aragonite crystal fans in neoproterozoic cap carbonates a case study from brazil and implications for the post snowball earth coastal environment abstract neoproterozoic cap carbonates are characterized by anomalous sedimentary features including sea floor precipitates represented by aragonite pseudomorph cement crusts and crystal fans these features are found in restricted periods of geological history and their generation in the context of the neoproterozoic has been attributed to very specific postglacial conditions leading to alkalinity oversaturation new sedimentary and geochemical results on well preserved neoproterozoic deposits of aragonite pseudomorph crystal fans at the base of the sete lagoas formation bambui group central brazil are reported the micrite settling facies shows the highest abundance of crystal fans arranged in centimeter scale layers interfingered with the micrite matrix this facies is interpreted as a result of postglacial calcium carbonate oversaturation in restricted areas characterized by marine dysoxic waters a numerical model constrains the kinetics of formation of aragonite crystals or micrite by calculating the induction times and precipitation rates of both carbonate species for postglacial conditions of elevated temperature and high atmospheric pco2 in these conditions the mg ca ratio of the neoproterozoic seawater is calculated at ca 1 2 alkalinity oversaturation is monitored by a variable evaporation degree aragonite formation is kinetically favored and the discrepancy between calcite and aragonite precipitation rate is greater as atmospheric pco2 hence alkalinity is higher these modeling conditions do not preclude the contribution of incomplete organic matter degradation to alkalinity as suggested by negative carbon isotope signatures in addition the large number of aragonite micrite pairs suggests a seasonal or paleoclimatic forcing other cases of abiotic aragonite precipitation through time are also briefly examined by comparison

multiple deformation episodes at myra falls volcanic hosted massive sulfide camp central vancouver island british columbia canada a detailed deformation history for central vancouver island was determined at myra falls volcanic hosted massive sulfide camp with early ductile deformation overprinted by several distinct episodes of brittle deformation brittle structures were subdivided into separate groups based on their morphology geometry kinematics and crosscutting relations the central location of this study provides a link between previous deformation studies in northem and southem vancouver island late paleozoic northeast southwest compression d i produced open upright folds with variably developed north northwest striking axial planar cleavage zones si and subhorizontal stretching lineations li subparallel to fi fold axes renewed northeast southwest compression during the collision of wrangellia and north america produced a second foliation s2 in localized shear zones slightly oblique to the dominant si foliation these two events are recorded throughout vancouver island wherever the basement is exposed mid cretaceous northeastsouthwest compression during d3 produced early steep conjugate strike slip faults d3a overprinted by northeast and southwest dipping thrust faults and bedding parallel shears d3b d3 structures have been previously recognized in northem vancouver island but not as far south as myra falls north south extension d4 produced east north and east southeast striking normal faults these faults consistently crosscut earlier d i d3 structures and reactivate steep d3a faults normal faulting is correlated with the development of the upper cretaceous nanaimo basin but no faults of this age have previous been reported from onshore studies the youngest structures at myra falls are large northweststriking northeast dipping tbrust faults and steep west to west northwest striking sinistral strike slip faults formed during the ds event these faults are gouge rich wavy anastomosing structures with cleaved wall rock zones up to several metres wide the ds faults are correlated with eocene deformation caused by the accretion of the pacific rim and crescent terranes along the southwestern margin of vancouver island myra falls is the northemmost location to have been reported at which the structures formed as part of the cowichan fold and tbrust belt

stable and unstable damage evolution in rocks with implications to fracturing of granite summary we address the relation between the rock rigidity and crack density by comparing predictions of a viscoelastic damage rheology model to laboratory data that include direct microscopic mapping of cracks the damage rheology provides a generalization of hookean elasticity to a non linear continuum mechanics framework incorporating degradation and recovery of the effective elastic properties transition from stable to unstable fracturing and gradual accumulation of irreversible deformation this approach is based on the assumption that the density of microcracks is uniform over a length scale much larger than the length of a typical crack yet much smaller than the size of the entire deforming domain for a system with a sufficiently large number of cracks one can define a representative volume in which the crack density is uniform and introduce an intensive damage variable for this volume we tested our viscoelastic damage rheology against sets of laboratory experiments done on mount scott granite based on fitting the entire stress strain records the damage variable is constrained and found to be a linear function of the crack density an advantage of these sets experiments is that they were preformed with different loading paths and explicitly demonstrated the existence of stable and unstable fracturing regimes we demonstrate that the viscoelastic damage rheology provides an adequate quantitative description of the brittle rock deformation and simulates both the stable and unstable damage evolution under various loading conditions comparison between the presented data analysis of experiments with mount scott granite and previous results with westerly granite and berea sandstone indicates that granular or porous rocks have lower seismic coupling this implies that the portion of elastic strain released during a seismic cycle as brittle deformation depends on the lithology of the region hence upper crustal regions with thick sedimentary cover or fault zones with high degree of damage are expected to undergo a more significant inelastic deformation in the interseismic period compared to intact crystalline rocks

first ediacaran fauna found in western africa and evidence for an early cambrian glaciation ediacara type body fossils are reported here for the first time from the west african craton in algeria this assemblage comprises medusoids comparable to medusinites sp and nimbia a trace fossil and a new genus of body fossil with uncertain affinity the fossils are in sandstones of the neoproterozoic cover separated by a major unconformity from the overlying tillite considered until now to be late neoproterozoic most ediacaran fauna radiated after the varanger ice age and tillites associated in ahaggar with molasse of the pan african belt are overlain by carbonates that were deposited during deglaciation and that locally contain early cambrian shelly fossils therefore we interpret the glaciogenic diamictite as early cambrian in age

cratonic and foreland early cambrian phosphorites of west africa palaeoceanographical and climatical contexts abstract in western gondwana two types of pan african brasiliano fold belts have been distinguished the first type is characterized by an old long lived tectonic cycle 1000 600 ma and is generally oceanic the closure of these oceans resulted in the aggregation of western gondwana in late neoproterozoic time the second type is characterized by a young short lived cycle about 600 520 ma and is mostly intracontinental fold belts of the second type have various geodynamic significances and represent folded foreland intermontane or impactogen type basins formed during or slightly after the deformational closure of the old long lived cycle phosphorites of west africa are associated with the young short lived tectonic cycle they occur together with the upper member of a distinctive formation known all over west africa this formation is made up of three members and consists from base to top of diamictites generally tillites with detrital intercalations carbonate rocks with barite and bedded cherts with local shale or siltstone intercalations in eastern senegal in the cratonic taoudeni basin the carbonate member is palaeontologically dated as early cambrian deposited during a glacio eustatic transgression it can be considered as a chronostratigraphic marker for the entire west africa phosphorites associated with or immediately following the eustatic transgression are also possibly of early cambrian age they are located either in the lower part of the chert member in the upper part of the carbonate member or sandwiched between these two units in fersiga and namel in the taoudeni basin phosphorites are associated with stromatolites characterizing the initial stage of the transgression they are overlain by evaporites which can be related to an isostatic rebound in the volta foreland basin phosphorites are associated with the chert member there they were deposited on a shelf ramp either on its proximal portion where they are strongly reworked kodjari and arli occurrences or in its distal part where they are interbedded with sediments deposited under anoxic conditions tapoa mekrou and aloub djouana occurrences the depth of marine sedimentation as indicated by the sedimentological characteristics of phosphorites and associated sediments was controlled by the combined effect of glacio eustatic sea level rise subsidence rate and isostatic rebound numerous textural features are similar in the phosphorites from the two basins phosphatic grains occurring as oncolites and stromatolitic fragments together with intraclasts show a noticeable biogenic contribution of microbial origin microbial build ups were formed in submergent emergent environments in the taoudeni basin and in the outer shelf of the volta basin apatites from these basins have similar ree contents which suggest a continental origin for the phosphorus early cambrian phosphorites of west africa were deposited soon after glacially derived sediments according to the available palaeocontinental maps both were laid down at palaeolatitudes of about 40 s west african early cambrian phosphorites thus formed at higher latitudes than their modern analogues which are confined within the inter tropical zone

