radiocarbon dates on deglaciation cordillera central northern peruvian andes abstract three radiocarbon dates along with relative dating criteria place limits on the deglaciation history of manachaque valley cordillera central ice retreated from the late glacial maximum by at least 12 100 yr b p during ice retreat numerous moraines were deposited throughout the valley glacier cover was reduced to about half that of the last glacial maximum by at least 9700 yr b p and to less than a tenth by at least 6450 yr b p because all dates are minimum the dates and field data are consistent with little or no ice remaining by early holocene no unambiguous younger dryas moraines are present

delta progradation and neoglaciation laguna paron cordillera blanca peru the history of holocene glaciation serves as an important record of glacier mass balance and therefore of climatic change the moraine record of holocene glaciation in the tropical andes however is fragmentary and poorly dated in contrast increases in the rate of accumulation of inorganic sediment in glacier fed lakes have been linked to periods of neoglaciation in many mountain regions the interpretation of such a record of neoglaciation from sediment cores in glacier fed lakes in the tropical andes can provide the continuity and chronologic control that is lacking in the existing moraine record unusual exposures of glacial lacustrine sediment in the cordillera blanca peru provide a rare opportunity to assess the link between climatic change glaciation and lacustrine sedimentation intentional lowering of water levels in laguna paron 9 s 77 44 w 4200 m a s l in 1985 resulted in the incision and exposure of at least 20 m of deltaic deposits at the eastern end of the lake three deltaic units can be identified horizontal topset beds steeply dipping and deformed foreset beds and horizontally laminated fine grained sediment six radiocarbon ages ranging from 1800 210 to 465 95 14c yr bp on wood indicate that the average rate of delta progradation in the late holocene has been approximately 290 m per 1000 yr the lake formed during deglaciation at least 10 000 yr ago and if such a rate of progradation of the delta had prevailed over the entire holocene then the delta would be at least three times as extensive as it is today thus the rate of delta progradation has varied significantly over the holocene we suggest that the rate of delta progradation was at least three times greater when glaciers were in advanced positions these positions are clearly delimited by neoglacial moraines which are within 1 2 km of the exposures studied and within 1 km of modern ice limits the most recent increase in the rate of delta progradation is evidenced by an increase in sedimentation rate ca 575 90 14c yr bp coincident with the onset of the little ice age copyright 2005 john wiley sons ltd

population wide garnet growth zoning revealed by la icp ms mapping implications for trace element equilibration and syn kinematic deformation during crystallisation the strong partitioning of many trace elements into garnet and their slow diffusivities in both garnet and the rock matrix means that their distribution may record valuable petrogenetic information not documented by major elements in metamorphic rocks complex trace element growth zoning in garnet porphyroblasts from a garnet grade metapelite from the barrovian sequence of the sikkim himalaya is assessed using quantified la icp ms raster mapping coupled with x ray micro computed tomography the data document systematic changes in the zoning patterns from early to late nucleated crystals and also suggest that the ree y chemistry incorporated into garnet is dependent on persistent disequilibrium in the rock volume there is evidence for hree y diffusion haloes surrounding growing garnets and a heterogeneous hree y distribution in the rock matrix annuli superimposed on oscillatory zoning are not consistent with formation during some rock wide event but are dependent on the spatial disposition of the garnet annuli are interpreted to reflect an integrated history of varying growth rates and the incorporation of pre existing heterogeneities due to relatively slow matrix diffusivities conversely smooth zoning of many transition metals indicate that their distribution in garnet may be controlled by equilibrium partitioning between garnet and the rock matrix significant rotation of garnet porphyroblasts during growth is revealed due to immobility of cr over the duration of the crystallisation interval and overprinting of the heterogenous precursor cr distribution strain rate estimates derived from this zoning are on the order of 10 11 10 12 hbox s 1

controls on metamorphic equilibration the importance of intergranular solubilities mediated by fluid composition a dramatic demonstration of the role of intergranular solubility in promoting chemical equilibration during metamorphism is found in the unusual zoning of garnet in pelitic schist exposed at harpswell neck maine usa many garnet crystals have irregular patchy distributions of mn cr fe and mg in their inclusion rich interiors transitioning to smooth concentric zoning in their inclusion poor outer rims in contrast zoning of ca and y is comparatively smooth and concentric throughout we re assess the disputed origin of these zoning features by examining garnet growth in the context of the thermal and structural history of the rocks and by evaluating the record of fluid rock interaction revealed in outcrop scale veining and fluid inclusion assemblages the transition in the character of garnet zoning correlates with the onset of a synkinematic simple shear dominated phase of garnet growth and with a shift in the composition of the intergranular fluid from co2 rich to h2o rich compositional variations in garnet are therefore best explained by a two stage growth history in which intergranular diffusive fluxes reflect differences in the concentration of dissolved species in these two contrasting fluids interiors of garnet crystals grew in the presence of a co2 rich fluid in which limited solubility for mn and cr and perhaps fe and mg produced patchy disequilibrium overprint zoning while appreciable solubility for ca and y permitted their rock wide equilibration rims grew in the presence of an h2o rich fluid in which high intergranular concentrations for all elements except cr enabled diffusion over length scales sufficient for rock wide equilibration this striking example of partial chemical equilibrium during reaction and porphyroblast growth implies that thermal effects may commonly be subsidiary in importance to solubilities in the intergranular medium as determinants of length scales for metamorphic equilibration

crystal size distribution and composition of garnets in eclogites from the dabie orogen central china crystal size and spatial distributions of minerals in metamorphic rocks provide insight into their nucleation growth environment and the metamorphic evolution of their host rocks episodic nucleation and growth histories for garnets in eclogites from the dabie orogen are revealed by variations in crystal size geochemical zoning and mineralogy of inclusions in garnets the studied garnets show pseudo lognormal crystal size distributions csds prograde chemical zoning patterns indexed by mineral inclusions and are mainly distributed at random constant growth rate for each episode is proposed based on the mineralogy of inclusions in garnets and the chemical zoning patterns the csd shapes were evaluated in terms of a size dependent proportionate growth model and a thermally accelerated diffusion controlled model but neither is consistent with the geochemical data and the concordant occurrence of mineral inclusions in garnet initial increasing nucleation rate followed by a subsequent medial stage of nearly constant growth and finally declining nucleation rate is inferred from the csd data this study suggests that linking chemical analysis with textural analysis is crucial to avoid misleading interpretation solely through csd shapes of minerals in metamorphic rocks

a comparison of microstructural and chemical patterns in garnet from the fleur de lys supergroup newfoundland this study uses compositional analyses of garnet porphyroblasts to test a previously published microstructure based model of garnet growth in the fleur de lys supergroup x ray maps reveal significant compositional anomalies within garnet including zoning reversals and steepened compositional gradients these anomalies occur at the margin of the proposed first stage of garnet growth g1 and coincide with truncations of inclusion trails and changes in the inclusion assemblage intervals of reversed composition zoning and steepened compositional gradients across this boundary are interpreted to represent a hiatus in garnet growth possibly accompanied by garnet consumption during which changes in the garnet forming reaction p t conditions and deformation kinematics occurred the junction of the proposed second and third stages of garnet growth g2 and g3 coincides with the transition between successive crenulation cleavages without substantial microstructural truncations or changes in the inclusion assemblage the g2 g3 boundary is generally marked by uninterrupted normal zoning with subtle compositional anomalies in some samples this boundary may in fact record continuous garnet growth or alternatively mark a relatively short intra orogenic pause in garnet growth with minimal affect on zoning patterns individual porphyroblasts with contrasting inclusion trail microstructures also have different zoning patterns and this supports the previous recognition of contrasting growth histories between individual porphyroblasts a combined structural metamorphic model is presented that integrates the timing of garnet growth and foliation development reaction history and the p t t path in the fleur de lys supergroup

