bismuth selenides from st andreasberg germany an oxidised five element style of mineralisation and its relation to post variscan vein type deposits of central europe carbonate veinlets at roter bar a former underground mine in the polymetallic st andreasberg vein district of the harz mountains germany host selenide minerals that are characterised as bi ag bearing clausthalite pbse tiemannite hgse guanajuatite bi2se3 and a number of selenides of bi zn cu ag and pd an unnamed bi pb ag selenide species with some hg and cu ideally bi4pb3ag2se10 is reported here specular hematite is disseminated within the clausthalite at the marginal zones of which other selenide minerals are located the occurrence of bohdanowiczite agbise2 and umangite cu3se2 constrains the formation temperature to 120 c and the selenide hematite assemblage plus barite in the carbonate gangue identifies highly oxidised conditions selenide assemblages of pb bi ag with and without co and ni occur in many parts of the variscan basement of central europe harz erzgebirge schwarzwald and bohemian massif and represent a high oxidation variety of five element ag as bi co ni veins

processes of forearc and accretionary complex formation during arc continent collision in the southern ural mountains the southern ural mountains of russia contain a well preserved well exposed paleozoic accretionary wedge and forearc that can be readily compared to those in active arc continent collision zones the early convergent history in the southern ural mountains is marked by the generation of boninite bearing arc tholeiites in the magnitogorsk forearc followed by arc tholeiite to calc alkaline volcanism with the entry of the east european craton continental crust in the subduction zone volcanism waned and stopped and high pressure metamorphism of its leading edge took place the arrival of the full thickness of the continental crust at the subduction zone is marked by increased sedimentation in the forearc basin and deposition of arc derived volcaniclastic turbidites across the subducting slab these together with offscraped continental material the exhumed high pressure rocks and a lherzolite massif formed an accretionary wedge a broad melange zone containing ultramafic fragments separates the forearc basement from the accretionary wedge and marks the damage zone that developed along the backstop region shallow water carbonates deposited unconformably on top of the mildly deformed arc record the end of the collision and the collapse of the arc

historical development of the gravity method in exploration the gravity method was the first geophysical technique to be used in oil and gas exploration despite being eclipsed by seismology it has continued to be an important and sometimes crucial constraint in a number of exploration areas in oil exploration the gravity method is particularly applicable in salt provinces overthrust and foothills belts underexplored basins and targets of interest that underlie high velocity zones the gravity method is used frequently in mining applications to map subsurface geology and to directly calculate ore reserves for some massive sulfide orebodies there is also a modest increase in the use of gravity techniques in specialized investigations for shallow targets gravimeters have undergone continuous improvement during the past 25 years particularly in their ability to function in a dynamic environment this and the advent of

paleomagnetism of the cu zn pb bearing kupferschiefer black shale upper permian at sangerhausen germany syngenetic diagenetic and epigenetic models have been proposed for the cu zn pb kupferschiefer mineralization at sangerhausen germany paleomagnetic and rock magnetic measurements have been made on 205 specimens from mine workings on the margin of the sangerhausen syncline the mineralization is richest in the 0 5 m thick upper permian 258 2 ma kupferschiefer black marly shale nine sites and dies out over 0 2 m in the underlying weisliegend sandstones three sites and overlying zechstein carbonates two sites except for one site of fault zone gypsum characteristic remanent magnetization directions were isolated for all 14 sites using alternating field and thermal step demagnetization these directions provide a negative fold test indicating that the remanence postdates jurassic fault block tilting rock magnetic measurements show that the kupferschiefer shale marks a redox front between the oxidized weissliegend sandstones and non oxidized zechstein carbonates the 14 site directions give a late jurassic paleopole at 149 3 ma it is significantly different from the paleopole reported by e c jowett and others for primary or early diagenetic rote faule alteration that gives an age of 254 6 ma on the current apparent polar wander path and is associated with kupferschiefer mineralization we suggest that the late jurassic extensional tectonic event that formed the nearby north german basin also reactivated variscan basement faults and extended them up through the overlying strata thereby allowing hydrothermal basement fluids to ascend and epigenetically mineralize the kupferschiefer shale the possibility of a 53 3 ma mineralization age is also considered

element and isotope geochemical investigations of the kupferschiefer in the vicinity of rote faule indicating copper mineralization sangerhausen basin g d r abstract based upon extensive data on the elemental and isotopic compositions of kupferschiefer of the sangerhausen basin and according to results of trace element and structural investigations of bitumen extracts trends of lateral and vertical distribution of various elements and genetic assertions are presented irregular positions of f v se au and u in the correlation diagram peculiarities of the lateral distribution of these elements abnormally high elemental concentrations in the rocks and in the bituminous extracts as well as alterations discovered in the composition of hydrocarbon groups and their structures support the idea of an influx of oxidizing metalrich waters moving through the rote faule from the rotliegendes basin into the kupferschiefer sediment isotope geochemical investigations carbon nitrogen and oxygen of organic carbonate and silicate fractions were carried out in order to characterize more precisely the conditions of sedimentation and the regime of diagenesis the contrary 13 c curves of pb zn facies and rote faule facies and the 13 c enrichment in the organic matter of rote faule can be explained by different redox conditions during sedimentation and or diagenesis furthermore the decreasing 18 o values of carbonates of the rote faule also suggest an influx of meteoric waters the results oppose a final syngenetic to early diagenetic fixation of the metal contents in kupferschiefer areas in the vicinity of rote faule the established model of influx of metalliferous fluids which arose from the rotliegendes is of local interest for element input and element redistribution

permian to early triassic magnetostratigraphy from the central european basin in poland implications on regional and worldwide correlations abstract permian early triassic rocks sampled in 15 outcrops 93 hand samples and 11 unoriented boreholes 630 hand samples from the polish part of the central european basin were studied paleomagnetically in spite of extensive remagnetization affecting 50 of samples from the boreholes a magnetic polarity sequence was compiled the polarity pattern is not only common for many sections from the investigated area but also convergent with the global synthetic magnetostratigraphic scale the lower rotliegend early permian rocks contain a reversed polarity record while the upper rotliegend late permian early triassic sediments are characterized by mixed polarity magnetization within the buntsandstein part of that mixed megazone 14 magnetic zones were found buntsandstein sedimentation started with a normal polarity zone which may be compared with that of early griesbachian defined in several places in the world the polarity record noted in the middle buntsandstein sediments could indicate significant stratigraphic gaps or condensations near the middle buntsandstein and rot boundary the comparison of the upper buntsandstein polarity with the early middle triassic magnetostratigraphic data from other basins suggests that the majority or even all the rot sediments should be included in the anisian

nature of the eastern boundary of the rio grande rift from cocorp surveys in the albuquerque basin new mexico reprocessing and synthetic seismic modeling of cocorp profiles across the eastern margin of the rio grande rift at abo pass new mexico suggest that synthetic and antithetic cenozoic normal faults sole into or are truncated by a northwest dipping listric master fault which bounds the eastern side of the basin and reaches a depth of at least 10 km beneath the southern albuquerque basin this fault appears to project toward the surface position of the los pinos cenozoic normal fault which lies basinward of and trends parallel to a mapped laramide duplex thrust zone the los pinos fault may sole into the older thrust reactivating this preexisting compressional structure at depth a lateral change in reflection amplitude and frequency is conspicuous across the eastern rift margin analysis demonstrates that source coupling is the main cause of a much deteriorated signal below the rift basin although complex ray paths and attenuation by the graben fill may contribute

re os age of non mineralized black shale from the kupferschiefer poland and implications for metal enrichment six samples of non mineralized black shale from a kupferschiefer section in the northern part of the polish zechstein basin zdrada ig 8 drill hole 1026 16 1026 90 m were studied for re os isotopes and selected major and trace elements these black shales averaging 5 82 wt corg and 1 69 wt stot display very low base metal values up to 106 ppb cu 792 ppb pb and 144 ppb zn and have abundances of 64 1376 ppb re and 0 37 1 25 ppb os with a 187os 188os ratio of 6 95 22 5 the regression of all re os data yields an age of 247 20 ma which is within the range of uncertainties of previous rb sr and k ar geochronological studies the scatter in the re os data can be explained in terms of fluctuations in sedimentary conditions i e restricted basin with terrestrial influence

melting of phase d in the lower mantle and implications for recycling and storage of h 2 o in the deep mantle we determined the melting phase relations and conditions of the dense hydrous magnesium silicate phase d nominally mgsi2o4 oh 2 on composition in mgo sio2 h2o msh mgo al2o3 sio2 h2o mash and feo mgo al2o3 sio2 h2o fmash and on a mixture of phase d olivine enstatite msh at 22 32 gpa and 1000 1800 c contrasting to previous studies we performed h2o undersaturated experiments bulk compositions were synthetic mixtures of brucite silica or brucite olivine enstatite on the silica rich side of the tie line perovskite h2o at 22 24 gpa the maximum thermal stability of phase d is between 1350 and 1400 c in msh and fmash but 1600 c at 24 gpa in the fe free al bearing bulk composition mash apparently addition of al2o3 increases the stability field of phase d by 200 c an effect that is counter balanced by addition of feo at 32 gpa the stability of phase d msh and fmash is between 1350 and 1400 c at 22 gpa phase d melts to a mg rich melt coexisting with mgsi ilmenite stishovite whereas at 24 32 gpa melt coexists with perovskite and stishovite even melts from bulk compositions in the silica rich part of the msh system molar bulk mg si 0 5 are magnesian rich mg si molar ratio of 2 5 and are distinct from aqueous fluids and hydrous melts at lower pressures the temperature stabilities determined in this study indicate that slabs that thermally relax when stagnating on top of the 660 km discontinuity or penetrating into the lower mantle will have their last dense hydrous magnesium silicate phase i e phase d melting and producing a magnesian and hydrous melt that will rise through the transition zone such a melt could be responsible for observed low velocity zones and may be neutrally buoyant at the 410 km discontinuity and will affect the structure and dynamics of the mantle

decomposition of phase d in the lower mantle and the fate of dense hydrous silicates in subducting slabs abstracthigh pressure high temperature quench type experiments were carried out on serpentine to pressures of 53 gpa andtemperatures between 800 1800oc x ray analyses show that recovered phase assemblages varied considerably for thedifferent high pressure and high temperature studies the dense hydrous magnesium silicate phases decompose sequentiallyas the pressure increases and appear to serve as reservoirs for h 2 o in the mantle eventually releasing it at the highestpressure superhydrous phase b is stable up to pressure equivalent to the boundary between the transition zone and lowermantle phase d decomposes at pressures of 44 gpa equivalent to about 1250 km depth this may de ne the lower depthlimit for the presence of dense hydrous magnesium silicates beyond this pressure only nominally anhydrous phases havebeen recovered in high pressure experiments this may indicate a lack of stoichiometric hydrogen bearing silicate phasesat higher pressure 1998 elsevier science b v all rights reserved keywords x ray diffraction analysis lower mantle serpentine high pressure

