episodic and short lived granitic pulses in a post collisional setting evidence from precise u pb zircon dating through a crustal cross section in corsica abstract in western corsica a large granitoid batholith was emplaced during carboniferous and permian times these rocks display an evolution through time from high mg k calc alkaline to calc alkaline then alkaline affinities moreover the magmatic processes can be observed at different crustal levels new and precise isotope dilution and thermo ionisation mass spectrometry id tims u pb dating suggests that granite magmatism in corsica did not simply reflect the continuous thermal evolution of a thickened crust a precise timing for the post collisional magmatism is documented with four distinct short lived episodes respectively at 345 338 305 and 280 ma separated by periods of inactivity these four magma pulses display variable nd isotopic signatures related to mantle crust interactions granite magma generation and emplacement is strongly connected to the thermal and tectonic activity of the lithosphere an increasing contribution of a depleted mantle to the magmatic processes is documented for the last igneous event this is interpreted to reflect the emplacement of depleted mantle materials in the lower crust which enhanced heat flow and triggered partial melting of previously underplated mafic rocks this increasing contribution of mantle materials marks the onset of a new geodynamic cycle characterised by an extensional tectonic regime preluding to the opening of the alpine orogenic tract

geochemical evolution of peraluminous plutons in southern nova scotia canada a pegmatite poor suite three southern nova scotia plutons crystallized rapidly at 375 ma from magma containing both mantle and crustal components isotopic and chemical data suggest that the crustal contribution included both lower crustal material and cambro ordovician turbidites of the host meguma group despite local evidence of mixing and mingling of magmas the bulk of the plutons evolved by assimilation and fractional crystallisation evolved portions of the plutons have compositions appropriate for development of rare metal pegmatite fields but pegmatites are relatively rare and little differentiated like parental plutons pegmatites fall into biotite plagioclase and muscovite potassium feldspar assemblages the latter locally contain mn rich garnet biotite giving calculated p t conditions of pegmatite crystallisation of 620 c 0 44 gpa under water saturated conditions host rocks at the time of emplacement experienced p t conditions varying from 500 to 620 c at 0 44 gpa beryl bearing pegmatites occur only where host rocks were below sillimanite grade and pegmatites of any kind are scarce in sillimanite grade host rocks rarity of pegmatites can be ascribed to a combination of insufficient amounts of f li and b in the magma with rapid cooling which prevented extensive fractionation and undercooling our data suggest rather that peraluminous suites produced by rapid heating due to incursions of lithospheric mantle into supracrustal rocks and typified by biotite rich cordierite bearing plutons are not favorable locales for major rare metal enriched pegmatite fields such fields appear to require relatively prolonged anatexis resulting from crustal thickening or an areally extensive mafic underplate

multiple crust reworking in the french armorican variscan belt implication for the genesis of uranium fertile leucogranites muscovite peraluminous granites mpgs form by partial melting of the continental crust and can be related to metalliferous deposits such as tin tungsten and uranium u metal enrichment in mpgs commonly results from fractional crystallization but the metal contents of the source play a major role for their fertility between ca 320 and 300 ma late carboniferous the french armorican variscan belt was intruded by numerous u fertile mpgs that contain inherited zircon grains with a wide range of ages from archean to carboniferous u pb and hf isotopic data of zircon grains from brioverian to carboniferous sediments cambrian to early carboniferous granitoids and late carboniferous mpgs indicate that the crust of the armorican massif is made up by detritus mainly derived from the west african craton 3500 1600 ma tdm 3 8 2 3 ga grenvillian belt 1200 900 ma tdm 2 7 1 2 ga and avalonian cadomian belt 800 550 ma tdm 2 5 0 8 ga and that the crust was affected by magmatic events at 510 470 ma tdm 1 6 0 6 ga 410 330 ma tdm 1 6 1 ga and 320 300 ma furthermore they reveal that the late carboniferous mpgs were mainly formed by partial melting of brioverian sediments with cambro ordovician and devonian carboniferous granitoids which are all genetically linked with each other and characterized by th u 4 the new data suggest that the u fertile mpgs result from multiple reworking of u rich brioverian sediments deposited ca 550 ma ago on the northern margin of gondwana and partially molten during several paleozoic events causing a successive increase in u content in the middle upper crust

accelerating shrinkage of patagonian glaciers from the little ice age ad 1870 to 2011 davies b j glasser n f 2012 accelerating shrinkage of patagonian glaciers from the little ice age similar to ad 1870 to 2011 journal of glaciology 58 212 1063 1084

an early paleoproterozoic high k intrusive complex in southwestern tarim block nw china age geochemistry and tectonic implications abstract systematic geochronologic geochemical and nd isotopic analyses were carried out for an early paleoproterozoic high k intrusive complex exposed in southwestern tarim nw china the results provide a better understanding of the paleoproterozoic tectonic evolution of the tarim block zircon u pb age dating indicates two paleoproterozoic magmatic episodes occurring at ca 2 41 ga and ca 2 34 ga respectively which were followed by a ca 1 9 ga metamorphic event the 2 41 ga granodiorite adamellite suite shares characteristics of late to post orogenic metaluminous a type granites in its high alkalinity na2o k2o 7 6 9 3 total ree 410 788 ppm zr 370 660 ppm and y 21 7 58 4 ppm contents end t values for the suite range from 3 22 to 4 71 and accordingly the nd modal ages t2dm vary between 3 05 ga and 3 17 ga based on geochemical data the 2 34 ga suite can be subdivided into two sub suites namely a type and s type however both types have comparable nd isotope compositions end t 0 41 to 2 08 and similar narrow t2dm ranges 2 76 2 91 ga geochemical and nd isotopic data for the high k intrusive complex in conjunction with the regional geological setting suggest that both the 2 41 ga suite and the 2 34 ga a type sub suite might have been produced by partial melting of the archean mafic crust in a continental rift environment the s type sub suite is thought to have formed by partial melting of felsic pelites and or metagreywackes recycled from archean crust ttg gabbro enclaves with positive end t value 2 15 have been found to be intermingling within the 2 34 ga suite ca 2 34 2 36 ga gabbroic dykes and adamellites have previously been documented in eastern tarim these observations indicate that the high k intrusions may reflect the emergence of depleted mantle upwelling beneath the tarim block at that time we suggest a three stages model for the precambrian crustal evolution in the tarim block 1 the formation of proto crust ttg by ca 2 5 ga 2 episodes of felsic magmatism possibly occurring in continental rift environments at ca 2 41 ga and ca 2 34 2 36 ga and 3 ca 1 9 ga metamorphism that may represent the solidification of the precambrian basement of the tarim block

from arc accretion to continental collision in the eastern jiangnan orogen evidence from two phases of s type granites abstract the ne jiangxi ophiolitic melange separates the huaiyu and jiuling terranes in the eastern jiangnan orogen of the south china block two phases of s type granites which are geochemically and mineralogically similar to the himalayan leucogranites are newly recognized in mantle peridotites of the ne jiangxi ophiolite the first phase a tourmaline bearing granite porphyry has a sims zircon u pb age of 904 4 4 8 ma and is strongly enriched in k2o 4 00 4 26 wt and strongly peraluminous a cnk 2 94 3 24 it further shows high rb sr ratios and highly fractionated ree patterns indicating an origin due to fluid absent melting of metapelites at relatively high temperatures the granite porphyry exhibits highly evolved zircon hf 6 0 to 1 0 and whole rock nd 4 2 to 5 1 isotopes which is in contrast to juvenile derived magmatic rocks in the huaiyu terrane we thus propose that the granite porphyry was formed by melting of the metapelites sourced from the yangtze block subsequent to the accretion of the huaiyu arc to the jiuling terrane the continental margin of the yangtze block the second phase a muscovite bearing quartz porphyry is strongly peraluminous a cnk 1 29 1 34 with low cao na2o ratios 0 11 0 14 and low feot mgo tio2 contents 2 39 2 75 wt similar to melts derived from fluid fluxed melting of metapelites zircon grains from the quartz porphyry yielded u pb ages of ca 803 801 ma with mainly positive ehf t values 1 9 to 8 7 which are younger than the depositional ages of the basement sequences and nearly identical to the accumulation of the overlying unmetamorphosed cover in the jiangnan orogen therefore it is suggested that the quartz porphyry was formed in a post collisional extensional setting subsequent to the final assembly of the yangtze and cathaysia blocks in conjunction with published data we conclude that multiple subduction accretion events may have been involved in the formation of the south china block during neoproterozoic times

