glaciers and rock glaciers distribution at 28 sl dry andes of argentina and some considerations about their hydrological significance the area studied includes a little known portion on the dry andes of the san juan frontal cordillera argentina where the hydrological significance of glaciers and rock glaciers was earlier never studied the surveyed sector includes cerro el potro 5 870 m asl and nearby mountain chains 28 s the predominant landforms in these areas were shaped in a periglacial environment superimposed on an earlier glacial landscape these regions comprise abundant rock glaciers a noteworthy rock glacier zone in the world of which little is known in south america this work employs geomorphological mapping to analyze the distribution of active rock glaciers in relation to altitude aspect and slope using optical remote sensing techniques with gis statistical estimation techniques were used based on a digital elevation model dem and aerial photos and spot images interpretation the specific density of rock glaciers estimation in the surveyed area argentine border is 1 56 with corresponds to 38 rock glaciers with an area of 5 86 km2 and 0 12 km3 of water equivalent furthermore the analytical results show that elevations 4 270 m asl a southeast facing aspect and slope between 2 and 40 favor the existence of rock glaciers finally a comparison with glacier water equivalent which covers an area of 16 km2 and 0 9 km3 of water equivalent shows that glaciers are the main stores of water at 28 s cerro el potro glacier however the importance of rock glaciers as water reserves in this portion of argentina should not be underestimated

permafrost activity and atmospheric warming in the argentinian andes abstract rock glaciers are permafrost or glacial landforms of debris and ice that deform under the influence of gravity recent estimates hold that in the semiarid chilean andes for example active rock glaciers store more water than glaciers however little is known about how many rock glaciers might decay because of global warming and how much this decay might contribute to water and sediment release we investigated an inventory of 6500 rock glaciers in the argentinian andes spanning the climatic gradient from the desert andes to cold temperate tierra del fuego we used active rock glaciers as a diagnostic of permafrost assuming that the toes mark the 0 c isotherm in climate scenarios for the twenty first century and their impact on freezing conditions near the rock glacier toes we find that under future worst case warming up to 95 of rock glaciers in the southern desert andes and in the central andes will rest in areas above 0 c and that this freezing level might move up more than twice as much 500 m as during the entire holocene 200 m many active rock glaciers are already well below the current freezing level and exemplify how local controls may confound regional prognoses a bayesian multifactor analysis of variance further shows that only in the central andes are the toes of active rock glaciers credibly higher than those of inactive ones elsewhere in the andes active and inactive rock glaciers occupy indistinguishable elevation bands regardless of aspect the formation mechanism or shape of rock glaciers the state of rock glacier activity predicts differences in elevations of toes to 140 m at best so that regional inference of the distribution of discontinuous permafrost from rock glacier toes cannot be more accurate than this in the argentinian andes we conclude that the central andes where rock glaciers are largest cover the most area and have a greater density than glaciers is likely to experience the most widespread disturbance to the thermal regime of the twenty first century

climate tectonics and the morphology of the andes large scale topographic analyses show that hemisphere scale climate variations are a first order control on the morphology of the andes zonal atmospheric circulation in the southern hemisphere creates strong latitudinal precipitation gradients that when incorporated in a generalized index of erosion intensity predict strong gradients in erosion rates both along and across the andes cross range asymmetry width hypsometry and maximum elevation reflect gradients in both the erosion index and the relative dominance of fluvial glacial and tectonic processes and show that major morphologic features correlate with climatic regimes latitudinal gradients in inferred crustal thickening and structural shortening correspond to variations in predicted erosion potential indicating that like tectonics nonuniform erosion due to large scale climate patterns is a first order control on the topographic evolution of the andes

rock glaciers and mountain hydrology a review abstract in mountainous regions climate change threatens cryospheric water resources and understanding all components of the hydrological cycle is necessary for effective water resource management rock glaciers are climatically more resilient than glaciers and contain potentially hydrologically valuable ice volumes and yet have received less attention even though rock glacier hydrological importance may increase under future climate warming in synthesising data from a range of global studies we provide the first comprehensive evaluation of the hydrological role played by rock glaciers we evaluate hydrological significance over a range of temporal and spatial scales alongside the complex multiple hydrological processes with which rock glaciers can interact diurnally seasonally annually decadally and both at local and regional extents we report that although no global extent complete inventory for rock glaciers exists currently recent research efforts have greatly elaborated spatial coverage using these research papers we synthesise information on rock glacier spatial distribution morphometric characteristics surface and subsurface features ice storage and hydrological flow dynamics water chemistry and future resilience from which we provide the first comprehensive evaluation of their hydrological contribution we identify and discuss long intermediate and short term timescales for rock glacier storage allowing a more balanced assessment of the contrasting perspectives regarding the relative significance of rock glacier derived hydrological contributions compared to other water sources we show that further empirical observations are required to gain a deeper hydrological understanding of rock glaciers in terms of i their genesis and geomorphological dynamics ii total ice water volume iii water discharge and iv water quality lastly we hypothesise that at decadal and longer timescales under future climate warming degradation of ice within rock glaciers may represent an increasing hydrological contribution to downstream regions and thus increased hydrological significance while rock glacier water stores persist

