digital elevation model resolution effects on terrain attribute calculation and quantitative soil landscape modeling the accuracy of digital elevation models dem and dem derived products depends on several factors including the horizontal resolution and vertical precision at which the elevation data are represented and the source of the elevation data this accuracy becomes increasingly important as we extend the use of dem data for spatial prediction of soil attributes our objective was to compare terrain attributes and quantitative soil landscape models derived from grid based dem represented at different horizontal resolutions 10 and 30 m represented at different vertical precisions 0 1 and 1 m and acquired from different sources decreasing the horizontal resolution of the field survey dem produced lower slope gradients on steeper slopes steeper slope gradients on flatter slopes narrower ranges in curvatures larger specific catchment areas in upper landscape positions and lower specific catchment areas values in lower landscape positions overall certain landscape features were less discernible on the 30 m dem than on the 10 m dem decreased vertical precision produced a large proportion of points with zero slope gradient and zero slope curvature and a large number of steeply sloping and more highly curved areas differences among dem from different sources were more significant with less accurate representation of depressions and drainage pathways with the usgs dem as compared to the field survey dem empirical models developed from different dem included similar predictive terrain attributes and were equally successful in predicting a horizon depth ahd in the validation data set

geomorphic threshold conditions for ephemeral gully incision abstract ephemeral gully erosion in cultivated land is an important source of sediment that is frequently being overlooked and not accounted for in soil erosion studies furthermore little is known about the factors controlling ephemeral gully erosion in this paper the available information on the initiation and location of ephemeral gullies is summarised focusing on the relationship between the upslope drainage area a and the critical slope gradient s cr for ephemeral gully initiation by plotting the non linear relationship between critical slope gradient measured immediately upstream of the incision head and drainage area at the incision head for gullied sites it was possible to draw a straight line on log log paper through the lower most points for each of the available datasets representing a critical slope area relationship for incision consequently below this line no incision occurs this line or critical relation can also be written as a power function between critical slope and area although many factors vary between the different datasets the exponent of the drainage area relationship 0 4 showed very little variation the observed critical slope area relationship can be related to a simple model of channel initiation by overland flow furthermore this relationship can be used to identify potentially unstable sites where control measures should be undertaken

distribution of local landforms at head and end points of gullies on different grid spacing abstract local landforms described by signs of curvatures can be considered as potential indicators of gully formation however the role of these landforms is not generally investigated in literature hence the goals of the present research are i identification of the relationships of land surface attributes at the head and end points of gullies with the size of these gullies at different grid spacings of a digital elevation model dem ii explanation of the frequency of occurrence fo of local landforms investigations were conducted on the example of 439 gullies of the hronska pahorkatina hill land in slovakia the sizes of the gullies were described by their area and perimeter altitude slope steepness maximal catchment area mca and curvatures were calculated at the head and end points of these gullies 12 types of main local landforms mllfs were identified by the signs of six curvatures for calculation of land surface attributes a set of dems with grid spacings at every 10 m interval from 10 m to 100 m was prepared at the head points of gullies significant spearman s rank correlation coefficients rs show that mca and curvatures related with gully size at dem grid spacings from 10 m to 30 m at the end points such relationships are observed at all grid spacings a negative rs between gully size and slope steepness is obtained at the head points it is demonstrated that the large gullies reached more flat locations in comparison with small gullies at the end points negative rs indicates that large gullies are characterized by flatter outlets in comparison with small gullies the fo of mllfs at the head and end points of gullies relative to their frequency for the whole dem indicate that only four types of mllf are systematically related to gully occurrence

evidence for silicate liquid immiscibility in monzonites and petrogenesis of associated fe ti p rich rocks example from the raftsund intrusion lofoten northern norway

