dolomitic slates from uruguay petrophysical and petromechanical characterization and deposit evaluation slates are internationally known as roof and facade cladding material since prehistoric times the methods required to mine and manufacture these dimensional stones are relatively simple in comparison to those utilized in granitic dimensional stones this has led to a worldwide rentable commercialization of slate in the last centuries and also to the development of characteristic cultural landscapes in uruguay several slates are mined and used in architecture especially as facade cladding and floor slabs the most important slates regarding their production and utilization are the dolomitic slates these dolomitic slates are associated with the neoproterozoic thrust and fold belt of the dom feliciano belt representative samples have been geochemically and petrographically characterized as well as petrophysically and petromechanically analyzed the petrophysical and petromechanical properties were investigated in a very systematic way with respect to the new european standards showing values comparable to those registered for internationally known slates detailed structural and deposit analysis were carried out in uruguay in order to evaluate the dolomitic slate deposits the slates are linked to calc silicate strata in a greenschist facies volcano sedimentary sequence and the deposits are located in the limb of a regional fold where bedding and cleavage are parallel the main lithotype is a layered and fine grained dolomitic slate with a quite diverse palette of colors light and dark green gray dark gray reddish and black the mined slate is split into slabs 0 5 2 cm thick in the past the average production in uruguay was around 4 000 tons year and a historical maximum of 13 000 tons was reached in 1993 oyhantcabal et al in z dt ges geowiss 158 3 417 428 2007 the oscillations in the regional demand were the cause of several flourishing and decay cycles in the activity but our investigation shows a considerable volume of indicated resources and therefore a very good potential

the initiation and development of metamorphic foliation in the otago schist part 1 competitive oriented growth of white mica the 3d shape size and orientation data for white mica grains sampled along two transects of increasing metamorphic grade in the otago schist new zealand reveal that metamorphic foliation as defined by mica shape preferred orientation spo developed rapidly at sub greenschist facies conditions early in the deformation history the onset of penetrative strain metamorphism is marked by the rapid elimination of poorly oriented large clastic mica in favour of numerous new smaller grains of contrasting composition higher aspect ratios and a strong preferred orientation the metamorphic mica is blade shaped with long axes defining the linear aspect of the foliation and intermediate axes a partial girdle about the lineation once initiated foliation progressively intensified by an increase in the aspect ratio size and alignment of grains although highest grade samples within the chlorite zone record a decrease in aspect ratio and reduction in spo strength despite continued increase in grain size these trends are interpreted in terms of progressive competitive anisotropic growth of blade shaped grains so that the fastest growth directions and blade lengths tend to parallel the extension direction during deformation the competitive nature of mica growth is indicated by the progressive increase in size and resultant decrease in number of metamorphic mica with increasing grade from c 1000 relatively small mica grains per square millimetre of thin section at lower grades to c 100 relatively large grains per square millimetre in higher grade samples reversal of spo intensity and grain aspect ratio trends in higher grade samples may reflect a reduction in the strain rate or reduction in the deviatoric component of the stress field

estimating groundwater exchange with lakes 1 the stable isotope mass balance method groundwater inflow and outflow contributions to the hydrologic budget of lakes can be determined using a stable isotope 18o 16o mass balance method the stable isotope method provides a way of integrating the spatial and temporal complexities of the flow field around a lake thereby offering an appealing alternative to the traditional time and labor intensive methods using seepage meters and an extensive piezometer network in this paper the method is applied to a lake in northern wisconsin demonstrating that it can be successfully applied to lakes in the upper midwest where thousands of similar lakes exist inflow and outflow rates calculated for the wisconsin lake using the isotope mass balance method are 29 and 54 cm yr respectively which compare well to estimates derived independently using a three dimensional groundwater flow and solute transport model of 20 and 50 cm yr such a favorable comparison lends confidence to the use of the stable isotope method to estimate groundwater exchange with lakes in addition utilization of stable isotopes in studies of groundwater lake systems lends insight into mixing processes occurring in the unsaturated zone and in the aquifer surrounding the lake and verifies assumed flow paths based on head measurements in piezometers

temporal geomagnetic and related attributes of kimberlite magmatism at ekati northwest territories canada abstract this paper outlines the development of a multi disciplinary strategy to focus exploration for economic kimberlites on the ekati property high resolution aeromagnetic data provide an over arching spatial and magnetostratigraphic framework for exploration and kimberlite discovery at ekati and hence also for this investigation the temporal geomagnetic spatial and related attributes of kimberlites with variable diamond content have been constrained by judiciously augmenting the information gathered during routine exploration with detailed laboratory based or field based investigations the natural remanent magnetisation of 36 ekati kimberlites has been correlated with their age as determined by isotopic dating techniques and placed in the context of a well constrained geomagnetic polarity timescale kimberlite magmatism occurred over the period 75 to 45 ma in at least five temporally discrete intrusive episodes based on current evidence the older kimberlites 75 to 59 ma have low diamond contents and are distributed throughout the property younger kimberlites 56 to 45 ma have moderate to high diamond contents and occur in three distinct intrusive corridors with nne to ne orientations economic kimberlite pipes erupted at 55 4 0 4 ma along the a154 lynx intrusive corridor which is 7 km wide and oriented at 015 and at 53 2 0 3 ma along the panda intrusive corridor which is 1 km wide and oriented at 038 the intrusion ages straddle a paleopole reversal at chron c24n consistent with the observation that the older economic kimberlites present as aeromagnetic low anomalies while the younger economic pipes are characterised as aeromagnetic highs the aeromagnetic responses for these kimberlites are generally muted because they contain volcaniclastic rock types with low magnetic susceptibility kimberlites throughout the ekati property carry a primary natural magnetic remanence nrm vector in ti bearing groundmass magnetite and it dominates over vectors related to induced magnetisation magnetostratigraphic correlation of ekati kimberlites may therefore present a powerful adjunct to existing exploration techniques mainly because the diamond content of ekati kimberlites apparently is related more to the age of eruption than to any other parameter investigated in this work

influence of changing atmospheric circulation on precipitation δ18o temperature relations in canada during the holocene postglacial precipitation 18o history has been reconstructed for two regions of canada long term shifts in the oxygen isotope composition of annual precipitation 18op in southern ontario appear to have occurred with a consistent isotope temperature relation throughout the past 11 50014c yr the modern isotope temperature relation in central canada near present boreal treeline evidently became established between 5000 and 4000 years ago although the relation during the last glacial maximum and deglaciation may also have been similar to present in the early holocene however unusually high 18opapparently persisted in spite of low temperature locally probably associated with high zonal index a rudimentary sensitivity analysis suggests that a small reduction in distillation of moisture in pacific air masses traversing the western cordillera perhaps accompanied by a higher summer winter precipitation ratio could have been responsible for the observed effect equivalent isotope temperature anomalies apparently occurred elsewhere in western north america in response to changing early holocene atmospheric circulation patterns suggesting that a time slice map of 18opfor north america during this period might provide a useful target for testing and validation of atmospheric general circulation model simulations using isotopic water tracers

geochemistry and origin of early proterozoic dongargarh rapakivi granite complex central india an example for magma mixing and differentiation abstract early proterozoic dongargarh granite complex of central india intruding the tonalitic to granodioritic amgaon gneisses and the nandgaon group bimodal volcanic suite comprises three different textural and compositional types viz porphyritic granodiorite pg coarse equigranular granite eg and microgranite mg synplutonic mafic dykes are common in the granite complex the pg is characterised by rapakivi texture and the eg is the dominant facies and exhibits sporadically developed rapakivi texture microgranular enclaves are common in the eg while they are rare in pg major and trace element geochemistry of pg shows marked i type and some occasional a type granite characters unusual for a rapakivi granite while the eg shows a type granite signatures the field petrographic chemical and isotopic data of these granites suggest their derivation by mixing of mantle derived basic magma with a crustal derived partly crystalline granitic magma episodic mafic magma underplating caused the anatexis of the archaean lower continental crust in a continental margin tectonic setting resulting first in the formation of the i type granodiorite followed by a type granite the i type granodiorite is mixed with the basic magma synplutonic dykes while the eg is formed by mingling of a type granite magma and the intruding basic magma