melting of continental crust during subduction initiation a case study from the chaidanuo peraluminous granite in the north qilian suture zone the chaidanuo granite batholith is a similar to 500 km 2 homogeneous high level intrusion in the north qilian oceanic suture zone three types of enclaves have been recognized including 1 supracrustal xenoliths 2 biotite gneiss that represents restite of the upper crustal melting and 3 coeval mantle derived mafic magmatic enclave mme the batholith consists dominantly of peraluminous biotite monzogranite with sio2 69 73 wt and a cnk 1 05 1 28 and shows geochemical affinity with the upper continental crust e g enrichment of large ion lithophile elements liles k rb u th pb depletion of high field strength elements hfses nb ta ti p eu and sr and enriched sr sr 87 sr 86 i 0 731 to 0 744 nd epsilon nd t 6 0 to 7 1 isotopes zircon u pb dating indicates that this batholith formed at 516 505 ma coeval with the mmes 510 ma which represent the early stage of seafloor subduction in the north qilian suture zone the hf isotopic composition of the mme epsilon hf t 6 0 to 2 1 is more depleted than that of the host granite epsilon hf t 14 8 to 4 7 suggesting mixing of mantle and crust derived melts the inherited zircon cores in the host granite yield an age peak at similar to 750 ma with a few detritals of 591 1683 ma zircons from a biotite gneiss enclave yield a protolith age of 744 ma and a metamorphic melting event at 503 ma sr nd isotopic modeling reveals that the batholith was generated by melting of neoproterozoic granitic rocks with the addition of 10 18 mantle derived magma therefore peraluminous granite can be produced by melting of crustal materials heated by mantle derived magmas during the early stage of subduction initiation at the site of a prior passive continental margin c 2014 elsevier ltd all rights reserved

ice loss from the southern patagonian ice field south america between 2000 and 2012 1 a time series composed of 156 aster derived digital elevation models dems and a radar penetration bias corrected version of the shuttle radar topography mission srtm dem is used to derive ice surface height and volume changes at the southern patagonian ice field spi in southern south america the observations made between february 2000 and march 2012 indicate that the ice field is rapidly losing volume at many of the largest outlet glaciers and in most cases thinning extends to the highest elevations of the ice field mass loss is occurring at a rate of 20 0 1 2 gt a 1 which when summed with mass loss at the adjacent northern patagonian ice field results in a combined rate of 24 4 1 4 gt a 1 equivalent to 0 067 0 004 mm a 1of sea level rise our decade long mass loss rates are substantially higher than those derived during the last three decades of the 20th century but are in good agreement with recent grace observations our volume loss estimate is sensitive to constraints applied to the amount of thickening in the accumulation zone new field measurements and a continued dem time series will be required to refine our estimates

dating the onset of variscan crustal exhumation in the core of the bohemian massif new u pb single zircon ages from the high k calc alkaline granodiorites of the blatna suite central bohemian plutonic complex abstract the variscan central bohemian plutonic complex crops out between the upper crustal tepla barrandian and the high grade moldanubian units bohemian massif much of the complex is made up of calc alkaline plutonic rocks 1 the geochemically more primitive na rich 354 4 ma sazava suite which was emplaced syntectonically during regional shortening 2 the younger more evolved potassic blatna suite which records both the shortening along its nw contact and the onset of normal shearing related to exhumation of the moldanubian unit to the se new ion microprobe u pb zircon ages for the high k calc alkaline blatna suite pinpoint this major switch in the tectonic regime both blatna and kozarovice granodiorites 346 2 ma and 347 2 ma 2 were generated by melting of heterogeneous crust and were emplaced contemporaneously to form the blatna composite pluton from age spectra preserved in inherited zircons and whole rock sr nd isotope signatures the likely crustal sources for the magmas were immature greywackes rich in neoproterozoic 615 10 ma kozarovice or late cambrian early ordovician 492 4 ma blatna volcanogenic detritus an additional important petrogenetic process was variable mixing with enriched mantle derived monzonitic magmas which may also have supplied the extra heat for crustal anatexis supplementary material analytical techniques selected whole rock major and trace element geochemical analyses and u th pb data are available at http www geolsoc org uk sup18391

geochronology geochemistry and petrogenesis of late permian to early triassic mafic rocks from darongshan south china implications for ultrahigh temperature metamorphism and s type granite generation abstract the role of the mantle in generating ultrahigh temperature metamorphism and peraluminous s type granites and the extent of crust mantle interaction are topics fundamental to our understanding of the earth s evolution in this study we present geochronological geochemical and sr nd hf isotopic data for dolerites and mafic volcanic rocks from the darongshan granite complex belt in western cathaysia south china la icp ms u pb zircon analyses yielded magma crystallization ages of ca 250 248 ma for the dolerites which are coeval with eruption of the mafic volcanic rocks ultrahigh temperature metamorphism and emplacement of s type granites in the darongshan granite complex belt the mafic volcanic rocks are high k calc alkaline or shoshonitic enriched in th u and light rare earth elements and depleted in nb ta and ti the dolerites are characterized by high fe2o3tot 11 61 20 39 wt and tio2 1 62 3 17 wt and low mgo 1 73 4 38 wt cr 2 8 10 8 ppm and ni 2 5 11 4 ppm isotopically the mafic volcanic rocks have negative whole rock end t values 6 7 to 9 0 and high isr values 0 71232 to 0 71767 which are slightly depleted compared with the dolerite samples end t 10 3 to 10 4 and isr 0 71796 to 0 71923 zircons in the dolerites have ehf t values of 7 6 to 10 9 the mafic volcanic rocks are interpreted to have resulted from the partial melting of an enriched lithospheric mantle source with minor crustal contamination during ascent whereas the dolerites formed by late stage crystallization of enriched lithospheric mantle derived magmas after fractionation of olivine and pyroxene the formation of these mantle derived mafic rocks may be attributed to transtension along a ne trending strike slip fault zone that was related to oblique subduction of the paleo pacific plate beneath south china such underplated mafic magmas would provide sufficient heat for the generation of ultrahigh temperature metamorphism and s type granites and act as a mafic end member for s type granite genesis

