petrology and textural classification of the jericho kimberlite northern slave province nunavut canada the paper presents data on petrology bulk rock and mineral compositions and textural classification of the middle jurassic jericho kimberlite slave craton canada the kimberlite was emplaced as three steep sided pipes in granite that was overlain by limestones and minor soft sediments the pipes are infilled with hypabyssal and pyroclastic kimberlites and connected to a satellite pipe by a dyke the jericho kimberlite is classified as a group ia lacking groundmass tetraferriphlogopite and containing monticellite pseudomorphs the kimberlite formed during several consecutive emplacement events of compositionally different batches of kimberlite magma core logging and thin section observations identified at least two phases of hypabyssal kimberlites and three phases of pyroclastic kimberlites hypabyssal kimberlites intruded as a main dyke hk1 and as late small volume aphanitic and vesicular dykes massive pyroclastic kimberlite mpk1 predominantly filled the northern and southern lobes of the pipe

toward process based modeling of geochemical soil formation across diverse landforms a new mathematical framework we present a mathematical model that integrates geochemical and geomorphic processes responsible for soils elemental and mineralogical evolution on diverse landforms eroding to depositional to level grounds this new model combines a hillslope sediment mass balance and a soil geochemical mass balance we model soils as the sum of a physically disturbed zone pdz and the underlying physically undisturbed but chemically altered zone caz the model considers processes including the production of pdz weathering front propagation mineral specific dissolution colloidal translocation and colluvial transport thus this study serves to 1 review preexisting models of pedogenic processes and to 2 offer a framework to integrate the geochemical and geomorphic processes active in soils we further discuss the implications of our model in 1 scaling chemical weathering reactions from mineral grains to pedons to soil catenas 2 understanding the emergence of geochemical soil catenas and 3 coupling physical and chemical weathering processes

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

organic metamorphism as a key for reconstructing tectonic processes a case study from the austroalpine unit eastern alps at the northwestern margin of the gurktal alps eastern alps eoalpine cretaceous thrusting of carbonaceous material cm bearing metasediments formed a very low to low grade metamorphic nappe stack above higher grade metamorphic basement nappes sedimentary burial as well as progressive metamorphism transformed the enclosed cm to anthracite metaanthracite and semigraphite in a kinematically well constrained section at the northwestern frontal margin of the nappe stack this transformation has been investigated by vitrinite reflectance measurements and raman spectroscopy of carbonaceous materials rscm automated interactive fitting of raman spectra estimates the metamorphic peak temperatures in a complete section through the upper part of the upper austroalpine unit a rscm trend indicates a temperature profile of ca 250 600 c the top part of the gradient is reconstructed by one dimensional thermal modeling the certainty of ca 25 c at a confidence level of 0 9 resembles the data variability within a sample location due to the large calibration range the method is able to reconstruct a thermal crustal profile in space and time the study highlights the versatility of rscm which characterizes almost 250 ma of a complex and polyphase tectonic history rscm data characterize the variscan metamorphic grade in nappes now imbricated in the eoalpine nappe stack they additionally constrain a numerical model which emphasizes the significance of an increased thermal gradient in a continental margin towards the western neotethyan ocean during permo triassic lithospheric extension it finally characterizes the eoalpine metamorphic gradient during nappe stacking and a significant metamorphic jump related to exhumation and normal faulting

a quaternary solution model for white micas based on natural coexisting phengite paragonite pairs a thermodynamic model for the quaternary white mica solid solution with end members muscovite mg celadonite paragonite feceladonite ms mgcel pg fecel is presented the interaction energies for the mgcel pg join the fecel pg join and the ternary interactions were obtained from natural coexisting phengite paragonite pairs phengite paragonite pairs were selected based on the criteria that their chemical compositions may be represented as a linear combination of the model end member compositions and that the respective formation conditions 350 650 c 4 21kbar are accurately known previously published excess free energy expressions were used for the ms pg ms mgcel and ms fecel binaries the suggested mixing model was tested by calculating multicomponent equilibrium phase diagrams this proved to be particularly well suited to reproduce compositional variations of white micas from amphibolite facies metapelites

the elements and richness of particle diffusion during sediment transport at small timescales the ideas of advection and diffusion of sediment particles are probabilistic constructs that emerge when the master equation a precise probabilistic description of particle conservation is approximated as a fokker planck equation the diffusive term approximates nonlocal transport it looks upstream and downstream for variations in particle activity and velocities whose effects modify the advective term high resolution measurements of bed load particle motions indicate that the mean squared displacement of tracer particles when treated as a virtual plume primarily reflects a nonlinear increase in the variance in hop distances with increasing travel time manifest as apparent anomalous diffusion in contrast an ensemble calculation of the mean squared displacement involving paired coordinate positions independent of starting time indicates a transition from correlated random walks to normal fickian diffusion this normal behavior also is reflected in the particle velocity autocorrelation function spatial variations in particle entrainment produce a flux from sites of high entrainment toward sites of low entrainment in the case of rain splash transport this leads to topographic roughening where differential rain splash beneath the canopy of a desert shrub contributes to the growth of a soil mound beneath the shrub with uniform entrainment rain splash transport often described as a diffusive process actually represents an advective particle flux that is proportional to the land surface slope particle diffusion during both bed load and rain splash transport involves motions that mostly are patchy intermittent and rarefied the probabilistic framework of the master equation reveals that continuous formulations of the flux and its divergence the exner equation represent statistically expected behavior analogous to reynolds averaged conditions key topics meriting clarification include the mechanical basis of particle diffusion effects of rarefied conditions involving patchy intermittent motions and effects of rest times on diffusion of tracer particles and particle borne substances this article is protected by copyright all rights reserved

influence of chemical denudation on hillslope morphology 1 models of hillslope evolution involving diffusion like sediment transport are conventionally presented as an equation in which the changes in land surface elevation or soil thickness are balanced by the divergence of soil transport and tectonic uplift soil production or both these models typically do not include the loss or gain of mass in hillslope soils due to processes of chemical weathering and deposition we formulate a more general depth integrated equation for the conservation of soil mass on a hillslope that includes a term representing chemical deposition or denudation this general depth integrated equation is then simplified to determine the one dimensional form of a steady state hillslope which experiences both mechanical and chemical denudation the differences in morphology between hillslopes only experiencing diffusion like mechanical sediment transport and hillslopes experiencing both diffusion like mechanical sediment transport and chemical denudation are explored under the conditions of a downslope increase in local soil lowering rate due to chemical weathering the hillslope profile will depart from the parabolic shape predicted by models that incorporate only linear diffusion like mechanical sediment transport in addition hillslopes that experience both chemical and mechanical denudation may have a convex concave profile at steady state a necessary condition for such steady state profiles is that the chemical denudation rate must exceed the mechanical denudation rate we further suggest that combinations of other physical parameter values such as total denudation rate average soil depth sediment diffusivity and the increase in soil depth away from the divide that lead to steady state convex concave hillslope profiles may exist in a wide variety of natural settings

mixing properties of phengitic micas and revised garnet phengite thermobarometers mixing properties for muscovite celadonite ferroceladonite solid solutions are derived from combining available experimental phase equilibrium data with tabulated thermodynamic data for mineral end members when a partially ordered solution model is assumed the enthalpy of mixing among the end members muscovite celadonite ferroceladonite is nearly ideal although the gibbs energies of muscovite celadonite and muscovite ferroceladonite solutions are asymmetric due to an asymmetry in the entropy of mixing thermodynamic consistency is achieved for data on phengite compositions inassemblages with a pyrope kyanite quartz coesite b almandine kyanite quartz coesite c talc kyanite quartz coesite and d garnet phengite pairs equilibrated both experimentally at high temperatures and natural pairs from low grade schists the muscovite paragonite solvus has been reanalysed using the asymmetric van laar model and the effects of the phengite substitution into muscovite have been quantitatively addressed in order to complete the simple thermodynamic mixing model for the solid solution among the mica end members results are applied to a natural pyrope coesite phengite talc rock from the western alps and to investigate the conditions under which biotite bearing mica schists transform to whiteschist like biotite absent assemblages for average pelite bulk compositions

reconstruction of a kimberlite eruption using an integrated volcanological geochemical and numerical approach a case study of the fox kimberlite nwt canada abstract an integrated approach involving volcanology geochemistry and numerical modelling has enabled the reconstruction of the volcanic history of the fox kimberlite pipe the observed deposits within the vent include a basal massive poorly sorted matrix supported lithic fragment rich eruption column collapse lapilli tuff extensive vent widening during the climactic magmatic phase of the eruption led to overloading of the eruption column with cold dense country rock lithic fragments dense juvenile pyroclasts and olivine crystals triggering column collapse 40 dilution of the kimberlite by granodiorite country rock lithic fragments is observed both in the physical componentry of the rocks and in the geochemical signature where enrichment in al2o3 and na2o compared to average values for coherent kimberlite is seen the wide deep open vent provided a trap for a significant proportion of the collapsing column material preventing large scale run away in the form of pyroclastic flow onto the ground surface although minor flows probably also occurred a massive to diffusely bedded poorly sorted matrix supported accretionary lapilli bearing lithic fragment rich lapilli tuff overlies the column collapse deposit providing evidence for a late phreatomagmatic eruption stage caused by the explosive interaction of external water with residual magma correlation of pipe morphology and internal stratigraphy indicate that widening of the pipe occurred during this latter stage and a thick granodiorite cobble boulder breccia was deposited ash and accretionary lapilli rich tephra deposited on the crater rim during the late phreatomagmatic stage was subsequently resedimented into the vent incompatible elements such as nb are used as indicators of the proportion of the melt fraction or kimberlite ash retained or removed by eruptive processes when compared to average coherent kimberlite the ash rich deposits exhibit 30 loss of fines whereas the column collapse deposit exhibits 50 loss this shows that despite the poorly sorted nature of the column collapse deposit significant elutriation has occurred during the eruption indicating the existence of a high sustained eruption column the deposits within fox record a complex eruption sequence showing a transition from a probable violent sub plinian style eruption driven by instantaneous exsolution of magmatic volatiles to a late phreatomagmatic eruption phase mass eruption rate and duration of the sub plinian phase of the eruption have been determined based on the dimensions of milled country rock boulders found within the intra vent deposits calculations show a short lived eruption of one to eleven days for the sub plinian magmatic phase which is similar in duration to small volume basaltic eruptions this is in general agreement with durations of kimberlite eruptions calculated using entirely different approaches and parameters such as predictions of magma ascent rates in kimberlite dykes

reconstruction of a multi vent kimberlite eruption from deposit and host rock characteristics jericho kimberlite nunavut canada abstract the jericho kimberlite 173 1 1 3 ma is a small 130 70 m multi vent system that preserves products from deep 1 km portions of kimberlite vents pit mapping drill core examination petrographic study image analysis of olivine crystals grain size distributions and shape studies and compositional and mineralogical studies are used to reconstruct processes from near surface magma ascent to kimberlite emplacement and alteration the jericho kimberlite formed by multiple eruptions through an archean granodiorite batholith that was overlain by mid devonian limestones 1 km in thickness kimberlite magma ascended through granodiorite basement by dyke propagation but ascended through limestone at least in part by locally brecciating the host rocks after the first explosive breakthrough to surface vent deepening and widening occurred by the erosive forces of the waxing phase of the eruption by gravitationally induced failures as portions of the vent margins slid into the vent and in the deeper portions of the vent 1 km by scaling as thin slabs burst from the walls into the vent at currently exposed levels coherent kimberlite ck dykes

