analytical solution for groundwater flow in an anisotropic sloping aquifer with arbitrarily located multiwells this paper presents a new analytical solution to describe the hydraulic head distribution and flow system in an anisotropic unconfined aquifer with a sloping bed and arbitrarily located multiwells under transient recharge unlike the existing analytical solutions for delineating the capture zones the solution presented in this study is easy and convenient to calculate flow field in some complicated systems and it can provide useful information for the pump and treat design in addition the presented solution may have the possible application in evaluating the sensitivity of hydrogeological parameters or estimating the hydraulic parameters when coupled with an optimization approach to analyze the aquifer data

volume loss fluid flow and state of strain in extensional mylonites from the central mojave desert california abstract compositional changes in mylonitic rocks from the central mojave metamorphic core complex california indicate that large volume loss 20 70 attended formation of mylonite along the waterman hills detachment fault strong silica depletion and significant mobility of normally immobile elements imply large fluid rock ratios during mylonitization possibly as a result of multiple pass hydrothermal convection connecting near surface and mid crustal alteration regimes dissolution of quartz during mylonitization indicates that the fluid was undersaturated with respect to silica and therefore was probably not magmatic or connate large volume loss in a shear zone should result in apparent flattening strains yet mylonites throughout the complex including the mylonites that record large volume loss exhibit constrictional strains this inconsistency raises questions about the applicability of the shear zone model to cordilleran metamorphic core complexes

clay mineralogy and geochemistry investigations in the host rocks of the chelungpu fault taiwan implication for faulting mechanism abstract the chelungpu fault with northward propagating ruptures was ruptured as a result of the m w 7 6 earthquake which struck central taiwan on 21st september 1999 to understand the consequences of clays in fault gouges we examined the clay mineralogy and major element geochemistry of the host rocks of the chelungpu fault from four outcrops shallow boreholes at fengyuan 455 3 m in depth nantou 211 9 m in depth and a deep borehole of the taiwan chelungpu fault drilling project 2003 m in depth results revealed different degrees of chemical weathering the intensity as documented by differences in the smectite content could be further understood through the relative clay percentage of smectite illite chemistry index and illite crystallinity these mineralogical proxies combined with the chemical index of alteration cia and the intensity of chemical weathering indicate that the degree of chemical weathering is a function of depth i e the most severe on the surface and the mildest in the tcdp samples the mineralogical and geochemical data obtained in this study also suggest that chemical weathering rather than leaching seems to be the main driving force for the phase changes of clays the amount of smectite produced by chemical weathering varies with depth and it suggests that the previous idea of weak fault caused by the presence of smectite in the fault zone will be risky without considering weathering processes the observations of clay mineralogy and major element geochemistry in this study indicate that the presence of smectite in the outcrops may not play a significant role during faulting and suggest that fault weakening as a result of the presence of smectite cannot be applied to the chelungpu fault

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

mass removal and clay mineral dehydration rehydration in carbonate rich surface exposures of the 2008 wenchuan earthquake fault geochemical evidence and implications for fault zone evolution and coseismic slip 1 we report variations in the mineralogical geochemical and isotopic 13c 18o composition of fault rocks sampled in transects across the zhaojiagou and pingxi exposures of the wenchuan earthquake or longmenshan fault zone where the gouge rich fault core and principal slip surface cuts through carbonate rich strata pervasive fluid infiltration was found to modify the mineralogical and geochemical architecture of the fault zones studied enrichment depletion patterns element partitioning and a very large implied volume loss are quite different from those characterizing faults in granites and clastic sedimentary rocks and can be explained by a mass removal model involving dissolution and advective transport enhanced by pressure solution an increasing enrichment in smectite observed toward the principal slip surface a high abundance of elements such as ba mg and f the deposition of minerals such as barite and fluorapatite as well as the distinct depletion in 13c in vein material consistently suggest reactions involving a hydrothermal fluid originating at depth illitization of black gouges caused by coseismic frictional heating was found to be widespread we propose that coseismic frictional heating along with the action of postseismic hydrothermal fluids controlled the transformation and distribution of smectite and illite within the fault core of the longmenshan fault zone the coseismic dewatering reactions are expected to have been more extensive at depth possibly helping generate excess pore pressure assisting dynamic slip weakening during the wenchuan earthquake

