weathering regime and geochemical conditions in a polar desert environment haughton impact structure region devon island canada this study examines the physical and geochemical properties of near surface sediments as well as the geochem ical and stable o h c isotope composition of ground surface waters in and around the haughton impact structure region devon island nunavut to determine the types of weathering mechanical bio chemical and their relative contribution in this polar desert environment the surface sediments collected from the allen bay and thumb mountain formations surrounding the impact crater are dominated by sand sized particles whereas the impact melt breccias inside the crater have a greater abundance of silt sized particles the subsurface sediments in the allen bay formation show a near equal amount of sand and silt sized particles however the micromorphologies of the sand sized particles collected at the sur face revealed that these grains irrespective of the local geology were heavily fractured by contrast fractures and rounded pits are observed on the surface of the sand grains located within the active layer whereas those located just above the permafrost table have only rounded cavities on their surface the ground waters also show variations in their solute con centration with depth the highest concentrations being found in the groundwaters near the top of permafrost taken to gether these observations suggest that there is a progressive evolution from a mechanically dominated weathering regime near the surface to increasing chemical weathering with depth the transition from mechanical weathering near the surface to increasing chemical weathering with depth can be attributed to the decreasing frequency and intensity of mechanical weathering processes i e frost action wetting drying thermal dilation with depth and to the presence of permafrost which allows a greater availability of water for chemical aqueous reactions at the base of the active layer

relict non glacial surfaces in formerly glaciated landscapes abstract relict non glacial surfaces occur within many formerly glaciated landscapes and contain important information on past surface processes and long term landscape evolution relict non glacial surfaces are distinguishable from glacial surfaces by large scale morphologies including rounded summits fluvial valleys and cryoplanation terraces and pediments and the presence of tors blockfields and or saprolites preservation during glaciation occurs either through coverage by non erosive cold based ice or as nunataks although surface morphologies and denudation rates indicate a continuous non glacial surface history since preglacial times relict non glacial surfaces are dynamic features that have evolved during the quaternary depending on spatial variables such as lithology slope regolith depth and the abundance of fine matrix and water some surfaces are denuding very slowly while others display more rapid denudation high spatial variability in denudation rates results in changing surface morphologies over time denudation rates also display high temporal variability with much surface evolution having perhaps occurred soon after the initial onset of glaciation or during paraglacial phases while some parts of non glacial landscapes are currently active others may be largely inactive relicts of past higher energy regimes although non glacial surfaces are dynamic much remains to be determined regarding surface denudation rates and the magnitude of morphological changes over time

comparison of radiocarbon dating of buried paleosols using arbuscular mycorrhizae spores and bulk soil samples ten paleosols from four separate soil pits located in karkevagge a glaciated trough in swedish lapland were dated using radiocarbon each soil was dated using both conventional bulk soil organic material som and a pure sample of arbuscular mycorrhizae am fungal spores the latter are produced by ubiquitous mycorrhizal fungi associated with the roots of many plant genera and may be viewed as a fossil material that has not interacted with any soil constituent subsequent to its emplacement in the soil at a time presumed to mark the cessation of a favorable soil forming environment regional deglaciation is presumed to have been about 10 000 bp while a cosmogenic exposure date obtained from the valley floor in karkevagge dated at 13 100 1638 bp the youngest paleosol buried at similar to 6 cm in soil pit m3 produced a spore date of 0 281 cal yr bp 1 sigma however bulk som dates of the same paleosol a horizon gave widely divergent dates and varied with the sample pretreatment ie the combustion temperature and the acid base treatment for example the bulk som dates for that paleosol ranged from a post bomb date of 0 314 cal yr bp 1 sigma to 2366 2710 cal yr bp 1 sigma when subjected to different pretreatments acid only acid base acid and the ignition temperatures 400 800 or 900 degrees c the oldest paleosol in the set buried at similar to 61 cm in soil pit m6 dated at 5479 5698 cal yr bp 1 sigma using spores but beyond calibration using bulk som the spore dates were all within the range to be expected of postglacial paleosols but the bulk som dates were frequently beyond the generally accepted time of deglaciation in addition all of the spore dates followed a conventional age depth pattern while the bulk som dates did not there are known possible sources of geogenic carbon contamination in karkevagge which may well account for the obviously invalid older bulk som dates an additional complication is that the spore dates vary somewhat with their density and diameter however where other types of fossil or charcoal are unavailable it appears that the enormously broad distribution of spores and their lack of interaction within the soil and persistence may well offer the prospect of an unusually useful radiocarbon dating medium within paleosols

surface wave profiling of the lithosphere beneath the mojave desert using terrascope data we have applied surface wave analysis to the mojave desert in southern california to extract the regional lithosphere velocity structure seismograms from teleseismic sources recorded by the terrascope stations a recently established network of broadband instruments were used to determine the phase velocity dispersion data of rayleigh waves for wave paths crossing the mojave desert an inversion analysis on the dispersion data for each path gave the shear wave velocity structure beneath the path inversion results show that there is a low velocity layer at the middle and lower crust which is particularly pronounced for paths traversing the western part of the mojave desert this low velocity layer at the midcrust may reflect the existence of a transition zone from the brittle to the ductile regimes where there is an absence of earthquake occurrence

chemical weathering of mafic rocks in boreal subarctic environment northwest russia under influence of glacial moraine deposits abstract chemical weathering of mafic rocks represents substantial sink of atmospheric co2 yet the mechanismes of this process in high latitude regions are poorly understood this work addresses geochemical migration and partitioning of major and trace elements between rock soil and surface waters during chemical weathering of mafic rocks and soil formation under the influence of a glacial moraine in the northwestern russian subarctic we used multidisciplinary approach which included major and trace element chemical analysis sr isotopic measurements and mineralogical structural and microscopic investigations quaternary pleistocene deposits were observed even in the deepest horizons of soil profiles and confirm a strong moraine influence as most soils showed podzolic features chemical and sr isotopic analyses revealed a strong impact of the moraine on soil chemistry and mineralogy mineralogical studies showed the presence of non aeolian quartz and zircon in soils which were not linked to the nature of the parental rocks i e mafic and felsic at the same time we observed the presence of etch pit corrosion on the surface of zircons and feldspars and a newly formed matter adjacent to the surface of primary phases the chemical index of alteration cia showed weak or no weathering of rocks within the soil profile and the weathering intensity scale confirmed the felsic chemical composition of soils developed over mafic and ultramafic rocks analysis of sr radiogenic isotopes demonstrated preferential removal of easily weatherable and less radiogenic minerals over the full depth of soil profile and a more radiogenic signature of the granitic moraine compared to mafic and felsic bedrocks the composition of most surface waters reflected the weathering of silicate rocks but did not allow for distinguishing purely mafic source the chemical weathering rates of ultramafic rocks were calculated to be higher than those for the granitic till but the moraine depositions which dominate this region hide evidence of the real weathering process this could be due to retention of mg and ca in soil due to precipitation of secondary phases such as mg vermiculite or divalent cation adsorption on mineral organic or organo mineral phases as a result weathering rates estimated for the olivinite rock appear to be lower than the weathering rates of mafic rocks reported in other boreal and subarctic regions overall the felsic moraine deposits are capable to sizably decrease the weathering intensity of mafic rocks which should be taken into account for chemical weathering modelling of high latitude regions subjected to glaciation in the past

contrasting behaviour of boron during crustal anatexis the study of volatile elements in crustal anatectic terranes may provide information about the role of fluid flow and fluid pathways during high temperature metamorphism we have studied the distribution of li and b in two migmatitic areas the pena negra anatectic complex central spain and the migmatites and leucogranites associated with the ronda peridotites southern spain they represent two contrasting cases in the behaviour of volatiles particularly b during anatexis the pena negra migmatites are dominated by diatexites where it is possible to distinguish granitic leucosomes melanosomes metric to decimetric leucogranitic segregates and decimetric to metric sillimanite rich restitic enclaves all lithologies are characterized by low b concentrations mean values 30 ppm and b is enriched in melanosomesrrestites with respect to leucosomesrleucogranites this may be due to the fact that a notable proportion of b can reside in restitic sillimanite b concentrations in leucosomes and leucogranites can be explained by closed system anatexis at ronda metatexitic and diatexitic migmatites underlie the ronda peridotites and diatexite and leucogranite dikes intrude the peridotites diatexites underlying the peridotites are characterized by cordierite q biotite garnet as ferromagne sian phases with rare or absent tourmaline low b contents 10 ppm and cordierite garnet leucosomes leucogranite dikes have high b concentrations mean valuef 400 ppm with tourmaline being a common and sometimes the most abundant ferromagnesian phase a genetic relationship between diatexites and leucogranites is strongly suggested by the presence of dikes of diatexites intruding the bottom of the peridotites we conclude that b in the leucogranites may stem from the dissolution of tourmaline originally present in the metasediments or infiltration of b rich aqueous fluids into the anatectic zone according to recent experimental work textures in some tourmaline rich ronda leucogranites suggest initial b o 23 contents in the melt higher than the present measured concentrations preliminary experimental results presented in this paper propose that this difference is not due to water activities in the melt rapid crystallization of the melts following undercooling may explain the existence of abundant euhedral tourmaline in leucogranites with low aluminium saturation index asis molar al o r caoq na oq k o and relatively low b contents q 2001 elsevier science b v all rights 23 2 2 reserved