oscillatory zoned crystals of pyrochlore group minerals from the guaniamo kimberlites venezuela abstract oscillatory zoned crystals of pyrochlore group minerals are found in the la ceniza diamondiferous kimberlites guaniamo region venezuela this is the first known occurrence of the pyrochlore group minerals in kimberlites worldwide the minerals occur in the kimberlite groundmass in association with olivine zoned spinel phlogopite carbonates dolomite calcite magnesite apatite tetraferriphlogopite fe ni cu sulfides and serpentine they form discrete octahedral crystals or intergrowths up to 50 m with a red brown core and light brown rim individual zones in the cores are remarkably enriched in tio 2 up to 14 3 wt ta 2 o 5 up to 10 1 wt zro 2 up to 23 7 wt tho 2 up to 22 3 wt and uo 2 up to 8 0 wt at moderate nb 2 o 5 contents whereas the outer regions contain significant cao up to 17 5 wt na 2 o up to 5 7 wt nb 2 o 5 up to 58 9 wt and f up to 4 6 wt approaching the ideal formula na ca 2 nb 2 o 6 f following the ima recommendations and the 50 rule the interior is classified as uranoan zr rich thoriobetafite thoriopyrochlore or thorian zr rich betafite pyrochlore and the outer part as pyrochlore or thorian pyrochlore strong compositional zoning is consistent with two substitutions 2 th u 4 ti zr 4 o 2 3ca 2 nb 5 f oh and 2 th u 4 2 ti zr 4 o 2 2ca 2 na 2nb 5 f oh the zoning patterns and the absence of perovskite indicate the dominant role of f among fluid components and relatively high alkalinity during crystallization of the silicate carbonate groundmass of the la ceniza kimberlite the composition and zoning of the la ceniza pyrochlore group minerals are very specific but in general strongly resemble those of some pyrochlores from carbonatites

a gis based approach for gully erosion susceptibility modelling a test in sicily italy the aim of this study is to analyze the susceptibility conditions to gully erosion phenomena in the magazzolo river basin and to test a method that allows for driving the factors selection the study area is one of the largest 225 km2 watershed of southern sicily and it is mostly characterized by gentle slopes carved into clayey and evaporitic sediments except for the northern sector where carbonatic rocks give rise to steep slopes in order to obtain a quantitative evaluation of gully erosion susceptibility statistical relationships between the spatial distributions of gullies affecting the area and a set of twelve environmental variables were analyzed stereoscopic analysis of aerial photographs dated 2000 and field surveys carried out in 2006 allowed us to map about a thousand landforms produced by linear water erosion processes classifiable as ephemeral and permanent gullies the linear density of the gullies computed on each of the factors classes was assumed as the function expressing the susceptibility level of the latter a 40 m digital elevation model dem prepared from 1 10 000 scale topographic maps was used to compute the values of nine topographic attributes primary slope aspect plan curvature profile curvature general curvature tangential curvature secondary stream power index topographic wetness index ls usle factor from available thematic maps and field checks three other physical attributes lithology soil texture land use were derived for each of these variables a 40 m grid layer was generated reclassifying the topographic variables according to their standard deviation values in order to evaluate the controlling role of the selected predictive variables one variable susceptibility models based on the spatial relationships between each single factor and gullies were produced and submitted to a validation procedure the latter was carried out by evaluating the predictive performance of models trained on one half of the landform archive and tested on the other large differences of accuracy were verified by computing geometric indexes of the validation curves prediction and success rate curves roc curves drawn for each one variable model in particular soil texture general curvature and aspect demonstrated a weak or a null influence on the spatial distribution of gullies within the studied area while on the contrary tangential curvature stream power index and plan curvature showed high predictive skills hence predictive models were produced on a multi variable basis by variously combining the one variable models the validation of the multi variables models which generally indicated quite satisfactory results were used as a sensitivity analysis tool to evaluate differences in the prediction results produced by changing the set of combined physical attributes the sensitivity analysis pointed out that by increasing the number of combined environmental variables an improvement of the susceptibility assessment is produced this is true with the exception of adding to the multi variables models a variable as slope aspect not correlated to the target variable the addition of this attribute produces effects on the validation curves that are not distinguishable from noise and as a consequence the slope aspect was excluded from the final multi variables model used to draw the gully erosion susceptibility map of the magazzolo river basin in conclusion the research showed that the validation of one variable models can be used as a tool for selecting factors to be combined to prepare the best performing multi variables gully erosion susceptibility model

