the zechstein supergroup using semi regional 2d and 3dseismic data constrains the geological evolution of the northwestern margin of the north permian basinin uk offshore quadrants 14 15 19 20 and 21 four depositional zones are identified on the basis of mappable seismic facies which are assumed to vary with halite content well control characterizes the most reflective seismic facies as an interbedded carbonate and anhydrite shelf succession which grades laterally through clastic rich sequences to the least reflective a thick halite basinal equivalent the trendsof the depositional zones illustrate the geometry of the north permian basin and may have been locally controlled by basement lineaments within the north permian basin a n s trending axis devil s hole high characterized by thick reflective facies separates the central north sea from the forth approaches basin basement fault blocks control facies type and thickness along the northwest margin of the north permian basin in the moray firth area permian tilt of the zechstein shelf related to regional flexure played a role in precipitating gravity driven tectonics within the seismically reflective facies on the east flank of the devil s hole high this permian phase of salt tectonics resulted in numerous intra zechstein structures which can be interpreted as rafted and folded zones of interbedded halite carbonate sulphate and clastics the rafts initially slid downdip towards the main halite basin then their evolution became dominated by differential subsidence of the interbeds which forced salt layers into adjacent passive diapirs this episode predates deposition of the triassic smith bank shales which rest upon the zechstein with local angular unconformity the spatial distribution of zechstein facies influenced the tectonostratigraphy of the triassic jurassic and cretaceous systems boundaries between zechstein facies correspond to the limit of triassic halokinesis on the west central shelf and the limit of detachment of jurassic and lower cretaceous thin skinned tectonics in moray firth half graben

plume related oceanic plateaus as a potential source of gold mineralization we propose that the formation of anomalously gold enriched provinces on opposite sides of the pacific basin at ca 120 ma can be traced back to the formation of a mantle plume related oceanic plateau in the permian fertile fragments of this oceanic plateau travelled across the developing pacific basin and arrived at the accretionary margin of the north china and american cratons respectively some time earlier than 120 ma formation of the oceanic plateau proximal to a midoceanic rise or triple junction implies a long cooling history and reduced buoyancy by the time it arrived at an active subduction zone consequently in this model at least a part of the plateau material could have subducted like normal oceanic crust metamorphic devolatilization caused the release of gold into the overlying crust thereby fertilizing the advective hydrothermal system which gave rise to among others gold provinces in the sierra nevada foothills california and jiaodong peninsula china this process could be a mechanism for the complete temporal and spatial decoupling of the initial mantle plume activity formation of a fertile primitive oceanic source rock and the establishment of a highly endowed gold province at an accretionary margin

textural and compositional relationships of ca amphiboles in metabasites of the cape smith belt northern quebec implications for a miscibility gap at medium pressure

salt dissolution and salt related deformation of the forth approaches basin uk north sea abstract this paper addresses the potential role of regional scale salt dissolution as a mechanism responsible for salt related deformation this analysis is based on an investigation of the late permian to triassic succession of the forth approaches basin on the nw margin of the north permian basin and makes use of a regional 2d seismic grid tied to five key exploration wells this basin is ideal for this study because it consists of a deformed central region with a ne sw trending axis and an undeformed periphery which provides a template and key datums for reconstruction of the adjacent zone of deformation structural styles in this zone include simple salt cored anticlines salt walls salt diapirs detachment faults and unusually for the north sea intra zechstein salt cored folds pre triassic detailed mapping was carried out in uk block 26 10 and this shows that the dominant structural trend is ne sw suggesting that basement tilting influenced structural development the stratal geometry of the numerous triassic mini basins is used to constrain the way in which accommodation space in the mini basins was created by depletion of mobile salt the spatial pattern of salt depletion can be accounted for by two contrasting mechanisms or some combination thereof 1 deformation through downbuilding during a phase of regional subsidence or 2 flow induced by regional salt dissolution volumetric arguments necessary to discriminate between these two mechanisms are inconclusive due to later deformation of the top zechstein datum selective preservation of z3 and z4 cycles of the zechstein over large parts of the block 26 10 study area suggests that much of the salt depletion process preferentially removed z2 halite this observation is compatible with a process of subjacent dissolution possibly resulting from low salinity groundwater circulating in the pre zechstein aquifers

