origin of a washboard moraine of the des moines lobe inferred from sediment properties abstract geometric characteristics of the washboard moraines of the des moines lobe dml of the laurentide ice sheet agree with their proposed origin as crevasse squeeze ridges but study of their sediments is required to help further test this hypothesis a 70 m long 3 5 m high section through a moraine ridge in central iowa revealed till with irregular isolated lenses of silt sand and gravel that dip to varying extents upglacier the texture and density of the till are like those of the basal till of the dml studied elsewhere in iowa and preconsolidation pressures determined from tests on till and silt of the ridge indicate that it developed subglacially rather than at the glacier margin preconsolidation pressures additionally demonstrate that pore water pressures in the bed supported most of the glacier s weight which would have contributed to till mobility fabrics based on the anisotropy of magnetic susceptibility of 3125 intact till specimens collected at 125 locations in the section indicate two end member states of strain that varied with location in the ridge and caused sediment mounding simple shear that was directed downglacier along shear planes inclined upglacier together with pure shear where an overlying crevasse allowed the sediment bed to extend upward and laterally meltwater that likely flowed along the crevasse deposited sorted sediments that were incorporated in till deformed and rotated this positive test of the crevasse squeeze hypothesis indicates that the dml was in longitudinal extension near its margin reinforcing previous arguments that the lobe surged the predominance of fabrics caused by simple shear demonstrates that crevasse filling was underway before the surge had fully halted this study should prompt caution in using similar transverse ridges such as those geophysically imaged in some submarine glacier forefields as indicators of retreat rates

the effect of phosphorus on manganocolumbite and mangaotantalite solubility in peralkaline to peraluminous granitic melts solubility experiments of mn columbite mnnb2o6 and mn tantalite mnta2o6 were conducted under water saturated conditions in synthetic haplogranitic melts containing different amounts of phosphorus at 800 c and 100 mpa all experiments were carried out in cold seal rapid quenching pressure vessels rqv with water as a pressure medium experimental results show that 1 the solubilities of mnnb2o6 and mnta2o6 in peralkaline melts are higher than those in peraluminous melts 2 phosphorus has strong influence on the solubilities of mnta2o6 and mnnb2o6 in peralkaline melts kspnb and kspta decrease from 104 89 10 4 mol2 kg2 and 107 62 10 4 mol2 kg2 for melts without p2o5 to 16 11 10 4 mol2 kg2 and 7 96 10 4 mol2 kg2 for melts containing 4 00 wt p2o5 respectively 3 phosphorus has less influence on the solubilities of mnta2o6 and mnnb2o6 in peraluminous melt kspnb decrease from 4 50 10 4 mol2 kg2 for melts without p2o5 to 0 73 10 4 mol2 kg2 and kspta from 3 57 10 4 mol2 kg2 to 0 14 10 4 mol2 kg2 for melts contaning 5 00 wt p2o5 taking the structural role of phosphorus into account p decreases the solubility of mn columbite and mn tantalite via competing for network modifiers

microstructural interpretations of modern and pleistocene subglacially deformed sediments the relative role of parent material and subglacial processes analysis of till micromorphology represents a relatively new technique that has been used most frequently to infer the importance of subglacial shear in till genesis this study aims to calibrate the technique by comparing pleistocene tills from united kingdom with a modern till the upb till from beneath ice stream b west antarctica despite the fact that all of the tills examined have been interpreted as deforming bed deposits the modern till has significantly less abundant and diverse microstructures than those found in the pleistocene tills seventeen examined thin sections of the upb till contain recognisable microstructures over only 0 30 of individual thin section area the most common microstructures are i birefringent clay patterns that are interpreted as shear zones and ii adherent matrix structures which we interpret as uncomminuted remnants of the parent glacial glaciomarine diamictons fourteen thin sections of the pleistocene tills were covered by microstructures in 10 95 of their area the pleistocene microstructures include birefringent clays and adherent matrix structures as in the upb till but also laminations and deformed pods made of chalk and sorted sediments we conclude that the same till forming process i e subglacial deformation may result in distinctly different till micromorphology this is a consequence of the fact that microstructural characteristics are strongly influenced by factors other than shear deformation we identify three controls that may be important for forming contrasting microstructural assemblages i strain magnitude ii the degree of heterogeneity of parent material and iii relative importance of sediment sorting by flowing water in the subglacial environment thus till micromorphology is sensitive to multiple factors which with proper calibration may enhance the existing capability to interpret past subglacial conditions from microstructures copyright 2001 john wiley sons ltd

the solubility of nb ta zr hf w in granitic melts with li and li f constraints for mineralization in rare metal granites and pegmatites tantalum mineralization is associated with granites and pegmatites that invariably are rich in lithium this in part is due to the extreme fractionation that is necessary for melts to reach saturation in either a ta or an li phase however there may also be chemical interactions in melts that explain this association experiments therefore were conducted to determine the effect of lithium on the solubility of tantalite mnta 2 o 6 in water saturated granitic melts other important elements in rare metal granites include nb zr hf and w consequently the effect of li on the solubilities of columbite mnnb 2 o 6 zircon zrsio 4 hafnon hfsio 4 and hbnerite mnwo 4 in granitic melts was also investigated the haplogranitic melt compositions used in these experiments have constant mole percent si and al and the al li na k ratio was 1 0 for all experiments i e the lithium content was the only compositional variable columbite and tantalite solubilities in the granitic liquids increase by a factor of approximately 2 to 3 with the addition of 2 wt percent li 2 o to haplogranite at 750 degrees to 1 035 degrees c 2 kbars and water saturated conditions the solubility data were extrapolated to a lower temperature more reasonable for columbite tantalite crystallization then compared to compositions representative of evolved liquids from which rare metal granites and pegmatites crystallize it is estimated that at 600 degrees c these melt compositions could be saturated in columbite but not tantalite however tantalite saturation is predicted if the melts contained less li and f therefore the genesis of tantalum mineralization may be explained by ta being retained in the melt because of high li f concentrations tantalite crystallization is delayed until an li or f or p mineral crystallizes which lowers tantalite solubility and results in a general association of ta with li in mineralized granitic rocks in contrast to columbite and tantalite the solubility of wolframite is not affected by the lithium content of the melt with up to 3 8 wt li 2 o in starting glasses and the solubilities of zircon and hafnon decrease with increasing li content of the melt one possible interpretation of the hbnerite solubility data is that the melt contains dominantly w super 6 which behaves as a network former the decrease in zircon hafnon solubility with li may reflect the lower field strength of zr super 4 and hf super 4 compared to nb super 5 and ta super 5 i e zr and hf are less able to compete with li for nonbridging oxygens whereas nb and ta are more able to compete it is also significant that the solubility of hafnon is greater than that of zircon similar to the higher solubility of tantalite compared to columbite this can explain why zr hf and nb ta ratios both decrease with fractionation

a morphometric analysis of tunnel valleys in the eastern north sea based on 3d seismic data a 1250 km2 3d seismic volume is used to provide a detailed spatial and geometrical analysis of fifteen pleistocene tunnel valleys in the danish north sea all the valleys are buried they are up to 39 km long 3 4 km wide and up to 350 m deep the valleys are part of a vast tunnel valley province covering an area of some 0 5 million km2 of the formerly glaciated lowland areas of north west europe the valleys consist of non branching non anastomosing troughs they exhibit strongly undulating bottom profiles with numerous sub basins and thresholds and are characterised by adverse end slopes cross cutting relationships and theoretical considerations suggest the occurrence of seven major episodes of valley incision attributed to ice marginal oscillations within a few glacials calculations considering the valley end gradients and theoretical ice surface profiles suggest that the valleys were formed by pressurised subglacial meltwater erosion given a range of theoretical ice surface profiles the adverse end slopes are well beyond the supercooling threshold which suggests that the water was not in thermal equilibrium with the basal ice and that flow was concentrated in substantial conduits with sufficient mass and flux to maintain water temperature well above the freezing point copyright 2007 john wiley sons ltd

influence of fluorine on the solubility of manganotantalite mnta2o6 and manganocolumbite mnnb2o6 in granitic melts an experimental study abstract solubility experiments of manganotantalite mnta 2 o 6 and manganocolumbite mnnb 2 o 6 were conducted under nearly fluid saturated conditions in synthetic haplogranitic hpg and natural granitic ng melts containing different amounts of fluorine at 800 to 1000 c and 200 mpa the experiments were carried out in cold seal pressure vessels at 800 c with water or ar as a pressure medium and in internally heated pressure vessels 1000 c with ar as a pressure medium the f contents vary from 0 to 11 43 wt in experiments using hpg melts and from 0 61 to 3 78 wt in experiments using ng melts additionally the ng melt contains minor amounts of p 2 o 5 0 44 to 0 64 wt in hpg melts alumina saturation index including mn asi mn 0 88 to 0 99 the solubility product values at 800 c yield log k sp ta and log k sp nb ranging from 3 36 0 10 to 2 92 0 10 mol kg and from 3 01 0 11 to 2 87 0 06 mol kg respectively in ng melts the log k sp ta and log k sp nb vary from 3 00 0 04 to 2 35 0 13 mol kg and from 2 83 0 06 to 2 67 0 18 mol kg at 800 c respectively the solubility products of both mnta 2 o 6 k sp ta and mnnb 2 o 6 k sp nb are not significantly affected by the f content for a given melt composition data are virtually identical within error the variation of the solubility products observed in this study is rather attributed to the changes in melt structure e g polymerization and in particular to the alumina saturation index by contrast there is no evidence for the formation of complexes associating f and nb and or ta our results also indicate that the structural changes caused by the incorporation of f in natural water rich silicate melts are not expected to significantly influence the maximum concentrations of nb and ta in granitic or pegmatitic melts coexisting with manganotantalite and manganocolumbite

