turbulent velocity profiles for smooth and rough open channel flow velocity measurements using a laserdoppler anemometer are carried out in a fully developed rectangular subcritical open channel flow on smooth and rough beds the average roughness heights of t

holocene palaeoclimates from peat stratigraphy macrofossil proxy climate records from three oceanic raised bogs in england and ireland quantified analyses of plant macrofossil remains have been made from three profiles of peat from raised bogs spanning a distance of 425 km from western ireland to northern england the reconstructed vegetation of each profile is related to changing bog surface wetness bsw and since the bogs are ombrotrophic these bsw changes are interpreted in terms of changing climate using age depth models based on a total of 49 radiocarbon dates a number of wetter and drier phases are identified and phase shifts to wetter and or cooler climates are defined prominent coincident changes to wetter conditions are dated in at least two of the profiles to ca 4400 4000 1750 1400 and 1000 cal bp and in all three profiles at 3200 2750 2350 2250 and around 700 cal bp these phases are related to proxy climate changes in other terrestrial data sets from northwest europe and a broad degree of synchroneity is demonstrated

high temperature deformation during continental margin subduction exhumation the ultrahigh pressure western gneiss region of norway abstract a new dataset for the high pressure to ultrahigh pressure western gneiss region allows the definition of distinct structural and petrological domains much of the study area is an e dipping homocline with e plunging lineations that exposes progressively deeper more strongly deformed more eclogite rich structural levels westward although eclogites crop out across the wgr scandian deformation is weak and earlier structures are well preserved in the southeastern half of the study area the scandian reworking increases westward culminating in strong scandian fabrics with only isolated pockets of older structures the dominant scandian deformation was coaxial e w stretching the sinistrally sheared more trondelag fault complex and nordfjord mylonitic shear zone bound these rocks to the north and south there was moderate top e amphibolite facies deformation associated with translation of the allochthons over the basement along its eastern edge and the nordfjord sogn detachment zone underwent strong lower amphibolite facies to greenschist facies top w shearing a northwestward increase in exhumation related melting is indicated by leucosomes with hornblende plagioclase and scandian sphene in the western 2 3 of the study area exhumation related amphibolite facies symplectite formation in quartzofeldspathic gneiss postdated most scandian deformation further deformation was restricted to slip along biotite rich foliation planes and minor local folding that the western gneiss region quartzofeldspathic gneiss exhibits a strong gradient in degree of deformation implies that continental crust in general need not undergo pervasive deformation during subduction

remote monitoring of volumetric discharge employing bathymetry determined from surface turbulence metrics current methods employed by the united states geological survey usgs to measure river discharge are manpower intensive expensive and during high flow events require field personnel to work in dangerous conditions indirect methods of estimating river discharge which involve the use of extrapolated rating curves can result in gross error during high flow conditions due to extrapolation error and or bathymetric change our goal is to develop a remote method of monitoring volumetric discharge that reduces costs at the same or improved accuracy compared with current methods while minimizing risk to field technicians we report the results of large scale particle image velocimetry lspiv and acoustic doppler velocimetry adv measurements conducted in a wide open channel under a range of flow conditions i e channel aspect ratio b h 6 6 31 9 reynolds number reh 4 950 73 800 and froude number fr 0 04 0 46 experiments were carried out for two different channel cross sections rectangular and asymmetric compound and two bathymetric roughness conditions smooth glass and rough gravel bed the results show that the mean surface velocity normalized by the depth averaged velocity the velocity index decreases with increasing h where is the boundary layer displacement thickness and that the integral length scales l11 1 and l22 1 calculated on the free surface vary predictably with the local flow depth remote determination of local depth averaged velocity and flow depth over a channel cross section yields an estimate of volumetric discharge

tethyan and indian subduction viewed from the himalayan high to ultrahigh pressure metamorphic rocks abstract the himalayan range is one of the best documented continent collisional belts and provides a natural laboratory for studying subduction processes high pressure and ultrahigh pressure rocks with origins in a variety of protoliths occur in various settings accretionary wedge oceanic subduction zone subducted continental margin and continental collisional zone ages and locations of these high pressure and ultrahigh pressure rocks along the himalayan belt allow us to evaluate the evolution of this major convergent zone 1 cretaceous 80 100 ma blueschists and possibly amphibolites in the indus tsangpo suture zone represent an accretionary wedge developed during the northward subduction of the tethys ocean beneath the asian margin their exhumation occurred during the subduction of the tethys prior to the collision between the indian and asian continents 2 eclogitic rocks with unknown age are reported at one location in the indus tsangpo suture zone east of the nanga parbat syntaxis they may represent subducted tethyan oceanic lithosphere 3 ultrahigh pressure rocks on both sides of the western syntaxis kaghan and tso morari massifs formed during the early stage of subduction exhumation of the indian northern margin at the time of the paleocene eocene boundary 4 granulitized eclogites in the lesser himalaya sequence in southern tibet formed during the paleogene underthrusting of the indian margin beneath southern tibet and were exhumed in the miocene these metamorphic rocks provide important constraints on the geometry and evolution of the india asia convergent zone during the closure of the tethys ocean the timing of the ultrahigh pressure metamorphism in the tso morari massif indicates that the initial contact between the indian and asian continents likely occurred in the western syntaxis at 57 1 ma west of the western syntaxis the higher himalayan crystallines were thinned rocks equivalent to the lesser himalayan sequence are present north of the main central thrust moreover the pressure metamorphism in the kaghan massif in the western part of the syntaxis took place later 7 m y after the metamorphism in the eastern part suggesting that the geometry of the initial contact between the indian and asian continents was not linear the northern edge of the indian continent in the western part was 300 to 350 km farther south than the area east of the nanga parbat syntaxis such en baionnette geometry is probably produced by north trending transform faults that initially formed during the late paleozoic to cretaceous gondwana rifting farther east in the southern tibet the collision occurred before 50 6 0 2 ma finally high pressure to ultrahigh pressure rocks in the western himalaya formed and exhumed in steep subduction compared to what is now shown in tomographic images and seismologic data

late holocene post 4000 years bp coastal dune development in northumberland northeast england the recent environmental history of coastal dune systems in northumberland northeast england has been examined using geomorphological stratigraphical and sedimentological techniques linked to radiocarbon and infrared stimulated luminescence irsl dating stratigraphies were determined from 22 vibracores and three sections and dune chronology was based on 28 14 c dates from peat and soil organic horizons and 26 irsl dates on k feldspar grains from within sand layers almost all dune systems are associated with regressive shorelines consequent upon a fall in relative sea level rsl from its holocene peak and indicate rsl functioned as a macroscale control on dune development where dunes are anchored on terrestrial sediment dune expansion may have been either transgressive or regressive in nature where near shore marine sediments form the dune substrate a regressive prograding dune model seems most likely most dune building occurred during the little ice age lia probably in a

anatexis of ultrahigh pressure eclogite during exhumation in the north qaidam ultrahigh pressure terrane constraints from petrology zircon u pb dating and geochemistry plagioclase rich leucosomes and k feldspar rich veins are widely distributed within retrogressed eclogite in the xitieshan area of the north qaidam ultrahigh pressure metamorphic terrane western china in this contribution a combined study of petrology zircon internal structure zircon u pb age zircon trace element composition whole rock geochemistry and sr nd isotopes in plagioclase rich leucosomes and k feldspar rich veins provides insight into the nature and timing of partial melting in these rocks petrological evidence for partial melting is provided by elongated highly cuspate feldspars quartz along grain boundaries e g muscovite garnet and clinopyroxene and felsic veinlets composed of quartz and feldspar along the boundaries of garnet clinopyroxene and clinopyroxene plagioclase symplectite in the metabasite whole rock geochemistry suggests that the plagioclase rich leucosomes have lower contents of both rare earth elements rees and high field strength elements hfses but higher large ion lithophile elements liles e g rb ba k sr and pb than the metabasite hosts the plagioclase rich leucosomes may be divided into two subgroups according to their distinct ree patterns 1 higher total ree content with or without weak negative eu anomalies and 2 lower total ree content with conspicuous positive eu anomalies the eu rich group also shows higher sr content than those in the eu poor group however the k feldspar rich veins show higher ree hfse and lile concentrations than the plagioclase rich leucosomes and metabasites the inherited cores of k feldspar rich veins are of typical magmatic origin oscillatory zoning with high th u ratios enriched heavy h rees and negative eu anomalies yielding 206 pb 238 u ages ranging from 904 8 ma to 915 28 ma the zircon cores of plagioclase rich leucosomes and mantles of k feldspar rich veins exhibit no zoning or weak zoning with flat hree patterns and no negative eu anomalies and they contain mineral inclusions of garnet and clinopyroxene implying that these zircon domains were formed during an episode of eclogite facies metamorphism with 206 pb 238 u ages ranging from 444 10 ma to 452 9 ma internal textures and mineral inclusions quartz plagioclase and k feldspar and trace element systematics steep hree patterns with negative eu anomalies and low th u ratios of the zircon rims from plagioclase rich leucosomes and k feldspar rich veins are similar to anatectic zircon these anatectic zircon domains yielded 206 pb 238 u ages ranging from 430 10 ma to 440 12 ma and 406 12 ma to 430 13 ma respectively an integrated study of petrology geochronology and geochemistry demonstrated that the metabasites of the north qaidam ultrahigh pressure terrane likely experienced initial partial melting with plagioclase rich leucosome formation under eclogite facies conditions and partial melt crystallization during the granulite facies stage triggered by dehydration melting involving zoisite and rare muscovite the k feldspar rich veins within the metabasites may be the result of injected melts that were derived from partial melting of nearby gneisses

measuring stream discharge by non contact methods a proof of concept experiment this report describes an experiment to make a completely non contact open channel discharge measurement a van mounted pulsed doppler 10ghz radar collected surface velocity data across the 183 m wide skagit river washington at a usgs streamgaging station using bragg scattering from short waves produced by turbulent boils on the surface of the river surface velocities were converted to mean velocities for 25 sub sections by assuming a normal open channel velocity profile surface velocity times 0 85 channel cross sectional area was measured using a 100 mhz ground penetrating radar antenna suspended from a cableway car over the river seven acoustic doppler current profiler discharge measurements and a conventional current meter discharge measurement were also made three non contact discharge measurements completed in about a 1 hour period were within 1 of the gaging station rating curve discharge values with further refinements it is thought that open channel flow can be measured reliably by non contact methods

