structure and diffusive properties of fluid filled grain boundaries an in situ study using infrared micro spectroscopy the rate of numerous diagenetic deformation and metamorphic processes in crustal rock systems ultimately depends on the structure and diffusive properties of water bearing grain boundaries we present the first in situ spectroscopic study of the nature of aqueous films present in mineral interfaces undergoing stress induced dissolution or pressure solution using infrared micro spectroscopy we show that during active pressure dissolution of the 111 plane of halite nacl against a caf2 plate the confined intercrystalline liquid has an average thickness of 85 185 nm and occupies a rough non equilibrium grain boundary structure the hydrogen bonding of the water within the grain boundary film is modified due to increased polymerization towards ice like hard water simultaneous pressure solution rate measurements show that diffusion within the grain boundary fluid is about one order of magnitude slower than in bulk solution during active pressure solution of the 100 plane of halite a similar non equilibrium grain boundary structure develops but the average thickness of the confined water film is only 40 nm and no evidence is found for modification of the hydrogen bonding of the water the difference in hydrogen bonding between the two orientations studied is attributed to differences in surface charge distribution on the 111 and neutral 100 interfaces in nacl the difference in mean film thickness is attributed to differences in crystallographically controlled roughness of the dissolving nacl surface if similar grain boundary thickness and diffusivity effects occur in other rock forming minerals pressure solution in such systems will tend to be interface reaction controlled and may be capable of producing significant seismic anisotropy

petrology of the great abitibi dyke superior province canada the great abitibi dyke gad which can be traced northeast for 700 km across the abitibi belt in the southeastern superior province of the canadian shield is composed of olivine gabbro to monzodiorite weakly saturated to undersaturate d in silica all rocks of the gad can be derived by mainly plagioclase and olivine fractionation from a parental magma corresponding in composition to chilled margin samples two units can be distinguished a marginal unit unit 1 representing 0 50 crystallization and a central unit unit 2 found over about half of the dyke length representing 50 70 crystallization modelling using pearce elemental ratio analysis quantifies the fractionation history and allows mass balance calculations over the present exposure level of the dyke the approximate balance between the amounts of cumulate and fractionated rocks suggests that unit 1 differentiated essentially in situ as a closed system in contrast unit 2 rocks were formed by loss of substantial plagioclase and olivine from the parental magma this fractionate must have either been lost to depth or left behind in an external chamber unit 2 rocks show depletion in plagioclase and enrichment in mafic minerals along strike towards the southwest deeper exposure level a trend explained by density stratification regional variation in unit 1 chemistry is interpreted in terms of lateral magma injection towards the northeast from the locus of keweenawan rift volcanism feldspar olivine and augite compositions are linearly correlated with equilibrium temperature and extent of magma evolution the parent magma had a trace element chemistry corresponding to a within plate setting and was probably derived from an incompatible element enriched mantle similar to the source for ocean island basalts oibs

constraints from 40ar 39ar geochronology on the tectonothermal history of the kapuskasing uplift in the canadian superior province the kapuskasing uplift ku in the superior province of the canadian shield has been interpreted as an oblique cross section through the archean mid crust however the time of juxtaposition of the granulites of the ku against the lower grade rocks of the abitibi greenstone belt agb along the ivanhoe lake fault zone is problematic to constrain the postmetamorphic tectonothermal history of the ku we have conducted 57 40ar 39ar step heating analyses on mineral and rock samples collected in a transect across the southern ku and adjacent agb the age spectra record a complex thermal history amphiboles from the agb in the footwall of the ivanhoe lake fault zone have ca 2 66 ga dates similar to closure ages for amphiboles from farther east in the agb amphibole dates of 2 46 2 52 ga from the deepest structural levels of the ku place an upper limit on the time of major uplift of the granulites and their juxtaposition with the agb biotite and muscovite dates from the transect cluster into three age groups

superplastic nanofibrous slip zones control seismogenic fault friction understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults displacement in such fault zones is frequently localized on highly reflective mirrorlike slip surfaces coated with thin films of nanogranular fault rock we show that mirror slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions these microstructures and associated frictional data suggest a fault slip mechanism resembling classical ashby verrall superplasticity capable of producing unstable fault slip diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains with nanogranular fault surfaces becoming increasingly recognized in crustal faults the proposed mechanism may be generally relevant to crustal seismogenesis

a pressure solution creep law for quartz from indentation experiments 1 indenter experiments have been performed on quartz crystals in order to establish a pressure solution creep law relevant at upper to middle crustal conditions this deformation mechanism contributes to earth s crust geodynamics controlling processes as different as fault permeability strength and stress evolution during interseismic periods or mechanochemical differentiation during diagenesis and metamorphism indenter experiments have been performed at 350 c and 20 120 mpa during months with differential stress varying from 25 to 350 mpa several experimental parameters were varied nature of quartz synthetic or natural nature of fluid manner in which the solid solution solid interface was filled and orientation of the indented surfaces versus quartz crystallographic c axis significant strain rates could only be obtained when using high solubility solutions naoh 1 mol l 1 displacement rates of the indenter were found activated by differential stress with exponential dependence as theoretically predicted the mean thickness of the trapped fluid phase below the indenter was estimated in the range 2 10 nm moreover the development of this trapped fluid phase was relatively fast and allowed fluid penetration into previously dry contact regions by marginal dissolution the indenter displacement rate was driven by differential stress and its kinetics was controlled by diffusion along the trapped fluid and the development of a morphological roughness along the interface conversely marginal strain energy driven dissolution was observed around the indenter and its kinetics was controlled by free surface reaction these experimental results are applied to model the interactions between pressure solution and brittle processes in fault zones providing characteristic time scales for postseismic transitory creep and sealing processes in quartz rich rocks

flow patterns of magma in dikes makhtesh ramon israel directions of magma flow were measured in a system of radial dikes in makhtesh ramon israel the flow directions were determined from field observations of segments fingers grooves and groove molds of the dikes the study indicates that the mean axis of magma flow is subhorizontal toward the north in agreement with the direction of divergence of the radial dike system two modes of flow were observed 1 regular bedding parallel flow in the well stratified rock units and 2 irregular meandering flow in the massive rock units it is suggested that corrugated dike walls in well stratified host rocks cause magma channelization and random or self generated restrictions in massive host rocks cause the apparent meanders furthermore the major lithologic boundaries in the host units strongly affect segmentation of the dikes

mid tertiary 25 21 ma lamprophyres in nw mexico derived from subduction modified subcontinental lithospheric mantle in an extensional backarc environment following steepening of the benioff zone abstract the mid tertiary lamprophyre dike swarm 8 km 2 5 km in size from hermosillo sonora nw mexico has calc alkaline characteristics and includes nnw striking amphibole phyric spessartite 85 of the swarm and nne striking phlogopite phyric kersantite the 40 ar 39 ar geochronology of amphibole and phlogopite gives overlapping plateau ages ranging from 25 to 21 ma although all the lamprophyres are enriched in incompatible elements and display negative nb ta and ti anomalies on the primitive mantle normalized plots kersantite has higher k na la yb p ti and incompatible trace elements e g zr compared to spessartite the lamprophyres have radiogenic sr and nd isotopic signatures 87 sr 86 sr 0 7057 0 7065 and e nd 1 to 2 3 suggesting derivation from the subcontinental lithospheric mantle that was previously modified by subduction related fluids this mantle is similar to that beneath the southern grenvillian orogen which has younger t dm ages than the 1 6 1 7 ga t dm ages of the caborca block the lamprophyric magmas were generated at various mantle depths at the southwestern edge of north america intrusion of the lamprophyres was synchronous with extension that produced normal faults and core complexes with wsw vergence extension occurred immediately following steepening of the benioff zone during which the magmatic arc migrated from east to west of hermosillo and the lamprophyres were intruded just behind the contemporaneous arc