petrogenesis of the late yanshanian mantle derived intrusions in southeastern china response to the geodynamics of paleo pacific plate subduction abstract several late yanshanian syenitic and gabbroic rocks from the coastal area of southeastern se china have been studied to determine zircon u pb ages and hf isotopic compositions as well as whole rock elemental and sr nd isotopic compositions to constrain their sources and tectonic settings the systematic la icp ms zircon u pb dating results indicate that they can be divided into two main stages the early stage 141 118 ma and the late stage 98 86 ma which temporally correspond to the regional lower and upper volcanic series respectively the early stage syenitic and gabbroic rocks are accompanied by vast rhyolitic and dacitic volcanic rocks with minor granites their parental magma was derived from an enriched mantle metasomatized by subducted sedimentary materials the late stage syenitic rocks mainly occur as the central intrusion of the caldera with ages close to the accompanied volcanics forming a caldera related volcanic intrusive ring complex they were produced by magma mixing between depleted asthenosphere melts and subduction related enriched mantle melts it is suggested that the late yanshanian tectonic settings of se china transformed from a compressional environment to an extensional environment corresponding to the transformation from forward to rollback subduction of the paleo pacific plate at approximately 110 ma

logistic regression modeling of rock glacier and glacier distribution topographic and climatic controls in the semi arid andes abstract logistic regression is applied to a random sample of surface points in the semi arid andes of santiago and mendoza chile argentina 32 45 34 30 s 12 000 km 2 above 3000 m a s l to identify local and regional controls on rock glacier and glacier distribution the study area is among the areas with the greatest abundance of rock glaciers worldwide the explanatory variables used for model selection are related to local and regional morphometric and climatic characteristics the models achieve a very good fit area under the roc curve 0 84 for rock glaciers and 0 95 for glaciers and are able to reproduce the regional distribution pattern model results are used to determine the optimal morphographic and climatic niche of rock glaciers and glaciers in the study area and help explain the presence of low elevation rock glaciers under favorable topoclimatic conditions

hazardous processes and events from glacier and permafrost areas lessons from the chilean and argentinean andes glacier and permafrost hazards such as glacial lake outburst floods and rock ice avalanches cause significant socio economic damages worldwide and these processes may increase in frequency and magnitude if the atmospheric temperature rises in the extratropical andes nearly 200 human deaths were linked to these processes during the twentieth century we analysed bibliographical sources and satellite images to document the glacier and permafrost dynamics that have caused socio economic damages in this region in historic time including glacial lake outburst floods ice and rock ice avalanches and lahars to unravel their causes and geomorphological impacts in the extratropical andes at least 15 ice dammed lakes and 16 moraine dammed lakes have failed since the eighteenth century causing dozens of floods some floods rank amongst the largest events ever recorded 5000 106 m3 and 229 106 m3 respectively outburst flood frequency has increased in the last three decades partially as a consequence of long term decades to centuries climatic changes glaciers shrinkage and lake growth short term days to weeks meteorological conditions i e intense and or prolonged rainfall and high temperature that increased meltwater production have also triggered outburst floods and mass movements enormous mass failures of glaciers and permafrost 10 106 m3 have impacted lakes glaciers and snow covered valleys initiating chain reactions that have ultimately resulted in lake tsunamis and far reaching 50 km flows the eruption of ice covered volcanoes has also caused dozens of damaging lahars with volumes up to 45 106 m3 despite the importance of these events basic information about their occurrence e g date causes and geomorphological impact which is well established in other mountain ranges is absent in the extratropical andes a better knowledge of the processes involved can help to forecast and mitigate these events copyright 2014 john wiley sons ltd

andean flat slab subduction through time the analysis of magmatic distribution basin formation tectonic evolution and structural styles of different segments of the andes shows that most of the andes have experienced a stage of flat subduction evidence is presented here for a wide range of regions throughout the andes including the three present flat slab segments pampean peruvian bucaramanga three incipient flat slab segments carnegie guanacos tehuantepec three older and no longer active cenozoic flat slab segments altiplano puna payenia and an inferred palaeozoic flatslab segment early permian san rafael based on the present characteristics of the pampean flat slab combined with the peruvian and bucaramanga segments a pattern of geological processes can be attributed to slab shallowing and steepening this pattern permits recognition of other older cenozoic subhorizontal subduction zones throughout the andes based on crustal thickness two different settings of slab steepening are proposed slab steepening under thick crust leads to delamination basaltic underplating lower crustal melting extension and widespread rhyolitic volcanism as seen in the caldera formation and huge ignimbritic fields of the altiplano and puna segments on the other hand when steepening affects thin crust extension and extensive within plate basaltic flows reach the surface forming large volcanic provinces such as payenia in the southern andes this last case has very limited crustal melt along the axial part of the andean roots which shows incipient delamination based on these cases a palaeozoic flat slab is proposed with its subsequent steepening and widespread rhyolitic volcanism the geological evolution of the andes indicates that shallowing and steepening of the subduction zone are thus frequent processes which can be recognized throughout the entire system

