curved vein fibres an alternative explanation abstract veins occurring at the edge of the dextral indian islands fault newfoundland are folded in response to a fault parallel ductile shear the veins which locally constitute a penetrative fabric element at outcrop scale are composed mainly of calcite and have a narrow rim of quartz and chlorite both the calcite and quartz are generally fibrous and lattice distortion in the calcite is not commensurate with the observed degree of fibre curvature this observation supports the popular view that curved fibres grow curved as they track the vein opening vector it is demonstrated however that the curvature in the material described here is due to deformation and that the lack of strong lattice distortion is due in part to polygonization and to recrystallization all observations are consistent with both the calcite and the quartz fibres having grown perpendicular to the vein walls the chlorite orientation is controlled by the orientation of mica grains in the country rock in some veins markers make it possible to define the net opening direction and in all examples it is demonstrated that the direction has not been tracked by the fibres since this conclusion may be more generally applicable caution should be exercised in interpreting kinematics on the basis of fibre geometry where vein density is high the veins and country rock screens separating them form a multilayer sequence that is folded into fairly harmonic folds the folds appear to have a cleavage transected relationship to the regional cleavage but the cleavage is shown to predate the folds

a laboratory simulation of fibrous veins some first observations abstract following work by stephen taber 80 years ago we describe vein like arrays of parallel fibrous crystals that grow evaporatively between pairs of brine soaked porous ceramic substrates crystals of solute grow antitaxially from fixed sites on the substrate forcing older parts of the crystals away from the growth site without benefit of any long range cracking parallel to the substrate the nutrients for growth are fed to the growth site advectively or diffusively through the substrate blocks themselves not along the plane of the vein we call such crystallization taber growth and suggest as taber did that it might be an important mechanism for non evaporative fibrous vein development in nature the taber growth model provides a ready explanation for the ability of fibers to track vein opening directions and tracking is indeed the rule in our samples though exceptions are also seen our results lend support to ideas already in the literature that fibrous veins are not necessarily products of a crack seal process and that fibrous veins are not necessarily syntectonic our observations also raise questions about criteria for recognition of syntaxial fibrous veins and underscore the importance of finding new criteria for recognition of the younging direction along fibers

the use of syntectonic fibres to determine strain estimates and deformation paths an appraisal abstract fibrous pressure shadows developed adjacent to rigid brittle inclusions are familiar features in many tectonites belief that these structures reflect the deformation path as once adjacent grains move apart has led to the derivation of a variety of techniques to determine both incremental and finite strain estimates these methods which can be divided into rigid fibre models e g durney and ramsay and deformable fibre models e g ellis display potentially serious problems when applied to field examples recent studies of microstructures within veins and pressure shadows support the concept that syntectonic fibre complexes can reflect deformation paths and are therefore useful markers of incremental and finite strain the problems mentioned therefore stem directly from the application of the techniques worked examples using these techniques give a variety of strain values dependent upon the extent to which a particular technique allows for volume change or fibre deformation this is useful locally however if the results are to be meaningful on a regional scale then it is imperative that the same technique be applied in the analysis of all fibres regardless of the local deformation path in such studies the merits of a particular technique in determining a correct strain value come second to allowing the spatial distribution of strain to be determined semi quantitatively and thus allowing comparison of similarly derived results with one another

sheared bedding parallel quartz vein as an indicator of deformation processes abstract monomineralic veins are well known as good recording of filling and precipitation processes however they are also able to register the action of deformation in rocks we used monomineralic quartz veins from quadrilaterro ferrifero brazil to represent how the deformation actuated during the transformation of different structures they were analyzed using a combination of a u stage and ebsd two main types of quartz aggregates are distinguished single crystals with subgrain development and strain free grains of quartz we interpret the microstructures and textures as the result of a combination of concurrent crystal plasticity microfracturing solution transfer and recrystallization the single quartz grains were deformed by dislocation glide however as the c axis orientation of the grain was not favorable for further glide on basal planes the deformation was accommodated by microfracturing new grains were formed along the deformed zones with crystallographic orientations suitable for gliding on basal planes as the deformation proceeded the new grains continue to develop until the vein was completely recrystallized into an aggregate of granular grains