origination and extinction through the phanerozoic a new approach abstract temporal patterns of origination and extinction are essential components of many paleontological studies but it has been difficult to obtain accurate rate estimates because the observed record of first and last appearances is distorted by the incompleteness of the fossil record here i analyze observed first and last appearances of marine animal and microfossil genera in a way that explicitly takes incompleteness and its variation into consideration this approach allows estimates of true rates of origination and extinction throughout the phanerozoic substantial support is provided for the proposition that most rate peaks in the raw data are real in the sense that they do not arise as a consequence of temporal variability in the overall quality of the fossil record even though the existence of rate anomalies is supported their timing is nevertheless open to question in many cases if one assumes that rates of origination and extinction are constant through a given stratigraphic interval then

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

the kapuskasing uplift a geological and geophysical synthesis over the past decade the kapuskasing uplift has been the subject of intense geological and geophysical investigation as lithoprobe s window on the deep crustal structure of the archean superior province enigmatic since its recognition as a positive gravity anomaly in 1950 the structure has been variably interpreted as a suture rift transcurrent shear zone or intracratonic thrust diverse studies including geochronology geothermobarometry and various geophysical probes provide a comprehensive three dimensional image of archean 2 75 2 50 ga crustal evolution and proterozoic 2 5 1 1 ga cooling and uplift the data favour an interpretation of the structure as an intracratonic uplift related to hudsonian collision eastward across the southern kapuskasing uplift erosion levels increase from 10 km in the michipicoten greenstone belt through the wawa gneiss domain 10 20 km into granulites 20 30 km of the kapuskasing structural zone juxtaposed against the low grade swayze greenstone belt al

kinetics of pressure solution at halite silica interfaces and intergranular clay films pressure solution is widely regarded as a potentially important deformation mechanism along crustal faults and during aliagenesis yet the mechanisms and kinetics of this process remain highly controversial to better understand the fundamental factors controwing the rates of pressure solution at the grain to grain scale we conducted experiments in which convex halite lenses were pressed against fiats of fused silica in brine fluid pressures were maintained at 0 1 mpa temperatures and mean contact normal stresses ranged from 8 3 o to 90 2oc and 0 5 to 13 5 mpa respectively the geometry and growth rate of the contact spot between the two lenses and the rate at which the lenses approached one another convergence were monitored using reflected light interferometry and transmitted light photomicrography convergence occurred when halite and silica lenses were pressed together in brine halite silica experiments no undercutting was observed and dry control experiments indicated negligible dislocation creep convergence rates in experiments at 50 2oc ranged from 0 01 to 0 05 m d depending on mean normal stress and contact spot radius the data are consistent with intergranular pressure solution ips rate limited by diffusion through an intergranular film with a very high diffusion coefficient 10 5 10 7 cm2 s the data further suggest that the diffusion coefficient and or thickness of this film increases with decreasing normal stresses at least for normal stresses less than about 4 mpa as no island channel boundary structures were observed we propose that this film consists of a continuous layer of strongly adsorbed i e structured water that is maintained between the halite and silica lenses during deformation convergence rates in similar experiments conducted at a constant load of 0 11 n but at 8 3 o 50 2 o and 90 2oc were approximately constant at a given normal stress and contact spot size the cause of this temperature insensitivity is unknown but might result from changes in interphase boundary structure or thickness with increasing temperature that are sufficient to offset the expected thermal activation an experiment was also conducted in which a halite lens was pressed against a fused silica fiat coated with an 0 8 m thick film of na montmorillonite in brine this clay film produced an approximately fivefold increase in convergence rates over those observed in a halite silica experiment conducted without clay at the same load and temperature the strong sensitivity of ips rates both to contact spot radius and to the presence of second phases along grain boundaries suggests that fine grained clay rich fault gouges and multiphase granular aggregates should be particularly susceptible to pressure solution creep in the middle to upper crust

mineral deposits of the mesoproterozoic midcontinent rift system in the lake superior region a space and time classification abstract the mesoproterozoic midcontinent rift system mrs of north america hosts a diverse suite of magmatic and hydrothermal mineral deposits in the lake superior region where rift rocks are exposed at or near the surface historically hydrothermal deposits such as michigan s native copper deposits and the white pine sediment hosted stratiform copper deposit were major mrs metal producers on going exploration for and potential development of copper nickel sulfide deposits hosted by the duluth complex of minnesota and the opening of the eagle nickel mine in michigan indicate an expanding interest in mrs magmatic deposits mrs hydrothermal and magmatic mineral deposits many of which are significant past present and likely future providers of critical minerals here are placed into a space and time metallogenic framework to construct this framework regional mrs mineral deposits extracted from the u s geological survey mineral resources data system mrds and the ontario ministry of energy northern development and mines mineral deposit inventory mdi were supplemented by other known and recently recognized mineral deposits described in the literature all mineral deposits were classified by deposit type host rock age and type and estimated timing of mineralization deposits were then put into a tectonic evolutionary framework stages for the mrs which shows that deposits formed within discrete spatial and temporal stages of rift evolution each stage of rift evolution is characterized by specific mineral deposit types that are largely confined both by their physical location in rift rocks and type and timing of mineralization examples include mrs nickel rich conduit type magmatic sulfide deposits which are restricted to an early magmatic stage mrs history when magma compositions were characterized by ni rich picrites and high mg basalts in contrast contact type magmatic sulfide deposits with cu ni were derived from more evolved al rich tholeiitic magmas that dominated a later time of voluminous magmatic activity hydrothermal sediment hosted stratiform chalcocite mineralization along the margins of western lake superior in michigan is economic only where fluid flow through red beds was concentrated by structures along the margins of a post volcanic mrs sedimentary basin widespread native cu and native ag mineralization occurred about 40 million years after formation of host basalt lava flows and interflow sedimentary rocks these descriptions of the diverse mineral deposits in the lake superior region cataloged within the space of the local and regional geology and over the more than 60 million year mineralizing history of the mrs are indicative of the complex and at times overlapping magmatic and hydrothermal mineral systems that operated within this major large igneous province

dynamics of abundance of the mid to late pridoli conodonts from the eastern part of the silurian baltic basin multifractals state shifts and oscillations

roughness of natural fault surfaces the roughness of fault surfaces is important in the mechanics of fault slip and could play a role in determining whether sliding occurs via earthquakes or fault creep we have made preliminary measurements of the power spectral density of several fault surfaces over the wavelength range from 10 5 to 1 m using field and laboratory scale profilimeters the fault surfaces are strongly anisotropic profiles parallel to the slip direction have amplitudes about one order of magnitude lower than those perpendicular to the slip direction over most of the wavelength interval measured fault roughness perpendicular to the slip direction is similar to the roughness of natural joints the greater smoothness in the slip direction presumably represents wear resulting from slip combining our data with previous measurements of the roughness spectrum of the san andreas fault shows that fault surfaces are fractal over nearly eleven orders of magnitude in wavelength

