lovehovden fault and billefjorden rift basin segmentation and development spitsbergen norway the carboniferous billefjorden rift basin is a well known example of a suite of carboniferous basins on the barents shelf and ne greenland the basin has a clastic carbonate and evaporite fill with complex and disputed stratigraphic relationships especially regarding the ebbadalen and minkinfjellet formations geometrically the basin is considered a simple half graben a n s trending fault and monocline structure within the northern portion of the basin the lovehovden fault has lithological and thickness differences across it within the minkinfjellet and possibly ebbadalen formations the fault shows w side down movement defining a sub basin within the larger half graben significant along strike changes occur down throw to the west is at least 150 metres and possibly 400 metres as shown by across fault thickness differences of ebbadalen and or minkinfjellet formations to the east of the fault the contact between the ebbadalen and minkinfjellet formations is a disconformity with significant local relief and is interpreted to represent exposure from footwall uplift and associated near or at surface solution producing basal stratiform breccias a similar contact is not exposed west of the fault monoclinal deformation and thickening of the younger wordiekammen formation above and across the monocline constrain a later movement component kinematic data and the structural style clearly indicate the lovehovden fault is a normal fault with associated tri shear zone development consistent with the regional carboniferous rift setting earlier interpretations describe the lovehovden fault and monocline as tertiary contractional features in contrast our work advocates that they are an important architectural basin element defining a sub basin within the billeforden trough during minkinfjellet formation deposition with insignificant if any tertiary reactivation the lovehovden fault is aligned with and represents the southern termination of the lemstromfjellet fault to the north thus the billefjorden basin changes from a narrow graben to a broader half graben to the south these along strike changes have important implications for the stratigraphic architecture of the basin and for palaeogeographic reconstructions these results and application of 3 d models for extension related tri shear zones may help inform interpretation of other carboniferous basins on the barents shelf

variable parent magmas and recharge regimes of the parinacota magma system n chile revealed by fe mg and sr zoning in plagioclase abstract zoning patterns of an content and fe mg and sr concentrations in plagioclase phenocrysts in andesites from parinacota volcano n chile reflect alternating recharge events with two chemically distinct mafic magmas these magmas are characterized by low and high sr contents similar to two recent mafic flank eruptions one end member basaltic andesite shows large sr enrichment and heavy rare earth depletions and thus equilibrated with lower crustal rocks at depth where plagioclase high sr is unstable and garnet high hree y is stable a second end member magma is lower in sr ba contents and has ree patterns typical for parent magmas elsewhere in the central andes the number of recorded recharge events increases after a catastrophic sector collapse and during the subsequent rebuilding of the stratocone variations of an fe and mg contents and morphology of zones suggest also changes in water pressure including decompression under water under saturated and water saturated conditions evidence for decompression is more present in post collapse samples suggesting that the change in the volcano dynamics involves changes in magma chamber location this shows the importance of the cone collapse event in the volcano s magmatic evolution we propose that both end members are only seen at the surface of parinacota volcano because of the particular dynamics of this volcanic system and that similar processes might occur in other volcanic centres of the central volcanic zone

development of incisions on a periodically emergent carbonate platform natih formation late cretaceous oman abstract subaerial exposure of carbonate platforms is generally recorded by karstification and pedogenesis whereas erosion features such as incisions along emersion surfaces have seldom been observed and studied however the recognition of incisions and the characterization of their fill may facilitate definition and hierarchy of sequence boundaries especially along exposure surfaces that do not otherwise present clear petrographic evidence for emersion in the natih formation late albian early turonian oman two successive incision surfaces are present in the upper part of the first third order depositional sequence seismic interpretation of regional subsurface data has allowed the quantification of progradational geometries within the natih sequence i carbonate platform and the correlation of incision surfaces with forced regressive prograding wedges on the margins of the intrashelf basin detailed geological sections and correlations have been made from three outcrop localities allowing a precise description of geometries and facies of incision fills morphology orientation and extent of these incisions have been assessed from detailed seismic interpretation coupled with forward seismic modeling the integration of outcrop and seismic data sets at the regional and local scales allows the interpretation and discussion of the origin and factors controlling the development of these incisions and a refinement of the stratigraphic model these two incisions record rapid sea level variations 500 ky with a magnitude of approximately 20 and 30 m that occurred during the early cenomanian this is probably not a unique case since for the same time interval incisions have been observed in siliciclastic systems in western canada and india and in carbonate systems on the arabian plate

localisation of normal faults in multilayer sequences abstract existing conceptual growth models for faults in layered sequences suggest that faults first localise in strong and brittle layers and are later linked in weak and ductile layers we use the discrete element method for modelling the growth of a normal fault in a brittle ductile multilayer sequence the modelling reveals that faults in brittle ductile sequences at low confining pressure and high strength contrast localise first as mode i fractures in the brittle layers low amplitude monoclinal folding prior to failure is accommodated by ductile flow in the weak layers the initially vertically segmented fault arrays are later linked via shallow dipping faults in the weak layers faults localise therefore as geometrically and kinematically coherent arrays of fault segments in which abandoned fault tips or splays are a product of the strain localisation process and do not necessarily indicate linkage of initially isolated faults the modelling suggests that fault tip lines in layered sequences are more advanced in the strong layers compared with weak layers where the difference in propagation distance is most likely related to strength and or ductility contrast layer dependent variations in fault localisation rates generate fringed rather than smooth fault tip lines in multilayers

prolonged residence times for the youngest rhyolites associated with long valley caldera 230th 238u ion microprobe dating of young zircons abstract we describe a new ion microprobe method for dating magmatic zircon growth that is based on in situ measurement of the magnitude of238u 230th disequilibrium our results support independent inferences that zircon can remain suspended for long periods 100 ka in the convecting potions of the magma from which it crystallizes because the crystallization ages date when the magma cooled to its zircon saturation temperature even when the zircons have long magmatic residence times 238u 230th zircon dating can be used to constrain the thermochemical evolution of silicic magmas 238u 230th ages have been determined for individual zircons from rhyolites associated with the long valley magmatic system of eastern california the samples are from deer mountain an 115 3 ka low silica moat rhyolite and from the coarsely porphyritic low silica rhyolite of south deadman dome one of the 0 6 ka inyo domes previous investigations have suggested that the two lavas were derived from the same magma reservoir a few of the zircon model ages calculated with respect to the isotopic characteristics of the whole rocks are within error of that for eruption of the deer mountain rhyolite however the majority of zircons from both lavas cluster around an age of 230 ka this common interval of zircon nucleation and growth for petrologically similar lavas suggests that the younger inyo dome lava may have tapped the same magma body from which the deer mountain rhyolite erupted more than 100 ka before on the other hand most of the zircon model ages are younger than previous episodes of silicic volcanism in the long valley caldera suggesting that the rhyolites may have been generated during development of a silicic upper crustal magma chamber in the western portion of long valley caldera zircon saturation temperatures for the rhyolites studied 795 810 c are the same as those obtained from coexisting fe ti oxides 809 4 c showing that the magma cooled to

pull aparts shear fractures and pressure solution vein arrays are often composed of pull aparts which are linked by shear fractures good examples of which occur in the lower jurassic limestones of somerset southwestern england such pull apart arrays have displacement distance characteristics which are similar to fault zones with maximum displacement indicated by the largest pull apart widths near the centre of the array and with displacement decreasing towards the tips pull apart arrays usually die out into enechelon or pinnate veins evidence for pressure solution along the shear fractures which connect pull aparts include their dark and braided nature their obliquity to the displacement direction the high dihedral angles often 90 between conjugate shear fractures and the dissolution of earlier structures a range of geometries occurs with varying relative amounts of veins and pressure solution being related to varying amounts of transtension or transpression there is a general trend for an increase in the angle between vein segments and the shear fractures as contraction increases there is therefore a trend for increased pressure solution on the shear fractures in more contractional arrays the concentration of insoluble material along shear fractures has important implications for the mechanics and sealing of faults