assessing hydrothermal alteration intensity in volcanic hosted massive sulfide systems using portable x ray fluorescence analysis of drill core an example from myra falls canada current portable x ray fluorescence pxrf technology can rapidly and inexpensively yield concentrations of geologically significant elements typically with instrument detection limits below several tens of parts per million based on conventional xrf whole rock geochemical data both the ishikawa alteration index and the chlorite carbonate pyrite index increase with proximity to sulfide mineralization at myra falls however available pxrf technology is typically unable to detect all the elements required to calculate these alteration indices as a result there is a need to utilize the elements that are readily detectable using pxrf and apply these to hydrothermal alteration assessment we propose that rb sr ratios provide a robust proxy for the ishikawa alteration index and demonstrate that conventional whole rock xrf analytical results for rb and sr can be reproduced using pxrf analysis from drill core surfaces at myra falls the rb sr ratios vary from 2 0 for intensely altered rocks downhole profiles of alteration intensity generated from systematic pxrf analysis of drill core surfaces can be used to inform drilling and targeting decisions the application of the rb sr ratio as a proxy for alteration intensity extends beyond this case study and can be applied to other hydrothermal systems that produce phyllosilicate minerals as alteration products of feldspar

stratigraphic evidence for shear in structural development of the triassic levant margin new borehole data on the epicontinental to deep marine transition in israel abstract triassic tectonic movements that include shear along a significant portion of the levant margin are evidenced from microfacies analysis of material recovered from the asher atlit 1 ga ash 2 meged 2 devora 2 and ramalla 1 onshore boreholes seismic studies showed that structural lineaments attributed to early mesozoic extension underlie coastal and central israel trending ne sw beneath southern israel and sub parallel to the then extensional palmyride basin of syria a more curved trend approximately nnw sse lies to the north beneath central israel coast parallel sedimentary domains formed above these lineaments which constitute the newly formed passive margin of the levant coast in the triassic the sedimentary history of these domains indicates that some were linked to each other and others disconnected the relative vertical movement between one domain and another is explained by activation of transpressional and trans tensional shear movements on the underlying curved faults these subordinate vertical movements also created the discontinuous barriers and small subsiding basins that separate the epicontinental sedimentary domain from the open tethys causing partial restriction necessary for the intermittent development of thick evaporites in the internal domains alternating with a regionally suppressed carbonate system this zone is here named the onshore levant margin shear zone olmsz shear was invoked theoretically in a number of models for the tectonic evolution of the eastern mediterranean as part of a neotethyan opening system this paper provides rock based evidence for such shear applicable to 20 of the eastern levant margin in the triassic

neonereites uniserialis from c 600 ma year old rocks in western scotland and the emergence of animals a chain of pellets neonereites uniserialis usually attributed to a coelomate or pseudocoelomate metazoan is described from the middle dalradian bonahaven formation of western scotland in sandstones not far above the port askaig tillite this trail lies more than 8 km below u pb zircon dated tayvallich lavas 595 4 ma and predates early deformation plus intrusion by granites at ben vuirich dated at 597 11 and 590 2 ma u pb zircon chronology for early metazoan evolution suggests that this is the earliest putative evidence for coelomates or pseudocoelomate discovered so far with a minimum interglacial age of c 600 ma bp it is from about this time that a fall takes place in the maximum 13 c of carbonates suggestive of a decline in the long term rate of carbon burial one explanation for this decline is the increasing impact of metazoan bioturbation through the late neoproterozoic to cambrian interval

the ediacaran sedimentary architecture and carbonate productivity in the atar cliffs adrar mauritania palaeoenvironments chemostratigraphy and diagenesis abstract the neoproterozoic strata of the taoudeni basin west african craton display a single glaciogenic deposit late cryogenian in age and included within a stratigraphic marker triad of tillite carbonate and bedded chert this work is focused on the analysis of the sedimentary architecture and episodic carbonate productivity related to its transgressive deglaciation recorded in the atar cliffs of adrar mauritania it offers a joint chemo event and sequence stratigraphic analysis that allows us to control problems of stratigraphic completeness and time resolution necessary for regional and worldwide stratigraphic correlation in the atar cliffs the cap carbonate sequence is underlain by a composite unconformity that comprises the pan african i discordance and an inherited palaeorelief associated with the glaciation the transgressive sequence began with accumulation of a sheet like apron onlapped by a toe of slope to basin transition with cap carbonates bedded cherts and distal turbidites tichilit el beida shales the carbonate strata of the atar cap carbonate sequence have recorded both dolomitization and dedolomitization processes destroying the original cement textures carbon isotope values from the sheet like apron range from 0 to 0 6 were directly controlled by the reworking of the underlying atar strata and do not reflect primary variations in seawater composition the general pattern of 13 c fluctuations within the overlying incomplete cap carbonate sequence is consistent with other post late cryogenian strata except in the initial shift from slightly to moderately negative values recognized elsewhere that is not preserved in the study area carbon isotope values in the preserved upper part of the cap carbonate record a pronounced rise in 13 c from 6 2 to highly enriched values 3 7 followed by the final demise of carbonate productivity the cap carbonate sequence is topped by an erosive unconformity succeeded by the recovery of carbonate accumulation represented by an onlapping dolostone deposited in coastal to foreshore environments there the carbon isotope values reflect the return to moderately negative values ranging from 0 9 to 2 0 the palaeogeographic development of a palaeorelief associated with the end of glacial conditions and deposition of the onlapping atar cap carbonate is related to the presence of interbedded felsic bentonites and phenocrysts and reflects the intermittent influence of a neighbouring explosive volcanism

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

dynamic rupture on a material interface with spontaneous generation of plastic strain in the bulk abstract we discuss 2d simulations of in plane ruptures on a fault between different solids in a model that includes dynamic generation of plastic strain off the fault the fault is governed by a regularized friction with a gradual response to abrupt changes of normal stress while plastic strain in the bulk is governed by a coulomb yielding criterion the occurrence of off fault damage stabilizes the slip velocity on the fault stable self sustaining ruptures propagate on the material interface as narrow unidirectional pulses in the direction of slip on the more compliant side of the fault plastic strain is generated only on the stiffer side of the fault the tensional quadrant in the direction of rupture propagation in a strip of approximately constant width that is correlated with the slip velocity on the fault simulations for various values of confining normal stress material contrast and cohesion in the bulk suggest that significant generation of off fault damage is limited to conditions that correspond to the top few kilometers of the crust the results are compatible with field observations of shallow asymmetric damage patterns in the structure of several large faults

chemostratigraphy of the lower arroyo del soldado group vendian uruguay and palaeoclimatic implications abstract new c and o isotopic determinations from the vendian lower arroyo del soldado group are reported and combined with sedimentologic and biostratigraphic data on the basis of different geochemical and petrographic criteria the primary nature of the c and sr isotopic signature is shown positive d 13 c values characterize the mainly siliciclastic upper yerbal formation which contains oxide facies bif and a diverse assemblage of skeletal fossils including cloudina riemkeae a series of positive and negative d 13 c excursions occur up section in the overlying polanco formation mainly composed of limestones and limestone dolostone rhythmites the transition to the overlying barriga negra and cerro espuelitas formation which consists of conglomerates and shales cherts bif respectively is marked by a further negative excursion on the basis of sedimentary structures a correlation of d 13 c with palaeobathymetry is established positive d 13 c peaks are associated with high sea level stand high organic carbon burial and relatively higher microfossil diversity while negative d 13 c excursions occur in carbonates with less organic matter less microfossil diversity and are always associated to regressions these observations can be readily explained by palaeoclimatic models which postulate that enhanced bioproductivity due to higher availability of nutrients p n fe was the key factor controlling neoproterozoic glaciations the mentioned models are discussed in view of the new data the occurrence of at least four cold periods in the upper vendian is envisaged these cold periods led to sea level fall and possibly glaciation at higher latitudes the absence of glacigenic rocks associated to negative d 13 c excursions in the arroyo del soldado group is probably due to the tropical setting of the basin finally the upper vendian age of the lower arroyo del soldado group is confirmed on the basis of c and sr isotopes the onset of carbonate deposition at the base of the polanco formation is estimated at 580 ma by comparison with existing global isotopic curves

