a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

the structure of an exhumed intraplate seismogenic fault in crystalline basement abstract the 600 m thick gole larghe fault zone glfz is hosted in jointed crystalline basement and exposed across glacier polished outcrops in the italian alps ancient seismicity is attested by the widespread occurrence of cataclasites associated with pseudotachylytes solidified frictional melts formed at 9 11 km depth and ambient temperatures of 250 300 c previous work focused on the southern part of the fault zone here we quantitatively document fault zone structure across the full width of the glfz and surrounding tonalite host rocks by using a combination of structural line transects and image analysis of samples collected across fault strike these new datasets indicate that the glfz has a broadly symmetric across strike damage structure and contains distinct southern central and northern zones distinguished by large variations in fracture density distribution of pseudotachylytes volume of fault rock materials and microfracture sealing characteristics the c 100 m wide central zone is bound by two thick 2 m and laterally continuous 1 km protocataclastic to ultracataclastic horizons within and immediately surrounding the central zone fracture density is relatively high due to cataclastic fault fracture networks that reworked earlier formed pseudotachylytes the fault fracture networks were associated with pervasive microcracking and fluid rock interaction resulting in the development of a c 200 m thick alteration zone delimited by lobate fluid infiltration fronts in the c 250 m thick southern and northern zones fracture densities are much lower and pseudotachylytes systematically overprint cataclastic faults that exploited pre existing magmatic cooling joints analysis of the structure of the glfz suggests that it shares certain characteristics with the seismogenic source responsible for the 2002 au sable forks intraplate earthquake sequence in the northeastern usa including seismicity distributed across a fault zone 500 1000 m thick and large 100 mpa static stress drops associated with frictional melting

earthquakes produce carbon dioxide in crustal faults abstract fourier transform infrared ftir microanalysis of pseudotachylytes i e friction induced melts produced by seismic slip from the nojima fault japan reveals that earthquakes almost instantaneously expel 99 wt of the wall rock co 2 content carbon is exsolved because it is supersaturated in the friction melts by extrapolation to a crustal scale fault rupture large events such as the m7 2 kobe earthquake 1995 may yield a total production of 1 8 to 3 4 10 3 tons co 2 within a few seconds this extraordinary release of co 2 can cause a flash fluid pressure increase in the fault plane and therefore enhance earthquake slip or trigger aftershocks it may also explain the anomalous discharge of carbon monitored in nearby fault springs after large earthquakes because carbon saturation in silicate melts is pressure dependent ftir can be used as a new tool to constrain the maximum depth of pseudotachylyte formation in exhumed faults

channelized fluid flow and mass transfer along a rift related detachment fault eastern alps southeast switzerland remnants of a rift related low angle detachment system are spectacularly exposed in the continental err nappe and occur discontinuously in the underlying oceanic platta nappe in southeast switzerland rocks along the detachment fault exhibit systematic changes in mineralogy fabrics and structures that are related to deformation and hydration of granite to form cataclasite and subsequent gouge structural mineralogical and geochemical data indicate a continuous evolution of fluid flow and mass transfer along the detachment fault mass balance calculations together with stable isotope data suggest 1 an altered seawater source and local interaction with mantle rocks 2 limited fluid rock interaction and mass transfer during initial cataclasis at deeper crustal levels and temperatures of 150 to 200 c 3 increased fluid flux and mass transfer at slightly lower temperatures 100 150 c during gouge formation at shallower crustal levels and 4 strongly localized fluid rock interaction at low temperatures 65 80 c near the sea floor at a final stage of detachment faulting we propose a model in which seawater dominated fluids penetrated and locally interacted with mantle rocks before they were caught and channelized along large scale detachment faults flow direction is upward along the detachment from higher to lower temperatures suggesting that the driving force of fluid flow was thermal fluid convection associated with mantle exhumation our study suggests that this large scale detachment fault is a good analog for extensional structures along present day nonvolcanic rifted margins such structures along ocean continent transitions are important in controlling fluid pathways and mass transfer between mantle and continental crust