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

origin of late variscan granitoids from ne bavaria germany exemplified by ree and nd isotope systematics sm nd isotopic results are presented for late and post tectonic granitoids comprising peraluminous granites and subordinate metaluminous dioritic rocks redwitzites from the fichtelgebirge fg and northern oberpfalz nop ne bavaria the data combined with a number of earlier geochromological studies on these granitoids place severe constraints on the crustal evolution of this region during the carboniferous and pre carboniferous epoch redwitzites range in nd t from 4 to 0 inclusive data from p k holl and coworkers the nd t values of the granites s s are restricted to overlapping ranges of 8 to 3 fg and 8 to 2 nop in both domains the older granites 330 325 ma are characterized by nd t values of 4 whilst the younger granites 315 305 and 290 ma have nd t values of 4 the diversity observed in nd isotopic characteristic is interpreted in terms of different source material the nd isotopic compositions of the redwitzites exhibit source heterogeneity suggesting mixing between mantle magma and crust the nd isotopic features of the older granites are consistent with the magmatic precursors having been generated by partial melting of pre existing mature crust variably contaminated by mantle material or alternatively by melting of chemically less evolved crust resembling paragneisses of teh zev structural unit the origin of the younger granites can be confidently linked to anatexis of common moldanubian and saxothuringian metasediments two stage nd model ages tdm of the granitoids are in the range 1 1 1 7 ga these ages provide further support of substantial involvement of pre phanerozoic crust in the generation of the granitoids the leuchtenberg granite and the g2 and g3 granites yield late variscan sm nd isochron ages which are concordant with previous rb sr data on these granites by contrast the nd isotopic data for barnau and flossenburg define pseudo isochrons suggestive of mixing between contrasting felsic melts

u pb zircon geochronology of coesite bearing eclogites from the southern dulan area of the north qaidam uhp terrane northwestern china spatially and temporally extensive uhp metamorphism during continental subduction coesite bearing eclogites from 100 km 2 in the southern dulan area north qaidam mountains nqm of western china contain zircon that records protolith crystallization and ultra high pressure uhp metamorphism sensitive high resolution ion microprobe mass spectrometer and laser ablation inductively coupled plasma mass spectrometry u pb analyses from cathodoluminescence cl dark zircon cores in a coesite bearing eclogite yield an upper intercept age of 838 50 ma and oscillatory zoned cores in a kyanite bearing eclogite gave a weighted mean 206 pb 238 u age of 832 20 ma these zircon cores yield steep heavy rare earth element hree slopes and negative eu anomalies that suggest a magmatic origin thus c 835 ma is interpreted as the eclogite protolith age unzoned cl grey or bright zircon and zircon rims from four samples yield weighted mean ages of 430 4 438 2 446 10 and 446 3 ma flat hree patterns without eu anomalies and contain inclusions of garnet omphacite rutile phengite and rare coesite these ages are interpreted to record 16 5 myr of uhp metamorphism these new uhp ages overlap the age range of both eclogite and paragneiss from the northern dulan area suggesting that all uhp rock types in the dulan area belong to the same tectonic unit our results are consistent with slow continental subduction but do not match oceanic subduction and diapiric exhumation uhp model predictions these new data suggest that similar to eclogites in other hp uhp units of the nqm and south altyn tagh protoliths of the eclogites in the dulan area formed in a continental setting during the neoproterozoic and then subducted to mantle depth together with continental materials during the early palaeozoic

boundary lines within petrologic diagrams which use oxides of major and minor elements use of some petrologic diagrams applied to analyses of volcanic rocks is unnecessarily difficult due to lack of data for construction of discriminant lines between rock series coordinates are provided for sufficient points to enable accurate plotting of the boundary lines within seven diagrams viz 1 tas total alkalies na2o k2o vs sio2 2 k2o vs sio2 3 afm 4 jensen 5 ktp k2o tio2 p2o5 6 fms feo mgo vs sio2 and 7 taktip k2o na2o k2o vs tio2p2o5 different versions of these boundaries are collated to indicate their variable position and it is demonstrated that inter laboratory analytical precision suffices to account for almost all of their spread on the tas and k2o vs sio2 diagrams

multiple sources of the early mesozoic gouli batholith eastern kunlun orogenic belt northern tibetan plateau linking continental crustal growth with oceanic subduction orogenic belts have been among the most important locations to investigate the growth of continental crust cc the eastern kunlun orogenic belt ekob which contains widespread permian triassic granitoids is volumetrically comparable to the cenozoic gangdese magmatic belt in the tibetan plateau and is an ideal region to investigate the mechanism of the paleozoic mesozoic cc growth in this region the gouli batholith at the eastern end of the ekob consists of the synchronous xiangride granodiorite asiha quartz diorite ca 242 ma and adamellite the granodiorite and quartz diorite both of which contain magmatic enclaves show medium high k calc alkalic and metaluminous signatures and have similar rare earth element and trace element patterns to those of bulk cc besides the xiangride granodiorite displays distinct adakitic signatures average sr y of 47 the sr nd isotopic values for the different types of rocks are roughly similar 87sr 86sr i 0 708167 0 713553 end t 6 8 to 5 3 while hf isotopes are distinguishable with ehf t granodiorite 0 3 to 5 1 and ehf t diorite 1 6 to 0 7 these geochemical and petrographic signatures suggest that the granodiorite originated from the partial melting of subducting oceanic crust and terrigenous sediments and the quartz diorite and enclaves formed via the mixing of slab derived magma and enriched mantle derived melt further comprehensive analyses of the spatial and temporal distribution of regional magmatic rocks metamorphism and sedimentary facies reveal that the gouli batholith and most of the permian triassic granitoids in the ekob formed during the subduction of the paleo tethys ocean instead of subsequent syn collision setting thus we contend that the permian triassic cc growth of the ekob occurred in a slab subduction setting and that both oceanic slab and subcontinental mantle significantly contributed to this process

first record and timing of uhp metamorphism from zircon in the xitieshan terrane implications for the evolution of the entire north qaidam metamorphic belt the xitieshan terrane is one of four metamorphic terranes in the north qaidam metamorphic belt which is an early paleozoic high pressure to ultrahigh pressure hp uhp metamorphic belt in nw china however conclusive evidence and precise timing of uhp metamorphism in the xitieshan terrane have not been well documented in this study we report an integrated study of zircon grains from an amphibolite in the xitieshan terrane in terms of mineral inclusions trace elements and u pb age systematics the first record of coesite is reported as an inclusion in a metamorphic zircon which provides unambiguous evidence for the uhp metamorphism of the xitieshan terrane the metamorphic zircon domains have weak or no zoning very low th u ratios insignificant eu anomalies and flat hree patterns zircon grains contain inclusions of garnet omphacite and rutile in addition to the coesite inclusion these inclusions indicate that the metamorphic zircon grains formed under uhp metamorphic conditions the metamorphic zircon grains were dated by the sims and la icpms methods and yield weighted mean ages of 432 14 and 441 9 ma respectively combined with previous results the hp uhp metamorphism of the xitieshan terrane may have lasted 460 440 ma with the peak uhp metamorphism at 441 9 ma a compilation of the reported geochronological data reveals that all four terranes of the north qaidam metamorphic belt might have experienced coeval uhp metamorphism during the early paleozoic 420 450 ma and thus may have suffered a coherent subduction uhp metamorphism and exhumation cycle

the cretaceous huangdaoshan cu bearing intrusion in chuzhou petrogenesis and implications for the cu mineralization in the middle lower yangtze river valley metallogenic belt eastern china abstract the huangdaoshan mineral deposit in the middle lower yangtze river valley metallogenic belt is located on the northern margin of the yangtze craton eastern china it is hosted by the high k calc alkaline quartz monzonite porphyry and quartz diorite porphyry of huangdaoshan intrusion the molybdenite re os age for the mineral deposit suggests that mineralization occurred at 128 9 2 3 ma and was coeval with the ore bearing intrusion 130 1 ma both porphyries are enriched in light rare earth elements lree and large ion lithophile elements lile depleted in heavy rare earth elements hree and high field strength elements hfse and have positive eu anomalies they also show adakitic affinities with high sr 914 1227 ppm and sr y ratios 125 212 and low y 5 40 9 00 ppm and yb 0 46 0 75 ppm contents petrography micro fabric features and sr nd hf isotopic results suggest that these adakite like magmas were derived from magma mixing between mantle and crustal derived materials the strong ree fractionations as well as the high la sm 6 0 7 1 and intermediate sm yb 4 5 5 6 ratios suggest that hornblende crystallization was the dominant control on fractionation apparent temperatures based on ti in zircon thermometry show that the mineralization related porphyries crystallized at 711 c 790 c the oxygen fugacity fo2 estimated from hornblende mg contents and biotite fe3 fe2 and mg contents indicates that the mineralized magma possessed a high oxidation state nno 0 15 to nno 1 62 the geochemical characteristics of the intrusions enrichment in liles depletion in hfses and nb ta anomalies indicate that the mafic magma was derived from partial melting of the enriched lithosphere mantle which had been metasomatized by slab derived fluids from a subducted oceanic plate therefore the parental magma contained high contents of h2o and metal e g cu with high fo2 the extensive contemporaneous magmatism metallogenic events and volcanic basins in the region suggest an extensional tectonic setting we further correlated this extension regime with slab roll back of the paleo pacific plate

