simplified quantitative risk assessment of rainfall induced landslides modelled by infinite slopes abstract rainfall induced landslides vary in depth and the deeper the landslide the greater the damage it causes this paper investigates quantitatively the risk of rainfall induced landslides by assessing the consequence of each failure the influence of the spatial variability of the saturated hydraulic conductivity and the nature of triggering mechanisms on the risk of rainfall induced landslides for an infinite slope are studied it is shown that a critical spatial correlation length exists at which the risk is a maximum and the risk is higher when the failure occurs due to a generation of positive pore water pressure

seepage beneath water retaining structures founded on spatially random soil the effect of stochastic soil permeability on confined seepage beneath water retaining structures has been studied random field concepts for the generation of soil permeability properties with a fixed mean standard deviation and spatial correlation structure have been combined with finite element methods to perform monte carlo simulations of the seepage problem analyses have been performed for a dam with two cut off walls the results of parametric studies to gauge the effect of the standard deviation and correlation structure of the permeability on the output statistics relating to seepage quantities exit gradients and uplift pressures are presented in all cases comparison is made with results that would be achieved on a deterministic basis flow rates and other quantities are shown to be affected significantly by the standard deviation and the correlation structure of soil permeability l article etudie l influence de la permeabilite d un sol stochastique sur l infiltration confinee existant sous

strain decoupling across the decollement in the region of large slip during the 2011 tohoku oki earthquake from anisotropy of magnetic susceptibility abstract the integrated ocean drilling program iodp expedition 343 japan trench fast drilling project jfast drilled and cored across the plate boundary decollement at site c0019 near the japan trench where large slip occurred during the 2011 tohoku oki earthquake m w 9 0 anisotropy of magnetic susceptibility ams data obtained from core samples show a striking change in magnetic fabric across the decollement in the frontal prism above the decollement the maximum ams axes display a strong preferred orientation in the northeast southwest direction with the intermediate and minimum ams axes distributed in the vertical plane in the underthrust sediments below the decollement the maximum and intermediate ams axes are subhorizontal but variable in direction and the minimum ams axes display an approximately vertical preferred orientation the ams ellipsoids for all samples have an oblate component but the ams ellipsoids of the underthrust sediments are generally less oblate than those of the frontal prism the magnetic fabric of the sediments in the prism are consistent with horizontal tectonic shortening nearly parallel to the plate convergence direction in the japan trench while that in the underthrust sediments represents a vertical uniaxial strain the magnetic fabrics of the frontal prism and underthrust sediments indicate an abrupt change in strain across the decollement at shallow depths and imply that large co seismic slip occurred along a weak plate boundary decollement that is mainly decoupled over the long term

carbonate silicate inclusions in garnet as evidence for a carbonate bearing source for fluids in leucocratic granitoids associated with granulites of the southern marginal zone limpopo complex south africa abstract we present a study of carbonate bearing polyphase inclusions in garnets from leucocratic granitoids intruding metapelitic granulites of the southern marginal zone smz of the neoarchean limpopo high grade complex south africa during the post peak stage 2710 2650 ma u pb ages for zircons and monazites ternary feldspar thermometry suggests that the granitoid magma cooled from temperatures 800 900 c at a pressure of ca 6 5 kbar abundant co2 fluid inclusions in quartz and t xco2 phase equilibria modeling via perple x imply action of an essentially carbonic fluid in the granitoids cores of almandine rich garnet grains from the granitoids contain polyphase carbonate bearing inclusions with a distinct negative crystal shape the major carbonate in the inclusions is a strongly zoned magnesite siderite variety whereas pyrophyllite is the predominant silicate phase raman spectra of unexposed inclusions revealed a presence of co2 as well as ch4 and h2o the carbonate bearing inclusions coexist with larger polyphase inclusions composed of biotite quartz k feldspar plagioclase sillimanite which are interpreted as relics of granitic melts modeling the mineral assemblage preserved within the carbonate bearing inclusions shows that their present mineral and chemical compositions are a product of interaction of the trapped aqueous carbonic fluid with host garnet during cooling below 400 c despite strong modifications the inclusions bear evidence for initial saturation of the fluid with mg carbonate this is taken as an evidence for an origin of the fluids by devolatilization of the mg rich carbonate bearing ultrabasic greenstone rocks of the kaapvaal craton that were buried under the smz being generated at temperatures between 650 and 700 c the fluid subsequently participated in anatexis and coexisted with the granite magma during exhumation and interaction of the smz granulites with cratonic rocks

structural geological and metamorphic significance of the kaapvaal craton limpopo belt contact abstract the hout river shear zone forms the terrane boundary between the granite greenstone terrane of the kaapvaal craton cratonic terrane and the high grade granulite terrane high grade gneiss province of the limpopo belt this structure is superimposed onto a thin skinned northward verging thrust system which exercises a significant control on the distribution of the ene wsw trending greenstone belts the hout river shear zone however dips steeply to the north and flattens out toward the south this structure was responsible for the emplacement of hot granulites against and over the cooler granite greenstone terrane and strongly influenced the metamorphic evolution of the area the shear zone acted as a conduit for infiltrating co2 rich h2o bearing fluids into still hot crust producing a retrograde isograd and associated zone of rehydration in the granulitic hanging wall of the structure retrogressed granulites in the hanging wall are characterized by fine grained kyanite as part of the retrograde assemblages while the greenstones in the footwall are characterized by coarse grained prograde kyanite the terrane boundary appears to be in thermal equlibrium with the lithologies in both the footwall and hanging wall so that tectonically mixed prograde greenstones and retrogressed granulites in and adjacent to the shear zone are apparently at a similar metamorphic grade the granulites appear to have had a hot iron effect on the cooler footwall rocks over which they have been displaced

the structural framework of the southern margin of the limpopo belt south africa abstract the southern marginal zone is characterized by two prominent regional structural features i massive crustal wedges 20 km 50 km containing large oval shaped closed fold structures which are related to an early d 1 phase of deformation and which are bounded by ii major ductile shear zones that strike in a general e w direction the hout river shear zone forms the southern boundary of the southern marginal zone where granulites are juxtaposed against lower grade granite greenstones of the kaapvaal craton this fault system also acted as the sole thrust for the other high grade shear zones in the southern marginal zone and played a major role in the development of the zone of retrogression and the establishment of the orthoamphibole isograd in the southern marginal zone the hout river shear zone and related faults within the southern marginal zone clearly post date d 1 and a period of peak metamorphism m 1 they are composite structures showing dominantly reverse sense displacements and are responsible for the emplacement of the granulite terrane over and onto the kaapvaal craton in contrast to these older structures are the reactivated shear zones these structures clearly cross cut and displace the high grade shear zones in the southern marginal zone as well as the retrograde orthoamphibole isograd the fact that the hout river and related shear zones are in metamorphic equilibrium with the surrounding wall rocks suggests their age is that of the metamorphism i e 2670 ma barton and van reenen 1992

volcaniclastic debris avalanche on motomachi area of izu oshima japan triggered by severe storm phenomenon and mechanisms abstract heavy rainfall and strong wind associated with typhoon wipha hit izu oshima island japan and triggered catastrophic landslides on the western slope of oshima volcano on 16 october 2013 these landslides were shallow but large in scale and the displaced landslide materials were characterized by rapid and long runout movement a massive landslide resulted in 36 people dead and 3 missing with 46 buildings being completely destroyed in the downstream area of motomachi district to understand the initiation and movement of these shallow landslides we surveyed the landslide area and found that in addition to heavy rainfall strong wind may also have played a key role in increasing the instability of the slopes we took samples from the source areas and examined their static and dynamic shear behaviors under naturally drained or undrained conditions test results showed that high pore water pressure can be built up and maintained within the displaced landslide material and increase landslide mobility even though the thickness of displaced landslide materials is 0 7 1 2 m this may then give a rational explanation on the fluidization process of the displaced landslide materials we also examined the windthrow features of trees subjected to different wind speed through monitoring the ground motion by seismometer and portable anemometer and then performed cyclic shear tests on the materials laying above the sliding surface the test results suggest that the windthrow may have promoted the buildup of excess pore water pressure within the saturated soil layer and thus favoured the occurrence of slope failure therefore it is suggested that in the prediction of shallow landslides on forested slopes subjected to heavy storm both the effects of rainfall and strong wind should be taken into account

