comparison of smectite and illite rich gouge frictional properties application to the updip limit of the seismogenic zone along subduction megathrusts along plate boundary subduction thrusts the transformation of smectite to illite within fault gouge at temperatures of 150 c is one of the key mineralogical changes thought to control the updip limit of seismicity if correct this hypothesis requires illite rich gouges to exhibit frictionally unstable velocity weakening behavior here we report on laboratory experiments designed to investigate the frictional behavior of natural and synthetic clay rich gouges we sheared 5 mm thick layers of commercially obtained pure ca smectite a suite of smectite quartz mixtures and natural illite shale grain size ranging from 2 to 500 m in the double direct shear geometry to shear strains of 7 30 at room humidity and temperature xrd analyses show that the illite shale contains dominantly clay minerals and quartz within the clay sized fraction 40 mpa our data specifically the velocity strengthening behavior of illite shale under a wide range of conditions do not support the hypothesis that the smectite illite transition is responsible for the seismic aseismic transition in subduction zones we suggest that other depth and temperature dependent processes such as cementation consolidation and slip localization with increased shearing may play an important role in changing the frictional properties of subduction zone faults and that these processes in addition to clay mineralogy should be the focus of future investigation

frictional resistance of faults during accelerating and decelerating earthquake slip the dynamic friction along faults controls earthquake ruptures in the crust but many previous studies have quantified this value only for constant slip rates experiments accounting for the more realistic condition of changing slip rates suggest that faults undergo a sequence of strengthening weakening and healing during acceleration and deceleration of slip the dynamic friction of faults during earthquake slip is a critical control on earthquake ruptures in the crust extrapolation of brittle crack theories to natural earthquakes1 2 3 has led to the commonly held view that fault friction reduces during rapid earthquake slip a process known as slip weakening1 high velocity gouge experiments4 5 and recent analyses of thermal pressurization6 7 and frictional melting8 support such a notion however these studies dealt with constant rates of slip along faults here we present the results of experiments aimed at understanding the frictional behaviour of fault zone materials under variable slip rates conditions that are more representative of natural earthquakes our results show that faults undergo a sequence of strengthening weakening and healing during acceleration and deceleration of slip such a sequence may be explained by the extrapolation of rate and state frictional behaviour9 10 at low slip velocities to more realistic slip rates but involving different physical mechanisms and a different scale the initial strengthening should impose a barrier for rupture growth into large earthquakes the healing on decelerating fault motion may lead to pulse like earthquake ruptures11 12 13 14 and static stress drops that are low in comparison with the dynamic stress changes15

effects of simulated fault gouge on the sliding behavior of tennessee sandstone nonclay gouges stick slip has been considered to be a mechanism of shallow focus earthquakes along pre existing faults and thus laboratory studies relevant to stick slip may lead to a better understanding of the mechanisms of the earthquakes and eventually to an effective prediction and or control of them this paper deals with the effects of various simulated gouges on the sliding behavior of rocks with special emphasis on how fault gouge alters potentially unstable behavior of a brittle rock about 150 specimens of tennessee sandstone with various simulated gouges along a 35 precut are deformed dry in a triaxial apparatus at room temperature with shortening rate of about 2 10 4cm s and at confining pressures to 300 mpa tennessee sandstone is a brittle and strong rock quartz cemented quartzose sandstone which consistently shows stick slip without simulated gouge at confining pressures above 30 40 mpa sliding behavior with a gouge layer depends markedly on the material used to simulate the gouge experimental results from monomineralic gouges show that mohs hardness of a mineral is a useful parameter to predict the general sliding behavior the most unstable sliding is associated with gouge composed of minerals with intermediate hardness dolomite anhydrite and calcite these gouges undergo the transition from stable sliding to stick slip at pressures of 50 80 mpa gouge composed of hard mineral such as quartz or feldspar behave more stably but stick slip occurs at pressures above 250 mpa only stable sliding is observed for gouge composed of soft minerals like halite although anhydrite gouge shows violent stick slip at 100 mpa pressure whereas only stable sliding occurs for quartz at the same pressure when they are mixed the behavior changes systematically with composition the inclusion of only 10 anhydrite permits stick slip and hence even a minor constituent mineral of fault gouge may alter the sliding mode for gouge composed of two distinct layers the more stabilizing member of the two dominates the behavior and the behavior is considerably different from that of homogeneously mixed gouge with the same bulk composition this suggests the significance of internal structures of natural fault zone in understanding the effects of fault zone materials on the fault motion the gouge composed of calcite or a mineral harder than calcite all show high and approximately the same ultimate frictional strength with an exception of fluorite the frictional strength is intermediate for fluorite galena and barite gouges and it is low for halite gouge

frictional sliding of dolomite a variation in constitutive behavior fault slip occurs via earthquakes or stable creep depending on the manner in which frictional resistance varies with sliding velocity and displacement if the form of this dependence is a function of rock type observed spatial variations in slip behavior along faults could be explained by lithologic variation we have used a rotary shear apparatus to investigate the frictional response of dolomite marble to changes in sliding velocity we have modeled the results using a state variable constitutive law for rock friction and a numerical method to solve for the interaction between the friction law and the compliance of our machine dolomite marble displays steady state velocity strengthening as contrasted with granite and quartzite which show velocity weakening at the same conditions to model the dolomite results it is necessary to use two state variables and surprisingly the parameters specifying the decay magnitudes associated with these state variables differ in sign from each other the magnitude of the parameter associated with the longer decay is negative leading to a downward decay of frictional strength associated with a decrease in velocity if the shorter decay is of sufficient magnitude as we observe at low velocity it is possible for the machine rock system to exhibit instability and oscillatory behavior even though the steady state response is velocity strengthening another way in which dolomite contrasts with granite and quartzite is that the friction parameters vary strongly with velocity a transition from unstable to stable sliding with increasing velocity has been observed previously and our observed variation of the constitutive parameters with velocity can explain this behavior there is some indication that the evolution of the state variables for dolomite occurs as a function of time rather than displacement in contrast with granite and quartzite the frictional behavior of dolomite shows that the constitutive laws that have been developed based on results from granite and quartzite are inadequate to describe all rock types and that more general laws are required