a structural metamorphic study of the broken hill block nsw australia the prograde pressure temperature p t path for the complexly polydeformed proterozoic broken hill block australia has been reconstructed through detailed structural analysis in conjunction with calculation of compositionally specific p t pseudosections of pelitic rock units within a high temperature shear zone that formed early in the tectonic evolution of the terrane whilst the overall p t path for the broken hill block has been interpreted to be anticlockwise the prograde portion of this path has been unresolved our results have constrained part of this prograde path showing an early heating event m1 at p t conditions of at least c 600 c and c 2 8 4 2 kbar associated with an elevated geothermal gradient c 41 61 c km 1 this event is interpreted to be the result of rifting at c 1 69 1 67 ga or at c 1 64 1 61 in the broken hill block early rifting was followed by an episode of lithospheric thermal relaxation and burial during which time sag phase sediments of the upper broken hill stratigraphy paragon group were deposited following sedimentation a second tectonothermal event m2 d2 occurred this event is associated with peak low pressure granulite facies metamorphism c 1 6 ga and attained conditions of at least 740 c at c 5 kbar a regionally pervasive high temperature fabric s2 developed during the m2 d2 event and deformation was accommodated along lithology parallel high temperature shear zones the larger scale deformation regime extensional or shortening of this event remains unresolved the m2 d2 event was terminated by intense crustal shortening during the olarian orogeny during which time the first mappable folds within the broken hill block developed

development of garnet porphyroblasts by multiple nucleation coalescence and boundary misorientation driven rotations two types of garnet porphyroblast occur in the schneeberg complex of the italian alps type 1 porphyroblasts form ellipsoidal pods with a centre consisting of unstrained quartz decussate mica and small garnet grains and a margin containing large garnet grains orientation contrast imaging using the scanning electron microscope shows that the larger marginal garnet grains comprise a number of orientation subdomains individual garnet grains without subdomains are small 50 m faceted and idioblastic and have simple zoning profiles with ca rich cores and ca poor rims subdomains of larger garnet grains are similar in size to the individual small garnet grains type 2 porphyroblasts comprise only ellipsoidal garnet with small subdomains in the centre and larger subdomains at the margin each subdomain has its own ca high ca dropping towards subdomain boundaries garnet grains with or without subdomains all have the same ca poor composition at rims in contact with other minerals the compositional zonation patterns are best explained by simultaneous multiple nucleation followed by growth and amalgamation of individual garnet grains the range of individual garnet and garnet subdomain sizes can be explained by a faster growth rate at the porphyroblast margin than in the centre the difference between type 1 and type 2 porphyroblasts is probably related to the growth rate differential across the porphyroblast electron backscatter diffraction shows that small individual garnet grains are randomly oriented large marginal garnet grains and subdomain bearing garnet grains have a strong preferred orientation clustering around a single garnet orientation misorientations across subdomain boundaries are small and misorientation axes are randomly oriented with respect to crystallographic orientations the only explanation that fits the observational data is that individual garnet grains rotated towards coincident orientations once they came into contact with each other this process was driven by the reduction of subdomain boundary energy associated with misorientation loss rotation of garnet grains was accommodated by diffusion in the subdomain boundary and diffusional creep and rigid body rotation of other minerals quartz and mica around the garnet an analytical model in which the kinetics of garnet rotation are controlled by the rheology of surrounding quartz suggests that at the conditions of metamorphism the rotation required to give a strong preferred orientation can occur on a similar time scale to that of porphyroblast growth

an overgrowth model to explain multiple dispersed high mn regions in the cores of garnet porphyroblasts the central portions of garnet porphyroblasts from harpswell neck maine exhibit small discrete regions of high mn content dispersed in three dimensions orientation contrast imaging oci and quantitative crystallographic orientation measurements from electron backscatter diffraction ebsd patterns show that most garnet porphyroblasts contain no variations in crystallographic orientation it is difficult to reconcile these data with a model in which each high mn region represents a discrete garnet nucleus an alternative hypothesis invokes a model of garnet growth in which precursor phases rich in mn are overgrown and their mn is incorporated locally into the garnet structure although this model requires length scales for equilibration of mn during the early stages of garnet growth that are shorter than any previously documented that inference is consistent with the very low temperatures of garnet nucleation in these rocks and with compositional evidence for progressively larger scales of equilibrium as reaction progressed very short length scales for equilibration of mn identified in this study for the lowest grade portion of the history of the rocks call into question the common assumption of rock wide equilibrium for mn during garnet growth at low temperature the absence of rock wide equilibrium for mn at low grade has potential negative implications for all common interpretive methods based in phase equilibria including thermobarometric studies and thermodynamic analysis of the origin and meaning of zoning in low grade garnet

soil catena variation along an alpine climatic transect northern peruvian andes abstract morphological and chemical properties of soils developed on end moraines of mostly quartzitic and granitic composition in the puna region of the northern peruvian andes vary with slope position and climate soil development was assessed on two catenas of similar age range 8 12 ka in two different precipitation zones at summit backslope and footslope positions soil properties that show trends downslope and with increased rainfall are greater clay content greater organic carbon content and greater pedogenic fe content in addition ph is lower in the higher rainfall area eolian material mixed loess forms the surface layer a horizon and may be responsible for the remarkable slope stability in the area it is suggested that mixed loess provided material for chemical alteration and translocation of clay and fe vertically and downslope in quartz rich parent materials soil data suggest that the amount of climate change during the holocene is limited it is doubtful if the climate at the wetter end of the transect ever existed at the drier end

evidence for holocene stability of steep slopes northern peruvian andes based on soils and radiocarbon dates summary radiocarbon dating and soil relationships indicate that landscapes in highaltitude glaciated valleys of the northern peruvian andes have been remarkably stable during the holocene radiocarbon dates show that deglaciation was underway by 12 ka and that slopes and alluvial fans at the bases of slopes were essentially stabilized by at least 8 ka the soils consist of fine grained loessial a horizons overlying bw horizons in gravelly till or alluvial fan gravel following deglaciation widespread gullying took place in till on the steep maximum angle 37 sideslopes of most valleys the eroded material was deposited as fans at the bases of the slopes loess was then deposited as a fairly uniform blanket across most elements of the landscape soil formation began during or following loess deposition and because soil profile morphology is sufficiently similar at most sites soil formation has been a dominant process during much of the holocene this remarkable stability especially for such steep slopes is attributed to a combination of tight packing of the till permeability of the capping loess rapid revegetation following ice retreat and roots from the present grassland vegetation and possibly former forests

subdivision of late pleistocene moraines in the cordillera blanca peru based on rock weathering features soils and radiocarbon dates abstract the progressive development of unusual rock weathering features and soils and minimum limiting radiocarbon dates provide a basis for subdividing four groups of late pleistocene moraines on the west side of the cordillera blanca northern peru 9 20 1 000 s 77 10 77 30 w boulders on the youngest late pleistocene moraines have 10 to 14 cm tall weathering posts soils on these moraines yield mean profile development index pdi values of 0 05 0 04 1 these moraines date between ca 13 500 and 9700 500 yr b p older than previously postulated the next older moraines have boulders with weathering post heights between 20 and 25 cm and soils with pdi values of 0 08 0 07 and were deposited prior to 13 280 190 yr b p probably during the last glacial maximum marine isotope stage 2 moraines from an older glaciation have boulders with weathering posts between 39 and 50 cm high soils that yield pdi values of 0 21 0 07 and are older than 19 700 340 yr b p boulders on moraines from a still older glaciation have lost ca 50 of their above ground volume and have weathering posts between 62 and 70 cm high pdi values for soils on these moraines are 0 32 0 06 linear and logarithmic models of weathering post and soil development with time are used to estimate minimum and maximum ages for the two oldest moraine groups linear models suggest that the second oldest moraines are between ca 20 500 and 46 500 yr b p and that the oldest moraines are between ca 29 000 and 72 000 yr b p in contrast logarithmic models suggest ages of greater than ca 75 500 yr b p and greater than ca 500 000 yr b p respectively

