variations of chemical features in a monsoon glacier watershed southeastern tibet plateau the ph ec electric conductivity 18o and major ions in melt water precipitation runoff and groundwater samples which were collected in baishui basin were analyzed based on chemical analysis the characteristic variations are analyzed in this paper the melt water precipitation runoff and groundwater were ca2 mg2 hco3 type with similar ion compositions but showed different ion concentrations normally the content is high in groundwater and runoff water but low in melt water and precipitation from the upper basin glacier downward there was a general increasing trend for the total ion concentrations in basin hco3 and ca2 accounted for more than 80 of total ions in samples indicating that ions mainly came from limestone and water typical of carbonate solution water water rock interaction is the significant contributor to water geochemistry the concentration of inorganic ion in melt water had an obvious diurnal variation with temperature change the 18o values increases with the altitude decrease the similarity of 18o in runoff and groundwater samples was due to their frequent transformation in karst regions

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

tonian ediacaran tectonomagmatic evolution of west avalonia and its ediacaran early cambrian interactions with ganderia an example of complex terrane transfer due to arc arc collision

decompression induced growth of albite porphyroblasts fleur de lys supergroup western newfoundland abstract albite porphyroblasts are widely distributed in pelitic and semi pelitic schists of the fleur de lys supergroup western newfoundland textures and mineral assemblages indicate that albite grew during nearly isothermal decompression from p t conditions of about 500 c 9 kbar to conditions of 550 c 6 5 kbar three compositional varieties of albite bearing schists here termed pmaq paragonite muscovite albite quartz mmaq microcline muscovite albite quartz and pmmq paragonite muscovite margarite quartz can be distinguished on the basis of pre porphyroblast mineral assemblages analysis of these assemblages in terms of the composition of the coexisting fluid log a na h versus log a k h suggests that as pressure and temperature changed the stability field of albite expanded at the expense of coexisting matrix phyllosilicates this promoted growth of albite on pre existing or newly formed nuclei late oligoclase in pmaq and pmmq samples is associated with replacement of matrix garnet by plagioclase mica chlorite particularly in strongly sheared samples

metamorphic evolution of a subduction complex south shetland islands antarctica a subduction complex composed of ocean floor material mixed with arc derived metasediments crops out in the elephant island group and at smith island south shetland islands antarctica with metamorphic ages of 120 80 ma and 58 47 ma respectively seven metamorphic zones i vii mapped on elephant island delineate a gradual increase in metamorphic grade from the pumpellyite actinolite facies through the crossite epidote blueschist facies to the lower amphibolite facies geothermometry in garnet amphibole and garnet biotite pairs yields temperatures of about 350 c in zone iii to about 525 c in zone vii pressures were estimated on the basis of si content in white mica al2o3 content in alkali amphibole nam4 aliv in sodic calcic and calcic amphibole alvi si in calcic amphibole and jadeite content in clinopyroxene mean values vary from about 6 7 5 kbar in zone ii to about 5 kbar in zone vii results from the other islands of the elephant island group are comparable to those from the main island smith island yielded slightly higher pressures up to 8 kbar with temperatures estimated between 300 and 350 c zoned minerals and other textural indications locally enable inference of p t t trajectories all with a clockwise evolution a reconstruction in space and time of these p t t paths allows an estimate of the thermal structure in the upper crust during the two ductile deformation phases d1 d2 that affected the area this thermal structure is in good agreement with the one expected for a subduction zone the arrival and collision of thickened oceanic crust may have caused the accretion and preservation of the subduction complex in this model d1 represents the subduction movements expressed by the first vector of the clockwise p t t path d2 reflects the collision corresponding to the second vector with increasing temperature and decreasing pressure and d3 corresponds to isostatic uplift accompanied by erosion under circumstances of decreasing temperature and pressure