geochemistry and zircon u pb ages of adakitic rocks from the dulan area of the north qaidam uhp terrane north tibet constraints on the timing and nature of regional tectonothermal events associated with collisional orogeny abstract geochemistry and u pb ages of leucosomes and tonalites in a high pressure granulite unit of the dulan area have been determined to constrain the tectonothermal evolution related to collision and thickening of lower crust in the north qaidam mountains nqd leucosomes and tonalites show a marked chemical resemblance to adakites 1 high la yb and sr y and low y and hree 2 high al 2 o 3 and low mg values with obvious positive eu anomalies and 3 slightly positive e nd t values zircon u pb analysis of leucosomes and tonalites yielded 206 pb 238 u ages of 428 437 ma and 436 437 ma respectively which constrain the emplacement ages of the adakitic rocks petrological geochronological and geochemical characters indicate that the adakitic rocks may have been derived from partial melting of a thickened mafic lower crust 50 km suggesting a dominating source regime of synchronous high pressure mafic granulites contemporary magmatism in other units of the nqd shows evidence of a widespread tectonothermal event during early silurian 420 450 ma that includes metamorphism magmatism and anatexis related to collision and thickening of lower crust

the tectonic transition from oceanic subduction to continental subduction zirconological constraints from two types of eclogites in the north qaidam orogen northern tibet abstract in the plate tectonics theory continental subduction is pulled by subduction of dense oceanic crust in practice however it is not easy to demonstrate that preceding oceanic crust exposes as oceanic type eclogite together with continental type eclogite in collisional orogens the north qaidam orogen in northern tibet is an ultrahigh pressure uhp metamorphic belt that contains the two types of eclogites providing us with an excellent opportunity to study the tectonic transition from oceanic subduction to continental subduction in order to constrain the protolith nature and metamorphic evolution of eclogites we performed a combined study of zircon u pb ages trace elements mineral inclusions and o hf isotopes for various eclogites from the orogen we discriminate the two types of eclogites by their differences in zircon u pb ages and o hf isotopes cl dark zircon domains exhibit high th u ratios steep hree patterns and significantly negative eu anomalies indicating that they are protolith zircons of magmatic origin with different extents of metamorphic recrystallization relict magmatic zircon domains in type i eclogites yield neoproterozoic protolith ages of 830 ma and hf model ages of 850 1100 ma whereas those in type ii eclogites yield cambrian protolith u pb ages of 489 ma and hf model ages of 500 650 ma most of the cl bright zircon domains show low th u ratios flat hree patterns and no negative eu anomalies and contain mineral inclusions of garnet omphacite and rutile indicating their growth under eclogite facies metamorphic conditions these metamorphic domains have consistent eclogite facies metamorphic ages of 433 440 ma throughout the north qaidam orogen regardless of the eclogite types and locations the metamorphic zircon domains in type i eclogites mostly exhibit 18o values higher than normal mantle values whereas type ii eclogites mostly have 18o values lower than the normal mantle values the difference in the 18o values indicates that their protoliths underwent different temperatures of hydrothermal alteration at different tectonic settings combining zircon u pb ages and o hf isotope compositions with local tectonics it is inferred that type i eclogites were metamorphosed from neoproterozoic continental mafic rocks whereas type ii eclogites were metamorphosed from oceanic mafic rocks that were subducted prior to the continental subduction the consistent eclogite facies metamorphic ages for the two types of eclogites indicate that the exhumed oceanic type eclogite was detached from the subducted oceanic crust and then entrained by the exhuming continental crust therefore the coexistence of oceanic and continental type eclogites in the north qaidam orogen demonstrates the tectonic transition from oceanic subduction to continental collision in the early paleozoic

syn collisional adakitic granodiorites formed by fractional crystallization insights from their enclosed mafic magmatic enclaves mmes in the qumushan pluton north qilian orogen at the northern margin of the tibetan plateau the qumushan qms syn collisional granodiorite which is located in the eastern section of the north qilian orogen at the northern margin of the greater tibetan plateau has typical adakitic characteristics and also contains abundant mafic magmatic enclaves mmes this recognition offers an unprecedented insight into the petrogenesis of both the adakitic host granodiorite and the enclosed mmes the mmes and their host granodiorites share many characteristics in common including identical crystallization age similar to 430 ma same mineralogy similar mineral chemistry and whole rock isotopic compositions indicating their genetic link the mmes are most consistent with being of cumulate origin formed at earlier stages of the same magmatic system that produced the qms adakitic granodiorite subsequent replenishment of adakitic magmas could have disturbed the cumulate piles as mmes dispersed in the adakitic granodiorite host during emplacement the geochemical data and petrogenetic modeling of trace elements suggest that the qms adakitic host granodiorite is most consistent with fractional crystallization dominated by the mineral assemblage of the mmes the parental magma for the qms granodiorite is best explained as resulting from partial melting of the ocean crust together with recycled terrigenous sediments during continental collision which may have also experienced interaction with mantle peridotite during ascent c 2016 elsevier b v all rights reserved

wind tunnel simulation of aeolian sandy soil erodibility under human disturbance abstract inappropriate anthropogenic activities such as overcultivation and overgrazing of steppe and excessive collection of fuelwood are largely responsible for current desertification in china however quantitative information concerning the impacts of human disturbance on soil erosion remains sparse this study investigated aeolian sandy soil erodibility under human disturbance by wind tunnel simulation the fixed aeolian sandy soils were taken from an artificial vegetation protective system on mobile dunes at the southeastern edge of the tengger desert the results indicate that 1 human disturbance such as cultivation can accelerate the erodibility of the fixed aeolian sandy soil the ratio between total soil loss from the undisturbed soil and the cultivated soil is about 0 004 2 surface vegetation and microbiotic crust are the main factors responsible for the natural wind erodibility of the fixed sandy soil wind erosion rate increases with decreasing percent of the vegetation and crust cover 3 the grain size distribution shows a higher percentage of particles in the range 1 0 mm and a lower percentage in the range

the dynamic effects of moisture on the entrainment and transport of sand by wind abstract there is an increasing awareness of the influence of surface moisture on aeolian entrainment and transport of sediment existing wind tunnel studies have shown the impact of a limited range of moisture contents on entrainment thresholds but similar investigations are lacking in the field the research reported here investigated the influence of changes in surface moisture content on sand entrainment and transport on a meso tidal beach in anglesey north wales high frequency 1 hz wind velocities measured with hot wire anemometers were combined with grain impact data from a sensit monitor and mass flux measurements from a standard sand trap surface and near surface moisture contents were assessed gravimetrically from surface sand scrapes and also directly by using a thetaprobe critical threshold values for entrainment were specified using a modified form of the time fraction equivalence method stout j e zobeck t m 1996a establishing the threshold condition for soil movement in wind eroding fields proceedings of the international conference on air pollution from agricultural operations mwps c 3 kansas city 7 9 february 1996 pp 65 71 results indicate a time dependent change in dominant control of the sand transport system from moisture to wind speed dependent upon the moisture content of the surface sediment this interchange between controlling parameters on both entrainment and transport was very sensitive to prevailing moisture conditions and took place over a period of minutes to hours under conditions experienced in the experiments presented here the critical moisture threshold for sediment entrainment was determined to be between 4 and 6 higher than the 1 4 specified in previous wind tunnel experiments furthermore a moisture content of nearly 2 where moisture was adhered to transported sediment appeared to have little or no impact on the rate of sand flux

metamorphic evolution of the coesite bearing ultrahigh pressure terrane in the north qaidam northern tibet nw china widespread evidence for ultrahigh pressure uhp metamorphism is reported in the dulan eclogite bearing terrane the north qaidam altun hp uhp belt northern tibet this includes 1 coesite and associated uhp mineral inclusions in zircon separates from paragneiss and eclogite identified by laser raman spectroscopy 2 inclusions of quartz pseudomorphs after coesite and polycrystalline k feldspar quartz in eclogitic garnet and omphacite and 3 densely oriented sio2 lamellae in omphacitic clinopyroxene these lines of evidence demonstrate that the dulan region is a uhp metamorphic terrane in the north dulan belt ndb eclogites are characterized by the peak assemblage grt omp rt phn coe pseudomorph and retrograde symplectites of cpx ab and hbl pl the peak conditions of the ndb eclogites are p 2 9 3 2 gpa and t 631 687 c the eclogite shows a near isothermal decompression p t path suggesting a fast exhumation in the south dulan belt sdb three metamorphic stages are recognized in eclogites 1 a peak eclogite facies stage with the assemblage grt omp ky rt phn at p 2 9 3 3 gpa and t 729 746 c 2 a high pressure granulite facies stage with grt cpx jd 30 pl an24 29 scp at p 1 9 2 0 gpa t 873 948 c and 3 an amphibolite facies stage with the assemblage hbl pl ep czo at p 0 7 0 9 gpa and t 660 695 c the clockwise p t path of the sdb eclogites is different from the near isothermal decompression p t path from the ndb eclogites which suggests that the sdb was exhumed to a stable crustal depth at a slower rate in essence these two sub belts formed in different tectonic settings they both subducted to mantle depths of around 100 km but were exhumed to the earth s surface separately along different paths this uhp terrane plays an important role in understanding continental collision in north western china

