sector trilling in cordierite and equilibrium overstepping in metamorphism the origin of sector trilling in cordierite is due to the hexagonal orthorhombic al si ordering transformation which under non equilibrium conditions proceeds via a short range ordered modulated structure the growth of these distortion waves associated with progressive ordering produces a strain field which is minimized by a cyclic distribution of symmetrically equivalent modulations sector and complexly trilled cordierites in metamorphic rocks grew as the hexagonal polymorph with a considerable degree of al si disorder the enthalpy and entropy of disorder are evaluated from recent experimental work the implication is that in metamorphic rocks substantial overstepping of stable equilibrium phase boundaries is required to nucleate hexagonal cordierite moreover its composition coexisting with other phases will also be significantly different from that of the stable ordered form

reenvisioning velocity reversal as a diversity of hydraulic patch behaviours past research investigated the surpassing of mean velocity at riffle cross sections by that at pool cross sections for flows up to bankfull termed velocity reversals to understand one mechanism by which riffle pool relief is maintained this study reenvisioned the classic velocity reversal by documenting stage dependent changes to the locations of peak velocity without cross sections instead the dynamics of peak velocity patches were considered for flows spanning 0 2 to 22 times bankfull discharge through the use of a high resolution dem and two dimensional hydrodynamic modelling a remarkable diversity in peak velocity patch behaviour was found across discharges including gradual expansion and shifting as well as abrupt disappearance and emergence relative to the low flow patch locations these behaviours blended together to varying degrees to produce many reversals in peak velocity across morphological units but it took substantially higher than bankfull discharge for peak velocities to move from riffles and chutes to fast glides and pools the discharges at which reversals occurred among morphological units were significantly higher for the valley confined reach than for the anastomosing reach copyright 2016 john wiley sons ltd

dendritic cordierite in argillaceous hornfels from the toki area gifu prefecture central japan dendritic cordierite occurs in argillaceous hornfels from the toki area gifu prefecture japan the cordierite crystal consists of c arms elongated parallel to the c axes and a arms perpendicular to the c axis the latter arms could be divided into six kinds of untwinned a arms with different growth directions elongated parallel to the respective a axis and twinned a arms elongated parallel to the 110 twin plane a arms branch out from c arms or other a arms with different growth directions and c arms sometimes branch out from a arms leading to a tree like structure each of the c arms contains three kinds of domains related by a three fold axis about the c axis these domains are irregularly distributed without any relation to the shape of the c arm and the domain boundaries are of zigzag shape this domain arrangement suggests that c arms grew as hexagonal cordierite and were later transformed into orthorhombic cordierite the fact that each untwinned a arm has a fixed growth direction to its orientation suggests that the a arms grew as an orthorhombic cordierite from the growth directions of c and a arms orthorhombic and hexagonal phases are considered to grow preferentially along the c and a axes respectively the branching of a new arm is explained by nucleation on an old arm with a different preferred growth direction the preferential growth is discussed in terms of a significant chemical potential gradient of the cordierite component this has been preserved in the mineral zoning observed in the matrix around the cordierite porphyroblast

origin of sector trilling in cordierite in daimonji hornfels kyoto japan sector trilling of cordierite in hornfels in the inner part of a contact aureole at daimonji japan is a new type which consists not only of six 100 sectors a sectors forming trilling but also of 001 sectors c sectors and high index sectors h sectors complex twins within and among these sectors were studied from a viewpoint of a pseudo twin the complex texture originated from both growth and transformation processes the c sector consists of three groups of domains which are related by a pseudo twin this intrasector pseudo twin indicates that the initial phase of the c sector was hexagonal cordierite indialite which later transformed to orthorhombic the a sector is related to adjacent sectors by a rotation of 120 around the c axis resulting in an intersector pseudo twin the a sector is interpreted to have formed by overgrowth of orthorhombic cordierite on prism faces of indialite the h sector with the dendritic texture is also interpreted to have grown as orthorhombic cordierite in hornfels in the middle part of the aureole cordierites with sector trilling often coexist with single crystals of cordierite and the sector trilling has no c and h sectors this trilling type suggests that nucleation of indialite was subsequently followed by growth of orthorhombic cordierite in its stable field

velocity reversals and sediment sorting in pools and riffles controlled by channel constrictions abstract keller keller e a 1971 areal sorting of bed load material the hypothesis of velocity reversal geological society of america bulletin 82 753 756 hypothesized that at high flow near bed velocities in pools exceed velocities in riffles and create pool scour pools however typically have larger cross sectional areas of flow at bankfull discharge this condition raises an inconsistency with keller s velocity reversal hypothesis and the one dimensional continuity of mass equation to address this problem a model of pool maintenance and sediment sorting is proposed that relies on constriction of flow by recirculating eddies and flow divergence over the exit slopes of pools according to the model a narrow zone of high velocity occurs in the center of pools creating scour along the downstream end of pools an uphill climb of particles up the pool exit slope promotes sediment deposition the model is tested with field and flume measurements of velocity water surface elevation and size of bed sediments in recirculating eddy influenced pools local reversals of the water surface gradient were measured in the field and a velocity reversal was created in the flume the reversals that were measured indicate higher gradients of the water surface over the upstream portions of pools and higher velocities in pools at high flow the distribution of bed sediments collected in the field also support the proposed model of pool maintenance

the periodic nature of step pool mountain streams rhythmic sequences of steps and pools in steep mountain streams have captured the attention of numerous workers but whether periodicities exist in the occurrence of step pools has not been investigated in a comprehensive way and the implications for such periodicities have not been explored spectral analysis was applied to bed elevation data from streams in the santa monica mountains of southern california to investigate periodicity in the occurrence of step pools results indicate significant step pool periodicities confirmed by independent field measurements that vary from 0 43 channel widths to 2 40 channel widths spectral analysis of channels affected by external influences tends to indicate multiple significant peaks that reflect higher variance in step pool spacing underlying periodicities are nevertheless de tected suggesting that external factors obscure but do not destroy the effects of more general internal mechanisms periodicity in the occurrence of step pools suggests that step pools are bedforms that represent a fundamental mutual adjustment between flow channel morphology and energy expenditure a rhythmic channel thalweg supports the notion that step pools are analogous to meandering in the vertical dimension and implies that because step pool channels are not able to adjust energy expenditure in the plane dimension they instead adjust boundary roughness in the vertical dimension a continuum of rhythmic gravel bedforms that displays the results of such adjustments and that shows how step pools merge into pools and riffles in the stream channel system is discussed and illustrated with empirical data from the santa monica mountains although many differences exist between steep mountain streams and broad alluvial rivers the findings of this study suggest that generalized principles of uniform energy expendi ture may also apply to rhythmic step pool streams these findings are potentially valuable in the management and design of steep channels