holocene provenance shift of suspended particulate matter in the amazon river basin abstract the strontium sr neodymium nd and lead pb isotope signatures of suspended particulate matter spm in rivers reflect the radiogenic isotope signatures of the rivers drainage basin these signatures are not significantly affected by weathering transport or depositional cycles but document the sedimentary contributions of the respective sources we report new sr nd and pb isotope ratios and element concentrations of modern spm from the brazilian amazon river basin and document the past evolution of the basin by analyzing radiogenic isotopes of a marine sediment core from the slope off french guiana archiving the last 40 kyr of amazon river spm and the holocene section of sediment cores raised between the amazon river mouth and the slope off french guiana the composition of modern spm confirms two main source areas the andes and the cratonic shield in the marine sediment core notable changes occurred during the second phase of heinrich stadial 1 i e increased proportion of shield rivers spm and during the last deglaciation i e increased proportion of madeira river spm together with elsewhere constant source contributions furthermore we report a prominent offset in sr and nd isotopic composition between the average core value end 11 7 0 9 2sd 87sr 86sr 0 7229 0 0016 2sd and the average modern amazon river spm signal end 10 5 0 5 2sd 87sr 86sr 0 7213 0 0036 2sd we suggest that a permanent change in the amazon river basin sediment supply during the late holocene to a more andean dominated spm was responsible for the offset

comments on c m clapperton s glacier readvances in the andes at 12500 10000 yr bp implications for mechanism of late glacial climatic change

diffusion limited ree uptake by eclogite garnets and its consequences for lu hf and sm nd geochronology garnets from the zermatt saas fee eclogites contain narrow central peaks for lu yb tm er and at least one additional small peak towards the rim the ree sm eu gd tb dy are depleted in the cores but show one prominent peak close to the rim these patterns cannot be modeled using rayleigh fractionation accompanied by mineral breakdown reactions instead the patterns are well explained using a transient matrix diffusion model where ree uptake is limited by diffusion in the matrix surrounding the porphyroblast observed profiles are well matched if a roughly linear radius growth rate is used the secondary peaks in the garnet profiles are interpreted to reflect thermally activated diffusion due to temperature increase during prograde metamorphism the model predicts anomalously low 176lu 177hf and 147sm 144nd ratios in garnets where growth rates are fast compared to diffusion of the ree and these results have important implications for lu hf and sm nd geochronology using garnet

cathodoluminescence imaging and titanium thermometry in metamorphic quartz cathodoluminescence cl of quartz from metamorphic rocks representing a range of conditions from the garnet grade to the migmatite grade reveals a variety of textures that is a function of metamorphic grade and deformation history ti concentrations determined by electron microprobe and ion microprobe generally correlate with cl intensity blue wavelengths and application of the ti in quartz thermometer titaniq reflects the temperature of quartz growth or recrystallization and in some settings modification by diffusion quartz from garnet grade samples is not visibly zoned records temperatures of 425 475 c and is interpreted to have recrystallized during fabric formation quartz grains from staurolite grade samples are zoned in cl with markedly darker cores and brighter rims some of which are interpreted to have been produced by the dominant staurolite producing reaction whereas others are interpreted as having formed by diffusion of ti into quartz rims quartz from the matrix of kyanite and sillimanite grade samples are generally unzoned although locally displays slightly brighter rims higher ti quartz inclusions within garnet and staurolite have distinctly brighter rims which are interpreted as having been produced by diffusive exchange with the host mineral quartz from migmatite grade samples displays highly variable cl intensity which is dependent on the location of the grain matrix grains in melanosomes are largely unzoned or rarely zoned with darker cores leucosome quartz is strongly zoned with bright cores and dark rims and is interpreted as having formed during crystallization of the melt locally within the leucosome is observed oscillatory zoned quartz which is interpreted as a subsolidus recrystallization to achieve strain relaxation quartz inclusions within garnet or plagioclase crystals often show bright domains separated by zones of dark cl these enigmatic textures possibly reflect local melting fluxed by fluid inclusions temperatures calculated from the ti in quartz thermometer are a function of the metamorphic grade of the sample the textural setting of the quartz the reaction history and the deformation history of the rock the titaniq temperatures can be used to constrain the conditions at which various metamorphic processes have occurred

a reevaluation of the evidence for a younger dryas climatic reversal in the tropical andes abstract a review of the evidence for a younger dryas equivalent climatic reversal in the tropical andes shows that a number of hypotheses need to be reassessed assumptions of the el abra cold and humid phase in colombia are compromised by insufficient dating control periods of glacier advance in peru and bolivia lack sufficient dating control to be correlated with the european younger dryas only glaciers on the quelccaya ice cap in peru may have advanced shortly before the onset of the european climatic reversal but even there a correlation is questionable a late glacial advance in the chimborazo area in ecuador is considerably older than previously suggested the same glacier advance has been dated to earlier than 12 000 bp in other areas of ecuador the emerging picture suggests two phases of glacier advances in the tropical andes 13 000 12 000 bp and 9000 10 000 bp both may have been caused by increasing precipitation unequivocal evidence for a cold younger dryas event in the tropical andes has yet to emerge

the pleistocene holocene transition in peru and its effects upon human use of the landscape abstract this paper reviews the state of our knowledge regarding the effects of the pleistocene holocene transition on the kinds and range of human adaptations in what is now peru following a discussion of geological paleoclimatic and archaeological data the paper focuses upon four aspects of environmental change with specific regard to how these would have affected human adaptations environmental changes on the pacific littoral the extinction of pleistocene faunal and floral species and their replacement with modern faunas the adaptive radiation of these modern flora and fauna especially into the andean highlands and characteristics of newly available high elevation environments that would have affected the process by which foraging peoples moved into them although pleistocene fauna have been discovered in peru none of these finds have been made in the context of indisputable human activity and therefore the effect of their extinction on early foraging peoples is unknown the earliest acceptable archaeological sites in peru date around 11 12 000 years ago and are found on the coastal lowlands the highlands were not occupied until after 11 000 years ago while high elevation environments were attractive after 11 000 years ago they were only slowly occupied by humans due to the constraints of the combined effects of hypoxia and cold