the gurupi belt northern brazil lithostratigraphy geochronology and geodynamic evolution abstract the gurupi belt is located in northern brazil on the southern margin of the sao luis craton which is dominated by juvenile calc alkaline rocks formed in intra oceanic island arcs between 2240 and 2150 ma the gurupi belt consists of i small lenses of an archean metatonalite of 2594 ma ii calc alkaline ttg tonalites and gneisses of 2147 2168 ma and juvenile nd isotope signature formed in intra oceanic arc setting iii an i type monzogranite that intruded by ca 2159 ma formed by the reworking of the oceanic arcs iv a metavolcano sedimentary succession with calc alkaline volcanic rocks of 2148 2160 ma and juvenile nd isotope signature formed in arc systems v several peraluminous muscovite bearing collision type granites of 2070 2100 ma with nd isotopes indicating variable reworking partial melting and or erosion of paleoproterozoic and archean crust vi a sub greenschist to greenschist facies supracrustal sequence of unknown age tentatively considered to be older than 2159 ma vii an amphibolite facies metasedimentary sequence in which the youngest detrital zircon has age of 1100 ma and nd isotopes and sedimentological evidence indicating archean paleoproterozoic mesoproterozoic and neoproterozoic sources viii a deformed gneissic nepheline syenite of 732 ma formed by mixing of mantle and crustal sources ix a peraluminous muscovite bearing post tectonic granite of 549 ma combined geological and geochronological information indicate that the paleoproterozoic rocks are part of a trans amazonian eburnean orogen initiated by an accretionary phase 2240 2150 ma better represented in the adjacent sao luis craton and terminated by a collisional event 2100 2080 ma that amalgamated juvenile and reworked paleoproterozoic terrains and an archean terrain existing to the south this landmass amalgamated in the paleoproterozoic broke up before 732 ma forming a rift as suggested by the emplacement of the nepheline syenite pluton the rift received detritus coming from archean paleoproterozoic mesoproterozoic and neoproterozoic sources we infer that the rift evolved to an oceanic basin and that the closure of this basin occurred at the end of the neoproterozoic 580 550 ma as part of the brasiliano pan african cycle of orogenies

the timing and evolution of the post glacial transgression across the sea of marmara shelf south of istanbul high resolution reflection seismic profiles with core analyses of sedimentary sequence near the sea of marmara som entrance to the strait of istanbul soi bosphorus provide detailed record of sealevel changes since the late glacial maximum lgm the sequence is deposited over the lgm erosional surface at a maximum depth of 105 m it includes seven seismic units that can be confidently correlated with 14c dated sedimentary units in the cores unit 6 represents levee deposits of the paleo soi channel that was deposited by a black sea outflow during 11 2 10 6 kyr bp the reflection surfaces at base of unit 5 and 4 correspond to wave cut terraces at 71and 63 m respectively and are estimated to be 10 6 and 9 8 kyr bp the seismic unit 2 overlaying a mud drape unit 3 comprises deltaic sediments that was deposited during 6 400 3200 yr 14c bp isopach map and

petrogenesis of juvenile type birimian paleoproterozoic granitoids in central cote d ivoire west africa geochemistry and geochronology abstract the birimian paleoproterozoic granitoids of central cote d ivoire are associated either with greenstone belts or with basin sedimentary rocks field data indicate two stages of granitoid emplacement which according to singlezircon and monazite 207 pb 206 pb age determinations occurred within a short period of time the first generation of granitoids 2123 2108 ma intruded and metamorphosed the greenstone belts whereas the second generation 2108 2097 ma intruded and metamorphosed the sedimentary pile and subordinate andesitic volcanic rocks of the bandama basin unconformably overlying the greenstone belts geochemical and isotopic data show that the various granitoids belong to four magmatic groups 1 sodic calc alkaline nacg 2 potassic calc alkaline kcg 3 peraluminous alg and 4 alkaline alkg all the granitoids show juvenile features with mantle like low initial sr isotopic compositions 0 700 0 702 and positive epsilon nd values 1 5 2 7 these data indicate that a the nacg may have formed by partial melting of a garnet amphibolite crust b the kcg and alkg derived from partial melting of crustal mafic to intermediate metaigneous rocks and c the alg epsilon nd 1 5 represent infracrustal melting of young sialic igneous materials during a regional crustal shortening in a transcurrent tectonic context sm nd model ages 2 25 2 4 ga preclude the existence of an archean crust reworked in the birimian magmas an underplating model is discussed

the frequency and magnitude of post glacial explosive eruptions at volcan mocho choshuenco southern chile abstract volcan mocho choshuenco 39 55 s 72 2 w is one of the most hazardous volcanoes in chile s southern volcanic zone svz to better evaluate these hazards we have reconstructed a high resolution eruption history the most detailed to date for a volcano in chile from detailed field observations and geochemical analyses mocho choshuenco has experienced ca 75 post glacial 3 plinian eruptions neltume pirehueico and huilo and a large pyroclastic density current and associated sub plinian event enco poor preservation and lack of exposure made it difficult to distinguish between medial to distal deposits solely on field observations instead deposits have been correlated using a combination of glass chemistry and fe ti oxide compositions new radiocarbon dates were obtained and integrated with existing dates in a bayesian age model oxcal to constrain the tempo of the volcanism based on preserved deposits we derive a post glacial eruptive frequency of one explosive eruption every 220 years with the youngest confirmed eruption from mocho choshuenco in 1864 the total post glacial volume of tephra erupted is estimated at 20 km 3 ca 50 with a dacitic or rhyolitic glass composition with 4 km 3 erupted from the monogenetic cones on the flanks making mocho choshuenco one of the most productive ca 1 km 3 kyr and active volcanoes in the svz during post glacial times many tephra deposits from mocho choshuenco could be preserved in one or more lakes in the region and have the potential to form regional tephra markers in particular the neltume deposits which are dispersed to the nne are found interbedded with tephra deposits from the villarrica quetrupillan lanin chain and should be preserved around sollipulli and llaima 140 km nne of mocho choshuenco this study highlights how a multi technique approach enables a complicated tephrostratigraphy to be unravelled so more robust estimates of the past eruptive frequency and size can be determined

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

hybridization of a shallow i type granitoid pluton and its host migmatite by magma chamber wall collapse the tokuwa pluton central japan the miocene tokuwa pluton of i type granitoid affinity was emplaced discordantly into a cretaceous to paleogene accretionary complex and induced a contact aureole in which various thermally metamorphosed rocks were developed including hornfels metatexite diatexite and cordierite bearing tonalite crd tonalite of s type granite affinity the thermally metamorphosed rocks show low pressure reaction textures culminating in partial melting peak p t conditions of 3 kbar at 7808c are estimated on the basis of the twq thermobarometer for the garnet bearing rocks the rocks in the contact aureole exhibit a gradual transition from hornfels through metatexite and diatexite to crd tonalite the sr isotopic composition at the time of tokuwa pluton emplacement at 12 ma decreases systematically from metatexite 0 7100 0 7112 through diatexite 0 7078 0 7094 to crd tonalite 0 7067 0 7068 this trend is interpreted in terms of mixing between the tokuwa magma and the aureole migmatites the field relationships geochemical data and isotopic data collectively suggest that the emplacement of the tokuwa pluton triggered partial melting of the surrounding metasedimentary rocks subsequent hybridization of the tokuwa magma with the metatexite in variable proportions produced the crd tonalite and diatexite the hybridization was caused by invasion of the tokuwa magma into the migmatite zone accompanied by gravitational collapse of the previously crystallized wall of the magma chamber the data presented demonstrate that even a relatively low temperature shallow i type granitoid pluton can induce contact anatexis and hybrid s type granitoid formation at the intrusive contact