high temperature hydration of ultramafic granulites from the southern marginal zone of the limpopo belt by infiltration of co2 rich fluid abstract the peak metamorphic assemblage of olivine orthopyroxene calcic amphibole spinel is replaced by a variety of high temperature retrograde assemblages in ultramafic granulites from the southern marginal zone of the limpopo belt the observed replacement of olivine according to the reaction forsterite co2 enstatite magnesite is restricted to the zone of rehydration which bounds the granulite zone in the south this observation is consistent with the post peak metamorphic infiltration of an externally derived co2 rich fluid during the high temperature post peak metamorphic history of the limpopo belt this event established a retrograde orthoamphibole isograd conditions of the retrogression are estimated to be near 670 c 6 kbar and xco2 fluid 0 67 c isotopic compositions of co2 extracted from magnesite produced by the high temperature breakdown of olivine supports a deep seated mantle source for the co2 rich retrograde fluid

fluid assisted interaction of peraluminous metapelites with trondhjemitic magma within the petronella shear zone limpopo complex south africa abstract the principal problem concerning the evolution of precambrian granulite complexes located between granite greenstone cratons is their interaction with the underthrusted greenstone belts during exhumation from the lower crust besides evidence for pervasive and localized fluid fluxes arising from devolatilization of the greenschist and amphibolite facies rocks in the course of their burial underneath the granulites this interaction might also be expressed in formation of diverse magmas of granitic trondhjemitic and granodioritic composition we present results of a petrological fluid inclusion and thermobarometric study of interaction between fluidized trondhjemitic magma and peraluminous metapelitic granulites associated with the regional high grade petronella shear zone located in the southern marginal zone smz of the limpopo granulite complex south africa the hot t 1000 c trondhjemitic magma which presumably originated from partial melting of a basaltic amphibolite material at the base of the granulite complex or at the top of the underthrusted greenstone blocks intruded granulites at p 8 0 9 5 kbar 24 28 km depth at 2 667 0 9 ga during the exhumation of the smz the magma heated and assimilated orthopyroxene cordierite metapelites and dragged them to a depth of 18 20 km 6 3 6 5 kbar the magma was heterogeneously saturated with mgo feo al 2 o 3 by the dissolved metapelites this process provoked crystallization of several garnet generations from the trondhjemitic melt various mineral assemblages included in the different generations of garnet allowed application of twq method combined with perple x pseudo sections to trace sub isobaric cooling of the magma from t 900 600 c at 5 5 6 5 kbar the isobaric cooling also affected the associated metapelites fluid inclusions trapped in garnet and quartz in the trondhjemite show that the magma transported carbonic fluid with densities corresponding to the late stages of magma cooling 600 650 c and 5 5 6 5 kbar carbonic fluids coexisted with aqueous salt fluids preserved as inclusions with salinity up to 20 58 wt nacl eq these low water activity fluids a h 2 o 0 3 bearing na k and ca salts being exsolved from the magma on cooling and solidification provoked formation of complex na gedrite biotite sillimanite quartz staurolite plagioclase bearing assemblages after cordierite in metapelites at temperatures 630 570 c and pressures 5 5 6 5 kbar these data provide evidence that hot trondhjemitic melts played a critical role in the exhumation of granulites onto the adjacent granite greenstone craton the trondhjemite transferred heat from the lower to the middle crust and transported large volumes of external aqueous carbonic salt fluids that participated in the rehydration of a significant portion of the smz

melt segregation and magma interactions during crustal melting breaking out of the matrix abstract differentiation of the continental crust begins with its partial melting the products of crustal melting are silicic hydrous h2o undersaturated granitic liquids that are generated within matrices of residual crystals crustal differentiation requires that felsic magmas form and escape from these solid residua an important question is whether granitic magmas collect into large batches within or near their sources which then give rise to ascent or alternatively bleed out of the sources in smaller streams or pulses we demonstrate that the physical reality is closer to the second alternative and thus question the validity of the concepts of magma segregation and source fertility as they are sometimes visualised granitic plutons contain chemically distinct sub populations formed by source level entrainment of the peritectic assemblages into the melts rapid evacuation at source levels and high ascent rates protect the magmas from wall rock interactions during their tenure at source depths and during their ascent through cool upper crust the existence of different types of granites and hence of clearly defined chemically different magmas within plutons dictates that felsic magmas must separate efficiently from their anatectic sources and must ascend to the sites of their emplacement with minimal chemical interaction with crust through which the magma must move exposed deep crustal sections are typically lithologically diverse with the more fertile rocks commonly forming discrete layers surrounded by rocks with contrasting compositions if the melts were required to segregate and accumulate into large volumes within their hot sources especially by slow gravity driven melt percolation it is very likely that they would be substantially modified by reaction with diverse source rocks thus the processes mooted to occur in melting assimilation storage and homogenisation mash or deep crustal hot dch zones would act to erase original compositional heterogeneities and produce larger batches of more homogeneous magma perhaps carrying evidence of extensive magma mixing from various lines of evidence we conclude that mash and dch zones may not exist and even if they do they cannot form the sources of most granitic magmas the intrinsic heterogeneity in crustal source rocks the likely occurrence of peritectic assemblage entrainment and the inefficiency of magma mixing decree that granitic rocks will retain source inherited chemical and isotopic heterogeneities rapid semi continuous and disequilibrium withdrawal of small magma batches from source rocks means that elements of whole rock trace element chemistry and accessory mineral chemistry will be decoupled from major element variations this also means that a large source with low nominal fertility due to low hydrous mineral content for example could still produce a substantial granitic pluton by additions of individually small increments of magma

involvement of fluids in the metamorphic processes within different zones of the southern marginal zone of the limpopo complex south africa an oxygen isotope perspective abstract we present oxygen isotope data obtained by laser fluorination for three outcrops from the south marginal zone smz of the limpopo granulite complex south africa these outcrops are located within the granulite zone bandelierkop quarry on the retrograde anthophyllite in isograd manamead locality and within the zone of rehydrated granulite south of the retrograde isograd klipbank locality studied samples also include felsic granitoid rocks that occur as intrusive bodies veins and veinlets in the host tonalite gneisses or the metapelite the tonalite gneiss tg and the k feldspar rich segregations kfs g at klipbank have marginally different 18 whole rock wr values 7 9 and 7 3 correspondingly the kfs g may have formed by partial melting of the tg in the presence of external saline h 2 o co 2 fluid metapelites at manamead locality have 18 o values 9 5 10 3 lower than those at bandelierkop quarry 10 0 11 4 the two mineral oxygen isotope temperature estimates for metapelite minerals from manamead cluster around two values 620 30 and 730 40 c oxygen isotope temperature estimates for the metapelites from bandelierkop quarry define a narrow temperature range of 700 740 the oxygen isotope temperatures are in reasonable agreement with the results of classical geothermobarometry the 18 values of the whole rocks and individual constituent minerals of metapelites strongly negatively correlate with the rocks volatile content loi values this suggests that a fluid phase was involved in the hydration of metapelites in the vicinity of the regional anthophylite in isograd of the southern marginal zone the fluid may have been released during crystallization of leucogranite melt oxygen isotope and geochemical features of the leucogranite indicate genetic relation to the tonalitic baviaanskloof gneisses but do not support the formation of leucogranite via in situ partial melting of metapelites

