from migmatite to magma crustal melting and generation of granite in the camboriu complex south brazil abstract partial melting of continental crust and granite genesis were investigated in the camboriu region south brazil structural geology and geochemistry were used in order to characterize the link between the high ba sr itapema granite ig and the syntectonic melting of orthogneisses and amphibolites of the camboriu complex cc the ig is a sheet like intrusive body of biotite monzogranite to granodiorite with large amount of migmatitic amphibolite and gneiss xenoliths and a well developed magmatic foliation concordant with the main gneissic banding discordant m thick granitic dykes which crosscut the migmatitic sequence and transport magma and xenoliths to feed the ig main body mark the transition from the migmatitic to the magmatic system within the complex whole rock geochemical data reveal important contamination and assimilation processes of xenoliths during ig magmatic flow which give rise to different facies and geochemical signatures the generation of the ig is an example of a continuous exposure from source to sink formed through a continuous and efficient deformation driven melting extraction transport system generated during coeval folding and anatexis of the cc metamorphic sequence

the coastal terrane of the kaoko belt namibia outboard arc terrane and tectonic significance abstract the coastal terrane or westernmost part of the kaoko belt outboard of the three palms mylonite zone has distinct feldspathic arenite sedimentary sequences no basement distinct nd sediment signatures excluding the archaean and suggesting mesoproterozoic neoproterozoic provenance sources and primitive arc like geochemical signatures for i type granitoids it contains evidence for an older metamorphic event at 650 645 ma not present in any other part of the kaoko belt this metamorphism m1 was of high t low p granulite to upper amphibolite facies and includes migmatisation associated with i type granitic magmatism of arc affinity arc growth at 650 640 ma took place outboard within the adamastor ocean while swakop group facies turbidite sedimentation continued inboard along the passive margin overprinting m1 and m2 fabrics and metamorphic assemblages constrain the docking to have occurred between 650 and 580 ma lack of ophiolite fragments and evidence of intermediate to high p metamorphism along the three palms mylonite zone suggest that it is not a suture and more likely to be part of an arc backarc wrench shear system that developed inboard of an e dipping subduction system where the adamastor ocean was subducted beneath the leading edge of the attenuated congo craton oblique collision between 650 and 580 ma due to docking of this outboard coastal terrane with arc affinities caused i crustal scale oblique overriding of the arc terrane over the passive margin of the congo craton ii crustal scale sinistral shear partitioned into two major ductile shear zones iii high t granulite facies metamorphism in an extruded shear zone bounded core and iv outwards or cratonwards verging basement cored fold nappes

linking the basement geology along the africa south america coasts in the south atlantic the work was financially supported by the czech science foundation 15 05988s we thank martin whitehouse and lev ilyinsky for their support while using the nordsim ion probe in stockholm the nordsim facility is jointly funded by denmark finland norway sweden and iceland this is nordsim publication 446 we appreciate the discussions with stano ulrich and pedro oyhantcabal during various stages of this project the paper benefited from the reviews of cees passchier and an anonymous reviewer cees passchier directed us to the work of abraham ortelius mentioned in the introduction and kindly provided the translation from latin

the climate memory of an arctic polythermal glacier knowledge of glacier equilibrium line altitude ela changes and trends in time is essentialfor future predictions of glacier volumes we present a novel method for determining trends in elachange at mccall glacier alaska usa over the last 50 years based on mapping of the cold temperatetransition surface cts marking the limit between cold and temperate ice of a polythermal glacier latent heat release from percolating meltwater and precipitation keeps the ice column temperate in theaccumulation area a change from accumulation to ablation zone reduces this heat release leadinglocally to glacier ice cooling by mapping the cts along the whole glacier length using radio echosounding and employing a thermodynamic model the timing of the cooling was determined fromwhich past elas were constructed these are in accord with mass balance measurements carried out onmccall glacier since the 1950s we show that with a warming climate mccall glacier tends to cool ina counter intuitive way

geology and petrogenesis of the edgecumbe volcanic field se alaska the interaction of basalt and sialic crust the edgecumbe volcanic field is a holocene volcanic province located on kruzof island se alaska exposed within the 260 km2 field are basalt andesitic basalt andesite dacite and rhyodacite the rhyodacites were erupted after the basalts and before the andesites the volcanics which are al rich 14 18 wt and lack an iron enrichment trend range from tholeiites 47 wt sio2 through rhyodacites 72 but a compositional gap of approximately 9 wt separates the dacites and rhyodacites initial 87sr 86sr ranges from 0 70297 in the basalts to 0 70440 in a pyroxene andesite 18o increases across the suite 5 8 to 7 9 plagioclase an32 86 is the dominant phenocryst in all but one lava olivine fo58 86 occurs in the basic lavas 53 wt sio2 but is replaced by orthopyroxene en43 73 and clinopyroxene en31wo41 en48wo40 in the more siliceous volcanics in the basalts and rhyodacites plagioclase is weakly zoned but extreme zoning 30 mole an is characteristic of phenocrysts in the intermediate lavas fractionation of the observed phenocryst assemblages could not have produced the more silicous volcanics instead they were generated by partial melting of intrusive basement 87sr 86sr 0 70487 18o 8 7 9 3 by basaltic magma and subsequent assimilation mass balance calculations show the rhyodacites are almost pure partial melt 5 basaltic component whereas the intermediate lavas contain between 30 and 60 partial melt

space time relation of post collisional granitic magmatism in santa catarina southern brazil u pb la mc icp ms zircon geochronology of coeval mafic felsic magmatism related to the major gercino shear zone abstract la mc icp ms u pb zircon dating was performed on syntectonic early post collisional granitic and associated mafic rocks that are intrusive in the brusque metamorphic complex and in the florianopolis batholith major tectonic domains separated by the neoproterozoic major gercino shear zone mgsz in south brazil the inferred ages of magmatic crystallization are consistent with field relationships and show that the syntectonic granites from both domains are similar with ages around 630 620 ma for high k calc alkaline metaluminous granites and ca 610 ma for slightly peraluminous granites although ca 650 ma inherited zircon components are identified in granites from both domains important contrasts on the crustal architecture in each domain are revealed by the patterns of zircon inheritance indicating different crustal sources for the granites in each domain the granites from the southern domain florianopolis batholith have essentially neoproterozoic 650 700 ma and 900 950 ma inheritance with a single 2 0 2 2 ga inherited age obtained in the peraluminous mariscal granite in the northern brusque metamorphic complex the metaluminous rio pequeno granite and associated mafic rocks have scarce inherited cores with ages around 1 65 ga whereas the slightly peraluminous serra dos macacos granite has abundant paleoproterozoic 1 8 2 2 ga and archean 2 9 3 4 ga inherited zircons our results are consistent with the hypothesis that the mgsz separates domains with distinct geologic evolution however the contemporaneity of 630 610 ma granitic magmatism with similar structural and geochemical patterns on both sides of this major shear zone indicates that these domains were already part of a single continental mass at 630 ma reinforcing the post collisional character of these granites

a connection between the neoproterozoic dom feliciano brazil uruguay and gariep namibia south africa orogenic belts evidence from a reconnaissance provenance study abstract a provenance study of neoproterozoic siliciclastic successions in the stratigraphically and tectonically lowermost and uppermost parts of the pan african gariep belt stinkfontein subgroup and oranjemund group respectively in southwestern africa as well as in the rocha group of the punta del este terrane dom feliciano belt in uruguay revealed that the oranjemund and rocha groups can be correlated and most likely formed in the same basin thus the rocha group is considered to represent the fill of the westernmost part of a re activated ediacaran gariep basin the lower parts of the oranjemund and rocha groups reflect erosion of mafic rocks whereas the upper parts are derived from a predominantly felsic source area first major and trace element geochemical data are consistent with oceanic islands of within plate geochemistry in the immediate vicinity as the most likely source of the mafic input into the lower part of the oranjemund group whereas a combination of continental margin and island arc is indicated as source for the bulk of the younger sediments in the upper oranjemund group age spectra obtained by shrimp u pb analyses of detrital zircon grains from the stinkfontein subgroup port nolloth group the oranjemund group and the rocha group are very similar except for a lack of the youngest age group around 600 ma in the stinkfontein subgroup in all three units zircon grains of 1000 1200 ma dominate with a further peak in the age distribution between 1700 and 2000 ma these ages compare well with the pre gariep basement geology in southwestern africa where the former age range corresponds to magmatic and high grade metamorphic activity in the mesoproterozoic namaqua natal belt and the latter to an extensive palaeoproterozoic andean type volcanic arc richtersveld terrane comparable ages are conspicuously absent in the basement of the rio de la plata craton in south america derivation of the rocha group sediments from a similar source as the contemporaneous oranjemund group sediments is therefore suggested the most likely source of the youngest detrital zircon grains in these two stratigraphic units is the 640 590 ma magmatic arc of the dom feliciano belt this interpretation explains the continental island arc component in the sediment provenance and takes into account the absence of comparable magmatism in the gariep belt two stages of basin evolution are distinguished for the gariep basin an early failed continental rift that subsequently became re activated as back arc basin related to the cryogenian dom feliciano arc consequently the gariep basin does not represent the main suture between the rio de la plata and the kalahari cratons this suture is now suspected to be west of the dom feliciano volcanic arc and might be connected with the sierra ballena major gercino lineament

a 700 ma sm nd garnet whole rock age from the granulite facies central kaoko zone namibia evidence for a cryptic high grade polymetamorphic history continental collision of the kalahari and the congo craton in africa and the rio de la plata craton in south america resulted in a structurally complex neoproterozoic belt system the kaoko dom feliciano ribeira belt it is uncertain whether these three cratons collided more or less simultaneously during one single orogenic event at 580 550 ma or whether the belt owe its structural and metamorphic features to several so far poorly constrained events the kaoko belt nw nambia representing the belt system between the southern congo craton and the rio de la plata craton is an ideal object to study these complexities within this belt high grade meta igneous and metasedimentary rocks of the sillimanite k feldspar zone contain large garnet porphyroblasts that grew at ca 730 10 c at 6 7 1 2 kbar during peak metamorphic granulite facies conditions a sm nd garnet whole rock errorchron n 7 mswd 6 0 obtained on a siliceous metasediment yielded an unexpected old age of 692 14 ma which is interpreted as an inherited metamorphic age of an older granulite facies event it is evident that the dated garnets survived the younger high grade granulite facies metamorphism that occurred between ca 570 and 520 ma and preserved their old sm nd isotope systematics implying that the closure temperature for sm nd in garnet is higher than ca 730 c in this case these results imply fast cooling rates at different times during the pan african orogeny that prevent isotopic homogenization at sample scale moreover it is suggestive that trace element ree diffusion in garnet is considerably slower than major element diffusion from a regional point of view it is possible that these specific siliceous metasedimentary rocks may be unrelated to the pan african metamorphic evolution of the kaoko belt between 570 and 520 ma and may represent lithological units that belong to so far unrecognized terranes in the kaoko belt 2007 elsevier b v all rights reserved