an inventory and estimate of water stored in firn fields glaciers debris covered glaciers and rock glaciers in the aconcagua river basin chile abstract an inventory of firn fields glaciers debris covered glaciers and rock glaciers was conducted in the aconcagua river basin of the semiarid andes of central chile a total of 916 landforms were identified of which rock glaciers were the most abundant 669 and occupied the most total area glaciers and debris covered glaciers were less numerous but were about five times larger in comparison the total area occupied by glaciers and debris covered glaciers was roughly equivalent to the total area of rock glaciers debris covered glaciers and rock glaciers were subcategorized into six ice content classes based on interpretation of surface morphology with high resolution satellite imagery over 50 of rock glaciers fell within a transitional stage 85 of debris covered glaciers were either fully covered or buried most landforms occupied elevations between 3500 and 4500 m glaciers and firn occurred at higher elevations compared to rock glaciers and debris covered glaciers rock glaciers had a greater frequency in the northern part of the study area where arid climate conditions exist firn and glaciers were oriented south debris covered glaciers west and rock glaciers southwest an analysis of water contribution of each landform in the upper andes of the aconcagua river basin was conducted using formulas that associate the size of the landforms to estimates of water stored minimum and maximum water storage was calculated based on a range of debris to ice content ratios for debris covered glaciers and rock glaciers in the aconcagua river basin rock glaciers accounted for 48 to 64 of the water stored within the landforms analyzed glaciers accounted for 15 to 25 debris covered glaciers were estimated at 15 to 19 firn fields contained only about 5 to 8 of the water stored expansion of agriculture prolonged drought and removal of ice rich landforms for mining have put additional pressure on already scarce water resources to develop long term sustainable solutions the importance of the water stored in rock glaciers or other alpine permafrost landforms such as talus slopes must be weighed against the economic value of mineral resources

zircon texture and chemical composition as a guide to magmatic processes and mixing in a granitic environment and coeval volcanic system this study documents the chemical and textural responses of zircon in the elba igneous complex with particular reference to the 7 to 7 8 ma old monte capanne pluton in relation to its coeval volcanic counterpart capraia using bse imaging and quantitative electron microprobe analyses the monte capanne pluton displays multiple field and geochemical evidence for magma mixing the samples we have investigated including monzogranitic mafic enclave and dyke samples display similar zircon textures and are associated with an extremely large range of trace and minor element hf y hree th u compositions which contrast with relatively simple textures and zoning patterns in zircons from a capraia dacite we have used a relatively simple textural classification patchy zoning homogenous cores oscillatory zoning and unzoned zircon as the basis for discussing the chemical composition and chemical variation within zircons from the monte capanne pluton based on these data and other works dini et al 2004 in lithos 78 101 118 2004 it is inferred that mixing between metaluminous and peraluminous melts occurred early in the evolution of the monte capanne magma chamber in particular mixing was responsible for the development of the patchy zoning texture in the zircon cores which was associated with reactions between other accessory phases including monazite apatite allanite which we infer to have significantly affected the th distribution in zircon zircons from the mc pluton displaying homogeneous cores have chemical affinities with zircons in the coeval capraia volcanic system consistent with the participation of a capraia like mantle end member during mixing further zircon growth in the mc pluton produced the oscillatory zoning texture which records both long term crystal fractionation and transient recharge with both silicic and mafic magmas events in a hybrid magma chamber it is inferred that hf and the th u ratio cannot be used alone to infer magmatic processes due to their dependency on temperature nor are they a diagnostic feature of xenocrystic grains this study shows that zircon chemistry coupled with detailed textural analysis can provide a powerful tool to elucidate the complex evolution of a magma system