dynamic cause of marginal lithospheric thinning and implications for craton destruction a comparison of the north china superior and yilgarn cratons we present a comparative tectonic analysis of the north china craton ncc which has lost parts of its root with the yilgarn and superior cratons which preserve their roots we compare the geophysical structure and tectonic histories of these cratons to search for reasons why some cratons lose their roots while others retain them based on the comparison and analysis of geological geophysical and geochemical data it is clear that the lithospheric thinning beneath craton margins is a common phenomenon which may be caused by convergence between plates however craton destruction is not always accompanied by lithospheric thinning except for cratons that suffered subduction and collision from multiple sides the western block also known as the ordos block of the ncc yilgarn and superior cratons have not experienced craton destruction the common ground among them is that they are surrounded by weak zones e g mobile belts or orogens that sheltered the cratons from deformation which contribute

evidence for a concealed midcontinent rift related northeast iowa intrusive complex abstract large amplitude aeromagnetic and gravity anomalies over a 16 000 km2 area of northeast iowa and southeast minnesota have been interpreted to reflect the northeast iowa intrusive complex neiic a buried intrusive igneous complex composed of mafic ultramafic rocks in the yavapai province 1 8 1 7 ga hundreds of meters of paleozoic sedimentary cover and a paucity of basement drilling have prevented detailed studies of the neiic long considered but not proven to be related to the 1 1 ga midcontinent rift system mrs the neiic is comparable in areal extent to the richly mineralized duluth complex and is similarly located near the margin of the mrs new geochronological and geophysical data together support an mrs affinity for the neiic a dike swarm imaged in aeromagnetic data is cut by intrusions of the neiic and a new apatite u pb date of 1170 ma on one of the dikes thus represents a maximum age for the neiic a minimum age constraint is suggested by 1 large volume magmatism associated with the mrs that was the last such event to affect the region and 2 the presence of reversely magnetized dikes similar in character to mrs related dikes elsewhere that cut several intrusions of the neiic the neiic is largely characterized by the presence of multiple zoned intrusions many of which contain large volumes of mafic ultramafic rocks and have strong geophysical similarities to alkaline intrusive complexes elsewhere including the mrs related coldwell complex of ontario the largest of the zoned intrusions are 40 km in diameter and are interpreted to have thicknesses of many kilometers suspected faults alignments of intrusions and intrusive margins tend to be aligned along northwest and northeast trends that match the trends of the belle plaine fault zone and fayette structural zone both previously interpreted as pre mrs possibly lithospheric scale discontinuities that may have controlled neiic emplacement these interpretations collectively imply notable potential for the neiic to host several different types of undiscovered base metal and critical mineral deposits

40ar 39ar phlogopite and u pb perovskite dating of lamprophyre dykes from the eastern lake superior region evidence for a 1 14 ga magmatic precursor to midcontinent rift volcanism thin lamprophyre dykes are abundant in the vicinity of the ca 1 1 ga midcontinent rift system and the late archean early proterozoic kapuskasing uplift in the canadian shield northeast of lake superior however the relationship between these dykes and spatially associated alkalic carbonatite complexes has been unclear to ascertain the temporal relationship between the two we have determined by 40ar 39ar and u pb dating precise emplacement ages for six lamprophyre dykes from the region the ma u pb date for perovskite from the western marathon and wawa areas is indistinguishable from the 1144 7 ma 40ar 39ar date for phlogopite from the eastern kapuskasing uplift and it is concluded that these dykes are part of a regional 1 14 ga swarm that extends over 300 km these dykes were therefore emplaced some 35 ma prior to the 1109 ma commencement of midcontinent rift volcanism and coeval alkaline complex activity but essentially simultaneously with emplacement of the 1141 2 ma abitibi diabase dyke

marathon dikes rb sr and k ar geochronology of ultrabasic lamprophyres from the vicinity of mckellar harbour northwestern ontario canada the ultrabasic lamprophyre dikes from the vicinity of mckellar harbour northwestern ontario are composed essentially of a mixture of phlogopite olivine primary carbonate spinel and apatite with associated perovskite and melilite petrologically and chemically they have strong affinities with alnoites and magmas derived from upper mantle sources in stable continental regimes rb sr isotopic studies give an isochron age of 1 65 0 12 ga 2 with an initial 87sr 86sr ratio of 0 70167 0 00036 2 this age is considerably older than the neohelikian keweenawan magmatic event associated with the development of the lake superior basin e g 950 1170 ma k ar data indicate a mean whole rock age for the dikes of 1144 ma and a pseudoisochron age of 1120 34 ma 2 these ages are thought to reflect partial degassing of phlogopite and incomplete updating of the rocks under thermal influences induced by the intrusion of the coldwell alkaline complex at 1044 ma ages of carbonatitic and alkaline rock

u pb baddeleyite crystallization age for a corson diabase intrusion possible midcontinent rift magmatism in eastern south dakota the largely buried basement of the northern great plains includes suture zones and terrane boundaries that represent a significant part of the growth of laurentia in the proterozoic basement exposures in this region east of the black hills are rare in southeastern south dakota southwestern minnesota northeastern nebraska and northwestern iowa small outcrops of the proterozoic sioux quartzite occur in southeastern south dakota corson diabase sills or dykes have intruded the quartzite u pb id tims baddeleyite data from a corson diabase sample yield an upper intercept date of 1149 4 7 3 ma suggesting the diabase is related temporally to the midcontinent rift mcr the similarity in age of this diabase to the inspiration sill pigeon river kipling and abitibi dykes suggests that early midcontinent rift development was not localized within the nipigon embayment but extended along a roughly east northeast zone from the abitibi dykes to the corson diabase the presence of the corson intrusions 25

multifractal and white noise evolutionary dynamics in jurassic cretaceous ammonoidea for more than a decade there has been interdisciplinary debate on whether fossil origination and extinction time series show evidence of self organized criticality soc or some other more complex hierarchical structure analyses of a new data set of jurassic and cretaceous ammonoid genera demonstrate that these taxonomic subgroups do not reproduce the patterns seen in larger data sets that pool disparate taxa rather originations and extinctions in these ammonoids show no evidence of soc limited evidence for a hierarchical multifractal pattern and at least within the suborder ammonitina evidence consistent with a white noise signal although a white noise pattern has been identified previously in an ammonoid family diversity time series the significance of such a result for ammonoid genus originations and extinctions is discussed here for the first time this white noise pattern indicates that processes acting on short time scales less than a few million years dominate the ammonitina origination and extinction records producing a nonhierarchical diversity dynamic because origination events in one interval do not appear to trigger originations in subsequent intervals ammonite evolutionary radiations were likely to be extremely rapid and driven by physical rather than biological opportunities for diversification