control of the geometry of precursor brittle structures on the type of ductile shear zone in the adamello tonalites southern alps italy abstract amphibolite facies ductile shear zones developed during the immediate post intrusive cooling history of the adamello tonalites southern alps italy shear zones include i thin a few mm s thick fault like shear zones that accommodate shear strain values up to several 100 s the dominant type ii mylonitic horizons dm s thick in sharp contact with the undeformed wall rock iii continuous shear zones with sigmoidal shaped s or composite s c foliations a transition between the different types occurs along strike over short distances discontinuous shear zones are also localized on pegmatite dykes and quartz veins and both i and ii are discontinuously outlined by quartz layers detailed surface mapping reveals that most fault like shear zones are arranged en echelon mainly forming contractional steps markers crosscut by shear zones allow the displacement to be measured at several positions along shear zones and this reveals very steep displacement gradients close to the shear zone tips differential displacement is mainly accommodated at contractional steps by the development of foliated domains geochemical analyses of major and trace elements show that there is no compositional change along strain gradients the overall features are consistent with nucleation of shear zones on former sets of en echelon joints in many cases intruded by pegmatite dykes or filled with quartz reactivation of joints produced strongly localized shear zones whereas broader foliated zones evolved from the contractional jogs between adjacent stepped joint terminations during progressive shearing these jogs were progressively involved in the accommodation of shear displacement and overall shear zone development

direct dating of quaternary phreatic maar eruptions by luminescence methods the suitability of quartz optically stimulated luminescence osl and feldspar infrared stimulated luminescence irsl for the direct dating of phreatic eruptions was tested on examples from the eifel volcanic field germany the mean irsl age of 11 6 0 5 ka for ulmener maar tephra is in excellent agreement with the independent age control 11 0 1 ka but the mean osl age of 14 2 0 6 ka overestimates the known age by 3 ka for meerfelder maar tephra consistent irsl mean 74 9 5 0 ka and osl ages 74 9 5 5 ka have been observed the consistent results from meerfelder maar imply that the overestimation observed for ulmener maar quartz osl might not be relative to the eruption age but rather represents a small absolute offset in samples taken from deposits of the eruption of laacher see volcano no resetting of the osl signal and highly scattered irsl estimates were found this implies that phreatomagmatic eruptions are less well suited for this dating approach compared to pure phreatic maar eruptions where the effect of high pressure shock waves probably dominates the process of resetting the luminescence signal

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

microstructural and chemical changes associated with cataclasis and frictional melting at shallow crustal levels the cataclasite pseudotachylyte connection in pelitic schists of the nason terrane of washington state pseudotachylyte can be demonstrated to have developed subsequent to the formation of foliation parallel cataclasite zones numerous microstructural lines of evidence point to a genetic link between pseudotachylyte and cataclasite and chemical evidence indicates that cataclasis played an important role in controlling pseudotachylyte chemistry besides optical and textural differences between the cataclasite and pseudotachylyte which may occur together there is unambiguous evidence of a melt origin for the pseudotachylyte while such evidence within the cataclasite is absent tem evidence indicates that glass is present in at least some of the veins as demonstrated by a lack of electron diffraction microlites present in the glass lack dislocations high temperature microlites of a mineralogy and composition not present in the host schist occur in various habits which depend on the distance from the vein margin also present are assimilation textures apparently quenched sulfide droplets and vesicles and amygdules in a pseudotachylyte vein studied in detail five microstructural domains occur these include vein margin cataclasite a transitional dark pseudotachylyte vein interior glass opaque and sulfide rich blebs and translucent haloes surrounding some of the blebs the cryptocrystalline cataclasite matrix grades into the dark pseudotachylyte which optically grades into the glass after adjustment for silica the host schist and cataclasite matrix are chemically very similar the dark pseudotachylyte and glass with the exception of na2o and cao are chemically quite similar to the cataclasite matrix the main difference may be the result of the segregation of the opaque plagioclase blebs thus the pseudotachylyte chemistry is strongly dependent upon the chemistry of the material comprising the cataclasite matrix which in turn is dependent on mineral susceptibility to incorporation into the cataclasite matrix fluids infiltrated along the cataclasite zones prior to pseudotachylyte generation as recorded by hydration reactions sulfide veining na2o loss and fluid inclusions this demonstrates that pseudotachylytes can form under fluid rich conditions as opposed to the commonly assumed dry conditions