p t d histories from quartz a case study of the application of the titaniq thermobarometer to progressive fabric development in metapelites 1 this study investigates the ability of quartz to record segments of the pressure temperature deformation p t d path in poly deformed metamorphic terranes and the associated application of the ti in quartz thermobarometer titaniq metapelites from the strafford dome eastern vermont were selected for this study because they record progressive fabric development during prograde metamorphism and have well constrained p t d histories from previous work results of this investigation are in agreement with previous studies and demonstrate that quartz in these samples records additional distinct intervals of the p t d path six preserved quartz equilibration events include 1 early prograde growth during burial 2 kyanite in quartz producing reactions 3 prenappe emplacement equilibration during isobaric heating 4 precipitation of quartz in quartz feldspar domains during crenulation cleavage development due to solution transfer 5 quartz producing chlorite out reactions during heating postnappe emplacement and 6 retrograde quartz overgrowths from an influx of siliceous fluids modeling quartz volume allows for the identification of quartz producing reactions in p t space the same may be done for ti phases to better constrain activities during reequilibration events an integration of cathodoluminescence imaging microstructural and petrographic investigation isochemical forward stability modeling and thermobarometry allows identification and interpretation of zoning patterns in quartz to unravel histories that would otherwise not be obtainable

parental carbonatitic melt of the koala kimberlite canada constraints from melt inclusions in olivine and cr spinel and groundmass carbonate abstract this study of the hypabyssal kimberlite with particularly fresh olivine from the palaeogene koala pipe ekati cluster slave craton canada is focused on reconstruction of the kimberlite parental melt the koala kimberlite sample is a typical ultramafic rock archetypal or group i kimberlite containing large abundance of forsteritic olivine set in a carbonate rich matrix the euhedral olivine ii shows significant zoning in terms of forsterite content and trace elements only the rims of olivine ii are considered to be magmatic they are uniform in terms of fo 91 5 0 2 mol and host primary crystal apatite cr spinel and melt inclusions the magmatic spinel phenocrysts are strongly zoned from titanian magnesian chromite to pleonaste with the cores having the same composition as spinel inclusions in olivine the primary and pseudo secondary melt inclusions in both magmatic cr spinel and olivine comprise a complex assemblage of daughter phases dominated by carbonate minerals dolomite eitelite na 2 mg co 3 2 shortite na 2 ca 2 co 3 3 nyerereite na 2 ca co 3 2 zemkorite na k 2 ca co 3 2 and fairchildite k 2 ca co 3 2 in addition to the dominant carbonates the melt inclusions contain phosphates chlorides and sulphates bradleyite na 3 mg po 4 co 3 halite sylvite aphthitalite na 0 25 k 0 75 2 so 4 but the silicate component is represented by tetraferriphlogopite only the melt inclusions in olivine studied in heating experiments show immiscibility of two carbonate liquids on heating and cooling and homogenise at low temperature 2 o sro and bao in wt 0 37 0 65 1 17 2 40 2 37 4 18 respectively such compositions are compared to secondary calcite replacing nyerereite and shortite in the natrocarbonatite lavas of the modern oldoinyo lengai volcano the results on mineralogy composition and homogenisation temperature of melt inclusions and the groundmass of the koala kimberlite imply that the parental kimberlite liquid was a si poor ca mg carbonate enriched in alkali elements lithophile trace elements phosphorus chlorine and sulphur

effective resource estimates for primary diamond deposits from the ekati diamond mine canada abstract primary economic diamond deposit modelling has rarely been documented in the public domain this paper presents information collected from significantly diamondiferous kimberlite pipes located near lac de gras in the arctic region of canada s northwest territories the resource estimation process is widely accepted as a cyclical iteration of data collection and evaluation processes a resource database is typically assembled from a large inventory of exploration data these data must be methodically quality checked before accepting the information for interpretive analysis the foundation of a mineral resource model is based on clear understanding of the geology model along with subsidiary grade volume and density models defining these models is an iterative process of statistical analyses and interpretation as a deposit progresses along a path towards development reducing risk to acceptable levels is critical for identifying and realizing its maximum value

quantification of electron microprobe compositional maps of rock thin sections an optimized method and examples quantification of discrete pressure temperature domains in deformed chlorite white mica bearing metapelites was undertaken on mineral compositions derived by two dimensional microprobe compositional mapping of selected areas of rock thin sections in order to achieve compositional information at sufficient analytical precision spatial resolution and sample coverage within a typical analysis time of 1 day an optimization of measurement methods was necessary the method presented here allows collection of raw counts for eight different element concentrations at an analytical precision of 1 2 wt x ray intensity multiplane maps one map per measured chemical element are translated into concentration multiplane maps utilizing selected conventionally measured spot analyses combined with the castaing approximation for each mineral as this step requires identification of the different minerals present in the mapped area a statistical clustering technique to identify different groups of composition was developed guided by simple petrographic inspection of the thin section to delineate the important minerals in the mapped area finally the compositions of each pixel are translated into a mineral structural formula thus yielding a new kind of image with a high content of petrological information the reliability of the mineral composition images was emphasized by carrying out precision tests on the analytical data the possible use of chemical maps to infer the p t deformation history of metamorphic rocks is illustrated with two samples from the spitzbergen and the sambagawa blueschist facies belts in both samples a strong correlation between structures and chemistry is observed qualitative estimates of p t conditions from the si content of mica and chlorite are in good agreement with their location in microstructures that formed at different times therefore the combination of chemical maps with microstructural observations is a very powerful approach to understand both the evolution of complex metamorphic rocks and the control by deformation of mineral reactivity

hillslope lowering rates and mobile regolith residence times from in situ and meteoric 10be analysis boulder creek critical zone observatory colorado cosmogenic radionuclides crns are commonly employed to quantify both the production rates and residence times of mobile regolith meteoric and in situ crns have different accumulation mechanisms and can independently constrain landscape evolution rates here we use both in situ and meteoric 10 be to investigate where in the regolith 10 be is stored and to quantify production rates and residence times of mobile regolith on active hillslopes in gordon gulch within the boulder creek critical zone observatory czo colorado usa our data reveal that two thirds of in situ 10 be in regolith is produced within saprolite and at least one tenth of the meteoric 10 be inventories is stored in saprolite highlighting the importance of consistent terminology and identification of the mobile regolith saprolite boundary we find that mobile regolith production rates are on average 3 1 cm k y and residence times are between 10 and 20 k y a notable exception exists at the depositional north facing footslope where residence times likely exceed 40 k y close agreement between the meteoric and in situ results indicates that upper and mid slope positions are consistent with steady uniform lowering of the landscape in addition to comparing the two methods we develop a one dimensional analytical model for the 10 be concentration fields on an active steady state catena with uniform erosion we then compare model predictions with measurements to evaluate how well our sites adhere to the steady state assumption underlying the calculations for mobile regolith residence time and production rates such comparisons suggest that calculated residence times and lowering rates are likely no closer than 25 of the geomorphic reality

deep bedded ultramafic diatremes in the missouri river breaks volcanic field montana usa 1 km of syn eruptive subsidence the ultramafic eocene missouri river breaks volcanic field mrbvf montana usa includes over 50 diatremes emplaced in a mostly soft substrate the current erosion level is 1 3 1 5 km below the pre eruptive surface exposing the deep part of the diatreme structures and some dikes five representative diatremes are described here they are 200 375 m across and have sub vertical walls their infill consists mostly of 55 90 bedded pyroclastic rocks fine tuffs to coarse lapilli tuffs with concave upward bedding and 45 10 non bedded pyroclastic rocks medium lapilli tuffs to tuff breccias the latter zones form steep columns 15 135 m in horizontal dimension which cross cut the bedded pyroclastic rocks megablocks of the host sedimentary formations are also present in the diatremes some being found 1 km or more below their sources the diatreme infill contains abundant lithic clasts and ash sized particles indicating efficient fragmentation of magma and country rocks the spherical to sub spherical juvenile clasts are non vesicular they are accompanied by minor accretionary lapilli and armored lapilli the deposits of dilute pyroclastic density currents are locally observed our main interpretations are as follows 1 the observations strongly support phreatomagmatic explosions as the energy source for fragmentation and diatreme excavation 2 the bedded pyroclastic rocks were deposited on the crater floor and subsided by 1 0 1 3 km to their current location with subsidence taking place mostly during the eruption 3 the observed non bedded pyroclastic columns were created by debris jets that punched through the bedded pyroclastic material the debris jets did not empty the mature diatreme occupying only a fraction of its width and some debris jets probably did not reach the crater floor 4 the mature diatreme was nearly always filled and buttressed by pyroclastic debris at depth there was never a 1 3 1 5 km deep empty hole with sub vertical walls otherwise the soft substrate would have collapsed inward which it only did near the surface to create the megablocks we infer that syn eruptive subsidence shifted down bedded pyroclastic material and shallow sedimentary megablocks by 0 8 1 1 km or more after which limited post eruptive subsidence occurred this makes the mrbvf diatremes an extreme end member case of syn eruptive subsidence in the spectrum of possibilities for maar diatreme volcanoes worldwide

a cosmic trip 25 years of cosmogenic nuclides in geology terrestrial cosmogenic nuclides produced by secondary cosmic ray interactions in the atmosphere and in situ within minerals in the shallow lithosphere are widely used to date surface exposure of rocks and sediments to estimate erosion and weathering rates and to date sediment deposition or burial their use has transformed geomorphology and quaternary geology for the first time allowing landforms to be dated and denudation rates to be measured over soil forming time scales the application of cosmogenic nuclides to geology began soon after the invention of accelerator mass spectrometry ams in 1977 and increased dramatically with the measurement of in situ produced nuclides in mineral grains near earth s surface in the 1980s the past 25 yr have witnessed the development of cosmogenic nuclides from their initial detection to their prevalence today as a standard geochronological and geochemical tool this review covers the major developments of the past 25 yr by comparing the state of the field in 1988 with that of today and by identifying key advances in that period that moved the field forward we emphasize the most commonly used in situ produced nuclides measured by ams for geological applications but we also discuss other nuclides where their applications overlap our review covers ams instrumentation cosmogenic nuclide production rates the methods of surface exposure dating measurement of erosion and weathering and burial dating and meteoric 10 be in memoriam devendra lal 1929 2012 whose vision inspired the field

composition and emplacement of the benfontein kimberlite sill complex kimberley south africa textural petrographic and melt inclusion constraints abstract the benfontein kimberlite is a renowned example of a sill complex and provides an excellent opportunity to examine the emplacement and evolution of intrusive kimberlite magmas we have undertaken a detailed petrographic and melt inclusion study of the benfontein upper middle and lower sills these sills range in thickness from 0 25 to 5 m new perovskite and baddeleyite u pb dating produced ages of 85 7 4 4 ma and 86 5 2 6 ma respectively which are consistent with previous age determinations and indicate emplacement coeval with other kimberlites of the kimberley cluster the benfontein sills are characterised by large variations in texture e g layering and mineral modal abundance between different sill levels and within individual samples the lower sill is characterised by carbonate rich diapirs which intrude into oxide rich layers from underlying carbonate rich levels the general paucity of xenogenic mantle material in the benfontein sills is attributed to its separation from the host magma during flow differentiation during lateral spreading the low viscosity is likely responsible for non explosive emplacement of the benfontein sills while the rhythmic layering is attributed to multiple magma injections the benfontein sills are marked by the excellent preservation of olivine and groundmass mineralogy which is composed of monticellite spinel perovskite baddeleyite ilmenite apatite calcite dolomite along with secondary serpentine and glagolevite namg6 si3alo10 oh o 8 h2o this is the first time glagolevite is reported in kimberlites groundmass spinel exhibits atoll textures and is composed of a magnesian ulvospinel magnetite mum or chromite core surrounded by occasional pleonaste and a rim of mg al magnetite we suggest that pleonaste crystallised as a magmatic phase but was resorbed back into the residual host melt and or removed by alteration analyses of secondary inclusions in olivine and primary inclusions in monticellite spinel perovskite apatite and interstitial calcite are largely composed of ca mg carbonates and to a lesser extent alkali carbonates and other phases these inclusions probably represent the entrapment of variably differentiated parental kimberlite melts which became progressively more enriched in carbonate alkalis halogens and sulphur during crystal fractionation carbonate rich diapirs from the lower sill contain more exotic phase assemblages e g ba fe titanate barite ancylite pyrochlore which probably result from the extreme differentiation of residual kimberlite melts followed by physical separation and isolation from the parental carbonate rich magma it is likely that any alkali or halogen rich minerals crystallising in the groundmass were removed from the groundmass during syn post magmatic alteration or in the case of na remobilised to form secondary glagolevite the benfontein sill complex therefore provides a unique example of how the composition of kimberlites may be modified after magma emplacement in the upper crust