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

low temperature thermochronologic record of eocene migmatite dome emplacement and late cenozoic landscape development shuswap core complex british columbia exhumed mid to lower crustal rocks offer an opportunity to determine the mechanisms conditions timing and consequences of the ascent of hot rocks from deep to shallow crustal levels we used results of low t thermochronology zircon and apatite u th he apatite fission track to document the very shallow emplacement 1800 m have preserved eocene fission track ages and evidence of rapid cooling 60 c myr this eocene cooling event corresponds to rapid exhumation by upward flow of partially molten crust and final exhumation by detachment faulting samples collected below 1800 m in elevation display a wide range of apatite fission track ages 43 15 ma and track length distributions that reflect prolonged residence in the apatite partial annealing zone these age elevation relations imply that the dome rocks reached the near surface 2 km during initial upward flow and tectonic exhumation in the eocene and that little erosion of the eocene surface has occurred since that time thermal modeling of the lowest elevation samples 600 m and intrasample apatite u th he age variations reveal enhanced erosion and relief production at the onset of continental glaciations at 3 ma our work illustrates the dynamic links between deep and shallow crustal processes and the evolution of topography in a deeply incised hot orogen

long wavelength s wave velocity structure throughout the mantle summary long wavelength s wave velocity anomalies are obtained for the entire mantle by inverting 6ooo long period 40 100s sh body waves and lo00 long period 100 500 s love waves in the shallow mantle the patterns of fast and slow velocity anomalies correlate well with age and tectonics in the depth range of 400 1000 km we find two antipodal fast velocity anomalies one in the western pacific and the other in south america they form a fairly strong i 2 anomaly moreover the 1 2 anomaly is the largest spherical harmonic component throughout the entire mantle except for in the layer of 1000 1300 km depth a fast velocity anomaly near the caribbean previously reported by several other investigators is found between the depths of 1000 and 1300km with diminishing amplitudes it can be traced to canada and the aleutians and may be related to old subducted slabs in the same depth interval similar size anomalies can be found in the middle of the pacific and in the indian ocean these could be checked by more detailed studies to judge the reliability of this study heterogeneity power has a peak at the surface and a secondary peak at the bottom of the mantle d consistent with the existence of chemical and or thermal boundary layers at the base of the mantle we also find a fast velocity anomaly which surrounds the pacific ocean this feature has been found by other researchers previously but its interpretation is difficult due to the trade off between velocity anomaly and core mantle boundary deformation

pyrite enhanced chemical weathering in karkevagge swedish lapland conventional wisdom once held that weathering in cold climates was overwhelmingly due to physical processes however that convention was challenged when chemical weathering was identified but unexplained as the dominant landscape denudation process in karkevagge an alpine valley in swedish lap land the research reported here involved scanning electron microscopy and energy dispersive x ray fluorescence of rock coatings to investigate chemical weathering in karkevagge analyses revealed that white coatings associated with streams emerging on the valley cliff face are commonly an amorphous aluminum oxyhydroxide sulfate such as basaluminite al 4 so 4 oh 10 h 2 o efflorescence on seasonal vegetation in stream channels demonstrates that this is an active process the white coating chemistry exhibited no systematic spatial patterns along the valley axis or with position on the cliff face although the white coatings were not crystalline and did not contain appreciable amounts of fe or ca in sheltered overhangs among boulders on the valley floor there were other well crystallized secondary sulfate minerals commonly associated with pyrite oxidation including gypsum jarosite and amorphous fe compounds this difference is due presumably to the ph of the associated waters because fe compounds tend to precipitate only at ph 5 which is the ph of the stream water pyrite oxidation may be an important early weathering process in this and in many other environments however it largely goes unrecognized because it occurs relatively rapidly in a geological sense and typically is only identified in recently disturbed landscapes associated with mining or other large scale earth moving activities karkevagge demonstrates that subarctic conditions do not preclude intense chemical weathering where conditions are favorable but it does not establish that strong chemical weathering is a widespread attribute of subarctic conditions

terrestrial and aquatic ecosystem responses to late holocene climate change recorded in the sediments of lochan uaine cairngorms scotland abstract we summarise the results of a range of sediment based studies at lochan uaine a remote corrie lake in the heart of the cairngorm massif in scotland the site lies above the holocene forest limit and has been minimally affected by human activities the results presented are mainly based on magnetic measurements element analysis granulometry organic geochemical analysis and pollen analysis carried out over a period of some 15 years the magnetic properties and element concentrations record a coherent sequence of changes reflecting mainly stages in catchment erosion in terms of the chronology developed for the sedimentary record from the site increases in allochthonous minerogenic sediment delivery to the lake occurred around 1000 bc ad 330 480 and ad 1260 1410 the only notable change in the pollen diagram records a period of deforestation at lower altitude predating the last of the periods of increased erosion the organic geochemistry analyses record a series of higher frequency responses in the aquatic ecosystem already noted in previous papers e g battarbee et al 2001 these include fluctuations in organic carbon content and in the concentrations of biomarkers indicative of changing lake productivity both the terrestrial and aquatic ecosystem responses are superimposed on a longer term trend of declining aquatic productivity progressive catchment weathering and increasing erosion the sediments of lochan uaine thus appear to have recorded complex system responses on three timescales reflecting a the long term decline in northern hemisphere insolation during the holocene b the millennial scale forcing of the kind found in many other mid late holocene records and c much shorter term quasi cyclic but clearly a periodic sub millennial fluctuations

a classification scheme for mantle derived garnets in kimberlite a tool for investigating the mantle and exploring for diamonds abstract a new empirical method has been devised for classification of mantle derived garnets in kimberlite simple chemical screens have been developed to distinguish between garnets from different parageneses based on mg fe ca cr ti and na values of published analyses of garnets from 2000 ultramafic xenoliths in kimberlite although crustal garnets are typically uncommon as xenocrysts in kimberlite the first step in the classification is to screen these from the mantle population using data from 600 garnet bearing crustal rocks such a screen may also prove useful in evaluating the source crust vs mantle of garnet in kimberlite exploration samples subsequent steps divide mantle garnets into eclogite peridotite and cr poor megacryst groupings and sub groups of the peridotite lherzolite harzburgite wehrlite and eclogite groups i and ii and a b c and grospydite populations important features of this classification include the fact that it is based on distinctions between groups of fundamental geological significance e g peridotite vs eclogite and it is based on a large well documented and well understood xenolith database as it utilizes oxide values and molar ratios of major and minor elements the rationale for the screens is readily understood and it is simple to use

analogue models of melt flow networks in folding migmatites we have modelled the formation and the layer parallel shortening of layered stromatic migmatites the model consists of thin superposed layers of partially molten microcrystalline wax the melt 30 vol has a negative buoyancy and a high viscosity contrast with its solid matrix as soon as the shortening begins melt filled veins with high aspect ratios open along foliation the melt is segregated into the veins forming a stromatic layering during incipient folding crescent shaped saddle reefs open at the hinges of open sinusoidal folds further shortening and melt enhanced shear displacements on interlayer interfaces cause chevron folds to develop and the saddle reefs to become triangular in comparison a melt free experiment shows only a few layer parallel openings and no saddle reefs in chevron folds on the basis of our experimental results we propose that in migmatites 1 mesoscale melt migration is a combination of flow in immobile veins and movements of veins as a whole 2 the changes in the geometry of the mesoscale melt flow network create the pressure gradients that drive melt migration 3 the melt flow network does not need to be fully interconnected to allow local expulsion 4 melt expulsion is episodic because the temporal evolution of the network combines with the spatial heterogeneity of the deformation

variations in weathering processes and rates with time in a chronosequence of soils from glen feshie scotland chemical and mineralogical characteristics have been determined for a chronosequence of six soil profiles ranging in age from 80 13 000 years bp developed on river terraces in the western cairngorms of scotland the c horizons are similar chemically and mineralogically and the soils have similar pedogenetic histories exchangeable ca and mg decrease with time and base saturation decreases exponentially from 24 6 in the ah horizon of the youngest profile to 2 8 in the comparable horizon of the 10 000 year old profile according to the chronofunction y 3 372 22 612 exp 0 0007365t long term weathering rates of base cations calculated from the loss of these cations relative to zr appear to decrease exponentially with time but this may be due to the method of calculation the magnitude of loss of base cations decreases in the sequence na k mg ca but when the relative mobilities of these elements are considered the loss is in the order mg na ca k this reflects the dissolution of chlorite and loss of mg and the more rapid weathering of plagioclase feldspar and loss of na and ca particularly in the coarse sand fraction than k feldspar the clay fractions although 2 of all horizons also show distinct patterns with age in that chlorite and mica are less abundant in older soils and vermiculite is more abundant the latter phase often having hydroxyaluminium polymers in the interlayer region the chemical and mineralogical trends in the soil sequence are closely associated and are induced by pedogenic weathering

ice sheet erosion and the stripping of tertiary regolith from baffin island eastern canadian arctic abstract the erosion of glaciated regions and concomitant changes in ice sheet dynamics through the pleistocene are poorly documented the baffin island landscape which has been shaped by the foxe sector of the laurentide ice sheet lis contains a variety of glacial and proximal glaciomarine sedimentary archives spanning the pleistocene we examine these records to better understand when tertiary regolith was stripped from beneath the foxe sector of the lis till on the interior plateaux of the island in areas with scoured bedrock have low chemical index of alteration cia values low meteoric 10 be 10 be met concentrations and clay mineralogy consistent with erosion from an unweathered bedrock source however in some areas in between fiord onset zones more weathered till is present containing considerably higher cia values high 10 be met concentrations and secondary clay mineral weathering products implying that the till has persisted on the landscape and weathered during successive glaciations using these weathering signatures we analyze the coastal glaciogenic deposits of the clyde foreland formation cff at two sites for evidence of tertiary regolith removal from the interior of baffin island by lis erosion provenance indicators within the cff demonstrate that pleistocene lis ice flow lines across baffin island have remained generally constant the oldest cff glaciogenic unit likely representing one of the first if not the first lis advances across baffin island had high 10 be met concentrations at the time of deposition consistent with extensive regolith erosion evidence of notably weathered sediment is absent in all younger units suggesting that tertiary regolith was likely largely stripped from the interior of the island by 1 6 0 2 ma

global mantle shear velocity model developed using nonlinear asymptotic coupling theory we present a three dimensional shear velocity model of the whole mantle developed using s h waveform data the model is expressed horizontally in terms of spherical harmonics up to degree 12 and vertically in terms of legendre polynomials up to degrees 5 and 7 in the upper and lower mantle respectively what distinguishes this model from other tomographic models published to date is 1 the theoretical normal mode based wave propagation approach where we include across branch mode coupling terms in order to model the body wave sensitivity to structure along the path more accurately 2 the wave packet weighting scheme which allows to balance contributions from high amplitude and low amplitude phases increasing the resolution in some parts of the mantle we also relax the constraints on the moho depth which is allowed to vary in the inversion thus absorbing some uncertainties in crustal structure the resulting model is generally in good agreement with other recent global mantle s velocity models and with some regional models the rms profile with depth has more power than other models in the upper mantle lower mantle transition region and the zone of increased power and low degree structure near the base of the mantle is confined to the last 500 km in depth this model provides a particularly good fit to the non hydrostatic geoid through harmonic degree 12 79 variance reduction as well as good fits to observed splitting functions of s velocity sensitive mantle modes indicating that both large scale and small scale features are really well constrained