early paleoproterozoic magmatism in the yangtze block evidence from zircon u pb ages sr nd hf isotopes and geochemistry of ca 2 3 ga and 2 1 ga granitic rocks in the phan si pan complex north vietnam abstract our understanding of the early evolution of the yangtze block is limited by the sparsely dispersed nature of pre neoproterozoic exposures new integrated petrographic zircon u pb age and hf nd isotope analyses and whole rock geochemical data for early paleoproterozoic granites in the phan si pan complex provides new insights into the evolution of the yangtze block as well as its role in the pre nuna supercontinent la icp ms zircon u pb dating of magmatic zircons from quartz monzonite and gneissic granite yielded 207pb 206pb ages of 2306 12 ma and 2096 15 ma respectively zircons from the quartz monzonite have ehf t values ranging from 4 1 to 2 1 corresponding to tdm2 model ages of 3002 2890 ma whereas zircons in the gneissic granite have ehf t values between 0 95 and 1 72 and corresponding tdm2 model ages of 2660 2516 ma which are consistent with their whole rock nd isotope values geochemically the quartz monzonites are i type granites combined with their relatively high sr y ratios and low y concentrations as well as fractionated ree patterns with relatively high lree but low hree concentrations they were probably generated by partial melting of the thickened middle lower crust under elevated temperature geochemical and isotopic signatures suggest that the ca 2 1 ga gneissic granites are high k calc alkaline ferroan a type granites formed by partial melting of juvenile crustal source at high temperature and low pressure with little involvement of ancient crustal material the phan si pan complex has a distinct early paleoproterozoic crustal evolution history compared with the other crustal provinces of the yangtze block suggesting independent histories that were not unified until the late paleoproterozoic during the assembly of nuna moreover the magmatism and tectonic evolution of the north vietnam region is broadly similar to that of the arrowsmith orogen of the rae craton in laurentia suggesting a potential spatial linkage the geologic record of the yangtze block does not support an early paleoproterozoic shutdown of plate tectonics

geochemistry and petrogenesis of mashhad granitoids an insight into the geodynamic history of the paleo tethys in northeast of iran mashhad granitoids in northeast iran are part of the so called silk road arc that extended for 8300 km along the entire southern margin of eurasia from north china to europe and formed as the result of a north dipping subduction of the paleo tethys the exact timing of the final coalescence of the iran and turan plates in the silk road arc is poorly constrained and thus the study of the mashhad granitoids provides valuable information on the geodynamic history of the paleo tethys three distinct granitoid suites are developed in space and time ca 217 200 ma during evolution of the paleo tethys in the mashhad area they are 1 the quartz diorite tonalite granodiorite 2 the granodiorite and 3 the monzogranite quartz diorite tonalite granodiorite stock from dehnow vakilabad 217 4 215 4 ma intruded the pre late triassic metamorphosed rocks large granodiorite and monzogranite intrusions comprising the mashhad batholith were emplaced at 212 5 2 ma and 199 8 3 7 ma respectively the high initial 87 sr 86 sr ratios 0 708042 0 708368 low initial 143 nd 144 nd ratios 0 512044 0 51078 and low e nd t values 5 5 to 6 1 of quartz diorite tonalite granodiorite stock along with its metaluminous to mildly peraluminous character al 2o 3 cao na 2o k 2o mol 0 94 1 15 is consistent with geochemical features of i type granitoid magma this magma was derived from a mafic mantle source that was enriched by subducted slab materials the granodiorite suite has low contents of y 18 ppm and heavy ree hree yb 594 ppm and high ratio of sr y 35 that resemble geochemical characteristics of adakite intrusions the metaluminous to mildly peraluminous nature of granodiorite from mashhad batholiths as well as its initial 87 sr 86 sr ratios 0 705469 0 706356 initial 143 nd 144 nd ratios 0 512204 0 512225 and e nd t values 2 7 to 3 2 are typical of adakitic magmas generated by partial melting of a subducted slab these magmas were then hybridized in the mantle wedge with peridotite melt the quartz diorite tonalite granodiorite stock and granodiorite batholith could be considered as arc related granitoid intrusions which were emplaced during the northward subduction of paleo tethys ocean crust beneath the turan micro continent the monzogranite is strongly peraluminous al 2o 3 cao na 2o k 2o mol 1 07 1 17 alkali rich with normative corundum ranging between 1 19 and 2 37 has high initial 87 sr 86 sr ratios 0 707457 0 709710 and low initial 143 nd 144 nd ratios 0 512042 0 512111 and e nd t values 5 3 to 6 6 that substantiate with geochemical attributes of s type granites formed by dehydration melting of heterogeneous metasedimentary assemblages in thickened lower continental crust the monzogranite was emplaced as a consequence of high temperature metamorphism during the final integration of turan and iran plates the ages found in the mashhad granites show that the subduction of paleo tethys under the turan plate that led to the generation of arc related mashhad granites in late triassic finally ceased due to the collision of iran and turan micro plates in early jurassic

the petrogenesis of leucogranitic dykes intruding the northern semail ophiolite united arab emirates field relationships geochemistry and sr nd isotope systematics the khawr fakkan block of the semail ophiolite united arab emirates exhibits a suite of 10 100 m scale metaluminous to peraluminous granitic intrusions ranging from cordierite andalusite biotite monzogranites to garnet tourmaline leucogranites which intrude mantle sequence harzburgites and lower crustal sequence cumulate gabbros structural constraints suggest that the subduction of continental sedimentary material beneath the hot proto ophiolite in an intra oceanic arc environment led to granulite facies metamorphism at the subduction front and the generation of granitic melts which were emplaced up to the level of the ophiolite moho compositions indicate the analysed granitoids were largely minimum melts that crystallised at variable a h2o and pressures of 3 to 5 kbar the lile sr rb and ba covariation modelling suggests that the granitoids formed largely by the dehydration melting of muscovite rich metasediments initial 87sr 86sr ratios of analysed dykes vary between 0 710 and 0 706 at initial nd values of between 6 3 and 0 5 cogenetic units of a composite sill from ra s dadnah yield a sm nd isochron age of 98 8 9 5 ma mswd 1 18 geochemical and isotopic characteristics of the analysed granitic intrusions indicate that the subducted continental material was derived from oceanic trench fill haybi complex sediments preserved as greenschist asimah area to granulite facies bani hamid area ophiolitic metamorphic sole terranes the sr nd isotope systematics suggest that hybrid granitic melts were derived from pre magmatic mixing of two contrasting subduction zone sources

paleoproterozoic arc magmatism imposed on an older backarc basin implications for the tectonic evolution of the trans hudson orogen canada compositional data from 72 granitoids and associated mafic rocks in the paleoproterozoic kisseynew domain trans hudson orogen canada were used to evaluate the tectonic setting of magma generation between 1840 and 1820 ma these data thus provide insights into the development of the trans hudson orogen just prior to amphibolite grade metamorphism and the final stages of continental collision the granitoid rocks are hornblende or orthopyroxene bearing medium to high k calc alkalic and weakly peraluminous the trends on harker variation diagrams are consistent with crystal fractionation processes although the range in values is related to the temporal and spatial distribution of samples the extent of lree light rare earth element enrichment increases with increasing sio 2 as does variability in hree heavy rare earth element fractionation and magnitude of eu anomalies most samples have gd yb n 10 suite ia although five have gd yb n 17 24 suggesting the presence of garnet residua suite ib the range in rock types calc alkalic character and negative nb and ti anomalies are all characteristic of arc environments magma generation within the trans hudson orogen including the kisseynew domain between 1 84 and 1 82 ga was related to interaction between the sask craton and the flin flon glennie complex a decrease in subduction angle likely resulted from northward directed subduction of more buoyant crust with associated changes in thermal conditions leading to melting over a wide area most magmas formed in a slab dehydration dominated regime although localized slab melts may have been generated ultimately subduction ceased and the slab foundered into the mantle potentially resulting in the generation of alkalic and potassic magmas within the rae and hearne cratons