the influence of volcanological and sedimentological processes on diamond grade distribution in kimberlites examples from the ekati diamond mine nwt canada the distribution of diamonds within individual kimberlite pipes is poorly documented in the public domain due to the proprietary nature of the data the study of the diamond distribution within two pipes fox and koala from the ekati diamond mine nwt canada in conjunction with detailed facies models has shown several distinct relationships of deposit type and grade distribution in both pipes the lithological facies represent grade units which can be distinguished from each other in terms of relative size and abundance of diamonds a positive relationship between olivine grain size and abundance with diamond size and abundance is observed indicating that sorting of fragmental kimberlites influences diamond distribution though surface geological processes do not control the diamond potential of the erupting magma they can be responsible for concentrating diamonds into economically significant proportions a good understanding of the eruption transport and depositional processes responsible for the individual lithological units and the diamond distribution within them is important for successful resource estimation this may lead to recognition of areas suitable for selective mining making a marginal deposit economic

chalcophile and platinum group element pge concentrations in the sulfide minerals from the mccreedy east deposit sudbury canada and the origin of pge in pyrite magmatic sulfide deposits consist of pyrrhotite pentlandite chalcopyrite pyrite and platinum group minerals pgm understanding the distribution of the chalcophile and platinum group element pge concentrations among the base metal sulfide phases and pgm is important both for the petrogenetic models of the ores and for the efficient extraction of the pge typically pyrrhotite and pentlandite host much of the pge except pt which forms pt minerals chalcopyrite does not host pge and the role of pyrite has not been closely investigated the ni cu pge ores from the south range of sudbury are unusual in that sulfarsenide pgm rather than pyrrhotite and pentlandite are the main carrier of pge probably as the result of arsenic contribution to the sulfide liquid by the as bearing metasedimentary footwall rocks in comparison the north range deposits of sudbury such as the mccreedy east deposit have as poor granites in the footwall and the ores commonly contain pyrite our results show that in the pyrrhotite rich ores of the mccreedy east deposit os ir ru rh ipge and re are concentrated in pyrrhotite pentlandite and surprisingly in pyrite this indicates that sulfarsenides which are not present in the ores were not important in concentrating pge in the north range of sudbury palladium is present in pentlandite and together with pt form pgm such as ptpd tebi 2 platinum is also found in pyrite two generations of pyrite are present one pyrite is primary and locally exsolved from monosulfide solid solution mss in small amounts 2 wt together with pyrrhotite and pentlandite this pyrite is unexpectedly enriched in ipge as pt and the concentrations of these elements are oscillatory zoned the other pyrite is secondary and formed by alteration of the mss cumulates by late magmatic hydrothermal fluids this pyrite is unzoned and has inherited the low concentrations of ipge and re from the pyrrhotite and pentlandite that it has replaced

what controls sheet intrusion in volcanoes structure and petrology of the stromboli sheet complex italy abstract a multidisciplinary study has been conducted on 109 intrusive sheets of stromboli the relation between sheet injection conditions with the magmatic and structural variations of the volcano and the parameters governing the preferential intrusion geometry inside the volcano in a time perspective have been determined during its subaerial activity the last 100 ka stromboli experienced periods of extrusive growth and sheet intrusions alternated to caldera and lateral collapses of the nw sciara del fuoco flank the sheet intrusions similar to the extrusive rocks span a large compositional range from calc alkaline to potassic through high k calc alkaline and shoshonitic series the most evolved compositions of the effusive rocks however have not been found as intrusions whereas some mafic and basic magmas of sheets were never erupted the repeated time change of location of the intrusions from strombolicchio to the ne sw trend passing trough the inferred paleostromboli summit cone and the southern flank could represent the expression of the shift of the magma chamber towards the southeast and the subsequent onset of a clear ne sw elongated magma chamber located along the main stromboli weakness zone the stromboli evolution in the last 100 ka has been characterized by the persistent n 10 55 e intrusion direction which reflects the influence of the edifice s state of stress on the magma feeding paths after 13 ka ago sheets mainly intruded along to the sector collapse scarps in a circum amphitheatre geometry which has been demonstrated to be influenced by the new cone morphostructure and not by different magma rheological characters

the lami pyroclastic succession lipari aeolian islands a clue for unravelling the eruptive dynamics of the monte pilato rhyolitic pumice cone abstract the lami succession piled up during the explosive activity of the monte pilato on lipari island central aeolian arc italy it comprises a repetitive alternation of fall and pyroclastic density current beds which define 13 units separated by fine ash beds despite the homogeneous rhyolitic composition the juveniles fragments show strong textural heterogeneities from highly vesicular pumice to dense black obsidians the pumice types are termed i tube which shows elongated tubular vesicles ii frothy highly vesicular with large sub rounded vesicles and iii agglomerated and welded two types of obsidian pyroclasts are recognized i aphyric black obsidian and ii grey obsidian showing spherulitic texture all these pyroclastic types occur throughout the stratigraphic succession and mixed in the same bed they account for changing physical conditions along the conduit which is hypothesised to be filled by a melt plug during the eruption of 12 out of 13 units the strong textural heterogeneities of the juvenile fragments testify for the existence of differential shear rates which can be explained though two shear mechanism i simple shear producing horizontal zonation of texture in the conduit with black obsidians along the conduit walls passing to tube and frothy pumice to the centre and ii pure shear producing a vertical zonation in the conduit with black obsidians at the top overlying frothy pumice agglomerated and welded pumice of unit 13 is thought to represent the portion of magma heated by a batch of hotter melt that entered the magma chamber and triggered the eruption the deposits of unit 13 represent a unique case of spatter accretion due to accumulation of hot low viscous rhyolitic pumice fragments emplaced from pyroclastic fountaining

the geology and emplacement history of the pigeon kimberlite ekati diamond mine northwest territories canada abstract the pigeon kimberlite is located approximately 6 km to the northwest of the koala cluster of the ekati diamond mine and is presently one of ten kimberlite occurrences in the ekati resource development plan it was emplaced along a regional lithological contact between syn yellowknife supergroup granitoid rocks and yellowknife supergroup metasedimentary rocks that were covered by a now eroded veneer of poorly consolidated muddy sediments detailed age dating has not been undertaken however the emplacement age is inferred from sedimentary xenoliths present within the pipe to range between 45 75 ma pigeon is a small kimberlite body estimated to be approximately 3 5 ha at surface consisting of a steep sided pipe that can be separated into four main geological domains that are characterized by contrasting textures different diamond characteristics and unique mineral abundance and compositional signatures the uppermost portion of the body consists of mud rich resedimented volcaniclastic kimberlite that was formed by the deposition of extra crater deposits by debris flow type processes into an open diatreme texturally complex kimberlite is present within the lower portion of the kimberlite and includes rocks that display a range of features consistent with coherent magmatic and less common volcaniclastic fragmental rocks this texturally complex zone is interpreted to represent a clastogenic deposit formed by a low energy eruption within an open diatreme

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

hydrological factors in the interpretation of stable isotopic proxy data present and past a european perspective in the context of this paper stable isotopic proxies are those preserving directly or via known or calculable fractionation factors a record of 18o 16o and or 2h 1h in the water which contributed to their growth suitable proxies include amongst others tree ring cellulose bone phosphate lake sediment minerals and speleothem fluid inclusions a principal aim of studying isotopic proxies is to gain more information about past climates through a knowledge of how rainfall isotope compositions have changed over time however converting back from proxy to rainfall is not necessarily straightforward because however well the isotopic fractionation due to proxy growth or formation is understood a variety of modifying processes may have intervened between this and the actual rainfall events three main reservoirs of environmental water may contribute to the isotopic compositions of terrestrial proxy indicators surface waters soil moisture and groundwater each of these can in principle be isotopically modified compared to rainfall in the locality this review examines these effects and how they may change under different european climate types at the present day it is concluded that while groundwater isotopic compositions typically represent closely the bulk composition of rainfall under a variety of climatic regimes soil and particularly lake waters require detailed study if their isotope systematics are to be adequately understood the review also finds that to a large extent the present is the key to the past in terms of recharge processes during the late pleistocene though glaciation may have had profound isotopic consequences in certain areas while a more general aridity led to the apparent absence of recharge in most areas for much of the late devensian

the economic implications of kimberlite emplacement abstract the economic potential of kimberlite bodies is defined by the volume and diamond content of all their internal units which are summarised in three dimensional geological models canadian geological models reveal distinct types of kimberlite bodies characterised by fundamentally different emplacement processes and products data for representative samples of canadian kimberlites are used to show that qualitative and quantitative macroscopic petrography olivines and xenoliths are powerful and practical techniques in assessing the economic implications of emplacement within individual phases of kimberlite kimberlite bodies result from the near surface emplacement of multiple discrete batches of mantle derived magmas each carrying different diamond populations and in some instances subsequent resedimentation processes magmas containing 25 modal of olivine macrocrysts the average maximum load of solids that can be carried to surface by a kimberlite magma have the greatest potential to be significantly diamondiferous modifications to the abundance and size distribution of the olivine macrocrysts in each batch of magma commonly occur during emplacement the modifications to the olivine macrocrysts which vary with different emplacement processes and products are mirrored in the macrodiamond content dilution by xenoliths is important in predicting diamond contents but it is also reflected in reduced olivine contents thus olivine macrocrysts can act as a proxy for macrodiamonds the abundance and size distribution data for olivine can improve the prediction of diamond grade and distribution within and between kimberlite units summary geological models and macroscopic petrography together improve the evaluation of newly discovered bodies resulting in enhanced resource estimates and increased degrees of confidence