zircon record of the plutonic volcanic connection and protracted rhyolite melt evolution the potential petrogenetic link between a crystal poor rhyolite the rhyolite canyon tuff and its associated subvolcanic intrusion and crystal rich post caldera lavas from turkey creek arizona usa is examined using zircon chemical abrasion thermal ionization mass spectrometry u pb geochronology and inductively coupled plasma mass spectrometry trace element analyses u pb ages indicate that zircon growth within the rhyolite and the dacite monzonite porphyry magmas was coeval over 300 k y prior to the large eruptive event trends in zircon trace elements hf y dy sm yb eu eu through time in the dacitic monzonitic units and rhyolite reflect melt evolution dominated by crystal fractionation importantly the y dy ratio in zircons in both units remains mostly similar for the first 150 k y of the system s evolution but the dominant population in the rhyolitic unit diverges from that of the dacite monzonite porphyry 150 k y before eruption we interpret this divergence in trace element composition to record the assembly time of the melt rich cap within its intermediate mush zone in the upper crustal reservoir these results are consistent with 1 a connection between plutonic and volcanic realms in the upper crust 2 a protracted time scale for constructing an intermediate mush large enough to hold 500 km 3 of rhyolite and 3 the prolonged extraction of that melt prior to eruption

structure and genesis of the thabor rock glacier northern french alps determined from morphological and ground penetrating radar surveys landform analysis and ground penetrating radar gpr were used to investigate the thabor rock glacier in the northern french alps the surface features of the rock glacier were classified and described with emphasis on massive ice exposures the retreat of the former thabor glacier since the little ice age lia was documented through an analysis of historical sources and recent movements of the rock glacier were inferred from orthophoto based measurements two dimensional 2 d models of the radar wave velocity were derived from the raw gpr data using the numerous diffraction hyperbolae for local determinations of the velocity and kriging interpolation techniques subsequently the profiles were migrated through a 2 d kirchhoff migration method using the interpolated velocities the 2 d velocity models exhibit pronounced spatial variations and in several locations high values 0 15 m ns 1 potentially corresponding to massive ice on the other hand while the migrated profiles show numerous layers the internal stratigraphy of the rock glacier is dominated by a few prominent internal boundaries the integration of morphology radar wave velocity and internal stratigraphy allowed us to identify the main structural units of the rock glacier as well as to explain its genesis the rock glacier was formed by the imbrication of a massive ice core originating from the retreat of the former thabor glacier since the lia into pre existing glacial deposits

the occurrence of alpine permafrost in the front range of colorado abstract permafrost distribution or ground that remains frozen for at least 2 years has been modeled using a combination of geographic information system gis techniques digital elevation model dem variables and land cover in alpine regions of the world in the front range however no such empirical models have been developed and field data are restricted in spatial extent but rock glaciers are in abundance here i present a probabilistic logistic regression model that is based on topoclimatic information elevation and aspect for rock glaciers derived from u s geological survey usgs 10 m dems classes of land cover obtained from an enhanced thematic mapper plus etm image classification were assigned weights and were then multiplied by the regression results to refine estimates the effectiveness of the model was evaluated by comparing mean probability scores with rock glacier activity categories mean annual air temperature maat from climatic stations on niwot ridge and bottom temperature of winter snow bts measurements while a monte carlo simulation was used to detect uncertainty associated with the original dem permafrost scores 50 covered about 8 9 242 km 2 of the study area 2722 km 2 with the highest scores clustered around longs and rowe peaks permafrost locations showed a strong correlation with rock glacier activity classes the 1 0 c maat isotherm and bts measurements less than 3 0 c the uncertainty analysis revealed that slight global differences exist between the original and error prone dem however local variations in aspect caused the most uncertainty these results indicate that the model accurately represents regional distribution of permafrost therefore topoclimatic information from rock glaciers and land cover when combined with an uncertainty analysis can effectively be used to map the occurrence of front range permafrost providing an imperative tool for cartographers planners and geocryologists

the significance of rock glaciers in the glacial periglacial landscape continuum rock glaciers are distinct landforms whose wide distribution occurrence and significance often go unrecognised they are deposits of poorly sorted angular blocky to tabular debris which are held together by an ice core or a matrix of ice cemented fine clastics rock glaciers have formed in glaciated and non glaciated areas many researchers have suggested that the absence of an ice core or the lack of movement indicates relict or fossil status active and inactive states can be viewed as the end members of a movement continuum movement rates derived from world wide locations as reported in the literature range from less than 1 cmyr 1 to greater than 130cmyr 1 unfortunately lack of observed movement has been equated incorrectly with an inactive status rock glacier movement must be considered from a rheological point of view movement is controlled by the transformation of potential energy to kinetic energy as the system attempts to reach thermal equilibrium or stability whereas a glacier can completely disappear or redevelop reactivation of a rock glacier requires only the re establishment of the conditions responsible for development and maintenance of interstitial ice although it might not be possible to re establish an ice core interstitial areas can definitely be recharged with ice and thus facilitate movement the concept of active versus inactive should be abandoned in favor of the view that a spatial and temporal continuum of form and movement exists