rock magnetic expression of fluid infiltration in the yingxiu beichuan fault longmen shan thrust belt china fluid infiltration within fault zones is an important process in earthquake rupture magnetic properties of fault rocks convey essential clues pertaining to physicochemical processes in fault zones in 2011 two shallow holes 134 and 54 m depth respectively were drilled into the yingxiu beichuan fault longmen shan thrust belt china which accommodated most of the displacement of the 2008 mw 7 9 wenchuan earthquake fifty eight drill core samples including granitic host rock and various fault rocks were analyzed rock magnetically mineralogically and geochemically the magnetic behavior of fault rocks appears to be dominated by paramagnetic clay minerals magnetite in trace amounts is identified as the predominant ferrimagnetic fraction in all samples decreasing from the host rock via fault breccia to proto cataclasite significant mass losses 10 7 45 6 are determined for the latter two with the isocon method volatile contents and alteration products i e chlorite are enriched toward the fault core relative to the host rocks these observations suggest that magnetite depletion occurred in these fault rocks exhumed from the shallow crust plumbed by fluid assisted processes chlorite interpreted to result from hydrothermal activity occurs throughout almost the entire fault core and shows high coefficients of determination r2 0 6 with both low and high field magnetic susceptibility close relationships with r2 0 70 are also observed between both low and high field magnetic susceptibility and the immobile elements e g tio2 p2o5 mno h2o and the calculated mass losses of fault rocks hence magnetic properties of fault rocks can serve as proxy indicators of fluid infiltration within shallow fault zones

fluid infiltration associated with seismic faulting examining chemical and mineralogical compositions of fault rocks from the active chelungpu fault abstract in order to understand the fault zone architecture and mechanisms that caused the chi chi earthquake the chelungpu drilling project was conducted during april 2000 through a collaborative project between japan and taiwan in this study chemical and mineralogical variations within the overall chelungpu fault zone including variations between less damaged host rocks damaged zones and fault cores caused by the chi chi earthquake were examined slopes of tio2 immobile isocons were consistently 1 for analyses comparing host rocks with rocks from damaged zones or with gouges from fault cores indicating that volume loss occurred in damaged zones and the fault cores these results strongly imply that pervasive fluid infiltration occurred within the fault zone volume loss within the damaged zone and fault core is interpreted to result from a two stage process involving i coseismic mechanical wearing and or dissolution in the fault core and ii fluid infiltration within the fault zone during postseismic and interseismic periods along cracks caused by seismic failure semi quantitative xrd analysis indicates that the kaolinite content consistently increases from the less damaged host rocks to the damaged zone and gouges in each fault core mineralogic changes indicate that pervasive acidic fluid infiltration occurred within the fault zones and reacted with the feldspars or muscovite to form kaolinite enrichment of kaolinite and illite found in the fault zones of southern drilling site could play some role on the slipping behavior of the southern part of the chelungpu fault greater volume loss in the fault core may have resulted from moderate permeability combined with the very fine grain nature of pulverized material in the fault core which enhanced chemical reactions including transformation of feldspars and muscovite to clay minerals the study results indicate that pervasive fluid infiltration occurred and changed the mineralogical and chemical architecture of fault zones caused by the cyclic earthquakes

deep fluid circulation in fault zones massive fluid circulation in retrogressive ductile shear zones is a well established but poorly understood phenomenon in some cases surface derived fluids which must initially have been at hydrostatic pressures can be shown to have entered shear zones in which fluids would normally be expected to be at lithostatic pressure in these circumstances thermal convection is an unlikely driving force for fluid movement underthrusting of a surficial fluid reservoir beneath shear zones is a viable mechanism in some cases but not for metasomatic shear zones in the pyrenees where insufficient underthrusting has occurred seismic pumping provides an alternative mechanism to explain the paradox of fluid access into ductile shear zones a kinematic analysis of a hypothetical fault zone shows that stress and dilatancy cycles will be out of phase above and below the frictional quasiplastic transition if this effect is sufficiently large hydraulic gradients may force fluid downward across the transition immediately after earthquake rupture through highly permeable microcrack networks between earthquake cycles plastic creep in mylonites will overprint microcrack networks increase fluid pressure and promote slow upward movement of fluid at low permeability for smaller shear zones such as those in the pyrenees seismic pumping could occur down a shallow decollement with subsequent upward fluid flow through shear zones in the hanging wall of the decollement

