a study of planetary waves in the southern winter troposphere and stratosphere part i wave structure and vertical propagation abstract planetary wave propagation in the southern winter troposphere and stratosphere is studied in an attempt to trace the origins of upward propagating disturbance daily geopotential girds from 1000 to 1 mb are analyzed for two 120 day winter seasons a cross correlation analysis technique is developed which allows coherent wave structure to be traced in time significant correlations are observed between the troposphere and stratosphere at finite time lags indicative of vertically propagating waves the observed vertical propagation time scales between the middle troposphere and middle stratosphere are on the order of 4 days for zonal wavenumber 1 k 1 1 2 days for k 2 and 1 day for k 3 the cross correlation analysis also delineates the meridional and vertical structures of the transient in time planetary waves zonal wavenumber 1 fluctuations exhibit a vertical out of phase relationship between the midlatitude troposphere and atmosphere three out of phase maxima in latitude are observed in

dissolved constituents and sr isotopes in river waters from a mountainous island the danshuei drainage system in northern taiwan abstract taiwan is a typical active orogenic belt situated at the collision boundary between the eurasian continental plate and the philippine sea plate dissolved major and trace constituents as well as sr and sr isotopes in river waters collected from the danshuei river basin in northern taiwan have been studied to evaluate chemical weathering processes the results of principal component analysis show that the ion sources in these river waters can be categorized into 3 major components chemical weathering seasalt contribution and local anthropogenic input the chemical weathering is the most dominant factor that contributes about 85 of total variances significantly increased na cl and ca cl as well 87 sr 86 sr were observed in most upper stream samples the na cl and ca cl ratios in the dahan stream however are much higher than the shindien stream even though average rainfall is stronger in the shindien drainage basin chemical evidence from river waters supports less intense weathering in the region selective dissolution of secondary calcites explains the observed high ca cl sr cl and ca na in the dahan stream these results highlight the potential importance of tectonic factors such as uplift and physical erosion in studying chemical weathering in an active orogenic belt the variations of 87 sr 86 sr in the danshuei river are quite large reflecting some strata that released sr most of the upstream waters exhibit more radiogenic 87 sr 86 sr 0 713243 0 714338 due to weathering of ambient low grade metamorphic rocks 0 71678 0 72216 the distributions of cl sr and 87 sr 86 sr in the main stream were affected by somewhat conservative mixing with sources varing between ambient rocks and seasalt in the upper dahan stream heavy 87 sr 86 sr ratios were coincident with large deviations of na cl from the average seawater value as high as 40 the degree of chemical weathering in ambient rocks plays a dominant role in affecting the distribution of sr and 87 sr 86 sr in the danshuei river this isotopic characteristic makes 87 sr 86 sr an invaluable tracer for studying source mixing migration pathways and chemical weathering in an active orogenic belt

cretaceous deformation in the western foothills of the sierra nevada california deformation of metamorphic rocks the tonalite of blue canyon several bodies of granite and granodiorite and the leucotonalite of ward mountain within an area of about 600 km 2 in the western foothills of the sierra nevada just south of the south end of the western metamorphic belt is attributed to emplacement of the leucotonalite in a nearly solid state the east flanks of two plutons of leucotonalite of ward mountain in the west central part of the deformed area dip gently beneath the area of deformed rocks whereas their west flanks are vertical or dip steeply east cata clastic planar and linear structures in the metamorphic rocks and in the tonalite of blue canyon form coherent and related patterns the planar structures generally strike parallel to contacts with the leucotonalite and dip outward between the two plutons of leucotonalite they form a synform lineations generally plunge outward from the leucotonalite but trend parallel to contacts within the synform heat and possibly volatiles that accompanied emplacement of the rising and westward moving mass of leucotonalite may have increased the susceptibility of the overlying rocks to attenuate normal to the planar structures and to stretch in the direction of the linear structures isotopic u pb and k ar determinations indicate that the age of the tonalite of blue canyon is about 114 m y and that the age of the leucotonalite of ward mountain coincides with the time of deformation at about 113 m y ago the isotopic age of the granodiorite of knowles which truncates cataclastic structures in the tonalite of blue canyon and the leucotonalite of ward mountain is 110 m y

tropical midlatitude interaction on the time scale of 30 to 60 days during the northern summer of 1979 abstract the relationship between the low frequency oscillation of convective activity in the tropics and the intensity of planetary scale upper tropospheric 200 mb systems in the subtropics during the northern hemisphere nh summer is studied using data obtained in the first garp global experiment fgge the mid pacific trough and the south asian tibetan and mexican anticyclones undergo cycles of amplification and decay with the 30 60 day fluctuation of convective activities in the indonesia western pacific iwp region and in the intertropical covergence zone itcz over central america the thermal contrast between the asian continent and the north pacific and the resulting east west circulation show similar time variations this circulation regulates the intensity of the south asian anticyclone and the mid pacific trough divergent circulation associated with convection over central america maintains the mexican anticyclone the low frequency transients in the upper troposphere around the mid pa

on the linkage of mesospheric planetary waves with those of the lower atmosphere and ionosphere a case study from indian low latitudes 1 in this paper we study the planetary scale wave features using concurrent observations of mesospheric wind and temperature ionospherich f and tropospheric wind from tirunelveli gadanki and kolhapur all located in the indian low latitudes made during february 2009 our investigations reveal that 3 to 5 day periodicity characterized as ultrafast kelvin ufk waves was persistent throughout the atmosphere during this period these waves show clear signatures of upward wave propagation from troposphere to the upper mesosphere linking the ionosphere through a clear correlation between mesospheric winds and h f variations we also note that the amplitude of this wave decreased as we moved away from the equator these results are the first of their kind from indian sector portraying the vertical as well as latitudinal characteristics of the 3 to 5 day ufk waves simultaneously from the troposphere to the ionosphere

episodic metamorphism and deformation in low pressure high temperature terranes in many cases low pressure high temperature metamorphism must be the consequence of advective heat transfer e g the ascent of granitic magma whereas such heating mechanisms are necessarily short lived the lifetime of the underlying orogenic processes is likely to be much longer and it is conceivable that during the evolution of an orogen repeated transient heating at shallow crustal levels is caused by episodes of segregation and upward passage of melts generated at deep crustal levels the number and timing of these events would depend on such factors as critical melt segregation volume moho temperature and strain rate evolution we investigate some of the controls on this multiple event superposition using a simple thermomechanical model designed to predict simultaneously the strain rate and the isostatic and thermal evolution of convergent orogenesis subject to a constant driving force an appealing aspect of this formulation is that in contrast to models that have attempted to explain event cyclicity through episodic processes acting on the orogenic boundaries it accounts for the repeated occurrence of events through processes inherent to the orogenic system itself

one to two month oscillations observed high latitude tropospheric and stratospheric response to tropical forcing abstract careful spectral correlation and coherence analyses of low frequency fluctuations in global geopotential height data are presented attention is paid to proper statistical assessments the main points are 1 one to two month oscillating quasi stationary wavetrains have recently been reported in the extratropical southern hemisphere troposphere as far south as the edge of antarctica however only weak correlations were observed with the supposed tropical forcing region leading to the question of whether the wavetrain is a response to tropical forcing or possibly due to in situ instabilities on 1 2 month time scales the present paper clears up this enigma with analyses of other tropical datasets which reveal clear correlation between low latitude source regions and the sh extratropical troposphere 2 an earlier investigation found strong correlations between 1 2 month oscillations in the upper stratosphere and tropical troposphere yet no vertical propagation was found directly above the tro

high resolution simulation of the boreal summer intraseasonal oscillation in met office unified model the present study investigates the fidelity and resolution sensitivity of met office unified model global atmosphere 3 0 in simulating the intra seasonal oscillation iso of the east asia and western north pacific summer monsoon two sets of model simulations at horizontal resolutions of n216 60km and n96 130km forced by observed daily high resolution sea surface temperature are examined and compared with the observations diagnostic results show that the model can well reproduce the gross spatio temporal features of observed summer iso over the east asia and western north pacific in terms of period dominant reof mode variance northward propagation cycle evolution and vertical structure the intra seasonal change in intensity and position of western north pacific subtropical high and upper troposphere westerly jet associated with the northward propagating isos are also reasonably captured in the model moreover increasing horizontal resolution improves most aspects of the iso simulation especially the intensity and northward propagation of the iso related convection and circulation systems further analysis indicates that the improvement as resolution increases is related to the weakening in background state of east asian summer monsoon which is due to the realistic simulation of land sea thermal contrast at higher resolution model this study suggests that enhanced model resolution can have some beneficial impacts on the iso simulation

estimating erosion rates and exposure ages with 36cl produced by neutron activation the isotopic composition of water soluble cl extracted from mineral grains in granitic rocks appears to reflect the relative age of debris flow fan surfaces and the erosion rate of bedrock outcrops our data indicate that some granitic landforms are stable landscape elements eroding on the order of meters to tens of meters per million years samples collected from debris flow fan surfaces of three distinct relative ages show the expected increase of model age with time but the 36cl exposure ages for boulders on any particular surface vary by a factor of more than five the method we used for extracting cl was designed to isolate the 35cl n 36cl production pathway and to simplify the chemical preparation of samples such isolation from fluid inclusions allows direct interpretation of measured 36cl cl ratios but requires a model to predict the thermal neutron production and absorption profile below the rock surface using such a model we find good agreement between measured and predicted 36cl cl for eight samples collected below the ground surface as well as consistency between several groups of samples collected near one another using elemental abundance data for 129 granitic rocks we modeled 36cl cl supported by radiogenic neutrons and find that it varies from 4 to 125 10 15 mean 21 18 1 however from the surface to a depth of 10 m thermal neutrons resulting from muon interactions have the potential to generate more 36cl than do radiogenic neutrons the production of 36cl in the subsurface has important implications for surface exposure dating of young low altitude samples collected from moraines and debris flow or alluvial fans especially at ages where erosion of the boulder surface is significant or where the source area for boulders is at altitudes much higher than the landform to be dated

carbonate versus silicate weathering in the raikhot watershed within the high himalayan crystalline series the major element and sr isotope geochemistry of surface waters bedrock and river sands was investigated in the raikhot watershed within the high himalayan crystalline series hhcs in northern pakistan mass balance calculations of mineral weathering contributions to the dissolved flux of ions from the watershed indicate that 82 of the hco 3 flux is derived from the weathering of carbonate minerals and only 18 is derived from silicate weathering even though the bedrock is predominantly quartzofeldspathic gneiss and granite with only 1 carbonate in the watershed this study demonstrates the importance of trace amounts of bedrock carbonate in controlling the water chemistry of glacial watersheds we suggest that the flux of sr with a high 87 sr 86 sr ratio in the major himalayan rivers may be derived in large part from weathering of trace amounts of calcite within the largely silicate hhcs models that use the flux of radiogenic sr from the himalayas as a proxy for silicate weathering rates may therefore overestimate the amount of co 2 consumption due to silicate weathering in the himalaya