unified structural representation of the southern california crust and upper mantle we present a new 3d description of crust and upper mantle velocity structure in southern california implemented as a unified structural representation usr the usr is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity vp vs measurements and incorporates the locations and displacement of major fault zones that influence basin structure these basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure which were subsequently iterated and improved using 3d waveform adjoint tomography a geotechnical layer gtl based on vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component the resulting model provides a detailed description of the structure of the southern california crust and upper mantle that reflects the complex tectonic history of the region the crust thickens eastward as moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust deep sedimentary basins and underlying areas of thin crust reflect neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late pliocene to illustrate the impact of this complex structure on strong ground motion forecasting we simulate rupture of a proposed m 7 9 earthquake source in the western transverse ranges the results show distinct basin amplification and focusing of energy that reflects crustal structure described by the usr that is not captured by simpler velocity descriptions we anticipate that the usr will be useful for a broad range of simulation and modeling efforts including strong ground motion forecasting dynamic rupture simulations and fault system modeling the usr is available through the southern california earthquake center scec website http www scec org

lithospheric deformation beneath the san gabriel mountains in the southern california transverse ranges high resolution tomographic images from los angeles region seismic experiment larse array and southern california seismic network scsn teleseismic data suggest that the entire lithosphere below the san gabriel mountains and san andreas fault in the transverse ranges has thickened in a narrow vertical sheet p wave travel time inversions of the combined data support the presence of the well documented upper mantle high velocity anomaly that extends 200 km into the mantle under the northernmost los angeles basin and transverse ranges and is associated with mantle downwelling due to oblique convergence we find that the high velocity high density upper mantle anomaly comprises a 60 80 km wide sheet of mantle material that lies directly below a substantial crustal root in the san gabriel mountains the velocity perturbations are as large as 3 in the anomaly corresponding to a 2 density increase the tomographic images suggest that deformation in the ductile lower crust and mantle lithosphere may be partially coupled mechanically and thermally if the thickening is occurring together in response to convergence and that it may be a local compressional feature

biota and geomorphic processes as key environmental factors controlling soil formation at elephant point maritime antarctica abstract we examined the main soil forming factors affecting the soil composition soil properties and the associated soil forming processes at elephant point a small ice free environment in the south shetland islands maritime antarctica for this purpose we collected twenty soil samples from each of ten different sites distributed along a linear transect running from the coast to the front of the rotch dome glacier the samples were obtained from surface layers 0 10 cm and at depth 40 50 cm although collection was limited in the moraine area by the permafrost table we determined ph electrical conductivity size particle distribution total organic carbon total nitrogen and total concentrations of al fe ca and p for physical and chemical characterization of the samples we also analysed the samples to determine the bioavailability of nutrients and fe al and p partitioning and finally examined them by isotopic 15n and x ray diffraction xrd analysis the results of the analyses revealed two clear geochemical environments corresponding to the two most extensive geomorphological units in this peninsula moraine and marine terraces soils from the moraine were characterized by alkaline reaction and high quantity of minerals with a low degree of crystallinity whereas soils from the marine terraces showed acid reaction high concentration of organometallic complexes and a high diversity of phosphate minerals taranakite minyulite struvite hydroxylapatite and leucophosphite which seem to be generated by phosphatization of faecal matter deposited by seabirds and seals consequently biota activity is the most relevant soil differentiating factor in the marine terraces which add organic matter and activate geochemical cycles on the other hand geomorphic processes strongly affected by physical weathering processes such as glacial abrasion by grinding process frost shattering and wind abrasion are the main soil forming factors in moraine these forces break up the parent material transform it and translocate the products formed

viscoelastic flow in the lower crust after the 1992 landers california earthquake space geodesy showed that broad scale postseismic deformation occurred after the 1992 landers earthquake three dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation whereas viscoelastic flow can explain the horizontal and near vertical displacements the viscosity of a weak about 10 km thick layer in the lower crust beneath the rupture zone that controls the rebound is about 10 18 pascal seconds the viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the basin and range province and it may be used for the analysis of earthquake hazard

structural analysis and deformation characteristics of the yingba metamorphic core complex northwestern margin of the north china craton ne asia abstract the presence of the yingba yinggete bagemaode metamorphic core complex mcc is confirmed near the sino mongolian border in china we report its structural evolution and the rheological features of ductile shear zones within this complex three deformations ds dm and db since the late jurassic are identified ds is characterized by ductile structures that resulted from early nw oriented low angle extensional ductile shearing dm is associated with partial melting and magmatic diapirism which accelerated the formation of the dome like geometry of the yingba mcc synchronously with or slightly subsequently to ds and dm the yingba mcc was subjected to brittle extensional faulting db which was accompanied by the exhumation of the lower crust and the formation of supracrustal basins the ductile shearing ds developed under greenschist to amphibolite facies metamorphic conditions 400 650 c as indicated by microstructures in quartz and feldspar quartz c axis fabrics and two feldspar geothermometry the mean kinematic vorticity estimates of 48 62 show a pure shear preferred flow during ds the yingba mcc provides an excellent sample that recorded an intermediate to high temperature shearing which also implies the widely extensional regime in northeastern asia at that time

tomographic image of the southern california mantle p wave teleseismic travel time delays recorded by the southern california array are inverted by the method of backprojection tomography to obtain images of variations in the p wave velocity structure to a depth of 750 km two major upper mantle features arc resolved one beneath the transverse ranges region and another beneath the salton trough region the transverse ranges feature appears as a curtainlike east trending high velocity anomaly this feature is 60 km thick extends most deeply on its eastern end to 250 km and attains a maximum velocity 3 greater than average southern california mantle of the same depth the salton trough feature which is not as well resolved as the transverse ranges feature is composed of low velocities in the upper 70 100 km these p wave velocities arc depressed 3 4 compared to average southern california mantle tests of the inversion indicate the major aspects of the imaged structure are authentic

upper mantle shear velocities beneath southern california determined from long period surface waves we used long period surface waves from teleseismic earthquakes recorded by the terrascope network to determine phase velocity dispersion of rayleigh waves up to periods of about 170 sec and of love waves up to about 150 sec this enabled us to investigate the upper mantle velocity structure beneath southern california to a depth of about 250 km ten and five earthquakes were used for rayleigh and love waves respectively the observed surface wave dispersion shows a clear love rayleigh wave discrepancy that cannot be accounted for by a simple isotropic velocity model with smooth variations of velocity with depth separate isotropic inversions for love and rayleigh wave data yield velocity models that show up to 10 anisotropy transverse isotropy however tests with synthetic love waves suggest that the relatively high love wave phase velocity could be at least partly due to interference of higher mode love waves with the fundamental mode even after this interference effect is removed about 4 anisotropy remains in the top 250 km of the mantle this anisotropy could be due to intrinsic anisotropy of olivine crystals or due to a laminated structure with alternating high and low velocity layers other possibilities include the following upper mantle heterogeneity in southern california such as the transverse range anomaly may affect love and rayleigh wave velocities differently so that it yields the apparent anisotropy higher mode love wave interference has a stronger effect than suggested by our numerical experiments using model 1066a if the high love wave velocity is due to causes other than anisotropy the rayleigh wave velocity model would represent the southern california upper mantle velocity structure the shear velocity in the upper mantle moho to 250 km of this structure is on average 3 to 4 slower than that of the tna model determined for western north america

geologic nitrogen and climate change in the geochemical budget of karkevagge swedish lapland abstract while nitrogen is an essential nutrient for plant growth in the terrestrial environment and generally fixed by biological processes in soils in arctic and alpine environments n is a severely limited nutrient because of both climatic and soil constraints it is widely believed that geologic nitrogen is such a small component of the nitrogen cycle that this source is generally not viewed as being a significant component however it has been estimated that in fact as much as 20 of the total nitrogen budget may be stored in geological materials and where n is severely limited such as in arctic and alpine environments geologic n may in fact be a dominant source of n for biological processes nitrogen saturation may therefore have substantial impacts on geochemical cycles involving both soil and water chemistry in order to determine the potential for the rocks and soils of karkevagge to be significant sources of n samples of the principal rock units of the valley along with soil developed on a variety of rock types were sampled ammonia ammonium contents were determined using ion chromatography ammonia ammonium contents of the sampled rock materials display a wide range of abundances with marble containing a mean nh4 abundance of 4300 mg n kg quartz schist 1600 mg n kg biotite schist 4300 mg n kg and garnet mica schist 4500 mg n kg soil ammonia ammonium abundances were found to be 1600 mg n kg n pool abundances range from 2 5 kg m3 for marble to 8 7 for garnet mica schist soil n pools were found to be 3 0 kg m3 the inorganic n present as ammonia ammonium measured in bedrock represents substantial n input into the geochemical budget the n in bedrock originates from organically bound nitrogen associated with sediment or geothermal waters representing a mixture of sedimentary mantle and meteoric sources nitrogen in the soil originates from the weathering of n rich rocks the presence of unweathered nitrate minerals or fluid inclusions released to the soil and ultimately to plants by assimilation by biota or nitrification geologic nitrogen in karkevagge rocks and soils may represent a large and reactive pool with the potential for considerable impact on the geochemical system to investigate the potential responses of nitrogen release as well as other nutrients to increasing co2 concentration scenarios flow through leaching experiments were conducted on crushed rock samples and soils from the study area leaching experiments revealed two to three fold increases in both n and k release with a tripling of carbon dioxide concentrations ammonium shows more rapid release than potassium which suggests substantial changes in nitrogen cycling with increasing co2 enrichment of the atmosphere