the onset of india asia continental collision early steep subduction required by the timing of uhp metamorphism in the western himalaya ultrahigh pressure uhp rocks in the nw himalaya are some of the youngest on earth and allow testing of critical questions of uhp formation and exhumation and the timing of the india asia collision initial collision of india with asia is widely cited as being at 55f1 ma based on a paleomagnetically determined slowdown of india s plate velocity and as being at ca 51 ma based on the termination of marine carbonate deposition even relatively small changes in this collision age force large changes in tectonic reconstructions because of the rapid india asia convergence rate of 134 mm a at the time of collision new u pb shrimp dating of zircon shows that indian rocks of the tso morari complex reached uhp depths at 53 3f0 7 ma given the high rate of indian subduction this dating implies that indian continental crust arrived at the asian trench no later than 57f1 ma providing a metamorphic age for comparison with previous paleomagnetic and stratigraphic estimates india s collision with asia may be compared to modern processes in the timor region in which initiation of collision precedes both the slowing of the convergence rate and the termination of marine carbonate deposition the indian uhp rocks must have traveled rapidly along a short hence steep path into the mantle early continental subduction was at a steep angle probably vertical comparable to modern continental subduction in the hindu kush despite evidence for modern day low angle subduction of india beneath tibet oceanic slab break off likely coincided with exhumation of uhp terranes in the western himalaya and led to the initiation of low angle subduction and leucogranite generation d 2005 elsevier b v all rights reserved

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

mineralogical and isotopic characterization of graphite deposits in the western part of the north qaidam orogen and east kunlun orogen northeast tibetan plateau china abstract medium to high grade metamorphic rocks comprising numerous graphite deposits are widely distributed in the periphery of the qaidam basin northern tibetan plateau china we present textural xrd and raman spectroscopy characteristics of graphite 13c results of graphite and cogenetic calcite and 18o results of calcite in three graphite occurrences located at the periphery of qaidam basin graphite displays hexagonal platy flaky irregular polygonal ovate morphologies with occasional spherulitic textures graphite morphologies combined with xrd and raman spectroscopy indicate that graphite has relatively high crystallinity raman microspectroscopy of graphite shows that peak metamorphic temperatures vary between 690 and 801 c graphite 13cv pdb values range between 26 3 and 21 6 indicating organic carbon as the major carbon source for graphite calcite 13cv pdb and calcite 18ov smow values range between 10 8 and 3 9 and between 6 6 and 29 5 respectively calcite 13cv pdb results show that organic carbon was mixed with inorganic carbon which resulted in an increase of 13cv pdb calcite 18ov smow values indicate that the graphite deposits experienced late stage water rock interaction the positive and negative anomalies of calcite 13cv pdb indicate that organic matter oxidation and recycling locally occurred during the final stage of the great oxidation event the wide distribution of regional metamorphic organogenic graphite deposits provides evidence for large scale paleoproterozoic biological activity in the periphery of the qaidam basin

geochemistry and trace element behaviors of eclogite during its exhumation in the xitieshan terrane north qaidam uhp belt nw china abstract the xitieshan terrane located in the central part of the north qaidam ultrahigh pressure uhp metamorphic belt china is mainly composed of orthogneiss and paragneiss and a few intercalated eclogite layers and boudins based on their bulk rock tio 2 contents the eclogites can be subdivided into a high ti group tio 2 2 and a low ti group tio 2 e nd t and restricted i sr values and therefore provide further evidence for the formation of the protoliths of the eclogites in an oceanic environment on the other hand the sr nd isotopes of high ti eclogites show mainly positive but also some negative e nd t values and relatively broadly distributed i sr values indicating minor crustal contamination of the ocean floor basalts considering available 750 877 ma protolith ages preserved in zircon cores it is inferred that some of the eclogites derived from neoproterozoic protoliths were emplaced onto the crust far ahead of the paleozoic deep subduction while the other eclogites originate from a different oceanic crust e g the paleo qilian ocean indicating multiple orogenies in the geological history of the xitieshan terrane china whole rock and in situ la icp ms mineral trace element analyses of eclogites revealed two stages of fluid behavior during retrogression that correspond to the two exhumation stages uncovered by phase equilibrium calculations the mineral scale trace element distributions and trace element inheritance of newly formed amphibole from its precursors indicate that at the peak metamorphic stage m1 and at the earlier eclogite facies overprint m2 the fluid was internally controlled by the rock itself within a mafic lens the amount of water soluble elements e g rb sr ba u pb and lree observed in the whole rock compositions as well as in amphiboles increases from the core phengite bearing eclogite to the rim amphibolite and implies an external fluid source for the amphibolite facies retrogression m3 which should be helpful for the final exhumation of uhp eclogite

macroturbulent structure of open channel flow over gravel beds the turbulent structure of open channel flow over a mobile gravel bed was investigated in an 8 m long 0 3 m wide and 0 3 m deep tilting flume a flow visualization technique was used and complemented by measurements of flow velocity fluctuations near the bed the experiments reveal that turbulent flow consists of a sequence of large scale eddies with a vertical size close to the flow depth an average length equal to four to five depths and a width of about two depths the downstream motion of these eddies causes quasiperiodic fluctuations of the local flow velocity components the development of longitudinal troughs and ridges on the mobile bed and preferential transport of bed particles along troughs are related to the effect of the eddies the experimental results indicate that the depth scale eddies are an important turbulence mechanism contributing to sediment transport

first record of k cymrite in north qaidam uhp eclogite western china inclusions of polycrystalline k feldspar aggregates after k cymrite kalsi 3 o 8 nh 2 o were discovered in garnet from a dulan eclogite in the qaidam ultrahigh pressure uhp terrane western china the eclogite consists of garnet alm 56 grs 23 prp 20 sps 01 omphacite jd 35 aeg 6 aug 59 and minor rutile and apatite the 20 to 200 m inclusions vary in shape from prismatic hexagonal to rounded and exhibit palisade and mosaic textures host garnets show radial fractures similar to those surrounding quartz pseudomorphs after coesite some inclusions consist of almost end member k feldspar or 99 100 ab 0 1 polycrystalline aggregates whereas others are composed of 90 vol k feldspar or 96 99 ab 1 4 with minor secondary albite occurring along the margins of the inclusions raman spectra of k feldspar crystalline aggregates vary slightly reflecting various degrees of si al ordering and show a raman peak at 390 395 cm 1 typical for cymrite structure these characteristics of the k feldspar polycrystalline inclusions imply the presence of former k cymrite in the dulan eclogite formed at 3 gpa at 720 c the occurrence of k cymrite in uhp eclogite is significant because of its potential as an important carrier of crustal k and h 2 o to the upper mantle

river discharge measurements by using helicopter mounted radar 1 the united states geological survey and the university of washington collaborated on a series of initial experiments on the lewis toutle and cowlitz rivers during september 2000 and a detailed experiment on the cowlitz river during may 2001 to determine the feasibility of using helicopter mounted radar to measure river discharge surface velocities were measured using a pulsed doppler radar and river depth was measured using ground penetrating radar surface velocities were converted to mean velocities and horizontal registration of both velocity and depth measurements enabled the calculation of river discharge the magnitude of the uncertainty in velocity and depth indicate that the method error is in the range of 5 percent the results of this experiment indicate that helicopter mounted radar can make the rapid accurate discharge measurements that are needed in remote locations and during regional floods

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

geochemistry of high grade metamorphic rocks of the north qaidam mountains and their geological significance the high grade metamorphic basement in the north qaidam mountains nqd is composed mainly of jinning age metasedimentary rocks and crustally derived granites possibly accompanied by minor paleoproterozoic and archaean material based on their geochemistry the metasedimentary rocks are divided into two groups type i which makes up the bulk of the high grade metamorphic basement in the nqd is characterized by high k2o low na2o relatively high total rare earth elements treez114 357 ppm and weak fractionation of light lree and heavy hree rare earth elements la yb nz8 27 these rocks also have strong negative eu anomalies eu eu z0 3 0 6 type ii rocks crop out mainly in the wulan area and are characterized by relatively high mgo 2 2 4 1 wt lower total ree and strong fractionation of lree and hree la yb nz29 48 both types of metasedimentary rocks have similar nd isotope compositions with tdmz1 9 2 2 ga and 3ndzk4 1 to k8 5 the granites are compositionally similar to the type i metasedimentary rocks the high grade metamorphic basement of the nqd is similar to that in the qilian orogenic belt and the yangtze platform the central qilian nqd terrane was separated from the dunhuang alxa terrane before the jinning period and the two terranes belong to the south china block and north china craton respectively q 2006 elsevier ltd all rights reserved