microstructural evolution in bitaxial crack seal veins a phase field study bitaxial crack sealing by epitaxial crystal growth is the most common vein forming process in earth s crust but the details of the microstructural processes in these are not well understood here we model the evolution of bitaxial crack seal quartz veins in two and three dimensions using the phase field method our numerical simulations show the influence of different parameters such as the obliquity of crack opening and crack location grain size and orientations on the evolving vein microstructure we examine the underlying growth competition observed during epitaxial growth of quartz results show many similarities with natural microstructures such as stretched crystals and compare well with the previous numerical findings as the ratio of crack aperture and matrix grain size for the present studies is chosen to be sufficiently large for growth competition to occur before complete sealing it leads to the formation of crystal fragments along the crack opening trajectory we explain how such fragment trails act as potential indicators of the opening of crack seal veins if they are confirmed to be common in natural microstructures finally we highlight the importance of accounting for the third dimension in the numerical simulations by analyzing the evolution of fluid connectivity in 2 d and 3 d during the sealing process

development of crystal morphology during unitaxial growth in a progressively widening vein ii numerical simulations of the evolution of antitaxial fibrous veins the development of fibrous morphology and capability of fibres for tracking the opening trajectory were investigated using numerical simulations of a natural antitaxial fibrous vein starting from a non unique best case variation of fracture opening velocity grain size wall roughness growth anisotropy and crystal growth velocity shows that these parameters differ in importance for crystal morphology and tracking capability fibrous veins can be simulated using crack seal opening of the fracture grain boundaries track the opening trajectory if the wall roughness is high opening increments are small and crystals touch the wall before the next crack increment starts

development of crystal morphology during unitaxial growth in a progressively widening vein i the numerical model abstract a two dimensional numerical model for the simulation of the formation of microstructures in crack seal veins is presented here the grain aggregate in the vein is described by grain boundary nodes that link short straight boundary segments growth of crystals into a crack takes place by many small incremental movements of nodes the rate of growth depends on the chosen growth morphology of the vein forming material different growth morphologies can be defined for every user defined number of steps the wall rock is moved a user defined distance and direction which simulates the opening of a crack after which sealing can proceed again the shape of the crack surface e g smooth or with ridges can be set by the user and can be made to match fracture surfaces found in real rocks the model is capable of reproducing realistic crack seal textures and can be used to systematically investigate the role of different parameters on the microstructures of veins first applications of the model are presented in part ii of this paper this volume

vein reactivation and complex vein intersection geometries in the taconic slate belt abstract this paper describes some complex intersection geometries for veins in the taconic slate belt of western new england u s a the complexity is primarily a result of the preferential reactivation during slaty cleavage development of one set of veins within an orthogonal system of pre cleavage veins the relative age of the precleavage veins also influences the intersection geometry in that the non reactivated veins which form the younger set of pre cleavage veins act as barriers to the propagation of the syn cleavage veins these types of intersection geometries are easily misinterpreted without microscale observations of vein textures and may be more common than is currently appreciated