evidence for reactivation of eocene joints and pre eocene foliation planes in the okanagan core complex british columbia canada we studied the brittle deformational history of the okanagan metamorphic core complex and its hanging wall carapace in the canadian cordillera in southern british columbia by an extensive structural investigation at mesoscopic scale the deformational history reveals that the transition from ductile to brittle deformation occurred during the early middle eocene and was associated with cooling due to tectonic and or extensive erosional unroofing of the okanagan portion of the sushwap metamorphic core complex our study is based on mesostructures because in this region macro structures are rarely exposed although their existence can be deduced from field relationships measured fault systems that are either perpendicular to bedding or which were sub vertical to inferred paleohorizontal and with very small dispersion of strike are interpreted as faulted joints i e joints that were reactivated by subsequent shear due to a relative change in stress orientation the faulted joints are similar to observed open mode i fracture system that exhibit no evidence for subsequent reactivation in this study we suggest that fault sets characterized by consistent attitude with a very small dispersion can be interpreted as faulted joints using only their stereographic projection pattern relative to the inferred paleohorizontal the first brittle deformation was a pervasive open mode fracturing in the hanging wall carapace of both eocene sedimentary and volcanic rocks and eocene and older igneous rocks characterized by a n s trend with a very small dispersion which formed either perpendicular to bedding or was sub vertical with respect to the inferred paleohorizontal these fractures are of similar trend to a middle eocene dyke swarm in part of the study area and beyond the okanagan core complex metamorphic rocks exhibit brittle fractures that are interpreted as metamorphic foliation planes which were reactivated as faults in response to the same e w extension recorded by the joints and dykes subsequent shear deformation associated with normal dip slip motion along the open mode fractures is explained by either regional tilting of the area in the presence of a similar stress orientation accompanying continued extension or as the result of a minor reorientation of the stress field later deformations suggested by strike slip and reverse motions indicate significant changes in the stress field orientation

evolution of north himalayan gneiss domes structural and metamorphic studies in mabja dome southern tibet field structural and metamorphic petrology investigations of mabja gneiss dome southern tibet suggest that contractional extensional and diapiric processes contributed to the structural evolution and formation of the domal geometry the dome is cored by migmatites overlain by sillimanite zone metasedimentary rocks and orthogneiss metamorphic grade diminishes upsection and is defined by a series of concentric isograds evidence for three major deformational events two older penetrative contractional and extensional events and a younger doming event is preserved metamorphism migmitization and emplacement of a leucocratic dike swarm were syntectonic with the extensional event at mid crustal levels metamorphic temperatures and pressures range from 500 8c and 150 450 mpa in chloritoid zone rocks to 705 65 8c and 820 100 mpa in sillimanite zone rocks we suggest that adiabatic decompression during extensional collapse contributed to development of migmatites diapiric rise of low density migmatites was the driving force at least in part for the development of the domal geometry the structural and metamorphic histories documented in mabja dome are similar to kangmar dome suggesting widespread occurrence of these events throughout southern tibet q 2004 elsevier ltd all rights reserved

clockwise p t paths for crustal melting and h2o recycling in granite source regions and migmatite terrains abstract clockwise pressure temperature p t paths of metamorphism pass through two kinds of melting reactions with increasing temperature the first generates h 2 o saturated partial melts at the h 2 o saturated solidus only if excess h 2 o is present usually this accounts for less than 3 melt the second generates h 2 o undersaturated melts through dehydration melting reactions dmrs of micas or other hydrous minerals and occurs at temperatures higher than the h 2 o saturated solidus if h 2 o undersaturated melts remain in situ and the source regions are not exhumed then the crystallisation reactions encountered along the near reverse p t path may produce the same mineralogy as in the source rock in regions of exhumation along the decompression segments of clockwise p t paths two other types of crystallisation reactions occur the better known type occurs at the recrossing of the pelite h 2 o saturated solidus at shallower depth this can occur at mid crustal depths or much shallower at pressures lower than the appropriate invariant point which relates all of these reactions and will result in granitic pegmatites at the other type remaining mica can react with hydrous melt to generate anhydrous granulite with free h 2 o fluid such suprasolidus decompression dehydration reactions sddrs result in freezing of pelitic melts at mid crustal depth to k feldspar quartz assemblages and release of h 2 o which can induce h 2 o saturated melting in adjacent fertile lithologies lacking h 2 o e g psammite older granite distinct mineral proportions and textures will result from each reaction the actual reactions occurring are related through specific invariant points whose locations are known in the p t space the displacement of these invariant points due to additional components in the solid melt and fluid phases is reasonably well known the flat lying sddr very low d p d t will extend to much higher pressures if a low ah 2 o fluid is present sddr involving amphibole or epidote will occur in mafic to intermediate compositions over a large depth range depending on fe mg ca na etc of the rock compositions

melt segregation in the continental crust distribution and movement of melt in anatectic rocks the grain and outcrop scale distribution of melt has been mapped in anatectic rocks from regional and contact metamorphic environments and used to infer melt movement paths at the grain scale anatectic melt is pervasively distributed in the grain boundaries and in small pools consequently most melt is located parallel to the principal fabric in the rock typically a foliation short branched arrays of linked melt bearing grain boundaries connect melt depleted parts of the matrix to diffuse zones of melt accumulation protoleucosomes where magmatic flow and alignment of euhedral crystals grown from the melt developed the distribution of melt leucosome and residual rocks normally melanocratic in outcrop provides different but complementary information the residual rocks show where the melt came from and the leucosomes preserve some of the channels through which the melt moved or sites where it pooled different stages of the melt segregation process are recorded in the leucosome melanosome arrays regions where melting and segregation had just begun when crystallization occurred are characterized by short arrays of thin branching leucosomes with little melanosome a more advanced stage of melting and segregation is marked by the development of residual rocks around extensive branched leucosome arrays generally oriented along the foliation or melting layer places where melting had stopped or slowed down before crystallization began are marked by a high ratio of melanosome to leucosome because most of the melt has drained away very few leucosomes remain to mark the melt escape path this is common in melt depleted granulite terranes many migmatites contain abundant leucosomes oriented parallel to the foliation mostly these represent places where foliation planes dilated and melt drained from the matrix via the branched grain boundary and larger branched melt channel leucosome arrays collected melt collected in the foliation planes was partially or fully expelled later when discordant leucosomes formed leucosomes or veins oriented at high angles to the foliation layering formed last and commonly lack melanocratic borders hence they were not involved in draining the matrix of the melting layer discordant leucosomes represent the channels through which melt flowed out of the melting layer

structures and melt fractions as indicators of rheology in cordierite bearing migmatites of the bayerische wald variscan belt germany a melt but the degree of their shape preferred orientation increases the relation between melt volume fraction melt segregation and with increasing melt segregation and differential stress the mideformation mechanisms of minerals in migmatites and the concrostructures suggest that deformation mechanisms and hence the trolling effects of all these factors on the bulk mechanical behaviour bulk mechanical behaviour of migmatites change in space and time were investigated using rocks from the bayerische wald bohemian during partial melting the observed complex interplay of melt massif variscan belt germany biotite dehydration melting at volume fraction melt segregation bulk strength contrasts mechanical 800 850 c and 0 5 0 7 gpa was the migmatite forming process properties of different minerals and time cannot be described by a in this area four migmatite types were distinguished that alternate single flow law detailed mapping of migmatite areas along with on the scale of several decimetres to several tens of metres type microstructural observations deformation experiments considering mig1 is massive and undeformed types mig2 and mig3 are heterogeneous melt distribution and numerical models that integrate both stromatic leucosome mesosome interlayering but differ in the different flow laws for various stages of partial melting may serve degree of deformation type mig4 has an interlayering of meto derive quantitative models for the bulk mechanical behaviour of lanosome and leucosome and is strongly deformed melt volume crustal sections in the future fractions found by volume estimation of pure melt leucosomes on outcrop hand specimen and thin section scales are 20 40 vol and coincide fairly well with melt volume fractions produced in dehydration melting experiments with similar bulk compositions at the relevant pressure and temperature conditions 20 30 vol the degree of melt removal from mesosomes and melanosomes melt

chemical weathering of monsoonal eastern china implications from major elements of topsoil major element compositions of 36 bulk samples and 41 clay samples which were obtained from 47 topsoils collected in monsoonal eastern china were investigated with conventional wet chemistry and x ray fluorescence xrf spectrometry respectively based on major element analyses the mobility of major elements and latitudinal distributions of sio2 al2o3 ratio chemical index of alteration cia chemical index of weathering ciw and weathering index of parker wip were analyzed meanwhile the suitability of these chemical weathering indices to topsoils in monsoonal eastern china and its controls were discussed these investigations indicate that na k ca mg and si are relatively depleted while mn p fe and ti are relatively enriched in topsoils of the study area by comparison with their contents in the upper continent crust ucc and that alkali metal na k and alkaline earth metal ca mg elements are generally easier to be depleted from their parent materials than other major elements during chemical weathering the latitudinal distributions of cia ciw and wip show that they are suitable to both bulk and clay samples but sio2 al2o3 is only suitable to clay samples not suitable in bulk ones all these investigations indicate a significant dependence of grain size in major element abundance and latitudinal distributions of sio2 al2o3 cia ciw and wip but parent rock type has little effect on them except its impact on the latitudinal distribution of wip in clay samples the significant grain size dependence probably indicates the presence of unaltered minerals in bulk samples thus we suggest that clay samples are more suitable to investigating chemical weathering of sediments on continents than bulk samples the trivial effect of parent rock type probably indicates a relatively uniform chemical weathering on various parent rocks correlation analyses indicate that climate is the dominant control of chemical weathering of topsoils in the study area and the significant latitude effect indicated by the spatial distributions of chemical weathering indices actually reflect the climate control on chemical weathering of topsoils chemical weathering indices actually reflect the integrated weathering history in the study area besides the dominant control of climate other factors like tectonics parent rock biology landform and soil depth and age might also have some effect on the chemical weathering of topsoils in the study area which needs further research c 2013 elsevier ltd all rights reserved

crustal scale rheological transitions during late orogenic collapse abstract orogeny involves crustal thickening followed by thermal relaxation and radiogenic heat production in the thickened crust culminating in crustal melting and magma intrusion which decrease the crustal viscosity by several orders of magnitude and cause late orogenic collapse collapse of the canadian cordillera is expressed in the early tertiary shuswap metamorphic core complex british columbia which displays a three layer crustal section separated by two fundamental rheological discontinuities 1 the brittle ductile transition across which high angle normal faults in the upper crust control basin formation merge into a low angle detachment zone where leucogranite laccoliths ponded and deformed progressively under submagmatic to low temperature conditions and 2 the metatexite diatexite transition across which the rocks lose their solid framework and behave like a viscous magma this transition has the potential to mechanically decouple the upper crust from the rest of the lithosphere during a late orogenic gravitational collapse