petrology of pelitic schists in the oligoclase biotite zone of the sanbagawa metamorphic terrain japan phase equilibria in the highest grade zone of a high pressure intermediate type of metamorphic belt the oligoclase biotite zone of the bessi area central shikoku is characterized by sodic plagioclase xca 0 10 0 28 bearing assemblages in pelitic schists and represents the highest grade zone of the sanbagawa metamorphic terrain mineral assemblages in pelitic schists of this zone all with quartz sodic plagioclase muscovite and clinozoisite or zoisite are garnet biotite chlorite paragonite garnet biotite hornblende chlorite and partial assemblages of these two types correlations between mineral compositions mineral assemblages and mineral stability data assuming ph2o psolid suggests that metamorphic conditions of this zone are about 610 25 c and 10 1 kbar based upon a comparative study of mineralogy and chemistry of pelitic schists in the oligoclase biotite zone of the sanbagawa terrain with those in the new caledonia omphacite zone as an example of a typical high pressure type of metamorphic belt and with those in a generalized upper staurolite zone as an example of a medium pressure type of metamorphic belt progressive assemblages within these three zones can be related by reactions such as

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

the isotopic record at an alpine glacier and its implications for local climatic changes and isotopic homogenization processes stratigraphic variations of oxygen isotopes in the snow which accumulates during the winter at the norwegian glacier austre okstindbreen are not entirely eliminated after 1 2 months of ablation in the following summer the relationship between regional temperature changes and 18 o values in the snowpack is affected by many natural factors but 1989 90 winter air temperatures were reflected in the snow which remained on austre okstindbreen at 1350 m a s l in july 1990 there were many variations of 18 o values in the 4 1 m of snow above the 1989 summer surface but variations in the underlying firn were relatively small meltwater percolation modifies the initial variations of 18 o values in the snowpack at a site below the mean equilibrium line altitude on austre okstindbreen increased isotopic homogenization within a 10 day period in july accompanied an increase of the mean 18 o value although the isotopic record at a temperate glacier is likely to be influenced by more factors than is that at polar glaciers it can provide an estimate of the approximate trend of local temperature variations

a comparison of the age and composition of the shelburne dyke nova scotia and the messejana dyke spain new 40ar 39ar age determinations on biotite from the shelburne dyke of nova scotia and from the messejana dyke of spain are identical at 203 2 ma in addition both dykes have similar chemical compositions and probably represent similar magma sources petrogenetic processes and tectonic settings related to an early phase of opening of the north atlantic ocean

isotope studies of ice cores from a temperate alpine glacier vernagtferner austria with respect to the meltwater flow core drillings were carried out in 1979 and 1983 on the temperate alpine glacier vernagtferner otztal alps austria in addition studies on the variation of the water table of the firn were carried out in the bore holes the 18 0 2h and 3h content of the cores as well as the electrical conductivity were measured the isotope profiles and the electrical conductivity of the 1983 core display a strong damping in comparison with the profiles from the 1979 core for the depth from 17 to 20 m l0 5 to 13 m water equivalent below the surface in the 1983 core the 3h contents are lower and the 2h and 18 0 contents are more homogenized this core section lies between the lower and upper limits of the water table fluctuations from 1979 to 1982 and it is also assumed that the transition from firn to ice takes place at this depth of the glacier the most reasonable explanation for this damping is that within the range of the firn water table important isotopic and chemical exchanges between the meltwater and the porous medium firn take place it is also possible that a small amount of meltwater is included in the firn while it is changing into ice

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

the age of blueschist metamorphism in anglesey north wales evidence from 40ar 39ar mineral dates of the penmynydd schists the 9penmynydd9 schists of se anglesey include several high p low t lithologies including 1 metasedimentary quartz phengite schist and 2 mafic blueschist with barroisite crossite assemblages that appear to have developed from an earlier actinolitic greenschist facies protolith one phengite and three amphibole concentrates have been analysed by incremental release 40 ar 39 ar dating methods and display discordant age spectra with anomalously young apparent ages recorded in low t increments ages increase systematically throughout intermediate t portions of the analyses to define high t plateaux of c 550 560 ma barroisite crossite rich concentrates and c 580 590 ma actinolite rich concentrate the phengite concentrate also displays an internally discordant spectrum with intermediate t increments defining ages similar to those recorded by barroisite crossite and high t increments giving ages similar to those of actinolite the amphibole and phengite ages are interpreted as dating post metamorphic cooling following a regional low p ml greenschist metamorphism c 580 590 ma and a high p m2 metamorphism c 550 560 ma 40 ar 39 ar ages suggest multiple metamorphism of oceanic crust before the arrival of the blueschist terrane and its accretion to the late precambrian basement of southern britain immediately prior to development of the welsh basin an age of c 550 560 ma for blueschist metamorphism on anglesey provides a likely maximum age for ignimbrites within the pre late lower cambrian arfon group exposed in nw wales