petrography and isotopic geochemistry of bedding parallel fibrous gypsum veins in the neogene qingshuiying formation of the ningnan basin north china insights for growth model of antitaxial fibrous veins abstract bedding parallel fibrous gypsum veins which are widely developed in the neogene qingshuiying formation of the ningnan basin a tertiary basin located in the northeastern margin of the tibetan plateau provide valuable information on stress field fluid origin and host rock deformation during their formation the systematic petrographic observation and isotope analysis of both of veins and wall rocks were carried out to investigate the formation mechanism of bedding parallel fibrous gypsum veins the distribution of fibrous gypsum veins shows vertical heterogeneity and mainly occurs in the middle and lower part of the qingshuiying formation with relatively high gypsum content single fibrous gypsum veins consist of a median zone and two fibrous zones the median zone is characterized by blocky gypsum crystals and multiple host rock fragments formed by crack seal events the fibrous zone is composed of parallel gypsum fibres a high angle to the vein walls indicating shear component vein opening is considered to be the result of fluid overpressure caused by horizontal compression in low permeability mudstone during basin inversion fibrous gypsum crystals grow continuously without obvious growth competition between adjacent crystals this indicates that growth of gypsum fibres occurs in limited space even without fractures the main driving force for vein dilation is force of crystallization of gypsum fibre growth and fluid pressure also has a certain contribution the sulfur and strontium isotopes of gypsum veins exhibit a high degree of consistency with wall rocks which indicates the material of the fibrous gypsum veins is derived from the wall rock a suitable growth model of bedding parallel fibrous gypsum veins in the ningnan basin is established which explains the process of vein interaction and the formation of v shaped or u shaped solid inclusions

influence of p t conditions on the style of normal fault initiation and growth in limestones from the se basin france abstract a conventional and cathodoluminescence microscopy stable isotope and fluid inclusion study was undertaken on normal fault zones exposed on vertical cliffs in tithonian limestones of the french se basin the aim was to determine the chronology of deformation and factors controlling normal fault nucleation and evolution in carbonate rocks two models are proposed for fault zone development depending on the depths at which deformation takes place at depths of 3 3 5 km incipient shear zones consist of en echelon veins filled by fibrous calcite and confined to limestone layers bounded by thin clayey interlayers as deformation increases and the layers rotate slip occurs along the clay rich interlayers a system of pull aparts forms allowing displacement to increase pull aparts are commonly filled by fibrous calcite crystals at depths of 1 5 2 km faults initiate as small slip surfaces early nucleating in some limestone layers their propagation is impeded by thin clayey interlayers which enhances fracturing and bending of the limestone layers as slip surfaces propagate they overlap and can connect with one another by means of dilational jogs that are filled by large euhedral calcite crystals in the first case pull aparts are coupled with the solution seams that reuse preexisting rotated clay rich interlayers as they formed they progressively filled and the fluid circulation remained local in the second case longer slip planes connect by dilation jogs that are not immediately filled which enhance the circulation of fluids which show chemical variations it appears that p t conditions strongly control the relative role of brittle processes and solution crystallization mechanisms and the style of the early stages of normal faulting in the same limestone rocks

cyclic fluid flow through a regionally extensive fracture network within the kodiak accretionary prism two types of periodic textures observed in veins from the kodiak accretionary prism attest to cyclic fluid flow through a regionally extensive fracture network buried at 8 12 km depth 1 crack seal microstructures with bands of mica inclusions and 2 collapse microstructures with jagged bands of residue embedded within euhedral crystals of quartz the difference in texture reflects the closure of cracks crack seal microstructures record the complete chemical sealing of the crack after each fracture event whereas the collapse features record longer fluid filled periods followed by more rapid draining of fractures collapse features consist of pressure solution selvages trapped within veins and in the wall rock adjacent to euhedral growth terminations the high concentrations of immobile elements in these selvages indicate that these fractures closed by collapse and penetration of quartz crystals into wall rock analysis of chemical composition on either side of four large euhedral growth veins and whole rock analysis of slates across the kodiak formation reveal local depletion of silica adjacent to veins but no evidence for long distance silica transport within the system both crack seal and collapse textures are observed in a regionally extensive vein system that displays a regular geometry with thin closely spaced 0 5 3 cm near vertical crack seal veins that connect vertically and laterally with thicker euhedral growth veins arranged in widely spaced 500 mm southeast dipping en echelon sets the mesoscopic distribution and textural variability of the vein network suggests that the development of the vein system involved early nucleation and growth of vertical hydrofractures as the fracture density increased arrays of fractures locally provided zones of weakness and southeast dipping brittle ductile shear zones nucleated these en echelon cracks remained open and provided small reservoirs of fluid textures show that en echelon fractures remain open but periodically grow by upward and downward propagation crack tips are then sealed with locally derived silica and fluid drains back into en echelon fracture arrays this local fluid movement is punctuated by less frequent events where the system links up over a greater distance fractured reservoirs become interconnected and the fluid within reservoirs is drained upward or laterally periodic inflation and deflation of en echelon arrays may reflect periodic slip on crosscutting faults and rupture of the seals that separate reservoirs