fracture analysis of a volcanogenic massive sulfide related hydrothermal cracking zone upper bell river complex matagami quebec application of permeability tensor theory located in the matagami mining district of the abitibi greenstone belt quebec the bell river complex is a 5 km thick tholeiitic layered gabbro and or anorthosite body 2724 6 2 5 1 9 mau pb which likely acted as the heat source that drove hydrothermal convection and volcanogenic massive sulfide vms hydrothermal mineralization in the area abundant fractures and veins crosscutting the western lobe of the bell river complex formed over a range of temperatures from 250 to 700 c the 250 to 400 c assemblage quartz epidote sericite chlorite plagioclase is the most widespread and occurs as orthogonal anastomosing and random vein sets vein densities average between 15 and 25 veins per m2 locally reaching as high as 40 to 60 veins per m2 these veins typically 1 to 3 mm wide are interpreted to represent thermal cracking associated with hydrothermal fluid mineralization in the district furthermore they crosscut earlier higher temperature pyroxene plagioclase 600 c and magnetite rich 300 600 c veins 1 10 mm wide densities commonly 0 5 veins per m2 detailed field measurements of quartz epidote vein geometries coupled with permeability tensor theory have produced a first order approximation of the maximum model permeability structure veins unfilled of the hydrothermal cracking zone representative district wide values indicate maximum model bulk permeabilities of 10 10 to 10 8 m2 for the hydrothermal cracking zone similar to permeabilities calculated for the fractured sheeted dike complexes of the semail and troodos ophiolites however a high flow zone located within the central parts of the hydrothermal cracking zone is characterized by a maximum model permeability of 10 7 m2 locally 1 m2 the high flow zone reaches maximum model permeability values as high as 10 6 to 10 5 m2 where two or more veins occur with apertures in excess of 2 cm mapping has shown that the hydrothermal cracking zone is confined to an 350 m thick interval located within a strongly layered gabbro and or anorthosite horizon of the layered zone upper bell river complex the base of this interval is 1 000 m below the top of the bell river complex furthermore in and around the town of matagami the dominant orientation of quartz epidote veins parallels the orientation of the layering 110 15 this parallelism is further reflected in the orientation of the calculated quartz epidote vein permeability tensors 94 30 1 n 71 the parallelism suggests that heterogeneities associated with the layer contacts provided planes of low tensile strength along which the hydrothermal cracks preferentially developed such an interpretation further explains why the hydrothermal cracking zone appears to be restricted to the strongly layered zone there are many more low tensile strength planes zones of quartz epidote veining approximately orthogonal to layering are also present the orthogonal veins are usually less continuous and commonly truncated but not crosscut by layer parallel veins the orthogonal subset of veins is interpreted to represent short pathways that allowed fluids to travel between adjacent layer parallel veins however locally longer layering orthogonal quartz epidote veins showing offsets of 10 to 30 cm normal to the layering of the bell river complex may represent initial conduits that allowed fluids to travel into overlying stratigraphy and through to the paleosea floor although volumetrically small in comparison with the permeability structure of the bulk sea floor the significantly higher permeability of the hydrothermal cracking zone indicates its importance in controlling the flow paths and fluxes of fluids deep within the hydrothermal system

three dimensional patterns of garnet nucleation and growth three dimensional compositional zoning patterns in garnet zone garnets from harpswell neck maine united states suggest complex patterns of nucleation and growth compositional zoning is often asymmetric and core compositions do not always coincide with the geometric center of the garnet in detail garnet zoning patterns show multiple isolated high mno areas that we interpret as sites of garnet nucleation if it is assumed that garnet growth is close to equilibrium and the mn zoning is not significantly modified by diffusion then the mno contours or isosurfaces can serve as a proxy for patterns of garnet nucleation and growth computer generated three dimensional animations of these patchwork mno zoning patterns reveal that many garnets contain multiple nuclei that grew and coalesced to form a single crystal new nuclei often appeared next to preexisting porphyroblasts and became incorporated into the growing crystal contrary to the widely held idea that garnets grow radially outward from a single nucleus we propose that many of the garnets examined in this study grew by the coalescence of multiple nuclei

potential glacial evidence for the younger dryas event in the cordillera of north and south america there is debate as to whether or not the younger dryas yd climatic event affected areas outside of the north atlantic region the potential of alpine glacial deposits to record the yd is of interest because alpine glaciers would be likely to leave a morainal record even during minor short lived advances caused by a period of deteriorating climate in the cordilleran ranges of north and south america there are several candidate moraines many bracketed between radiocarbon ages of ca 12 and 10 ka which may be yd in age the best examples are in the canadian and american rockies the ecuadorian peruvian and bolivian andes and around the patagonian ice cap in most cases temporal brackets are not narrow enough and some radiocarbon ages may not be accurate enough to allow correlation at the present time there are two cases of lateglacial readvance whose ages are interpreted to match or fall within the yd interval an advance of the crowfoot glacier in canada is interpreted to have occurred within the period ca 11 3 and 10 14c ka bp and an advance of the reschreiter glacier in ecuador is interpreted to have culminated in the period ca 11 to 10 6 14c ka bp the latter interpretation depends on an assumption that lake level variations were caused by glacier advances and retreats

enhanced heat transfer in partially saturated hydrothermal systems the role of capillarity is potentially important for determining heat transfer in hydrothermal regions capillarity allows mixing of phases in liquid vapor systems and results in enhanced two phase convection comparisons involving a numerical model with capillarity and analytical models without indicate that heat transfer can be enhanced by about an order of magnitude whether capillarity can be important for a particular hydrothermal region will depend on the nature of mineral precipitation as well as pore and fracture size distributions

microstructure and crystallographic preferred orientation of polycrystalline microgarnet aggregates developed during progressive creep recovery and grain boundary sliding abstract optical microscopy electron probe microanalysis and electron backscatter diffraction methods have been used to examine a broad range of garnet microstructures within a high strain zone that marks the western margin of a major transpression zone in the southern new england appalachians garnet accommodated variable states of finite strain expressed as low strain porphyroclasts type 1 high strain polycrystalline aggregates type 2 and transitional morphologies type 3 that range between these end members type 1 behaved as rigid porphyroclasts and is characterized by four concentric ca growth zones type 2 help define foliation and lineation are characterized by three ca zones and possess a consistent bulk crystallographic preferred orientation of 100 symmetrical to the tectonic fabric type 3 show variable degrees of porphyroclast associated with aggregate where porphyroclasts display complex compositional zoning that corresponds to lattice distortion low angle boundaries and subgrains and aggregate cpo mimics porphyroclast orientation all aggregates accommodated a significant proportion of greenschist facies deformation through grain boundary sliding grain rotation and impingement and pressure solution which lead to a cohesive behavior and overall strain hardening of the aggregates the characteristic cpo could not have been developed in this manner and was the result of an older phase of partitioned amphibolite facies dislocation creep recovery including chemical segregation and recrystallization of porphyroclasts this study demonstrates the significance of strain accommodation within garnet and its affect on composition under a range of pt conditions and emphasizes the importance of utilizing ebsd methods with studies that rely upon a sound understanding of garnet

development of the alluvial and lacustrine terraces on the northern margin of the hetao basin inner mongolia china implications for the evolution of the yellow river in the hetao area since the late pleistocene abstract terrace formation processes can reflect the evolution of large rivers the hetao basin is a floodplain of the yellow river and there are two to three terraces that extend e w on the northern margin based on a detailed field geological survey and measurement of the terrace sections combined with sedimentological and chronological analyses we reconstructed the developmental processes of the three terraces and inferred that three river terraces were formed by the yellow river the osl dating results show that the time of deposition of terrace 3 was prior to 118 ka bp subsequently the terrace began to experience incision and formed the geomorphic surface of terrace t3 similarly terrace 2 and terrace 1 were mainly deposited from 109 and 59 ka respectively and began to be incised prior to 71 and 46 ka respectively the three terraces in the northern hetao basin are the products of the combined actions of climatic shifts and tectonic uplift the yellow river s evolutionary history in the hetao area since the late pleistocene is discussed before about 120 ka bp the yellow river may have flowed through the northern hetao basin between 110 and 70 ka bp the yellow river experienced at least two changes between river and lake sedimentation from 60 to 50 ka a very large river connected lake of the yellow river was developed in the hetao basin after 50 ka the hetao river connected paleolake of the yellow river gradually dried

the chemistry of fumarolic vapor and thermal spring discharges from the nevado del ruiz volcanic magmatic hydrothermal system colombia on the basis of three sets of gas samples taken during the three months preceding the november 13 1985 eruption of nevado del ruiz from fumaroles on the crater floor the composition of the vapors discharged following minor eruptive activity in september corresponded to that of an essentially magmatic gas during the subsequent quiet period in october the proportion of a hydrothermal component in the vapor discharge increased steadily up until the major eruption the gases were found to be exceptionally high in total sulfur and are super saturated with respect to elemental sulfur their thermodynamic equilibration temperatures range from 200 to 600 c gases and waters from fumaroles and thermal springs on the flanks of the volcano are likely to be derived from a two phase vapor brine envelope surrounding the magmatic system the chemistry of the fumarole discharges is compatible with the assumption of an eruptive mechanism involving the build up of pressure in an extensive vapor zone by gas released from an essentially stagnant already extensively degassed body of magmatic material at depth production of such a residual gas over extended periods may account for the large amount of so2 discharged from the volcano in relation to the small amount of ejected solids