the subsolidus segregation of layer parallel quartz feldspar veins in greenschist to upper amphibolite facies metasediments layer parallel i e parallel to foliation or bedding vein formation in the graywackes and pelites of the quetico metasedi mentary belt occurred during synchronous prograde metamorphism and regional dj com pression in a traverse across metasediments which change in metamorphic grade from green schist to upper amphibolite migmatite facies layer parallel veins show the following trends 1 an increase in thickness and internal corn plexity the latter due to successive boudinage 2 low grade veins are parallel to planes of anisotropy due to the original sedimentary fabric of the host rocks but at higher grades other sites are also used and 3 a systematic increase in plagioclase quartz ratio in the veins towards higher grade adjacent mafic selvedges first exhibit quartz depletion then in the amphibolite facies plagioclase depletion mineralogical zoning is often preserved in a single vein older parts are more quartz rich than younger mass balance calculations and whole rock geochemistry based on veins mafic selvedges and country rock are consistent with a closed system subsolidus segregation origin the layer parallel veins are syntectonic and migration of the mobile components required to form their mineralogy is a stress induced mass transfer the source of these components appears to be dominantly pressure solution of the same minerals in the host rocks although metamor phic reactions may also have contributed veins nucleated first at those sites where initial sedimentary heterogeneites such as fine scale graded bedding provided gradients of normal stress across grain boundaries and hence of chemical potential necessary to drive the sub solidus segregation process the earliest veins are thus parallel to bedding later nucleation of the veins could also occur along more randomly distributed sites within the metasediments and these veins grew parallel to the schistosity rather than bedding if the two were distinct once formed the veins themselves which are more competent than the surrounding rock provide the stress heterogeneity required for their further growth the increasing plagioclase quartz ratio in the veins may be due to a tem perature dependent increase in plagioclase com ponent mobility relative to quartz alterna tively the increasing transfer distances for silica resulting from prior quartz depletion in the inner parts of the mafic selvedge may increase the relative mobility of plagioclase component

quantitative risk assessment of landslides triggered by earthquakes and rainfall based on direct costs of urban buildings abstract this paper outlines a framework for risk assessment of landslides triggered by earthquakes and rainfall in urban buildings in the city of medellin colombia applying a model that uses a geographic information system gis we applied a computer model that includes topographic geological geotechnical and hydrological features of the study area to assess landslide hazards using the newmark s pseudo static method together with a probabilistic approach based on the first order and second moment method fosm the physical vulnerability assessment of buildings was conducted using structural fragility indexes as well as the definition of damage level of buildings via decision trees and using medellin s cadastral inventory data the probability of occurrence of a landslide was calculated assuming that an earthquake produces horizontal ground acceleration a h and considering the uncertainty of the geotechnical parameters and the soil saturation conditions of the ground the probability of occurrence was multiplied by the structural fragility index values and by the replacement value of structures the model implemented aims to quantify the risk caused by this kind of disaster in an area of the city of medellin based on different values of a h and an analysis of the damage costs of this disaster to buildings under different scenarios and structural conditions currently 62 of valle de aburra where the study area is located is under very low condition of landslide hazard and 38 is under low condition if all buildings in the study area fulfilled the requirements of the colombian building code the costs of a landslide would be reduced 63 compared with the current condition an earthquake with a return period of 475 years was used in this analysis according to the seismic microzonation study in 2002

a physically based multi hazard risk assessment platform for regional rainfall induced slope failures and debris flows abstract rainfall induced slope failures and debris flows are two major hazards in mountainous areas a physically based multi hazard risk assessment platform for regional rainfall induced slope failures and debris flows has been developed in this study the platform enables prompt assessment of risks posed by regional rainfall induced slope failures and debris flows across multiple catchments which is required in landslide risk management in a large area it considers the contribution of slope failures to debris flows and the scenario of a location impacted by multiple slope failures or debris flows or both the contribution of slope failures to debris flows is considered by adding the increased amount of channel deposit from slope failures to the source material of debris flows the platform is applied to a highway near the epicentre of the 2008 wenchuan earthquake the platform predicts the impact areas and runout distances of regional debris flows reasonably well the risk assessment results indicate that both slope failures and debris flows pose a great danger to travellers along the road shortly after the earthquake due to the presence of a large amount of loose landslide deposits on steep terrains the materials from the slope failures triggered during a storm substantially increase the channel deposit volume leading to significantly increased debris flow volume and risk a multi hazard risk assessment approach is necessary to consider the scenario of a location impacted by multiple slope failures or debris flows or both since assessing risks of slope failures and debris flows separately may underestimate the risk

undrained failure mechanisms of slopes in random soil abstract since the charts of taylor 1937 it has been well known in engineering geological investigations that the location of the critical failure mechanism in a homogeneous undrained clay slope goes either deep tangent to a firm base or shallow through the toe depending on whether the slope angle is less than or greater than about 53 in reality natural soils always exhibit spatial variability and the above expectations no longer hold true the objective of this note is to investigate the failure mechanisms and probability of failure of slopes in random undrained soil over a wide range of slope angles an elastic perfectly plastic finite element method in combination with random field generation well known as the random finite element method rfem is employed rfem represents a powerful tool for slope stability analyses that allow mechanisms to develop naturally within soil masses it is found that for certain combinations of random field properties relatively flat slopes may display a significant number of shallow mechanisms and steeper slopes may display a significant number of deep mechanisms for a steep slope the more variable the undrained shear strength the less likely the slope is to display a toe mechanism understanding the uncertainty of failure mechanisms is important because the consequences may be more serious in a deep failure as it involves a greater volume of soil

fluid inclusions in hydrated granulite facies rocks southern marginal zone of the limpopo belt south africa abstract the archean granulite terrane of the southern marginal zone of the limpopo belt south africa was rapidly uplifted and thrust over a low grade granite greenstone terrane van reenen et al 1987 during cooling the granulites were rehydrated in a zone parallel to the contact with the low grade terrane a sharply defined retrograde orthoamphibole isograd at conditions of 6 kbar 625 650 c x co 2 0 8 van reenen 1986 was established we made microthermometric analyses of over 1000 fluid inclusions in four samples representing a traverse across the isograd with the goal of characterizing the hydrating fluid we found patterns of composition and density of inclusions to be similar to those reported from other granulite facies terranes a few apparently pure co 2 inclusions with densities appropriate for the p t conditions many co 2 inclusions with lower densities and aqueous inclusions of variable salinity and containing no detectable co 2 the results suggest that the hydrating fluid may be represented by secondary co 2 rich fluid inclusions because of their small size most between 5 and 10 m and equant shapes h 2 o contents of the co 2 rich inclusions of up to 0 3 mole fraction may not be detectable a model for hydration of the granulites includes infiltration of a fluid into the partially cooled overthrust granulites with a temperature gradient decreasing towards the underthrust greenstone terrane the fluid was probably generated by devolatilization of the greenstones as they were heated by the overthrust granulites the high co 2 content of the calculated fluid and of the fluid inclusions suggests the hydrating fluid was co 2 rich at the p t conditions of the retrograde isograd

hydrological responses and stability analysis of shallow slopes with cohesionless soil subjected to continuous rainfall understanding the hydrological and physical responses of shallow slopes subject to rainfall events is vital for the efficiency of a warning system setup in this research a series of experiments were undertaken to evaluate the hydrological responses of shallow slopes of varying steepness and when subjected to varying intensities periods and inter storm periods of rainfall an analysis of infinite slopes was also undertaken to develop a fundamental understanding of rainfall induced shallow slope failure characteristics the hydrological and physical responses were characterized in the infiltration and saturation phases during the infiltration phase the maximum magnitude of water content was found behind the wetting front termed as the water content behind the wetting front wb for a certain soil type the magnitude of wb was found to be dependent on the magnitude of rainfall intensity regardless of the slope gradient and initial water content based on the relative depth of the failure plane th

rainfall infiltration in a landslide soil deposit importance of inverse particle segregation abstract coarse particles move towards the front and surface of the deposit while fine particles stay in the rear and bottom accordingly the coefficient of permeability of the soil statistically tends to decrease from the surface to the bottom and from the toe to the apex of the deposit this feature can be described by trend functions that describe the changes in particle size and permeability inside the soil deposit in this paper attempts are made to include the physical background in the characterization of geotechnical uncertainties the objectives of this paper are to simulate non stationary fields of particle size and coefficient of permeability in a landslide soil deposit and to analyse rainfall infiltration in the non stationary random fields the soil deposit is assumed to consist of inter layers parallel to the slope surface the soil deposit is also assumed to be axisymmetric therefore any vertical section of the deposit can be selected to generate two dimensional non stationary random fields each of the non stationary random fields is formulated by adding a trend surface to a residual stationary random field with orthogonal major and minor scales of fluctuation the produced random fields follow an exponential correlation structure subsequently steady state rainfall infiltration in the anisotropic non stationary heterogeneous random fields is analysed the effects of variations of saturated permeability and scale of fluctuation on the pore water pressure regime are also investigated