crack seal microstructure evolution in bi mineralic quartz chlorite veins in shales and siltstones from the rwth 1 well aachen germany abstract in core samples from the deep geothermal well rwth 1 we studied variscan quartz chlorite veins formed by crack seal processes in siliciclastics at the brittle to ductile transition these sheared veins are common in sections of the well which are interpreted as variscan thrust zones based on image logs and seismic data microstructures interpreted to reflect different stages in the evolution of such crack seal veins suggest the veins started in microcracks sealed by quartz and chlorite to veinlets crossing multiple grains and bundles of veinlets evolving by progressive localization into low angle extensional shear veins and high angle dilational jog veins in the sheared veins chlorite and quartz ribbons show evidence for crack seal and simultaneous ductile shearing during vein evolution forming peculiar fin shaped microstructures in quartz ribbons in high angle dilational jogs fibrous crystals of quartz and chlorite point to multiple crack seal events with simultaneous growth of two different mineral phases this is interpreted to be the basic microstructural process in the veins we extend earlier models of polycrystal growth in fractures and present a series of 2d simulations of the kinematics of crystal growth in these bi mineralic veins for both localized and non localized cracking results are compared with the observed microstructures we show that when the relative growth rates of the two mineral phases are different serrated grain boundaries evolve the similarities between observation and model suggest that the assumption of our model is valid although many second order processes require a more detailed study we propose that the principles observed here can be applied to other bi mineralic crack seal veins

structural control magmatic hydrothermal evolution and formation of hornfels hosted intrusion related gold deposits insight from the thaghassa deposit in eastern anti atlas morocco in the moroccan eastern anti atlas the thaghassa intrusion related gold deposit is hosted in hornfelsed metasedimentary rocks that lie adjacent to the ikniwn granodiorite fields studies reveal three tectono magmatic stages controlling the formation of the deposit i the first stage refers to the top to the south asymmetry and the syn kinematic ikniwn pluton emplacement controlled by a compressional or transpressional strain regime ii the second stage is characterized from older to younger and further away from the intrusion by metatexite with leucocratic stromatic bands aplo pegmatite sills intermediate veinlets composed of quartz k feldspar and muscovite and then gold bearing striped foliation veins all these features are assumed to have been emplaced during a large scale ene wsw dextral shearing process that results from an ese wnw shortening direction during transtensive tectonics we suggest that the progressive and continuous shearing was initiated since the aplo pegmatite stage and achieved during the hydrothermal phase the existence of intermediate veins characterized by quartz rich core and apatite muscovite feldspar rich rims demonstrates the progressive evolution from the magmatic to the hydrothermal stage and evidence for the persistence of the magmatic character at least until the onset of the hydrothermal process iii the late stage developed large volcanic dyke swarm and brittle faulting zircon u pb la icp ms dating yields a concordia age of 563 5 6 3 ma for the ikniwn granodiorite intrusion the fluid inclusions data besides the mineral thermometry indicate that two main types of fluids can been highlighted i a hot aquo carbonic h2o nacl co2 fluid with n2 and ch4 evolving from vapour rich n2 and ch4 inclusions for the magmatic stage 550 c to ch4 co2 biphased inclusions for the ongoing hydrothermal stage 450 300 c and ii an always secondary low t 200 c saline aqueous type probably nacl free from volatiles with very variable salinity eventually we highlight that in the hornfels hosted irg deposits fluid sources may originate from both magmatic processes and devolatization of the metamorphic host rocks