vesicles amygdales and similar structures in fault generated pseudotachylytes amygdales in fault generated pseudotachylytes from the outer hebrides thrust scotland and the ikertoq shear belt west greenland contain mineral assemblages dominated by k spar sphene epidote quartz and carbonates respectively these contrasting assemblages indicate that vesicle infilling took place under differing environmental conditions other filled cavities resembling amygdales in form and mineralogy are recognized as replacement pseudomorphs after porphyroclasts using published data relating vesicle abundance and solubility functions for h2o and co2 to pressure a palaeoseismic depth estimate equivalent to the depth of vesiculation of about 1 6 km is inferred for the greenland pseudotachylytes described in this paper

earth s ion upflow associated with polar cap patches global and in situ observations we report simultaneous global monitoring of a patch of ionization and in situ observation of ion upflow at the center of the polar cap region during a geomagnetic storm our observations indicate strong fluxes of upwelling o ions originating from frictional heating produced by rapid antisunward flow of the plasma patch the statistical results from the crossings of the central polar cap region by defense meteorological satellite program f16 f18 from 2010 to 2013 confirm that the field aligned flow can turn upward when rapid antisunward flows appear with consequent significant frictional heating of the ions which overcomes the gravity effect we suggest that such rapidly moving patches can provide an important source of upwelling ions in a region where downward flows are usually expected these observations give new insight into the processes of ionosphere magnetosphere coupling

contemporaneous plutonism and strike slip faulting a case study from the tonale fault zone north of the adamello pluton italian alps 1 a field microstructural and geochronological study of contemporaneous plutonism and strike slip faulting along the eastern tonale fault zone provides new insights into the interrelationships between magmatic emplacement contact metamorphism and shearing and it places new time constraints for the periadriatic fault system although pluton emplacement and shearing were not caused by each other they mutually interacted during contact metamorphism the character of the composite tonale fault zone varies considerably with its proximity to the northern margin of the adamello pluton from a paired greenschist facies mylonite belt northern mylonite zone and cataclastic fault zone in the west to a fault zone consisting of northern mylonite zone cataclastic fault zone and a second mylonite belt southern mylonite zone formed by contemporaneous shearing and contact metamorphism in the east ongoing strike slip motion led to telescoping and advective cooling of the deforming contact aureole new u pb zircon ages for the northernmost adamello intrusions the avio at 34 6 1 0 ma and the presanella at 32 0 2 3 ma date the onset of contact metamorphism rb sr and k ar cooling ages and new zircon fission track ages provide evidence that postintrusive cooling to below 300 c was achieved rapidly i e approximately 30 myr ago being consistent with a shallow crustal emplacement at ambient temperatures of approximately 250 c cataclastic dextral strike slip faulting continued until about 20 ma when the tonale fault zone became offset by a number of minor sinistral shears and by the giudicarie fault hence dextral strike slip motion along the periadriatic fault system east of the bergell pluton lasted from approximately 35 20 myr ago

brittle ductile brittle deformation during cooling of tonalite adamello southern italian alps abstract late to post magmatic deformation in slightly diachronous contiguous intrusions of the north western adamello batholith southern alps italy is recorded as from oldest to youngest i joints ii solid state ductile shear zones iii faults associated with epidote k feldspar veins and iv zeolite veins and faults structures ii to iv are localized on the pervasive precursory network of joints i which developed during the earliest stages of pluton cooling high temperature 500 c ductile overprinting of joints produced lineations defined by aligned biotite and hornblende on the joint surfaces and highly localized mylonites the main phase of faulting producing cataclasites and pseudotachylytes occurred at 250 c and was associated with extensive fluid infiltration cataclasites and pseudotachylytes are clustered along different e w striking dextral strike slip fault zones correlated with the activity of the tonale fault a major tectonic structure that bounds the adamello batholith to the north ductile deformation and cataclastic veining episodes occurred at p 0 25 0 3 gpa during rapid cooling of the batholith to the ambient temperatures 250 c that preceded the exhumation of the batholith timing of the sequence of deformation can be constrained by 39 ar 40 ar ages of 30 ma on pseudotachylytes and various existing mineral ages in the whole composite adamello batholith multiple magma pulses were intruded over the time span 42 30 ma and each intrusive body shows the same ductile to brittle structural sequence localized on the early joint sets this deformation sequence of the adamello might be typical of intrusions undergoing cooling at depths close to the brittle ductile transition