late devonian transpressional tectonics in spitsbergen svalbard and implications for basement uplift of the sorkapp hornsund high abstract the late devonian svalbardian event relates to the final activity in the caledonian orogen and affected devonian strata in spitsbergen by major folding oblique thrusting and basement uplift in southern spitsbergen the devonian deformation and the complementary presumed mid carboniferous adriabukta event deformation caused uplift of the sorkapp hornsund basement high or horst this high is fault bounded by devonian sandstones and a questionably aged early or mid carboniferous mudstone unit adriabukta formation the adriabukta formation at hornsund occurs in the core of a major syncline with underlying devonian strata in the west limb all truncated in the footwall by a steep east side up oblique reverse fault mid to late carboniferous rifting reversed the motion and produced rift fill deposits and these strata overlie the deformed devonian rocks and the adriabukta formation with an angular unconformity a similar basin architecture and major syncline bounded by a reverse fault with lateral movement characterize the svalbardian deformation in the mimerdalen pyramiden area at billefjorden farther north similarity also exists between a late devonian unit planteklofta formation at mimerdalen and the adriabukta formation at hornsund and we question the previous interpretation of the adriabukta formation as carboniferous rather we suggest that the adriabukta and svalbardian deformation events may have been part of the same event

the frictional behavior of lizardite and antigorite serpentinites experiments constitutive models and implications for natural faults laboratory studies of the frictional behavior of rocks can provide important information about the strength and sliding stability of natural faults we have conducted friction experiments on antigorite and lizardite serpentinites rocks common to both continental and oceanic crustal faults we conducted both velocity step tests and timed hold tests on bare surfaces and gouge layers of serpentinite at room temperature we find that the coefficient of friction of lizardite serpentinite is quite low 0 15 0 35 and could explain the apparent low stresses observed on crustal transform faults while that of antigorite serpentinite is comparable to other crustal rocks 0 50 0 85 the frictional behavior of both types of serpentinite is well described by a two mechanism model combining state variable dominated behavior at high slip velocities and flow dominated behavior at low velocities the two mechanism model is supported by data from velocity step tests and timed hold tests the low velocity behavior of serpentinite is strongly rate strengthening and should result in stable fault creep on natural faults containing either antigorite or lizardite serpentinite

uplift of deep crust during orogenic extensional collapse a model based on field studies in the sogn sunnfjord region of western norway the western gneiss region wgr in norway experienced high pressure metamorphism during silurian devonian continent continent collision the eclogite bearing lower crust is separated from the middle and upper crust by major detachment zones formed during extensional collapse of the orogen formation of the devonian basins is related to the extension the footwall of the detachment zones comprises three structural and metamorphic zones the upper zone zone 1 is characterized by penetrative homogeneous down to the west simple shear developed under retrograde greenschist facies metamorphism zone 2 suffered inhomogeneous simple shear of the same polarity petrography and mineral chemistry data from the lower zone zone 3 show a record of initial eclogite facies metamorphism at 600 c and 16 kbar which was decompressed almost isothermally to amphibolite facies conditions at 550 c and 10 12 kbar both the eclogite and amphibolite facies metamorphism developed in a regime of pure shear with vertical shortening the rapid decompression records an approach of approximately 20 km to the surface related to uplift that was probably the result of the removal of a thickened thermal boundary layer in the mantle lithosphere the pure shear regime which developed initially in the lower crust was truncated by zones of simple shear as the lower crust was uplifted to middle and upper crustal levels extension by simple shear in the upper crust was rooted in the lower crust where extension occurred by pure shear the shear zones in zones 1 and 2 did not penetrate the pure shear regime of the lower crust a considerable amount of tectonic stripping of the orogenic welt predates deposition of the devonian sedimentary basins

segmentation of the caledonian orogenic infrastructure and exhumation of the western gneiss region during transtensional collapse the ultra high pressure western gneiss region of the norwegian caledonides represents an archetypical orogenic infrastructure of a continent continent collision zone to test established exhumation models we synthesize the geochronology and structures of major basement windows and provide new ages from poorly dated areas migmatite u pb zircon samples date melt crystallization at c 405 ma in the oygarden complex expanding the spatial extent of devonian migmatization micas from shear zones in the oygarden and gulen domes yield 40ar 39ar ages mostly between 405 and 398 ma recording the exhumation of metamorphic core complexes on a larger scale the youngest ages of various geochronometers in different segments of the western gneiss region show abrupt breaks 10 30 myr across low angle detachments and sinistral transfer zones which also correspond to metamorphic and structural discontinuities we explain the segmentation of the orogenic infrastructure by partitioned post orogenic transtension due to lateral and vertical rheological contrasts in the orogenic edifice strong cratonic foreland and orogenic wedge v soft infrastructure differential crustal stretching dragged out deep levels of the orogenic crust below low angle detachments and became progressively dominated by sinistral transfer zones collapse obliterated the syn collisional structure of the orogenic root and resulted in the diachronous exhumation of distinct infrastructure segments supplementary material complete analytical results are available at https doi org 10 6084 m9 figshare c 5241710

a microphysical model for fault gouge friction applied to subduction megathrusts a microphysical model is developed for the steady state frictional behavior of illite quartz fault gouge and applied to subduction megathrust p t conditions the model assumes a foliated phyllosilicate supported microstructure which shears by rate independent frictional slip on the aligned phyllosilicates plus thermally activated deformation of the intervening quartz clasts at low slip rates or high temperatures the deformation of the clasts is easy accommodating slip on the foliation without dilatation with increasing velocity or decreasing temperature the shear of the clasts becomes more difficult increasing bulk shear strength until slip is activated on inclined portions of the phyllosilicate foliation where it anastomoses around the clasts slip at these sites leads to dilation involving clast matrix debonding balanced at steady state by compaction through thermally activated clast deformation model predictions taking pressure solution as the thermally activated mechanism show three regimes of velocity dependent frictional behavior at temperatures in the range of 200 500 c with velocity weakening occurring at 300 400 c in broad agreement with previous experiments on illite quartz gouge effects of slip rate normal stress and quartz fraction predicted by the model also resemble those seen experimentally extrapolation of the model to earthquake nucleation slip rates successfully predicts the onset of velocity weakening behavior at the updip seismogenic limit on subduction megathrusts the model further implies that the onset of seismogenesis is controlled by the thermally activated initiation of fault rock compaction through pressure solution of quartz which counteracts dilatation due to slip on the fault rock foliation