development and controlling factors of gullies and gully complexes east coast new zealand sequential aerial photographs of a small headwater catchment in the waiapu basin east coast region north island new zealand were interpreted to measure and analyse temporal changes in active area of gullies and gully complexes for a longer time span 1939 2003 and with higher temporal resolution compared to previous studies we focus on the conditions leading to the development of gullies and gully complexes under pasture and forest by using topographic thresholds slope area relationships of catchments for the initiation of gullies and gully complexes in addition the influence of two different lithologies as well as the occurrence of major rainfall events was related to gully activity twenty gullies and four gully complexes occupying 62 5 ha or 12 5 per cent of the catchment area occurred in the study catchment between 1939 and 2003 however the majority of these were not active at all of the dates studied gullies developed in the sandstone dominated tapuwaeroa formation tended to attain their maximum size by 1957 with a mean catchment area of 2 1 ha gullies developed in mudstone of the whangai formation attained their maximum size in 1939 with a mean catchment area of 4 31 ha exceptions are gullies which developed into mass movement deposits or into an earth flow deposit as well as gullies developed under indigenous forest topographic threshold values for gullies under pasture and indigenous forest show that values for gullies under forest plot far above the threshold line of gullies under pasture indicating that the topographical threshold for gully development under forest is higher compared to under pasture a threshold value of 9 4 ha in catchment area is needed for the development of gully complexes under pasture all located in the whangai formation and with the same orientation as the strike of the mudstones gully complex area and dominance of mass movement erosion increased with larger catchment area a decreasing distance to the threshold line for gullies under pasture indicates a later development for gully complexes no gully complexes developed under indigenous forest indicating that the threshold value for gully complex development is higher than for gully complexes under pasture and was not reached in the study area a model of shifting topographical threshold for gully development for a given catchment is developed which depends on land use when a catchment has an indigenous forest cover the topographical threshold is very high after conversion to pasture threshold values decrease drastically with the invasion of scrub the threshold slowly increases and returns to a similar level to that under indigenous forest after reforestation development of gullies and gully complexes is a highly dynamic phenomenon and phases of expansion and inactivity indicate that models describing only unidirectional advancing stages without periods of inactivity are not suitable therefore this study adds more phases to models of gully and gully complex development in the east coast region the threshold line for gully initiation under pasture and a value of 9 4 ha in catchment area for gully complex initiation permits one to predict which catchments under similar environmental settings develop gullies and gully complexes on a physical basis this enables land managers to implement sustainable land use strategies to reduce erosion rates of gullies and gully complexes copyright 2006 john wiley sons ltd

crystalline inclusions and c isotope ratios in diamonds from the snap lake king lake kimberlite dyke system evidence of ultradeep and enriched lithospheric mantle abstract u type paragenesis inclusions predominate 94 7 among the crystalline inclusion suite of 115 diamonds 4 2 mm obtained from the recently discovered snap lake king lake skl kimberlite dyke system southern slave canada the most common inclusions are olivine 90 and enstatite 22 sulfide cr pyrope chromite and cr diopside inclusion are less abundant 15 10 5 and 1 respectively results of the inclusion composition study demonstrate the following a the relatively enriched character of the mantle parent rocks of the u type diamonds the average mg of olivine inclusions is 92 1 and of enstatite inclusions average 93 3 cao content in cr pyrope inclusions is relatively high 3 73 5 75 wt b four of ten u type cr rich pyrope inclusions contain a majoritic component up to 16 8 mol which requires pressures of 110 kbar carbon isotopes compositions for 34 diamonds with u type inclusions have a 13c range from 3 2 to 9 with a strong peak around 3 5 this is much heavier than the ratios of u type diamonds from siberia and south africa 4 5 diamonds with olivine inclusions can be divided into two groups based on their 13c values as well as the mg and ni fe ratio in the olivines most show a narrow range of 13c values from 3 2 to 4 8 average 3 72 and have olivine inclusions with mg less than 92 3 and relatively high fe ni ratios a second group is characterized by a much wider variation of c isotope composition 13c varies from 3 8 to 9 0 average 5 97 and the olivine inclusions having a higher mg up to 93 6 and relatively low fe ni ratios this difference in the c isotope composition may have several explanations a peculiarities of asthenosphere degassing coupled with an abnormal thickness of lithosphere b the abnormal thickness and enriched character of lithospheric mantle c involvement of subducted c of crustal origin in the processes of the diamond formation the presence of subcalcic cr rich majorite up to 17 mol pyropes of low ca harzburgite paragenesis among the crystalline inclusion suite of skl diamonds is strong evidence for the existence of diamondiferous depleted peridotite in lithospheric mantle at depth near 300 km beneath southern slave area and is postulated to be one of the main reasons for the much heavier c isotope composition of skl u type diamonds in comparison with those from siberian and south african kimberlites

unusual paired pattern of radiohaloes on a diamond crystal from guaniamo venezuela abstract an octahedral diamond crystal from guaniamo venezuela shows a multitude of round radiocolouration spots that indicate a remarkable formation history spots always occur in pairs with similar spacing and intensity ratio between the two spots of each pair we interpret this pattern to be the result of long term irradiation of the stone emanating from a multitude of radioactive point sources at some point during the irradiation the stone must have experienced a translational movement which shifted it ca 50 m relative to the adjacent material i e the 111 crystal face was a fault plane after which irradiation continued the neoproterozoic age of the guaniamo kimberlites and the high degree of radiation damage suggest that both of the two irradiation periods lasted over hundreds of millions of years this interpretation is supported by results of he irradiation experiments