the magnetization of clay rich rocks in sedimentary basins low temperature experimental formation of magnetic carriers in natural samples abstract rocks are often magnetically altered during burial thus providing a useful method to study their thermo chemical history in order to improve the understanding of burial diagenetic magnetization we experimentally synthesized magnetite in natural samples lower jurassic argillites from the paris basin were heated to 150 c under a confined atmosphere of argon when a magnetic field was applied during the heating a chemical remanent magnetization was acquired rock magnetism studies reveal that most of the newly formed magnetic carriers were magnetite using anhysteretic remanent magnetization as a measure of the quantity of magnetite an increase of up to 150 after heating was observed ferrimagnetic iron sulphide and hematite are observed to have formed in samples composed of less than 3 calcite and new magnetite is sometimes completely absent in samples containing less than 0 5 calcite hysteresis measurements suggest that the new magnetite is in the pseudo single domain state scanning electron microscope studies indicate that the new magnetic carriers are associated with pre existing pyrite the magnetic transformations during the experiments involved a fluid which reacted with iron bearing and sulfur bearing minerals in ways depending on local redox conditions this study shows that magnetite can be produced in argillaceous sediments at the normal temperatures and pressures found in sedimentary basins without any external supply from long range fluid flow

phase stability and thermal equation of state of δ alooh implication for water transportation to the deep lower mantle abstract in this study we present new experimental constraints on the phase stability and thermal equation of state of an important hydrous phase alooh using synchrotron x ray diffraction up to 142 gpa and 2500 k our experimental results have shown that alooh remains stable at the whole mantle pressure temperature conditions above the d layer yet will decompose at the core mantle boundary because of a dramatic increase in temperature from the silicate mantle to the metallic outer core at the bottom transition zone and top lower mantle the formation of alooh by the decomposition of phase egg is associated with a 2 1 2 5 increase in density and a 19 7 20 4 increase in bulk sound velocity v the increase in across the phase egg to alooh phase transition can facilitate the subduction of alooh to the lower mantle compared to major lower mantle phases alooh has the lowest but greatest v leading to an anomalous low v ratio which can help to identify the potential presence of alooh in the region more importantly water released from the breakdown of alooh at the core mantle boundary could lower the solidus of the pyrolitic mantle to cause partial melting and or react with fe in the region to form the low velocity feo2hx phase the presence of partial melting and or the accumulation of feo2hx phase at the cmb could be the cause for the ultra low velocity zone alooh is thus an important phase to transport water to the lowermost mantle and helps to understand the origin of the ultra low velocity zone

8 precambrian geodynamics and ore formation the fennoscandian shield abstract compared with present day global plate tectonics archaean and palaeoproterozoic plate tectonics may have involved faster moving hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle this scenario also fits with the complex geodynamic evolution of the fennoscandian shield from 2 06 to 1 78 ga when rapid accretion of island arcs and several microcontinent continent collisions in a complex array of orogens was manifested in short lived but intense orogenies involving voluminous magmatism with a few exceptions all major ore deposits formed in specific tectonic settings between 2 06 and 1 78 ga and thus a strong geodynamic control on ore deposit formation is suggested all orogenic gold deposits formed syn to post peak metamorphism and their timing reflects the orogenic younging of the shield towards the sw and west most orogenic gold deposits formed during periods of crustal shortening with peaks at 2 72 to 2 67 1 90 to 1 86 and 1 85 to 1 79 ga the ca 2 5 to 2 4 ga ni cu pge deposits formed both as part of layered igneous complexes and associated with mafic volcanism in basins formed during rifting of the archaean craton at ca 2 5 to 2 4 ga svecokarelian ca 1 89 to 1 88 ga ni cu deposits are related to mafic ultramafic rocks intruded along linear belts at the accretionary margins of microcratons all major vms deposits in the fennoscandian shield formed between 1 97 and 1 88 ga in extensional settings prior to basin inversion and accretion the oldest cyprus type deposits were obducted onto the archaean continent during the onset of convergence the pyhasalmi vms deposits formed at 1 93 to 1 91 ga in primitive bimodal arc complexes during extension of the arc in contrast the skellefte vms deposits are 20 to 30 million years younger and formed in a strongly extensional intra arc region that developed on continental or mature arc crust deposits in the bergslagen uusimaa belt are similar in age to the skellefte deposits and formed in a microcraton that collided with the karelian craton at ca 1 88 to 1 87 ga the bergslagen uusimaa belt is interpreted as an intra continental or continental margin back arc extensional region developed on older continental crust iron oxide copper gold iocg deposits are diverse in style at least the oldest mineralizing stages at ca 1 88 ga are coeval with calc alkaline to monzonitic magmatism and coeval and possibly cogenetic subaerial volcanism more akin to continental arcs or to magmatic arcs inboard of the active subduction zone younger mineralization of similar style took place when s type magmatism occurred at ca 1 80 to 1 77 ga during cratonization distal to the active n s trending subduction zone in the west possibly interaction of magmatic fluids with evaporitic sequences in older rift sequences was important for ore formation finally the large volumes of anorthositic magmas that characterize the sveconorwegian orogeny formed a major concentration of ti in the sw part of the sveconorwegian orogenic belt under granulite facies conditions about 40 million years after the last regional deformation of the sveconorwegian orogeny between ca 930 and 920 ma

the role of the kupferschiefer in the formation of hydrothermal base metal mineralization in the spessart ore district germany insight from detailed sulfur isotope studies the spessart district sw germany located at the southwestern margin of the permian kupferschiefer basin in central europe hosts abundant stratabound and structurally controlled base metal mineralization the mineralization styles identified are 1 stratabound cu pb zn ag ores in zechstein sedimentary rocks 2 structurally controlled cu as ag ores in zechstein sedimentary rocks 3 crosscutting co ni bi as and cu fe as veins 4 stratabound metasomatic fe mn carbonate ores in zechstein dolomite 5 barren barite veins and 6 fe mn as veins in permian rhyolites building on previous work that involved mineralogical textural and chemical characterization of the major mineralization types we have performed a comprehensive sulfur isotope study that applied both conventional and novel laser ablation multi collector inductively coupled plasma mass spectrometry techniques the 34s values of sulfide minerals from the different ore types are consistently negative and highly variable in the range between 44 5 and 3 9 whereas the 34s values of barite are all positive in the range between 4 7 and 18 9 remarkably stratabound and structurally controlled mineralization in zechstein sedimentary rocks has the least negative 34s values whereas vein type deposits have consistently more negative 34s values the observed pattern of sulfide 34s values can be best interpreted in terms of fluid mixing at the basement cover interface hydrothermal fluids originating from the crystalline basement migrated upward along subvertical fault zones and were periodically injected into groundwaters that were flowing in the post variscan sedimentary cover these groundwaters had interacted with the zechstein sedimentary rocks resulting in fluids characterized by elevated concentrations of reduced sulfur with negative 34s values and alkaline ph repeated mixing between both chemically contrasting fluids caused rapid and efficient precipitation of sulfide ore minerals in hydrothermal veins with highly variable but distinctly negative 34s values

copper deposition during quartz dissolution by cooling magmatic hydrothermal fluids the bingham porphyry abstract scanning electron microscope cathodoluminescence imaging is used to map successive generations of fluid inclusions in texturally complex quartz veinlets representing the main stage of ore metal introduction into the porphyry cu au mo deposit at bingham utah following conventional fluid inclusion microthermometry laser ablation inductively coupled plasma mass spectrometry la icpms is applied to quantify copper and other major and trace element concentrations in the evolving fluid with the aim of identifying the ore forming processes textures visible in cathodoluminescence consistently show that the bulk of vein quartz q1 characterized by bright luminescence crystallized early in the vein history cu fe sulfides are precipitated later in these veins in a microfracture network finally filled with a second generation of dull luminescing q2 quartz mapping of brine and vapor inclusion assemblages in these successive quartz generations in combination with la icpms microanalysis shows that the fluids trapped before and after cu fe sulfide precipitation are very similar with respect to their major and minor element composition except for copper copper concentrations in inclusions associated with ore formation drop by two orders of magnitude in a tight pressure temperature interval between 21 and 14 mpa and 425 350 c several hundred degrees below the temperature of fluid exsolution from the magma copper deposition occurs within a limited p t region in which sulfide solubility shows strong normal temperature dependence while quartz solubility is retrograde this permits copper sulfide deposition while secondary vein permeability is generated by quartz dissolution the brittle to ductile transition of the quartz feldspar rich host rocks occurs in the same temperature range which further enhances vein reactivation and promotes cooling and expansion of fluids ascending across the transition from lithostatic to hydrostatic conditions

the aguablanca ni cu pge deposit sw spainossa morena zone lat 37 57 n long 6 11 w

the southern rhine graben a new view of the initial phase one of the puzzling features of the southern end of the rhine graben is the dinkelberg tabular jura block on the eastern shoulder of the graben it is dissected by a large number of faults the most notable ones forming a field of narrow little grabens and half grabens whose bordering faults converge at the level of the middle triassic evaporites which points to decollement at that horizon the little grabens were traditionally considered to be of oligocene age coeval with the main taphrogenesis of the rhine graben two hypotheses were offered for their formation one ascribing them to extension on the extrados of large basement folds the other to gravity sliding on paleoslopes recent field work uncovered overwhelming evidence for an eocene age of the little grabens the time of the initial phase of rhine graben formation at that time there were neither large basement folds nor paleoslopes of any significance and therefore the two hypotheses offered until now do not work however the map view pattern of the field of faults offers a somewhat unusual way out of the dilemma this pattern is most prominently displayed in the dinkelberg area north of the rhine there a lane of narrow decollement grabens with a mean nne strike is confined within the nw striking dinkelberg graben which is much wider and rooted in the basement it is also very shallow with a subsidence on the order of 100 m the lane of decollement grabens forms a dextral en echelon pattern with respect to the dinkelberg graben suggesting stretching of the post evaporite sequence above a basement essentially extended by strike slip this model though not as clearly expressed is also compatible with the data in the rest of the dinkelberg tabular jura block it also fits surprisingly well a theoretical model by withjack and scheiner 1982 that predicts a dominance of strike slip in the marginal area of a system consisting of extension superimposed on doming

unusually large shear wave anisotropy for chlorite in subduction zone settings using first principle simulations we calculated the elasticity of chlorite at a density 2 60 g cm 3 the elastic constant tensor reveals significant elastic anisotropy vp 27 vs1 56 and vs2 43 the shear anisotropy is exceptionally large for chlorite and enhances upon compression upon compression the shear elastic constant component c44 and c55 decreases whereas c66 shear component stiffens the softening in c44 and c55 is reflected in shear modulus g and the shear wave velocity vs our results on elastic anisotropy at conditions relevant to the mantle wedge indicates that a 10 20 km layer of hydrated peridotite with serpentine and chlorite could account for the observed shear polarization anisotropy and associated large delay times of 1 2 s observed in some subduction zone settings in addition chlorite could also explain the low vp vs ratios that have been observed in recent high resolution seismological studies

neogene quaternary magmatism and geodynamics in the carpathian pannonian region a synthesis in the carpathian pannonian region in neogene times westward dipping subduction in a land locked basin caused collision of two lithospheric blocks alcapa and tisia with the southeastern border of the european plate calc alkaline and alkaline magmatism was closely related to subduction rollback collision and extension from the spatial distribution of the magmatic activity four segments can be defined western segment magmatism occurring on the alcapa block central segment magmatism occurring on both alcapa and the tisia blocks south eastern segment and interior segment both on the tisia block most calc alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment assimilation and fractionation processes at shallow crustal levels occurred in most of the segments strongly masking the deeper source processes long term subduction rollback and or delamination led to contamination of the asthenosphere beneath the western segment here large volume partial melts of the contaminated mantle caused underplating and crustal anatexis leading to mixing of mantle derived calc alkaline magmas with crustal melts in the central segment calc alkaline magmas were formed by subduction and rollback followed by back arc extension and slab breakoff avariable mantle source is indicated in the back arc setting and larger amount of fluid induced metasomatism source enrichment and assimilation nearer to the trench in the interior segment evolution from typical calc alkaline magmas to adakite like ones was related to extension due to fast rotations and transtensional tectonics here calc alkaline magmas formed by decompression melting of a heterogeneous crust mantle lithosphere while adakite like melts resulted from fliud dominated melting of the lithosphere along the south eastern segment slab breakoff was responsible for the generation of typical calcalkaline magmas but in the extreme south of the segment shallow level tearing of the slab followed breakoff strike slip tectonics allowed the rise of hot asthenosphere and generation of adakite like magmas via slab melting along the torn edge of the east european plate alkalic basaltic volcanism with an oib like asthenosphere source followed the calc alkaline stage