controls on surface water chemistry in the upper merced river basin yosemite national park california surface water draining granitic bedrock in yosemite national park exhibits considerable variability in chemical composition despite the relative homogeneity of bedrock chemistry other geological factors including the jointing and distribution of glacial till appear to exert strong controls on water composition chemical data from three surface water surveys in the upper merced river basin conducted in august 1981 june 1988 and august 1991 were analysed and compared with mapped geological hydrological and topographic features to identify the solute sources and processes that control water chemistry within the basin during baseflow water at most of the sampling sites was dilute with alkalinities ranging from 26 to 77 pequiv i alkalinity was much higher in two subcatchments however ranging from 51 to 302 pequiv 1 base cations and silica were also significantly higher in these two catchments than in the rest of the watershed concentrations of weathering products in surface water were correlated to the fraction of each subcatchment underlain by surficial material which is mostly glacial till silicate mineral weathering is the dominant control on concentrations of alkalinity silica and base cations and ratios of these constituents in surface water reflect the composition of local bedrock chloride concentrations in surface water samples varied widely ranging from 1 to 96 pequiv 1 the annual volume weighted mean chloride concentration in the merced river at the happy isles gauge from 1968 to 1990 was 26 pequiv l which was five times higher than in atmospheric deposition 4 5 pequiv l suggesting that a source of chloride exists within the watershed saline groundwater springs whose locations are probably controlled by vertical jointing in the bedrock are the most likely source of the chloride sulphate concentrations varied much less than most other solutes ranging from 3 to 14 pequiv 1 concentrations of sulphate in quarterly samples collected at the watershed outlet also showed relatively little variation suggesting that sulphate may be regulated to some extent by a within watershed process such as sulphate adsorption

quasi periodic oscillations in a symmetric general circulation model abstract long lime integrations with a symmetric version of the clas climate model with hydrology have shown that the hadley circulation has well defined strong and weak episodes this oscillation of the hadley circulation seems to occur in two dominant range of periodicities one with periods between 10 and 15 days and another with periods between 20 and 40 days this quasi periodic behavior of the hadley circulation is seen only when the moist convective heating is determined by dynamics if the latent beating in the atmosphere is prescribed and kept artificially fixed this oscillation of the hadley circulation disappears thus this oscillation of the hadley circulation appears as a result of interactions between moist convective and dynamical processes a wave phenomenon is seen in the lower atmosphere that propagates toward the position of maximum radiative beating this wave perturbation has a length scale of about 15 20 degrees latitude in the north south direction this phenomenon has large ampli

subglacially precipitated carbonates record geochemical interactions and pollen preservation at the base of the laurentide ice sheet on central baffin island eastern canadian arctic the mineralogy and isotopic compositions of subglacially precipitated carbonate crusts spccs provide information on conditions and processes beneath former glaciers and ice sheets here we describe spccs formed on gneissic bedrock at the bed of the laurentide ice sheet lis during the last glacial maximum on central baffin island geochemical data indicate that the ca in the crusts was likely derived from the subglacial chemical weathering ca bearing minerals in the local bedrock c and sr isotopic analyses reveal that the c in the calcite was derived predominantly from older plant debris the 18o values of the spccs suggest that these crusts formed in isotopic equilibrium with basal ice lis preserved in the barnes ice cap bic columnar crystal fabric and the predominance of sparite over micrite in the spccs are indicative of carbonate precipitation under open system conditions however the mean 18o value of the calcite crusts is 10 higher than those of primary lis ice preserved in the bic demonstrating that spccs record the isotopic composition of only basal ice palynomorph assemblages preserved within the calcite and basal bic ice include species last endemic to the arctic in the early tertiary the source of these palynomorphs remains enigmatic

geochemistry of high grade supracrustal rocks from the kerala khondalite belt and adjacent massif charnockites south india abstract the kerala khondalite belt kkb comprises a suite of supracrustal rocks of probable proterozoic age that was metamorphosed to the granulite facies the kkb consists of an interlayered sequence of 1 garnet biotite orthopyroxene graphite gneisses 2 khondalites graphite garnet biotite sillimanite cordierite gneisses and 3 cordierite gneisses garnet biotite cordierite orthopyroxene as well as less abundant mafic granulites calc silicates and quartzites petrologic and geochemical data suggest that these rocks were originally arkosic and argillaceous sediments possibly accompanied by felsic volcanic rocks along with minor intercalations of basalts carbonates and quartz rich sandstones the ree patterns of the metasediments are typically lree enriched with large negative eu anomalies indicating a continental provenance the major and trace element compositions of some of the arkosic rocks of the kkb resemble those of the massif charnockites that bound the kkb to the north which suggests that the massif charnockites may have been the source of some of the kkb sediments modern day analogues of the pelite arkose lithologic association observed in the kkb occur in intracratonic rifts and rifted continental margins this association is clearly distinct from the graywacke mafic volcanic association found in the southern indian greenstone belts and many other lower grade archean sedimentary sequences the kkb supracrustals show both lithologic and chemical similarities to many proterozoic supracrustal successions

the intraseasonal 30 50 day oscillation of the australian summer monsoon abstract the tropical intraseasonal 30 50 day oscillation manifests itself in the australian summer monsoon by a pronounced modulation of the monsoonal westerlies these 30 50 day fluctuations of the monsoonal westerlies are coherent with rainfall and olr across northern australia the olr fluctuation originates in the indian ocean and systematically propagates eastward at 5 m s 1 consistent with previous studies of the intraseasonal oscillation the detailed evolution of the intraseasonal oscillation of the monsoon is studied via composites of upper air data in and about the australian tropics during the summer periods 1957 87 91 events were identified at darwin australia the composite oscillation at darwin has a very deep baroclinic structure with westerlies extending up to 300 mb the westerly phase lasts about ten days and lags a similar duration rainfall event by about four days during the westerly phase the upper troposphere is warm and the extreme lower troposphere is cool this structure

a rift drift delamination model of continental evolution palaeozoic tectonic development of eastern australia the adelaide lachlan and new england fold belts of eastern australia record the continental growth of eastern gondwanaland during the palaeozoic the new england fold belt nefb represents a tectonic collage formed by subduction accretion during the late paleozoic but contains remnants of subduction related rocks that date from the cambrian the lachlan fold belt lfb developed inboard from the nefb initially as an amalgam of proterozoic continental and cambrian oceanic fragments that formed by rift and drift at the leading edge of eastern gondwanaland convergent tectonism at 500 ma welded the fragments to the craton and formed the adelaide fold belt oceanward dispersal of detritus across the lfb produced an overlap assemblage of quartzose ordovician turbidites and a new subduction zone developed at the eastern margin the tectonic setting was similar to the modern philippines plate of the western pacific behind the arc silurian devonian convergent tectonics converted the 1700 2000 km wide continental margin of the proto lfb into a 750 km wide thin skinned fold magmatic belt within 60 ma the driving force was delamination which produced a ubiquitous basaltic underplate that generated 1 regional low p metamorphism 2 local anticlockwise p t t paths and crustal scale isobaric cooling 3 voluminous syn to late tectonic granitoids emplaced at rates approximately twice that of modern arcs and 4 normal thickness crust despite an average of 60 shortening delamination occurred in two separate areas originally 1000 km apart first in the eastern then in the western part of the lfb the lfb and its northern counterpart the thomson fold belt represent approximately one fifth of the australian continent and evolved from dispersed fragments into stable continental crust in 300 ma such rapid growth rates are typical of the 2 7 2 5 ga and 1 9 1 7 ga periods when voluminous widespread granitoids and large turbidite dominated low p metamorphic belts were produced in settings that are not obviously subduction related therefore a similar process of rift drift delamination riddel tectonics may have periodically operated throughout earth history

intraseasonal variability of high resolution doppler imager winds in the equatorial mesosphere and lower thermosphere analyses of high resolution doppler imager hrdi daytime equatorial zonal winds indicate significant variability on time scales of 20 121 days these appear as transient oscillations in the equatorial zonal mean zonal wind between 70 and 100 km the oscillations are characterized by two maxima near 75 and 95 km that are out of phase separated by a minimum near 80 km these features move downward in time and exhibit equatorial symmetry with maximum values at the equator during 1994 maximum amplitudes of the intraseasonal oscillation are 20 m s 1 in january and 30 m s 1 in june the intraseasonal variability present in hrdi winds is qualitatively consistent with variations on similar timescales reported at christmas island it has been hypothesized that the wind patterns at christmas island result from modulated gravity wave driving eckermann et al 1997 the results of the present study strongly support this view

neutralization of atmospheric acidity by chemical weathering in an alpine drainage basin in the north cascade mountains the most important weathering reaction that neutralizes incoming atmospheric acidity in the south cascade lake basin is weathering of calcite which occurs in trace amounts in veins on joint surfaces and as a subglacial surficial deposit although the basin is underlain by igneous and high grade metamorphic rocks weathering of plagioclase is quantitatively negligible the principal silicate weathering reaction is alteration of biotite to vermiculite these conclusions are based on mass balance calculations involving runoff compositions and on mineralogical observations for predictive modeling of the effects of increased acid deposition it is essential to identify the relevant weathering reactions feldspar weathering is commonly not an important source of solutes in alpine basins underlain by granitic rocks 30 references 2 figures 1 table

atmospheric co2 sink silicate weathering or carbonate weathering it is widely accepted that chemical weathering of ca silicate rocks could potentially control long term climate change by providing feedback interaction with atmospheric co2 drawdown by means of precipitation of carbonate and that in contrast weathering of carbonate rocks has not an equivalent impact because all of the co2 consumed in the weathering process is returned to the atmosphere by the comparatively rapid precipitation of carbonates in the oceans here it is shown that the rapid kinetics of carbonate dissolution and the importance of small amounts of carbonate minerals in controlling the dissolved inorganic c dic of silicate watersheds coupled with aquatic photosynthetic uptake of the weatheringrelated dic and burial of some of the resulting organic c suggest that the atmospheric co2 sink from carbonate weathering may previously have been underestimated by a factor of about 3 amounting to 0 477 pg c a this indicates that the contribution of silicate weathering to the atmospheric co2 sink may be only 6 while the other 94 is by carbonate weathering therefore the atmospheric co2 sink by carbonate weathering might be significant in controlling both the short term and long term climate changes this questions the traditional point of view that only chemical weathering of ca silicate rocks potentially controls long term climate change

tectonic evolution in the archaean and proterozoic kre high heat flow probably favoured global hotspot activity with crustal growth of iceland type through vertical magmatic accretion the tectonic environment for the generation of about 3 9 2 5 ga granite gneiss greenstone terrains with volurnlnous production of tonalite trondhjemite granodlorite magmas is still uncertain and both piate ma and intrapiate scenarios arc possible deformanon atylea in greenstones and adjacent high grade orthognersses with intercalated shallow water supracrustal assemblages suggest extensive horizontal shortening and crustal interstacking this probably resulted from collisional and or rotational motion and produced significant intracrustal melting as early as 3 9 ga by the end of the archaean and locally much earlier crustal thicknesses reached 35 50 km or more and the cxtl aordinary hhlding to erogenic deformation may have been due to delamination and crustal subduction towards the end of the proterozoic evidence for modern style plate tectonics becomes abundant through the recognition of laland a16 accretion ophiolite obducdon foreland thrust and fold belts and exotic terranes one of the best documented example for this tectonic environment is the arabian nubian shield 4lthough it is doubtful whether modern plate tectonic settings can serve as analogues for all precambrian tectonic styles it i clear that global crustal evolution since the early archaean was governed by the motion of plates which repeatedly came togethel tv fotm supercontinents and then dlspersetl again we shall not understand the detailed mechanism of precambrian crustal itlton cs before we learn horn lo irltejpret recent large scale crustal deformation and its causes