an experimental study of grain scale melt segregation mechanisms in two common crustal rock types creation of pathways for melt to migrate from its source is the necessary first step for transport of magma to the upper crust to test the role of different dehydration melting reactions in the development of permeability during partial melting and deformation in the crust we experimentally deformed two common crustal rock types a muscovite biotite metapelite and a biotite gneiss were deformed at conditions below at and above their fluid absent solidus for the metapelite temperatures ranged between 650 and 800 c at pc 700 mpa to investigate the muscovite dehydration melting reaction for the biotite gneiss temperatures ranged between 850 and 950 c at pc 1000 mpa to explore biotite dehydration melting under lower crustal conditions deformation for both sets of experiments was performed at the same strain rate e 1 37 10 5 s 1 in the presence of deformation the positive v and associated high dilational strain of the muscovite dehydration melting reaction produces an increase in melt pore pressure with partial melting of the metapelite in contrast the biotite dehydration melting reaction is not associated with a large dilational strain and during deformation and partial melting of the biotite gneiss melt pore pressure builds more gradually due to the different rates in pore pressure increase melt enhanced deformation microstructures reflect the different dehydration melting reactions themselves permeability development in the two rocks differs because grain boundaries control melt distribution to a greater extent in the gneiss muscovite dehydration melting may develop melt pathways at low melt fractions due to a larger volume of melt in comparison with biotite dehydration melting generated at the solidus this may be a viable physical mechanism in which rapid melt segregation from a metapelitic source rock can occur alternatively the results from the gneiss experiments suggest continual draining of biotite derived magma from the lower crust with melt migration paths controlled by structural anisotropies in the protolith

a granulometry and secondary mineral fingerprint of chemical weathering in periglacial landscapes and its application to blockfield origins abstract a review of published literature was undertaken to determine if there was a fingerprint of chemical weathering in regoliths subjected to periglacial conditions during their formation if present this fingerprint would be applied to the question of when blockfields in periglacial landscapes were initiated these blocky diamicts are usually considered to represent remnants of regoliths that were chemically weathered under a warm neogene climate and therefore indicate surfaces that have undergone only a few metres to a few 10s of metres of erosion during the quaternary based on a comparison of clay and silt abundances and secondary mineral assemblages from blockfields other regoliths in periglacial settings and regoliths from non periglacial settings a fingerprint of chemical weathering in periglacial landscapes was identified a mobile regolith origin under at least seasonal periglacial conditions is indicated where clay 0 5 silt 8 across a sample batch this contrasts with a mobile regolith origin under non periglacial conditions which is indicated where clay 0 5 silt 6 across a sample batch with clay 0 5 silt 8 in at least one sample a range of secondary minerals which frequently includes interstratified minerals and indicates high local variability in leaching conditions is also commonly present in regoliths exposed to periglacial conditions during their formation clay silt ratios display a threshold response to temperature related to the freezing point of water but there is little response to precipitation or regolith residence time lithology controls clay and silt abundances which increase from felsic through intermediate to mafic compositions but does not control clay silt ratios use of a sedigraph or coulter counter to determine regolith granulometry systematically indicates lower clay abundances and intra site variability than use of a pipette or hydrometer in contrast to clay silt ratios secondary mineral assemblages vary according to regolith residence time temperature and or precipitation a microsystems model is invoked as a conceptual framework in which to interpret the concurrent formation of the observed secondary mineral ranges according to the fingerprint of chemical weathering in periglacial landscapes there is generally no evidence of blockfield origins under warm neogene climates nearly all blockfields appear to be a product of quaternary physical and chemical weathering a more dominant role for periglacial processes in further bevelling elevated low relief non glacial surface remnants in otherwise glacially eroded landscapes is therefore indicated

frozen bed fennoscandian and laurentide ice sheets during the last glacial maximum the areal extents of the laurentide and fennoscandian ice sheets during the last glacial maximum about 20 000 years ago are well known1 but thickness estimates range widely from high domed2 to thin3 with large implications for our reconstruction of the climate system regarding for example northern hemisphere atmospheric circulation and global sea levels this uncertainty stems from difficulties in determining the basal temperatures of the ice sheets and the shear strength of subglacial materials4 a knowledge of which would better constrain reconstructions of ice sheet thickness here we show that in the absence of direct data the occurrence of ribbed moraines in modern landscapes can be used to determine the former spatial distribution of frozen and thawed bed conditions we argue that ribbed moraines were formed by brittle fracture of subglacial sediments induced by the excessive stress at the boundary between frozen and thawed bed conditions resulting from the across boundary difference in basal ice velocity maps of glacial landforms from aerial photographs of canada and scandinavia reveal a concentration of ribbed moraines around the ice sheet retreat centres of quebec keewatin newfoundland and west central fennoscandia together with the evidence from relict landscapes that mark glacial areas with frozen bed conditions the distribution of ribbed moraines on both continents suggest that a large area of the laurentide and fennoscandian ice sheets was frozen based and therefore high domed and stable during the last glacial maximum

pervasive melt migration from migmatites to leucogranite in the shuswap metamorphic core complex canada control of regional deformation abstract the shuswap metamorphic core complex exhumed in the hinterland of the canadian cordillera displays a 15 km structural section from migmatites to leucogranite it comprises a lower unit dominated by anatectic migmatites exposed in the core of domes at higher structural level the transition from a middle amphibolite facies unit to an upper crustal unit is marked by a low angle detachment associated with the emplacement of laccoliths of leucogranite the amphibolite facies middle unit is permeated by a network of granitic veins feeding the laccoliths and structurally connected to the migmatites of the lower unit this paper describes the geometric textural and structural characteristics and the distribution of the granitic fraction at the outcrop scale in the amphibolite facies unit separating the migmatites from the leucogranite this analysis constrains the mechanisms of melt migration within a plurikilometer scale section across high grade rocks of the middle crust in fertile lithologies metapelites felsic amphibolites the granitic fraction in part generated in situ forms a diffuse network of concordant veins feeding discordant veins and structural sites such as the foliation shear zones and boudin necks discordant granitic veins are oriented perpendicular and to a lesser extent parallel to the mineral and stretching lineation in refractory lithologies the granitic fraction is dominantly intrusive and displays sharp contacts with the host rock however distribution of the granitic fraction shows the same characteristics as for fertile lithologies the melt fraction migrated through a network of fractures taking advantage of mechanical weaknesses such as the foliation plane or forming dikes oriented dominantly perpendicular to the regional stretching and mineral lineations these geometric and textural characteristics suggest that granite migration in these rocks is achieved dominantly by viscous flow of the melt solid through the solid matrix driven by its buoyancy and controlled by mechanical anisotropy of the rock and local dilation created by heterogeneous deformation the relationship between the regional fabric and the distribution of the granitic fraction indicates that regional deformation incremental and finite played a major role in providing pathways for melt migration the formation of laccoliths of leucogranite at higher structural levels suggests that upward melt migration led to accumulation of granitic magmas these observations are consistent with a model of pervasive melt migration through a network of interconnected concordant and discordant granitic veins feeding laccolithic plutons extracted from the dominantly solid matrix during vertical thinning and compaction at a regional scale the presence of both transposed and intact granitic networks indicate an overlap between deformation and granite migration as a continuum or in pulses the methodology and terminology proposed in this paper provide some insights on the behavior of the granitic fraction in the middle crust this approach should be applicable to other high grade terrains exhumed in the cores of orogenic belts

a model for neogene crustal rotations transtension and transpression in southern california two episodes of crustal rotation have occurred in the regions of southern california and the mojave desert since the beginning of miocene time an early miocene episode of clockwise crustal rotation is associated with widespread north south to north northeast south southwest crustal extension throughout southeast california and western arizona this episode is apparently related to changing subduction parameters of the farallon plate a middle miocene and later episode of clockwise rotation in the transverse ranges and bordering areas is related to shear between the pacific and north american plates in both episodes clockwise crustal rotations first occur in a deforming zone which has a component of extension across its trend and shear along its trend the effects of extension are most pronounced in the earlier episode but clear in the later one also the pacific north american deforming zone began contracting in width during pliocene time but clockwise rotations continued and are probably in progress today

parent material and chemical weathering in alpine soils on mt mansfield vermont usa we compared the elemental composition of soil and bedrock samples to determine the extent of chemical weathering and the nature of the soil parent material in alpine soils on vermont s highest summit previously it was unclear whether these soils formed through weathering of bedrock glacial till or eolian sediment or solely through the accumulation of organic matter in eighteen profiles no evidence was found to indicate that soils have developed in glacial till despite evidence that the mountain was completely inundated by the laurentide ice sheet in contrast results strongly support the theory that pedogenesis in this environment involves in situ bedrock weathering under a thickening blanket of acidic organic litter weathering indices reveal an increase in weathering intensity upwards from the bedrock and trends of normalized rare earth elements demonstrate a strong similarity between bedrock and soil samples leaching has concentrated less mobile elements such as al cr la p pb and ti in soil horizons and removed mobile elements such as co fe k mg mn si and zn x ray diffraction reveals that chlorite which is present in all bedrock samples and some saprolites has weathered completely from upper soil horizons and that hydrobiotite vermiculite kaolinite gibbsite and goethite have formed in the soil ratios of immobile elements ce cr nb ta ti y and zr in soil and bedrock samples are however notably different furthermore the moderately mobile trace elements cu mo and sr are actually more abundant in soil than in bedrock and soil concentrations of zr are up to an order of magnitude greater than in bedrock samples together these data argue for at least a modest eolian influx which may have arrived during the regression of lake vermont during the latest pleistocene or from an outwash source in the immediate post glacial period similarly increased ca and na concentrations in soil samples may signify modern deposition of dust bearing ca from agricultural fields and na from roads

timescales of migmatization melt crystallization and cooling in a cordilleran gneiss dome valhalla complex southeastern british columbia 1 integration of in situ and conventional ion microprobe u th pb zircon and monazite geochronology with 40ar 39ar hornblende biotite and muscovite thermochronology provides a temporal record of metamorphism partial melting fluids and cooling of exhumed midcrustal to lower crustal rocks the valhalla complex southeastern british columbia is one of a series of elongate gneiss domes within the omineca belt of the canadian cordillera we have performed u th pb and 40ar 39ar age measurements on migmatitic gneisses from a range of structural levels and settings within the valhalla complex in an effort to better document the timing of migmatization and exhumation stromatic migmatites and leucosomes crystallized in boudin necks yield concordant u pb zircon ages that cluster near 60 ma and th pb monazite ages of circa 60 50 ma in situ analyses of monazite in samples that contain 60 50 ma however the combined data also suggest that melt crystallization circa 60 ma in the valhalla complex occurred rapidly and before the other domes within the omineca belt cooling at 49 ma throughout the omineca is associated with regional extension and exhumation of migmatites in the domes the presence of abundant migmatites and the similarity in timing of melt crystallization and cooling in domes along the 400 km long omineca belt is consistent with localization of exhumation at the boundary between the flowing crust of the hinterland and the rigid colder crust of the rocky mountain foreland

