constitutive relationships and physical basis of fault strength due to flash heating 1 we develop a model of fault strength loss resulting from phase change at asperity contacts due to flash heating that considers a distribution of contact sizes and nonsteady state evolution of fault strength with displacement laboratory faulting experiments conducted at high sliding velocities which show dramatic strength reduction below the threshold for bulk melting are well fit by the model the predicted slip speed for the onset of weakening is in the range of 0 05 to 2 m s qualitatively consistent with the limited published observations for this model earthquake stress drops and effective shear fracture energy should be linearly pressure dependent whereas the onset speed may be pressure independent or weakly pressure dependent on the basis of the theory flash weakening is expected to produce large dynamic stress drops small effective shear fracture energy and undershoot estimates of the threshold slip speed stress drop and fracture energy are uncertain due to poor knowledge of the average contact dimension shear zone thickness and gouge particle size at seismogenic depths

deformation textures and mechanical behavior of a hydrated amorphous silica formed along an experimentally produced fault in chert 1 we conducted a series of friction experiments on chert at intermediate to high slip velocities v 0 87 104 mm s and at low normal stress n 1 5 mpa to better understand the process of fault weakening by silica gel formation as identified in previous friction experiments on quartz rocks fault weakening in chert samples occurred in association with the formation of a 0 1 mm thick fault gouge layer that contains a thin foliated layer of fine grained material and a cataclastically fragmented zone characterized by clast matrix texture mft ir and xrd analyses reveal that the fault gouge consists of a mixture of hydrated amorphous silica and quartz grains the mechanical behavior of the fault gouge at a small magnitude of strain 0 008 as examined independently of the friction experiments using a rheometer is characterized by a negative dependence of shear stress on strain rate with a notable hysteresis behavior

quartz c axis fabric differences between porphyroclasts and recrystallized grains discussion recently kirschner teyssier 1991 identified differences between quartz c axis fabrics of porphyroclasts and recrystallized grains in mylonitic quartzites heavitree quartzites and interpreted these differences as indicating a change in the kinematic framework during the deformation history in this discussion we suggest an alternative interpretation of such fabrics derived from our current research on sheared granitoids see the appendix for a description from the archean bonfim metamorphic complex in the quadrilatero ferrifero southeast brazil in these rocks differences between c axis fabrics shown by old and new grains resulted from the heterogeneous disappearance of porphyroclasts with increasing recrystallization the porphyroclasts that disappeared faster were ones more favourably oriented to undergo dynamic recrystallization by subgrain rotation heterogeneous disappearance of porphyroclasts gradually altered the deformation fabric initially shown by porphyroclasts by reinforcing the orientations most resistant to recrystallization in the most recrystallized samples it is suggested that the porphyroclast fabrics displayed by kirschner teyssier 1991 have a similar origin before we deal with kirschner and teyssier s paper itself a brief comment on both selective recrystallization and residual fabric is necessary as these are the keys to our reinterpretation of the heavitree quartzite fabrics the concept of residual fabric expected firstly in the strength and distribution of the maxima and then in the fabric skeleton itself thus a fabric that portrays the orientation of the porphyroclast relicts most resistant to recrystallization the residue of the recrystallization might be gradually displayed in this discussion it is called the residual fabric unfortunately residual fabrics have not received attention in studies on quartz microfabric probably because they are more noticeable when the amount of porphyroclasts is relatively low commonly there are insufficient porphyroclasts in a single thin section to permit the construction of fabric diagrams in these cases two or more thin sections of the same sample are required to obtain a representative plot

frictional melting processes in planetary materials from hypervelocity impact to earthquakes frictional melting is the result of the conversion of mechanical deformation to heat under adiabatic conditions of slip within planetary materials which are mainly natural ceramics frictional melting occurs at high strain rates typically 10 2 s 1 and at slip velocities greater than 0 1 m s 1 t he pathway to friction melting is controlled by the mechanical properties of a rock s constituent minerals especially fracture toughness minerals with the lowest fracture toughnesses and breakdown temperatures are preferentially comminuted and fused to form the melt the product is a polyphase suspension comprising mineral and rock fragments enclosed in a liquid matrix this cools to form the rock type known as pseudotachylyte and at even higher strain rates it forms shock veins in meteorites and in impact craters which may contain high pressure mineral polymorphs the generation of melt on sliding surfaces can lubricate earthquake faults facilitate the post shock modification of impact craters and make landslides more hazardous

tectonics of the kola collision suture and adjacent archaean and early proterozoic terrains in the northeastern region of the baltic shield as preparation for the deep seismic and other geophysical experiments along the polar profile which transects the granulite belt and the kola collision suture structural field work has been performed in northernmost finland and norway and published geological information including data from the neighbouring soviet territory of the kola peninsula have been compiled and reinterpreted based on these studies and a classification according to crustal and structural ages the northeastern region of the baltic shield is divided into six major tectonic units these units are separated and outlined by important low angle ductile shear or thrust zones of late archaean to early proterozoic age the lateral extension of these units into soviet territory and their involvement in large scale crustal deformation structures are described using the view down the plunge method a generalised tectonic cross section that predicts the crustal structures along the polar profile is compiled and the structures around the kola deep drill hole are reinterpreted the kola suture belt through parts of which the kola deep bore hole has been drilled is considered to represent a ca 1900 ma old arc continent and continent continent collision suture it divides the northeastern shield region into two major crustal compartments a northern compartment comprising the murmansk and sorvaranger units and a southern compartment including the inari unit the granulite belt and the tanaelv belt as well as the more southernly situated south lapland karelia craton of the karelian province of the svecokarelian fold belt the kola suture belt is outlined by a 2 40 km wide and ca 500 km long crustal belt composed of 1 1 early proterozoic ca 2400 2000 ma old metavolcanic and metasedimentary sequences which originally formed part of the attenuated margin of the northern archaean compartment and 2 2 the remains of a ca 2000 1900 ma old predominantly andesitic island arc terrain this island arc terrain was built up above a sw plunging subduction zone initiated ca 2000 ma ago in the southern part of a newly formed oceanic domain the kola ocean due to continued subduction and complete consumption of this ocean the northern passive margin deposits and the island arc terrain were brought into tectonic juxtaposition and during the final arc continent and continent continent collision they were overthrusted onto the northern archaean continent along its southern boundary the kola suture belt is tectonically overlain by the archaean rocks of the inari unit this unit was derived from a microcontinent split from the southern compartment the depositional basin of the protoliths of the granulite belt being formed to the south of the microcontinent the inari microcontinent appears to have wedged out towards the southeast as the continuation of the granulite belt north of the white sea is in direct tectonic contact with the kola suture belt the granulite belt is composed of high grade paragneisses and minor amounts of meta igneous rocks the paragneisses formed from thick turbidite and mass flow deposits lain down in a back arc basin south of the inari microcontinent a thermal anomaly beneath the partly oceanic basement of the back arc basin is believed to have contributed to the ca 2000 1900 ma old granulite facies metamorphism of the granulite assemblages granulite facies conditions still prevailed when the inari microcontinent overrode the granulites and when the granulite belt as such was formed and was overthrusted for at least 100 km towards the southwest in conjunction with the latter event the rocks of the basement of the basin also became involved in thrust movements these now form the tanaelv belt which shows gradational tectonic contacts towards underlying cover and basement rocks of the south lapland karelia craton although not all parts of this craton were affected by the svecokarelian deformation it is considered to belong to the karelian province of the svecokarelian fold belt a ca 1900 1800 ma old episode of wrench faulting and the intrusion of 1790 1770 ma old post kinematic granites concluded the svecokarelian evolution of the northeastern shield region