evidence of subduction and crust mantle mixing from a single diamond abstract cathodoluminescence cl imaging of polished sections of a diamond from the guaniamo region of venezuela suggests a history of the diamond involving two periods of growth separated by a period of resorption and possibly brittle deformation in situ electron probe analysis of multiple eclogitic garnet inclusions reveals a correlation between garnet composition and location in the stone an early formed garnet in the diamond core has higher ca ca mg and lower mg mg fe values than later garnets associated with the second period of diamond growth this variation conforms to an extensive trend of variation in the suite of eclogitic garnets extracted from venezuelan diamonds the diamond is zoned in carbon isotope composition in situ secondary ion mass spectrometry sims data the core compositions 13c pdb corresponding to the first stage of growth average 17 7 the second period of growth is apparently in two sub sets of cl zones with mean values of 13 0 and 7 9 nitrogen contents of diamond are low 30 300 atomic ppm and do not correlate with carbon isotope composition oxygen isotope ratios of the garnet inclusions are elevated substantially above those expected for common mantle 18o vsmow of early garnet is approximately 10 5 and two late garnets average 8 8 the evolutionary trend of magnesium enrichment in garnet is unlikely to represent igneous fractionation the stable isotope data are consistent with diamond formation in subducted meta basic rocks that had interacted with sea water at low temperatures at or near the sea floor and contained a substantial biogenic carbon component during or following subduction diamonds continued to form in an evolving system that was progressively modified by interaction with mantle material

suitability of lidar point density and derived landform curvature maps for channel network extraction this study uses landform curvature as an approach for channel network extraction we considered a study area located in the eastern italian alps where a high quality set of lidar data was available and where channel heads and related channel network were mapped in the field in the analysis we derived 1 m dtms from different ground lidar point densities and we used different smoothing factors for the landscape curvature calculation in order to test the suitability of the lidar point density and the derived curvature maps for the recognition of channel network this methodology is based on threshold values of the curvature calculated as multiples 1 3 times of the standard deviation of the curvature our analyses suggested that i the window size for curvature calculations has to be a function of the size of the features to be detected ii a coarse ground lidar point density could be as useful as a finer one for the recognition of main channel network features and iii rougher curvature maps are not optimal as they do not explore a sufficient range at which features occur while smoother curvature maps overcome this problem and are more appropriate for the extraction of surveyed channels copyright 2010 john wiley sons ltd

rapid development and infilling of a buried gully under cropland central belgium abstract analysis of contemporary and past gully erosion and infilling processes allowed to reconstruct the long term evolution of a permanent gully system under cropland an active and a buried gully under cropland were investigated the recent sediment deposits within the active gully adjacent to the buried gully showed that the recent gully was filling in at a mean rate of 6 4 cm a 1 in the buried gully several erosion and deposition phases could be identified and the type of deposited sediments revealed a complex infilling history charcoal pottery and brick fragments of different sizes were found at all depths of the gully infilling their age indicates that the first gully incised after the midst of the 17th century most probably in the second half of the 18th century or the early 19th century gully morphology and analogy with the processes in the recent gully indicate that the buried gully filled in rapidly overall five cycles of cut and fill occurred in 350 years or less and four cycles even within little less than a few decades indicating that gully development and infilling under cropland can be very rapid processes

phase relations in the camgsi 2 o 6 kalsi 3 o 8 join at 6 and 3 5 gpa as a model for formation of some potassium bearing deep seated mineral assemblages the join camgsi2o6 kalsi3o8 has been studied at 6 gpa 890 1 500 c and 3 5 gpa 1 000 1 100 c k rich melts in the join produce assemblages cpx grt cpx opx cpx san and cpx grt san at 1 100 1 300 c at nsansystem 90 mol this explains a scarcity of san in mantle cpx rich assemblages and its association with high k aluminosilicate melt inclusions in diamonds in absence of san kcpx is the only host for potassium the k jadeite content in kcpx systematically increases with decreasing temperature and reaches 10 12 mol near the solidus however kcpx coexists with san at nsansystem 70 mol and 4 gpa to cpx san at p 4 gpa similar sequence of assemblages is observed in some eclogitic xenoliths from kimberlites and grt cpx rocks of the kokchetav complex northern kazakhstan