rate and mechanism in prograde metamorphism for a given rate of heat input into a prograde metamorphic sequence the extent of overstep of reaction temperature disequilibrium depends on the slowest of three sequential steps a surface detachment of reactant minerals b transport of material to the site of mineral growth and c nucleation and growth of the product mineral we have developed analytical expressions which enable determination of the rates of mineral dissolution and growth and of advective and diffusive mass transport during metamorphism the dissolution and growth steps are linear functions of the driving force g of the overall reaction while diffusion may take place either through a grain boundary fluid film or through the disorganized grain boundary itself

equilibrium pool dimensions and sediment sorting patterns in coarse grained new england channels abstract pools and riffles are natural bedforms that produce variations in width and depth along channels deemed critical for aquatic habitat an understanding of this morphology is necessary for the successful design of a reconstructed or restored channel to better understand pool geometry and sorting characteristics of new england channels characterizations of pool geometry were performed on 145 different pools strongly influenced by channel constrictions characterizations of channel bed sediments were also performed at 34 of these locations data from 120 pools were used in least squares multiple regression analysis with 19 different independent variables to develop prediction equations for pool depth length and exit slope gradient these equations were then tested using the 25 remaining pools eighteen different geometric variables were then used to predict sediment 50 values in pool centers pool exit slopes and riffles for the subset of 34 samples the regression analyses for pool geometry indicate that pool depth is significantly influenced to a decreasing degree by pool exit slope width constriction gradient constriction width drainage area upstream channel width and the exit slope expansion ratio with an r 2 value of 0 53 similarly pool length is influenced by channel gradient location of the channel constriction pool width drainage area and constriction length with an r 2 value of 0 72 the gradient of pool exit slope is influenced by drainage area channel gradient and constriction gradient with an r 2 value of 0 34 however r 2 values for exit slope increased to 0 65 when sediment d 50 data were utilized using the resulting regression equations to predict dimensions for the 25 verification pools yields average residuals near zero although moderate variations do exist a tukey kramer hsd comparison of the means for sediment 50 values indicates pool sediments are significantly coarser than pool exit slope and riffle sediments for the subset of 34 pools regression analyses also suggest significant relations between the size of sediments in pools and riffles and a combination of geometric variables with r 2 values that range from 0 45 to 0 62 the results suggest that pool dimensions are related to basin wide variability and local hydraulic conditions the findings also suggest that the characteristics of constrictions and the downstream section of pools provide an important control on scouring and sorting characteristics throughout the pool riffle morphology

the linkage between velocity patterns and sediment entrainment in a forced pool and riffle unit a field based project was initiated in order to characterize velocities and sediment entrainment in a forced pool and riffle sequence three dimensional velocities and turbulence intensities were measured with an acoustic doppler velocimeter at 222 different points at three similar flows that averaged approximately 4 35 m 3 s 1 within a large pool riffle unit on north saint vrain creek colorado sediment sorting patterns were observed with the introduction of 500 tracer particles painted according to initial seeding location tracer particles moved sporadically during a 113 day period in response to the annual snowmelt peak flow which reached a maximum level of 14 8 m 3 s 1 velocity data indicate high instantaneous velocities and turbulence levels in the centre of pools patterns of sediment deposition support the notion that stream competence is higher in the pool than the downstream riffle flow convergence around a large channel constriction appears to play a major role in multiple processes that include helical flow development and sediment routing and backwater development with low velocities and turbulence levels above the constriction that may locally limit sediment supply jet flow flow separation vortex scour and turbulence generation enhance scour in the centre of pools ultimately multiple processes appear to play some role in maintenance of this forced pool and the associated riffle copyright 2008 john wiley and sons ltd

stage dependent variability in tractive force distribution through a riffle pool sequence high resolution data on spatial and temporal variability in flow hydraulics and sediment transport within riffle pool sequences are required to improve understanding of how fluvial processes maintain these meso scale bedforms this paper addresses this issue by providing velocity and boundary shear stress data over a range of discharges from base flow 0 07 m3 s 1 to just over bankfull 8 52 m3 s 1 from a sequence of four pools and three riffles in the river rede northumberland the data supports the reversal hypothesis of keller geol soc am bull 87 1971 753 as the primary explanation for the maintenance of the riffle pool sequence although they also indicate that spatial variability in tractive force is highly stage dependent and complex section averaged velocity data indicate reversal to be evident at four out of six riffle pool units an equalisation in velocity was found for the other two riffle pool units close to bankfull stage the spatial patterns of tractive force exhibited in the study reach as a result of increased discharge demonstrate that riffle pool units operate independently of one another shear stress reversals were observed in individual riffle pool units at different river stages during a flood hydrograph and in some instances two occurred in the same riffle pool unit during a single flow event pools were characterised by coarser bed sediments and narrower channel widths in comparison to riffles increasing the likelihood of tractive force reversal in the river rede areas of predicted bed sediment entrainment obtained from o c matched observed channel changes in the upper part of the study reach but over estimated change in the middle portion of the reach

estimation of viscosity contrast and finite strain from deformed elliptical inclusions a method of strain analysis is described which takes into account a possible competence difference between the strain markers and the rest of the rock using data consisting of the sectional shapes and orientations of groups of inclusions from conglomerate like rocks limits are placed on the possible effective viscosity contrast between the inclusions and the rock as a whole as well as on the bulk finite strain suffered by the rock these results are calculated using a computer program based on the theory for the deformation of elliptical cylinders the method can be considered an extension of the rf method but provides more information and involves less restrictive assumptions

mid crustal horizontal shear zone in the forearc region of the mid cretaceous sw japan arc inferred from strain analysis of rocks within the ryoke metamorphic belt abstract the strain geometry of a cretaceous low p high t metamorphosed accretionary complex in sw japan is one of the key geological constraints in understanding the cretaceous tectonics of the forearc region at the eastern margin of eurasia we studied the strain geometry of upper greenschist to lower amphibolite facies metamorphic rocks from the mid cretaceous low p high t ryoke metamorphic belt which during the mid cretaceous were located at mid crustal depths close to the volcanic front strain analysis focused on deformed radiolarian fossils in metachert and sandstone chert clasts within metapelite the maximum stretching direction x direction of the strain ellipsoid of the schistosity forming deformation at the peak metamorphism is oriented e w and the xy plane of the strain ellipsoid developed parallel to schistosity the metachert and metapelite exhibit plane strain to general flattening strain that probably largely resulted from the schistosity forming deformation based on the results of the previous strain analyses and this study it reveals that the schistosity forming deformation occurred under bedding normal shortening resulting in general flattening strain throughout the ryoke metamorphic belt the x direction of the strain ellipsoid of the schistosity forming deformation is oriented parallel to the length of the ryoke metamorphic belt throughout the sw japan arc the schistosity formed parallel to bedding planes that developed horizontally in non metamorphosed accretionary complexes of sw japan indicating horizontal xy plane of the strain ellipsoid these observations indicate the occurrence of horizontal shear deformation within the middle crust 15 km depth at the time of the low p high t metamorphism the deep seated horizontal shear zone and the shallower incipient median tectonic line mtl fault system could result in a crustal scale detachment fault in the forearc region of the mid cretaceous sw japan arc after the formation of the detachment the left lateral pull apart forearc basins onogawa izumi group distributed on the north side of the mtl and the southern marginal mylonite zone might be formed by the sinistral movement along the detachment fault