cenozoic thermal mechanical and tectonic evolution of the rio grande rift careful documentation of the cenozoic geologic history of the rio grande rift in new mexico reveals a complex sequence of events at least two phases of extension have been identified an early phase of extension began in the mid oligocene about 30 ma and may have continued to the early miocene about 18 ma this phase of extension was characterized by local high strain extension events locally 50 100 regionally 30 50 low angle faulting and the development of broad relatively shallow basins all indicating an approximately ne sw 25 extension direction consistent with the regional stress field at that time extension events were not synchronous during early phase extension and were often temporally and spatially associated with major magmatism a late phase of extension occurred primarily in the late miocene 10 5 ma with minor extension continuing to the present it was characterized by apparently synchronous high angle faulting giving large vertical strains with relatively minor lateral strain 5 20 which produced the modern rio grande rift morphology extension direction was approximately e w consistent with the contemporary regional stress field late phase graben or half graben basins cut and often obscure early phase broad basins early phase extensional style and basin formation indicate a ductile lithosphere and this extension occurred during the climax of paleogene magmatic activity in this zone late phase extensional style indicates a more brittle lithosphere and this extension followed a middle miocene lull in volcanism regional uplift of about 1 km appears to have accompanied late phase extension and relatively minor volcanism has continued to the present we have estimated geotherms and calculated lithospheric strength curves for the two phases of extension using geologic data to constrain earlier events and geophysical data to constrain the modern geotherm and crustal structure a high geotherm was deduced for early phase extension resulting in a shallow crustal brittle ductile transition and negligible mantle strength the lithosphere cooled after early phase extension resulting in a deeper crustal brittle ductile transition and perhaps more significantly a considerable zone of mantle strength immediately beneath the moho these results indicate that early phase extensional style was controlled by a crustal decollement near the brittle ductile transition which was prevented during late phase extension by significant strength in the uppermost mantle late cenozoic uplift of the rift zone cannot be explained by crustal thinning during extension and geotherm evolution predicted from simple cooling however this uplift does not appear to be restricted to the rift zone and pliocene to recent volcanism and heat flow data suggest that uplift may be caused by magmatic thickening of the crust perhaps unrelated to rifting the complex interrelationship among regional and local prerifting synrifting and postrifting events in the rio grande rift suggests that rifting at least in this region should not be considered in isolation of other geologic events

la primavera caldera mexico structure inferred from gravity and hydrogeological considerations la primavera geothermal field mexico is associated with a pleistocene rhyolitic caldera this gravity study was conducted to assist its development and explotation digital processing of the gravity data upward and downward continuations vertical derivatives enabled delineation of the main features of the caldera s subsurficial structure a 3 d structural model was established which could be supported by gravity modeling 2 d and 3 d forward modeling accordingly the caldera is featured by an asymmetric subsurface structure a major depression in its northern half and a boomerang shaped structural high to the south lineaments reflecting the regional northwest southeast and northeast southwest structural fabric were observed the basal volcanics units are affected by lineaments of the northwest southeast system whereas the northeast southwest system affects only the shallower units the structural high has a northwest southeast trend at the western and southwestern portion of the caldera from i

reos and s isotopic constraints on the origins of two mineralization events at the tangdan sedimentary rock hosted stratiform cu deposit sw china abstract the tangdan stratiform cu deposit in the kangdian region of south china is hosted in sedimentary rocks of the late paleoproterozoic to early mesoproterozoic dongchuan group orebodies mainly occur in dolostone and black shale above a thick sequence of hematitic sandstone and siltstone mineralization consists mainly of bedding parallel stratiform ores with minor amounts of discordant vein type ores both stratiform and vein type ores are composed of bornite and chalcopyrite with minor chalcocite and digenite associated with gangue minerals including ankerite dolomite calcite and quartz cu sulfides from vein type ores contain 122 293 ppb re much higher than those of stratiform ores 0 6 14 ppb re they have highly radiogenic os with re os model ages ranging from 1413 to 1457 ma and a weighted mean re os model age of 1432 19 ma 2 mswd 0 30 which is within uncertainty in agreement with isochron ages of 1401 30 ma 2 mswd 0 67 and 1397 71 ma 2 mswd 0 22 using 187 re 188 os versus 187 os 188 os and 187 re versus 187 os regression respectively in contrast sulfides from stratiform ores did not yield meaningful model ages due to the extremely low concentrations of re and radiogenic os however early studies have shown that the stratiform ores were likely formed at 1700 ma during the diagenesis of the host strata sulfides from the vein type ores have 34 s values ranging from 15 to 8 significantly lower than those of stratiform ores 3 to 10 suggesting that organic matter may have been involved in the formation of the vein type ores contrasting re os and s isotopes suggest that the two types of ores at the tangdan deposit were likely formed from different ore forming fluids we propose that stratiform ores were precipitated from basinal fluids during the early evolution of the rift basin whereas the vein type ores were formed due to a much younger thermal event during which hydrothermal fluids interacted with overlying black shale to account for the high re and negative 34 s values this study demonstrates that re os isotopes of sulfides can be used to study the origin of hydrothermal system

7 4 kupferschiefer copper deposits of sw poland lubin sieroszowice district lat 51 35 n long 16 6 e

9 processes of tectonism magmatism and mineralization lessons from europe abstract metallogenic provinces in europe range in age from the archaean to the neogene deposit types include porphyry copper and epithermal cu au volcanic hosted massive sulphide vms orogenic gold fe oxide cu au anorthosite fe ti oxide and sediment hosted base metal deposits most of them formed during short lived magmatic events in a wide range of tectonic settings many can be related to specific tectonic processes such as subduction hinge retreat accretion of island arcs continental collision lithosphere delamination or slab tear in contrast most sediment hosted deposits in europe evolved in extensional continental settings over significant periods of time in europe as elsewhere ore formation is an integral part of the geodynamic evolution of the earth s crust and mantle many tectonic settings create conditions conducive to the generation of water rich magma but the generation of ore deposits appears to be restricted to locations and short periods of change in temperature and stress imposed by transitory plate motions crustal influence is evident in the strong structural controls on the location and morphology of many ore deposits in europe crustal scale fault fracture systems many involving strike slip elements have provided the fabric for major plumbing systems rapid uplift as in metamorphic core complexes and hydraulic fracturing can generate or focus magmatic hydrothermal fluid flow that may be active for time spans significantly less than a million years once a hydrologically stable flow is established ore formation is strongly dependent on the steep temperature and pressure gradients experienced by the fluid particularly within the upper crust in europe significant fracture porosity deep in the crystalline basement 1 is not only important for magmatic hydrothermal systems but allows brines to circulate down through sedimentary basins and then episodically upward expelled seismically to produce sediment hosted base metal deposits and kupferschiefer copper deposits emerging research stimulated by geode can improve the predicting power of numerical simulations of ore forming processes and help discover the presence of orebodies beneath barren overburden

phase relations of peridotites under h2o saturated conditions and ability of subducting plates for transportation of h2o phase relations of peridotites under h2o saturated conditions up to 28 gpa and 2600 c have been clarified based on the high pressure experimental results in the mgo feo sio2 h2o mgo sio2 al2o3 h2o cao mgo al2o3 sio2 h2o and natural systems based on the phase assemblages deduced and the chemical compositions of the phases the maximum h2o contents for two bulk rock compositions lherzolite and harzburgite have been calculated using mass balance then the potential ability of subducting plates for transportation of h2o is discussed by simple models combining the phase relations and the thermal structures of subduction zones as a function of the age of subducting plate a 15 130 ma the subduction velocity u0 2 25 18 cm year and angle 30 and 60 and the mantle potential temperature tp 1300 and 1350 c the results confirm the importance of choke point a cusp around 6 2 gpa and 550 c at which the stability field of major hydrous phases is minimized in terms of temperature although the choke point is exceeded by the mg sursassite bearing assemblage that has the maximum h2o content of 0 4 0 7 wt around 5 7 gpa and 550 700 c if the geotherm of the coldest part across the subducting plate passes below the choke point maximum 4 6 wt h2o can subduct whereas h2o less than 0 4 0 7 wt can subduct above the choke point the critical conditions are clarified as follows if 30 and tp 1300 c a 15 ma with u0 9 cm year or a 30 ma with u0 2 25 cm year is the critical condition if 60 and tp 1300 c or 30 and tp 1350 c the critical conditions slightly shift to an older age or a greater velocity e g a 30 ma with u0 3 5 cm year the slab thermal parameter au0sin is useful to predict roughly the critical condition however within the younger plate the spatial extent of a cold region with major hydrous phases is thinner hence less h2o is subducted even with the same slab thermal parameter this indicates that the age of the plate and the subduction velocity act differently on the h2o transportation ability of subducting plates

kinematic evolution of the romanian carpathians abstract the regional pattern of contraction and extension directions and the evolution of the strain field from paleogene to neogene times enabled a reconstruction of the migration path of the carpathian collision front the carpathian nappes were thrust around the moesian plate during paleogene and early neogene times and protruded into a small oceanic embayment between the moesian and european plates the arc structure of the carpathian fold thrust belt was formed in late neogene times as a result of the eastward escaping tisza dacia block due to n directed convergence of the adriatic plate and the retreating subduction of an oceanic slab brittle deformation structures in the romanian carpathians suggest three tectonic events related to major plate motions 1 paleogene to middle miocene ne to ene contraction caused right lateral curved strike slip faults 2 middle miocene to pliocene fan shaped orientations of contraction directions were caused by right lateral oblique convergence in the southern carpathians frontal convergence in the southern eastern carpathians and left lateral convergence in the northern eastern carpathians 3 pleistocene to holocene general e w extension and n s contraction in the carpathian arc and local ese wnw contraction in the vrancea area is related to the late roll back stage and break off of the subducted slab in the bend area

spatially dependent seismic anisotropy in the tonga subduction zone a possible contributor to the complexity of deep earthquakes abstract the deep part of the tonga subduction zone consists of two differently oriented slab segments the northern segment within latitudes 17 19 s and the southern segment within latitudes 19 5 27 s the orientation of the slab is strike dip 110 57 in its northern part and 210 46 in its southern part both segments are seismically active at depths from 500 to 700 km the mechanisms of deep focus earthquakes reported in the harvard moment tensor catalogue contain compensated linear vector dipole clvd components that behave differently in both segments the mean value of the clvd is 3 for the northern segment but 10 for the southern segment the mean absolute value of the clvd is 12 for the northern segment and 16 for the southern segment the complex behaviour of the clvd is explained by spatially dependent seismic anisotropy in the slab the inversion for anisotropy from the non double couple components of moment tensors points to orthorhombic anisotropy in the both slab segments the anisotropy seems to have a uniform strength of 5 7 for p waves and 9 12 for s waves and is oriented according to the orientation of each segment and the stress acting in it the spatial variation of velocities is roughly similar in both segments the retrieved anisotropy might have several possible origins it can be 1 intrinsic caused by preferentially aligned anisotropic minerals such as wadsleyite ringwoodite ilmenite or others 2 effective caused for example by intra slab layering or 3 partly apparent produced by systematic errors in the moment tensors due to neglecting 3d slab geometry and the slab mantle velocity contrast when calculating the green functions in the moment tensor inversion