geochemistry and isotopic characteristics of mafic phulad ophiolite and related rocks in the delhi supergroup rajasthan india implications for rifting in the proterozoic abstract regionally metamorphosed mafic rocks phulad ophiolite in the delhi supergroup n w india have tholeiitic compositions the data indicate that there are two independent rock suites phulad barr jetgarh pbj meta basalts with element abundances and ratios resembling midocean ridge basalts morb and ranakpur desuri r d meta basalts and meta gabbros with relatively high al2o3 and low tio2 for similar mgo and high lil element rb ba sr coupled with low hfs zr nb and ree sm nd abundances the compositions of these rocks are characteristic of ocean arc basalts dioritic rocks at ranakpur exhibit low k tholeiitic differentiation trends and have close chemical affinity with the spatially associated meta basalts ranakpur diorites define a sm nd whole rock isochron corresponding to an age of 1012 78 ma with an initial nd isotopic composition that is similar to bulk earth sm nd mineral isochrons for a meta gabbro diorite and quartz diorite at ranakpur correspond to ages of 838 36 835 43 and 791 43 ma respectively these younger ages reflect metamorphic re equilibration of isotope compositions during widespread granite and granodiorite emplacement in this region during the late proterozoic model sm nd ages for the meta basalts calculated relative to undepleted mantle vary between 1300 1700 ma the chemistry of both mafic rock suites indicates derivation from source regions which had been depleted during previous melting episodes so the model ages are a maximum age constraint ranakpur desuri mafic rocks have negative initial nd 1 0 to 4 5 and low sm nd ratios suggesting crustal contamination or reworking with a few exceptions the pbj meta basalts have positive initial nd 1 5 to 4 8 indicating that they were derived from heterogeneously enriched although longterm depleted mantle the chemical data support the hypothesis that the pbj meta basalts are fragments of proterozoic ocean crust

stratigraphy and geochemistry in the proterozoic mafic volcanic rocks of the nagu korpo area sw finland the volcanic rocks of the nagu korpo area in sw finland form a thin 1000 m formation that is folded into narrow synforms separated by migmatite filled antiforms in nagu the volcanic formation comprises three units a lower unit of subvolcanic banded gabbro sills a middle unit of amphibolitic volcanic rocks and an upper unit consisting of a thin ultramafic volcanic rock layer the volcanic formation is interlayered within a thicker sequence of metasedimentary gneisses geochemically the metavolcanic rocks are tholeiitic and plots based on ti y zr and other trace elements show that they resemble recent within plate lavas morb and mantle normalised trace element plots show patterns strongly differing from those of recent arc lavas indicating a tectonic environment of plate boundary related initial rifting the upper ultramafic lavas are enriched in lree relative to the lavas of the much thicker amphibolitic middle unit below a model for the initial formation of the volcanic rocks of the svecofennian fold belt must acknowledge both the episode of initial rifting and the later evolution of an island arc like environment

mass balance modeling of mineral weathering rates and co2 consumption in the forested metabasaltic hauver branch watershed catoctin mountain maryland usa mineral weathering rates and a forest macronutrient uptake stoichiometry were determined for the forested metabasaltic hauver branch watershed in north central maryland usa previous studies of hauver branch have had an insufficient number of analytes to permit determination of rates of all the minerals involved in chemical weathering including biomass more equations in the mass balance matrix were added using existing mineralogic information the stoichiometry of a deciduous biomass term was determined using multi year weekly to biweekly stream water chemistry for a nearby watershed which drains relatively unreactive quartzite bedrock at hauver branch calcite hosts 38 mol of the calcium ion ca2 contained in weathering minerals but its weathering provides 90 of the stream water ca2 this occurs in a landscape with a regolith residence time of more than several ka kiloannum previous studies indicate that such old regolith does not typically contain dissolving calcite that affects stream ca2 na ratios the relatively high calcite dissolution rate likely reflects dissolution of calcite in fractures of the deep critical zone of the carbon dioxide co2 consumed by mineral weathering calcite is responsible for approximately 27 with the silicate weathering consumption rate far exceeding that of the global average the chemical weathering of mafic terrains in decaying orogens thus may be capable of influencing global geochemical cycles and therefore climate on geological timescales based on carbon balance calculations atmospheric derived sulfuric acid is responsible for approximately 22 of the mineral weathering occurring in the watershed our results suggest that rising air temperatures driven by global warming and resulting in higher precipitation will cause the rate of chemical weathering in the hauver branch watershed to increase until a threshold temperature is reached beyond the threshold temperature increased recharge would produce a shallower groundwater table and reduced chemical weathering rates copyright 2013 john wiley sons ltd

vertical and lateral propagation characteristics of intraseasonal oscillation from the tropical lower troposphere to upper mesosphere 1 using a mesosphere stratosphere troposphere mst radar and a rayleigh lidar collocated at the indian tropical station gadanki 13 5 n 79 2 e european centre for medium range weather forecasts ecmwf re analysis data and the horizontal wind velocities measured by the thermosphere ionosphere mesosphere energetics and dynamics timed doppler interferometer tidi instrument onboard the timed satellite the present study makes a report on the lateral and vertical propagation characteristics of an intraseasonal oscillation iso 20 40 day period band propagating from the lower troposphere to the upper mesosphere region during the winter november december january and february months of the years 2004 2005 it is found that the iso had its origin in the tropical lower troposphere and propagated laterally and vertically to the upper mesosphere through the subtropical latitudes by partial refraction and reflection processes about the subtropical westerly jet corresponding enhancements in the wavelet spectrum of outgoing long wave radiation olr noaa interpolated indicate that convective forces in the lower troposphere are one of the main sources for the generation of the iso from the phase of the iso in the horizontal winds as observed by the mst radar it is found that the iso propagated upward from the lower troposphere up to near the tropopause where it got sharply attenuated from the ecmwf data it is observed that the iso was refracted to the subtropical latitudes through the tropical tropopause from where it got radiated upward into the stratosphere the phase propagation of the filtered winds shows that the iso arched back toward the tropical latitudes and propagated to the mesospheric region

analysis of hot fluid infiltration in fractured granite by fluid inclusion study abstract the la peyratte granite deux sevres france is crosscut by veins of hydrothermal origin petrographie analysis shows that most of these veins were sealed by phengite crystals during a single hydrothermal event one of these veins 300 m width was chosen for detailed investigations of fluid inclusions inside the wall rock a thermal gradient was determined 335 c inside the vein to 260 c at 11 mm inside the wall rock theoretical modelling shows that the thermal gradient cannot originate from a permanent heat source continuous flow but from a variable one pulsed regime the modelling is based on a periodic function for simplifying the calculations in this case the fluid residence time 0 5 h must be short compared to the period 1 d in order to fit the measured thermal gradient the thermal gradient was established during a period of time long enough for alteration mineral reactions to proceed it disappeared when the vein was sealed it was then that the fluid inclusions were trapped at homogenization temperatures

regional geodynamic implications of the may july 1990 earthquake sequence in southern sudan abstract several large earthquakes occurred in the south of the sudan in may and july 1990 the focal mechanism solution of the main shock may 20 1990 one of the largest events in africa ever recorded shows left lateral strike slip faulting one of the nodal planes is parallel to the aswa fault zone a major proterozoic tectonic feature a line connecting the epicenters of the main events of may and july also strikes in the same direction field observations and satellite imagery also indicate left lateral horizontal reactivation movement along this large structural feature during cenozoic times the fault plane solutions of the harvard centroid moment tensor catalog for earthquakes between 1977 and 1989 in the east african rift system show extensional horizontal slip component striking about northwest southeast all these facts lead the interpretation of this wide diffuse fault zone as an active intracontinental transform area linking the two main branches of the rift system if one considers this displacement and the slip directions obtained from the centroid moment tensors solutions as characterizing the motion between the nubian and somalian plates new constraints on the regional geodynamics can be inferred the somalian block appears to be moving southeastwards relative to the african block the rupture occurred in at least three steps affecting a zone roughly 50 km long the large aftershocks of 24th may have significantly different fault plane solutions indicating the complexity of the rupture process nevertheless the tension axes of the main aftershocks always strike n s thus there is an exchange of the intermediate and pressure axes for the aftershocks on may 24 relative to the main shock

an experimental evaluation of the reaction of granite with streamwater seawater and nacl solutions at 200 c abstract experiments reacting granite with streamwater seawater and nacl solutions have been conducted at 200 c 50 mpa under batch conditions using direct sampling autoclaves for durations up to 80 days granite streamwater experiments at 10 1 and 2 1 water rock ratios produced fluids of low tds the reaction of granite with seawater produced a fluid of low ph 3 5 and principal changes in the fluid chemistry as follows a gain of sio2 and losses of sulphate magnesium and calcium appreciable mobilisation of heavy metals into the fluid phase such as fe up to 15 mg l and mn up to 2 mg l were noted solid precipitates consisted of anhydrite caminite magnesium hydroxide sulphate hydrate and a mixed layer smectite chlorite clay the low ph of the evolved fluid is attributed to the precipitation of the hydroxyl consuming mineral phases caminite and the smectite chlorite clay the reaction of granite with nacl solutions 0 008 and 0 028 m produced fluids which were similar to those of the streamwater experiments however ph was lower in the nacl experiments 7 4 7 8 so that the steady state concentrations of a number of the cationic constituents of the fluids were slightly greater in these experiments compared with the streamwater experiments the dominant constituent of the product fluids excepting nacl was sio2 the concentration of which was buffered by quartz solubility the sole secondary solid product identified was a sparsely developed illitic clay the injection of a li rb cs na cl fluid into the experiments after 1000 hours demonstrated that the concentrations of the rare alkalis in the fluids were controlled by non equilibrium processes other chemical components perturbed by dilution returned to the steady states developed prior to the injection process demonstrating buffering by metastable reactions with the rock the steady state composition of the fluids was adequately predicted using an assumption of chemical equilibrium between the principal minerals of the granite and thermodynamic data for pure mineral compositions

water percolating behavior indicated by the water chemistry within a decomposed granite slope central japan abstract monitoring rainfall discharge amount and the chemistry of water from just beneath the groundwater table yielded a conceptual model of water percolation behavior within a decomposed granite slope in central japan providing a clue to evaluate a landslide hazard potential by rainstorms when rainfall is strong enough more than about 50 mm a day in this case air pressure in the vadose zone probably increases temporarily because of the downward movement of a wetting front pushing down the water of the capillary fringe the capillary water has sio2 concentrations controlled by the precipitation of cristobalite the water is rich in ca which is supplied from plagioclase with sio2 after the pushing down of the capillary water rainwater with soil water in the unsaturated zone reaches the groundwater surface the cation concentrations in the unsaturated soil water and the capillary water are affected by ion exchange

monazite chemical weathering rare earth element behavior and paleoglaciohydrology since the last glacial maximum for the loch vale watershed colorado usa rare earth element ree release from weathering of accessory monazite ree po4 since the last glacial maximum at 18 1 ka was investigated in sediment recovered from an outlet lake within the glaciated loch vale watershed colorado usa labile rees in the sediments reveal monazite weathering increased during the younger dryas chronozone ydc 13 2 to 11 1 ka when alpine glaciers advanced as climate cooled and bedrock comminution increased monazite dissolution peaked at approximately the pleistocene holocene transition 10 5 ka during the holocene ree concentrations decline reflecting a reduction in monazite weathering the ree cerium ce may occur as trivalent or tetravalent cations and the ce anomaly ce n ce n in sediment permits interpretations of paleoredox conditions the ce n ce n decreases from 18 1 ka to the pleistocene holocene boundary initially oxidizing conditions within the watershed increased because of enlargement of the proglacial area as the ice retreated at the onset of the ydc oxidation further escalated in response to enhanced chemical weathering associated with glacial advance a more stable holocene climate and landscape resulted in relatively small changes in ce n ce n values slightly decreasing ce n ce n values over the last several hundred years are consistent with present day stream water values and may reflect the onset of present day hydrobiogeochemical conditions