geochemical and strontium isotopic characteristics of parental aleutian arc magmas evidence from the basaltic lavas of atka eighteen flows from a basal stratigraphic sequence on the aleutian island of atka were analyzed for major elements trace elements and initial 87sr 86sr ratios petrographically these lavas contain abundant plagioclase 24 45 and lesser amounts of olivine 7 magnetite and clinopyroxene phenocrysts compositionally the lavas are high alumina 20wt basalts 48 51 wt sio2 with low tio2 1 and mgo 5 within the section compositional variations for all major elements are quite small while mgo content correlates with olivine phenocryst contents no such relationship exists between the other oxides and phenocryst content these lavas are characterized by 8 10 ppm rb high sr 610 669 ppm 308 348 ppm ba and very constant zr 23 29 ppm and sc 23 29 ppm abundances ni and cr display extremely large compositional ranges 12 118 ppm and 12 213 ppm respectively no correlation exists between trace element concentrations and phenocryst contents strontium isotopic ratios show a small but significant range 0 70314 0 70345 and are slightly elevated with respect to typical morb no systematic correlation between stratigraphic position and petrography or geochemistry is evident ree abundances measured on six samples are lree enriched la yb n 2 20 2 81 and display similar chondrite normalized patterns one sample has a slight positive eu anomaly but the other lavas do not compared to other aleutian basalts of similar silica content these lavas are less lree enriched and have lower overall abundances the geochemical characteristics of these basalts suggest they represent true liquid compositions despite their highly porphyritic nature published phase relations indicate fractionation of a more mgo rich magma could not have produced these lavas the high al2o3 and low mgo and compatible element abundances suggest a predominantly oceanic crustal source for parental high alumina basalts

evidence of 1 7 to 1 8 ga collisional arc in the kaoko belt nw namibia detailed structural and isotopic analyses in the hoanib and ugab river valleys indicate the existence of an exotic 1 7 to 1 8 ga terrane in the pan african kaoko belt this crustal block called as mudorib complex is imbricated between autochthonous and para autochthonous rocks of congo craton kaoko basin and western kaoko batholith units during the main tectono thermal phase of kaoko belt collision around 580 ma involving the rio de la plata congo and kahalari paleoplates this terrain is positioned between the 1 9 ga pruwes complex units of sw edge of the congo craton and the 0 58 to 0 55 ga amspoort suite granitoids of the western kaoko batholith it is coincident with a regional positive aeromagnetic anomaly trending from nnw in the ugab region to the namibia angola border internally mudorib complex consists in 1 73 to 1 81 ga tonalitic trondhjemitic dioritic granodioritic sequence of gneisses associated with cogenetic gabbroic and anothositic gneisses in the core zone of this pan african structure field relationship and u pb zircon and sm nd whole rock isotope data combined with geochemical information suggest the existence of two rock associations in the mudorib complex namely late paleoproterozoic tonalitic trondhjemitic dioritic gneisses with island arc affinity and tholeiitic metabasites of juvenile origin showing nd model age of 1 73 2 17 ga and end t of 2 05 4 3 this 1 8 to 1 7 ga complex is also intruded by granitic dykes formed at 1 49 1 50 ga with nd model age of 1 75 2 34 ga during stable tectonic conditions in addition to widespread pan african tectono metamorphic events a secondary metamorphic event of 1 3 ga is also recognized in the mudorib rocks which may be associated with accretion process of the complex to the paleoproterozoic to archean nucleus of the kaoko belt in the hoanib river valley

estimating the risk of glacier cavity collapse during artificial drainage the case of tete rousse glacier 1 during the summer of 2010 the presence of a pressurized water filled subglacial cavity of at least 50 000 m3 was detected within the tete rousse glacier french alps artificial drainage was started to avoid an uncontrolled rupture of the ice dam but was interrupted soon after to evaluate the capacity of the cavity roof to bear itself the risk was that the release of pressure within the cavity during the artificial drainage would precipitate the collapse of the cavity roof and potentially flush out the remaining water flooding the valley below an unprecedented modeling effort was deployed to answer the question of the cavity roof stability we set up a model of the glacier with its water cavity solved the three dimensional full stokes problem predicted the upper surface and cavity surface displacements for various drainage scenarios and quantified the risk of the cavity failure during artificial drainage we found that the maximum tensile stress in the cavity roof was below the rupture value indicating a low risk of collapse a post drainage survey of the glacier surface displacements has confirmed the accuracy of the model prediction this practical application demonstrates that ice flow models have reached sufficient maturity to become operational and assist policy makers when faced with glaciological hazards thus opening new perspectives in risk management of glacier hazards in high mountain regions

evolution of the major gercino shear zone in the dom feliciano belt south brazil and implications for the assembly of southwestern gondwana the dom feliciano belt developed during the brasiliano pan african orogenic cycle due to the tectonic interaction between the rio de la plata congo and kalahari cratons along with the amalgamation of smaller continental fragments together with its prolongations to the south the major gercino shear zone constitutes one of the main lineaments of the orogenic system establishing a more than 1000 km long ne trending tectonic boundary between a granitic batholith and a metavolcano sedimentary association based on combined field structural microstructural and textural data together with new and published geochronological data a refined model for the geological evolution of the major gercino shear zone is presented regional nw verging low dipping structures were generated between 650 and 615 ma preceding the formation of the shear zone this was followed by the main deformation phase corresponding to pure shear dominated dextral strike slip interpreted do be controlled by regional transpression during oblique convergence of the continental terranes this stage lasted until ca 585 ma and was coeval with the continuous emplacement of granitic magmatism along the structure strain partitioning and localization led to the development of mylonitic belts along the intrusion borders mostly under greenschist facies metamorphic conditions late stage ductile deformation along the structure was active during the cooling of the intrusions until ca 550 ma while the deformation front of the orogenic system migrated to counterpart orogenic belts in the african continent after tectonic stabilization the major gercino shear zone recorded episodic brittle reactivation possibly related to the phanerozoic evolution of the active margins and intracratonic basins in gondwana 2018 springer verlag gmbh germany part of springer nature

oblique collision and evolution of large scale transcurrent shear zones in the kaoko belt nw namibia abstract early structures in the central part of the kaoko orogenic belt of nw namibia suggest that the initial stage of collision was governed by underthrusting of the medium grade central kaoko zone below the high grade western kaoko zone resulting in the development of an inverted metamorphic gradient in the western zone early structures were overprinted by a second phase of deformation which is associated with localization of the transcurrent puros shear zone along the contact between the western and central zones during this second phase extensive partial melting and intrusion of 550 ma granitic bodies occurred in the high grade western zone in the central zone the second phase of deformation led to complete overprinting of the early foliation in the zone adjacent to the puros shear zone and to the development of kilometre scale folds in the more distal parts strain partitioning into transcurrent deformation along the puros shear zone and ne sw oriented shortening in the central zone is consistent with a sinistral transpressional regime during the second phase of deformation transcurrent deformation continued during cooling of the entire belt giving rise to the localized low temperature village mylonite zone that separates a segment of elevated mesoproterozoic basement from the rest of the western zone in which only pan african ages have so far been observed the data suggest that the boundary between the western and central kaoko zones represents a modified thrust zone controlling the tectonic evolution of the pan african kaoko belt

natural deformation and recrystallization of some intermediate plagioclase feldspars abstract intermediate an25 an48 plagioclase feldspars from the nordre stromfjord shear zone central west greenland have undergone extensive ductile deformation by intracrystalline slip and by twinning the plagioclases were deformed under low granulite facies conditions optical substructures include undulatory extinction deformation bands subgrains and deformational twins mainly on the albite law dynamic recrystallization occurred primarily by subgrain rotation with bulge nucleation migration of a high angle boundary as a secondary mechanism in some cases recrystallization is accompanied by a small decrease in the an content which is thought to indicate prograde metamorphic conditions the plagioclases exhibit a good crystallographic preferred orientation which is compatible with 010 001 being the principal slip system quartz has in the same rocks undergone more plastic deformation and more extensive recovery than plagioclase this is at least in part due to the fact that most dislocations in plagioclase are dissociated

timing of terrane accretion in the neoproterozoic eopaleozoic ribeira orogen se brazil abstract new id tims u pb geochronological data of the oriental terrane combined with detailed geological data of other terranes support the presented tectonic evolutionary model for the central segment of the neoproterozoic ribeira belt southeastern brazil that can be subdivided in four major tectonic units a the occidental terrane regarded as the reworked margin of the sao francisco craton to the northwest b the paraiba do sul klippe c the oriental terrane comprising arc complexes and d the cabo frio terrane to the southeast the oriental terrane and the cabo frio terrane were progressively accreted to the reworked continental margin of the sao francisco paleoplate the occidental terrane contains pre 1 8 ga basement slivers interlayered with neoproterozoic passive margin successions andrel ndia group the oriental terrane focus of the work was firstly accreted to the sao francisco margin at ca 580 ma it displays three structural domains thrusted to nw toward the reworked sao francisco margin from west to east a the cambuci domain that is interpreted as the fore arc association b the costeiro domain that contains a distal passive margin succession intruded by the ca 790 and 635 620 ma rio negro arc complexes and c the italva domain that comprises marbles psamitic gneisses and amphibolites of ca 840 and is regarded both as the proximal passive margin of the oriental terrane or a back arc basin syn to late collisional granitoids and three metamorphic episodes ca 605 580 and 550 ma indicate a complex history for the collision i they were also described for the kaoko damara and west congo only the youngest one pan african belts located at occidental africa and are supposed to record the main episode of convergence in western gondwana a second collisional stage at ca 530 ma accreted the cabo frio terrane to the oriental terrane and is possibly related with the closure of a back arc basin located between the oriental terrane and kalahari craton that remained open until the ordovician the effects of the collision ii were also detected at the oriental terrane finally late to post tectonic granites marked the tectonic collapse of the orogenic building between 513 480 ma