residence resorption and recycling of zircons in devils kitchen rhyolite coso volcanic field california zircons from the devils kitchen rhyolite in the pleistocene coso volcanic field california have been analyzed by in situ pb u ion microprobe shrimp rg and by detailed cathodoluminescence imaging the zircons yield common pb corrected and disequilibrium corrected pb u ages that predate a previously reported k ar sanidine age by up to 200 kyr and the range of ages exhibited by the zircons is also approximately 200 kyr cathodoluminescence imaging indicates that zircons formed in contrasting environments most zircons are euhedral and a majority of the zircons are weakly zoned but many also have anhedral embayed cores with euhedral overgrowths and multiple internal surfaces that are truncated by later crystal zones concentrations of u and th vary by two orders of magnitude within the zircon population and by 10 20 times between zones within some zircon crystals indicating that zircons were transferred between contrasting chemical environments a zircon saturation temperature of 750 c overlaps within error a previously reported phenocryst equilibration temperature of 740 25 c textures in zircons indicative of repeated dissolution and subsequent regrowth are probably caused by punctuated heating by mafic magma input into rhyolite the overall span of ages and large variation in u and th concentrations combined with calculated zircon saturation temperatures and resorption times are most compatible with crystallization in magma bodies that were emplaced piecemeal in the crust at coso over 200 kyr prior to eruption and that were periodically rejuvenated or melted by subsequent basaltic injections

rapid remobilization of magmatic crystals kept in cold storage we lack thermal histories for magma reservoirs but here the magma under mount hood oregon usa is shown to have been too cold to mobilize for most of the time it has been stored which implies that magma mobilizes at which point it can be imaged geophysically very quickly prior to eruption this paper presents a novel approach to constraining the thermal history of the subsurface magma bodies that feed eruptions by combining temporal information from a variety of sources kari cooper and adam kent combine timescales derived from uranium series disequilibria textural information and trace element zoning in crystals they show that at mount hood oregon only a small fraction of the total storage duration has been spent at temperatures above the critical crystallinity the point at which magma is easily mobilized they conclude that largely liquid bodies that could be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption the processes involved in the formation and storage of magma within the earth s upper crust are of fundamental importance to volcanology many volcanic eruptions including some of the largest result from the eruption of components stored for tens to hundreds of thousands of years before eruption1 2 3 although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes they remain relatively poorly known4 5 eruptions of crystal rich magma are often suggested to require the mobilization of magma stored at near solidus conditions6 7 8 however accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures7 8 9 what has been lacking in this debate is clear observational evidence linking the thermal and therefore physical conditions within a magma reservoir to timescales of storage that is thermal histories here we present a method of constraining such thermal histories by combining timescales derived from uranium series disequilibria crystal sizes and trace element zoning in crystals at mount hood oregon usa only a small fraction of the total magma storage duration at most 12 per cent and probably much less than 1 per cent has been spent at temperatures above the critical crystallinity 40 50 per cent at which magma is easily mobilized partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near solidus temperatures is common magma storage at low temperatures indicates that although thermobarometry calculations based on mineral compositions may record the conditions of crystallization they are unlikely to reflect the conditions of most of the time that the magma is stored our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption

a 10 300 year old permafrost core from the active rock glacier lazaun southern otztal alps south tyrol northern italy two cores were drilled on rock glacier lazaun in the southern otztal alps n italy the average ice content of core lazaun i is 43 vol and of core lazaun ii is 22 vol radiocarbon dating of plant macrofossil remains of core lazaun i yielded ages ranging from 8960 cal yr bp at a depth of ca 23 5 m to 2240 cal yr bp at a depth of 2 8 m indicating that the ice near the base is approximately 10 300 yr old the rock glacier was intact since that time and the ice persisted even during warm periods of the holocene an ice free debris layer between 16 8 and 14 7 m separates the rock glacier into two frozen bodies inclinometer measurements indicate that both frozen bodies are active and that deformation occurs within a shear horizon at a depth of 20 25 m at the base of the lower frozen body and to a minor extent at a depth of approximately 14 m at the base of the upper frozen body the ice free debris layer in the middle of the lazaun rock glacier indicates a more than five centennial long drought period which dates to about 4300 3740 cal yr bp

pdf orientations in shocked quartz grains around the chicxulub crater we measured 852 sets of planar deformation features pdfs in shocked quartz grains in impactite samples of the yaxcopoil yax 1 core and from 4 cretaceous tertiary k t boundary deposits the monaca the cacarajcara and the pealver formations in cuba and dsdp site 536 within 800 km of the chicxulub crater in order to investigate variations of pdf orientations in the proximity of the crater orientations of pdfs show a broad distribution with peaks at 1013 1012 and 1112 plus r z 1011 orientations with minor c 0001 s 1121 t 2241 plus x 5161 and m 1010 plus a 11 20 orientations planar deformation features with c 0001 orientation are relatively more abundant in the proximity of the chicxulub crater than in distal sitessuch as north america the pacific ocean and europe this feature indicates that in the proximity ofthe crater part of the shocked quartz grains in the k t boundary deposits were derived from the lowshock pressure zones moreover the orientations of pdfs with 1122 plus r z 1011 are high in our studied sites and frequencies of these orientations decrease with increasing distance from the crater on the other hand absence of c 0001 and the rare occurrence of pdfs with 1122 plus r z 1011 orientations in the sample from the yax 1 core that was taken at the top of the impactite layer of the chicxulub crater suggests that the sampling horizon that reflects a certain cratering stage is also an important factor for variations in shocked quartz