geochronology of the hout river shear zone and the metamorphism in the southern marginal zone of the limpopo belt southern africa abstract in this paper monazite u pb and zircon evaporation dates stepleaching pb pb results on garnet staurolite and kyanite and hornblende ar ar data are presented which constrain the timing of granulite facies metamorphism in the southern marginal zone of the limpopo belt and its thrusting onto the kaapvaal craton the southern marginal zone of the limpopo belt is considered to be a lower crustal equivalent of the northern kaapvaal craton granulite exhumation is associated with southward thrusting along the hout river shear zone which is a set of thrust and strike slip shear zones zircon ages for the matok intrusive complex which was emplaced within the zone during this thrusting charno enderbites 2671 4 ma granodiorites between 2667 and 2664 ma have previously been interpreted as evidence for rapid exhumation of the southern marginal zone within only 7 ma we have obtained a u pb date of 2691 7 ma for monazite from the bandelierkop quarry in the southern marginal zone interpreted as the age of high grade metamorphism a single zircon evaporation pb pb date of 2643 1 ma from a leucosome band at the same locality may indicate longer lasting metamorphism or decompression melting during exhumation anatexis of metapelitic xenoliths within the matok intrusive complex was dated at 2663 4 ma by u pb on monazite indistinguishable from existing zircon ages for this complex pb pb step leaching dates obtained on synkinematically grown garnet 2691 20 ma staurolite 2712 37 ma and kyanite 2672 51 ma from the khavagari hills in the giyani greenstone belt in the immediate footwall of the hout river shear zone indicate that early thrusting was contemporaneous with peak metamorphism in the southern marginal zone ar ar dating and geochemistry on syntectonic hornblende separates from the same shear zone system yielded disturbed spectra and indicated multiple populations probably reflecting repeated or continuous tectonic activity of the hout river shear zone up to about 2600 ma

insights into the complexity of crustal differentiation k2o poor leucosomes within metasedimentary migmatites from the southern marginal zone of the limpopo belt south africa differentiation of the continental crust is the result of complex interactions between a large number of processes which govern partial melting of the deep crust magma formation and segregation and magma ascent to significantly higher crustal levels the anatectic metasedimentary rocks exposed in the southern marginal zone of the limpopo belt represent an unusually well exposed natural laboratory where the portion of these processes that operate in the deep crust can be directly investigated in the field the formation of these migmatites occurred via absent incongruent melting reactions involving biotite which produced cm to m scale k2o poor garnet bearing stromatic leucosomes with high ca na ratios relative to their source rocks field investigation combined with geochemical analyses and phase equilibrium modelling designed to investigate some aspects of disequilibrium partial melting show that the outcrop features and compositions of the leucosomes suggest several steps in their evolution 1 melting of a portion of the source with restricted plagioclase availability due to kinetic controls to produce a magma melt entrained peritectic minerals in variable proportions relative to melt 2 segregation of the magma at near peak metamorphic conditions into melt accumulation sites mas a k a future leucosome 3a reequilibration of the magma with a portion of the bounding mafic residuum via chemical diffusion h2o k2o which triggers the co precipitation of quartz and plagioclase in the mas 3b extraction of melt dominated magma to higher crustal levels leaving peritectic minerals entrained from the site of the melting reaction and the minerals precipitated in the mass to form the leucosome in the source the key mechanism controlling this behaviour is the kinetically induced restriction of the amount of plagioclase available to the melting reaction this results in elevated melt h2o and k2o and chemical potential gradient for these components across the leucosome mafic residuum contact the combination of all of these processes accurately explains the composition of the k2o poor leucosomes these findings have important implications for our understanding of melt segregation in the lower crust and minimum melt residency time which according to the chemical modelling is 5 years we demonstrate that in some migmatitic granulites the leucosomes constitute a type of felsic refractory residuum rather than evidence of failed magma extraction this provides a new insight into the ways that source heterogeneity may control anatexis this article is protected by copyright all rights reserved

effects of degree of saturation on shallow landslides triggered by rainfall the empirical rainfall threshold concept and the physical based model are two commonly used approaches for the assessment of shallow landslides triggered by rainfall to investigate in detail the rainfall triggered shallow landslides many physical based models coupling the infinite slope stability analysis with the rainfall infiltration modeling in variably saturated soil were developed however in those physical based shallow landslide models the unit weight and the unsaturated shear strength were assumed constant rather than depending on the degree of saturation in this study the effects of the unit weight and the unsaturated shear strength as function of degree of saturation on rainfall triggered shallow landslides are examined several designed scenarios and a real case scenario are used to conduct the examinations the results show that not only the occurrence of shallow landslides but also the failure depth and the time to failure could be misassessed if the influences of degree of saturation on the unit weight and the unsaturated shear strength are neglected

hydration of cordierite and hypersthene and a description of the retrograde orthoamphibole isograd in the limpopo belt south africa

influence of co2 on melting of model granulite facies assemblages a model for the genesis of charnockites it is shown that partial melting studies at crustal pressures in sio2 rich portions of the system kalsio4 mg2sio2 h2o co2 can be used in modeling the anatectic origin of charnockites the univariant reaction phlogopite sanidine quartz vapor enstatite liquid yields an sio2 rich melt granite analog at 3 kbar the vapor composition at the solidus is buffered to high h2o contents by virtue of the coexistence of phlogopite with its breakdown products with higher pressures 8 and 15 kbar the fluid phase is buffered to higher co2 contents and the melt composition becomes enriched in k2o and mgo charnockite analog melting relations are controlled through the expansion of the quartz liquidus field relative to the enstatite and sanidine fields with increasing pressure it is noted that partial melts generated at the base of the crust in the presence of co2 rich fluid will be of an alkaline nature and will crystallize enstatite at lower pressures co2 saturated melting of similar sio2 rich bulk compositions phlogopite absent through the reaction enstatite sanidine quartz co2 liquid occurs at temperatures above 1000 c to about 15 kbar

the magmatic metamorphic and tectonic evolution of the northern marginal zone of the limpopo belt in zimbabwe the northern marginal zone of the limpopo belt in southern africa comprises a plutonic assemblage of granitoids including a distinctive suite of porphyroclastic granites and a much less abundant supracrustal assemblage of metabasites and iron formations these rocks are at granulite facies above a normal thickness of continental crust most of the plutonic assemblage are intrusive rocks that crystallized from dry melts from 2800 to 2600 ma with a relatively simple thermal history they may have been derived from partial melting of a mafic source some supracrustal rocks have experienced two thermal events at granulite facies a reverse sense shear zone forms the boundary of the northern marginal zone with the zimbabwe craton the southern boundary is the triangle shear zone which is proven as a continuous structure along a much greater strike length than previously documented a widespread sub vertical foliation in the northern marginal zone and the reverse shear zone formed during progressive nnw sse shortening crustal thickening occurred both magmatically and tectonically in the late archaean and was accompanied by synchronous uplift protracted magmatism provides a mechanism to incorporate supracrustal rocks into the lower crust and can explain the occurrence of more than a single thermal event