deformation mechanisms in granitic rocks at shallow crustal levels abstract microstructural observations of naturally faulted granitic gneisses show that feldspar grains are weaker than quartz grains at temperatures below 325 c and at depths of less than 8 10 km feldspar grains sustained most of the deformation by grain scale faulting slip along cleavage controlled fractures and cataclasis fracture of feldspar grains within fault zones promoted their alteration to kaolinite quartz grains also deformed by fracturing and often healed to form quartz porphyroclasts and mosaics in a comminuted matrix of feldspar and kaolinite syntectonic alteration of the feldspar grains may have weakened the fault zones over time and resulted in foliated textures within the fault zones this study of naturally deformed rocks confirms published experimental results on the behavior of granitic rocks at low temperatures and pressures and taken together these data show that the theology of the upper 10 km of the crust is greatly influenced by cataclastic processes in feldspar

a solution of the nonlinear boussinesq equation for phreatic flow using an integral balance approach abstract an analytical solution of the nonlinear boussinesq equation is presented using the integral balance method the solution obtained is the same as that obtained by basak 1979 following a different approach

lateral variations in the long term slip rate of the chelungpu fault central taiwan from the analysis of deformed fluvial terraces the chelungpu fault ruptured during the september 1999 mw 7 6 chi chi earthquake in central taiwan this event was characterized by coseismic displacements increasing along strike and updip from south to north previous studies suggested that such lateral variations also existed in the long term fault slip rate but this has not yet been clearly documented to address this we investigate deformed fluvial terraces along the choushui and tatu wu rivers in the southern and central segments of the thrust fault optical ages of 13 ka to 38 ka obtained for these terraces enable estimation of fault slip rates of 5 8 2 0 and 10 3 1 6 3 0 mm yr for the southern and central segments respectively we combine these findings with the fault slip rate determined by other authors for the northern segment statistical analysis of the data suggests lateral variations in the long term fault slip rate with values increasing toward the north this pattern in the slip rate averaged over approximately tens of thousand years is similar to that observed for coseismic displacements during the chi chi earthquake the similarities in the deformation pattern observed for one earthquake or cumulated over several events suggest that the chi chi earthquake could be characteristic of the earthquakes breaking the chelungpu fault with respect to slip distribution our results also allow for discussing the plausible evolution of major rivers draining the foothills of central taiwan over the last 40 60 kyr

fluid rock interactions in seismic faults implications from the structures and mineralogical and geochemical compositions of drilling cores from the rupture of the 2008 wenchuan earthquake china we describe the structural features and mineralogical and geochemical compositions of the fault rocks recovered from boreholes at the golden river site on the yingxiu beichuan fault which activated and slipped along a 240 km long main surface rupture zone during the 2008 wenchuan earthquake the fault which accommodated co seismic slip cuts granitic rocks from the pengguan complex in which this earthquake most likely nucleated fault rocks including cohesive cataclasite unconsolidated breccia and three fault gouges with distinct colors were identified from the drilling cores on going uplift and erosion in the area means that the fault rocks formed at different depth were exhumed to the shallow surface during the uplift history of the longmenshan fault zone a clear change from fracturing and comminution in the cataclasites and breccia to more pervasive shear formation of fine grained materials in the gouges has been observed the gouges are distinct and have accommodated significant displacement in multiple increments of shear furthermore fault rocks recovered from the boreholes display numerous features indicative of fluid infiltration and fluid rock interaction toward the fault core clay minerals have replaced feldspars the element enrichment depletion patterns of the fault rocks show general fluid infiltration trends such as 1 mobile elements are generally depleted in the fault rocks 2 the microstructural mineralogical and geochemical results of the fault rocks consistently indicate that pervasive fluid infiltration and fluid rock interactions altered feldspars and mafic minerals to clay minerals the fluid was mg2 and fe2 rich facilitating formation of chlorite isocon analyses further reveal that a large rock volume has been lost which is attributed to the removal of mobile elements associated with fluid infiltration and perhaps enhanced by pressure solution these results reflect the accumulated effects of cataclasis and fluid infiltration fluid rock interaction during the long evolution history of the longmenshan fault zone fluid rock interactions in seismic faults implications from the structures and mineralogical and geochemical compositions of drilling cores from the rupture of the 2008 wenchuan earthquake china