neoproterozoic substrate condition vis a vis microbial mat structure and its implications sonia sandstone rajasthan india dst fast track project young scientist scheme no sr ftp es 03 2011 cas phase v upe ii programme of jadavpur university national research foundation and university of pretoria south africa

earthquake ruptures modulated by waves in damaged fault zones faults are usually surrounded by damaged zones of lower elastic moduli and seismic wave velocities than their host rocks if the interface between the damaged rocks and host rocks is sharp enough earthquakes happening inside the fault zone generate reflected waves and head waves which can interact with earthquake ruptures and modulate rupture properties such as rupture speed slip rate and rise time we find through 2 d dynamic rupture simulations the following 1 reflected waves can induce multiple slip pulses the rise time of the primary pulse is controlled by fault zone properties rather than by frictional properties 2 head waves can cause oscillations of rupture speed and in a certain range of fault zone widths a permanent transition to supershear rupture with speeds that would be unstable in homogeneous media 3 large attenuation smears the slip rate function and delays the initial acceleration of rupture speed but does not affect significantly the rise time or the period of rupture speed oscillations 4 fault zones cause a rotation of the background stress field and can induce plastic deformations on both extensional and compressional sides of the fault the plastic deformations are accumulated both inside and outside the fault zone which indicates a correlation between fault zone development and repeating ruptures spatially periodic patterns of plastic deformations are formed due to oscillating rupture speed which may leave a permanent signature in the geological record our results indicate that damaged fault zones with sharp boundaries promote multiple slip pulses and supershear ruptures

micro scale damage characterized within part of a dismembered positive flower structure san jacinto fault southern california usa abstract to better understand the processes that control sub grain fracturing in fault damage zones we studied micro scale damage in sandstones adjacent to the san jacinto fault sjf where it is exhumed from a total depth of 220 m beneath a northeast verging thrust that comprises part of a relic and dismembered flower structure the thrust places high grade gneiss of the pre middle cretaceous burnt valley complex over sedimentary rocks of the pleistocene bautista formation an 10 12 cm thick zone of cataclasite is present along the northeast side of the fault adjacent to a narrow black ultracataclasite core non pervasive microscopic damage characterized by pulverized sand grains extends outward from the zone of cataclasites tens of meters such textures are better developed in sandstones that contain

pulverized fault rocks and damage asymmetry along the arima takatsuki tectonic line japan abstract we present field and laboratory data on pulverized rocks at the hakusui kyo outcrop of the arima takatsuki tectonic line attl which is a dextral strike slip fault with 17 km displacement juxtaposing granite to the south against rhyolite to the north the majority of slip at the surface is localized to a clay rich gouge fault core 8 10 cm in width surrounded by a coarsening outwards fault breccias up to 3 m wide fault damage is highly asymmetric with respect to the slipping zone the granite south of the fault has a pulverized damage zone up to 200 m wide while the rhyolite to the north has only about 3 m wide non pulverized fault breccia the degree of pulverization in the granite decreases approximately logarithmically with normal distance from the slip zone the highly fractured pulverized rocks exhibit several distinct textural characteristics in thin section grains appear to be highly comminuted but the original grain shapes and margins are recognizable microfractures tend to be tensile in no preferred orientation grain fragments display little to no rotation and lack evidence of in situ shear consequently at macroscale the rocks appear to preserve original granitic textures despite being highly fractured and friable the observed pulverization and rock damage asymmetry are most consistent with generation mechanism involving ruptures on a bimaterial interface with statistically preferred propagation direction leading to damage primarily on the side with higher seismic velocity at depth this is supported by laboratory measurements of p wave ultrasonic velocities on intact samples which indicate that the granites have consistently higher velocity than the rhyolite with increasing confining pressure

chemical and physical characteristics of pulverized tejon lookout granite adjacent to the san andreas and garlock faults implications for earthquake physics we present new detailed analyses of samples of pulverized tejon lookout granite collected from sections adjacent to the san andreas and garlock faults in southern california the tejon lookout granite is pulverized in all exposures within about 100 m from both faults chemical analyses indicate no or little weathering in the collected samples although xrd analysis shows the presence of smectite illite and minor kaolinite in the clay size fraction weathering products may dominate in the less than 1 micron fraction the average grain size in all samples of pulverized tejon lookout granite ranges between 26 and 208 microns silt to fine sand with the particle size distribution in part a function of proximity to the primary slip zone the san andreas fault samples that we studied are generally finer grained than those collected from adjacent to the garlock fault the particle size distribution for each studied sample from both faults follows a pseudo power law with a continuously changing exponent which suggests that pulverization is not simply a consequence of direct shear the average particle size that we determined for our samples is considerably coarser than reported in previous investigations which we attribute to possible measurement errors in the prior work our data and observations suggest that dynamic fracturing in the wall rock of the san andreas and garlock faults only accounts for about 1 or less of the earthquake energy budget

particle size and energetics of gouge from earthquake rupture zones surprisingly considering the forces that we see at the surface not all the energy involved in an earthquake is transformed into ground motion much of it is consumed by frictional heating and rock pulverization an analysis of pulverized rock or gouge collected from the san andreas fault in california and from a rupture zone at 2 km depth in a south african gold mine contradicts the commonly held view that gouge surface energy is a negligible component of earthquake energy balance the analysis reveals unexpected diminutive particles in gouge samples indicating that pulverization not frictional heating is the major consumer of earthquake energy at depth this might explain the heat flow anomaly seen in the san andreas fault system and perhaps some other long standing puzzles in earthquake energetics grain size reduction and gouge formation are found to be ubiquitous in brittle faults at all scales1 2 3 4 and most slip along mature faults is observed to have been localized within gouge zones5 6 this fine grain gouge is thought to control earthquake instability3 6 7 8 and thus understanding its properties is central to an understanding of the earthquake process7 9 here we show that gouge from the san andreas fault california with 160 km slip and the rupture zone of a recent earthquake in a south african mine with only 0 4 m slip display similar characteristics in that ultrafine grains approach the nanometre scale gouge surface areas approach 80 m2 g 1 and grain size distribution is non fractal these observations challenge the common perception that gouge texture is fractal10 11 and that gouge surface energy is a negligible contributor to the earthquake energy budget3 9 12 we propose that the observed fine grain gouge is not related to quasi static cumulative slip but is instead formed by dynamic rock pulverization during the propagation of a single earthquake

mechanics of grain size reduction in fault zones 1 recent observations of nanometer scale particles in the cores of exhumed fault zones raise questions about how such small particles are formed and how they survive especially if significant shear heating is produced during an earthquake commercial crushing and grinding operations encounter a grind limit near 1 mm below which particles deform plastically rather than fracturing a fragmentation model and low temperature plasticity mechanics indicate that it is not possible to produce under compressive loading and short timescale significantly smaller particles at any strain rate however shock loading and subcritical crack growth can produce nanometer scale fragments in compression under tensile loading the fragment size is determined by a competition between the nucleation of cracks and stress relaxation in their neighborhoods therefore higher tensile strain rates produce smaller fragments the ultimate limit is determined by the availability of elastic strain energy which does not place a significant constraint on the minimum grain size grain growth kinetics suggests that survivability of grains is very temperature sensitive a 10 nm quartz fragment will double its size in 0 1 s at 1000c in 20 s at 800c in 14 h at 600c and in 10 years at 400c the observation of grains smaller than 10 nm places meaningful constraints on the dynamic fields and permeability of the fault zone during a large earthquake microstructural analysis of the grains and rock damage may be used to infer whether fragmentation occurred under macroscopic tension or compression