provenance of detrital muscovite in cambrian avalonia of maritime canada 40ar 39ar ages and chemical compositions we report single grain ages for detrital muscovite separated from sandstone samples from five localities in southern new brunswick and southeastern cape breton island nova scotia and from two qua

le batholite de de pas nouveau quebec infrastructure composite d arc magmatique proterozoique the de pas batholith in new quebec is a mass of granitoids elongated in a n s direction covering 7000 km2 in the southeastern part of the archean rae province it is located between the paleopro

magmatic history of the avalon terrane of southern new brunswick canada based on u pb zircon geochronology u pb zircon dates from volcanic and plutonic units confirm that igneous activity throughout the caledonian highlands of southern new brunswick occurred in two main episodes ca 620 ma and ca 560 550 ma the ca 620 ma episode is represented by mainly metatuffaceous rocks of the broad river group and associated dioritic to granitic plutons that form most of the eastern highlands igneous rocks of similar age and type have been documented in avalonian areas throughout the northern appalachian orogen and are interpreted generally to have formed during subduction at a continental margin in contrast the ca 560 550 ma igneous episode may be unique to the caledonian highlands it is represented by tuffs and bimodal flows of the coldbrook group and co genetic gabbroic and granitic plutons that occur mainly in the western highlands this voluminous magmatism may have taken place in a volcanic arc and intra arc extensional setting perhaps like that represented by older but lithologically similar rocks of th

spatial and temporal variations of oxygen isotopes in snowpacks and glacial runoff in different types of glacial area in western china in order to improve understanding of spatial and temporal variations of stable isotopes in atmospheric precipitation snow cover and glacier meltwater in different regions of china samples were collected for isotopic analysis in four areas yulong mountain yunnan himalaya temperate glacier area samdain kangsang mountain nyainqentanglha shan subpolar glacier area the headwater area of the urumqi river tien shan subpolar glacier area and muztag mountain pamirs polar glacier area sampling was undertaken in both summer and winter between 2000 and 2003 the d 18 o values show a temperature altitude effect in new winter snow on yulong mountain reflecting the condensation and fractionation processes associated with the winter monsoon but a different more complex pattern in residual snow deposited during the summer monsoon this old snow is influenced by the precipitation amount effect solar radiation and evaporation and the water content of the snowpack the summer precipitation at samdain kangsang mountain is associated with the summer monsoon there is a marked precipitation amount effect during the long passage of the southwest india monsoon from the distant moisture source to samdain kangsang mountain and the summer precipitation is strongly depleted of the heavy isotope above 6000 m the high radiation flux causes much evaporation from the snow surface the associated 18 o enrichment of the snow is reflected in a reverse altitude effect the d 18 o values in the summer snowpack of the tien shan and muztag mountain decrease with increasing altitude and decreasing air temperature indicating a temperature altitude effect post depositional processes cause isotopic changes during the transformation of snow firn ice to meltwater the effects are much stronger at temperate than at polar glaciers moreover changes in the isotopic signal at both temperate and polar glaciers can result from evaporation sublimation ablation and drifting