the bed morphology of upland single thread channels in semi arid environments evidence of repeating bedforms and their wider implications for gravel bed rivers single thread gravel bed streams of moderate slope in the northern negev are characterized by three channel units bars exhibit steeper than average slopes and poorly sorted mixtures of small medium cobbles and coarse very coarse pebbles flats are associated with more gentle slopes and well sorted medium fine pebbles and granules and transitional units have intermediate slopes and grain size in general all three units are planar span the full channel width and have well defined boundaries bars and flats are more common than the transitional units and alternate downstream for distances of several hundred metres forming sequences that are reminiscent of the riffle pool structure commonly observed in humid temperate gravel bed rivers a notable contrast is the absence of significant bed relief bars lack crests and flats lack depressions the relative lack of bed relief in bar flat sequences is attributed to the high rate of sediment supply from the sparsely vegetated hillslopes which promotes the infilling of depressions and to the erosion of crests under conditions of intense transport this reduction of bed relief lowers channel roughness which in turn increases flow velocity and therefore the ability of the channel to transmit the large sediment loads it receives although our analyses pertain to a semi arid river system the results have wider implications for understanding the adjustment of channel bedform to high sediment loads in other fluvial environments copyright 2012 john wiley sons ltd

glass bearing crustal xenoliths buchites erupted during the recent activity of stromboli aeolian islands abstract three xenoliths erupted as ejecta during recent violent explosion of stromboli volcano aeolian islands were investigated in this paper they consist of high temperature mineral association cordierite hercynite spinels sillimanite plagioclase mullite corundum and abundant glass 10 70 vol and may be classified as buchites the peraluminous composition of the xenoliths their trace element distribution and ree patterns support their origin from granulite and amphibolite facies metapelites of the calabrian continental crust which is considered the crystalline basement beneath stromboli buchites have an isotopic composition comparable to that of stromboli extrusives and significantly different from that of the calabrian basement the glass is generally colourless and has a si al alkali rich composition except for one sample where a fe mg ca rich reddish brown glass also occurs these two kinds of glass show complicated textures where patches of reddish brown glass are often surrounded by plagioclase and or cordierite or forms streaks and swirls with the colourless glass cordierite plagioclase and oxides have different compositions according to their position in the xenoliths ca rich plagioclase an72 95 mg poor cordierite mg values 47 66 and al rich spinels are in the inner portions of the xenoliths and associated with colourless glass on the contrary close to the contact with the host lava or associated with coloured glass cordierite shows higher mg values ti fe bearing oxides occur and plagioclase is chemically similar to the basalt phenocrysts an66 71 the abundant and fresh glass and the idiomorphic shape of the high temperature minerals suggest that the xenoliths were hold in the basaltic magma before its extrusion for a significant time to allow their partial or nearly complete melting and subsequent nucleation and growth of new phases during this stage the interaction between the anatectic liquid and the basaltic magma affected the original isotopic composition of the xenoliths and in some cases produced glass and mineral phases cordierite plagioclase and oxides with different composition

spatial variations in surface sediment structure in riffle pool sequences a preliminary test of the differential sediment entrainment hypothesis dseh riffle pool sequences are maintained through the preferential entrainment of sediment grains from pools rather than riffles this preferential entrainment has been attributed to a reversal in the magnitude of velocity and shear stress under high flows however the differential sediment entrainment hypothesis dseh postulates that differential entrainment can instead result from spatial sedimentological contrasts here we use a novel suite of in situ grain scale field measurements from a riffle pool sequence to parameterise a physically based model of grain entrainment field measurements include pivoting angles lift forces and high resolution dems acquired using terrestrial laser scanning from which particle exposure protrusion and surface roughness were derived the entrainment model results show that grains in pools have a lower critical entrainment shear stress than grains in either pool exits or riffles this is because pool grains have looser packing hence greater exposure and lower pivoting angles conversely riffle and pool exit grains have denser packing lower exposure and higher pivoting angles a cohesive matrix further stabilises pool exit grains the resulting predictions of critical entrainment shear stress for grains in different subunits are compared with spatial patterns of bed shear stress derived from a 2d computational fluid dynamics cfd model of the reach the cfd model predicts that under bankfull conditions pools experience lower shear stresses than riffles and pool exits however the difference in sediment entrainment shear stress is sufficiently large that sediment in pools is still more likely to be entrained than sediment in pool exits or riffles resulting in differential entrainment under bankfull flows significantly this differential entrainment does not require a reversal in flow velocities or shear stress suggesting that sedimentological contrasts alone may be sufficient for the maintenance of riffle pool sequences this finding has implications for the prediction of sediment transport and the morphological evolution of gravel bed rivers

the behaviour of deformable ellipsoidal particles in three dimensional slow flows implications for geological strain analysis abstract eshelby s equations governing the motion of a viscous inclusion embedded in a matrix of contrasting viscosity are solved numerically for arbitrarily shaped and arbitrarily oriented ellipsoidal particles the theory has important implications for geological strains and strain analysis specifically it predicts that particles more competent than their matrix will have deformed shapes with larger k values than equivalently shaped and oriented passive markers the effect is significant even for viscosity ratios as low as r 1 5 and increases with increase in r for general applications numerical solutions must be sought nevertheless there are useful exceptions 1 1 the two dimensional deformed shape of viscous particles can be computed graphically provided the matrix strain is irrotational pure shear and the section ellipse is a principal plane of the particle ellipsoid for sections through a three dimensional system with arbitrarily oriented particles this method and those based on sections through an elliptic cylinder is inaccurate the reliability is further diminished for simple shear 2 2 irrotational deformations in three dimensions can be computed on transformed flinn plots if the particle or average particle axial orientations are parallel with the applied flow similar diagrams may be used to make independent estimates of viscosity contrasts in polymict conglomerates

omphacite microstructures as time temperature indicators of blueschist and eclogite facies metamorphism omphacites from a wide range of geological environments have been examined by transmission electron microscopy their microstructures are sufficiently variable as to be potential indicators of thermal history for blueschist and eclogite metamorphism in particular the average size of equiaxed antiphase domains apd s arising from cation ordering appears to be a characteristic feature of each environment and increases in the sequence franciscan blueschist 1 turkey blueschist 2 guatemala jadeitic blocks in serpentinite 3 syros blueschist 9 red wine complex canada amphibolite 1 maksyutov complex urals blueschist 3 zermatt saas blueschist 5 allalin metagabbro 4 tauern eclogite 1 franciscan eclogite 5 nybo norway eclogite 2 numbers in brackets indicate the number of hand specimens for which omphacite microstuctures are known a relationship between apd size annealing time and temperature has been derived by analogy with the known apd coarsening behaviour in other systems where apd size n text apd size text n propto text e text text q rt cdot text time text most omphacites fit into a self consistent scheme with n 8 2 if the activation energy q is assumed to be that of cation disordering 75 kcal mole 1 available estimates of peak metamorphic temperature t are used and a reasonable geological time scale is taken as 104 108 years according to this model apd sizes are set in a relatively short interval of the total history of a rock when its temperature is close to its peak value apd sizes are much more sensitive to temperature than to time and may be used as a geothermometer which has the advantage of not being reset by re equilibration at low temperatures petrological implications arising from the model are that allalin metagabbros were metamorphosed at a similar peak temperature to zermatt saas blueschists franciscan eclogites reached higher temperatures than has been previously supposed and that the microstructures in some sesia lanzo omphacites are consistent with a high temperature pre blueschist origin deviation from an ideal coarsening law with n 2 implies that the apd s are not simply stacking mistakes but have some associated structural or compositional modification locally excess titanium concentrated at apd s in red wine complex omphacites may account for their anomalously low observed apd size