multimode surface wave tomography for the australian region using a three stage approach incorporating finite frequency effects 1 a three stage inversion technique for surface wave tomography is applied to the australian region the inversion procedure consists of three independent processes in the first stage path specific one dimensional 1 d shear velocity profiles are derived from multimode waveform inversion to provide dispersion information the information from all paths is then combined to produce multimode phase speed maps as a function of frequency the first version of these phase speed maps is derived from linearized inversion based on the assumption of surface wave propagation along great circle paths subsequently the 2 d phase speed maps are updated by including ray tracing and finite frequency effects through the influence zone around the surface wave paths over which the phase is coherent finally in the third stage the 3 d shear wave speed distribution is reconstructed from the set of updated multimode phase speed maps this three stage inversion of surface waves has significant benefits because it is possible to incorporate multimode dispersion off great circle propagation and finite frequency effects for surface waves in a common framework the final 3 d model which includes the effects of ray bending and finite frequency shows improvement in the definition of the model in regions with high gradients in shear velocity such as near tectonic boundaries especially in eastern australia despite the natural smoothing imposed by considering the influence zone around the surface wave paths the final models still require rapid change in shear wave properties in the neighborhood of the edge of the craton

the influence of schistocity on soil weathering on large boulder tops karkevagge sweden abstract weathering and soil development was examined on large boulder tops in karkevagge a deglaciated valley in northern sweden soil and weathered rock was collected from 15 mica schist and 5 garnet mica schist boulders the boulders approximated closed systems as their tops were essentially horizontal and assumed inputs were minimal with the possible exception of rainwater and aeolian sediment this provided a relatively uniform sample to determine influential soil forming factors results showed that the soils were shallow and exhibited minimal horizonation mostly a over c horizons particle size was predominantly coarse sandy loam with a significant percentage of silt and clay on a number of the boulders clay content was higher on the garnet mica schist than on the mica schist boulders soil ph was acidic deeper soils had developed overlying vertical schistocity emphasizing the role of microenvironment muscovite chlorite and mixed layer minerals were the predominant clay minerals in the boulder soils secondary clay formation in soils indicated that chemical weathering was occurring results concurred with previous research that chemical weathering is an active geomorphic process in karkevagge

clay mineralogy chemical weathering and landscape evolution in arctic alpine sweden abstract the purpose of this research was to 1 characterize the clay mineralogy of soils in and adjacent to karkevagge a recently deglaciated valley in arctic sweden 2 document chemical weathering in a periglacial environment and 3 use the mineralogy to help explain landscape evolution soil samples were analyzed from 11 sites that differ in elevation parent material drainage slope and vegetation parent materials include residuum alluvium colluvium and glaciofluvial material derived from garnet mica schist plus in one locality a till of granitic origin x ray diffraction xrd was used to characterize the clay size fraction

simulating loss of primary silicate minerals from soil due to long term weathering using allogen comparison with soil chronosequence lake sediment and river solute flux data this paper presents allogen a process model of soil mineral chemical weathering though designed principally to aid interpretation of lake sediment geochemical records by providing mass balance constraints for competing interpretations the model is also applicable to more general questions about long term weathering and soil development the model is constructed around a generalised version of the mineral weathering submodel of profile modified to minimise the need for site specific data and to optimise performance for long term change comparison with observed weathering rate data river flux studies chronosequences and lake sediment chemical stratigraphy suggests that soil mineral depletion can be usefully simulated over timescales applicable to quaternary and holocene studies to illustrate this the plausibility of a weathering interpretation is demonstrated for sediment records at lake hope simpson and moraine lake and the lake chronosequence at glacier bay while long term soil mineral depletion appears predictable reliable simulation of past runoff quality is hampered by lack of a suitable long term model for soil carbon

melt segregation in migmatites anatectic stromatic migmatites have a symmetrical layered structure with a low ratio of thickness to length and a periodicity features that have not been explained satisfactorily but which are related to physical processes of melt segregation we evaluate the compaction model for segregation as it applies to migmatites and develop models for melt segregation based upon convection driven by volume change and upon advection down pressure gradients that result from applied differential stress acting on an anisotropic multilayer protolith compaction by gravity driven two phase flow results in asymmetric separation yields calculated segregation times that are slow or geologically unreasonable and yields relative volumes that are not consistent with the abundance of leucosome seen in natural migmatites although calculated segregation times for very wet granite might allow segregation by compaction some driving force in addition to gravity is needed to cause widespread melt segregation in the crust for segregation at low volume fraction of melt we develop a two dimensional two phase matrix and fluid viscous flow cell model length much greater than thickness with phase changes which predicts either expansion or contraction convection depending on whether volume change vr is positive or negative convection leads to melt segregation to form a stromatic structure in a geologically reasonable timescale at moderate volume fraction of melt segregation may occur by filter pressing in compositionally layered rocks in response to applied differential stress melt migration is by porous medium flow driven by differences in mean normal stress between the layers as a consequence of differences in rheology and shear enhanced matrix collapse calculated segregation rates are fast and the model yields adequate volume of leucosome the positive vr for volatile phase absent melting reactions under crustal pressures promotes melt escape unless extensional deformation facilitates melt accumulation if the rate of melt production exceeds the rate of melt escape then the increase in melt pressure may lead to melt enhanced embrittlement and fracture and melt may migrate out of the system in contrast water rich volatile phase present melt producing reactions have a negative vr which promotes melt retention after segregation unless deformation generates melt escape pathways evolution of stromatic structure through anatectic erosion of mesosome by increasing the melt fraction in situ may lead to breakdown of the solid matrix and will lead to instability due to buoyancy and magma may become mobile and entrain residual material restite

mantle heterogeneities and the scec reference three dimensional seismic velocity model version 3 we determine upper mantle seismic velocity heterogeneities below southern california from the inversion of teleseismic travel time residuals teleseismic p wave arrival times are obtained from three temporary passive experiments and southern california seismic network scsn stations producing good raypath coverage the inversion is performed using a damped least squares conjugate gradient method lsqr the inversion model element spacing is 20 km before the inversion the effects of crustal velocity heterogeneities represented by the southern california earthquake center scec seismic velocity model version 2 are removed from the teleseismic travel times the p wave inversion produces a variance reduction of 43 s wave velocities are determined from laboratory vp vs ratios the most prominent features imaged in the results are high p wave velocities 3 in the uppermost mantle beneath the northern los angeles basin and the previously reported tabular high velocity anomaly 3 to depths of 200 km beneath the transverse ranges crosscutting the san andreas fault we incorporate the upper mantle seismic velocity heterogeneities into the scec southern california reference seismic velocity model the prior accounting for the crustal velocity heterogeneity demonstrates the utility of the top down method of the scec seismic velocity model development

effects of melt loss melt retention and protolith composition on differentiation of anatectic metapelites a case study of the wet mountains colorado abstract two metasedimentary migmatite samples from the same outcrop in the northern margin of the oak creek pluton in the wet mountains colorado have distinct mineralogy textures and major and trace element geochemistry sample w6 a garnet biotite migmatite has trace element characteristics consistent with a sedimentary protolith this sample is also rich in silica and lacks sillimanite and cordierite sample w6a a garnet sillimanite cordierite migmatite has strong heavy rare earth element hree enrichment low silica and contains abundant aluminum rich minerals both rocks are relatively oxidized consistent with sedimentary protoliths for both based on textural and geochemical evidence we interpret the differences in mineralogy between the two samples to be the result of differing degrees of melt extraction and variations in protolith composition such differences were assessed using isocon analysis and calculated p t phase diagrams melt retention in sample w6 resulted in the absence of sillimanite and cordierite and back reaction between minerals and melt in the peak assemblage by contrast melt extraction in w6a left garnet in the residuum and imparted a strong heavy rare earth element enrichment on the sample allowing preservation of the peak mineral assemblage consequently w6a records peak conditions of 743 c and 7 6 kbar whereas w6 yields lower p t estimates that may represent the prograde and retrograde metamorphic paths our results indicate that melt extraction can be heterogeneous even at outcrop scale and differing mineralogy may reflect variable proportions of melt loss and local variations in the composition of the protolith moreover at least at small scale migmatization of iron rich protoliths is a plausible mechanism for the production of ferroan alkaline granitic magmas

geochemistry and mineralogy of saprolite in finnish lapland abstract an ancient saprolite has developed on the palaeoproterozoic granulite granite gneiss and amphibolite bedrock of the vuotso tankavaara area of central finnish lapland the present day climatic regime in finnish lapland lies within the northern boreal zone and so the saprolite there can be regarded as fossil cores of saprolite were collected from 4 sections 42 samples and analyzed chemically and mineralogically in the study area progressive weathering of the rocks has been marked by gradual enrichment in al fe and ti and depletion of na k and ca the higher concentration of fe iii and water and reduced na and ca in weathered bedrock in the 4 sections are indicative of oxidation hydration and leaching processes involved during weathering the primary minerals in the saprolite are plagioclase feldspar k feldspar quartz garnet almandine and hornblende the common secondary minerals are kaolinite halloysite and vermiculite in addition to minor amounts of sericite intense weathering is indicated by 1 the presence of kaolinite and halloysite in 4 sections of different bedrock types and 2 the comparatively lower sio2 al2o3 wt ratio 2 30 of weathered granulites 3 sections as compared to fresh granulite 4 33 and that of weathered amphibolite 2 68 as compared to fresh amphibolite 3 56 in general kaolinite and halloysite have formed through the weathering of feldspars garnet and biotite vermiculite is the most probable alteration product of biotite the formation of kaolinite and halloysite in finnish lapland indicates wetter and warmer climatic conditions during the time of their formation than at present the possible time for formation of the saprolite is early cretaceous early tertiary into middle miocene