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

shear sense a new approach that resolves conflicts between criteria in metamorphic rocks investigation of microstructural relationships in major movement zones in metamorphic rocks where the sense of displacement is known from regional geological relationships indicates numerous problems with current concepts of shear sense criteria and their application the direction of apparent shearing commonly conflicts from one criterion to another e g from the symmetry of quartz c axis orientation diagrams to the asymmetry of extensional crenulation cleavages this implies that interpretations of shear sense along foliations from some mesoscale and microscale criteria have been erroneous a new approach to interpreting shear sense involving the use of strain fields resolves conflicts in mesoscopic and microscopic criteria and provides a method for determining coherent shear sense histories extending back before the last shearing event for any foliated metamorphic rock it also provides a powerful tool for determining the structural metamorphic path that a rock has followed within an orogen for determination of the shear sense on the last foliation developed in a rock this approach uses geometries developed around competent heterogeneities such as quartz pebbles pegmatite pods veins porphyroclasts porphyroblasts and breccia clasts a shear sense history is derived by applying this approach to earlier foliations preserved within the heterogeneities and their strain shadows

thermo mechanical pressurization of experimental faults in cohesive rocks during seismic slip earthquakes occur because fault friction weakens with increasing slip and slip rates since the slipping zones of faults are often fluid saturated thermo mechanical pressurization of pore fluids has been invoked as a mechanism responsible for frictional dynamic weakening but experimental evidence is lacking we performed friction experiments normal stress 25 mpa maximal slip rate 3 ms 1 on cohesive basalt and marble under 1 room humidity and 2 immersed in liquid water drained and undrained conditions in both rock types and independently of the presence of fluids up to 80 of frictional weakening was measured in the first 5 cm of slip modest pressurization related weakening appears only at later stages of slip thermo mechanical pressurization weakening of cohesive rocks can be negligible during earthquakes due to the triggering of more efficient fault lubrication mechanisms flash heating frictional melting etc

an interlinked system of folds and ductile shear zones late stage svecokarelian deformation in the central fennoscandian shield finland abstract the svecokarelian deformation of the karelian and svecofennian provinces in finland involved four main phases isoclinal folding and associated thrusting were the main processes of d 1 which was followed by more open folding in d 2 subsequent deformation was localized during d 3 and d 4 this paper focuses on the late stage d 4 svecokarelian deformation that created most of the ductile shear zones in the central fennoscandian shield and was the last penetrative deformational event to affect the entire palaeoproterozoic domain deformation during d 4 occurred approximately from 1 85 1 80 ga and left a greater imprint in the rocks than has commonly been supposed the shear zones formed during d 4 are referred to collectively as the finlandia shear system the karelian province is composed of archaean basement and its autochthonous allochthonous palaeoproterozoic sedimentary cover svecokarelian tectonics split the basement into separate complexes the rheological properties of which differed markedly from those of the adjacent proterozoic supracrustal units on the northern and southern margins of the archaean complexes folding with steep e w trending axial surfaces was the main response to d 4 deformation whereas on the eastern and western margins of the complexes the response to d 4 was the development of sinistral and dextral shear zones trending ne sw and nw se respectively on a large scale these areas of folding and of shearing form an interlinked system the changes from one style of deformation to the other being gradual the principal d 4 elements in the area of juvenile svecofennian crust are folds with e w trending axial surfaces

proterozoic tectonic evolution and late svecokarelian plate deformation of the central baltic shield the continental crust of the central baltic shield evolved by accretion towards the west during the svecokarelian orogeny 1700 2200 ma ago the following features are consistent with a plate tectonic mechanism involving subduction of oceanic crust below an archean craton in the east flysch sediments with serpentinite masses and pillow lavas linear high grade metamorphic zones island arc type volcanic belts and late tectonic batholiths with porphyry type cu mo deposits semi consolidated new crust was affected by late svecokarelian deformation dn after 1850 ma nne trending folds with crenulation cleavage were overprinted on older structures together with associated nw trending ductile transcurrent shear zones that curve the fn folds into gentle s and z shapes the late tectonic batholiths intruded partly at the same time as and partly after the dn deformation

hydrological effects and nutrient losses of forest plantation establishment on tropical rainforest land in sabah malaysia abstract new measurements of field saturated hydraulic conductivity soil moisture rain intensity surface runoff and erosion are presented with earlier published data on soil physical properties stream water quality and runoff and dissolved nutrient losses from a paired catchment experiment in sabah malaysia the catchment experiment compared crawler tractor extraction and burning normal practice catchment w5 versus manual extraction and no burning w4 another catchment where secondary vegetation after forest fire was cleared and burned before planting was also studied w1 2 two separate control catchments were also included one was for rainforest w6 and the other comprised secondary vegetation w3 although hydraulic conductivity was reduced in clay soils at 20 and 40 cm depths under tractor tracks the decrease was less drastic than for steady state infiltrability on both clay and sand topsoils since control topsoils 0 20 cm were well aggregated in contrast to more compact subsoils with higher clay content topsoils were close to saturation at all times also after treatments but control forest surface runoff in slopes excluding valley bottom comprised only 2 9 of rainfall in a wet year except for just after burning clear felling did not increase slope surface runoff on undisturbed clay topsoils and surface erosion was not increased except for the erosion of ash after burning on tractor tracks extensive surface runoff caused surface and gully erosion elevated concentrations of suspended sediment in stormflow in w5 were back to pretreatment levels within 2 years under manual extraction suspended particulate loss was approximately half most of which emanated from sediments activated by increasing stream runoff dissolved nutrient losses from catchment w5 in kilograms per hectare were 39 9 n 1 3 p 189 k 27 ca and 16 mg in the 33 months during and after treatments these amounts were equivalent to between 10 and 185 of the removal in the harvest for the minimum disturbance of w4 the increased nutrient loss was halved except for ca burning of residues in w1 2 and w5 increased dissolved losses dramatically over a short period the bulk of soil water was concluded to move quickly as troughflow in topsoil hence bypassing of retention possibilities in the largest pores with small specific surfaces led to large dissolved nutrient stream losses in this humid tropical environment even without soil disturbance and extensive surface runoff

low frictional strength of quartz rocks at subseismic slip rates 1 laboratory experiments on rocks at low sliding velocity typically yield values of the friction coefficient of 0 6 0 85 here we demonstrate that an extraordinary decrease in friction coefficient accompanies sliding of room dry quartz rocks at rates faster than in most laboratory experiments but slower than seismic slip rates in some cases the friction coefficient decreases from low speed values by more than a factor of 3 this extraordinary weakening likely results from the formation of finely comminuted amorphous wet material on the sliding surface

ring permeametry design operation and error analysis assessment of slope stability soil management or contaminant transport problems usually requires numerous yet accurate point measurements of permeability this technical note describes a new method for the rapid field assessment of permeability in near surface soils or unconsolidated sediments the procedure is known as ring permeametry and is an ex situ core based method giving measurements which can be guaranteed to be stratum specific unlike measurements from some in situ techniques the potential sources of precision and bias error within the method are quantified and their effect on the uncertainty of permeability estimates is illustrated 1997 john wiley sons ltd

early proterozoic deposition and deformation at the karelian craton margin in southeastern finland abstract the margin of the karelian craton underwent complex though not chaotic deformation during the svecokarelian orogeny the resultant structural sequence can be subdivided into an early phase that involved translation of thrust nappes and recumbent folds verging towards the craton and a younger phase having more zonal and upright structures these latter include nw trending ductile shear zones associated with widespread pluton emplacement and later n trending faults and shear zones having substantially vertical displacements these features are interpreted in terms of a relative increase in vertical crustal stresses resulting from gravitational and thermal disequilibrium in the overthrust archaean basement despite this structural complexity two distinct depositional provinces are recognized in north karelia separated by a major thrust zone the more easterly hoytiainen province is a narrow essentially intracratonic feature containing locally derived archaean and proterozoic detritus an early phase of chemogenic and pelitic deposition with sporadic tholeiitic volcanism was followed by an influx of coarse clastic detritus largely deposited from turbidity currents within a prograding submarine fan the province apparently records deposition in a transtensional en echelon system of basins initiated near the craton margin at about 2 1 ga in contrast the savo province is largely allochthonous and includes the distinctive outokumpu assemblage commonly interpreted as a remnant of lower proterozoic oceanic crust provenance for the bulk of the overlying metasediments remains problematical although local evidence for deposition on archaean basement exists if an accretionary margin context is considered several potential niches for savo province deposition can be found that appear to satisfy constraints imposed by both isotopic data relating to provenance and the sequence and geometry of svecokarelian deformation

effect of water on the frictional behavior of cohesive rocks during earthquakes fluid rock interactions can control earthquake nucleation and the evolution of earthquake sequences experimental studies of fault frictional properties in the presence of fluid can provide unique insights into these interactions we report the first results from experiments performed on cohesive silicate bearing rocks microgabbro in the presence of pressurized pore fluids h2o drained conditions at realistic seismic deformation conditions the experimental data are compared with those recently obtained from carbonate bearing rocks carrara marble contrary to theoretical arguments and consistent with the interpretation of some field observations we show that frictional melting of a microgabbro develops in the presence of water in microgabbro the initial weakening mechanism flash melting of the asperities is delayed in the presence of water conversely in calcite marble the weakening mechanism brittle failure of the asperities is favored this opposite behavior highlights the importance of host rock composition in controlling dynamic frictional weakening in the presence of water cohesive carbonate bearing rocks are more prone to slip in the presence of water whereas the presence of water might delay or inhibit the rupture nucleation and propagation in cohesive silicate bearing rocks 2013 geological society of america