eskolaite associated with diamond from the udachnaya kimberlite pipe yakutia russia the mineral eskolaite cr 2 o 3 has been discovered in association with natural diamond from the udachnaya pipe in yakutia where it is intergrown with an octahedral diamond mostly as an inclusion in the diamond but also exposed at its surface a detailed study was performed on fragments extracted from the outer surface of the diamond using single crystal x ray diffraction xrd high resolution electron microscopy hrtem analytical electron microscopy aem including line scan and elemental mapping emp and sims these applied techniques confirmed the nature of the eskolaite with 86 8 wt cr 2 o 3 and notable impurities of tio 2 3 99 wt al 2 o 3 2 00 wt fe 2 o 3 5 83 wt and mgo 1 11 wt trace elements including v 4900 ppm mn 129 ppm zr 56 ppm and nb 32 ppm were also detected the entire range of ree is just at or below the limits of detection a small picrochromite inclusion x mg 81 2 y cr 94 7 was detected in the eskolaite its chemistry is typical of chromite diamond inclusions it also contains minute inclusions of perovskite corundum and an unidentified ti phase nano sized cavities in picrochromite were determined to consist of carbonate and quench products including si mg ca p k and cl this may represent relics of the diamond forming metasomatic fluids the eskolaite containing a picrochromite inclusion was formed at high pressure within the diamond stability field from c o h bearing fluids containing ca k cl p and possibly even peridotitic u type oxides and silicates

extreme crustal oxygen isotope signatures preserved in coesite in diamond the anomalously high and low oxygen isotope values observed in eclogite xenoliths from the upper mantle beneath cratons have been interpreted as indicating that the parent rock of the eclogites experienced alteration on the ancient sea floor1 recognition of this genetic lineage has provided the foundation for a model of the evolution of the continents whereby imbricated slabs of oceanic lithosphere underpin and promote stabilization of early cratons2 early crustal growth is thought to have been enhanced by the addition of slab derived magmas leaving an eclogite residuum in the upper mantle beneath the cratons3 but the oxygen isotope anomalies observed in eclogite xenoliths are small relative to those in altered ocean floor basalt and intermediate stage subduction zone eclogites and this has hindered acceptance of the hypothesis that the eclogite xenoliths represent subducted and metamorphosed ocean floor basalts we present here the oxygen isotope composition of eclogitic mineral inclusions analysed in situ in diamonds using an ion microprobe secondary ion mass spectrometer the oxygen isotope values of coesite a polymorph of sio2 inclusions are substantially higher than previously reported for xenoliths from the subcratonic mantle but are typical of subduction zone meta basalts and accordingly provide strong support for the link between altered ocean floor basalts and mantle eclogite xenoliths

neoproterozoic anomalous kimberlites of guaniamo venezuela mica kimberlites of isotopic transitional type in venezuela kimberlites have so far only been found in the guaniamo region where they occur as high diamond grade sheets in massive to steeply foliated paleoproterozoic granitoid rocks the emplacement age of the guaniamo kimberlites is 712f6 ma i e neoproterozoic the guaniamo kimberlites contain a high abundance of mantle minerals with greater than 30 olivine macrocrysts the principal kimberlite indicator minerals found are pyrope garnet and chromian spinel with the overwhelming majority of the garnets being of the peridotite association chrome diopside is rare and picroilmenite is uncommon chemically the guaniamo kimberlites are characterized by high mgo contents with low al2o3 and tio2 contents and higher than average feo and k2o contents these rocks have above average ni cr co th nb ta sr and lree concentrations and very low p yand particularly zr and hf contents the nb zr ratio is very distinctive and is similar to that of the aries australia kimberlite the guaniamo kimberlites are similar in petrography mineralogy and mantle mineral content to ilmenite free group 2 mica kimberlites of south africa the nd sr isotopic characteristics of guaniamo kimberlites are distinct from both kimberlite group 1 and group 2 being more similar to transitional type kimberlites and in particular to diamondiferous kimberlites of the arkhangelsk diamond province russia the guaniamo kimberlites form part of a compositional spectrum between other standard kimberlite reference groups they formed from metasomatised subcontinental lithospheric mantle and it is likely that subduction of oceanic crust was the source of this metasomatised material and also of the eclogitic component which is dominant in guaniamo diamonds d 2004 published by elsevier b v