exhumation of the high pressure tsakkok lens swedish caledonides insights from the structural and white mica 40ar 39ar geochronological record

using chemical tracers in hillslope soils to estimate the importance of chemical denudation under conditions of downslope sediment transport 1 we present a model of hillslope soils that couples the evolution of topography soil thickness and the concentration of constituent soil phases defined as unique components of the soil with collective mass equal to the total soil mass the model includes both sediment transport and chemical denudation a simplified two phase model is developed the two phases are a chemically immobile phase which has far lower solubility than the bulk soil and is not removed through chemical weathering for example zircon grains and a chemically mobile phase that may be removed from the system through chemical weathering chemical denudation rates in hillslope soils can be measured using the concentration of immobile elements but the enrichment of these immobile elements is influenced by spatial variations in chemical denudation rates and spatial variations in the chemical composition of a soil s parent material these considerations cloud the use of elemental depletion factors and cosmogenic nuclide based total denudation rates used to identify the relationship between physical erosion and chemical weathering if these techniques do not account for downslope sediment transport on hillslopes where chemical denudation rates vary in space estimates of chemical denudation using techniques that do not account for downslope sediment transport and spatial variations in chemical denudation rates may be adequate where the chemical denudation rate is a significant fraction of the total denudation rate but are inadequate in regions where chemical weathering rates are small compared to the total denudation rate we also examine relationships between transient mechanical and chemical denudation rates soil particle residence times may affect chemical weathering rates and the relationship between total landscape lowering rates and soil particle residence times can thus be quantified

estimates of the rate of regolith production using and from an alpine hillslope abstract the production of regolith is a fundamental geomorphic process because most surface processes transport only unconsolidated material we use concentrations of the cosmogenic radionuclides crns 10 be and 26 al in regolith and bedrock to deduce the rate of production of regolith on an alpine hillslope in the wind river range wy these calculations are based on a theoretical model which we develop here this model shows that it is important to consider dissolution of regolith in regolith production and in basin averaged erosion rate studies rates of production of regolith are uniform along the hillslope and the mean rates for the entire hillslope deduced from 10 be and 26 al are 14 3 4 0 and 13 0 4 0 m ma 1 respectively rates of production of regolith deduced from 10 be concentrations in regolith mantled bedrock support the rates deduced from regolith concentrations in the alpine environment examined here the rate of production of regolith beneath 90 cm of regolith is nearly twice as fast as the average rate of production of regolith on bare rock surfaces which small et al small e e anderson r s repka j l finkel r 1997 erosion rates of alpine bedrock summit surfaces deduced from in situ 10 be and 26 al earth and planetary science letters 150 413 425 previously documented rock mantled with regolith probably weathers more rapidly than bare rock because the water required for frost weathering is limited on bare rock surfaces because the hillslope examined here is convex with constant curvature and regolith production and thickness are uniform down the slope the regolith volume flux must be proportional to the local slope of the hillside therefore our results are consistent with gilbert s gilbert g k 1909 the convexity of hilltops journal of geology 17 344 350 steady state hillslope hypothesis if tor height and the difference between rates of weathering on bare and regolith mantled rock provide a fair estimate of the age of summit flats steady state hillslope conditions have been attained in less than several million years

soil transport on a moraine foreslope abstract recent work has demonstrated that glacial moraine erosion and soil mixing occur at rates high enough to influence chemical weathering processes and the determination of depositional ages in this study we complement previous moraine crest studies by investigating a 1 8 m deep soil profile from the foreslope of a terminal bull lake age moraine 140 ky in the wind river mountains wyoming usa techniques applied include measurement of the grain size distribution major element concentrations and cosmogenic 10 be concentrations in quartz results suggest a 30 cm thick moving soil layer overriding a previously eroded mixed soil layer mass balance calculation based on the cosmogenic nuclide concentration in the different soil layers of the slope profile as well as a previously investigated crest profile suggests that one third of the 30 cm thick layer is coming from the crest area and two thirds of the material from the eroding moraine slope foreslope denudation rates are 0 015 to 0 018 mm y 1 based on the 10 be concentration of the lowermost samples and assuming a depositional age of 140 ky the 10 be concentration of the foreslope surface sample suggests a denudation rate of 0 020 mm y 1 for the sediment source area analysis of major elements in a limited number of surface samples reveals that the immobile element ti is enriched downslope whereas more mobile elements are generally depleted downslope the internal structure of a moraine foreslope is complex and care must be taken in calculating moraine age and denudation rate with depth profiles

optically stimulated luminescence dating of sediments over the past 200 000 years optical dating of sediment using optically stimulated luminescence has become important for studying earth surface processes and this technique continues to develop rapidly a group of closely linked luminescence methods can be used to estimate the time since grains of quartz and feldspar were last exposed to daylight by detecting their subsequent response to environmental ionizing radiation exposure the technique is well suited to the dating of deposits as young as one year to several hundred thousand years recent technical developments have established a dating protocol with improved precision a high degree of reliability and an in built means to detect incomplete signal removal during deposition this approach has been extended to age estimation for single grains opening up a wider range of potential environments and new possibilities for understanding postdepositional grain movement ongoing research offers the possibility of significant age range extension and novel applications including low t

tracing hillslope sediment production and transport with in situ and meteoric 10be 1 we use in situ produced and meteoric 10be analyzed in soils from 28 pits on four hillcrest parallel transects along a 14 hillslope in the great smoky mountains north carolina as tracers of soil production and transport we rely upon amalgamation both to investigate and smooth spatial variability in 10be concentrations lidar indicates that the hillslope is topographically complex and that soil is moved downslope diffusively until it encounters the ephemeral channel network and is rapidly exported in situ produced 10be measured in depth profiles indicates that over millennial timescales soils are mixed above the soil saprolite boundary in contrast meteoric 10be concentrations increase with depth and are correlated to concurrent increases of dithionite extractable al and ph observations explained by similar al and be mobility in the soil the concentrations of both meteoric and in situ produced 10be increase downslope proportional to the maximum soil particle path length the data suggest virtual downslope soil velocities of 1 1 1 7 cm yr 1 in a well mixed active transport layer 60 cm thick the thickness of this transport layer is constant downslope and depends on the rooting depth and consequent root wad thickness of downed trees on the slope both of which reflect depth to the soil saprolite boundary both meteoric and in situ produced 10be suggest that soil production is balanced by surface denudation at rates between 10 and 13 m myr 1 soil residence times on the slope range from 21 to 33 kyr based on the meteoric 10be inventories major element geochemical analysis suggests little if any elemental loss during soil transport downslope

quantifying glacial moraine age denudation and soil mixing with cosmogenic nuclide depth profiles 1 glacial boulders and soils on moraines are often dated to quantify the timing of glaciations and or rates of chemical weathering in moraine chronosequences a common assumption is that moraine crest erosion and soil mixing are unimportant however several studies suggest moraine denudation may be substantial we evaluate the magnitude of moraine denudation and soil mixing in the pinedale 21 ka and bull lake 140 ka moraines at fremont lake wyoming united states using cosmogenic nuclide depth profiles and a numerical model of moraine erosion and nuclide production and decay depth profiles indicate mixing of the surface layer from 40 to 60 cm depth age constraints from depth profile dating of cosmogenic nuclides result in ages of 17 24 ka for the pinedale moraine and 70 127 5 ka for the bull lake moraine these ages are comparable to ages based on the lal and chen approach which uses a sample from the mixed layer and the unmixed layer however the lal and chen approach is difficult to apply in real environments as the mixing depth needs to be determined independently we find our best fit model based ages for the bull lake moraine are younger than independent age constraints from boulder exposure dating due to incomplete mixing exposure age constraints from boulders are more straightforward for moraines than ages based on depth profile dating finally we find that moraine crests do significantly erode and are mixed suggesting that previous weathering and dust accumulation rate studies on moraines provide minimum estimates for these processes

which geomorphic processes can be informed by luminescence measurements abstract luminescence signals from quartz and feldspar contain a wealth of information about exposure to heat and sunlight while many studies have focused on quantifying individual processes such as grain transport and burial cooling during exhumation or bleaching of freshly exposed rock surfaces not much work has yet been done to illustrate how these effects might interact for example how might a geologist geomorphologist interpret the luminescence signals within a riverine cobble or within a recent rockfall from an uplifting terrain this study attempts to address this issue by first presenting a simple kinetic expression for osl signal accumulation in response to background radiation and osl loss by exposure to heat or to direct or attenuated sunlight this model is then used to simulate three example sample histories simulation results demonstrate how much information can be embedded within one sample s luminescence signal and how disparate geomorphic histories can produce strikingly similar signals the temperatures and timescales which can be examined with luminescence signals are presented in comparison to those of various geomorphic processes finally simulation results illustrate the benefit of using signals of different stability to better understand a sample s recent geologic history

metamorphic evolution and 40ar 39ar geochronology of the wuguan complex eastern qinling area china implications for the late paleozoic tectonic evolution of the qinling orogen abstract the late paleozoic tectonic evolution of the qinling orogen is poorly constrained the wuguan complex which lies between the north qinling and south qinling tectonic belts represents a late paleozoic metamorphic belt of the qinling orogen in this contribution we report new metamorphic pressure temperature p t constraints and 40ar 39ar ages of garnet amphibolites and garnet bearing metapelites from the wuguan complex textural observations and mineral compositions especially garnets with two stages of growth indicate the wuguan complex experienced two distinct metamorphic events conventional geothermobarometry and phase equilibria modelling indicate that the earlier metamorphism had peak p t conditions of 660 725 c and 8 0 12 0 kbar with a clockwise p t path whereas the later metamorphic overprint records p t conditions of 560 610 c and 7 5 9 0 kbar hornblendes from amphibolites yield 40ar 39ar ages of 306 299 ma whereas muscovites from garnet bearing metapelites yield 40ar 39ar ages of 252 251 ma the two groups of 40ar 39ar ages correspond to the cooling time of the two distinct metamorphic events respectively combining with previously published zircon u pb ages from the wuguan complex and two groups of metamorphic ages from the guishan complex and the xiongdian eclogite belt we infer that the earlier metamorphism probably occurred at the hangingwall of a subduction zone during carboniferous subduction of oceanic crust the later metamorphic overprint might have been related to the initial collision between the sino korean and yangtze cratons during the late permain