hydrologic effects of clearcutting and wildfire on steep granitic slopes in idaho many of the environmental impacts of logging and wildfire are caused by changes in the hydrologic response of slopes after disturbances this study was conducted to evaluate changes in inflow storage and outflow for 3 year periods before and after clearcut logging and wildfire on two steep granitic microwatersheds in idaho clearcutting alone and clearcutting plus wildfire increased annual peak snow water equivalent and snowmelt rates an average of 41 and 30 respectively the greater volume and rate of snowmelt caused respective increases in the peak piezometric rise and in total piezometric storage amounting to 47 and 27 accordingly the total volume of subsurface flow intercepted by the roadcut was increased 96 and was accompanied by 27 greater peak flow rates none of the above responses were detectable on an adjacent watershed that was burned by wildfire alone evapotranspiration was reduced on both watersheds after clearcutting or wildfire as indicated by increases in the unsaturated soil water content at the end of the growing season amounting to 44 and 72 respectively accelerated mass erosion on clearcut slopes and accelerated surface and mass erosion on roads and in channels below roads can result from such changes

comments on the interpretation of deformation textures in rocks abstract in rocks that undergo ductile deformation preferred orientation develops as a result of intracrystalline slip and mechanical twinning the orientation distribution is a consequence of the microscopic mechanisms and of the strain path it can be used to get some insight into the deformation history however it is never unique the interpretation relies largely on polycrystal plasticity theory the concepts of stress equilibrium and strain compatibility which are two extreme assumptions made to model deformation are discussed new approaches such as the viscoplastic self consistent theory are a compromise and may be applicable to mineral systems which display a high degree of plastic anisotropy important extensions allow for heterogeneous deformation in the polycrystal from grain to grain and even within grains in correspondence with microstructural observations all these theories defy the popular notion which is becoming entrenched in the geological literature that the microscopic slip plane normal aligns with the axis of maximum principal compressive stress and that in simple shear the crystallographic slip plane rotates into the macroscopic shear plane and the slip direction into the macroscopic shear direction an orientation referred to by geologists as easy glide it is emphasized that future work on texture development of rocks should be based on rigorous physics rather than ingenious intuition in accordance with an old recommendation of walter schmidt

petrology and geochemistry of metabasalts from the 1 95 ga jormua ophiolite northeastern finland the jormua ophiolite exposes a unique fragment of red seatype oceanic crust formed in a setting related to continental break up 1950 ma ago two distinct types of basalt are represented the early dykes and the main basalt suite early dykes have fractionated h ree patterns oib like trace element patterns low 2j nb 6 and ejwfyss ga 0 6 indicative of their derivation from an enriched source the remaining dykes and all lavas belong to the second e morb like main basalt suite which is characterized by high mg number and cr contents flat ree patterns zr b 6 17 chondritic th ta and only moderately depleted isotopic signatures zjufi gs a 4 1 9j most main suite samples cannot be related solely by fractional crystallization to a common parental magma rather they represent distinct melt fractions that underwent variable amounts of chromite olivine plagioclase fractionation during ascent a significant part of the compositional diversity of the main basalt suite can be explained by mixing a depleted source with a relatively uniform proportion of an enriched component similar to that represented by the oib like early dykes it is probable that during the latest stages of continental rifting the oib type melts metasomatized the upper part of the depleted asthenospheric mantle which became the source of the main basalt suite soon after the old continental lithosphere was ruptured the complete absence of any evidence for a subduction related component in the basalts implies that jormua is not a back arc ophiolite

sediment production from forest road surfaces erosion on roads is an important source of fine grained sediment in streams draining logged basins of the pacific northwest runoff rates and sediment concentrations from 10 road segments subject to a variety of traffic levels were monitored to produce sediment rating curves and unit hydrographs for different use levels and types of surfaces these relationships are combined with a continuous rainfall record to calculate mean annual sediment yields from road segments of each use level a heavily used road segment in the field area contributes 130 times as much sediment as an abandoned road a paved road segment along which cut slopes and ditches are the only sources of sediment yields less than 1 as much sediment as a heavily used road with a gravel surface

archean proterozoic collision boundary in central fennoscandia revisited abstract archean proterozoic ap collision boundary in central fennoscandia is a complex collage of archean basement rocks its paleoproterozoic supracrustal cover rocks and svecofennian 1 93 1 78 ga supracrustal and plutonic rocks the apparent steep nature and complexity of the ap boundary has led to contradictory tectonic models varying from arc continent collision via back arc closure to accretion of arc terranes along a strike slip shear zone we present new geochronology data from detrital zircons combined with whole rock geochemical and sm nd isotopic data on paleoproterozoic sedimentary and volcanic rocks across the boundary to revise its nature the 2 06 ga siilinjarvi volcanic complex and associated turbidites with an inferred deposition age at 2 1 2 06 ga are part of the cover sequence the siilinjarvi volcanic rocks derive from both plume oib and sub continental lithospheric mantle sclm magma sources and are often contaminated by the archean crust the sahara suite sedimentary cover rocks are derived from local 1 95 1 92 ga bimodal volcano plutonic source which source also explains the common age population found in younger sedimentary rocks the nalantojarvi suite psammites with maximum depositional ages of 1 97 1 93 ga are continental slope to deep water sediments deposited at the continental margin contemporaneous mafic magmatism seen as lavas and dykes show a change from sclm dominated present east to asthenospheric depleted mantle dm dominated present west melts the interpretation of the nalantojarvi suite as cover rocks of the lower plate indicates that the archean crust continues at least 50 km more to the west than thought earlier parautochthonous sedimentary rocks from salahmi eastern kansanneva and loutemaki with maximum depositional ages at 1 92 1 91 ga are inferred as collision related foredeep deposits from local sources both the lampaanjarvi suite and pyhajarvi suite sedimentary rocks have deposited at 1 89 1 88 ga or later whereas the lampaanjarvi suite rocks are dominated by a local source and the pyhajarvi suite rocks derive from a mixture of older sediments and 1 89 1 88 ga granitoids at least two tectono metamorphic stages separated with a major unconformity can be differentiated in the study area the early deformation and metamorphic stage in the nalantojarvi suite has occurred before the intrusion of the late to post collisional pyroxene granitoids at 1 88 ga the pyhajarvi suite sedimentary rocks have been deposited after the intrusion of these granitoids between 1880 and 1875 ma and then subsequently deformed and metamorphosed at 1875 ma we propose a tectonic model where the continental breakup occurred at 2 1 2 06 ga followed by a new spreading within the pre existing passive margin at 1 98 1 93 ga during initial continent arc collision the subducted slab steepened strongly at high angle subduction ceased rapidly and finally detached and shallow slab breakoff occurred at 1 92 1 91 ga followed subsequently by ophiolite obduction and a formation of a foreland fold and thrust belt mantle crust decoupling of the archean lithosphere occurred and a crocodile jaw formed where the arc rocks are partly buried beneath the bounding archean continent similar features have been recorded in other ap collision zones which could indicate that the buoyant nature of the archean lithosphere combined with denser paleoproterozoic lithosphere may be a general cause for decoupling of archean crust and mantle during arc continent collision in paleoproterozoic

diapirism and gravity tectonics report of a tectonic studies group conference held at leeds university 25 26 march 1980 ir is now almost two decades since hans ramberg began his well known research of simulating diapiric structures in the laboratory and his application of this model work to the origin of major structures in orogenic belts ramberg 1963 1967 since then there has been a revolution of ideas in structural geology ideas ofhorizontal tectonics based on the movements of the earth s plates have largely taken preference to ideas based on vertical tectonics related to diapirism it was therefore considered timely to review the relative role of diapirism in regional deformation and hence the tectonic studies group affiliated to the geological society of london held a meeting on this theme on 25 26 march 1980 at the university of leeds this report includes the abstracts of all the contributions and it also summarises some of the conclusions most of which emerged during discussion following the contributions

persistence of road runoff generation in a logged catchment in peninsular malaysia measurements of saturated hydraulic conductivity ks and diagnostic model simulations show that all types of logging road trail in the 14 4 ha bukit threk experimental catchment 3 btec3 generate substantial horton overland flow hof during most storms regardless of design and level of trafficking near surface ks 0 0 05 m on the main logging road skid trails and newly constructed logging terraces was less than 1 2 and 34 min h 1 respectively near surface ks on an abandoned skid trail in an adjacent basin was higher 62 mm h 1 owing to the development of a thin organic rich layer on the running surface over the past 40 years saturated hydraulic conductivity measured at 0 25 m below the surface of all roads was not different all 6 mm h 1 and corresponded to the ks of the adjacent hillslope subsoil as most roads were excavated into the regolith more than 0 5 1 m after 40 years only limited recovery in near surface ks occurred on the abandoned skid trail this road generated hof after the storage capacity of the upper near surface layer was exceeded during events larger than about 20 mm thus excavation into low ks substrate had a greater influence on the persistence of surface runoff production than did surface compaction by machinery during construction and subsequent use during logging operations overland flow on btec3 roads was also augmented by the interception of shallow subsurface flow traveling along the soil saprolite bedrock interface and return flow emerging from the cutbank through shallow biogenic pipes the most feasible strategy for reducing long term road related impacts in btec3 is limiting the depth of excavation and designing a more efficient road network including minimizing the length and connectivity of roads and skid trails copyright 2007 john wiley sons ltd