u pb dating of perovskite by la icp ms an example from the oka carbonatite quebec canada abstract the potential for u pb dating of the mineral perovskite using laser ablation inductively coupled plasma mass spectrometry la icp ms has been evaluated perovskite can have relatively elevated u and th contents making it a potentially useful geochronometer kimberlite lamprophyre and carbonatite intrusions are prone to alteration and typically contain abundant xenocrysts thus standard techniques for dating the magmatic emplacement of these rocks becomes highly problematic perovskite however is commonly present as a primary magmatic mineral in these rocks and has been used to constrain the timing of kimberlite and lamprophyre emplacement the main limitations to the production of accurate la icp ms u pb ages for perovskite are the lack of suitable standards coupled with the large common pb correction required 204 hg can produce large isobaric interference on the non radiogenic 204 pb isotope and methods based on 208 pb 206 pb and u th ratios are hampered by the enhanced th content present in most perovskite crystals after careful calibration using zircon reference materials common pb corrected 206 pb 238 u ages can be determined on each individual la icp ms analysis by using the measured 207 pb 206 pb ratio which is dominated by the common pb proportion in phanerozoic rocks this method assumes that the perovskite crystals analyzed are cogenetic and have the same initial pb ratios the la icp ms method has been applied to data collected on two large single perovskite crystals from the oka carbonatite complex quebec canada the weighted mean 206 pb 238 u age of 131 7 ma n 25 mswd 0 42 is consistent with published geochronology data from the region and suggests that la icp ms dating of perovskite could be a useful low cost alternative to compliment existing techniques

diversity and morphological evolution of jurassic belemnites from south germany abstract belemnites are extinct cephalopods whose evolutionary history is representative of successful adaptive radiations during the mesozoic nevertheless a detailed understanding of the dynamics and palaeoenvironmental drivers of this evolution is still lacking in order to fill this gap we analyze the diversity and morphological disparity of jurassic rostra from south germany and compare these patterns with other euro boreal trends we show that after an early apparition of few dissimilar groups during the hettangian sinemurian interval belemnites experienced four periods of diversification i e early pliensbachian middle late toarcian early bajocian and oxfordian marked by morphological disparifications of rostra towards forms potentially optimized for different hydrodynamic properties these adaptive radiations were interrupted at regional scale by four biological crises corresponding to morphological bottlenecks i e pliensbachian toarcian aalenian late bajocian and kimmeridgian most of them were morphoselective except the aalenian extinction which could be related to a prominent sea level fall by comparing our results to palaeoenvironmental data we show that warm temperate seawater temperatures might have favoured the diversification of belemnites potentially by accelerating their metabolic rates the population turnovers and the evolutionary rates on the long term conversely cooling or hyperthermal events correspond with biological crises migrations towards refuge areas located in the arctic and mediterranean domains could have been key factors for rapid post crisis recoveries finally the available data suggest a trend towards increased streamlining of the rostrum through the jurassic

dating of archean auriferous quartz vein deposits in the abitibi greenstone belt canada 40 ar 39 ar evidence for a 70 to 100 m y time gap between plutonism metamorphism and mineralization the sigma mine at val d9or quebec in the abitibi belt is typical of vein type gold deposits in archcan greenstone belts although the relative timing of gold mineralization with respect to magmatism metamorphism deformation and hydrothermal events in the mine is well documented precise isotopic age constraints have until recently been lacking this paper presents the results of a 40 ar 39 ar dating study of the sigma mine and of the davidson tisdale deposit in the abitibi belt in the sigma mine dates on metamorphic amphibole indicate that the regional metamorphism which predates the vein formation occurred at ca 2 68 ga muscovite from the gold bearing quartz veins yields a plateau date of 2579 or 9 ma 2sigma whereas biotite from the veins shows disturbed saddle shaped age spectra the mild disturbance of the biotite is attributed to later diabase dike emplacement and a 40 ar 39 ar date on a dike indicates that this event is younger than 2 3 ga thermal effects of the grenville orogeny 1 2 1 0 ga may also be present a muscovite separate from a gold bearing quartz vein at the davidson tisdale deposit yields a 2607 or 10 ma 2sigma plateau date although the amphibole and muscovite dates at the sigma mine bracket the gold mineralization event at between ca 2 68 and 2 58 ga a number of tectonothermal histories are possible for this time interval it is concluded based on all evidence that the muscovite plateau dates are the time of vein and gold formation which thus occurred in the sigma mine ca 100 m y and in the davidson tisdale deposit ca 70 m y after syn to post tectonic magmatism and regional metamorphism

petrologic hypothesis testing with pearce element ratio diagrams derivation of diagram axes in petrology pearce element ratio per diagrams have been used i to determine whether members of a rock suite are co genetic ii to identify the minerals involved in differentiation processes and iii to evaluate the extent to which those mineral are involved the axis coefficients of each diagram are chosen such that sorting of minerals or combinations of minerals will generate unique and predictable trends unfortunately selection of the optimal combination of axis coefficients is a difficult task especially if the system being investigated has a large number of phases or complicated solid solution minerals our work has established a formal set of rules and matrix operations which facilitate the determination of per diagram axes coefficients this methodology can be used to determine the unit molar vector displacement caused by the addition or subtraction of a specific mineral given a set of axis coefficients it can also be used to create per diagrams on which minerals have predetermined vector displacements by designating all vector displacements to be parallel axis coefficients for assemblage test diagrams can be determined to test the following hypothesis the observed chemical variation is due to the addition or removal of a specific set of minerals alternatively by designating all vector displacements to be mutually perpendicular phase discrimination diagrams can be created which test whether the observed chemical variations require a specific phase to be involved in differentiation phase discrimination diagrams also provide a means to estimate the extent of that involvement this methodology facilitates construction of powerful yet simple per diagrams which provide an effective means of testing alternative differentiation hypotheses

no fractals in fossil extinction statistics statistical analyses of the fossil record seek to discover the mechanisms controlling biotic diversity throughout the earth s history sole et al 1 reported that many extinction time series are statistically self similar with 1 f power spectra suggesting that extinctions are driven by self organized criticality or by other scale free internal dynamics of the biosphere here we show that the apparent self similarity and 1 f scaling reported by sole et al are artefacts of their interpolation methods extinction records that are not interpolated show no evidence of fractal scaling

geologic transect across the grenville orogen of ontario and new york revised cross sections of the western grenville province incorporate new geologic results and reprocessed seismic reflection data the geology is presented in terms of three tectonic elements 1 pre grenvillian laurentia and its margin with ca 1740 and 1450 ma continental arc plutons and associated supracrustal rocks 2 composite arc belt of allochthonous 1300 1250 ma volcanic arcs and sedimentary rocks and 3 frontenac adirondack belt characterized by supracrustal and granitoid rocks and anorthosites of uncertain affinity that may represent a distinctive part of the composite arc belt or an offshore micro continent rocks of the composite arc and frontenac adirondack belts were amalgamated with each other by ca 1160 ma were then thrust over laurentia during ca 1080 1035 ma and ca 1010 980 ma phases of convergence and were dissected and exhumed by 1040 ma normal faults penetrative deformation was restricted to that part of the pre grenvillian laurentian margin that lies to the southeast of the grenville front and parts of the accreted composite arc and frontenac adirondack belts the laurentian rocks in the grenville province are bounded to the northwest and southeast by southeast dipping ductile thrust and or normal shear zones the composite arc and frontenac adirondack belts to the southeast are bounded by ductile and brittle ductile thrust and or normal faults that separate domains with contrasting cooling histories despite a long pre grenvillian tectonic and plutonic history the present crustal architecture and much of the seismic reflectivity were acquired during 1080 980 ma phases of compression and extension