petrology of hp metamorphic veins in coesite bearing eclogite from western tianshan china fluid processes and elemental mobility during exhumation in a cold subduction zone abstract a petrological study was carried out for high pressure hp veins which cut through the host coesite bearing eclogites at habutengsu kebuerte in western tianshan china the results place constraints on the origin and property of metamorphic fluids during subduction zone metamorphism omphacite clinozoisite and quartz dominated veins occur on centimeter to meter scales within lens shaped and layered eclogites or cutting into the country rocks of garnet phengite schists coesite bearing eclogites mainly consist of fibrous fine grained omphacite and porphyroblastic garnet with minor amounts of amphibole mainly barroisite clinozoisite white mica mainly paragonite and rutile the veins are pronouncedly coarse grained compared to the host eclogites and commonly consist of quartz clinozosite rutile white mica phengite and paragonite and garnet with or without omphacite titanite apatite carbonate mainly dolomite and glaucophane fluid inclusions are abundant in vein omphacite titanite and apatite but are rare in the equivalent minerals of host eclogites rounded vein garnets usually occur close to the sharp interface of vein and host eclogite omphacite in the veins is characterized by its euhedral form surrounded by quartz or coarse bladed aggregates in contrast to the fibrous or patchy one suggesting dynamic recrystallization in the host rocks omphacite in both veins and host eclogites has similar jadeite contents jd 40 50 indicating formation at eclogite facies metamorphic conditions vein phengite uniformly contains certain amounts of ba with maximum bao content of 3 16 4 25 wt suggesting that ba was mobilized during the exhumation of uhp rocks specific textures of vein minerals such as the enclosure of magnesite or calcite in dolomite rutile in titanite and the occurrence of zoned ba rich phengite indicate the chemical variability of channelized fluids over time based on zr content in rutile and the presence of paragonite omphacite phengite glaucophane as well as the little deformed textures of hp veins it is estimated that the vein forming fluids would flow at about 1 3 2 1 gpa and 540 580 c corresponding to the stage of retrograde eclogite facies recrystallization during exhumation of the uhp eclogites that formed at peak p t conditions of 2 7 gpa and 460 520 c the hp veins occur as a consequence of a regional tectonothermal event triggering breakdown of lawsonite within the uhp eclogites based on the petrology of vein minerals it is inferred that the hp fluids were enriched in si ca na al and ba this suggests that these elements could be mobilized during the retrograde metamorphism of uhp eclogites in a cold subduction zone coeval pervasive flow of hp metamorphic fluids through the uhp eclogites at this stage may be an important process to eliminate most mineralogical evidence of the uhp metamorphism

recalibration of the garnet muscovite gm geothermometer and the garnet muscovite plagioclase quartz gmpq geobarometer for metapelitic assemblages the garnet muscovite gm geothermometer and the garnet muscovite plagioclase quartz gmpq geobarometer have been simultaneously calibrated under conditions of t 1 4 450 760 c and p 1 4 0 8 11 1 kbar using a large number of metapelitic samples in the compositional ranges x grt fe 1 4 0 53 0 81 x grt mg 1 4 0 05 0 24 x grt ca 1 4 0 03 0 23 in garnet x pl ca 1 4 0 17 0 74 in plagioclase and fe 1 4 0 04 0 16 mg 1 4 0 04 0 13 al 1 4 1 74 1 96 in muscovite on the basis of 11 oxygens the resulting gm thermometer yielded similar temperature estimates mostly within 50 c to that of the garnet biotite thermometer and successfully discerned the expected systematic temperature change of prograde sequences thermal contact zones and an inverted metamorphic zone the resulting gmpq barometer yielded similar pressure estimates mostly within 1 0 kbar to the garnet aluminum silicate plagioclase quartz gasp barometer and placed the aluminosilicate bearing samples in the appropriate aluminosilicate stability fields application of the gmpq barometer to thermal contact aureoles or rocks within limited geographical areas confirmed the expected constant pressures that should exist in these settings the random errors of the gm thermometer and the gmpq barometer are estimated to be 16 c and 1 5 kbar respectively when biotite or aluminosilicate is absent in metapelites metamorphic p t conditions may be determined by simultaneously applying the gm thermometer and the gmpq barometer

refining the timing of eclogite metamorphism a geochemical petrological sm nd and u pb case study from the pohorje mountains slovenia eastern alps high pressure metamorphism in the pohorje mountains of slovenia austroalpine unit eastern alps affected n morb type metabasic and metapelitic lithologies thermodynamic calculations and equilibrium phase diagrams of kyanite phengite bearing eclogites reveal pt conditions of 2 1 gpa at t 750 c but within the stability field of quartz metapelitic eclogite country rocks contain the assemblage garnet phengite kyanite quartz for which calculated peak pressure conditions are in good agreement with results obtained from eclogite samples the eclogites contain a single population of spherical zircon with a low th u ratio combined constraints on the age of metamorphism come from u pb zircon as well as garnet whole rock and mineral mineral sm nd analyses from eclogites a coherent cluster of single zircon analyses yields a 206pb 238u age of 90 7 1 0 ma that is in good agreement with results from sm nd garnet whole rock regression of 90 7 3 9 and 90 1 2 0 ma end 8 for two eclogite samples the agreement between u pb and sm nd age data strongly suggests an age of approximately 90 ma for the pressure peak of the eclogites in the pohorje mountains the presence of garnet omphacite and quartz inclusions in unfractured zircon indicates high pressure rather than ultrahigh pressure conditions the analysed metapelite sample yields a sm nd garnet whole rock scatterchron age of 97 15 ma these data probably support a single p t loop for mafic and pelitic lithologies of the pohorje area and a late cretaceous high pressure event that affected the entire easternmost austroalpine basement including the koralpe and saualpe eclogite type locality in the course of the complex collision of the apulian microplate and europe

a new approach to kimberlite facies terminology using a revised general approach to the nomenclature of all volcanic rocks and deposits descriptive to genetic although kimberlite pipes bodies are usually the remains of volcanic vents in vent deposits and subvolcanic intrusions the terminology used for kimberlite rocks has largely developed independently of that used in mainstream volcanology existing kimberlite terminology is not descriptive and includes terms that are rarely used used differently and even not used at all in mainstream volcanology in addition kimberlite bodies are altered to varying degrees making application of genetic terminology difficult because original components and depositional textures are commonly masked by alteration this paper recommends an approach to the terminology for kimberlite rocks that is consistent with usage for other volcanic successions in modern terrains the eruption and emplacement origins of deposits can often be readily deduced but this is often not the case for old variably altered and deformed rock successions a staged approach is required whereby descriptive terminology is developed first followed by application of genetic terminology once all features including the effects of alteration on original texture and depositional features together with contact relationships and setting have been evaluated because many volcanic successions consist of both primary volcanic deposits as well as volcanic sediments terminology must account for both possibilities

low pressure temperature stability of pyrope quartz relative to orthopyroxene kyanite a new model for aluminous orthopyroxene with vacancies determination of the stability of pyrope with quartz could provide theoretical pressure temperature p t constraints on silica saturated eclogites as well as near end member pyrope bearing terrains the lower p t stability of pyrope in the presence of quartz in the system mgo al2o3 sio2 can be modeled by the reaction 3 enstatite 2 kyanite 2 pyrope 2 quartz reaction reversals were experimentally obtained using a in diameter piston cylinder press and a 1000 t multi anvil press besides natural quartz all other starting materials including orthopyroxene pyrope and kyanite were synthesized the reaction has been bracketed at 1 50 gpa at 1040 1080 c 1 69 1 79 gpa at 1000 c 2 26 gpa at 920 940 c 2 90 gpa at 840 860 c the bracketed boundary is higher in temperature and pressure than that calculated using the newest dataset of holland et al j petrol 59 881 900 https doi org 10 1093 petrology egy048 2018 particularly at higher pressures aluminum is usually thought to be taken into orthopyroxene in the form of mg tschermak s pyroxene mgts mgal2sio6 under these experimental p t conditions in contrast the observed orthopyroxene composition indicated the involvement of a non stoichiometric component mg eskola pyroxene mges mg0 5 0 5alsi2o6 an aluminous orthopyroxene with octahedral vacancies end member thermodynamic properties for mges as well as a mixing model for the ternary enstatite mgts mges solid solution have been derived the thermodynamic calculations employing the mixing model are in good agreement with the experimental brackets the new model has potential applications to constrain p t conditions of tectonic settings such as ultrahigh pressure and ultrahigh temperature metamorphisms

geological constraints on the eruption of the jwaneng centre kimberlite pipe botswana abstract geological mapping has allowed constraints to be placed on the eruption mechanisms involved in the formation of the late permian early triassic jwaneng centre kimberlite pipe botswana twelve lithofacies and three lithofacies associations lfa 1 3 are recognised lfa 1 comprises massive to bedded volcaniclastic kimberlite and marginal shale breccias and outcrops over 65 of the surface area of the pipe it is characterised by a lithic population dominated by transvaal shale clasts lfa 1 grades into lfa 2 which comprises massive and bedded volcaniclastic kimberlite and volcaniclastic breccias and outcrops over 19 of the surface area of the pipe the lithic population of lfa 2 is dominated by contorted and fluidal outlined karoo age mudstones and siltstones lfa 3 comprises a wedge shaped unit in the north of the pipe and consists of a series of allochthonous megablocks of sedimentary and volcaniclastic strata the juvenile clast type and matrix mineral assemblages of the volcaniclastic deposits in the centre pipe differ from those in many other southern african kimberlite pipes various emplacement models for kimberlite pipes are discussed and evaluated in the light of the new geological data both a maar diatreme model and an explosive volatile driven eruption model could account for much of the geology of the centre pipe and distinguishing between the two models based on deposits alone is difficult there is strong circumstantial evidence for ambient conditions favourable to phreatomagmatism at the time of the eruption and the influence of external water may explain the differences between the jwaneng centre pipe and the class 1 kimberlites common across southern africa in terms of both the juvenile clasts and of the inter clast cement however low abundances of some types of lithic inclusions derived from major country rock units pose an unresolved problem for a classic maar diatreme model of pipe formation

microdiamond on areskutan confirms regional uhp metamorphism in the seve nappe complex of the scandinavian caledonides metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust here we present a new occurrence of diamond within the seve nappe complex snc of the scandinavian caledonides on areskutan in jamtland county sweden microdiamond is found in situ as single and composite diamond carbonate inclusions within garnet in kyanite bearing paragneisses the rocks preserve the primary peak pressure assemblage of ca mg rich garnet phengite kyanite rutile with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite calculated p t conditions for this stage are 830 840 c and 4 1 4 2 gpa in the diamond stability field the ultrahigh pressure uhp assemblage has been variably overprinted under granulite facies conditions of 850 860 c and 1 0 1 1 gpa leading to formation of ca mg poor garnet biotite plagioclase k feldspar sillimanite ilmenite quartz this overprint was the result of nearly isothermal decompression which is corroborated by ti in quartz thermometry chemical th u pb dating of monazite yields ages between 445 and 435 ma which are interpreted to record post uhp exhumation of the diamond bearing rocks the new discovery of microdiamond on areskutan together with other evidence of ultrahigh pressure metamorphism uhpm within gneisses eclogites and peridotites elsewhere in the snc provide compelling arguments for regional at least 200 km along strike of the unit uhpm of substantial parts of this far travelled allochthon the occurrence of uhpm in both rheologically weak gneisses and strong lithologies eclogites peridotites speaks against the presence of large tectonic overpressure during metamorphism

statistical description of slope dependent soil transport and the diffusion like coefficient 1 for hillslopes undergoing diffusive soil transport it is often assumed that the soil flux is proportional to the local land surface gradient where the coefficient of proportionality is like a diffusion coefficient inasmuch as transport involves quasi random soil particle motions related to biomechanical mixing and similar dilational processes a slope dependent relation arises from a balance between particle fluxes that tend to loft a soil and gravitational settling of particles into available pore space a specialized form of the fokker planck equation adapted to such particle motions clarifies how the particle flux involves advective and diffusive parts this in turn contributes to a kinematic description of the diffusion like coefficient ingredients of this coefficient include an active soil thickness a characteristic particle size the porosity in excess of a consolidated porosity and the rate of particle activation as a function of depth these last two ingredients vertical porosity structure and activation rate in effect characterize the magnitude and frequency of settling particle motions related to biological activity and thereby set the rate constant of the transport process the significance of land surface slope is that it is a measure of the downslope component of slope normal lofting that is balanced by settling because the diffusion like coefficient contains the soil thickness the analysis suggests that the soil flux is proportional to the depth slope product the analysis is consistent with published profiles of soil creep displacement and with published estimates of soil flux obtained by downslope integration of soil production rates for hillslopes in california and australia