origin of middle triassic high k calc alkaline granitoids and their potassic microgranular enclaves from the western kunlun orogen northwest china a record of the closure of paleo tethys abstract the western kunlun orogen the northwest tibet plateau occupies a key tectonic position at the junction between the pan asia and the tethyan tectonic domains it is related to subduction of proto and paleo tethys and terrane collision from early paleozoic to early mesozoic this paper presents the first detailed shrimp zircon u pb chronology mineral chemistry major and trace element and sr nd hf isotope geochemistry of three middle triassic plutons yuqikapa muztaga and taer and their microgranular enclaves in the western kunlun orogen shrimp zircon u pb dating shows that the yuqikapa pluton was emplaced in the anisian 243 ma and the muztaga and taer plutons that contain microgranular enclaves were emplaced in the ladinian 234 227 ma the yuqikapa pluton is composed of peraluminous high k calc alkaline two mica granites monzogranite syenogranite alkali feldspar granite with initial 87sr 86sr ratios of 0 7071 0 7077 end t of 4 4 to 6 3 and ehf t in situ zircon of 3 3 elemental and isotopic data suggest that they were formed by wet anatexis of the precambrian metasedimentary and metaigneous rocks in the continental collision overthrust zone the muztaga and taer plutons consist of metaluminous to weakly peraluminous high k calc alkaline granitoids granodiorite monzogranite with initial 87sr 86sr ratios of 0 7052 0 7104 end t of 3 6 to 7 3 and ehf t in situ zircon of 3 1 to 1 0 elemental and isotopic data suggest that they were formed by partial melting of the precambrian metasedimentary and metaigneous rocks in the normal lower crust

geochronology petrogenesis and tectonic significance of peraluminous granites from the chinese altai nw china abstract the paleozoic granites in the chinese altai are important for the study of tectonic evolution and crustal growth in the central asian orogenic belt caob four representative peraluminous granitic intrusions were selected for systematic studies of zircon u pb and hf isotopic compositions and whole rock geochemical and nd sr isotopic analyses these rocks have high asi alumina saturation index al 2 o 3 cao na 2 o k 2 o 1 01 1 46 molecular ratios with 0 6 5 6 wt of normative corundum and are characterized by moderately negative eu anomalies eu eu 0 38 0 98 and strong depletion in ba nb and sr elements our data suggest that these intrusions were emplaced from 419 to 393 ma consistent with a period of intensive magmatic activities and high temperature metamorphism in the chinese altai while in situ zircon hf isotopic analyses for these granites give predominantly positive e hf t values 0 8 to 12 8 a few inherited zircons yield negative e hf t values from 12 5 to 1 53 the u pb age and hf isotopic data of these inherited zircons are similar to that of the widespread metasediments in addition the peraluminous granitic rocks have near zero or negative e nd t values 3 3 to 0 5 and relatively high initial 87 sr 86 sr ratios 0 7079 0 7266 distinct from those of the i type granites in the study region but similar to the early paleozoic habahe sediments these isotopic compositions suggest that the newly accreted metasediments of habahe group may be the major source rock of the peraluminous granites the geochemical compositions indicate that their precursor magmas were derived from a relatively shallow crustal level p 5 kbar and zircon saturation temperatures suggest that these granitic intrusions were emplaced at 672 861 c the peraluminous granitic magmas were generated by dehydration melting of newly accreted materials which were possibly brought to at least middle crustal depth by subduction related processes in an active margin and were subsequently molten by strikingly high ambient temperature probably caused by upwelling of the hot asthenosphere associated with ridge subduction in the paleozoic

tectono magmatic rejuvenation of the qaidam craton northern tibet abstract ascertaining the enigmatic characteristics of the crystalline basement of the qaidam basin the deepest intracontinental basin yet located in the highest orogenic plateau with the thickest continental crust has broad implications for the cenozoic basin evolution in particular and intracontinental tectonics of asia in general we carried out a comprehensive investigation on the ages and geochemical isotopic characteristics of the qaidam and suganhu basement rocks obtained from drill cores petrological observations and u pb zircon dating la icp ms of granitoid samples from drill cores indicate that early neoproterozoic early paleozoic and late paleozoic mesozoic intrusions are largely represented suggesting that the qaidam and suganhu blocks were involved into three tectono magmatic episodes similar whole rock geochemistry and sr nd isotopic characteristics between the early neoproterozoic granitoids beneath the qaidam basin and the contemporaneous basement rocks in the surrounding orogenic belts confirm the existence of pervasive early neoproterozoic metamorphism and magmatism along the present day northern tibetan plateau by comparing the trace and rare earth elements patterns as well as the sr nd compositions of the ordovician arc related granitoids and silurian devonian post collisional granitoids beneath the qaidam and suganhu basins with the corresponding granitoids from the surrounding orogenic belts we assert that the proto tethys subduction events that were recorded within the eastern kunlun altyn tagh and the qilian shan orogenic belts were different they generated distinctive subduction related arc magmas whereas the closure of the oceanic basins resulted in the amalgamation of the orogenic belts inducing subsequent extensive post collisional magmatism within the qaidam block the widespread permian and triassic granitoids beneath the northwestern northern qaidam basin mainly involved a lower crust or a crust mantle source including mesoproterozoic crust they demonstrate that the influence of the paleo tethys evolution penetrated the qaidam block northwards reaching to the northern edges of the block we conclude that the qaidam block is not a craton as typical as the rigid tarim block but pertains to a tectono magmatic rejuvenated craton which is not mechanically stronger than its surrounding regions however trapped between the lithospheric left lateral strike slip altyn tagh fault system to the northwest and the qilian shan transpressional system to the northeast the qaidam block forms a relatively stable domain that escaped from significant cenozoic deformation

geochemical character and petrogenesis of pan african amspoort suite of the boundary igneous complex in the kaoko belt nw namibia abstract in the kaoko belt of northwestern namibia syn tectonic granitoids of the boundary igneous complex intruded a nnw sse trending suture between the neoproterozoic coastal terrane and archaean neoproterozoic congo craton derived foreland typical representatives of this syn collision igneous association are ca 550 ma old k feldspar phyric bt cam granites granodiorites of the amspoort suite with minor cpx gabbro and rare two pyroxene dolerite bodies the scarce opx cpx bt dolerites could come from a chur like mantle source 87sr 86sr550 0 7045 e550nd 0 the rest of the amspoort suite is interpreted as a product of ht anatexis of a heterogeneous lower crust built mainly by immature metapsammites rich in arc derived detritus with minor metabasite and intermediate metaigneous bodies the most likely source appears to be the anatectic coastal terrane gneisses yet partial melting of so far little constrained congo craton cover if formed by immature and youthful detritus unrelated to the basement cannot be discounted in any case the rather primitive sr nd isotopic compositions of the amspoort suite apart from dolerites e550nd 3 4 to 5 3 87sr 86sr550 0 7063 0 711 rule out any major role for the congo craton basement derived material which is in sharp contrast to other more southerly pan african granitoid complexes of the kaoko belt