boron geochemistry of the central american volcanic arc constraints on the genesis of subduction related magmas boron contents were measured in representative quaternary lavas from the central american volcanic arc to evaluate along strike variations in subduction processes despite the significant range in b concentrations 2 37 ppm in the mafic lavas b la ratios vary in a systematic fashion along the arc higher values 1 are typical between guatemala and northern costa rica whereas low values most 0 5 typify central costa rica and western panama b la is highly correlated with 10be 9be r2 0 94 excluding one sample and appears to be a useful indicator of subduction contributions to the magma sources if enrichments of both b and 10be are proportional to the flux of subducted sediment along strike variations in b la suggest at least a twofold variation in this flux with maximum values below western nicaragua and minimum values below costa rica and western panama where the cocos ridge is being subducted these data may also reflect significant differences in thermal state of the descending slab which in turn differentially affects release patterns of fluids and fluid mobile trace elements and possibly melting processes beneath different parts of the arc the following scenario is suggested to explain the geochemical results beneath the northwestern part of the arc steep subduction of older relatively cold slab favors more efficient subduction of fluid components to depths beneath the volcanic front the released fluids carry fluid mobile elements to the overlying mantle which upon melting produces calcalkalic magmas shallow subduction of warmer slab beneath the southeastern part of the arc favors shallow release of fluids and limits fluid related metasomatism of sub arc mantle beneath the volcanic front under such conditions b la and ba la ratios in the sub arc mantle vary little from values seen in oceanic island basalts magmas in this part of the arc nevertheless display the highest la yb and lowest ba la and b la ratios which are consistent with prior light rare earth element enrichment in the source significantly lower degrees of melting or a combination thereof because some of the largest volcanoes occur in costa rica and magma flux there is nearly an order of magnitude higher than elsewhere in the arc source enrichment is considered to be the more plausible explanation it is proposed that quaternary magma production below costa rica involved lithospheric sources containing trapped or stored melt components but this enrichment process is unlikely to have involved typical arc magmas or subduction fluids because we see no b enrichment

mass balance calculations with end member compositional variability applications to petrologic problems although end member compositional variability is quite common most quantitative mass balance procedures cannot accommodate this variability in a systematic manner by rearranging the traditional mass balance relations a series of equations can be derived to account for such heterogeneity while this approach can be applied ton component systems the results are difficult to represent graphically accordingly the procedure is most useful for two and three component systems for two components the concentration of an element in a mixture is cpm chmx 1 1x c1 and the isotopic signature is epmc pm ehmc hmx 1 1x e1c 1 where pm hm and 1 refer to parental magma hybrid magma and component 1 respectively x is the proportion of parental magma c is concentration is isotopic ratio and c the concentration of the denominator isotope in the particular isotopic ratio of interest these equations describe straight lines termed isoproportional or ip lines of fixed mixing proportion in the cpm c1 concentration or epmc pm e1c 1 planes only those ip lines intersecting the rectangle defined by observed end member compositions represent viable mixing proportions for three component systems the mass balance equations are y chm c2 x cpm c2 c1 c2 and y c hmehm c 2e2 x c pmepm c 2e2 c 1e1 c 2e2 where y is now the proportion of component 1 and the proportion of component 2 z is simply 1 x y using major trace and rare earth element as well as isotopic data a region of the x y plane representing possible mixing combinations can be defined due to the compositional variability of most magmatic end members this new mass balance procedure should be applicable to a diverse range of petrologic problems this procedure has been applied to three different petrologic processes aleutian parental magma genesis assimilation contamination and crust mantle differentiation

cumulatic diorites related to post collisional brasiliano pan african mafic magmatism in the vila nova belt southern brazil abstract the capivaras diorite in the vila nova region nw of the sul rio grandense shield is composed of six ne to nne oriented rock bodies of late tectonic emplacement relative to the d3 deformation phase which forms subvertical high strain zones in basement gneiss sequences within these intrusive bodies a shape foliation is present generally parallel to contacts and displaying a local solid state deformational component the internal structure of the capivaras diorite main intrusion is marked by a zone of intense flow and mingling characterized by strong shape foliation and layers of variable texture and composition which result from cumulative processes heterogeneous flow and interaction of coeval compositionally contrasting magmas the central part of this intrusion is texturally homogeneous and slightly foliated even though cumulative processes have remained important during its formation along the contact with basement gneisses fine grained diorites are found which are considered to be compositionally close to the parental magma of the capivaras diorite this magma has a mildly alkaline affinity and shows moderate to high contents of zr ti and p highly fractionated ree patterns low nb contents as well as high contents of k sr ba and rb are suggestive of its provenance from mantle sources which have been previously affected by subduction processes such as those of mature magmatic arcs or post collisional settings magmatic evolution was controlled by cumulative processes and gave origin to pyroxene orthocumulates plagioclase pyroxene orthocumulates pyroxene adcumulates and more rarely plagioclase adcumulates the cumulative origin of these rocks is indicated by field textural and geochemical features which are distinct from those of crystallized liquids the compositional diversity of cumulates has led to the generation of compositionally different melts the early formed pyroxene cumulates have caused ca al na ba and sr enrichment in the magmatic liquid leading to plagioclase crystallization and accumulation coarse grained mafelsic cumulates were formed during the late stages of magmatic crystallization due to volatile enrichment of the intercumulus liquid considering geological relations as well as tectonic and compositional features of the capivaras diorite it is interpreted as part of neoproterozoic magmatism related to the post collisional stage of brasiliano pan african orogenic cycle in southern brazil

snow accumulation and ice flow at dome du gouter 4300 m mont blanc french alps glaciological experiments have been carried out at dome du gouter 4300 m a s l mont blanc in order to understand the flow of firn ice in this high altitude alpine glacierized area accumulation measurements from stakes show a very strong spatial variability and an unusual feature of mass balance fluctuations for the alps i e the snow accumulation does not show any seasonal patterns measured vertical velocities which should match with long term mean mass balance are consistent with observed accumulations therefore the measurement of vertical velocities seems a good way of quickly obtaining reliable mean accumulation values for several decades in such a region a simple flow model can be used to determine the main flowlines of the glacier and to propose snow ice age of core samples from the two boreholes drilled down t the bedrock in june 1994 these results coincide with radioactivity measurements made to identify the well known radioactive snow layers of 1963 and 1986 we can hope to obtain ice samples 55 60 years old about 20 or 30 m above the bedrock 110 m deep below the deformation of the ice layers is loo great to be dated accurately

twenty years of cold surface layer thinning at storglaciaren sub arctic sweden 1989 2009 this paper presents the changes in the thermal structure of the polythermal glacier storglaciaren northern sweden over the 20 year period 1989 2009 derived by comparing maps of the depth of the englacial transition between cold ice permanently frozen and temperate ice which contains water inclusions the maps are based on interpreted ice penetrating radar surveys from 1989 2001 and 2009 complex thinning of the cold layer first identified between 1989 and 2001 is still ongoing a volume calculation shows that storglaciaren has lost one third of its cold surface layer volume in 20 years with a mean thinning rate of 0 80 0 24 m a 1 we suggest that the thinning of the cold layer at storglaciaren is connected to the climatic warming experienced by sub arctic scandinavia since the 1980s and we argue that repeated ice penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate

very high elevation mont blanc glaciated areas not affected by the 20th century climate change 1 this paper analyses the impact of climate change over the last 100 years on high elevation glaciated areas of the mont blanc range comprising ice fields covering the top of the mont blanc 4808 m and dome du gouter 4300 m areas surface ablation is negligible for these high elevation areas and the surface mass balance is mainly controlled by snow accumulation at dome du gouter ice fluxes have been calculated through two transversal sections by two independent methods in order to assess long term surface accumulation a comparison between these results and recent accumulation observations together with the strong relationship between valley precipitation and snow accumulation suggests that surface accumulation rates did not change significantly over the entire 20th century moreover the small ice thickness changes less than 3 m on the average observed at mont blanc and dome du gouter between 1905 and 2005 clearly reveal that these high elevation glaciated areas have not been significantly affected by climate change over the last 100 years

tracking the sources and the evolution of the late neoproterozoic granitic intrusions in the brusque group dom feliciano belt south brazil la icp ms and shrimp geochronology coupled to hf isotopic analysis abstract the central domain of the neoproterozoic dom feliciano belt in the brazilian state of santa catarina is mainly composed of a metavolcano sedimentary sequence the brusque group and its crystalline basement such as the camboriu complex this association was intruded in its late deformational stage by voluminous granitic magmatism related to the metamorphic climax of the area the intrusions share a distinct crustal affinity and are divided into three suites from oldest to youngest as indicated by field criteria sao joao batista valsungana and nova trento we present seven new la icp ms and two shrimp u pb zircon ages coupled with in situ analysis of hf isotopes and use them to discuss the magmatic sources and evolution of the intrusions and propose an evolutionary model for this plutonic association intrusion mostly took place at 615 585 ma but the field stratigraphy is not necessarily reflected by u pb ages which establish considerable overlaps between intrusions from different suites inherited zircon crystals are common and reflect a long geological history that matches the geochronological record of the brusque group and the camboriu complex hf ratios are remarkably widespread but strengthen the characteristic crustal signature of the magmatism and partially overlap with whole rock isotopic data for the same rocks we propose that the intrusions were caused by a regional heating event within the central domain of the dom feliciano belt in santa catarina with limited direct mantellic contribution and more significant indirect thermal contribution through the voluminous magmatism of the recently juxtaposed florianopolis batholith this triggered large scale partial melting of the local continental crustal and formed the studied granites the long lasting magmatic event promoted the protracted generation and emplacement of numerous distinct intrusions synchronically leading to contrasts between the field and u pb stratigraphy the suites varied geochemical and isotopic characteristics probably reflect a combination of the heterogeneities of their source rocks with the impact of different magmatic processes during granitogenesis and emplacement while the valsungana and nova trento suites were probably generated within a deeper crustal level and underwent some degree of magmatic interaction the peraluminous sao joao batista suite has an upper crust signature that indicates the assimilation of metasedimentary rocks

