retreat of glaciar tyndall patagonia over the last half century we report measurements of ice surface elevation ice thickness and surface area for glaciar tyndall patagonia made in 1999 2002 the measurements together with previously published observations show acceleration over the last few decades of the rates of thinning and retreat of the main calving front the acceleration of shrinkage appears to be driven by a combination of climate and feedback processes the dominant feedback being increased melting associated with lowering of the glacier surface elevation feedback the melting capacity in the main terminus lake is now too small to be a major factor accelerating the retreat the glacier bed has low slope and remains below the elevation of the lake spillway for 14 km upstream from the 2000 calving front indicating the potential for extensive retreat under the influence of strong elevation feedback and increasing interaction with the lake as it enlarges

growth mechanisms structural defects and composition of synthetic tremolite what are the effects on macroscopic properties amorphous gels and oxides corresponding to ca2mg5si8o23 in bulk composition have been reacted to phase assemblages containing tremolitic amphibole using routine hydrothermal methods in the pressure temperature range from 1 22 kbar and 600 875 c the products have been characterized by x ray diffraction optical microscopy and high resolution electron microscopy the nature of the amphibole microstructure and the types of intergrown biopyriboles vary markedly as a function of synthesis temperature and pressure reflecting different amphibole growth mechanisms at p h2o 10 kbar within or very near the stability field of fale amphibole forms by topotactic reaction from this metastably crystallized intermediate phase chain multiplicity faults cmfs with m 3 are numerous the bulk compositional shift in the disordered amphibole crystals is compensated in the run product by coexisting diopside at p h2o 10 kbar but still in the talc stability field amphibole grows topotactically from and also nucleates preferentially on metastable diopside by a dissolution regrowth process the two phases form fine 100 a lamellar intergrowths with almost no cmfs with m 3 and the compositional shift induced by armoured diopside relics is compensated by discrete talc the same lamellar amphibole diopside microstructure is observed at temperatures above the talc stability field and at all pressures investigated but the compositional shift is compensated by enstatite quartz varying the experimental parameters run duration h2o content does not significantly affect the above observations for the wide range of pressures and temperatures investigated the synthetic amphiboles of the present study appear to correspond very closely to end member tremolite the observed product assemblages and apparent compositional shifts of the amphibole equivalent in ca mg ratio to as much as 11 mol magnesiocummingtonite component can be explained by the incorporation of cmfs in this phase we argue that cmf induced shifts in ca mg ratios also play a significant role for the 10 mol magnesiocummingtonite component commonly assumed in analogous experiments in the present literature the genuine magnesiocummingtonite solid solution component may be much less than 10 mol empirical high resolution transmission electron microscopy observations of preferential corrosion structures at crystal terminations suggest that to a first approximation structurally disordered tremolites exhibit the reaction behaviour of mechanical mixtures down to the unit cell scale the thermodynamic properties of synthetic tremolite even in small intergrown lamellae within disordered crystals should therefore closely approach those of discrete ideal tremolite single crystals in accord with the converging agreement shown by recent comparative experimental studies on the phase relationships of natural and synthetic tremolite

the role of h 2 o in rapid emplacement and crystallization of granite pegmatites resolving the paradox of large crystals in highly undercooled melts granite pegmatite sheets in the continental crust are characterized by very large crystals there has been a shift in viewing pegmatites as products of very slow cooling of granite melts to viewing them as products of crystal growth in undercooled liquids with this shift there has been a renewed debate about the role of h2o in the petrogenesis of pegmatites based on data on nucleation of minerals and new viscosity models for hydrous granite melts it is argued that h2o is the essential component in the petrogenesis of granite pegmatites h2o is key to reducing the viscosity of granite melts which enhances their transport within the crust it also dramatically reduces the glass transition temperature which permits crystallization of melts at hundreds of degrees below the thermodynamic solidus which has been demonstrated by fluid inclusion studies and other geothermometers published experimental data show that because h2o drastically reduces the nucleation rates of silicate minerals the minerals may not be able to nucleate until melt is substantially undercooled in a rapidly cooling intrusion nucleation starts at its highly undercooled margins followed by inward crystal growth towards its slower cooling hotter core delay in nucleation may be caused by competition for crystallization by several minerals in the near eutectic melts and by the very different structures of minerals and the highly hydrated melts once a mineral nucleates however it may grow rapidly to a size that is determined by the distance between the site of nucleation and the point in the magma at which the temperature is approximately that of the mineral s liquidus assuming components necessary for mineral growth are available along the growth path granite pegmatites are apparently able to retain h2o during most of their crystallization histories within the confinement of their wall rocks pegmatitic texture is a consequence of delayed nucleation and rapid growth at large undercooling both of which are facilitated by high h2o li b f and p contents in granite pegmatite melts without retention of h2o the conditions for pegmatitic textural growth may be difficult to achieve loss of h2o due to decompression and venting leads to microcrystalline texture and potentially glass during rapid cooling as seen in rhyolites in contrast slow cooling within a large magma chamber promotes continuous exsolution of h2o from crystallizing magma growth of equant crystals and final solidification at the thermodynamic solidus these are the characteristics of normal granites that distinguish them from pegmatites

the evolution of the patagonian ice sheet from 35 ka to the present day patice abstract we present patice a gis database of patagonian glacial geomorphology and recalibrated chronological data patice includes 58 823 landforms and 1 669 geochronological ages and extends from 38 s to 55 s in southern south america we use these data to generate new empirical reconstructions of the patagonian ice sheet pis and subsequent ice masses and ice dammed palaeolakes at 35 ka 30 ka 25 ka 20 ka 15 ka 13 ka synchronous with the antarctic cold reversal 10 ka 5 ka 0 2 ka and 2011 ad at 35 ka the pis covered of 492 6 x103 km2 had a sea level equivalent of 1 496 mm was 350 km wide and 2090 km long and was grounded on the pacific continental shelf edge outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams the pis reached its maximum extent by 33 28 ka from 38 s to 48 s and earlier around 47 ka from 48 s southwards net retreat from maximum positions began by 25 ka with ice marginal stabilisation then at 21 18 ka which was then followed by rapid irreversible deglaciation by 15 ka the pis had separated into disparate ice masses draining into large ice dammed lakes along the eastern margin which strongly influenced rates of recession glacial readvances or stabilisations occurred at least at 14 13 ka 11 ka 6 5 ka 2 1 ka and 0 5 0 2 ka we suggest that 20th century glacial recession a 1 is occurring faster than at any time documented during the holocene

melt inclusions in pegmatite quartz complete miscibility between silicate melts and hydrous fluids at low pressure fluorine boron and phosphorus rich pegmatites of the variscan ehrenfriedersdorf complex crystallized over a temperature range from about 700 to 500 c at a pressure of about 1 kbar pegmatite quartz crystals continuously trapped two different types of melt inclusions during cooling and growth a silicate rich h2o poor melt and a silicate poor h2o rich melt both melts were simultaneously trapped on the solvus boundaries of the silicate fluorine boron phosphorus water system the partially crystallized melt inclusions were rehomogenized at 1 kbar between 500 and 712 c in steps of 50 c by conventional rapid quench hydrothermal experiments glasses of completely rehomogenized inclusions were analyzed for h2o by raman spectroscopy and for major and some trace elements by emp electron microprobe both types of melt inclusions define a solvus boundary in an xh2o t pseudobinary system at 500 c the silicate rich melt contains about 2 5 wt h2o and the conjugate water rich melt about 47 wt h2o the solvus closes rapidly with increasing temperature at 650 c the water contents are about 10 and 32 wt respectively complete miscibility is attained at the critical point 712 c and 21 5 wt h2o many pegmatites show high concentrations of f b and p this is particularly true for those pegmatites associated with highly evolved peraluminous granites the presence of these elements dramatically reduces the critical pressure for fluid melt systems at shallow intrusion levels at t 720 c water is infinitely soluble in a f b and p rich melt simple cooling induces a separation into two coexisting melts accompanied with strong element fractionation on the water rich side of the solvus very volatile rich melts are produced that have vastly different physical properties as compared to normal silicate melts the density viscosity diffusivity and mobility of such hyper aqueous melts under these conditions are more comparable to an aqueous fluid

hasty retreat of glaciers in northern patagonia from 1985 to 2011 mapping changes in glacier extent from repeat optical satellite data has revealed widespread glacier decline in nearly all regions of the world over the past few decades while numerous studies have documented the changes of the outlet glaciers of the northern and southern patagonia icefields npi spi information about glacier changes in the patagonian andes to the north of the npi is much scarcer here we present an assessment of area changes for glaciers mainly located in the palena district of chile based on glacier inventories for 1985 2000 and 2011 that were derived from two consecutive landsat scenes and a digital elevation model the analysis revealed a dramatic area decline for the largest glaciers and total area loss of 25 from 1985 to 2011 the lower parts of several larger glaciers 10 km 2 melted completely area loss below 1000 m elevation was 50 100 in both periods and 374 glaciers out of 1664 disappeared the number of proglacial lakes increased from 223 to 327 and their area expanded by 11 6 km 2 59 between 1985 and 2011 seasonal snow persisting at high elevations in the 2011 scene was a major obstacle to glacier delineation so the obtained area change rate of 1 a 1 over the entire period is a lower bound estimate the observed climate trends e g cooling in puerto montt are in contrast to the observed shrinkage