post taconic blueschist suture in the northern appalachians of northern new brunswick canada a narrow belt of late ordovician early silurian blueschist at least 70 km long separates an allochthonous fragment of back arc oceanic crust of the middle ordovician fournier group from underlying rift related volcanic rocks of the middle ordovician tetagouche group in northern new brunswick canada the basalts on both sides of the blueschist belt are predominantly metamorphosed to greenschist facies conditions the blueschist belt is interpreted to be an out of sequence thrust zone that accommodated tectonic transport of higher pressure rocks on top of lower pressure rocks during post peak blueschist facies metamorphism the blueschists have higher fe sub 2 o sub 3 feo ratios and total iron contents in comparison to otherwise chemically equivalent basalts of the fournier and tetagouche groups that have been metamorphosed into greenschists the blueschist belt was probably the site of channelized flow of oxidizing fluids during active deformation ina subduction complex formed during the closure of a wide taconic back arac basin in late ordovician silurian time

40ar 39ar white mica ages reveal neoproterozoic paleozoic provenance and an alleghanian overprint in coeval upper ordovician lower devonian rocks of meguma and avalonia abstract 40ar 39ar analyses ir single grain total fusion of white micas from upper ordovician lower devonian sedimentary strata in the meguma annapolis section and avalon arisaig section terranes of the canadian appalachians complement recent detrital zircon studies by providing constraints on local source areas and identifying the age of low temperature a remarkable outcome of the study is that many muscovite ages are significantly younger than the depositional age of the strata they do not record the middle late devonian age of acadian folding or adjacent intrusions but instead preserve a precise age of 322 6 2 1 ma 16 analyses although the sections sampled display no discernable evidence for carboniferous tectonism these ages are coeval with documented alleghanian deformation in both avalonian and meguma terrane rocks and we interpret them to reflect distributed fluid flow coeval with dextral shear along the avalon meguma terrane boundary

tectono stratigraphic terranes in cape breton island nova scotia implications for the configuration of the northern appalachian orogen cape breton island is divided into four terranes on the basis of contrasts in pre carboniferous geology the blair river complex in the north is an exposure of north american grenvillian basement analogous to the humber zone basement in newfoundland ordovician to devonian metavolcanic metasedimentary gneissic and granitic rocks of the aspy terrane are correlative with parts of the gander terrane of newfoundland and new brunswick the bras d9or terrane characterized by low pressure gneisses a carbonate clastic platform sequence and late precambrian early cambrian plutons may be correlative with units previously included in the gander terrane in southern newfoundland and the avalon terrane in southern new brunswick the mira terrane in southeastern cape breton island including late precambrian to early cambrian volcanic and sedimentary sequences and fossiliferous cambrian ordovician units is clearly part of the avalon terrane therefore with the exception of the dunnage terrane which is not represented in cape breton island the terranes of newfoundland continue through cape breton island they are offset to the northwest to the mainland part of the appalachian orogen in new brunswick

metamorphism of an early palaeozoic continental margin western baie verte peninsula newfoundland metamorphic mineral assemblages and textures from early palaeozoic continental margin rocks in north western newfoundland indicate that different structural levels have contrasting metamorphic histories rocks of the east pond metamorphic suite which represent the older structurally lower level of the margin experienced an early high pressure low temperature stage of metamorphism 10 12 kbar minimum 450 500 c which produced eclogite in mafic dykes and phengite garnet assemblages in pelites this was overprinted by higher temperature lower pressure amphibolite facies metamorphism 700 750 c 7 9 kbar minimum which produced complex symplectic textures in rocks of all compositions rocks of the fleur de lys supergroup which were deposited in the stratigraphically higher levels of the rifted margin reached pressures of 7 8 5 kbar at about 450 c during the early stages of metamorphism overprinted by assemblages which indicate maximum temperatures of 550 600 c at about 6 5 kbar the metamorphic history of both units is interpreted to be the result of thermal relaxation following initial burial of a continental margin by overriding thrust sheets since there is no evidence that maximum pressures or temperatures within the fleur de lys supergroup were ever as high as those reached in the east pond metamorphic suite these rocks may have followed parallel nested p t t paths with the more deeply buried east pond metamorphic suite subjected to greater thermal relaxation effects quantitative modelling of p t t paths is not possible with the present data owing to both large uncertainties in p t estimates and in the time of metamorphism