structural and chemical characterization of shear zones in the freshly activated nojima fault awaji island southwest japan behavior and role of each shear zone in a shallow fault zone of granitic origin during seismic cycles are revealed by comprehensive examinations of petrographic and chemical characterization on a fault zone in the geological survey of japan gsj drill core penetrating the nojima fault which was activated during the 1995 hyogoken nanbu earthquake m 7 2 the gsj core consists of granodiorite and porphyritic intrusive rocks including a nojima fault zone which involves seven thin shear zones main shear zone msz 625 m depth upper cataclasite zone ucz upper shear zone usz lower shear zones lsz 1 and lsz 2 and lower cataclasite zones lcz 1 and lcz 2 these shear zones are generally surrounded by weakly pulverized and altered fault related rocks wpar which generally show volume gain the fault zone architecture is clarified as follows 1 total thickness of the nojima fault zone is 70 m 2 all shear zones except the older cataclasite zones ucz 1 lcz 1 and lcz 2 were evolved from wpar indicating that pulverization and alteration of recent activity were more diffused at the initial stage of faulting and gradually localized to each shear zone 3 the msz 2 m thick can be regarded as a high velocity frictional zone with accompanying volume loss compaction and possibly with heat generation during coseismic periods 4 the lsz 1 3 6 m thick located just beneath the msz and typically showing explosion brecciation texture is also regarded as a coseismic shear zone this zone could function as a trap zone for fluid or gas during postseismic interseismic periods 5 the lsz 2 2 7 m thick located around 710 m depth contains foliated fault gouge enriched with clay minerals and characterized by a large degree of volume gain possibly a result of slow velocity motion or creep during the interseismic and or postseismic periods

effects of simulated clay gouges on the sliding behavior of tennessee sandston abstract the effects of simulated fault gouge on the sliding behavior of tennessee sandstone are studied experimentally with special reference to the stabilizing effect of clay minerals mixed into the gouge about 30 specimens with gouge composed of pure clays of homogeneously mixed clay and anhydrite or of layered clay and anhydrite along a 35 precut are deformed dry in a triaxial apparatus at a confining pressure of 100 mpa with a shortening rate of about 5 10 4 sec and at room temperature pure clay gouges exhibit only stable sliding and the ultimate frictional strength is very low for bentonite mont morillonite intermediate for chlorite and illite and considerably higher for kaolinite anhydrite gouge shows violent stick slip at 100 mpa confining pressure when this mineral is mixed homogeneously with clays the frictional coefficient of the mixed gouge determined at its ultimate frictional strength decreases monotonically with an increase in the clay content the sliding mode changes from stick slip to stable sliding when the frictional coefficient of the mixed clay anhydrite gouge is lowered down below 90 95 of the coefficient of anhydrite gouge the stabilizing effect of clay in mixed gouge is closely related to the ultimate frictional strength of pure clays that is the effect is conspicuous only for a mineral with low frictional strength only 15 20 of bentonite suppresses the violent stick slip of anhydrite gouge in contrast violent stick slip occurs even if the gouge contains as much as 75 of kaolinite the behavior of illite and chlorite is intermediate between that of kaolinite and bentonite bentonite anhydrite two layer gouge exhibits stable sliding even when the bentonite content is only 5 thus the presence of a thin clay rich layer in a fault zone stabilizes the behavior much more effectively than do the clay minerals mixed homogeneously with the gouge this result brings out the mechanical significance of internal structures of a fault zone in understanding the effects of intrafault materials on the fault motion based on the present experimental results incorporated with some other experimental data it is argued that although the stabilizing effect of montmorillonite and vermiculite is indeed remarkable at room temperature the effect should be much less pronounced at elevated temperatures due perhaps to the dewatering of the clays in most geological environments where shallow earthquakes occur the stabilizing effect of clays is probably not so conspicuous as to completely suppress the unstable motion of a fault

water table rise in a semiconfined aquifer due to surface infiltration and canal recharge abstract a general solution to the fluctuation of water table for unsteady state flow in a semiconfined and finite aquifer with recharge from canals and surface infiltration is presented the flow is assumed to be one dimensional in a horizontal direction with the recharging canals at different elevations the laplace transformation method is employed in the solution a numerical example is given for a flow situation in a hypothetical finite aquifer bounded by two recharging canals under vertical infiltration giving water table changes with respect to time