hydrochemical and stable isotope indicators of pyrite oxidation in carbonate rich environment the hamersley basin western australia abstract sulphur s is a commonly occurring element in most aquifers primarily in oxidised sulphates and reduced sulphides forms sulphides often constitute a risk to groundwater quality due to acid rock drainage especially in catchments that are subject to mining excavations or groundwater injection however in semi arid regions detection of the acid rock drainage risk can be challenging and traditional methods based on observations of increasing so 4 concentrations or so 4 cl ratios in surface and groundwater are not necessarily applicable in addition decreasing ph usually accompanying pyrite oxidation can be masked by the high ph neutralisation capacity of carbonate and silicate minerals analysis of 73 surface and groundwater samples from different water bodies and aquifers located in the hamersley basin western australia found that most of the samples are characterised by neutral ph but there was also a large spatial variability in the dissolved sulphate so 4 concentrations that ranged from 1 mg l to 15 000 mg l not surprisingly groundwater in aquifers that contained pyrite had high sulphate concentrations 1000 mg l this was associated with low 34 s so4 values 1 2 to 4 6 and was consistent with the values obtained from aquifer matrix pyritic rock samples 1 9 to 4 4 it was also found that the so 4 concentrations and acidity levels were not only dependent on 34 s so4 values and existence of pyrite but also on the presence of carbonate minerals in the aquifer matrix the groundwater in aquifers containing both pyrite and carbonate minerals had a neutral ph and was also saturated with respect to gypsum and had high magnesium concentrations of up to 2200 mg l suggesting de dolomitisation as the process buffering the acidity generated by pyrite oxidation based on the findings from this study a classification scheme has been developed for identification of the acid rock drainage contribution to groundwater that encompasses a myriad of geochemical processes that occur in aqueous systems the classification uses five proxies so 4 so 4 cl si of calcite 34 s so4 and 18 o so4 to improve assessment of the oxidation of sulphide potential contribution to overall sulphate ion concentrations regardless of acidity levels of the aqueous system

strain and displacement in the harts range detachment zone a structural study of the bruna gneiss from the western margin of the entia dome central australia abstract a detailed structural and strain study has been carried out on the bruna granitic gneiss and its bounding thrusts from the western margin of the entia dome in the eastern harts ranges the zone containing the bruna gneiss has been described recently as comprising the harts range detachment zone hrdz a major low angle lithospheric detachment along which both major extensional and contractional movements have occurred the bruna gneiss contains a ductile fabric which varies from an augen streaky foliation through a ribbon gneiss to protomylonite and mylonite in what is predominantly a granitic gneiss conformably overlying the bruna gneiss is a distinctive dark coloured megacrystic gneiss layer which intruded independently from the bulk of the bruna gneiss and followed a different subsequent strain history principal stretch lineations are consistently north plunging or horizontal n s except where folded the bruna gneiss fabrics are complexly folded about axes in an asymmetric manner which suggests interruption of ductile slip and crumpling of the fabrics followed by continuing slip on other discrete surfaces and shear zones strain measurements of elongated feldspars and aggregates indicate moderate to high strains with predominantly plane strain symmetries strain is partitioned into planar parallel zones and suggests dominant heterogeneous simple shear as the main non coaxial flow mechanism flattening strains occur near the bases of two major zones and constrictional strains occur within some zones a strain integration profile across the detachment zone produces total displacements of only a few kilometres suggesting that much of the overall indicated displacement is partitioned into the discrete bounding thrusts asymmetric augen pressure shadows and shear bands provide kinematic indicators in the bruna gneiss most show reverse sense displacement of the overlying harts range cover in a southerly direction over the entia gneiss basement opposite extensional sense movements occur in some zones and especially at the margins of the detachment zone

the loess deposits of buca dei corvi section central italy revisited loess deposits have been described in the past for the upper section of buca dei corvi succession central italy in this paper the deposits were re analysed to clarify the depositional environment and to attempt a paleoclimate reconstruction two radiocarbon dates on pedogenic carbonate constrain the ages to the late glacial and are consistent with previous osl dating of the top of the succession the non marine mollusc assemblage shows typical character of cold and dry climatic conditions testified by strong oligotypical composition mineralogy and geochemistry of the sediments indicate the abundant presence of exotic quartz mineral which can be explained only by wind transport probably wind transport was also responsible of deposition of carbonate which then dissolved and re precipitated producing pedogenic concretions stable isotopes 13c 12c and 18o 16o ratios of the concretions are consistent with a climate drier than present conditions with an environment characterized by sparse vegetation

chemical weathering of a soil chronosequence on granitoid alluvium ii mineralogic and isotopic constraints on the behavior of strontium the use of strontium isotopes to evaluate mineral weathering and identify sources of base cations in catchment waters requires an understanding of the behavior of sr in the soil environment as a function of time our approach is to model the temporal evolution of 87sr 86sr of the cation exchange pool in a soil chronosequence developed on alluvium derived from central sierra nevada granitoids during the past 3 ma with increasing soil age 87sr 86sr of ammonium acetate extractable sr initially decreases from values typical of k feldspar to those of plagioclase and hornblende and then remains constant even though plagioclase and hornblende are absent from the soils after approximately 1 ma of weathering the temporal variation of 87sr 86sr of exchangeable sr is modeled by progressively equilibrating sr derived from mineral weathering and atmospheric deposition with sr on exchange sites as waters infiltrate a soil column observed decreases in quartz normalized modal abundances of plagioclase hornblende and k feldspar with time and the distinct87sr 86sr values of these minerals can be used to calculate sr flux from weathering reactions hydrobiotites in the soils have nearly constant modal abundances chemistry and 87sr 86sr over the chronosequence and provide negligible sr input to weathering solutions the model requires time and soil horizon dependent changes in the amount of exchangeable sr and the efficiency of sr exchange as well as a biologic cycling term the model predicts that exchangeable sr initially has 87sr 86sr identical to that of k feldspar and thus could be dominated by sr leached from k feldspar following deposition of the alluvium the maximum value of 87sr 86sr observed in dilute stream waters associated with granitoids of the yosemite region is likewise similar to that of the k feldspars suggesting that k feldspar and not biotite may be the dominant source of radiogenic sr in the streams this study reveals that when attempting to use strontium isotopes to identify sources of base cations in catchment waters and biomass both preferential leaching of sr from minerals during incipient soil development and changing sr exchange efficiency must be considered along with chemical contributions due to mineral dissolution

first observations of intraseasonal oscillations in the equatorial mesosphere and lower thermosphere we present the first evidence of strong intraseasonal 10 100 day variability of the equatorial mesosphere and lower thermosphere drawn from spectral analysis of three years of radar wind measurements of the region at christmas island 2 n 157 w oscillations in the zonal wind as large as 20 m s 1 are observed with periods 60 days at 85 95 km amplitudes attenuate near 80 km then reintensify near 75 km where they are usually of longer period and are out of phase with the upper level oscillations oscillations with periods 35 40 days are also observed at 85 95 km these oscillations are transient and usually appear when the background flow is westward similar signals are not observed in the meridional winds these facts suggest that they could be kelvin waves similar to intraseasonal variability in the equatorial lower atmosphere associated with the madden julian oscillation somewhat different time height activity at 20 days could be related to the 1 3 rossby normal mode or the 20 25 day tropospheric oscillation as it is unlikely that any of these oscillations could propagate to these heights from the lower atmosphere we postulate that they arise due to variations in gravity wave activity and transmissivity induced by intraseasonal oscillations lower down which is transferred into the mean flow when these gravity waves dissipate in the mesosphere this may mean that this intraseasonal activity is a time varying mean wind rather than a forced planetary wave

alkalinity dynamics in an unacidified alpine lake sierra nevada california gem lake a small unacidificd high elevation lake in the sierra nevada undergoes an annual cycle of low alkalinity between 30 and 40 pcq liter during the ice free season and high alkalinity 240 peq liter in fall and winter both ph and alkalinity decrease drastically up to one unit for ph and 200 peq liter for alkalinity during spring snowmelt but chemistry of the snow snowmelt and runoff indicate that the declines in alkalinity are due to dilution rather than acidification the hydraulic residence time in the lake incrcascs from about 135 d in winter to 7 d during snowmclt high alkalinity water is simply flushed from the lake and replaced by water with an ionic composition very near that of the snowmclt runoff increases in alkalinity in fall and winter can be accounted for by the rates of weathering in the watershed a mass balance approach is used to reconstruct weathering reactions in the basin it suggests that the lake receives both surface runoff with the weathering products of the hydrolysis of granodiorite minerals to kaolinite and deep water from subterranean circulation with the products of granodiorite weathering to both kaolinitc and smectite the relative importances of low alkalinity surface runoff and high alkalinity groundwater to the recharge of the lake are proposed as factors controlling the seasonal bicarbonate concentration of the lake

vertical variation of low frequency oscillations in uhf radar derived winds at a tropical indian station 1 signatures of the low frequency intraseasonal oscillations and their vertical variation in the lower troposphere are studied using multilevel wind observations made at a tropical indian station pune 18 32 n 73 51 e from wind profiler uhf radar during the period june 2003 to may 2006 spectral analysis using fast fourier transform showed the presence of oscillations 30 40 days and 50 70 days in daily mean zonal winds and revealed their evolution in height period structures the 30 40 days oscillation mode has the largest amplitude compared to the other modes in zonal and meridional winds all oscillation modes have much less amplitude in the vertical wind component the high temporal 3 hourly zonal and meridional wind observations obtained during the southwest monsoon period june to september jjas during the years 2003 2004 and 2005 showed a prominent regime of oscillation namely 30 40 days and a moderate signature of 10 20 day mode in all three years it is seen that these oscillations are not occurring as a single frequency sinusoidal oscillation but are seen as broadband spectrum the amplitude of these wave modes showed significant vertical variation the vertical structures of radar observed intraseasonal oscillations 30 40 days mode and tropical rainfall measuring mission derived mean precipitation intensity during the monsoon period jjas during the years 2003 2005 showed a reasonable comparison the results presented in this study show significant intraseasonal and interannual variability in lower tropospheric winds which are closely related to the performance of the southwest monsoon

the synchronism of crustal thickening and high t low p metamorphism in the mount isa inlier australia 1 an example the central soldiers cap belt abstract in the soldiers cap group of the central eastern part of the early to middle proterozoic mount isa inlier tracing of mesoscopic structures has led to the recognition of an early nw closing fold nappe with an e w trending coaxially shortened frontal zone d1 folded around a n s trending upright syncline d2 an andalusite sillimanite prograde metamorphic event indicating a paleo geothermal gradient of approximately 50 c km occurred during early d2 times the coexistence of such moderately high paleo geothermal gradients and crustal thickening is common in the early to middle proterozoic mobile belts of northern australia crust mantle delamination has been suggested by etheridge et al 1987 to explain this coexistence here the thermal implications of this model and the additional thermal effects of waning crustal extension magmatic events and of the radioactive selfheating of the thickened crust are qualitatively discussed

the synchronism of crustal thickening and low pressure facies metamorphism in the mount isa inlier australia 2 fast convective thinning of mantle lithosphere during crustal thickening the mount isa inlier is like some other northern australian early to middle proterozoic fold belts characterized by an anti clockwise p t t path i e regional prograde low p facies metamorphic assemblages grew during crustal thickening p t and were overprinted by a phase of essentially isobaric cooling p 0 t in this study two possible models for the synchronism of regional low p facies metamorphism and crustal thickening are quantitatively evaluated using a one dimensional finite difference technique 1 extreme elevation of isotherms immediately before the thickening event due to e g lithospheric extension magmatic activity or crust mantle delamination and 2 crustal thickening accompanied by convective thinning of the mantle lithosphere only the latter results in prograde low p facies metamorphism during crustal thickening it is the preferred model for the mount isa inlier