fluid inclusion examination of the transition from magmatic to hydrothermal conditions in pegmatites from san diego county california thermometric properties and compositions of fluid inclusions in quartz are used to constrain the roles that fluid soluble elements principally li b cl and f have in controlling the transition from magmatic to hydrothermal mineral paragenesis in pegmatites and to ultimately understand why some pegmatites in the san diego county pegmatite district contain abundant gem quality li bearing minerals in pockets whereas others do not in this district lithium cesium tantalum type pegmatites occur in the mesozoic peninsular ranges batholith emplacement of the dikes occurred at low pressures 200 300 mpa that resulted in the formation of large miarolitic cavities pockets some of which contain gem quality li bearing minerals two pegmatite suites were studied the gem bearing himalaya and the more barren la posta the inclusions measured in this study further underscore highly undercooled crystallization of pegmatites pressure corrected homogenization temperatures t h of 400 to 515 and 70 to 425 c were obtained for primary inclusions in the intermediate zone and the core respectively of a la posta dike primary inclusions in the intermediate zone and the massive quartz core of the himalaya pegmatite have t h ranges of 350 to 420 and 150 to 300 c respectively the high portion of the latter temperature range is interpreted to represent the conditions that existed during the initial crystallization of minerals that line pegmatite pockets the most important cations in fluid inclusions in both pegmatites are na b3 and li lithium concentrations are much higher in inclusions in the himalaya pegmatite up to 51 at of all cations within the massive quartz in the core zone in the la posta pegmatite few primary inclusions contain appreciable li the b content of inclusions in both pegmatites is high up to 65 at of cations the dominant anions in the inclusions are cl f and formula 1 the data suggest that hydrothermal fluids that collected in pockets were acidic and promoted the growth of tourmaline and other minerals that are stable in acidic solutions in both pegmatites na and b dominate secondary inclusions these inclusions reveal fluids stripped of li and k by crystallization of lepidolite within fractures of primary minerals throughout the pegmatites and sometimes as an alteration product in pockets the lowering of alkali h ratios in the fluid stabilized clays including kaolinite that line the walls of pockets coeval crystallization of terminated quartz crystals with clays is consistent with its precipitation from the fluids 1 embed mml math 1 gif

a study of strontium diffusion in k feldspar na k feldspar and anorthite using rutherford backscattering spectroscopy abstract sr chemical diffusion has been measured in orthoclase anorthoclase and anorthite under dry 1 atm conditions a strontium oxide aluminosilicate powder mixture was used as the source material with rutherford backscattering spectroscopy rbs used to measure diffusion profiles over the temperature range 725 1075 c the following arrhenius relations were obtained orthoclase normal to 001 d 5 97 10 0 0060 0 0030exp 67900 1600rtcm 2 s 1 measurements of diffusion perpendicular to 010 and 100 indicate little diffusional anisotropy in orthoclase anorthoclase normal to 010 d 4 51 10 1 358 5 6exp 89100 4800rt cm 2 s 1 normal to 001 d 2 25 10 2 1615 31exp 89300 4600rt cm 2 s 1 anorthite normal to 010 d 3 85 10 2 0 380 0 0039 exp 78800 5400rt cm 2 s 1 the correlation of sr uptake with a reduction of k and ca in orthoclase and anorthite respectively indicates that sr is exchanging with these species nuclear reaction analysis nra measurements of al in orthoclase suggests that the coupled exchange sr 2 al 3 k 1 si 4 is taking place as expected sr closure temperatures for feldspars calculated with the above parameters are relatively high compared to those of some other minerals e g biotite muscovite apatite however closure temperatures of feldspars may be significantly depressed if they are exsolved or twinned leading to small effective diffusion lengths feldspar crystals of millimeter size should retain 87 sr 86 sr ratios except when subjected to thermal events of extreme temperature or duration

the dunbar gneiss granitoid dome implications for early proterozoic tectonic evolution of northern wisconsin the dunbar dome in northeastern wisconsin is a critical structural feature in the early proterozoic penokean orogen it provides exposures of gneisses dunbar gneiss that structurally underlie the voluminous metavolcanic rocks of northeastern wisconsin and exposures of abundant granitoid rocks ranging from tonalite to granite the granitoid rocks cut both the gneisses in the core and the supracrustal cover metavolcanic rocks and were emplaced essentially along the core cover boundary the dunbar gneiss is calc alkaline and was derived from volcanic and intrusive rocks of intermediate composition the various intrusive rocks have calcic calc alkaline and alkali to alkali calcic compositions and they progress with time to more sio 2 and k 2 rich compositions u pb zircon ages indicate that accumulation of the layered rocks in the core and cover deformation and metamorphism and intrusion of the granitoid rocks spanned a relatively short time 1865 1835 ma we interpret the dome as being a large scale fold interference structure resulting from polydeformation modified by diapirism northeast oriented folds f 3 and a related mylonitic foliation s 3 nearly confined to the dome are superposed on northwest oriented folds f 2 that developed during regional deformation in the core cover boundary these structures are obliterated by a zone of intense deformation a mylonitic foliation and a steeply plunging stretching lineation as much as 500 m wide which we interpret as resulting from diapirism metamorphic zoning is concentric amphibolite facies in inner parts of the mantle and greenschist facies in the outer part of the mantle the wisconsin magmatic terrane as represented by the rocks in the dunbar dome differs from the epicratonic early proterozoic sedimentary volcanic sequence marquette range supergroup in michigan to the north in stratigraphy structure and volume and composition of igneous rocks whereas the basalts in northern michigan are compositionally similar to continental rift basalts the volcanic rocks in the dunbar dome have over all island arc compositional affinities the over all calc alkaline compositions of the intrusive rocks are similar to those in magmatic arcs formed at convergent plate margin settings accordingly we interpret the wisconsin magmatic terrane as an oceanic arc complex that was sutured to the north american continent during development of the penokean orogen similar interpretations based on broad regional observations have been proposed previously

crystallization of the little three layered pegmatite aplite dike ramona district california subhorizontally layered pegmatite aplite bodies are characterized by fine grained sodic to granitic aplite that is usually juxtaposed abruptly above by much coarser grained commonly graphic potassic pegmatite although well studied there currently is little concensus as to how such dikes form the little three dike near ramona california is representative of such zoned bodies in this and other regions and contains discontinuous miarolitic pockets near the base of the graphic pegmatite zone tourmaline garnet biotite and muscovite show no changes in major or minor element compositions indicative of progressive magmatic fractionation until the immediate vicinity of the main miarolitic zone where they record abrupt and extreme enrichments in li f and mn there is no correlation of chemical changes in the dike with the appearance of small miarolitic vugs well below the main miarolitic zone nor is there any indication that the aplite graphic pegmatite or miarolitic pockets represent separate magma injections the chemistries of tourmaline garnet and micas however preclude conventional models of rayleigh fractionation or traditional zone refining textural features and modeled cooling histories indicate that the dike cooled quickly and might have solidified partially or totally to glass before crystallization commenced geothermometry based on the compositions of coexisting plagioclase and homogeneous nonperthitic k feldspar indicates inward crystallization of the dike from 400 435 c at the margins to 350 390 c within 20 30 cm of the pocket horizon then a sharp decrease to 240 275 c in the pockets where k feldspar is perthitic we interpret the feldspar geothermometry except perhaps in the miarolitic cavities to reflect the temperatures at crystallization fronts that advanced into the pegmatite first from the foot wall and eventually joined by a similar front downward from the hanging wall crystallization down from the hanging wall may have commenced after 70 80 of the foot wall aplite had crystallized the very abrupt increases of li mn and f in tourmaline and garnet near the miarolitic zone appear to be explained best by the process of constitutional zone refining in which a fluxed crystallization front sweeps an incompatible element enriched boundary layer through a solid or semi solid after these two highly fluxed boundary layers merged near the main miarolitic zone compositional evolution could have proceeded by crystal melt fractionation

estimation of snow ablation under a dust layer covering a wide range of albedo ablation processes of snow under a thin dust cover are complicated compared with those under a thick cover mainly owing to the effects of aggregation redistribution of dust particles on the conditions of surface melting aggregation of dust particles causes the snow surface to brighten after the initial dust configuration thus affecting the relationship between initial dust concentration and surface albedo in order to estimate snow ablation rate under a thin dust cover we used a composite energy balance model in which the surface albedo is taken as a measured input variable the estimated results of snow ablation agreed reasonably well with the observation considering the measurement errors inherited in the snow depressions comparison of the two cases that is one considering the aggregation of dust particles observation albedo variable and the other without aggregation assumption albedo constant showed that the ablation rates were noticeably lower on the former case this suggests that the aggregation of dust particles induces a reduction of snow ablation copyright 2002 john wiley sons ltd

penetration depth of interferometric synthetic aperture radar signals in snow and ice digital elevation models of glaciated terrain produced by the nasa jet propulsion laboratory jpl airborne interferometric synthetic aperture radar insar instrument in greenland and alaska at the c 5 6 cm wave length and l band 24 cm frequencies were compared with surface elevation measured from airborne laser altimetry to estimate the phase center of the interferometric depth or penetration depth p on cold polar firn at greenland summit p 9 2m at c and 14 4m at l band on the exposed ice surface of jakobshavn isbrae west greenland p 1 2 m at c and 3 3 m at l band except on smooth marginal ice where p 15 5 m on colder marginal ice of northeast greenland p reaches 60 to 120 m at l band on the temperate ice of brady glacier alaska p is 4 2 m at c and 12 6 m at l band with little dependence on snow ice conditions the implications of the results on the scientific use of insar data over snow ice terrain is discussed