recycling of crustal materials through study of ultrahigh pressure minerals in collisional orogens ophiolites and mantle xenoliths a review abstract newly recognized occurrences of ultrahigh pressure uh p minerals including diamonds in ultrahigh temperature uh t felsic granulites of orogenic belts in chromitites associated with ophiolitic complexes and in mantle xenoliths suggest the recycling of crustal materials through deep subduction mantle upwelling and return to the earth s surface this circulation process is supported by crust derived mineral inclusions in deep seated zircons chromites and diamonds from collision type orogens from eclogitic xenoliths in kimberlites and from chromitities of several alpine himalayan and polar ural ophiolites some of these minerals contain low atomic number elements typified by crustal isotopic signatures ophiolite type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone in addition to ringwoodite and inferred stishovite a number of nanometric minerals have been identified as inclusions employing state of the art analytical tools reconstitution of now exsolved precursor uh p phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier uh p conditions for example tibetan chromites containing exsolution lamellae of coesite diopside suggest that the original chromitites formed at p 9 10 gpa at depths of 250 300 km the precursor phase most likely had a ca ferrite or a ca titanite structure both are polymorphs of chromite and at 2000 c would have formed at minimum pressures of p 12 5 or 20 gpa respectively some podiform chromitites and host peridotites contain rare minerals of undoubted crustal origin including zircon feldspars garnet kyanite andalusite quartz and rutile the zircons possess much older u pb ages than the time of ophiolite formation these uh p mineral bearing chromitite hosts evidently had a deep seated evolution prior to extensional mantle upwelling and partial melting at shallow depths to form the overlying ophiolite complexes these new findings together with stable isotopic and inclusion characteristics of diamonds provide compelling evidence for profound underflow of both oceanic and continental lithosphere recycling of surface organic carbon into the lower mantle and ascent to the earth s surface through mantle upwelling intensified study of uh p granulite facies lower crustal basement and ophiolitic chromitites should allow a better understanding of the geodynamics of subduction and crustal cycling

the crustal structure of the guayana shield venezuela from seismic refraction and gravity data abstract we present results from a seismic refraction experiment on the northern margin of the guayana shield performed during june 1998 along nine profiles of up to 320 km length using the daily blasts of the cerro bolivar mines as energy source as well as from gravimetric measurements clear moho arrivals can be observed on the main e w profile on the shield whereas the profiles entering the oriental basin to the north are more noisy the crustal thickness of the shield is unusually high with up to 46 km on the archean segment in the west and 43 km on the proterozoic segment in the east a 20 km thick upper crust with p wave velocities between 6 0 and 6 3 km s can be separated from a lower crust with velocities ranging from 6 5 to 7 2 km s a lower crustal low velocity zone with a velocity reduction to 6 3 km s is observed between 25 and 25 km depth the average crustal velocity is 6 5 km s the changes in the bouguer anomaly positive 30 mgal in the west and negative 20 mgal in the east cannot be explained by the observed seismic crustal features alone lateral variations in the crust or in the upper mantle must be responsible for these observations

factors related to gully erosion in woody encroachment in south eastern australia abstract gullies initiate when the equilibrium within a drainage line is upset by increased discharge or decreased soil resistance to detachment and transport of soil particles and is triggered and accelerated by human induced changes to vegetation cover woody encroachment is the increase in density cover extent and biomass of woody plants and can result in low ground cover which increases the potential of soil erosion this paper reports the relationships between gully erosion and site characteristics such as topography vegetation cover and road infrastructure in a 120 km study area of semi arid woodland subject to woody encroachment in south eastern australia this study characterised gully morphology and activity identified the factors related to gully volume and estimated the topographic thresholds for sub catchments subject to woody encroachment firstly relationships between gully volume activity topography vegetation cover and road infrastructure were explored secondly site characteristics of 32 sub catchments with and without gullies were compared finally the topographic thresholds for unstable and stable sub catchments with and without gullies respectively were estimated using the slope drainage area relationship s aa b all gullies were active and high gully volume was related to large sub catchments long gullies and short distances to roads stable sub catchments without gullies had gentler slopes higher foliage projective cover and ground cover than unstable sub catchments with gullies when data for sub catchments with and without gullies were combined the main factors related to gully volume were drainage area at the gully or stream heads and their local slope and ground cover the mean topographic threshold for gully development provided insights into the drainage area and slope conditions needed for gully development gully erosion in the study area is most likely the result of interactions among topography vegetation and human made structures roads in space and time the results of the study advance our understanding of gully erosion dynamics in areas of woody encroachment and can be used to identify areas susceptible to gullying