assimilation of crustal material by basaltic magma strontium isotopic and trace element data from the edgecumbe volcanic field se alaska the edgecumbe volcanics which range from basalt through rhyodacite have sr contents between 125 and 370 p p m rb contents of 1 to 70 p p m ba ranging from 50 550 p p m and initial l7sr sr ratios between 0 70291 and 0 70404 no simple correlation exists between these components and silica the highest sr sr values occur in a group of intermediate lavas 55 60 wt per cent sio2 while the rhyodacites have initial ratios between 0 7035 and 0 7038 with increasing silica sr increases to a maximum in the andesites and then steadily decreases ba and rb increase over the same compositional range the highest l7sr 86sr lavas have major and trace element concentrations which depart from trends defined by most of the lavas the variation in strontium isotopic compositions suggests interaction between parental basaltic magma and crustal material attempts to model the assimilation process using fixed end member assimilation and assimilation fractional crystallization models have failed to produce the observed chemical trends because the parental basaltic liquid underwent little fractionation the variability in hybrid lavas is attributed to variation in contaminant composition initial melts were low in cao al2oj mgo and sr and enriched in sio2 k2o na2o rb and ba as melting progressed melts became enriched in the more refractory components because hybrid strontium isotopic composition is a function of sr concentration as well as isotopic compositions the sr content of the assimilant strongly influences resultant isotopic systematics the development of the assimilants suggests plagioclase was a residual phase during early melting this model of crustal assimilation represents one end member in the spectrum of processes responsible for the generation of continental volcanic suites

atmospheric temperature changes over the 20th century at very high elevations in the european alps from englacial temperatures 1 given the paucity of observations a great deal of uncertainty remains concerning temperature changes at very high altitudes over the last century englacial temperature measurements performed in boreholes provide a very good indicator of atmospheric temperatures for very high elevations although they are not directly related to air temperatures temperature profiles from seven deep boreholes drilled at three different sites between 4240 and 4300 m above sea level in the mont blanc area french alps have been analyzed using a heat flow model and a bayesian inverse modeling approach atmospheric temperature changes over the last century were estimated by simultaneous inversion of these temperature profiles a mean warming rate of 0 14 c decade between 1900 and 2004 was found this is similar to the observed regional low altitude trend in the northwestern alps suggesting that air temperature trends are not altitude dependent

plagioclase microfabrics in a ductile shear zone from the jotun nappe norway abstract gabbroic and anorthositic rocks from the jotun nappe are transected by small ductile shear zones in which a high grade paragenesis and a new foliation are formed most plagioclase grains show evidence of plastic deformation and have recrystallized by subgrain rotation and bulge processes to fine grained mylonite during these processes a plagioclase grain shape fabric was destroyed and with increasing strain a pre existing plagioclase crystal fabric was successively modified enhanced and finally obliterated this could be evidence of superplastic flow inverse pole figure analysis of the typical plagioclase crystal fabric in the shear zone indicates that 021 a could be an operative slip system and planes close to 132 could be possible slip planes

assessment of thermal change in cold avalanching glaciers in relation to climate warming high elevation glaciers covered by cold firn are undergoing substantial warming in response to ongoing climate change this warming is affecting the ice rock interface temperature the primary driver of avalanching glacier instability on steep slopes prediction of future potential instability therefore requires appropriate modeling of the thermal evolution of these glaciers application of a state of the art model to a glacier in the french alps taconnaz has provided the first evaluation of the temperature evolution of a cold hanging glacier through this century our observations and three dimensional modeling of the glacier response velocity thickness temperature density and water content to climate change indicate that taconnaz glacier will become temperate and potentially unstable over a large area by the end of the 21st century the risk induced by this glacier hazard is high for the populated region below and makes observation and modeling of such glaciers a priority

structure and strain variation at mid crustal levels in a transpressional orogen a review of kaoko belt structure and the character of west gondwana amalgamation and dispersal abstract the neoproterozoic cambrian kaoko belt is an orogen scale 800 180 km transpressional system important in the amalgamation of west gondwana mid crustal transpression at amphibolite to granulite facies conditions is dominated by two major 400 km exposed strike slip shear zones bounding a 20 40 km wide high grade orogen core to the east a deeply buried nappe dominated escape zone has inverted metamorphic sequence and verges outwards onto a platformal foreland to the west an arc like neoproterozoic coastal terrane was amalgamated and variably reworked during transpression the major purros and three palms mylonite zones have calculated shear displacements on the order of 120 180 km these shear zones are moderately to steeply dipping mylonite zones of 1 5 km width are arcuate and curvilinear in map view and show along strike variation in slip kinematics also highly curved in vertical section the shear zones define a flower to half flower geometry for the orogen core an oblique network of mylonitic shear zones akin to riedel shears links the major shear zones and defines regional scale shear lozenges internally deformed by tight upright folding and shear fabrics these shear zones create domains in the orogen core with varying dominance of pure shear in shear lozenges and simple shear in shear zones however absence of dip slip domains and the smoothly continuous traces of sub horizontal to shallow and acute oblique stretching lineations across all parts of the belt preclude marked kinematic partitioning and the internal part of the belt resembles large scale triclinic shear clast aspect ratios boudin train extension sheath fold aspect geometry degree of rotation of planes producing flanking folds composite s c foliations pressure fringes on pyrite and garnet porphyroclasts provide a semi quantitative measure of strain intensity average strain ratios are x z 40 1 for the major shear zones x z 12 1 for the orogen core x z 8 1 for the escape zone and x z 3 1 for the coastal terrane a more continuous pattern of strain intensity across the whole belt is mapped using a qualitative foliation intensity index foliation traces have a sigmoidal pattern in the orogen core swinging from sub parallel to the boundary shear zones to higher acute angles in the internal parts deformation character also varies from upright open folding in amphibolite facies domains in the north upright tight chevron folding in a low grade central domain to a high grade domain of tight to isoclinal inter folded basement and cover with inclination decreasing towards the south the kaoko belt is a well exposed sector of an extensive 3000 km long broad 400 km arcuate orogenic system adamastor orogen that amalgamated west gondwana bringing the south american sao francisco and rio de la plata cratons and african kalahari and congo cratons components together though a complex system most sectors involved oblique collision and accretion of magmatic arcs of 660 610 ma age followed by peak metamorphism and main phase transpressional orogenesis between 585 and 560 ma with shear zones remaining active until 530 ma this e w amalgamation immediately pre dates the final n s amalgamation of gondwana along the kuunga orogen between 535 and 510 ma the large scale adamastor orogen consisting of kaoko dom feliciano ribeira aracuai and west congo mobile belts also shows broadly similar and symmetric structural architecture throughout the high grade thermally softened core partitioned intense wrench dominated strains and networks of transcurrent shear zones that dip inwards with listric form either side of the internal zone containing amalgamated arcs and high grade core are nappe fold and thrust belts that rework attenuated passive margin basement and adamastor ocean sediments and structures verge outward at moderate to high angles onto both foreland margins the kaoko belt well illustrates the highly partitioned nature of transpressional systems in general and patterns in common throughout the greater adamastor orogen such as metamorphic zonation and heterogeneous distribution of deformation style flow regime and highly variable degrees of reworking strain and recrystallization this highly partitioned and steep structural grain localized lithospheric extension and rifting 415 ma later during breakup and dispersal of gondwana

geochronological constraints on the evolution of the southern dom feliciano belt uruguay abstract new u pb sensitive high resolution ion microprobe k ar and ar ar data from the southernmost dom feliciano belt allow the identification of four major events orthogneisses from the punta del este terrane indicate a magmatic episode at c 770 ma and high grade metamorphism at 641 17 ma granitoid emplacement at 627 23 ma was roughly coeval with peak metamorphism volcaniclastic rocks of the las ventanas formation dated at 573 11 ma can be correlated with the peripheral foreland basin 571 8 ma transpression and coeval high k calc alkaline magmatism is recorded in the maldonado granite dated at 564 7 ma the following events are postulated 1 magmatism at 850 750 ma related to rifting 2 metamorphism and granite emplacement at 650 600 ma 3 molasse sequences and foreland basins at c 573 ma 4 late magmatism at 580 560 ma associated with transpression the data indicate that 1 the punta del este terrane could be a portion of the coastal terrane of the kaoko belt 2 granitoid emplacement at 650 600 ma in the punta del este and nico perez terranes favours westward subduction and 3 widespread post collisional synkinematic magmatism occurred in the dom feliciano and kaoko belts between 580 and 550 ma supplementary material analytical methods and data are available at http www geolsoc org uk sup18369

a test of a quartz eclogite source for parental aleutian magmas a mass balance approach the observation that magmatic conduits evolve with time has provided a new framework within which to interpret aleutian compositional and isotopic data accordingly a two stage physical model of aleutian magma genesis has been developed and used to model quantitatively geochemical and isotopic mass balance relations parental magmas approximated by high alumina basalts are presumed to be generated by partial melting of eclogite and subducted sediment the incorporation of sediment produces elevated parental magma sr and pb isotopic ratios but lowered epsilon nd relative to morb if these magmas ascend along well established conduits their isotopic characteristics are little changed during ascent in immature conduits interaction with oceanic lithosphere produces significant isotopic variability according to this model the isotopic and geochemical characteristics of parental magmas are fixed by mixing eclogite and sediment melts as a test we have quantitatively examined the mass balance rel