low stable isotope ratios of tropical cyclone rains tropical cyclone rains have distinctly lower stable isotope ratios than rains in other tropical and summer precipitation systems with a mean value slightly above that of water vapor near the sea surface the isotope ratios also decrease radially inward to the eye wall but appear to be anomalously low even near the periphery of the rain shield these findings indicate that tropical cyclones are highly efficient precipitation systems and suggest the use of stable isotope ratios as dynamic tracers of a tropical cyclone s water and energy budgets

hydrogen isotope ratios of recent lacustrine sedimentary n alkanes record modern climate variability abstract hydrogen isotope ratios were measured on n alkanes n c12 to n c31 extracted from recent lake surface sediments along a n s european transect to test if modern climate variability is recorded in these biomarkers d values of the n alkanes are compared to d values of meteoric water from the iaea gnip database spanning a range from 119 in northern sweden to 41 in southern italy to lake water d values and to mean annual temperatures varying between 2 0 c in the north and 13 7 c in the south d values of the short chained n alkanes n c12 to n c20 excluding algal derived n c17 and n c19 are higher in the north and lower in the south the isotopic fractionation e for hydrogen between meteoric water and the short chained n alkanes is increasing from n to s by more than 100 and is significantly correlated to mean annual temperature for n c16 and n c18 this suggests that these n alkanes may originate from a different source in the northern lakes possibly due to petroleum contamination or are synthesized using a different biochemical pathway the n c17 and n c19 alkanes of algal origin the n c21 and n c23 alkanes originating from water plants and the long chain n alkanes n c25 n c27 n c29 and n c31 of terrestrial origin clearly correlate with d values of meteoric water lake water and mean annual temperature indicating that they excellently record the d value of meteoric water the mean hydrogen isotope fractionation ec17 w of 157 sd 13 between n c17 and meteoric water is fairly constant over the wide range of different climates and lake environments suggesting only minor influence of environmental factors on this biochemical fractionation this suggests that d values of n c17 are suitable to reconstruct the isotopic composition of source water the mean fractionation between the long chain n alkanes and water is 128 sd 12 the mean difference of 31 between both e values is likely due to evaporative enrichment of deuterium in the leaf water if this is the only influence on the enrichment the difference between the d values of terrestrial and aquatic compounds might be suitable to reconstruct terrestrial evapotranspiration of the lake environment

characterization of tectono metamorphic events using crystal size distribution csd diagrams a case study from the acebuches metabasites sw spain crystal size is one of the main characteristics of a metamorphic rock since it is the result of several processes including prograde metamorphism as well as retrometamorphism and static and dynamic recrystallisation in this paper crystal size histograms mean crystal size crystal size distribution diagrams mean aspect ratio and proportion of prismatic sections of amphiboles have been used to describe two tectono metamorphic events that affected the acebuches metabasites in the southwestern part of the iberian massif the diagrams depicting the crystal size distribution csd of metamorphic rocks show typically a straight segment that reflects the kinetic conditions during prograde metamorphism as well as retrometamorphic and dynamic recrystallisation processes and a bell shaped curve formed during the last stages of growth the geometrical characteristics of the straight lines of csd diagrams from different samples of the acebuches metabasites vary consistently with the structural and metamorphic features indicative of the tectono metamorphic history suffered by these rocks this suggests that csd diagrams can be a useful tool of microstructural analysis in metamorphic rocks

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

experimental geochemical mineralogical and o isotope constraints on the late magmatic history of the fichtelgebirge granites germany mineralogical experimental geochemical and stable isotope data give evidence for an aqueous late stage fluid which develops increasingly from the less to the more highly evolved granites of the fichtelgebirge g1 g4 in less evolved granites particularly g1 only minor chloritization and sericitization minor hydration and corrosion of zircons low leachable fractions of sr and zr the nearly chondritic ratios of zr hf and y ho and rare earth element ree patterns lacking the tetrad effect provide evidence of a less differentiated granitic melt system poor in complexing agents and water with insignificant late magmatic fluid rock interaction the subsequent low temperature alteration which is suggested by oxygen isotope composition of quartz and biotite did not affect the whole rock chemical composition in the highly evolved granites particularly g4 albitization sericitization and fluoritization ubiquitous hydration and corrosion of zircons high leachable fractions of sr and zr zr hf and y ho ratios very different from the chondritic ratios and ree patterns showing a marked tetrad effect point to the presence of a highly specialized fluid system rich in water and complexing agents such as fluorine leading to a marked magmatic hydrothermal alteration the oxygen isotopes also indicate alteration by high temperature fluids which were likely exsolved during the final stage of crystallization

black dimensional stones geology technical properties and deposit characterization of the dolerites from uruguay dimensional stones with a black color occupy a prominent place on the international market uruguayan dolerite dikes of andesitic and andesitic basaltic compo sition are mined for commercial blocks of black dimen sional stones a total of 16 dikes of both compositions were studied and samples collected for geochemical and petro graphical analysis color measurements were performed on different black dimensional stones in order to compare them with the uruguayan dolerites samples of the two commercial varieties absolute black and moderate black were obtained for petrophysical analysis e g density porosity uniaxial compressive strength tensile strength etc detailed structural analyses were performed in sev eral quarries geochemistry and petrography determines the intensity of the black color the uruguayan dolerite absolute black is the darkest black dimensional stone analyzed in this study the petrophysical properties of uruguayan dolerites make them one of the highest quality black dimensional stones structural analyses show that five joint sets have been recognized two sub vertical joints one horizontal and two diagonal these joint sets are one of the most important factors that control the deposits since they control the block size distribution and the amount of waste material

canadian kimberlites geological characteristics relevant to emplacement in canada more than 770 kimberlites have erupted in diverse tectonic settings over a period of 1000 ma and over an area at least 5000 km across the kimberlites represent at least 30 comagmatic fields one pipe type dominates each of the different kimberlite fields even with the discovery of a significant number of new kimberlite fields this review of recent data substantiates the previous proposal that there are at least three distinct classes of kimberlite pipes which show a correlation with the nature of the country rocks into which they were emplaced new data show that a variation on the prairies pipe type occurs when kimberlites were emplaced into competent paleozoic sediments resulting in steeper sided pipes infilled with similar pyroclastic kimberlite new data for each pipe type are summarised and the contrasting characteristics of the three pipe types are considered to reflect fundamentally different styles of eruption and deposition apparently uniform near surface olivine and volatile rich kimberlite magmas were modified differently during the contrasting emplacement processes resulting in distinct textural rock types pyroclastic kimberlite pk tuffisitic kimberlite tk and associated hypabyssal kimberlite hk or resedimented kimberlite rvk dominating each type of pipe the substantiated correlation of pipe type with country rock geology could indicate variable constraints on volatile exsolution which affected the nature of the magmatic eruptions in different settings