formation of extremely f rich hydrous melt fractions and hydrothermal fluids during differentiation of highly evolved tin granite magmas a melt fluid inclusion study quartz crystals from topaz zinnwaldite albite granites from zinnwald erzgebirge germany contain in addition to primary and secondary fluid inclusions fis abundant crystalline silicate melt inclusions mis with diameters up to 200 m these mis represent various stages of evolution of a highly evolved melt system that finally gave rise to granite related sn w mineralization the combination of special experimental techniques with confocal laser raman microprobe spectroscopy and empa permits precise measurement of elevated contents of h2o f and b in re homogenized mis the contents of h2o and f were observed to increase from 3 to 30 and 1 9 to 6 4 wt respectively during magma differentiation however there is a second mi group very rich in h2o with values up to 55 wt h2o and an f concentration of approximately 3 wt ongoing enrichment of volatiles h2o f b and cl and of cs and rb can be explained in terms of magma differentiation triggered by fractional crystallization and thus is suggested to reflect elemental abundances in natural magmas and not boundary layer melts partitioning between melt and cogenetic fluids has further modified the magmatic concentrations of some elements particularly sn the coexistence of two types of mis with primary fis indicates fluid saturation early in the history of magma crystallization connected with a continuous sequestration of sn f and b the results of this study provide additional evidence for the extraordinary importance of the interplay of h2o f and b in the enrichment of sn during magma differentiation by decreasing the viscosity of and increasing the diffusivity in the melts as well as by the formation of various stable fluoride complexes in the melt and coexisting fluid

an experimental study of b p and f rich synthetic granite pegmatite at 0 1 and 0 2 gpa extreme enrichment in h2o b p and f is characteristic of many evolved granites and pegmatites we report experimental phase relations of a synthetic peraluminous pegmatite spiked with p2o5 b 2o3 and f 5 wt of each rb2o cs2o 1 wt of each and li2o 0 5 wt experiments were carried out in h2o satu rated conditions in cold seal rapid quench pressure vessels at 0 1 0 2 gpa crystallisation starts at about 820 c with berlinite and topaz quartz appears at 700 750 c topaz is replaced by muscovite at about 600 c at near solidus temperatures 450 500 c amblygonite lacroixite and a cs bearing aluminosilicate crystallise in all charges aluminosilicate melt coexists with low density hydrous fluid and hydrosaline melt the latter is strongly enriched in na3alf6 and h3bo3 components experi mental evidence of the liquid immiscibility and mineral reactions documented in our study offers new explana tions of many enigmatic features of natural pegmatites

three basaltic earth approaching asteroids and the source of the basaltic meteorites we report five color photometry near infrared spectra 0 8 2 5 m and thermal observations of the earth approaching asteroids 3551 1983 rd 3908 1980 pa and 4055 1985 do2 we derive their diameters as 1 2 1 0 and 3 4 km respectively apart from greater absorption band depths the spectra of these three small asteroids are nearly identical to that of vesta which is known to have a differentiated basaltic surface the deeper pyroxene bands 0 9 and 1 9 m relative to vesta are consistent with more pyroxene rich surfaces larger mineral grain sizes in their optically immature regoliths more bare rock surfaces or all of these factors these small earth approaching asteroids have similar orbits with perihelia near earth s orbit in july august they are probably not fragments of vesta but may be fragments of one or more vesta like parent bodies the spectra of vesta and the three earth approachers resemble those of the basaltic meteorites i e eucrites howardites and diogenites hed meteorites we find that hed fall times show a weak peak in july august suggesting that 3551 3908 and 4055 may be fragments of the source bodies of the hed meteorites or perhaps of a single common hed parent body the kilometer size asteroids have regoliths with significant insulating properties but these regoliths differ from that of the moon in that the particle sizes are larger than on the moon and lunar like glasses and agglutinates are largely absent the causes of these differences are related to impact velocities impact shaking and debris retention on small bodies differentiated basalt or mantle like asteroids may have impacted earth and left discontinuities in the geologic climatic record without leaving the chemical signatures associated with the k t boundary event

contribution of the patagonia icefields of south america to sea level rise digital elevation models of the northern and southern patagonia icefields of south america generated from the 2000 shuttle radar topography mission were compared with earlier cartography to estimate the volume change of the largest 63 glaciers during the period 1968 1975 2000 these glaciers lost ice at a rate equivalent to a sea level rise of 0 042 0 002 millimeters per year in the more recent years 1995 2000 average ice thinning rates have more than doubled to an equivalent sea level rise of 0 105 0 011 millimeters per year the glaciers are thinning more quickly than can be explained by warmer air temperatures and decreased precipitation and their contribution to sea level per unit area is larger than that of alaska glaciers

cooling rates and crystallization dynamics of shallow level pegmatite aplite dikes san diego county california pegmatites of the pala and mesa grande pegmatite districts san diego county california are typically thin sheet like composite pegmatite aplite dikes aplitic portions of many dikes display pronounced mineralogical layering referred to as line rock characterized by fine grained garnet rich bands alternating with albite and quartz rich bands thermal modeling was performed for four dikes in san diego county including the 1 m thick himalaya dike the 2 m thick mission dike the 8 m thick george ashley dike and the 25 m thick stewart dike calculations were based on conductive cooling equations accounting for latent heat of crystallization a melt emplacement temperature of 650 c into 150 c fractured gabbroic country rock at a depth of 5 km and an estimated 3 wt initial h 2o content in the melt cooling to 550 c at the center of each dike occurred in 9 years for the stewart dike 340 days for the george ashley dike 22 days for the mission dike and 5 days for the himalaya dike based on these calculations growth rates for large pegmatitic minerals such as the 10 cm long himalaya hanging wall tourmaline crystals may have been on the order of 10 5 cm s crystal size distribution csd studies of garnet from layered aplites suggest growth rates of about 10 6 cm s these results indicate that the dikes cooled and crystallized rapidly with variable nucleation rates but high overall crystal growth rates initial high nucleation rates coincident with emplacement and strong undercooling can account for the millimeter size aplite grains lower nucleation rates coupled with high growth rates can explain the decimeter size minerals in the hanging walls cores and miarolitic cavities of the pegmatites the presence of tourmaline and or lepidolite throughout these dikes suggests that although the melts were initially h 2o undersaturated high melt concentrations of incompatible or fluxing components such as b f and li h 2o aided in the development of large pegmatitic crystals that grew rapidly in the short times suggested by the conductive cooling models

southern hemisphere origins of the 1976 climate shift 1 observations from the tropical pacific ocean identify an abrupt climate shift in 1976 with surface temperatures changing from cooler than normal to warmer than normal in the span of about 1 year model results show that this climate shift originates with subsurface temperature anomalies in the south tropical pacific ocean which propagate first to the western boundary then northward to the equator and finally eastward along the equator to 140 w where they rise to the surface the results suggest that changes in the north pacific respond to changes in the tropical pacific

ice volumetric changes on active volcanoes in southern chile most of the glaciers in southern chile have been retreating and shrinking during recent decades in response to atmospheric warming and decrease in precipitation however some glacier fluctuations are directly associated with the effusive and geothermal activity of ice covered active volcanoes widely distributed in the region the aim of this paper is to study the ice volumetric changes by comparing several topographic datasets a maximum mean ice thinning rate of 0 81 0 45 m a 1 was observed on the ash debris covered ablation area of volcan villarrica between 1961 and 2004 whilst on volcan mocho the signal to noise ratio was too small to yield any conclusion an area reduction of 0 036 0 019 km 2 a 1 since 1976 was obtained on glaciar mocho while on volcan villarrica the area change was 0 090 0 034 km 2 a 1 between 1976 and 2005 glaciers on active volcanoes are therefore shrinking mainly in response to climatic driving factors however volcanic activity is affecting glaciers in two opposite ways ash debris advection is helping to reduce surface ablation at lower reaches by insulating the ice from solar radiation while geothermal activity is probably enhancing melting and water production at the bedrock resulting in negative ice elevation changes

meteor storm evidence against the recent formation of lunar crater giordano bruno it has been suggested that the formation of the 22 km diameter lunar crater giordano bruno was witnessed in june 1178 a d to date this hypothesis has not been well tested such an impact on the earth would be civilization threatening previous studies have shown that the formation of giordano bruno would lead to the arrival of 10 million tonnes of ejecta in the earth s atmosphere in the following week i calculate that this would cause a week long meteor storm potentially comparable to the peak of the 1966 leonids storm the lack of any known historical records of such a storm is evidence against the recent formation of giordano bruno other tests of the hypothesis are also discussed with emphasis on the lack of corroborating evidence for a very recent formation of the crater