an early proterozoic ophiolite the jormua mafic ultramafic complex northeastern finland abstract the 1 96 ga old jormua complex comprises a fault bounded unit 2 5 20 km in the centre of the kainuu schist belt at the eastern margin of the early proterozoic svecokarelides the complex was dismembered and metamorphosed to lower amphibolite facies during the svecokarelian orogeny in the intact complex the basal unit was formed by serpentinites the middle unit of mafic dykes and the uppermost extrusive unit of basaltic pillow lavas gabbroic rocks are present as intrusive bodies in the serpentinites and narrow interdyke screens within the dyke unit trondhjemitic rocks occur as minor segregations in the gabbroic rocks or as cross cutting narrow dykes in the mafic dyke unit the dyke unit is locally composed exclusively of subparallel metabasalt and metadolerite dykes in places interdyke metagabbro and serpentinite screens are abundant well preserved chilled margins are common and many dykes are split and intruded by younger dykes the chemical composition of the serpentinites indicates derivation from harzburgitic dunitic mantle peridotites the gabbroic rocks which represent obvious tholeiitic cumulates show extreme differentiation similar to gabbros of the high ti ophiolites and gabbros dredged from present midocean ridges in chemistry the trondhjemitic rocks are close to granitic rocks from mid ocean ridges and high ti ophiolites the similar chemical composition of the dykes and lavas of the complex indicates that they are cogenetic both being tholeiitic metabasalts with chondrite normalized ree patterns ranging from slightly lree depleted to slightly lree enriched ones compared with modern rocks the jormua metabasalts most closely resemble transitional midocean ridge basalts it is suggested that the jormua complex and related mafic ultramafic bodies in eastern finland originated as divergent margin ophiolites concomitantly with the break up of the archaean craton in the extensional stage of the svecokarelian orogeny which culminated in the opening of a major ocean after 1 97 ga the tectonic emplacement of these ophiolites into their present locations occurred in connection with thrusting during the compressional stage of the orogeny about 1 9 ga ago

the atnarpa igneous complex southeast arunta inlier central australia implications for subduction at an early mid proterozoic continental margin abstract three distinctive igneous suites have been identified from the atnarpa igneous complex southeast margin of the arunta inlier central australia the 1879 11 10 ma gabbro diorite tonalite trondhjemite suite sio2 49 78 shows both calc alkaline and trondhjemitic affinities the overall depletion of nb ti y k and rb in this suite indicates that its parental magma must have been depleted in these elements it is the oldest zircon age so far obtained in the arunta inlier the 1873 11 10 ma low al tonalite trondhjemite granodiorite suite is also depleted in k and rb however unlike either the 1879 ma or the 1751 ma suites it has lower al2o3 and sr at comparable sio2 levels and display flat hrees and negative eu anomalies the 1751 12 ma younger tonalite suite is high in sr sr y and al2o3 and low in zr ti nb y th and u and displays a strongly fractionated ree pattern with hree depletion typical of archaean high al tonalite trondhjemite granodiorite suites such geochemical features contrast with the 1850 1880 ma old k rb ree th enriched na sr depleted barramundi igneous association widespread in proterozoic terrains of northern australia the parental magma of the 1879 11 ma suite is considered to be derived by subduction related partial melting of a metasomatised hybridised mantle wedge with phlogopite retained in the residue the parental magma of the 1873 11 ma low al suite by relatively low pressure partial melting of a mafic source with residual plagioclase left in the residue and the 1751 12 ma younger tonalite suite by partial melting of a subducted oceanic crust at mantle depth with residual garnet amphibole these processes contrast with models of restite unmixing of a geochemically uniform but fractionated preexisting mantle derived underplate previously proposed for the k rich barramundi igneous association combining geochemical features of the atnarpa igneous complex with reported data from the harts range and the alice springs areas we propose that the southeast margin of the arunta inlier represents a convergent continental margin during the early to middle proterozoic which has undergone at least two episodes of subduction related magmatism 1860 1880 ma and 1730 1770 ma such continental margin subduction could provide additional driving force for crust mantle delamination and ensialic a subduction within the preexisting continental crust further north both within plate vertical underplating and marginal lateral accretion could be important processes for proterozoic crustal evolution

direct effects of co2 and temperature on silicate weathering possible implications for climate control a critical uncertainty in models of the global carbon cycle and climate is the combined effect of organic activity temperature and atmospheric co2 on silicate weathering here we present new dissolution rates of anorthite and augite which indicate that silicate weathering in organic rich solutions is not directly affected by soil co2 but is very sensitive to temperature apparently co2 accelerates silicate weathering indirectly by fertilizing organic activity and the production of corrosive organic acids the weathering dependencies highlight the ability of silicate weathering to act as a global thermostat and damp out climate change when used as input in steady state carbon cycle and climate models

amphibolites from the entia gneiss complex eastern arunta inlier geochemical evidence for a proterozoic transition from extensional to compressional tectonics geochemically distinct metabasic amphibolite suites within the dominantly quartzo feldspathic entia basement gneiss complex egc harts range central australia imply two separate magmatic episodes of contrasting tectonic affinity that contributed to the early mid proterozoic crustal evolution of the eastern arunta inlier the metabasic suites directly reflect a distinctive style of proterozoic tectonics involving sequential mantle plume generated extension crustal thinning and subsequent compression crustal thickening that took place on a lithospheric detachment zone during ensialic orogenesis metabasic rocks from an early formed supracrustal association were generated in an intra continental rift environment they have the geochemical characteristics of continental tholeiites similar to metabasites in other eastern arunta basement gneiss terranes younger basic to ultrabasic amphibolites comprise thick massive deformed and metamorphosed sills and small layered igneous bodies that intruded the earlier formed supracrustal sequence trace element characteristics of these rocks e g high la nb and zr nb typify subduction related magmas the data imply an arc or collisional type environment this regime post dating the tensional i e rifting stage a metacumulus origin is proposed for many of these rocks their continuous geochemical trends imply extensive pyroxene dominated fractionation of mantle derived parental magmas in differentiating sill complexes emplaced at depths in the range 20 25 km incompatible element distributions and continuous overlapping major element trends indicate that the cumulate metapyroxenite bodies are related to the early fractionation of voluminous tonalite granodiorite orthogneiss intrusives that comprise a significant portion of the entia dome and which closely resemble intrusive suites commonly observed in cordilleran settings anomalously high k zr rb zr and ba zr ratios for these entia amphibolites together with variations in sio2 ce yb n and k rb ratios indicate contamination of some of the entia magmas by continental crust most likely by small degrees of melting of easily fusible felsic gneiss component aided by high surface area to volume ratio of the sills

depositional age and provenance of the marboo formation from shrimp u pb zircon geochronology implications for the early palaeoproterozoic tectonic evolution of the kimberley region western australia abstract the marboo formation is the oldest rock unit in the hooper complex in the west kimberley region of western australia the complex forms an elongate belt 350 km long and at least 100 km wide of deformed and metamorphosed palaeoproterozoic low to high grade metasedimentary rocks and mafic and felsic igneous rocks the marboo formation consists of a sequence of turbiditic metasedimentary rocks derived from the northwest an area of crust now buried beneath the unconformably overlying speewah and kimberley basins shrimp u pb dating of detrital zircons from a low grade quartz wacke indicate that the provenance terrain contributed zircons dated at around 2500 to 2400 ma 2300 ma 2200 to 2050 ma 1970 ma and 1910 ma the mount joseph migmatite formed by in situ melting of the marboo formation and zircons interpreted as detrital in origin give ages of 2500 to 2000 ma a maximum depositional age is provided by a population of zircon cores dated at 1872 9 ma growth of rims on zircons is dated at 1861 5 ma and is interpreted as the age of high grade metamorphism a minimum age for deposition is provided by the richenda microgranodiorite which forms a high level intrusive stock into the marboo formation and is dated at 1858 5 ma comparison with recent shrimp ages from the halls creek group in the east kimberley indicates that the turbidites of the marboo formation were deposited deformed metamorphosed and intruded by granitoid before the majority of the turbiditic metasedimentary rocks in the olympio formation were deposited this is not consistent with deposition of the turbiditic rocks in the same basin the assumption of contemporaneous turbidite deposition throughout the kimberley region has been taken as evidence of intracratonic palaeoproterozoic orogeny however these results provide support for plate tectonic models and the recognition of tectonostratigraphic terranes within the kimberley region detrital zircons from the marboo formation suggest that unexposed crust beneath the speewah and kimberley basins is largely early palaeoproterozoic in age rather than archaean as previously assumed the spread in ages indicates that the time period between formation of late archaean basement in northern australia and the formation of palaeoproterozoic orogens was marked by ongoing crust formation and was not a period of quiessence

the intra cratonic evolution of the central eastern mount isa inlier northwest queensland australia the central eastern part of the mount isa inlier can be subdivided into three major tectono stratigraphic domains from west to east i the mitakoodi anticlinorium a tight northeast plunging composite anticline which is developed within subaerial to shallow marine continental rift facies lithologies ii the marimo staveley block in which tight to isoclinal folds are developed within a marine shelf iii the central part of the soldiers cap group belt which is dominated by a series of metaturbidites and which hosts a fold nappe refolded about n s to ne sw trending axes the transition from subaerial sediments in the west through marine shelf sediments to turbidites in the east has been one of the main arguments used by advocates for a proterozoic continental margin at this locality here however it is argued that folding and differential uplift along late fault and shear zones led to the juxtaposition of different stratigraphic levels and to the apparent deepening of palaeobasins from subaerial in the west to deep water in the east the age of the soldiers cap group is poorly constrained but it is likely to be older than that of rocks cropping out in the marimo staveley block the marimo staveley block lithologies overlie those of the mitakoodi anticlinorium so here time transgression rather than eastward deepening may be deduced thus a palinspastic reconstruction based on an eastwards progressive deepening is not justified this adds to other evidence that refutes the continental margin model previously proposed for the eastern margin of the mount isa inlier instead the lithostratigraphic sequences reflect several stages of intra continental rifting all without formation of oceanic crust the pervasive post depositional deformational event is associated with regional low p facies metamorphism which indicates a further ensialic history

the northern margin of the capricorn orogen western australia an example of an early proterozoic collision zone abstract the early proterozoic 2200 1600 ma capricorn orogen is a major zone of deformation metamorphism and granite emplacement between the archaean yilgarn and pilbara cratons of northwest australia capricorn orogen structures are recognized along the southern margin of the pilbara craton deforming the archaean granite greenstone terrain of the sylvania inlier together with rocks of the hamersley ashburton and blair basins in the sylvania inlier deformation is characterized by large scale shear zones interpreted as nne directed thrusts in the hamersley basin orogenic deformation forms the ophthalmia fold belt and can be divided into two groups of structures in the southwest large scale dome and basin folds pre ashburton basin are present in the southeast folds and faults are part of a younger syn ashburton basin n directed foreland fold and thrust belt directly linked to deformation in the sylvania inlier the deformed ashburton basin and adjacent parts of the hamersley basin form the ashburton fold belt two periods of deformation are recognized early recumbent folding d1a post ashburton basin pre blair basin and later dextral wrench faulting and associated folding d2a syn or post blair basin capricorn orogen structures are interpreted as the result of an oblique continent continent collision between the pilbara and yilgarn cratons along the southern pilbara margin collision first occurred in the southeast and migrated northwest with the ashburton basin evolving as a foreland basin late stage dextral wrench faulting was the result of westward extrusion of material caught between the opposing craton margins