deformation induced garnet zoning compositional zoning patterns in garnet porphyroblasts from kyanite bearing samples of the devonian littleton formation north central massachusetts reveal complex patterns of growth that are related to multiple deformation and metamorphic events garnet porphyroblasts exhibit asymmetrical and irregular zoning patterns in xmn xca and fe fe mg zoning reversals in mn and fe fe mg and patch distribution in ca appear to occur around the boundaries of the textural zones also the compositions of the garnet at the textural boundaries are variable for all traverses these observations suggest that the garnet zoning was not only modified from diffusion processes but was also influenced by pre existing microfabrics through the effects of preferential dissolution and resorption in partial disequilibrium relationships between chemical and textural truncations indicate that the zoning patterns of garnet were strongly modified from preferential dissolution and precipitation during the development of successive foliations that occurred in zones of high strain stress cleavage seams and zones of low strain stress respectively

getting the inside story using computed x ray tomography to study inclusion trails in garnet porphyroblasts this study demonstrates how high resolution x ray computed tomography can be used to determine the geometry of curved inclusion trails in garnet porphyroblasts for the first time the three dimensional geometry of these features is shown as an animation a stereo pair a vrml model and two dimensional sections the spatial resolution of the data in this study approximately 10 m is high enough to resolve inclusions and finer resolutions are possible comparisons of scan imagery with thin section and microprobe data demonstrate that many typical inclusion phases in garnet porphyroblasts can be clearly distinguished including quartz ilmenite and monazite a sodium metatungstate solution with a density of 1 19 g cm3 was used for a wedge calibration during scanning reducing artifacts to a minimum and allowing maximum image contrast the overall conclusion of this study is that high resolution x ray computed tomography is a quick non destructive technique that is invaluable in the study of porphyroblast microstructure the three dimensional data generated by this technique can be compared with geometries predicted by the varying theoretical models for the formation of curved inclusion trails in garnet porphyroblasts they can also be analyzed to determine the three dimensional orientation of curvature axes in individual porphyroblasts which has not been possible until now

scales of disequilibrium and rates of equilibration during metamorphism mounting evidence suggests that partial disequilibrium meaning disequilibrium for some elements but not for others may be a common but rarely detected phenomenon during metamorphic mineral growth even in ordinary prograde reactions that progress to completion detailed examination of compositional variations in garnet crystals over a range of metamorphic grade suggests distinctly different scales of equilibration for common elements with strong temperature dependence under lower greenschist facies conditions fe and mg may equilibrate at hand sample scale whereas mn and ca may not equilibrate even at millimeter scale although mn may achieve hand sample scale equilibration under upper greenschist facies conditions ca and many trivalent cations e g rees may not do so until temperatures exceed those of the middle amphibolite facies even in the lower granulite facies some elements e g y yb show indications of disequilibrium at sub centimeter scales during garnet growth analysis and numerical modeling of undisputed disequilibrium textures demonstrate that the most common impediment to equilibration during metamorphism is the sluggishness of intergranular diffusion the same mechanism known to govern porphyroblast crystallization in many metamorphic environments despite this importance to petrology few quantitative determinations exist of inter granular diffusion rates under metamorphic conditions using numerical simulations of coupled intergranular and intracrystalline diffusion processes in coronal textures around partially resorbed garnet crystals from the llano uplift u s a a very precise and relatively accurate estimate is obtained for the rate of intergranular diffusion of al in fluid undersaturated systems this result and an earlier estimate for fluid saturated systems provide bracketing values for al diffusivity during metamorphism

garnet polycrystals and the significance of clustered crystallization polycrystalline garnets are common in metamorphic rocks and may form as a result of close spacing of nuclei if clustering is early or impingement of larger grains if clustering occurs later in the growth history the timing of clustering relative to garnet growth is relevant to understanding the formation and evolution of porphyroblasts and evaluating the significance if any of clustering electron backscattered diffraction ebsd analysis of garnet bearing metamorphic rocks reveals the presence of polycrystalline garnet in nine localities examined in this study the northern appalachians vermont maine new york usa north american cordillera north cascades range washington snake range nevada usa western rocky mountains british columbia canada southern menderes massif turkey santander massif colombia and the sanandaj sirjan zone hamadan iran in some samples polycrystals comprise 20 30 of garnets analyzed and chemical and textural evidence suggests that early coalescence of garnet polycrystals is common some early coalescing polycrystals exhibit growth zoning that is concentric about the geometric center of the polycrystal in thin section these garnets may be undetectable as polycrystals based on morphology or zoning in some polycrystals zoning is unrelated to the location of internal grain boundaries in others fe mn mg zoning has a different pattern than that of ca zoning patterns may vary on the scale of a single thin section in addition some polycrystals are characterized by high angle misorientation boundaries that may be in special non random orientations an observation that indicates that these polycrystals are not random clusters of grains the presence of internal grain boundaries may affect diffusion pathways and length scales and may facilitate communication of porphyroblast interiors with matrix phases thereby influencing reaction history of the rock and the composition zoning of garnet

late quaternary vegetational change in the central peruvian andes abstract new fossil pollen records from the central peruvian andes at elevations above 4000 m including pollen concentration data and additional radiocarbon dates provide information on late quaternary vegetation change for the region a pollen assemblage typical of superpuna plus low pollen concentrations and organics in the late glacial section of laguna tuctua indicate a cold dry climate but strong evidence for a late glacial climate reversal i e the younger dryas is not presently confirmed an abrupt increase in urticales pollen as compositae and polylepis acaena type pollen decline signals the beginning of the holocene subsequent increases in urticales and plantago rigida type pollen point to increased moisture as well as higher temperatures from about 11 000 to 7000 yr b p a possible correlation exists between the rapid expansion of puna and closed continuous forest and the rise in importance of camelids in the early holocene in the mid holocene plantago rigida cushion bogs and continuous montane forest elements decline suggesting a drier climate grasses and cheno ams then increase reaching maxima about 4000 yr b p pastoralism and agriculture are thought to have developed at this time according to ethnobotanical studies from this area and pollen evidence seems to support these findings between 3000 and 2000 yr b p pollen percentages of poaceae plantago rigida type and other local taxa decline as glacial activity was renewed in the higher mountains zea mays is present by 2000 yr b p and pollen of weeds and secondary successional plants associated with increasing agricultural disturbance are evident

glacier readvances in the andes at 12 500 10 000 yr bp implications for mechanism of late glacial climatic change radiocarbon dates from two sites in the andes ecuador and peru confirm that glaciers culminated a readvance after 11 000 yr bp a moraine stage equivalent in altitude and position relative to existing glaciers is present in most glacierized ranges but its age is equivocal broadly limiting dates from colombia and peru suggest that the stage may be late glacial as it is younger than 12100 yr bp but formed before the early holocene in southern chile a comparable moraine stage is older than ca 9100 yr bp andean glaciers appear to have advanced at least twice during the late glacial interval glacier reconstruction from these moraine limits suggests depression of the equilibrium line altitude by at least 300 400 m in the northern and north central andes and possibly less than this farther south late glacial climatic change occurred globally and possibly reflects north atlantic temperature and circulation changes forced by deglaciation of the northern ice sheets migrations north and south of the atlantic polar front and the switching off and on of a dust pump in low midlatitudes