recent extreme slope failures in glacial environments effects of thermal perturbation abstract this paper describes recent exceptional slope failures in high mountain glacial environments the 2002 kolka karmadon rock ice avalanche in the caucasus a series of ice rock avalanches on iliamna volcano alaska the 2005 mt steller rock ice avalanche in alaska and ice and rock avalanches at monte rosa italy in 2005 and 2007 deposit volumes range from 10 6 to 10 8 m 3 and include rock ice and snow here we focus on thermal aspects of these failures reflecting the involvement of glacier ice and permafrost at all sites suggesting that thermal perturbations likely contributed to the slope failures we use surface and troposphere air temperatures near surface rock temperatures satellite thermal data and recent 2d and 3d thermal modeling studies to document thermal conditions at the landslide sites we distinguish between thermal perturbations of volcanic geothermal and climatic origin and thermal perturbations related to glacier permafrost interaction the data and analysis support the view that recent current and future climatic change increases the likelihood of large slope failures in steep glacierized and permafrost terrain however some important aspects of these settings such as the geology and tectonic environment remain poorly understood making the identification of future sites of large slope instabilities difficult in view of the potentially large natural disasters that can be caused by such slope failures improved data and understanding are needed

comparing three different methods to model scenarios of future glacier change in the swiss alps ongoing atmospheric warming causes rapid shrinking of glaciers in the european alps with a high chance of their near complete disappearance by the end of the 21st century here we present a comparison of three independent approaches to model the possible evolution of the glaciers in the swiss alps over the 21st century the models have different levels of complexity work at a regional scale and are forced with three scenarios of temperature increase low moderate high the moderate climate scenario gives an increase in air temperature of 28c and 48c for the two scenario periods 2021 50 and 2070 99 respectively resulting in an area loss of 60 80 by 2100 in reality the shrinkage could be even faster as the observed mean annual thickness loss is already stronger than the modelled one the three approaches lead to rather similar results with respect to the overall long term evolution the choice of climate scenarios produces the largest spread 40 in the final area loss while the uncertainty in present day ice thickness estimation causes about half this spread

the influence of snow cover thickness on the thermal regime of tete rousse glacier mont blanc range 3200 m a s l consequences for outburst flood hazards and glacier response to climate change 1 tete rousse glacier french alps was responsible for an outburst flood in 1892 that devastated the village of st gervais le fayet close to chamonix causing 175 fatalities changes in the hydrothermal configuration of the glacier are suspected to be the cause of this catastrophic outburst flood in 2010 geophysical surveys of this glacier revealed a subglacial lake that was subsequently drained artificially the processes controlling the thermal regime of the glacier have been investigated on the basis of measurements and snow firn cover and heat flow models using meteorological data covering the last 200 years temperature measurements show a polythermal structure with subglacial water trapped by the cold lowest part of the glacier 2 c the modeling approach shows that the polythermal structure is due to temporal changes in the depth of the snow firn cover at the glacier surface paradoxically periods with negative mass balances associated with warmer air temperature tend to cool the glacier whereas years with colder temperatures associated with positive mass balances tend to increase the glacier temperature by increasing the firnpack depth and extent the thermal effect of the subglacial lake is evaluated and shows that the lake was formed around 1980 according to future climate scenarios modeling shows that the glacier may cool again in the future this study provides insights into the thermal processes responsible for water storage inside a small almost static glacier which can lead to catastrophic outburst floods such as the 1892 event or potentially dangerous situations as in 2010

a review of the relationships between granitoid types their origins and their geodynamic environments abstract granitoids are divided into several types according to their mineral assemblages their field and petrographical features and their chemical and isotopic characteristics this typology complements most of the recent classifications because it is not based solely on chemical and isotopic criteria but also on the field petrographical and mineralogical criteria it thus has the advantage of distinguishing the various granitoid types in the field in most cases the proposed classification shares many similarities with the twenty most used genetic classifications of granitoids both types of peraluminous granitoids are of crustal origin the tholeiitic alkaline and peralkaline granitoids are of mantle origin and both types of calc alkaline granitoids are of mixed origin and involve both crustal and mantle materials each granitoid type is generated and emplaced in a very specific tectonic setting each stage of the wilson cycle is characterised by typical associations of granitoids well typed and precisely dated granitoids can then complement structural approaches and indicate on the geodynamic environment with reference to some case studies the use of granitoids as tracers of the geodynamic evolution is also proposed and discussed

climate warming revealed by englacial temperatures at col du dome 4250 m mont blanc area 1 temperatures were measured in two deep boreholes drilled at the same location in the ice at col du dome 4250 m in 1994 and 2005 providing clear evidence of atmospheric warming the 1994 temperature profile was already far from steady state conditions results from a heat transfer model reveal that the englacial temperature increase cannot be explained solely by atmospheric temperature rise the latent heat produced by the refreezing of surface meltwater below the surface also contributes to the englacial temperature increase although surface melting is normally very low at this altitude this contribution became significant after 1980 for temperatures at the top of the borehole simulations for different climatic scenarios show that glaciated areas located between 3500 and 4250 m could become temperate in the future this warming could have a major impact on the stability of hanging glaciers frozen to their beds if the melting point is reached

isotope geochemistry and geochronology of the nico perez terrane rio de la plata craton uruguay u pb shrimp zircon geochronology bulk rock geochemistry and sr nd isotopic data are herein presented in order to better constrain the tectonic evolution of the nico perez terrane npt uruguay the studies are focused on two key geological units located in the southern part of the npt namely carape complex cc and lavalleja metamorphic complex lmc the carape complex previously interpreted as part of a remnant magmatic arc formed at 1 75 ga mainly by partial melting of archean crust t dm model ages between 2 8 and 3 0 ga with strong negative e nd t values the lavalleja metamorphic complex previously interpreted as a back arc basin has volcanic units formed at 0 59 ga during the brasiliano cycle but may also contain older paleoproterozoic units the geochemistry of the lmc meta igneous rocks indicates a complex scenario two distinct signatures have been recognized one similar to morbs and the other similar oibs sm nd t dm model ages of basic rocks present a bimodal paleoproterozoic and archean distribution which is also recognized in several other units of the npt in the light of new results we conclude that the npt represents a cratonic margin setting characterized by the stacking of lithotectonic assemblages with archean paleoproterozoic and neoproterozoic age at the margin of the rio de la plata craton

which empirical model is best suited to simulate glacier mass balances based on an extensive dataset of surface mass balances smb from four glaciers in the french alps for the period 1995 2012 and in the framework of enhanced temperature index models we investigate the sensitivity of seasonal glacier smb to temperature solar radiation precipitation and topographical variables our results reveal strong correlations between winter smb and precipitation although the precipitation gradient cannot explain the high accumulation rates based on the available point measurements we found no relevant relationship between winter smb and topographical variables temperature was found to be the main driver of ice snow ablation while solar radiation was found to strongly influence the spatial distribution of summer smb we compared the ability of several enhanced temperature index models to accurately simulate point smb and glacier wide mb our analyses revealed that the uncertainties in the simulated annual smb due to winter smb uncertainties are larger than differences between models and prevented us from concluding which model is the most suitable in contrast with results of previous studies including solar radiation in melt models did not improve the performances when modelling glacier wide mb we conclude that a classical degree day model is sufficient to simulate the long term glacier wide mb if the underlying processes are not required to be resolved

atmospheric warming at a high elevation tropical site revealed by englacial temperatures at illimani bolivia 6340 m above sea level 16 s 67 w in june 1999 a deep 138 7 m ice core was extracted from the summit glacier of illimani bolivia 6340 m above sea level 16 39 s 67 47 w and an englacial temperature profile was measured in the borehole using on site and regional meteorological data as well as ice core stratigraphy past surface temperatures were reconstructed with a heat flow model the englacial temperature measurements exhibit a profile that is far from a steady state reflecting an increasing atmospheric temperature over several years and nonstationary climatic conditions englacial temperature interpretation using air temperature data borehole temperature inversion and melting rate quantification based on ice core density shows two warming phases from 1900 to 1960 0 5 0 3 k starting approximately in 1920 1930 and from 1985 to 1999 0 6 0 2 k corresponding to a mean atmospheric temperature rise of 1 1 0 2 k over the 20th century according to various climate change scenarios the future evolution of englacial temperatures was simulated to estimate when and under what conditions this high elevation site on the illimani summit glacier could become temperate in the future results show that this glacier might remain cold for more than 90 years in the case of a 2 k rise over the 21st century but could become temperate in the first 20 m depth between 2050 and 2060 if warming reaches 5 k

west gondwana amalgamation based on detrital zircon ages from neoproterozoic ribeira and dom feliciano belts of south america and comparison with coeval sequences from sw africa

time constraints on magmatism along the major gercino shear zone southern brazil implications for west gondwana reconstruction the dom feliciano belt situated in southernmost brazil and uruguay contains a large mass of granite gneissic rocks also known as florianopolis pelotas batholith formed during the pre syn and post orogenic phases of the brasiliano pan african cycle in the ne extreme of this granitic mass pre syn and post tectonic granites associated with the major gercino shear zone mgsz are exposed the granitic manifestation along the mgsz can be divided into pre kinematic tonalitic gneisses peraluminous high k calc alkaline early kinematic shoshonitic and metaluminous post kinematic granites u pb zircon data suggest an age of 649 10 ma for the pre tectonic gneisses and a time span from 623 6 ma to 588 3 ma for the early to post tectonic magmatism negative ehf t values ranging from 4 6 to 14 6 and hf model ages ranging from 1 64 to 2 39 ga for magmatic zircons coupled with whole rock nd model ages ranging from 1 24 to 2 05 ga and end t values ranging from 3 84 to 7 50 point to a crustal derivation for the granitic magmatism the geochemical and isotope data support a continental magmatic arc generated from melting of dominant paleoproterozoic crust and a similar evolution for the granitic batholiths of the eastern dom feliciano belt and western kaoko belt

cold firn and ice of high altitude glaciers in the alps measurements and distribution modelling the thermal regime of high altitude accumulation areas in the swiss alps was systematically investigated on the jungfraufirn bernese alps on the breithornplateau valais alps and on grenzgletscher valais alps in 1991 1992 and 1994 temperatures were measured in a deep hole 120 m deep and in several shallow holes 14 30 m deep whereas the wide neve of the jungfraufirn at 3400 3600 m a s l and the 3800 m high breithorn plateau seems to be predominantly temperate cold firn and ice temperatures were measured throughout on grenzgletscher 3900 4450 m a s l mean firn temperatures on grenzgletscher vary strongly and range between 3 and 14 c a comparison between the measured temperature profiles and a one dimensional heat conduction calculation shows that the release of latent heat by penetrating and refreezing meltwater decisively influences the thermal pattern of the firn pack a multiple linear regression model based on measured firn temperatures from the european alps and the parameters altitude and aspect yields aspect dependent lower boundaries for the occurrence of cold firn ranging between 3400 northerly aspects and 4150 m a s l southerly aspects a total of 120 glaciers with cold firn areas are found when applying the model to glacier inventory data from the european alps