uplift deformation and fluid involvement within an active normal fault zone in the gulf of corinth greece the active pisia fault zone is exposed close to the crest of a rotated carbonate fault block that forms part of the southern margin to the gulf of corinth half graben in central greece the crest of the fault block lies above sea level whilst in the hanging wall a marine basin exists as a result the diagenetic and structural characteristics of the fault zone record complex fluid involvement both early phreatic carbonate syn kinematic cements characterized by drusy fabrics baroque dolomites and crack seal textures and late vadose carbonate syn kinematic cements characterized by flowstones containing cave collapse debris exist in the uplifted footwall to the fault downward percolation of vadose meteoric waters and the upwelling of pore waters with elevated temperatures produced the diagenetic features observed within the fault zone the co existence of early phreatic and late vadose cements within the fault zone is related to footwall uplift across the water table and subsequent erosional unroofing the present day elevation of phreatic cements to c 650m above current sea level provides a minimum estimate of footwall uplift along the fault the wider implication is that temporal changes in deformation and fluid flow may typify fault block evolution

dynamic development of fault rocks in a crustal scale detachment an example from western norway 1 the nordfjord sogn detachment nsd zone of western norway juxtaposes eclogites and gneisses of lower crustal affinity with sedimentary deposits suggesting that the zone experienced substantial displacement during devonian extensional denudation of the caledonides renewed activation occurred in permian and jurassic cretaceous times the detachment zone consists of a succession of fault related rocks reflecting various crustal positions and deformation mechanisms during activation and unroofing in more detail the lower 1 2 km thick section of the nsd zone consists of mylonites with various protoliths showing a general upward decrease in metamorphic grade the mylonitic section is truncated by the nsd fault defining the boundary toward hanging wall nappe rocks that are topped by sedimentary basins in an attempt to provide precise descriptions of the observed fault rocks we classify these rocks into 1 noncohesive breccias 2 cemented and indurated breccias of secondary cohesion and 3 cataclasites phyllonites and mylonites formed with primary cohesion along and across strike sections of the fault reveal the spatial and temporal relationships of the nsd fault the fault zone consists of a lower section of phyllonites and cataclasites reaching a total thickness of 50 70 m significant volumes of pseudotachylyte were injected into these fault rocks and were later reworked reactivation of the fault is suggested by overprinting carbonate cemented breccias that are cut by a discrete fault itself associated with breccias and gouge by comparing the various fault rocks and their formation mechanisms some constraints can be applied to the unroofing history the nsd fault developed in the ductile brittle transition zone of the crust where it experienced an initial shift from mainly frictional to plastic flow caused by reaction softening before hardening caused a return to frictional flow at the same time repeated pulses of pseudotachylyte were generated possibly lubricating the fault zone and contributing to strain localization these pseudotachylyte pulses also show that the fault was affected by seismic slip events before returning to a creep regime within a wider section than that ruptured by earthquakes younger cemented breccias and noncohesive breccias and gouge reflect earthquake rupturing and frictional flow within the seismogenic crust

identification of a suspected quaternary fault in eastern korea proposal for a paleoseismic research procedure for the mapping of active faults in korea abstract in terms of seismic hazard in the korean peninsula the occurrence of destructive earthquakes has long been overlooked because of no serious modern instrumental seismicity and lack of historical earthquake records of large earthquakes in recent years although the importance and uses of paleoseismological studies has significantly increased in seismic hazard assessments of critical facilities there is still a huge lack of paleoseismological data to improve our knowledge for korean active tectonics and relevant seismic hazards in this study we identified and characterized a suspected quaternary fault in the eastern part of the korea peninsula based on lineament analyses field observations and trench surveys we focus on a prominent lineament around the northern part of the previously reported but not sufficiently studied maeup fault firstly a potential fault lineament is recognized by geomorphic expressions in a mountainous area from satellite and digital elevation model dem generated images then fault related geomorphic and hydrologic features such as disconnected drainages sag ponds and asymmetric water leaking out on an artificial ditch were observed along the lineament in the field studies finally the existence of the fault is confirmed by an exposure of a 2 5 m wide fault core in trench surveys the internal structures of the fault core i e slip surfaces slickenlines and s c fabrics indicate that the fault evolved via a series of slip events under a variety of tectonic settings probably leading up to the current stress regime sustained during quaternary thus our results suggest that the newly identified fault could be a quaternary fault and hence it is necessary to perform more paleoseismic investigations around the study region this case study emphasizes the importance of the careful interpretation of tectonic landforms and fault zone structures in the study of active faults and proposes a suitable research procedure for the identification of active faults in korea

natural fractures in tight oil sandstones a case study of the upper triassic yanchang formation in the southwestern ordos basin china natural fractures are important storage spaces and fluid flow channels in tight oil sandstones intraformational open fractures are the major channels for fluid flow in tight oil sandstones small faults may provide fluid flow channels across different layers according to analogous outcrops cores and borehole image logs small faults and intraformational open fractures are developed in the tight oil sandstones of the upper triassic yanchang formation in the southwestern ordos basin china among them high dip angle intraformational open fractures are the most abundant northeast southwest trending fractures are the principal fractures for fluid flow because that is the present day maximum horizontal compressive stress direction combined with production data horizontal wells striking normal to or at a large angle relative to the major flow pathways are beneficial for tight oil production improvement fractures with high dip angles are the main factor that influences initial oil production linkage and tip damage zones are more favorable for oil production improvement than wall damage zones this study provides an example of natural fracture characterization and unravels fracture contributions to reservoir physical properties and oil production of tight oil sandstones which could provide a geological basis for oil exploration and development in tight sandstones

vertical coupling and decoupling in the lithosphere recent advancements in the understanding of mountain belts have focused on vertical coupling of the lithospheric layers this volume describes the extent to which observed or inferred sub horizontal coupling or attachment zones provide vertical kinematic linkage between rheologically distinct layers in the continental lithosphere a common theme is whether the deformation which partitioned differently in each layer is linked kinematically across attachment zones and driven by flow in the deeper crust and mantle lithosphere the papers are divided into six sections the first analyses the extent to which mantle flow controls deformation of the overlying layers the vertical axis block rotations section uses geological and palaeomagnetic data to constrain the role and magnitude of basal shear across mid crustal attachment zones the lower crustal flow and topography section addresses the time dependent development of orogenic plateaux and their role in the orogenic cycle multiple examples of the spatial and temporal development of lithospheric coupling are given in both the orogenic examples and subduction examples sections finally rheological constraints of vertical coupling in the lithosphere are investigated

percolation threshold and permeability of crystallizing igneous rocks the importance of textural equilibrium the permeability of a crystal mush fundamentally controls the ability of its melt to migrate or segregate with respect to the solid phase and thus controls the extent to which compaction and porous media convection can occur in crystallizing igneous cumulates in particular the existence of a percolation threshold which defines the porosity at which a crystallizing rock becomes impermeable can limit the effectiveness of these processes we present three dimensional numerical models of the topology of porosity in both texturally equilibrated and nonequilibrated crystal melt systems these models enable porosity vs permeability relationships and hence percolation thresholds to be calculated the permeability of the nonequilibrated models was calculated using a network simulation method these models confirm that there is no percolation threshold for a perfectly texturally equilibrated rock with dihedral angles of 20 these results suggest that the volume of trapped melt in an igneous cumulate may be controlled by the ability of the crystallizing crystal melt system to reach textural equilibrium