cordierite formation during the experimental reaction of plagioclase with mg rich aqueous solutions the reaction between plagioclase labradorite and oligoclase and mg rich aqueous solutions was studied experimentally at hydrothermal conditions 600 700 c 2 kbar during the experiments plagioclase grains were readily converted to cordierite and quartz within 4 days the cordierite crystals had well developed polyhedral shapes but showed skeletal internal morphologies suggesting that the initial growth occurred fast under high driving force conditions in pure mgcl2 solutions 0 5 5 m plagioclase dissolution and cordierite precipitation were spatially uncoupled indicating that al was to some extent mobile in the fluid cordierite crystals formed at 700 c showed orthorhombic symmetry whereas those formed at 600 c dominantly persisted in the metastable hexagonal form suggesting a strong increase in al si ordering speed between 600 and 700 c the thermodynamic evolution of the fluid solid system ultimately resulted in stabilization of ca rich plagioclase as demonstrated by partial anorthitization of unreacted plagioclase grains cordierite was also observed to form when mg was added to a potentially albitizing na silicate bearing solution in that case cordierite precipitation appeared to be more closely coupled to plagioclase dissolution and secondary alteration of remnant plagioclase grains did not occur most likely due to armoring of the plagioclase by the cordierite overgrowth the fast reaction rates observed in our experimental study have potential implications for mg metasomatism as a rock forming process

ductility of garnet as an indicator of extremely high temperature deformation discoidal shaped garnets alm63 prp33 grs3 sps1 occur in the foliation plane of lineated quartzofeldspathic mylonites of the morin shear zone located along the eastern boundary of the morin anorthosite complex grenville province quebec the flattened shape of garnets records a component of coaxial strain x y z different from the dominant rotational shear strain x y z in this mylonite tem observations indicate dislocation slip and recovery to be the main mechanism for the deformation of garnet extrapolation of available experimentally determined flow laws to natural strain rates shows an inversion of flow strength between quartz feldspar and garnet garnet much stronger than quartz and feldspar at temperatures below 700 c becomes weaker than quartz and feldspar above 900 c the coaxial ductile strain recorded by the garnets could be produced by a local uncharacterized deformation under extremely high temperature conditions at the roof of the rising anorthositic diapir 1155 ma subsequent lower temperature rotational deformation is related to strike slip movement along the morin shear zone 1020 ma

fracture controlled feldspar shape fabrics in deformed quartzo feldspathic rocks abstract the behaviour of feldspar in the brittle ductile transition region has often been discussed in models dominated by mechanisms of extension fracturing in this example a small caledonian granitic pluton from nw ireland feldspar shape changes are primarily accomplished by small displacements upon numerous shear fractures these fractures developed as riedel and anti riedel shears as the granite was synkinematically deformed in a regional shear zone the deformation took place under greenschist facies conditions at strain rates estimated between 10 13 and 10 14 s 1

rifting and reactivation of a cretaceous structural belt at the northern margin of the south china sea abstract the tiu tang lung fault hong kong special administrative region china is located on the northern stretched continental margin of the south china sea along this fault middle jurassic volcanic rocks of the tai mo shan formation are tectonically juxtaposed on lower cretaceous sedimentary rocks of the pat sin leng formation both extensional detachments and compressional features are observed and various genetic strain configurations are proposed for the tiu tang lung fault with implications for understanding the dynamics of the pre south china sea rifting during the cretaceous we have identified tilted bedding planes in the continental deposits of the pat sin leng formation which can be related to early cretaceous syn extensional deposition a mid cretaceous penetrative top to the south to top to the west shear fabric is also observed and serves as an indicator of the strain pattern this deformation is expressed by cleavages schistosity s c fabrics kink folds phacoids and stretched pebbles at both a macroscopic and microscopic scale cleavages and bedding are generally sub parallel to the local shear orientation the whole sedimentary pile is crosscut by cenozoic n70 and n150 normal faults these constraints together with previous fission track seismic and structural data allow us to reinterpret the kinematics of this domain during syn orogenic to syn extensional periods the observed top to the south thrusting event is coeval with ne sw strike slip sinistral fault movement subsequent n s extension can be correlated with south china sea rifting from eocene to oligocene these observations reveal a polyphase history associated with continental margin inversion which witnessed localized extension on previous compressional structures

monoclinic model shear zones abstract although many ductile shear zones are supposed to have developed by approximately simple shear flow some must have formed under different conditions a few types of such non simple shear zones have been proposed in the literature such as transpression transtension and stretching shear zones this paper presents a full three dimensional kinematic model of shear zones with monoclinic flow geometry monoclinic shear zone types can be classified according to flow parameters and according to the geometry and orientation of accumulating finite strain modelling of finite strain accumulation shows that a number of unusual and potentially problematic structural features may develop in monoclinic shear zones these include stretching lineations normal to the displacement direction foliations normal to the shear zone boundary switching of the position of principal finite strain axes x y and z during progressive deformation and strain gradients along shear zones that may give rise to obliqueness of fabric elements of the same age in adjacent rock volumes

basin scale methods for predicting salmonid spawning habitat via grain size and riffle spacing tested in a california coastal drainage basin scale predictive geomorphic models for river characteristics particularly grain size can aid in salmonid habitat identification however these basin scale methods are largely untested with actual habitat usage data here we develop and test an approach for predicting grain size distributions from high resolution lidar light detection and ranging derived topographic data for a 77 km2 watershed along the central california coast this approach improves on previous efforts in that it predicts the full grain size distribution and incorporates an empirically calibrated shear stress partitioning factor the predicted grain size distributions are used to calculate the fraction of the bed area movable by spawning fish we then compare the movable fraction with 7 years of observed spawning data we find that predicted movable fraction explains the paucity of spawning in the upper reaches of the study drainage but does not explain variation along the mainstem in search of another morphologic characteristic that may help explain the variation within the mainstem we measure riffle density a proxy for physical habitat complexity we find that field surveys of riffle density explain 64 of the variation in spawning in these mainstem reaches suggesting that within reaches of appropriate sized gravel spawning density is related to riffle density because riffle density varies systematically with channel width predicting riffle spacing is straightforward with lidar data taken together these findings demonstrate the efficacy of basin scale spawning habitat predictions made using high resolution digital elevation models copyright 2016 john wiley sons ltd