dynamic fracturing field and experimental observations abstract we analyzed a system of complex joints in thick dolomite layers that are exposed within the western margins of the dead sea basin these joints display two dominant features tree like branching and a gradual increase of density that leads to local fragmentation the development of this joint system is investigated in laboratory experiments with samples of brittle ductile layered composites the samples were subjected to layer parallel extension and displayed three styles of fracturing planar fractures known from previous tests branching fractures and clustering fractures observed here for the first time in layered composites based on fracture morphology we deduced that the branching and clustering fractures in the experiments and the tree like closely spaced joints in the field propagated at dynamic high velocity growth rates it is proposed that the morphological features described here could be used as field criteria to recognize dynamic rates of rock fracturing

dynamic branched fractures in pulverized rocks from a deep borehole pulverized rocks observed in outcrops near large faults are considered to be products of intense fragmentation occurring during strong earthquakes however the exact mechanism and depth of pulverization are controversial here we present an analysis of pulverized rocks along an 930 m interval in a deep borehole in the vicinity of a buried fault cuttings of carbonate lithology from below 4980 m host well preserved sets of dense fractures with a hierarchic branching geometry that was never affected by near surface processes branches are typically symmetric with consistent orientations and hierarchic splitting the main fractures are spaced at 0 1 mm with angular fragments ranging from a few microns to submicrons indicating further intense localized fragmentation splitting of fossils by fractures in the absence of lateral shear proves the tensile origin of the fractures the fracture geometry and density are consistent with dynamic tensile fractures that propagate at critical velocities in laboratory experiments thus these dense branching fractures are the first direct observation that pulverization in fault zones extends to a significant depth and originates from dynamic tensile fracturing

integrated chronostratigraphy of the vendian system of siberia implications for a global stratigraphy integrated 13 c chemostratigraphy and sequence stratigraphy are developed for a succession of vendian strata nokhtuisk section on the southern margin of the siberian platform the carbonates exhibit secular variations in 13 c and at least three major depositional sequences that encompass the last c 20 million years

temporal relationship between cratonization and glaciation the vendian early cambrian glaciation in western gondwana abstract cratonization has long been said to favour glaciation cratons would be ideal cradles for the development of continental ice caps in western africa the widespread continental glaciation developed near the proterozoic paleozoic boundary can no longer be considered as vendian according to the recent discovery of an early cambrian microfauna in eastern senegal it extends until atdabanian time 530 520 ma the age of its beginning lacks in precision it can be vendian or early cambrian in the hoggar fold belt it constitutes the lower part of molassic intermontane sequences where it is about 30 40 ma younger than the pan african cratonization dated at 600 ma this extensive cratonization closed the old long lived pan african brasiliano cycle 1000 600 ma and is responsible for the aggregation of west gondwana in the south american paraguay belt glacial sequences also postdate brasiliano cratonization dated at 590 ma they are probably vendian overlain by an ediacara like fauna and slightly older than those of western africa the glaciation was restricted to the shoulders of rifted basins initiating the young short lived pan african brasiliano cycle 600 or slightly younger to 520 ma world distribution of continents indicate that the widespread late vendian early cambrian ice cap glaciation of west africa developed at middle latitudes 50 30 whereas the probably vendian glaciation of the paraguay belt restricted to local highlands occupied high to middle latitudes 60 in western gondwana glaciation and cratonization occurring near the proterozoic cambrian boundary appear as distinct and temporary unrelated phenomena

subsea floor replacement in volcanic hosted massive sulfide deposits abstract recent research on volcanic hosted massive sulfide vms deposits indicates that syngenetic subsea floor replacement ores form an important component of many deposits in the context of vms deposits subsea floor replacement can be defined as the syn volcanic formation of sulfide minerals within pre existing volcanic or sedimentary deposits by infiltration and precipitation in open spaces fractures inter and intra granular porosity as well as replacement of solid materials there are five criteria for distinguishing subsea floor replacement in massive sulfide deposits 1 mineralized intervals are enclosed within rapidly emplaced volcanic or sedimentary facies lavas intrusions subaqueous mass flow deposits pyroclastic fallout 2 relics of the host facies occur within the mineral deposit 3 replacement fronts occur between the mineral deposit and the host lithofacies 4 the mineral deposit is discordant to bedding and 5 strong hydrothermal alteration continues into the hanging wall without an abrupt break in intensity criteria 1 3 are diagnostic of replacement whereas criteria 4 and 5 may suggest replacement but are not alone diagnostic because clastic sulfide ores contain accessory rock fragments collected by the parent sediment gravity flow s during transport criteria 2 can only be applied to massive semi massive disseminated or vein style deposits and not clastic ores the spectrum of vms deposit types includes deposits that have accumulated largely subsea floor and others in which sedimentation and volcanism were synchronous with hydrothermal activity and precipitation of sulfides occurred at and below the sea floor over the life of the hydrothermal system deposits that formed largely subsea floor are mainly hosted by syn eruptive or post eruptive volcaniclastic facies gravity flow deposits water settled fall autoclastic breccia however some subsea floor replacement vms deposits are hosted by lavas and syn volcanic intrusions sills domes cryptodomes burial of sea floor massive sulfide by lavas or sediment gravity flow deposits can interrupt sea floor mineralization and promote subsea floor replacement and zone refining the distance below the sea floor at which infiltration and replacement took place is rarely well constrained with published estimates ranging from less than 1 to more than 500 m but mainly in the range 10 200 m the upper few tens to hundreds of metres in the volcano sedimentary pile are the favoured position for replacement as clastic facies are wet porous and poorly consolidated in this zone and at greater depths become progressively more compacted dewatered altered and less amenable to large scale infiltration and replacement by hydrothermal fluids furthermore sustained mixing between the upwelling hydrothermal fluid and cold seawater is regarded as a major cause of sulfide precipitation in vms systems and this mixing process generally becomes less effective with increasing depth in the volcanic pile the relative importance of subsea floor replacement in vms systems is related principally to four factors the permeability and porosity patterns of host lithofacies sedimentation rate the relative ease of replacement of host lithofacies especially glassy materials and early formed alteration minerals during hydrothermal attack and physiochemical characteristics of the hydrothermal fluid