tectonic setting of avalonian volcanic and plutonic rocks in the caledonian highlands southern new brunswick canada the caledonian highlands of southern new brunswick consist of late proterozoic to cambrian rocks generally considered typical of the avalon terrane of the northern appalachian orogen mainly tuffaceous volcanic and sedimentary rocks of the broad river group and cogenetic dioritic to granitic plutons with ages ca 620 ma form most of the eastern caledonian highlands they have petrological features indicative of origin in a continental margin subduction zone significantly younger ca 560 550 ma dacitic to rhyolitic lapilli tuffs and flows laminated tuffaceous siltstone basaltic and rhyolitic flows and clastic sedimentary rocks of the coldbrook group form most of the western highlands and occur locally throughout the highlands the mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group this voluminous subaerial magmatism may have formed during postorogenic ex

proterozoic blueschist bearing melange in the anti atlas mountains morocco abstract blueschists from the bou azzer inlier provide compelling evidence for late proterozoic subduction in the anti atlas mountains of morocco high pressure low temperature metabasites containing blue amphibole minerals crossite and magnesioriebeckite record pressures in excess of 5 kbar together with regional relationships the geologic setting of the blueschists constrains the polarity of pan african subduction in this region which occurred from 750 to 600 ma blueschist facies rocks crop out in a heterogeneous assemblage of variably deformed and metamorphosed tectonic slices of ophiolitic fragments enclosed in a schistose serpentinite matrix the melange belt containing the blueschist facies rocks is intruded by a number of diorite plutons one of which has yielded a u pb radiometric age of 650 ma together with transaharan belt to the southeast the anti atlas suture zone exposed within the bou azzer inlier contains among the oldest known blueschist bearing ophiolitic melanges in the world

a groundwater conceptual model and karst related carbon sink for a glacierized alpine karst aquifer southwestern china summary in the jade dragon snow mountain jdsm region yunnan province sw china an extensive hydrochemical and stable isotopic study of a glacierized alpine karst aquifer was conducted during the period 2011 2014 the objectives of the study were first to establish a conceptual hydrogeological model of the karst groundwater system second to estimate the proportion of extra glacier melt water infiltrating the karst aquifer that is being induced by the regional climate warming third to calculate the karst related flux of carbon into the karst aquifer knowledge of the local hydrogeological background from previous work was the starting point of the hydrochemical and stable isotopic study some representative spring waters and recharge waters i e glacier melt water and rainwater were investigated both spatially and temporally by hydrochemical and isotopic techniques including analysis of major and some minor ions and o and h stable isotopes a conceptual hydrogeological model of a fracture diffuse flow karst groundwater aquifer was proposed the proportion of glacier melt water infiltrating into the karst aquifer was estimated by using the karst spring as a natural pluviometer and with stable isotope analysis results show that 1 the jdsm karst aquifer is a diffuse flow system 2 it has a number of discharge areas and the jinsha river is the karst drainage base level 3 the proportion of the glacier melt water penetrating the karst aquifer is 29 and 4 the karst related carbon sink is 26 67 3 44 t km 2 a 1 as co 2 which is lower than that in non glacierized karst aquifers but over ten times larger than the carbon sink flux from silicate weathering in non karst areas showing the control of both climate and lithology on the rock weathering related carbon sink and the significance of carbonate weathering in the global carbon cycle

tropical glacier meltwater contribution to stream discharge a case study in the cordillera blanca peru original abstract discharge measurements climate observations and hydrochemical samples gathered monthly 1998 99 in the yanamarey and uruashraju glacier fed catchments of the cordillera blanca peru permit an analysis of the glacier meltwater contribution to stream flow these glacier catchments feed the rio santa which discharges into the pacific ocean based on a water balance computation glacier melt contributes an estimated 35 of the average discharge from the catchments for comparison a volumetric end member mixing model of oxygen isotopes shows glacier melt contributes 30 45 to the total annual discharge based on stream geochemistry discharge from the yanamarey glacier catchment provides 30 of the annual volume discharged from the querococha watershed which is 10 glacierized by analogy the larger rio santa watershed also 10 glacierized receives at least 12 of its annual discharge from melting glacier ice tributary watersheds to the rio santa with larger fractions of glacier cover have less variable runoff and enhanced discharge demonstrating that the glaciers effectively buffer stream discharge seasonally with continued glacier melting stream flow will likely become more variable and there will be less dry season runoff