energy constrained open system magmatic processes iv geochemical thermal and mass consequences of energy constrained recharge assimilation and fractional crystallization ec rafc 1 a wealth of geochemical and petrological data provide evidence that the processes of fractional crystallization assimilation and magma recharge replenishment dominate the chemical signatures of many terrestrial igneous rocks previous work spera and bohrson 2001 bohrson and spera 2001 has established the importance of integrating energy species and mass conservation into simulations of complex magma chamber processes an extended version of the energy constrained formulation energy constrained recharge assimilation fractional crystallization ec rafc tracks mass and compositional variations of melt cumulates and enclaves in a magma body undergoing simultaneous recharge assimilation and fractional crystallization spera and bohrson 2002 because many ec rafc results are distinct from those predicted by extant rafc formulations the primary goal of this paper is to present a range of geochemical and mass relationships for selected cases that highlight issues relevant to modern petrology among the plethora of petrologic problems that have important well documented analogues in nature are the geochemical distinctions that arise when a magma body undergoes continuous versus episodic recharge the connection between erupted magmas and associated cumulate bodies the behavior of recharge fractionation dominated systems rfc thermodynamic conditions that promote the formation of enclaves versus cumulates and the conditions under which magma bodies may be described as chemically homogeneous investigation of the effects of continuous versus episodic recharge for mafic magma undergoing rafc in the lower crust indicates that the resulting geochemical trends for melt and solids are sensitive to the intensity and composition of recharge suggesting that ec rafc may be used as a tool to distinguish the nature of the recharge events compared to the record preserved in melts the geochemical and mass characteristics of solids associated with particular rafc events may record a more complete view of the physiochemical history of an open system magma body the capability of ec rafc to track melts and solids creates a genetic link that can be compared to natural analogues such as layered mafic intrusions and flood basalts or mafic enclaves and their intermediate composition volcanic or plutonic hosts the ability to quantify chemical and volume characteristics of solids and melts also underscores the need for integrated field petrologic and geochemical studies of igneous systems while it appears that a number of volcanic events or systems may be characterized by continuous influx or eruption of magma steady state systems reports describing compositional homogeneity for products that represent eruptions of more than one event are relatively rare in support of this ec rafc results indicate that very specific combinations of recharge conditions bulk distribution coefficients and element concentrations are required to achieve geochemical homogeneity during cooling of a magma body undergoing rafc in summary critical points are that ec rafc provides a method to quantitatively investigate complex magmatic systems in a thermodynamic context it predicts complex nonmonotonic geochemical trends for which there are natural analogues that have been difficult to model and finally ec rafc establishes the link between the chemical and physical attributes of a magmatic system application of ec rafc promises to improve our understanding of specific tectonomagmatic systems as well as enhance our grasp of the essential physiochemical principles that govern magma body evolution

a model for the structure and development of fault zones cross sections of fault zones commonly show two sub parallel slip surfaces which bound more or less deformed rock this characteristic geometry can be explained by a combination of 9tip line9 and 9asperity9 bifurcation processes fault tip line bifurcation is due to irregular tip line propagation resulting in leading edge segmentation fault overlap and eventual duplex formation asperity bifurcation removes a fault surface irregularity by the generation of a new slip surface which by passes the original slip surface repetitions of either or both bifurcation processes give rise to a fault zone with a complex and unpredictable internal geometry these processes are described mainly on the basis of observation of normal faults hut can be applied to other fault types fault zone thickening by bifurcation is intermittent rather than progressive and localised fault zone thinning may occur

dating crust mantle separation re os isotopic study of mafic xenoliths from central arizona mafic deep crustal and shallow upper mantle xenoliths hosted in the chino valley and camp creek latites of central arizona have 187os 188os 0 216 to 1 51 ratios dramatically higher than values typical of mantle peridotite 0 13 re os model ages for the xenoliths range from 0 57 to 2 3 ga with a mean of 1 1 0 6 ga consistent with the possibility that the xenoliths sample proterozoic lower crust and upper mantle underplated to the ca 1 6 1 8 ga basement combined os and sr nd pb data indicate that these xenoliths were not formed by crustal contamination of cenozoic asthenospheric melts but allow for recent interaction between old mafic materials in the lithosphere and high 87sr 86sr low 143nd 144nd melts of proterozoic lithospheric mantle the potassic latite hosts to the xenoliths also have radiogenic os indicating that they are melts of a mafic rather than a peridotitic source in the old lithosphere these data demonstrate the utility of the re os system in defining mantle separation ages or the initial time of melt extraction from a peridotitic mantle even in cases where the lithospheric mantle is remelted long after its formation

hydraulic characterization of a fault zone from fracture distribution abstract a quantitative assessment of how faults control the migration of geofluids is critical in many areas of geosciences we integrated geological fieldwork quantitative analysis of the fractures distribution and numerical modeling to build a geometrical representation of a fault zone and to characterize its hydraulic properties our target is a fault located in the majella mountain italy we collected 21 scan lines across the fault profile in order to characterize its architecture the numerical modeling of the fracture network of the damage zones and their hydraulic parameters was performed using both commercial move and open source software dfnworks and pflotran move was used to build a representative model of the fault zone using fracture spacing as a proxy and to model the hydraulic parameters of the different fault domains dfnworks and pflotran were employed to infer the hydraulic parameters of the damage zones of the fault and then upscale these properties to an equivalent continuum domain suitable for fluid flow simulations through the whole fault zone our findings show how even in a relatively small area it is possible to describe changes in terms of hydraulic properties of a fault zone and to build models capable to represent these variations

influence of p t conditions on the style of normal fault initiation and growth in limestones from the se basin france abstract a conventional and cathodoluminescence microscopy stable isotope and fluid inclusion study was undertaken on normal fault zones exposed on vertical cliffs in tithonian limestones of the french se basin the aim was to determine the chronology of deformation and factors controlling normal fault nucleation and evolution in carbonate rocks two models are proposed for fault zone development depending on the depths at which deformation takes place at depths of 3 3 5 km incipient shear zones consist of en echelon veins filled by fibrous calcite and confined to limestone layers bounded by thin clayey interlayers as deformation increases and the layers rotate slip occurs along the clay rich interlayers a system of pull aparts forms allowing displacement to increase pull aparts are commonly filled by fibrous calcite crystals at depths of 1 5 2 km faults initiate as small slip surfaces early nucleating in some limestone layers their propagation is impeded by thin clayey interlayers which enhances fracturing and bending of the limestone layers as slip surfaces propagate they overlap and can connect with one another by means of dilational jogs that are filled by large euhedral calcite crystals in the first case pull aparts are coupled with the solution seams that reuse preexisting rotated clay rich interlayers as they formed they progressively filled and the fluid circulation remained local in the second case longer slip planes connect by dilation jogs that are not immediately filled which enhance the circulation of fluids which show chemical variations it appears that p t conditions strongly control the relative role of brittle processes and solution crystallization mechanisms and the style of the early stages of normal faulting in the same limestone rocks