petrogenesis and thermal overprint of s type granites in helanshan region north china craton constraints on the 1 90 ga khondalites decompression melting and 1 32 ga tectono thermal event abstract widespread paleoproterozoic s type granites and khondalites high grade sillimanite garnet gneisses are exposed in the khondalite belt of the north china craton ncc porphyritic biotite granites in the helanshan region from the western khondalite belt exhibit a gradual contact relationship with the neighboring khondalites in order to constrain the petrogenesis of these granites and their genetic relationship with the khondalites detailed geochronological data as well as geochemical and whole rock sm nd and zircon lu hf isotope compositions of these granites are reported la icp ms zircon u pb dating on magmatic zircon cores yields an emplacement age of 1902 22 ma whereas metamorphic rims define a metamorphic age of 1356 57 ma the unpolished surfaces of zircon crystals selected based on the presence of rims visible in cathodoluminescence were further analyzed by sims depth profiling which gave a more precise metamorphic age of 1317 18 ma the helanshan granites display typical s type geochemical characteristics e g high a cnk 1 16 1 29 and k2o 5 09 5 86 wt contents but low feot mgo 2 39 4 88 and p2o5 0 15 0 23 wt contents similar trace and rare earth element patterns and consistent zircon hf model ages 2366 2483 ma and whole rock nd model ages 2407 2499 ma between the porphyritic biotite granites and the khondalites suggest that they were derived from partial melting of khondalites the geochemical character of the porphyritic biotite granites including significant negative eu anomalies high rb ba and rb sr ratios and variable hree contents and la yb n ratios suggest that they are probably related to the post peak decompression stage that was characterized by biotite breakdown and the progressive replacement of garnet with the presence of k feldspar and plagioclase in the residues homogeneous zircon ehf t values mostly from 0 5 to 1 7 combined with low bulk rock fe2o3t content and cao na2o ratios preclude the contribution from mafic magma following the continental collision the emplacement of the porphyritic biotite granites at ca 1 90 ga provides the latest limit on the timing of post peak decompression metamorphism of the khondalites and their formation supports a post collisional mantle upwelling model to account for the 1 92 1 90 ga regional metamorphic magmatic events on the other hand the metamorphic zircon rims indicate that s type granites were overprinted by a 1 32 ga tectono thermal event which was probably related to the breakup of the columbia supercontinent

pathways for neoarchean pyrite formation constrained by mass independent sulfur isotopes it is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the neoarchean it is puzzling therefore that the sulfur isotope record of the neoarchean is characterized by a signal of atmospheric mass independent chemistry rather than a strong overprint by sulfate reducers here we present a study of the four sulfur isotopes obtained using secondary ion ms that seeks to reconcile a number of features seen in the neoarchean sulfur isotope record we suggest that neoarchean ocean basins had two coexisting significantly sized sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record one of these pools is suggested to be a soluble sulfate pool and the other pool atmospherically derived elemental sulfur is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide we suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite forming environments we also suggest that the existence of a significant nonsulfate pool of reactive sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record

syn and post collisional granitoids in the central tianshan orogen geochemistry geochronology and implications for tectonic evolution abstract the eastern part of the central tianshan belt in china is characterized by abundant granitoids which are not only indicators of the interaction between crust and mantle but also can be used for tracking the tectonic evolutionary history of the orogen four granitic plutons muscovite granites mg biotite monzonitic granites bmg biotite granites bg and alkali granites ag have been recognized to have intruded in the mishigou area central tianshan belt the mg has pronounced a s type affinity which is strongly peraluminous with a high aluminum saturation index and displays positive rb th u and lree anomalies with a strong negative ba nb sr p ti and eu anomalies therefore the magma of the mg is considered to have been derived from melting of thickened continental crust which is composed mainly of the sediments eroded from a pre silurian continental island arc the u pb zircon age of 424 5 2 6 ma constrains the age of mg and crust thickening the bg and bmg granitoids display i type geochemical features and have affinities to subduction arcs both of them are characterized by calc alkaline peraluminous granites with a significant lree enrichment and a negative eu anomaly as well as a depletion in ba nb ta sr p and ti and an enrichment in rb th u nd zr and sm these characteristics indicate that they were derived from a mixed magma source between lower continental crust and the input of components derived from the mantle wedge above the subduction zone the la icpms zircon u pb ages of 411 4 7 ma and 402 3 4 ma represent the formation ages of the bg and bmg granitoids respectively which also constrain that the subduction of the south tianshan oceanic crust also occurred during early devonian time the ag shows a typical a type granite affinity with depletion of nb ta sr p ti and y it is interpreted that ag was formed in a within plate tectonic setting and related to continental up doming and rifting zones as a consequence of the extensional collapse after the collision of the tianshan orogen the u pb zircon age of 290 5 1 ma represents the formation age of the ag and the time of the extensional collapse and rifting

comparison of mass balances for vernagtferner oetzal alps as obtained from direct measurements and distributed modeling the direct comparison of modeled glacier mass balance distribution with field measure ments could be problematic as the methodology of determination and the processes considered at the point or catchment scale could differ strongly moreover direct measurements cover only small parts of a glacier and model performance is thus difficult to assess outside these regions remaining opportunities for model validation include comparison of snowlines as derived from remote sensing data and maps of the mass balance distribution as interpreted by observers with local knowledge this study compares such hand drawn maps of the vernagtferner oetzal alps mass balance with the modeled pattern as obtained from a distributed energy mass balance model of intermediate complexity the model is driven by measured daily values of temperature global radiation and precipitation from a nearby climate station and grids of mean daily potential global radiation and climatologic annual precipitation sums compared with the direct measurements the calculated mean mass balance and equilibrium line altitude agreed very well in both balance years although the spatial pattern of the mass balance distribution displayed larger deviations in regions influenced by snowdrift or local topographic undulations however compared with the remaining snow as visible on a satellite image from 1999 the modeled snowline pattern for a larger sample of glaciers is in very good agreement

different melting conditions and petrogenesis of peraluminous granites in western qinling china and tectonic implications abstract the qinling orogen records the prolonged amalgamation history between the north china block ncb and the south china block scb accompanied by major granitoid intrusions during the triassic however the petrogenesis of these granitoids especially that of the peraluminous granites remains a matter of debate detailed study of these peraluminous granites which are the products of crustal melting will give insights into the melting process and petrogenesis of peraluminous magmas and will further constrain the regional geological evolution in this study xiahe xh tourmaline bearing two mica granite and baijiazhuang bjz two mica granite were selected for systematic analysis of their mineralogy petrology zircon u pb geochronology and geochemistry the zircon u pb dating showed that the xh and bjz granites were emplaced at approximately 242 ma and approximately 214 ma respectively the presence of muscovite and tourmaline high peraluminosity at 1 1 low oxygen fugacity o2 conditions below the fayalite magnetite quartz fmq buffer and low zircon saturation temperatures indicate sedimentary protolith s type granitic affinity the low cao na2o ratios

glass rich cordierite biotite rhyodacite valle ninahuisa puno se peru petrological evidence for hybridization of lachlan s type and potassic mafic magmas

petrogenesis of the mesozoic shuikoushan peraluminous i type granodioritic intrusion in hunan province south china middle lower crustal reworking in an extensional tectonic setting abstract the mesozoic shuikoushan granitoid intrusion in the jiangnan orogen between the yangtze and the cathaysia blocks in southern hunan province south china provides an opportunity to probe deep crustal composition and structure and to investigate the geodynamic evolution of south china the intrusion is composed of granodiorite with i type geochemical affinities and contains zircon with an u pb concordant age of 158 3 1 2 ma rocks from the intrusion have variable sio2 from 58 4 wt to 65 2 wt al2o3 from 15 0 wt to 17 2 wt tio2 from 0 57 wt to 0 76 wt and p2o5 from 0 27 wt to 0 52 wt they have a cnk from 0 97 to 1 23 1 04 on average and are dominantly peraluminous they are characterized by enrichment in lree la sm n 3 47 5 19 and lil e g k rb and depletion in hfse e g u th in primitive mantle normalized trace element diagrams these geochemical features indicate that the rocks are i type granodiorites and have undergone extensive fractional crystallization of hornblende biotite titanite and apatite all samples show negative ehf t 10 6 to 8 1 and end t 5 92 to 6 13 values with relatively high initial 87sr 86sr isr 0 7101 0 7102 and 18o ratios 8 4 9 7 these values significantly differ from mantle values suggesting that they are generated by the amphibole dehydration melting of a mafic source in the middle to lower crust beneath the jiangnan orogen the emplacement of the shuikoushan granitoid intrusion is contemporaneous with the late jurassic to early cretaceous extension within the shi hang rift zone indicating that it may have been formed under an extensional regime in response to both the pacific superplume activity and westward subduction of the pacific plate the extensional processes along with asthenosphere upwelling and basaltic underplating may have triggered the widespread late jurassic granitoid intrusion in southern hunan province and possibly in south china