preconsolidation pressures in the battleford formation southern saskatchewan canada soft surficial unoxidized till of the battleford formation overlies hard oxidized and unoxidized till of the floral formation the difference in hardness between these two formations is the result of preconsolidation pressures that range from 1500 to 2200 kpa in the floral formation and from 350 to 750 kpa in the lower till unit of the battleford formation the upper till and clay unit of the battleford formation which represents a conformable contact between this formation and the overlying glaciolacustrine clay is normally consolidated preconsolidation of the floral formation apparently took place upglacier where the potentiometric surface for subglacial beds was 170 240 m below the ice surface the lower till unit of the battleford formation was deposited from and consolidated under stagnant ice the upper normally consolidated till and clay unit of the battleford formation was let down upon the lower till unit by ablation the calculated minimum stagnant ice thickness required for consolidation

glacial geological implications of overconsolidated sediments on the lomonosov ridge and yermak plateau with the coupled use of multibeam swath bathymetry high resolution subbottom profiling and sediment coring from icebreakers in the arctic ocean there is a growing awareness of the prevalence of quaternary ice grounding events on many of the topographic highs found in present water depths of 1000 m in some regions such as the lomonosov ridge and yermak plateau overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin however there exists no comprehensive analysis of the geotechnical properties of these sediments or how their inferred stress state may be related to different glacigenic processes or types of ice loading here we combine geophysical stratigraphic and geotechnical measurements from the lomonosov ridge and yermak plateau and discuss the glacial geological implications of overconsolidated sediments the degree of overconsolidation determined from measurements of porosity and shear strength is shown to result from consolidation and or deformation below grounded ice and with the exception of a single region on the lomonosov ridge cannot be explained by erosion of overlying sediments we demonstrate that the amount and depth of porosity loss associated with a middle quaternary w790e950 thousand years ago e ka grounding on the yermak plateau is compatible with sediment consolidation under an ice sheet or ice rise conversely geotechnical properties of sediments from beneath late quaternary ice groundings in both regions independently dated to marine isotope stage mis 6 indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf

response of sediment to ice sheet loading in northwestern germany effective stresses and glacier bed stability laboratory tests on sediment over ridden by the last ice sheet in northwestern germany reveal very low ice induced pre consolidation and high palaeo pore water pressures sediment consolidation at the base of the glacier was largely controlled by hydraulic properties of the substratum generally low permeabilities of the bed caused sustained high pore water pressure in over ridden sediments close to the flotation point this implies a serious possibility of hydraulic lifting of the ice sheet it is believed that the reduced basal coupling limited the transformation of glacier shear stress on to the bed sediments which is indicated by a lack of sedimentological evidence for widespread pervasive bed deformation ice motion was probably focused at the glacier sole by some combination of sliding and ploughing however isolated spots with deformation occur so that the subglacial system in the study area can be characterized as a stable deforming mosaic

evolution of mid channel bars in a braided river and complex response to reservoir construction an example from the middle hanjiang river china using the middle hanjiang river as an example this paper deals with the development of mid channel bars in a braided river as controlled by channel boundary conditions runoff and sediment load as well as reservoir construction relations have been established between indices describing the mid channel bars and the controlling variables such as the channel width the percentage silt clay content in the channel boundary and the energy expenditure of flowing water bank erosion provides space and material for mid channel bar formation so bank erosion rate can be closely related to mid channel bar indices the middle channel bars exhibit a complex evolutionary response to the reservoir regulated hydrological regime in the middle hanjiang river a descriptive model showing the complex response has been established 1997 john wiley sons ltd

coarse sediment storage and connectivity and off highway vehicle use board camp creek arkansas abstract upper board camp creek bcc in western arkansas drains the wolf pen gap wpg trail complex a designated off highway vehicle ohv area in use since the 1990s the mixed bedrock alluvial channel is quite active with extensive bars and eroding banks present within the higher order main valley channels this study was conducted to determine the relative magnitudes of sediment storage and production within the channel and whether geomorphic changes are synchronous with establishment and increasing ohv use levels on the trail system fourteen geomorphically active reaches within the main valley channels representing the range of conditions of bcc within the wpg complex were examined in detail all sites had significant alluvial storage in the form of point lateral or mid channel bars dominated by cobble and gravel sediment storage volumes ranged from 140 to nearly 10 000 m3 per kilometer of channel with a mean of about 3400 eleven of 14 reaches also had actively eroding banks ten reaches 71 exhibited net sediment storage two are possible net sources and two may be in approximate steady state storage erosion the imbalance between local bank erosion sources and in channel storage and the evidence of activity and mobility of most of the bars indicates a connected system with coarse sediment mobile during banktop flow events and no evidence of sediment starvation finer

physical conditions at the base of a fast moving antarctic ice stream boreholes drilled to the bottom of ice stream b in the west antarctic ice sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1 6 bars of the ice overburden pressure these conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick the mechanics of ice streaming plays a role in the response of the ice sheet to climatic change

flow mechanism of the des moines lobe of the laurentide ice sheet rapid flow of the des moines lobe of the laurentide ice sheet may have been related to its unlithified substrate new reconstructions of the lobe based on moraine elevations sediment subsidence during moraine deposition and flow direction indicators indicate that the lobe may have been 3 times thicker than in previous reconstructions nevertheless implied basal shear stresses are 15 kpa so internal ice deformation was not significant instead the lobe likely moved by a combination of sliding plowing of particles through the bed surface and bed shear consolidation tests on basal till yield preconsolidation stresses of 125 300 kpa so effective normal stresses on the bed were small a model of sliding and plowing indicates that at such stresses most particles gripped by the ice may have plowed easily through the till bed resulting in too small a shear traction on the bed to shear it at depth consistent with this prediction measurements of orientations of clasts in basal till yield a weak fabric implying pervasive bed shear strain less than 2 although some stronger fabrics have been reported by others we infer tentatively that movement was principally at the bed surface by plowing

sources of radiogenic helium in a clay till aquitard and its use to evaluate the timing of geologic events abstract concentrations of dissolved gases he ne ar and n 2 were measured in pore waters collected from a pleistocene 0 80 m depth and cretaceous 80 156 m depth aged clay rich aquitard system using both a conventional copper tube method and in situ diffusion samplers both methods yielded similar results he data revealed a well defined increase in concentration with depth from 1 7 10 8 cm 3 he stp g 1 water near the water table at 2 3 m below ground surface to 6 9 10 6 cm 3 he stp g 1 water at 80 m below ground surface b g the concentration at depth greatly exceeded values for atmospheric solubility at in situ temperatures and could not be attributed to steady state production from decay of u and th within the aquitard system trends in he isotope ratios and concentrations suggest accumulation as a result of both release of residual 4 he from within the pleistocene clay rich till ca 87 and an ascending radiogenic helium flux from underlying cretaceous age sediments ca 13 one dimensional transport modeling of the he data suggests that between 15 ka and 25 ka were required to produce the observed profile this time frame agrees with studies utilizing isotope tracers i e d h and 14 c dic to estimate the timing of deposition for the till at this site our results demonstrate the utility of using helium a nonreactive tracer for delineating hydrogeologic processes in slow permeability geologic strata and also support the contention that thick clay rich surficial aquitards can provide long term containment of contaminants including hazardous wastes

the denholm landslide saskatchewan part i geology the denholm landslide whose surface is composed of scarps ridges and elongated depressions is 160 m high 2000 m wide and up to 100 m thick the shear zone is in silty montomorillonitic clay of the upper part of the lea park formation and upper colorado group unit the upper cretaceous judith river formation and the quaternary empress sutherland and saskatoon groups were affected by the landslide although these sediments were fractured and gravity faulted by tension when the landslide moved they can be readily traced through the landslide particularly the upper part the scarps gravity faults ridges horsts and elongated depressions grabens are the surface expression of tension resulting from the stretching of beds during the landslide the movement of the landslide is thought to have started when the north saskatchewan spillway eroded to the level of the present shear zone about 11 000 years ago established by radiocarbon dating and is believed to have stopped in recent time during th

a petrologic assessment of internal zonation in granitic pegmatites abstract cameron et al 1949 devised the nomenclature and delineated the patterns of internal zonation within granitic pegmatites that are in use today zonation in pegmatites is manifested both in mineralogy and in fabric mineral habits and rock texture although internal zonation is a conspicuous and distinctive attribute of pegmatites there has been no thorough effort to explain that mineralogical and textural evolution in relation to the zoning sequence presented by cameron et al 1949 or in terms of the comprehensive petrogenesis of pegmatite bodies pressure temperature and whole rock composition this overview of internal zonation within granitic pegmatites consists of four principal parts 1 a historic review of the subject 2 a summary of the current understanding of the pegmatite forming environment 3 the processes that determine mineralogical and textural zonation in pegmatites and 4 the applications of those processes to each of the major zones of pegmatites based on the concepts presented in london 2008 the fundamental determinates of the internal evolution of pegmatite zones are 1 the bulk composition of melt 2 the magnitude of liquidus undercooling prior to the onset of crystallization 3 subsolidus isothermal fractional crystallization by which eutectic or minimum melts fractionate by sequential non eutectic crystallization 4 constitutional zone refining via the creation of a boundary layer liquid chemically distinct from but continuous with the bulk melt at the crystallization front and 5 far field chemical diffusion the long range and coordinated diffusion of ions particularly of alkalis and alkaline earths through melt