petrographic geochemical and fluid inclusion evidence for the origin of siliceous cap rocks above volcanic hosted massive sulfide deposits at myra falls vancouver island british columbia canada massive sulfides at the myra falls volcanic hosted massive sulfide vhms camp vancouver island british columbia canada are overlain by white chert black chert argillite and siltstone white chert is best developed above the battle orebody where it forms a siliceous caprock 3 5 m thick above the massive sulfides there is a gradational lateral change from white chert above massive sulfides to black chert and unaltered argillite 100 to 150 m south of the battle orebody chert horizons are also located above the ridge and extension ore zones but only minor chert lies above the hw orebody which is instead overlain by a thick argillite sequence the chert and argillite share similar sedimentologic and petrologic features including abundant parallel laminations interbedded turbidites radiolarian rich layers soft sediment deformation scours flame structures and small phosphatic concretions these features indicate that white and black chert formed as a replacement of mudstone rather than as exhalative or biogenic deposits silicification occurred early in the depositional history of the fine grained sediments and was contemporaneous with some ore formation early syndepositional features are still visible in the chert with primary pore spaces such as radiolarian tests filled by silica rutile apatite and minor sulfides displaying open space crystal growth the presence of minor ore clast breccias above the orebody indicates that at least parts of the battle orebody were exposed on the sea floor metal zoning is observed in the cap rock horizon above the battle orebody with higher cu zn and cd contentrations in chert directly above massive sulfides higher pb sb and ag contentrations in black chert at the edge of the siliceous cap rocks and lower metal concentrations in the distal argillite primary fluid inclusions in spherical quartz patches in chert above the battle orebody indicate that hydrothermal fluids passing through sediment were between 135 to 250c and had salinities ranging from 3 0 to 12 1 wt percent nacl equiv these data are similar to those for fluid inclusions measured in quartz interstitial to sulfides in the underlying battle orebody which have temperatures of homogenization ranging from 140 to 250c and salinities from 3 0 to 12 4 wt percent nacl equiv fluid inclusions in the battle orebody display a slight increase in salinity and homogenization temperature with depth which may reflect the overprinting of earlier high temperature stages by cooler fluids as the hydrothermal system waned or varying degrees of mixing between hydrothermal fluids and seawater a minimum depth for deposition of the cap rocks 200 m is estimated based on sedimentologic features such as fine parallel laminations and interbedded sandstone turbidites which indicate deposition below storm wave base greater water depths 1 000 1 500 m are suggested by the lack of evidence of boiling in fluid inclusions low o2 concentrations in the bottom water of the battle basin are suggested by the absence of bioturbation lack of fossils of benthic fauna degree of pyritization values 0 90 elevated zn pb cu cd as sb ag ba and v low fe and mn and v v ni 0 8 in the unaltered argillite paleosea floor reconstructions indicate that the battle and hw orebodies formed in small basins along a northwest trending ridge the finegrained sediments were deposited in depocenters within paleotopographic lows hydrothermal fluid densities estimated from fluid inclusions at myra falls range from 0 88 to 1 05 g cm3 and are higher than for many other vhms deposits however they are close to the density of seawater at 2c and a 2 000 m depth 1 028 g cm3 replacement textures in the siliceous cap rocks above the battle deposit the sheetlike morphology of the siliceous cap rocks and lateral metal zonation indicates that diffuse lateral flow of hydrothermal fluids through the porous sea floor sediments was more important than the buoyant rise of hydrothermal fluids into the water column however buoyant venting during formation of the battle deposit is indicated by positive eu anomalies and elevated metal values in argillite of the battle basin reflecting the wide dispersal of plume particulates the range of fluid densities indicate that the hydrothermal fluids emerging onto the sea floor and flowing laterally through porous sea floor sediments would have varied from buoyant to neutrally buoyant to negatively buoyant

the palaeobiology and geochemistry of precambrian hydrocarbon source rocks abstract organic carbon productivity and formation of hydrocarbon source rocks during the early precambrian was almost exclusively the product of the growth of microbial mats indirect evidence of microbial mats can be traced back to at least 2 6 2 7 ga neoarchaean with the earliest evidence of mat development in siliciclastic sediments coming from the 2 9 ga mesoarchaean predominantly marine sedimentary rocks of the mozaan group in south africa the earliest direct evidence for terrestrial microbial mats in siliciclastic sediments comes from the 2 75 ga palaeoproterozoic fluviolacustrine sediments of the hardey formation of the pilbara craton in western australia well preserved proterozoic hydrocarbons provide valuable information about the early evolution of the biosphere eukaryotic steranes biomarker for eukaryotic cells and therefore evolved forms of life are present in the geological record from about 2 7 ga but they are not abundant or diverse within archaean communities which tend to be dominated by archaea isoprenoids some hydrocarbons have been generated and migrated from archaean organic rich shales but they were probably not of sufficient volume to be of commercial interest the world s oldest significant hydrocarbon source rocks are palaeoproterozoic in age and include the shungite deposits 2 0 ga in the lake onega region of arctic russia there is strong evidence of a global biospheric oxygenation event at c 1300 1250 ma mesoproterozoic in conjunction with a first order positive shift in the marine carbon isotope record this is supported by the appearance of the oldest bedded marine gypsum deposits and of the earliest unambiguously multicellular eukaryotes at this time this oxygenation event probably played a significant role in supporting the more diverse eukaryotic communities preserved in the neoproterozoic molecular record and provided the volume of organic material required to generate commercial volumes of hydrocarbons hydrocarbon source rocks of late mesoproterozoic and early neoproterozoic age are widespread and include highly organic rich shales deposited in restricted basinal settings adjacent to stromatolitic carbonate banks by c 850 ma the neoproterozoic molecular record is dominated by hopanes from cyanobacteria with a significant abundance and diversity of eukaryotic steranes including those of multicellular eukaryotes red and green algae as well as molecular evidence for heterotrophic protists the most widespread hydrocarbon source rocks of mid to late neoproterozoic age are commonly transgressive organic rich black shales associated with inter glacial and post glacial phases of the neoproterozoic global scale glaciations the relative dominance of microbial mats in the contribution of organic matter as a source for hydrocarbon generation probably decreased significantly during the late neoproterozoic and earliest cambrian perhaps as a result of the rapid growth of grazing metazoan communities or possibly as a result of changes in seawater chemistry and or nutrient supply precambrian and infracambrian petroleum systems are relatively abundant and widespread the oldest live oil recovered to date is sourced from mesoproterozoic rocks within the velkerri formation roper group of the mcarthur basin of northern australia dated at 1361 21 ma and 1417 29 ma re os dates with at least the initial phase of oil generation and migration having taken place before 1280 ma however the geologically oldest commercial production is currently from the somewhat younger mid to late neoproterozoic cryogenian ediacaran petroleum systems of the lena tunguska province in east siberia and in southern china from the latest neoproterozoic to early cambrian huqf supergroup in oman and potentially in the near future from the age equivalent mawar supergroup in western india

chemostratigraphy and diagenetic constraints on neoproterozoic carbonate successions from the sierras bayas group tandilia system argentina carbon and oxygen isotopic data combined with a detailed diagenetic study obtained from undeformed and unmetamorphosed dolomite and limestone from the neoproterozoic sierras bayas group argentina provide a new record of isotopic stratigraphic variations useful for regional and global correlations the sierras bayas group is subdivided into the villa monica sandstones and dolomites cerro largo siliciclastic rocks and loma negra limestones formations unconformably overlain by the cerro negro formation siliciclastic rocks with basal marls and grouped into four depositional sequences bounded by unconformities the

short wavelength infrared spectral characteristics of the hw horizon implications for exploration in the myra falls volcanic hosted massive sulfide camp vancouver island british columbia canada short wavelength infrared swir spectrometry has been used to identify previously unmapped hydrothermal alteration zones around volcanic hosted massive sulfide vhms orebodies at myra falls vancouver island british columbia hydrothermal alteration assemblages are uniformly dominated by fine grained white mica with poor development of mineralogical zonation swir spectrometry is an ideal exploration tool for characterizing this fine grained hydrothermal alteration at myra falls swir spectrometry has identified subtle shifts in the wavelengths of the aloh absorption feature of white mica corresponding to compositional changes in altered rhyolite distal and proximal to ore aloh absorption occurs at shorter wavelengths 2 198 nm and corresponds to lower fe fe mg and si al and higher na na k in strongly altered samples proximal to ore slightly sodic muscovites aloh absorption occurs at longer wavelengths 2 206 nm and corresponds to higher fe fe mg and si al and lower na na k in samples distal to ore nonsodic slightly phengitic muscovites white mica in siltstone within a meter of vhms ore has higher zn v fe and mg contents than white mica distal to these altered samples chlorite compositions identified by swir also show systematic changes with intensity of alteration and distance from ore the average wavelength of the feoh absorption feature for chlorite in rhyolitic samples proximal to ore is 2 241 nm intermediate mg chlorite whereas wavelengths in background samples average 2 247 nm intermediate fe chlorite similar changes are observed in footwall and hanging wall andesites with samples near the battle mine containing muscovite to phengitic muscovite average wavelength of the aloh absorption feature of 2 200 nm and mg rich chlorite average wavelength of the feoh absorption feature of 2 245 nm to regional andesite samples with phengitic muscovite average wavelengths of the aloh absorption feature of 2 209 nm and fe rich chlorite average wavelength of the feoh absorption feature of 2 249 nm in weakly altered rocks white mica compositions also vary with host lithology the aloh absorption feature occurs at longer wavelengths in white mica in dacite and andesite compared to adjacent rhyolitic rocks suggesting that higher fe and mg in the host lithology affects the composition of white mica two zones of intense hydrothermal alteration above the battle and hw orebodies have distinctive swir spectral characteristics with the aloh and feoh features occurring at shorter wavelengths 2 197 and 2 240 nm respectively small anomalous zones of alteration were also identified in the thelwood valley area where minor mineralized zones are present as broad zones of fine grained white mica sericite alteration are ubiquitous throughout the myra falls property alteration proximal to ore cannot be identified simply by visual logging of drill core alteration zonation may be determined by subtle shifts in white mica spectral characteristics this study indicates that swir analysis may be an effective field based exploration tool for quantifying the intensity of alteration associated with vhms orebodies and that trends in mineral compositions even in very fine grained rocks can be used as mine scale vectors to ore