precipitation of caco3 in pressure solution experiments the importance of damage and stress abstract pressure solution ps is a widespread phenomenon in the earth s upper crust which influences many important natural processes including porosity evolution of sedimentary rocks and fault healing ps is a creep process effecting porous rocks involving microscale dissolution and precipitation reactions mediated by diffusion of solutes in the fluid phase this paper presents an experimental study in carbonates aiming to advance basic understanding of the physical chemistry controlling ps the experiments utilize a newly developed method which enables imaging the precipitation stage of ps with a confocal microscope via a fluorescent marker that binds to precipitating carbonate we use this method to study the relative role of the various driving forces and the dominant mechanisms controlling the amount and spatial distribution of precipitation in carbonates undergoing ps using a clamping apparatus we performed dozens of experiments in which carbonate samples were indented by quartz grains in the presence of water carbonate precipitation was observed to occur relatively fast hours days within and around all indented pits irrespective of the imposed experimental conditions such as stress and fluid saturation yet the amount and distribution of the precipitation varies between experiments two major factors were found to control the amount of precipitation degree of damage inflicted by pitting and the application of stress fluid saturation was seen to affect the spatial distribution of precipitates in light of these results we reexamine the traditional chemical potential equations of ps in order to explain the comparable effects of damage and stress on precipitation

evolution and extinction of maastrichtian late cretaceous cephalopods from the lopez de bertodano formation seymour island antarctica one of the most expanded records to contain the final fortunes of ammonoid cephalopods is within the lopez de bertodano formation of seymour island james ross basin antarctica located at 65 south now and during the cretaceous this sequence is the highest southern latitude onshore outcrop containing the cretaceous paleogene k pg transition we present comprehensive new biostratigraphic range data for 14 ammonite and one nautiloid species based on the collection of 700 macrofossils from high resolution sampling of parallel sedimentary sections dated maastrichtian to earliest danian in age across southern seymour island we find evidence for only a single abrupt pulse of cephalopod extinction at the end of the cretaceous when the final seven ammonite species disappeared consistent with most evidence globally in the lead up to the k pg extinction in the james ross basin starting during the campanian ammonite diversity decreased overall but the number of endemic taxa belonging to the family kossmaticeratidae actually increased this pattern continued into the maastrichtian and may be facies controlled linked to changes in sea level and seawater temperature during the early maastrichtian ammonite diversity dropped significantly with only two species recorded from the basal lopez de bertodano formation on seymour island the subsequent diversification of endemic taxa and reappearance of long ranging widespread species into the basin resulted in an increase in ammonite diversity and abundance during the mid maastrichtian this was coincident with an apparent period of warming temperatures and sea level rise interpreted from palynology and sedimentology perhaps reflecting a high latitude expression of the mid maastrichtian event late maastrichtian diversity levels remained stable despite reported climatic and environmental variation ammonite diversity patterns during the maastrichtian parallel those of microfossil species such as nannofossil and planktonic foraminifera suggesting that dynamic climatic and environmental changes affected many planktonic and nektonic organisms during the latest cretaceous however we suggest that these perturbations had a minimal effect on overall diversity prior to the catastrophic extinction event at the k pg boundary

evidence of self organization in planktic foraminiferal evolution implications for interconnectedness of paleoecosystems we analyzed planktic foraminiferal evolutionary data using techniques of nonlinear dynamics a methodology new to paleontology the data set comprises 196 extinction and speciation horizons derived from biostratigraphic ranges of 662 reliably defined species bothextinctionandspeciationdatasetsarewellcharacterizedbypower lawmodels however return maps and a predictor technique indicate that the extinction data are more highlydeterministicthanspeciationdata weinterprettheanalysis particularlyextinction data to be consistent with planktic foraminiferal evolution being organized and not randomly driven our results do not preclude periodic large extinction events driven by external forces as predetermined by another system e g large body impact or internally driven extinction processes where spontaneously derived interdependencies cascade through the ecosystem or some combination thereof our data support a model whereby the internal organization of an ecosystem regulates the response to changes in a deterministic manner the relative scales of disturbances and extinctions depending on the degreeofinterdependencywithinthesystem thusanycontentionthatspeciesinteractions are not sufficiently intense to generate mass extinctions can be dismissed random walks generated by genetic drift and the transitory nature of n dimensional niche space may explain why speciation is less deterministic than extinction

ratio correlations and major element mobility in altered basalts and komatiites attempts have been made in the recent literature to constrain major element mobility in altered basalts and komatiites using the molecular proportion ratio mpr diagrams developed by t h pearce 1970 the method involves ratioing the molecular proportions of two oxides against a third oxide and presenting the results as an oxide oxide ratio plot the transformation appears to clean up scatter plots with low correlations and produces highly correlated ratio plots these plots have been taken to be indicative of igneous fractionation trends and thus of minimal bulk chemical change during alteration there are however inherent statistical problems in ratio correlation which have received much attention in the mathematical literature this paper explains the implications of enhanced correlations for work on altered rocks using ratio plots and suggests that extreme caution must be exercised in the interpretation of mpr diagrams

paleomagnetism and geochemistry of 1144 ma lamprophyre dikes northwestern ontario implications for the north american polar wander and plate velocities

low stress pressure solution experiments on halite single crystals abstract pressure solution experiments on halite single crystals in saturated solution were carried out at atmospheric pressure under uniaxial stress ranging from 0 1 to 2 0 mpa and at temperatures of 303 and 323 k the experiments were performed in ceramic loading rigs with damp proofed sample chambers the low uniaxial stress is applied by loading the piston with steel weights ranging from 0 5 to 5 0 kg the position of the piston is measured by an electronic displacement transducer connected to a data acquisition system deviations caused by fluctuations of temperature and output voltage of the power supply are corrected after data acquisition the halite cubes 100 with edge dimensions of 3 9 mm are prepared by cleaving and placed with a 100 cleavage face on the 001 face of a muscovite single crystal 10 10 0 1 mm a polished quartz 0001 plate or another halite crystal oriented to form a 45 twist boundary the four free 100 faces of the halite cube are in contact with the surrounding nacl solution the initial displacement rate of the piston after flooding of the system and loading is up to 50 0 m day attributed to smoothing of the halite face and elimination of point contacts with high stress concentration within 2 to 3 days this stage grades into steady state displacement with rates of 0 1 2 0 m day in some experiments stages of higher displacement rates 2 0 5 0 m day lasting for 3 5 days are observed episodically with intervals of 10 15 days these cycles appear not to be triggered by external events experiments with a dry mica halite interface carried out for comparison at the same temperature and at an uniaxial stress of 2 mpa result in a displacement rate below the limits of detection this rules out a significant contribution of crystal plastic deformation in the wet experiments the experimental results show no simple correlation between displacement rate and magnitude of uniaxial stress crystal size type of the interface and temperature at the given conditions convergence at a single interface due to pressure solution is apparently not a steady state process the alternating stages of lower and higher displacement rates observed in many experiments suggest that the mechanisms of transport or dissolution may change spontaneously during the experiment it is possible that the process itself leads to an unstable configuration causing episodic changes