inverted oligo miocene metamorphism in the lesser himalaya sequence arunachal pradesh india age and grade relationships the lesser himalaya sequence in the siyom valley eastern arunachal pradesh exposes a telescoped and inverted greenschist upper amphibolite facies sequence over 20 km tectonically overlain by an upright grade decreasing upward granulite to lower amphibolite facies sequence over 30 km such grade relationships would normally attribute the boundary to a main central thrust mct structure and predict a change from underlying lesser himalaya sequence lhs to greater himalaya sequence rocks across the boundary however all pelitic and psammitic samples have similar detrital zircon age spectra involving c 2500 1750 1500 1200 and 1000 ma gondwanan populations correlated with the lhs isograds are broadly parallel to a penetrative nw dipping s2 foliation developed contemporaneously with the inversion garnet growth in garnet staurolite and kyanite zone schists beneath the thrust commenced at 8 kbar and 550 c before syn to post s2 heating of staurolite and kyanite zone rocks to 640 c at 8 5 kbar most probably at c 18 5 ma kyanite rutile garnet migmatite immediately above the thrust records peak conditions of 10 kbar and 750 c and c 21 5 ma monazite ages slip on a se propagating thrust was likely contemporaneous with early miocene metamorphism based on the distribution of structure metamorphic textures and overlap of age relationships it is inferred to have initially controlled the uplift of granulite to mid crustal levels between 22 and 19 ma thermal relaxation within a disrupted lhs metamorphic profile inducing a post s2 thermal peak in lower grade footwall rocks

the central slave basement complex part i its structural topology and autochthonous cover new field and geochronological data are used to define the distribution of mesoarchean basement rocks in the south central slave province this distribution reflects a single contiguous basement terrane that we propose to call the central slave basement complex it shows a structural topology that is internally consistent and compatible with known regional folding and faulting events a sample of a proposed basement gneiss below the courageous lake greenstone belt central slave province has been dated by u pb methods and yields an age of 3325 8 ma consistent with the new basement distribution this sample also contains 2723 3 ma metamorphic zircon and ca 2680 ma titanite the central slave basement complex is overlain by a thin discontinuous but distinctive cover sequence that includes minor volcanic rocks clastic sedimentary rocks and banded iron formation all previously known and some new occurrences of this distinctive cover sequence occur in the immediate stratigraphic hanging wall of the

distinct kimberlite pipe classes with contrasting eruption processes abstract field and scott smith field m scott smith b h 1999 contrasting geology and near surface emplacement of kimberlite pipes in southern africa and canada proc 7th int kimb conf eds gurney et al 1 214 237 propose that kimberlite pipes can be grouped into three types or classes classical or class 1 pipes are the only class with characteristic low temperature diatreme facies kimberlite in addition to hypabyssal and crater facies kimberlite class 2 and 3 pipes are characterized only by hypabyssal and crater facies kimberlite in an increasing number of class 1 pipes a new kimberlite facies transitional facies kimberlite is being found in most cases this facies forms a zone several metres wide at the interface between the hypabyssal and diatreme facies the transitional facies exhibits textural and mineralogical features which are continuously gradational between the hypabyssal and the diatreme types the textural gradations are from a coherent magmatic texture to one where the rock becomes increasingly magmaclastic and this is accompanied by concomitant mineralogical gradations involving the decline and eventual elimination of primary calcite at the expense of microlitic diopside both transitional and diatreme facies kimberlites are considered to have formed in situ from intruding hypabyssal kimberlite magma as a consequence of exsolution of initially co 2 rich volatiles from the volatile rich kimberlite magma the transitional facies is initiated by volatile exsolution at depths of about 3 km below the original surface with subsequent cracking through to the surface and resultant rapid decompression the further catastrophic exsolution of volatiles and their expansion leads to the formation of the diatreme facies thus diatreme facies kimberlite and class 1 pipes are emplaced by essentially magmatic processes rather than by phreatomagmatism distinctly different petrographic features characterize crater facies kimberlite in each of the three pipe classes in crater facies kimberlites of class 1 pipes small pelletal magmaclasts and abundant microlitic diopside are characteristic these features appear to reflect the derivation of the crater facies material from the underlying diatreme zone most class 2 pipes have shallow craters and the crater facies rocks are predominantly pyroclastic kimberlites with diagnostic amoeboid lapilli which are sometimes welded and have vesicles as well as glass possible kimberlite lava also occurs at two class 2 pipes in n angola the possible presence of lava as well as the features of the pyroclastic kimberlite is indicative of hot kimberlite magma being able to rise to levels close to the surface to form class 2 pipes most class 3 kimberlites have very steep craters and crater facies rocks are predominantly resedimented volcaniclastic kimberlites in some cases characterized by the presence of abundant angular magmaclasts which are petrographically very similar to typical hypabyssal facies kimberlite found in class 1 pipes the differences in crater facies kimberlite of the three classes of pipe reflect different formation and depositional processes as well as differences in kimberlite composition specifically volatile composition kimberlite forming pipe classes 1 and 3 is thought to be relatively water rich and is emplaced by processes involving magmatic exsolution of volatiles the kimberlite magma forming class 2 pipes is co 2 rich can rise to shallow levels and can initiate phreatomagmatic emplacement processes

breaking ground pedological geological and ecological implications of soil bioturbation abstract soil and its biota are fundamental components of the critical zone earth s living skin that most directly sustains life within that zone geologically rapid soil and saprolite displacement by biota particularly invertebrate meso and macrofauna affects a large proportion of earth s soils this was first recognised by late 19th century observers on both sides of the atlantic ocean who regarded bioturbation as fundamental to soil formation throughout much of the 20th century however the agronomical focus of soil scientists and the dominant paradigm of landscape evolution relegated bioturbation as a result many aspects of bioturbation are still not widely appreciated only in the last few decades has a re evaluation commenced in a range of disciplines primary effects of bioturbation which we quantify herein include soil production from saprolite the formation of surface mounds soil burial and downslope transport rates of bioturbation can be as rapid as sustained maximum rates of tectonic uplift in concert with surface geomorphic processes bioturbation alters fundamental properties of soil including particle size distribution porosity the content of carbon and other nutrients and creep flux rate the precise influence of biotic mixing is regulated by its depth function earth s incredibly diverse soil biota also perform a number of functions at a range of spatial and temporal scales that extend beyond soil to landscape evolution ecosystem engineering niche construction and carbon cycling understanding these linkages which have operated since the evolution of trees in the devonian period is of growing importance as we seek a fuller picture of earth s history to predict and manage its future

macrocrystal phlogopite rb sr dates for the ekati property kimberlites slave province canada evidence for multiple intrusive episodes in the paleocene and eocene abstract new rb sr age determinations using macrocrystal phlogopite are presented for 27 kimberlites from the ekati property of the lac de gras region slave province canada these new data show that kimberlite magmatism at ekati ranges in age from at least late paleocene 61 ma to middle eocene time 45 ma older perovskite bearing kimberlites from ekati extend this age range to late cretaceous time 74 ma within this age range emplacement episodes at 48 51 53 55 56 and 59 61 ma can be recognized middle eocene kimberlite magmatism of the previously dated mark kimberlite 47 5 ma is shown to include four other pipes from the east central ekati property a single kimberlite aaron may be younger than the 47 5 ma mark kimberlite the economically important panda kimberlite is precisely dated in this study to be 53 3 0 6 ma using the phlogopite isochron method and up to six additional kimberlites from the central ekati property have early eocene ages indistinguishable from that of panda including the koala and koala north occurrences late paleocene 55 56 ma kimberlite magmatism represented by the diavik kimberlite pipes adjacent to the southeastern ekati property is shown to extend onto the southeastern ekati property and includes three and possibly four kimberlites a precise eight point phlogopite isochron for the cobra south kimberlite yields an emplacement age of 59 7 0 4 ma eight other kimberlites from across the ekati property have similar late paleocene rb sr model ages the addition of 27 new emplacement ages for kimberlites from the ekati property confirms that kimberlite magmatism from the central slave province is geologically young despite ages ranging back to cambrian time from elsewhere in the slave province with the available geochronologic database lac de gras kimberlites with the highest diamond potential are currently restricted to the 51 53 and 55 56 ma periods of kimberlite magmatism

diamond resorption features as a new method for examining conditions of kimberlite emplacement the study develops a new approach utilizing parameters of trigonal etch pits on diamond crystals to infer the conditions of diamond residence in kimberlite magma diamond crystals from dissolution experiments conducted at 1 gpa and 1150 1350 c in the presence of h2o rich or co2 rich fluid were studied with atomic force microscopy afm the afm data of resorbed diamond surfaces show that much deeper surface relief was produced in co2 fluid it also clearly distinguishes the profiles of the trigonal etch pits forming regular flat bottomed trigons in h2o fluid and round or pointed bottomed trigons in co2 fluid the relationship between the diameter and the depth of the trigonal pits is found to be another important indicator of the fluid composition dissolution in h2o fluid develops trigons with constant diameter and variable depth where the diameter increases with temperature trigons developed in co2 fluid have a large range of diameters showing a strong positive correlation with the depth the developed criteria applied to the natural diamond crystals from three ekati mine kimberlites indicate significant variation in co2 h2o ratio and temperature of their magmatic fluid this conclusion based on diamond resorption agrees with the mineralogy of microphenocrysts and groundmass of the studied kimberlites offering new method to study crystallization conditions of kimberlite magma

fragmentation in kimberlite products and intensity of explosive eruption the explosive eruption of kimberlite magma is capable of producing a variety of pyroclast sizes shapes and textures however all pyroclastic deposits of kimberlite comprise two main types of pyroclasts 1 pyroclasts of kimberlite with or without enclosed olivine crystals and 2 olivine crystals which lack coatings of kimberlite here we propose two hypotheses for how kimberlite magmas are modified due to explosive eruption 1 olivine crystals break during kimberlite eruption and 2 kimberlite melt can be efficiently separated from crystals during eruption these ideas are tested against data collected from field study and image analysis of coherent kimberlite and fragmental kimberlite from kimberlite pipes at diavik nt olivines are expected to break because of rapid pressure changes during the explosive eruption disruption of kimberlite magma and pyroclast production is driven by ductile deformation processes rather than by brittle fragmentation the extent to which melt separates from olivine crystals to produce kimberlite free crystals is a direct consequence of the relative proportions of gas melt and crystals lastly the properties of juvenile pyroclasts in deposits of pyroclastic kimberlite are used to index the relative intensity of kimberlite eruptions a fragmentation index is proposed for kimberlite eruption based on a crystal size distributions of olivine and on b ratios of selvage free olivine pyroclasts to pyroclasts of kimberlite with or without olivine crystals

temporal distribution of granitoid plutonic rocks in the archean slave province northwest canadian shield granitoid rocks in the slave province consist of 4 0 2 8 ga granitoid gneisses that predate the 2 71 2 65 ga volcanic and turbiditic rocks of the yellowknife supergroup and 2 70 2 58 ga granitoid plutons that intrude the yellowknife supergroup u pb zircon ages and nd and pb isotopic data indicate that the older granitoids are restricted to the western part of the slave province granitoid gneisses in the eastern slave province previously suspected to predate the yellowknife supergroup are similar in age to the volcanic rocks in this paper the results of a detailed geochronological study of plutonic rocks of the contwoyto lake nose lake area of the northcentral slave province are reviewed and integrated with the available age data base for plutonic rocks elsewhere in the slave province the data indicate that the timing of the later 2 7 ga plutonism is bimodal consisting of two distinct magmatic periods separated by approximately 20 ma of apparent magmatic quiescence the first period was synvolc