the competition between rates of deformation and solidification in syn kinematic granitic intrusions resolving the pegmatite paradox abstract while fully crystallized granites rich in feldspar generally serve to strengthen the continental crust their precursor melts are assumed to be important agents of crustal weakening many syn tectonic granitic pegmatites are deformed within shear zones but ubiquitously preserve undeformed primary magmatic textures implying that they were largely molten during shearing yet the shapes of pegmatite bodies indicate that they deformed with a greater competence than their surroundings this co located pair of material behaviours is paradoxical we interpret field relationships in a typical pegmatite shear zone association torrisdale nw scotland and propose a mechanism by which syn tectonic granitic melts may in effect act as competent bodies while not yet fully crystallized competence was rapidly increased by preferential crystallization on intrusion margins that served to encapsulate residual melt inside stiff rinds further crystallization may have been pulsed as the concentrations of crystallization inhibitors fluxes increased in residual fluids postulating the existence of initial stiff rinds also consistent with modern estimates for rates of feldspar crystallization cms yr from undercooled hydrous silicic magma to form pegmatites these greatly outpace strain rate estimates for shear zones thus fully liquid granitic melts may only be present fleetingly and have little opportunity to weaken deforming crust before crystallization begins

the physical and chemical evolution of fluids in rare element granitic pegmatites associated with the lacorne pluton quebec canada abstract co magmatic rare element be li nb ta granitic pegmatites associated with the lacorne monzogranite pluton of the preissac lacorne batholith quebec range from a least evolved beryl type in the pluton through a transitional beryl spodumene type to a most evolved spodumene type in mafic country rocks they possess internal lithologic fabrics and primary fluid inclusions that provide evidence for saturation of the magma with aqueous fluids immediately after the formation of aplite in the beryl pegmatite and pene contemporaneously with formation of the beryl spodumene and spodumene pegmatites the early fluids are represented by aqueous liquid vapor type 1a and aqueous liquid vapor solid type 2 inclusions in beryl from beryl and beryl spodumene pegmatites and are estimated to have been trapped between 500 and 550 c and at 3 5 kb on the basis of microthermometric measurements analyses of the compositions of the precipitates from decrepitated inclusions and the nature of the solids trapped these fluids are interpreted to have been nacl dominated 16 wt nacl eq and to have contained appreciable fe and dissolved co2 in spodumene pegmatite the equivalent fluid which was trapped at 450 to 500 c contained significant mn li and cs in place of fe consistent with corresponding trends in the chemical evolution of the host rock volatile rich mainly secondary aqueous fluid inclusions type 1b trapped in beryl are interpreted to reflect temporary sharp drops in pressure later in the crystallization history of the beryl bearing pegmatites due to local fluid overpressures that led to brecciation and consequent pressure release these inclusions have high salinity are cacl2 rich and are considered to represent magmatic hydrothermal fluids that acquired their calcium as a result of their interaction with the host lacorne pluton incursion of cacl2 rich fluids into the spodumene pegmatites is interpreted to have occurred earlier in their crystallization history i e upon emplacement of the pegmatites as shown by the fact that a high proportion of primary inclusions in spodumene in these pegmatites contains considerable calcium and calcium contents are generally higher in inclusions in spodumene than in beryl the inclusions in the spodumene pegmatites are thought to have acquired their calcium through interaction of the fluids with the amphibolites metabasalts that host these intrusions the crystallization of the pegmatites terminated with the entrapment of low salinity aqueous carbonic fluids type 3 inclusions in quartz 6 10 wt nacl eq which most likely formed as a result of the unmixing of the magmatic fluid into separate aqueous and carbonic fluids probably at temperatures between 250 and 350 c the results of this study show that aqueous fluid saturation can take place at an early stage of pegmatite emplacement and that magma evolution is matched by changes in the solute chemistry of the exsolving aqueous fluid they also show that evolution to a more volatile rich composition h2o f li may have contributed to the increased mobility of later magma batches thereby helping to explain the regional zonation of the pegmatites from beryl type within the pluton to spodumene type in the adjacent amphibolite

comparative study of lahars generated by the 1961 and 1971 eruptions of calbuco and villarrica volcanoes southern andes of chile abstract the villarrica and calbuco volcanoes of the andean southern volcanic zone are two of the most active volcanoes in chile and have erupted several times in the xx century the 1961 eruption at calbuco volcano generated lahars on the north east and southern flanks while the 1971 eruption at villarrica volcano generated lahars in almost all the drainages towards the north west and south of the volcano the deposits from these eruptions in the voipir and chaillupen river villarrica and the tepu river calbuco are studied the 1971 lahar deposits on villarrica volcano show a great number of internal structures such as lamination lenses grading of larger clasts and a great abundance of large floating blocks on top of the deposits the granulometry can be unimodal or bimodal with less than 5 by weight of silt clay material sem images reveal a great variety of forms and compositions of clasts the 1961 lahar deposits on calbuco volcano have a scarce number of internal structures steeper margins and features of hot emplacement such as semi carbonized vegetal rests segregation pipes and a more consolidated matrix the granulometry usually is bimodal with great quantities of silt clay material 10 by weight sem images show a uniformity of composition and forms of clasts differences on deposits reveal different dynamics on both lahars the villarrica lahar was generated by sudden melt of ice and snow during the paroxysmal phase of the 1971 eruption when a high fountain of lava was formed the melted water flowed down on the flanks of the volcano and incorporated sediments to become transition flows highly energetic and were emplaced incrementally dilution of the flows occurs when the lahars reached unconfined and flatter areas in cases where the lahar flow found large water streams dilution is enhanced the calbuco lahars were generated by the dilution of block and ash pyroclastic flows by flowing over the ice or snow or by entering active rivers transforming to debris flows the differences on dynamics of both flows show the importance to understand initiation processes of lahars in order to make better hazard assessment due to laharics flows

diffusion effects on oxygen isotope temperatures of slowly cooled igneous and metamorphic rocks recently obtained data on oxygen diffusion in feldspars quartz and hornblende permit the prediction of the apparent18o16o temperatures that would be measured in a rock that consisted only of those three minerals and cooled slowly from high temperature the computed temperatures would be based on the differences in the18o16o ratios between coexisting pairs of minerals the present calculation takes into account the diffusion rates for oxygen as a function of temperature the cooling rate of the rock the mineral grain sizes and the mode of the rock for mineral grains 1 mm in radius and a cooling rate of 10 c m y the minimum difference in apparent temperature between quartz feldspar and feldspar hornblende pairs will be 115 c despite the assumption of a normal uneventful slow cooling history to room temperature further the apparent quartz hornblende temperature will range over 30 c 590 620 c depending on the mode of the rock for a cooling rate of 1000 c m y the apparent difference in temperature can be as much as 400 c consequently consistency in temperatures obtained by oxygen isotope analysis should not be expected in most high grade metamorphic rocks or igneous rocks which are cooled slowly departures from the pattern of temperatures obtained in this model would imply a very rapid quench from high temperature or a complex history for the rock for some minerals including hornblende the relation between temperature and the equilibrium fractionation of oxygen isotopes between coexisting phases has been derived from observed relations in natural specimens the choice of the specimens used for such calibrations needs to be re evaluated in light of these findings this may result in a change in the equilibrium equation constants an example from the literature the san jose tonalite baja california mexico was modelled and yields 18o concentrations in the minerals that correspond closely with the measured values this suggests that the model used is appropriate that the rock has had a simple thermal history and that it cooled at 100 200 c m y over the temperature range 800 500 c the set of paleotemperatures obtained for a rock will in general yield neither the mineral closure temperatures nor the formation or crystallization temperatures on the other hand the cooling rate of the rock may be derived from the data this in turn may have important tectonic implications with regard to denudation and uplift rates

non explosive constructional evolution of the ice filled caldera at volcan sollipulli chile a radar and gravity survey of the ice filled caldera at volcan sollipulli chile indicates that the intra caldera ice has a thickness of up to 650 m in its central part and that the caldera harbours a minimum of 6 km3 of ice reconnaissance geological observations show that the volcano has erupted compositions ranging from olivine basalt to dacite and have identified five distinct volcanic units in the caldera walls pre or syn caldera collapse deposits the sharkfin pyroclastic unit comprise a sequence which evolved from subglacial to subaerial facies post caldera collapse products which crop out along 17 of the 20 km length of the caldera wall were erupted almost exclusively along the caldera margins in the presence of a large body of intra caldera ice the alpehue crater formed by an explosive eruption between 2960 and 2780 a bp in the southwest part of the caldera is shown to post date formation of the caldera sollipulli lacks voluminous silicic pyroclastic rocks associated with caldera formation and the collapse structure does not appear to be a consequence of a large magnitude explosive eruption instead lateral magma movement at depth resulting in emptying of the magma chamber may have generated the caldera the radar and gravity data show that the central part of the caldera floor is flat but within a few hundred metres of the caldera walls the floor has a stepped topography with relatively low density rock bodies beneath the ice in this region this coupled with the fact that most of the post caldera eruptions have taken place along the caldera walls implies that the caldera has been substantially modified by subglacial marginal eruptions sollipulli caldera has evolved from a collapse to a constructional feature with intra caldera ice playing a major role the post caldera eruptions have resulted in an increase in height of the walls and concomitant deepening of the caldera with time

evidence for lithium aluminosilicate supersaturation of pegmatite forming melts new experimental data on the solubility of lithium li at spodumene lialsi2o6 and petalite lialsi4o10 saturation at 500 mpa and 550 750 c reveal evidence for lithium supersaturation of pegmatite forming melts before the formation of li aluminosilicates the degree of li enrichment in granitic melts can reach 11 000 ppm above the saturation value before the crystallization of li aluminosilicate minerals at lower temperatures comparison of the experimental results with the spodumene rich moblan pegmatite quebec is consistent with extreme li enrichment of the pegmatite forming melt prior to emplacement which cannot be explained with equilibrium crystallization of li aluminosilicates from a common granitic melt the results of this study support the model of disequilibrium fractional crystallization through liquidus undercooling as the most plausible mechanism for the generation of such li rich ore resources