pleistocene stratigraphy of the saskatoon area saskatchewan canada an update pleistocene deposits in the saskatoon area are divided into the sutherland and saskatoon groups the sutherland group is divided into the mennon dundurn and warman formations and the saskatoon group is divided into the floral and battleford formations the floral formation is subdivided into the lower till the riddell member and the upper till each formation is composed of a sequence of deposits including basal proglacial sediment till upper proglacial sediment and nonglacial sediment each formation is defined primarily on the basis of carbonate content and stratigraphic position of its till and commonly it is bounded by weathered zones and or nonglacial sediments the sutherland group is pre illinoian in age and the lower till of the floral formation is illinoian in age the riddell member between the lower and upper tills of the floral formation is late rancholabrean probably sangamon in age radiocarbon ages of sediments lying between the upper till of the floral formation early wis

preconsolidation of tills and intertill clays by glacial loading in southern saskatchewan canada preconsolidation of pre battleford tills and intertill clays resulted in a narrow range of effective pressures 1800 200 kpa at 10 sites along a 1300 km transect across southern saskatchewan these data suggest an almost invariant loading system that is independent of total ice thickness which ranged from 1150 to 2000 m the preconsolidation process apparently took place in a temperate glacier environment the loading system is characterized as a variable thickness of ice related to distance from the glacier terminus a steady hydraulic grade line sustained a potentiometric surface within the subglacial sediments at an elevation consistently 69 76 of the total ice thickness this mechanism maintains small fluctuations in effective stress

internal differentiation of rare element pegmatites effects of boron phosphorus and fluorine lithium rich rare element pegmatites are characterized by high concentrations of b p and f the interactions of these components with h2o and rare alkalis lower liquidas and solidus temperatures enhance silicate liquid h2o miscibility and control partitioning and concentration of group i elements and higher field strength cations boron f and perhaps p may form peralkaline na and li species that promote early saturation in mica quartz activities of f p and especially b are largely unbuffered throughout crystallization concentration of these components through fractional crystallization involving muscovite generates a peralkaline na aluminosilicate rich melt or vapor from which albitites rich in tourmaline phosphates f rich micas beryl zircon and nb ta sn oxides crystallize phase equilibrium experiments with peraluminous b p f rich rhyolite obsidian macusanite simulate many features of rare element pegmatites especially at h2o undersaturated conditions

petrogenesis of tourmaline granites and topaz granites the contribution of experimental data abstract fluorine and boron are generally only minor components of granitic rocks but may be found highly concentrated in certain tourmaline granites and topaz granites up to 1 wt b2o3 and 3 2 wt f respectively studies of various examples of these granite types which occur as small bodies emplaced at shallow levels p lithostatic textural and petrographic data indicate that the tourmaline and topaz granite magmas crystallized at low to moderate temperatures below 700 c and that a fluid phase may have been present during the crystallization interval both granites varieties are peraluminous co up to 5 characterized by the presence of white micas lithium micas or muscovite aluminium silicates and other al rich minerals garnet cordierite boron and fluorine are hosted by tourmaline schorl rich member of the schorl dravite series topaz and mica respectively these granites have low ca fe mg and ti contents each the crystallization of tourmaline granite and topaz granite magmas is discussed using experimental data derived from studies of granitic systems with added boron and fluorine both elements act as a flux enabling boron and fluorine enriched melts to persist to temperatures as low as 650 c at 1 kbar in addition the effect of increasing fluorine content displaces the minimum in q ab or at ph2o 1 kbar toward the albite apex plots of fluorine rich topaz granites coincide with this trend suggesting that the role of fluorine in magmatic processes may have affected the rock composition as well as crystallization temperatures boron rich granites plot near the low ph2o minima in qz ab or suggesting that boron has less of an influence on minimum melt compositions the low temperatures of crystallization permits phases such as muscovite or andalusite topaz and two alkali feldspars to crystallize directly from f and b enriched melts at low pressures in addition the limited available experimental data are used to compare the effects of fluorine and boron on major and trace element distribution during melt vapour interaction

preconsolidation pressures in intertill glaciolacustrine clay near blaine lake saskatchewan soft intertill glaciolacustrine clays are of concern for stability of slopes and foundations an intertill clay deposit between 32 and 54 m below the surface was continuously cored index properties were determined for 46 samples and 10 samples were tested on the oedometer stratigraphic evidence indicates that the glaciolacustrine clay blaine lake member lying between the till of the sutherland and saskatoon groups was glaciated three times however preconsolidation pressures of this intertill clay show the degree of consolidation is less than 20 based on a total stress from an estimated ice thickness extrapolated from the cypress hills this low preconsolidation pressure suggests there was insufficient time for dissipation of excess pore water pressure created by thickening of the advancing glacier key words preconsolidation pressure excess pore water pressure glaciers intertill clay

melt inclusions in quartz from an evolved peraluminous pegmatite geochemical evidence for strong tin enrichment in fluorine rich and phosphorus rich residual liquids abstract we have investigated the magmatic evolution of a late stage f and p rich pegmatite forming aluminosilicate liquid and the geochemical controls on magmatic mineralizing processes by remelting totally crystallized melt inclusions in quartz and analyzing the quenched glass by epma and sims the quartz phenocrysts were sampled from a pegmatite that occurs in a variscan granite genetically associated with cassiterite and wolframite mineralized greisen veins at the ehrenfriedersdorf sn w deposit central erzgebirge se germany the melt inclusion compositions imply that the pegmatite forming liquid achieved extreme levels of chemical differentiation it contained high abundances of sn f p li rb cs nb ta and be and abnormally low concentrations of ca y sr and ree for a granite and it was strongly peraluminous the molar al 2 o 3 cao na 2 o k 2 o ranged from 1 3 to 2 0 fractions of the pegmatite forming liquid were extremely enriched in p 2 o 5 f al 2 o 3 and the molar abundances of f p in the glasses correlate strongly with moles of network modifying al ions implying that the bulk liquid included f p and al bearing complexes formation of these complexes reduced the activities of f p and al in bulk liquid suppressed the crystallization of magmatic topaz and p rich minerals and allowed the liquid to become enriched in these constituents some fractions of the ehrenfriedersdorf aluminosilicate liquid contained 1000 2000 ppm sn these levels of sn enrichment were up to 2 orders of magnitude greater than that ever reported for nonmineralized metaluminous and peraluminous igneous materials and are consistent with some experimentally derived sn solubilities in cassiterite saturated granitic liquids at geologically relevant pressures and temperatures this concordance implies that cassiterite could have crystallized directly from this highly evolved p and f rich peraluminous granitic liquid without the involvement of hydrothermal fluids

the meandering braided river threshold a reappraisal abstract the concept of a threshold discharge slope q s combination that separates braided from meandering streams is critically re examined partly by review of previous data and partly by analysis of new data from south island new zealand it is argue d that discriminant functions that use mean annual discharge provide a poor physical basis for interpretations based on natural processes while bankfull discharge is also deficient because it is not a fully independent variable the common use of channel rather than valley slope adds a further misleading component because channel slope is partly dependent on channel pattern sinuosity most previous studies have inadequately treated the role of bed particle size in pattern discrimination failing to recognize that active gravel streams must plot higher on a q s chart than sand bed channels irrespective of pattern because of the greater power requirements for bed material movement within any one size class of bed material there is no evidence to indicate a clear discrimination between braiding and meandering only a weak statistical association between pattern and slope discharge values while this association may be explicable in terms of the high shear stress and stream power that accompany high qs values promoting braiding the real prerequisite for braiding appears to be high loads of bed calibre material producing wide shallow channels a factor that is only partly controlled by stream power accordingly the search for a pattern threshold based on discharge and slope seems to be a futile exercise an interpretation of existing pattern discriminant functions from the perspective of the threshold shear stress for particle movement is made it is concluded that in effect these functions merely state that gravel bed streams are more likely to be braided than channels in finer sediment statistically this appears to be valid and reasons for that difference are offered based on the balance between imposed bed material load and channel capacity