the role of disseminated calcite in the chemical weathering of granitoid rocks accessory calcite present at concentrations between 300 and 3000 mg kg 1 occurs in fresh granitoid rocks sampled from the merced watershed in yosemite national park ca usa loch vale in rocky mountain national park co usa the panola watershed ga usa and the rio icacos puerto rico calcite occurs as fillings in microfractures as disseminated grains within the silicate matrix and as replacement of calcic cores in plagioclase flow through column experiments using de ionized water saturated with 0 05 atm co2 produced effluents from the fresh granitoid rocks that were dominated by ca and bicarbonate and thermodynamically saturated with calcite during reactions up to 1 7 yr calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates principally biotite mass balance calculations indicate that most calcite had been removed during this time and accounted for 57 98 of the total ca released from these rocks experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution the lack of excess ca and alkalinity indicated that calcite had been previously removed by natural weathering the extent of ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks high ca na ratios relative to plagioclase stoichiometries indicate excess ca in the yosemite loch vale and other alpine watersheds in the sierra nevada and rocky mountains of the western united states this ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains in contrast ca na flux ratios are comparable to or less than the ca na ratios for plagioclase in the subtropical panola and tropical rio icacos watersheds in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport limited weathering these results indicate that the weathering of accessory calcite may strongly influence ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces

zonal mean temperature variations inferred from saber measurements on timed compared with uars observations 1 in the zonal mean meridional winds of the upper mesosphere oscillations with periods between 1 and 4 months have been inferred from uars measurements and independently predicted with the numerical spectral model nsm the wind oscillations tend to be confined to low latitudes and appear to be driven at least in part by wave mean flow interactions winds across the equator should generate due to dynamical heating and cooling temperature oscillations with opposite phase in the two hemispheres investigating this phenomenon we have analyzed saber temperatures from timed in the altitude range between 55 and 95 km to delineate with an empirical model the year long variability of the migrating tides and zonal mean components the inferred seasonal variations of the diurnal tide characterized by amplitude maxima near equinox are in substantial agreement with uars observations and results from the nsm for the zonal mean the dominant seasonal variations in the saber temperatures with annual 12 months and semiannual 6 months periodicities agree well with those derived from uars measurements the intraseasonal variations with periods between 2 and 4 months have amplitudes close to 2 k almost half as large as those for the dominant seasonal variations their amplitudes are in qualitative agreement with the corresponding values inferred from uars during different years the saber and uars temperature variations reveal pronounced hemispherical asymmetries consistent with meridional wind oscillations across the equator the phase of the semiannual temperature oscillations from the nsm agrees with the observations from uars and saber however the amplitudes are systematically smaller which may indicate that planetary waves are more important than is allowed for in the model for the shorter period intraseasonal variations which can be generated by gravity wave drag the model results are generally in better agreement with the observations

carbonate composition and its impact on fluvial geochemistry in the ne tibetan plateau region using co variations of sr ca and mg ca we examined the carbonate compositions of various bedrocks silicate and carbonate rocks and sediments eolian and fluvial sediments sand and topsoil found in the ne tibetan plateau tp region a combined carbonate composition dataset based on our results and other reported data shows that bedrock carbonate composition on the ne tp displays a much broader range of sr ca and mg ca ratios than restricted source carbonate endmembers reported upon in previous studies this has clear implications for modern weathering studies in addition to paleo reconstructions in this tectonically active and climatically variable area during the late cenozoic bedrock carbonate compositions are characterized by disseminated carbonates with higher sr ca and mg ca ratios and sedimentary carbonates mostly marine with lower sr ca but variable mg ca ratios the mostly authigenic carbonates found in sediments show similar trends with a gradient 0 97 1 00 in a plot of log sr ca versus log mg ca suggesting that calcite precipitation processes i e the sources of the dissolved cations in the water control their chemistry based on observations and modeling we conclude that the mixing of authigenic and bedrock carbonate endmembers plus the incongruent dissolution of bedrock carbonates accounts for the bulk carbonate composition of sediments e g loess sand and topsoil a comparison of bedrock and sedimentary carbonate composition with reported fluvial water data in the ne tp suggests that weathering of carbonates in terrigenous sediments rather than in bedrock is mostly responsible for the changes in fluvial sr mg and ca compositions our study suggests that interactions between carbonates and water occur widely during the exposure transport and deposition of sediments significantly modifying regional carbonate compositions and fluvial geochemistry

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

the nature of proterozoic reworking of early archaean gneisses mukalo creek area southern gascoyne province western australia abstract the gascoyne province a key segment of the early proterozoic capricorn orogen which separates the archaean pilbara and yilgarn cratons of western australia may be divided into northern central and southern zones the southern zone comprises predominantly archaean granulite facies quartzo feldspathic gneisses and passes southwards into the western gneiss terrain of the yilgarn block this area was part of the lower crust of a stabilized continental landmass at the end of the archaean development of the capricorn orogen 2 ga ago resulted in discontinuous deformation of the northern part of this landmass deformation was concentrated in ductile shear zones leaving blocks of relatively undeformed gneiss between them the shear zones trend between ene wsw and ese wnw and dip to the south at 50 60 strong down dip stretching lineations and asymmetric feldspar porphyroclasts indicate that the shear zones are reverse faults however metamorphic assemblages in early proterozoic dolerite dykes which post date the shear zones show that the area was still in the lower crust following the earliest proterozoic deformation isothermal uplift of the southern gascoyne province northern yilgarn block by 10 km or more occurred 1 7 1 5 ga ago and was accompanied by granitoid intrusion deformation within e w trending shear zones continued after uplift and was accompanied by patchy greenschist facies retrogression of both static and dynamic style on the local scale the effects of early proterozoic deformation on the early archaean gneisses are generally confined to shear zones and their immediate surroundings they comprise 1 realignment of gneissic trends from n s to e w 2 development of quartz ribbon mylonites by elongation of quartz grains into lenses and ribbons and reduction of feldspar grainsize by crystal plastic processes 3 growth of porphyroblastic and corona garnet in felsic and mafic gneisses the later proterozoic deformation occurred at lower temperatures and resulted in 1 further realignment of gneissic trends from northerly to easterly 2 reduction of quartz grainsize by crystal plastic processes and reduction of feldspar grainsize largely by brittle fracture 3 greenschist facies retrogression that the earliest deformation in the southern gascoyne province resulted in crustal shortening and was followed by significant uplift and granitoid intrusion indicates that proterozoic reworking of this area resulted from regional n s compression this favours development of the capricorn orogen in a collision zone between the pilbara and yilgarn cratons rather than in an ensialic mobile zone

denudation rates determined from the accumulation of in situ produced 10be in the luquillo experimental forest puerto rico we present a simple method for estimation of long term mean denudation rates using in situ produced cosmogenic 10be in fluvial sediments procedures are discussed to account for the effects of soil bioturbation mass wasting and attenuation of cosmic rays by biomass and by local topography our analyses of 10be in quartz from bedrock outcrops soils mass wasting sites and riverine sediment from the icacos river basin in the luquillo experimental forest puerto rico are used to characterize denudation for major landform elements in that basin the 10be concentration of a discharge weighted average of size classes of river sediment corresponds to a long term average denudation of 43 m ma 1 consistent with mass balance results

strontium 87 strontium 86 as a tracer of mineral weathering reactions and calcium sources in an alpine subalpine watershed loch vale colorado sr isotopic ratios of atmospheric deposition surface and subsurface water and geologic materials were measured in an alpine subalpine watershed to characterize weathering reactions and identify sources of dissolved ca in stream water previous studies have noted an excess of ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals mixing calculations based on 87 sr 86 sr indicate that on an annual basis 26 67 of ca export in streams is atmospherically derived 23 61 is from weathering of plagioclase and the remainder is from weathering of calcite present in trace amounts in the bedrock a potential source of error when applying sr isotopes in catchment studies is determination of the 87 sr 86 sr of sr released by mineral weathering which is complicated by the wide range of mineral isotopic compositions particularly in older rocks and the variable rates at which the minerals weather in this study base flow stream chemistry was used to represent the 87 sr 86 sr of sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of sr released by weathering in the alpine environment

geodynamic regimes in the precambrian of the urals abstract of all precambrian rocks in the urals the late proterozoic is best represented the archaean and lower proterozoic are reconstructed from separate blocks massifs which are roughly correlated with the crystalline basement of the adjacent platforms radiometric dates for the majority of early precambrian blocks exceed 2 ga features of very old 2 9 ga protocrustal material have been identified with grey gneiss complexes archaean blocks represent remnants of charnockite granulite and migmatite amphibolite complexes and the geodynamic regime of their generation is the most primitive and does not occur in later periods of geological history the karelian age blocks appear to be relics of nongeosynclinal mobile belts their petrochemical characteristics and ree patterns suggest rift related conditions of their formation late proterozoic deposits 1650 590 ma comprise thick terranes both at the western slope and in the axial zone of the urals revision of rock associations disclosed that these terranes were previously wrongly interpreted as geosynclinal formations they consist of platform sediments and include magmatic rocks which are typical of zones of diaschysis tectonomagmatic activation and rifting recurrent rifting of the elsonian grenville and baikal assynthian cycles of diastrophism was responsible for crustal extension and thinning followed by complete continental breakup and development of oceanic basins in the early palaeozoic only extension in the lower crust during rifting was responsible for dynamometamorphism under different temperature conditions and dropping lithostatic pressure blastomylonites and schists produced during this process were previously mistaken for products of orogenic metamorphism they were considered as evidence of geosynclinal cycles occurring in the late proterozoic and similar to those of the palaeozoic diaschysis and rifting were probably predominant geodynamic regimes in the late precambrian of the urals they resulted in destruction or extensive reworking of the original archaean and early proterozoic crust to variable degrees and in the accumulation of volcano sedimentary and terrigenous rifted depressional successions there is no reliable evidence for the existence of an oceanic basin in the late proterozoic of the urals

origin age and paleoenvironmental significance of carbonate precipitates from a granitic environment akshayuk pass southern baffin island canada this study documents the discovery of calcite crusts on the upper surface of clasts within morainic complexes in akshayuk pass southern cumberland peninsula baffin island a region underlain by granitic and gneissic rocks of the precambrian canadian shield strontium isotope ratios 87 sr 86 sr indicate that the major source of calcium is derived from the local dissolution of fracture filling calcite and a minor source is derived from silicate weathering the calcite crusts have 13 c values between 1 6 and 12 0 and 18 o values in the 13 0 and 7 9 range these values are highly enriched over the predicted isotopic values based on the 13 cdic and 18 o of the local water and temperature at which calcite precipitation occurred the isotopic enrichments are attributed to a combination of both equilibrium and kinetic evaporation and were verified experimentally the series of evaporative experiments indicate that kinetic evapo ration produces a far from equilibrium isotope effect on both the 13 c and 18 o composition of the precipitating calcite 13 ckie caco3 co2 between 20 2 and 40 5 vpdb 18 okie averaging 34 9 3 7 vsmow based on these re sults the formation of the calcite crusts is ascribed to the evaporation of stagnating ephemeral lakes and streams fol lowing the retreat of valley glaciers given the 1500 m difference in heights between the highland and the valley the katabatic winds originating from the penny ice cap can act as a catalyst to increase the rate of evaporation in ad dition radiocarbon dating of ten of these crusts yielded holocene ages 7640 cal calibrated bp to modern these re sults suggest that the maximum expansion of holocene valley glacier in akshayuk pass previously thought to have occurred during the little ice age is probably much older

granite weathering and the sensitivity of alpine lakes to acid deposition lake chemical data from the national surface water survey nsws were corrected for the effects of regional atmospheric deposition and then used to evaluate the role of weathering in supplying base cations silica sulfate and alkalinity to surface waters in alpine vs subalpine and in glaciated vs unglaciated granitic terrane of the western and southeastern united states thermodynamic models idealized reaction stoichiometry and multivariate regression involving solutes and geographic variables indicate that irreversible weathering can largely account for lake chemistry by contrast relatively minor roles are played by reversible ion exchange in soils and sediments terrestrial bioaccumulation and transformations in lakes the regional patterns in lake acidity components no so4 doc co3 and statistical relationships between acidity and base cations demonstrate that rock weathering is limited by acid inputs in many alpine catchments prior to fall overturn the empirical success of the henriksen alkalinity model depends on a high ca na weathering ratio the latter increases with increasing physical disturbance of the catchment iuvenility hence under natural circumstances attains a maximum as a result of on going or recent glaciation the henriksen model fails in geochemically old terrane where cation losses accompanying silicate weathering attain steady state proportions