strontium diffusion kinetics in amphiboles and significance to thermal history determinations abstract strontium tracer diffusion coefficients have been determined in hornblende and tremolite single crystals using experiments conducted at a confining pressure of 200 mpa at temperatures ranging from 700 to 960 c a quasi hydrothermal experimental technique was devised to avoid solution precipitation effects depth profile analyses were made with an ion microprobe the arrhenius relation for diffusion parallel to the c crystallographic direction in the gore mountain hornblende over this temperature interval has an activation energy q 260 12 kj mol and a pre exponential factor d 0 4 9 18 1 3 10 8 m 2 s at 800 c transport rates parallel to the c axis measured in the two tremolite samples amnh 30563 and barrie township ontario are 3 2 10 21 m2 s and 2 0 10 21 m2 s respectively these values are factors of 3 and 5 slower than those observed for the hornblende sample at the same temperature transport rates parallel and perpendicular to the c axis are the same within the estimated uncertainty for all three compositions experiments that differed in o 2 by a factor of 6 107 mno mn3o4 mno and magnetite wustite mw for the hornblende gave the same strontium diffusion rates within a factor of two crystals with cleavage faces or polished with alumina or diamond gave the same d values provided the crystals were annealed prior to the diffusion experiment using a combination of closed system rb sr systematics and strontium diffusion kinetics it is now possible to determine the thermal histories of hornblende bearing igneous and metamorphic rocks since the diffusion rates for strontium in amphiboles are relatively slow hornblende will be more retentive of sr than of other species for which transport rates are known ar o h and will be a useful tool to record higher temperature portions of cooling paths

age of volcanic rocks and syndepositional iron formations marquette range supergroup implications for the tectonic setting of paleoproterozoic iron formations of the lake superior region a rhyolite in the hemlock formation a mostly bimodal submarine volcanic deposit that is laterally correlative with the negaunee iron formation yields a sensitive high resolution ion microprobe shrimp u pb zircon age of 1874 9 ma but also contains inherited archean zircons as old as 3 8 ga this precise age determination for the classic paleoproterozoic stratigraphic sequence of northern michigan the marquette range supergroup mrs necessitates modification of previous depositional and tectonic models our new data indicate that the menominee group previously ascribed to continental rifting during early pre collision phases of the penokean orogenic cycle is coeval with arc related volcanic rocks now preserved as accreted terranes immediately to the south and is more aptly interpreted as a foredeep deposit we interpret these to be second order basins created by oblique subduction of the continental margin rather than basins formed on a rifting margin along with a recently reported age for the gunflint formation in ontario of 1878 2 ma our data suggest that an extensive foredeep in the western lake superior region was the locus of iron formation deposition during arc accretion from the south further we interpret the lower mrs chocolay group a glaciogenic and shallow marine succession that lies atop archean basement to be equivalent to the upper part of the huronian supergroup of ontario and to represent the original continental rifting and passive margin phase of the penokean cycle the upper mrs baraga group represents deeper marine basins dominated by turbidites and lesser volcanic rocks resulting from increased subsidence and continued collision a stitching pluton which cuts correlatives of the hemlock formation in a thrust sheet yielded a u pb zircon age of 1833 6 ma consistent with other post tectonic plutons in wisconsin and northern michigan indicating that penokean convergence lasted no longer than 40 million years

quantifying the effects of climate and surface change on glacier mass balance when a mass balance is computed using an outdated map that computation does not reveal the actual mass change but older maps often must be used for practical reasons we present a method by which with a few additional measurements each year a mass balance computed with an outdated map can be transformed into an actual mass change this is done by taking into account the influence of changes in areal extent and changes in the surface elevation of the glacier since the map was made this method is applied to south cascade glacier washington u s a as an example the computed cumulative mass balance from 1970 to 1997 would have been 16 too negative if the 1970 map had not been updated while the actual volume change of a glacier is relevant to hydrological studies the change that would have occurred on a constant or static surface is more relevant to certain glacier dynamics problems and most climate problems we term this the reference surface balance and propose that such a balance which deliberately omits the influence of changes in area and surface elevation is better correlated to climatic variations than the conventional one which incorporates those influences

topography and penetration of the greenland ice sheet measured with airborne sar interferometry a digital elevation model dem of the geikie ice cap in east greenland has been generated from interferometric c band synthetic aperture radar sar data acquired with the airborne emisar system gps surveyed radar reflectors and an airborne laser altimeter supplemented the experiment the accuracy of the sar dem is about 1 5m the mean difference between the laser heights and the sar heights changes from 0 m in the soaked zone to a maximum of 13 m in the percolation zone this is explained by the fact that the snow in the soaked zone contains liquid water which attenuates the radar signals while the transparency of the firn in the percolation zone makes volume scattering dominate at the higher elevations for the first time the effective penetration has been measured directly as the difference between the interferometric heights and reference heights obtained with gps and laser altimetry

synthetic fluid inclusions xiv coexisting silicate melt and aqueous fluid inclusions in the haplogranite h2o nacl kcl system coeval silicate melt and aqueous synthetic fluid inclusions were introduction formed at 800 c and 2000 bars in the quartz saturated haploin recent years the study of silicate melt inclusions has granite h2o nacl kcl system the equilibrium assemblage congained considerable popularity as a method to charsisted of ab19 2or31 1qtz49 1 melt quartz and an aqueous solution acterize the ptx evolution of igneous processes andwith a composition of 7 4 wt nacl 5 9 wt kcl the erson 1974 roedder 1979 lowenstern 1995 of melt contained 0 18 wt cl and 5 5 wt h2o the special interest has been the study of melt inclusions calculated partition coefficient of chloride between the melt and trapped in an immiscible fluid melt system roedder aqueous fluid d m aq cl c m cl c aq cl is 0 021 the calculated dis1979 1984 1992 hansteen lustenhouwer 1990 tribution coefficient of na and k between the melt and the aqueous frezzotti 1992 naumov et al 1992 1996 yang phase d m aq na k c m na c m k c aq na c aq k is 0 40 homogenization bodnar 1994 student bodnar 1996 microtemperatures of synthetic silicate melt inclusions obtained by heating thermometric data from such inclusions can be used in 10 0 c day increments in a tube furnace agreed with known directly to determine formation temperatures and presformation temperatures with no size dependence when measured sures without the necessity of invoking difficult to prove in a high temperature heating stage a heating rate of 1 c min assumptions or requiring an independent geobarometer produced homogenization temperatures that were about 10 c lower or geothermometer roedder bodnar 1980 than those obtained from the same inclusions using a heating rate roedder 1992 described specific types of magmatic of 3 c min although both heating rates produced homogenization immiscibility immiscibility being defined as the existence temperatures above the formation temperature a positive correlation of two or more non crystalline multi component sobetween inclusion size and th was observed for both heating rates lutions which differ in properties and composition at results confirm that microthermometric data from coeval silicate equilibrium including silicate melt silicate melt silicate melt and aqueous fluid inclusions can be used to accurately predict melt sulfide melt and silicate melt aqueous fluid in this p t formation conditions if data from the smallest melt inclusions study we have investigated the behavior of synthetic fluid are used or if the melt inclusions are homogenized using a slow inclusions trapped under conditions of silicate melt heating rate 1 c min aqueous fluid immiscibility in the haplogranite

the surface energy balance of an active ice covered volcano villarrica volcano southern chile the energy balance of bare snow and tephra covered ice near the glacier equilibrium line elevation on villarrica volcano southern chile was investigated during 2004 and 2005 combining meteorological surface temperature and ablation measurements with energy balance modelling a tephra thermal conductivity of 0 35 w m 1 k 1 and a critical tephra thickness of 0 1 m tephra windblown tephra impurities lowered snow albedo but increased snowmelt by only an estimated 0 28 m w e over the same period the net mass balance impact of supraglacial tephra at villarrica volcano is therefore positive as thick ash and lapilli mantle most of the glacier ablation zones probably reducing annual ablation by several metres w e in the accumulation seasons frequent melting events were recorded with modelled daily snowmelt rates of up to 50 mm w e

geological setting and timing of the world class sn nb ta and li mineralization of manono kitotolo katanga democratic republic of congo the central african mesoproterozoic kibara belt in katanga drcongo forms a metallogenic province that hosts a variety of granite related mineralization rich in cassiterite columbite tantalite wolframite ferberite spodumene and beryl this mineralization is mainly present in pegmatites and quartz veins that are thought to be associated with the youngest granite generation in the kibara belt i e so called e group granite generation manono kitotolo is one of the world s largest sn nb ta and li mineralized pegmatites with a large resource of spodumene columbite tantalite and cassiterite still remaining mineralized pegmatites have intruded along the foliation in the mesoproterozoic metasedimentary rocks and dolerites of the manono kitotolo area the pegmatites have been emplaced very late during the climax of the kibaran orogeny probably during the transition from orogenic collapse to extensional tectonics based on their structural position the emplacement of the pegmatites resulted in an intense alteration of the doleritic and metasedimentary host rocks resulting in muscovitization tourmalinization and silicification a mineralogical and geochemical zonation typical for granitic pegmatites has been identified that was affected by metasomatic hydrothermal alteration mainly albitization and greisenization the latter alteration is associated with the main phase of cassiterite mineralization a first stage with nb ta li and minor sn however already formed pre alteration directly associated with pegmatite crystallization 40ar 39ar muscovite dating of unaltered pegmatites resulted in ages of 938 8 5 1 ma and 934 0 5 9 ma these ages are overlapping with the u pb age of the nb ta mineralization 940 5 1 ma also giving new temporal constraints on the fertile e group granite generation in the kib the 40ar 39ar muscovite age of a mineralized greisen is 923 3 8 3 ma which is younger but still partly within error of the 40ar 39ar ages of the unaltered pegmatites based on the partial overlap in age but also on field and paragenetic relationships and the stable isotope composition of the fluids this greisenization and associated cassiterite mineralization can still be linked to the pegmatite crystallization