genesis of kupferschiefer cu ag deposits by convective flow of rotliegendes brines during triassic rifting extensive and rich cu ag sulfide mineralization occurs in poland across the contact between the upper permian zechstein restricted marine sequence and the lower permian rotliegende continental volcanic and clastic sequence geologic evidence suggests that the mineralization was formed during late diagenesis when metalliferous brines migrated through the rotliegende leaching metals from the volcanic detritus and up the flanks of basement highs possibly along fracture porosity to the pyritic kupferschiefer and zechstein limestone above thick evaporites in the lower zechstein preclude a vertical flow through model but metal zoning attitudes suggest that the brines overturned where the rotliegende pinched out against the highs and moved laterally along the base of the zechstein toward the basin centers presumably to sink back down into the rotliegende completing a convection cell a middle triassic paleomagnetic age for the metal zoning and kimmerian attitudes of dilatant sulfide veinlets indicate that the mineralizing event coincided with continental rifting associated with the opening of the tethys ocean slow unicellular convection may be commonplace in sandstone basins where small lateral temperature gradients delta t exist but greater velocities are necessary to form large orebodies an anomalous tensional and thermal event such as rifting can increase velocities by increasing permeability slope angle or delta t the paleothermal structure of southwestern poland was determined by modeling the conductive heat flow in 14 one dimensional geologic sections which described the evolution of the basin architecture for 10 m y in the early triassic rifting was simulated by increasing the lower boundary condition from 500 degrees to 1 000 degrees c at 25 km this thermal pulse produced a surprisingly high delta t of 25 degrees c across the lubin ore district solely from differences in thermal conductivities between the basement high 4 2 w m degrees c the sandstone 2 5 w m degrees c and the shale basin center 1 25 w m degrees c unicellular convection patterns would be induced by the lateral boundary conditions of warm basement highs and cold shale centers and by the greater horizontal permeability these cells were 15 to 20 km long 400 m high and subhorizontal a slope angle of 2 degrees and a permeability of 1 d produces a convection velocity of 13 cm yr which with a copper solubility of 1 000 mg kg in 20 to 30 percent ca na cl brines in equilibrium with hematite can form the lubin deposit in less than 6 m y using a fracture permeability of 2 d and a solubility of 300 mg kg the time needed is less than 10 m y the konrad mine can be formed in similar time periods without the continuous recycling of the brine inherent in convective flow 20 times or more the metal solubilities needed to form the lubin deposits by a flow through model would be unreasonably high natural gases likely migrated along with the metalliferous brines and helped convection by creating secondary porosity and increasing the buoyancy of the fluids because the fluids are recirculated and not expelled convection provides a way in which secondary migration of methane and petroleum can occur effectively in solution as well as in separate phases

stability of dense hydrous magnesium silicate phases and water storage capacity in the transition zone and lower mantle abstract we evaluated the water storage capacity in the mantle based on the phase relations of silicate systems containing water we conducted high pressure and temperature synthesis experiments on some silicate systems such as the superhydrous phase b phase c and phase g phase d and f compositions in the mgo sio2 h2o system and the cmas pyrolite 2 wt h2o system up to the uppermost part of the lower mantle superhydrous phase b is stable at temperatures below 1200 c at 18 gpa and below 1300 c at 20 gpa the following reaction sequences were observed with increasing temperature from 1200 to 1600 c in the pressure range from 18 to 20 gpa superhydrous phase b phase b liquid wadsleyite periclase liquid anhydrous phase b periclase liquid phase g is stable at temperatures below 1000 c at 18 gpa below 1100 c at 20 22 gpa and below 1200 c at 25 gpa wadsleyite stishovite liquid are stable above 1000 c at 18 gpa ringwoodite or phase e stishovite liquid above 1100 c at 22 gpa ilmenite stishovite liquid above 1100 c at 23 5 gpa and perovskite stishovite liquid above 1200 c at 25 gpa superhydrous phase b is stable at 1200 c at 18 5 and 25 gpa in cmas pyrolite 2 wt h2o composition whereas it decomposes at around 1400 c at 25 gpa in the composition there may be a layered structure in the mantle in its water storage potential solubility of water per unit mass i e the upper and lower mantles have relatively small water storage potentials whereas the transition zone has a larger potential the water content in the transition zone might be large because the primordial water trapped in the lower mantle and the recycled water transported by the slab subduction might have been released upwards and stored in the transition zone during geological time

clay mineralogy crystallinity and k ar ages of illites within the polish zechstein basin implications for the age of kupferschiefer mineralization a discussion sir bechtel et al 1999 suggest that the formation of diagenetic illite in the kupferschiefer of the polish zechstein basin was coeval with the mineralizing event the ages estimated for the diagenetic illites are in the range of 190 to 216 ma a middle to late triassic date 240 220 ma for the high grade mineralization in the kupferschiefer was inferred from the remanent magnetization of hematite inside the rote faule zone in southwestern poland and the polar wander paths of europe and russia jowett et al 1987 in conclusions p 271 bechtel et al 1999 stated within limits of error the ages inferred for the diagenetic illites inside the mining district of the polish kupferschiefer 190 216 ma are in agreement with the date of the kupferschiefer mineralization proposed by jowett et al 1987 from paleomagnetic measurements thus paleomagnetic data were used for verification of indirect age determination of the main mineralizing event according to bechtel et

gravity models of the albuquerque basin rio grande rift new mexico as part of a hydrologic study gravity anomalies over the albuquerque basin were modeled to determine the thickness of the low density neogene basin deposits the major aquifer of the basin the models are constrained by substantial density log and well data fifteen two dimensional 2 d models include four major density units the upper unit density 2 20g cm3 corresponds to the neogene syn rifting deposits thickness of this unit averages about 1 5 km and exceeds 2 0 km in a strip along the east side of the basin the thickness is about 1 0 km between the albuquerque and the santo domingo basins at the south end of the albuquerque basin the thickness is less than 0 5 km the configuration of the remaining density units less constrained by well data raises significant questions about the history of the basin that cannot be answered with existing data

metal accumulation during and after deposition of the kupferschiefer from the sangerhausen basin germany abstract a densely sampled profile 58 cm in thickness composed of 13 samples of the kupferschiefer and overlying zechstein carbonates from the sangerhausen basin germany has been analysed by various geochemical and microscopic methods in order to clarify the mechanism of base metal accumulation in this location the kupferschiefer is only slightly influenced by the hematite bearing oxidized fluids called rote faule the determination of facies dependent parameters along the profile indicates that kupferschiefer from the sangerhausen basin was largely deposited in a marine environment only at the beginning of kupferschiefer sedimentation did euxinic conditions prevail the bottom part of the profile is significantly enriched in trace elements such as cu ph zn as co ag and u the cu concentration amounts to 19 88 wt post depositional oxidation of the organic matter is observed only in the transition zone between the kupferschiefer and the zechstein conglomerate indicating the influence of ascending oxidizing brines microscopic analyses show that only fe sulfides form framboidal textures cu minerals are present along the total profile preferentially in fractures and as patchy structures composed of chalcocite chalcopyrite and bornite in the highly mineralized bottom section cu sulfides are associated with pyrobitumen sparry calcite and arsenopyrite results from maturation studies of organic matter suggest that the maximum temperature affecting the kupferschiefer was approximately 130 c a 3 step process of metal accumulation is proposed during deposition of the sediment framboidal pyrite and pyrite precursors were precipitated by bacterial so 4 2 reduction bsr during diagenesis the pyrite and pyrite precursors were largely replaced by mixed cu fe minerals and by chalcocite pr in the section with very high cu contents 8 reduced sulfur from fe sulfides was not sufficient for precipitation of cu and other trace metals from ascending solutions in this part of the profile thermochemical so 4 2 reduction tsr occurred after pyrite replacement as indicated by the presence of pyrobitumen and sparry calcite

4 transpressional tectonics lower crust decoupling and intrusion of deep mafic sills a model for the unusual metallogenesis of sw iberia abstract sw iberia is interpreted as an accretionary magmatic belt resulting from the collision between the south portuguese zone and the autochthonous iberian terrane in variscan times 350 to 330 ma in the south portuguese zone pull apart basins were filled with a thick sequence of siliciclastic sediments and bimodal volcanic rocks that host the giant massive sulphides of the iberian pyrite belt massive sulphides precipitated in highly efficient geochemical traps where metal rich but sulphur depleted fluids of dominant basinal derivation mixed with sulphide rich modified seawater massive sulphides formed either in porous reactive volcanic rocks by sub seafloor replacement or in dark shale by replacement of mud or by exhalation within confined basins with high biogenic activity crustal thinning and magma intrusion were responsible for thermal maturation and dehydration of sedimentary rocks while magmatic fluids probably had a minor influence on the observed geochemical signatures the ossa morena zone was a coeval calc alkaline magmatic arc it was the site for unusual mineralization particularly magmatic ni cu and hydrothermal fe oxide cu au ores iocg most magmatism and mineralization took place at local extensional zones along first order strike slip faults and thrusts the source of magmas and iocg and ni cu deposits probably lay in a large mafic ultramafic layered complex intruded along a detachment at the boundary between the upper and lower crust here juvenile melts extensively interacted with low grade metamorphic rocks inducing widespread anatexis magma contamination and further exsolution of hydrothermal fluids hypersaline fluids 18 o fluid 5 4 to 12 were focused upward into thrusts and faults leading to early magnetite mineralization associated with a high temperature 500 c albite actinolite salite alteration and subsequent copper gold bearing vein mineralization at somewhat lower temperatures assimilation of sediments by magmas led in turn to the formation of immiscible sulphide and silicate melts that accumulated in the footwall of the layered igneous complex further injection of both basic and sulphide rich magmas into the upper crust led to the formation of ni cu rich breccia pipes younger 330 to 280 ma peraluminous granitoids probably reflect the slow ascent of relatively dry and viscous magmas formed by contact anatexis these granitoids have w sn and pb zn related mineralization that also shows geochemical evidence of major mantle crust interaction late epithermal hg cu sb and pb zn ag mineralization was driven by convective hydrothermal cells resulting from the high geothermal gradients that were set up in the zone by intrusion of the layered igneous complex in all cases most of the sulphur seems to have been derived from leaching of the host sedimentary rocks 34 s 7 to 20 with only limited mixing with sulphur of magmatic derivation the metallogenic characteristics of the two terranes are quite different in the ossa morena zone juvenile magmatism played a major role as the source of metals and controlled the styles of mineralization in the south portuguese zone magmas only acted as heat sources but seem to have had no major influence as sources of metals and fluids which are dominated by crustal signatures most of the magmatic and tectonic features related to the variscan subduction and collision seem to be masked by those resulting from transpressional deformation and deep mafic intrusion which led to the development of a metallogenic belt with little resemblance to other accretionary magmatic arcs