the keisarhjelmen detachment records silurian devonian extensional collapse in northern svalbard at the junction of the atlantic and arctic margins the crustal scale keisarhjelmen detachment of northwest svalbard records previously unrecognized magnitudes of extension the detachment separates a corrugated metamorphic core complex in the footwall from a mantling devonian supradetachment basin in the hanging wall the detachment has a top n displacement of more than 50 km which is aligned with the map scale corrugations and an upwards ductile to brittle transition with shear related footwall retrogression this configuration has striking similarities to extensional collapse detachments in the paired scandinavian greenland caledonides but orientation and position link the detachment with the ellesmerian orogen this article is protected by copyright all rights reserved

effects of temperature and co2 on the frictional behavior of simulated anhydrite fault rock the frictional behavior of anhydrite bearing faults is of interest to a the safety and effectiveness of co2 storage in anhydrite capped reservoirs b seismicity induced by hydrocarbon production and c natural seismicity nucleated in evaporite formations we performed direct shear experiments on simulated anhydrite fault gouges at a range of temperatures 80 150 c and sliding velocities 0 2 10 ms 1 under a fixed effective normal stress of 25 mpa four types of experiments were conducted 1 dry experiments 2 experiments pressurized with water 3 dry experiments pressurized with co2 and 4 wet experiments pressurized with co2 fluid pressures of 15 mpa were used when applied over the temperature range investigated water saturated samples were found to be up to 15 frictionally weaker than dry equivalents wet samples containing co2 were also up to 15 weaker than co2 free equivalents dry sample strength without co2 was independent of temperature whereas wet samples without co2 strengthened 10 from 80 to 150 c samples containing co2 weakened by 4 dry and 10 wet from 80 to 150 c under the p t conditions investigated only dry anhydrite fault gouge showed velocity weakening behavior above 120 c required for faults to potentially generate earthquakes assuming natural fault gouges are wet in situ seismicity is unlikely to nucleate in anhydrite rich faults though the presence of dolomite or reaction produced calcite may change seismic potential co2 penetration into wet anhydrite rich faults may trigger slip on critically stressed faults due to the observed short term co2 weakening effects excluding possible formation of secondary minerals but is not expected to influence slip stability

compaction creep of simulated anhydrite fault gouge by pressure solution theory v experiments and implications for fault sealing the sealing and healing behaviour of faults filled with anhydrite gouge by processes such as pressure solution is of interest in relation both to the integrity of faults cutting geological storage systems sealed by anhydrite caprocks and to seismic events that may nucleate in anhydrite bearing sequences such as those present in the seismogenic zone beneath the apennines we have developed a detailed series of kinetic models for pressure solution in anhydrite fault gouge allowing for dissolution diffusion and precipitation control to estimate the time scale on which such sealing and healing effects occur we compare the models obtained with previously reported experimental data on compaction creep rates in simulated anhydrite fault gouge tested under wet upper crustal conditions the results confirm earlier indications that compaction under these conditions likely occurs by diffusion controlled pressure solution applying our most rigorous model for diffusion controlled pressure solution constrained by the fit to the experimental data we infer that anhydrite fault sealing will occur in a few decades at most which is rapid compared with both co2 storage time scales and with the recurrence interval for seismicity in the apennines

new insights into crustal structure cenozoic magmatism co2 degassing and seismogenesis in the southern apennines and irpinia region from local earthquake tomography we present high resolution vp and vp vs models of the southern apennines italy computed using local earthquakes recorded from 2006 to 2011 with a graded inversion scheme that progressively resolves the crustal structure from the large scale of the apennines belt to the local scale of the normal fault system high vp bodies defined in the upper crust and midcrust under the external apennines are interpreted as extensive mafic intrusions revealing anorogenic magmatism episodes that broadened on the adriatic domain during paleogene under the mountain belt a low vp region annular to the neapolitan volcanic district indicates the existence of a thermal fluid anomaly in the midcrust coinciding with a shallow moho and diffuse degassing of deeply derived co2 in the belt axial zone low vp vs gas pressurized rock volumes under the apulian carbonates correlate to high heat flow strong co2 dominated gas emissions of mantle origin and shallow carbonate reservoirs with pressurized co2 gas caps we hypothesize that the pressurized fluid volumes located at the base of the active fault system influence the rupture process of large normal faulting earthquakes like the 1980 mw6 9 irpinia event and that major asperities are confined within the high vp apulian carbonates this study confirms once more that preexisting structures of the pliocene apulian belt controlled the rupture propagation during the irpinia earthquake the main shock broke a 30 km long ne dipping seismogenic structure whereas delayed ruptures both the 20 s and the 40 s subevents developed on antithetic faults reactivating thrust faults located at the eastern edge of the apulian belt

frictional properties of sedimentary rocks and natural fault gouge from the longmen shan fault zone sichuan china in this paper we report friction experiments performed on samples collected from the region hit by the 2008 wenchuan earthquake in the longmen shan fault zone lfz of sichuan southwestern china the materials tested consisted of simulated gouges prepared from intact clay rich mudstone and sandstone a calcite limestone plus a natural fault gouge from a trenched surface rupture cutting the mudstone and sandstone the clay rich samples including the natural gouge were dominated by illite and quartz in our experiments we sheared 1 mm thick gouge layers between saw cut driver blocks using a triaxial testing machine at conditions corresponding to 2 km depth in the lfz temperature was varied from 25 c to 150 c and to investigate the velocity dependence of friction we stepped the shear displacement rate between 1 22 and 0 122 m s our results show that the natural gouge was more illite rich and much weaker than the protolith mudstone and sandstone and showed a steady state friction coefficient of 0 4 compared with 0 6 for the latter the limestone gouge displayed values of 0 6 0 7 all samples except the limestone showed stable velocity strengthening slip the limestone showed velocity strengthening at 25 c 50 c but quasi static oscillations at 100 c 150 c along with velocity weakening behavior at 150 c we apply our results to discuss the role of the sedimentary rocks studied during events such as the wenchuan earthquake and argue that the clay rich sediments of the region may have a damping effect upon ruptures propagating from depth whereas the limestone may accelerate propagation producing significant stress drops

deciphering late devonian early carboniferous p t t path of mylonitized garnet mica schists from prins karls forland svalbard this is the peer reviewed version of the following article ko minska k spear f s majka j faehnrich k manecki m piepjohn k dallmann w k 2020 deciphering late devonian early carboniferous p t t path of mylonitized garnet mica schists from prins karls forland svalbard journal of metamorphic geology which has been published in final form at https doi org 10 1111 jmg 12529 this article may be used for non commercial purposes in accordance with wiley terms and conditions for use of self archived versions