rb and sr diffusion in alkali feldspars with implications for cooling histories of rocks volume diffusion of sr and rb have been measured in orthoclase feldspar as well as sr diffusion in albite using isotope exchange hydrothermal solutions and analysis by ion microprobe for water pressures of 1000 bars the kinetics of diffusion parallel to the c axis are given by the arrhenius relations strontium transport in the or is isotropic to within a factor of four the measurements use a new procedure in which only the elements in question are present in the starting fluid cooling rates of igneous rocks can now be determined from closure temperatures material balance and the rb sr dating method based on the departures of the mineral data from the whole rock isochron for cooling rates less than approximately 100 c my

the 1925 meteorite fall near ellemeet and serooskerke the netherlands two meteorites impacted in 1925 around the town of serooskerke on the isle of schouwen the netherlands the largest mass is widely known as the ellemeet diogenite while a second mass heavily weathered due to environmental exposure also survived until the present day this work aims to reconstruct the history of the 1925 fall and for the first time documents the second mass known as the serooskerke by integrating a historical and experimental approach the study of historical news archives and cadastral records redefined the 1925 impact site at n 51 42 086 e 3 49 789 environmental exposure experiments reproducing the effects of rainfall and frost weathering identified the latter as the main cause for the second mass reported disintegration in the field sometime during the 1925 1926 winter the bulk mineralogy of the second mass was established using xrd powder diffraction for a 2 range of 3 70 and was found to be identical to an ellemeet reference sample uv vis nir spectroscopy 300 2500 nm was subsequently used to broadly compare the second mass to hed clan meteorites bouvante eet87503 johnstown and asteroid 4 vesta in order to corroborate its vestan origin the historical and geographic relationship of the two masses and the comparable bulk mineralogy supported the pairing of these two meteorites this makes the serooskerke a valuable legacy of the 1925 fall especially as the location of 50 of the remaining ellemeet mass is presently unknown

intercrystalline stable isotope diffusion a fast grain boundary model we formulated a numerical model for stable isotope interdiffusion which predicts the temperatures recorded between two or more minerals and the intragranular distribution of stable isotopes in each mineral as functions of mineral grain sizes and shapes diffusivities modes equilibrium isotopic fractionations and the cooling rate of a rock one of the principal assumptions of the model is that grain boundaries are regions of rapid transport of stable isotopes this fast grain boundary fgb model describes interdiffusion between any number of mineral grains assuming that local equilibrium and mass balance restrictions apply on the grain boundaries throughout the volume modeled the model can be used for a rock containing any number of minerals and number of grain sizes of each mineral several grain shapes and any thermal history or domain size desired previous models describing stable isotope interdiffusion upon cooling have been based on dodson s equation or an equivalent numerical analogue the closure temperature of dodson is the average bulk temperature recorded between a mineral and an infinite reservoir by using dodson s equation these models have treated the closure temperature as an innate characteristic of a given mineral independent of the amounts and diffusion rates of other minerals such models do not accurately describe the mass balance of many stable isotope interdiffusion problems existing models for cation interdiffusion could be applied to stable isotopes with some modifications but only describe exchange between two minerals under specific conditions the results of fgb calculations differ considerably from the predictions of dodson s equation in many rock types of interest actual calculations using the fgb model indicate that closure temperature and diffusion profiles are as strongly functions of modal abundance and relative differences in diffusion coefficient as they are functions of grain size and cooling rate closure temperatures recorded between two minerals which exchanged stable isotopes by diffusion are a function of modal abundance and differences in diffusion coefficient and may differ from that predicted by dodson s equation by hundreds of degrees c either or both of two minerals may preserve detectable zonation which may in some instances be larger in the faster diffusing mineral rocks containing three or more minerals can record a large span of fractionations resulting from closed system processes alone the results of fgb diffusion modeling indicate that the effects of diffusive exchange must be evaluated before interpreting mineral fractionations concordant or discordant recorded within any rock in which diffusion could have acted over observable scales the predictions of this model are applicable to thermometry evaluation of open or closed system retrogression and determination of cooling rates or diffusion coefficients

a late holocene explosive mafic eruption of villarrica volcano southern andes the chaimilla deposit abstract villarrica chile is one of the most active volcanoes in south america having erupted about 60 times in the last 460 years although its historical eruptive activity has been mainly effusive and weakly explosive it had strong explosive behaviour in postglacial times chaimilla

velocity of radio waves in glaciers as an indicator of their hydrothermal state structure and regime the results of measurements of radio wave velocities rwv by wide angle reflection war methods in the temperate abramov glacier in the alai mountain ridge and the two layered sub polar fridtjovbreen and hansbreen on svalbard using a low frequency 2 13 mhz radar are considered and discussed the experimental data obtained and the data from the literature show that the values of rwv could be a good indicator of the hydrothermal state of glaciers as such these data enable the identification of cold temperate and transitional two layered glaciers and can be used for estimation of the water content in glaciers and changes in the hydrothermal state

use of remotely sensed and field data to estimate the contribution of chilean glaciers to eustatic sea level rise a synthesis of glaciological studies carried out in chile during recent decades is presented including inventories and records of glacier variations fluctuations of whicharerelatedtoregionalclimate changeandtheircontributionto eustatic sea level rise basedupon satelliteimagery aerialphotographsandhistorical records newdata for 20 glaciersarepresented these newdata arecombinedwithpreviousrecordsto coverthe historicalvariations of95 chileanglaciers oftheseglaciers only 6 showa netadvance during the study period 6 show no significant change while 88 have retreated the contributionof chileanglaciersto eustatic sea levelrisehasbeenestimatedtobeapproxi mately 8 2 of the worldwide contribution of small glaciers on earth during the last 51years most of the glacier variations are thought to have been driven by a temperature increase which has been documented by several stations in chile anomalies in rainfall and the decreasing trend in annual precipitation shown at a few stations have probably also contributedtoglacier recession basedonobservedclimatictrends itisexpectedthat the glacier retreat will continue that the mass balance will continue to show a negative trend and that thinning rates will increase all of these changes will ultimately affect the availability of water resources in chile that depend on glacierizedbasins

glacier melting during lava dome growth at nevado de toluca volcano mexico evidences of a major threat before main eruptive phases at ice caped volcanoes abstract nevado de toluca volcano is one of the largest stratovolcanoes in the trans mexican volcanic belt during late pleistocene its activity was characterized by large dome growth and subsequent collapse emplacing large block and ash flow deposits intercalated by plinian eruptions morphological and paleoclimate studies at nevado de toluca and the surrounding area evidenced that the volcano was affected by extensive glaciation during late pleistocene and holocene during the older recognized glacial period 27 60 ka mis 3 the glacier was disturbed by the intense magmatic and hydrothermal activity related to two dome extrusion episodes at 37 ka and 28 ka glacier reconstruction indicates maximum ice thickness of 90 m along main valleys as at the cano ravines the major glacial valley on the northern slope of the volcano along this ravine both 37 and 28 ka block and ash deposits are exposed and they directly overlay a fluviatile sequence up to 40 m thick which 14 c ages clearly indicate that their emplacement occurred just before the dome collapsed these evidences point to a clear interaction between the growing dome and its hydrothermal system with the glacier during dome growth a large amount of melting water was released along major glacial valleys forming thick fluvioglacial sequences that were subsequently covered by the block and ash flow deposits generated by the collapse of the growing dome even though this scenario is no longer possible at the nevado de toluca volcano the data presented here indicate that special attention should be paid to the possible inundation areas from fluviatile lahar activity prior to the main magmatic eruption at ice capped volcanoes

pyribole evolution during tremolite synthesis from oxides the formation mechanisms of tremolite in a time series of hydrothermal experiments at 850 c and 6 1 kbar were studied using transmission electron microscopy tem analytical tem and x ray diffraction the starting materials were unseeded mixtures of reagent grade oxides after the first 8 min of reaction the synthesis products were diopside enstatite clinoenstatite quartz and minor c centered and primitive monoclinic amphibole 13 wt total the compositions of the first formed amphiboles vary considerably from essentially pure cummingtonite ca mg 0 to nearly ideal tremolite ca mg 0 4 three groupings of amphiboles with successively higher ca mg ratios were identified respectively 0 1 0 22 and 0 35 over a period of 97 h the proportions of mg rich amphibole gradually decrease and the average ca mg ratios of all amphiboles steadily increase from about 0 22 to 0 35 other changes include 1 a decrease in the aspect ratio of amphibole crystals with increasing time 2 a decrease in the number of non amphibole chain multiplicity faults cmfs from early a 2 values as low as 0 81 to a final value of 0 94 and 3 a distinct change in the rate of amphibole growth after 1 h of synthesis these observations suggest that two mechanisms of amphibole formation are dominant 1 formation of pyroxene modules with subsequent hydration and arrangement into the double chain amphibole structure and 2 direct nucleation and growth of amphibole from hydrothermal solution a third mechanism involving formation of talc like modules followed by their breakdown into double chain modules incorporation of ca and ordering into the amphibole structure may also occur but probably only at the lamellar or unit cell scale because these syntheses were performed outside the stability field of talc