characterization of pulverized granitoids in a shallow core along the san andreas fault littlerock ca summary we present results on the composition structure and particle size distribution psd of pulverized and damaged granitic rocks in a 42 m deep core adjacent to the san andreas fault near littlerock ca the cored section is composed of pulverized granites and granodiorites and is cut by numerous mesoscopic secondary shears the analysis employs xrd xrf thin sections and semi automated particle size analyser methods including a novel calibration method the mean particle size for the majority of samples falls between 50 and 470 m the psds can be fitted by a power law with d values ranging between 2 5 and 3 1 as well as by a superposition of two gaussians fracture surface energy calculations based on the observed particle distributions provide very low values indicating that the part of the total earthquake energy budget expended for breaking or shattering rocks is small shear deformation is likely to dominate near secondary faults the most pronounced fault related alteration occurs along the secondary shears and is a function of both composition and depth the alteration to clay appears to be the result of fluid rock interaction and brittle deformation under low temperature conditions rather than of surface related weathering the particle size reduction noted in the core reflects multiple mechanisms of comminution the zones of pulverization that lack significant weathering likely result from repeating episodes of dynamic dilation and contraction

rupture mechanism and interface separation in foam rubber models of earthquakes a possible solution to the heat flow paradox and the paradox of large overthrusts abstract spontaneous stick slip along the interface between stressed foam rubber blocks is a simple analog of earthquake rupture and stick slip results from this model are used to elucidate the role of normal stress variations along the interface in the stick slip process observations indicate significant normal interface vibrations and separation during slip suggesting that dynamic changes in normal stress rather than a drop in the coefficient of friction may control stick slip as suggested for example by tolstoi oden and martins and brune and co workers observations of particle trajectories indicate that stick slip shear motion is associated with various degrees of fault separation for an asymmetric model the motion is consistent with slipping motion of the type suggested by schallamach and price for a symmetric model the motion is similar to that suggested by comninou and dundurs if interface waves of this type involving separation during slip occur in earthquakes they may be a solution to the heat flow paradox since a major part of the slip occurs during separation and during low normal stress thus frictional heat generation is reduced normal interface vibrations during stick slip may explain the high corner frequency of p wave spectra and the generally high levels of p wave spectra beyond the corner frequency schallamach comninou type waves are consistent with the partial stress drop abrupt locking self healing models of brune and heaton

the epicontinental subsiding margin of the triassic in northern israel north arabian plate abstract the triassic sedimentary pattern of the north arabian margin represents a transition from continental to deep marine we here present a transect part of this suite from southern to northern israel cuttings from the ramalla s and devora n boreholes were studied by petrographic and cathodoluminescence microscopy biotic and sedimentological components were grouped into microfacies upon which a carbonate evaporitic depositional facies model was based mid to inner ramp conditions persisted along the transect essentially following a s n depositional strike with outer ramp to basinal facies to the west five low order lo cycles were identified and integrated into a sequence stratigraphic model with eustatic tectonic and differential subsidence components lo cycle 1 is late anisian pelsonian cycle 2 is late anisian to longobardian cycle 3 is early carnian cycle 4 is late carnian and cycle 5 is at the carnian norian transition facies range from supratidal via lagoonal facies in late hst or lst to calcarenitic shoals and short term deepening to offshore at maximum flooding cycles 1 and 2 are non evaporitic with a clastic influx event in cycle 2 cycles 3 and 4 contain sabkha or salina evaporites in the lagoonal facies that end in the lower part of cycle 5 these facies group into a higher order cyclicity with discrete events that can be correlated between the boreholes depositional and burial history were correlated to alpine and arabian plate stratigraphy over 20 myr from the anisian pelsonian to the norian siliciclastic carbonate and evaporite dominated environments indicate climates ranging from relatively humid to extremely arid rapid subsidence in the late anisian is attributed to neotethyan rifting of northeastern gondwana from latest anisian to early carnian reduced subsidence took place in the face of eustatic sea level rise renewed subsidence in the carnian is attributed to further neotethyan rifting subsidence terminated in the norian with uplift to the north attributed to pre volcanic doming

first evidence for cambrian glaciation provided by sections in avalonian new brunswick and ireland additional data for avalon gondwana separation by the earliest palaeozoic abstract the first evidence for cambrian glaciation is provided by two successions on the avalon microcontinent the middle lowest cambrian middle terreneuvian series and fortunian stage stage 2 boundary interval has an incised sequence boundary overlain by a fluvial lowstand facies and higher olive green marine mudstone on hanford brook southern new brunswick this succession in the lower mystery lake member of the chapel island formation may be related to melting of an ice sheet in avalon the evidence for this interpretation is a muddy diamictite with outsized up to 10 cm in diameter proterozoic marble and basalt clasts that penetrated overlying laminae in the marine mudstone that eustatic rise was associated with the mudstone deposition is suggested by an approximately coeval rise that deposited sediments with watsonella crosbyi zone fossils 650 km away in avalonian eastern newfoundland a sea level rise within the watsonella crosbyi chron at ca 535 ma may correspond to a unnamed negative 13 c excursion younger than the basal cambrian excursion bace and the zhuce excursion in stage 2 of the upper terreneuvian series cambrian dropstones are now also recognized on the northern gander margin of avalon in continental slope rise sedimentary rocks in southeast ireland although their age early middle cambrian is poorly constrained dropstones in the booley bay formation provide additional evidence for cambrian glaciation on the avalon microcontinent besides providing the first evidence of cambrian glaciation these dropstone deposits emphasize that avalon was not part of or even latitudinally close to the terminal ediacaran cambrian tropical carbonate platform successions of west gondwana

gouge formation by dynamic pulverization during earthquake rupture it is proposed here that fault gouge forms by rock pulverization within the tip region of a fast propagating earthquake due to the intensity of stress and rates of strain in this zone to examine this mechanism we calculate the deformation conditions of a dynamic shear fracture propagating close to the limiting rayleigh wave velocity the mechanical conditions close to the fracture tip are extreme tensile stresses approach 5 gpa volumetric strain rates exceed 105 s 1 and volumetric expansion alternates with volumetric contraction it is expected that a localized zone a few millimeters wide will be pulverized under these conditions this mechanism of dynamic gouge formation provides new insight to recent observations of the texture of gouge from the san andreas fault zone and from rupture zones in south african mines further as such extreme conditions develop only during fast propagating earthquakes presence or absence of pulverized gouge may serve as an indicator of earthquake propagation velocity