1 subduction slab detachment and mineralization the neogene in the apuseni mountains and carpathians abstract the inner carpathians comprise several distinct neogene late stage orogenic pb zn cu ag au ore districts the mineral deposits in these districts are closely related to volcanic and subvolcanic rocks and represent mainly porphyry and epithermal vein deposits which formed within short periods of time in each district here we discuss possible geodynamic and structural controls that suggest why some of the neogene volcanic districts within the carpathians comprise abundant mineralization while others are barren the neogene period has been characterized by an overall geodynamic regime of subduction where primary roll back of the subducted slab and secondary phenomena like slab break off and the development of slab windows could have contributed to the evolution location and type of volcanic activity structural features developing in the overlying lithosphere and visible in the carpathian crust such as transtensional wrench corridors block rotation and relay structures due to extrusion tectonics have probably acted in focusing hydrothermal activity as a result of particular events in the geodynamic evolution and the development of specific structural features mineralization formed during fluid channelling within transtensional wrench settings and during periods of extension related to block rotation in the slovakian ore district of the western carpathians neogene volcanism and associated mineralization were localized by sinistral ne trending wrench corridors which formed part of the extruding alcapa block the baia mare ore district in the eastern carpathians reflects a transtensional wrench setting on distributed oversteps close to the termination of the dragos voda fault there mineralization was spatially controlled by the transtensional dragos voda master fault and associated cross fault systems the golden quadrangle cu au ore district of the southern apuseni mountains reflects an unusual rotated transtensional extensional setting close to the termination of a graben system there fluid flow was probably localized by fault propagation at the inner tip of the graben system the spatial and temporal evolution of the magmatism and its changing geochemical signature from n w to s e strongly suggests a link with the contemporaneous northeastward roll back of the subducted slab and a progressive southeastward detachment during accelerating roll back this geodynamic evolution is further supported by the present day overall and detailed mantle lithospheric density images the present day heat flow patterns the crustal architecture and its interpreted evolution and the spatial and temporal evolution of depocentres around the carpathian arc in contrast to all these features the mineral deposits in the west carpathians east carpathians and apuseni mountains are too synchronous with respect to their individual volcanic history and contrast too much with younger volcanics of similar style but barren in southeastern parts of the carpathians to simply link them directly to the slab evolution in all three districts the presence of magmatic fluids released from shallow plutons and their mixing with meteoric water were critical for mineralization requiring transtensional or extensional local regimes at the time of mineralization possibly following initial compressional regimes these three systems show that mineralization was probably controlled by the superposition of favourable mantle lithospheric conditions and partly independent evolving upper crustal deformation conditions in the 13 to 11 ma period the dominant mineralization formed all across the carpathians and was superimposed on structurally favourable crustal areas with at that time volcanic hydrothermal activity the period may reflect the moment when the upper part of the crust failed under lithospheric extension imposed by the slab evolution this crustal failure would have fragmented the overriding plate possibly breaking up the thermal lid to provoke intensive fluid flow in specific areas and allowed subsequent accelerated tectonic development block rotation and extrusion of a family of sub blocks that are arbitrarily regarded as the tisia dacia or alcapa blocks even though they have lost their internal entity

geochemistry of the kupferschiefer poland cu pb and zn are the main metals occurring in sulfides in the kupferschiefer they are arranged in the three distinct zones around rote faule in the order cu pb and zn copper zones are enriched in transition metals i e ag ni co v and mo ranging from 600 to 1500 ppm they are concentrated especially in the bottom part of black shale re is associated with mo the re mo ratio in cu pb and k castaingites is about 1 70 in copper zones near the contact with lead zones au platinum group metals pgm and u are concentrated ranging from traces to several hundred ppm the main mechanism of concentration of transition metals was catalytic autooxidation and dehydrogenation of organic matter the noble metals form either independent minerals or are present in organic matter and thucholite in the lead zones at the contact with cu zones an increased content of ag 100 1500 and hg 5 800 ppm is present the average hg content for the black shale of the zone is 61 ppm a natural gas exploited from the rotliegendes beneath the kupferschiefer carries in aerosols significant amount of pb cu mn fe ag and hg this suggests the rotliegendes as a pathway or as a source of metals for the kupferschiefer the presence of k castaingite intergrown with silvinite kcl may suggest k dominated brines as the mineralizing fluids

early cretaceous mineralizing activity in the st andreasberg ore district southwest harz federal republic of germany in the st andreasberg ore district southwest harz at some time between the main and subsequent stages of mineralization sensu wilke 1952 potassium feldspar adularia was formed hydrothermally based on isotopic dating rb sr 40ar 39ar the formation of this mineral is ascribed to the early cretaceous thus part of the st andreasberg mineralization is proved to have been formed in the late mesozoic the mineralization process forming feldspar does not coincide with magmatic phases of the area

water transport into the deep mantle and formation of a hydrous transition zone abstract the phase relations in the peridotite water system to the top of the lower mantle reveal that a certain amount of water can be transported and stored in the transition zone by various hydrous minerals resulting in formation of a hydrous transition zone results of preliminary experiments to clarify the effect of water on kinetics of the olivine wadsleyite transformation are given and show that water enhances the transformation kinetics significantly there are potential dehydration sites in the deep mantle four sites along the descending slabs depending on their temperature profiles i e the mantle wedge of the subduction zone mantle transition zone top of the lower mantle where hydrous ringwoodite and superhydrous phase b decompose and deep in the lower mantle around 1200 1500 km depth where decomposition of phase d g occurs we also expect one site of dehydration melting at the base of the upper mantle where the hot mantle plume hydrated in the transition zone can be dehydrated the transition zone can serve as a water absorber for the mantle scale water circulation system some of the recent seismic works including the p wave tomography images reveal the existence of low velocity anomalies in the transition zone suggesting possibly a wet transition zone elevation of the 410 km discontinuity and lack of clear evidence for a metastable olivine wedge in cold slabs may be consistent with the equilibrium phase transformation from olivine to wadsleyite in cold and wet slabs on the basis of our kinetic study of the transformation under wet conditions

mid mantle anisotropy in subduction zones and deep water transport the earth s transition zone has until recently been assumed to be seismically isotropic increasingly however evidence suggests that ordering of material over seismic wavelengths occurs there but it is unclear what causes this we use the method of source side shear wave splitting to examine the anisotropy surrounding earthquakes deeper than 200 km in slabs around the globe we find significant amounts of splitting 2 4 s confirming that the transition zone is anisotropic here however there is no decrease in the amount of splitting with depth as would be the case for a metastable tongue of olivine which thins with depth suggesting this is not the cause the amount of splitting does not appear to be consistent with processes in the ambient mantle such as lattice preferred orientation development in wadsleyite ringwoodite or mgsio3 perovskite we invert for the orientation of several mechanisms subject to uncertainties in mineralogy and deformation and the best fit is given by updip flattening in a style of anisotropy common to hydrous phases and layered inclusions we suggest that highly anisotropic hydrous phases or hydrated layering is a likely cause of anisotropy within the slab implying significant water transport from the surface down to at least 660 km depth

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

the composition of brines in the early diagenetic mineralization of the permian kupferschiefer in germany the kupferschiefer is an approximately 0 5 m thick black marly shale of lower zechstein age in germany if one includes some of its footwall and hanging wall it contains 300 mt cu 800 mt zn and 300 mt pb the regional pattern of metal distribution demonstrates its relationship to variscan and permian tectonic structures faults and the topographic relief of the basement apparently controlled the uprise and lateral migration of reducing and slightly acid hot brines from deeper crustal levels to supply the metals for the mineralization of the proto kupferschiefer deep fluids are mainly richer in zn than pb and richer in pb than cu mixing of such slightly acid fluids with slightly alkaline formation waters seawater caused a gradient in ph from about three to eight and in sulfide concentration most of the sulfide came from dissolved pyrite which was very light in sulfur isotopes this gradient controlled the sequential precipitation of bornite chalcopyrite chalcocite galena and sphalerite which is observed in a lateral and vertical zoning of these sulfides the fluids experienced a fractionation of the metals during migration over meter to kilometer distances from the tectonically controlled vents within the unconsolidated proto kupferschiefer close to the vents the sulfide deposits attained concentrations up to 2 zn pb cu the migration of the metals over large distances took place in unconsolidated sediment thus the major mineralization of the kupferschiefer has to be classed as an early diagenetic process

the role of organically bound sulphur in stratiform ore sulphide deposits abstract low and high molecular weight organic sulphur compounds were analyzed in a selected number of samples of the permian kupferschiefer poland their significant presence in these mature samples supports the hypothesis that during deposition and shortly thereafter labile organic sulphur compounds must have been very abundant this assumption has led to a new model for metal accumulation based on a slow and gradual release of sulphur from these labile organic sulphur compounds during increasing diagenesis

seismic low velocity layer at the top of subducting slabs observations predictions and systematics abstract layered structure persists at the tops of subducting plates to depths in excess of 150 km a low velocity channel several km thick produces guided seismic guided waves which indicate that the top of the downgoing plate remains coherent and probably has not eclogitized to 150 km depth the surrounding medium has seismic velocities 3 6 faster than standard earth models as inferred from direct travel times presumably because the waveguide lies atop cold descending lithosphere however guided waves travel more slowly several tests with full waveform synthetics show that the guided waves can be observed only if excited by sources that lie near or within the low velocity channel thus the frequent observation of dispersed body waves indicates that intermediate depth earthquakes tend to lie in waveguides also receivers must be favorably placed observations for seven circum pacific subduction zones show such signals which can be explained as low velocity channels 2 8 km thick velocity anomalies within low velocity channels are largest at shallowest depths up to 14 slower than surroundings at depths less than 150 km diminishing to

provenance of cretaceous clastics in the subhercynian basin constraints to exhumation of the harz mountains and timing of inversion tectonics in central europe the harz mountains and the adjacent subhercynian cretaceous basin figure as the most prominent surface representative for late cretaceous inversion structures in central europe facies depositional architecture and provenance of the basin fill reflect mechanisms and timing of the exhumation of the harz from hauterivian to early santonian there is no evidence for detrital input from the nearby harz area sediments are mature quartzarenites derived from paleozoic basement rocks and or recycled permian to mesozoic sedimentary rocks this situation changed drastically in middle to late santonian when freshly exhumed and eroded mesozoic sedimentary cover rocks of the harz were delivered into the basin feldspar and lithoclasts reflect erosion of triassic and in places jurassic to turonian strata apatite and garnet in heavy mineral spectra are derived from largely unweathered lower triassic buntsandstein as indicated by apatite and garnet chemistry in early campanian paleozoic lithoclasts indicate erosion cutting down into the basement of the harz simultaneous strong decrease of feldspar garnet and apatite suggest an almost complete removal of the 2 3 km thick mesozoic cover of the harz within only 2 4 myr this translates into an exhumation rate of approximately 1 mm a consistent with apatite fission track data from granitoid rocks of the harz mountains

stability of hydrous magnesium silicates in the mantle transition zone phase relations in the mg oh 2 sio2 system have been studied up to 18 gpa a new hydrous phase phase e mg2 3si1 3h2 4o6 was encountered at 13 17 gpa and 1000 c phase f mg1 2si1 8h2 4o6 another new hydrous phase was observed at 15 5 gpa and 800 c the stability field of phase a was also briefly studied these new hydrous phases might be stabilized in the mantle transition zone especially in subducting slabs at those depths