sodic amphibole exsolutions in garnet from garnet peridotite north qaidam uhpm belt nw china implications for ultradeep origin and hydroxyl defects in mantle garnets two types of amphibole exsolution lamellae were discovered in garnet from a few garnet peridotites from the north qaidam ultrahigh pressure metamorphic belt northern tibet nw china the amphibole lamellae are strictly oriented in four directions corresponding to the isometric form 111 i e octahedron planes of garnet observations by transmission electron microscopy tem show that amphibole lamellae are topotaxtially concordant with the host garnet and possess 9 8 to 10 a lattice c spacing electron microprobe analysis reveals that these exsolved amphibole lamellae are high in na and ti the tem observations and recalculated compositions indicate that the oriented amphibole lamellae exsolved from original supersilicic majorites with high concentrations of na2o 0 3 wt and hydroxyl up to 1000 ppm by weight these results imply that the host garnet peridotites were formed at depths greater than 200 km and that garnet can be an important reservoir of water at such depths in the mantle

early paleozoic polyphase metamorphism in northern tibet china abstract the altun qilian kunlun orogenic system in the northern tibetan plateau is considered as the northernmost orogenic collage of the proto tethyan domain early paleozoic polyphase tectonothermal events related to the subduction of the proto tethyan ocean and subsequent collisional orogeny produced two dominant metamorphic belts the north altun nat north qilian nql hp lt metamorphic belt and south altun sat north qaidam nqd uhp metamorphic belt the nat nql hp lt metamorphic belt mainly consists of blueschist eclogite and hp metasediments eclogites record metamorphic conditions of 420 550 c and 21 25 kbar at 510 460 ma the hp lt metamorphic belt is associated with ophiolite subduction accretion complex and arc magmatic rocks suggesting that the nat nql is a typical early paleozoic accretionary orogenic belt in contrast the sat nqd uhp metamorphic belt is characterized by eclogite and garnet peridotite enclosed within continental orthogneiss and paragneiss these rocks record uhp metamorphism at t 700 c and p 27 kbar geochronology suggests that the uhp metamorphism occurred at 500 423 ma and eclogite protolith ages of 850 750 ma suggest that protoliths are related to neoproterozic continental rifting field relationships petrology and geochronology suggest that the sat nqd uhp metamorphic belt resulted from the deep subduction of continental crust moreover in the sat nqd uhp metamorphic belt two types of hp granulites have been recognized the first type of hp granulite was formed by overprinting of eclogites during exhumation the second type of hp granulite has a single metamorphic history and similar age to that of uhp eclogite penecontemporaneous metamorphic ages but different geothermal gradients between hp granulites and related uhp eclogite define a possible paired metamorphic belt which may be considered to be a diagnostic characteristic of collisional orogens high grade metamorphic rocks in the sat nqd commonly record barrovian type metamorphism although it remains unclear whether or not all of these rocks have an earlier u hp metamorphic history the low medium p barrovian metamorphism and associated magmatism are about 20 50 ma later than uhp metamorphism newly recognized eclogites in the northern part of the east kunlun mountains to the south of qaidam basin have a similar field relationship enclosed in continental gneiss and mineral assemblage to the nqd eclogites and a similar or slightly younger metamorphic age 410 430 ma the occurrence of similar continental type eclogites on two sides of the qaidam basin makes it necessary to reconsider the nature of the qaidam block the polyphase metamorphism in northern tibet can be linked to accretion and collisional orogenesis related to the evolution of prototethys through the early paleozoic

storminess variation during the last 6500 years as reconstructed from an ombrotrophic peat bog in halland southwest sweden cores taken from an ombrotrophic peat bog in the coastal zone of halland southwest sweden were examined for wind transported mineral grains pollen and humidity indicators the core covers the period from 6500 cal yr bp to present ombrotrophic conditions existed from ca 4200 cal yr bp onwards bog surface wetness fluctuated strongly until ca 3700 cal yr bp with an apparent dominance of dry summer conditions from 4800 4500 cal yr bp local wet shifts occurred around 4300 2800 2400 and 1500 cal yr bp whereas the most recent 600 years of the record show increasingly dry conditions mineral grain content interpreted as aeolian sand influx asi was used as a proxy for winter storm frequency and intensity until ca 1500 cal yr bp after which increasing human impact as reconstructed by pollen analysis became a second important potential cause for increased sand drift strongly increased storminess occurred at 4800 4200 2800 2200 1500 1100 and 400 50 cal yr bp indicating a dominance of cold and stormy winters during these periods many of these storm periods apparently coincide with storm events in other sites in southwestern scandinavia suggesting that our asi record reflects a regional scale climatic signal furthermore these stormy periods correlate to well known cold phases in the north atlantic region suggesting a link to large scale fluctuations in atmospheric circulation patterns less

geochronology geochemistry and isotope compositions of piaochi s type granitic intrusion in the qinling orogen central china petrogenesis and tectonic significance abstract s type peraluminous granite can crop out in various tectonic settings the paleozoic piaochi granitic intrusion is a large s type peraluminous intrusion located in the north qinling orogen and has important implication for its tectonic evolution though intensively studied the age and tectonic setting of this intrusion are still controversial in this study we carried out an integrated study of zircon u pb age major and trace elements and sr nd hf o isotope compositions for the piaochi intrusion with aims to constrain its petrogenesis and tectonic significance sims and la icpms u pb zircon data obtained from magmatic zircons indicate that the piaochi intrusion was emplaced at 473 4 ma and contained ca 490 ma inherited zircons the granite samples from the piaochi intrusion show typical s type characteristics such as the relatively moderate aluminum saturation index 1 00 1 08 low zirconium saturation temperatures occurrences of muscovite and high zircon 18 o values 8 70 to 9 54 the relatively low sm nd 0 13 0 20 and feo t mgo ratios 2 21 3 9 suggest that the granites are unfractionated the geochemical compositions reveal that they were derived from partial melting of a clay poor but plagioclase and biotite rich psammitic source similar to metasedimentary rocks outcropping in the north qinling unit moreover the piaochi granites are moderately depleted in eu and heavy rare earth elements and have relatively high la yb n values 22 8 56 8 implying a high pressure plagioclase poor and garnet rich residual assemblage the piaochi granites have high and variable initial 87 sr 86 sr ratios 0 72167 0 72511 and low e nd t from 10 23 to 8 71 values with two stage nd model ages t dm2 of 1 91 2 03 ga which are comparable with those of supracrustal materials in the north qinling unit in addition our results show that the ca 470 ma magmatic zircons display a narrow e hf t array within those of the inherited cores these imply that the piaochi granites inherited their isotopic characteristics wholly from their sources and the hf isotopes might have been differently homogenized during the partial melting our new zircon u pb ages indicate that the piaochi granites were emplaced after the climax of the uhp metamorphism coeval with later retrograde metamorphism during exhumation therefore we suggest that the formation of the early paleozoic piaochi intrusion was triggered by the exhumation of the uhp rocks

geochemistry zircon upb geochronology and luhf isotopic composition of eclogites and their host gneisses in the dulan area north qaidam uhp terrane new evidence for deep continental subduction abstract in this study we link zircon u pb shrimp and la icp ms geochronology and the lu hf isotopic composition of eclogites and their host gneisses schists with whole rock geochemistry of eclogites in the dulan area to constrain their protoliths and metamorphic relationships u pb dating suggests that the protolith of one of the eclogites was a neoproterozoic mafic intrusive rock 828 58 ma and the protolith of enclosing orthogneiss was an early neoproterozoic granitoid 923 12 ma detrital zircons from grt bearing mica schists yield ages of 0 9 2 5 ga with a dominant range of 1 0 1 8 ga indicating sedimentary sources from neoproterozoic to neoarchean crust and a depositional age 0 9 ga the matching metamorphic ages of eclogites 438 5 ma 436 4 ma and their country rocks grt bearing mica schists 438 4 ma 439 8 ma orthogneiss 427 8 ma indicate that all studied samples experienced coeval early paleozoic hp uhp metamorphism the u pb ages and hf isotopic compositions of the inherited magmatic zircon cores of an eclogite sample e hf 800 2 6 9 2 t dm1 1 0 1 3 ga t dm2 1 1 1 4 ga suggest that the protolith may be derived from neoproterozoic depleted mantle with variable proportions of an older crustal component the magmatic zircon cores of the orthogneiss e hf 900 7 3 to 0 2 t dm2 1 8 2 1 ga suggest that the parental magma was derived from a paleoproterozoic crustal source hf isotopic compositions of the detrital zircons from the metasediments e hf t 19 4 to 10 6 suggest three crust formation and reworking events 1 archean t dm2 2 7 2 9 ga juvenile crust reworked at 2 5 ga 2 early paleoproterozoic t dm2 2 3 2 5 ga juvenile crust reworked at 1 8 ga and 3 late paleoproterozoic t dm2 1 5 1 9 ga juvenile crust reworked in the neoproterozoic whole rock geochemical data suggest that the protoliths of the dulan eclogites were probably derived from a continental rift or an incipient oceanic basin rather than a large long lived ocean basin thus combined with field relationships petrology geochemistry zircon u pb dating and the lu hf isotopic analysis presented in this paper and reported from previous studies we suggest that the dulan eclogites and their country rocks experienced a common uhp metamorphism during late ordovician deep continental subduction

slab breakoff a model for caledonian late granite syn collisional magmatism in the orthotectonic metamorphic zone of scotland and donegal ireland abstract none of the existing models for calc alkaline late granite siluro devonian genesis in the metamorphic caledonian orogenic belt of ireland and scotland fully explains their spatial age or chemical character a consistent model must involve the closure of iapetus ocean where slab breakoff is a natural consequence of attempted subduction of continental crust expected outcome is a long linear belt of high k calc alkaline magmas some with characteristic trace element signatures specifically high ba sr and zr other features include the critical magmatic association of coeval appinite and granite rapid uplift erosion and the low grade regional metamorphism in the southern uplands the linear heat pulse on breakoff is spatially intensity and time limited producing small volume melts emplaced as separated plutons over a short time span magmatism in the caledonian metamorphic belt is accurately accounted for by slab breakoff on collision of baltica with the scoto greenland margin during the scandian orogeny following iapetus ocean closure the two chemically isotopically and areally distinctive suites in the metamorphic belt in scotland viz the argyll and cairngorm suites can be modelled by reference to the donegal granites where sequential partial melting of new lamprophyric underplated crust then shallower old crust as heat conduction moved up through the crust on slab breakoff produced magmas characteristic of the two suites