coal fly ash interaction with environmental fluids geochemical and strontium isotope results from combined column and batch leaching experiments abstract the major element and sr isotope systematics and geochemistry of coal fly ash and its interactions with environmental waters were investigated using laboratory flow through column leaching experiments sodium carbonate acetic acid nitric acid and sequential batch leaching experiments water acetic acid hydrochloric acid column leaching of class f fly ash samples shows rapid release of most major elements early in the leaching procedure suggesting an association of these elements with soluble and surface bound phases delayed release of certain elements e g al fe si signals gradual dissolution of more resistant silicate or glass phases as leaching continues strontium isotope results from both column and batch leaching experiments show a marked increase in 87 sr 86 sr ratio with continued leaching yielding a total range of values from 0 7107 to 0 7138 for comparison the isotopic composition of fluid output from a fly ash impoundment in west virginia falls in a narrow range around 0 7124 the experimental data suggest the presence of a more resistant highly radiogenic silicate phase that survives the combustion process and is leached after the more soluble minerals are removed strontium isotopic homogenization of minerals in coal does not always occur during the combustion process despite the high temperatures encountered in the boiler early released sr tends to be isotopically uniform thus the sr isotopic composition of fly ash could be distinguishable from other sources and is a useful tool for quantifying the possible contribution of fly ash leaching to the total dissolved load in natural surface and ground waters

antitaxial crack seal vein microstructures and their relationship to displacement paths abstract the microstructures developed in an example of a syntectonic crack seal vein indicate that antitaxial fibres do not necessarily track the incremental opening history during crack seal vein growth this observation serves as a caution against the uncritical use of fibrous microstructures to make inferences about displacement histories during fibre formation it is demonstrated that crack seal processes can lead to the development of both irregular and laminated vein microstructures as well as fibrous microstructures the types of microstructures which develop in crack seal veins and the extent to which they reflect the opening paths of veins depend on a range of factors the most important of these include the nucleation and growth kinetics of phases precipitated from fluids in opening fractures and the location of sites of material accretion during successive crack seal increments

fractures in mudrocks advances in constraining timing and understanding mechanisms abstract recent advances in fracture timing techniques have led to new insights about sequences and mechanisms of fracture formation in mudrocks methods to constrain fracture timing in mudrocks include i field evidence including crosscutting relationships and evidence of compaction ii petrographic evidence including signs of soft sediment deformation and diagnostic mineral assemblages or textures iii stable isotopic evidence iv thermometric dating using burial history modelling and v radiometric age dating in this contribution we briefly review each method with salient examples from the literature many documented examples of mudrock hosted fractures formed during early burial a non intuitive finding that demands a re assessment of our assumptions about what types of materials can develop opening mode fractures in general the style and distribution of fractures varies dramatically based on fracture timing highlighting the importance of constraining timing for predicting fracture patterns and interpreting their mechanisms including the role of fluid flow

computer experiments to investigate complex fibre patterns in natural antitaxial strain fringes antitaxial non deforming strain fringes from lourdes france show complex quartz calcite and chlorite fibre patterns that grew around pyrite in a slate during non coaxial progressive deformation development of these fringes was modelled using a computer program fringe growth 2 0 which can simulate incremental growth of crystal fibres around core objects of variable shape it uses object centre paths as input which are obtained from fibre patterns in thin section the numerical experiments produced fibre patterns that show complex intergrowth of displacement controlled face controlled and intermediate fibres similar to those in the natural examples the direction of displacement controlled growth is only dependent on the relative movement between core object and fringe so that core object rotation with respect to the fringe influences the fibre patterns and produces characteristic asymmetric fibre curvature object centre paths should be used for kinematic analysis of strain fringes instead of single fibres since these paths represent the fringe as a whole the length along the path can be interpreted in terms of finite strain and path curvature in terms of rigid body rotation of fringes with respect to an external reference frame