comparison of satellite derived with ground based measurements of the fluctuations of the margins of vatnajokull iceland 1973 92 vatnajokull iceland is the earth s most studied ice cap and represents a classical glaciological field site on the basis of s palsson s seminal glaciological field research in the late 18th century since the 19th century vatnajokull has been the focus of an array of glaciological studies by scientists from many nations including many remote sensing investigations since 1951 landsat derived positions of the termini of 11 outlet glaciers of vatnajokull were compared with frontal positions of six of these 11 outlet glaciers determined by field observations during the period 1973 92 the largest changes during the 19 year period 1973 92 occurred in the large lobate surge type outlet glaciers along the southwestern western and northern margins of vatnajokull tungnaarjokull receded 1413 112 m 1380 1 m from ground observations and bruarjokull receded 1975 191 m 2096 5 m from extrapolated ground observations between 1973 and 1992 satellite images can be used to delineate glacier margin changes on a time lapse basis if the glacier margin can be spectrally discriminated from terminal moraines and sandur deposits and if the advance recession is larger than maximum image pixel size local knowledge of glaciers is critically important however in the accurate delineation of glacier margins on landsat images

experimental study of boron solubility and speciation in the na2o b2o3 sio2 h2o system abstract the na2o b2o3 sio2 h2o system has been studied at 520 c and 1 5 kbar in order to understand boron solubility and speciation under hydrothermal conditions at different sodium content within the studied compositional range excess of sio2 na2o 0 5 8 wt b2o3 3 5 6 7 wt and h2o 50 5 68 2 wt the system contains three phases aqueous fluid quartz and borosilicate liquid at na2o raman spectroscopy has not detected known sodium borate and borate polyanionic meta ortho tri tetra and pentaborate species in inclusions from all experiments within 20 400 c dissolved orthoboric acid line 876 cm 1 was the only raman spectral feature determined in fluid inclusions within the region typical for aqueous borate species 500 1200 cm 1 high temperature raman spectroscopy along with microthermometrical data suggests that a significant part of boron in the fluid and borosilicate liquid at the experimental temperature and pressure is bonded to sodium borosilicate species it was shown that boron has no significant effect on the phase relations within the studied part of the system na2o b2o3 sio2 h2o and under the studied conditions the system can be regarded as na2o sio2 h2o to a first approximation the obtained experimental data show that under natural hydrothermal conditions slightly alkaline aqueous fluids can transport significant amounts of boron and silica far away from the hydrothermal fluid source on the other hand in natural systems with relatively high alkalinity one can expect that boron does not migrate too far from the fluid source and being accumulated in the borosilicate liquid will form borosilicate mineralization at appropriate conditions

mapping thermal and hydrological conditions beneath a polythermal glacier with radio echo sounding spatial patterns in residual bed reflection power brp r derived from ground based radio echo sounding were mapped and interpreted in terms of the thermal and hydrological conditions at the base of a high arctic polythermal glacier john evans glacier ellesmere island canada brp r is the residual from a statistical relationship between measured bed reflection power and ice thickness that describes the rate of dielectric loss with depth in the glacier we identified three types of thermal structure a positive brp r and an internal reflecting horizon occur over the glacier terminus the reflecting horizon is interpreted as the boundary between warm and cold ice and suggests the presence of a warm basal layer b positive brp r occurs without an internal reflector in the upper part of the ablation zone this suggests that ice is at the pressure melting point only at the bed c negative brp r without an internal reflector occurs in all other regions suggesting cold ice at the bed where brp r is positive its pattern is similar to the pattern of subglacial water flow predicted from the form of the subglacial hydraulic equipotential surface this suggests that hydrological conditions at the glacier bed are a major control on brp r probably because the dielectric contrast between ice and water is higher than that between ice and other subglacial materials

compositional changes of minerals associated with dynamic recrystallizatin the rate of compositional and isotopic exchange between minerals may be enhanced significantly if the rock is deformed simultaneously the enhanced exchange rate may result from a reduction in grain size shorter distance for volume diffusion dissolution and growth of grains by diffusion creep pressure solution or the movement of high angle grain boundaries through strained grains during recrystallization in the dislocation creep regime the migration of high angle grain boundaries provides high diffusivity paths for the rapid exchange of components during recrystallization the operation of the latter process has been demonstrated by deforming aggregates consisting of two plagioclases an1 and an79 at 900 c 1 gpa confining pressure and a strain rate of 2x10 6s 1 the polygonal recrystallized grains were analyzed using an analytical transmission electron microscope and have a variable but often intermediate composition at the conditions of these experiments the volume interdiffusion rate of nasi caal is too slow to produce any observable chemical change and microstructural chemical relations indicate that the contribution from diffusion creep was insignificant except for initially fine grained 2 10 m aggregates these results indicate that strain induced recrystallization can be an effective mechanism for enhancing the kinetics of metamorphic reactions and for resetting the isotope systematics of minerals such as feldspars pyroxenes and amphiboles

meteorite falls in june two sets of observations two types of meteoritic events are associated with the calendric period june 13 30 one is an excess of falls of certain basaltic meteorites these comprise a new subgrouping of achondrites designated nuj whose lithologies suggest possibly similar preterrestrial histories historical high energy impact like events on the earth and moon have also occurred in late june in addition to much studied events in 1178 1908 tunguska and 1975 these include an impact like lunar event known to islamic scholars whose occurrence in 617 a d may have been june 26 27

macflincor and its application to fluids in archean lode gold deposits abstract macflincor was developed to process laboratory data gathered on fluid inclusions and to calculate isochores for geologically important fluids composed of h2o c02 ch4 nacl and n2 within the program interactive diagrams are available to describe those chemical systems which cannot be adequately constrained numerically the user can choose from various published equations of state describing fluid behavior and can easily compare the results obtained by using different equations the program once the basic fluid parameters have been established allows the data to be used to determine the p t trapping conditions to evaluate possible pressure corrections and to compare different depths of formation based on the pressure calculations and given geothermal gradients for illustrative purposes macflincor has been utilized here to constrain different physical chemical parameters of fluid inclusions trapped in ore related quartz veins and breccias of archean lode gold deposits in western australia inferred pressures from individual deposits show a wide range of values which may be due to post entrapment modifications and or observational uncertainties including estimation of liquid vapor ratios

experimental phase equilibria in the system lialsio4 sio2 h2o a petrogenetic grid for lithiumx rich pegmatites phase relations for the bulk composition lia1sis01z system lia1si04 sioz hzo have been investigated experimentally over the range 340 950 c and 0 5 6 0 kbar p hzo stability relations among eucryptite spodumene petalite b spodumene tetragonal and virgilite hexagonal have been determined for quartz saturated subsolidus conditions the result is a quantitative p t phase diagram that is applicable to quartz saturated lithium aluminosilicate assemblages in pegmatites and some volcanic rocks thermochemical data derived from these experimental results are internally consistent and in close agreement with values obtained from calorimetry under the quartz saturated conditions that prevail in pegmatites stability relations among the lithium aluminosilicates are a function of p and t and are largely independent of the nature and proportions of other phases in the chemically complex pegmatite system thus the lithium aluminosilicate phase diagram constitutes a petrogenetic grid from which p t conditions of emplacement and crystallization can be ascertained for many lithium alumino silicate bearing pegmatites

rapid crystallization of the animikie red ace pegmatite florence county northeastern wisconsin inclusion microthermometry and conductive cooling modeling we evaluated the crystallization regime of a zoned pegmatite dike and the degree of magma undercooling at the onset of crystallization by analyzing coeval fluid and melt inclusion assemblages the liquidus temperature of the pegmatite magma was 720 c based on re melting of crystallized melt inclusions in heating experiments the magma crystallized sequentially starting with a thin border zone which formed in less than one day at an average temperature of 480 c based on primary fluid inclusions meaning 240 c undercooling the primary inclusions from the outer zones were postdated by secondary inclusions trapped between 580 and 720 c representing fluid exsolved from hotter still crystallizing inner pegmatite units the huge temperature contrast between the pegmatite s inner and outer zones was simulated by conductive heat numerical modeling a 2 5 m wide dike emplaced in 220 c rocks cools entirely to 400 c in less than 50 days unidirectional and skeletal textures also indicate rapid disequilibrium crystallization

combining geomorphometry feature extraction techniques and earth surface processes research the way forward abstract in recent years the wealth of technological development revolutionised our ability to collect data in geosciences due to the unprecedented level of detail of these datasets geomorphologists are facing new challenges giving more in depth answers to a broad er range of fundamental questions across the full spectrum of the earth s and planetary processes this contribution builds on the existing literature of geomorphometry the science of quantitative land surface analysis and feature extraction translate land surface parameters into extents of geomorphological elements it provides evidence of critical themes as well as emerging fields of future research in the digital realm supporting the likely effectiveness of geomorphometry and feature extractions as they are advancing the theoretical empirical and applied dimension of geomorphology the review further discusses the role of geomorphometric legacies and scientific reproducibility and how they can be implemented in the hope that this will facilitate action towards improving the transparency and efficiency of scientific research and accelerate discoveries in geomorphology in the current landscape substantial changes in landforms ecosystems land use hydrological routing and direct anthropogenic modifications impact systems across the full spectrum of geomorphological processes although uncertainties in the precise nature and likelihood of changes exist geomorphometry and feature extraction can aid exploring process regimes and landscape responses taken together they can revolutionise geomorphology by opening the doors to improved investigations crossing space and time scales blurring the boundaries between traditional approaches and computer modelling and facilitating cross disciplinary research ultimately the exploitation of the available wealth of digital information can help to translate our understanding of geomorphic processes which is often based on observations of past or current conditions into the rapidly changing future