calculated phase relations in high pressure metapelites in the system nkfmash na2o k2o feo mgo al2o3 sio2 h2o using an internally consistent thermodynamic dataset and updated models of activity composition relation for solid solutions petrogenetic grids in the system nkfmash na2o k2o feo mgo al2o3 sio2 h2o and the subsystems nkmash and nkfash have been calculated with the software thermocalc 3 1 in the p t range 5 36 kbar and 400 810 c involving garnet chloritoid biotite carpholite talc chlorite kyanite sillimanite staurolite phengite paragonite albite glaucophane jadeite with quartz coesite and h2o in excess these grids together with calculated afm compatibility diagrams and p t pseudosections are shown to be powerful tools for delineating the phase equilibria and p t conditions of na bearing pelitic assemblages for a variety of bulk compositions from high p terranes around the world these calculated equilibria are in good agreement with petrological studies moreover contours of the calculated phengite si isopleths in p t pseudosections for different bulk compositions confirm that phengite barometry is highly dependent on mineral assemblage

on the welding of pyroclasts from very low viscosity magmas examples from kimberlite volcanoes abstract lithofacies in kimberlite pipes in southern africa exhibit features consistent with welded pyroclastic rocks these include flared conduit filling geometries abundant lithic clasts lithic clast layers subhorizontal clast fabrics gradational contacts with volcaniclastic rocks and sintered and coalesced globular ash and lapilli and melt coated particles the welding dynamics of kimberlite pyroclasts differ from those of glassy vesiculated pyroclasts in silicic volcanic systems low melt viscosity 0 1 pa s results in the efficient separation of volatiles and melt and the breakup of magma into nonvesicular spherical droplets the glassy state is difficult to form in silica deficient magmas because the crystallization kinetics are fast in low viscosity melts three pyroclastic lithofacies are recognized that primarily relate to the state of the initial melt phase in the pyroclasts on deposition 1 densely welded kimberlite forms where the initial melt phase in pyroclasts remains as pure mel

empirical garnet muscovite plagioclase quartz geobarometry in medium to high grade metapelites abstract based on the net transfer reactions among garnet muscovite plagioclase and quartz for both mg and fe end member models the garnet muscovite plagioclase quartz gmpq geobarometry was empirically calibrated under the physical conditions of p 1 0 11 4 kbar and t 505 745 c for 128 natural metapelitic rock samples collected from the literature the input temperatures and pressures were simultaneously determined by the garnet biotite thermometer and the garnet aluminosilicate plagioclase quartz gasp barometer the gmpq calibrations adopted the same asymmetric quaternary solid solution model of garnet and the same al avoidance asymmetric ternary model of plagioclase as the calibrations of the garnet biotite geothermometer and the gasp geobarometer a symmetric fe mg al vi ternary solid solution model of muscovite was adopted and the margules parameters of muscovite were obtained through regression the mg and fe model reactions along with the assumption of whether the ferric iron content in muscovite is 0 or 50 resulted in four gmpq barometry formulae the gmpq barometry formulae reproduce the input gasp pressures well within 1 0 kbar mostly within 0 5 kbar for both aluminosilicate bearing and aluminosilicate absent samples the gmpq barometry formulae yield identical pressures for every sample whether the sample was included or not in calibrating the barometers for each of the mg or fe model reaction the formulae gave identical pressures within 40 bars the random error of the gmpq barometry may be expected as 1 4 kbar the d p d t slopes of these gmpq formulae are close to that of the gasp barometer in the p t space applications of the gmpq barometry to aluminosilicate absent metapelites within a limited geographic area without postmetamorphic structural discontinuity generally show no pressure difference it may be concluded that the gmpq barometry formulae derived in this work may be used as practical tools for metamorphic pelites under the conditions of 505 745 c and 1 11 4 kbar in the composition range of x gros 3 in garnet and x an 17 in plagioclase

the geology of kimberlite pipes of the ekati property northwest territories canada abstract this paper reviews key characteristics of kimberlites on the ekati property nwt canada to date 150 kimberlites have been discovered on the property five of which are mined for diamonds the kimberlites intrude archean basement of the central slave craton numerous proterozoic diabase dykes intrude the area the precambrian rocks are overlain by quaternary glacial sediments no phanerozoic rocks are present however mudstone xenoliths and disaggregated sediment within the kimberlites indicate that late cretaceous and tertiary cover likely

accretion of the archean slave province continental rift models have long been applied to the archean slave province of northwestern canada a reassessment of these models shows them to be incompatible with observed geological relations and suggests that contractional tectonic models may be more appropriate than extensional ones regions composed of different rock suites e g orthogneisses vs mafic volcanics are separated by high strain zones recording large displacements it is proposed that the high strain zones separate four distinct terranes that have been juxtaposed during collisional orogenesis from west to east these include the anton terrane interpreted as an archean microcontinent the sleepy dragon terrane possibly an exhumed more eastern part of the anton terrane the contwoyto terrane a westward verging fold and thrust belt containing tectonic slivers of greenstone volcanics and the hackett river volcanic terrane interpreted as an archean island arc the contwoyto and hackett river terranes represent a paired accretionary prism and island arc system that formed above an east dipping subduction zone these collided with the anton microcontinent producing a basement nappe expressed as the sleepy dragon terrane during the main accretion event within the slave province the whole tectonic assemblage was intruded by late kinematic to postkinematic granitoids

application of mineral equilibria modeling to constrain t and x co2 conditions during the evolution of the magdala gold deposit stawell victoria australia mineral equilibria modeling involving solid solution calculations has been combined with mineral assemblage information from the alteration zones associated with gold mineralization to determine the t and xco2 conditions for the formation of the magdala gold deposit at stawell victoria australia economic gold mineralization is primarily hosted within the stilpnomelane alteration zone of the stawell facies that is adjacent to the magdala basalt evolution of the magdala gold deposit involved at least three fluid infiltration events 1 a co2 bearing fluid during the d2 deformation event produced carbonate spots throughout the chlorite zone 2 a co2 s k bearing fluid accompanied the d3 4ab deformation and produced a muscovite zone and siderite rims on ankerite and 3 a co2 k s au bearing fluid during the d4c deformation event produced the stilpnomelane zone of the stawell facies the proximal and distal alteration zones within the magdala basalt and the main economic gold mineralization mineral equilibria modeling constrains the temperature of formation of the magdala deposit to t 345 390 c at 3kbar substantially lower than indicated by other previous classical thermobarometry methods furthermore this method has allowed the characterization of the mineralizing fluid and constrained its composition to xco2 0 08 at 3kbar the timing and composition of the mineralizing fluids are similar to that of metamorphic fluid generated from devolatilization of a greenstone pile with peak of metamorphism occurring earlier and at deeper levels in the crust

bioturbation and erosion rates along the soil hillslope conveyor belt part 1 insights from single grain feldspar luminescence the interplay of bioturbation soil production and long term erosion deposition in soil and landscape co evolution is poorly understood single grain post infrared infrared stimulated luminescence post ir irsl measurements on sand sized grains of feldspar from the soil matrix can provide direct information on all three processes to explore the potential of this novel method we propose a conceptual model of how post ir irsl derived burial age and fraction of surface visiting grains change with soil depth and along a hillslope catena we then tested this conceptual model by comparison with post ir irsl results for 15 samples taken at different depths within four soil profiles along a hillslope catena in the santa clotilde critical zone observatory southern spain in our work we observed clear differences in apparent post ir irsl burial age distributions with depth along the catena with younger ages and more linear age depth structure for the hill base profile indicating the influence of lateral deposition processes we noted shallower soils and truncated burial age depth functions for the two erosional mid slope profiles and an exponential decline of burial age with depth for the hill top profile we suggest that the downslope increase in the fraction of surface visiting grains at intermediate depths 20 cm indicates creep to be the dominant erosion process our study demonstrates that single grain feldspar luminescence signature depth profiles provide a new way of tracing vertical and lateral soil mixing and transport processes in addition we propose a new objective luminescence based criterion for mapping the soil bedrock boundary thus producing soil depths in better agreement with geomorphological process considerations our work highlights the possibilities of feldspar single grain techniques to provide quantitative insights into soil production bioturbation and erosion deposition

soil creep and convex upward velocity profiles theoretical and experimental investigation of disturbance driven sediment transport on hillslopes the movement of unconsolidated materials near the earth s surface is often driven by disturbances that occur at a range of spatial and temporal scales the nature of these disturbances ranges from highly variable such as tree turnover to periodic and predictable such as frost heave or creep to explore the effect of probabilistic disturbances on surface processes we formulated a granular creep model with analogy to rate process theory rpt used for chemical reactions according to the theory individual particles must be energized to a height greater than adjacent particles in order for grain dilation and transport to occur the height of neighbouring particles which is akin to activation energy in chemical reactions varies with slope angle such that energy barriers get smaller in the downslope direction as slopes steepen when slopes approach the friction limited angle of repose the height of energy barriers approaches zero and grains ow in the absence of disturbance an exponential function is used to describe the probability distribution of particle excitation height although alternative distributions are possible we tested model predictions of granular dynamics in an experimental sandpile in the sandpile acoustic energy serves as the disturbance agent such that grains dilate and shear in response particle velocities are controlled by the frequency of energy pulses that result in grain displacement using tracer particles we observed a convex upward velocity pro le near the surface of the sandpile consistent with predictions of our rpt based velocity model in addition we depth integrated the velocity model to predict how ux rates vary with inclination of the sandpile and observed non linear ux gradient curves consistent with model predictions by varying the acoustic energy level in the experimental sandpile we documented changes in the rate of grain movement similar changes in modelled velocities were achieved by varying the exponent of the particle excitation probability distribution the general agreement between observed and modelled granular behaviour in our simple laboratory sandpile supports the utility of rpt based methods for modelling transport processes e g soil creep frost heave and till deformation thus enabling us to account for the probabilistic nature of disturbances that liberate sediment in natural landscapes copyright 2004 john wiley sons ltd

quantifying the rate and depth dependence of bioturbation based on optically stimulated luminescence osl dates and meteoric 10be both the rate and the vertical distribution of soil disturbance modify soil properties such as porosity particle size chemical composition and age structure all of which play an important role in a soil s biogeochemical functioning whereas rates of mixing have been previously quantified the nature of bioturbation s depth dependence remains poorly constrained here we constrain for the first time the relationship between mixing rate and depth in a bioturbated soil in northeast queensland australia using a novel method combining osl optically stimulated luminescence ages and meteoric beryllium 10 10be inventories we find that the best fit mixing rate decreases non linearly with increasing soil depth in this soil and the characteristic length scale of 0 28 m over which the mixing coefficient decays is comparable to reported rooting depth coefficients in addition we show that estimates of surface mixing rates from osl data are highly dependent on erosion rate and that erosion rate must be constrained if accurate mixing rates are to be quantified we calculate surface diffusion like mixing coefficients of 1 8 10 4 and 2 1 10 4 m2 yr 1 for the studied soil for two different estimates of soil erosion 2014 the authors earth surface processes and landforms published by john wiley sons ltd