experimental constraints on the effect of phosphorous and boron on nb and ta ore formation abstract evolved granites and pegmatites are important sources for critical metals including niobium nb and tantalum ta the ore deposits that are commonly associated with these granitic rocks are commonly enriched in phosphorous p and boron b yet there are few experimental constraints on the influence of these fluxing compounds on ore forming processes here the effects of phosphorous p boron b temperature and melt alkalinity on the solubility of manganocolumbite mnnb 2 o 6 and manganotantalite mnta 2 o 6 in evolved fluid saturated granitic melts were studied solubility experiments were performed at 100 mpa and 800 to 1000 c using three haplogranitic melt compositions with alumina saturation indices asi of 0 8 peralkaline 1 0 subaluminous and 1 2 peraluminous the possible effect of p and the influence of b in p rich granitic systems were investigated by adding 4 wt p 2 o 5 and 4 wt p 2 o 5 4 wt b 2 o 3 respectively to the starting compositions the addition of p decreased the solubility of manganocolumbite and manganotantalite in peralkaline granitic melts in agreement with previous studies we suggest that p was present as network forming alkali phosphate complexes such as m x po y in the peralkaline melt structure m k na etc resulting in the observed effect of p at asi 0 8 the presence of p had a positive effect on the solubility of manganocolumbite and manganotantalite in subaluminous granitic melts which became less significant in peraluminous systems this may reflect the formation of complexes such as al x po y and ta nb x po y in the melt empirical relationships describing the effect of p on manganocolumbite and manganotantalite solubility in the aforementioned haplogranitc melts at 100 mpa and 800 c were determined the addition of b to p rich peralkaline melts had a minor effect on manganocolumbite solubility but resulted in an increase of manganocolumbite and manganotantalite solubility in subaluminous systems for peraluminous melts a minor increase of the solubility of manganocolumbite and manganotantalite with the addition of b was typically observed we propose that the addition of b to the p enriched melts resulted in the formation of network forming boro phosphate complexes until the b p molar ratio in the melts reached unity once the b p molar ratio was greater than one polymerizing mbo 2 complexes were probably formed in peralkaline melts while b acted presumably as a network modifier in subaluminous and peraluminous systems with b p 1 in combination with literature data we determined similar dissolution enthalpies for manganocolumbite and manganotantalite for given a asi and pressure where the dissolution enthalpy increased with asi from 60 kj mol at asi 0 6 to 150 kj mol at asi 1 2 cooling is thus likely to be of greater importance for magmatic mineralization in peraluminous compared to peralkaline systems the primary influence of b and p in peraluminous systems is to act as fluxes lowering the crystallization temperature of melts which allows for the crystallization of primary magmatic tantalite

apatite in felsic rocks a model for the estimation of initial halogen concentrations in the bishop tuff long valley and tuolumne intrusive suite sierra nevada batholith magmas

decompression experiments as an insight into ascent rates of silicic magmas an experimental study of h2o exsolution bubble growth and microlite crystallisation during ascent decompression of silicic magmas in the volcanic conduit is presented isobaric and decompression experiments were performed on a rhyolitic melt at 860 c nno 1 h2o saturation and pressures between 15 and 170 mpa two sets of decompression experiments were performed with decompression rates varying between 0 001 and 960 mpa min 1 from 150 to 50 mpa high pressure decompression and 2 from 50 to 15 mpa low pressure decompression the experiments highlight incomplete h2o exsolution for decompression rates 100 mpa min incomplete bubble growth for decompression rates 0 1 mpa min crystal nucleation time lags and incomplete chemical re equilibration to final pressures the observed crystallisation process i e growth versus nucleation depends on the decompression range indeed decompression induced crystallisation during high pressure decompressions is dominated by growth of existing crystals whereas during low pressure decompressions crystal nucleation is the dominating process this study provides a means to infer magma ascent rates in eruptions of silicic magmas through a combined petrologic and experimental approach

modeling the subglacial hydrology of the james lobe of the laurentide ice sheet to investigate the drainage conditions that might be expected to develop beneath soft bedded ice sheets we modeled the subglacial hydrology of the james lobe of the laurentide ice sheet from hudson bay to the missouri river simulations suggest the james lobe had little effect on regional groundwater flow because the poorly conductive upper cretaceous shale that occupies the upper layer of the bedrock would have functioned as a regional aquitard this implies that general northward groundwater flow out of the williston basin has likely persisted throughout the quaternary moreover the simulations indicate that the regional aquifer system could not have drained even the minimum amount of basal meltwater that might have been produced from at the glacier bed therefore excess drainage must have occurred by some sort of channelized drainage network at the ice till interface using a regional groundwater model to determine the hydraulic conductivity for an equivalent porous medium in a 1 m thick zone between the ice and underlying sediment and assuming conduit dimensions from previous theoretical work we use a theoretical karst aquifer analog as a heuristic approach to estimate the spacing of subglacial conduits that would have been required at the ice till interface to evacuate the minimum water flux results suggest that for conduits assumed to be on the order of a tenth of a meter deep and up to a meter wide inter conduit spacing must be on the order of tens hundreds of meters apart to maintain basal water pressures below the ice overburden pressure while evacuating the hypothesized minimum meltwater flux r 2007 elsevier ltd all rights reserved

basal mechanics of ice stream b west antarctica 1 till mechanics data from laboratory geotechnical tests on till recovered from beneath ice stream b west antarctica at the upstream b camp hereinafter the upb till show that failure strength of this till is strongly dependent on effective stress but is practically independent of strain and strain rate these data support use of a coulomb plastic rheology in modeling of ice stream behavior and subglacial till deformation our testing program combined triaxial ring shear and confined uniaxial tests to investigate till strength and compressibility results show that the upb till follows closely coulomb s equation in which shear strength is a linear function of normal effective stress apparent cohesion near zero and internal friction angle equal to 24 till compressibility is best described by a logarithmic function that relates void ratio to normal effective stress in general the behavior of the upb till is consistent with other experimental evidence regarding mechanical behavior of granular materials based on our laboratory results we formulate the compressible coulomb plastic till model in which there are three interrelated primary state variables shear strength void ratio and normal effective stress this model is used in the second part of our study to simulate response of subglacial till to realistic effective stress forcings these simulations demonstrate that the model is capable of reproducing fundamental aspects of subglacial till kinematics 1 occurrence of tilt rate oscillations and negative tilt rates in tiltmeter records and 2 distributed till deformation to depths of 0 1 1 0 m beneath the ice base our laboratory and modeling results substantiate application of the compressible coulomb plastic model in simulations of the motion of ice stream b over its weak till bed

underlying gravel layers in a large sand bed river and their influence on downstream dam channel adjustment due to the changes in environmental factors during a river s historical development underlying gravel layers are found in many large plain rivers when the buried depth of this gravel layer is within the reach of down cutting by clear water scour after reservoir construction it may be exposed and exert a far reaching influence on channel adjustment in hanjiang river the longest tributary of the yangtze river in china down cutting has been greatly reduced and even stopped due to the total change of bed material composition the exposure of a gravel layer results in a dramatic increase in the bed s hydraulic roughness so the channel slope may increase after a decline during the period prior to the exposure of the gravel layer moreover the exposed gravel layer increases the erosion resistance of bed material making a lower relative erosion resistance of bank to bed material where the bank s erosional resistance is weak this may lead to a tendency towards channel widening

textural features and chemical evolution in tantalum oxides magmatic versus hydrothermal origins for ta mineralization in the tanco lower pegmatite manitoba canada tantalum a key element in the electronics industry is produced mainly from rare element granitic pegmatites although their internal structure mineralogy and petrogenesis have been extensively investigated the processes that control tantalum mineralization remain poorly understood in particular the role of fluids in the crystallization of tantalum ore one of the major problems arises from the difficulty in distinguishing primary magmatic from secondary hydrothermal textures in such complex rocks in the tanco pegmatite manitoba canada tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite eight different families of tantalum oxides occur in various associations and compositions the tanco lower pegmatite is an isolated body beneath the main pegmatite body that contains abundant tantalum associated with mica alteration tantalum mineralization in the tanco lower pegmatite occurs as three different styles facies 1 is hosted by the wall zone and hosts primary magmatic ta oxides with simple textures progressive and oscillatory zoning facies 2 is hosted by the lower and upper intermediate zones where most mineralization occurs with dendritic amblygonite facies 3 is hosted by the central zone which is affected by mica alteration in this latter facies the oxides show particularly complex textures evident from x ray mapping by combining information obtained from textural observations and chemical analyses we are able to determine the paragenesis for each ta oxide bearing mineral assemblage and hence to evaluate the relative contributions of magmatic versus hydrothermal processes in complex associations we observe relics of primary ta phases that are replaced or overgrown by secondary ta phases we propose the paragenetic sequence columbite group minerals microlite early primary magmatic columbite wodginite group minerals microlite late primary magmatic wodginite group minerals microlite secondary magmatic ferrotapiolite secondary magmatic in addition chemical variations were identified in the columbite and wodginite group minerals both at the crystal scale and at the pegmatite scale columbite and wodginite group minerals show the typical ta ta ta nb and mn mn mn fe atomic ratios increase from earlier to later zones at the crystal scale the increase in ta and mn with fractionation in the columbite group is explained by the higher solubility of the ta end member relative to the nb end member and the crystallization of other minerals that shift the melt composition toward mn enrichment the fractionation trend in the wodginite group shows fe enrichment which is consistent with experimental results that show a higher solubility of the fe end member relative to the mn end member in columbite group minerals considering the available experimental data as well as the intimate association of ta oxides with zircon observed in this study we conclude that tantalum mineralization is a product of direct crystallization from the melt rather than hydrothermal in origin fluids are attributed an indirect role only as they could have brought minor elements fe mn or ca into the melt which resulted in the crystallization of secondary ta phases textural evidence shows that the late secondary phases were formed at the same time as mica alteration we suggest that mica alteration was due to a late melt rather than a hydrothermal fluid that reacted with the blocky k feldspar of the central zone during the alteration event tantalum was remobilized from primary phases and incorporated in new secondary ta oxide species