late glacial and late holocene moraines in the cerros cuchpanga central peru abstract small ice fields on the western cordillera northeast of lima were expanded to three times their present size in the recent past and the regional snow line was probably about 100 m lower than it is today outwash from the expanded glaciers formed deltas of silt in valley bottom lakes when the ice lobes retreated the reduced outwash was trapped behind recessional moraines and the clear meltwater infiltrated into the limestone bedrock and emerged at the heads of the deltas in spring pools the delta surfaces then became covered with peat and radiocarbon dates for the base of the peat 1100 70 and 430 70 yr b p for two different deltas indicate that the maximum ice advance was older than those dates and thus older than the little ice age of many north temperate regions much older moraines date from expansion of the same local summit glaciers to even lower levels in the main valleys which had previously been inundated by the cordilleran ice field the cordilleran deglaciation and this expansion of local glaciers probably occurred between 12 000 and 10 000 yr ago on the basis of slightly contradictory radiocarbon dates

lava water interaction and hydrothermal activity within the 2014 2015 holuhraun lava flow field iceland abstract lava that erupted during the 2014 2015 holuhraun eruption in iceland flowed into a proglacial river system resulting in aqueous cooling of the lava and an ephemeral hydrothermal system we carried out a monitoring study of this system from 2015 to 2018 to document the cooling of the lava over this time using thermocouple measurements and data logging sensors the heat loss rate from advection through this hydrothermal system in august 2015 was 5 5 108 w since eruption aqueous cooling likely accounted for 1 of the total heat loss from the lava this estimate excludes steam losses from fumaroles as well as any groundwater that was not released to the surface and thus is a lower bound near the terminus of the flow advection of heat by flowing water may have locally accounted for tens of percent of the total cooling of that part of the flow our data quantify the importance of water cooling for this lava flow and can be compared with models to better understand lava water interactions more generally we also provide detailed methods for simple low cost monitoring of similar instances in the future

geological constraints on the kinematics and fault plane solution of the quiches fault zone reactivated during the 10 november 1946 ancash earthquake northern peru the ancash earthquake of 10 november 1946 mw 6 8 produced surface faulting along the quiches normal slip fault field studies reported discontinuous nw se to nnw sse striking seismic scarps that displace quaternary glacial moraines and outwash as well as mesozoic sedimentary rocks structural analyses show that the 1946 normal displacement was accompanied by a small left lateral slip component morphological analysis of the fault scarp and observations in a trench excavated across the scarp show evidence of a single normal fault displacement before the 1946 seismic event that offset late pleistocene glacial moraines this indicates an approximate recurrence interval of more than 13 000 1 000 years for the major events suggesting a rate of net vertical displacement on the fault of less than 0 25 mm yr kinematic analysis along the quiches fault in comparison with other regional studies suggests that the state of stress in the high andes is regionally and locally homogeneous with only minor changes in the stress directions adjacent to major structures such as the maranon thrust and fold belt the minimum horizontal stress 3 axis is oriented n10 25 e the intermediate horizontal stress 2 axis is oriented n100 115 e and the maximum stress 1 axis is vertical we suggest that the 60 sw dipping quiches surface fault plane is connected at depth to a low angle dipping fault plane this seismic fault is a reactivated thrust fault of the tertiary maranon thrust and fold belt

hydrogeochemistry of high temperature geothermal systems in china a review as an important part of the mediterranean himalayas geothermal belt southern tibet and western yunnan are the regions of china where high temperature hydrothermal systems are intensively distributed of which rehai yangbajing and yangyi have been investigated systematically during the past several decades although much work has been undertaken at rehai yangbajing and yangyi to study the regional geology hydrogeology geothermal geology and geophysics the emphasis of this review is on hydrogeochemical studies carried out in these geothermal fields understanding the geochemistry of geothermal fluids and their environmental impact is critical for sustainable exploitation of high temperature hydrothermal resources in china for comparison the hydrogeochemistry of several similar high temperature hydrothermal systems in other parts of the world are also included in this review it has been confirmed by studies on cl and stable isotope geochemistry that magma degassing makes an important contribution to the geothermal fluids from rehai yangbajing and yangyi though meteoric water is still the major source of recharge for these hydrothermal systems however the mechanisms of magma heat sources appear to be quite different in the three systems as recorded by the 3he 4he ratios of escaping geothermal gases a mantle derived magma intrusion to shallow crust is present below rehai although the intruding magma has been heavily hybridized by crustal material by contrast the heat sources below yangbajing and yangyi are inferred to be remelted continental crust besides original sources the geochemistry of characteristic constituents in the geothermal fluids have also been affected by temperature dependent fluid rock interactions boiling and redox condition changes occurring in the upper part of hydrothermal systems and mixing with cold near surface waters the geothermal fluids from rehai yangbajing and yangyi contain very high concentrations of some toxic elements since local drinking water sources may be mixed with geothermal water and irrigation with water containing geothermally derived harmful elements possibly leading to accumulation in crops consumed by human beings the natural geothermal spring discharge or anthropogenic geothermal wastewater drainage of these fields poses a threat to the environment and human health future research work should focus on estimation of stable o and h isotope compositions of magmatic water related to high temperature hydrothermal systems in china which is of significance for the quantitative source study of geothermal fluid recharged by degassed magmatic waters attention should also be paid to some constituent species in geothermal fluid of strong environmental significance such as thioarsenate that is crucial for the fate of as discharged from geothermal springs especially sulfidic hot springs

metamorphic history suggested by garnet growth chronologies in the isua greenstone belt west greenland abstract compositional maps for garnets from the five tectonic domains of the isua greenstone belt in west greenland are used to identify episodes of garnet growth during the metamorphism of the greenstone belt three distinct episodes of garnet growth are recorded in domains iii v two in domain ii and one in domain i a wide variety of garnet textures are observed including growth zoning post growth homogenisation replacement rim resorption and oscillatory zoning there is no simple correlation of garnet growth events among domains indicating that at least some events are related to localised metasomatic processes in the greenstone belt however the relative growth chronology combined with the available geochronology indicates that the observed metamorphic processes span both the early and late archaean

cenozoic glaciation in the southern hemisphere with the end of glaciation in gondwana in early permian time a prolonged interval began when the earth was without ice sheets though not necessarily free of mountain glaciers not until sometime during the tertiary era did ice sheets build up once more first in antarctica and later in the northern hemisphere the fundamental cause of the cooling that led to the formation of the antarctic ice sheet and eventually to major glaciation in lower latitudes is generally held to have been the increasing thermal isolation of antarctica as australia and later south america separated from it allowing zonal oceanic circulation to develop rifting between australia and antarctica began between 1 10 and 90 m y ago cande mutter 1982 but not until much later probably sometime between 30 and 25 m y ago had it progressed far enough for deep circulation to begin as the south tasman rise cleared north victoria land kennett et a1 1974 kennett 1977 weissel et ai 1977 however antarctica did not reach its present high level of thermal isolation until south america had separated from it enabling the antarctic circumpolar current to become established savin et ai 1975 according to barker burrell 1977 1982 coherent spreading between the antarctic peninsula and tierra del fuego started about 29 m y ago and deep circulation began 23 5 2 5 m y ago thereafter increasing in volume the initial ice fields and ice caps that later expanded to become the

formation of garnet clusters during polyphase metamorphism pre alpine garnets of variscan age from metapelitic basement units in northern italy were strongly retrogressed at near surface conditions prior to alpine contact metamorphism the replacement by sheet silicates caused a significant volume increase during retrogression producing pervasive fracturing up to several hundreds of angular fragments formed from each crystal electron backscatter diffraction analysis documents a maximum misorientation of 22 of some fragments as a result of local rotation during fracturing new garnet growth is observed on the garnet fragments during contact metamorphic overprinting resulting in garnet clusters fragments can be identified due to calcium rich domains fragment orientations were inherited and only minor new nucleation occurred these garnets develop features typically associated with multiple nucleation models but here they reflect multiple metamorphic events we propose that clusters can be indicative of multiple metamorphic events which were separated by a period of intense retrograde alteration