the oxygen isotopic composition of granulites and retrogressed granulites from the limpopo belt as a monitor of fluid rock interaction abstract from the southern marginal zone of the limpopo belt three rock systems cordierite bearing metapelites mafic rocks and ultramafic rocks are studied by whole rock oxygen isotope analysis in order to decide wether the observed variation in the o isotopic composition of the metapelites is due to granulite facies fluid rock interactions or due to earlier processes a discrimination index pelite index pi is proposed in combination with the whole rock oxygen isotopic composition this index enables one to put some constraints on the origin of the precursor rocks in the case of the limpopo metapelites it is concluded that the cordierite anthophyllite bearing metapelites are only in part true metasediments a metasomatic alteration of mafic precursors in an ocean crust environment could be responsible for both low pi indices and high with respect to unaltered mantle material 18 o values fluid rock interactions in this environment are also thought to be responsible for the observed chemical and o isotopic variation of mafic and ultramafic rocks the data do not support significant large scale co 2 infiltration during granulite facies metamorphism the retrograde regionally extended anthophyllite formation in the southern marginal zone of the limpopo belt is certainly triggered by some fluid infiltration model calculations show that the amount of fluids necessary for this readjustment is too small to have an imprint on the whole rock oxygen isotope composition

mid crustal granulite facies metamorphism in the central kaapvaal craton the bushveld complex connection abstract the numerous greenstone remnants which occur as inclusions in the archaean gneissic granitoid basement exposed in the core of the vredefort dome display evidence of very high grades of granulite facies metamorphism and an unusually complex three stage metamorphic history 1 in metapelites migmatites and refractory restites were produced in a mid crustal 0 5 gpa m1 anatectic event at temperatures in excess of 900 c in the restites 2 in the migmatites the peak metamorphic assemblages are variably overprinted by a high grade retrograde reaction which involved crystallizing anatectic melts m2 3 both the peak metamorphic assemblages and the retrogression textures are cross cut by pseudotachylitic breccia veins which mark a shock metamorphic event associated with the formation of the vredefort dome and 4 the peak metamorphic assemblages and the m2 retrogression textures are overprinted by new generations of remarkably fine grained post shock high grade phases which crystallised at a pressure some 0 25 gpa lower than that of both the peak metamorphic conditions and the retrogression m3 these data indicate an anticlockwise p t evolution where mid crustal anatexis most probably resulted from the intraplating of bushveld complex related ultramafic magmas at 2 06 ga a period of approximately isobaric cooling and retrogression was followed by the vredefort catastrophe which resulted from the impact of a large meteorite into the terrane at 2 02 ga this shock event halted the natural mid crustal metamorphic progression prior to the terrane cooling below 650 c and resulted in the rapid exhumation of the terrane by some 9 km in the process it provided a window into the deep levels of the central kaapvaal craton not seen elsewhere in the region

comment on ultrahigh temperature granulites and magnesian charnockites evidence for the neoarchean accretion along the northern margin of the kaapvaal craton by rajesh et al

deep crystal response to continental collision the limpopo belt of southern africa the limpopo belt is an example of an archean 2700 ma continental collisional zone in which the thickened crust 70 km has virtually attained equilibrium with the adjacent non thickened plates by a process of upward movement and lateral spreading of the underthrust high grade metamorphosed plates

influence of spatial variability of permeability property on steady state seepage flow and slope stability analysis in recent years spatial variability modeling of soil parameters using random field theory has gained distinct importance in geotechnical analysis in the present study commercially available finite difference numerical code flac 5 0 is used for modeling the permeability parameter as spatially correlated log normally distributed random variable and its influence on the steady state seepage flow and on the slope stability analysis are studied considering the case of a 5 0 m high cohesive frictional soil slope of 30 degrees a range of coefficients of variation cov from 60 to 90 in the permeability values and taking different values of correlation distance in the range of 0 5 15 m parametric studies using monte carlo simulations are performed to study the following three aspects i e i effect ostochastic soil permeability on the statistics of seepage flow in comparison to the analytic dupuit s solution available for the uniformly constant permeability property ii strain and deformation pattern and iii stability of the given slope assessed in terms of factor of safety fs the results obtained in this study are useful to understand the role of permeability variations in slope stability analysis under different slope conditions and material properties c 2009 elsevier b v all rights reserved

evolution of the northern high grade margin of the kaapvaal craton south africa the northern kaapvaal craton is divided into three distinctive crustal zones 1 the high grade southern marginal zone smz of the limpopo belt in the north 2 a transitional zone of technically stacked metamorphic rocks which includes the area from the sutherland belt in the north to the pietersburg and murchison belts in the south and 3 a low grade granite greenstone terrane farther to the south the change across the smz boundary is expressed by an overall increase in the grade of metamorphism a strip of retrogression related to a zone of thrusting abrupt changes in intensity of deformation rock densities magnetic lineament patterns and isotopic ages in compositionally similar rocks regional metamorphism in the northern kaapvaal craton is demonstrably not a continuum in the sense that the highest grade rocks underwent all earlier stages of metamorphism rather that rapid local tectonic processes must have occurred a proposed evolutionary path for the smz was initiated with crustal thicke

paleoproterozoic amphibolite facies retrogression and exhumation of archean metapelitic granulites in the southern marginal zone of the limpopo belt south africa abstract granulite facies terrains that have undergone extensive retrogression provide insights into the recycling of volatiles in the crust during orogenesis the timing of retrogression is key to understanding the geodynamic circumstances of such events this study has investigated amphibolite facies retrogression of melt depleted granulite facies metapelites from the south marginal zone smz of the limpopo belt the granulites formed via incongruent partial melting reactions that consumed biotite and produced garnet and rutile as prominent peritectic products at 2 7 ga under conditions of 11 kbar and 875 c peak metamorphic garnet is replaced by cordierite orthopyroxene symplectites with cordierite subsequently partially replaced by fine grained intergrowths of amphibolite facies assemblages including rutile zr in rutile thermometry yielded a temperature range of 731 846 c for the granulite facies rutiles and 629 690 c for rutile in the retrograde assemblage all rutile generations yielded a youngest u pb age of 2 1 ga some granulite facies rutiles record older dates 2 55 2 25 ga which are non systematic with regard to crystal size and represent non reset relicts of metamorphic recrystallization during a potentially complex history of amphibolite facies metamorphism between 2 7 and 2 2 ga the youngest 2 1 ga rutile u pb age represents the time of final exhumation related cooling of the rocks following a discrete paleoproterozoic amphibolite facies retrograde event coexisting orthoamphiboles in the peak metamorphic assemblage indicate a maximum peak temperature of 625 c the lack of age size correlation and intragrain age zoning in rutile suggest fast cooling following the amphibolite facies retrograde event which is inferred to be not much older u pb dating of zircon from the same rocks confirms that the metapelites underwent granulite facies metamorphism at 2695 35 ma thus the metapelites of the smz record both an archean granulite facies event and a polymetamorphic paleoproterozoic amphibolite facies history that culminated in a mid amphibolite facies peak inducing partial retrogression of the granulites the paleoproterozoic amphibolite facies event is tentatively correlated with mantle melting documented between 2 3 and 2 1 ga to produce mafic and intermediate volcanic rocks in the pretoria group on the kaapvaal craton

himalayan tibetan analogies for the evolution of the zimbabwe craton and limpopo belt abstract the limpopo orogeny which lasted from 2700 to 2600 ma was characterised by nnw sse directed shortening this resulted in both crustal thickening accommodated by folding and nnw directed thrusting and associated crustal extrusion whereby a number of crustal blocks including the central zone of the limpopo belt was displaced to the west southwest along wsw ene trending shear zones this was part of a regionally distributed phase of orogenic deformation which affected the adjoining kaapvaal and zimbabwe cratons from the witwatersrand basin in the south to the harare greenstone belt in the north this deformation which migrated northwards with time postdated an earlier phase of crustal accretion during which the archaean crustal unit now marked by the kaapvaal and zimbabwe cratons and the limpopo belt grew towards the north northwest shortening of this unit during the limpopo orogeny may be regarded as the last stage of the crustal accretion process this tectonic process of continental growth by accretion followed by crustal shortening with associated crustal extrusion has many features in common with tibetan tectonics from the mesozoic to the present

model for the prediction of shear strength with respect to soil suction experimental studies on unsaturated soils are generally costly time consuming and difficult to conduct shear strength data from the research literature suggests that there is a nonlinear increas