the influence of mechanically weak layers in controlling fault kinematics and graben configurations examples from analog experiments and the norwegian continental margin fault systems in extensional basins commonly display geometries that vary with depth reflecting depth and lithology dependent mechanical strength using an experimental approach we investigate this relationship by deploying physical analog models with stratified sequences consisting of brittle ductile sand silicone polymer sequences subject to single and polyphase deformation the experiments were used as analogs for a sandstone sequence interlayered by beds of evaporates or overpressured or unconsolidated mudstone in nature the latter being representative of decollement horizons experiments series 1 s1 using homogeneous and stratified quartz and feldspar sand produced asymmetric composite single grabens with diverse fault frequencies and fault styles for the graben margin faults for the mechanically stratified experiments with one decollement level series 2 contrasting graben configurations were produced in that the lowermost sequence was characterized by graben geometries of similar type to that of the s1 experiments whereas the sequence above the decollement was characterized by large fault blocks delineated by steepened or oversteepened faults the experiments with two decollements series 3 were displayed similarly but included graben geometries that widened upward with each level being characterized by independent fault systems the results can be used to explain strata bound fault patterns and depth dependent extension as seen in several places along the norwegian continental margin and elsewhere

a comparison of amphiboles from medium and low pressure metabasites a comparison of published metabasite amphibole analyses from medium and low pressure metamorphic terrains reveals that there is no systematic variation in na nam4 al or alvi as a function of pressure this may be due to blurring of the differences by variation in oxidation state or by analytical differences between laboratories it is not due to variable mg fe in whole rocks differences that can be recognised are generally higher ti al ratios in the low pressure amphiboles and a very poorly developed compositional gap between actinolite and hornblende compared with a well developed gap at medium pressures these features together with the relatively low grade appearance of calcic plagioclase at low pressures provide the best means of distinguishing metabasites from the two facies series

5 late variscan mineralizing systems related to orogenic processes the french massif central abstract the french massif central constitutes an exceptional study area due to the diversity of its metallic deposits its internal position in the variscan belt and the abundance of available geological geophysical and metallogenic data obtained within the geofrance 3d programme the deposits formed towards the end of the orogenic evolution represent the economic products of two distinct mineralizing systems a au sb hydrothermal system and a w sn and rare metals magmatic hydrothermal system which were simultaneously active during a short time span between ca 310 and 300 ma two types of gold deposit can be distinguished on the basis of their depth of emplacement deep seated gold deposits developed under lithostatic to hydrostatic pressure during rapid exhumation and shallow gold deposits emplaced under hydrostatic pressure with no significant uplift deposits of w sn and rare metals were emplaced in the upper crust during final crystallization of specialized magmas after their rapid ascent perhaps enhanced by simultaneous regional uplift the gold bearing systems are associated with a complex network of re activated crustal scale faults initially active during the period between 335 and 315 ma normal motion along the faults coeval with 335 to 315 ma granite migmatite domes played a major role in the 3d distribution of the hydrothermal plumbing system gold and related metals were carried within huge hydrothermal cells which reached ca 100 km by 10 km in area and 30 km in depth in contrast granites rich in magmatophile elements w sn rare metals generated smaller hydrothermal cells 10 km by 10 km in area and

mantle fluids in the karakoram fault helium isotope evidence abstract the karakoram fault kkf is the 1000 km long strike slip fault separating the western himalaya from the tibetan plateau from geologic and geodetic data the kkf is argued either to be a lithospheric scale fault with hundreds of km of offset at several cm a or to be almost inactive with cumulative offset of only a few tens of kilometers and to be just the upper crustal localization of distributed deformation at depth here we show 3he 4he ratios in geothermal springs along a 500 km segment of the kkf are 3 100 times the normal ratio in continental crust providing unequivocal evidence that a component of these hydrologic systems is derived from tectonically active mantle mantle enrichment is absent along the indus yarlung suture zone isz just 35 km southwest of the kkf suggesting that the mantle fluids flow only within the kkf within the last few ma the kkf must have accessed tectonically active tibetan mantle northeast of the mantle suture which we therefore locate vertically beneath the kkf very close to the surface trace of the isz hence in southwestern tibet indian crust may not now be underthrusting substantially north of the isz even though miocene underthrusting may have placed indian crust north of the isz in the lower half of the tibetan plateau crust this is in significant contrast to central and eastern tibet where underthrust indian material not only forms the lower half of the tibetan crust but is also currently underthrusting for 200 km north of the isz our new constraint on kkf penetration to the mantle allows an improved description of the continuously evolving karakoram fault as a tectonically significant yet perhaps geologically ephemeral lithospheric structure