diffusion control of garnet growth harpswell neck maine usa a detailed analysis of chemical zoning in two garnet crystals from harpswell neck maine forms the basis of an interpretation of garnet nucleation and growth mechanisms garnet apparently nucleates initially on crenulations of mica and chlorite and quickly overgrows the entire crenulation giving rise to complex two dimensional zoning patterns depending on the orientation of the thin section cut contours of ca zoning cross those of mn fe and mg indicating a lack of equilibrium among these major garnet constituents zoning of fe mg and mn is interpreted to reflect equilibrium with the rock matrix whereas ca zoning is interpreted to be controlled by diffusive transport between the matrix and the growing crystal image analysis reveals that the growth of garnet is more rapid along triple grain intersections than along double grain boundaries moreover different minerals are replaced by garnet at different rates the relative rate of replacement by garnet along double grain boundaries is ordered as muscovite chlorite plagioclase quartz flux calculations reveal that replacement is limited by diffusion of si along double grain boundaries to or from the local reaction site it is concluded that multiple diffusive pathways control the bulk replacement of the rock matrix by garnet with si and al transport being rate limiting in these samples

recent glacial history and paleoclimate of the peruvian bolivian andes abstract radiocarbon dates of glacial deposits in the peruvian bolivian andes are used to place the observed phases of glaciation in a common chronological framework the climatic conditions that may determine modern snowline are examined in order to understand the types of climatic forcing to which glaciers may have been sensitive in the past also considered are independent proxies of climatic change including pollen sequences lake level history and ice core data late pleistocene glaciation in central peru between 24 ka and 12 ka bp appears to have occurred during colder and perhaps drier conditions in bolivia a glacial maximum is dated to phases of late holocene glaciation in peru that correspond in part to the little ice age in the northern hemisphere appear to have been caused by a combination of colder and wetter conditions an overall warming trend may be the cause for the retreat of many glaciers in the region since the mid 19th century

regional synthesis of last glacial maximum snowlines in the tropical andes south america the modern glaciers of the tropical andes are a small remnant of the ice that occupied the mountain chain during past glacial periods estimates of local last glacial maximum lgm snowline depression range from low e g 200 300 m in the junin region peru through intermediate 600 m at laguna kollpa kkota in bolivia to high e g 1100 1350 m in the cordillera oriental peru although a considerable body of work on paleosnowlines exists for the tropical andes absolute dating is lacking for most sites moraines that have been reliably dated to 21 cal kyr bp have been identified at few locations in the tropical andes more commonly but still rarely moraines can be bracketed between about 10 14 c kyr 11 5 cal kyr bp and 30 14 c kyr bp typically only minimum limiting ages for glacial retreat are available cosmogenic dating of erratics on moraines may be able to provide absolute dating with sufficient accuracy to identify deposits of the local lgm ongoing work using cosmogenic 10 be and 26 al in peru and bolivia suggests that the local lgm may have occurred prior to 21 cal kyr bp r 2005 elsevier ltd and inqua all rights reserved

vent temperature trends at the vulcano fossa fumarole field the role of permeability between 1994 and 2010 we completed 16 thermal surveys of vulcano s fossa fumarole field aeolian islands italy in each survey between 400 and 1 200 vent temperatures were collected using a thermal infrared thermometer from distances of 1 m the results show a general decrease in average vent temperature during 1994 2003 with the average for the entire field falling from 220 c in 1994 to 150 c by 2003 however between 2004 and 2010 we witnessed heating with the average increasing to 190 c by 2010 alongside these annual scale field wide trends we record a spatial re organisation of the fumarole field characterised by shut down of vent zones towards the crater floor matched by rejuvenation of zones located towards the crater rim heating may be expected to be associated with deflation because increased amounts of vaporisation will remove volume from the hydrothermal system gambino and guglielmino j geophys res 113 b07402 2008 however over the 2004 2010 heating period no ground deformation was observed instead the number of seismic events increased from a typical rate of 37 events per month during 1994 2000 to 195 events per month during 2004 2010 as part of this increase we noticed a much greater number of high frequency events associated with rock fracturing we thus suggest that the heating event of 2004 2010 was the result of changed permeability conditions rather than change in the heat supply from the deeper magmatic source within this scenario cooling causes shut down of lower sectors and re establishment of pathways located towards the crater rim causing fracturing increased seismicity and heat flow in these regions this is consistent with the zone of rejuvenation which lies towards and at the rim being the most favourable location for fracturing given the stress field of the fossa cone schopa et al j volcanol geotherm res 203 133 145 2011 it is also the most established zone having been active at least since the early twentieth century our data show the value of deploying multi disciplinary geophysical campaigns at degassing fumarolic hydrothermal systems this allows more complete and constrained understanding of the true heat loss dynamics of the system in the case study presented here it allows us to distinguish true heating from apparent heating phases while the former are triggered from the bottom up i e they are driven by increases in heat supply from the magmatic source the latter are triggered from the top down i e by changing permeability conditions in the uppermost portion of the system to allow more efficient heat flow over zones predisposed to fracturing

late quaternary glaciation of the cordillera real bolivia glacial geological studies in tropical mountain areas of the southern hemisphere can be used to address two issues of late pleistocene climate change the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics radiocarbon dates from the cordillera real and from other areas in peru and bolivia suggest that late pleistocene glaciation culminated between 14 000 and 12 000 yr bp followed by rapid deglaciation because deglaciation was apparently synchronous with that in northern hemisphere regions insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time late pleistocene glaciation in the cordillera real culminated when precipitation was 200 mm yr 1 higher and temperatures were 3 5 1 6 c lower than today this produced an equilibrium line altitude depression of about 300 100 m on the western side of the cordillera prior to this conditions were drier and probably at least as cold however the lack of moraines in the cordillera real dated to the last glacial maximum ca 18000 yr bp precludes using the equilibrium line altitude method to quantitatively evaluate the discrepancy between warm sea surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period

magma differentiation rates from 226ra 230th and the size and power output of magma chambers we present a mathematical model for the evolution of the 226ra 230th activity ratio during simultaneous fractional crystallization and ageing of magma the model is applied to published data for four volcanic suites that are independently known to have evolved by fractional crystallization these are tholeiitic basalt from ardoukoba djibouti morb from the east pacific rise alkali basalt to mugearite from vestmannaeyjar iceland and basaltic andesites from miyakejima izu bonin arc in all cases 226ra 230th correlates with indices of fractional crystallization such as th and the data fall close to model curves of constant fractional crystallization rate the best fit rates vary from 2 to 6 10 4 yr 1 consequently the time required to generate moderately evolved magmas f 0 7 is of the order of 500 to 1500 yrs and closed magma chambers will have lifetimes of 1700 to 5000 yrs these rates and timescales are argued to depend principally on the specific power output i e power output per unit volume of the magma chambers that are the sites of fractional crystallization equating the heat flux at the epr to the heat flux from the sub axial magma chamber that evolves at a rate of ca 3 10 4 yr 1 implies that the magma body is a sill of ca 100 m thickness a value which coincides with independent estimates from seismology the similarity of the four inferred differentiation rates suggests that the specific power output of shallow magma chambers in a range of tectonic settings covers a similarly narrow range of ca 10 to 50 mw km 3 their differentiation rates are some two orders of magnitude slower than that of the basaltic makaopuhi lava lake hawaii that cooled to the atmosphere this is consistent with the two orders of magnitude difference in heat flux between makaopuhi and the east pacific rise 226ra 230th data for magma suites related by fractional crystallization allow the magma differentiation rate to be estimated and from this the thermal budget of the magma chamber addressed and where an independent measurement of heat flux exists to place constraints on the size of the magma chamber such results have the potential to constrain the likely timescale and size of future eruptions of evolved magmas