the stable isotope evolution in shiyi glacier system during the ablation period in the north of tibetan plateau china in order to firstly explore the stable isotope evolution of shiyi glacier system in the central qilian mountains a total of 167 samples have been collected from newly deposited snow surface snow snowpits meltwater and glacier fed river water from july 2012 to november 2013 the results indicated that only the newly deposited snow in 23 november 2013 showed a significant altitude effect whereas surface snow had a reverse altitude effect owing to evaporation and sublimation in summer 2012 and 2013 the d

chronology of sanbagawa metamorphism by collating age data based on the fossil age of the protoliths radiometric dating of the metamorphic minerals and sedimentary records of erosion at the earth s surface the history of the sanbagawa metamorphism can be summarized as follows 1 the pre metamorphic sedimentary rocks carboniferous jurassic early cretaceous became mixed and formed a thickened packet in the vicinity of an ancient trench through a variety of subduction related tectono sedimentary processes probably in early cretaceous time c 130 120 ma 2 the subducted protoliths underwent progressive metamorphism reaching a maximum depth of c 30 km in late early cretaceous time c 116 10 ma 3 the high p t metamorphic rocks began to rise toward the surface during the interval 110 50 ma with minimum estimates for the average cooling rate around 9 12 c ma and an average uplift rate around 0 4 0 5 mm year 4 finally at some stage after reaching the erosional surface the high p t metamorphic rocks were covered unconformably by the middle eocene c 50 42 ma kuma group on the basis of the present chronological summary of the sanbagawa metamorphism the areal extent of the sanbagawa metamorphism is also discussed with respect to the weakly metamorphosed subduction accretion complex of the next tectonic belt to the south the northern chichibu belt

contribution of glacier meltwater to streamflow in the wind river range wyoming inferred via a bayesian mixing model applied to isotopic measurements the wind river range wrr of wyoming has the largest concentration of alpine glaciers in the american rockies and contributes to several major river systems in the western united states declines in the areal extent and volume of these glaciers are well documented and eventual loss of alpine glaciers will reduce the amount of water available for agricultural and domestic use the contribution of glacial melt to streamflow remains largely unquantified in wyoming we used isotope measurements and bayesian modeling to estimate the fractional contribution of glacier meltwater to dinwoody creek dc in the wrr on bi weekly and seasonal spring summer and fall time scales over 2 years in 2007 and 2008 we made temporally intensive measurements of the stable isotope composition of water from the dc watershed samples of the primary sources of streamflow snowmelt glacier melt rain and baseflow were collected during field campaigns and automated collection of stream samples occurred over the melt season isotope data d and 18o were analyzed within a hierarchical bayesian framework that incorporated temporal and spatial correlations glacial melt contributed a significant proportion 53 59 to streamflow in a low flow year 2007 or when streamflow was low during a high flow year 2008 in 2008 a large and persistent snowpack contributed significantly 0 42 51 to streamflow in mid summer the large contribution of glacial melt to streamflow suggests that the loss of glaciers may impact riparian ecosystems and human water supplies in the late summer and in years with low snowpack copyright 2011 john wiley sons ltd

oxygen isotopes in glacier river water austre okstindbreen okstindan norway there is no discernible river discharge from austre okstindbreen norway in winter any water formed by basal melting is likely to be stored in isolated cavities or sediments at the bed in summer a baseflow component of discharge relatively depleted of 18 o is diluted by water more enriched in 18 o glacier ice meltwater with a high 18 o value passes rapidly through channelized systems and emerges in the glacier river within a few hours headward extension of the systems in late summer may tap water stored within the glacier since the previous summer s close down stored water also is released during early melt season events when the low capacity drainage systems cannot accommodate inputs the high 18 o value indicates that the probable source of the released water is glacier ice or low altitude snowfall stratigraphic variations of 18 o values resulting from changing weather conditions characterize the accumulating winter snowpack during the melt season the mean 18 o value of the residual pack rises the water leaving it depleted of 18 o passes slowly through the glacier smoothing out variations of supply 18 o values of rain vary between and within events and their effect on glacier river 18 o values is unpredictable