probabilistic analysis of seepage that considers the spatial variability of permeability for an embankment on soil foundation abstract in this study probabilistic analysis of seepage through an embankment on soil foundation was performed the traditional seepage analysis method was extended to develop a probabilistic approach that accounts for the uncertainties and spatial variation of the hydraulic conductivity in a layered soil profile the hydraulic conductivity of soil shows significant spatial variations in different layers because of stratification further it varies on a smaller scale within each individual layer it was assumed that the statistics of the hydraulic conductivity is different for different layers and that the hydraulic conductivity in a layer is uncorrelated with that in the other layers two dimensional random fields were generated on the basis of the karhunen loeve expansion in a manner consistent with a specified marginal distribution function and an autocorrelation function a series of seepage analyses of embankment foundation systems were performed using the generated random fields to study the effects of uncertainty due to the spatial heterogeneity of the hydraulic conductivity on the seepage flow the results showed that the probabilistic framework can be used to efficiently consider the various flow patterns caused by the spatial variability of the hydraulic conductivity in seepage assessment for an embankment on soil foundation

fluids p t paths and the fates of anatectic melts in the earth s crust this paper presents a model for the longevity and physical behaviour of anatectic melts in the earth s crust it is assumed that a thermal anomaly has caused partial fusion of biotite plagioclase quartz rocks to produce a granitic melt and restitic solids the focus is on the potential chemical and physical outcomes as a function of the various p t fluid conditions rocks undergoing fluid present melting will sustain an increase in bulk density and will become more gravitationally stable diapiric up welling of such material should not occur in fluid absent melting the bulk density will decrease and foster gravitational instability stresses in the surrounding rocks could however lead to fracture and rapid evacuation of the melt with excess fluid and without melt segregation isobaric cooling will cause immediate freezing if t rises above the biotite quartz melting reaction freezing will still occur at the original reaction t diapiric up welling should not occur biotite bearing diatexites might be formed by large degrees of fusion but magma ascent is unlikely in isothermal decompression immediate freezing will ensue and the migmatite should contain orthopyroxene rather than biotite with excess fluid and melt segregation cooling will induce freezing at the fluid saturated granite solidus magma ascent could however occur even for xflh2o 1 in isothermal decompression melt will persist to the granite solidus for the imposed xflh2o limited magma ascent could occur all granites should contain primary igneous biotite for fluid deficient rocks without melt segregation freezing will occur at the t of the original melting if the reaction is overstepped solidification will occur at the original xflh2o magma formation is unlikely migmatites should contain either pyroxene retrogressed to biotite or biotite alone on decompression immediate freezing is likely if t remains at the biotite quartz reaction for higher t melt will survive decompression and freeze at the fluid saturated solidus for some increased xflh2o magma ascent is possible and the melt will freeze very close to the wet granite solidus in fluid deficient rocks with melt segregation cooling and crystallization will cause fluid saturation in situ segregated melt will freeze at the original xflh2o melt ascent will however cause exsolution of a co2 rich fluid with fluid escape melt will freeze close to the wet granite solidus an increase in melt proportion may accompany magma ascent or source up welling any low p granite intrusion should be charnockitic for fluid absent rocks without melt segregation freezing will occur on cooling to the t of the original reaction only transitory migmatites could be formed but melt will survive decompression almost to the h2o saturated granite solidus the rocks will reveal former melt presence only in the existence of veins of coarse retrograde biotite with isothermal decompression further melting may occur forming an orthopyroxene bearing granulite facies migmatite in fluid absent situations with melt segregation magma could be efficiently transported to higher crustal levels if the melt proportion were insufficient for magma formation granulite facies migmatites would result ascending melt would progressively dissolve any entrained restite the granites produced should be charnockitic to aid in interpretation of the modelling results we suggest that it may be slightly more common for the highest grade metamorphic terranes to exhibit isobaric cooling paths that fluid present anatexis is normally limited to the shallower parts of the crust and that fluid absent reactions are more likely at greater depths we conclude that the best models for natural fluid present anatexis are those dealing with essentially pure h2o fluid and that fluid deficient conditions will dominate over fluid excess we also believe that it is common for melts to be physically segregated on scales larger than the diffusion paths of many elements

fluids in granulites of the southern marginal zone of the limpopo belt south africa the southern marginal zone of the limpopo belt in south africa is characterised by a granulite and retrograde hydrated granulite terrane the southern marginal zone is therefore perfectly suitable to study fluids during and after granulite facies metamorphism by means of fluid inclusions and equilibrium calculations isolated and clustered high salinity aqueous and co2 ch4 fluid inclusions within quartz inclusions in garnet in metapelites demonstrate that these immiscible low h2o activity fluids were present under peak metamorphic conditions 800 850 c 7 5 8 5 kbar the absence of widespread high temperature metasomatic alteration indicates that the brine fluid was probably only locally present in small quantities thermocalc calculations demonstrate that the peak metamorphic mineral assemblage in mafic granulites was in equilibrium with a fluid with a low h2o activity 0 2 0 3 the absence of water in co2 rich fluid inclusions is due to either observation difficulties or selective water leakage the density of co2 inclusions in trails suggests a retrograde p t path dominated by decompression at t 600 c re evaluation of previously published data demonstrates that retrograde hydration of the granulites at 600 c occurred in the presence of h2o and co2 rich fluids under p t conditions of 5 6 kbar and 600 c the different compositions of the hydrating fluid suggest more than one fluid source

influences of soil water characteristic curve on rainfall induced shallow landslides the analysis of slope instability induced by rainfall was usually performed using the main drying curve as the measurement of the main wetting curve is a more time consuming and costly task in this study the influences of the main drying and wetting curves on rainfall induced shallow landslides are examined three designed scenarios and a real case scenario are used to conduct this examination the prediction of shallow landslide occurrence is related to the main drying and wetting curves due to the strong relation between groundwater pressure head and hysteresis effect the main wetting curve may have a less minimum landslide triggering rainfall amount and a less rainfall duration threshold for landslide occurrence than the drying wetting curve for safety s sake an underestimation of shallow landslide occurrence may be produced by the commonly used main drying curve in addition besides the shallow landslide occurrence the failure depth and the time to failure are also influenced by the main drying and wetting curves the hysteresis effect should be taken into account for assessing rainfall induced shallow landslides

stability analyses of rainfall induced landslides the slope stability issues concerning rainfall induced slope failures are investigated and presented specifically the effect of both negative and positive pore water pressures on the stability of initially unsaturated slopes are carefully explained and coupled with infinite slope analysis methods in order to present a predictive formulation of slope failures that occur as a result of rainfall events the formulation serves as a baseline analysis method for evaluating potentially unstable soil slopes that are subject to surface infiltration and explains the various triggering mechanisms that may occur based on individual combinations of the slope geometry soil strength and infiltration parameters a procedural method is outlined for utilizing the analytical formulation to predict the change in the factor of safety for a slope subject to infiltration and a detailed analysis of a case study is presented to verify the method quantitative statements are made concerning the time and depth of failure in relationship to the soil slope and rainfall parameters

random finite element method for spudcan foundations in spatially variable soils abstract spudcans are large diameter 20 m conical foundations holding up mobile jack up platforms for offshore oil and gas developments in shallow to moderate water depths during self installation the spudcan often penetrates several tens of meters into seabed soils where large variations often occur in the shear strength of the soils although the failure mechanisms and bearing capacity of spudcan foundations have been studied in homogeneous soil and layered uniform soil the effect of the spatial variability in soil strength on the spudcan response is still unclear this study presents a random finite element method rfem for assessing the failure mechanisms and the bearing capacity of a spudcan foundation embedded in spatially varied seabed soils a comprehensive review of seabed soils discusses typical ranges of the mean the coefficient of variation and the scale of fluctuation of the undrained shear strength random fields are generated and mapped into a non linear finite element analysis to reveal the failure mechanisms of the spudcan in spatially varied soils the influence of the scale of fluctuation in different directions is investigated the results indicate that ignoring the spatial variability of soil strength leads to an overestimation of the bearing capacity it is unconservative for the foundation design to assume an isotropic random field model in the rfem analysis

shear strength characteristics of a residual soil shallow landslides in natural residual soils slopes are common all over the world the slip surfaces associated with these landslides are often situated above the groundwater table therefore it i