an integrated approach to the late stages of neoproterozoic post collisional magmatism from southern brazil structural geology geochemistry and geochronology of the corre mar granite abstract the neoproterozoic post collisional stage in south brazil is marked by intense granitic magmatism controlled by transcurrent shear zones related to the southern brazilian shear belt sbsb the sbsb has controlled the ascent and emplacement of magmas from crust and mantle in such scenario the corre mar granite cmg represents a small intrusion emplaced in a low strain zone located between two important segments of the sbsb the major gercino and itajai perimbo shear zones the cmg has a diagnostic subvertical s c foliation pair present in all intrusions regardless of their size it was emplaced within a conjugate system where sinistral nne shearing and nw se extension were both active generating space along the ne direction solid state deformation associated to the nne shearing is attested to by microstructures as feldspar recrystallization and asymmetric recrystallization tails the opening is attributed to the regional dextral transcurrent dynamics of the major gercino and itajai perimbo shear zones and magma emplacement was essentially conditioned by the nw extension component zircon u pb la mc icp ms crystallization age of cmg at 615 4 ma very close to other regional granites as the 611 ma serra dos macacos smg and 620 ma rio pequeno granite rpg points these three granitic bodies as synchronous the strong deformation features present in the cmg as opposed to the other neoproterozoic granites demonstrate that space rather than time must be called upon to explain the difference in structural patterns identified in the cmg geochemical and sr nd isotopic signatures as the slightly peraluminous character high k contents high lree hree ratios moderate rb nb zr and ree contents to regular sio 2 together with low 87 sr 86 sr i and the strongly negative nd t values indicate that the cmg is derived from old crustal sources possibly related to the paleoproterozoic camboriu complex quartz feldspathic orthogneisses the coincidence of cmg archean to paleoproterozoic inheritance ages with the age of a migmatization event identified in the camboriu complex and moreover the coincidence of the crystallization age intervals of the granites 615 611 ma with the last migmatization event at 640 610 ma reinforces the genetic link between them the paleoproterozoic tdm ages the geochemical and isotopic signatures the zircon u pb crystallization and inheritance age and the resemblance of the cmg and the smg suggest that they represent comagmatic and contemporaneous granitic pulses with a possible genetic link with the neoproterozoic migmatization event in the camboriu complex

origin of the outburst flood from glacier de tete rousse in 1892 mont blanc area france extensive field measurements and historical data have been used to re analyse the cause of the outburst flood from glacier de tete rousse that devastated the village of saint gervais le fayet french alps in 1892 causing 175 fatalities the origin of this disaster was the rupture of an intraglacial cavity in glacier de tete rousse that released 200 000 m 3 of water and ice all previous studies have concluded that the intraglacial cavity was formed from a crevasse that was filled and enlarged by meltwater the re analysis presented here suggests that the reservoir of the upper cavity did not originate as an enlarging crevasse the origin of the meltwater reservoir was more likely a supraglacial lake formed before 1878 during a period of negative mass balance following a period of positive mass balance after 1878 the lake was hidden until the outburst flood of 1892 this means that such hazards may be detected by checking regularly for the formation of a lake on the surface of the glacier before it is hidden

first geophysical and shallow ice core investigation of the kazbek plateau glacier caucasus mountains first ever ice core drilling at mt kazbek caucasus mountains took place in the summer of 2014 a shallow ice core 18 m was extracted from a plateau at 4500 m a s l in the vicinity of the mt kazbek summit 5033 m a s l a detailed radar survey showed that the maximum ice thickness at this location is 250 m borehole temperature of 7 c was measured at 10 m depth the ice core was analyzed for oxygen and deuterium isotopes and dust concentration from the observed seasonal cycle it was determined that the ice core covers the time interval of 2009 2014 with a mean annual snow accumulation rate of 1800 mm w eq multiple melt layers have been detected 18o values vary from 25 to 5 the dust content was determined using a particle sizing and counting analyzer the dust layers were investigated using scanning electron microscopy and x ray diffraction analysis dust can be separated into two categories by its origin local and distant samples reflecting predominantly local origin consisted mainly of magmatic rocks while clay minerals were a characteristic of dust carried over large distances from the deserts of the middle east and sahara the calculated average dust flux over three years at kazbek was of 1 3 mg cm2 a 1 neither 18o nor dust records appear to have been affected by summer melting overall the conditions on kazbek plateau and the available data suggest that the area offers good prospects of future deep drilling in order to obtain a unique environmental record

vapour absent melting from 10 to 20 kbar of crustal rocks that contain multiple hydrous phases implications for anatexis in the deep to very deep continental crust and active continental margins

the role of xenoliths and flow segregation in the genesis and evolution of the paleoproterozoic itapema granite a crustally derived magma of shoshonitic affinity from southern brazil abstract the paleoproterozoic itapema granite ig is a large granitic body that intrudes orthogneisses and amphibolites altogether representing part of the basement for neoproterozoic granitic magmatism in southern brazil it is composed of fine to medium grained hornblende biotite monzogranites to granodiorites that host abundant country rock xenoliths and irregularly distributed mafic aggregates interaction between magmatic flow and low flow velocity zones related to xenolith rich portions resulted in flow segregation and mineral fractionation as the main mechanisms that led to compositional and textural diversity expressed also in geochemical trends the geometry and distribution of flow foliation suggest that the itapema granite is a subhorizontal sheet like intrusion and that its emplacement was controlled by thrusting under upper amphibolite facies conditions many geochemical characteristics of the itapema granite are similar to those of shoshonitic granitoids however lower alkali contents lack of basic or intermediate associated rocks and intimate temporal association with high grade gneisses and migmatites suggest that it was crustally derived its origin is compatible with melting of amphibolitic orthogneisses derived from continental tholeiitic or shoshonitic sequences under high geothermal gradient conditions where temperatures reached at least 850 c

baseline characteristics of a debris covered snow covered gorge in a typical japanese mountainous terrain abstract debris covered snow covered gorges dsgs are common in the mountainous environment of the japanese alps in the western pacific region but are almost absent in subdued landscapes where snow melting rates are higher our study demonstrates that the effect of debris coverage on the shrinkage of snow covered gorges of the japanese alps results in differences in how the gorges respond to climate change which has been neglected in predictions of future water availability snow covered gorges and glacial meltwater make important contributions to drinking water irrigation water and hydropower supply in the japanese alps region global warming is expected to increase mountainous river discharge and snowmelt in the short term but long term predictions are uncertain therefore detailed and reliable baseline data about the mountainous environment of the japanese alps and its effects on the cryosphere are essential for predicting the future hydrosphere of japan however field investigations in this region are difficult and to date studies have not collected enough data to fully understand the processes involved supraglacial debris influences the terminus dynamics and can thereby modify the migration of a snow covered gorge under climate change recent studies have found several dsgs that are stagnant i e almost non flowing in the mountainous environments of southwest saskatchewan canada two surface samples were taken on 24 june 2014 and 27 june 2014 to determine the mean grain size of sediment at the site it was found that dsgs extended for several kilometres through valleys in this region our results indicated that the maximum temperature within 10 cm of the ground surface varied from 10 c to 15 c which may be the crucial baseline factor for the existence of dsgs although the increasing rates of meltwater discharge and surface lowering indicate that these snow covered gorges are currently shrinking their fronts remain remarkably stable a phenomenon that has also been observed in other regions the significance of debris cover and its impact on regional differences in the mountainous environment of the japanese alps has not been established in the mountainous valley belt of the region in this study we report the baseline characteristics of dsg during the beginning of the snowmelt period in the extreme mountainous environment region of the japanese alps

petrogenesis of syntectonic granites emplaced at the transition from thrusting to transcurrent tectonics in post collisional setting whole rock and sr nd pb isotope geochemistry in the neoproterozoic quatro ilhas and mariscal granites southern brazil abstract the neoproterozoic post collisional period in southern brazil 650 580 ma is characterized by substantial volumes of magma emplaced along the active shear zones that compose the southern brazilian shear belt the early phase syntectonic magmatism 630 610 ma is represented by the porphyritic high k metaluminous to peraluminous quatro ilhas granitoids and the younger heterogranular slightly peraluminous mariscal granite quatro ilhas granitoids include three main petrographic varieties muscovite biotite granodiorite mbg biotite monzogranite bmz and leucogranite lcg that although sharing some significant geochemical characteristics are not strictly comagmatic as shown by chemical and sr nd pb isotope data the most primitive muscovite biotite granodiorite was produced by contamination of more mafic melts possibly with some mantle component with peraluminous crustal melts the biotite monzogranite although more felsic has higher ca mgo tio 2 and ba and lower k 2 o feo t sr and rb contents possibly reflecting some mixing with coeval mafic magmas of tholeiitic affinity the leucogranite may be derived from pure crustal melts the mariscal granite is formed by two main granite types which occur intimately associated in the same pluton one with higher k 5 6 5 wt k 2 o high rb and lower cao na 2 o ba and zr as compared to the other 3 5 wt of k 2 o the two mariscal granite varieties have compositional correspondence with fine grained granites fgg that occur as tabular bodies which intruded the quatro ilhas granoitoids before they were fully crystallized and are inferred to correspond to the mariscal granite feeders an interpretation that is reinforced by similar u pb zircon crystallization ages the initial evolution of the post collisional magmatism marked by the emplacement of the quatro ilhas granitoids varieties activated sources that produced mantle and crustal magmas whose emplacement was controlled both by flat lying and transcurrent structures the transition from thrust to transcurrent related tectonics coincides with the increase in the proportion of crustal derived melts the transcurrent tectonics seems to have played an essential role in the generation of mantle derived magmas and may have facilitated their interaction with crustal melts which seem to be to a large extent the products of reworking of orthogneiss protoliths