tracing fluid saturation during pegmatite differentiation by studying the fluid inclusion evolution and multiphase cassiterite mineralisation of the gatumba pegmatite dyke system nw rwanda abstract aqueous fluid saturation during the internal evolution of phosphorus and boron rich pegmatites in nw rwanda has been investigated using petrography fluid inclusion microthermometry and microanalysis of minerals and fluid inclusions raman microspectroscopy and la icp ms the gatumba dyke system gds in rwanda has been selected for this study because it hosts a multiphase cassiterite mineralisation in wall core and internal replacement zones suggesting an advancing influence of magmatic hydrothermal conditions during dyke solidification as such multiphase cassiterite precipitation is applied as a tracer for magmatic to hydrothermal crystallisation processes in granitic pegmatites the gds consists of a group of six major lct lithium caesium tantalum family dykes which all belong to the most differentiated rare element pegmatites in the gatumba gitarama field petrography identified a well developed internal anatomy consisting of a border wall intermediate and a quartz core zone in addition replacement zones developed as cleavelandite after perthitic microcline units in the intermediate zone and as muscovite quartz pockets in the intermediate and wall zones the latter replacement zone display muscovitisation reactions with the formation of greisens texturally the greisen pockets replace the secondary cleavelandite units during internal differentiation multiphase cassiterite mineralisation formed in 1 large microcline crystals of the wall zone cst1 2 assemblage with quartz f poor montebrasite and carbonate and boron enriched mn fluorapatite in the core zone cst2 and 3 the greisen replacement units in the wall and intermediate zones cst3 fluid inclusion micro analyses demonstrate that a saline aqueous h2o nacl kcl co2 n2 l1 type fluid 20 wt nacl and 3 wt kcl was saturated during onset of crystallisation of the wall and intermediate zones and precipitation of the disseminated magmatic hydrothermal cst1 mineralisation in and around large perthitic k feldspars isochore reconstructions of this l1 fluid indicate crystallisation conditions of 535 560 c and 5 1 5 6 kbar for the gds extensive microcline fractionation and subsequent replacement reactions of cleavelandite after microcline in the intermediate zone were induced by a li enriched and more na depleted h2o nacl licl co2 n2 l2 type fluid which was present during solidification of the core zone and present during precipitation of cst2 phase mineralisation 6 12 wt nacl 1 10 wt licl late stage hydrothermal cst3 mineralisation in the greisen pockets precipitated from a cs enriched h2o nacl kcl co2 n2 l3 type fluid 15 wt nacl distinctly after the formation of the cleavelandite replacement units subsolidus cst3 precipitation is dominantly driven by metasomatic hydrolytic fluid rock reactions combining textural microthermometric and fluid compositional data with reported sn melt fluid partitioning and solubility data demonstrate that primary cassiterite i e cst1 and cst2 in the wall and core zone of the gds precipitated from the exsolved saline aqueous l1 and l2 fluid present at the interface of the highly fractionated melt phase fast disequilibrium growth of near anhydrous mineral assemblages likely caused the formation of flux rich and at least locally water saturated melt compositions at the crystallisation front of the large crystals this study emphasises the importance of local magmatic hydrothermal conditions and the presence of an immiscible aqueous fluid phase during the internal crystallisation and cassiterite mineralisation of rare element pegmatites

geomorphology and till architecture of terrestrial palaeo ice streams of the southwest laurentide ice sheet a borehole stratigraphic approach abstract a multidimensional study utilising geomorphological mapping and the analysis of regional borehole stratigraphy is employed to elucidate the regional till architecture of terrestrial palaeo ice streams relating to the late wisconsinan southwest laurentide ice sheet detailed mapping over a 57 400 km2 area of southwestern saskatchewan confirms previous reconstructions of a former southerly flowing ice stream demarcated by a 800 km long corridor of megaflutes and mega scale glacial lineations ice stream 1 and cross cut by three formerly southeast flowing ice streams ice streams 2a b and c analysis of the lithologic and geophysical characteristics of 197 borehole samples within these corridors reveals 17 stratigraphic units comprising multiple tills and associated stratified sediments overlying preglacial deposits the till thicknesses varying with both topography and distance down corridor reconciling this regional till architecture with the surficial geomorphology reveals that surficial units are spatially consistent with a dynamic switch in flow direction recorded by the cross cutting corridors of ice streams 1 2a b and c the general thickening of tills towards lobate ice stream margins is consistent with subglacial deformation theory and variations in this pattern on a more localised scale are attributed to influences of subglacial topography including thickening at buried valley margins thinning over uplands and thickening in overridden ice marginal landforms

red deer hill a drumlinized glaciotectonic feature near prince albert saskatchewan canada red deer hill is 5 km long 3 km wide and 70 m high the hill is a glaciotectonic structure formed by a single 106 m thick thrust block presumably derived from the 80 m deep upglacier holmes depression the thrust block became dislodged by displacement along a presheared horizontal gouge zone where the shearing resistance of the clay was reduced to a residual state by the first mennon glaciation the hill depression structure was formed by the battleford glacier which drumlinized red deer hill before depositing a veneer of till over the structure the holmes depression was filled with glacial lake saskatchewan lacustrine and deltaic sediments horizontal displacement along a decollement in the direction of the activating force resulted in a stress environment changing from extension to compression in the zone of extension holmes depression an active rankine state developed and beds stretched and thinned in the zone of compression red deer hill conversely a passive rankine state developed an

statistical analysis of lateral migration of the rio grande new mexico abstract the lateral migration rates of alluvial rivers are affected by changes in water and sediment regimes the rio grande downstream from cochiti dam exhibits spatial and temporal variability in lateral movement rates documented since 1918 a tremendous database exists that documents planform bed material size channel geometry and water and sediment regimes a statistical analysis reveals that migration rates primarily decreased with decreasing flow energy r2 0 50 p 60 the findings show that lateral movement increases with increasing flow energy and with degree of braiding

columbite solubility in granitic melts consequences for the enrichment and fractionation of nb and ta in the earth s crust the behaviour of niobium and tantalum in magmatic processes has been investigated by conducting mnnb2o6 and mnta2o6 solubility experiments in nominally dry to water saturated peralkaline aluminium saturation index a s i 0 64 to peraluminous a s i 1 22 granitic melts at 800 to 1035 c and 800 to 5000 bars the attainment of equilibrium is demonstrated by the concurrence of the solubility products from dissolution crystallization mn doped and nb or ta doped experiments at the same pressure and temperature the solubility products of mnnb2o6 ksp nb and mnta2o6 ksp ta at 800 c and 2 kbar both increase dramatically with alkali contents in water saturated peralkaline melts they range from 1 2 10 4 and 2 6 10 4 mol2 kg2 respectively in subaluminous melt a s i 1 02 to 202 10 4 and 255 10 4 mol2 kg2 respectively in peralkaline melt a s i 0 64 this increase from the subaluminous composition can be explained by five non bridging oxygens being required for each excess atom of nb5 or ta5 that is dissolved into the melt the ksp nb and ksp ta also increase weakly with al content in peraluminous melts ranging up to 1 7 10 4 and 4 6 10 4 mol2 kg2 respectively in the a s i 1 22 composition columbite tantalite solubilities in subaluminous and peraluminous melts a s i 1 02 and 1 22 are strongly temperature dependent increasing by a factor of 10 to 20 from 800 to 1035 c by contrast columbite tantalite solubility in the peralkaline composition a s i 0 64 is only weakly temperature dependent increasing by a factor of less than 3 over the same temperature range similarly ksp nb and ksp ta increase by more than two orders of magnitude with the first 3 wt h2o added to the a s i 1 02 and 1 22 compositions whereas there is no detectable change in solubility for the a s i 0 64 composition over the same range of water contents solubilities are only slightly dependent on pressure over the range 800 to 5000 bars the data for water saturated sub and peraluminous granites have been extrapolated to 600 c conditions at which pegmatites and highly evolved granites may crystallize using a melt concentration of 0 05 wt mno 70 to 100 ppm nb or 500 to 1400 ppm ta are required for manganocolumbite and manganotantalite saturation respectively the solubility data are also used to model the fractionation of nb and ta between rutile and silicate melts predicted rutile melt partition coefficients increase by about two orders of magnitude from peralkaline to peraluminous granitic compositions it is demonstrated that the nb2o5 ta2o5 activity coefficient ratio in the melt phase depends on melt composition this ratio is estimated to decrease by a factor of 4 to 5 from andesitic to peraluminous granitic melt compositions accordingly all the relevant accessory phases in subaluminous to peraluminous granites are predicted to incorporate nb preferentially over ta this explains the enrichment of ta over nb observed in highly fractionated granitic rocks and in the continental crust in general