southern carpathian rock glaciers inventory distribution and environmental controlling factors abstract rock glaciers are valuable diagnostic landforms indicating permafrost creeping during their genesis and activity based on the analysis of high quality air orthophoto and field work a first polygon based inventory of rock glaciers from the southern carpathians has been elaborated in total 306 rock glaciers were included in the inventory comprising 79 debris and 227 talus rock glaciers most of these landforms were classified as relict 258 while only 48 covering 2 81 km 2 were considered intact the size of rock glaciers considered as a proxy for past environmental conditions and the relationships with the predictor variables lithology aspect contributing area geographic coordinates elevation and slope range were analysed using bivariate statistics analysis of variance anova and various post hoc tests the statistical analysis revealed that the rock glaciers occurring in the highest mountain ranges in areas composed of granites and granodiorites are considerably larger than the others because their duration of activity is greater strong dependences between rock glacier size and other topographic attributes contributing area aspect and slope range were also confirmed the rock glacier distribution in the southern carpathians is clearly controlled by topography lithology and debris availability the abundance of rock glaciers increases with altitude but their size decreases slightly in mountain units where granites and granodiorites predominate retezat and par ng mountains the density of rock glaciers and the mean specific area covered by these spectacular landforms are considerably higher than in other areas the higher continentality effects of the southern carpathians enabled the formation of rock glaciers at substantially lower elevations than in the alps the mean altitude of intact rock glaciers front which could be used as a morphological indicator of discontinuous permafrost is located at 2088 m

magma emplacement differentiation and cooling in the middle crust integrated zircon geochronological geochemical constraints from the bergell intrusion central alps abstract u th pb zircon geochronology is an essential tool for quantifying the emplacement differentiation and thermal evolution of crustal magmatic systems however the power of u pb zircon dates can be enhanced through complementary characterization of mineral texture and geochemistry as this permits more detailed interpretations of geochronological datasets than conventionally achieved our approach to better relating zircon dates and geological processes consists of a multi method analytical workflow including cathodoluminescence imaging cl in situ la icpms epma zircon geochemistry u pb zircon id tims geochronology and solution icpms zircon trace element analysis u pb tims tea these methods are here applied to zircon from the bergell intrusion a composite alpine pluton preserving a 10 km mid crustal transect hand samples of tonalite granodiorite and hybridized granitoid each record 250 700 kyr of autocrystic zircon growth bergell zircons are ubiquitously zoned with ca 10 4 10 6 yr growth histories as evidenced by id tims analysis of microsampled fragments from single crystals u pb tims tea data exhibit compositional trends on multiple spatiotemporal scales including the handsample scale representing in situ differentiation at the emplacement level e g th u lithology scale defining trajectories corresponding to the production of tonalitic versus granodioritic magmas lu hf and pluton scale indicating increasingly evolved melts over 1 6 myr of pluton assembly zr hf these absolute tims tea temporal trends are corroborated by relative la icpms epma core to rim geochemistry we compare records of trace element evolution from tims tea bergell whole rock geochemistry and a global compilation of whole rock geochemical data these findings support zircon compositional evolution as a robust indicator of differentiation at local and crustal scales and provide key empirical constraints on melt differentiation and cooling timescales in the middle crust

gas driven filter pressing in magmas insights into in situ melt segregation from crystal mushes gas driven filter pressing is the process of melt expulsion from a volatile saturated crystal mush induced by the buildup and subsequent release of gas pressure filter pressing is inferred to play a major role in magma fractionation at shallow depths 10 km by moving melt and gas relative to the solid crystalline framework however the magmatic conditions at which this process operates remain poorly constrained we present novel experimental data that illustrate how the crystal content of the mush affects the ability of gas driven filter pressing to segregate melt hydrous haplogranite 2 1 wt water in the melt and dacite 4 2 wt water in the melt crystal mushes with a wide range of crystallinities 34 80 vol crystals were investigated using in situ high temperature 500 800 c synchrotron x ray tomographic microscopy with high spatial 3 m pixel and temporal resolution 8 s per three dimensional data set our experimental results show that gas driven filter pressing operates only below the maximum packing of bubbles and crystals 74 vol above this threshold the mush tends to fracture and gas escapes via fractures therefore the efficiency of gas driven filter pressing is promoted close to the percolation threshold and in situations where a mush inflates slowly relative to build up of pressure and expulsion of melt such observations offer a likely explanation for the production of eruptible crystal poor magmas within earth s crust