permeable convection above magma bodies abstract thermal convection above large shallow magma bodies in the crust is treated as a one dimensional bottom heated convection process in permeable media solutions for single phase convection are briefly reviewed and a solution is developed for two phase permeable convection in bottom heated media heat flow measurement techniques are discussed for permeable geologic zones above magma bodies and these techniques give consistent results for solidifying lava lakes in hawaii kilauea iki q 257 w m2 and iceland heimaey q 465 w m2 the heat loss from a magma body is a strong function of the permeability when a two phase convection zone occurs above the magma body and the heat loss is independent of the thickness of the two phase convection zone in steady state two phase convection zones where permeability does not vary appreciably with depth convective heat flow restrictions tend to limit the maximum saturation temperatures at depth to around 250 c an effect observed in many geothermal steam fields a conduction dominated transition zone tends to occur between the two phase zone and the magma body and the thickness of this transition zone may easily range from a few meters to several kilometers depending on the permeability

formation of garnet polycrystals during metamorphic crystallization garnet polycrystals may form throughout the metamorphic history of a rock starting at the earliest stages of garnet growth when closely spaced nuclei coalesce in mica schist from townshend dam vt electron back scattered diffraction ebsd analysis shows that garnet polycrystals possess two or more distinct lattice orientations separated by high angle boundaries 28 61 the minimum rotational displacements required to bring these lattice orientations into concordance with each other are commonly normal to the same low energy planes that occur as crystal faces of euhedral garnet there is no evidence for intracrystalline deformation and the polycrystals therefore probably represent individual garnet crystals that coalesced during growth the boundaries cross cut growth zoning and inclusion trails of the polycrystals indicating that early formed polycrystals once coalesced behave chemically and physically as single crystals statistical analysis of a 3d high resolution x ray computed tomographic data set of a large sample 912 cm3 of a townshend dam schist combined with microprobe and ebsd analyses of garnet are consistent with a high degree of clustering at all stages of garnet growth the formation and prevalence of polycrystals implies that garnet nuclei impinged on each other and coalesced and that coalescence was a common feature throughout garnet growth in the rock

glaciation in the andes during the lateglacial and holocene this review updates the chronology of andean glaciation during the lateglacial and the holocene from the numerous articles and reviews published over the past three decades the andes which include some of the world s wettest and driest mountainous regions offer an unparalleled opportunity to elucidate spatial and temporal patterns of glaciation along a continuous 68 degree meridional transect the geographic and altitudinal extent of modern glaciers and the sensitivity of both modern and former glaciers to respond to changes in specific climatic variables reflect broad scale atmospheric circulation and consequent regional moisture patterns glaciers in the tropical andes and in the mid latitude andes are likely to have been far more sensitive to changes in temperature than glaciers in the dry subtropical andes broad scale temporal and spatial patterns of glaciation during the lateglacial are apparent in the southernmost andes the lateglacial chronology appears to have a strong antarctic signature with the best dated moraines correlating closely with the antarctic cold reversal the southernmost andes do not appear to have experienced a significant ice advance coeval with the younger dryas yd climatic reversal at the other end of the andes from w 0t o 9 n a stronger yd connection may exist but critical stratigraphic and geochronologic work is required before a yd ice advance can be fully demonstrated in the central andes of peru well dated moraines record a significant ice readvance at the onset of the yd but ice was retreating during much of the remaining yd interval the spatial temporal pattern of holocene glaciation exhibits tantalizing but incomplete evidence for an early to mid holocene ice advance s in many regions but not in the arid subtropical andes where moraines deposited during or slightly prior to the little ice age lia record the most extensive advance of the holocene in many regions there is strong evidence for neoglacial advances in the interval between 1 0 and 2 5 ka moraines that correlate with the lia of the northern hemisphere are seen in all presently glacierized mountain ranges most of these date to within the past 450 years outboard of these moraines in many regions are moraines of a slightly more extensive advance that occurred several hundred years prior to the onset of the lia priorities for future work include filling in several prominent spatial gaps in the distribution of chronologic studies for the lateglacial these gaps include the arid regions of northern chile and argentina the southern peruvian andes between 11 5 and 13 5 s and the andes of northern peru and

measuring and interpreting heat fluxes from shallow volcanic bodies using vertical temperature profiles a preliminary test to test the potential of heat flux prospecting in active volcanic areas using shallow temperature data taken along vertical profiles we carried out two thermal profile surveys one not far from yasur cone on tanna island and another inside the caldera of ambrym new hebrides arc southwestern pacific the basic steady heat flux of internal volcanic origin was determined taking into account both conductive and convective heat transfers at both locations there exists over small distances significant differences in the heat flux these differences correspond to shallow sources of heat the use of a network of vertical profiles allowed a heat flux mapping b location of shallow volcanic heat sources and c observation of the detailed structure of the heat release at quiescent but active volcanoes

practical evaluation of steady heat discharge from dormant active volcanoes case study of vulcarolo fissure mount etna italy abstract from a theoretical approach combined with experimental study i propose a method to compute both sensible and latent heat transfer in a thermally active volcanic area this method is applied to a fumarolic thermal fissure located on the south flank on mount etna italy the method involves four steps 1 mapping of self potential sp to quickly identify thermal anomalies 2 mapping of ground temperature t at constant depth in the area defined by sp mapping 3 measurement of vertical t profiles at selected representative stations including the coldest and hottest and 4 direct measurements of vapor flow where the convective heat flux reaches the surface when heat flux values vary in the range 10 300 w m 2 t measurements at a depth equal to about 1 m are sufficient to estimate the absolute flux value to within an absolute error less than 30 and 10 for the relative value ground temperature measurement is an easy and accurate method for estimating heat discharge on a limited surface to define the fissure system monitor time variations of heat flux or to calibrate remote sensing results on the ground

a review of lateglacial pollen records from ecuador and peru with reference to the younger dryas event abstract published biostratigraphic records from ecuador spanning the lateglacial period of approximately 13 000 to 10 000 bp lack radiocarbon dates delineating the younger dryas and records with extrapolated dates do not exhibit evidence of a climatic reversal for peru fossil pollen data from four sites suggest one and possibly two climatic oscillations in the lateglacial but only one site laguna junin has dates that delimit a short term climatic change and this occurs between 12 000 and 11 000 bp pollen records from laguna baja and rio blanco pond give the strongest indication of a climatic reversal but bracketing dates are not available other pollen records from peru have tenuous dating or data and do not support a lateglacial climatic reversal at the time of the younger dryas

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids

a late glacial holocene pollen record from the eastern andes of northern peru abstract a pollen and sediment record of a core 4 2 m long from laguna baja 7 42 s 77 32 w 3575 m in the cordillera oriental of northern peru suggests several episodes of major vegetational and climatic change over the past 13 000 yr the oldest pollen assemblage consists of a mixture of paramo elements tropical alpine vegetation including high percentages of poaceae 40 that decline upward moist montane forest compositae and polylepis and wet montane forest e g hedyosmum and podocarpaceae organic carbon content range from 60 with high percentages of jamesonia a fern characteristic of paramo and decreasing values of plantago tubulosa and the wet montane forest elements hedyosmum and podocarpaceae charcoal percentages are at a maximum during this period magnetic susceptibility and sand percentages are high and percentages of organic matter are low several explanations for these changes are possible including a reduction in temperature and moisture more frequent periods of aridity with increased fires or natural succession the holocene record begins with pronounced increases in organic carbon and pollen of wet montane forest primarily hedyosmum podacarpaceae and urticales high values of podocarpaceae pollen 35 and a decline in charcoal suggest temperature and moisture levels above modern day values wet montane forest pollen remain high and charcoal values are low from about 10 000 to 6000 yr b p suggesting that warm and moist conditions prevailed for about 4000 yr subsequently podocarpaceae and urticales decline and for a brief time alnus is prominent in the pollen record following the alnus maximum at about 5000 yr b p poaceae ambrosia and chenopodiaceae amaranthaceae become frequent increased paramo and disturbance indicator pollen suggest increased anthropogenic activities in this region from the middle holocene to the present