structure and petrology of newly discovered volcanic centers in the northern kermadec southern tofua arc south pacific ocean 1 the nzaplume iii expedition of september october 2004 to the northern kermadec southern tofua nkst arc between 28 52 s and 25 07 s resulted in the discovery of at least seven new submarine volcanic centers and a substantial caldera complex adjacent to the previously known monowai seamount the volcanic centers form a sublinear chain that coincides with the kermadec ridge crest in the south hinetapeka and diverges 45 km westward of the ridge crest in the north v just to the south of where the louisville ridge intersects with the arc all of the centers contain calderas or caldera like structures as well as multiple cones domes fissure ridges and vent fields all show signs of recent eruptive and current hydrothermal activity there are strong structural controls on edifice location with cones and fissure ridges typically associated with faulting parallel to the regional 12 strike of the arc front several of the calderas are ellipsoidal orientated northwest southeast in the general direction of least compressive stress sampled volcanic rocks representing the most recently erupted lavas are all low k tholeiites two of the centers gamble and rakahore yielded only high silica dacite to rhyolite 69 74 wt silica whereas two others monowai and v yielded only basalt to andesite 48 63 wt silica mineral assemblages are plagioclase pyroxene dominated with accessory fe ti oxides apatite olivine and quartz tridymite cristobalite typical of dry volcanic arc systems hornblende occurs only in a felsitic rhyolite from hinepuia volcanic center and zircon is absent glass contents range to 57 in basalts andesites mean 20 and 97 in andesites rhyolites mean 59 and other quench textures including swallow tailed plumose or dendritic crystal forms and crystallites are common most lavas are highly vesicular 63 mean 28 and have low volatile contents mostly 2 wt which together with the occurrence of tridymite or cristobalite indicates explosive eruption and rapid cooling exceptions are rocks from u volcanic center which have low vesicularity and low glass contents across a wide compositional range indicating effusive eruption disequilibrium mineral textures the frequent occurrence of xenoliths and xenocrysts and macroscopic evidence for magma mingling indicate that many of the lavas are hybrids having resided only a short time in upper crustal reservoirs prior to eruption silicic magmas are major components of nkst arc volcanism and caldera formation is the dominant eruptive style the scale of silicic magmatism is in marked contrast to the dominant basaltic andesitic magmatism in the southern kermadec arc with evidence from other arcs silicic magmatism is now recognized as a major feature of intraoceanic arcs globally

climate change in the turkana basin as deduced from a 4000 year long δo18 record abstract a model of the oxygen isotopic composition of lake turkana waters sheds insight into the paleoclimatic interpretation of a 18 o profile of inorganic calcite from a core taken from the lake the model indicates that high frequency fluctuations seen in the isotopic record are probably due to shifts in lake level while the long term increase of 1 4 seen from 4 to 2 kyr bp cannot be due solely to lake level change it must be due to changes in other climatic parameters such as the isotopic composition of the inflow these findings suggests that the abrupt change observed in lake turkana and many other african lakes at 4 ka was the precursor to a 2000 year long adjustment in the climate over the ethiopian plateau the isotopic record from lake turkana agrees with other paleoclimate records from the basin including the diatom stratigraphy and radiocarbon dates on exposed shoreline deposits

asymmetric shape preferred orientations as shear sense indicators abstract mineral shape preferred orientations can be characterized by plotting aspect ratios against grain length orientation and such plots commonly display asymmetric patterns in xz sections perpendicular to foliation and parallel to the direction of maximum elongation in most cases the asymmetries cannot be discerned by superficial examination of thin sections the sense of asymmetry can be defined by a the shape of the highest aspect ratio per grain length orientation curve and b the relative orientations of the most elongate grain and the mean or median of the population as a whole observed senses of asymmetry display consistent relationships to known senses of shear and they therefore provide a useful alternative to or check on other methods of shear sense determination examples of quartz plagioclase microcline amphibole and biotite shape preferred orientations are described and they include recrystallized mosaics as well as populations of discrete mineral grains the examples include mineral preferred orientations that evolved by plastic deformation anisotropic crystal growth and mechanical rotation of inequidimensional grains

geology of the victor kimberlite attawapiskat northern ontario canada cross cutting and nested craters abstract the pipe shapes infill and emplacement processes of the attawapiskat kimberlites including victor contrast with most of the southern african kimberlite pipes the attawapiskat kimberlite pipes are formed by an overall two stage process of 1 pipe excavation without the development of a diatreme sensu stricto and 2 subsequent pipe infilling the victor kimberlite comprises two adjacent but separate pipes victor south and victor north the pipes are infilled with two contrasting textural types of kimberlite pyroclastic and hypabyssal like kimberlite victor south and much of victor north are composed of pyroclastic spinel carbonate kimberlites the main features of which are similar clast supported discrete macrocrystal and phenocrystal olivine grains pyroclastic juvenile lapilli mantle derived xenocrysts and minor country rock xenoliths are set in serpentine and carbonate matrices these partly bedded juvenile lapilli bearing olivine tuffs appear to have been formed by subaerial fire fountaining airfall processes the victor south pipe has a simple bowl like shape that flares from just below the basal sandstone of the sediments that overlie the basement the sandstone is a known aquifer suggesting that the crater excavation process was possibly phreatomagmatic in contrast the pipe shape and internal geology of victor north are more complex the northwestern part of the pipe is dominated by dark competent rocks which resemble fresh hypabyssal kimberlite but have unusual textures and are closely associated with pyroclastic juvenile lapilli tuffs and country rock breccias volcaniclastic kimberlite current evidence suggests that the hypabyssal like kimberlite is in fact not intrusive and that the northwestern part of victor north represents an early formed crater infilled with contrasting extrusive kimberlites and associated breccias the remaining main part of victor north consists of two macroscopically similar but petrographically distinct pyroclastic kimberlites that have contrasting macrodiamond sample grades the juvenile lapilli of each pyroclastic kimberlite can be distinguished only microscopically the nature and relative modal proportion of primary olivine phenocrysts in the juvenile lapilli are different indicating that they derive from different magma pulses or phases of kimberlite and thus represent separate eruptions the initial excavation of a crater cross cutting the earlier northwestern crater was followed by emplacement of phase i a low grade olivine phenocryst rich pyroclastic kimberlite and the subsequent eruption of phase ii a high grade olivine phenocryst poor pyroclastic kimberlite as two separate vents nested within the original phase i crater the second eruption was accompanied by the formation of an intermediate mixed zone with moderate grade thus the final pyroclastic pipe infill of the main part of the victor north pipe appears to consist of at least three geological macrodiamond grade zones in conclusion the victor kimberlite was formed by several eruptive events resulting in adjacent and cross cutting craters that were infilled with either pyroclastic kimberlite or hypabyssal like kimberlite which is now interpreted to be of probable extrusive origin within the pyroclastic kimberlites of victor north there are two nested vents a feature seldom documented in kimberlites elsewhere this study highlights the meaningful role of kimberlite petrography in the evaluation of diamond deposits and provides further insight into kimberlite emplacement and volcanism

systematics of internal zircon morphology in major variscan granitoid types the internal morphologies of zircon crystals from different types of granitoids alkaline calcalkaline and anatectic are revealed by cathodoluminescence imaging and are described in terms of growth rates of the crystal faces relative to each other zircons in the alkaline granitoids are characterized by high and constant growth rates of 010 relative to the pyramidal forms and by symmetric grwoth of 011 zircons in the calcalkaline and anatectic granitoids are characterized by fluctuating or gradually decreasing relative growth rates of 010 by asymmetric and highly variable growth of 011 and by a tendency of 110 to become grwoth inhibited corrosion events are interspersed during zircon growth in the calcalkaline magmas in the calcalkaline and anatectic magmas a discontinuity breaks the morphological evolution at late stages of crystallization the discontinuity coincides with a sharp drop in cathodoluminescence the growth behaviour of each crystal form is analysed and compared with predictions made by the periodic bond chain pbc theory it is argued that the relative growth rate of 010 depends on supersaturation that the growth rates of 011 faces are changed in response to different ratios of adsorbing cations na k al and that 110 faces become growth inhibited by the adsorption of h2o or trace elements enriched in the residual liquid morphological and chemical discontinuities at late stages of crystallization are reasonably explained by the formation of larger growth units from smaller ionic entities in the residual liquid important factors controlling the zircon morphology in different types of granitoids are high cooling rates alkaline magmas magma mixing calcalkaline magmas enrichment of h2o and trace elements in residual liquids calcalkaline and anatectic magmas and the major element chemistry of the magma possibly the ratio of na and k to al agpaicity

the effects of heterogeneity in magma water concentration on the development of flow banding and spherulites in rhyolitic lava abstract this study focuses on the origin of flow banded rhyolites that consist of compositionally similar darker and lighter flow bands of contrasting texture and color infrared radiation was used to obtain fourier transform infrared ftir spectra from which water concentrations were calculated and to map variations in water concentrations across zones of spherulites and glass from the 23 million year old sycamore canyon lava flow of southern arizona lighter colored thicker flow bands consist of gray glass fine grained quartz and large 1 0 to 1 5 mm spherulites darker colored thinner flow bands consist of orange glass and smaller 0 1 to 0 2 mm spherulites the centers of both large and small spherulites are occupied by either 1 a quartz or sanidine crystal 2 a granophyric intergrowth or 3 a vesicle mapping of water concentration dominantly oh in glass and oh and h2o in sanidine crystals illustrates fluctuating water availability during quenching of the host melt textures of large spherulites in the lighter gray bands in some cases indicate complex quenching histories that suggest that local water concentration controlled the generation of glass versus crystals small spherulites in darker orange bands have only one generation of radiating crystal growth both the glass surrounding spherulites and the crystals in the spherulites contain more water in the gray flow bands than in the orange flow bands flow banding in the sycamore canyon lava flow may have originated by the stretching of a magma that contained pre existing zones vesicles or proto vesicles of contrasting water concentration as the magma flowed in the conduit and on the surface variation in the original water concentration in the alternating layers is interpreted to have resulted in differences in undercooling textures in spherulites in the lighter compared to the darker flow bands