under the hood of the earthquake machine toward predictive modeling of the seismic cycle advances in observational laboratory and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power to explore that possibility we developed an integrative and fully dynamic model of the parkfield segment of the san andreas fault the model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude m w 6 0 main shocks including events similar to the ones in 1966 and 2004 and provides an excellent match for the detailed interseismic coseismic and postseismic observations collected along this fault during the most recent earthquake cycle such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins

velocity dependence of strength and healing behaviour in simulated phyllosilicate bearing fault gouge abstract despite the fact that phyllosilicates are widespread in fault zones little is known about the strength of phyllosilicate bearing fault rocks under brittle ductile transitional conditions in this study we explored the steady state strength and healing behaviour of a simulated phyllosilicate bearing fault rock i e muscovite plus halite and brine at room temperature normal stresses of 1 9 mpa atmospheric fluid pressure and sliding velocities of 0 001 13 m s using a rotary shear apparatus while 100 halite and 100 muscovite samples exhibit rate independent frictional brittle behaviour the strength of mixtures containing 10 50 muscovite is both normal stress and sliding velocity dependent at low velocities 1 m s velocity weakening frictional behaviour occurs along with the development of a structureless intermixed cataclastic microstructure the steady state porosity of samples deformed in this regime increases with increasing sliding velocity we propose that this behaviour involves competition between dilatation due to granular flow and compaction due to pressure solution towards higher sliding velocities dilatation increasingly dominates over pressure solution compaction so that porosity increases and frictional strength decreases during periods of zero slip pressure solution compaction occurs causing a significant strength increase on reshearing our results imply that cataclastic overprinting of mylonitic rocks in natural fault zones does not require any changes in temperature or effective pressure conditions but can simply result from oscillating fault motion rates our healing data suggest that foliated aseismically creeping fault segments will remain weak and aseismic whereas segments that have slipped seismically will rapidly re strengthen and remain in the unstable velocity weakening regime

the effects of lateral variations in rock composition and texture on anhydrite caprock integrity of co2 storage systems abstract we investigated the effect of rock texture and composition on the mechanical strength and volumetric behaviour of anhydrite rich caprock conventional triaxial experiments were performed at 80 c confining pressures of 1 5 35 mpa and strain rates of 10 5 s 1 both dry and in the presence of fluids we determined the failure envelope and the effect of fluids upon it for anhydrite displaying an equigranular texture consisting of euhedral grains we observed a general pattern of increasing peak compressive strength with increasing confining pressure consistent with a previous study on anhydrite from the same formation which showed an irregular texture consisting of interlocking acicular grains embedded in a fine grained matrix the peak strength of euhedral anhydrite was found to be 15 65 lower than that of acicular anhydrite no chemical effects were observed for the fluids tested hydraulic fracturing experiments showed the tensile strength to be approximately 4 mpa for euhedral and 6 mpa for acicular anhydrite we combined the failure envelopes with simple analytical calculations on the effect of cooling on in situ stress showing that tensile caprock failure due to cooling would be unlikely for both types of anhydrite assuming a hypothetical reservoir at a depth of 3800 m however it should be noted that tensile failure may pose an issue for shallower reservoirs or weaker caprock formations

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

frictional properties of simulated anhydrite dolomite fault gouge and implications for seismogenic potential the frictional properties of anhydrite dolomite fault gouges and the effects of co2 upon them are of key importance in assessing the risks associated with co2 storage in reservoir formations capped by anhydrite dolomite sequences and in understanding seismicity occurring in such formations such as the italian apennines therefore we performed velocity stepping direct shear experiments on simulated dolomite anhydrite and 50 50 anhydrite dolomite gouges at representative in situ conditions 120 c and ne 25 mpa they were conducted under vacuum or else using water or co2 saturated water as pore fluid pf 15 mpa friction coefficients varied between 0 55 and 0 7 all dry samples exhibited velocity weakening behavior whereas all wet samples exhibited velocity strengthening behavior without or with co2 this is consistent with trends previously reported for such gouges a compilation of literature data shows that the transition from velocity strengthening to velocity weakening occurs in these materials between 80 and 120 c when dry and between 100 and 150 c when wet this implies little seismogenic potential for wet dolomite anhydrite and mixed gouges under co2 storage conditions at 2 4 km depth seismic slip in the italian apennines at depths of 6 km and beyond may be explained by the velocity weakening behavior expected in anhydrite and especially dolomite at temperatures above 150 c

carbon dioxide earth degassing and seismogenesis in central and southern italy 1 we present the first regional map of co2 earth degassing from a large area most of central and south italy derived from the carbon of deep provenance dissolved in the main springs of the region the investigation shows that a globally significant amount of deeply derived co2 10 of the estimated global co2 emitted from subaerial volcanoes is released by two large areas located in western italy the anomalous flux of co2 suddenly disappears in the apennine in correspondence to a narrow band where most of seismicity concentrates here at depth the gas accumulates in crustal traps generating co2 overpressurized reservoirs which induce seismicity

comment on the keisarhjelmen detachment records silurian devonian extensional collapse in northern svalbard this is the peer reviewed version of the following article dallmann w piepjohn k 2018 comment on the keisarhjelmen detachment records silurian devonian extensional collapse in northern svalbard terra nova 30 4 319 321 which has been published in final form at https doi org 10 1111 ter 12335 this article may be used for non commercial purposes in accordance with wiley terms and conditions for use of self archived versions

tourmaline in the central swedish ore district more than 40 recently discovered tourmaline occurrences have been investigated in the mid proterozoic bergslagen ore district of central sweden some are spatially associated with ores others with zones of leaching remobilization and migmatization among the tourmaline bearing ore deposits are the dammberg znpb fe sulphide deposit the sala pb zn ag deposit the dalkarlsberg pershyttan and haksberg fe oxide deposits the leja cu deposit and the zinkgruvan zn pb ag deposit tourmaline has been recorded a as tourmalinites and tourmaline bearing chemical sediments b in tourmaline bearing skarns c in tourmaline quartz veins d as disseminations along the foliation in schists e in tourmaline pegmatites f in tourmalinized haloes in metavolcanites along tourmaline pegmatites and g in late joints tourmalinites tourmaline bearing chemical sediments and tourmaline bearing skarns are spatially associated with sulphide and oxide mineralizations the dravite components in these tourmalines are proportional to the size of zn pb sulphide mineralizations tourmalines from quartz veins close to and within ore deposits contain high zr and cr contents with increasing distance away from these deposits the zr and cr contents fall significantly tourmalines from pegmatites have inherited a number of trace element enrichments through partial melting and assimilation of volcaniclastic sediments into granitic melts despite magmatic homogenization zn contents in these tourmalines reflect the proximity of zn pb sulphide deposits decreasing away from them tourmalines from late joints with zn contents above the 100 ppm level are also indicative for the proximity of zn pb sulphide mineralizations thus some trace elements in these tourmalines may represent suitable exploration tools