genesis of natural hydraulic fractures as an indicator of basin inversion abstract satin spar fibrous gypsum veins which occur in evaporite basins worldwide provide significant insights into host rock deformation and fluid flow although the genetic mechanism remains obscure satin spar veins in the red marls of the triassic mercia mudstone of the bristol channel basin were characterized in the context of regional and local setting the vein network in the keuper marl lower mercia exhibits a lack of systematic cross cutting between three distinct vein sets two sets of veins are observed in the overlying tea green marl with one set clearly crossing the other the gypsum veins commonly contain a blocky median zone of multiple thin bands of host rock inclusions and alabastrine gypsum crystals exhibiting crack seal patterns fibrous zones on either side of the median zone consist of pure parallel aligned gypsum fibres that are oblique to vein walls indicating a hybrid shear extensional mode of vein widening veins developed within reverse reactivated faults contain fibre lineations in the median zones and also on vein surfaces suggesting a minimum of two phases of fault slip the veins are interpreted to have formed as a result of overpressure in the low permeability mudstones by tectonic compression during basin inversion giving rise to the median zone growth of gypsum fibres commenced when the initial fractures were completely sealed the timing of vein formation is suggested to be miocene based on cross cutting relationships with folds formed during the latest phase of basin inversion because the fractures initiated in response to fluid overpressures they provide a useful analog to subsurface hydraulic fracture systems in low permeability rocks subjected to tectonic compression the fibrous widening of the veins post dates their initiation and led to continued propagation and increased connectivity

microstructures in a banded iron formation gua mine india this paper provides a detailed documentation of microstructures developed in the banded iron formation bif of gua mine located in the bonai synclinorium eastern india where the rocks have been subjected to three deformations d 1 to d 3 folded iron ores quartz strain fringes around rigid core objects and folded iron ore layers and refracted quartz veins are described from samples taken from d 2 folds in the banded iron formation orientations of microstructures are compared with mesoscopic structures to interpret the generations of ore minerals planar structures and the time relationship between deformation and development of different microstructures the mechanism of d 2 folding is worked out and its bearing on microstructure development is discussed the d 2 folds are inferred to have developed by a combination of tangential longitudinal strain in the competent layer flexural flow in the incompetent layers and flexural slip at the interface between layers of differing competence homogeneous flattening strain superposed the earlier strain which led to modification of the folds in the competent layer from class 1b to 1c this strain is quantified and is found to be higher in the limb than the hinge of a fold diffusive mass transfer by solution and bulging dynamic recrystallization in quartz are inferred as the dominant deformation processes during folding moreover based on comparison with published deformation microstructure maps the microstructures of the present study are estimated to have developed between 300 and 350 c temperatures at a strain rate of 10 14 10 12 s 1 which are geologically realistic conditions for naturally deformed rocks

kinematics of crystal growth in syntectonic fibrous veins abstract detailed observations of a set of fibrous antitaxial calcite veins in a slate reveal that some of the calcite fibres do not connect material markers on both sides of the vein and can therefore not have tracked the full opening trajectory during vein growth this calls for a better understanding of the mechanisms of fibre formation and reliable criteria to test the tracking hypothesis based on surface roughness characteristics of the vein wall we develop a simple model for shape growth of crystals in a crack seal environment which can account for both tracking and non tracking behaviours and propose a set of tracking criteria for antitaxial veins finally we discuss ways by which the model can be tested against natural examples