stress induced grain boundary migration in very soluble brittle salt abstract grain boundary migration gbm was studied in situ at room temperature atmospheric pressure and an applied diffmfwerential stress of 9 5 mpa under the optical microscope in a wet aggregate of an elastic brittle salt sodium chlorate the aggregate was previously deformed predominantly by a combination of grain boundary sliding pressure solution and cataclastic solution creep after deformation but when the sample was still under differential stress undeformed fracture free grains were observed to grow at the cost of deformed intensely fractured grains gmb rates typically fell in the range 2 10 m day gbm took place only as long as the sample was under stress boundaries stopped to migrate as soon as stress was taken off and started to migrate again as soon as the sample was stressed again our observations suggest that gbm in this material and under the prevailing experimental conditions is a stress induced process i e driven by differences in elastic strain between fractured and unfractured grains

first evidence for high grade himalayan age synconvergent extension recognised within the western syntaxis nanga parbat pakistan we present evidence for horizons of medium to high grade 400 600 c deformation accompanying normal sense displacement in high strain himalayan gneisses and schists from the southeastern nanga parbat massif the western syntaxis in the pakistan himalaya in their present orientation the broadly n s trending steeply dipping gneisses show microstructural and outcrop scale evidence for dextral and sinistral shear in discrete layers we interpret these as horizons of thrust and normal motion within the footwall of the original main mantle thrust once neogene antiformal folding is removed this is the first report of significant normal motion in the main mantle thrust footwall in the nanga parbat syntaxis and may indicate that synconvergent extension in the himalaya extended to the western syntaxis this episode of extension could correspond to a period of similar normal motion in the central himalaya or represent a separate event earlier in the orogeny

morphological and textural diversity of the steens basalt lava flows southeastern oregon usa implications for emplacement style and nature of eruptive episodes this study focuses on middle miocene tholeiitic flood basalt lava flows from the oregon plateau northwestern usa steens basalt and is the first to comprehensively document and evaluate their morphology field observations of flows from several sections within and proximal to the main exposures at steens mountain have been supplemented with textural and geochemical data and are used to offer preliminary insights into their emplacement compound pahoehoe flows of variable thickness appear to be common throughout the study area laterally and vertically these tend to be plagioclase phyric and the morphology and disposition of constituent flow lobes are quite similar to those from other provinces such as hawaii and the snake river plain classic a a flows with brecciated upper and basal crusts are not abundant but by no means uncommon flows with characters different from typical pahoehoe and a a are also common such flows display a range in morphology flows with preserved upper crusts but brecciated basal crusts as well as those displaying well developed flow top breccias and preserved basal crusts rubbly pahoehoe are observed the steens basalt appears to display greater morphological and textural diversity at the outcrop scale than that described for some other flood basalt provinces the abundant compound pahoehoe flows often rich in plagioclase phenocrysts were likely emplaced during slow but sustained eruptive episodes their constituent lobes show clear evidence for endogenous growth the relatively aphyric flows with brecciated surfaces including a a hint at higher strain rates and or higher viscosity probably caused by higher effusion rates a couple of sections are characterized by compositionally similar but morphologically different flows that were possibly part of the same eruption while differences in pre eruptive topography could explain this it is also possible that certain physical parameters changed substantially and abruptly during eruption and that such changes were accompanied by differentiation processes within the plumbing system it is possible that such observations indicate temporal fluctuations within complex magmatic and eruptive systems and deserve closer scrutiny

constraining kimberlite geology through integration of geophysical geological and geochemical methods a case study of the mothae kimberlite northern lesotho abstract the cretaceous mothae kimberlite is located in northern lesotho on the southeast margin of the kaapvaal craton historical work suggests that mothae has a low average diamond grade of 3 cpht and the economic viability therefore depends on the presence of large high quality and thus value diamonds as does that of the nearby letseng diamond mine defining such a diamond population requires a very large and representative bulk sample the near surface geology of the mothae kimberlite was investigated using ground geophysical surveys pit mapping petrography measurements of the mantle components and whole rock compositions integration of data from these different approaches clearly defines the outline of the kimberlite at the surface and permits definition with varying confidence levels of at least six geologically distinct domains within the body the domains are defined primarily on the basis of variations in the relative abundances of certain mantle derived minerals extracted from exploratory pit samples supported to varying extents by geophysically defined zones variations in kimberlite type established petrographically and variations in whole rock composition the domains are interpreted to reflect the presence of multiple phases of volcaniclastic kimberlite each with a potentially different diamond content the map of the near surface geology constructed on the basis of the work described in this paper provides a valuable framework for planning of further drilling and sampling work aimed at constraining the diamond resource at mothae this study illustrates the value of an integrated multidisciplinary approach to understanding the geology of a complex kimberlite body during the early stages of evaluation

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

geochemical and petrographic studies of ta mineralization in the nuweibi albite granite complex eastern desert egypt the nuweibi albite granite is one of 14 known sn ta nb bearing granitoids in the eastern desert region of egypt the granite is a highly leucocratic albite rich rock with accessory columbite tantalite cassiterite microlite and ixiolite as well as topaz garnet and white mica ages of 450 600 ma were obtained from zircons by the 207pb 206pb evaporation method great uncertainty is caused by the small size and poor quality of the grains but the precision is sufficient to indicate that the granite is late or postorogenic with respect to the panafrican orogeny the nuweibi granite is divided into a western and an eastern part by a regional fault both parts of the granite are compositionally similar but there are important differences and a clear compositional gap between them so they are considered separate facies of an intrusive complex the eastern part of the granite is more highly mineralized has higher modal albite contents and higher ta nb ratios both in the whole rock and in the ore minerals it is suggested that the two parts of the granite evolved from a common source and were emplaced sequentially the eastern part representing a later more fractionated magma textural evidence strongly suggests that the granite has a magmatic origin overall but disturbance of geochemical trends at the whole rock scale and at the scale of zoning profiles in individual grains of columbite tantalite indicate post magmatic overprinting by analogy with other ta bearing albite granites the sodic bulk composition of the nuweibi granite can be explained by fluorine enrichment in the magma fluorine contents in the magma were high enough to stabilize topaz and muscovites contain 2 4 wt f however whole rock f contents are low we speculate that the low ca al and p contents of the magma prevented abundant f bearing minerals to form and led to loss of fluorine to now eroded roof rocks

a review of the oxygen isotope composition of lacustrine diatom silica for palaeoclimate reconstruction diatom silica frustules are a form of biogenic opal and contain oxygen isotopes that are being increasingly used in palaeoclimate studies frustules are comprised of an inner tetrahedrally bonded silica skeleton si o si with an outer hydrous layer the hydrous layer is freely exchangeable and must be removed prior to oxygen isotope measurement using oxidising reagents and or high temperatures analysis of the oxygen isotope composition of diatom silica requires samples that are almost pure diatomite since extraction techniques will liberate oxygen from all the components in the sediment there is a generally acceptable protocol involving chemistry sieving and settling techniques and more recently laminar flow separation recent studies of lacustrine diatoms have shown that even a small proportion of contaminant can have a significant influence on the oxygen isotope value all lake sediments require their own specific procedure and every sample must be scrutinised by microscopy to check for the level of contamination prior to analysis where sediment cannot be purified sufficiently a semi quantitative assessment of the diatom content can facilitate mass balance techniques when robust preparation methods are used diatom silica offers an important palaeoclimate proxy providing an additional complementary rather than an alternative host of oxygen isotopes in carbonates in lacustrine isotope studies it is often assumed but rarely proven that diatom silica form in isotope equilibrium and hence empirically derived palaeotemperature equations usually made in vitro can be used most studies lack the detailed investigation of contemporaneous materials from natural waters of the region under study to test these equations further investigations need to be conducted in order to understand the systematic relationship between temperature water isotope composition and diatom isotope composition to enable quantitative interpretation of the sediment record experiments to test for vital effects and inter specific differences have so far revealed little variation it is useful to know when and where the diatom silica is formed in the modern environment so details of diatom ecology are important in the interpretation of isotope data here we show that valuable palaeoclimate data can be gained from the oxygen isotope composition of diatom silica 18odiatom especially since diatoms are abundant in many lakes sensitive to climate variation where other hosts e g carbonates are absent to date the most successful studies have been conducted in areas where the 18odiatom registers changes in the oxygen isotope composition of the lake water rather than temperature which is then related to other aspects of climate in these studies the range of values obtained is often greater than the error introduced by contaminating materials