determination of the h3bo3 concentration in fluid and melt inclusions in granite pegmatites by laser raman microprobe spectroscopy a method of determining the boric acid h3bo3 concentration in fluid inclusions and volatile rich glasses using laser raman microprobe spectroscopy is described the h3bo3 content of melt and fluid inclusions is determined with good accuracy and precision in the concentration range of 0 to 20 wt and with a minimum detection limit mdl of 0 05 wt h3bo3 the method is applicable to complex solutions that contain components such as nacl kcl rbcl or cscl which do not form stable hydrated borates with boric acid at room temperature this raman study demonstrates that boric acid is an abundant component in volatile rich melt inclusions and in genetically linked primary and pseudosecondary fluid inclusions particularly in tourmaline bearing granites and boron rich pegmatites in quenched pegmatite melt boron occurs predominantly as a trigonal coordinated b oh 3 complex the analytical method is applied to a series of melt and fluid inclusions from different localities and geological environments namely hydrothermal tin and tungsten deposits granite pegmatites and rhyolites special emphasis is given to the analysis of fluorine phosphorus and boron rich pegmatites of the variscan ehrenfriedersdorf complex central erzgebirge germany in this pegmatite system boron in combination with water fluorine and phosphorous is responsible for immiscibility of two coexisting silicate melts a silicate rich h2o poor melt and a silicate poor h2o rich melt accompanied by strong element fraction ation between the two boron fractionates into the water rich silicate melt by factors between 1 8 at 500 c and 1 0 at 712 c if at low pressure a vapor phase is additionally formed boron is partitioned into the vapor phase the utility of the developed method was also quantitatively tested by experiments with a hydrothermal diamond anvil cell

stratigraphy and structure of a late wisconsinan salt collapse in the saskatoon low south of saskatoon saskatchewan canada an update the saskatoon low is a collapse structure that formed as a result of dissolution of salt from the middle devonian prairie evaporite formation in this study the collapse has affected the upper cretaceous lea park judith river and bearpaw formations of the montana group the early and middle pleistocene mennon dundurn and warman formations of the sutherland group and the late pleistocene floral battleford and haultain formations of the saskatoon group locally the collapse is about 180 m which is about equal to the thickness of the salt the first phase of collapse took place after deposition of the ardkenneth member of the bearpaw formation and before glaciation or during a pre illinoian glaciation the second phase of collapse occurred during the battleford glaciation late wisconsinan prior to deposition of the battleford formation the saskatoon low was glacially eroded removing the sutherland group and the floral formation after the glacial erosion up to 110 m of soft till of the battle

river morphology and thresholds the regime geometry and channel patterns of alluvial rivers are analyzed wing an energy approach together with physical relationships of flow continuity flow resistance and sediment transport because of the discontinuity in flow resistance and thus in power expenditure between lower and upper flow regimes the adjustment in river regime consists of sudden changes in channel geometry channel pattern and sometimes silt clay content when such a discontinuity is crossed thresholds or discontinuities in river morphology are obtained in the analysis in accordance with such thresholds rivers of distinct morphological features are classified into four regions based upon the bankfull discharge channel slope and median size of bed sediment their respective features are described and certain regime relationships for channel width and depth are established the predicted channel geometries are compared with river data

gold solubility in oxidized and reduced water saturated mafic melt abstract we have performed experiments to evaluate au solubility in natural water saturated basaltic melts as a function of oxygen fugacity experiments were carried out at 1000 c and 200 mpa and oxygen fugacity was controlled at the fayalite magnetite quartz fmq oxygen fugacity buffer and fmq 4 all experiments were saturated with a metal chloride aqueous solution loaded initially as a 10 wt nacl eq fluid the stable phase assemblage at fmq consists of basalt melt olivine clinopyroxene a single phase aqueous fluid and metallic au the stable phase assemblage at fmq 4 consists of basalt melt clinopyroxene magnetite spinel solid solution a single phase aqueous fluid and metallic au silicate glasses i e quenched melt and their contained crystalline material were analyzed by using both electron probe microanalysis epma and laser ablation inductively coupled plasma mass spectrometry la icp ms measured au concentrations in the quenched melt range from 4 8 g g 1 to 0 64 g g 1 at fmq 4 and 0 54 g g 1 to 0 1 g g 1 at fmq the measured solubility of au in olivine and clinopyroxene was consistently below the la icp ms limit of detection i e 0 1 g g 1 these melt solubility data place important limitations on the dissolved au content of water saturated cl and s bearing basaltic liquids at geologically relevant fo2 values the new data are compared to published experimentally determined values for au solubility in dry and hydrous silicate liquids spanning the compositional range from basalt to rhyolite and the effects of melt composition oxygen fugacity pressure and temperature are discussed

solubility of wodginite titanowodginite microlite pyrochlore columbite mn and tantalite mn in flux rich haplogranitic melts between 700 and 850 c and 200 mpa abstract ore minerals of niobium and tantalum are typically associated with pegmatites and rare metal granites these include columbite tantalite wodginite titanowodginite microlite and pyrochlore solubility and crystallization mechanisms for columbite mn and tantalite mn have been extensively studied in haplogranitic melts with little research into other ore minerals in this study the solubilities of wodginite titanowodginite microlite and pyrochlore are compared to those for columbite mn and tantalite mn in a flux rich haplogranitic melt of alumina saturation index asi 1 0 asili of 0 83 at 700 850 c and 200 mpa the effect of melt composition on the solubilities of wodginite titanowodginite and microlite compared to tantalite mn is also investigated in highly fluxed haplogranitic melts of asi 1 0 1 10 and 1 24 asili of 0 83 0 90 1 02 at 700 c and 800 c and 200 mpa the log solubility product logksp at 750 c and melt asi of 1 0 is highest for tantalite mn 2 32 mol2 kg2 followed by columbite mn 2 68 mol2 kg2 and pyrochlore 3 71 mol3 kg3 titanowodginite 3 73 mol3 kg3 wodginite 3 77 mol3 kg3 and microlite 3 78 mol3 kg3 the latter four of which are almost identical within error however solubility can also be expressed as a mineral melt partition coefficient with higher partition coefficients reflecting lower solubilities the tantalum mineral melt partition coefficients of wodginite 27 0 titanowodginite 30 2 and tantalite mn 29 6 are identical within error microlite is higher 80 3 reflected by lower concentrations of tantalum in the melt for stoichiometric saturation because it contains a major melt cation sodium the niobium mineral melt partition coefficient for columbite mn 66 1 is higher than for pyrochlore 50 1 wodginite titanowodginite pyrochlore columbite mn and tantalite mn have similar temperature and melt composition dependences but conversely microlite solubility increases with asi as all studied minerals have been shown to have similar relative solubilities at stoichiometric saturation it can be concluded that in general the presence of bivalent ca mn fe and some tetravalent cations sn ti control which tantalum and niobium phases crystallize in rare metal deposits

sulfur partitioning between apatite and melt and effect of sulfur on apatite solubility at oxidizing conditions the effect of sulfur on phosphorus solubility in rhyolitic melt and the sulfur distribution between apatite anhydrite melt and fluid have been determined at 200 mpa and 800 1 100 c via apatite crystallization and dissolution experiments the presence of a small amount of sulfur in the system 0 5 wt s under oxidizing conditions increases the solubility of phosphorus in the melt probably due to changing calcium activity in the melt as a result of the formation of ca s complexing cations apatite solubility geothermometers tend to overestimate temperature in ca poor s bearing system at oxidizing conditions in crystallization experiments the sulfur content in apatite decreases with decreasing temperature and also with decreasing sulfur content of the melt the sulfur partition coefficient between apatite and rhyolitic melt increases with decreasing temperature kdsapatite melt 4 5 14 2 at t 1 100 900 c under sulfur undersaturated conditions no anhydrite the sulfur partition coefficient is lower in anhydrite saturated melt 8 at 800 c than in anhydrite undersaturated melt suggesting that kdsapatite melt depends not only on the temperature but also on the sulfur content of the melt these first results indicate that the sulfur content in apatite can be used to track the evolution of sulfur content in a magmatic system at oxidizing conditions

fluoride silicate melt immiscibility and its role in ree ore formation evidence from the strange lake rare metal deposit quebec labrador canada pegmatites and adjacent subsolvus granites two alkali feldspars of the mid proterozoic strange lake pluton quebec labrador canada host potentially economic concentrations of high field strength elements hfse including the rare earth elements ree zirconium and niobium previous studies have proposed that these concentrations were the result of a com bination of extreme fractionation of a peralkaline granitic magma and later hydrothermal remobilization however the recent discovery of melt inclusions which after heating to 900 or 950 c quench to immiscible fluoride and silicate glasses suggests an additional mechanism of hfse concentration crystallized melt inclusions are common in quartz phenocrysts of the early hypersolvus and transsolvus granite after heating four types of inclusions were discerned type 1 inclusions quench to a single silicate glass containing a high concen tration of zr nb and ti quenching of type 2 inclusions produces a zr nb ti rich silicate glass containing a globule of calcium rich fluoride glass with a high concentration of the ree the third inclusion type is similar to type 2 except that the calcium rich fluoride glass contains a globule of ree fluoride glass up to 50 wt total ree type 4 inclusions contain calcium fluoride glass with multiple silicate globules we propose that during or soon after emplacement the early granitic magma exsolved a calcium fluoride melt into which rare earth elements ree partitioned preferentially the conjugate silicate melt was consequently depleted in ca and the ree and enriched in zr nb and ti crystallization of the fluoride melt occurred late in the crystallization history of the silicate magma allowing it to accumulate in the volatile rich residual magma that formed the pegmatites this played a major role in the extreme enrichment of the pegmatites in ca f and ree crystallization of the pegmatites proceeded inwards from an outer zone in which feldspars quartz arfvedsonite and zirconosilicate minerals dominate to a core where the immiscible fluoride liquid collected and crystallized fluorite and ree minerals fluid exsolved from the silicate melt reacted with the products of both the silicate and fluoride melts remobilizing most of the hfse including the ree this study reports a rare example of silicate fluoride melt immiscibility and the first in which such immiscibility played a role in concentrating the ree to potentially economic levels 2014 elsevier ltd all rights reserved