neoproterozoic peraluminous granitoids in the jiangnan fold belt implications for lithospheric differentiation and crustal growth abstract neoproterozoic magmatism in the jiangnan fold belt of south china is characterized by voluminous ca 820 ma peraluminous granitoids which show a large range of chemical compositions the meixian dioritic and the lantian granitic intrusions from the central jiangnan fold belt were emplaced at 821 6 ma and 823 7 ma respectively the meixian diorites are mainly composed of amphibole 10 40 biotite 5 30 plagioclase 30 60 and quartz 5 10 they have low sio 2 59 42 63 15 wt moderate mgo 2 96 3 56 wt and na 2 o 3 51 4 39 wt and relatively high v 102 137 ppm and cr 47 1 58 7 ppm they show nearly zero end 0 6 to 0 1 and high ehf values 2 3 to 10 6 these mineralogical and geochemical features suggest that mantle derived melts were involved in their petrogenesis modeling calculations reveal that the meixian diorites were formed by fractional crystallization of mantle derived melts associated with 10 30 contamination by the country rocks however the lantian granites are fractionated i type granites that are composed of plagioclase 10 25 quartz 30 40 k feldspar 15 20 biotite 5 15 and amphibole 5 they have high sio 2 72 3 80 2 wt moderate k 2 o 1 58 4 11 wt and na 2 o 2 78 3 94 wt and low mgo 0 50 0 80 wt and cao 0 16 0 50 wt their negative end 2 3 to 1 4 and positive ehf values 0 4 to 9 9 are similar to those of the neoproterozoic arc affinity mafic rocks in the region suggesting that the lantian granites were derived from the mafic juvenile crust the neoproterozoic igneous rocks in the jiangnan fold belt are mainly composed of peraluminous granites with minor diorites the large volume of peraluminous granitoids are generally partial melts of the continental crust whereas the limited diorites are differentiation products of the basaltic magmas the petrogenesis of the granitoids in the jiangnan fold belt suggests that basaltic magma underplating triggered crustal anatexis during or after collision between the yangtze and cathaysia blocks

early palaeozoic crustal melting in an extensional setting petrological and sm nd evidence from the izera granite gneisses polish sudetes the izera block in the west sudetes which is composed of granites gneisses and transitional granite gneisses and minor mica schists is one of the largest outcrops of early palaeozoic ca 500 ma metagranitoid rocks in the basement units of the variscides of central europe the izera granites show s type features magmatic cordierite relict garnet and sillimanite lack of mafic enclaves and absence of coexisting tonalites and diorites the paucity of pegmatites indicates that the granitic magma was relatively dry the s type character of these granites is further supported by their peraluminous character a cnk 1 0 1 63 high content of normative corundum up to 3 5 and relatively high 87sr 86sr initial ratio the chemical variation of these rocks was controlled by the fractional crystallization of plagioclase cao sr eu eu biotite and cordierite al2o3 mgo feo zircon zr hf and monazite ree initial end values range from 5 2 to 6 9 mean 5 9 sd 0 6 these largely negative end values imply that the granitic magmas emplaced ca 500 ma were extracted from a source reservoir that was strongly enriched in lree i e with low sm nd ratio on a time integrated basis the relatively consistent depleted mantle model ages 1 730 2 175 ma mean 1 890 ma is in agreement with the earlier reported presence of ca 2 1 ga old inherited pb component in zircon from the closely related rumburk granite this points to an old early proterozoic crustal residence age of the inferred metasedimentary protoliths of the izera granitoids with only minor contribution to their protoliths of juvenile components of late proterozoic early palaeozoic age although the izera granites show some trace element features reminiscent of syn collisional or post collisional granitoids they more likely belong to the broad anorogenic class our data corroborate some previous interpretations that granite generation was connected with the early palaeozoic rifting of the passive margin of the saxothuringian block well documented in the region by bimodal volcanic suites of similar age kaczawa unit eastern and southern envelope of the karkonosze izera block in this scenario granite magmatism and bimodal volcanism would represent two broadly concomitant effects of a single major event of lithospheric break up at the northern edge of gondwana

petrogenesis of jurassic fractionated i type granites in southeast china constraints from whole rock geochemical and zircon u pb and hf o isotopes abstract whole rock geochemical and sr nd hf isotopic data and zircon in situ u pb ages and hf o isotopes are reported for twelve granitic intrusions from inland to coastal areas of the cathaysia block southeast se china in order to constrain their magma sources and petrogenesis they are mainly composed of biotite granites with minor granodiorites zircon u pb dating by la icpms and sims methods gave emplacement ages of 165 154 ma for these rocks which are metaluminous to weakly peraluminous a cnk 0 95 1 10 with variable sio 2 contents and high k 2 o contents they are all depleted in high field strength elements hfses and enriched in light rare earth elements lrees and large ion lithophile elements liles and show negative sr ba and eu anomalies in the spidergrams petrographic and geochemical features suggest the granodiorites that contain hornblende to be typical of i type while the biotite granites without hornblende are fractionated i type granites their variable major and trace element concentrations are due to fractional crystallization of feldspar biotite hornblende and accessory minerals including apatite allanite and monazite moreover our data indicate significant variations in isotopic compositions of these granitoids from inland to coastal areas the inland granites from the lapu fogang xinfengjiang and baishigang plutons have relatively high initial 87 sr 86 sr ratios 0 7105 0 7155 and low e nd t 11 2 to 7 3 and e hf t 10 9 to 6 3 values for whole rocks and variable 18 o values of 7 69 9 25 and e hf t values of 13 5 to 6 7 for zircons in contrast the coastal granites from the longwo wushikeng lianhuashan shigushan chiliao hulutian mantoushan and fenghuang plutons show relatively low initial 87 sr 86 sr ratios 0 7056 0 7110 and high e nd t 7 6 to 6 2 and e hf t 6 5 to 2 8 values for whole rocks together with e hf t values of 7 2 to 3 9 and 18 o values of 6 69 8 38 for zircons the spatial isotopic variations suggest that these jurassic granitoids were generated by different percentage mixing of mantle and ancient paleoproterozoic crust derived magmas with subsequently minor crustal assimilation our results highlight that jurassic fractionated i type granites occur widely from inland to coastal areas of se china arguing against the previous view that jurassic granites occur only in inland while coastal granites are mainly cretaceous the widespread occurrence of jurassic granitoids in se china is attributed to ascending of mantle derived magmas which provide heat for partial melting of lower crustal materials in an extensional setting