energy constrained recharge assimilation and fractional crystallization ec raχfc a visual basic computer code for calculating trace element and isotope variations of open system magmatic systems 1 volcanic and plutonic rocks provide abundant evidence for complex processes that occur in magma storage and transport systems the fingerprint of these processes which include fractional crystallization assimilation and magma recharge is captured in petrologic and geochemical characteristics of suites of cogenetic rocks quantitatively evaluating the relative contributions of each process requires integration of mass species and energy constraints applied in a self consistent way the energy constrained model energy constrained recharge assimilation and fractional crystallization ec ra fc tracks the trace element and isotopic evolution of a magmatic system melt solids undergoing simultaneous fractional crystallization recharge and assimilation mass thermal and compositional trace element and isotope output is provided for melt in the magma body cumulates enclaves and anatectic i e country rock melt theory of the ec computational method has been presented by spera and bohrson 2001 2002 2004 and applications to natural systems have been elucidated by bohrson and spera 2001 2003 and fowler et al 2004 the purpose of this contribution is to make the final version of the ec ra fc computer code available and to provide instructions for code implementation description of input and output parameters and estimates of typical values for some input parameters a brief discussion highlights measures by which the user may evaluate the quality of the output and also provides some guidelines for implementing nonlinear productivity functions the ec ra fc computer code is written in visual basic the programming language of excel the code therefore launches in excel and is compatible with both pc and mac platforms the code is available on the authors web sites http magma geol ucsb edu and http www geology cwu edu ecrafc as well as in the auxiliary material

assimilation of felsic crust by basaltic magma thermal limits and extents of crustal contamination of mantle derived magmas basaltic magma is the most widely used probe of mantle chemistry and structure chemical characterization of the sources for mantle derived magma is possible only after quantitative evaluation of possible contamination by crustal wall rocks the most commonly invoked contamination mechanisms are the combined processes of crustal assimilation and magmatic fractional crystallization afc because of the energetic link between these processes predicting assimilation and crystallization progress requires modeling both heat and mass transfer in the magma country rock system using the melts software package we modeled isenthalpic heat balanced afc between two common types of basaltic magma and several types of felsic crust at 1 kbar our simulations show that during the early stages of isenthalpic afc the ratio of rates of assimilation to crystallization r may be substantially greater than one 2 0 2 7 allowing assimilation of a mass of country rock up to 5 18 of the initial magma mass with only 3 7 crystallization the second stage of afc beginning with plagioclase and or pyroxene saturation is characterized by lower r 0 5 1 0 the initial high r stage results from suppression of crystallization associated with the change in magma composition as assimilation progresses under certain conditions even small degrees of crystallization of olivine alone coupled with cooling of the magma can accommodate relatively large amounts of crustal assimilation and cause large shifts in isotopic and trace element geochemical indices with little differentiation

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

variations in trace element partition coefficients in sanidine in the cerro toledo rhyolite jemez mountains new mexico effects of composition temperature and volatiles trace element partition coefficients have been measured for one plagioclase and five sanidine mineral separates from the cerro toledo rhyolite new mexico sanidine partition coefficients vary substantially and systematically within the cerro toledo rhyolite partition coefficients for ca sr zn la and eu are lowest in the most evolved rhyolites whereas sm and hree partition coefficients are highest rubidium partition coefficients remain constant while those for ba ce and th are variable variations of the sr zn la and eu partition coefficients are correlated with the ca contents and partition coefficients of the sanidines calcium may have controlled the distribution of these elements in the sanidine by modifying the feldspar structure the low ca partition coefficients in sanidines for the most evolved rhyolites may be the consequence of modification of the melt structure possibly due to increased volatile contents at the top of the magma chamber s during evolution of the cerro toledo rhyolite the zn and la partition coefficients between sanidine and melt also may have been controlled by this change in melt structure modelling using major elements and the constant rb partition coefficient for sanidine indicates 70 crystallization of magma during cerro toledo rhyolite time by removal of 68 sanidine and 32 quartz estimates of the volume 1 of initial parental magma and 2 of the magma that crystallized during this period are 11 670 km3 and 8170 km3 respectively the average intrusion rate of silicic magma during cerro toledo rhyolite activity was 35 10 3 km3 a

strain rate dependent rheology of partially molten rocks coupling or decoupling in the lithosphere is often related to the absence or the presence of a layer of partially molten rocks although the rheology of such rocks remains unsolved theoretical arguments correlated with structural observations provide new insights on the rheology of partially molten rocks namely migmatites and magma these rocks are simplified to two phase pseudofluids constituted of a quasi solid matrix and a variable amount of melt previous experiments indicate that the matrix deforms plastically according to a power law the melt is newtonian and weakens at high shear strain rates because of the heterogeneous distribution of matrix and melt phases their rheologies cannot be averaged to obtain the rock rheology four behaviours are identified i at high stress and strain rates the viscosity contrast between melt and matrix is lowest both phases can accommodate strain at a comparable rate allowing migmatite and magma bodies to deform as quasi solid units ii at low strain rates the viscosity contrast between melt and matrix is highest melt deforms and relaxes much faster than the matrix the simultaneous coexistence of a weak and a strong phase is expressed in a 3d viscosity strain rate melt fraction diagram in which a cusp shaped surface represents viscosity the cusp graphically shows that the viscosity of partially molten rocks may jump several orders of magnitude these jumps leading to sudden melt segregation are timely erratic iii at low strain rates strain partitioning may lead to internal instabilities and segregation between melt and restitic phases as observed in the leucosome melanosome separation iv cyclic processes follow hysteresis loops and trigger strain localisation

petroleum geology and potential hydrocarbon plays in the gulf of suez rift basin egypt the gulf of suez in egypt has a north northwest south southeast orientation and is located at the junction of the african and arabian plates where it separates the northeast african continent from the sinai peninsula it has excellent hydrocarbon potential with the prospective sedimentary basin area measuring approximately 19 000 km 2 and it is considered as the most prolific oil province rift basin in africa and the middle east this basin contains more than 80 oil fields with reserves ranging from 1350 to less than 1 million bbl in reservoirs of precambrian to quaternary age the lithostratigraphic units in the gulf of suez can be subdivided into three megasequences a prerift succession pre miocene or paleozoic eocene a synrift succession oligocene miocene and a postrift succession post miocene or pliocene holocene these units vary in lithology thickness areal distribution depositional environment and hydrocarbon importance geological and geophysical data show that the northern and central gulf of suez consist of several narrow elongated depositional troughs whereas the southern part is dominated by a tilt block terrane containing numerous offset linear highs major prerift and synrift source rocks have potential to yield oil and or gas and are mature enough in the deep kitchens to generate hydrocarbons geochemical parameters sterane distribution and biomarker correlations are consistent with oils generated from marine source rocks oils in the gulf of suez were sourced from potential source rock intervals in the prerift succession that are typically oil prone type i and in places oil and gas prone type ii or are composites of more than one type multiple types i ii or iii for oil prone oil and gas prone or gas prone respectively the reservoirs can be classified into prerift reservoirs such as the precambrian granitic rocks paleozoic cretaceous nubian sandstones upper cretaceous nezzazat sandstones and the fractured eocene thebes limestone and synrift reservoirs such the miocene sandstones and carbonates of the nukhul rudeis kareem and belayim formations and the sandstones of south gharib zeit and