the geometrical relationship between the stretching lineation and the movement direction of shear zones abstract the geometrical relationship between foliations and lineations in shear zones is considered quantitatively assuming that the internal structures of shear zones have monoclinic symmetry the common practice of directly correlating the pitch or plunge of the stretching lineation with the obliquity of the shear direction is challenged it is the orthogonal projection of the stretching lineation on the shear zone boundary that is parallel to the shear direction a shear zone is parallel to a plane containing both the pole to the symmetry plane and the strike of the shear zone and the shear direction is parallel to the intersection of the symmetry plane and the shear zone boundary the symmetry plane is determined by the stretching lineation and the poles to the s foliation the implications of this study for the interpretation of shear zones are discussed with reference to an actual example

metamorphic and structural evolution of the early proterozoic puolankajarvi formation finland i structural and textural relations the amphibolite facies puolankajarvi formation pjf occupies the western margin of the early proterozoic kainuu schist belt ksb of northern finland the lower and middle parts of the pjf consist of turbiditic psammites and pelites and tempestitic semipelites this report concentrates on the pelitic lithologies which include quartz two mica plagioclase schists with variable amounts of garnet staurolite andalusite and biotite porphyroblasts as well as sillimanite and cordierite segregations the ksb forms a major north south trending synclinorium between two archaean blocks it contains both autochthonous and allochthonous units and is cut by faults and shear zones the pjf lies on the western side of the ksb and is probably allochthonous the formation has undergone six major deformation phases d1 d2 d3a d3b d4 and d5 during d3a d5 the maximum principal stress 1 changed in a clockwise direction from south west to north east between d2 and d3 the intermediate principal stress 2 changed from horizontal to vertical and the interval between d2 and d3 marks a transition from thrust to strike slip tectonics relict structures in the porphyroblasts indicate the following mineral growth deformation evolution in the pjf 1 throughout the pjf there was a successive crystallization of garnet syn d1 poryphyroblastic biotite inter d3 4 and staurolite inter d3 4 during the pre d4 stage 2 a syn d4 inter d4 5 crystallization of kyanite sillimanite fibrolite porphyroblastic tourmaline magnetite rutile cordierite and muscovite biotite plagioclase pseudomorphs after staurolite was most localized at and near d4 shear zones 3 a syn to post d5 generation of andalusite ilmenohematite and sheet silicates after staurolite and after cordierite occurred near d5 faults the evolution outlined here permits the relative dating of the pjf parageneses which is used in the second part of the study tuisku laajoki 1990 and together with the knowledge of the pressure temperature conditions during various growth events makes it possible to compile pressure temperature deformation paths for the pjf

2 45 ga break up of the archaean continent in northern fennoscandia rifting dynamics and the role of inherited structures within the archaean basement abstract constraints from restoration of minor rift related faults preserved from subsequent palaeoproterozoic overprint along the southern margin of the perapohja belt northern fennoscandia indicate local ne sw extension directions prevailed at the time of 2 44 ga rifting of the archaean continent this palaeostress field is attributed to pull apart setting of the perapohja belt at a left overstepping zone of major sinistral n s trending deformation zones consequently the variably overprinted nw se trending structures of the perapohja belt including the nw se central graben were originally generated as normal faults the proposed setting is compatible with a conducted reconnaissance sandbox analogue model where the orientation of the major normal faults was controlled by the ambient stress field within the step over zone between strike slip faults by contrast the faults bounding e w to ene wsw trending basement horsts are the result of reactivation of older basement structures underlying the pull apart basin based on the results we infer that the final break up of the archaean continent in northern fennoscandia utilized the 2 44 ga rift related nw se trending crustal anisotropy parallel with dyke swarms with pre existing archaean n s trending structures reactivated as second order shear zones in between the voluminous syn rift 2 5 2 4 ga and later pulses of mafic magmatism 2 32 1 98 ga are considered indicative of active type rifting which onset was controlled by a mantle plume centred within a supercraton formed by the superior hearne and karelian kola cratons the presented model supports the continuity of the archaean craton beyond the caledonian orogen towards north west and explains its segmentation suggesting a model for the localization of the palaeoproterozoic supracrustal belts of northern fennoscandia moreover this paper provides an approach to understand the basement cover relationships and the structural signatures within these relatively shallow supracrustal belts which are highly prospective for mineral deposits

strong velocity weakening and powder lubrication of simulated carbonate faults at seismic slip rates 1 high velocity friction tests were conducted on solid and hollow cylinders of carrara calcite marble dolomite marble silicate bearing calcite marble and calcite gouge to investigate the strength of carbonate faults during seismic slip the experiments performed at normal stresses of 0 6 14 7 mpa slip rates of 0 03 1 60 m s and room temperature in a rotary shear friction testing machine yielded an extraordinarily low steady state friction coefficient 0 1 at slip rates of 1 1 1 2 m s the slip weakening distance of 4 28 m became shorter at higher normal stress or frictional work rate strong velocity weakening was observed not only in steady state but also in nonsteady state friction while the slip rate was changing thus slip deceleration was accompanied by fault strength recovery large rapid temperature rises in narrow shear localization zones less than a few micrometers induced carbonate decomposition such as the breakdown of calcite into aggregates of cao nanograins and co2 in carrara marble scanning electron microscope observation revealed that the shear localization zone in the highly porous decomposition product was a layer of scattered small grains mostly 1 m in diameter these microstructures and the measured high permeability 10 14 m2 of the decomposed marble indicate that the dominant weakening mechanism in our experiments was possibly powder lubrication powder rheology at high slip rates is not yet well understood but the frictional behavior of nanograins appears to be strongly velocity dependent if decarbonation occurs during seismic slip in natural carbonate faults powder lubrication may make the faults slippery even under fluid drained conditions

multiple post svecofennian 1750 1560 ma pegmatite dykes in archaean palaeoproterozoic rocks of the west troms basement complex north norway geological significance and regional implications abstract the west troms basement complex north norway consist of meosarchaean neoarchaean and palaeoproterozoic crust which likely represent the continuation of the karelian craton of the fennoscandian shield beneath and across the caledonian nappes the complex is transected by several meta sedimentary volcanic belts with ages from ca 2 7 to 1 9 ga and linear ductile shear zones that record polyphase deformation after emplacement of several late svecofennian plutonic complexes 1 80 1 79 ga the astridal supracrustal belt of the senja shear zone was intruded by various generations of granite pegmatite dykes which yield zircon and titanite u pb ages ranging between 1758 and 1562 ma with evidence of a weak caledonian overprint at about 400 ma that formed or reset some but not all titanites the age range indicates that formation of the pegmatites occurred after termination of the main svecofennian orogeny 1 92 1 79 ga of the karelian craton comparison within the larger scale context of the fennoscandian shield suggests that emplacement of these pegmatites may have been caused by late stage reactivation of intracratonic shear zones possibly reflecting distal effects of deeper magmatic processes such as intrusion of coeval aged rapakivi granite suites ca 1 65 1 5 ga in finland and or the mesoproterozoic gothian orogeny and magmatism affecting the southwestern parts of fennoscandia the mesoproterozoic ages however also correspond to late laxfordian ca 1 7 1 6 ga tectonic events in the lewisian basement on the laurentian margin of scotland suggesting a potential early link between these basement complexes

the precambrian supracrustal rocks of finland and their tectono exogenic evolution abstract the precambrian supracrustal rocks of finland were produced during four main evolutionary stages 1 late archaean pre svecokarelidic greenstone schist evolution on an unknown basement 2 at least four cycles of early proterozoic karelian continental epi pericontinental sedimentation and volcanism on or next to the cratonized late archaean basement 3 early proterozoic svecofennian eugeosynclinal evolution west of or in part on the late archaean basement and its cratonic cover and 4 middle to late proterozoic jotnia continental sedimentation on the stabilized early proterozoic post svecokarelidic basement

interference fold patterns in regional unidirectional stress fields a result of local kinematic interactions abstract folds are commonly found in association with ductile shear zones however superimposed folding contemporaneous with shearing is rarely reported here we describe a macroscopic fold interference pattern with geometry intermediate between types 1 and 2 related to development of adjacent transcurrent shear zones the interference fold pattern is located in a compartment bounded on the eastern side by an ene trending dextral shear zone that connects with a ne trending sinistral shear zone and on the western side by a ne trending sinistral shear zone a first folding episode produced nw trending sw verging inclined folds and a later one ne trending upright folds folds of the first event are attributed to a local contractional strain field induced by the growth of the shear zones with opposed kinematics whereas the later folding episode and nucleation of the western shear zone reflects regional nw se contraction folding of a macro scale nw trending fold by ne trending folds produced the fold interference structure in contrast with most cases of types 1 and 2 fold interference patterns in the present case no change on the orientation of regional stress axes is required

growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting 1 to understand how frictional melting affects fault instability we performed a series of high velocity friction experiments on gabbro at slip rates of 0 85 1 49 m s 1 at normal stresses of 1 2 2 4 mpa and with displacements up to 124 m experiments have revealed two stages of slip weakening one following the initial slip and the other immediately after the second peak friction the first weakening is associated with flash heating and the second weakening is due to the formation and growth of a molten layer along a simulated fault the two stages of weakening are separated by a marked strengthening regime in which melt patches grow into a thin continuous molten layer at the second peak friction the frictional coefficient decays exponentially from 0 8 1 1 to 0 6 during the second weakening the host rocks are separated completely by a molten layer during this weakening so that the shear resistance is determined by the gross viscosity and shear strain rate of the molten layer melt viscosity increases notably soon after a molten layer forms however a fault weakens despite the increase in melt viscosity and the second weakening is caused by the growth of molten layer resulting in the reduction in shear strain rate of the molten layer very thin melt cannot be squeezed out easily from a fault zone so that the rate of melting would be the most critical factor in controlling the slip weakening distance effect of frictional melting on fault motion can be predicted by solving a stefan problem dealing with moving host rock molten zone boundaries

nature of a major tectonic discontinuity in the svecofennian province of northern sweden abstract the volcanic rocks of the skellefte ore district ca 1 89 1 87 ga like other volcanic complexes of similar age in the svecofennian orogenic province have been regarded as juvenile arc material developed over a contemporaneous subduction zone and subsequently accreted to the continent during a period of very rapid crustal growth a modelled geoelectric anomaly dipping ne beneath the district from the southern province has provided support for the subduction collision hypothesis we have used recently acquired geological and geophysical evidence to suggest an alternative to this model regional aeromagnetic and gravity data indicate that the skellefte district is the site of a major tectonic discontinuity the province to the north of this discontinuity provides evidence of an archaean basement to within 100 km of skelleftea the skellefte group on the southern margin of this province displays a narrow belt of strong upright folding trending w to wnw we correlate this folding with the second major deformation episode d 2 of similar trend in the metamorphic complex of the southern province here informally called the robertsfors group the family of d 2 structures on both sides of the province boundary defines the 80 km wide skellefte zone d 2 in the robertsfors group consists of discrete ductile shear zones and associated upright folds these zones are consistently steep display southside up kinematics and are superposed on earlier ne trending folding d 1 and migmatisation in the robertsfors group we infer from the style of d 2 that it could not be responsible for the accretion of an exotic volcanic arc to the continent upper crustal thickening was probably largely achieved during d 1 we conclude from the style and orientation of the d 1 structures in the robertsfors group their absence from the skellefte group and their relation to granitoid intrusions that d 1 pre dates deposition of the skellefte group we infer that the robertsfors group forms part of the previously unknown basement of the skellefte group the latter is therefore regarded as a supracrustal sequence deposited in a rift setting rather than a juvenile volcanic arc it is also concluded that the basement stratigraphic package which also occurs to the southwest of the skellefte ore district and has variable internal structures is responsible for the modelled geoelectric anomaly we therefore interpret the tectonic discontinuity as the boundary between pre and post 1 9 ga rock groups both of which have been intruded by post 1 9 ga granitoids and affected by the localised upright d 2 post 1 87 ga deformation in the skellefte zone the volcanism of the skellefte ore district and the ni bearing mafic intrusions of the southern province are attributed to an episode of extension between d 1 and d 2 which was probably related to a contemporaneous active margin lying west of the present exposure of svecofennian rocks d 1 in the robertsfors group is attributed to the closure of an extensive marginal basin possibly involving subduction prior to skellefte group deposition i e before 1 9 ga geochronological data from the robertsfors group on the ages of d 1 and d 2 and the regional significance of pre 1 9 ga metamorphic complexes are discussed in a companion paper

weakening of quartz rocks at subseismic slip rates due to frictional heating but not to lubrication by wear materials of hydrated amorphous silica or silica gel abstract in order to clarify the weakening mechanism of quartz rocks at subseismic slip rates of 0 1 10 cm s we conducted two series of rotary shear friction experiments at a normal stress of 1 5 mpa and equivalent slip rates veq of 0 1 10 cm s one on intact agate controlling background temperature tbg and atmosphere and the other on intact agate and silica gel gouge monitoring temperature t adjacent to the slip surface or the gouge layer in the former experiments at veq 1 cm s agate samples at room tbg showed similar steady state friction coefficients ss 0 62 0 63 irrespective of humid or dry condition in the latter case of which hydration of amorphous wear materials was hampered while agate sample at tbg 100 c exhibited weakening to ss 0 35 in the latter experiments ss of both intact agate and silica gel gouge decreased with increasing veq from 0 6 0 7 at veq 0 1 cm s to 0 03 0 16 at veq 10 cm s while the maximum t increased with increasing veq from 25 28 c at veq 0 1 cm s to 88 93 c at veq 10 cm s spikes of high friction followed by t maxima and subsequent weakening suggest that slip at strong asperity contacts induced frictional heat which in turn resulted in weakening these two series of friction experiments indicate that the frictional strength of quartz rocks at subseismic slip rates is controlled by temperature which increases by frictional heating but not by wear materials of hydrated amorphous silica or silica gel indentation strength of quartz is much higher than that of other common rock forming minerals so that much more amount of frictional heat would be induced at asperity contacts in quartz rocks than in other rocks which is likely responsible for weakening of quartz rocks at subseismic slip rates

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

amorphous material formed by the mechanochemical effect in natural pseudotachylyte of crushing origin a case study of the iida matsukawa fault nagano prefecture central japan abstract pseudotachylytes from the iida matsukawa fault central japan iida pseudotachylytes are described down to the nanometer scale using high resolution electron microscopy scanning electron microscopy analyses of chemical compositions and mercury intrusion porosimetry the pseudotachylyte matrix chiefly consists of nanoscale particles and elongated submicron fragments with biotite composition amorphous material of several tens of nanometers in size is also observed despite the absence of melt textures lattice fringe images reveal that the amorphous phase coexists with lattice distortion in deformed biotite fragments that are several hundreds of nanometers in size the presence of these submicrostructures indicates that the amorphous material formed by mechanical stress during the comminution process that is via the mechanochemical effect we conclude that amorphous material does not always provide evidence of the rapid cooling of melt in pseudotachylyte the amorphous materials present in the iida pseudotachylyte resulted from the mechanochemical effect due to both shear stress and normal stress during the comminution process that accompanied fault motion

major palaeoproterozoic shear zones of the central fennoscandian shield abstract employing two recently studied crustal scale shear zones as type examples this paper summarizes the major palaeoproterozoic svecokarelian shear tectonics of the central fennoscandian shield and demonstrates that this part of the shield was not as stable during the svecokarelian orogeny as commonly assumed the collision of the svecofennian island arc with the karelian continent first created numerous nw se trending folds and thrusts of stages d1 and d2 which were then modified by successive shearing during stages d3 and d4 stage d3 built up a system of n s trending shear zones here named the savolappishearsystem the type example of which is the hirvaskoski shear zone this is a dextral strike slip shear zone at least 150 km long and 10 30 km wide characterized by blastomylonitic fault rocks and various structures such as hook folds z folds and sheath folds associated with the principal displacement zone synthetic riedel shears and pinnate shears the traces of the axial planes of f3 en echelon folds deviate 15 30 anticlockwise from the plane of the principal displacement zone other members of the savolappi shear system are the pajala shear zone in northern sweden and the russian north karelia shear zone in the east stage d4 created a conjugate shear system called the finlandia shear system the type example of which is the oulujarvi shear zone this is a ne sw trending sinistral strike slip shear zone more than 250 km long and 20 30 km wide across its southwestern end it is composed of a ne sw trending principal displacement zone synthetic riedel shears and pinnate shears with antithetic riedel shears in a nw se direction typical fault rocks within these shears are s c mylonites the axial plane traces of f4 folds of all scales diverge by 20 40 clockwise from the plane of the principal displacement zone the kuopio shear zone is a conjugate nw se trending counterpart of the oulujarvi shear zone as a whole the finlandia shear system forms a conjugate network of nw se and ne sw trending shear zones which occupies most of the northern and central fennoscandian shield

sources of suspended sediment within a tropical catchment recovering from selective logging quantification of the source of suspended sediments generated by selective forestry activities is central to the development of sustainable forestry guidelines this assessment is hampered by a dearth of available studies particularly from the tropics this study involved the monitoring at 10 s intervals of surface discharge and turbidity from 15 contributory areas of a 44 ha catchment the catchment is located within lowland dipterocarp rain forest on borneo island in a region recovering from the first episode of selective timber removal that took place some 5 years previously both the within storm dynamics of the sediment flux and the time integrated sediment yields were analysed to link the source landforms to the catchment behaviour a 10 year rainfall event of 167 mm occurred during the monitoring period and triggered a debris slide and several log culvert collapses along the area s main timber haulage road the sampling design captured this event s dynamics and allowed lumped catchment response to be traced to the new landforms during the 1 day period of the 10 year event some 33 t of suspended sediment were transported from one debris slide comprising a significant proportion of the 105 t discharging from the whole catchment which itself constituted 40 of the annual yield of 592 t km 2 the contributory areas with only ephemeral waterflows including former haulage roads and tracks generated relatively little sediment during this 10 year event or in other storms this work suggests that though some sediment sources recover from the impacts of forest road construction and harvesting collapse of roadfill materials or more local log culvert failure persists for several years after harvesting sustainable forestry guidelines that do not focus on ameliorating these persistent instabilities may not significantly mitigate the geomorphic impacts of conventional selective harvesting copyright 2004 john wiley sons ltd