stylolites a review abstract stylolites are ubiquitous geo patterns observed in rocks in the upper crust from geological reservoirs in sedimentary rocks to deformation zones in folds faults and shear zones these rough surfaces play a major role in the dissolution of rocks around stressed contacts the transport of dissolved material and the precipitation in surrounding pores consequently they play an active role in the evolution of rock microstructures and rheological properties in the earth s crust they are observed individually or in networks in proximity to fractures and joints and in numerous geological settings this review article deals with their geometrical and compositional characteristics and the factors leading to their genesis the main questions this review focuses on are the following how do they form how can they be used to measure strain and formation stress how do they control fluid flow in the upper crust geometrically stylolites have fractal roughness with fractal geometrical properties exhibiting typically three scaling regimes a self affine scaling with hurst exponent 1 1 0 1 at small scale up to tens or hundreds of microns another one with hurst exponent around 0 5 to 0 6 at intermediate scale up to millimeters or centimeters and in the case of sedimentary stylolites a flat scaling at large scale more complicated anisotropic scaling scaling laws depending of the direction of the profile considered is found in the case of tectonic stylolites we report models based on first principles from physical chemistry and statistical physics including a mechanical component for the free energy associated with stress concentrations and a precise tracking of the influence of grain scale heterogeneities and disorder on the resulting micro structures experimental efforts to reproduce stylolites in the laboratory are also reviewed we show that although micrometer size stylolite teeth are obtained in laboratory experiments teeth deforming numerous grains have not yet been obtained experimentally which is understandable given the very long formation time of such geometries finally the applications of stylolites as strain and stress markers to determine paleostress magnitude are reviewed we show that the scalings in stylolite heights and the crossover scale between these scalings can be used to determine the stress magnitude its scalar value perpendicular to the stylolite surface during the stylolite formation and that the stress anisotropy in the stylolite plane can be determined for the case of tectonic stylolites we also show that the crossover between medium millimetric scales and large pluricentimetric scales in the case of sedimentary stylolites provides a good marker for the total amount of dissolution which is still valid even when the largest teeth start to dissolve which leads to the loss of information since the total deformation is not anymore recorded in a single marker structure we discuss the impact of the stylolites on the evolution of the transport properties of the hosting rock and show that they promote a permeability increase parallel to the stylolites whereas their effect on the permeability transverse to the stylolite can be negligible or may reduce the permeability depending on the development of the stylolite

paleomagnetism and upb geochronology of volcanic rocks from michipicoten island lake superior canada precise calibration of the keweenawan polar wander track abstract paleomagnetic poles have been determined for normally magnetized samples of late proterozoic volcanic rocks from 23 sites on michipicoten island lake superior canada the results are in general accord with an earlier less precise study by one of the authors and indicate a small polar shift between rocks of the mamainse point formation 186 e 38 n and the michipicoten island formation 175 e 26 n a quartz feldspar porphyry intruding the lower mamainse point formation but unconformably overlain by the michipicoten island formation was sampled for u pb zircon dating the zircons define an age of emplacement of 1086 5 1 3 3 0 ma this age and the pole positions are consistent with and supplement ages previously determined for the keweenawan paleomagnetic polar wander curve these data define an apparent polar wander rate of 14 cm a 1 this age combined with previously published u pb ages indicates a time span of 22 ma for most keweenawan igneous activity in addition the time of the keweenawan paleomagnetic reversal is constrained to be between 1086 5 1 3 3 0 and 1097 6 3 6 ma the age of the upper part of the reversely magnetized osler group the zircon population contained an inherited component from a source 1403 50 ma old this suggests that the porphyry magma was at least partly derived by melting of an anorogenic pluton emplaced during the mid proterozoic

upper bound on stylolite roughness as indicator for amount of dissolution stylolites are rough surfaces that form by localized dissolution despite their abundance in carbonates and sandstones and their importance for fluid flow and rock deformation many fundamental issues concerning their structure and evolution are still unresolved this manuscript studies the roughening of long parallel stylolites here we report measurements of stylolite surface roughness at a scale larger than ever measured before 10 2 10 1 m measurements were performed using ground based lidar on 6 naturally exposed surfaces of 4 km long stylolites in northern israel producing a topographic map of the surfaces from which roughness characteristics were derived our results show that for length scales below 50 cm the stylolite morphology exhibits self affine behavior with a hurst exponent h 0 65 consistent with previous studies made on smaller samples the self affine behavior changes for measurements made on scales above 50 cm with h decreasing almost to zero on long length scales this observed upper bound of self affine roughness is measured here for the first time but has been previously predicted by theory ebner et al 2009b koehn et al 2007 our measurements support these theoretical models and together with them present a scenario in which the investigated stylolites evolve from preferential dissolution along an existing surface that was initially smooth and progressively roughened with time such a mechanism of stylolites growth is different from previously suggested mechanisms for other classes of stylolites which might propagate sideways from an initial defect based on the theoretical roughening model that we adopted the upper limit to fractality for this class of stylolites may be used as a measure of the amount of dissolution on stylolites indeed the amount of dissolution on the stylolites in our field site which we calculated from the upper limit to fractality is comparable to though slightly larger than our estimates of dissolution from two additional independent techniques reflecting compactive strain of 50

pressure solution and hydrothermal recrystallization of carbonate sediments an experimental study reply abstract the extent of calcite recrystallization was determined in pressure solution and hydrothermal experiments which were conducted on deep sea carbonates of low mg calcite iceland spar and reagent grade calcite powder in the pressure solution experiments wet sediments were subjected to confining pressures of 500 1500 bars and pore pressures of 150 500 bars at temperatures between 22 and 180 c for 21 240 h the hydrothermal experiments were performed in sealed teflon coated bombs at 200 c zero effective stress in sulfate free sea water for two weeks the hydrothermal system was solution dominated the extent of calcite recrystallization was determined by measuring the oxygen isotopic compositions of the pore fluids and solids before and after each experiment scanning electron microscope observations porosity and specific surface area measurements were performed in fine grained carbonate samples subjected to high effective stresses the mechanism for recrystallization apparently involves both relief of strain energy at grain to grain contacts and decrease in surface free energy by decreasing the surface area while in coarse grained carbonates relief of strain energy appears to be the most important control of recrystallization in the hydrothermal experiments however decrease in surface free energy is the only driving force for recrystallization effective stress increased the rate of calcite recrystallization in both pressure solution and hydrothermal experiments clay minerals retarded the reaction the effects of diatomite and basaltic glass on the extent of calcite recrystallization was investigated only in the hydrothermal experiments both admixed non carbonate materials retarded the reaction diatomite being the most effective inhibitor surface chemical reactions seem to be responsible for the observed inhibitions of calcite recrystallization increases in the extent of calcite recrystallization with increasing ionic strength were observed in hydrothermal experiments in nacl solutions of five different ionic strengths

effects of phosphate ions on intergranular pressure solution in calcite an experimental study abstract intergranular pressure solution ips is a coupled chemical mechanical process of widespread importance that occurs during diagenesis and low temperature deformation of sedimentary rocks laboratory experiments on ips in halite quartz and calcite have largely concentrated on the mechanical aspects of the process in this study we report the effects of pore fluid chemistry specifically varying phosphate ion concentration on the mechanical compaction by ips of fine grained calcite powders at room temperature and 1 to 4 mpa applied effective stress phosphate was investigated because of its importance as a biogenic constituent of sea and pore waters increasing the pore fluid phosphate concentration from 0 to 10 3 mol l systematically reduced compaction strain rates by up to two orders of magnitude the sensitivity of the compaction strain rate to phosphate concentration was the same as the sensitivity of calcite precipitation rates to the addition of phosphate ions reported in the literature suggesting that the rate of ips in phosphate bearing samples was controlled by calcite precipitation on pore walls the results imply that ips and associated porosity permeability reduction rates in calcite sediments may be strongly reduced when pore fluids are enriched in phosphates for example through high biologic productivity or a seawater origin future modeling of ips related processes in carbonates must therefore take into account the effects of pore fluid chemistry specifically the inhibition of interfacial reactions