the partitioning of trace elements between ilmenite ulvospinel armalcolite and silicate melts with implications for the early differentiation of the moon mineral melt trace element partition coefficients for a large number of trace elements zr hf ta nb v co cu zn sr ree sb sn mo cr w u th were determined experimentally for ilmenite fetio3 ulvospinel fe2tio4 minerals of the armalcolite solid solution fe mg ti2o5 the measured partition coefficients indicate that the high field strength elements zr hf nb and ta and some transition metals v cr co sn are moderately compatible in iron titanium oxides whereas other elements ree y sr u th mo sb and w are strongly incompatible the partition coefficients for u are always significantly higher than the th partition coefficients which makes fe ti oxides efficient in fractionating u from th our data also indicate that ilmenite and other iron titanium oxides are able to fractionate w from hf the latter of which is much more compatible this makes the iron titanium oxides very effective agents to influence hf w isotopic ratios during the evolution of the moon in addition we also present some trace element partition coefficients for iron and titanium bearing orthopyroxene

biot number and thermos bottle effect implications for magma chamber convection thermal boundary conditions model the coupling between a convecting magmatic body and its host such conditions need to be considered in models of igneous systems that involve thermal histories crystallization and fractionation of melt formation of aureoles by contact metamorphism and any other processes in which transport of heat plays a role usually investigations of magmatic systems have tended to emphasize modeling the interior convective regime relative to treatment of the thermal coupling yet it is found that the thermal nature of an intrusion is likely to be influenced more by coupling to its host than by the details of internal convective flows evaluation of a parameter having the form of a biot number bi provides a basis for estimating which boundary conditions are most appropriate it is found that bi 0 1 constant heat flux limit for models of several caldera systems for such values of the biot number the host regime behaves somewhat like a thermos bottle by limiting the flow of heat through the magma host system so that convective stirring of magma has little effect on the cooling rate of the intrusion because of this insulating effect boundary temperatures assumed in convection models should approach magmatic values even if an active hydrothermal system is present however high boundary temperatures do not imply that melting and assimilation of host rock by magma must occur despite the thermos bottle effect magmatic convection can still be quite vigorous

compositional convection in a reactive crystalline mush and melt differentiation fractional crystallization and partial melting involve relative motion of liquid and solid phases and chemical and thermal interactions between them to elucidate some physical principles of thermosolutal convection in a reactive porous medium we describe experiments on the directional solidification of aqueous ammonium chloride solutions the addition of small amounts of a polymerizing agent permits variation of the solution viscosity independently of thermal conditions the phase diagram and permeability solutions were cooled from below and crystallization developed at the base of the tank generating at first a field of thin plumes of light residual fluid released from the boundary layer at the top of the mush the interstitial fluid within the mush also became unstable eventually the onset of convection occurring when the porous medium rayleigh number of the mush reached a critical value this threshold value was found to be 25 at low initial superheat and to decrease with increasing superheat local thermodynamic equilibrium between crystals and liquid within the mush coupled the evolution of temperature composition and porosity convective motions locally caused dissolution and precipitation and hence fluctuations of porosity developed dissolution occurred preferentially in the central parts of upwellings and the upflow gradually focused being ultimately channelized into narrow chimneys devoid of crystals all else being equal the areal density of chimneys was greater the lower the viscosity chimney diameter increased with increasing solution viscosity in the liquid above the growing mush the convective plumes were very similar to salt fingers depending on solution viscosity and temperature gradient they exhibited a phenomenon of collective instability such that vertical motion was disrupted by wave instabilities the base plate temperature chosen was above the eutectic and hence the total amount of crystals at the end of experiments with the same initial composition and the same final temperature was a constant fixed by the phase diagram the spatial distribution of crystals and the final porosity of the mush were however determined by the strength of compositional convection as measured by the porous medium rayleigh number when no convection occurred mush thickness finally became equal to the initial layer thickness and the system was homogeneous when compositional convection occurred the overlying reservoir underwent chemical evolution and mush growth slowed dramatically in experiments with progressively lower solution viscosity and hence more vigorous convection final mush thickness was progressively less and final porosity lower final mush thickness was found to scale with solution viscosity to the power 0 33 during fractional crystallization of magma the effects of compositional convection can be recorded in the chemical and mineralogical features of cumulate rocks we speculate that fossil chimney structures can be found in the lower zone of the bushveld ultramafic complex in the form of iron rich platinum bearing dunite pipes this could explain the adcumulate nature of the lower zone rocks and the chemical and mineralogical similarities between the pipes and the overlying merensky reef the merensky reef would be interpreted as a hiatus in mush growth the results may also have applications to the flow structure in regions of partial melting and in the earth s core

extensional faults in fine grained carbonates analysis of fault core lithology and thickness displacement relationships abstract a study of 103 extensional faults hosted by fine grained carbonates in western sinai svalbard and oman reveals that faults vary geometrically between simple cores and cores comprising fault splays lenses segment linkages and overlap structures fault core rocks are typically carbonate breccias carbonate and shale gouge shale smear secondary calcite cement and veins and host rock lenses there is a significant scatter in the core thickness for any given displacement but the overall pattern is that the thickness increases with displacement this increase best fits a power law function 0 29d 0 56 that describes a gradual decrease in the thickness displacement relationship for increasing slip along faults in more detail the general function can be seen as the sum of two power law trend lines the first representing thin localized fault cores with generally simple and planar geometry the second representing thicker fault cores with complex geometry of lenses and overlap structures and with fault rock membranes the studied faults show a significant change in composition and geometry from small 0 1 m to moderate 1 10 m and to large offset faults 10 400 m the overall pattern is that fault initiates as fractures filled with calcite veins and thin shear fractures that hosts gouge membranes with increased fault offset complexity increases with breakdown of veins more extensive fault rock membranes and a trend towards development of lenses when offset exceeds 100 m cores become complex with multiple slip zones cemented breccia and shale smear membranes and various types of lenses we envision that the fault development as reflected by offset is dominated by forces extension compression acting in the fault mechanical heterogeneity of wall rocks the core lithologies and their developing rheology and especially geometric effects arising from fault irregularities

recharge in volcanic systems evidence from isotope profiles of phenocrysts strontium isotope ratios measured from core to rim across plagioclase feldspar crystals can be used to monitor changes in the isotope composition of the magma from which they grew in samples from three magma systems from convergent margin volcanoes sudden changes in major element composition petrographic features and strontium isotope composition were found to correspond to discrete magmatic events most likely repeated recharge of more mafic magma with lower ratios of strontium 87 to strontium 86 into a crustally contaminated magma

non linear feedback loops in the rheology of cooling crystallizing felsic magma and heating melting felsic rock at least six major parameters control the rheology of partially molten systems melt content rate of melt production reaction to strain of the solid component reaction to strain of the molten component temperature and chemical composition of the source rocks we examine their interactions to understand the rheology of partially molten rocks and partly crystallised magmas this paper especially focuses on the rheology in the transitional domains between two pairs of thresholds that bracket a transitional regime between a solid state and a fluid behaviour during melting and crystallisation respectively we review related information and point out non linear effects that develop during heating of melting rocks and cooling of crystallising magmas owing to the non linear interactions positive or negative feedback loops accelerate or damp the system melt in migmatite experiences shear softening which along with strain partitioning facilitates melt segregation conversely the augmenting number of rigid crystals during cooling increases the suspension viscosity shear hardening which soon inhibits magma movement those effects reinforce the asymmetry between solid to melt and melt to solid transitions they severely contradict the concept of one rheological critical melt percentage valid for both melting and crystallisation transitions fabric acquisition competes with nucleation and crystal growth thus leading to hysteresis of the stress stain rate curves implications to field observations include horizontal magma segregation magma extraction and successive magma intrusions