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

road surface drainage channel initiation and slope instability field surveys of road drainage concentration at three sites in the western united states are used to test simple models relating channel initiation and shallow landsliding to ground slope and contributing area thresholds the form of boundaries between data for locations where road drainage concentration is associated with either shallow landsliding channel initiation by overland flow or no observable geomorphic effect is consistent with theoretically derived drainage area slope relations comparison of survey data with results of previous studies in these areas indicates that the drainage area required to support a channel head is smaller for road related runoff than for undisturbed slopes contrary to current land management paradigms in the pacific northwest drainage concentration from ridgetop roads may cause both landsliding and integration of the channel and road networks road drainage concentration increases the effective length of the channel network and strongly influences the distribution of erosional processes in each of the study areas the approach of using field reconnaissance to establish thresholds for erosion associated with road drainage provides a useful method to define regional criteria for road design that should reduce impacts on downstream channel systems

towards better design and management of tsunami evacuation routes a case study of ao jak beach road among the thousands of people killed or reported missing in thailand during the 2004 indian ocean tsunami were villagers in small communities on the andaman coast a combination of factors contributed to loss of life including the lack of defined evacuation routes this vulnerability to tsunami attacks has recently been addressed with the demarcation of evacuation routes along both well maintained arteries and native surface unpaved roads however poor location design and irregular maintenance will reduce the lifetime that the latter can provide safe egress from remote coastlines in this work we identified 10 major gullies and 18 landslides along a critical 0 5 km section of a tsunami evacuation road accessing a remote beach of the andaman coast in southern thailand erosion rates from landslides and gullies approached 9500 mg ha 1 in less than a year following widening of the road importantly the degradation features landslides in particular reduced the effectiveness of the road to serve as a safe passageway to escape future tsunamis or large storm surges this study demonstrates that greater attention should be given to appropriate road location design and maintenance in integrated programmes aimed at reducing tsunami vulnerability in remote coastal areas not only on the andaman coast but worldwide

growth of contact area between rough surfaces under normal stress the contact area between deforming rough surfaces in marble alabaster and quartz was measured from thin sections of surfaces bonded under load with low viscosity resin epoxy the marble and alabaster samples had contact areas that increased with stress at an accelerating rate this result suggests that the strength of the asperity contacts decreased progressively during the deformation following some form of strain weakening relationship this conclusion is supported by petrographic observation of the thin sections that indicate that much of the deformation was cataclastic with minor twinning of calcite and kinking of gypsum in the case of the quartz the observed contact area was small and increased approximately linearly with normal stress only the irreversible cataclastic deformation was observed however strain induced birefringence and cracking of the epoxy not observed with the other rocks suggests that significant elastic deformation occurred but recovered during unloading

energy partition for grain crushing in quartz gouge during subseismic to seismic fault motion an experimental study abstract brunauer emmett teller bet surface area of quartz gouge was measured before and after shearing deformation at subseismic to seismic slip rates to determine how much of frictional work and fracture energy was consumed during grain crushing measurement of bet surface area provides more direct data on surface area change than grain size measurement does twenty four experiments on quartz gouge composed of ottawa sands or crushed quartz were conducted dry with room humidity or wet with added water at slip rates of 0 006 1 3 m s and normal stresses of 0 76 3 37 mpa using a high velocity friction apparatus and a low to high velocity friction apparatus about 1 mm thick gouge was placed between cylindrical specimens of belfast dolerite of 25 mm in diameter results show that grain crushing absorbed only 0 02 0 22 of frictional work and only 0 05 1 06 of fracture energy under dry and wet conditions thus grain comminution is unlikely to be an important energy sink at least for mature faults with well developed slip zone surface area of gouge decreases with deformation at seismic slip rates this and sem observations suggest partial sintering due to frictional heating thus a simple scenario of grain crushing as an energy sink does not hold for estimating the energy budget during earthquakes

uraniferous bitumen nodules in the talvivaara ni zn cu co deposit finland influence of metamorphism on uranium mineralization in black shales in the central part of the fennoscandian shield the talvivaara ni zn cu co deposit hosted by palaeoproterozoic metamorphosed black schists contains low uranium concentrations ranging from 10 to 30 ppm the talvivaara black schists were deposited 2 0 1 9 ga ago and underwent subsequent metamorphism during the 1 9 1 79 ga svecofennian orogeny anhedral uraninite crystals rimmed by bitumen constitute the main host of uranium u pb secondary ion mass spectrometry dating indicates that uraninite crystals were formed between 1 878 17 and 1 871 43 ma during peak metamorphism rare earth element patterns and high th content average 6 38 wt in disseminated uraninite crystals indicate that u was concentrated during high temperature metamorphism 400 c the formation of bitumen rims around uraninite may be explained by two distinct scenarios a a transport of u coincident with the migration of hydrocarbons or b post metamorphic formation of bitumen rims through radiolytic polymerization of gaseous hydrocarbons at the contact with uraninite

earthquake slip weakening and asperities explained by thermal pressurization for the earth s crust to release accumulated stress in the form of an earthquake a fault must weaken and give way otherwise the movement would quickly grind to a halt due to the surrounding pressure this weakening is not really understood laboratory experiments simply don t match seismologists estimates of the distance a fault must slip before it becomes very weak a new study concludes that the missing ingredient is water geological studies and measurements show the slip zones to be narrow impermeable structures water already in the fault zone can quickly become pressurized by frictional heating as the rocks start to move catalysing large earthquakes from minor movements an earthquake occurs when a fault weakens during the early portion of its slip at a faster rate than the release of tectonic stress driving the fault motion1 2 this slip weakening occurs over a critical distance dc understanding the controls on dc in nature is severely limited however because the physical mechanism of weakening is unconstrained conventional friction experiments typically conducted at slow slip rates and small displacements have obtained dc values that are orders of magnitude lower than values estimated from modelling seismological data for natural earthquakes3 4 5 6 here we present data on fluid transport properties of slip zone rocks and on the slip zone width in the centre of the median tectonic line fault zone japan we show that the discrepancy between laboratory and seismological results can be resolved if thermal pressurization of the pore fluid7 8 9 10 is the slip weakening mechanism our analysis indicates that a planar fault segment with an impermeable and narrow slip zone will become very unstable during slip and is likely to be the site of a seismic asperity

high velocity frictional properties of gabbro high velocity friction experiments have been performed on a pair of hollow cylindrical specimens of gabbro initially at room temperature at slip rates from 7 5 mm s to 1 8 m s with total circumferential displacements of 125 to 174 m and at normal stresses to 5 mpa using a rotary shear high speed friction testing machine steady state friction increases slightly with increasing slip rate at slip rates to about 100 mm s velocity strengthening and it decreases markedly with increasing slip rate at higher velocities velocity weakening steady state friction in the velocity weakening regime is lower for the non melting case than the frictional melting case due perhaps to severe thermal fracturing a very large peak friction is always recognized upon the initiation of visible frictional melting presumably owing to the welding of fault surfaces upon the solidification of melt patches frictional properties thus change dramatically with increasing displacement at high velocities and such a non linear effect must be incorporated into the analysis of earthquake initiation processes