an integrated model for transitional pressure solution in sandstones abstract a key aspect of the deformation of sedimentary rocks during diagenesis is pressure solution however it is often not clear why some rocks of a given mineralogy depth and pressure exhibit a great deal of pressure solution while very similar rocks under similar conditions do not to address such difficulties which we believe arise from the natural non linear physico chemical processes a quantitative model for pressure solution applied to sandstones has been developed this model subsumes various factors 1 pressure temperature and burial rate 2 grain size shape and packing of the mineral grains 3 the variability of water film thickness and coefficient of diffusion between any two grains in contact as a function of stress across the contact pore fluid pressure salinity ph and temperature in this study we distinguish several types of surface sites over quartz grains in a sandstone with corresponding differences in chemical potential thus allowing the diffusive transfer of matter from one site to another the contact between two grains is divided into two parts the actual true contact between two grains is a site of water film diffusion and the inclusions inside the contact the free face inclusion contacts are sites of free face pressure solution on the pore surface site precipitation occurs it is shown that a kinetics transition from a reaction limited deformation to a diffusion limited deformation occurs in the upper crust a geometric transition occurs too due to the textural evolution of the rock with deformation the main goal of this paper is to show the dynamics of the shifting importance of actual and free face inclusion contacts using a unified model including both features the result is a predictive model for porosity variations with depth due to pressure solution in sandstones

sedimentary stylolite networks and connectivity in limestone large scale field observations and implications for structure evolution stylolites are rough surfaces formed by localized rock dissolution and prevalent in carbonates and other sedimentary rocks their impact on porosity and permeability and capacity to accommodate compactive strain are well documented this paper presents a meso scale field study on sedimentary stylolites in carbonates characterizing large scale distributions of stylolites including measurements conducted on longer than kilometer long stylolites our field study suggests that on large scales connections between stylolites become important since connectivity and also lack of connectivity are expected to play a significant role in strain accommodation and hydraulic rock properties we suggest that large scale analysis may require a new characterization scheme for stylolites populations based on their connectivity we therefore divide sedimentary stylolite populations into three end member types which are correlated with the three possibilities for percolation of such systems isolated stylolites with zero percolation connectivity long parallel stylolites with 2 dimensional percolation connectivity and interconnected stylolite networks with 3 dimensional percolation connectivity new statistical parameters and measures are devised and used to quantitatively characterize the different population types schematic mechanistic models are then offered to explain the evolution of the three end member connectivity classes in addition we discuss the effect on fluid flow of the different population types

the geochemistry geochronology and paleomagnetism of dikes and sills associated with the mesoproterozoic midcontinent rift near thunder bay ontario canada abstract the midcontinent rift mcr of north america comprises a series of basaltic sheets flows and intrusive rocks emplaced in the lake superior region during the mesoproterozoic the mafic rocks preserved on the northern flank of lake superior represent the older portions of the rift sequence and offer insights into the early development of the rift new geochronological geochemical and paleomagnetic data are presented for the dikes and sills located in and south of thunder bay ontario three sill suites are recognized within the study area an earlier spatially restricted ultramafic unit termed the riverdale sill the predominant logan sills and nipigon sills in the north of the study area in addition three dike sets are recognized the north east trending pigeon river swarm the north west trending cloud river dikes and the mt mollie dike the geochemical data demonstrate that the majority of sills south of thunder bay are of logan affinity and distinct from those of broadly similar age in the nipigon embayment to the north the pigeon river dikes that intrude the sills are geochemically coherent but distinct from the logan sills and could not be feeders to the sills the new age of 1109 2 4 2 ma for the cloud river dike and its r polarity are consistent with published magnetostratigraphy the mt mollie dike age 1109 3 6 3 ma indicates that it is not coeval with the spatially associated crystal lake gabbro as previously thought the complexity of the dike and sill suites on the northern flank of suggests that the early phases of rifting occurred in distinct and changing stress fields prior to the main extensional rifting preserved in younger rocks to the south the geochemistry and geochronology of the intrusions suggest a long lived and complex magmatic history for the midcontinent rift

a fractal analysis of quaternary cenozoic mesozoic and late pennsylvanian sea level changes sea level changes are related to both climatic variations and tectonic movements the fractal dimensions of several sea level curves were compared to a modern climatic fractal dimension of 1 26 established for annual precipitation records a similar fractal dimension 1 22 based on 18o 16o in deep sea sediments has been suggested to characterize climatic change during the past 2 m y our analysis indicates that sea level changes over the past 150 000 to 250 000 years also exhibit comparable fractal dimensions sea level changes for periods longer than about 30 m y are found to produce fractal dimensions closer to unity and missourian late pennsylvanian sea level changes yield a fractal dimension of 1 41 the fact that these sea level curves all possess fractal dimensions less than 1 5 indicates that sea level changes exhibit nonperiodic long run persistence the different fractal dimensions calculated for the various time periods could be the result of a characteristic overprinting of the sediment record by prevailing processes during deposition for example during the quaternary glacio eustatic sea level changes correlate well with the present climatic signature during the missourian however mechanisms such as plate reorganization may have dominated resulting in a significantly different fractal dimension

compaction creep of wet granular calcite by pressure solution at 28 c to 150 c 1 uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone analytical grade calcite and superpure calcite the tests were performed at 28 c 150 c effective stresses of 20 47 mpa and a pore pressure of 20 mpa using presaturated caco3 solution as the pore fluid sample grain sizes ranged from 12 to 86 m the aim was to determine if creep occurs by intergranular pressure solution ips under these conditions and to identify the rate controlling process the wet samples showed significant creep while dry and oil flooded samples did not wet samples were also characterized by microstructures such as sutured grain contacts grain indentations and overgrowths suggesting the operation of ips the behavior of the wet samples at low strains 4 5 agreed well with the predictions of standard models for diffusion controlled pressure solution however at higher strains 5 10 creep slowed down compared with the model predictions transient flow through tests performed in this regime led to an acceleration of creep consistent with models for precipitation controlled ips and demonstrated an increase in the impurity content of the pore fluid toward higher strains since some of these impurities notably mg2 retard precipitation in calcite we suggest that creep occurred by diffusion controlled ips at low strain giving way to precipitation control at larger strains as impurities accumulated fitting of the diffusion controlled ips model to the low strain data yielded values of the grain boundary diffusion product ds in calcite of 10 19 m3 s 1 at 150 c

structural evolution of the hemlo greenstone belt in the vicinity of the world class hemlo gold deposit a complex history of volcano sedimentary deposition polyphase strain multiple intrusive events and various stages of porphyroblastesis is indicated for the hemlo gold deposit area within the hemlo greenstone belt structural elements can be assigned to at least six stages of development d1 d6 d1 generated small scale folds and low angle faults thrusts with no planar fabric except within strain aureoles around the earliest intrusions d2 was a progressive event resulting from northeast directed compression which generated regional predominantly s shaped folds early d2 penetrative planar and linear fabrics overturned stratigraphy and formation of an inflection in the strike of the greenstone belt mid d2 and development of high strain zones with dominant sinistral and local dextral shear sense late d2 d3 was a distinctly separate progressive event resulting from northwest directed transpression which generated variably penetrative east to northeast striking foliation s3 ductile de