petrogenesis of coexisting high silica aluminous and peralkaline rhyolites from yunshan yongtai southeastern china abstract the late cretaceous bimodal yunshan yongtai volcanics in fujian province contain peralkaline rhyolites the only presence of such rhyolites in southeastern china whole rock and mineral chemical compositions are analyzed for the coexisting aluminous metaluminous to weakly peraluminous peralkaline high silica rhyolites from the yunshan volcanics they are sparsely porphyritic and contain k feldspar ferromagnesian minerals quartz magnetite and titanomagnetite phenocrysts as well as accessory minerals such as fayalite chevkinite apatite and zircon the mineral assemblage indicates an oxidizing pre eruption condition these rhyolites exhibit diagnostic geochemical features of a type granites such as elevated 10 4 ga al mostly greater than 2 6 and feo t feo t mgo ratios enrichment in high field strength elements hfse such as zr 400 ppm and nb and strong depletion in al 2 o 3 2 o poor meta granitic igneous rocks in the deep crust and cannot be fractionated from the coeval yunshan mafic magmas geochemical variations of major and trace elements indicate the possible fractionation of k feldspar calcium rich pyroxene fe ti oxides and minor chevkinite during the magma evolution in peralkaline rhyolites we found that the pre existing fe ti oxide and hedenbergite phenocrysts had been transformed into aegirine oxide and aegirine oxide fluorite assemblages respectively these mineral assemblages are the products of the subsolidus reaction of pre existing phenocrysts and extraneous na f rich fluids such na f rich fluids may be derived from the degassing of the subvolcanic rocks the reactions indicate that the yunshan peralkaline rhyolites could be generated through the reaction of highly fractionated aluminous silica magmas and na f rich fluids

magmatic perturbations in the okataina volcanic complex new zealand at thousand year timescales recorded in single zircon crystals abstract using single crystals to trace the chemical evolution of a magmatic system has long been a goal of igneous petrology crystals utilized for in situ dating hold great potential to link compositional and temporal information to better understand the evolution of a magmatic system if micron scale zoning of trace elements within a single zircon can be directly associated with volcanic events in magmatic systems then new insights into long term maintenance and storage of eruptible magma can be unlocked this study presents new data that directly links the geochemical history recorded in individual zircon crystals with over 50 000 yrs of changing physical and chemical conditions within a magma reservoir trace elements hf and y in zircon have not diffusively equilibrated with their host melt so that they store information about the melt when that zone crystallized thus different stages of growth can be associated with discrete time periods in the magmatic system zircon from the two most recent rhyolite eruptions kaharoa and whakatane within the okataina volcanic complex ovc new zealand have both isotopic age and trace element signatures that correspond with distinct changes in the temperature and phase assemblage of pulses of erupted magma within the caldera system this discrete change is associated with caldera collapse and reflects a change from cold wet source rhyolite to a relatively hotter and drier source rhyolite and back the kaharoa and whakatane eruptions are separated by 4000 yrs and 15 km distance yet the zircon populations record the same distinct thermal and chemical pulse that occurred following caldera collapse suggesting an interconnected magmatic system that houses at least small volumes of rhyolite melt for timescales of 10 3 to 10 5 yrs that is periodically extracted during eruption

a preliminary inventory of rock glaciers at 30 s latitude cordillera frontal of san juan argentina abstract the dry andes of the cordillera frontal of san juan 30 s latitude is characterized by high relief with peaks up to 5000 m a s l this geological province is mainly made up of a suite of triassic to miocene volcanic rocks modern ice glaciers are small and few in number and persistent snow fields are similarly small and scattered the predominant landforms in these areas have been shaped in a periglacial environment superimposed on an earlier glacial landscape a preliminary inventory map of rock glaciers was constructed using optical remote sensing techniques digital topographic analysis and aerial photograph data organized in a geographic information system gis over 140 rock glaciers have been identified 90 are active or inactive and the rest are fossil a total of 88 rock glaciers are considered active the most common periglacial features recognized in the area are talus glaciers and only 23 are tongue shaped glaciers