fault and fluid interaction in a rifted margin integrated study of calcite sealed fault related structures southern corinth margin this work integrates microstructural petrologic microthermometric and geochemical analysis of calcite sealed fault related structures of the major faults of the southern margin of the corinth rift greece it draws attention to the main deformational processes and fault fluid inter action in fault zones along the whole margin data analysed come from the compact breccia located immediately adjacent to major fault planes samples were collected at different positions alongside different faults juxtaposing synrift continental deposits hanging wall against the prerift pindus limestones footwall this implies hectometric fault displacements and that the fault zones have recorded a relatively long evolution of deformation our study identifies four main defor mation features common to all studied faults calcite cemented breccia extensional veins shear veins and fault slip surfaces the integrated data analysis shows that deformation structures and fault rocks that coexist in the same outcrop formed at different depths and times during inferred upward fault propagation the style of deformation evolved from distributed brecciation to loca lized slip surfaces and from a closed system with fluid rock equilibrium during brecciation to a more open one with limited influx of meteoric water during extensional and shear fracturing this implies relative uplift of the footwall during fault propagation and fault interaction with different water aquifers as the fault propagates upwards the results demonstrate similar fault evolution and fault fluid interaction through the entire rifted margin and during the whole rifting period

a complex magma mixing origin for rocks erupted in 1915 lassen peak california the eruption of lassen peak in may 1915 produced four volcanic introduction rock types within 3 days and in the following order 1 hybrid magma mixing is an important process among interblack dacite lava containing 2 undercooled andesitic inclusions mediate magmas in volcanic arcs e g turner 3 compositionally banded pumice with dark andesite and light campbell 1986 philpotts 1990 and references therein dacite bands and 4 unbanded light dacite all types represent laboratory studies of synthetic analogs of silicate magma stages of a complex mixing process between basaltic andesite systems and mathematical modeling of mixing viscous and dacite that was interrupted by the eruption they contain liquids have suggested a range of possible mixing mechdisequilibrium phenocryst assemblages characterized by the coanisms e g cashman bergantz 1991 however use existence of magnesian olivine and quartz and by reacted and of these results to interpret magmatic systems is limited unreacted phenocrysts derived from the dacite the petrography and by the applicability of synthetic analogs to magmatic crystal chemistry of the phenocrysts and the variation in rock conditions and by the imprecise knowledge of the effective compositions indicate that basaltic andesite intruded dacite magma viscosity of silicate liquid crystal mixtures at magmatic and partially hybridized with it phenocrysts from the dacite magma temperatures and pressures if magmas mix incompletely were reacted cooling crystallization and vesiculation of the hybrid i e mingle features such as compositional banding or andesite magma converted it to a layer of mafic foam the decreased undercooled inclusions are usually apparent but if they density of the andesite magma destabilized and disrupted the foam mix completely mineralogical disequilibrium may be the blobs of foam rose into and were further cooled by the overlying dacite magma forming the andesitic inclusions disaggregation of only direct evidence for a mixing origin andesitic inclusions in the host dacite produced the black dacite and if the thermal and compositional contrasts between light dacite magmas formation of foam was a dynamic process two magmas are great and the ratio of silicic to mafic removal of foam propagated the foam layer downward into the magma is large there is little interaction between them hybrid andesite magma eventually the thermal and compositional and the mafic magma is undercooled e g bacon 1986 contrasts between the hybrid andesite and black dacite magmas were many undercooled inclusions contain reacted phereduced then they mixed directly forming the dark andesite magma nocrysts inherited from their host silicic magma heiken about 40 50 andesitic inclusions were disaggregated into the eichelberger 1980 and bacon 1986 pointed out host dacite to produce the hybrid black dacite thus disaggregation that undercooled inclusions are typically formed from of inclusions into small fragments and individual crystals can be hybrid magmas in general the formation of undercooled an efficient magma mixing process disaggregation of undercooled inclusions retards further mixing sakuyama 1984 inclusions carrying reacted host magma phenocrysts produces cothompson dungan 1985 sparks marshall 1986 existing reacted and unreacted phenocryst populations koyaguchi blake 1991 however fragmentation and or disaggregation of undercooled inclusions plays an important role in hybridization in some magma systems thompson dungan 1985 coulon et al 1986 clynne christiansen 1987 clynne 1989 linneman myers

incipient magma chamber formation as a result of repetitive intrusions an analytical solution for periodic magma intrusions in conduits was developed to study the onset of shallow magma chamber formation the solution is based on determining when a repetitive series of intrusions can cause the wall rock of a conduit to reach its melt temperature the results show that magma chamber formation in conduits is a strong function of the volume rate of intrusion and that magma chamber formation is likely when the intrusion rate exceeds 10 3 km3 yr which agrees with observations by other investigators once this critical value of intrusion rate is reached magma chambers are likely to begin forming after only a few intrusive pulses less than ten results for both cylindrical conduits and dikes show cylindrical conduits are more favourable for the formation of shallow magma chambers

isotope and chemical microsampling constraints on the history of an s type rhyolite san vincenzo tuscany italy fine scale heterogeneities in strontium isotope ratios 40ar 39ar ages and chemical com sition have been determined for individual mineral grains and enclaves in the rhyolites of san vincenzo italy the rhyolites are peraluminous with phenocrysts of alkali feldspar piagioclase biotite and cordierite and have previously been divided into two groups on the basis of whole rock major element chemistry group b lavas are distinguished from group a in having higher mgo and cao contents as well as containing two pyroxenes and chilled latite enclaves the group b lavas show textural evidence for d sequilib um such as resorption and sieve zones in feldspars laser fusion 40ar 39ar dating of individual alkali feldspar crystals suggests that the eruption of these rhyolites took place 4 38 0 04 ma though small amounts of excess argon are present in subhedral and cloudy crystals the groundmass in the group a sample has a higher initial r7sr 86sr 0 725 than that of the group b 0 7 13 the sr isotope compositions of chemically and texturally characterized individual grains reveal marked disequilibrium between minerals and the host glass as well as within grain zonation the feldspars and coarse grained biotites have initial 87sr 8 sr that are intermediate between those of the group a and b glasses with alkali feldspar generally having higher initial 87sr 86sr ratios than plagioclase chilled latite enclaves which are present in only the group b lavas have relatively low initial 8 sr 86sr ratios in the range 0 7082 0 7088 the mineral chemistry and isotope data indicate that restite does not form a significant portion of the crystalline assemblage and therefore cannot be the source of the strontium isotope dis equilibrium xenocrysts mixed into the rhyolite from a mafic magma were identified as clinopyroxene megacrysts clinopyroxene orthopyroxene clots orthopyroxene plagioclase clots and plagioclase with extensive sieve textures these grains all have relatively low initial 87sr 86sr ratios other grains that may be xenocrysts are cordierites with cores containing inclusions of biotite spinel and sillimanite and alkali feldspars with excess 4 ar the strontium isotope di quilib um in phenocrysts of plagioclase alkali feldspar and biotite is attributed to a changing melt chemistry that was too rapid for strontium diffusive equilibration a mode1 for the san vincenzo magma chamber is proposed in which the sr isotope evolution of the group b rhyolites is due to magma mixing of a crustal melt with latite magma containing unra diogenic strontium the variable initial strontium isotope compositions of group a phenocrysts may be due to assimilation or crystallization along the interface between mingled group a and b magmas