late paleoproterozoic to early mesoproterozoic tangdan sedimentary rock hosted strata bound copper deposit yunnan province southwest china sedimentary rock hosted strata bound copper deposits are widespread in the kangdian region of the central yunnan and southern sichuan provinces southwest china the deposits occur within weakly metamorphosed rocks of the late paleoproterozoic to early mesoproterozoic dongchuan group and are spatially associated with discordant breccia bodies that are interpreted as having formed from salt diapirs the tangdan deposit the largest in the region consists of stratiform and discordant orebodies predominantly hosted in dolostones immediately above hematitic sandstones and siltstones and in black shales above the dolostones host rocks for the deposit display a complex paragenetic sequence of alteration and mineralization early sodic alteration resulted in the growth of both albite and ferroan dolomite later potassic alteration resulted in the precipitation of potassium feldspar and locally biotite in argillaceous layers sulfide mineralization was temporally and spatially associated with silicification that postdated both sodic and potassic alteration textures suggest that silicification may have preferentially affected evaporite minerals in the dolostones copper sulfides form bedding parallel disseminations veinlets and to a lesser extent stockworks copper sulfides are dominated by chalcopyrite with lesser bornite and chalcocite hypogene chalcopyrite and bornite from the tangdan deposit have 34s values that range from 12 7 to 9 3 and cluster between 3 to 5 the values suggest derivation from mesoproterozoic marine sulfates the dolostone host rocks have relatively homogeneous c and o isotope values ranging from 0 2 to 1 3 13cv pdb and from 19 1 to 22 4 18ov snow carbonate minerals in quartz sulfide veins display both a trend toward lighter oxygen isotope values and a trend to significantly lighter carbon isotope values the light carbon isotope values suggest involvement of organic carbon in the mineralizing process alteration and mineralization at tangdan probably occurred via interaction of oxidized saline brines derived from the underlying red bed sequence with partially to wholly lithified dolostones sulfide precipitation was likely due to both redox reactions and mineralizing fluid ph changes resulting from dolomite and sulfate dissolution the styles of alteration and mineralization at the tangdan deposit are similar to those observed in the central african copperbelt particularly the dolostone hosted orebodies in the mines series of the democratic republic of congo

shear wave anisotropy in textured phase d and constraints on deep water recycling in subduction zones abstract regions of low seismic velocity and high shear anisotropies in cold subducted slabs have often been related to anisotropic fabrics in hydrous phases mainly induced by slab deformation the interpretation of these seismic anomalies in terms of hydration thus relies on a better knowledge of the elasticity and plastic deformation mechanisms of candidate hydrous phases here we investigate the development of lattice preferred orientations lpo in phase d mgsi 2 h 2 o 6 10 18 wt h 2 o the ultimate water carrier in hydrous subducted peridotite the samples were deformed non hydrostatically up to 48 gpa in a diamond anvil cell and the texture and strength were obtained from analysis of the x ray diffraction patterns collected in radial diffraction geometry we find that at low strains the layered structure of phase d displays strong 0001 texture where the stacking fault axis c axis preferentially align parallel to the compression axis a subsidiary 1 0 1 0 texture develops at higher strains plasticity simulations in polycrystalline aggregates using a viscoplastic self consistent model suggest that these lpo patterns are consistent with shape preferred orientation mechanism during the first compaction steps and with dominant easy glide on basal planes and harder first order pyramidal slip respectively upon further compression we find that phase d displays the lowest strength and the highest anisotropy among phases in hydrous peridotite in the uppermost lower mantle and might thus control the shear wave anisotropy generated in subducted slabs below the transition zone we further evaluate the effect of textured phase d on the seismic velocity structure and shear wave anisotropy of deformed hydrous peridotite and compare the results to seismic observations in tonga subduction we show that 16 vol of phase d in hydrous subducted peridotite is required to explain the negative velocity anomalies of 3 the extent of shear wave splitting 0 9 0 3 and the shear wave ray polarization geometry v sh v sv observed in a detached fragment of the tonga slab laying sub horizontally below the transition zone seismic observations may thus place constraints on the degree of hydration of the tonga slab beyond the transition zone leading to the requirement that a minimum of 1 2 wt h 2 o is retained in the slab by hydrous peridotite below 670 km depth

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

the kupferschiefer cu ag ore deposits in poland a re appraisal of the evidence of their origin and presentation of a new genetic model the kupferschiefer stratiform copper deposits in central europe have long been considered a classic example of syngenetic mineralization however metal zoning and host rock relationships determined during exploration around the recently discovered lubin district orebodies in southwest poland suggest that the ore may instead be late diagenetic the mineralization occurs as thin extensive blankets of sulphides in the pyritic organic rich basal units of the late permian zechstein restricted marine sequence and in the eolian weissliegendes sandstone at the top of the early permian rotliegendes continental rift sequence of bimodal volcanic rocks and redbeds it is directly underlain and controlled by irregular oval zones of rote faule rf a barren oxidized and reddened portion of the normally dark grey pyritic basal zechstein rocks in plan view the metals occur as successive belts enriched in copper silver lead and zinc which developed laterally from and encircle the rf zones the ore transgres

clausthalite pbse and tiemannite hgse from the type locality new observations and implications for metallogenesis in the harz mountains germany abstract clausthalite and tiemannite from the type locality clausthal in the harz mountains germany have virtually gone undocumented since their discovery in the nineteenth century the minerals and their selenide assemblages are here documented in historical samples from the konigin charlotte mine in the former clausthal pb zn ag mining district clausthalite and tiemannite are the main selenide components naumannite is generally subordinate whereas klockmannite and eskebornite are accessory minerals the absence of inversion lamellae in naumannite constrains the formation temperature to 87 sr 86 sr values of 0 70914 and 0 71133 for two samples of tiemannite aggregates containing celestine anhydrite inclusions the clausthal selenide assemblages postdated the main sulfide bearing polymetallic vein style mineralisation of the harz mountains

evidence from rayleigh wave data for magma in an upper crustal dike in the albuquerque belen basin of the rio grande rift new mexico we have found evidence for a dikelike structure in the middle of the albuquerque belen basin of the rio grande rift from our interpretation of two station rayleigh wave amplitude and phase velocity data two dimensional finite element modeling suggests that the structure is about 200 m thick extends vertically from a depth of about 2 1 2 km to at least 20 km and contains material characterized by a shear wave velocity of about 1 2 km s simple physical arguments suggest that the length of the structure may be at least 28 km long nearby high heat flow values historical swarmlike seismicity recent 0 14 ma volcanism and an extensive sill like magma body at midcrustal depths all suggest that the structure is a magma filled dike source characteristics and seismometer response limit our reliable data to the frequency band of 0 08 hz to 0 250 hz thus we cannot tell whether the dike is solely an upper crustal feature or whether it extends through the crust and in to the upper mantle copyright american geophysical union 1987

predicted elastic properties of the hydrous d phase at mantle pressures implications for the anisotropy of subducted slabs near 670 km discontinuity and in the lower mantle the dense hydrous magnesium silicate called the d phase is the most likely candidate to recycle hydrogen into the lower mantle in subduction zones as seismology represents the preferred method to detect this mineral in subduction zones the single crystal elastic tensor has been calculated using first principle methods a triple cell p3 m1 was used to account for an ordered ideal composition of the d phase to lower mantle pressures the elastic tensor of the mineral at ambient conditions is predicted to be c11 387 7 c33 287 7 c44 100 4 c12 108 0 c13 51 1 c14 14 6 in gpa with bulk modulus at zero pressure ko 163 gpa and a statistical error of about 4 0 gpa for all constants the pressure derivatives of the elastic constants have been determined to pressure of 80 gpa our tensor correctly predicts the published experimental measurements of linear compressibility along the a and c axes the logarithmic pressure derivative of the c a axial ratio and bulk modulus at zero pressure it contradicts the experimentally measured elastic tensor reported by liu l g okamoto k yang y j chen c c lin c c 2004 elasticity of single crystal phase d a dense hydrous magnesium silicate by brillouin spectroscopy solid state commun 132 517 520 which fails to reproduce the experimental compressibility data using the elastic constants and density predicted to 85 gpa the seismic anisotropy of p and s waves has been calculated as a function of pressure the single crystal has high p wave velocities and shear wave splitting in the basal plane below 20 gpa at high pressures the maximum p wave velocities have threefold symmetry normal to a axes in the basal plane whereas the maximum shear wave splitting is parallel to a axes with twofold symmetry the d phase has high vp and vs anisotropy at ambient pressure 17 6 for vp and 19 9 for vs the vp anisotropy decreases with increasing pressure to about 30 gpa while it remains constant at 8 from 30 to 85 gpa the vs anisotropy decreases to 17 at 20 gpa and then increases to 22 at 85 gpa the isotropic velocity ratios of s to p rs p bulk sound to s r s and density to s r s are calculated as a function of pressure the rs p shows very little variation with pressure with low value of 0 6 whereas both r s and r s increase with pressure to peak values of 2 8 and 2 0 respectively at about 60 gpa the presence of the d phase in subducted horizontal stagnant plates in the circum pacific could contribute to a number of seismic observations such as the observed velocity heterogeneity at depths between 500 and 1000 km and the fast s waves travelling horizontally with horizontal polarization in this depth range further the lower density of the d phase compared with

elasticity of superhydrous phase b seismic anomalies in cold slabs and implications for deep water transport abstract seismic anomalies in the vicinity of cold slabs including low velocity zones and enhanced seismic shear wave splitting have been commonly attributed to the presence of hydrated slab material the dense hydrous magnesium silicate dhms superhydrous phase b shyb mg 10 si 3 h 4 o 18 is considered an important water carrier to transition zone depth due to its large pressure stability and abundance up to 20 vol in hydrous peridotites to interpret the observed seismic anomalies in terms of hydration and to assess the role of shyb in deep water recycling we have investigated the sound velocities and single crystal elasticity of shyb to pressures of 17 5 gpa at ambient temperature by brillouin scattering spectroscopy in diamond anvil cells the voigt reuss hill averages for the adiabatic bulk moduli k s shear moduli and their pressure derivatives yield k s 150 2 gpa 99 1 gpa k s p 4 7 2 and p 1 44 5 the aggregate compressional and shear wave velocities of shyb at transition zone pressures are comparable to those of hydrous iron bearing ringwoodite but are significantly lower than anhydrous phases in peridotites the calculated velocity contrast between dry and shyb bearing hydrous peridotite containing 1 2 wt of water indicate that 17 vol of shyb decreases both compressional v p and shear v s wave velocities by at most 2 5 at transition zone depths our results combined with data for the deformation mechanisms of shyb indicate that shyb aggregates develop strong textures under down dip compression regime and yield a maximum shear wave splitting of 1 1 in the plane perpendicular to the compression axis at 17 5 gpa although shyb in hydrous subducted peridotite would reduce its seismic velocities the splitting geometry v sv v sh generated by shyb fabrics in peridotite is incompatible with the pattern observed in tonga and sangihe and would require the contribution of other phases to be explained textured phase d is a plausible candidate to explain the shear wave splitting in the lower transition zone while at intermediate transition zone depths the coexistence of textured phase d and shyb in hydrous deformed peridotite would generate the observed array polarization however the later scenario will require locally very high water concentrations at depth