a gis physically based emergency methodology for predicting rainfall induced shallow landslide zonation abstract this study proposes an original approach for predicting shallow translational slide hazards which are triggered by irregular rainfall events via the method of zonation at a regional scale in emergency situations the proposed model incorporates the infinite slope method in a gis platform to assess hazard and risk associated with slope instability this application can be integrated into the emergency management software simge 1 0 sge 2 0 the objective of the work is to provide a quick tool for managing emergencies and predicting shallow rainfall induced landslides rils the originality of this approach includes the relationship between two variables m z with m being a hydrological pattern of steady state simulating the effects of rain that cause translational slides and z being the characteristic sliding depth based on the bounded lithological unit this method provides hazard maps including zonation based on a factor of safety towards shallow landslides where stable and unstable conditions depending on precipitation are determined for managing emergencies this approach was applied in the guadalmansa river basin in benahavis malaga andalusia where numerous shallow landslides occurred in 2010 caused by extreme rainfall events and a lithological unit has been isolated for this research alpujarride schist the results obtained through this method have been verified after analysing the studied area s landslide inventory

combined roles of saturated permeability and rainfall characteristics on surficial failure of homogeneous soil slope abstract both rainfall characteristics rainfall intensity and duration and saturated permeability of soil may influence the type and mechanism of surficial slope failures in general the failures can be initiated by two mechanisms i e loss of matric suction through propagation of wetting front and rise of water table up to date there are still no clear indicators to identify the dominant parameters that control the type of failure for these shallow landslides this paper investigates the hydraulic responses of soils to the variations of rainfall characteristics and soil permeability through numerical analyses the results showed that the hydraulic responses to rainfall for a homogeneous infinite slope underlain by an impermeable layer can be divided into two stages 1 the propagation of wetting front and 2 the rise of water table based on these hydraulic responses the type and mechanism of failures were deduced from the analytical analyses both the rainfall characteristics and saturated permeability were found to be predominant in controlling the hydraulic responses of soil and hence the occurrence time depth of failure plane and type of surficial slope failures

probabilistic stability analysis of rainfall induced landslides considering spatial variability of permeability abstract many regions around the world are vulnerable to rainfall induced landslides a variety of methods have been proposed for revealing the mechanism of landslide initiation current analysis methods however do not consider the effects of non homogeneous soil profiles and variable hydraulic responses on rainfall induced slope failures in korea where the depth of weathering is very shallow many slope failures occur in the layer of weathered residual soil that overlays the bedrock these failures are characterized by shallow failure surfaces located near the interface between the weathered soil and the underlying bedrock in this study probabilistic stability analyses were conducted for a weathered residual soil slope with shallow impermeable bedrock to study the failure mechanism of rainfall related landslides a series of seepage and stability analyses of an infinite slope based on one dimensional random fields were performed to study the effects of uncertainty due to the spatial heterogeneity of hydraulic conductivity on the failure of unsaturated slopes due to rainfall infiltration the results showed that a probabilistic framework can be used to efficiently consider various failure patterns caused by spatial variability of hydraulic conductivity in rainfall infiltration assessment for a shallow infinite slope

fluid absent melting and the roles of fluids in the lithosphere a slanted summary abstract the presence or absence nature and compositions of lithospheric fluids are crucial factors in the evolution of igneous and metamorphic rocks despite this confusion still surrounds perceptions of the degrees of fluid involvement in many geological settings however experimental and field investigations constrain these roles and we are able to make some valid generalizations studies of prograde metamorphism have highlighted the spatial heterogeneity of fluid concentrations in many crustal environments this commonly indicates internal lithological control of volatile activities under fluid present conditions crustal fluids do not appear to mix readily fluid flow is generally structurally or lithologically controlled the transition from amphibolite to granulite facies is characterized by a decrease in ah2o as well as a temperature increase in many terranes these phenomena correlate with the appearance of migmatites some granulites are not migmatitic but have chemical and mineralogical characteristics of melt depleted restites this indicates efficient extraction of melts incongruent melting reactions involving the breakdown of crystalline hydrates in crustal rocks produce granitoid melts plus denser restites that are nearly or actually anhydrous experimental and theoretical treatments of fluid absent melting show that micas and amphiboles decompose at 700 to 900 c for mid to lower crustal pressures the melts resemble the compositions of s and i type granitoids pervasive aqueous fluids could not generally have been present during this melting since exposed granulite terranes are not characterized by high melt proportions and the magmas themselves are water undersaturated likewise the general presence of very h2o poor pervasive fluids is unlikely since this would allow only subsolidus dehydration at normally attainable crustal temperatures in this case the amphibolite granulite transition is possible at relatively low temperatures and the resultant rocks would not contain evidence of in situ melting the granulite granite connexion and effective crustal differentiation seem viable only during high temperature fluid absent metamorphism data on continental geotherms show that the lower crust is not entirely granulitic granulites are produced in regions of anomalously high heat flow the mantle connexion thus inferences on the nature of the lower crust should not be entirely based on studies of exposed granulite terranes mineral assemblages in eclogites also indicate widespread internal buffering of volatile activities and probable fluid absent conditions mantle derived basaltic magmas too are volatile bearing and it is plausible that volatile fixing phases also occur in the mantle volatiles may largely be introduced into the mantle through subduction processes and only released during the melting attending the breakdown of hydrous minerals as in the crust

partial melting and the origin of metapelitic granulites in the southern marginal zone of the limpopo belt south africa abstract two potentially realistic models exist to explain the origin of the granulite facies rocks of the southern marginal zone i co2 fluxing inducing the necessary high temperature dehydration reactions and ii melting of hydrous minerals to yield an h2o undersaturated granitic melt in equilibrium with a dehydrated granulitic assemblage petrographic and field evidence from the bandelierkop quarry in the southern marginal zone indicate a sequence of melting reactions involving muscovite and biotite relict textural evidence indicates that the reaction responsible for the generation of most of the melt bi sil qz plag melt ga ksp was fluid absent the melting reactions can be shown to have occurred during the prograde metamorphic path with the highest temperature reaction bi qz plag hy cord melt occurring at approximately peak metamorphic conditions 850 c and less than 9 5 kbar this suggests a fluid absent mode of granulite formation a subsequent retrograde reaction cord ksp h2o ky qz related to a rise in h2o during in situ crystallisation of the melt did not destroy the granulite assemblages and hypersthene remains stable in areas of the southern marginal zone that record pressures of greater than 6 5 kbar during retrogression

fluid inclusions in rocks from the amphibolite facies gneiss to charnockite progression in southern karnataka india direct evidence concerning the fluids of granulite metamorphism fluid inclusion studies of rocks from the late archaean amphibolite facies to granulite facies transition zone of southern india provide support for the hypothesis that co2 rich h2o poor fluids were a major factor in the origin of the high grade terrain charnockites closely associated leucogranites and quartzo feldspathic veins contain vast numbers of large co2 rich inclusions in planar arrays in quartz and feldspar whereas amphibole bearing gray gneisses of essentially the same compositions as adjacent charnockites in mixed facies quarries contain no large fluid inclusions inclusions in the northernmost incipient charnockites as at kabbal karnataka occasionally contain about 25 mol of immiscible h2o lining cavity walls whereas inclusions from the charnockite massif terrane farther south do not have visibile h2o microthermometry of co2 inclusions shows that miscible ch4 and n2 must be small probably less than 10mol combined densities of co2 increase steadily from north to south across the transitional terrane entrapment pressures calculated from the co2 equation of state range from 5 kbar in the north to 7 5 kbar in the south at the mineralogically inferred average metamorphic temperature of 750 c in quantitative agreement with mineralogic geobarometry this agreement leads to the inference that the fluid inclusions were trapped at or near peak metamorphic conditions calculations on the stability of the charnockite assemblage biotite orthopyroxene k feldspar quartz show that an associated fluid phase must have less than 0 35 h2o activity at the inferred p and t conditions which agrees with the petrographic observations high tio2 content of biotite stabilizes it to lower h2o activities and the steady increase of biotite tio2 southward in the area suggests progressive decrease of ah2o with increasing grade oxygen fugacities calculated from orthopyroxene magnetite quartz are considerably higher than the graphite co2 o2 buffer which explains the absence of graphite in the charnockites the present study quantifies the nature of the vapours in the southern india granulite metamorphism it remains to be determined whether co2 flushing of the crust can by itself create large terranes of largeion lithophile depleted granulites or whether removal of h2o bearing anatectic melts is essential