textural elemental and isotopic characteristics of pleistocene phreatic cave deposits jabal madar oman abstract two main types of karst formation are commonly known the surficial meteoric one and the subsurface hypogenic karst which can be related to both carbonic h2co3 and sulfuric h2s acids this paper documents evidence for a third co2 regime related type of karst that is less commonly described petrographic and geochemical properties of exhumed pleistocene phreatic cave deposits from the diapiric jabal madar dome in northern oman are documented and discussed in a process oriented context these calcites form at the interface between two fundamentally different diagenetic and hydrogeological domains the deep seated hydrothermal and the near surficial meteoric vadose one four calcite phases are recognized i acicular ii blocky to stubby elongated iii proto palisade and iv macro columnar calcites the macro columnar calcites forming the last stage of precipitation are conspicuous due to their cyclical red zonation and they form the main geochemical focus of this study fluid inclusion data point to fluid temperatures of between 30 to 50 c monophase liquid inclusions and elevated salinities 1 6 to 7 3 wt nacl equivalent low carbon isotope data 8 to 9 are in agreement with the influx of soil zone co2 whereas decreasing 18o 15 values might point to mixing of saline hydrothermal and 18o depleted meteoric freshwater i e two fluid sources trace element and stable isotope data shift between the different cement phases and vary cyclically across the red zoning in macro columnar calcites with respect to the intra crystal variability these patterns are perhaps best explained in the context of redox potential two interpretations are presented the one favored here suggests that the cyclical red zoning in macro columnar calcites is controlled by pleistocene monsoonal climate patterns

reactivation history of the long lived billefjorden fault zone in north central spitsbergen svalbard new geological mapping has revealed further details of the tectonic and stratigraphic effects of devonian and later reactivations of the billefjorden fault zone one of a number of important north south trending lineaments in svalbard analysis of offsets along the many steeply dipping faults within the zone and effects on the subsidence and deformation of the adjacent crustal blocks is presented as a series of tectonic maps from the late devonian through to the tertiary late devonian sinistral transpression suggested previously cannot be ruled out and carboniferous reactivation was dominated by extension with possibly a slight dextral strike slip component after late carboniferous to early cretaceous platform subsidence during which the fault zone had little effect on sedimentation development of the tertiary west spitsbergen fold belt related to the opening of the arctic ocean involved compressive and transpressive reactivation of basement seated structures further east including the billefjorden fault zone in the billefjorden austfjorden area this produced a large monoclinal fold across the fault zone which was later cross cut by extensional structures to produce the present day billefjorden syncline this localized late extension is related to a slight variation in the trend of the billefjorden fault zone through this area

isotopic evidence for multiple contributions to felsic magma chambers gouldsboro granite coastal maine abstract the gouldsboro granite forms part of the coastal maine magmatic province a region characterized by granitic plutons that are intimately linked temporally and petrogenetically with abundant co existing mafic magmas the pluton is complex and preserves a felsic magma chamber underlain by contemporaneous mafic magmas the transition between the two now preserved as a zone of chilled mafic sheets and pillows in granite mafic components have highly variably isotopic compositions as a result of contamination either at depth or following injection into the magma chamber intermediate dikes with identical isotopic compositions to more mafic dikes suggest that closed system fractionation may be occurring in deeper level chambers prior to injection to shallower levels the granitic portion of the pluton has the highest nd isotopic composition e nd 3 0 of plutons in the region whereas the mafic lithologies have nd isotopic compositions e nd 3 5 that are the lowest in the region and similar to the granite and suggestive of prolonged interactions and homogenization of the two components sr and nd isotopic data for felsic enclaves are inconsistent with previously suggested models of diffusional exchange between the contemporaneous mafic magmas and the host granite to explain highly variable alkali contents the felsic enclaves have relatively low nd isotopic compositions e nd 2 1 indicative of the involvement of a third lower e nd melt during granite petrogenesis perhaps represented by pristine granitic dikes contemporaneous with the nearby pleasant bay layered intrusion the dikes at pleasant bay and the felsic enclaves at gouldsboro likely represent remnants of the silicic magmas that originally fed and replenished the overlying granitic magma chambers the large isotopic and chemical contrasts between the enclaves and granitic dikes and granitic magmas may be in part a consequence of extended interactions between the granitic magmas and co existing mafic magmas by mixing mingling and diffusion alternatively the granitic magmas may represent an additional crustal source using granitic rocks such as these with abundant evidence for interactions with mafic magmas complicate their use in constraining crustal sources and tectonic settings fine grained dike rocks may provide more meaningful information but must be used with caution as these may also have experienced compositional changes during mafic felsic interactions

partition coefficients for rare earth elements in mafic minerals of high silica rhyolites the importance of accessory mineral inclusions abstract ree concentrations of mafic mineral separates from high silica rhyolites measured by inaa are high and variable compared to electron microprobe analyses of the minerals themselves the mafic phases commonly contain inclusions or have adhering grains of accessory rare earth element ree rich minerals optical and electron microscopic observation revealed discrete grains of chevkinite rare earth titano silicate included within clinopyroxenes from the sierra la primavera mexico rhyolite and monazite grains adhering to ortho and clinopyroxenes from the bishop tuff california during hand picking of mineral separates inclusions are only partly removed as a result the magnitude and variability of true mineral melt partition coefficients for light ree have been overestimated the true ree partition coefficients of la primavera and bishop tuff pyroxenes obtained by microprobe are only slightly higher than they are in lower silica rhyolites and are not as variable as previously thought the partitioning slope is positive as in less silicic systems the relative partitioning behavior of ree in high silica rhyolites is dominated by crystal chemical controls and not by liquid structural effects when a partition coefficient is used for crystallization calculations adhering phases and inclusions should be retained or the minor phases must be accounted for separately alternatively a bulk distribution coefficient can be calculated using whole rock and glass compositions and the glass mode

fault deformation mechanisms and fault rocks in micritic limestones examples from corinth rift normal faults abstract a multidisciplinary study investigates the influence of different parameters on fault rock architecture development along normal faults affecting non porous carbonates of the corinth rift southern margin here some fault systems cut the same carbonate unit pindus and the gradual and fast uplift since the initiation of the rift led to the exhumation of deep parts of the older faults this exceptional context allows superficial active fault zones and old exhumed fault zones to be compared our approach includes field studies micro structural optical microscope and cathodoluminescence geochemical analyses 13 c 18 o trace elements and fluid inclusions microthermometry of calcite sin kinematic cements our main results in a depth window ranging from 0 m to about 2500 m are i all cements precipitated from meteoric fluids in a close or open circulation system depending on depth ii depth in terms of p t condition determines the development of some structures and their sealing iii lithology marly levels influences the type of structures and its cohesive non cohesive nature iv early distributed rather than final total displacement along the main fault plane is the responsible for the fault zone architecture v petrophysical properties of each fault zone depend on the variable combination of these factors