predicting the susceptibility to gully initiation in data poor regions permanent gullies are common features in many landscapes and quite often they represent the dominant soil erosion process once a gully has initiated field evidence shows that gully channel formation and headcut migration rapidly occur in order to prevent the undesired effects of gullying there is a need to predict the places where new gullies might initiate from detailed field measurements studies have demonstrated strong inverse relationships between slope gradient of the soil surface s and drainage area a at the point of channel initiation across catchments in different climatic and morphological environments such slope area thresholds s a can be used to predict locations in the landscape where gullies might initiate however acquiring s a requires detailed field investigations and accurate high resolution digital elevation data which are usually difficult to acquire to circumvent this issue we propose a two step method that uses published s a thresholds and a logistic regression analysis lr s a thresholds from the literature are used as proxies of field measurement the method is calibrated and validated on a watershed close to the town of algiers northern algeria where gully erosion affects most of the slopes the gullies extend up to several kilometres in length and cover 16 of the study area first we reconstruct the initiation areas of the existing gullies by applying s a thresholds for similar environments then using the initiation area map as the dependent variable with combinations of topographic and lithological predictor variables we calibrate several lr models it provides relevant results in terms of statistical reliability prediction performance and geomorphological significance this method using s a thresholds with data driven assessment methods like lr proves to be efficient when applied to common spatial data and establishes a methodology that will allow similar studies to be undertaken elsewhere

modelling the occurrence of gullies in rangelands of southwest spain gully erosion has been recognized as an important soil degradation process in rangelands of southwest spain in this paper a relatively new data mining technique called multivariate adaptive regression splines mars was applied to construct a model capable of predicting the location of gullies a large database was used to support the model composed of a target variable presence or absence of gullies and 36 independent variables related to topography lithology soils rainfall land use and vegetation cover the performance of the model was evaluated using the receiver operating characteristic roc curve for five external datasets the model had high predictive power with values for the area under the roc curve of the external validation datasets varying from 0 75 to 0 98 1 0 being perfect prediction the most important variables explaining the spatial distribution of gullies were lithology and soil type finally the model was compiled and implemented into a geographical information system to obtain maps of susceptible areas for gully erosion these maps show that approximately 7 of the study area presents favourable conditions for the development of gullies the results demonstrate that mars constitutes a valuable model in geomorphic research and could also be a useful tool for assessing the impacts of changing climate and land use on gully erosion copyright 2009 john wiley sons ltd

the history of soil erosion and fluvial deposits in small catchments of central europe deciphering the long term interaction between humans and the environment a review abstract during the last few decades many case studies focused on the dynamics of fluvial systems in response to hillslope erosion land use impact and climate changes this paper will review the current state of knowledge of the dynamics of past soil erosion and gullying in small catchments

micrometer scale cavities in fibrous and cloudy diamonds a glance into diamond dissolution events abstract micrometer sized internal cavities in diamonds preserve evidence of diamond dissolution events combining the methods of focused ion beam fib sample preparation and transmission electron microscopy tem enables these features to be studied in detail micrometer scale cavities are found in the inner parts of fibrous and cloudy kimberlitic diamonds their filling consists of amorphous matrix secondary nano crystals volatiles and in some cases larger resorbed crystals trapped minerals include corundum kappa alumina quartz olivine moissanite 6h and ca mg carbonates this is the first observation of kappa alumina in nature secondary nano minerals are observed within the amorphous matrix and include carbonates al oxide fluorite ilmenite and secondary diamond crystals the amorphous matrix is spongy and its composition is dominated by amorphous carbon nitrogen chlorine and also contains water when no crystalline phases are observed the matrix is also enriched in alumina silica and in some cases calcium we propose that micrometer scale cavities in diamonds form during dissolution events induced by the introduction of oxidizing hydrous fluids into the diamond growth area hydrous fluids are the main dissolving agents for most kimberlitic diamonds fedortchouk y canil d semenets e 2007 mechanisms of diamond oxidation and their bearing on the fluid composition in kimberlite magmas am mineral 92 1200 1212 at diamond forming conditions silica and alumina are enriched in hydrous fluids that are in equilibrium with eclogites kessel r ulmer p pettke t schmidt m w thompson a b 2005 the water basalt system at 4 to 6 gpa phase relations and second critical endpoint in a k free eclogite at 700 to 1400 c earth planet sci lett 237 873 892 this is consistent with the increased solubility of alumina with increased pressure and temperature in the na cl bearing fluids manning c e 2006 mobilizing aluminum in crustal and mantle fluids j geochem explor 89 251 253 manning c e 2007 solubility of corundum kyanite in h2o at 700c and 10 kbar evidence for al si complexing at high pressure and temperature geofluids 7 258 269 additionally hydrous fluids may leach grain boundaries that are enriched in alumina in peridotitic environments hiraga t anderson i m kohlstedt d l 2004 grain boundaries as reservoirs of incompatible elements in the earth s mantle nature 427 699 703 wirth r 1996 thin amorphous films 1 2 nm at olivine grain boundaries in mantle xenoliths from san carlos arizona contrib mineral petrol 124 44 54 diamond dissolution will form oxidized carbon species and may decrease the solubility of silica and alumina in the dissolving agent leading to their precipitation diamond forming fluids that are trapped in sub micrometer inclusions in the same fibrous diamonds are the dominant fluid component in the diamond growth area corrosive hydrous fluids are less common and appear as short discrete events followed by the return of the common diamond forming fluids and continued diamond precipitation