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

dehydration of dioctahedral aluminous phyllosilicates thermodynamic modelling and implications for thermobarometric estimates we propose a solid solution model for dioctahedral aluminous phyllosilicates accounting for the main compositional variations including hydration observed in natural smectites interlayered illite smectite illites and phengites from diagenetic to high grade metamorphic conditions the suggested formalism involves dehydrated micas and hydrated pyrophyllite like thermodynamic end members with these end members the equilibrium conditions of quartz water k bearing mica like phyllosilicates of fixed 2 1 composition are represented by a line in p t space along which the interlayer water content varies the relevant thermodynamic properties required for the calculation of equilibrium conditions were derived using a set of 250 natural data of known maximal temperature and pressure conditions which covers a range between 25 c and few mpa to 800 c and 5 gpa the temperatures calculated at fixed pressure with our model are in fair agreement with those reported in the literature for the 250 natural data at low temperature and pressure the amount of interlayer water in k deficient phengite and illite is predicted to reach 100 of the apparent vacancies which is consistent with previous values reported in the literature although the amount of interlayer water is predicted to decrease with pressure and temperature it is calculated to be significant in k deficient phengite from lt hp pelites metamorphosed at about 350 c 10 kbar the presence of molecular water in the interlayer site of such phengites has been confirmed by ftir mapping its implications for p t estimates are discussed

syn and posteruptive hazards of maar diatreme volcanoes abstract maar diatreme volcanoes represent the second most common volcano type on continents and islands this study presents a first review of syn and posteruptive volcanic and related hazards and intends to stimulate future research in this field maar diatreme volcanoes are phreatomagmatic monogenetic volcanoes they may erupt explosively for days to 15 years above the preeruptive surface a relatively flat tephra ring forms below the preeruptive surface the maar crater is incised because of formation and downward penetration of a cone shaped diatreme and its root zone during activity both the maar crater and the diatreme grow in depth and diameter inside the diatreme which may penetrate downwards for up to 2 5 km fragmented country rocks and juvenile pyroclasts accumulate in primary pyroclastic deposits but to a large extent also as reworked deposits ejection of large volumes of country rocks results in a mass deficiency in the root zone of the diatreme and causes the diatreme fill to subside thus the diatreme represents a kind of growing sinkhole due to the subsidence of the diatreme underneath the maar crater is a subsidence crater and also grows in depth and diameter with ongoing activity as long as phreatomagmatic eruptions continue the tephra ring grows in thickness and outer slope angle syneruptive hazards of maar diatreme volcanoes are earthquakes eruption clouds tephra fall base surges ballistic blocks and bombs lahars volcanic gases cutting of the growing maar crater into the preeruptive ground formation of a tephra ring fragmentation of country rocks thus destruction of area and ground changes in groundwater table and potential renewal of eruptions the main hazards mostly affect an area 3 to possibly 5 km in radius distal effects are comparable to those of small eruption clouds from polygenetic volcanoes syneruptive effects on infrastructure people animals vegetation agricultural land and drainage are pointed out posteruptive hazards concern erosion and formation of lahars inside the crater a lake usually forms and diverse types of sediments accumulate in the crater volcanic gases may be released in the crater compaction and other diagenetic processes within the diatreme fill result in its subsidence this posteruptive subsidence of the diatreme fill and thus crater floor is relatively large initially but will decrease with time it may last millions of years various studies and monitoring are suggested for syn and posteruptive activities of maar diatreme volcanoes erupting in the future the recently formed maar diatreme volcanoes should be investigated repeatedly to understand more about their syneruptive behaviour and hazards and also their posteruptive topographic limnic and biologic evolution and potential posteruptive hazards for future maar diatreme eruptions a hazard map with four principal hazard zones is suggested with the two innermost ones having a joint radius of up to 5 km areas that are potentially endangered by maar diatreme eruptions in the future are pointed out

the critical role of climate and saprolite weathering in landscape evolution landscapes evolve in response to external forces such as tectonics and climate that influence surface processes of erosion and weathering internal feedbacks between erosion and weathering also play an integral role in regulating the landscapes response our understanding of these internal and external feedbacks is limited to a handful of field based studies only a few of which have explicitly examined saprolite weathering here we report rates of erosion and weathering in saprolite and soil to quantify how climate influences denudation by focusing on an elevation transect in the western sierra nevada mountains california we use an adapted mass balance approach and couple soil production rates from the cosmogenic radionuclide crn 10be with zirconium concentrations in rock saprolite and soil our approach includes deep saprolite weathering and suggests that previous studies may have underestimated denudation rates across similar landscapes along the studied climate gradient chemical weathering rates peak at middle elevations 1200 2000 m averaging 112 3 9 7 t km 2 y 1 compared to high and low elevation sites 46 8 5 2 t km 2 y 1 measured weathering rates follow similar patterns with climate as those of predicted silica fluxes modeled using an arrhenius temperature relationship and a linear relationship between flux and precipitation furthermore chemical weathering and erosion are tightly correlated across our sites and physical erosion rates increase with both saprolite weathering rates and intensity unexpectedly saprolite and soil weathering intensities are inversely related such that more weathered saprolites are overlain by weakly weathered soils these data quantify exciting links between climate weathering and erosion and together suggest that climate controls chemical weathering via temperature and moisture control on chemical reaction rates our results also suggest that saprolite weathering reduces bedrock coherence leading to faster rates of soil transport that in turn decrease material residence times in the soil column and limit soil weathering copyright 2009 john wiley sons ltd

volcanology of the aries micaceous kimberlite central kimberley basin western australia abstract the neoproterozoic 815 4 4 3 ma aries kimberlite intrudes the king leopold sandstone and the carson volcanics in the central kimberley basin northern western australia aries is comprised of a n nne trending series of three diatremes and associated hypabyssal kimberlite dykes and plugs the diatremes are volumetrically dominated by massive clast supported accidental lithic rich kimberlite breccias that were intruded by hypabyssal macrocrystic phlogopite kimberlite dykes and plugs with variably uniform to globular segregationary textured groundmasses lower diatreme facies accidental lithic rich breccias probably formed through fall back of debris into the vent with a major contribution from the collapse of the vent walls these massive breccias are overlain by a sequence of bedded volcaniclastic breccias in the upper part of the north lobe diatreme abundant poorly vesicular to nonvesicular juvenile kimberlite ash and lapilli with morphologies that are indicative of phreatomagmatic fragmentation processes occur in a reversely graded volcaniclastic kimberlite breccia unit at the base of this sequence this unit and overlying bedded accidental lithic rich breccias are interpreted to be sediment gravity flow deposits including possible debris flows derived from the collapse of the crater walls and or tephra ring deposits that surrounded the crater diatreme forming eruptions may have been initiated by magma water interactions along fracture and joint controlled aquifers within the king leopold sandstone the current level of exposure of the diatremes probably extends from the lower diatreme facies up into the base of a bedded upper diatreme sequence

reservoir theory for studying the geochemical evolution of soils 1 linking mineral weathering rates measured in the laboratory to those measured at the landscape scale is problematic in laboratory studies collections of minerals are exposed to the same weathering environment over a fixed amount of time in natural soils minerals enter are mixed within and leave the soil via erosion and dissolution leaching over the course of soil formation the key to correctly comparing mineral weathering studies from laboratory experiments and field soils is to consistently define time to do so we have used reservoir theory residence time of a mineral as defined by reservoir theory describes the time length between the moment that a mineral enters via soil production and leaves via erosion and dissolution leaching the soil age of a mineral in a soil describes how long the mineral has been present in the soil turnover time describes the time needed to deplete a species of minerals in the soil by sediment efflux from the soil these measures of time are found to be sensitive to not only sediment flux which controls the mineral fluxes in and out of a soil but also internal soil mixing that controls the probability that a mineral survives erosion when these measures of time are combined with published data suggesting that a mineral s dissolution reaction rate decreases during the course of weathering we find that internal soil mixing by partially controlling the age distribution of minerals within a soil might significantly alter the soil s mass loss rate via chemical weathering

the evolution of geological models for the do 27 kimberlite nwt canada implications for evaluation abstract this contribution reviews the evolution of geological models for the do 27 kimberlite located in the lac de gras kimberlite province northwest territories canada the do 27 kimberlite was discovered as a geophysical anomaly in 1992 and early models of the kimberlite models 1 2 were based largely on geophysical surveys with early core drilling confirming the presence of kimberlite core drilling completed in 1993 was used to create the first geological model model 3 model 3 interpreted the dominant pipe infill to be diatreme facies kimberlite influencing the interpretation of model 3 was the understanding of kimberlites at the time which assumed most kimberlites were comparable to southern african style kimberlites these kimberlites were typically large steep sided bodies infilled by diatreme facies kimberlite however this was inconsistent with the much smaller kimberlites being discovered in the early 1990s in the lac de gras area bulk sample evaluation in 1994 was conducted based on the interpretation in model 3 targeting the diatreme facies kimberlite the resulting diamond grades were below expectations and the project was not evaluated further however several partners in the project questioned the validity of model 3 and acquired a re assessment of the same 1993 drill cores the resulting geological model model 4 interpreted pyroclastic kimberlite to be the dominant pipe infill this pipe was located south of where the 1994 evaluation was focused the diatreme facies kimberlite of model 3 was reinterpreted to be low volume intrusive sills not infilling a pipe like body based on this re interpretation do 27 was re evaluated from 2005 2007 by peregrine diamonds ltd through bulk sampling and core drilling these new data were used to create model 5 which builds on the interpretations of model 4 diamond grades obtained from the 2005 2007 bulk sampling were substantially higher than those from the 1994 evaluation which has significant implications for the economic viability of the do 27 kimberlite the progression in understanding and geological modeling of do 27 demonstrates the importance of reliable and accurate geological models in the economic assessment of kimberlite pipes

strong tectonic and weak climatic control of long term chemical weathering rates the relationships among climate physical erosion and chemical weathering have remained uncertain because long term chemical weathering rates have been difficult to measure here we show that long term chemical weathering rates can be measured by combining physical erosion rates inferred from cosmogenic nuclides with dissolution losses inferred from the rock to soil enrichment of insoluble elements we used this method to measure chemical weathering rates across 22 mountainous granitic catchments that span a wide range of erosion rates and climates chemical weathering rates correlate strongly with physical erosion rates but only weakly with climate implying that by regulating erosion rates tectonic uplift may significantly accelerate chemical weathering rates in granitic landscapes

structural controls of fluid flow and gold mineralization in the easternmost parts of the karagwe ankole belt of north western tanzania abstract gold mineralization in the biharamulo region of western tanzania is confined to the sheared low angle basement cover contact between archaean basement gneisses of the tanzania craton and the structurally overlying low grade metamorphic metasediments of the mesoproterozoic karagwe ankole belt regional scale fluid flow along this detachment is indicated by the pervasive silicification and retrogression of wall rocks to pervasively foliated phyllonites and pyritization of particularly metasediments commonly graphite rich in the hanging wall of the shear zone gold mining centres on specific structural sites along the detachment but also in stratigraphically higher sections in the structurally overlying metasediments zones of gold mineralization along the detachment correlate with ne trending ramp structures dip angles 20 35 that are most ideally orientated for slip and reactivation within the low angle phyllonitic detachment repeatedly overprinted auriferous quartz vein stockworks in quartzofeldspathic gneisses immediately below the detachment indicate brittle fracturing of the competent footwall lithotypes during slip along the weaker detachment in cases of massive silicification up to 50 m thick quartz blows are formed along the contacts between detachment phyllonites and footwall gneisses the multiple overprinting relationships of successive quartz vein generations in these zones of massive silicification suggests that the quartz blows acted as competent blocks in the weak detachment causing the repeated overprint of earlier silicification by later fracturing and quartz veining events gold mineralization above the detachment and in stratigraphically higher metasediments is closely associated with fold structures that form part of the low grade metamorphic fold and thrust belt veining is particularly abundant in competent lithotypes such as quartzite and chemically reactive ferruginous mafic sills overprinting relationships between quartz vein sets illustrate fluid flow during fold amplification and importantly the final lock up stage of folds during which much of the mineralization was introduced oxygen isotope values for quartz veins indicate fluids were likely derived from clastic mainly metapelitic sedimentary sequences of the karagwe ankole fold belt the data also implies that the partially reworked archaean granitoid greenstone basement of the tanzania craton has not contributed to the fluid evolution and possibly gold mineralization the extent 100 km of the basement cover detachment and associated alteration is indicative for a regional scale fluid system gold mineralization is however controlled by local structures and lithological contrasts that require the detailed mapping and sampling of the regional structure