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

the petrology and geochemistry of granitic gneisses from the east arunta inlier central australia implications for proterozoic crustal development the entia gneiss complex is an early to middle proterozoic inlier composed of upper amphibolite facies orthogneisses and paragneisses in the eastern end of the arunta block in central australia it is separated from overlying structurally distinct compositionally different and probably younger gneisses of the harts range complex by a subhorizontal detachment zone this paper discusses the petrology of four major granitic gneiss bodies one of these the bruna gneiss has intruded this detachment zone the other three are components of the structurally underlying entia gneiss complex the entia gneiss complex has a distinctive subhorizontally layered character with recumbent folds and flat lying schistosity the granitic gneisses that are components of this complex appear to have intruded an actively deforming terrain and are folded sheet like bodies the orthogneisses of the entia complex range from gabbro to true granite in composition and the granites are i type on both geochemical and petrographic criteria they are significantly different from the relatively alkali rich granites of equivalent age which occur in some of the other northern australian proterozoic blocks and are most like the granites of the modern cordilleran belts particularly in the association of diorite and gabbro with granodiorite it is suggested they are formed in narrow collisional belts formed as a result of closure of intracratonic rift basins the high surface area to volume ratio of these granites which is a consequence of the deformational environment into which they were intruded has resulted in considerable wall rock exchange in the more differentiated end members of the suites this has led to contamination by a net gain of k2o rb and ba and loss of relatively compatible elements including the ree y nb and tio2 compared with the syn tectonic entia granites the bruna granite gneiss is post tectonic and shows geochemical affinities with a type or anorogenic palaeozoic granites most of this granite is confined to the detachment zone but the very latest phases also intrude the harts range cover sequence an important conclusion of this study is that detachment zones of the type described from this area of the eastern arunta block exercise strong control on plutonism into the early to middle proterozoic crust as long as the very mobile style of early proterozoic tectonics continues the intracrustal dislocation zone confines syn tectonic granitic magmatism to deeper levels

intra seasonal oscillations observed in the mlt region above uk 52 n 2 w and esrange 68 n 21 e 1 analyses of intra seasonal oscillations i e oscillations with periods of 30 100 days in the mlt region made by meteor radars at middle uk five years of data and high latitudes esrange three years of data are presented in this work there is clear evidence of 75 day variability in the mean winds this intra seasonal oscillation appears to be a prominent feature of the mean zonal circulation and was observed quite regularly in the time intervals december 1996 september 2001 over uk and october 1999 december 2002 over esrange the intra seasonal oscillations observed over esrange are coherent in both amplitude and phase over the height range of 80 100 km covered by the radar they are especially strong in the range 90 97 km weaker near 87 88 km and stronger again near 81 km at these lower heights the intra seasonal oscillations are usually of longer period 80 days than and are out of phase with the oscillations at the upper heights we also note that this oscillation is a common feature in the meridional winds over the uk it is present but intermittent in the meridional winds over esrange

collision tectonics in the late precambrian eastern ghats mobile belt mesoscopic to satellite scale structural observations regional mapping of a section across the eastern ghats mobile belt egmb north of the godavari graben in eastern peninsular india by using landsat thematic mapper data enables recognition of a number of shear zones lineaments and structural domes and basins a conspicuous megashear occurs at the western boundary of the granulite facies rocks of the egmb adjacent to the archean granite greenstone craton the confinement of a suite of alkaline igneous rocks to this shear zone is a notable feature the strike extensions of this shear belt extend through to the elchuru alkaline complex prakasam district andhra pradesh and the syenite plutons of koraput district orissa the contrasting lithologies metamorphism and structural history on either side of the shear zone suggests that it might be a precambrian suture zone the mesoscopic structural features in the egmb include prominent foliation with moderate to steep dips folds faults shears s c fabrics pinch and swell structures and other linear fabric elements these observations favour the consideration of drastic crustal shortening and thickening and a complex deformational sequence the major rock units in this part of egmb comprise garnetiferous sillimanite gneisses quartzites and calc granulites forming the khondalitic suite of rocks and a wide variety of charnockitic rocks the contact of the two rock units is generally sheared and often migmatised the structural fabric suggests two major tectonic events an essentially horizontal tectonic regime resulting in thrust systems and associated structures subsequently followed by strike slip tectonics characterized by high shear strains features such as westward verging thrusts large scale recumbent folds major shear zones structural domes and basins indications of tectonic crustal shortening extensive calc alkali magmatism and widespread migmatization in the region are attributed to collisional processes during proterozoic times the spatial disposition of the egmb and its linkage with the distribution of similar rock units during the late precambrian time in a global tectonic scenario are discussed

petrology geochemistry and origin of a major australian 1880 1840 ma felsic volcano plutonic suite a model for intracontinental felsic magma generation in australia a major period of felsic volcanism and granite emplacement occurred between 1880 and 1840 ma towards the end of the early proterozoic these volcanics and granites covering at least 37 000 km2 are compositionally uniform over large areas the felsic magmas are predominantly i type being derived from infracrustal sources which have never been exposed to surficial weathering processes when compared with early archaean and phanerozoic i type granites the 1880 1840 ma suite has distinctively high levels of k2o rb zr la ce th u and low mgo and cao contents even at relatively low sio2 levels of 60 65 the 1880 1840 ma rocks are characterized by low initial 87sr 86sr ratios and negative nd values chemical and isotopic modelling on these volcanics and granites suggest that they formed from mantle derived sources that are around 2300 2000 ma old there is no evidence of a major archaean component in these granites the sources are interpreted to have formed as a result of polygonal small scale mantle convection which led to extensive underplating of archaean crust during this underplating event large volumes of incompatible element enriched mantle derived material accreted to the base of the lower crust and fractionated significantly the more fractionated part of this source was remelted between 1880 1840 ma to produce the voluminous felsic volcanics and comagmatic granites present in nearly every proterozoic domain of australia the actual underplating event between 2300 2000 ma is believed to have triggered the formation of early proterozoic sedimentary basins which occur in a polygonal pattern and appear to wrap around archaean nuclei the composition of these felsic melts and the tectonic setting operating during their emplacement precludes genesis by contemporaneous subduction of oceanic crust all are generated by processes of vertical accretion in an intracontinental environment

reconnaissance geochronology tectonothermal evolution and regional significance of the middle proterozoic choma kalomo block southern zambia abstract new u pb zircon 40 ar 39 ar rb sr and sm nd data provide the first numerical chronology for the tectonothermal evolution of the choma kalomo block an extensive middle proterozoic terrane in southern zambia to the south of the pan african zambezi belt the choma kalomo batholith a large plutonic body in the central part of the block is shown to be a composite intrusion emplaced from c 1345 to 1200 ma based on u pb zircon ages and detailed mapping of intrusive relations early phases of the batholith were intruded as syntectonic to late syntectonic plutons during development of a penetrative s 1 fabric in the metasedimentary country rocks of the choma kalomo block d 2 folding produced the regional ne sw structural trends in the block and possibly occurred at c 1230 ma based on an rb sr isochron from an early phase of the batholith containing a penetrative s 2 foliation an u pb zircon age of c 1200 ma from post tectonic granite provides a younger limit to the timing of d 2 40 ar 39 ar mineral ages from the posttectonic granite and sm nd and 40 ar 39 ar mineral ages from amphibolites in country rock paragneisses range from c 1200 to 500 ma recording post d 2 cooling followed by subsequent low grade pan african overprinting along the southern margin of the zambezi belt d 1 in the choma kalomo block at c 1345 ma is substantially younger than early proterozoic orogenesis in adjacent terranes to the east in zimbabwe indicating that a major precambrian discontinuity beneath the mid zambezi valley separates these regions d 1 in the block is similar in age to plutonic and deformational events dated at c 1350 1400 ma in the irumide belt of central and northern zambia suggesting that these two terranes on each side of the younger cross cutting zambezi belt are parts of a single originally continuous middle proterozoic mobile belt continuity between the choma kalomo block and broadly coeval terranes to the southwest in namibia and south africa also appears likely and all of these areas are considered to form parts of a middle proterozoic orogenic province lying west of the kaapvaal and zimbabwe cratons

chemical weathering in the krishna basin and western ghats of the deccan traps india rates of basalt weathering and their controls rates of chemical and silicate weathering of the deccan trap basalts india have been determined through major ion measurements in the headwaters of the krishna and the bhima rivers their tributaries and the west flowing streams of the western ghats all of which flow almost entirely through the deccan basalts samples n 63 for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002 the total dissolved solid tds in the samples range from 27 to 640 mg l 1 the rivers draining the western ghats that flow through patches of cation deficient lateritic soils have lower tds average 74 mg l 1 whereas the bhima except at origin and its tributaries that seem to receive na cl and so4 from saline soils and anthropogenic inputs have values in excess of 170 mg l 1 many of the rivers sampled are supersaturated with respect to calcite the chemical weathering rates cwr of selected basins which exclude rivers supersaturated in calcite and which have high cl and so4 are in range of 3 to 60 t km 2 y 1 this yields an area weighted average cwr of 16 t km 2 y 1 for the deccan traps this is a factor of 2 lower than that reported for the narmada tapti wainganga ntw systems draining the more northern regions of the deccan the difference can be because of i natural variations in cwr among the different basins of the deccan ii selection of river basin for cwr calculation in this study and iii possible contribution of major ions from sources in addition to basalts to rivers of the northern deccan traps silicate weathering rates swr in the selected basins calculated using dissolved mg as an index varies between 3 to 60 t km 2 y 1 nearly identical to their cwr the ca mg and na mg in these rivers after correcting for rain input are quite similar to those in average basalts of the region suggesting near congruent release of ca mg and na from basalts to rivers comparison of calculated and measured silicate ca in these rivers indicates that at most 30 of ca can be of nonsilicate origin a likely source being carbonates in basalts and sediments the chemical and silicate weathering rates of the west flowing rivers of the deccan are 4 times higher than the east flowing rivers this difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates the silicon weathering rate swr in the krishna basin is 15 t km 2 y 1 within a factor of 2 to those in the yamuna bhagirathi and alaknanda basins of the himalaya suggesting that under favourable conditions intense physical weathering high runoff granites and the other silicates in the himalaya weather at rates similar to those of deccan basalts the co2 consumption rate for the deccan is deduced to be 3 6 105 moles km 2 y 1 based on the swr the rate though is two to three times lower than reported for the ntw rivers system it still reinforces the earlier findings that in general basalts weather more rapidly than other silicates and that they significantly influence the atmospheric co2 budget on long term scales

weathering rates of bedrock by lichens a mini watershed study the chemical weathering rate of rock substrates by saxicolous lichens was measured quantitatively and compared with the weathering rate of bare rock in the cone pond area at hubbard brook experimental forest usa the experiments used mini watersheds 1 m2 on outcrops of mica schist a laboratory mini watershed experiment and a thin section analysis were also conducted during the course of the study computed cumulative flux ratios of the weathering rate of lichen covered versus bare rock mini watersheds for mg2 16 7 and si 4 0 3 were significant the rate of denudation of the rock was calculated to be higher for the lichen mini watershed than the bare rock mini watershed a laboratory mini watershed experiment demonstrated the same trend of higher elemental fluxes for the lichen mini watershed than the bare rock mini watershed for k mg2 na and si the weathering rind beneath the lichen was measured to be between 0 2 and 0 5 mm thick these results show the significance of biotic enhancement of chemical weathering this research also calculated the rate of denudation of the rock by lichens and supported the mini watershed studies as a reliable method to study the chemical weathering by lichens bryophytes and plants in thin soil and alpine areas