earthquake rupture propagation inferred from the spatial distribution of fault rock frictional properties abstract the frictional properties of fault rocks that rupture during earthquakes are expected to affect the nucleation and propagation of seismic slip but these properties and their variation under in situ earthquake conditions are typically unknown here we present experimental results on the variation of frictional properties of fault rocks from the alhama de murcia fault amf in se spain which ruptured in the 2011 lorca earthquake in the epicentral area the fault zone is characterized by the presence of abundant phyllosilicate rich gouges that surround more competent fractured lenses of the phyllitic basement measurements of lineaments and orientations of r shears in the gouges are consistent with cmt solutions of the 2011 lorca earthquake suggesting that the bulk of displacement on the amf was accommodated within similar gouges at depth in order to evaluate the frictional properties of the fault rocks of the amf we performed rotary shear experiments under hydrothermal conditions of samples obtained from surface outcrops of the amf zone progressively simulating deeper levels in the crust by stepping temperature effective normal stress and fluid pressure a negative velocity dependence of friction expressed as a negative value of the rate and state friction rsf parameter a b and which is a prerequisite for the nucleation of an instability was observed only for samples derived from competent lenses under hydrothermal conditions gouge derived samples exhibited only velocity strengthening properties i e positive values of a b which increase with deeper conditions in particular with increasing effective normal stress combined with our outcrop observation of the anastomosing nature of gouges surrounding more competent lenses of fractured protolith our results suggest that the 2011 lorca earthquake nucleated in the competent lenses followed by propagation of slip into the frictionally weaker gouges the inferred upward propagation direction of the 2011 lorca earthquake is consistent with propagation of the rupture into the velocity strengthening gouges which at shallower levels provide a smaller barrier to seismic slip due to lower values of effective normal stress and a b our results suggest that the spatial variation of the frictional properties along the amf was an important factor controlling the nucleation and propagation of seismic slip which together with the shallow hypocenter close to the city of lorca led to serious damage we infer that understanding of such variations in frictional properties may significantly improve seismic hazard evaluations in tectonically active regions

interseismic re strengthening and stabilization of carbonate faults by non dieterich healing under hydrothermal conditions abstract friction experiments consisting of a velocity stepping stage a slide hold slide shs stage and a second velocity stepping stage have been performed to study the frictional healing behavior of carbonate fault gouge and the effects of healing on the velocity dependence of friction at 20 140 c and at 50 mpa effective normal stress dry experiments show classical dieterich healing characterized by a transient peak in friction after each hold period with no effects of shs testing on steady state friction or velocity dependence by contrast the wet tests show 1 an increase in apparent steady state friction upon re sliding after a hold period and 2 a pronounced increase in the velocity dependence parameter a b after the shs stage while the first of these non dieterich type healing effects has been observed in previous hydrothermal experiments on simulated quartz gouges it has not been reported previously for carbonate gouges the observed effect of shs testing on a b has never been reported our findings suggest that under in situ hydrothermal conditions interseismic fluid assisted deformation processes such as pressure solution can significantly promote fault re strengthening in carbonates and can cause slip stabilization if the results are applicable to active faults in carbonate terrains they have important implications for understanding how the extent of the seismogenic zone and how earthquake magnitude and aftershock distributions may evolve with repeated cycles of natural seismicity and interseismic healing

crustal structure of northwestern svalbard and the adjacent yermak plateau evidence for oligocene detachment tectonics and non volcanic breakup summary in 1999 new seismic refraction data were collected off northwestern svalbard and the adjacent yermak plateau a 260 km long profile provides detailed velocity information for the northeastern edge of the eurasian continent and the adjacent yermak plateau north of forlandsundet graben the depth of the moho varies between 23 and 28 km and remains at this depth to the northern edge of the profile at 81 n the crustal lithology off western svalbard can be related to the basement province west of the raudfjorden fault zone off the northern shoreline of svalbard the structure of the tertiary danskoya basin is mapped below this a late silurian early devonian basin with seismic velocities between 5 1 and 5 8 km s 1 and a thickness of up to 8 km is present a palaeozoic sequence of up to 6 km thickness is expected below the tertiary cover north of the danskoya basin an earlier suggestion that oligocene rift processes affected the southern yermak plateau is confirmed a detachment structure is situated below the palaeozoic basin below danskoya basin which is probably a consequence of simple shear tectonics the middle crust exhibits low seismic velocities above the detachment fault the lowermost crust beneath is slightly contaminated by mantle derived melts which is deduced by the slightly elevated velocities of the lowermost crust these melts can be attributed to decompressive melting caused by modest uplift of the moho during stretching the velocity depth model provides no evidence for large magmatic activity which implies a non volcanic rifted margin history this leads to the assumption that the proposed yermak hotspot during the breakup of svalbard from northern greenland did not exist

frictional properties of a low angle normal fault under in situ conditions thermally activated velocity weakening the zuccale fault is a regional low angle normal fault exposed on the isle of elba in central italy that accommodated a total shear displacement of 6 8 km the fault zone structure and fault rocks formed at 8 km crustal depth the present day fault structure is the final product of several deformation processes superposed during the fault history in this study we report results from a series of rotary shear experiments performed on 1 mm thick powdered gouges made from several fault rock types obtained from the zuccale fault the tests were done under conditions ranging from room temperature to in situ conditions i e at temperatures up to 300 c applied normal stresses up to 150 mpa and fluid saturated the ratio of fluid pressure to normal stress was held constant at either 0 4 or 0 8 to simulate an overpressurized fault the samples were sheared at a constant sliding velocity of 10 m s for at least 5 mm after which a velocity stepping sequence from 1 to 300 m s was started to determine the velocity dependence of friction this can be represented by the rate and state parameter a b which was determined by an inversion of the data to the rate and state equations friction of the various fault rocks varies between 0 3 and 0 8 similar to values obtained in previous studies and decreases with increasing phyllosilicate content friction decreases mildly with temperature whereas normal stress and fluid pressure do not affect friction values systematically all samples exhibited velocity strengthening conditionally stable behavior under room temperature conditions and a b increased with increasing sliding velocity in contrast velocity weakening accompanied by stick slips was observed for the strongest samples at 300 c and sliding velocities below 10 m s an increase in fluid pressure under these conditions led to a further reduction in a b for all samples so that they exhibited unstable stick slip behavior at low sliding velocity the results suggest that phyllosilicate bearing fault rocks can deform by stable aseismic creep at low resolved shear stress and low shear rate conditions an increase in fluid pressure or loading of stronger portions could lead to a runaway instability the runaway instability might be limited in size because of 1 the fault heterogeneity 2 the observed strengthening at higher sliding velocities and 3 a co seismic drop in pore fluid pressure