the poisonous rocks of karkevagge abstract the black schist in karkevagge swedish lapland has been reported to weather easily and produce a poisonous effect on vegetation this research was an investigation of that phenomenon as part of a larger study of weathering in karkevagge in july 1999 soil and plant samples were collected downslope of a poisonous boulder samples from the adjacent unaffected slope served as references biomass plant elemental composition and soil fertility were determined most plants within 1 4 m downslope of the poison boulder were dead and effects on plant growth could be seen to about 6 m plants near the boulder had elevated levels of k b al cd se and fe and lower levels of ca mn and ba compared to reference plants in the soil near the poison boulder extractable s cd and fe and salt contents were greater while ph and extractable cl p ca mg k ba ni and cr were lower than in the reference soil at 10 m downslope of the boulder soil and plant chemistry was more similar to the reference materials but some effects were still noted elemental analyses of the poison boulder and soil revealed no particular plant toxins although contents of fe and s were higher and ca lower than in reference materials we believe the poison is sulfuric acid which forms as a consequence of pyrite oxidation the dark color of the boulder is consistent with a pyrite bearing lithology and other field observations and laboratory analyses support the hypothesis coatings on local rocks include jarosite gypsum and copiapite secondary minerals associated with pyrite oxidation and weathering accelerated by sulfuric acid radiocarbon dating indicates that the rock fell off the cliff some time before 245 14 c years bp

ice sheet growth under dirty conditions implications of debris cover for early glaciation advances abstract debris covered glaciers respond differently to any given set of climatic conditions than clean glaciers this difference stems from change in ablation rate caused by a debris cover approaching zero ablation with sufficiently thick protective cover a mechanism not yet considered in the context of ice sheet growth critical to applying the mechanism to ice sheets is supply of debris we postulate that periods after major interglacials offer the best conditions for dirty advances this is because the volume of debris previously deposited and weathered in interglacial time the latter a function of exposure length should be at a maximum advances of dirty ice sheets generate landforms and in positions deviating from clean ice advances under similar climatic conditions hence inferences of both ice sheet properties inferred from such dirty ice advances and the climate conditions related to such advances must be cautious furthermore modeling of past ice sheets must consider the effect of debris cover whenever indications exist for such a cover

preglacial surface remnants and quaternary glacial regimes in northwestern sweden abstract we present a detailed map of the distribution of preglacial surface remnants in the kebnekaise region of northwestern sweden in this mountain area we discern four important large scale geomorphological units each representing a specific set of erosional agents and formative conditions these are i intact preglacial surface remnants characterized by gentle slopes round summits wide shallow valleys and an absence of rock basins ii preglacial surface remnants showing signs of minor glacial erosion and deposition iii glacially scoured surfaces including glacial troughs iv deep fluvial valleys cut into the preglacial surface the pattern of glacial erosion is explained as the result of three specific modes of glaciation known to have existed during the last 120 000 years and inferred to have repeatedly prevailed during the last 2 75 million years cirque glaciation mountain ice sheets and fennoscandian ice sheets a deep ocean oxygen isotope record of foraminifera from the north atlantic dsdp 607 was used to infer the temporal extent of these modes of glaciation during the last 2 75 million years we interpret the preglacial landscape preservation and the pattern of glacial erosion in terms of the configuration the basal thermal regime and the duration of such glaciation events the average subglacial thermal regime of both ice sheet types was frozen on the uplands and melting in the main valleys where outlet glaciers and ice streams formed the pre glacial landscape is best preserved at intermediate elevations low enough not to have been covered by cirque glaciers and apparently high enough not to have experienced melted bed conditions and subglacial erosion during ice sheet overriding events in a narrow high relief zone along the elevation axis interglacial fluvial erosion was morphologically important the absence of glacial erosion on uplands in this zone allowed fluvial erosion to commence on the same locations during each ice free interval in contrast no persistent fluvial valley pattern could develop in zones subjected to repeated glacial scouring and hence derangement of fluvial patterns

morphology and stratigraphy from several deglaciations in the transtrand mountains western sweden the transtrand mountains western sweden are characterised by an abundance of glaciofluvial meltwater channels crossing lateral channels and channel systems overprinted by fluting occur at several localities drainage channel systems from three older deglaciations are interpreted to have been preserved despite overriding by later ice sheets deep sections machine excavated into the summit surface of the hundfjallet mountain revealed the presence of two lower diamictons into which two older generations of lateral channels were cut and subsequently buried by a late weichselian basal till buried frost sorted structures and frost fractured bedrock below the lowermost till indicate the repeated occurrence of periglacial condil conditions an organic layer between the two older units yielded an infinite radiocarbon age of 45000 yr bp the pollen content of this layer indicates a local mountain heath flora dominated by ericaceous dwarf shrubs and graminids the climate phase is interstadial or the beginning or end of an interglacial the different diamictons also display different pollen spectra during the last deglaciation the ice flow was from the north northeast the second youngest system of drainage channels corresponds to ice flow from approximately west northwest there are still older traces of separate deglaciation events from the east and north a frozen bed is interpreted to have been the standard basal regime for the last ice sheets to cover the transtrand mountains

the influence of partial melting on the electrical behavior of crustal rocks laboratory examinations model calculations and geological interpretations abstract the complex electrical impedance of a granulite has been determined over the frequency range 10 1 to 105 hz at temperatures between 600 and 1200 c at normal pressure and different oxygen fugacities in the stability field of magnetite the impedance spectroscopic is measurements are compared with the results of melting experiments performed under the same experimental conditions and with the same rock sample as the is measurements a strong increase in the electrical conductivity of about one and a half orders of magnitude is observed during partial melting this increase is explained by the formation of an interconnected network of melt the wetting of the grain surfaces starts slightly above the solidus however complete interconnection of the network is detected at higher temperatures 1070 c and hence higher melt fractions 10 vol this is explained by deviations from the equilibrium fabric of the partially molten sample with a modified brick layer model mblm the electrical conductivity is calculated as a function of the observed melt portion this model is valid if the melt forms a complete interconnected network at the grain boundaries the electrical conductivity at different temperatures was modeled using the results of the melting experiments and the mblm melt 10 s m with ea melt 1 ev solid 0 01 s m with ea solid 1 4 ev the results of the laboratory examinations were applied to different crustal regions where partially molten rocks are assumed to exist the same mblm is used to estimate the melt fraction that is necessary to explain the high conducting zones hczs observed in the crust beneath the andean orogen the pyrenees and the tibetan plateau at least 14 4 and 4 vol of interconnected melt are necessary to produce the observed conductivity respectively the actual amount of melt should be higher due to perturbation problems and melt trapped in pockets

preservation of landforms under ice sheets and ice caps abstract this article addresses the question of whether or not distinct glacial and non glacial landforms can survive beneath ice sheets and ice caps with little or no morphological alteration a review of recent work documents the existence of pre last stadial landforms and landscapes in areas covered by the fennoscandian and laurentide ice sheets a substantial number of independent works indicate that landforms such as eskers drainage channels and boulder fields have escaped destruction despite complete ice overriding during several tens of millenia full preservation of former ground surfaces or delicate landforms probably is linked to areas where the ice sheet base was continuously frozen to its bed larger robust landforms such as large drumlins appear to have been preserved even under wet based conditions in glaciated areas patches preserved under dry cold based conditions provide important windows towards the past showing landscapes that were destroyed in surrounding areas affected by wet based and eroding ice some consequences for the research fields of non glacial geomorphology archaeology and botany include the possibility of subglacial museums and refugia a time space model describes geomorphological access to information from older events in glaciated areas

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

ten years 1994 2004 of potential weathering in karkevagge swedish lapland this paper reports the findings of a ten year study of potential weathering of machine polished dolomite granite and limestone discs buried in shallow pits beneath a variety of vegetation cover types in karkevagge and on an adjoining ridge in swedish lapland the paper extends a previously published five year 1994 1999 record by adding the period 1999 2004 comparing the two periods and integrating results to provide a decadal record the field and laboratory procedures of the first period were faithfully replicated during the second period with the notable modification that only a segment of each original disc was replaced in the field for the second portion of the study a total of 48 dolomite 36 granite and 19 limestone discs were buried at shallow depths 60 cm beneath alpine tundra birch forest dryas heath heath meadow solifluction meadow and willow cover types with the exception of the willow which had only two each cover type had three replicated pits relationships identified during period 1 were generally repeated during period 2 salient results are the expected weathering rate order of limestone dolomite granite and statistically distinguishable differences in weathering rate by vegetation cover type differentiation of the two heath categories from the other vegetation cover types is the most important spatial distinction in weathering rate statistical distinctions among other measures were variable with soil horizon and burial depth being non significant ph variability being weakly distinguishable and drainage variability being important granite mass losses were generally too low to be useful for statistical separation dolomite discs experienced a statically higher loss rate during period 2 which had both a warmer and wetter air climate than period 1 minimum and maximum total decadal percentage losses from the discs were 0 2 and 25 7 for dolomite 0 07 and 0 57 for granite and 0 2 and 32 1 for limestone in general dolomite was the most useful material for monitoring mass loss with limestone weathering tending to be too rapid and granite weathering being too slow copyright 2006 john wiley sons ltd

weathering implications of water chemistry in an arctic alpine environment northern sweden this paper reports on some of the chemical characteristics of late melt season water from karkevagge valley of the boulders above the arctic circle in northern sweden included in the analyses were temperature electrical conductivity ph so4 no3 k sio2 mg mn na fe and al these were measured in rain late lying snow and water from the major stream and lake as well as from pond tributary and seep sources in the valley a total of 71 samples was collected at 57 sites between august 6 and august 23 1996 for the purpose of characterizing the present weathering regime within this classic u shaped glacial valley evidence of chemical weathering included increases in solute concentrations over precipitation inputs and a source related wide variation in water chemistry the dominant anion measured in surface water was so4 that along with the presence of caso4 coatings on streambeds indicates that pyrite oxidation may contribute to the weathering regime high so4 concentrations were associated with gypsum coated streambeds and seeps that emerge from the bedrock low so4 concentrations were associated with tributaries flowing primarily on fresh rock and originating from melting snow estimated chemical denudation rate for the valley corrected for atmospheric inputs was 19 2 tons km2 yr although this is lower than previously reported our research supports earlier work indicating that chemical weathering is a major component of mass wasting in this arctic alpine environment