kinematic and thermal evolution of the haymana basin a fore arc to foreland basin in central anatolia turkey abstract gondwana tauride kirsehir blocks and eurasia pontides derived continental blocks delimit the haymana basin central turkey to the south and the north respectively the boundaries of these blocks define the izmir ankara erzincan and intra tauride suture zones which are straddled by a number of late cretaceous to oligocene marine to continental basins the haymana basin is located at the junction of the iaesz and itsz and comprises upper cretaceous to middle eocene basin infill deposited in response to the interaction of these blocks the basin provides a unique opportunity to unravel spatio temporal relationships related to the timing of late stage subduction history of neo tethys ocean and subsequent collision of the intervening continental blocks we have conducted a multidisciplinary study in the region that includes mapping of major structures combined with fault kinematic analyses e w striking folds dominate the basin cross section balancing of these structures indicates around 25 roughly n s shortening in the region paleostress studies indicate that the basin was initially subjected to n s to nne ssw extension until the middle paleocene phase 1 and then n s directed syn depositional compression and coeval e w directed extension until the middle miocene phase 2 implying strike slip deformation and pure shear shortening in the basin these different deformation phases are attributed to first fore arc subduction basin development then foreland collision stages of the basin apatite u th he dating of 5 samples indicate that exhumation of the se segment of the basin started in early oligocene whereas the nw segment of the basin exhumed in the early miocene the differential uplift is possibly related to progressive north westwards movement of derekoy basin bounding fault at the north we propose that the haymana basin evolved from extensional forearc basin during the late cretaceous to early paleocene and foreland basin after the terminal subduction and subsequent collision of tauride and pontide blocks

late paleozoic subduction accretion along the southern margin of the north qinling terrane central china evidence from zircon u pb dating and geochemistry of the wuguan complex abstract the qinling orogen separating the north china plate from the yangtze plate is a key area for understanding the timing and process of aggregation between the two plates two competing and highly contrasting tectonic models currently exist to explain the timing and nature of collision one advocates a devonian continental collision while the other favors a triassic collision the wuguan complex between the early paleozoic north qinling and the mesozoic south qinling terranes can provide important constraints on the late paleozoic evolutionary processes of the qinling orogen metamorphosed sedimentary rock of the wuguan complex have a detrital zircon age spectrum with two major peaks at 453 ma and 800 ma several minor age populations of 350 430 ma and 1000 2868 ma and a youngest weighted mean age of 358 3 ma indicating a mixed source from the north qinling terrane the recrystallized zircons yield a weighted mean age of 333 2 ma representing the metamorphic age geochemical analyses imply that the sedimentary rocks were originally deposited in an active continental margin dominated by an acidic arc source with a subordinate mafic ultramafic source the youngest population of detrital zircons 358 ma suggests that the wuguan complex developed as forearc basin along the southern accreted margin of the north qinling terrane during the early carboniferous whereas the ca 520 460 ma mafic rocks with e morb n morb oib or island arc basalt signatures probably derived from the danfeng group in combination with regional data we suggest that the depositional age of the wuguan complex is ca 389 330 ma but it was subsequently incorporated into tectonic melange by the northward subduction of the paleo qinling ocean a long lived southward facing subduction accretionary system in front of the north qinling terrane probably lasted until at least the early carboniferous