reconsidering the glacier to rock glacier transformation problem new insights from the central andes of chile abstract the glacier to rock glacier transformation problem is revisited from a previously unseen angle a striking case in the juncal massif located in the upper aconcagua valley chilean central andes is documented there the presenteseracae debris covered glacier has advanced several tens of metres and has developed a rock glacier morphology in its lower part over the last 60 years the conditions for a theoretically valid glacier to rock glacier transformation are discussed and tested permafrost probability in the area of the studied feature is highlighted by regional scale spatial modelling together with on site shallow ground temperature records two different methods are used to estimate the mean surface temperature during the summer of 2014 and the sub debris ice ablation rates are calculated as ranging between 0 05 and 0 19 cm d 1 i e 0 04 and 0 17 m over the summer these low ablation rates are consistent with the development of a coherent surface morphology over the last 60 years furthermore the rates of rock wall retreat required for covering the former glacier at presenteseracae lie within the common 0 1 2 mm y 1 range assuming an average debris thickness and a range of debris covering time intervals the integration of the geomorphological observations with the numerical results confirms that the studied debris covered glacier is evolving into a rock glacier

timing and conditions of formation of granitoid clasts erupted in recent pyroclastic deposits from tarawera volcano new zealand abstract granitoid clasts in pyroclastic deposits of the 0 7 ka kaharoa eruption from the intra caldera tarawera volcano of the okataina volcanic centre ovc new zealand provide an insight to the plutonic processes beneath one of the most productive quaternary rhyolite centers on earth sims u th data for 79 granitoid zircon crystals from six clasts reveal a unimodal age spectrum yielding a weighted average model age of 208 4 ka mswd 1 2 n 72 the remaining crystals are at secular equilibrium and u pb analyses indicate that a few of these outliers date back to 750 ka a period significantly longer than the known volcanic record at ovc probably 550 ka in contrast zircon crystallization in co erupted pumice and lava of the 0 7 ka kaharoa event and that of the three preceding rhyolite eruptions occurred mostly during 0 50 ka reflecting a separate magmatic history brittle deformation features incipient alteration and low 18o whole rock compositions 3 are consistent with a shallow solid intrusion that has interacted with meteoric hydrothermal fluids however 18o sims analyses of zircons 5 4 0 2 n 11 are consistent with magmatic compositions and thus meteoric interaction occurred post emplacement the kaharoa granitoids contrast with those ejected in the 40 60 ka caldera forming rotoiti event that were partly molten and display zircon age spectra indistinguishable from those for co erupted pumices suggesting the latter were derived from contemporaneous crystal mush the 0 7 ka kaharoa case shows that zones of the magmatic system remained solid despite frequent and voluminous magma production that included caldera forming events such long lived sub solidus zones in magma systems would act as barriers to melt connectivity and interaction with country rock but are also a potential source for antecrysts xenocrysts in subsequent eruptions this exemplifies how plutonic and volcanic evolution can diverge even in close proximity

tracking crystal melt segregation and magma recharge using zircon trace element data abstract the cretaceous yunshan caldera complex in se china consists of an unusual coexisting assemblage of peraluminous and peralkaline rhyolites and a resurgent intra caldera porphyritic quartz monzonite in this study we use zircon trace element data to study the compositional differences of zircons from cogenetic magmas and to track the evolution of the entire magmatic system our results indicate that the zircons from the peraluminous and peralkaline rhyolites formed from highly evolved compositions with high hf concentrations and low ti contents and low th u and zr hf ratios which are distinct from those of the intrusive porphyritic quartz monzonite zircons from the peraluminous and peralkaline rhyolites display overlapping zr hf and hf but the zircons from the peralkaline rhyolites have extremely low eu eu ratios

application of frequency ratio and logistic regression to active rock glacier occurrence in the andes of san juan argentina this study employs statistical modeling techniques and geomorphological mapping to analyze the distribution of active rock glaciers in relation to altitude aspect slope lithology and solar radiation using optical remote sensing techniques with gis the study area includes a portion of the dry andes of the cordillera frontal of san juan around 30 s latitude where few geomorphological studies have been conducted over 155 rock glaciers have been identified and 85 are considered active the relationship between the variables and the rock glaciers distribution was analyzed using the frequency ratio method and logistic regression models the analytical results show that elevations 3824 m a s l a south facing or east facing aspect areas with relatively low solar radiation and slope between 2 and 20 favor the existence of the rock glaciers and demonstrate that lithology and slope exert major influences

trace element composition of igneous zircon a thermal and compositional record of the accumulation and evolution of a large silicic batholith spirit mountain nevada hafnium u th and ree content of zircons from the spirit mountain batholith in southern nevada correlate with calculated temperatures from the ti in zircon thermometer to support field and petrologic evidence of rejuvenation of crystal mush and melt extraction events during the 2 million year accumulation of the granitoid batholith marked variation in zircon composition from sample to sample from grain to grain within individual samples and from zone to zone within individual grains documents in detail a history of fluctuating conditions with repeated episodes of replenishment reheating crystal mush rejuvenation fractional crystallization and melt segregation the zircons exhibit compositional and thermal variability indicative of variations in host melt composition due to 1 melt rejuvenation mixing and fractionation 2 coeval growth of other ree rich accessory minerals and possibly 3 fluctuation in fo2