energy constrained open system magmatic processes 3 energy constrained recharge assimilation and fractional crystallization ec rafc 1 geochemical data for igneous rock suites provide conclusive evidence for the occurrence of open system processes within thermally and compositionally evolving magma bodies the most significant processes include magma recharge with possible enclave formation and magma mixing assimilation of anatectic melt derived from wallrock partial melting and formation of cumulates by fractional crystallization rafc in this study we extend the energetically constrained assimilation and fractional crystallization ec afc model spera and bohrson 2001 bohrson and spera 2001 to include the addition of compositionally and thermally distinct recharge melt during simultaneous assimilation and fractional crystallization energy constrained recharge assimilation and fractional crystallization ec rafc tracks the trace element and isotopic composition of melt cumulates and enclaves during simultaneous recharge assimilation and fractional crystallization ec rafc is formulated as a set of 3 t i s coupled nonlinear differential equations where the number of trace elements and radiogenic and stable isotope ratios modeled are t i and s respectively solution of the ec rafc equations provides values for the average wallrock temperature ta mass of melt within the magma body mm mass of cumulates mct and enclaves men mass of wallrock involved in the thermal interaction mao mass of anatectic melt assimilated m a concentration of t trace elements and i s isotopic ratios in melt cm cumulates cct enclaves cen and anatectic melt ca as a function of magma temperature tm input parameters include the equilibration temperature teq the initial temperature and composition of pristine melt tmo cmo emo recharge melt tro cro ero and wallrock tao cao eao temperature dependent trace element distribution coefficients dm dr da heats of transition for wallrock ha pristine melt hm and recharge melt hr and the isobaric specific heat capacity of assimilant cp a pristine melt cp m and recharge melt cp r the magma recharge mass function mr tm is specified a priori and defines how recharge magma is added to standing magma the present ec rafc simulator incorporates a weak coupling to major element mass balance and phase relations based on laboratory experiments or gibbs energy minimization e g ghiorso 1997 ec rafc can be applied to a variety of magmatic systems including volcanic suites that show evidence of magma mixing layered mafic intrusions and granitoid plutons predictions for masses as well as compositions of magmatic products are part of the ec rafc solution the systems approach provides an opportunity to quantitatively assess the roles of assimilation fractional crystallization and magma recharge in magma evolution using trace element and isotopic constraints together with energy conservation

transient two dimensional dynamics in the upper conduit of a rhyolitic eruption a comparison of closure models for the granular stress to elucidate the role of particle collisions in redistributing momentum after fragmentation a numerical study was performed comparing the behavior of an inviscid or collision less granular material with a granular material whose viscosity and pressure were modeled using kinetic theory the granular viscosity calculation is sensitive to particle size and three particle sizes were considered 0 0002 m 0 002 m and 0 02 m a critical volume fraction of gas 0 75 identifies the onset of fragmentation dividing the region of rhyolitic magma with dispersed bubbles from the region of turbulent gas with dispersed particles the transient simulations can be divided into two dynamic regimes an initial shock followed by a transition to steady state during the initial shock phase treatment of the granular pressure and viscosity led to greater particle velocities relative to the inviscid calculation due to the development of higher gas pressure at fragmentation however as steady state is approached the viscosity slows the particle phase relative to the inviscid counterpart for particles greater than a millimeter the modeled sub millimeter particle velocity was insensitive to the treatment of the granular pressure and viscosity centimeter scale particles have a much higher granular viscosity up to 10 1 pa s and the kinetic theory calculation is thus relevant in these conditions after reaching steady state the differential velocity between gas and particles at the conduit exit correlates with particle size for both the inviscid and granular viscosity calculations negligible differential velocity develops for sub millimeter particles but centimeter scale particles exit the conduit with 5 differential velocity between phases

evolution of fracture and fault controlled fluid pathways in carbonates of the albanides fold thrust belt the process of fracture and fault formation in carbonates of the albanides fold thrust belt has been systematically documented using hierarchical development of structural elements from hand sample outcrop and geologic map scales the function of fractures and faults in fluid migration was elucidated using calcite cement and bitumen in these structures as a paleoflow indicator two prefolding pressure solution and vein assemblages were identified an overburden assemblage and a remote tectonic stress assemblage sheared layer parallel pressure solution surfaces of the overburden assemblage define mechanical layers shearing of mechanical layers associated with folding resulted in the formation of a series of folding assemblage fractures at different orientations depending on the slip direction of individual mechanical layers prefolding and folding related fracture assemblages together formed fragmentation zones in mechanical layers and are the sites of incipient fault localization further deformation along these sites was accommodated by rotation and translation of fragmented rock which formed breccia and facilitated fault offset across multiple mechanical layers strike slip faults formed by this process are organized in two sets in an apparent conjugate pattern calcite cement and bitumen that accumulated along fractures and faults are evidence of localized fluid flow along fault zones by systematic identification of fractures and faults their evolution and their fluid and bitumen contents along with subsurface core and well log data we identify northeast southwest trending strike slip faults and the associated structures as dominant fluid pathways in the albanides fold thrust belt

on the origin of high alumina arc basalt and the mechanics of melt extraction most models of high alumina arc basalt petrogenesis rely heavily on the supposition that the abundances of certain trace elements in particular the relatively unfractionated rare earth element ree patterns and the unusually high concentrations of k rb sr and ba are incompatible with a garnet bearing subducted oceanic crustal quartz eclogite source rock we have carefully examined this apparently unequivocal evidence in light of recent progress on the physics of melt extraction and the heat transfer and mechanics of magma ascent the weakest element of all trace element models involving a quartz eclogite source is the assumption that the element concentrations are fixed at the source and only later modified in the near surface environment we expand on such models by monitoring the concentrations of r ee and major and trace elements during initial melting ascent and extraction of magma this is done by combining calculated cooling curves for ascending magmatic bodies with high pressure phase equilibria the amount that each phase contributes to the melt is monitored along with the composition of the melt and residual solids with quartz eclogite initial melting initiates gravitational instability of the entire source material melt plus solids before melt extraction can occur during ascent of this mush melting increases until the solids can be repacked to free the melt this extraction takes place some 15 20 km above the slab after about 50 per cent melting at which point the melt has a pattern of ree and other trace element concentrations almost identical to those observed in high alumina arc basalts assuming an initial composition equivalent to altered oceanic crust plus 5 per cent pelagic sediment sr abundances are the only ones which are not well matched by this process the major element concentrations of the extracted melt also closely match those of high alumina arc basalt a similar but less detailed evaluation of both fertile and depleted peridotite source rocks yields good agreement for the ree and other trace element concentrations assuming a lree enriched source rock strongly enriched in k rb sr and ba ni cr and co abundances are satisfied only through substantial low pressure fractionation of mafic phases in particular olivine though not rigorously tested such a process may be compatible with the observed major element concentrations of high alumina basalt however the experimentally verified fact that high alumina basalts could never have been in equilibrium with either an olivine beari ng magma or source rock eliminates this possibility altogether thus the simultaneous consideration of the mechanics of ascent and melt extraction along with phase equilibria clearly shows that partial melting of quartz eclogite best satisfies the chemical constraints of major trace and ree characteristics of high alumina arc basalts

extensional fault cores in micritic carbonate case studies from the gulf of corinth greece abstract the major pisia and doumena faults of the corinth rift greece are both hosted by micritic carbonate rock their common fault elements are principal slip surfaces layers of fault rocks fault rock and host rock lenses corrugations and smaller shear and tension fractures along planar fault segments a corrugated slip surface with an associated thin fault rock layer is formed well developed down dip corrugations indicate movement along the same surface over many fault increments bends jogs in the faults are sites of complex structural relations hosting frequent lenses more porous fault rocks and dense networks of fractures major jogs in the slip surfaces have both strike and dip oriented undulating curvature that are associated with higher order fracture networks as well as frequent lenses fault core lens shapes of the doumena fault show relationship of length vs width of 3 2 similarly principal slip surfaces of the two faults show undulations with aspect ratios of amplitude vs wavelength 1 19 and 1 14 in strike direction despite a prominent difference in down dip geometry the intrinsic deformation in fault cores of micritic carbonate supports a model in which fluids entered the core by damage zone fractures that are linked to the principal slip surface flow along the fault core was controlled by the fracture system of lenses and thereby lens connectivity but may have been hampered by flow retarding fault rocks the flow potential is especially well developed in fault bends and breached relays due to frequent lenses and well developed fracture networks