characteristics of ophiolite related metamorphic rocks in the beysehir ophiolitic melange central taurides turkey deduced from whole rock and mineral chemistry small outcrops of the metamorphic rocks of the beysehir ophiolite appear to the west of gencek and to the south of durak south of beysehir lake in the central tauride belt in turkey amphibolitic rocks in the ophiolitic melange have an igneous origin protoliths of these rocks were probably alkali basalts gabbros or some ultramafic cumulates such as pyroxenite the amphibolites of the beysehir ophiolite can be divided into four groups 1 amphibolecgarnetcplagioclasegepidote as secondary minerals gopaque such as ilmeniteg accessory minerals such as sphene and apatite 2 amphibolecpyroxenecplagioclasegepidotegaccessory minerals such as sphene apatitegchlorite calcite as secondary mineral 3 amphibolegplagioclasegopaquegaccessory minerals 4 amphibolec plagioclasegepidotegbiotite and muscovitegopaquegaccessory minerals these metamorphic rocks show mainly granoblastic grano nematoblastic porphyroblastic and or poikiloblastic textures all amphiboles in the amphibolites are calcic and cluster in the range from magnesio hastingsite pargasite to actinolite amphibole compositions are characterized by sio2z 38 02 54 3 al2o3z 1 5 12 8 feoz 10 03 14 67 k2oz 0 2 1 8 mgoz 5 5 15 7 mg z 0 3 0 8 the amphibolites show an alkaline to subalkaline character however the primitive mantle normalized incompatible trace element diagram shows close similarity with the typical ocean island basalt oib pattern the rock chondrite normalized ree diagram of the amphibolites also confirms their oib signature tectonomagmatic discrimination diagrams based on the immobile trace elements suggest a mostly within plate alkali basalt wpb environment beysehir ophiolitic melange contains amphibolites from ophiolite related metamorphic rocks but the matrix of the beysehir ophiolitic melange is not metamorphosed blocks of metamorphic rocks and the ophiolitic rocks may have been incorporated into the ophiolitic melange in an oceanic environment during the late cretaceous by tectonic forces q 2005 elsevier ltd all rights reserved

the gold carbonate association source of co2 and co2 fixation reactions in archaean lode deposits abstract abundant carbonate is a ubiquitous feature of archaean lode gold deposits both in domains of alteration enveloping veins and in rocks enclosing auriferous sediments detailed studies of chemical mass balance in metabasalts progressively altered towards gold bearing quartz carbonate veins disposed within shear zones at yellowknife reveal massive additions of co2 k si and fe accompanying mineralisation with concomitant depletions of na coherent behaviour of al sc zr also v and nb provides a reference for constraining the volume relations during hydrothermal alteration in the peripheral regions of alteration depletions of ca and mg result in overall volume reduction but these elements are added to veins and their immediate alteration envelopes where there is a large positive volume change precious metals together with cr ni cu zn pb rb cd and ba have been added to the veins and altered wall rocks whereas quartz noble metals and other trace elements have been precipitated from hydrothermal fluids solution of ca mg and some fe indigenous to peripheral alteration regions combining with co2 from the mineralising reservoir appears to be the process for forming the abundant ferri dolomite gangue observations of many archaean au deposits reveals that carbonate chemistry reflects the nature of wall rocks with wall rocks donating the bivalent metal cations and hydrothermal fluids the co2 alteration reactions at yellowknife involved hydrolysis of albite accompanied by fixation of kaqueous to produce muscovite with na loss and hydrolysis of chlorite epidote with co2 fixation to form ferri dolomite studies of oxygen isotopes fe 2 fe 2 fe 3 and structure reveal that au quartz and carbonate were precipitated in the presence of fluids of probable metamorphic origin 18 o 8 9 at low redox potential and at ambient temperatures of 400 450 c during episodes of hydrofracturing the abundant co2 and k required for extensive carbonate muscovite replacement alteration could be supplied by fluids released during prograde metamorphism under greenschist or greenschist amphibolite facies conditions where the relative proportion of co 2 h 2 o is in the order of 0 2 to 0 5 and k na 1 given high co2 co in the hydrothermal reservoir these molecules may act as complexing agents for transport of au and other rare elements e g w pd ni cr