kimberlite eruptions as triggers for early cenozoic hyperthermals 1 the early cenozoic experienced at least three short but major hyperthermals associated with disruptions of the global carbon cycle the largest among those the paleocene eocene thermal maximum was associated with a negative carbon isotopic excursion of 2 5 that appears to be best explained by the thermal dissociation of methane hydrates due to an initial period of warming the cause of the initial warming has been attributed to a massive injection of carbon co2 and or ch4 into the atmosphere however the source of the carbon is as yet unknown the emplacement of a large cluster of kimberlite pipes at 56 ma in the lac de gras region of northern canada may have provided the carbon that triggered early warming in the form of exsolved magmatic co2 our calculations indicate that the estimated 900 1100 pg of carbon required for the initial 3 c of ocean water warming associated with the paleocene eocene thermal maximum could have been released during the emplacement of a large kimberlite cluster the coeval ages of two other kimberlite clusters in the lac de gras field and two other early cenozoic hyperthermals indicate that co2 degassing during kimberlite emplacement is a plausible source of the co2 responsible for these sudden global warming events

bioturbation and erosion rates along the soil hillslope conveyor belt part 2 quantification using an analytical solution of the diffusion advection equation particles on soil mantled hillslopes are subject to downslope transport by erosion processes and vertical mixing by bioturbation both are key processes for understanding landscape evolution and soil formation and affect the functioning of the critical zone we show here how the depth age information derived from feldspar based single grain post infrared infrared stimulated luminescence pirir can be used to simultaneously quantify erosion and bioturbation processes along a hillslope in this study we propose for the first time an analytical solution for the diffusion advection equation to calculate the diffusivity constant and erosion deposition rates we have fitted this model to age depth data derived from 15 soil samples from four soil profiles along a catena located under natural grassland in the santa clotilde critical zone observatory in the south of spain a global sensitivity analysis was used to assess the relative importance of each model parameter in the output finally the posterior probability density functions were calculated to evaluate the uncertainty in the model parameter estimates the results show that the diffusivity constant at the surface varies from 11 4 to 81 9 mm2 a 1 for the hilltop and hill base profile respectively and between 7 4 and 64 8 mm2 a 1 at 50 cm depth the uncertainty in the estimation of the erosion deposition rates was found to be too high to make a reliable estimate probably because erosion deposition processes are much slower than bioturbation processes in this environment this is confirmed by a global sensitivity analysis that shows how the most important parameters controlling the age depth structure in this environment are the diffusivity constant and regolith depth finally we have found a good agreement between the soil reworking rates proposed by earlier studies considering only particle age and depth and the estimated diffusivity constants the soil reworking rates are effective rates corrected for the proportion of particles actually participating in the process

h2o and co2 in kimberlitic fluid as recorded by diamonds and olivines in several ekati diamond mine kimberlites northwest territories canada abstract surface dissolution features on diamonds and fourier transform infra red spectroscopy ftir of phenocrystal and xenocrystal olivines from kimberlites contain a record of magmatic fluid in kimberlite magmas we investigated composition and behavior of kimberlitic fluid and the effect of volatiles on the eruption style and geology of kimberlites using microdiamonds and olivine concentrates from six kimberlite pipes with different lithologies and the character of diamond resorption ekati diamond mine northwest territories canada the study showed a clear correlation between the resorption style of diamond population of the kimberlites and the type of infrared ir spectra of their olivines four kimberlites have high quality diamonds with smooth regular surface features and high h 2 o content of the olivines indicating the presence of h 2 o rich fluid during the emplacement fast ascent rates of fluid rich magma can explain explosive eruption and filling the pipes with volcaniclastic kimberlite facies conversely grizzly and leslie kimberlites have diamonds with complex sharp features diminishing diamond quality and indicating loss of the fluid the slower ascent rates and less explosive eruption of the fluid free magmas produced kimberlite pipes filled with magmatic facies kimberlite distinctive peaks in olivine ir spectra at 3356 and 3327 cm 1 were found to correlate with the presence of hydrous magmatic fluid character of diamond morphology suggests that during the whole ascent of all six kimberlites the magmatic fluid when present had a high h 2 o co 2 ratio

co existing fluid and silicate inclusions in mantle diamond we document the compositions of co existing silicate macro inclusions and fluid micro inclusions in the fibrous coats of eight coated diamonds from the panda kimberlite canada the mineral inclusions in the diamond coats come from either the peridotite suite cr pyrope orthopyroxene olivine and cr diopside or the eclogite suite omphacite therefore fibrous diamonds grow in the same paragenetic environments as octahedral diamonds the inclusions document a more fertile source composition lower mg and higher cao than for equivalent phases in octahedral diamonds from panda and worldwide however moderate to high cr2o3 contents in garnet and clinopyroxene inclusions suggest that this apparent fertility is due to a secondary process geothermometry of the silicate inclusions yields low equilibration temperatures of 930 to 1010 c the co existing fluid micro inclusions are dominated by h2o carbonate and kcl fluid inclusions in both the peridotitic and eclogitic samples fall along linear arrays between fe ca mg carbonate and kcl inclusions in the one eclogitic sample also contain quartz we suggest that the diamonds have trapped both metasomatised minerals and the metasomatic fluid and so provide a snap shot of a metasomatic event in the mantle

inverse ductile thinning via lower crustal flow and fold induced doming in the west carpathian eo alpine collisional wedge 1 continental core complexes are generally interpreted to result from extensional doming due to gravity driven upflow of lower crust in contrast the vepor dome is characterized by the lack of inverted density profile and relatively cold metamorphic field gradient which precludes an activation of rayleigh taylor instability instead the crustal structure of the vepor unit is marked by dense and weak metapelitic lower crust and light and strong granitoid upper crust inherited from variscan nappe stacking it is shown that the cretaceous eo alpine tectonic evolution of the vepor dome is controlled by the dynamics of two neighboring mechanically strong continental blocks i e the overthrusting of the suprastructural gemer unit from the south and the underthrusting of the fatric basement from the north structural metamorphic and geochronological data from the vepor unit imply two main phases of the convergent process 1 lower cretaceous crustal thickening due to overthrusting and internal deformation of the gemer unit together with upper crustal folding in the vepor unit led to the progressive development of the orogenic front parallel pressure gradient the instantaneous response of the lower crustal and low viscosity metapelites led to an along strike lower crustal flow accompanied by prograde barrovian type metamorphism 2 as the south vergent underthrusting of the fatric basement propagated to greater depths during the upper cretaceous the convergent process switched from top driven to bottom driven and the exhumation of the lower crust occurred via polyharmonic folding overall doming of the vepor unit induced upper crustal detachment faulting and eastward unroofing of the dome

particle trajectories on hillslopes implications for particle age and 10be structure many geomorphic systems act as conveyor belts onto which material is loaded at a particular rate and is transported in one direction toward another system that serves as a sink as the material travels it ages it changes in grain size it accumulates cosmogenic radionuclides it adsorbs or releases nutrients and it weathers here i address the hillslope conveyor as many geochemical processes are depth dependent the depth history of a particle becomes important to know i calculate soil particle trajectories in the horizontal depth plane and address three cases one in which horizontal speeds decline exponentially with depth a second in which they are uniform with depth and a third in which horizontal speeds are also uniform but all profile values are vertically well mixed vertical speeds are governed by continuity in an incompressible medium and by the boundary condition of zero vertical particle speed at the soil surface particle trajectories must therefore become surface parallel at the surface knowledge of soil particle trajectories allows calculation of residence times and concentration profiles of 10be in the soil the results inform strategies for interpretation of nuclide concentrations in soils and stream sediments and for inference of transport rate profiles in all steady cases the particle age and 10be structure is uniform with distance from the divide when significant vertical gradients in horizontal speed occur the patterns of particle age and of 10be concentration are dominated by the depth scale of the transport process in unmixed cases the particle age and 10be concentration in near surface samples can greatly exceed the vertically averaged values reflecting the fact that the vertical speeds of particles slow dramatically as they near the surface in cases in which horizontal speed varies significantly with depth the vertically averaged concentration of 10be within the soil can significantly under predict the mean 10be concentration of sediment delivered to the channel proper averaging requires weighting by particle speed these results provide the backdrop for addressing chemical evolution of soil on a hillslope

in vent column collapse as an alternative model for massive volcaniclastic kimberlite emplacement an example from the fox kimberlite ekati diamond mine nwt canada abstract the origins of massive poorly sorted fragmental kimberlite and kimberlite breccias in the diatremes of kimberlite volcanic pipes is currently poorly understood studies of the textural features of the major infill of the fox kimberlite ekati diamond mine nwt canada show that it may have formed as a result of the collapse of the explosive eruption column above the vent into the deep open pipe during the climactic stage of the eruption as the eruption intensity increased the column became critically overloaded with dense particles and rapidly collapsed onto itself unlike deposits typically preserved from column collapse events such as ignimbrites some portion of the collapsing mass was trapped in the deep pipe forming a distinct type of pyroclastic deposit in vent vent fill column collapse lapilli tuff this deposit has previously been tentatively identified as tuffisitic kimberlite tk or massive volcaniclastic kimberlite mvk based on broadly similar textural characteristics with these lithologies though every individual deposit will have formed under slightly different circumstances mass emplacement from column collapse is proposed as a viable model for massive volcaniclastic kimberlite emplacement based on extrapolation of modern volcanological processes

crystallization of groundmass spinel in kimberlite groundmass spinel grains in 46 kimberlite and related rocks have been analyzed and compared the majority of the spinel analyses are classified as high chromium chromite chr and magnesioulvo spinel magnetite mum and represent two significant stages of spinel growth there are also a significant number of spinel grains that are classified as xenocryst spinel xen pleonaste spinel ple and magnetite mag eight different spinel zoning trends are identified the majority of the chr spinel grains are interpreted as a primary phase that crystallized as small octahedra from kimberlite magma on the journey from the upper mantle to the final resting place in the upper crust three zoning trends lead directly away from primary chromite the major zoning trend trend 1 is from chromite to magnesio ulvo spinel magnetite this zoning trend is unique to spinel in kimberlite carbonatites and lamprophyres we suggest that this somewhat oxidizing and more magnesian trend was influenced by the high carbonate content of group i kimberlites and the rapid crystallization of the minerals during the evolution of volatiles the zoningtrend 2 involves increasing titanium and ferric iron as a function of increasing fe 2 fe 2 mg this trend is similar to the zoning of spinel in basalt and is thought to be due to co crystallization of magnesium and aluminum rich silicate minerals such as olivine and phlogopite in kimberlites or pyroxene and plagioclase in basalt zoning trend 3 in kimberlite leads away from primary chromite and towards an aluminous pleonaste ple spinel this trend is characterized by a large decease of cr cr al parallel to so called olivine spinel iso potential lines similar trends of lesser magnitude and cyclic al cr zoning have been identified in basaltic spinel this trend is thought to be due to very rapid crystallization under conditions of supersaturation where the crystallization of spinel affects the local environment ahead of the growing spinel crystal i e diffusion controlled crystallization the tendency for immiscibility between ferrite or titanate rich spinel and aluminate rich spinel pleonaste has a great influence on trends 1 and 3 zoning and also on atoll spinel formation very local conditions such as nucleation or lack of nucleation of other minerals can influence both the textural environment and composition of kimberlitic spinel