neoproterozoic high pressure low temperature metamorphic rocks in the avalon terrane southern new brunswick canada high p low t metamorphic rocks of the hammondvale metamorphic suite hms are exposed in an area of 10 km2 on the nw margin of the caledonian avalon terrane in southern new brunswick canada the hms is in faulted contact on the se with c 560 550 ma volcanic and sedimentary rocks and co magmatic plutonic units of the caledonian terrane the hms consists of albite and garnet porphyroblastic mica schist with minor marble calc silicate rocks and quartzite pressure and temperature estimates from metamorphic assemblages in the mica schist and calc silicate rocks using twq indicate that peak pressure conditions were 12 4 kbar at 430 c peak temperature conditions were 580 c at 9 0 kbar 40ar 39ar muscovite ages from three samples range up to 618 615 ma a minimum age for high p low t metamorphism in this unit these ages indicate that the hms is related to the c 625 600 ma subduction generated volcanic and plutonic units exposed to the se in the caledonian terrane the ages are also similar to those obtained from detrital muscovite in a neoproterozoic cambrian sedimentary sequence in the caledonian terrane suggesting that the hms was exposed by latest neoproterozoic time and supplied detritus to the sedimentary units the hms is interpreted to represent a fragment of an accretionary complex similar to the sanbagawa belt in japan it confirms the presence of a major cryptic suture between the avalon terrane sensu stricto and the now adjacent brookville terrane

tectonometamorphic evolution of the sebadani eclogitic metagabbro and the sambagawa schists central shikoku japan 40ar 39ar mineral age constraints the sambagawa metamorphic belt exposed in central shikoku records a high p t metamorphic event it is represented by the oboke nappe and structurally overlying internally imbricated besshi nappe complex these major structural units are in ductile thrust contact a melange is developed along a ductile internal tectonic contact within the besshi nappe complex tectonic emplacement of a high t enclave sebadani eclogite in the melange zone resulted in the development of a contact metamorphic aureole within the host sambagawa rocks 36ar 40ar versus 39ar 40ar isotope correlation ages recorded by hornblende from the sambagawa basic schists which surround the sebadani enclave are 83 4 0 3 ma within contact aureole and 83 6 0 5 ma outside aureole 40ar 39ar plateau ages recorded by muscovite from the same samples are 87 9 0 3 and 89 3 0 4 ma amphibole from the amphibolite within the sebadani enclave records isotope correlation ages of 93 7 1 1 and 96 5 0 7 ma massive interior and 84 6 1 2 ma marginal shear zone amphibole within the massive amphibolite is significantly higher in xmg than that within the host sambagawa basic schists the older ages recorded by amphibole within the sebadani enclave are interpreted to date cooling through somewhat higher closure temperatures than which characterize the more fe rich amphibole in surrounding schists the younger amphibole age recorded within the marginal shear zone probably indicates that crystallization of amphibole continued until cooling through the relatively lower amphibole closure temperatures these results together with the previously published 40ar 39ar ages of the sambagawa schists suggest i metamorphic culmination occurred in the besshi nappe complex at c 100 90 ma ii at c 95 ma the besshi nappe complex was internally imbricated and tectonic enclaves were emplaced iii at c 85 ma the composite besshi nappe was rapidly exhumed and tectonically emplaced over the oboke nappe which attained peak metamorphic conditions at c 75 ma iv the besshi and oboke nappe complexes were further exhumed as a coherent tectonic unit and unconformably overlain by the eocene kuma group at c 50 ma