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

timing and mechanism of formation and exhumation of the northern qaidam ultrahigh pressure metamorphic belt abstract the qilian caledonian orogenic belt on the north margin of the qinghai tibet plateau were formed by convergence and collision of the alxa terrain qilian terrain and qaidam terrain the 350 km long wnw ese trending north qaidam ultrahigh pressure uhp metamorphic belt lying between the qilian and qaidam terrains was formed between 495 and 440 ma by deep subduction of the south qilian sea and the qaidam continental crust beneath the qilian terrain the uhp belt was exhumed by a process of oblique extrusion during transformation from normal to oblique intracontinental subduction between the qilian and qaidam terrains exhumation began at 470 460 ma and was completed by 406 400 ma exhumation structures are well preserved in the uhp rocks and record extensive retrograde metamorphism

petrology geochemistry zircon u pb dating and lu hf isotope of granitic leucosomes within felsic gneiss from the north qaidam uhp terrane constraints on the timing and nature of partial melting abstract granitic leucosomes are widely distributed within felsic gneiss in the north qaidam ultrahigh pressure uhp metamorphic terrane in western china which is crucial to understanding the relationships between partial melting metamorphic evolution and orogenic processes we have applied petrology whole rock geochemistry and sr nd isotope zircon u pb geochronology trace element composition and lu hf isotope of these granitic leucosomes to determine the nature and timing of partial melting of these rocks anatexis of the felsic gneiss is evidenced by 1 highly cuspate elongated feldspar grains along quartz quartz and quartz feldspar boundaries 2 cuspate wedge shaped pockets of k feldspar quartz plagioclase muscovite along the boundaries of quartz and or plagioclase and 3 felsic veinlets of k feldspar quartz plagioclase muscovite along grain boundaries major elements feo t mno mgo and tio 2 as well as lrees hrees and hfses are mainly retained in the melanosomes whereas the large ion lithophile elements liles e g rb ba k sr pb are preferentially partitioned into the granitic leucosomes three discrete u pb ages are recorded in the zoned zircons from the melanosomes and granitic leucosomes the inherited magmatic pre metamorphic zircon cores from melanosomes and granitic leucosomes contain quartz feldspar inclusions and record a neoproterozoic protolith age of approximately 950 ma the unzoned zircon mantles in the melanosomes and granitic leucosomes show characteristics similar to metamorphic zircons in terms of such as remarkably flat heavy rare earth element hree patterns an absence of obviously negative eu anomalies and low th u ratios these zircon mantles record an eclogite facies metamorphic age of 444 449 ma the last discrete age at 433 435 ma is preserved in anatectic zircon rims which display pronounced oscillatory zoning and contain felsic mineral inclusions of k feldspar plagioclase quartz the anatectic zircons have negative eu anomalies and pronounced positive ce anomalies and their low th u ratios and lu hf isotope features that are indistinguishable from those of the metamorphic domains the similarity in lu hf signatures indicates a closed system whereby no hf was added either from the outside via fluids or surprisingly from the pre metamorphic cores during partial melting muscovite relicts coexist with cuspate feldspars in the granitic leucosomes suggesting that the anatectic melts originate from dehydration melting due to breakdown of the muscovite in the felsic gneiss in conclusion an integrated study of the petrology geochronology and geochemistry demonstrates that partial melting of felsic gneiss in the nqd uhp terrane could mainly occurred during the initial retrogression stage and anatectic melt crystallized probably under granulite facies conditions

rapid hydrological changes during the holocene revealed by stable isotope records of lacustrine carbonates from lake igelsjon southern sweden a holocene sediment sequence from lake igelsjon south central sweden was studied by stable oxygen and carbon isotope analyses of different carbonate components the deposit which covers the time span from ca 11 500 cal bp to the present was laid down in a small kettle hole lake the hydrological balance of which is presently dominated by groundwater flow isotopic records obtained on bulk carbonates originating mainly from summer produced calcitic algal encrustations exhibit several rapid shifts of more than 2parts per thousand likely reflecting pronounced hydrological variations corresponding isotopic data obtained on calcitic gastropod opercula from parts of the profile show subdued responses to major climatic shifts probably related to an extended calcification season the isotopic records were complemented by studies of modern isotope hydrology and our interpretations are based on a simplistic climate hydrology model in which variations in groundwater generation within the lake catchment produce changes in groundwater level and related adjustments of lake level and surface volume ratio of the basin during the ice free season assumed periods of decreased lake volume in a relatively dry climate low lake level are characterised by enrichment in o 18 and c 13 resulting from increased evaporation inflow ratio and atmospheric equilibration respectively in clear contrast to this situation intervals of more humid climatic conditions give rise to increased lake volume high lake level possibly surface over flow and relatively depleted isotopic ratios relatively humid conditions which may correlate to a wide spread cooling event recorded by various proxies across the north atlantic region are indicated by distinct isotopic shifts at ca 8300 and 8000 cal bp bracketing a period of o 18 depletion the period between ca 8000 and 4000 cal bp was characterised by relatively dry and stable climatic conditions whereas the subsequent part of the holocene experienced a more humid and variable climate following marked and coherent depletions in o 18 and c 13 at ca 4000 cal bp c 2002 elsevier science ltd all rights reserved less

remote measurement of river discharge using thermal particle image velocimetry piv and various sources of bathymetric information abstract although river discharge is a fundamental hydrologic quantity conventional methods of streamgaging are impractical expensive and potentially dangerous in remote locations this study evaluated the potential for measuring discharge via various forms of remote sensing primarily thermal imaging of flow velocities but also spectrally based depth retrieval from passive optical image data we acquired thermal image time series from bridges spanning five streams in alaska and observed strong agreement between velocities measured in situ and those inferred by particle image velocimetry piv which quantified advection of thermal features by the flow the resulting surface velocities were converted to depth averaged velocities by applying site specific calibrated velocity indices field spectra from three clear flowing streams provided strong relationships between depth and reflectance suggesting that under favorable conditions spectrally based bathymetric mapping could complement thermal piv in a hybrid approach to remote sensing of river discharge this strategy would not be applicable to larger more turbid rivers however a more flexible and efficient alternative might involve inferring depth from thermal data based on relationships between depth and integral length scales of turbulent fluctuations in temperature captured as variations in image brightness we observed moderately strong correlations for a site aggregated data set that reduced station to station variability but encompassed a broad range of depths discharges calculated using thermal piv derived velocities were within 15 of in situ measurements when combined with depths measured directly in the field or estimated from field spectra and within 40 when the depth information also was derived from thermal images the results of this initial proof of concept investigation suggest that remote sensing techniques could facilitate measurement of river discharge

island arc magmatism in relation to the evolution of the crust and mantle abstract one aspect of the evolution of the earth s mantle is the development through geologic time of the continental crust a popular hypothesis is that the earth s crust has developed through the magmatic events associated with plate movements a two stage melting process involving generation of ocean ridge basalts followed by subduction and partial remelting of the oceanic lithosphere to form andesitic suites has been invoked as the major continental crust forming magmatic cycle however there is chemical and isotopic evidence for the composition of continental crust and arcs that is in conflict with the broad consequences predicted by this hypothesis the average composition of the upper continental crust has been fairly readily determined as granodioritic but the composition of the lower crust is less certain seismological and petrological evidence suggest that a substantial portion of the lower crust is basaltic in character therefore it cannot be concluded that the bulk average crust corresponds to andesite again the rock type most frequently collected in many arcs is andesite but the conclusion that the whole arc pile is of this composition is illogical and not supported by much field and petrologic evidence the peripheral accretion of arcs to continents is well documented for post palaeozoic epochs so that the nature of arc magma sources is critically relevant to the processes of continental crustal growth a large body of data on arc magmas can be explained by the hypothesis that the superjacent upper mantle wedge rather than the subducted lithosphere itself is the major source of arc erupted melts for many oceanic arcs isotopic evidence 87 sr 86 sr 143 nd 144 nd rules out the possibility that they constitute appropriate bulk crustal additions for the development of continents continental crustal growth may therefore either have changed in essential chemical isotopic character since the cambrian or arc magmas derived from chondritic type or lil enriched sources may be the only volumetrically significant additions to continental crust