volume and frequency of ice avalanches from taconnaz hanging glacier french alps very large volumes of ice break off regularly from taconnaz hanging glacier french alps during winter when the snow mantle is unstable these collapses can trigger very large avalanches that represent a serious threat to inhabited areas below photogrammetric measurements have been performed over 1 year to assess the volume and frequency of the largest collapses major collapses occur when the glacier reaches a critical geometry after a major ice collapse the glacier is in a minimal position and subsequently recharges over 6 months to reach the maximum position again this critical geometry is a necessary but not sufficient condition for further large collapses large collapses do not systematically occur in the maximum position as ice is often removed by disintegration into small ice blocks for two major collapses the volume of ice breaking off has been assessed at 275000m 3 photogrammetric measurements were used to determine an ice flux of 820000m 3 a 1 through the studied ice stream in agreement with an assessment based on ice flow modeling this ice flux estimation was used to determine the average ice volumes breaking off over surveyed periods

post collisional late neoproterozoic high ba sr granitic magmatism from the dom feliciano belt and its cratonic foreland uruguay petrography geochemistry geochronology and tectonic implications abstract post collisional granitic magmatism with high barium strontium hibasr content and shoshonitic affinity has been recently recognized both in the southern section of the dom feliciano belt of uruguay and its cratonic foreland this group of granitic rocks has a distinctive age mineralogy chemistry and field characteristics new zircon u pb la icp ms data for three of the plutons confirm their late neoproterozoic age 634 7 3 sierra de los caracoles 604 3 0 ma cortez blanco and 597 3 6 ma guayabo similar ages were published previously for the solis de mataojo granitic complex 584 13 ma as well as las flores 586 2 7 ma and sobresaliente plutons 585 2 5 ma mineral assemblages of the studied quartz monzonites granodiorites and monzogranites comprise quartz orthoclase and microcline plagioclase ab 10 30 hornblende green biotite apatite titanite and allanite they plot predominantly in the high k calc alkaline field with the exception of a few that plot in the shoshonitic field characteristically they are relatively high in na 2 o normally 4 5 in acid varieties sio 2 65 decreasing to between 3 and 4 for more basic types k 2 o normally exceeds 3 5 but can be as low as 700 ppm sr 500 ppm and light rees alongside low nb ta and heavy rees the eu anomalies are negligible to slightly positive intermediate initial 87 sr 86 sr values 0 7077 to 0 7090 and very low initial epsilon nd values 15 8 to 19 3 at 600 ma with high nd tdm 2 2 2 8 ga suggest a recycling of ancient paleoproterozoic to late archaean sources late neoproterozoic granitoids of uruguay have been emplaced within a post collisional tectonic setting controlled by major shear zones and strike slip fault zones current field and analytical data suggest that these granitoids could have been mostly generated through the partial melting of an intermediate to lower mafic continental crust and or enriched crustal sources in the presence of garnet amphibole as stable residual mineral assemblage with a possible minor mantle component

a method for modelling mass balance in partial melting and anatectic leucosome segregation a method is proposed for adjusting the mass balance to characterize quantitatively the behaviour of minerals in anatexis the method is based on an unconstrained simple mixing model that can be expressed as where b a0 and a1 n are compositional vectors of segregate source rock and source minerals respectively the most important concepts are 1 degree of partial fusion fmm 1 a0 2 mineral fractionation index and 3 plagioclase differentiation index for a given mineral the mfi values have the following meaning a mfi mfi mfi 1 preferential incorporation into the segregate and e mfi a0 external contribution to the anatectic system defined by a0a0 to test the method and illustrate its use it was applied to two real problems of partial melting in the pena negra anatectic complex central spain the first is a very simple case of segregation of a diktyonitic neosome from an orthogneiss through partial melting located in vertical shear zones this process is characterized by 1 fmm 0 51 2 active incorporation of k feldspar plagioclase and biotite into the segregate 3 disequilibrium melting of plagioclase 4 residual behaviour of quartz and ilmenite the second case concerns the formation of a cordierite bearing granite from granodioritoid diatexites through an anatectic process whose most salient characteristics are 1 fmm 0 45 2 incongruent melting of biotite 3 residual behaviour of plagioclase which melted with a pdi of 1 22 4 preferential incorporation of quartz into the segregate 5 total extraction of k feldspar from the residue

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

temperature and accumulation of high altitude firn in the alps data on temperature and accumulation of high altitude firn in the alps are compiled and discussed firn temperature varies with incoming radiation slope aspect at a given altitude the altitudinal gradient of temperature in highly permeable firn bodies appears to be about twice as high as the mean lapse rate of air temperature cold infiltration takes place above about 3500 m a s firn temperatures on the highest peaks are around 15 c accumulation net balance also decreases with increasing altitude from about 3m h20 at 3500 m a s to around 0 5 m h20 at wind exposed sites between 4300 and 4800 m a s l probably this is strongly due to wind erosion and topographical effects however temperature and accumulation not only appear to be interrelated but also seem to be positively correlated to the heat applied to the surface assuming the observed altitudinal gradients have remained constant in time it can be estimated that high altitude firn bodies have become considerably warmer since the last century co2 induced atmospheric warming could lead to a drastic change in the mass turnover and flow activity of high glaciers in wind exposed places where wind erosion of the snowpack becomes a controlling factor of accumulation introduction studies on mass and heat exchange at the surface of alpine firn have usually been carried out at altitudes below about 3500 m a s where firn is temperate and accumulation is high eg lang and others 1977 muller 1977 access to firn regions of higher altitudes is difficult however rather unusual construction work eg refuge lenkins on mont blanc and a number of tunnels dug into the firn of the monte rosa region by j e fisher in the 1950s furnished some information which indicated that at high altitudes firn is cold and accumulation does not further increase with altitude interest in temperature and accumulation of high altitude firn has grown recently in connection with i englacial temperatures 2 ice avalanches and 3 alpine core drilling temperature distribution in the tongue of grenzgletscher one of the largest ice bodies in the alps must be caused by advection of cold ice from high altitudes blatter and haeberli 1984 the frequency of ice avalanches ultimately depends on the accumulation of firn alean 1985 and the stability of steep mountain glaciers seems to depend on firn and ice temperatures rothlisberger 198 1 alean 1984 finally core drilling projects in cold high alpine firn and ice provide important information about the evolution of the composition of the atmosphere in heavily industrialized regions over past decades and centuries eg wagenbach and others in press but require knowledge about the distribution of accumulation in space and time the aims of the present study are to compile information available and point to possible effects of recent atmospheric warming firn temperature temperature measurements from deep pits tunnels and shallow bore holes in high altitude firn of the alps have been compiled by haeberli 1976 cf also hooke and others 1983 new information is available from chli titlis jungfraujoch sphinxgrat and monte rosa colle gnifetti all swiss alps at chli titlis 3070 m a s i 15 m temperature in the summit s 22 m thick firn and ice was 0 7 c 1979 80 cf haeberli and others 1979 temperatures in the sphinxgrat crest were measured in a 70 m borehole through firn ice and perennially frozen rocks in connection with recent construction work at the jungfraujoch the ice rock interface 10 m below the surface at 3525 m a s had a temperature close to 6 c 198 1 temperatures around 14 c at 15 m depth were registered in all core drilling boreholes made so far on colle gnifetti 4450 m a s the fim ice transition in this cold firn saddle occurs about 40 m below the surface schotterer and others 1981 when presently known firn temperatures are compiled figure i two groups seem to exist group i incorporates summits crests and probably also very steep slopes 45 which mainly consist of impermeable ice or high density firn with high concentrations of ice layers temperatures in such ice bodies decrease with increasing altitude at a rate about i c ioo m which is slightly higher than the assumed lapse rate of mean annual air temperature 0 65 c ioo m no temperate firn bodies are known in such situations in contrast more gentle slopes and basins group 2 where highly permeable firn accumulates are temperate up to about 3600 m a s above this upper boundary of the warm infiltration zone of the alps percolating meltwater cannot

dynamic recrystallization in deformed plagioclase during progressive shear deformation grain size reduction of plagioclase accompanied with progressive ductile deformation was investigated in a centimeter scale small shear zone collected from the hatagawa shear zone northeast japan the angle between the foliation and the shear zone boundary decreases from the margin to the center of the shear zone indicating an increase of shear strain toward the center the volume fraction of fine plagioclase grains xpl diameter 15 m increases with progressive shear strain the value of xpl increases steeply from 30 to 60 between the angles 23 and 20 and then it gradually increases from 60 to 90 toward 0 the fine plagioclase grains have a variable dislocation density and a crystallographic preferred orientation suggesting that recrystallization accommodated dislocation creep transmission electron microscopy tem observations revealed that strain induced grain boundary bulging occurred along the grain boundaries of plagioclase porphyroclasts thus the grain size of plagioclase was reduced by strain induced grain boundary bulging the kinetic theory of dynamic recrystallization approximately predicts the formation of the above mentioned xpl curve and suggests that the inflection point of xpl at 23 20 is probably due to site saturation in which all of the original grain boundaries are covered by the recrystallized grains the kinetic theory of dynamic recrystallization also gives a physical basis for the classification of mylonite on the basis of the volume fraction of fine grains