slip weakening as a mechanism for slow earthquakes slow earthquakes form part of a spectrum of fault behaviour between steady creep and fast rupture during a normal earthquake laboratory simulations of slow slip in rock samples taken from the nankai subduction zone japan reveal similar characteristics to fast earthquakes implying that some slow slip events could be prematurely arrested earthquakes

reactivation of intrabasement structures during rifting a case study from offshore southern norway abstract pre existing structures within crystalline basement may exert a significant influence over the evolution of rifts however the exact manner in which these structures reactivate and thus their degree of influence over the overlying rift is poorly understood using borehole constrained 2d and 3d seismic reflection data from offshore southern norway we identify and constrain the three dimensional geometry of a series of enigmatic intrabasement reflections through 1d waveform modelling and 3d mapping of these reflection packages we correlate them to the onshore caledonian thrust belt and devonian shear zones based on the seismic stratigraphic architecture of the post basement succession we identify several phases of reactivation of the intrabasement structures associated with multiple tectonic events reactivation preferentially occurs along relatively thick c 1 km relatively steeply dipping c 30 structures with three main styles of interactions observed between them and overlying faults i faults exploiting intrabasement weaknesses represented by intra shear zone mylonites ii faults that initiate within the hangingwall of the shear zones inheriting their orientation and merging with said structure at depth or iii faults that initiate independently from and cross cut intrabasement structures we demonstrate that large scale discrete shear zones act as a long lived structural template for fault initiation during multiple phases of rifting

ultra thick triassic dolomites control the rupture behavior of the central apennine seismicity evidence from magnetic modeling of the l aquila fault zone high resolution tomography from the 2009 l aquila extensional seismic sequence has shown that the mw 6 1 main shock and most of the aftershocks occurred within a high velocity body 6 6 vp 6 8 km s located between depths of 3 and 12 km the nature of the high vp body has remained speculative although exhumed mafic deep crustal and upper mantle rocks serpentinites have been favored we used 3d magnetic anomaly modeling to investigate the plausibility of these favored sources for the l aquila body the modeling does not support the presence of high velocity serpentinites with a 30 50 serpentinization degree and gabbros accordingly we conclude that the high vp body may represent non magnetic upper triassic and possibly lower liassic dolomites that have been drilled in neighboring wells for 2 4 km this conclusion is also consistent with the lack of a coherent gravity anomaly for the body we speculate that ultra thick triassic dolomites reaching a thickness of 8 km may have been deposited in syntectonic wedges formed at the northern margin of the ionian sea where oceanic spreading occurred in mid late triassic times

healing and sliding stability of simulated anhydrite fault gouge effects of water temperature and co2 abstract anhydrite bearing faults are currently of interest to 1 co2 storage sites capped by anhydrite caprocks such as those found in the north sea and 2 seismically active faults in evaporite formations such as the italian apennines in order to assess the likelihood of fault reactivation the mode of fault slip and or fault leakage it is important to understand the evolution of frictional strength during periods of no slip and upon reloading healing and relaxation behavior and of the velocity dependence of friction of anhydrite fault gouge therefore we performed slide hold slide experiments combined with a velocity stepping sequence using simulated anhydrite fault gouge 95 wt caso4 vacuum dry and water wet experiments were performed at temperatures ranging from 20 to 150 c and at an effective normal stress of 25 mpa we also performed tests using dry co2 water wetted co2 and co2 saturated water as pore fluid but only at 120 c if pore fluid was present a fluid pressure of 15 mpa was present vacuum dry samples exhibit similar frictional healing to samples containing lab air but healing is significantly enhanced in wet samples dry samples exhibit velocity weakening behavior at t 120 c and wet samples exhibit velocity strengthening behavior over the full temperature range the presence of co2 does not influence the healing behavior or the velocity dependence of friction samples containing water wetted co2 exhibit behavior similar to wet samples we infer that the healing in dry samples is controlled by plastic asperity creep dieterich type possibly through dislocation creep and or twinning in wet samples healing is inferred to be controlled by increases in contact area and cohesion by pressure solution using a pressure solution rate model to extrapolate healing by contact area growth indicates that the maximum re strengthening through such a mechanism will only take days to tens of days

diagenetic compaction experiments on simulated anhydrite fault gouge under static conditions faults that crosscut subsurface co2 storage systems offer potential leakage pathways especially if fault reactivation and dilation occur after reactivation however newly formed fault gouge is expected to gradually compact and seal as a function of time to estimate the time scale on which this occurs the processes that control compaction must be understood we performed uniaxial compaction experiments on simulated anhydrite fault gouge to investigate the deformation mechanisms that operate under postslip conditions in faulted anhydrite caprocks this involved constant stress 5 12 mpa and stress stepping experiments 5 7 5 10 mpa performed at 80 c under dry and wet conditions on fault gouge samples prepared from crushed natural anhydrite sieved into different grain size fractions in the range 20 500 m dry samples showed little to no compaction creep whereas wet samples i e flooded with presaturated caso4 solution showed rapid compaction our mechanical data and microstructural observations on wet samples suggest that for fine grain sizes 50 m and low stresses gouge compaction is controlled by diffusion controlled pressure solution with increasing grain size and stress fluid assisted subcritical microcracking becomes dominant pressurizing solution flooded samples with co2 15 mpa led to no significant effect on compaction rates in fine grained material but it decreased compaction rates in coarse samples since fine grain sizes are expected in reactivated faults we infer that pressure solution will dominate in anhydrite cap rocks with extrapolation of our lab data to reservoir conditions suggesting sealing time scales of a few decades