how vein sealing boosts fracture widening rates the buckling enhanced aperture growth mechanism for syn tectonic veins abstract the paper introduces the mechanism of buckling enhanced aperture growth for syn tectonic veins that formed in simple shear dominated kinematic frameworks in the middle or lower crust apart from the well understood concepts of fracture widening driven by effective tensile stresses buckling enhanced fracture aperture growth relates widening to active outward buckling of more viscous incipient cement layers precipitated as hydrothermal minerals for the pore fluid on the walls of juvenile syn tectonic veins driven by fracture parallel compressive creep strain in the host rocks thus the mechanism proposed here follows similar principles as tectonic folding although important differences exist inspired by the structural record of low aspect ratio veins exposed in hp lt metamorphic rocks cropping out on south evia island greece generic numerical models are calculated to study development of buckling instabilities in such incompletely cemented veins and their impact on aperture growth rates the models indicate 1 that aperture growth rates increase with increasing viscosity contrast between the host rocks and the cement layers 2 an increase in the thickness of the cement layers cause acceleration of aperture growth 3 that support of restraining forces at the vein tips offered by the host rocks against buckling of the cement layers cause fully compressive states of stress ahead the fracture tips and 4 that fracture aperture growth is possible against fully compressive fracture normal stresses the buckling enhanced vein aperture growth mechanism yields important implications for the maintenance and decay of fracture bound permeability and for the mechanical state of the middle and lower crust in seismically active regions

microstructural evolution and grain boundary structure during static recrystallization in synthetic polycrystals of sodium chloride containing saturated brine the effects of brine on recrystallization in halite are well known however properties of brine such as morphology connectivity diffusivity and the resulting influences on deformation mechanisms are still a matter of debate this paper presents a microstructural study of dense statically recrystallizing synthetic polycrystalline halite containing small amounts of brine we used powders of two different grain size classes 10 m and 200 355 m the aggregates were compacted to brine filled porosities less than about 2 and annealed at room temperature without an external stress field

crack seal fibre growth mechanisms and their significance in the development of oriented layer silicate microstructures abstract an analysis of crack seal fibre growth mechanisms has shown two important implications of the crack seal process for the interpretation of microstructures in low grade metamorphic rocks 1 1 the ability of fibre growth to track the incremental separation history of crack walls depends on details of the nucleation and growth mechanisms 2 2 fibrous crystals may develop cristallographic preferred orientations in certain crack seal situations the microstructures of layer silicates and associated phases developed in several examples of syntectonic intragranular microfracture sites and veins indicates that layer silicate 001 and grain shape preferred orientation can develop during crack seal deformation by oriented growth mechanisms during successive crack seal increments preferred orientation may develop in response to an interaction between anisotropic growth kinetics and the displacement history resulting in preferential rejoining by syntaxial overgrowth of pulled apart grains having fast growth directions parallel to the incremental displacement direction across a microcrack preferred orientation may also be developed and enhanced in crack seal growth sites by overgrowth of previously oriented layer silicates in the microcrack walls in this case the crystallographic preferred orientation need not be simply related to the displacement history during crack seal fibre growth since crack seal processes may operate on all scales down to the minimum size of a microfracture in a deforming rock such mechanisms of layer silicate preferred orientation development are expected to be very significant in developing and enhancing foliation during deformation involving microfracture and solution transfer processes

evidence at lomax illinois for mid wisconsin 40 000 yr b p position of the des moines lobe and for diversion of the mississippi river by the lake michigan lobe 20 350 yr b p abstract an abrupt change in environment from a wetland to a deeper slackwater lake at 20 345 85 yr b p occurred in a second order valley tributary to the mississippi river near lomax illinois the age of this shift is associated with the overflow of glacial lake milan and diversion of the mississippi river from the princeton valley rock island to peoria to its present course rock island to st louis the diversion occurred due to blockage of the princeton valley segment of the ancient mississippi river by the lake michigan lobe impoundment of glacial lake milan and eventual overflow of the lake southwest of rock island across a former drainage divide near andalusia illinois fossil ostracode assemblages in the slackwater sediment at lomax indicate changes in the post diversion full glacial paleohydrology and based on multivariate analysis hint at the area s paleoclimate an older part of the succession at lomax is consistent with glaciation in the upper iowa river basin about 40 000 yr b p aggradation of sediment rich in coarse silt is attributed to a response of the ancient iowa river basin associated with deposition of the glacigenic sheldon creek formation by the des moines lobe