tectonic styles of early proterozoic ore deposition in the fennoscandian shield the early proterozoic metallogenic events of the fennoscandian shield are connected with two major stages of crustal evolution the karelian continental development 2 5 2 1 ga and the svecofennian orogeny 2 0 1 75 ga the karelian continental development was dominated by deposition of terrestrial sediments and tholeiitic volcanism on archaean crust a tensional regime probably associated with a mantle plume and partial melting of the upper mantle culminated in the generation of an ene wsw trending rift zone which was intruded by tholeiitic magma 2 44 ga ago some 15 layered igneous bodies hosting cr pge ni cu and fe v ti deposits are known in the kemi suhanko and koillismaa belts these mafic ultramafic bodies originally formed either several lopoliths or one single layered igneous complex with a minimum length of 260 km nw se and nnw sse trending dolerite dykes intruded the rifted and attenuated archaean crust 2 25 2 0 ga ago preceding ocean opening the coeval ne sw trending dolerite dykes in the northern part of the shield are interpreted as manifestation of an aulacogen the failed arm of a triple armed rift system oceanic crust is preserved in 1 96 ga old ophiolite complexes the cu co zn ni and cr contents of the outokumpu type deposits derive from hydrothermal leaching of oceanic crust and were discharged together with chemogenic cherts and carbonates from ascending hydrothermal fluids on the seafloor above fissure vents in the northern part of the shield rifting and probably ocean opening resulted in the formation of the layered tholeiitic sedimentary complex of the petsenga ni cu district intruded by mineralized mafic ultramafic magma the age of this event is poorly constrained the basin was subsequently closed and continental collision of the kola suture was accompanied by southward obduction of the lapland granulite belt on the archaean crust during the svecofennian orogeny the divergent continental margin was converted into an active margin early subduction of oceanic crust produced oceanic island arcs intruded by 1 93 1 9 ga old tonalites and trondhjemites subsequent subduction of oceanic crust generated 1 9 1 87 ga old continental island arcs associated with massive sulphide cu zn pb ag au deposits the island arcs were accreted to the archaean crust in a concave belt containing the ore districts of kiruna skellefte vihanti pyhasalmi aijala orijarvi and bergslagen bimodal volcanic suites with felsic calc alkaline and mafic tholeiitic volcanites are attributed to rifting of the overriding plate above subduction zones ni cu deposits in synorogenic 1 9 1 87 ga old mafic ultramafic intrusions occur in linear fault controlled belts at the margin of the archaean crust the generation of ni bearing tholeiitic to komatiitic magma is explained by partial melting of the mantle wedge above the early subduction zone magma differentiation and magma upwelling along transcurrent faults on the continental margin sulphur was probably assimilated from the supracrustal wall rocks 1 89 1 87 ga old early svecofennian granitoids are associated with porphyry type cu mo au deposits widespread late svecofennian s type 1 84 1 75 ga granitic magmatism generated minor mo u w sn and ree deposits emphasis is laid on the importance of geotectonic models as a basis for further exploration in the fennoscandian shield

impacts of logging disturbance on hillslope saturated hydraulic conductivity in a tropical forest in peninsular malaysia using a constant head permeameter we found an abrupt natural decrease in saturated hydraulic conductivity ks within the upper 1 0 m soil profile of an orthoxic tropudult at the bukit tarek experimental catchments research area in tropical peninsular malaysia the depth at which low ks could cause a perched water table in response to high intensity rainfall however was too great to generate saturation overland flow on planar hillslopes in the study area the effects of logging activity on ks at five subsurface depths 0 1 0 25 0 5 0 75 and 1 0 m on the non roaded portion of the harvest area were examined at the three following sites which differed in the degree of disturbance and recovery since timber harvesting 1 selective logging conducted in the 1960s 2 mechanized selective tree removal conducted 4 years ago and 3 high impact clear cutting just prior to measurement this recent logging greatly disturbed the soil surface via compaction topsoil subsoil mixing burning and produced comparatively high variability in near surface ks changes in ks at or below 0 25 m however were not detected with certainty at any sites in terms of hillslope hydrologic response the connectivity of zones of low ks in the harvest area with dense networks of skid trails and terraces was identified as one of the most important consequences of timber harvesting although this phenomenon was not quantified we estimate the recovery time for near surface ks on the non roaded hillslope to be less than 40 years d 2006 elsevier b v all rights reserved

structure and composition of the precambrian crust along the polar profile in the northern baltic shield abstract along the 500 km long polar profile the continental crust of the northern baltic shield consists of several archaean and early proterozoic crustal segments in the south in the karelian province the upper crust consists of a 3 1 2 6 ga old archaean substratum with a 0 6 km thick low to medium grade volcanosedimentary cover here shallow basin facies rocks of the central lapland complex have been thrust northwards onto the karasjok kittila greenstone belt the repeatedly folded cover rocks form linear troughs between domes and culminations of granitoids the 47 48 km thick crust of the karelian province is of a shield type it is characterised by a low velocity layer interpreted as a horizon of decollement below the supracrustal and granitoid rocks in the lapland granulite belt early proterozoic high grade metapelites and metapsammites with minor metaigneous intercalations have been thrust to the southwest they are separated from the underlying karelian province by the tectonic mixture zone of the tanaelv belt in the interpretations two alternative models are given for the shape of the lapland granulite belt it is either a synformal nappe or a ne dipping body pinching out at depth and overthrust from the north by the archaean inari terrain both the lapland granulite belt and the inari terrain have a 42 44 km thick crust with a relatively thin lower crust marked by lower seismic velocities the early proterozoic polmak pasvik pechenga belt separates the archaean inari terrain from the archaean sorvaranger terrain in the north this belt is interpreted as a suture zone which continues to depth it may either dip steeply towards irregularities in the moho or form a sw dipping low angle plane below the lapland granulite belt the northernmost part of the baltic shield is concealed beneath a 0 7 km thick very low grade metamorphic late proterozoic cover this cover is divided into two parts by the trollfjord komagelv strike slip fault here the crust is again of a normal shield type with a thickness of 42 46 km

toward a unified conceptual framework for shear sense indicators abstract the growing lexicon for shear sense indicators has created a need for a unified conceptual system of classification many common shear structures can be described by linear combinations of two kinematic variables which quantify the relative importance of objects vs foliations in controlling the shear zone velocity field

age of deformation episodes in the palaeoproterozoic domain of northern sweden and evidence for a pre 1 9 ga crustal layer it is proposed in a companion paper that the volcanic rocks of the skellefte group in northern sweden were deposited on a pre 1 9 ga basement rather than formed as a juvenile volcanic arc and subsequently accreted to the continent it is suggested that the proposed basement the robertsfors group to the south of skelleftea was already deformed during an early episode of deformation d1 prior to the deposition of the skellefte stratigraphic sequence during an extensional tectonic episode a younger episode of deformation d2 then affected both areas this hypothesis has important implications for the evolution of the svecofennian province to test it by constraining the ages of the principal deformation episodes we have undertaken both isotope dilution and ion microprobe studies of zircon and monazite from three localities in the robertsfors group a phase of migmatisation directly related to d2 shear zones allows the dating of d2 at 1860 ma other planar granitoid bodies which cut the d1 structures confirm the age of this event in the context of earlier published data we conclude that the correlation of d2 in the robertsfors group with the main folding in the skellefte group is valid another granitoid body folded by d2 but emplaced after d1 contains a suite of zircons of apparent magmatic aspect but with a spread of ages from 1870 to 1900 ma because of the high mswd the suite was divided into two groups with ages of 1896 and 1874 ma recognising the possibilities of inheritance and of updating by younger events we have preferred to interpret the younger age as a minimum age for magmatic intrusion this is consistent with the basement hypothesis but is our only definite constraint on the age of d1 however we infer using other evidence that d1 is probably older than 1900 ma xenocrysts interpreted as detrital zircons derived from the associated metasediments give ages between 2716 and 1941 20 ma the latter age provides a maximum age of deposition for part of the robertsfors group and a maximum age for d1 other sequences to the south and west considered broadly equivalent to the robertsfors group are intruded by granitoids dated between 1920 and 1960 ma providing local minimum ages of deposition for the sequences involved regional correlation with respect to age and deformation style can be made with the pre 1 9 ga kalevian rocks to the ne deposited on archaean basement on the sw margin of the karelian province we suggest that pre 1 9 ga complexes equivalent to the robertsfors group are widespread in the svecofennian province and were deposited in a marginal basin which may have been initiated as early as 2 2 ga ago this hypothesis of an extensive basement crustal layer evidently requires that a substantial volume of crustal growth occurred prior to 1 9 ga in contrast to previous hypotheses erosion of the pre 1 9 ga basin rocks after d1 is also the likely source of the 2 1 1 9 ga detrital zircons in younger sediments associated with the overlying post 1 9 ga volcanics the source of these detrital zircons has previously been problematical

high velocity frictional properties of a clay bearing fault gouge and implications for earthquake mechanics 1 frictional properties of natural kaolinite bearing gouge samples from the median tectonic line sw japan have been studied using a high velocity rotary shear apparatus and deformed samples have been observed with optical and electron scanning and transmission microscopy for a slip velocity of 1 m s 1 and normal stresses from 0 3 to 1 3 mpa a dramatic slip weakening behavior was observed x ray diffraction analysis of deformed samples and additional high velocity friction experiments on pure kaolinite indicate kaolinite dehydration during slip the critical slip weakening distance dc is of the order of 1 to 10 m these values are extrapolated to higher normal stresses assuming that dc is rather a thermal parameter than a parameter related to a true characteristic length the calculation shows that dimensionally dc 1 n2 where n is the normal stress applied on the fault the inferred dc values range from a few centimeters at 10 mpa normal stress to a few hundreds of microns at 100 mpa normal stress microscopic observations show partial amorphization and dramatic grain size reduction down to the nanometer scale localized in a narrow zone of about 1 to 10 m thickness fracture energy gc is calculated from the mechanical curves and compared to surface energy due to grain size reduction and energies of mineralogic transformations we show that most of the fracture energy is either converted into heat or radiated energy the geophysical consequences of thermal dehydration of bonded water during seismic slip are then commented in the light of mineralogical and poromechanical data of several fault zones which tend to show that this phenomenon has to be taken into account in most of subsurface faults and in hydrous rocks of subducted oceanic crust