regional metamorphic dehydration and seismic hazard we use a one dimensional model of coupled heat transport fluid transport porosity feedback and metamorphism to investigate how dehydration reactions proceeding during burial of hydrous rocks in the footwall of thrusts or the hanging wall of normal faults may influence the temporal evolution of pore fluid pressure pf based on a new interpretation of existing kinetic data for the dehydration of model serpentinite we advance the hypothesis that pf buildup to tensile failure may be possible within decades of the onset of dehydration in low permeability metamorphic rocks of the middle crust this model contrasts with both 1 typical earthquake nucleation models which involve preexisting fluids that play a passive role responding to tectonic stresses rather than generating them and 2 conventional treatments of pf generation based on equilibrium thermodynamics and constant rates of dehydration which require 10 106 years to produce significant pf increases our results suggest that repeated cycles dehydration induced seismicity are plausible in low permeability areas of the mid crust and can be sustained throughout an orogenic episode if fresh hydrous minerals descend into the metamorphic zone along the downgoing face of a thrust or normal fault system

bed material size and the riffle pool sequence relationships between the bed material size distribution and riffle pool geometry of a small coarse bedload upland stream channel are described downstream sequences of bed material size are highly variable although series analysis reveals some persistence in the data over short distances cross correlation of bed material series with bed elevation series indicates riffles tend to coincide with coarser bed material sequences comparison of the bed material size distributions of individual riffles pools and bars is however more revealing mean particle size was found to be the most useful criterion for distinguishing between bed forms and in these terms bars are the most distinctive features moreover riffles and pools can be viewed as simply downstream oscillations in elevation of a single coarser grained sedimentary unit coarse sediment supply from erosion scars created where the channel meets confining bluffs in valley fill deposits does mean that the average particle size of adjacent and downstream bed forms is increased however conclusions remained unchanged after reanalysis following the identification and subtraction of immobile particle diameters plan geometry and coarse sediment supply in the upland environment are also shown to influence bed material size distributions tightly curved pools tend to have the finest pool sediments but also the least difference between bar and pool sediments size of material in pools is also negatively related to an index of cross section asymmetry

objective identification of pools and riffles this paper presents a new technique for objectively identifying pools and riffles the technique is termed the bed form differencing technique and as its data base has bed elevations surveyed at a fixed interval along the channel these elevations are differenced and the difference or elevation change values are used to identify pools and riffles where the cumulative elevation change since the last bed form exceeds a certain tolerance value a new bed form is considered to exist the type of bed form being determined by the direction of the elevation change analysis of a small stream in western new york suggests that the most realistic pool riffle sequence is obtained where the tolerance value is 0 75 times the standard deviation of the difference values the bed form differencing technique can be used to identify bed forms other than pools and riffles such as ripples and dunes by simply modifying the surveying interval to reflect the scale of the bed forms

the role of initial fabric on strain determination from deformed ellipsoidal objects abstract twenty one samples of undeformed conglomerates sandstones tuffs oolites and pisolites from precambrian to pleistocene in age were collected from a variety of geologic environments each sample was sectioned on three mutually perpendicular faces with one face parallel to bedding selected samples were also sectioned at 60 and 30 degrees to the bedding plane the shape and orientation of at least 100 particles were measured on each section particle shape ranges from nearly circular in some samples to highly eccentric in others sections parallel with bedding have essentially random fabrics no preferred orientation of particles sections not parallel with bedding have a preferred orientation of particles along the bedding trace but particles with all orientations do exist the fabric distributions on the polar plot elliott 1970 are often irregular in shape and the initial circle point lies well within the distribution in all cases transformation equations for the final shape and orientation of an individual particle using known shapes and orientations of the initial particle and the strain ellipse are used to construct the resultant fabrics after homogeneous simulated strains of several directions and magnitudes the resultant fabrics can be used as a test of utility and accuracy of strain determination methods a simple algebraic method of strain determination is found to be fairly accurate if the initial fabrics measured in this study are representative the accuracy of the method can be increased with the use of an error function introduced herein

an appraisal of the velocity reversal hypothesis for stable pool riffle sequences in the river severn england the velocity reversal hypothesis is the linchpin for a number of recent conceptual models pertaining to sediment sorting and the maintenance of pool riffle sequences in gravel bedded streams the literature in support of the hypothesis together with published adverse criticism is reviewed it is concluded that convincing evidence for the ubiquitous occurrence of such a reversal in a range of channel geometries is currently unavailable continuity considerations indicate that riffles need to be considerably wider than pools for a reversal in the mean velocity to occur under conditions of subcritical flow high stage and stable morphology these observations are substantiated by a detailed study of the hydraulic geometry of stable pool riffle sequences in the river severn england neither the sectionally averaged velocity nor the near bed shear velocity is sensibly greater in the pools than over the riffles during bankfull or near bankfull flow instead a tendency towards equalization of the values of average hydraulic variables is noted as discharge increases a detailed investigation of the three dimensional character of the flow is required to demonstrate whether the entrainment forces within pools can locally exceed those over neighbouring riffles unusual behaviour of the energy gradient over riffles during moderate discharges is related to backwater effects as mediated by the spacing of the riffles the hydraulic data are used to comment on the stability of the test reaches in the context of the development of the river severn in the vicinity of shrewsbury

differential bed sedimentology and the maintenance of riffle pool sequences abstract riffle pools are the characteristic reach scale bedforms of gravel and mixed bedded channels of low to moderate slope the purpose of this paper is to clarify several aspects of the sedimentology of riffle pool sequences and to suggest how these both reflect and control riffle pool stability in the presence of spatial differences in the turbulent near bed flow field high frequency velocity measurements obtained using an array of electromagnetic current meters are combined with results from grid and transect sampling of bed sediments from 9 sites on 3 small upland rivers in n exmoor u k riffle sediments are shown to possess greater development of microtopographic structuring than adjacent pools which enhances riffle stability and which may reflect greater turbulent kinetic energy there over most of the flow range data on surface sediment arrangement and turbulent flow characteristics can be combined with different transport threshold equations to explain the maintenance of riffle pool sequences with respect to a particle queuing kinematic wave model without recourse to a competence reversal as conventionally assumed

sediment transport processes in pool riffle sequences this paper reviews the published data for sediment transport in pool riffle sequences which suggests that a velocity or shear stress reversal hypothesis does not explain all of the published evidence of sediment transport this conclusion is explored in more detail using observations of sediment transport from the regulated river north tyne sediment transport rates at discharges of 30 per cent bankfull are initially highest on riffles as discharge increases sediment transport rates in pools rise sharply and values locally exceed those on riffles tracing experiments using a combination of magnetic and painted tracers are used to show the downstream dispersal of fine and coarse sediments through the pool riffle sequence coarser particles experience longer transport paths and faster virtual rates of travel in pools during bankfull floods analysis of entrainment data reveals evidence for additional restraint operating on riffles and causing higher dimensionless entrainment thresholds an appraisal of the possible mechanisms controlling sediment entrainment transport and deposition in pool riffle sequences is made which reveals evidence for the operation of a combination of hydraulic sedimentological and interactive processes a descriptive model of sediment transport processes in pool riffle sequences is presented