resolution of regional fluid flow related to successive orogenic events on the laurentian margin seven localities distributed along a 180 km long outcrop within the uk sector of the laurentian margin were sampled and all showed two phases of authigenic k feldspar the first phase was precipitated from a cool fluid of moderate salinity and the second phase was precipitated from a hotter more saline fluid ar ar ages for the two episodes of authigenesis are ca 470 ma and ca 432 ma the data can be interpreted to represent two phases of regional scale fluid migration related to ordovician arc accretion and silurian continent continent convergence corresponding to the grampian and scandian episodes of the caledonian orogeny respectively

nd isotopic characteristics of terranes within the avalon zone southern new brunswick nd isotopic data are presented for rock units in four terranes within the traditional avalon zone of southern new brunswick initial end values for igneous rocks within the caledonia terrane range from 1 6 to 4 6 whereas values for sedimentary rocks range from 8 4 to 3 6 a granite within the kingston terrane has end 438 ma 4 0 nd isotopic compositions for the kingston and caledonia terranes are similar to those of the mira terrane in cape breton island the antigonish highlands of nova scotia and plutonic rocks of eastern newfoundland each of these regions may be a dismembered part of a single terrane the avalon terrane sensu stricto initial end values for rocks from the brookville terrane range from 1 3 to 2 8 the coverdale anorthosite within the brookville terrane has a present day end value of 12 1 and a depleted mantle model age of 1 3 ga similar to mesoproterozoic anorthosites in laurentia clastic sedimentary rocks in the green head group have end 750 ma values of 2 0 and 10 9

40ar 39ar ages for detrital white mica in meguma terrane nova scotia canada implications for provenance of the goldenville and halifax groups single grain 40 ar 39 ar ages are reported for detrital white mica along with conventional step heating data for whole rocks from low grade metasandstone samples from the goldenville halifax and rockville notch groups in the meguma terrane of southern nova scotia the majority 166 of single grains from 11 samples yielded ages between ca 615 and 350 ma and the remaining 12 grains yielded ages between ca 1900 and 870 ma the late neoproterozoic paleozoic age distributions are consistent with derivation of sediments from the rapidly uplifted flanks of an active rift where partial to complete resetting of white mica ages occurred at ca 520 500 ma preceding sediment deposition the ca 615 ma ages may be relics of the original detrital white mica that existed in the source rocks prior to the rifting event ages from the upper silurian white rock formation appear to reflect this same ca 520 500 ma event suggesting that sediments in the white rock formation were recycled from the goldenville and halifax groups the older precambrian ages are inferred to represent white mica in the source region likely amazonia the whole rock age spectra are discordant with pronounced age gradients and no well defined age plateaus initial gas released from five of the samples at low laboratory extraction temperatures ca 450 500 c yielded ages of ca 260 300 ma not seen in the single grain data whereas gas released at the highest extraction temperatures yielded ages in the range ca 510 530 ma possibly reflecting the principal result obtained from the single grain data

the peristerite gap in low grade metamorphic rocks coexisting na plagioclases from greenschists both in the thermal aureole of the kasugamura granite japan and in the low p metamorphic zone of yap island western pacific were analyzed in great detail the peristerite solvus was determined for each suite the asymmetric solvus has steep albite rich and gentle oligoclase rich limbs that are similar to those for higher pressure series the present results together with those from vermont new zealand and the sanbagawa belt indicate that the peristerite solvus shifts toward the albite component and higher temperature with increasing pressure with increasing pressure albite co existing with oligoclase an 100 ca ca na 20 varies in composition from an 8 9 in kasugamura through an 3 in yap island and vermont to an 1 in new zealand and an less than 0 5 in the sanbagawa belt the consolute temperatures for the peristerite solvus estimated from available geothermometry are 420 c in kasugamura 450 550 c in vermont and 550 600 c in the sanbagawa belt the variation of plagioclase composition in progressive metamorphic zones is explained by intersection of a plagioclase forming reaction and the peristerite immiscibility gap in an isobaric t xan diagram the greenschist zone is characterized by albite the transition zone by occurrence of peristerite pairs and the amphibolite zone by plagioclase of an 20 50