fe rich and k rich mafic spherules from slumped and channelized chicxulub ejecta deposits in the northern la sierrita area ne mexico spherule deposits commonly interpreted as ejecta from the chicxulub impact at yucatan mexico are present in many k t cretaceous tertiary sections geological mapping of the northern la sierrita area ne mexico revealed the presence of 1 multiple spherule deposits embedded in late maastrichtian marls which are folded or disaggregated breccia like they are up to 6 m thick locally present in two outcrop areas and show limited lateral continuity these deposits consist of mm cm sized spherical to drop shaped vesiculated spherules angular to filamentous ejecta fragments and abundant carbonate they are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps slides liquefaction and debris flows welded components suggest an initial ground surge like ejecta dispersion mode 2 a spherule deposit 10 60 cm thick that constitutes the base of a channelized sand siltstone deposit at or close to the k t boundary and is characterized by wide lateral continuity it is of similar petrologic composition to deposit 1 though slightly enriched in terrigeneous detritus thus reflecting influx from proximal shelf areas it is interpreted to result from debris flows and turbidite currents though no size sorting and abrasion of ejecta has been observed petrological mineralogical and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the chicxulub impact with multiple deposits produced by subsequent remolding reworking and redeposition spherules and fragments have an fe 25 30 wt al mg rich and si poor 25 wt sio2 composition and are altered to chlorite and iron oxides though rare k rich mafic glass 50 wt sio2 5 8 wt k is also present they contain ti fe k rich schlieren fe mg rich globules and rare m sized metallic and sulfidic ni co rich inclusions carbonate as clasts and within spherules and fragments shows textures indicative of quenching and or liquid immiscibility although potential ejecta fractionation and alteration make accurate evaluation difficult this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination

evaluating the origin of garnet cordierite and biotite in granitic rocks a case study from the south mountain batholith nova scotia evaluating the origin of garnet cordierite and biotite in granites provides important insight into closed and open system magma evolution we present field textural major and trace element mineral chemical and sr nd whole rock isotopic data on garnet cordierite and biotite rich zones from the peraluminous south mountain batholith we infer that 1 garnet rich zones of decimeter to meter size with 30 vol large subhedral garnet with abundant inclusions of detrital country rock monazite represent partially assimilated metapelitic country rocks where garnet is the incongruent product of biotite dehydration melting 2 cordieriterich zones tens of meters to kilometers in dimension with 5v ol large subhedral to euhedral zoned cordierite formed by crystallization from relatively evolved magmas and subsequent crystal accumulation 3 biotite rich zones with large subhedral to euhedral biotite with abundant euhedral apatite inclusions making up 80 vol centimeter scale or 25 vol kilometer scale of the rocks formed dominantly by fractional crystallization throughout the chemical evolution of the batholith our results suggest that for garnet and cordierite a combination of textural and mineral chemical characterization is probably sufficient to determine their origin in granites however for biotite and other readily equilibrated minerals evaluating both mineral and rock textures and majorelement trace element and isotopic compositions is essential

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

a 200 year mid european air temperature record preserved in lake sediments an extension of the δ18op air temperature relation into the past abstract a detailed history of the water oxygen isotope ratios of lake ammersee southern germany was established for the last two centuries by analyzing oxygen isotope ratios of ostracod shells from a sediment core in a three to five year resolution empirical analysis and modelling of the isotope hydrology of the lake show that the oxygen isotopic composition of the lake water is mainly controlled by the isotopic composition of local precipitation for the last 200 years the lake isotope record is strongly correlated to the air temperature record from hohenpeisenberg situated within the lake s catchment area thus the mid european relation between 18 o in precipitation and air temperature documented for the last 20 years can be extended over a longer time and a larger temperature range the results provide further support for the validity of ostracod 18 o from ammersee sediments as a quantitative proxy for mean annual air temperature probably extending back to the last glaciation

seasonality and the isotope hydrology of lochnagar a scottish mountain lake implications for palaeoclimate research the relationship between isotope ratios in precipitation and lake waters was monitored by bi weekly measurements taken over a five and a half year period between may 2000 and september 2005 a period of 1964 days at lochnagar a remote mountain lake in eastern scotland short term changes in the oxygen isotope composition of lake water 18ol at lochnagar follow a seasonal pattern similar to isotopes in local precipitation 18op however changes in catchment residence time snow accumulation lake ice cover and lake stratification modify the temporal structure of 18ol over the seasonal cycle of particular importance is precipitation amount which controls catchment and lake residence times and determines the degree of phase lag and amplitude change between 18ol and 18op a simple mass balance model replicates these effects and demonstrates that the degree of phase lag and amplitude reduction is predictable given known input volume ratio the implications of these observations for the use of 18o

late stage magmatic evolution of oceanic gabbros as a result of hydrous partial melting evidence from the ocean drilling program odp leg 153 drilling at the mid atlantic ridge petrographic observations within oceanic gabbros drilled by ocean drilling program odp at leg 153 from the mid atlantic ridge kane fracture zone mark area 23 n in combination with experimental findings suggest that the late stage magmatic evolution of these gabbros is characterized by pervasive hydrous partial melting water saturated melting experiments on a variety of natural gabbros between 900 and 1000 c at 200 mpa produced newly formed minerals forming a characteristic paragenesis consisting of plagioclase orthopyroxene and pargasitic amphibole clinopyroxene the an content of the new plagioclases is uniformly higher than that of the protolith olivine and clinopyroxene primocrysts react to form neoblastic orthopyroxene and pargasitic amphibole these features can also be observed in the gabbros from the mark area here we found zones at plagioclase grain boundaries showing a strong enrichment in an component with an contents up to 20 to 25 mol higher than those of the host plagioclase primary olivines and clinopyroxenes in contact with such zones react to orthopyroxene and pargasitic amphibole these phases rim olivine and clinopyroxene and grow interstitially typical petrographic characteristics of a late stage magmatic phase the observed late stage microstructures in the gabbros thus appear to be the results of partial melting processes triggered by water rich fluids and are not crystallization products of a percolating differentiated late melt here we demonstrate that hydrothermal circulation within the gabbroic layer starts at much higher temperatures 900 1000 c than up to now believed water rich fluids propagate on grain boundaries in a ductile regime causing hydrous partial melting on a large scale a cracks system a prerequisite in current models for enabling hydrothermal circulation is not necessary the observed process has the potential for transfer of heat and mass between the upper and lower oceanic crust provided that the water rich fluids triggering the partial melting process are seawater derived this process may have a significant influence on the cooling of the deep oceanic crust which is in concordance with new thermal models implying that high temperature hydrothermal circulation is regarded to play an important role in transport of heat in the deep oceanic crust copyright 2005 by the american geophysical union

heterogeneous nucleation as the predominant mode of crystallization in natural magmas numerical model and implications for crystal melt interaction crystallization of natural magmas is inherently a disequilibrium process which involves nucleation and growth kinetics melt crystal mechanical interactions and subsolidus modifications which are all recorded in the resulting rock texture we use a new high resolution three dimensional numerical model to address the significance and consequences of homogeneous versus heterogeneous crystal nucleation in silicate magmas with increasing amount of heterogeneous nuclei during crystallization initially equigranular textures evolve to porphyritic bimodal and spherulitic types the corresponding crystal size distributions csds become concave up curved the clustering index progressively decreases and the grain contact relationships record increased clustering concave up curved csds previously interpreted as resulting from multistage crystallization mixing of crystal populations grain agglomeration or size dependent growth are now predicted consistently with other size spatial and clustering parameters to form by heterogeneous crystal nucleation correlation relationships between various textural parameters and the fraction of heterogeneous nuclei are calibrated and used on representative volcanic and plutonic rocks including cumulate rocks to deduce the fraction of heterogeneous nuclei the results indicate that 60 to 99 of all nuclei are heterogeneous for plutonic and cumulate rocks the estimate of the heterogeneous nuclei fraction based on the clustering index is significantly lower than other estimates such discrepancies in general point to the occurrence of other processes and here the results imply that crystal mush compaction and interstitial melt extraction were involved during the magma solidification formation of crystals in clusters implicit for heterogeneous nucleation implies that greater efficiency of crystal melt separation is expected in these situations