grain size along two gravel bed rivers statistical variation spatial pattern and sedimentary links a new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel bed rivers in northeastern british columbia canada a preliminary assessment of grain size variability establishes a basis for examination of the spatial pattern of grain size change standard anova techniques are inappropriate because individual samples have unequal variances and are not normally distributed alternative tests for homoscedasticity and comparison of means are therefore utilized within site between sample variability is not significant the grain size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled in both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining textural variations along the two rivers studied here are complex and show negligible overall fining in over 100 km this is the consequence of a large number of tributary inputs and non alluvial sediment sources which are the legacy of late pleistocene glaciation the identification of lateral sources like these is fundamental for understanding textural changes within rivers the sedimentary link a channel reach between significant lateral sediment inputs provides a means of isolating fluvial maturation processes abrasion and sorting from contingent lateral inputs strong fining trends are apparent in most links and classification of grain size measurements according to their location within particular links greatly improves the statistical explanation of textural variation identification of sedimentary links provides a means of applying models of fluvial fining processes so isolation of link networks will aid the development of basin scale models of textural variation 1998 john wiley sons ltd

variation in cross sectional asymmetry of coarse bedload river channels alternative indices of cross section asymmetry are compared observed values of two preferred indices for 567 natural sections across eleven confined upland channels are predictably low along such low sinuosity reaches variation in asymmetry of sections located around confined unconfined but stable and freely migrating bends is evaluated consideration of the influence of bed topography emphasizes local plan curvature of bed forms as an important control on degree of asymmetry variation in indices for bed forms in similar planform locations indicates the levels of asymmetry at different stages of the transformation of channel geometry over time

the significance of cordierite hypersthene assemblages from the beitbridge region of the central limpopo belt evidence for rapid decompression in the archean

discussion bulk sampling of coarse clastic sediments for particle size analysis gale and hoare 1992 have provided a figure relating maximum particle diameter in a coarse clastic sediment to the size of sample required to generate a reproducible measure of the particle size distribution of that sediment however they fail adequately to justify the basis for the criterion of sample adequacy adopted in their proposal additionally there is a range of separate issues neglected by gale and hoare 1992 which makes their conclusion inapplicable in many situations a fundamental issue that they neglect is the purpose lying behind a grain size analysis this issue determines what grain size measures are appropriate rather than the empirical seemingly purpose independent approach of gale and hoare 1992

change in dominant mechanisms for phyllosilicate preferred orientation during cleavage development in the kitakami slates of ne japan abstract selected slates from the kitakami mountains of ne japan were studied by means of finite strain measurement x ray texture goniometry optical microscopy back scattered sem and x ray fluorescence and diffraction analyses finite strain recorded by radiolarians in slates although not equivalent to bulk strain shows a positive correlation with strength of phyllosilicate basal plane fabrics however there is a possible difference between the fabric pattern and radiolarian strain ellipsoid shape as well as a difference in fabric pattern between chlorite and illite mica these relationships between phyllosilicate fabrics and finite strains suggest that strain estimation from phyllosilicate fabrics based on the march model may be unreliable unless their relationship is established in each case optical and back scattered sem studies revealed a change in microstructures in accordance with increasing fabric strength in slates with weak fabric strength cleavage domains are dark to opaque in appearance and characterized by a concentration of insoluble residues such as carbonaceous matter sphene ilmenite rutile epidote and apatite as well as phyllosilicates phyllosilicates in cleavage domains are oriented subparallel to cleavage whereas those in intercleavage domains are variously oriented as fabric strength increases cleavage domains become transparent and composed mainly of phyllosilicates phyllosilicates become finer grained and more uniform in grain size they are well oriented in both cleavage and intercleavage domains as fabric strength further increases phyllosilicates tend to coarsen these lines of microstructural evidence suggest that the dominant mechanism for phyllosilicate preferred orientation changes as cleavage develops from pressure solution transfer through syntectonic crystallization recrystallization and possibly to oriented grain growth because fabric strength increases with increasing illite crystallinity metamorphic grade mainly temperature must be one of the major factors which control the dominance of phyllosilicate preferred orientation mechanisms

the development of δ clasts in non linear viscous materials a numerical approach abstract winged porphyroclasts are often used as kinematic or strain indicators in shear zones in particular it has been suggested that the geometry of clasts in mylonites can give information about the rheological behaviour of the matrix around the clast passchier et al 1993 we tested this hypothesis with a numerical finite element simulation of the flow field of a viscous matrix around a relatively rigid clast power law viscous flow properties of the matrix with stress exponents of 1 linear viscous 3 and 5 were tested as well as three different sets of approximately simple shear boundary conditions which are relevant to experimental and or natural situations the simulations show that the flow field is primarily determined by the boundary conditions the stress exponent is of secondary importance in general the different boundary conditions produce two types of flow fields about the rigid clast an eye shaped flow field and a bow tie shaped flow field the former is produced by boundary conditions that approximate simple shear applied at an infinite distance from the rigid clast and the latter is produced by boundary conditions which are equivalent to a shear box or ring shear apparatus although both the shear box and ring shear boundary conditions produce bow tie flow patterns the wing geometries which result from the flow patterns for these two cases can be significantly different the geometry of the wings that develop on a clast is a direct function of the flow field around the clast for linear and non linear rheologies only the ring shear boundary conditions produce wings that show stair stepping i e wings that are parallel but not in the same plane in natural shear zones clasts both with and without stair stepping are observed in comparing geologic observations with experimental or numerical modelling it is essential to understand which boundary conditions are appropriate

modelling three dimensional flow structures and patterns of boundary shear stress in a natural pool riffle sequence fluid sediment interactions control river channel forms and processes analysis of spatial hydraulic patterns and the resulting boundary shear stress are required to aid understanding of river system behaviour in this paper the hydraulic processes active in a natural pool riffle sequence are simulated using a three dimensional computational fluid dynamics cfd model methods employed for the prescription of model boundary conditions are outlined model calculations are assessed using comparisons with field observations acquired over a range of flows simulations are then used to illustrate flow structures and patterns of boundary shear stress for a near bankfull and an intermediate flow event results are used to assess existing theories that seek to explain the development and maintenance of pool riffle sequences simulated results suggest that near bed velocities and bed shear stresses decrease on riffles and increase in pools as discharge increases model simulations indicate that secondary flow acts to route near bed flow over the downstream side of riffles and into the pool head away from the centre of pools implications for sediment transport and pool maintenance are discussed