structural and fluid chemical properties of seismogenic normal faults abstract structures in extensional fault zones can be classified using the configuration of fault branch lines and tip lines important classes include the segment bend segment termination segment branch cross fault intersection and segment offset the effect of these structures on rupture history is not necessarily consistent neither between individual earthquakes nor between different fault zones rupture behavior is dependent on several other factors including loading conditions regional and localized rupture tip stress fields fluid mechanical processes and chemical processes fracture toughness is partly controlled by the angular discordance between slip directions on adjacent fault segments greater discordance between slip directions and intersection lines of fault segments results in greater strain incompatibility an internal fracture network generally evolves within a segment boundary to maintain compatibility and transfer slip between the segments the dimensions and structure of this fracture network may also partly control rupture propagation presumably activation of a fault network with large angular discordances between slip directions and intersection lines will generate numerous asperities as the subsidiary faults mutually interact and offset each other the geometry of a segment boundary may change with depth and the three dimensional nature of the structure may be important in controlling rupture history fluids influence rupturing via fluid pressure effects and time dependent chemical processes fracture propagation by stress corrosion may favor instability and chemical alteration may produce minerals of lower strengths allowing time dependent creep sealing and healing of fractures however may remove damage and increase strength elementary computations indicate that representative times for sealing and chemical alteration are between 1 and 1000 years for reasonable physical conditions well within the recurrence intervals of most large earthquakes time to failure for stress corrosion cracking is more highly variable and strongly sensitive to applied stress and fluid pressure

water table fluctuation in soils overlying semi confined aquifers in response to time varying replenishment abstract the water table height in drained agricultural land depends on time varying replenishment that is due to the vertical downward recharge from irrigation or rainfall and in some cases to the upward vertical leakage from a semi confined aquifer the downward recharge may be assumed to vary exponentially with time whereas the upward leakage may be expressed as a function of the unknown water table height furthermore the rising of the water level in the field drainage system that may cause an inverse flow from the drains towards the soil is introduced through a properly defined boundary condition a non homogeneous form of the boussinesq equation that is used to describe this particular drainage problem is solved for three different initial conditions the same drainage problems were solved numerically by using the finite element method comparison between analytical and numerical solutions shows satisfactory agreement from the analytical solutions we obtain the non dimensional water table height at the midpoint between the drains and the non dimensional discharge of the drains per unit drained area as functions of non dimensional time and constants describing the aforementioned drainage conditions variation of these functions has also been illustrated graphically in non dimensional diagrams these can be used to show the sensitivity to various sets of parameter values and to calculate easily the water table height and the drain discharge in practical problems

differences in magnetic properties of fragments and matrix of breccias from the rupture of the 2008 wenchuan earthquake china relationship to faulting abstract rock magnetic and mineralogical analyses were performed on fragments and matrix of six fault breccias from the zhaojiagou outcrop of yingxiu beichuan fault which was the main fault ruptured during the 2008 wenchuan mw 7 9 earthquake at leigu town beichuan county sichuan province china the matrix which is generally enriched in dolomite feldspar and clay minerals but depleted in calcite has much higher low field magnetic susceptibility and magnetization and lower coercivity in comparison with fragments and bulk samples magnetic behavior of the bulk samples and fragments is dominated by dia paramagnetic components in contrast small amounts of partially oxidized magnetite and lepidocrocite are present in the matrix a simple conceptual model associating faulting related effects was proposed to explain these significant differences in magnetic properties of fragments and matrix during coseismic slip intense shear may crush the pre existing magnetic grains in fault rocks into finer ones while stress and frictional heating to a little extent induce magnetic changes and thermochemical alterations of magnetic mineralogy in fault breccias respectively during interseismic periods meteoric fluids would infiltrate and percolate into fault zone and cause dissolution precipitation and recrystallization of fe bearing minerals as the diverse permeability structure and grain size of fragments and matrix these effects would modify their magnetic mineralogy at various levels consequently faulting related effects especially the fluid movements taking place over many previous earthquake cycles would be the most likely reasons for the observed different magnetic properties in fragments and matrix it further proposes that magnetic studies of fault breccias would provide clues to help understand seismic faulting and history of fault activity