geology lithogeochemistry and alteration of the battle volcanogenic massive sulfide zone buttle lake mining camp vancouver island british columbia volcanogenic polymetallic massive sulfide deposits within the buttle lake mining camp occur within the felsic volcanic and volcaniclastic rocks of the myra formation that immediately overlies price formation andesite these units comprise the lower exposed part of the paleozoic sicker group in the buttle lake uplift in central vancouver island the sicker group represents a volcanic island arc that forms the base of the allochthonous wrangell terrane the battle main zone contains 2 3 million tons mt of proven and probable reserves grading 1 3 g t au 25 3 g t ag 2 5 percent cu 0 5 percent pb and 13 2 percent zn overall the buttle lake camp hosts geologic reserves of about 12 5 mt the battle main massive sulfide zone occurs within the h w horizon the lowest member of the myra formation immediately above the price formation andesite price formation andesite is over 300 m thick in the vicinity of the camp and consists of feldspar or pyroxene porphyritic basaltic andesite flows synvolcanic block faulting of this unit formed the regional scale buttle lake camp basin with a strike length of at least 10 km local sub basins in this major structure contain the sulfides and felsic volcanic rocks of the h w horizon the h w horizon is a 15 to 200 m thick felsic package that extends throughout the basin it consists of eight members three of which represent periods of massive sulfide deposition from the stratigraphic base to the top of these members are 1 the battle main massive sulfide lens 2 fine rhyolitic tuffaceous deposits 3 h w mafic sills 4 gap massive sulfide lens 5 coarse rhyolite pyroclastic deposits 6 rhyolite tuffaceous and cherry sediments 7 battle upper massive sulfide lenses and 8 a tripartite rhyolite flow dome complex consisting of quartz porphyritic rhyolite quartz feldspar porphyritic rhyolite and green quartz feldspar porphyritic rhyolite volcaniclastic units in the felsic package evolved with interfingering of subaerial and submarine pyroclastic processes flow dome units evolved by fractionation of quartz and feldspar alteration evaluated petrographically and with pearce element ratios is most intense close to synvolcanic and synmineral feeder faults that channeled solutions through the price formation andesite proximal to the battle main massive sulfide lens envelopes to the feeder faults have distinctive mg addition anomalies and contain the mineral assemblage pyrite sericite quartz chlorite discharge feeder stockworks immediately below the battle main massive sulfide lens contain varying proportions of sericite quartz and pyrite but lack significant chlorite deposition of the h w horizon rhyolitic units on top of the battle main massive sulfide lens did not halt mineralization rather fluids continued to percolate upward through the newly deposited rhyolitic units and deposited the battle upper lenses close to the new sediment water interface alteration below the battle upper lenses consists of quartz sericite and pyrite with minor galena sphalerite and tennantite overall hydrolysis of feldspar in both the price formation and the h w horizon resulted in a halo surrounding the ore lenses marked by addition of k and concomitant na and ca depletion

chemostratigraphy of neoproterozoic cap carbonates from the volta basin west africa abstract the neoproterozoic era includes some of the most extreme ice ages in earth history the exact number of glaciations is unknown although there were at least two events of global reach and possibly an equal number of lesser advances neoproterozoic glacial deposits in west africa have proven particularly difficult to correlate with better constrained successions elsewhere in most west african successions only a single glaciogenic deposit is present generally within a stratigraphic triad of tillite carbonate and bedded chert the age of these deposits and their synchroneity across the craton remain controversial we report isotopic data from carbonates that cap tillites in the volta basin sud banboli group in the three sections measured 13 c pdb begins at 2 to 3 and drops to 5 to 8 correlated with a drop in both 18 o and mg ca this pattern both the drop in 13 c and its correlation with 18 o and lithology has been observed in neoproterozoic cap carbonates on other cratons suggesting that it reflects primary depositional variations in addition the strong positive correlation among lithology 13 c and 18 o suggests that lithological variation may have exerted a principal control on isotopic variation implying that the dolomite formed in isotopic equilibrium with seawater as a primary precipitate or very early diagenetic replacement this would require low levels of sulfate estimated to be 1 mm or less consistent with available s isotopic data the presence of barite crusts in association with some cap carbonates and the conditions of seawater chemistry hypothesized in the aftermath of a snowball earth the stratigraphic pattern of carbon isotope variation in the volta basin cap carbonates suggests that underlying tillites are likely marinoan 650 600 ma in age this interpretation is supported by distinctive lithological characters observed in volta basin cap carbonates and accepted marinoan correlatives tillites elsewhere on the craton have been assigned latest proterozoic or early cambrian ages either the basis for these proposals requires reexamination or west african tillites record more than one glacial event

northwest africa s ediacaran to early cambrian fossil record its oldest metazoans and age constraints for the basal taroudant group morocco abstract the anti atlas area in southern morocco preserves one of the most complete latest ediacaran to cambrian shallow marine carbonate records in the world and serves as a standard for global chemostratigraphic 13ccarb curves contrary to the excellent chemostratigraphic coverage neither metazoan fossils only stromatolites and calcified algae nor radiometric age constraints were hitherto available for the basal part of this carbonate record the tifnout member of the adoudou formation of the taroudant group we report an ediacara type fauna from shallow marine sandstones from the basal tabia member and microfossils from dolostones from both the tabia and the tifnout members of the adoudou formation the former are discoidal fossils and share many characteristics with the form genus aspidella and exhibit a peculiar style of preservation pointing towards an early diagenetic two stage carbonate followed by silica cementation history leading to good preservation of these supposedly once soft bodied organisms the dolostone hosted microfossils are preserved as sparite filled molds enclosed by a thin opaque envelope despite their small size they resemble late ediacaran calcifying metazoans such as namacalathus and tubular small shelly fossils together these fossils constitute the oldest known direct evidence for presumably metazoan life from northwest africa we also report new time constraints for the adoudou formation and fossils enclosed therein based on combined la icp ms and high precision ca id tims u pb zircon geochronology of detrital and volcanic zircons together with new chemostratigraphic 13ccarb and literature data these new age constraints suggest a late ediacaran age time span between ca 561 and 542 ma for the discoidal ediacara type fossils from the basal tabia member and a latest ediacaran to earliest cambrian time span between ca 544 and 540 ma and an early cambrian age time span between ca 528 and 523 ma for the two microfossil faunas from the tifnout member

rare earth element geochemistry of the woxi w sb au deposit hunan province south china the woxi w sb au deposit in hunan south china is hosted by proterozoic metasedimentary rocks a turbiditic sequence of slightly metamorphosed greenschist facies gray green and purplish red graywacke siltstone sandy slate and slate the mineralization occurs predominantly 70 as stratabound stratiform ore layers and subordinately as stringer stockworks the former consists of rhythmically interbedded banded to finely laminated stibnite scheelite quartz pyrite and silty clays whereas the latter occurs immediately beneath the stratabound ore layers and is characterized by numerous quartz pyrite gold scheelite stringer veins or veinlets that are typically either subparallel or subvertical to the overlying stratabound ore layers the deposit has been the subject of continued debate in regard to its genesis rare earth element geochemistry is used here to support a sedimentary exhalative sedex origin for the woxi deposit the ree signatures of the metasedimentary rocks and associated ores from the woxi w sb au deposit remained unchanged during post depositional processes and were mainly controlled by their provenance the original ore forming hydrothermal fluids as demonstrated by fluid inclusions in quartz from the banded ores are characterized by variable total ree concentrations 3 5 to 136 ppm marked lree enrichment lan ybn 28 248 lree hree 16 to 34 and no significant eu anomalies eu eu 0 83 to 1 18 they were most probably derived from evolved seawater that circulated in the clastic sediment pile and subsequently erupted on the seafloor the bulk banded ores are enriched in hree lan ybn 4 6 11 4 lree hree 3 to 14 and slightly depleted in eu eu eu 0 63 to 1 14 relative to their parent fluids this is interpreted as indicating the influence of seawater rather than a crystallographic control on ree content of the ores within a single ore layer the degree of hree enrichment tends to increase upward while the total ree concentrations decrease reflecting greater influence and dilution of seawater there is a broad similarity in chondrite normalized ree patterns and the amount of ree fractionation of the bandedoresinthisstudyandexhalitesfromothersedex typepolymetallicoredeposits suggestingasimilargenesisforthesedeposits