studies of strain and rheology of conglomerates abstract conglomerates can show significant strain variations among their component rock types previous studies have exploited this feature as a method of quantifying the effective viscosity ratios among different rock types using inclusion matrix models that we review here we further investigate the rheology of conglomerates via models of multiphase mixtures of spherical clasts with varying phase fractions using idealised models with two to four phases we can quantify the influence of phase viscosities and volume fractions on the bulk viscosity and reveal how this controls the strain partitioning among the different phases we consider practical methods of analysing conglomerates and choose r f analysis for measuring clast strain and fry analysis for whole rock strain the methods are illustrated through case studies of two very different conglomerates the port askaig tillite scotland and cesson conglomerate brittany we define the important rock phases in each and assess their strain variations although providing strain measurements of regional interest our main purpose is to quantify the viscosity ratios among the component rocks we find that among the most common rock types semipelite quartzite psammite volcanics granite the viscosity ratios span about one order of magnitude agreeing with previous studies these small numerical values for viscosity ratios among many rock types in many conglomerates lead us to conclude that these rocks each deformed at approximately constant viscosity i e as linearly viscous rather than according to a power law

competence contrasts in ductile deformation as illustrated from naturally deformed chert mudstone layers abstract a sample of chert mudstone layers provides a rare opportunity for quantitative analyses of competence contrasts in naturally deformed rocks this sample contains deformed quartz veins possibly formed subperpendicular to bedding during initial bedding normal compaction and abundant radiolarians as strain markers whose viscosity during deformation is approximated by that of chert under several assumptions these allow quantitative analyses of two types of competence contrast in ductile deformation layer competence contrast and inclusion matrix competence contrast layer competence contrast results in strain and cleavage refraction through the layers while inclusion matrix competence contrast is illustrated by the difference in strain state between radiolarians and their matrix a quartz vein presumed to be initially perpendicular to bedding provides estimates of layer parallel shear strains and chert mudstone layer viscosity ratios which were also used as radiolaria matrix viscosity ratios in different layers radiolarian shapes are factorized into cleavage strains and pre cleavage shapes cleavage strains in matrix are then determined from radiolarian strains applying eshelby s equations and their variations as well as the refraction of cleavage through the layers are compared with treagus s theoretical modeling of strain refraction with decreasing layer competence cleavage refracts toward bedding and increases in intensity so that cleavage bedding intersections vary slightly but systematically through the layers suggesting a threedimensional strain refraction all three principal axes of radiolarian and matrix cleavage strain ellipsoids estimated indeed refract from layer to layer strain magnitude systematically increases with decreasing layer competence these results are consistent with the strain refraction theory however no systematic change in strain ellipsoid shape associated with strain refraction is recognized

subsurface flow in lowland river gravel bars geomorphic and hydraulic processes which form gravel bars in large lowland rivers have distinctive characteristics that control the magnitude and spatial patterns of infiltration and exfiltration between rivers and their immediate subsurface environments we present a bedform infiltration relation together with a set of field measurements along two reaches of the san joaquin river ca to illustrate the conditions required for infiltration and exfiltration of flow between a stream and its undulating bed and a numerical model to investigate the factors that affect paths and residence times of flow through barforms at different discharges it is shown that asymmetry of bar morphology is a first order control on the extent and location of infiltration which would otherwise produce equal areas of infiltration and exfiltration under the assumption of sinusoidal bedforms hydraulic conductivity varies by orders of magnitude due to fine sediment accumulation and downstream coarsening related to the process of bar evolution this systematic variability not only controls the magnitude of infiltration but also the residence time of flow through the bed the lowest hydraulic conductivity along the reach occurred where the difference between the topographic gradient and the water surface gradient is at a maximum and thus where infiltration would be greatest into a homogeneous bar indicating the importance of managing sand supply to maintain the ventilation and flow through salmon spawning riffles numerical simulations corroborate our interpretation that infiltration patterns and rates are controlled by distinctive features of bar morphology

fry and rf ϕ strain methods constraints and fold transection mechanisms in the nw iberian variscides abstract apulia is a small portuguese sector in nw of central iberian zone that have been deformed in a non coaxial sinistral transpressive regime during the first and main variscan tectonic event d1 this deformation give rise to a major nw se anticline where the s1 n s cleavage transect the inverted short ne limb two and three dimensional strains analysis have been done in the low metamorphic grade ordovician quartzites of this limb using fry and rf methods the data show that most deformation was due to intergranular deformation mechanisms the intragranular deformation leading to the distortion of strain markers and to cleavage was very incipient and a latter event in the d1 phase the apparent plane strain ellipsoids if no volume change is assumed related to the intragranular mechanisms contrast with the more prolate strain ellipsoids related to the bulk deformation of apulia quartzites this constrictional bulk strain fabrics are characteristic of the sinistral transpressive regimes dominant in the northern sectors of the central iberian zone

metamorphic evolution of aluminous granulites from labwor hills uganda sapphirine cordierite quartz and spinel cordierite quartz form relic assemblages of probable archaean age in fe rich aluminous metapelites from labwor hills uganda and reflect an unusually high temperature metamorphism 1 000 c at pressures in the vicinity of 7 9 kbars and a o2 near the magnetite hematite buffer subsequent reaction textures include the replacement of spinel and cordierite by sillimanite and hypersthene and formation of sapphirine hypersthene k feldspar quartz symplectites which are interpreted as pseudomorphs after osumilite a petrogenetic grid appropriate to these assemblages suggests these reaction textures may be due to cooling at constant or increasing pressure and constant a o2 or decreasing a o2 at constant temperature and pressure the former interpretation is supported by the coexistence of ilmenohematite and magnetite during the development of the reaction textures and by the comparatively low al2o3 contents of secondary hypersthene this pressure temperature path implies that 1 metamorphism occurred at deep levels within normal thickness crust probably less than 40 45 km thick due to an extreme thermal perturbation induced either by emplacement of mantle derived magmas or by thinning of the subcontinental lithosphere in an extensional tectonic regime 2 the excavation and surface exposure of the granulites is due to a subsequent postgranulite facies metamorphism crustal thickening most probably involving their incorporation into an allochthonous upper crustal thrust sheet during the formation of the mozambique foldbelt

strain analysis and rheology contrasts in polymictic conglomerates an example from the seine metaconglomerates superior province canada deformed conglomerates typically display contrasting strains between different lithological clast populations and matrix which can be exploited to provide information about effective viscosity contrasts we analyzed three different clast populations granitoid mafic volcanic and felsic volcanic across a strain gradient in the seine metaconglomerates of ontario canada we calculated finite strain using the rf 4 method and bootstrap statistics granitoid clasts exhibited the least amount of strain while the mafic and felsic clasts had similar greater strains we assumed that the bulk finite strain was recorded by the mafic clasts given their large proportion of the rock and their similar composition to the matrix we calculated effective viscosity contrasts using the finite strain information assuming newtonian viscous rheology the two volcanic clast populations have similar effective viscosities regardless of strain magnitude with ratios of felsic mafic ranging from 0 27 to 2 12 and average ratio of 1 19 the granitoid clasts are significantly more competent than the mafic clasts with effective viscosity ratios ranging from 2 35 to 12 39 and average ratio of 5 61 the results are consistent with a qualitative