fluid channelling during ductile shearing transformation of granodiorite into aluminous schist in the tauern window eastern alps ductile shearing in the core of the tauern window austria transformed metagranodiorite into si undersaturated garnet chlorite staurolite schist at a depth of c 35 40 km during the alpine orogeny four distinct zones have been recognized extending from the wallrock into the centre of the shear zone zone i unaltered metagranodiorite with subordinate amphibolite zone ii biotite white mica garnet schist zone iii biotite phengite schist zone iv quartz absent garnet chlorite staurolite schist with garnets up to 10 cm across whole rock analyses show a dramatic decrease in sio2 from 65 wt in zone i to 35 wt in zone iv ca na and sr also decrease across the shear zone whereas al ti fe mg p cr ni zn and rb all increase towards zone iv mass balance calculations indicate that shearing was accompanied by up to 60 volume loss near the centre of the shear zone comparison of the tauern window samples with other shear zones in granitic hosts indicates that silica loss accompanied by gains in mg fe and ti is typical for volume loss shear zones but is distinctly different from the element behaviour exhibited in shear zones that are thought to represent approximately isovolumetric behaviour in the samples studied here volume loss appears to have resulted from channellized fluid flow during shearing producing time integrated fluid fluxes of 108 cm3 cm 2 in zone iv this large volume of fluid may have originated in part from dehydration of flysch carried beneath the metagranodiorites during eocene movement on the north penninic subduction zone development of an inverted thermal gradient during subduction would have allowed the fluid to scavenge large amounts of silica from the shear zone during ascent and heating

tropical precipitation and cross equatorial ocean heat transport during the mid holocene abstractsummertime insolation intensified in the northern hemisphere during the mid holocene resulting in enhanced monsoonal precipitation in this study the authors examine the changes in the annual mean tropical precipitation as well as changes in atmospheric circulation and upper ocean circulation in the mid holocene compared to the preindustrial climate as simulated by 12 coupled climate models from pmip3 in addition to the predominant zonally asymmetric changes in tropical precipitation there is a small northward shift in the location of intense zonal mean precipitation mean itcz in the mid holocene in the majority 9 out of 12 of the coupled climate models in contrast the shift is southward in simulations using an atmospheric model coupled to a slab ocean the northward mean itcz shift in the coupled simulations is due to enhanced northward ocean heat transport across the equator oht eq which demands a compensating southward atmospheric energy transport across the equator accomplished

water table fluctuation in a sloping aquifer with transient recharge abstract an analytical solution of the linearized boussinesq equation with a complex transient recharge function is presented to describe the water table fluctuation in a sloping aquifer of finite width the solution is obtained by using an eigenvalue eigenfunction expansion method some previously known solutions for different recharge functions have been shown to be special cases of the present general solution applications of the solutions in prediction of the spatio temporal distribution of the water table in a ditch drainage system are illustrated with the help of synthetic examples

fluid infiltration into fault zones chemical isotopic and mechanical effects fluid infiltration into fault zones and their deeper level counterparts brittle ductile shear zones is examined in diverse tectonic environments in the 2 7 ga abitibi greenstone belt major tectonic discontinuities with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism during reverse motion on the structures accommodating shortening of the belt these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids such fluids were characterised by 18o 6 2 d 50 20 13c 4 4 and temperatures of 270 to 450 c probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism hydrothermal fluids were more radiogenic 87sr 86sr 0 7010 to 0 7040 and possessed higher than did contemporaneous mantle komatiites or tholeiites and thus carried a contribution from older sialic basement a provinciality of87sr 86sr and 13c is evident signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres mineralised faults possess enrichments of large ion lithophile lil lil elements including k rb ba cs b and co2 and rare elements such as au ag as sb se te bi and w fluids were characterised by xco2 0 1 neutral to slightly acidic ph low salinity 3 wt k na 0 1 they carried minor ch4 co and n2 and they underwent transient effervescence of co2 during decompression clastic sediments occupy graben developed at fault flexures the40ar 39ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years

analytical and experimental solutions for drainage of sloping lands with time varying recharge m j boussinesq s 1904 nonlinear partial differential equation for unsteady state flow of water through a phreatic aquifer resting on a sloping impervious barrier and receiving time varying recharge has been solved two patterns of recharge rates i e linearly increasing and exponentially declining with time were considered the initial conditions of the water table were taken at the drain level transformations were devised to transform the resulting approximate linearized boussinesq equation to the form of a one dimensional heat flow equation for each case of recharge pattern and analytical solutions for the height of the water table between parallel drains were obtained in the form of a convergent series the analytical solutions were experimentally verified with a hele shaw model a reasonably close agreement was found in the computed and observed phreatic surfaces the results showed that the analytical solutions presented herein can be used with reasonable accuracy for designing subsurface drainage in sloping phreatic aquifers

two dimensional modelling of water table fluctuation in response to localised transient recharge abstract an analytical solution of the linearised boussinesq equation is presented and used to predict the spatio temporal variation of the water table in a finite aquifer system in response to a transient recharge from an overlying rectangular basin the boundary conditions of the finite aquifer are taken as fixed heads which would apply when the aquifer system is surrounded by open water bodies application of the solution is illustrated with the help of a numerical example the results would also have applications in studying stream aquifer interaction in the presence of transient recharge