mechanical behavior and microstructure of simulated calcite fault gouge sheared at 20 600 c implications for natural faults in limestones we report ring shear experiments on simulated calcite fault gouges performed at fixed temperatures t within the range from 20 to 600 c the experiments were performed wet using pore fluid pressures pf of 10 pf 60 mpa one series of experiments employed a constant effective normal stress neff of 50 mpa while in a second series neff was sequentially stepped from 30 to 100 mpa in all experiments sliding velocity v was stepped in the range from 0 03 to 100 m s the results showed stable velocity strengthening behavior at 20 c but velocity weakening at 100 to 550 c for all v steps to 3 m s which was frequently accompanied by stick slip at 600 c velocity strengthening occurred microstructural observations suggest increasing importance of ductile deformation with increasing temperature as reflected by a localized shear band structure at 20 c giving way to a pervasive shear plane parallel grain shape fabric at 600 c using existing flow equations for dense calcite polycrystals we show that dislocation and or diffusion creep of 10 30 m sized bulk gouge grains likely played a role in experiments performed at t 400 c we suggest that the observed velocity weakening behavior can be explained by a slip mechanism involving dilatant granular flow in competition with creep controlled compaction our results have important implications for the breadth of the seismogenic zone in limestone terrains and for the interpretation of natural fault rock microstructures specifically while samples sheared at 400 550 c exhibited essentially brittle frictional mechanical behavior stick slip the corresponding microstructures resembled that of a mylonite

plasticity and diffusion creep of dolomite abstract natural and synthetic dolomites have been shortened in triaxial compression experiments at temperatures of 400 850 c equilibrium co2 pore pressures effective confining pressures of 50 400 mpa and strain rates of 10 4 to 10 7 s 1 at low temperatures t 600 mpa both for coarse grained 240 m and fine grained 2 m and 12 m samples differential stresses vary little with strain rate or temperature and microstructures of coarse grained samples are dominated by f twins and undulatory extinction an exponential relation o exp 1 3 between strain rate and differential stress 1 3 describes the crystal plasticity of dolomite at a fixed pe and t with 0 079 0 01 mpa 1 and 0 023 07 03 mpa 1 for coarse and fine grained materials respectively however measured values of 1 3 increase with increasing temperature a trend that has been observed for dolomite single crystals but cannot be described by an arrhenius relation at high temperatures t 800 c for coarse t 700 c for fine dolomite strengths are reduced with increasing temperature and decreasing strain rate but the mechanisms of deformation differ depending on grain size high temperature flow strengths of coarse grained dolomite can be described by a power law o 1 3 nexp h rt with a large value of n 5 and a ratio of parameters h n 60 6 kj mol microstructures of coarse grained samples deformed at t 800 c show evidence of dislocation creep with little mechanical twinning high temperature flow strengths of fine grained synthetic dolomite fit a thermally activated newtonian law where the effective n 1 28 0 15 and h 280 45 kj mol consistent with diffusion creep the change in mechanical response of coarse grained natural dolomite with increasing temperature represents a transition from twinning and slip with little or no recovery to dislocation creep while the change in response of fine grained synthetic dolomite represents a transition from crystal plasticity to diffusion creep the combined results for coarse and fine grained dolomites define a deformation mechanism map with fields of crystal plasticity dislocation creep and diffusion creep strengths of coarse grained dolomite in the crystal plastic and dislocation creep fields are much larger than strengths of calcite rocks deformed by similar mechanisms in contrast strengths of fine grained dolomite deformed by diffusion creep are more comparable to those of fine grained calcite suggesting little contrast in rheology

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

devonian orogen parallel opposed extension in the central norwegian caledonides late orogenic early to middle devonian extension in the scandinavian caledonides was unidirectional in western norway new data from two detachment zones hoybakken and kollstraumen north of the more trondelag fault complex show that bidirectional opposed orogen parallel extension dominated in this region at this time the fault complex acted as a transfer zone for the hoybakken detachment extension and uplift in central norway triggered significant magmatic activity in contrast to the lack of granite intrusions during exhumation of western norway

frictional properties and microstructure of calcite rich fault gouges sheared at sub seismic sliding velocities we report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone 96 caco3 and pure calcite our experiments consisted of direct shear tests performed under dry and wet conditions at an effective normal stress of 50 mpa at 18 150 c and sliding velocities of 0 1 10 m s wet experiments used a pore water pressure of 10 mpa wet gouges typically showed a lower steady state frictional strength 0 6 than dry gouges 0 7 0 8 particularly in the case of the pure calcite samples all runs showed a transition from stable velocity strengthening to potentially unstable velocity weakening slip above 80 100 c all recovered samples showed patchy mirror like surfaces marking boundary shear planes optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands characterized by extreme grain comminution and a crystallographic preferred orientation cross sections of boundary shears cut normal to the shear direction using focused ion beam sem from pure calcite gouges sheared at 18 and 150 c revealed dense arrays of rounded 0 3 m sized particles in the shear band core transmission electron microscopy showed that these particles consist of 5 20 nm sized calcite nanocrystals all samples showed evidence for cataclasis and crystal plasticity comparing our results with previous models for gouge friction we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands with water facilitating pressure solution subcritical cracking and intergranular lubrication our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains contrary to recent claims our data also demonstrate that nanocrystalline mirror like slip surfaces in calcite rich faults are not necessarily indicative of seismic slip rates

rheology of dolomite large strain torsion experiments and natural examples a set of large strain deformation experiments is presented to better constrain the conditions in which grain size sensitive mechanisms are dominant during deformation of dolomite experiments were made on an internally heated gas apparatus equipped with torsion facilities the rheological data set was fitted to an empirical flow law that allows extrapolation to natural conditions fabric evolution with increasing strain was investigated by means of optical and electron microscopy electron backscattered diffraction extrapolation of the laboratory data to geologically relevant conditions of temperature and strain rate was tested on a natural case of a deformed dolomite calcite sequence across the contact aureole of the adamello pluton southern alps italy both the geological data and the laboratory measurements indicate that at high temperature an inversion of the relative strength occurs between the two carbonates with calcite being the weak phase at low temperature and dolomite being the weak phase at high temperature

metamorphic core complexes windows into the mechanics and rheology of the crust metamorphic core complexes are products of normal fault displacements sufficient to exhume rocks from below the brittle ductile transition these faults detachments may initiate within the brittle crust at steep angles but they sole into the ductile middle crust and during displacement rotate to gentler dips due to hanging wall extension the exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping low friction shallow segments of the detachment metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress strain localization and strain rate with decreasing temperature providing a window into physical conditions and deformational processes in the mid crust the metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault in addition to those accompanying exhumation these processes may include diapiric emplacement of gneiss domes or exhumation in a subduction channel and may not be directly related to formation of the core complex factors favouring core complex formation are high gravitational potential energy of the extending crust weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence

the formation environment of potassic chloro hastingsite in the nakhlites mil 03346 and pairs and nwa 5790 insights from terrestrial chloro amphibole potassic chloro hastingsite has been found in melt inclusions in mil 03346 its paired stones and nwa 5790 it is some of the most chlorine rich amphibole ever analyzed in this article we evaluate what crystal chemistry terrestrial analogs and experiments have shown about how chlorine dominant amphibole chloro amphibole forms and apply these insights to the nakhlites chloro amphibole is rare with about a dozen identified localities on earth it is always rich in potassium and iron and poor in titanium in terrestrial settings its presence has been interpreted to result from medium to high grade alteration 400 c of a protolith by an alkali and or iron chloride rich aqueous fluid ferrous chloride fluids exsolved from mafic magmas can cause such alteration as can crustal fluids that have reacted with rock and lost h2o in preference to chloride resulting in concentrated alkali chloride fluids in the case of the nakhlites an aqueous alkali ferrous chloride fluid was exsolved from the parental melt as it crystallized this aqueous chloride fluid itself likely unmixed into chloride dominant and water dominant fluids chloride dominant fluid was trapped in some melt inclusions and reacted with the silicate contents of the inclusion to form potassic chloro hastingsite

the effect of loading rate on static friction and the rate of fault healing during the earthquake cycle the seismic cycle requires that faults strengthen heal between earthquakes and the rate of this healing process plays a key role in determining earthquake stress drop1 2 3 4 rupture characteristics5 6 and seismic scaling relations2 3 4 7 frictional healing as evidenced by increasing static friction during quasi stationary contact between two surfaces1 8 9 10 11 12 is considered the mechanism most likely to be responsible for fault strengthening2 3 13 14 previous studies however have shown a large discrepancy between laboratory and seismic field estimates of the healing rate2 3 4 14 15 in the laboratory rock friction changes by only a few per cent per order of magnitude change in slip rate whereas seismic stress drop increases by a factor of 2 to 5 per order of magnitude increase in earthquake recurrence interval but in such comparisons it is assumed that healing and static friction are independent of loading rate here i summarize laboratory measurements showing that static friction and healing vary with loading rate and time as expected from friction theory16 17 18 applying these results to seismic faulting and accounting for differences in laboratory seismic and tectonic slip rates i demonstrate that post seismic healing is expected to be retardedfor a period of several hundred days following an earthquake in agreement with recent findings from repeating earthquakes13 14 19 20

compaction creep of wet granular calcite by pressure solution at 28 c to 150 c 1 uniaxial compaction experiments have been carried out on wet calcite powders prepared from milled limestone analytical grade calcite and superpure calcite the tests were performed at 28 c 150 c effective stresses of 20 47 mpa and a pore pressure of 20 mpa using presaturated caco3 solution as the pore fluid sample grain sizes ranged from 12 to 86 m the aim was to determine if creep occurs by intergranular pressure solution ips under these conditions and to identify the rate controlling process the wet samples showed significant creep while dry and oil flooded samples did not wet samples were also characterized by microstructures such as sutured grain contacts grain indentations and overgrowths suggesting the operation of ips the behavior of the wet samples at low strains 4 5 agreed well with the predictions of standard models for diffusion controlled pressure solution however at higher strains 5 10 creep slowed down compared with the model predictions transient flow through tests performed in this regime led to an acceleration of creep consistent with models for precipitation controlled ips and demonstrated an increase in the impurity content of the pore fluid toward higher strains since some of these impurities notably mg2 retard precipitation in calcite we suggest that creep occurred by diffusion controlled ips at low strain giving way to precipitation control at larger strains as impurities accumulated fitting of the diffusion controlled ips model to the low strain data yielded values of the grain boundary diffusion product ds in calcite of 10 19 m3 s 1 at 150 c

kinematics of the hoybakken detachment zone and the more trondelag fault complex central norway the tectonic disintegration of the caledonian orogen through combined extension contraction and strike slip was characterized by spatial and temporal strain partitioning through a period of at least 30 ma early to mid devonian exhumation of the central norway basement window was associated with retrograde top to the sw extensional shearing in the hoybakken detachment zone sinistral shearing along the more trondelag fault complex and formation of extension parallel folds progressive exhumation led to increasing strain localization and to the transition from ductile to brittle deformation in the interval between c 370 and 320 ma the hoybakken detachment fault cut previously folded detachment mylonites capturing mylonites in its hanging wall 40 ar 39 ar mica and k feldspar ages indicate a late devonian or younger age for the uppermost parts of the adjacent old red basin gentle folding of this stratigraphic level attests to the continuation of shortening and orogen oblique extension into late devonian carboniferous time shortening was intensified along strands of the more trondelag fault complex as shown by mutually cross cutting reverse and strike slip faults flower structures may be particularly common in constrictional strain systems where strike slip faults develop parallel to the principal elongation trend but normal to the principal axis of shortening

the middle devonian basins of western norway sedimentary response to large scale transtensional tectonics abstract the devonian basins of western norway were formed during late to post orogenic extension of overthickened caledonian crust the basins are situated in the hanging wall of the extensional nordfjord sogn detachment zone nsdz and display extensional half graben geometries in sections parallel to the local direction of principal extension based on overall facies configurations paleocurrent patterns and intrabasinal structures we infer an anticlockwise rotation of the syndepositional extension direction from nw se in the south solund basin to wsw ene in the north hornelen basin the axes of folds that are roughly parallel to the local extension direction are rotated correspondingly the kvamshesten basin is located between the solund and hornelen basins sedimentological and structural data show evidence of an early southeastwards tilt direction followed by a more eastwards tilt and associated e w flowing paleodrainage correspondingly nw se trending folds and reverse faults are superposed by e w trending ones at low to intermediate stratigraphic levels the variations in apparent tilt direction for the basins together with variations in intrabasinal structure is interpreted to reflect an anticlockwise rotation of the regional syndepositional strain field the above observations and inferences indicate that the devonian basins in western norway formed in a strain field dominated by regional transtension accommodated by extension along the nsdz and sinistral strike slip along orogen parallel shear zones and faults to the north of the basins alternatively nw directed extension preceded the introduction of a sinistral strike slip component the models are in accordance with recent work carried out in the footwall of the nsdz and illustrates the tectono sedimentary response to a complex interplay between extension and strike slip that appears to have been fundamental in the late stage disintegration of the caledonian orogen