geochemical and zircon u pb and hf isotopic study of the baijuhuajian metaluminous a type granite extension at 125 100 ma and its tectonic significance for south china abstract the early cretaceous baijuhuajian pluton is an a type granitic intrusion emplaced along the jiangshan shaoxing jssx fault zone in western zhejiang province se south china it intruded into a late jurassic volcanic basin bounded by proterozoic sandstone and siltstone the granite has a coarse grained porphyritic texture and is composed of alkali feldspar phenocrysts in a matrix of k feldspar quartz plagioclase and biotite the pluton has a clear a type geochemical signature e g it is metaluminous a cnk 1 0 and has high sio2 75 to 78 wt total alkalis na2o k2o 4 8 to 8 5 wt rare earth elements total ree 228 to 438 ppm hfse and fe feot feot mgo 0 87 to 0 97 on the other hand it is characterized by low cao 0 51 to 1 01 wt tio2 0 06 to 0 13 wt p2o5 below detection and sr 7 0 to 9 5 ppm the hypersolvus texture and fine grained groundmass indicate emplacement at a shallow depth shrimp u pb zircon dating yielded a weighted mean 206pb 238u age of 126 3 ma and zircons from this pluton give ehf t values between 0 52 and 4 24 suggesting the importance of juvenile material in the magma source most of the plutonic rocks in southeast china are calc alkaline subduction related intrusions of jurassic and cretaceous age previous studies suggested that the sparse a type granites in south china were emplaced in two episodes 190 155 ma in the inland area and 100 ma along the coastal area in se south china our study of the baijuhuajian granite together with the coeval suzhou a type granite 123 ma in jiangsu province defines an important extensional event between 125 and 100 ma considering the available data for the mesozoic igneous rocks in south china we suggest that subduction of the pacific plate in the mesozoic produced voluminous calc alkaline granitoids and volcanic rocks with a younging trend from west to east the a type granites were generated during periods of local extension at 190 155 ma and 125 100 ma perhaps corresponding to localized rollback of the pacific plate

geochemical constraints on the petrogenesis of granitoids in the east kunlun orogenic belt northern tibetan plateau implications for continental crust growth through syn collisional felsic magmatism early triassic syn collisional granitoids with mafic magmatic enclaves mmes crop out along the entire east kunlun orogenic belt ekob at the northern margin of the tibetan plateau they are andesitic in composition and enriched in light rare earth elements lrees with a flat heavy ree hree pattern their average composition resembles that of the bulk continental crust the enclosed mmes have the same mineralogy as their host granitoids but contain a greater mode of mafic minerals amphibole and biotite and thus have higher hree abundances zircon u pb dating shows that both the granitoid hosts and mmes have the same crystallization age of similar to 250 ma and indistinguishable bulk rock sr nd pb hf isotope compositions i sr of 0 7080 0 7116 varying pb 206 pb 204 i of 18 53 19 32 essentially constant epsilon nd t of 5 3 to 2 1 and a small range of positive epsilon hf t mostly 1 7 5 2 the complete isotopic overlapping between the granitoid hosts and the mmes is understood to reflect that the mmes are disintegrated cumulates formed at an early stage of the granitoid magma evolution within the same magmatic system the isotopic data set reveals that the granitoids are variably evolved melts produced by partial melting of the subducted paleo tethyan oceanic crust with terrigenous sediments under amphibolite facies conditions in response to the continental collision c 2014 elsevier b v all rights reserved

paleozoic granitic magmatism and tectonic evolution of the south altun block nw china constraints from zircon u pb dating and lu hf isotope geochemistry abstract the south altun orogenic belt saob consisting of the south altun block sab and the south altun continental block sacb is one of several important orogenic belts in nw china numerous granite bodies are widely distributed in the sab however the petrogenesis and tectonic environment of these granites and their relationships to those of the sacb central altun continental block cacb north altun block nab qilian block qlb and north qaidam block nqb remain unclear in this investigation we selected the sab granites for detailed study and explore the petrogenesis employing bulk rock geochemistry zircon u pb dating and hf isotopic analysis zircon u pb la icp ms dating of the granites from the sab identified seven spatially distinct paleozoic plutonic suites a yigan 352 343 ma b baiganhu 448 444 ma c west mangya 444 435 ma d aketishan 265 ma e chaishuigou 406 ma f changchungou 469 ma and g north mangya 462 ma based on previous research combined with our new u pb dating and bulk rock geochemical investigations in the sab we identdified six distinct episodes of granitoid emplacement episodes 1 and 2 quartz diorite granodiorite monzogranite with i type affinities and ages of 503 497 ma and 483 458 ma respectively episode 3 granodiorite monzogranite syenogranite with i and s type affinities and an age of 456 432 ma episode 4 monzogranite syenogranite alkali feldspar granite with a type affinities and an age of 424 385 ma episode 5 granodiorite monzogranite with s type affinities and an age of 352 338 ma and episode 6 quartz diorite monzogranite syenogranite with i type affinities and an age of 265 264 ma zircon lu hf isotope analyses from various episodes show that ehf t values are positive in most cases but negative for a small number of inherited xenocrystic zircons source rocks were mainly juvenile crust evidently mixed with minor ancient continental material based on our new results integrated with regional geological data we conclude that episodes 1 and 2 granitic magma generations were related to the subduction of oceanic crust episode 3 to post collisional partial melting episode 4 to the isostatic adjustment of orogenic blocks after plate suturing episode 5 to petrotectonic thickening of the altun crust and episode 6 to altun fault transcurrent slip attending kunlun paleo tethys subduction

estimating bed shear stress from remotely measured surface turbulent dissipation fields in open channel flows synoptic information on bed shear stress is necessary in predicting the transport of sediments and environmental contaminants in rivers and open channels existing methods of estimating bed shear stress typically involve measuring vertical profiles of streamwise velocity or reynolds stress and taking advantage of the logarithmic or the constant stress region respectively to determine friction velocity and subsequently bed shear stress while effective these methods yield local measurements of bed shear stress only direct measurements of bed shear stress can also be obtained through measurements with a drag plate however this method yields average shear stress information over the area of the plate and is impractical for large scale implementation in the field here we present a method capable of providing continuous synoptic measurements of bed shear stress over a large field of view a series of large scale particle image velocimetry lspiv and acoustic doppler velocimetry adv measurements were made in a variety of flows generated in a wide open channel facility turbulent dissipation is calculated on the free surface from the 2 d lspiv results and is correlated with near surface adv measurements of turbulent dissipation in the water column the adv results are consistent with the nezu 1977 established relationship for the vertical variation of turbulent dissipation in the water column knowledge of the correlation between free surface and near surface dissipation values coupled with nezu s 1977 relationship allow a robust and accurate estimate of friction velocity to be made and subsequently shear stress at the bed can be estimated this article is protected by copyright all rights reserved

syn collisional granitoids in the qilian block on the northern tibetan plateau a long lasting magmatism since continental collision through slab steepening in this paper we present a new model that can explain the large zircon age spectrum of similar to 510 420 ma within a single sample from the gangcha gcha biotite granodiorite and the huangyuan hy two mica monzogranite on the northern tibetan plateau the large age spread recorded in zircons is characteristic of granitoid samples from the studied region which is best explained by the long lasting magmatism since the onset of continental collision at similar to 500 ma followed by slab steepening and the ultimate slab break off at similar to 450 ma these granitoids have a large major and trace element compositional variation but limited initial sr i sr 450 0 709 to 0 715 nd epsilon nd 450 6 5 to 3 7 hf epsilon hf 450 4 3 to 1 5 and pb pb 206 pb 204 450 17 70 to 17 17 pb 207 pb 204 450 15 60 to 15 69 pb 208 pb 204 450 38 04 to 38 73 isotopic variation the small negative whole rock epsilon nd 450 and epsilon hf 450 values are most consistent with the granitoid source being dominated by subducted seafloor materials the inherited zircons with large negative epsilon hf 450 values e g 50 are indicative of input from the lower continental crust and subducted sediments the correlated variations among major elements trace elements and radiogenic isotopes are best interpreted as reflecting melting induced mixing of a compositionally heterogeneous source with superimposed effect of varying extent of fractional crystallization and crustal assimilation the inherited zircons of palaeo proterozoic age and the archean crustal model ages signify the involvement of ancient basement rocks c 2016 elsevier b v all rights reserved

remote determination of the velocity index and mean streamwise velocity profiles when determining volumetric discharge from surface measurements of currents in a river or open channel the velocity index is typically used to convert surface velocities to depth averaged velocities the velocity index is given by k ub usurf where ub is the depth averaged velocity and usurf is the local surface velocity the usgs united states geological survey standard value for this coefficient k 0 85 was determined from a series of laboratory experiments and has been widely used in the field and in laboratory measurements of volumetric discharge despite evidence that the velocity index is site specific numerous studies have documented that the velocity index varies with reynolds number flow depth relative bed roughness and with the presence of secondary flows a remote method of determining depth averaged velocity and hence the velocity index is developed here the technique leverages the findings of johnson and cowen 2017 and permits remote determination of the velocity power law exponent thereby enabling remote prediction of the vertical structure of the mean streamwise velocity the depth averaged velocity and the velocity index

early palaeozoic north qaidam uhp metamorphic belt on the north eastern tibetan plateau and a paired subduction model an early palaeozoic uhp metamorphic belt was recently discovered in the north qaidam mountains in the north eastern part of the tibet plateau the belt contains abundant eclogite with lesser amounts of garnet peridotite and gneiss the paragneiss contains abundant zircon with coesite inclusions whereas the eclogite has garnet with coesite pseudomorphs and omphacite with exsolved quartz the calculated peak metamorphic conditions for the eclogite are t 730 c and p 2 8 gpa the garnet peridotites are magnesium rich with mg s 100 mg mg fe up to 92 olivine in the peridotites is highly magnesian fo 91 5 and tio2 poor and is typical of low t garnet peridotites calculated peak metamorphic conditions for the peridotites are t 837 c and p 2 5 gpa u pb and sm nd isotope dating indicate that continental subduction started during the early ordovician 495 ma the north qaidam uhp together with the north qilian hp belt about 300 km to the north constitute a pair of genetically related early palaeozoic subduction zones along the northern margin of the tibet plateau