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

lateral variations in mylonite zone thickness as influenced by fluid rock interactions linville falls fault north carolina abstract over a distance of approximately 20 km along strike the linville falls mylonite varies in thickness from 1 m at linville falls to 60 m at banner elk along strike pressure temperature and displacement variations are minimized allowing this study to focus on the influences of fluid behavior and protolith mineralogy on fault zone development the protolith at linville falls contains mainly k feldspar perthite and quartz while at banner elk the protolith contains plagioclase and quartz at linville falls quartz deformed by dynamic recrystallization feldspar by intragranular fracturing and alteration to quartz and mica and mica by sliding along cleavage planes modal mineralogies change from the protolith to the mylonite with quartz decreasing from 39 to 19 and feldspar from 59 to 1 5 muscovite increases from mass balance calculations based on major and trace element geochemistry indicate approximately 75 volume loss at linville falls and 20 at banner elk fluid rock ratios estimated from the calculated depletions of si are an order of magnitude higher at linville falls than at banner elk fluids infiltrated the fault zone over a thicker zone at banner elk than at linville falls because the plagioclase altered more readily than k feldspar creating new pathways for fluids fluids migrated preferentially through channels along the fault zone creating a three dimensional network of higher fluid flow

fluid interaction and element mobility in the development of ultramylonites abstract shear zones are often characterized by the presence of mylonitic fabrics the textural development of such fabrics is enhanced by the presence of a fluid phase in a single specimen of rock from the brevard fault zone in north carolina we can demonstrate the development of ultramylonite domain by focused fluid flow the ultramylonite interface retains a sharp textural and chemical discontinuity this suggests that solute transport was dominantly parallel to the tectonic layering major chemical changes between the ultramylonite zone and the protolith include losses of si 2 na 2 0 and k 2 0 and gain of cao feo and hjo in the high strain domain introduction during the tectono thermal evolution of mountain belts zones of high strain are often recorded by the development of mylonites although mylonites and subcategories within mylonites sibson 1977 can be generated by numerous well documented physical processes their chemi cal and isotopic evolution is much more complex mechanical processes often associated with the development of high strain zones include micro fracturing dilatancy grain boundary sliding and dislocation glide these properties are strongly dependent on the modal mineralogy bulk compo sition heterogeneity of the rock and the temperature and pressure con ditions during deformation such variations in the mechanics of deforma tion have led to the more common classification of shear zones as either ductile or brittle sibson 1977 ramsay 1980 however most shear zones are characterized by the availability of fluids that cause a drastic change in the style of deformation by altering the behavior and assem blage of minerals hydration reactions and the rates of chemical and mechanical processes during progressive deformation the presence of a fluid phase during deformation enhances solution transport microfractur ing and recrystallization suc h chemically active zones generate mineral assemblages that record the metamorphic history of the mylonites al though it is not unusual to find minerals that persist through such an event these relict minerals if recognized can identify equilibrium vs nonequilibrium assemblages observed in shear zones clearly the pres ence of relict minerals would have a substantial impact on the trace element and isotopic signature of the rock to more carefully document the behavior of elements in a strain zone that has abundant fluid we have chosen to study a transect across the brevard fault zone near rosman north carolina within this tran sect one particular outcrop provided a single large specimen that over a distance of 25 cm showed the entire strain gradient fabric from proto mylonite to ultramylonite see sibson 1977 for mylonite series ob served by us as discontinuous patches in the longer 15 km transect we report petrographic textural and chemical data from this block and pro vide a physical model to explain these data

element mobility associated with syn metamorphic shear zones near scotchport nw mayo ireland three major blastomylonitic synmetamorphic epidote amphibolite to mid amphibolite facies shear zones are seen on the nw coast of the mullet peninsula in nw mayo these shear zones occur at the contacts of major structural units and in an imbricated slice where rocks of the erris complex are deformed and chemically modified chemical changes associated with individual shear zones have been deduced by comparing the compositions of various gneisses both within and adjacent to the shear zones compositional changes are different in the constituent rock types within each unit and many elements normally considered immobile have been selectively mobilized within the shear zones little evidence of wholesale metasomatic introduction of components into these shear zones was found to accompany the selective mobilization