tectonic model for the evolution of the limpopo belt abstract constraints on which any model for the tectonic evolution of the limpopo belt must be based include the following data crustal thickening to at least 65 km between 2700 and 2650 ma ago was responsible for the formation of the granulite terrane exposed in the limpopo belt today this crustal thickening probably resulted from the thrusting of the kaapvaal craton over the zimbabwe craton along the south dipping triangle tuli sabi shear zone other northwardverging thrusts related to this event occur in the kaapvaal craton south of the limpopo belt in the central and southern marginal zones and the kaapvaal craton this shortening is directed to the southwest while in the northern marginal zone it was directed to the north northwest peak metamorphism was superimposed on the thickened crust and then nearly isothermal decompression of several kbars occurred throughout the belt during this decompression rocks moved upward and spread outward onto the adjacent cratons from the zone of thickened crust along several inward directed shear zones creating a regional pop up high grade rocks were thrust over low grade rocks on the cratons producing along the terrane boundary retrograde metamorphism in the limpopo belt and prograde metamorphism on the cratons

partial melting and the formation of granulite facies assemblages in namaqualand south africa abstract dehydration melting reactions in which water from a hydrous phase enters the melt leaving an anhydrous solid assemblage are the dominant mechanism of partial melting of high grade rocks in the absence of externally derived vapour equilibria involving melt and solid phases are effective buffers of ah2 o the element partitioning observed in natural rocks suggests that dehydration melting occurs over a temperature interval during which for most cases ah2o is driven to lower values the mass balance of dehydration melting in typical biotite gneiss and metapelite shows that the proportion of melt in the product assemblage at t 850 c is relatively small 10 20 and probably insufficient to mobilize a partially melted rock body granulite facies metapelite biotite gneiss and metabasic gneiss in namaqualand contain coarse grained discordant unfoliated anhydrous segregations surrounded by a finer grained foliated matrix that commonly includes hydrous minerals the segregations have modes consistent with the hypothesis that they are the solid and liquid products of the dehydration melting reactions bt sil qtz pi grt crd kfs l metapelite bt qtz pl opx kfs l biotite gneiss and hbl qtz opx cpx pl l metabasic gneiss the size shape distribution and modes of segregations suggest only limited migration and extraction of melt growth of anhydrous poikiloblasts in matrix regions development of anhydrous haloes around segregations and formation of dehydrated margins on metabasic layers enclosed in migmatitic metapelites all imply local gradients in water activity also they suggest that individual segregations and bodies of partially melted rock acted as sinks for soluble volatiles the preservation of anhydrous assemblages and the restricted distribution of late hydrous minerals suggest that retrograde reaction between hydrous melt and solids did not occur and that h2o in the melt was released as vapour on crystallization this model combined with the natural observations suggests that it is possible to form granulite facies assemblages without participation of external fluid and without major extraction of silicate melt

metamorphism of reduced granulites in low co 2 vapour free environment pervasive flooding of co2 has been proposed as the cause of granulite facies metamorphism that is capable of producing many distinctive characteristics of the deep continental crust reduced water activity orthopyroxene bearing assemblages depletion of large ion lithophile lil elements and dehydration1 6 the calculations presented here of c o h fluid composition for conditions of granulite facies metamorphism show that oxygen fugacity f o2 estimates from many terranes are sufficiently low that the addition of co2 rich fluid causes graphite to precipitate for values of pressure p and temperature t common to granulites and with f o2 slightly below the quartz fayalite magnetite buffer qfm the addition of co2 sufficient to grow 10 vol orthopyroxene requires the precipitation of 1 5 vol graphite as 0 1 vol graphite is readily recognizable but is not reported in most low f o2 granulites these rocks have not been flooded by co2 and low f h2o is probably due to extraction of a magma or recrystallization of an already dry rock7 8 granulite terranes may thus result from a combination of these three processes and the dominance of any one cannot now be demonstrated on a regional basis

constraints on the composition of fluids involved in retrograde anthophyllite formation in the limpopo belt south africa abstract orthoamphibole occurs widely in the metapelitic gneisses and other lithologies within the southern marginal zone of the limpopo belt in southern africa petrographic relations indicate that the orthoamphibole formed as a retrogressive replacement of the granulite facies minerals cordierite and orthopyroxene the existence of a discrete retrograde orthoamphibole isograd that can be mapped for over 150 km has led previous workers to suggest that the orthoamphibole formed as a result of equilibrium high temperature reactions which occurred in response to regional influx of fluids at the close of the limpopo orogeny 2670 ma ago however in order to substantiate this interpretation it is necessary to show from phase equilibrium analysis that the metapelitic minerals and their retrograde products comprise assemblages stable at elevated pressure and temperatures rather than disequilibrium assemblages formed at unspecified lower temperatures by monotropic reactions some of the properties of the infiltrating fluids may in turn be specified if the alteration products represent equilibrium assemblages it is shown that the presence of anthophyllite and the absence of talc in two analysed metapelites from the retrograde isograd require an associated vapour phase to have been relatively low in water ah2o 0 7 and temperatures to have been below 620 c when the anthophyllite developed from the orthopyroxene the fast kinetics of formation of talc and the relatively sluggish kinetics of formation of anthophyllite in experimental systems make it highly unlikely that the orthoamphibole could have formed metastably at low temperatures and high water activities a more general phase equilibrium analysis based on the coexistence of cordierite garnet biotite enstatite plagioclase and quartz with retrograde anthophyllite and kyanite indicates that this assemblage was in equilibrium at temperatures between 450 to 650 c for pressures of 5 to 7 kbars and water activities between 0 6 and 0 1 the temperatures pressure and water activities are highly correlated and lower pressures and water activities are required for equilibrium at lower temperatures the reduced water activities calculated require that a substantial quantity of another volatile be present in the vapour phase in the absence of stable scapolite or carbonates this volatile cannot be confirmed to be co2 the required infiltration of late orogenic fluids with reduced water activities is apparently a major feature of the limpopo event and may have parallels in other large precambrian high grade terrains in as much as orthoamphibole replacing orthopyroxene is a commonly observed mineral assemblage

constraints on the form of the p t loop in the southern marginal zone of the limpopo belt south africa abstract a generalised clockwise p t path consisting of a prograde portion a high grade isothermal decompression portion and an essentially isobaric cooling portion has been suggested for the metamorphic evolution of the southern marginal zone previous studies have concluded that the high grade decompression path started in the kyanite stability field peak metamorphic mineral compositions have been reset during the equilibrium decompression event and hydration during the cooling dominated isobaric portion occurred in the kyanite stability field the present petrographic study from the bandelierkop quarry a locality in the granulite zone of the southern marginal zone identified a series of sequential anatectic reactions which record a period of prograde heating from approximately 700 c to 850 c during this period pressure is constrained to within the sillimanite stability field by the production and preservation of prograde generations of sillimanite the maximum temperature melting event is closely followed by two divariant reactions ga qz sil cord and ga qz cord hy which occur in response to a period of general isothermal decompression a subsequent cooling dominated rehydration period is indicated by a crystallisation hydration reaction cord ksp melt bi ky qz which occurred at a minimum temperature of approximately 640 c and pressure greater than 6 5 kbar the present data confirms the clockwise form of the loop and also supports the previously suggested flat slope of the retrograde cooling portion additional mineral chemistry data relating to the second decompression reaction indicate that the zonation profiles of cordierite and garnet as well as the growth of small quantities of garnet after the reaction are in strong support of the suggested p t path the present mineral compositions in the southern marginal zone reflect a near total re equilibration during the high grade cooling dominated portion of the p t path and as a result reflect p t conditions considerably lower than those of the peak metamorphism