morphology of riffle pool sequences in the river severn england despite the occurrence of pool riffle sequences in many rivers there are few data concerning pool riffle unit morphology of many criteria proposed to identify pool riffle units only two methods can be regarded as objective and robust these are the zero crossing and the control point methods in this paper statistics are developed from the zero crossing method to describe the streamwise morphology of 275 riffles and 285 pools which form a near continuous 32 1km of the bed of the river severn in shropshire england yalin s theoretical relationship between pool riffle unit length i p and channel width w i p 3w applies to the river severn reach average riffle height h is a constant proportion of bankfull depth h typically h i 0 16h riffle height is a positive function of riffle length pool depth is a positive function of pool length however both riffle length and pool length increase more rapidly than the bed level amplitude such that long riffles or pools are relatively flat as channel gradient reduces bedforms flatten and become more asymmetric as riffle stoss sides and the proximal slope of pools lengthen at the expense of riffle lee sides and pool distal slopes the statistical relationships between riffle height length and water depth are similar to those for equilibrium subaqueous dunes the severn data are partially consistent with yalin s theoretical analysis relating riffle bedform length lr to water depth i e lr i i2i h wherein i i i 1 for steep near equilibrium bedforms but i i i 2 to 3 as the relative depth decreases and riffles become long low features a consideration of turbulence data indicates that the frequency of coherent turbulent flow structures associated with the riffle pool mixing length is of the order of 60 seconds the morphological and dynamic similarity of the river severn riffles with dunes raises intriguing questions with respect to self similar convergent organization of periodic alluvial bedforms and to bedform dynamic classification particularly

experimental modeling of viscous inclusions in a circular high strain shear rig implications for the interpretation of shape fabrics and deformed enclaves 1 deformation experiments with initially spherical and prolate viscous inclusions suspended in a viscous newtonian matrix in a circular high strain annular shear rig provide insights on the shape development of inclusions in high strain shear zones during progressive deformation inclusions with a specific viscosity ratio with respect to the matrix material show distinct types of three dimensional shape development for instance at a high viscosity ratio between matrix and inclusion a pulsating ellipsoid develops which both continuously rotates and changes its shape from a sphere to an ellipsoid and back to a sphere the experiments show that the shape of an inclusion that has a viscosity different to the matrix material cannot be taken as a reliable indicator for the magnitude or type of finite strain in naturally formed shear zones in which strain rates are heterogeneous from boundary to center viscosity contrast and power law flow will result in a large number of different shape developments trends for inclusions such as mafic and microgranitic enclaves pebbles or mineral aggregates

mg cordierite si al ordering optical properties and distortion flux grown crystals of mg cordierite mg1 93 al3 95 si5 07 o18 synthesized by lee and pentecost 1976 appear biaxial 2vx 10 25 under the polarizing microscope whereas their distortion index 0 between crossed polars 001 sections display lamellar and cyclic twinning on 110 and less frequently 310 as duration of annealing at 1 300 c increased 2vx increased simultaneously undulatory extinction and intragrain variations in 2vx increased slightly up to 4 h annealing then steadily decreased for this mg cordierite which lacks significant channel h2o or co2 2vx and reach maxima of 88 589 nm and 0 25 after 42 h of annealing but other sectors still display lesser values for 2vx presumably to the extent 2vx is less than 88 these sectors represent intergrown submicros copically twinned orthorhombic domains and thus possess shortrange but not long range order annealing at 1 300 c likely increased long range order by promoting growth of larger domains at the expense of smaller ones ultimately two differently oriented domains growing toward each other by annexation and re orientation of smaller domains meet in a twin boundary that with time tends to become straight

the relationship between tectonic strain and the three dimensional shape fabrics of pebbles in deformed conglomerates the bias associated with the use of the shape of deformed inclusions to estimate bulk strain from conglomerate systems is examined mechanical considerations based on eshelby9s theory for the deformation of ellipsoidal inclusions supported by data from naturally deformed conglomerates with more than one type of inclusion reveal a discrepancy between the degree of prolateness oblateness shown by the inclusion and the bulk rock strain ellipsoid this bias is most marked in situations where the difference of competence between the inclusion and matrix is high and the volume fraction of inclusions is low in these situations an inclusion which is more competent than the matrix will deform to a shape which is more prolate than the bulk strain ellipsoid this has important implications for strain analysis of conglomeratic rocks and the interpretation of pebble shape fabrics in the context of regional tectonics

sediment routing hypothesis for pool riffle maintenance this paper provides comprehensive evidence that sediment routing around pools is a key mechanism for pool riffle maintenance in sinuous upland gravel bed streams the findings suggest that pools do not require a reversal in energy for them to scour out any accumulated sediments if little or no sediments are fed into them a combination of clast tracing using passive integrated transponder pit tagging and bedload traps positioned along the thalweg on the upstream riffle pool entrance pool exit and downstream riffle are used to provide information on clast pathways and sediment sorting through a single pool riffle unit computational fluid dynamics cfd is also used to explore hydraulic variability and flow pathways clast tracing results provide a strong indication that clasts are not fed through pools rather they are transported across point bar surfaces or around bar edges depending upon previous clast position clast size and event magnitude spatial variations in bedload transport were found throughout the pool riffle unit the pool entrance bedload trap was often found to be empty when the others had filled further supporting the notion that little or no sediment was fed into the pool the pool exit slope trap would occasionally fill with sediment thought to be sourced from the eroding outer bank cfd results demonstrate higher pool shear stresses 140 n m 2 in a localized zone adjacent to an eroding outer bank compared to the upstream and downstream riffles 60 n m 2 at flows of 6 2 m3 s 1 60 of the bankfull discharge and above there was marginal evidence for near bed velocity reversal near bed streamlines produced from velocity vectors indicate that flow paths are diverted over the bar top rather than being fed through the thalweg some streamlines appear to brush the outer edge of the pool for the 4 9 m3 s 1 to 7 8 m3 s 1 between 50 and 80 of the bankfull discharge simulations however complete avoidance was found for discharges greater than this copyright 2013 john wiley sons ltd

late cretaceous to early tertiary transtension and strain partitioning in the chugach accretionary complex se alaska abstract shear zones in the late cretaceous sitka graywacke of the chugach accretionary complex in southeast alaska record constrictional finite strains with maximum principal stretches plunging shallowly subparallel to strike of the shear zones macrostructural analysis indicates the finite strain formed during one deformation event microstructural analysis of the shear zones shows that this deformation is ductile promoted mostly through deformation of low strength lithic clasts and pressure solution kinematic indicators from some of the shear zones indicate dominantly dextral motion although multiple scenarios can explain constrictional finite strains in a shear zone these dextral strike slip shear zones must have experienced a component of extension across them in order to generate constrictional finite strains therefore the shear zones are dextral transtensional shear zones an uncommon tectonic regime in an accretionary complex the transtensional shear zones reflect strike slip motion related to partitioning of late cretaceous to early tertiary right oblique convergence between north america and the farallon plate the extensional component that was superposed on the strike slip shear zones to generate transtension resulted from contemporaneous collapse of the forearc following thickening related to underplating