isotopic characteristics of precipitation groundwater and stream water in an alpine region in southwest china the hydrological cycle has been enhanced under the warmer climatic conditions on the southeastern edge of the tibetan plateau china to investigate the complex hydrological system in the study area 18o and 2h were measured on waters in a mountainous region huangbengliu watershed the stream water tends to be isotopically more depleted in 18o and 2h than precipitation and groundwater but more enriched than meltwater a clear seasonality with higher isotopic values of stream water in summer and lower values in winter is evident coinciding with the timing of the peak discharge the correlation between 18o and 2h in stream water shows that the isotopic signature of precipitation is well preserved in stream flow and the evaporation during the stream flow is only minor the isotopic composition of stream water shows a decreasing trend from upstream to downstream which results from tributary water inputs with heavy isotope depleted water according to an isotopic mass balance model the fraction of meltwater inputs over the total stream flow ranged from 25 5 to 61 8 the study demonstrates that the ice snow melting and tributary inputs are the prevailing mechanisms regulating stream isotope hydrology in alpine regions on the edge of the tibetan plateau

mineral compositional and textural evidence for magma mingling in the saraykent volcanics abstract upper cretaceous paleocene calc alkaline dacitic and rhyodacitic lava flows and domes are exposed in the saraykent yozgat region within central anatolian crystalline complex cacc saraykent volcanics are generally plagioclase hornblende biotite titanomagnetite quartz augite phyric subrounded vesicular magmatic enclaves ranging from a few millimeters to a few centimeters in size are present in the saraykent dacites the enclaves are mainly holocrystalline and have similar mineral assemblage to the host dacites almost all phases in saraykent volcanics exhibit varying degrees of disequilibrium features indicative of magma mingling plagioclase phenocrysts display sieved and normal type populations a wide range in rim compositions and oscillatory zoning maximum core to rim compositional change in sieved rhyodacite plagioclases is up to 24 mol increase in an some plagioclase core compositions are unusually ca rich they range from an27 to an75 for the saraykent dacites and from an30 to an66 for the saraykent rhyodacites hornblende and biotite phenocrysts have reaction rims indicating disequilibrium crystallization with magma both hornblende and biotite crystals show reverse zoning in terms of decreasing mg mg fe quartz phenocrysts are corroded and embayed presence of normally and reversely zoned augites in the same sample and high ti high al augites more comparable with basaltic compositions are other lines of evidence for disequilibrium the enclave hornblendes are both edenitic and pargasitic the latter being more typical of mafic compositions the enclave biotite crystals have higher mg mg fe2 ratios than the host dacite biotite crystals and display normal reverse and oscillatory zoning plagioclase core compositions vary between an44 and an55 in the enclaves although the development of sieve texture in plagioclase and reaction rims on mafic minerals may be attributed to decompression this cannot explain the observed compositional change and normal type of plagioclase in the same sample similarly a cognate i e fractionation origin for the enclaves can be suggested due to their mineralogical similarity to the host dacite however other criteria such as oscillatory zoning and unusually calcic cores of plagioclases heterogeneity of plagioclase rims resorbed and embayed phenocrysts and augite compositions indicating a more mafic magma are enough to support the suggestion that magma mingling was a viable process in the generation of the saraykent volcanics

characterization of the lithological contact in the shergottite eeta79001 a record of igneous differentiation processes on mars elephant moraine eet a79001 is the only martian meteorite that consists of both an olivine phyric shergottite lithology a and a basaltic shergottite lithology b the presence of these lithologies in one rock has previously been ascribed to mixing processes either magmatic or impact induced here we present data regarding phase changes across the contact between the lithologies these data show that the contact is gradational and suggest that it is a primary igneous feature consistent with crystallization of a single cooling magma we present a model to establish a petrogenetic connection between an olivine phyric and a basaltic shergottite through differentiation the model involves the shallow or surface emplacement of a magma that contained pre eruptive solids phenocrysts and minor xenocrysts subsequent differentiation via crystal settling and in situ crystallization langmuir 1989 resulted in a layered sequence of lithology a overlain by lithology b with gradations in modal abundance of maskelynite increasing from a to b and pigeonite maskelynite decreasing from a to b and a gradational change in pattern of pyroxene zonation zones of magnesian augite separating magnesian and ferroan pigeonite appear and thicken into b across the contact a pigeonite phenocryst bearing zone near the contact in lithology b appears to be intermediate between lithology a and the bulk of lithology b which resembles basaltic shergottite queen alexandra range que 94201 re examination of sr isotopic compositions in lithology a and across the contact is required to test and constrain the model

late holocene climate change in central sweden inferred from lacustrine stable isotope data stable isotopes 18o and 13c of lacustrine carbonates chara spp algae and pisidium spp molluscs from a lake sedimentary sequence in central sweden were analysed to infer changes in lake hydrology and climate during the late holocene results from analysis of lake water isotopes 18o and 2h show that lake blektjarnen water isotope composition is responsive to the balance between evaporation and input water e i ratio a high e i ratio results from a dry and probably warmer climate decreasing the relative importance of precipitation input under such conditions evaporation and atmospheric equilibration probably enrich lake water in 18o and 13c respectively which is reflected in the isotopic composition of the carbonates in the lake from the relatively positive chara 18o values we infer that conditions were dry and warm between 4400 and 4000 cal a bp whereas more negative values indicate that conditions were wetter and probably cooler between 4000 and 3000 cal a bp a drier climate is inferred from more positive values between 2500 and 1000 cal a bp however a successive depletion after ca 1750 cal a bp also detected in several other 18o records carbonate and diatom suggest increasingly wetter conditions in scandinavia after that time which is probably related to increased strength of the zonal flow

the initiation and development of metamorphic foliation in the otago schist part 2 evidence from quartz grain shape data shape size and orientation measurements of quartz grains sampled along two transects that cross zones of increasing metamorphic grade in the otago schist new zealand reveal the role of quartz in the progressive development of metamorphic foliation sedimentary compaction and diagenesis contributed little to the formation of a shape preferred orientation spo within the analysed samples metamorphic foliation was initiated at sub greenschist facies conditions as part of a composite s1 bedding structure parallel to the axial planes of tight to isoclinal f1 folds an important component of this foliation is a pronounced quartz spo that formed dominantly by the effect of dissolution precipitation creep on detrital grains in association with f1 strain with increasing grade the following trends are evident from the spo data i a progressive increase in the aspect ratio of grains in sections parallel to lineation and the development of blade shaped grains ii the early development of a strong shape preferred orientation so that blade lengths define the linear aspect of the foliation lineation and the intermediate axes of the blades define a partial girdle about the lineation iii a slight thinning and reduction in volume of grains in the one transect and iv an actual increase in thickness and volume in the survivor grains of the second transect the highest grade samples within the chlorite zone of the greenschist facies record segregation into quartz and mica rich layers this segregation resulted largely from f2 crenulation and marks a key change in the distribution deformation and spo of the quartz grains the contribution of quartz spo to defining the foliation lessens as the previously discrete and aligned detrital quartz grains are replaced by aggregates and layers of dynamically recrystallized quartz grains of reduced aspect ratio and reduced alignment pressure solution now affects the margins of quartz rich layers rather than individual grains in higher grade samples therefore the rock structure is characterized increasingly by segregation layering parallel to a foliation defined predominantly by mica spo

a multi proxy study of lake development in response to catchment changes during the holocene at lochnagar north east scotland abstract this paper describes a multi core lake sediment study using pollen diatoms and chironomids together with magnetics and sediment biogeochemistry as biotic and abiotic proxies to infer lake development in response to environmental change during the holocene at lochnagar in the eastern highlands of scotland diatoms are used to infer ph chironomids to infer temperature with pollen and plant megafossils acting as an independent proxy to validate these records and to provide insights into changes in catchment vegetation and soils lipid biomarkers are explored for their potential to provide additional information on lake productivity the results indicate highly distinctive fluctuations in the loss on ignition loi record which are in phase with changes in some biotic chironomid head capsule concentration and abiotic coarse silt particle size fraction and lipid and chlorine fractions variables catchment driven changes due to the development and degredation of soils and the natural succession and human intervention on terrestrial catchment vegetation have the strongest influence on the diatom and chironomid assemblages these catchment processes resulted in the natural acidification of the lake water post industrial acidification of the lake was also influential on the lake biota climate driven temperature change appears to have had only a weak influence on the biota with declines in cold stenothermic chironomid taxa in response to early holocene warming and declines in thermophilic chironomids in response to cooling at about 2600 cal yr bp