ice loss rates at the northern patagonian icefield derived using a decade of satellite remote sensing abstract we use a satellite based survey of glacier surface elevation changes speeds and surface melt conditions between 2000 and 2011 to quantify mass loss from the northern patagonian icefield npi chile a history of ice elevation change is found by differencing aster digital elevation models dems relative to a void filled version of the dem collected by the shuttle radar topography mission srtm in february 2000 thinning rates have accelerated at lower elevations while above the equilibrium line altitude ela recent thinning rates are not significantly different from those observed in previous studies a volumetric change of 4 06 0 11 km 3 yr is found by summing surface elevation changes over all glaciers in the npi this is regarded as a lower bound because volume loss due to frontal retreat and sub aqueous melting is not included this volume change is converted to a mass loss of 3 40 0 07 gt yr taking into account density differences above and below the equilibrium line we find that the npi is providing at least 0 009 0 0002 mm yr to ongoing sea level change in agreement with previous estimates sub pixel offset tracking of aster image pairs is used to produce glacier displacements over intervals typically ranging from 6 days to 18 months the first whole icefield composite velocity map is presented the terminus of the san rafael glacier on the western side of the npi sustained a peak calving front speed of 19 7 1 2 m day for 7 days in the austral fall of 2007 passive microwave observations indicate that the surface of the accumulation basin of the glacier was wet during this period of rapid motion suggesting that the fast speed may be a consequence of a rise in sub glacial water pressure sourced from melt or rainwater making its way to the glacier bed and reducing basal friction several other outlet glaciers including the benito and hpn1 glaciers on the isolated western side of the icefield accelerated while thinning between 2007 and 2011 marked acceleration also occurred after 2007 at the front of the san quintin glacier the largest outlet glacier of the npi the paucity of thickness measurements at the outlet glaciers means it is impossible to accurately gauge the mass flux of the icefield and thus give a full estimate of the mass balance

neoproterozoic tourmaline bearing peraluminous granitoids in the western jiangnan orogen south china geochemistry petrogenesis and tectonic implications abstract neoproterozoic granitoids are widespread in the jiangnan orogen in south china that was formed by assemblage between the yangtze and cathaysia blocks the peraluminous s type granitoids from the guibei region in the western jiangnan orogen are composed of quartz alkali feldspar and plagioclase with subordinate biotite and muscovite they show large variable feo mgo 1 9 12 8 and k2o na2o cao 2 84 ratios indicating the rocks experienced fractional crystallization their end values 9 31 to 5 45 and two stage nd model ages 1 83 2 34 ga suggest that the guibei granitoids were derived from a mature source that was mainly composed of recycled supracrustal materials the tourmalines occurring as disseminated and nodular grains show high na k 0 56 0 77 apfu low ca 0 01 0 08 apfu and x site vacancy 0 18 0 51 apfu and belong to the alkali group their high fe 1 64 2 28 apfu low mg 0 14 0 80 apfu and mg mg fe 0 016 0 325 suggest that the minerals are dominated by schorl end member in the schorl dravite solid solution series the tourmalines have constant and strong negative 11b values 13 4 to 9 5 and the nodular tourmalines are isotopically lighter 11b 10 0 to 13 4 than the disseminated tourmalines 11b 9 5 to 12 5 the disseminated tourmalines are suggested to have been crystallized in melts at the early magmatic stage whereas the nodular tourmalines formed in fluid rich immiscible melts at the late magmatic stage the boron isotopic variations within or among the tourmaline generations are mainly controlled by rayleigh fractionation in combined with the regional geology the peraluminous granitoids in this study are considered to be partial melts of the supracrustal rocks in the post orogenic setting

the role of collisional tectonics in the metallogeny of the central andean tin belt abstract the inner arc of the central andes broadly corresponding to the eastern cordillera is the location of a rich tertiary and triassic sn w ag base metal metallogenic province commonly referred to as the bolivian tin belt we propose that the tertiary metallogeny which generated most of the tin ores was a direct consequence of discrete collisions between the south american plate and the nazca slab and sub slab mantle during the ongoing andean orogeny evidence supporting this proposal include 1 the coincidence of the tin province and the inner arc in a marked hump in the andean orogen which may represent tectonic indentation 2 the symmetry of the tin province with respect to the bolivian orocline the axis of which corresponds to the direction of highest compression 3 the relative symmetry of the magmatism and tin mineralization with respect to this axis 4 the concurrent timing of mineralization and compressional pulses 5 the similar host rock geochemistry and ore lead isotope data testifying to a common crustal reservoir and 6 the striking similarity of the igneous suites associated with the ore deposits to those from typical collisional orogens a number of studies have called upon a persistent tin anomaly to explain the metallogeny of the region we propose instead that the latter is better explained by periodic compressional interaction between the farallon nazca oceanic plate and the south american continent this led to the generation of peraluminous magmas which during fractional crystallization exsolved the fluids responsible for the voluminous sn w mineralization

genesis of the two main types of peraluminous granitoids two mica monzogranites to leucogranites and biotite rich cordierite bearing tonalites to monzogranites form two distinct groups of peraluminous granitoids they can be distinguished by mineral and rock associations and by the variation of their peraluminosity during differentiation except for the rare muscovite bearing granitoids produced by extreme fractionation or local contamination of metaluminous magmas the majority of peraluminous granitoids are produced by partial melting of crustal rocks production of either muscovite bearing granites or biotite rich cordierite bearing granitoids does not depend only on the nature of the sources but is also controlled by the physical parameters of partial melting and consequently by the way anatexis of a thickened crust is enhanced biotite rich cordierite bearing granitoids are generated where mantle derived magmas are injected into or have underplated crustal rocks two mica granites are generated where thickened crust is affected by major crustal shears or thrusts correlations between differentiation and peraluminosity indicate the dominant role of either restite unmixing or fractional crystallization in the production and evolution of the various types of peraluminous granitoids

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

u pb re os and 40ar 39ar geochronology of porphyry sn cu mo and polymetallic ag pb zn cu vein mineralization at bianjiadayuan inner mongolia northeast china implications for discrete mineralization events

the petrogenesis of some migmatites and granites central damara orogen namibia evidence for disequilibrium melting wall rock contamination and crystal fractionation

strong spatial variability of snow accumulation observed with helicopter borne gpr on two adjacent alpine glaciers the spatial distribution of snow accumulation plays an essential role for the mass balancedistribution on alpine glaciers traditional point measurements snow pits and probes are labour intensive and interpolation in between the points causes uncertainties airborne radar measurements have already been used for snow mapping innon glacierized terrain but not on alpine glaciers to enhance our understanding ofthe spatial distribution of accumulation and pin down reasons for observed variations we have conducted high resolution helicopter borne radar measurements on the temperatedglacier findel and neighbouring adler glacier in southwestern switzerland the radar sensor was mounted underneath a helicopter and operated at a centre frequencyof 500 mhz with a bandwidth of 400 mhz the results were validated withextensive ground based profiling of the snow cover the radar data allows a clearrecognition of the snow cover 6 of the total profile length of 10 km did not allowinterpretation due to missing or disturbed layering and agreed well with the groundbased measurements r2 0 85 reduced accumulation has been observed in allcrevassed zones statistical analysis of the correlation between observed accumulationand terrain characteristics have been performed in a gis environment revealing differingaccumulation patterns on the lower part of findel glacier accumulation showsa clear altitudinal trend while the upper part is dominated by strongly varying snowdepth without an altitudinal trend the accumulation characteristic on adler glacieris similar to the upper part of findel glacier but despite of their close vicinity accumulationis reduced by 40 compared to the same elevation on findel glacier thisstudy reveals a large potential of helicopter borne snow profiling for measurements ofaccumulation distribution on alpine glaciers