caterpillar tectonics in the harts range area a kinship between two sequential proterozoic extension collision orogenic belts within the eastern arunta inlier of central australia abstract we propose that in the harts range area of the arunta inlier of central australia a basement and cover relationship previously described by us represents a thick complexly deformed contact zone between an early middle proterozoic fold belt the strangways orogenic belt sob and a younger middle proterozoic orogenic belt the harts range orogenic belt both of which contain their own supracrustal sequences rocks of the sob were deposited and possibly metamorphosed to a maximum grade of granulite facies at 1800 ma during an early phase of crustal extension they were subsequently intruded by a significant proportion of acidic magmas at 1767 ma and compressed to form a distinctively nne ssw trending orogenic belt a wnw ese trending shallowly north dipping zone of intense and repeated deformation termed the harts range detachment zone hrdz formed initially during a period of nne ssw crustal extension as a major low angle normal shear detachment zone within and crosses at a high angle to the trend of the basement rocks of the sob the hrdz has been intermittently active as a zone of crustal weakness since its initiation the first extensional movement on this zone began the formation of the harts range mobile belt hrmb which displays many of the characteristics of modern tectonic zones activated by plate movement a supracrustal cover sequence the harts range cover hrc formed in the major geosynclinal basin which developed on the subsiding upper plate of the hrdz continued crustal extension juxtaposed the cover sequence which was then metamorphosed to a maximum grade of amphibolite facies and granulite facies basement of the hrdz before a fundamental change in movement sense led to crustal contraction and a collision related thrusting phase the hrmb which includes the hrdz and the hrc was then internally deformed over a relatively very short time span 15 20 ma before voluminous granitic magma intruded mainly along the hrdz during the harts range orogeny hro the intrusion of this major granitoid at 1747 ma precisely fixes the time scale of evolution for the earlier phases of the hro the hro is documented in detail as a peculiar orogenic style of crustal contraction which was largely taken up by reverse sense discrete thrusting and shearing on faults and shear zones associated with the hrdz displacement on the hrdz was a stick slip process with repeated punctuation of thrust slip movement by pinning at points located progressively to the south each period of cessation of thrust slip movement was followed by folding of discrete thrusts of captured basement lobes within the hrdz and of the overlying supracrustal sequence the individual discrete movement phases and folding episodes are each named and described as is a model of this unusual type of proterozoic tectonic activity

chemical variation in a proterozoic suite of granitoids extending across a mobile belt craton boundary contrary to earlier opinions the southwestern margin of the baltic shield was formed after the svecokarelian orogenic event 2 2 1 8 ga during the initial stages of its formation 1 7 1 6 ga granitoid rocks intruded the southwestern margin and simultaneously also the already cratonized part of the shield among these granitoids the most important chemical difference is between calc alkalic differentiated granitoids to the west and alkalicalcic more evolved granites to the east of an intraorogenic suture the mylonite zone the chemical differences between alkali calcic granites found on both sides of the interorogen boundary proper the protogine zone are less significant as yet a final choice cannot be made between wholly actualistic and non actualistic possibly intracratonic variants of precursory plate tectonic processes

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

sedimentary and volcanic evolution of a neoproterozoic continental margin bleida anti atlas morocco abstract a tentative geodynamic evolution of the neoproterozoic continental margin of the northern border of the west african craton is reconstructed using both sedimentological observations and geochemical arguments from volcanic rocks the rifting stage was marked first by intermittent subsidence of a very shallow shelf environment leading to deeper water sedimentation conditions with local surges of deltaic channels this rifting stage was also characterized by the eruption of a 500 m thick pile of submarine basic lava flows with geochemical characteristics similar to those generally observed in basaltic lavas erupted during continental rifting this first rifting stage 790 ma clauer 1976 was succeeded by a drastic change both in sedimentation and volcanism the younger sediments are deep water distal turbidites with associated pyritic black shales they include a few highly differentiated tholeiitic flows and sedimentary exhalative copper deposits linked to felsic volcanism these changes are attributed to the development of deep water oceanic basins along the northern border of the west african craton the closure of this pan african oceanic domain occurred by transpression tectonics along this major lithospheric transform zone which is roughly e w trending

pb and nd isotope and trace element constraints on the origin of basic rocks in an early proterozoic igneous complex minnesota abstract a suite of early proterozoic basic to granitic rocks exposed near st cloud minnesota are cut by northeast trending basaltic dikes pb isotope data for all of these rocks overlap and plot about an 1800 ma pb pb correlation line the basic rocks which are light ree enriched have nd values between 0 4 and 4 8 petrogenetic considerations suggest that the basic rocks were derived from a light ree enriched source which had an fe mg ratio greater than that for pyrolite the enrichment in fe mg is probably a result of the addition of basic melts to the source the light ree enrichment may have a mantle origin by the addition of mantle derived light ree enriched basic melts or fluids or a sedimentary origin by the addition of light ree enriched fluids or melts derived from subducted sediments with an early proterozoic provenance in either case the nd isotopes suggest that the light ree enriched component existed since c 2300 ma the igneous complex may have formed at a convergent margin an anorthositic gabbro near mora has an nd of 5 indicating that it was derived from a mantle source with a history of light ree depletion this gabbro may have been part of an early proterozoic ocean crust

basalt weathering in central siberia under permafrost conditions chemical weathering of basalts in the putorana plateau central siberia has been studied by combining chemical and mineralogical analysis of solids rocks soils river sediments and suspended matter and fluid solution chemistry altogether 70 large and small rivers 30 soil pore waters and groundwaters and over 30 solids were sampled during july to august 2001 analysis of multiannual data on discharge and chemical composition of several rivers of the region available from the russian hydrological survey allowed rigorous estimation of mean annual major element concentrations and dissolved and suspended fluxes associated with basalt weathering for the rivers tembenchi and taimura that drain monolithologic basic volcanic rocks the mean multiannual flux of total dissolved cations tds c ca mg na k corrected for atmospheric input is 5 7 0 5 t km 2 yr for the largest river nizhniya tunguska draining essentially basic rocks the tds c is 6 1 1 5 t km 2 yr the overall co2 consumption flux associated with basalt weathering in the studied region 700 000 km 2 achieves 0 08 10 12 mol yr which represents only 2 6 of the total co2 consumption associated with basalt weathering at the earth s surface the fluxes of suspended matter were estimated as 3 1 0 5 9 0 0 8 and 6 5 2 0 t km 2 yr for rivers taimura eratchimo and nizhniya tunguska respectively based on chemical analyses of river solutes and suspended matter the relative dissolved versus particulate annual transport of major components is cinorg corg na k ca mg si fe mn ti al which reflects the usual order of element mobility during weathering according to chemical and mineralogical soil and sediment analyses alteration of basalt consists of 1 replacement of the original basaltic glass by si al fe rich amorphous material 2 mechanical desegregation and grinding of parent rocks leading to accumulation of primary hydrothermal trioctahedral smectite and 3 transformation of these trioctahedral oxy smectites and mixed layer chlorite smectite into secondary dioctahedral smectite accompanied by removal of ca mg and fe and enrichment in al no vertical chemical differentiation of fluid and solid phases within the soil profile was identified all sampled soil pore waters and groundwaters were found to be close to equilibrium with respect to chalcedony gibbsite halloysite and allophanes but strongly supersaturated with respect to goethite nontronite and montmorillonite over the annual cycle the contribution of atmospheric precipitation permafrost melting underground reservoirs litter degradation and rock and soil mineral weathering for the overall tds c transport in the largest river of the region nizhniya tunguska is 9 3 3 10 5 10 5 5 25 20 and 45 30 respectively in the summertime direct contribution of rocks and soil mineral weathering via solid fluid interaction does not exceed 20 the main unknown factors of element mobilization from basalt to the river is litter degradation in the upper soil horizon and parameters of element turnover in the vegetation copyright 2005 elsevier ltd

chemical weathering and cation loss in a base poor watershed weathering of minerals in soils provides important plant nutrients and consumes acidity yet mineral weathering is difficult to observe and quantify we derived present day weathering flux estimates for soil minerals in a forested watershed in central new hampshire using a geochemical mass balance the cone pond watershed is characterized by low alkalinity surface waters and acidic spodosols developed on a thin mantle of locally derived till making it susceptible to continued inputs of acid precipitation weathering reactions were developed on the basis of observed patterns of mineral abundance in the soil profile and measured mineral chemistry the dissolution of approximately 171 mol ha 1 yr 1 of plagioclase feldspar is the predominant weathering reaction at cone pond weathering fluxes of hornblende biotite chlorite and potassium feldspar ranged from 3 to 20 mol ha 1 yr 1 an order of magnitude lower when normalized to their abundances in the soil however hornblende and chlorite had the fastest weathering rates as measured by cation release chemical weathering mainly of plagioclase resulted in the neutralization of only 52 of incoming acidity furthermore silicate weathering could only account for the release of about 53 mol ha 1 yr 1 of ca compared to the observed net output stream loss minus bulk precipitation input of 75 mol ha 1 yr 1 on the basis of these observations and a companion study we conclude that current acid inputs exceed the ability of cone pond soils to neutralize hydrogen ion and that depletion of approximately 22 53 mol ha 1 yr 1 of ca from labile soil pools is occurring in this area the rate of ca depletion is one third to one eighth of the rate estimated for a more base rich watershed nearby

low latitude mesospheric mean winds observed by gadanki mesosphere stratosphere troposphere mst radar and comparison with rocket high resolution doppler imager hrdi and mf radar measurements and hwm93 1 low latitude mesospheric winds are investigated using data collected from 1995 to 2006 11 years by indian mst radar located at gadanki 13 5 n 79 2 e clear eastward and westward flow in zonal wind is noticed during solstices and equinoxes respectively the meridional wind shows equatorward flow below 75 km and poleward flow above 75 km quite consistent with that observed with other techniques the winds show a clear semiannual oscillation sao with maxima during equinoxes the strength of the sao during spring is larger than that of fall equinox and the first peak occurs at higher altitudes than the second peak the observed features are compared with other techniques namely rocket high resolution doppler imager hrdi and medium frequency mf radar and also with horizontal wind model hwm93 in general good comparison is seen among various techniques with some discrepancy observed in amplitudes interestingly decrease in eastward wind with time during winter months is noticed the significance of the present results lies in showing the consistency inconsistency of various experimental techniques to measure the middle atmospheric winds which are very important to assess the climate variability

extra tropical atmospheric response to enso in the cmip5 models the seasonal mean extra tropical atmospheric response to el nino southern oscillation enso is assessed in the historical and pre industrial control cmip5 simulations this analysis considers two types of el nino events characterized by positive sea surface temperature sst anomalies in either the central equatorial pacific cp or eastern equatorial pacific ep as well as ep and cp la nina events characterized by negative sst anomalies in the same two regions seasonal mean geopotential height anomalies in key regions typify the magnitude and structure of the disruption of the walker circulation cell in the tropical pacific upper tropospheric enso teleconnections and the polar stratospheric response in the cmip5 ensembles the magnitude of the walker cell disruption is correlated with the strength of the mid latitude responses in the upper troposphere i e the north pacific and south pacific lows strengthen during el nino events the simulated responses to el nino and la nina have opposite sign the seasonal mean extra tropical upper tropospheric responses to ep and cp events are indistinguishable the enso responses in the merra reanalysis lie within the model scatter of the historical simulations similar responses are simulated in the pre industrial and historical cmip5 simulations overall there is a weak correlation between the strength of the tropical response to enso and the strength of the polar stratospheric response enso related polar stratospheric variability is best simulated in the high top subset of models with a well resolved stratosphere