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

soil formation and weathering in a permafrost environment of the swiss alps a multi parameter and non steady state approach spatially discontinuous permafrost conditions frequently occur in the european alps how soils under such conditions have evolved and how they may react to climate warming is largely unknown this study focuses on the comparison of nearby soils that are characterised by the presence or absence of permafrost active layer thickness 2 3 m in the alpine tundra and subalpine forest range of the eastern swiss alps using a multi method geochemical and mineralogical approach moreover a new non steady state concept was applied to determine rates of chemical weathering soil erosion soil formation soil denudation and soil production long term chemical weathering rates soil formation and erosion rates were assessed by using immobile elements fine earth stocks and meteoric 10be in addition the weathering index k ca ti the amount of fe and al oxyhydroxides and clay minerals characteristics were considered all methods indicated that the differences between permafrost affected and non permafrost affected soils were small furthermore the soils did not uniformly differ in their weathering behaviour a tendency towards less intense weathering in soils that were affected by permafrost was noted at most sites weathering rates the proportion of oxyhydroxides and the weathering stage of clay minerals were lower in permafrost soils in part erosion rates were higher at the permafrost sites and accounted for 79 97 of the denudation rates in general soil formation rates 8 8 86 7 t km2 y were in the expected range for alpine soils independent of permafrost conditions it seems that the local microenvironment particularly vegetation and subsequently soil organic matter has strongly influenced denudation rates as the climate has varied since the beginning of soil evolution the conditions for soil formation and weathering were not stable over time soil evolution in high alpine settings is complex owing to among others spatio temporal variations of permafrost conditions and thus climate this makes predictions of future behaviour very difficult this article is protected by copyright all rights reserved

the chemical weathering regime of karkevagge arctic alpine sweden abstract karkevagge is a valley located in swedish lapland at approximately 68 n and represents an arctic alpine landscape it is a presently periglacial glaciated trough incised into essentially horizontal metamorphic rocks some of which are presumably pyrite rich a set of coordinated studies was undertaken to investigate the nature of chemical weathering and pedogenesis in the valley and upon the abutting ridges august 1996 water quality measures reveal considerable spatial variation in solute totals with the highest total dissolved solute abundances being correlated with high sulfate abundances ridge crest soils exhibited poor horizonation but more extensive development of secondary clay minerals developed in situ than was found in valley flank and valley bottom soils valley soils exhibited multiple thin horizons many of which were buried and are taken to reflect great paraglacial and periglacial instability favorable microenvironments in the valley permit significant development of spodosols coarse debris along and across the valley bears both weathering rinds and rock coatings rock coatings in the valley include several types of iron films sulfate crusts carbonate skins and heavy metal skins karkevagge represents a mild arctic environment which does not preclude substantial chemical weathering in locations where abundant pyrite rich bedrock and water coincide this weathering follows pathways which are eminently expectable given that weathering of the pyrite rich rock permits generation of sulfuric acid which in turn weathers muscovite mica and calcite in local schists and marble respectively zones of intense chemical weathering also generate clearly visible deposits of gypsum and iron sulfate deposits such as jarosite not all arctic and or alpine environments are likely to be so active chemically but the results from karkevagge clearly show that dismissal of chemical weathering in cold regions on the basis of presumed first principles is erroneous consequently chemical weathering in such environments merits substantially more attention than it has hitherto received

three dimensional s wave velocity structure in southern california 1 the three dimensional s wave velocity structure was constructed from rayleigh wave phase velocities measured using teleseismic trinet data the s wave velocity maps show some features that are much more distinct than previous tomographic results in southern california there is a clear seismic velocity contrast across the san andreas fault the north american plate side is systematically slower than the pacific plate side under the eastern california shear zone there are distinct slow velocity anomalies in the crust suggesting a close connection to lower viscosity crust previously concluded from observation of the post seismic deformation after the landers earthquake major upper mantle features include a fast velocity root under the transverse ranges which is the dominant feature in the upper mantle and a slow velocity anomaly under the salton trough our results support that the velocity contrast across the san andreas fault extends below the moho

teleseismic surface wave study for s wave velocity structure under an array southern california summary teleseismic surface wave data from the dense seismographic network in southern california cisn california integrated seismic network are used to construct s wave velocity maps for the region surface wave phase velocity measurements are achieved by way of a waveform matching spectral domain technique that was developed for use within the cisn array a two station phase velocity measurement technique was developed which takes advantage of the fact that for surface wave arrivals from any azimuth there are multiple pairs of cisn stations which are almost exactly on the same great circle paths to ensure the validity of this assumption particle motions were analysed for measured pairs within the network showing that the deviation between expected backazimuth from ray theory and observed backazimuths are small enough to be analysed by a simple distance correction this method was applied to 114 large earthquakes for time periods between 1999 and 2002 and led to the retrieval of phase velocity maps for rayleigh waves between 20 and 55 mhz and for love waves between 25 and 45 mhz finite frequency effect for propagating surface waves was approximately taken into consideration using a geometrical technique an ellipse determined by wavelength and great circle distance between the source and receiver can describe an influence zone for the finite frequency effect phase velocity map reconstructions using a method which incorporates this effect show minimal changes in phase velocity maps for our region but do extend solvable velocity regions inversion for s wave velocity distribution with depth shows that deep structural contrast across the san andreas extends into the upper mantle a slow velocity anomaly is evident under the southern sierras and the salton sea the latter region indicating the northward extension of tectonic activity in the gulf of california fast velocity roots that reach 60 km are found under the western part of transverse ranges and the northern peninsular ranges reconstruction of past location of the western transverse range microplate implies that these two ranges may have been adjacent to one another historically both the western transverse range fast velocity root and the peninsular range fast velocity root may be a remnant of old oceanic plate

blockfields old or new evidence and implications from some plateaus in northern norway evidence is presented from investigations on plateau top blockfields in still glaciated regions of north norway pits dug into these blockfields typically show profile depths 0 5 m and sometimes in excess of 1 m analysis of fines shows enrichment in the silt and clay sized fraction suggestive of prolonged chemical weathering chemical alteration of parent material is supported by xrd analysis which identifies a number of clay minerals present in blockfield samples a chemical weathering origin suggests that these plateau top blockfields are features which have considerable longevity in the landscape and have been forming since perhaps tertiary times the original weathering profiles have been destroyed by frost heaving mechanisms protection of the blockfield by cold based ice occurred during periods of glacial coverage

landscape preservation under fennoscandian ice sheets determined from in situ produced 10be and 26al some areas within ice sheet boundaries retain pre existing landforms and thus either remained as ice free islands nunataks during glaciation or were preserved under ice differentiating between these alternatives has significant implications for paleoenvironment ice sheet surface elevation and ice volume reconstructions in the northern swedish mountains in situ cosmogenic 10be and 26al concentrations from glacial erratics on relict surfaces as well as glacially eroded bedrock adjacent to these surfaces provide consistent last deglaciation exposure ages 8 13 kyr confirming ice sheet overriding as opposed to ice free conditions however these ages contrast with exposure ages of 34 61 kyr on bedrock surfaces in these same relict areas demonstrating that relict areas were preserved with little erosion through multiple glacial cycles based on the difference in radioactive decay between 26al and 10be the measured nuclide concentration in one of these bedrock surfaces suggests that it remained largely unmodified for a minimum period of 845 418 461 kyr these results indicate that relict areas need to be accounted for as frozen bed patches in basal boundary conditions for ice sheet models and in landscape development models subglacial preservation also implies that source areas for glacial sediments in ocean cores are considerably smaller than the total area covered by ice sheets these relict areas also have significance as potential long term subglacial biologic refugia

weathering rates of buried machine polished rock disks karkevagge swedish lapland some 48 dolomite 37 granite and 19 limestone machine polished disks were buried at soil horizon boundaries in 16 soil pits to maximum depths of 0 5 0 6 m within karkevagge a presently periglacial glaciated trough in arctic sweden the objective of the ongoing study is to determine near surface potential weathering rates beneath birch forest dryas heath heath meadow solifluction meadow and willow vegetation cover types selected disks were excavated after 1 year and all disks were excavated after 4 or 5 years the limestone disks weathered fastest followed closely by the dolomite disks but the granite disks weathered at much slower rates mean annual percentage mass loss over 4 or 5 years was 0 473 0 145 two standard errors for dolomite disks 0 032 0 005 two standard errors for granite disks and 1 104 0 446 two standard errors for limestone disks for dolomite disks the dryas heath and heath environments weathered the most slowly a trend that was generally followed by the granite disks poor drainage i e increasing wetness and decreasing ph were found to promote dolomite weathering rates in a statistically significant manner surficial and subsurface weathering rates at individual sites were generally found to be correlated for dolomite but not granite copyright 2002 john wiley sons ltd

deciphering a non glacial glacial landscape mosaic in the northern swedish mountains relict surfaces contain information on past surface processes and long term landscape evolution a detailed investigation of relict non glacial surfaces in a formerly glaciated mountain landscape of northern sweden was completed based on interpretation of colour infrared aerial photographs analysis in a gis and fieldwork working backwards from landscape to process surfaces were classified according to large and small scale morphologies that result from the operation of non glacial processes the degree of weathering regolith characteristics and the style of glacial modification surfaces were also compared in the gis according to elevation slope angle and bedrock lithology the study revealed five types of relict non glacial surfaces but also two types of extensively weathered glacial surfaces that were transitional to relict non glacial surfaces illustrating spatially variable processes and rates of non glacial and glacial landscape evolution rather than being static preglacial remnants relict non glacial surfaces are dynamic features that have continued to evolve during the quaternary the classification provides hypotheses for landscape evolution that can be field tested through for example terrestrial cosmogenic nuclide studies and geochemical analyses of fine matrix materials the classification may be applicable to relict non glacial surfaces in other formerly glaciated landscapes

melt producing versus melt consuming reactions in pelitic xenoliths and migmatites abstract melt producing reactions have operated both in pelitic xenoliths and in pelitic migmatites but melt consuming reactions related to in situ melt crystallization are largely restricted to migmatites hence xenolith reaction textures may provide clues on the relative roles of both reaction types in migmatites a comparison of xenoliths and migmatites results in a catalogue of textural and chemical features some of which are argued to be diagnostic the results have implications for the identification of restite in igneous rocks and for the relative importance of prograde and retrograde processes in different domains of layered migmatites