zr complexation in high pressure fluids and silicate melts and implications for the mobilization of hfse in subduction zones abstract field observations and solubility experiments show evidence for the efficient mobilization of nominally insoluble hfse i e ti zr nb and hf by high pressure fluids probably via complexation with polymerized alkali silica dissolved species and halogens f and cl here we investigate the complexation of zr in subduction related fluids aqueous fluids and hydrous haplogranite melts up to 800 c and 2 4 gpa using x ray absorption spectroscopy xanes and exafs in a hydrothermal diamond anvil cell and provide evidence for the formation of zr o si na polymeric species in alkali alumino silicate fluids at high pressure zr 4 speciation in dilute fluids 2 5 wt hcl is dominated by 8 fold coordinated zr h 2 o 8 4 hydrated complexes at room conditions and no evidence for extensive zr cl complexation in the fluid was found up to 420 c as confirmed by ab initio xanes calculations of various zro 8 x cl x clusters the addition of na and si dissolved species from 35 to 60 wt dissolved na 2 si 2 o 5 ns2 into the fluid favors the formation of alkali zirconosilicate clusters zr o si na similar to those found in vlasovite na 2 zrsi 4 o 11 with zr 4 in octahedral coordination with oxygen zr o distance 2 09 0 04 a and 6 si na second neighbors zr si na distance 3 66 0 06 a this coordination environment also dominates zr speciation in f free and f bearing ns2 and haplogranite glasses and high pressure hydrous haplogranite melts 15 5 33 wt dissolved h 2 o in the investigated pressure temperature range the xas analyses assisted by ab initio xanes calculations are not conclusive concerning the extent of zr f complexation in hydrous granitic melts alkali zirconosilicate zr o si na clusters such as those identified in this study may explain the enhanced solubility of zircon zrsio 4 and other hfse bearing minerals in alkali aluminosilicate bearing aqueous fluids produced by dehydration and melting of the slab and provide a favorable mechanism for the mobilization of hfse in subduction zones fluid rock interactions and or p t variations as fluids migrate through the mantle wedge could affect the stability of these complexes triggering the precipitation of hfse bearing accessory phases that are eventually recycled into the mantle contributing to the dispersion of hfse these processes provide a possible explanation for the characteristic hfse depletion recorded in arc magmas

till beneath ice stream b 1 properties derived from seismic travel times seismic experiments conducted on ice stream b part of the marine ice sheet of west antarctica show a meters thick layer immediately beneath the 1000 m thick ice a seismic experiment consisting of wide angle reflection profiling along a line parallel to ice stream flow was conducted to determine the properties of this layer inversion of seismic travel times yields a compressional wave speed of less than 1700 m s 1 and a shear wave speed less than 160 m s 1 for the layer these very low wave speeds imply that the material in the layer is highly porous and is saturated with water at a high pore pressure based on wave speeds in other saturated unconsolidated sediments we believe that a porosity substantially greater than 0 32 probably around 0 4 and an excess of overburden pressure over pore pressure of only 50 kpa 0 5 bar characterize the layer at this location

maximum and minimum water contents of granitic melts generated in the crust a reevaluation and implications abstract recent results of studies aimed to determine the water solubilities and the liquidus temperatures in synthetic and natural granitic systems are used to constrain the minimum water contents of granitic melts generated in the crust as a function of pressure temperature melt composition and water activity it is concluded that melts generated in the crust at high temperature and low water activities such as a type granites contain higher water contents than previously assumed up to 20 at 800 900 c and 3 7 kbar as a consequence the melt fraction produced at a given amount of available water can be up to 20 lower the minimum water content of melts generated by partial melting of crustal protoliths especially quartzofeldspathic rocks can be predicted adequately from the liquidus curves in granitic systems this water content can be higher if the melt composition departs from a minimum or eutectic quartzofeldspathic composition melts generated from quartzofeldspathic rocks at low temperature 750 c and below are necessarily water rich 5 wt h 2 o and have approximately the same viscosity or even slightly lower viscosities than melts generated at higher temperatures viscosities in the range 10 4 3 10 5 4 pa s recent experimental data also show that the value of the positive d p d t slope of the liquidus curves for fixed water contents above 800 c is lower than predicted by previous models thus adiabatic decompression produces a higher amount of melt than previously assumed at high temperature the formation of melt by adiabatic decompression can be up to 50 higher than assumed

statistical models of fluvial systems abstract statistical methods have dominated quantitative analyses of fluvial systems over the last 40 years this paper assesses the utility of statistical models by examining methodological issues associated with empirical analysis of hydraulic and channel geometry relationships it also describes and presents examples of advanced statistical models that promise to enhance our understanding of the structure and dynamics of fluvial systems bivariate and multivariate power function models of fluvial systems provide objective numerical descriptions of the relationship between channel geometry and hydrologic hydraulic sedimentologic and biotic controls traditional regression models are limited in that they only describe simple input output relations between the states of dependent and independent variables advanced statistical models transcend these limitations simultaneous equation models continuously varying parameter models and distributed lag models are statistical tools for explicitly analyzing 1 mutual adjustments among fluvial variables 2 the factors controlling the spatial structure of channel geometry flow relations and 3 the equilibrium or disequilibrium dynamics of fluvial systems respectively these advanced statistical techniques can be used to empirically test conceptual models of fluvial systems at a variety of spatial and temporal scales

the effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts abstract the solubilities of columbite tantalite wolframite rutile zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts all experiments were conducted at 1035 c and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt h 2 o accessory phase solubilities are not affected by the water content of the peralkaline melt by contrast solubilities are affected by the water content of the subaluminous melt where the solubilities of all the accessory phases examined increase with the water content of the melt up to 2 wt h 2 o at higher water contents solubilities are nearly constant it can be concluded that water is not an important control of accessory phase solubility although the water content will affect diffusivities of components in the melt thus whether or not accessory phases will be present as restite material the solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies which have observed differences in the coordination of high field strength elements in dry vs wet subaluminous granitic glasses but not for peralkaline granitic glasses lastly the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species

verendrye valley and the glidden esker saskatchewan subglacial and ice walled features in southwestern saskatchewan canada verendrye valley is more than 100 km long about 1 km wide and at least 225 m deep southward the valley grades into the glidden esker the surface of which rises about 280 m above the lowest point in the valley the sediments in the valley and esker are 205 and 75 m thick respectively and form a fining upward sequence from sand and gravel at the base to silt with sand interbeds in the upper part of the sequence which in turn is covered by a blanket of glacial lake clay the concave upward longitudinal profile of verendrye valley the genetic relationship between verendrye valley and the glidden esker and the age of the features indicate the valley and esker were formed by a subglacial stream during the last deglaciation 15 500 14 000 years ago the fining upward sequence of sediments in the valley and esker suggests the sub glacial valley formed time transgressively by headward erosion while the glacier margin remained stationary at the glidden esker

rapid soft bed sliding of the puget glacial lobe the puget lobe of the late pleis inferred to be lodgment till based on the tocene cordilleran ice sheet advanced into presence of oriented stones oriented stria western washington over a thick sequence of tions on stones overconsolidation and unlithified sediments the basal drag due to deformation features sliding over this surface was calculated by 1 this paper investigates the rapid motion of idealizing the sediment bed as a rigid planar the puget lobe over its bed of deformable sedi surface scattered with roughness elements cor ment studies of large vanished glaciers com responding to individual sedimentary particles plement basal motion studies of modern glaci and 2 taking the minimum reconstructed slid ers in which the glacier geometry and velocity ing velocity to be 500 m yr 1 the calculated are well constrained but the characteristics of basal drag minimized by choices of parameters the bed can only be inferred from observations is 400 kpa much higher than the reconstructed over very limited areas kamb et al 1985 gravitational driving stress of 40 kpa indi seismic measurements blankenship et al 1986 cating that a rigid bed and low water pressure or modelling lingle and brown 1987 obser are not consistent with the glacierfs rapid vations on glacier beds recently exposed by motion high subglacial water pressure aver glacial retreat can provide information about aging 90 of the ice overburden 10 mpa is conditions during a somewhat greater time span inferred from overconsolidation of subglacial but are restricted to the marginal environ clays the occurrence and deformation of ment in addition inferences about the bed of water deposited sediments within the till and modern glaciers are limited by the short dura the requirement to drain large quantities of tion and seasonality of the observations a water from the interface suggest that water notable benefit of studying the beds of pieis pressure reached 99 of the ice overburden tocene glaciers is that they record basal ploughing of till by ice entrained clasts per conditions for intervals spanning entire glaci vasive shearing and finally ice bed separa ations and accessible far from the glacier tion become possible as water pressure margins increases at the low inferred effective nor after a brief summary of data available from mal stress the basal drag is reduced from the previous reconstructions of the puget lobe the rigid bed case by water layers which decouple basal conditions of the lobe are explored along the smallest particles from the glacier sole two complementary lines we first present cal and ploughing which reduces the resistance culations of basal drag due to glacier sliding offered by the largest particles the limited for different models of till bed roughness that shear strain observed in much of the till indicate that rapid sliding requires very low implies pervasive shearing did not contribute effective stresses and extensive ice bed significantly to ice motion basal motion was decoupling or ploughing second we summarize confined to the ice bed interface or to dis geological and geotechnical data that indicate tinct faults within the substrate