a mid triassic paleomagnetic age of the kupferschiefer mineralization in poland based on a revised apparent polar wander path for europe and russia extensive mineralization occurs in southwest poland as zoned blankets of cu ag pb zn sulphides in the kupferschiefer and zechstein limestone across the base of the late permian zechstein restricted marine sequence and in the weissliegendes sandstone at the top of the early permian rotliegendes continental volcanic and siliciclastic sequence the rote faule rf zone an oxidized hematitic equivalent of the normally pyritic basal zechstein directly underlies the copper ore and is part of the metal zoning although the origin has generally been considered to be syngenetic geologic controls of the rf ore systems in poland suggest a late diagenetic origin by converting metalliferous brines migrating through the rotliegendes clastic redbeds up along basement highs oxidizing the pyritic kupferschiefer to form the rf and precipitating base and precious metals on the reduced side of this oxidation reduction front a paleomagnetic study of the ore zone in five mines in poland the rf zone in three mines and of the barren pyritic basal zechstein from outcrops and quarries in poland germany and england was undertaken to determine the absolute age of the mineralization in the barren pyritic rocks and the copper sulphide ore thermal demagnetization and vector subtraction revealed an unstable low temperature first remanence component 76 9 n 12 2 e a63 1 6 parallel to the ambient field and a second higher temperature component 82 6 n 145 9 e a63 1 9 which could be miocene 10 20 ma or less likely cretaceous 110 ma or jurassic 180 ma this second component is erased at 350 400 c and is thought to be carried by a product of weathering after alpine age uplift and erosion no primary magnetization could be isolated in the copper or pyritic zones the rf hematite however contained a very stable third reversed component 49 0 n 157 2 e a63 2 2 which was revealed typically between 500 and 620 c and is considered to represent a secondary chemical remanent magnetization acquired during the mineralizing process in order to date the isolated magnetic components carboniferous to neogene apparent polar wander apw paths for europe and russia were constructed using paleopole catalogs mean paleopoles every 10 ma from 350 to 0 ma with a63 circles of confidence were calculated as running averages using overlapping 20 and 30 ma time intervals the rf pole corresponding to the third remanence component coincides extremely well with a middle triassic age of 240 ma on the 20 ma apw path and a late triassic age of 230 ma on the 30 ma apw path statistical analysis yields upper and lower age limits of 250 and 220 ma this triassic paleomagnetic age supports the proposed late diagenetic origin of the kupferschiefer ore deposits and suggests that the rf ore systems were formed immediately after triassic continental rifting associated with the opening of the tethys ocean to the south a likely source of the thermal anomaly necessary to initiate adequate convective velocities within the rotliegendes clastic basins

elasticity of single crystal superhydrous phase b at simultaneous high pressure temperature conditions we investigated the combined effect of pressure and temperature on the elasticity of single crystal superhydrous phase b shy b using brillouin scattering and x ray diffraction up to 12 gpa and 700 k using the obtained elasticity we modeled the anisotropy of shy b along slab geotherms showing that shy b has a low anisotropy and cannot be the major cause of the observed anisotropy in the region modeled velocities of shy b show that shy b will be shown as positive velocity anomalies at the bottom transition zone once shy b is transported to the topmost lower mantle it will exhibit a seismic signature of lower velocities than topmost lower mantle we speculate that an accumulation of hydrous phases such as shy b at the topmost lower mantle with a weight percentage of 17 26 in the peridotite layer as subduction progresses could help explain the observed 2 3 low shear velocity anomalies in the region

single crystal equation of state of phase d to lower mantle pressures and the effect of hydration on the buoyancy of deep subducted slabs 1 an understanding of the physical properties of the hydrous magnesium silicate phase d is important for the interpretation of the seismic anomalies observed in subducted slabs and to evaluate the effect of hydration on slab dynamics here we report the equation of state of phase d mg1 1si1 8h2 5o6 up to 65 gpa obtained from high precision single crystal x ray diffraction a single crystal of phase d was loaded in a diamond anvil cell using helium as pressure transmitting medium to ensure quasi hydrostatic conditions during the entire data collection the volume of phase d decreases smoothly over the entire pressure range without the anomalies in the compressibility reported at 40 gpa in previous powder diffraction studies if existing in phase d a hydrogen bond symmetrization transition as predicted by first principles calculation is therefore not associated with anomalies in the volume compression behavior the isothermal bulk modulus kt and its pressure derivative k t obtained from the fitting of the unit cell volumes using a third order birch murnaghan equation of state are kt 151 4 1 2 gpa and k t 4 89 0 08 respectively this bulk modulus is in good agreement with a recent single crystal brillouin scattering experiment the presence of 16 vol of phase d in hydrous peridotite lithologies reduces the density by up to 2 6 at upper most lower mantle pressure temperature conditions 1273 k and 30 gpa phase d is thus a potential candidate to influence the buoyancy of hydrated stagnant slabs below the transition zone

seismic anisotropy in the mantle transition zone beneath fiji tonga 1 we demonstrate a rare unequivocal case of anisotropy in the transition zone tz evident from many horizontal polarized shear waves sh that arrive up to 3 s earlier than vertical polarized shear waves sv the anisotropic region correlates with deep earthquakes away from the active subduction zone and known boundaries of lateral heterogeneities in compression and shear wave speeds we interpret the anisotropy as strong fabric associated with a large petrologic anomaly in the core of remnant lithosphere which is buoyant and stagnates in the tz fast subduction of cold slab actually favors such a configuration so slab penetration into the lower mantle does not uniformly occur

the chemical composition of specular hematite from tilkerode harz germany implications for the genesis of hydrothermal hematite and comparison with the quadrilatero ferrifero of minas gerais brazil the black shale hosted selenide vein type deposit at tilkerode eastern harz germany has specular hematite enclosed in clausthalite pbse the specular hematite has ti and v in amounts of up to 1 wt tio2 and 3 wt v2o5 and subordinate but important contents of mo 22 372 ppm and b up to 68 ppm the tilkerode hematite serves as a reference for hydrothermal hematite formed at relatively low temperatures 150 c the composition of the tilkerode hematite is compared with that of two generations of specular hematite from itabirite hosted iron ore deposits in the quadrilatero ferrifero of minas gerais brazil the first generation of specular hematite represents an early tectonic hematitisation of dolomitic itabirite at aguas claras and occurs as fine grained crystals reconnaissance data indicate that the aguas claras hematite is poorer in ti and v relative to the tilkerode hematite but has 5 10 ppm b and 7 11 ppm li the second generation of specular hematite defines the pervasive tectonic foliation of the gongo soco iron ore this hematite has ti contents of up to 2 wt tio2 and subordinate amounts of v 62 367 ppm its b and li concentrations are mostly below 2 ppm b and 1 ppm li the presence of ti and b in the tilkerode hematite can be explained by highly saline b bearing fluids that were capable of mobilising otherwise immobile ti the mo signature of the tilkerode hematite suggests that mo was derived from the host black shale in minas gerais b and li were incorporated into the early tectonic hematite from saline fluids at relatively low temperatures aguas claras and then released during metamorphic hematite growth at higher temperatures as suggested by the foliation defining hematite without b li signature gongo soco

global time scale and regional stratigraphic reference scales of central and west europe east europe tethys south china and north america as used in the devonian carboniferous permian correlation chart 2003 dcp 2003 the boundaries of the devonian carboniferous and permian stages of the global stratigraphic reference scale abbreviated to global stratigraphic scale gss are described in relation to the biostratigraphic and or lithostratigraphic units of the regional stratigraphic reference scales abbreviated to regional stratigraphic scales rss of central and west europe east europe tethys south china eastern tethys and north america in their type regions the boundaries of gss units rarely coincide with those of homonymous rss units moreover the definitions of some rss units have changed several times over the last decades and subsequent misunderstanding of the stratigraphical significance of these changes has often introduced errors into proposed global correlation charts the stratigraphic framework proposed in our global devonian carboniferous permian correlation chart 2003 dcp 2003 devonian carboniferous permian correlation chart 2003 menning m schneider j w alekseev a s amon e o becker g von bitter p h boardman d r bogoslovskaya m braun a brocke r chernykh v chuvashov b i clayton g dusar m davydov v i dybova jachowicz s forke h c gibling m gilmour e h goretzki j grunt t a hance l heckel p h izokh n g jansen u jin y g jones p kading k ch kerp h kiersnowski h klets a klug ch korn d kossovaya o kotlyar g v kozur h w laveine j p martens th nemyrovska t l nigmadganov a l paech h j peryt t m rohn r roscher m rubidge b schiappa t a schindler e skompski s ueno k utting j vdovenko m v villa e voigt s wahlman g p wardlaw b r warrington g weddige k werneburg r weyer d wilde v winkler prins c f work d m 2004 abschlusskolloquium dfg schwerpunktprogramm 1054 evolution des systems erde wahrend des jungeren palaozoikums im spiegel der sedimentgeochemie abstracts univ erlangen germany 2004 p 43 herein abbreviated to dcp 2003 and cited as dcp 2003 in references is an attempt to reduce these errors the dcp 2003 is the stratigraphic base for project 1054 of the deutsche forschungsgemeinschaft dfg the evolution of the late palaeozoic in the light of sedimentary geochemistry this composite time scale has been carefully balanced as far as data allows to remove unnecessary artificial compression and expansion of time intervals biozonations and depositional events the ages selected in dcp 2003 are markedly different to those in the geologic time scale 1989 gts 1989 harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge harland w b armstrong r l cox a v craig l e smith a g smith d g 1990 a geologic time scale 1989 cambridge univ press cambridge pp 1 263 and in gradstein and ogg gradstein f m ogg j 1996 a phanerozoic time scale episodes 19 1 2 3 4 insert whereas they are closer to those of the geologic time scale 2004 gts 2004 gradstein f m ogg j g smith a g 2004 a geologic time scale 2004 cambridge univ press cambridge pp 1 589 mostly the ages are rounded to the nearest 0 5 ma in order to avoid estimates of questionable accuracy whereas ages of 0 1 ma in the gts 2004 and their error bars of 0 4 ma to 2 8 ma for the devonian to permian stage boundaries suggest an improved accuracy in contrast in the dcp 2003 questionable ages and positions of stratigraphic boundaries are marked by arrows c 2006 elsevier b v all rights reserved

reconstructions of the continents around the north atlantic at about the 60th parallel abstract late carboniferous early tertiary apparent polar wander apw paths 300 40 ma for north america and europe have been tested in various reconstructions these paths demonstrate that the 500 fathom bullard et al fit is excellent from late carboniferous to late triassic times but the continental configuration in northern pangea changed systematically between the late triassic ca 214 ma and the mid jurassic ca 170 ma due to pre drift extension best fit north atlantic reconstructions minimize differences in the late carboniferous early jurassic and late cretaceous tertiary segments of the apw paths but an enigmatic difference exists in the paths for most of the jurassic whereas for the early cretaceous the data from europe are nearly non existent greenland s position is problematic in a bullard et al fit because of a late triassic early jurassic regime of compression 300 km that would be inherently required for the norwegian shelf and the barents sea but which is geologically not defensible we suggest a radically new fit for greenland in between europe and north america in the early mesozoic this fit keeps greenland locked to europe for the late paleozoic early mesozoic and maintains a reconstruction that better complies with the offshore geological history of the norwegian shelf and the barents sea pre drift a24 extension amounted to approximately 450 km on the mid norwegian shelf but with peak extension in the late cretaceous