high resistant sand injected marl and low resistant damaged marl to locate and characterize the thenia fault zone in boumerdes city north central algeria the purpose of this study was to locate and characterize the thenia fault zone tfz in the urban area of boumerdes city geological and electrical resistivity tomography surveys have targeted the plaisancian marl and its quaternary cover as a whole data indicate a complex near vertical fault zone with an asymmetric and zoned internal structure of at least 150 m wide and with a straight n120 overall trending the fault zone is traversed with two elongated parallel fault branches fb1 and fb2 generally 70 m distant from each other these fault branches locate two intense damage zones idzs of 10 15 m thick each situated at the margin of two damage zones each having a thickness of several tens of meters downward sand injections into idzs during pleistocene epoch possible pulverization of plaisancian marl rocks systematic deflection of actual stream channels and vertical displacement of at least 30 m affecting quaternary alluvial deposits show that the area would have undergone active tectonic driven by the tfz

the nama group revisited summary the nama group of southern namibia is a candidate for the terminal proterozoic global stratotype section and point gssp desirable characteridics of a gssp include a well preserved index fossil assemblage little deformation or metamorphism well constrained isotopic ages stable isotope records and magnetostratigraphic control the age of the nama group sediments is now constrained to between 570 and 510 ma assuming the gondwana assembly was nearly complete at this same time there is a discrepancy between the previously published nama poles a revised 55cl510 ma apparent polar wander path for gondwana and the preceding supercontinental assemblages of rodinia and panottia for these reasons the nama group sediments were resampled in an effort to evaluate the potential of detailing the magnetostratigraphy of the nama group and resolving the discrepancy between the nama poles and the apwp of gondwana collectively both the previous studies of the nama group and this one show a complex series of overprints and no easily discernible primary direction of magnetization we therefore urge caution in using the nama group poles in any tectonic models of the neoproterozoic early palaeozoic specifically the n1 component of magnetization previously identified as a primary magnetization was discovered in a younger suite of samples therefore previous tectonic models that used the n1 magnetization direction as representative of the time of nama deposition should be revised in light of these recent findings

integrated stratigraphy of the upper neoproterozoic succession in yunnan province of south china re evaluation of global correlation and carbon cycle abstract this study provides a chemostratigraphic and sequence stratigraphic framework of a relatively unfossiliferous sub cambrian marine sedimentary succession in yunnan province of south china our results allow its global stratigraphic correlation and provide an improved understanding of marine carbon cycle during the late neoproterozoic the succession has a basal glacial diamictite nantuo formation and comprises two large scale depositional cycles towards the precambrian cambrian pc c boundary each of which changes from siliciclastic to carbonate sediments with environments ranging from shallow subtidal to evaporitic supratidal in the absence of biostratigraphic control attribution of the tillite has remained equivocal between the 710 ma sturtian and 635 ma marinoan glaciations a compilation of known paleomagnetic and other geochronologic constraints suggests that the nantuo glaciation in south china was at least diachronous in which the nantuo tillite in yunnan belongs to the older glaciation stratigraphic patterns of the diagenetically screened 13c variation and depositional sequences during the carbonate dominated interval show a striking similarity with those of the upper cryogenian and entire terminal proterozoic carbonates at widely separated other localities rather than the terminal proterozoic alone supporting the view that deposition of the nantuo tillite in yunnan reflects the sturtian rather than marinoan glaciation further considerations of the 13c results provide three important implications for the late neoproterozoic marine carbon cycle first comparison of different 13c profiles suggests considerable variability in the absolute values of carbonate on both intra and inter basinal scales which differs profoundly from their relative homogeneity in marine phanerozoic counterparts and may therefore reflect lateral isotopic heterogeneity in the oceanic carbonate reservoir during the late neoproterozoic second an empirical correlation between the 13c and relative sea level changes was applied to evaluate hypothesized explanations for 13c temporal variation in surface sea yielding short term inverse and long term positive relationships the short term trend marks periods of the negative 13c excursions and is compatible to most of the existing arguments for the 13c events on the other hand mechanisms causing the long term trend remain enigmatic in the absence of comparable data from other localities our observation however suggests that at least two different mechanisms operated marine carbon cycle during the late neoproterozoic third the negative 13c anomaly characterizing the period following the marinoan glaciation worldwide was not coincident between kerogen and carbonate but occurs as a lagged drop in yunnan where a 7 depletion in kerogen preceded an 3 depletion in carbonate their lagged trends likely reflect different sources as kerogen and carbonate signals are considered to monitor surface and deeper waters respectively the negative 13c event would therefore have occurred in surface water followed by a smaller 13c depletion through the entire water column due to vertical mixing between surface and deeper waters at the studied site this mechanism supports the proposed hypothesis that injection of the 13c depleted atmospheric co2 into the surface sea deriving ultimately from quantitative dissociation of methane hydrate in terrestrial permafrost during the post glacial warming contributed to the negative 13c anomaly

rock pulverization at high strain rate near the san andreas fault rocks near the san andreas fault are pervasively crushed at distances of up to 400 m from its core laboratory experiments and calculations suggest that the rocks were pulverized at high strain rates 150 s 1 associated with a supershear rupture a rupture propagating at a velocity equal to greater than that of seismic shear waves

volcanism sedimentation and massive sulfide mineralization in a late cretaceous arc related basin eastern taurides turkey abstract late cretaceous arc volcanism and associated massive sulfide mineralizations occur in the eastern taurus mountains the mineralizations are related to felsic dacitic rhyolitic volcanic rocks which together with basement rocks form the lowermost levels of a 5000 m thick volcano sedimentary sequence and are restricted to a few levels within the sequence basaltic rocks which are intruded by tonalite and dacite form the base of the volcano sedimentary sequence the dacitic rhyolitic rocks are overlain by a volcano sedimentary succession with andesitic dacitic flows the flows do not contain any mineralization this succession starts with volcanic breccia and tuffs at the base passing into crystal rich sandstone and pelagic mudstone with tuffite intercalations and ends with marls intercalated with sandstones basalt and peridotite olistoliths the felsic rocks bear stockwork and disseminated types of mineralization the massive sulfide mineralization has a simple mineral assemblage of pyrite chalcopyrite bornite and sphalerite optical microscopic examination of pyrites from derince massive sulfide deposits reveals that the pyrites are commonly seen in framboidal and cubic forms the geochemistry of the magmatic rocks and sedimentary facies associations indicate that the mineralizations in the derince were developed in an intra arc environment

constrains on the origin and history of the eastern mediterranean basin abstract the basin formed along the northern passive margin of gondwanaland as a relict of the mesozoic neotethys in early mesozoic time though direct information from the basin itself is meagre the geology of its passive margins and the regional framework of the tethys evolution constrain the formation and history of the basin the eastern mediterranean and its passive margins are interpreted to have formed as a result of several faulting and continental breakup phases from early permian to middle jurassic times before pangaea s complete disintegration this led to the detachment of the eratosthenes and tauride blocks from the margins of the levant and herodotus basins respectively the latter merged in the northeast with the cyprus basin that extended along arabia s northern margin the main rifting probably occurred in the triassic leading to seafloor spreading in the herodotus and cyprus basins while along the levant margin important rifting also occurred in the jurassic during the initial rifting stages extension perpendicular to the levant margin was important but subsequently the tauride block drifted mainly northward the existence of the passive margins and slopes of the eastern mediterranean is documented at least from the end of the middle jurassic until then the basin was probably narrow 200 300 km but during the main phase of the africa laurasia separation it grew to twice its present width or more this scenario depends critically on the interpretation that the tauride block was originally located next to northeastern africa on the western side of the eratosthenes block plate convergence and consumption of the northern portion of the basin have taken place since mid cretaceous times but the active convergent boundary on its northern side formed only in the neogene by modification of earlier structures some intra plate deformation also took place especially in the neogene but it hardly changed the original configuration of the remaining portion of the basin