oxygen isotope ratios of sedimentary biogenic silica reflect the european transcontinental climate gradient oxygen isotope ratios of biogenic silica offer considerable potential in tracing past climate change using both marine and lacustrine sediment records despite recent improvements and standardisation in preparatory and analytical methods evidence for a systematic relationship between climate parameters and the oxygen isotope composition of sedimentary diatom silica 18osilica is contradictory in particular observed differences between the 18osilica of living and sedimentary diatom silica in both lake and marine environments question the validity of applying isotope fractionation models derived from living diatoms to reconstructing climate from sediment records in order to address this issue oxygen isotope ratios of biogenic silica 18osilica are examined from a suite of lake surface sediment samples which span a large climatic gradient across western europe 18osilica values are strongly correlated with air temperature and the isotope composition of precipitation 18op when evaporation of lake waters is accounted for the time averaged surface sediment data suggest a fractionation of 35 between water and biogenic silica however the effect of temperature appears less marked than that observed between contemporary diatoms and lake water over short timescales suggesting that diagenetic processes may lead to a reduction in the temperature sensitivity of sediment 18osilica records comparison of 18osilica data with d analysed from n alkanes of aquatic origin n c17 n c21 and n c23 demonstrates that the slope of the regional 18o d water line is preserved within the sediment record offering exciting potential for palaeoclimate research

uncertainty based grade modelling of kimberlite a case study of the jay kimberlite pipe ekati diamond mine canada abstract understanding uncertainty in resource models is a significant requirement of mineral resource evaluation geostatistical simulation is one method that can be used to quantify uncertainty and sequential gaussian simulation sgs is one of the easiest techniques to understand and implement using sgs provides both a spatial model of a given variable and the ranges around that variable at any number of scales the jay kimberlite pipe is located in the southeastern quadrant of the ekati property drilling to date has identified three kimberlitic domains characterized by varying lithological properties these domains are not separated by hard contacts but rather by boundaries that are transitional within these domains vertical trends exist in particular diamond grade increases with depth for these reasons jay required an in depth investigation of the best uncertainty based grade modelling method to use grade was modelled by organic sgs and by using the stepwise conditional transform sct to incorporate a trend into the simulation routine although the sgs results were valid they did not fully reproduce the trend and therefore the results did not fully match the geological interpretation of the deposit the sct results reproduced the trend however did not correspond to the variability of the data and therefore under represented the actual uncertainty in the model this was confirmed through detailed uncertainty calculation and probabilistic resource classification therefore the sgs model was chosen as the preferred uncertainty based grade model for the jay pipe

spider texture and amphibole preferred orientations abstract foliation in blueschist facies chert from california is defined by layers of oriented alkali amphibole which consistently curve towards and converge on pyrite and possibly pyrrhotite crystals these foliation nodes not previously described are called here spider texture the texture is interpreted in terms of perturbations of the stress field in a matrix undergoing strain about rigid pyrite or pyrrhotite crystals and it has important implications for understanding the mechanisms of amphibole preferred orientation development geometrical relationships between spider texture pressure shadows and quartz preferred orientations suggest that amphiboles grew with a strong preferred orientation along planes of maximum shearing stress the mechanism of foliation and preferred orientation development probably involved competitive anisotropic growth of amphibole prisms within the small gaps that open at steps on shear planes followed by additional micro porphyroblastic growth the first stage of the mechanism is similar to slickenfibre development

origin of internal flow structures in columnar jointed basalt from hreppholar iceland i textural and geochemical characterization basalt columns from hreppholar iceland show distinct internal structures produced by alternating brighter and darker bands through the column locally exhibiting viscous fingering features here we present geochemical and petrographic data retrieved from analyses of major and trace elements and mineral chemistry from a cross section of a single basaltic column this is combined with petrographic descriptions and data on crystal size distributions of plagioclase we use our data from hreppholar to test four existing models that have been proposed to explain banded structures inside columns 1 deuteric alteration 2 double diffusive convection 3 constitutional supercooling and 4 crystallization induced melt migration we find that the internal structures at hreppholar represent primary magmatic features because approximately 20 of the observed structures crosscut the column bounding fracture for each meter along the main axis of the column these features must thus have been formed before the column delimiting crack advanced major and trace element analyses show small but significant variations across the column and strong correlation between oxides like feo and tio2 as well as k2o and p2o5 the geochemical variations correlate with the presence of darker brighter bands visible on a polished surface and can be explained by a variation in the modal proportions of the main phenocryst phases specifically variable plagioclase and titanomagnetite content this banding enhances the internal structures apparent in the polished cross section from columnar joints at hreppholar the measured variations in major and trace element geochemistry as well as mineral chemistry are too small to distinguish between the proposed band forming models plagioclase crystal size distributions however display a systematic change across the column that is consistent with late stage migration of melt inside the column i e the crystallization induced melt migration hypothesis the central part of the columns have plagioclases indicative of slow cooling and these are also more steeply oriented i e subparallel to the column axis compared with plagioclases present in the more rapidly cooled edges this redistribution of melt within individual columns may significantly affect the cooling rate of columnar jointed lava flows and intrusions

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

assessment of rock geomechanical quality by quantitative rock fabric coefficients limitations and possible source of misinterpretations abstract rock microfabrics were quantified by image measurement system petrographic image analysis of thin sections along with common measured parameters grain area and size length of major and minor axes and their orientation some quantitative parameters aspect ratio grain boundary smoothness and fabric coefficients micropetrographic quality index k texture coefficient tc indexes of interlocking t and grain size homogeneity g were determined the reliability of these parameters for the evaluation of geomechanical properties was tested on the set of granitic rocks showing pronounced variability in rock mechanical properties none of the tested rock fabric coefficients or parameters proved a close correlation to rock mechanical properties except grain size based on experimental findings the grain size is along with porosity the controlling factor of rock mechanical properties of genetically and mineralogically similar rocks obliteration of the real effects of rock fabric parameters on the mechanical properties of rocks by application of complex fabric coefficients disables their practical use in petrography applied to geomechanics

structural analysis of flow related textures in lavas abstract the textures of coherent volcanic rocks including lavas and volcanic intrusives commonly contain features that are attributed to flowage previous applications of structural analysis to volcanic rocks are expanded here to provide a framework for analysis textures defined as the crystallinity granularity and shapes and arrangements of the components crystals glass and voids of a rock together with structures defined as individual features composed of the disposition attitude arrangement or relative positions of the components of a rock are first described second the spatial fabrics shapes and arrangements of the components of a rock and the orientation of textures and structures are identified third textures structures and fabrics are placed in the spatial and temporal geological context finally detailed interpretations of the kinematics and rheology of structures and fabrics is made leading to an integrated flow history of the rock illustrative case studies include rhyolite from the basal part of the tertiary minyon falls dome northeastern new south wales australia which has a texture comprising planar domains of differing crystal abundance flow bands multiple folds of these domains relatively homogeneous crystal alignment parallel to the fold axes and microfolding of these domains in the zone of interaction between phenocrysts and matrix including retrorotation of phenocrysts on short limbs of inequant folds trachyte dykes on fraser island queensland australia have a texture comprising crystal alignment planar concentration domains banding two planar domains of crystal alignment interpreted to be conjugate shear zones phenocrysts influence the spacing and distribution of the domains and interacted with shear zones by undergoing small amounts of rotation the shear zones overprinted a homogeneous crystal alignment during the last stage of flow before solidification as a result of dilatant granular interactions lava from miocene submarine banded silicic mafic domes on katsurajima on the coast of the shimane peninsula southwestern japan has a texture comprising crystal alignment irregular domains interpreted as the result of quenching local internal deformation of crystals including brittle boudinage and elongate vesicles and amygdales dacite from the late stages of the 1991 1995 eruption of mount unzen in western kyushu japan has a texture comprising crystal alignment deformation of phenocrysts and their surrounding matrix producing voids by mechanical means with the possible involvement of vapour phases the pervasive mechanical failure of the flowing magma may have triggered frontal collapse and the ensuing pyroclastic eruptions a spectrum of increasingly intense flow related textures can be recognised from simple planar alignments of crystals and vesicles to overprinting effects and domainal textures such as banding and shear zones and deformed domains pervasive ductile tearing and ultimately brittle fracture record flow during the transition from ductile magma to brittle rock the development of these flow related textures is controlled by the interplay of driving forces magma pressure gravity and resisting forces viscosity where driving forces are strong flow related textures are well developed when viscous resistance exceeds the driving forces flow and the development of flow related textures ceases