record of multiple stage channelized fluid and melt activities in deeply subducted slab from zircon u pb age and hf o isotope compositions abstract geochemical features of island arc rocks require two slab derived components of a melt and a fluid added to their sources these two liquids may unite to an intermediate aqueous melt at the base of volcanic arc direct evidence of this process has been scarce yet here we present an integrated study of in situ u pb age trace element and o hf isotope for zircons from a suite of a quartz vein a felsic vein their host eclogite and surrounding gneiss at the xitieshan uhp terrane of the north qaidam metamorphic belt nqmb oscillatory zoned zircons from the quartz vein are enriched in u li nb and ree with a formation age of 442 6 ma consistent with the timing of the peak uhp metamorphism this demonstrates there is no temporal gap between the uhp metamorphism and fluid flow in the xitieshan terrane in particular the oscillatory zoned zircons of the quartz vein have similar hf isotope compositions to zircons from the surrounding gneiss but variable o isotope compositions between the host eclogite and surrounding gneiss the fluid from surrounded gneiss was thus an aqueous melt with high transport ability for lu and hf and o while the fluid from the host eclogite was an aqueous fluid only with the ability to transport o according to the similar behaviors of granitic rock and sediment it is inferred that a channelized hydrous melt can be formed in the downgoing sediment layer where an aqueous fluid can be formed from underlying basalt and or peridotite layers at the sub arc depth the two types of fluid are fed to the overlying mantle wedge from subducting slab to form island arc rock by contrast the zircons in the felsic vein yield a weighted mean 206pb 238u age of 420 4 ma which can be regard as the timing of partial melting during the exhumed stage for the xitieshan uhp rocks the zircon o and hf isotopic features of the felsic vein are between the country gneiss and host eclogite compatible with their emanating from hydrous melt of both the eclogite and gneiss during the exhumation stage of the uhp rocks this indicates that hydrous melt would be released from both the sediment and basalt or peridotite layers of the subducting slabs at relatively shallow depth

the early paleozoic xitieshan syn collisional granite in the north qaidam ultrahigh pressure metamorphic belt nw china petrogenesis and implications for continental crust growth abstract syn collisional magmatism produced by partial melting of subducted oceanic and continental crust during the continental collision plays an important role in understanding the orogenic evolution and crustal growth this contribution reports zircon la icpms u pb ages and hf isotopic compositions whole rock major and trace elements and sr nd isotopic compositions of syn collisional xitieshan intrusion within the north qaidam ultrahigh pressure metamorphic uhpm belt to study its petrogenesis and contribution to continental crust growth la icpms zircon u pb dating of the xitieshan granite yields magmatic crystallization ages of 441 2 ma and 442 2 ma which are consistent with the peak age of ultrahigh pressure eclogite facies metamorphism in the xiteishan terrane the temporal correlation between them confirms that the xitieshan granite was products of syn collisional magmatism during the continental collision between qaidam and qilian blocks these granites show high k calc alkaline and slightly peraluminous signature low zirconium saturation temperatures and high contents of k2o with the s type characteristics they have rare earth element and trace element patterns resembling those of bulk continental crust with strong fractionation of light and heavy rare earth elements la yb n 19 26 moderately eu negative anomalies eu 0 65 0 71 and the obviously nb ta p and ti negative anomalies the xitieshan granite also exhibits remarkable sr nd isotopic differences initial 87sr 86sr 0 70920 0 71080 and end t 4 54 4 11 from the contemporaneous granites within north qaidam uhpm belt combined with the positive ehf t 0 5 5 3 and ages of inherited zircons 475 518 ma the magmatism is best explained as resulting from melting of subducted oceanic and continental crust during continental collision isotopic mixing calculations suggest that ca 28 35 ocean crust and ca 65 72 continental materials contribute to the origin of the xitieshan granite thus the syn collisional felsic magmatism represents juvenile crust with input of oceanic crustal materials derived from the depleted mantle and the hypothesis continental collision zones are primary sites for net continental crust growth is applicable in the north qaidam

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

post collisional magmatism consequences of uhpm terrane exhumation and orogen collapse n qaidam uhpm belt nw china exhumation of subducted slabs and extensional collapse of orogens are the main tectonic processes in ancient and modern continental collisional zones magmatism during these two processes may play important roles in understanding reworking and growth of the continental crust we report here that a series of plutonic magmas including intrusions of two mica granite tonalite granodiorite biotite monzogranite porphyritic biotite granite and diorite as well as contemporaneous mafic dykes have been recognized in dulan edogite bearing terrane the north qaidam ultra high pressure metamorphic uhpm belt the magmatism represented by these plutons is temporally similar to 20 30 million years mys younger than the uhpm age lasting for similar to 40 mys and derived from different sources with different mechanisms the magmatism was initiated by exhumation of uhpm terranes during which strongly peraluminous two mica granite and metaluminous tonalite were produced respectively by decompression melting of the exhumed uhpm upper and lower continental crust respectively the genesis of mafic magmatic enclave mme hosting granodiorite with a clear hybrid signature and coeval biotite monzogranite reflected the upwelling of asthenospheric mantle by extension of lithosphere during the orogen collapse it was induced by detachment of the subducted lithospheric mantle which then brought heat and mantle material into continental crust and triggered the partial melting of the exhumed uhpm continental crust and gave rise to mixing of crustal and mantle melts porphyritic biotite granite reflects a late melting event of continental crust diorite marked by high magnesium content represents mantle melts with slight crustal contamination which implies that the orogen has been unrooted and collapsed completely the post collisional magmatism of the north qaidam belt provides an improved understanding for the late thermal and tectonic evolution of a uhpm continental collision zone c 2014 elsevier b v all rights reserved

the growth of the continent through geological time studied by nd isotope analysis of shales abstract we determined the nd isotopic composition and the sm nd ratios in a series of australian shales ranging from 0 2 gy to 3 3 gy the first result of this study is the constancy of the sm nd ratio in these shales as in granitoids secondly the initial 143nd 144nd ratio gives a regular curve decreasing through geological time both results confirm that shales are representative samples of the continental crust when insoluble elements like ree are studied we calculated their nd model ages of crustal differentiation the model ages regularly decrease with the stratigraphic ages and after 2 gy the curve flattens and tends to an asymptotic value at around 1 8 gy the significance of the shales is that they represent a mixture of continental materials and we consider the model age of such a mixture directly linked with the mean age of the continental portion feeding the sedimentary basin from these results we deduce a quantitative model of the growth curve of the continental source of the shales taking into account the effects of erosion which selectively sample recent mountains relative to shield areas we propose that the results obtained here are representative of the whole gondwana continent having studied the case of the australian shales we try to extend our study first we applied our quantitative approach to the recent results obtained by o nions et al on north atlantic provinces the continental growth curves obtained by our inversion procedure are quite distinct from the australian shales showing the regional character of shales with these two cases studied we try to compare our results with the already developed model for continental growth the consideration of the surface conservative versus surface non conservative models clearly show the non uniqueness of the geological interpretation of the growth curve on the other hand we have calculated for each case the recycling rate versus geological time by comparing the growth curve with the hurley rand province age curve such recycling increases with time in agreement with the data obtained on nd and sr initial ratios on granitoids

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

p t t evolution of orogenic belts and the causes of regional metamorphism barrow 1893 introduced three important ideas that furthered understanding of metamorphic processes i the use of critical index minerals in argillaceous rocks to define metamorphic zones and elucidate spatial features of regional metamorphism ii the concept of progressive metamorphism and iii the concept of magmatic advection of heat as a possible cause of regional metamorphism this article expands upon these themes by reviewing our understanding of the dynamic evolution of orogenic belts as interpreted from the p t t paths of metamorphic rocks and by considering the likely causes of the different kinds of regional metamorphism that we observe within orogenic belts understanding metamorphic rocks allows the distinction of two fundamentally different types of orogenic belt defined by relative timing of maximum t and maximum p orogenic belts characterized by clockwise p t paths achieved maximum p before maximum t the metamorphic peak normally post dated early deformation within the belt and additional heating above the normal conductive flux has been related to the amount of overthickening by contrast orogenic belts characterized by counterclockwise p t paths achieved maximum t before maximum p the metamorphic peak normally pre dated or was synchronous with early deformation within the belt and additional heating above the normal conductive flux has been related to the emplacement of plutons techniques used to constrain portions of p t t paths include the use of mineral inclusion suites in porphyroblasts and reaction textures thermobarometry the use of fluid inclusions thermodynamic approaches such as the gibbs method radiogenic isotope dating fission track studies and numerical modelling we can utilize specific mineral parageneses in suitable rocks to determine individual p t t paths and a set of p t t paths from one orogenic belt allows us to interpret the spatial variation in dynamic evolution of the metamorphism recent advances are reviewed with reference to collision metamorphism high temperature low pressure metamorphism granulite metamorphism and subduction zone metamorphism and some important directions for future work are indicated

structure of turbulence in compound channel flows the structure of turbulence in compound channel flows is examined in a laboratory study shear stresses and turbulence intensities are measured in a channel comprised of a deep central section flanked on either side by wide shallow berms flood plains the study concerns the nature of turbulence in the mixing regions separating the deep and shallow zones also studied is the mixing region s effect on the compound flow field for both wide and narrow channel conditions under narrow channel conditions the mixing process extends to the center of the main channel flow field however under wide channel conditions the central region is not affected and observed turbulence levels at the center of the main channel are in close agreement with theoretical values for a two dimensional flow field apparent shear stress at the vertical main channel flood plain interface was measured directly and compared favorably with estimated values based on momentum considerations