nano inclusion suite and high resolution micro computed tomography of polycrystalline diamond framesite from orapa botswana abstract a single polycrystalline diamond aggregate from the orapa kimberlite botswana contains a syngenetic micro and nano inclusion suite of magnetite pyrrhotite omphacite garnet rutile and c o h fluid in order of abundance this suite of inclusions is distinctly different from those in fibrous diamonds although the presence of sub micrometer fluid inclusions provides evidence for a similarly important role of fluids in the genesis of polycrystalline diamond it is the first study of polycrystalline diamond by high resolution ct computed tomography reaching a resolution of 1 3 m using polychromatic x rays combined with focused ion beam assisted transmission electron microscopy the method reveals epigenetic replacement coatings of hematite and late stage sheet silicates around the magnetites showing that magnetites are often but not always interstitial to the diamond and thus were open to late stage overprinting it is proposed that the polycrystalline diamond formed by a redox reaction between a small scale carbonatitic melt and a sulfide bearing eclogite the water released from the melt during diamond precipitation fluxed local melting of the surrounding eclogite and oxidation of sulfide phases to magnetite which mingled with the carbonatitic melt and re precipitated locally

layered mantle structure beneath the western guyana shield venezuela evidence from diamonds and xenocrysts in guaniamo kimberlites abstract mantle xenoliths and xenocrysts from guaniamo venezuela kimberlites record equilibration conditions corresponding to a limited range of sampling in the lithosphere 100 150 km within this small range however compositions vary considerably but regularly defining a strongly layered mantle sequence major and trace element compositions suggest the following lithologic sequence highly depleted lherzolite from 100 to 115 km mixed ultra depleted harzburgite and lherzolite from 115 to 120 km relatively fertile lherzolite from 120 to 135 km and mixed depleted harzburgite and relatively fertile lherzolite from 135 to 150 km based on comparison with well documented mantle peridotites and xenocrysts from elsewhere we conclude that the meso proterozoic cuchivero province host to the guaniamo kimberlites is underlain by depleted and ultra depleted shallow archean mantle that was underplated and uplifted by proterozoic subduction perhaps more than once these proterozoic subduction events introduced less depleted oceanic lithosphere beneath the archean section which remains there and is the source of the abundant guaniamo eclogite suite diamonds that have ocean floor geochemical signatures although diamond indicative low ca cr pyrope garnets are abundant they are derived primarily from the shallow depleted layer within the field of graphite stability and the rare peridotite suite diamonds are either metastably preserved at these shallow depths or were derived from the small amount of depleted lithosphere sampled by these kimberlites that remains within the diamond stability field the mixture of archean and proterozoic mantle in the depth range 135 150 km

unusual upper mantle beneath guaniamo guyana shield venezuela evidence from diamond inclusions the geochemistry of mineral inclusions in diamond is an important source of information about the composition of the continental lithospheric mantle at depths exceeding 120 150 km at these depths two main types of geochemical environment support diamond formation they are ultramafic or peridotitic u type and eclogitic e type environments as shown by minerals that occur as inclusions in diamonds in primary diamond bearing kimberlite or lamproite rock the ratio of diamonds from these two geochemical environments varies widely between localities the u type environment dominates for the majority of diamond occurrences worldwide whereas the e type environment dominates for a very limited number of localities in south africa north america and australia the present study shows that an uncommonly high percentage 99 4 of e type diamonds with extremely variable inclusion assemblages is found in kimberlites in the northwestern part of the guyana shield at guaniamo venezuela these variations range from previously unknown silica undersaturated corundum eclogite to abundant silica rich coesite eclogite assemblages representing 22 of all e type diamonds some of which contain syngenetic ilmenite and magnetite the compositional variations of garnet and omphacite inclusions are extremely broad the wide variability of the eclogitic source in which diamonds formed beneath the guyana shield indicates a broadly basaltic chemistry in this environment which may represent ancient subducted oceanic crust such specific features have not been reported for any other diamond occurrence and reflect an unusual composition of the deep lithospheric mantle in this area