evidence for periodicity and nonlinearity in a high resolution fossil record of long term evolution the application of new signal analysis techniques provides increased insight into the study of the fossil record and processes of evolution the fossil record of 622 planktic foraminifera contains data from 200 stratigraphic stages of the past 127 m y time series analyses wavelet and fourier transform of the planktic foraminifera fossil record were used to discern periodic components in long term evolution the correlation function analysis was used to distinguish between random and deterministic behavior of the fossil record the analyses show that stationary 30 m y periodicity and complex deterministic patterns occur in the long term planktic foraminifera evolution in particular in the extinction record our results suggest that the occurrence of intense diversity fluctuations with 3 10 m y periodicity after major extinction events may be attributed to nonlinear self organized evolutionary response to the availability of new ecospace this coupled nonlinear periodic scenario may explain the repetitive appearance of similar morphotypes in 30 m y intervals

in situ u pb dating and nd isotopic analysis of perovskite from a rodingite blackwall associated with uhp serpentinite from southwestern tianshan china abstract metamorphic perovskite associated with diopside chlorite occurs in blackwalls surrounding rodingitized mafic dikes that are included in ultrahigh pressure uhp serpentinized ultramafic rocks from changawuzi chinese southwestern tianshan perovskite forms discrete crystals in the chlorite rich matrix or appears at the rim of ilmenite the metamorphic perovskites from the blackwalls are characterized by high concentrations of ree nb ta th and u the primitive mantle normalized patterns of perovskite are two to three orders of magnitude higher but parallel to the bulk rock patterns demonstrating that perovskite is a major host of these incompatible trace elements in the ultramafic rocks the bulk rock major and trace element compositions of rodingite dikes and associated blackwalls display variable patterns consistent with different mafic protoliths of the rodingites perovskites from three samples were analysed for u pb by in situ secondary ion mass spectrometry two samples contained essentially common pb whereas one sample had enough radiogenic pb to define a discordia in the tera wasserburg diagram with an age intercept of 317 11 ma if all analyses are pooled together a 238u 206pb age of 308 5 ma is obtained these ages are in agreement with the age of peak uhp metamorphism in chinese southwestern tianshan in situ nd isotopes of perovskite from the three samples were obtained by laser ablation multi collector inductively coupled plasma mass spectrometry the nd t 310 of two samples are 8 37 0 14 and 7 88 0 25 respectively which suggests that they have similar protoliths these samples plot close to a 310 ma sm nd isochron in contrast the third sample has a different nd t 310 of 0 90 0 51 indicating a completely different protolith thus in situ analyses of perovskite can provide important information on the protolith as well as the metamorphic evolution of reaction zones between mafic and ultramafic rocks

further refinement to the timing of mesoproterozoic magmatism lake nipigon region ontario the midcontinent rift in the lake superior region of north america is one of the best preserved examples of an aborted precambrian intercontinental rift one that hosts a diverse suite of rock types in addition to the well studied and voluminous rift fill flood basalts although there is a growing database of high precision age information for the main volcanic packages and the largest mafic intrusions there is relatively little information available on the absolute timing of mafic ultramafic intrusions dyke swarms and alkaline complexes especially in the ontario portion of the rift we report new high precision u pb ages for 29 samples primarily collected in the lake nipigon area ontario from these new age results it is now possible to expand the known distribution of geon 15 magmatism in the region confirm an early stage of midcontinent rift mafic magmatism between 1150 and 1130 ma provide evidence that significant mafic ultramafic magmatism occurred in the lake nipigon region slightly earlier

calcite twinning strains from syn faulting calcite gouge small offset strike slip normal and thrust faults we have evaluated the stress strain behavior of calcite precipitated and mechanically twinned in small offset strike slip normal and thrust faults of a variety of ages and from a variety of tectonic settings n 3001 twin measurements 63 strain analyses from 18 field sites five strike slip faults with syn faulting horizontally striated calcite rake 0 were studied and we report the orientations of the contemporaneous stress strain field associated with each fault intrusion of the marathon large igneous province mafic dikes 2 1 ga in archean crust minnesota usa post keweenaw rift 1 1 ga faulting island lake fault central ontario canada subduction associated with metamorphic core complex formation cretaceous china subduction cretaceous to miocene italy and continental extension recently active furnace creek fault death valley california usa seven normal faults with synfaulting dip slip striated calcite were studied and are from the following tectonic settings a normal fault slip surface in an ordovician piedmont fold appalachian s paleo subduction associated with cretaceous metamorphic core complex formation china 3 sites the paleo extensional atlantic margin 55 ma ireland 1 site with a u pb calcite age continental extension 1 active site mojave desert a transcurrent margin jamaica 1 active fault site and subduction 2 active faults along the eur african margin in italy with calcite u th disequilibria ages and crete respectively six thrust fault examples are all from convergent orogenic settings the basal thrust of the penokean 1850 ma fold and thrust belt the penokean orogen foreland in mesabi range banded iron formation folds an offset breccia body in the permian gondwanide belt ellsworth mountains antarctica the frontal thrust of the gondwanide cape belt south africa the paleocene frontal prospect thrust sevier belt wyoming and an alpine foreland back thrust lulworth cove u k for each strike slip fault system the twinning shortening strain is horizontal and at an angle of 0 60 to the respective fault plane dextral or sinistral although in the majority of cases the shortening axis is parallel to fault strike 13 of 23 results in each normal fault example dip slip kinematic striations dominate the faulted surface yet the orientation of the maximum principal compressive stress 1 and shortening strain axis e1 are not 45 to the fault plane as predicted but are sub horizontal and either strike parallel 25 of 35 results or strike normal 10 of 35 results thrust faults preserve shortening strain axes parallel to the dip slip kinematic direction within the fault plane plane strain and not at 45 to the principal plane 5 of 5 results none of the fault stress strain field results reported here support the andersonian or mohr coulomb criteria for stress strain relations predicted along faults

the abitibi dyke swarm a consequence of superior grenville interaction both the age 1150 ma and the strike of the abitibi dykes east of the kapuskasing structural zone in the superior province of the canadian shield can be explained as a consequence of the grenvillian orogeny in the adjacent grenville province modelling the superior province as an elastic brittle plate acted on its southeastern boundary by tectonic stresses consequent upon the grenvillian orogeny we obtain families of maximum and minimum horizontal stress trajectories that match very well the orientation of the dykes

analysis of petrologic hypotheses with pearce element ratios pearce element ratios can test whether the members of a rock suite are comagmatic and can illustrate the causes of chemical diversity in comagmatic suites comagmatic rocks have constant ratios for elements conserved in the system during changes that led to the chemical diversity in basaltic systems the incompatible elements ti k and p are often conserved the slope of the trend on a pearce element ratio diagram is sensitive to the stoichiometry of the crystallizing and segregating phases a judicious choice of ratios as axes for the diagram provides a signature for the phases involved and estimates of their compositions in basaltic rocks diagrams with ti k vs p k can provide a test of the comagmatic hypothesis diagrams with 0 5 mg fe k vs si k have trends that are distinct for each comagmatic suite and different mineral assemblage different suites are distinguished by the intercepts in diagrams whereas mineral assemblages are recognized by the slopes of the trends for example if olivine is the sole crystallizing and segregating phase the trend will have a slope of 1 diagrams with 2ca na k vs al k distinguish plagioclase from augite assemblages and in conjunction with 0 5 mg fe k diagrams unravel the crystallization sequences of suites that have suffered three phase crystallization and segregation analyses from the uwekahuna laccolith kilauea the 1955 and 1967 68 eruptions of kilauea diamond craters volcanic field oregon and experimental data on morb glasses provide illustrations of the interpretations that can be obtained from pearce element ratios