two brine model of the genesis of strata bound zechstein deposits kupferschiefer type poland these kupferschiefer deposits were probably formed as a result of a mixing of two brines the upper cold brine ucb is an unmineralized brine rich in na ca cl and so4 with a ph 7 and originating from evaporites overlying the metal bearing zechstein rocks the lower hot brine lhb rich in mg k cl so4 and co3 with a ph 7 formed in sediments in the central part of the zechstein basin at a depth of 7 000 m this brine was subjected to heating and upward convection toward the fore sudetic monocline along the bottom of the z1 carbonates during its migration it caused albitization serpentinization and leaching of the primary metal deposits in rocks underlying the zechstein becoming enriched in heavy metals the mineralization process being a result of the mixing of the two brines ucb and lhb and catalytic oxidation of the organic matter of the black shale were initiated at shallow depths in the area of the fore sudetic monocline the boundary of the two brines generally overlapped the strike of the black shale

elasticity of phase d and implication for the degree of hydration of deep subducted slabs 1 seismic anomalies in subducted slabs including low velocity zones and shear wave splitting have often been related to hydrous regions phase d mgsi2h2o6 10 18 wt h2o may be the ultimate water carrier in hydrous subducted peridotite and its seismic properties are thus essential for interpreting observed anomalies in terms of hydration here we report the sound velocities and elasticity of mg and al fe bearing phase d single crystals measured by brillouin spectroscopy the room conditions adiabatic bulk and shear modulus are ks0 154 8 3 2 gpa and 104 3 2 1 gpa for mg phase d and ks0 158 4 3 9 gpa and 104 7 2 7 gpa for alfe phase d suggesting minor effect of cation substitution on the elasticity of phase d based on the seismic velocity data we found that 16 vol of alfe phase d in hydrous subducted peridotite with 1 2 wt h2o could provide a plausible explanation for the negative velocity anomalies of 3 observed in fragments of the tonga slab below the transition zone

a multistage origin for kupferschiefer mineralization new re os age determinations on mineralized material from the polish kupferschiefer elucidate the timing of mineralization and thus the likely mechanisms of ore deposition three mineralization parageneses were analysed a chalcocite as pore space filling in sandstone b disseminated cu mo mineralization in shale and c massive bedded copper sulphides the resulting ages fall into two ranges 245 2 1 6 264 7 1 8 ma and 162 3 0 8 184 3 2 2 ma these results substantiate previous age determinations although no upper triassic ages were found in this study some of the younger ages for the mineralization could represent alteration and recrystallization of existing sulphides the results confirm that mineralization took place in several stages from soon after kupferschiefer sediment deposition in the upper permian and for at least 100 m y after until at least the cretaceous the genesis of the mineralization can be explained by the episodic release of hydrothermal fluids from the subsiding adjacent southern permian sedimentary basin although the relative importance of each successive mineralizing event for introducing additional metals is as yet unknown

lead isotope systematics of vein type antimony mineralization rheinisches schiefergebirge germany a case history of complex reaction and remobilization processes mesothermal vein type sb mineralization in the rheinisches schiefergebirge germany is characterized by two different mineralization styles which are 1 extensional quartz stibnite vein systems and 2 cu pb sb sulphosalt assemblages in overprinted pre existing pb zn veins a detailed pb isotope study of 52 representative samples from both mineralization types indicates distinct compositional patterns cu pb sb sulphosalts meneghinite boulangerite bournonite formed by reaction remobilization are characterized by pb isotope compositions 206pb 204pb 18 179 18 223 which are identical to the precursor galena 206pb 204pb 18 168 18 223 the pb isotope composition of sulphosalt minerals in these vein systems was controlled by lead inherited from pre existing galena stibnite and pb sulphosalts zinkenite semseyite plagionite formed in quartz stibnite vein systems display pb isotope ratios 206pb 204pb 18 250 18 354 which are more radiogenic than galenas from variscan pb zn ore veins 206pb 204pb 18 162 18 303 detailed small scale investigation of thrust zones hosting pb zn ores and crosscutting quartz ankerite fissure veins ramsbeck deposit indicates that the pb isotope compositions of recrystallized galena and remobilized phases boulangerite semseyite bournonite are arranged along a linear trend this is interpreted as mixing between primary galena with 206pb 204pb 18 206 and overprinting hydrothermal fluids with a more radiogenic composition 206pb 204pb 18 354 expressed by intermediate compositions 206pb 204pb 18 256 18 334 of newly formed sulphosalts the pb isotope systematics of the vein type sb mineralization is in accordance with a model of pb extraction from similar crustal sources palaeozoic sedimentary sequences at different times

red bed and basement sourced fluids recorded in hydrothermal mn fe as veins sailauf germany a la icpms fluid inclusion study the hydrothermal mn fe as vein mineralization at sailauf germany hosts a complex sequence of oxide and carbonate minerals that record a protracted fluid history the mineralization is related to a major unconformity that separates permian zechstein sedimentary rocks from underlying variscan crystalline basement the hydrothermal veins contain two principal mineralization stages which are mn oxides associated with calcite and hematite associated with mn calcite the fluid evolution of the hydrothermal system has been reconstructed from fluid inclusion petrography microthermometry and la icpms microanalysis coupled with stable isotope geochemistry of carbonate and oxide minerals the fluid inclusions are high salinity sodic calcic brines and the bulk fluid properties show no major differences between the mn oxide and the hematite stage la icpms analysis of major and trace elements demonstrates that the mineralization formed from chemically distinct fluid pulses characterized by variations in their k li b pb and zn concentrations the fluid that precipitated the mn oxide stage has anomalous pb zn and li b ratios which closely resemble fluids found in fracture fillings in red beds of the permian rotliegend basin by contrast the fluids associated with the hematite stage have pb zn and li b ratios typical of crustal fluids that were derived from interaction with crystalline basement both fluids possess characteristic element ratios including cl br but variable absolute concentrations of most metals this suggests that both fluids were modified by mixing with a common metal depleted brine that had a similar cl br ratio most likely a formation water from the overlying zechstein sedimentary rocks the sailauf mineralization provides insight into the protracted post variscan fluid evolution at the basement cover interface the compositionally anomalous fluid that precipitated the mn oxides is comparable to brines derived from interaction with red beds and likely represents the ore fluid of kupferschiefer type sediment hosted cu deposits conversely the fluid that deposited the hematite mineralization resembles fluids that typically form basement and sediment hosted pb zn deposits

relationship between extensional tectonic style and the paleoclimatic elements at laguna el fresnal chihuahua desert mexico abstract a multi disciplinary geomorphology ecology sedimentology geology gravimetry ground penetrating radar and direct current resistivity study established a relation among the subsurface structure of laguna el fresnal the geomorphic units and the vegetation according to gravity data laguna el fresnal is an asymmetric fault bounded basin typical of the basin and range province and the rio grande rift the geomorphic units along the eastern and western sides of el fresnal basin show marked differences the western slope is characterized by a variety of sedimentary deposits and geomorphic features such as alluvial fans debris flows braided stream deposits sheet flood deposits erosional surfaces paleosols and fluvial paleosystems of dendritic and parallel types in contrast the eastern slope has only aeolian deposits covering structures of alluvial origin the vegetation also shows this asymmetry along the western slope vegetation is composed from the highest to the lowest elevations of juniperus ssp yucca echinocereus ssp and prosopis ssp whereas on the eastern slope the vegetation is mostly composed of small prosopis ssp associated with larrea tridentata communities the juniperus ssp vegetation represents remnants of an environment upper pleistocene age more humid than at present the stratigraphy of the morphological units was tentatively established three depositional lobes qi qii and qiii and three generations of alluvial fans qiv qv and qvi were defined silty clayey sediments of aeolian origin loess from the basin constitute unit qvii the structure of the first 3 4 m of units qvii and qi were established using a ground penetrating radar vertical electric soundings indicate at least 40 m of clay sediments beneath the plain the contrasting differentiation between geomorphic units and vegetation at both slopes of the basin indicates that the western border of the basin is or was uplifting

application of the 187re 187os system to black shale geochronometry the decay of 187re to 187os provides a tool for determining depositional ages of black shales re and os concentrations and os isotopic compositions of whole rock samples of the bakken shale a mississippian devonian boundary black shale yield a whole rock isochron with an age of 354 49 ma this age is in agreement with the accepted age of the bakken shale 360 ma the initial 187os186os ratio of the isochron is 6 2 3 3 this value is indistinguishable from the 187os186os ratios observed in modern black sea sediments the concentration of common os in bakken shale samples is strongly correlated with total nitrogen indicating that a large fraction of the os in these samples is associated with a hydrogenous component which overwhelms any os supplied to the sediment in association with detrital material or cosmic dust the dominance of the hydrogenous component imparts a relatively homogeneous initial 187os186os ratio to the sediment at the time of deposition the degree of scatter about the isochron exceeds the degree of scatter expected from either analytical error or from the estimated degree of initial isotopic heterogeneity the pattern of scatter is consistent with postdepositional mobilization of re and or os on a small spatial scale we suggest that this mobilization may be a consequence of petroleum formation and migration in the bakken shale

kinematics of retreating subduction along the carpathian arc romania kinematic axes and resultant vectors of displacement along the carpathian arc and the apuseni mountains aid in the reconstruction of retreating subduction along the carpathians the recent vertical position of the subducted slab below the vrancea area of the eastern carpathians represents the final rollback stage of a small fragment of oceanic lithosphere formerly situated between the moesian and east european plates the ages and locations of the eruption centers of the andesitic volcanic chain along the carpathian arc in the overriding plate as well as the thrust directions are used as markers to reconstruct the rollback area of the subducted slab between the moesian and east european plates

3 geochronology and geodynamics of late cretaceous magmatism and cu au mineralization in the panagyurishte region of the apuseni banat timok srednogorie belt bulgaria abstract the apuseni banat timok srednogorie abts belt europe s most extensive belt of calc alkaline magmatism and cu au mineralization is related to the subduction of the tethys ocean beneath the european continental margin during the late cretaceous phase of the alpine himalayan orogeny economic deposits are restricted to certain segments along the belt and all major porphyry style and high sulphidation ore deposits in bulgaria are aligned on the panagyurishte corridor a narrow zone obliquely crossing the abts belt this paper reviews the geology geochemistry and geochronology of igneous and hydrothermal events along this corridor in a profile extending from the european continental basement in the north to the accretionary complex of the rhodopes in the south extensive u pb dating of zircons from subvolcanic intrusions and major plutons supplemented by published age data for magmatic rocks and hydrothermal ore deposits obtained by other methods reveals a general younging of magmatism from ca 92 ma in the north elatsite to ca 78 ma in the south capitan dimitrievo cu au deposits are restricted to the northern and central parts of the profile ranging in age from 92 to 86 ma while the southernmost part exposes more deeply eroded mid crustal plutons devoid of economic mineralization the age progression correlates with a north to south geochemical trend of decreasing crustal input into mantle derived magmas magmatism and ore formation in individual magmatic hydrothermal complexes along the profile is much shorter lived for example subvolcanic intrusions and porphyry cu au mineralization at the elatsite deposit and andesitic volcanism and high sulphidation au as cu mineralization at chelopech all occurred within a time span of about 1 million years the age progression of calc alkaline magmatism within the panagyurishte region bulgaria from north to south is explained as a consequence of slab retreat during oblique subduction this led to transtensional block faulting and subsidence and thus to the preservation of near surface magmatic hydrothermal products including economic cu au deposits accretion of continental fragments in the rhodopes south of the abts belt led to greater uplift of the youngest late cretaceous intrusions this removed any ore deposits that might have been formed in this area

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