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

melt collecting structures and the formation of extraction dykes during syntectonic anatexis of the camboriu complex south brazil abstract the camboriu complex metamorphic sequence comprises orthogneisses and amphibolites with widespread melting features generated at upper amphibolite facies conditions regional to mesoscale structures are shown to control generation collection and extraction of melts as partial melting starts it is locally focused as layer parallel leucosomes in banded gneisses and isolated pockets of in situ leucosomes in massive amphibolites the further tightening of cm to m scale upright folds and conjugate shear planes oblique to axial planar position trigger the coalescence and migration of melts first along the main banding then along axial planes of folds and finally giving rise to a network where melt is collected the melt network eventually acquires enough mobility to form m wide extraction dykes roughly parallel to axial planes of folds capable of transferring the products of migmatization to upper crustal levels to feed granitic plutons the orientation and geometry of pure shear dominated structures in the camboriu complex are in accordance with deformation partitioning between this and adjancent shear zones which is expected for the transpressive character of the neoproterozoic southern brazilian shear belt

ice core age dating and paleothermometer calibration based on isotope and temperature profiles from deep boreholes at vostok station east antarctica an interpretation of the deuterium profile measured along the vostok east antarctica ice core down to 2755 m has been attempted on the basis of the borehole temperature analysis an inverse problem is solved to infer a local geophysical metronome the orbital signal in the surface temperature oscillations expressed as a sum of harmonics of milankovich periods by correlating the smoothed isotopic temperature record to the metronome a chronostratigraphy of the vostok ice core is derived with an accuracy of 3 0 4 5 kyr the developed timescale predicts an age of 241 kyr at a depth of 2760 m the ratio 13d 13t i between deuterium content and cloud temperature fluctuations at the top of the inversion layer is examined by fitting simulated and measured borehole temperature profiles the conventional estimate of the deuterium temperature slope corresponding to the present day spatial ratio 9 per mil oc is confirmed in general however the mismatch between modeled and measured borehole temperatures decreases noticeably if we allow surface temperature responsible for the thermal state of the ice sheet to undergo more intensive precession oscillations than those of the inversion temperature traced by isotope record with this assumption we obtain the long term temporal deuterium temperature slope to be 5 8 6 5 per mil oc which implies that the glacial interglacial temperature increase over central antarctica was about 15oc in the surface temperature and 10oc in the inversion temperature past variations of the accumulation rate and the corresponding changes in the ice sheet surface elevation are simultaneously simulated

oxidized magnetite series rapakivi type granites of carajas brazil implications for classification and petrogenesis of a type granites abstract the varying geochemical and petrogenetic nature of a type granites is a controversial issue the oxidized magnetite series a type granites defined by anderson and bender anderson j l bender e e 1989 nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america lithos 23 19 52 are the most problematic as they do not strictly follow the original definition of a type granites and approach calc alkaline and i type granites in some aspects the oxidized jamon suite a type granites of the carajas province of the amazonian craton are compared with the magnetite series granites of laurentia and other representative a type granites including finnish rapakivi and lachlan fold belt a type granites as well as with calc alkaline i type orogenic granites the geochemistry and petrogenesis of different groups of a types granites are discussed with an emphasis on oxidized a type granites in order to define their geochemical signatures and to clarify the processes involved in their petrogenesis oxidized a type granites are clearly distinguished from calc alkaline cordilleran granites not only regarding trace element composition as previously demonstrated but also in their major element geochemistry oxidized a type granites have high whole rock feo t feo t mgo tio 2 mgo and k 2 o na 2 o and low al 2 o 3 and cao compared to calc alkaline granites the contrast of al 2 o 3 contents in these two granite groups is remarkable the cao feo t mgo tio 2 vs cao al 2 o 3 and cao feo t mgo tio 2 vs al 2 o 3 diagrams are proposed to distinguish a type and calc alkaline granites whole rock feo t feo t mgo and the feo t feo t mgo vs al 2 o 3 and feo t feo t mgo vs al 2 o 3 k 2 o na 2 o diagrams are suggested for discrimination of oxidized and reduced a type granites experimental data indicate that besides pressure the nature of a type granites is dependent of o 2 conditions and the water content of magma sources oxidized a type magmas are considered to be derived from melts with appreciable water contents 4 wt originating from lower crustal quartz feldspathic igneous sources under oxidizing conditions and which had clinopyroxene as an important residual phase reduced a type granites may be derived from quartz feldspathic igneous sources with a metasedimentary component or alternatively from differentiated tholeiitic sources the imprint of the different magma sources is largely responsible for the geochemical and petrological contrasts between distinct a type granite groups assuming conditions near the nno buffer as a minimum for oxidized granites magnetite bearing granites formed near fmq buffer conditions are not stricto sensu oxidized granites and a correspondence between oxidized and reduced a type granites and respectively magnetite series and ilmenite series granites is not always observed

improved discrimination of subglacial and periglacial erosion using 10be concentration measurements in subglacial and supraglacial sediment load of the bossons glacier mont blanc massif france deciphering the complex interplays between climate uplift and erosion is not straightforward and estimating present day erosion rates can provide useful insights glaciers are thought to be powerful erosional agents but most published glacial erosion rates combine periglacial subglacial and proglacial erosion processes within a glaciated catchment sediments found in subglacial streams originate either from glacial erosion of substratum or from the rock walls above the glacier that contribute to the supraglacial load terrestrial cosmogenic nuclides tcn are produced by interactions between cosmic ray particles and element targets at the surface of the earth but their concentration becomes negligible under 15 m of ice measuring tcn concentrations in quartz sand sampled in subglacial streams and in supraglacial channels is statistically compliant with stochastic processes e g rockfalls and may be used to discriminate subglacial and periglacial erosion results for two subglacial streams of the bossons glacier mont blanc massif france show that the proportion of sediments originating from glacially eroded bedrock is not constant it varies from 50 to 90 n 6 the difference between the two streams is probably linked to the presence or absence of supraglacial channels and sinkholes which are common features of alpine glaciers therefore most of the published mean catchment glacial erosion rates should not be directly interpreted as subglacial erosion rates in the case of catchments with efficient periglacial erosion and particularly rockfalls the proportion of sediments in the subglacial stream originating from the supraglacial load could be considerable and the subglacial erosion rate overestimated here we estimate warm based subglacial and periglacial erosion rates to be of the same order of magnitude 0 39 0 33 and 0 29 0 17 mm a 1 respectively

avalanching glacier instabilities review on processes and early warning perspectives avalanching glacier instabilities are gravity driven rupture phenomena that might cause major disasters especially when they are at the origin of a chain of processes reliably forecasting such events combined with a timely evacuation of endangered inhabited areas often constitute the most efficient action recently considerable efforts in monitoring analyzing and modeling such phenomena have led to significant advances in destabilization process understanding improving early warning perspectives the purpose of this paper is to review the recent progress in this domain three different types of instabilities can be identified depending on the thermal properties of the ice bed interface if cold 1 the maturation of the rupture is associated with a typical time evolution of surface velocities and passive seismic activity a prediction of the final break off is possible using these precursory signs for the two other types water plays a key role in the development of the instability if the ice bed interface is partly temperate 2 the presence of meltwater may reduce the basal resistance which promotes the instability no clear and easily detectable precursory signs are known in this case and the only way to infer any potential instability is to monitor the temporal evolution of the thermal regime the last type of instability 3 concerns steep temperate glacier tongues switching for several days weeks during the melting season into a so called active phase followed in rare cases by a major break off event although the prediction of such events is still far from being achievable critical conditions promoting the final instability can be identified

tectonic setting and u pb zircon dating of the plutonic socorro complex in the transpressive rio paraiba do sul shear belt se brazil the precambrian rio paraiba do sul shear belt comprises a 200 km wide anastomosing network of ne sw trending ductile shear zones extending over 1000 km of the southeastern coast of brazil granulitic gneissic migmatitic and granitoid terrains as well as low to medium grade metavolcano sedimentary sequences are included within it these rocks were affected by strong contractional tangential tectonics due to west northwestward oblique convergence of continental blocks subsequent transpressional tectonics accomodated large dextral orogen parallel movements and shortening the plutonic socorro complex is one of many deformed granites with a foliation subparallel to that of the shear belt and exposes crosscutting relationships between its tectonic magmatic and metamorphic structures these relationships point to a continuous magmatic evolution related to regional thrusts and strike slip ductile shear zones the tectonic and magmatic structural features of the serra do lopo granite provide a model of emplacement by sheeting along shear zones during coeval strike slip and cross shortening of country rocks geochronological data indicate that the main igneous activity of socorro complex spanned at least 55 million years from the late stage of the northwestward ductile thrusting 650 ma through right lateral strike slip 595 ma deformation the country rocks yield discordant age data which reflect a strong imprint of the transamazonian tectono metamorphic event 1 9 to 2 0 ma we propose a model for the origin of calc alkaline granites of the ribeira belt by partial melting of the lower crust with small contributions of the lithospheric mantle during transpressional thickening of plate margins which were bounded by deep shear zones the transpressional regime also seems to have focused granite migration from deeper into higher crustal levels along these shear zones

post collisional transition from calc alkaline to alkaline magmatism during transcurrent deformation in the southernmost dom feliciano belt braziliano pan african uruguay abstract in the southernmost dom feliciano belt of uruguay highly fractionated calc alkaline granites mildly alkaline granites shoshonitic volcanics and peralkaline intrusions and volcanics are spatially and temporal associated with the evolution of shear zones four representative magmatic unites of this diverse association were petrographic and geochemically investigated the solis de mataojo complex a medium to high k2o calc alkaline granite with signature typical of mature continental arcs and post collisional settings the maldonado granite highly fractionated calc alkaline to alkaline with characteristics that are transitional between both types of series the pan de azucar pluton with characteristics typical of post collisional alkaline granites and the las flores shoshonitic basalts geochemistry and geotectonic setting point out that slab breakoff was most likely the mechanism associated with the generation of high k calc alkaline magmas solis de mataojo and maldonado shortly after collision extension associated to the formation of molassic basins and emplacement of dolerites and basalt flows with shoshonitic affinity las flores 15and finally a shift to magmas with alkaline signatures pan de azucar simultaneous with a second transpressional phase were probably linked with lithospheric thinning through delamination this evolution took place between 615 and 575 ma according to available data contrary to previous proposals which considered this magmatism to represent the root of a continental magmatic arc a post collisional environment transitional from orogenic to anorogenic during transcurrent deformation is proposed

modelling heat flow in a cold high altitude glacier interpretation of measurements from colle gnifetti swiss alps modelling the heat flow in small cold high altitude glaciers is important for the interpretation of paleoclimatic data from ice cores coupled glacier flow and heat flow models are presented that incorporate the densification heat advection and possible phase transitions at the permafrost boundaries within the bedrock marked bends observed in the temperature profiles from two recent boreholes on colle gnifetti swiss alps are interpreted with the help of a transient heat flow model driven with a temperature history the conclusion is that substantial warming of the mean firn temperature at shallow depths has taken place over the last few decades this has not been observed before in cold firn regions of the alps modelled heat fluxes in the monte rosa massif are strongly influenced by the mountain topography this leads to a spatial variability of the temperature gradient near the glacier base which has been observed in boreholes to the bedrock in order to match the measured temperature profiles in the glacier the vertical heat flux at great depth must be set to an extremely low value it is shown with the help of the transient heat flow model that this is a paleoclimatic effect possibly enhanced by a degrading permafrost base