igneous emplacement in a shear zone termination the biotite granite at strontian scotland deformed xenolith strain data together with other structural information indicate that the biotite granite body 90 sq km of the strontian complex scotland was emplaced in the extensional termination of a dextral transcurrent shear zone this shear zone is a splay of the major great glen fault which lies along the southern boundary of the granite siting of the shear zone splay was probably controlled by a a slight releasing bend in the great glen fault in this area and b a large pre existing asymetric synform in proterozoic metasedimentary country rocks which intersects the great glen fault trace at a high angle a model is proposed in which moine thrust caledonian compression at ca 435 ma activated the great glen fault dextrally dextral movements around the releasing bend detached a flat segment from the inside fault wall and the biotite granite was emplaced side ways at depths of about 15 km as a sheet into this extensional listric fault bounded cavity

metamorphic and structural evolution of the early proterozoic puolankajrvi formation finland ii the pressure temperature deformation composition path the paragenetic relationships between sillimanite andalusite kyanite chlorite cordierite biotite garnet and staurolite in the early proterozoic puolankajarvi formation pjf together with mineral compositions are used to construct a partial petrogenetic grid for metapelites with significant mn content mno 0 1 0 5 by adding a six phase invariant point over the garnet absent invariant point for mn free amf phases the grid and textural relations of the pjf are used to construct part of the p t deformation path for the pjf relatively short deformation pulses and associated flow of oxidizing fluid along shear zones were responsible for the paragenetic and compositional changes during cooling and decompression at 600 500 c and 6 0 2 5 kbar oxidation led to decreased fe2 and further stressed the importance of mn increased mn divalent cations a tectonothermal evolution of the kainuu schist belt is presented which includes crustal thinning and steepening of a previously established thermal gradient this was followed by thrusting and folding of the isotherms into a thermal antiform on the western side of the belt

forest roads and geomorphic process interactions cascade range oregon a major flood in february 1996 triggered more than 100 geomorphic features affecting forest roads in a 181 km 2 study area in the western cascade range oregon eight types of features including mass movements and fluvial features were mapped measured and analysed using geographic information systems and sediment budgets for the road network although roads functioned as both production and depositional sites for mass movements and fluvial processes the net effect of roads was an increase in basin wide sediment production debris slides from mobilized road fills were the dominant process of sediment production from roads road related sedimentation features were concentrated in a portion of the study area that experienced a rain on snow event during the storm and was characterized by the oldest roads and steep slopes underlain by unstable highly weathered bedrock the downslope increase in frequency of features and volumes of sediment produced combined with the downslope increase in relative frequency of fluvial over mass wasting processes suggests that during an extreme storm event a road network may have major impacts on stream channels far removed from initiation sites overall this study indicated that the nature of geomorphic processes influenced by roads is strongly conditioned by road location and construction practices basin geology and storm characteristics published in 2001 by john wiley sons ltd

testing models for the development of spiral shaped inclusion trails in garnet porphyroblasts to rotate or not to rotate that is the question the formation of spiral shaped inclusion trails ssits is problematical and the two viable models for their formation involve opposite shear senses along the foliation in which the porphyroblasts are growing one model argues for porphyroblast rotation with respect to a geographically fixed reference frame whereas the other argues for no such porphyroblast rotation but instead rotation of the matrix foliation around the porphyroblast thus porphyroblasts with ssits cannot be used as shear sense indicators until it is conclusively determined which model best explains them any successful model must explain features associated with ssits including 1 foliation truncation zones 2 smoothly curving ssits 3 millipede microstructure 4 total inclusion trail curvature in median sections 5 porphyroblasts with ssits that have grown together 6 evidence for relative porphyroblast displacements 7 shear sense indicators inside and outside porphyroblasts 8 crenulations associated with porphyroblasts and 9 geometries in sections subparallel to spiral axes axes of rotation a detailed study of these features suggests that most if not all can be explained by both the rotational and non rotational models in spite of these models involving diametrically opposed movement senses therefore geometrical analysis of individual porphyroblast microstructures may not determine which model best explains ssits until the kinematics required to form these microstructures are better understood in particular the sense of shear along a developing crenulation cleavage specific tests for determining the shear sense along crenulation cleavages are proposed and results of such tests may conclusively resolve the debate over how ssits form

amorphous material in high strain experimental fault gouges the microstructures of gouges produced in room temperature rotary shear sliding experiments were examined by transmission electron microscopy gouges were produced by sliding on ground surfaces of granite quartzite or marble except for one experiment in which a 1 mm thick simulated gouge layer was used water was added to the sliding surfaces of all but one sample crystal plastic processes play no role in the granite and quartzite gouges and a minor role in the marbles all of the gouges consist of mostly submicron crystalline fragments in addition the granite gouges contain 5 60 amorphous material and the quartzite gouge contains 50 amorphous material in the granite samples the composition of the amorphous material commonly lies between k rich and na ca rich feldspars although portions may be silica rich the microstructural relations suggest that the amorphous material forms by comminution of fragments rather than by melting the amount of amorphous material increases and the size of the largest crystalline fragments decreases with an increase in average shear strain although the microstructure is nearly uniform throughout each granite gouge layer these observations suggest that after slip becomes localized on y shear surfaces and or r1 riedel shears the entire gouge layer must continue to undergo deformation it is suggested that cyclic deformation in the gouge must occur to accommodate the passage of geometric irregularities on the active slip surfaces

a model for the development of a domainal quartz c axis fabric in a coarse grained gneiss abstract quartz c axis fabrics in high grade coarse grained layered gneisses reveal a distinctive pattern with three perpendicular maxima which can be interpreted in terms of syntectonic recrystallization and growth mapping of the distribution of c axes within a single thin section demonstrates that the fabric is domainal fabric domains are on the scale of millimetres and are associated with individual quartz rich patches no single domain exhibits the overall fabric of the complete thin section within each domain weighting of the c axis fabric by the area of each quartz grain demonstrates that the largest grains have their c axes preferentially at the maxima a model is presented to account for the development of this fabric grains which can keep their stored strain energy to a minimum by the use of a single glide system oriented approximately parallel to the plane and direction of maximum resolved shear stress grow at the expense of other grains the largest most successful grains deform by glide on only one of either the basal a or the prism a systems depending on the crystallographic orientation of the grain each domain develops its own glide direction by co operation of the glide systems of its constituent grains the successful grains in a domain are those which can accommodate that direction the bulk strain of the rock is achieved by the addition of the strains distinct to each domain

microstructural shear criteria associated with grain boundary sliding during ductile deformation abstract experimental studies on rock analogues are described which establish that certain microstructures diamond grain structures tabular grain structures and asymmetric grain boundary bulges can be used to determine i if deformation was coaxial or non coaxial and ii the sense of shear in zones of non coaxial deformation mechanisms for the development of the structures are described which involve the linked operation of grain boundary sliding and migration

silica gel formation during fault slip evidence from the rock record dynamic reduction of fault strength is a key process during earthquake rupture many mechanisms for causing coseismic weakening have been proposed based on theory and laboratory experiments including silica gel lubrication however few have been observed in nature here we report on the fi rst documented occurrence of a natural silica gel coating a fault surface the corona heights fault slickenside in san francisco california is covered by a shiny layer of translucent silica microstructures in this layer show fl ow banding armored clasts and extreme comminution compared to adjacent cataclasites the layer is composed of 100 nm to 1 m grains of quartz hydrous crystalline silica and amorphous silica with 10 100 nm inclusions of fe oxides and ellipsoidal silica colloids kinematic indicators and mixing with adjacent cataclasites suggest the shiny layer was fl uid during fault slip the layer therefore represents a relict silica gel that formed during fault motion and which could have resulted in frictional instability these observations confi rm that the silica gels formed in rock friction experiments do occur in natural faults and therefore that silica gel formation can act as a dynamic weakening mechanism in faults at shallow crustal conditions

natural and experimental evidence of melt lubrication of faults during earthquakes melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake here we estimate the dynamic shear resistance f in the presence of friction induced melts from both exhumed faults and high velocity 1 28 meters per second frictional experiments exhumed faults within granitoids tonalites indicate low f at 10 kilometers in depth friction experiments on tonalite samples show that f depends weakly on normal stress extrapolation of experimental data yields f values consistent with the field estimates and well below the byerlee strength we conclude that friction induced melts can lubricate faults at intermediate crustal depths