time dependent behaviour of the bearpaw shale in oedometric loading and unloading time dependent behaviour can have a significant influence on the compressibility characteristics of soils however most of the research on this topic has investigated the behaviour of soft soils in this paper the time dependent behaviour of a hard clay shale bearpaw shale is investigated using both one dimensional multi staged loading msl oedometer and constant rate of strain crs oedometer consolidation tests conducted on 25 0 and 16 9 mm diameter specimens the results show that soft clays and hard clay shales that share the same c e cc ratio where c e is the secondary compression index and cc is the incremental compression index will show the same approximately 7 change in pre consolidation pressure for an increase of one log cycle of strain rate despite the many orders of magnitude difference in pre consolidation pressure in the case of the bearpaw shale this 7 change in pre consolidation pressure corresponds to approximately 700 kpa the time dependent behaviour of the bearpaw shale d

the dirt hills structure an ice thrust feature in southern saskatchewan canada the dirt hills structure is expressed at the surface as a broad arcuate moraine 7 5 km wide 120 m high and 40 km long the structure is composed mainly of bedrock and drift consisting of three slabs stacked to form a single block 215 m thick the shear zones that bound the slabs are mainly in clays of the bearpaw formation the dirt hills structure originated during the last deglaciation when the glacier under compressive flow readvanced up the missouri coteau escarpment and stacked the subglacial slabs of bedrock and drift the subparallel arcuate ice thrust ridges are formed presumably by imbricate thrust faults originating from the uppermost shear zone

logistic analysis of channel pattern thresholds meandering braiding and incising a large and geographically diverse data set consisting of meandering braiding incising and post incision equilibrium streams was used in conjunction with logistic regression analysis to develop a probabilistic approach to predicting thresholds of channel pattern and instability an energy based index was developed for estimating the risk of channel instability associated with specific stream power relative to sedimentary characteristics the strong significance of the 74 statistical models examined suggests that logistic regression analysis is an appropriate and effective technique for associating basic hydraulic data with various channel forms the probabilistic diagrams resulting from these analyses depict a more realistic assessment of the uncertainty associated with previously identified thresholds of channel form and instability and provide a means of gauging channel sensitivity to changes in controlling variables

anastomosis and the continuum of channel pattern anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables flow strength bank erodibility and relative sediment supply using an ordinal scaling l ow m oderate h igh the traditional forms of straight meandering and braided have respective representations of l l l m l m l m and h h m h in terms of those variables the anastomosing pattern is on average represented by l l m h but not so definitively as other forms specification of the third element sediment supply is particularly hampered by the paucity of data but aggradation a characteristic of many anastomosing rivers can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport a sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches a flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems

geochemical evidence for a multistage magmatic genesis of ta sn li mineralization in the granite at beauvoir french massif central the beauvoir rare metal granite at the southern edge of the echassieres granite massif french massif central is mineralized by disseminated ta sn and li the granite body formed from an independent melt which was emplaced soon after the main granite facies of the massif the geochemistry of the beauvoir granite relates it to the phosphorus rich type of ta bearing granites and geochemical and mineralogical data establish its similarity to pegmatite melts the beauvoir granite results built up from two distinct intrusions both intrusions are cogenetic and were emplaced within a short time interval a geochemical study of a deep drill hole bored down to 900 m under the surface to the floor of the granite sheet with selected key zones observed in greater detail has allowed the recreation step by step of a long process leading to the economic concentration of ta sn and li the comparison of major element trace element and isotopic geochemistry with the petrology makes it possible to unravel the numerous processes contributing to the ore formation local events need to be determined before main events can be identified constraints on the interpretation of the ore genesis are provided by a careful observation of data interpretations of these observations are strongly backed up by experimental data e g keppler 1993 the source rock was most likely enriched in sn and w at about 10 ppm precluding a slightly enriched granitic melt by partial melting it is not known whether the melt was already enriched in ta but this is not a prerequisite subsequently deep seated fractional crystallization produced granitic magma similar in composition ta nearly equal 9 m to the adjacent colettes granite and further fractionation processes led to a melt already strongly enriched in ta ca 40 ppm strongly peraluminous and enriched in the depolymerizing elements f and p the viscosity was therefore very low allowing easy ascent during transport small scale fluctuations in the viscosity were amplified by upward movement leading to an f and p rich melt preceding the magma batch this less viscous melt again underwent crystallization while moving through the upper

stream curvature and bank erosion a model based on the momentum equation based on the momentum equation of flow the force per unit area which the flow exerts radially on the outer bank of a stream bend is expressed by an equation in which the force is explicitly related to the curvature ratio r w curve radius channel width a dimensionless curvature coefficient c alpha is defined which is dependent on r w and the coefficient of dynamic bedload friction tan alpha exploring the changes of c alpha with r w reveals a functional relationship which for the known values of tan alpha shows maximal values of c alpha for r w values between 2 and 4 the theoretical results agree with field measurements of the relationship between r w and the rate of channel migration

a coupled consolidation shear model for the process of formation of glaciated soils it has been generally observed that the measured preconsolidation pressure values for glaciated soils are not compatible with the measured effective pressure values at the bed of the glacier if one dimensional consolidation alone is considered as the formation process for these soils in this paper a new model for the process of formation of glaciated soil termed the coupled consolidation shear ccs model is developed using the frameworks of critical state soil mechanics and small strain consolidation theory the ccs model includes simultaneous shearing and consolidation of subglacial sediments and is able to simulate profiles of preconsolidation pressure versus depth that closely resemble those observed in glaciated soils the ccs model is validated by successfully simulating the profile of preconsolidation pressure versus depth for an 80 m deep battleford till layer in birsay saskatchewan canada the ccs model suggests the existence of anisotropic yield strength and stiffness in glaciated soils as

combined measurements of subglacial water pressure and surface velocity of findelengletscher switzerland conclusions about drainage system and sliding mechanism interpretation des mesures de pression dans les forages et des vitesses superficielles la comparaison avec les modeles suggere que l on a neglige le frottement du aux debris dans les modeles et qu il n existe jamais de chenaux cylindriques rectilignes

solubility of manganotantalite zircon and hafnon in highly fluxed peralkaline to peraluminous pegmatitic melts the behavior of tantalum and zirconium in pegmatitic systems has been investigated through the determination of ta and zr solubilities at manganotantalite and zircon saturation from dissolution and crystallization experiments in hydrous li f p and b bearing pegmatitic melts the pegmatitic melts are synthetic and enriched in flux elements 0 7 1 3 wt li2o 2 5 5 wt f 2 8 4 wt p2o5 and 0 2 8 wt b2o3 and their aluminum saturation index ranges from peralkaline to peraluminous asili al na k li 0 8 to 1 3 with various k na ratios dissolution and crystallization experiments were conducted at temperatures varying between 700 and 1 150 c at 200 mpa and nearly water saturated conditions for dissolution experiments pure synthetic end member manganotantalite and zircon were used in order to avoid problems with slow solid state kinetics but additional experiments using natural manganotantalite and zircon of relatively pure composition i e close to end member composition displayed similar solubility results zircon and manganotantalite solubilities considerably increase from peraluminous to peralkaline compositions and are more sensitive to changes in temperature or asi of the melt than to flux content a model relating the enthalpy of dissolution of manganotantalite to the asili of the melt is proposed hdiss kj mol 304 asili 176 in the peralkaline field and hdiss kj mol 111 asili 245 in the peraluminous field the solubility data reveal a small but detectable competitivity between zr and ta in the melt i e lower amounts of zr are incorporated in a ta bearing melt compared to a ta free melt under the same conditions a similar behavior is observed for hf and ta the competitivity between zr or hf and ta increases from peraluminous to peralkaline compositions and suggests that ta is preferentially bonded to non bridging oxygens nbos with al as first neighbors whereas zr is preferentially bonded to nbos formed by excess alkalies as a consequence zr ta ratios when buffered by zircon and manganotantalite simultaneously are higher in peralkaline melts than in peraluminous melts

reconstruction of a pleistocene meandering river in east hungary by vhr seismic images and its climatic implications abstract the upper 20 30 m of the pleistocene alluvial sequence on the tisza river hungary is investigated by 200 km of vhr single channel seismic sections frequent internal configurations such as 1 bundles of inclined reflections 2 trough shaped converging and 3 horizontal parallel reflections are interpreted respectively as lateral accretion of point bars abandoned channel fills and floodplain deposits the series of 5 8 m thick inclined strata sets occurring at the same depth throughout the area suggest the presence of a meandering river dated to about 43 47 ka in the late pleistocene according to osl data newly recorded quasi 3d seismic profiles reveal that each 1 3 km long inclined series correlates with an individual point bar continuously migrating in the same direction small deviations in the direction of migration are caused by natural wandering of the meander bend morphometric parameters of point bars are used to calculate ancient channel parameters width and depth of 200 500 m and 5 8 m respectively values imply a channel forming discharge of q 400 900 m 3 s these results imply a greater amount of runoff and supply in the basin during mis3 compared to the present day long lasting meandering indicates the role of local factors and a different fluvial environment compared to the commonly anastomosing systems in nw europe our data support the thesis of the three axis drainage system for the basin new evidence is provided for the antecedent existence of a temporally active third trunk river in addition to the ancestors of danube and tisza rivers contrary to the present day two axis drainage pattern