crustal melts below 400 c we propose that the internally zoned li bearing tin mountain pegmatite in the harney peak granite pegmatite system of the black hills south dakota crystallized from fluid rich compositionally complex melts at 400 350 c the low crystallization temperatures resulted from the combined fluxing effects of li b p h 2 o and carbonate anions the presence of hydrous silicate melts at temperatures of 350 c is revealed by microthermometric data on primary fluid inclusions cogenetic with crystallized melt inclusions mineral assemblages of the crystallized melt inclusions and chemistry of bulk fluid leachates indicate that the melts and fluids contained significant amounts of li and na as carbonates and or borates that acted as powerful fluxes the low temperatures give a new perspective on the stability of silicate melts in the crust

glacier fluctuations in extratropical south america during the past 1000 years article i nfo this paper presents an updated extensive review of glacier fluctuations during the past 1000 years in the extratropical andes of south america between ca 17 and 55 s given the variety of environmental conditions and evidence available for glacier fluctuations across this wide latitudinal range regional accounts are given for the desert andes 17 31 s the andes of central chile and argentina 31 36 s and the north 36 45 s and south 45 55 s patagonian andes the techniques dating limitations and interpretations of the glacier records along this transect are also discussed information on glacier fluctuations in the desert andes is limited to the 20th century documentation on past glacier variations is more abundant in the central chilean argentinean andes but the number of chronologies dealing with glacier fluctuations prior to the 1900s is also limited most records indicate that glaciers were generally more extensive prior to the 20th century with dates of maximum expansion ranging from the 16th to the 19th centuries the number and extent of glaciers increase significantly in the patagonian region where the evidence available for dating glacier variations during the past centuries is more abundant and the dating control for glacier events is generally better than in the northern parts of the study area for some patagonian glaciers maximum little ice age lia or post lia advances have been precisely dated by dendro geomorphological determinations or in situ measurements however for most sites the evidence available is still preliminary and there is considerable variability in the extent and timing of events related to the maximum lia expansion identified in most areas between the 16th and 19th centuries evidence is starting to appear at a growing number of sites for glacier advances during the first half of the past millennium these events were generally less extensive than the lia maximum pulses despite the occurrence of several post lia readvances over the past 100 110 years most areas in the andes of extratropical south america have experienced a general pattern of glacier recession and significant ice mass losses the differences in the glacier histories observed at local and regional scales probably reflect the inherent limitations associated with the glacier records and or the dating techniques used in each case together with the varying dominance of precipitation temperature and other climatic and non climatic factors on glacier mass balance and glacier dynamics these differences indicate that the late holocene glacier history of southern south america is more complex than commonly assumed the evidence discussed in this study highlights not only the immense potential for glaciological studies of this region but also a significant need for an increased number of detailed well dated records of glacier fluctuations

beryllium mineral evolution beryllium is a quintessential upper crustal element being enriched in the upper crust by a factor of 30 relative to primitive mantle 2 1 vs 0 07 ppm most of the 112 minerals with be as an essential element are found in granitic pegmatites and alkalic rocks or in hydrothermal deposits associated with volcanic and shallow level plutonic rocks and skarns because of the extensive differentiation needed to enrich rocks sufficiently in beryllium for beryllium minerals to form these minerals are relative latecomers in the geologic record the oldest known is beryl in pegmatites associated with the sinceni pluton swaziland 3000 ma in general beryllium mineral diversity reflects the diversity in the chemical elements available for incorporation in the minerals and increases with the passage of geologic time furthermore the increase is episodic that is steep increases at specific times are separated by longer time intervals with little or no increase in diversity nonetheless a closer examination of the record suggests that at about 1700 ma the rate of increase in diversity decreases and eventually levels off at 35 species formed in a given 50 ma time interval between 1125 and 475 ma then increases to 39 species at 125 ma except for four spikes before dropping off to 30 species for the last 100 ma these features appear to reflect several trends at work 1 diversifications at 2475 1775 and 525 ma which are associated with highly fractionated rare element granitic pegmatites and with skarns at langban and similar deposits in the bergslagen ore region of central sweden and which are inferred to correspond to the collisional phases of the supercontinents kenorland nuna and gondwana respectively 2 diversification at 1175 ma due to the rich assemblage of beryllium minerals in the ilimaussaq peralkaline complex gardar province west greenland in an extensional environment 3 diversification at 275 ma which is largely attributable to granitic pegmatites appalachian mountains u s a and urals russia and the larvik alkalic complex norway but nonetheless related to continental collision and 4 limited exhumation of environments where beryllium minerals could have formed in the last 100 ma that the maximum diversity of be minerals in any one geologic environment could be finite is suggested by the marked slowing of the increase in the number of species formed in a given 50 ma time interval whereas the drop off at 100 ma could be due to 100 myr being too short a time interval to exhume the deep seated occurrences where many be minerals had formed the relative roles of chance vs necessity in complex evolving systems has been a matter of considerable debate one equally applicable to what extent the temporal distribution of beryllium minerals is a matter of contingency on the one hand the appearance of the most abundant be minerals such as beryl and phenakite early in the history of be mineralization appears to be a deterministic aspect since these minerals only require the abundant cations al and si and crystallize at relatively low concentrations of be in aqueous solution or granitic magmas on the other hand it could be argued that the very existence of most other be minerals as well as the temporal sequence of their appearance is a matter of chance since 55 of the 112 approved be minerals are known from a single locality and many of these phases require an unusual combination of relatively rare elements consequently we cannot exclude the possibility that other equally rare and thus contingent potential be minerals await discovery in as yet unexposed subsurface deposits on earth and we suggest that details of be mineral evolution on other earth like planets could differ significantly from those on earth

monitoring ice capped active volcan villarrica southern chile using terrestrial photography combined with automatic weather stations and global positioning systems volc an villarrica 39 25 12 s 71 56 27 w 2847ma s l is an active ice capped volcano located in the chilean lake district the surface energy balance and glacier frontal variations have been monitored for several years using automatic weather stations and satellite imagery in recent field campaigns surface topography was measured using javad gps receivers daily changes in snow ice and tephra covered areas were recorded using an automatic digital camera installed on a rock outcrop in spite of frequently damaging weather conditions two series of consecutive images were obtained in 2006 and 2007 these photographs were georeferenced to a resampled 90m pixel size srtm digital elevation model and the reflectance values normalized according to several geometric and atmospheric parameters the resulting daily maps of surface albedo are used as input to a distributed glacier melt model during a 12 day mid summer period the spatial pattern of cumulative melt is complex and controlled by the distribution of airfall and wind blown tephra with extremely high melt rates occurring downwind of the crater and exposed ash banks the camera images are also used to visualize the pattern of glacier crevassing the results demonstrate the value of terrestrial photography in understanding the energy and mass balance of the glacier including the generation of meltwater and the potential value of the technique for monitoring volcanic activity and potential hazards associated with ice volcano interactions during eruptive activity

seasonality of the enso related rainfall variability in central chile and associated circulation anomalies the seasonality of the enso rainfall relationship in central chile 308 418s and associated circulation anomalies are studied using correlation and compositing techniques during el nino episodes there is a tendency for the occurrence of above average precipitation between 308 and 358s in winter june july august jja and from 358 to 388s in late spring october november on while rainfall deficit is typically observed from around 388 to 418s during the following summer january february march jfm when el nino reaches its maximum development opposite rainfall anomalies are characteristic during la nina events this study confirms results from previous investigations indicating that enhanced blocking activity over the amundsen bellings hausen seas area in the southeastern se pacific during el nino is a key feature explaining the wet conditions in winter it is also shown that the same circulation anomaly explains the relatively wet conditions in late spring in the 358 388s region during el nino episodes furthermore the southward displacement from winter to late spring of the area with significant enso related rainfall anomalies seems associated with the seasonal migration of the boundary separating the region under the influence of the subtropical domain from the extratropical domain where the westerly regime and associated disturbances prevail blocking episodes in the se pacific during el nino seem to be part of a wave structure particularly intense during spring characterized by a sequence of positive and negative quasi barotropic height anomalies stretching southeastward from the equator toward the se pacific and back to the southwestern atlantic on the other hand anomalously dry conditions in winter and late spring during la nina are favored by long lasting and intense ridges at subtropical latitudes over the se pacific and south america resulting in a southward migration of the midlatitude storm tracks in summer a higher frequency of ridges in the southern tip of the south america during el nino episodes presumably contributes to reinforcement of the southern edge of the subtropical anticyclone in the se pacific which at this time of the year reaches its southernmost position resulting in the annual rainfall minimum on the other hand an increased frequency of cyclonic circulation anomalies crossing the southern tip of the continent is associated with relatively wet conditions in southern central chile particularly during la nina events