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

large scale convection patterns observed by dmsp the authors present a comprehensive compilation of the average distribution of the electrostatic potential across the high latitude ionosphere the averages are compiled from potentials along the satellite path calculated from thermal ion drift data from instrumentation on the defense meterological satellite program dmsp flights 8 and 9 satellites data were collected from the dmsp f8 satellite during the period september 1987 to december 1990 and from the dmsp f9 satellite during the period march 1988 to december 1990 the potential distributions are separated by geomagnetic position season and orientation of the interplanetary magnetic field imf and then averages of the distributions are calculated the average potential distributions clearly show the displacement of polar cap convection contours to the dusk or dawk flanks under the influence of the imf b sub y component the cross cap potential decreases as imf b sub z changes from southward to northward the average distributions indicate that the development of more than two convection cells for northward imf is either uncommon or nonexistent for imf b sub z 0 and b sub z vert bar b sub y vert bar a distorted pattern is observed in the average potential distribution not a four cell pattern as some previous studies suggest it should be for allmore orientations of the imf the convection reversal boundary at the poleward edge of the auroral zone is observed in the average distributions to be a rotational boundary it is not a shear boundary as suggested by some previous investigations on average the harang discontinuity convection reversal in the auroral zone near midnight is observed to exist weakly or not at all when examining individual passes a strong eastward flow is present sometimes in the region of the harang discontinuity especially on the poleward boundary but not at all times as implied by the heppner maynard model 39 refs 9 figs 2 tabs less

stable isotope and chemical systematics of pseudotachylyte and wall rock homestake shear zone colorado usa meteoric fluid or rock buffered conditions during coseismic fusion 1 a hydrous fluid phase is critical in controlling effective stress and fault mechanics and influencing the mineralogy and strength of materials within fault zones oxygen and hydrogen isotope and chemical analysis of wall rock gneiss pseudotachylyte and selected minerals in gneiss and pseudotachylyte from the homestake shear zone was used to assess whether melting occurred in the presence of meteoric water or involved only minor amounts of h2o derived from micas in wall rock gneiss bulk pseudotachylyte has slightly lower 18osmow than the whole rock protolith d for one bulk pseudotachylyte is essentially identical to biotite in gneiss d for two samples is lower by 20 bulk pseudotachylyte has lower sio2 and k2o and higher al2o3 feo mgo cao and h2o than gneiss the lower sio2 of pseudotachylyte compared to gneiss is explained by physical segregation of 25 to 72 volume of quartz clasts from the mobile melt phase samples of gneiss and pseudotachylyte define a sio2 18o mixing line between quartz and the most sio2 and 18o depleted pseudotachylyte physical segregation of quartz highest oxygen isotope composition in the pseudotachylyte gneiss system accounts for the slightly lower oxygen isotope composition of bulk pseudotachylyte relative to gneiss the similar d of pseudotachylyte and biotite from gneiss in one sample is consistent with dehydration melting of biotite during frictional heating and dissolution of biotite derived h2o in the melt late devitrification of glass and formation of greater amounts of fine grained muscovite accompanied by 10 30 loss of hydrogen as h2o results in lower d values in other samples in general melt generation occurred in a fault zone closed to infiltration of meteoric water there was no free h2o rich pore fluid present at the time of slip to potentially influence the behavior of the fault

the effects of fault orientation and fluid infiltration on fault rock assemblages at seismogenic depths abstract the factors controlling the development of different types of fault rock assemblages and more specifically the formation of friction melts are still not fully understood in this study we compared two exhumed strike slip faults in the adamello batholith southern alps the gole larghe and the passo cercen fault zones active at 9 11 km depth and temperatures of 250 300 c each fault zone consists of hundreds of sub parallel strands exploiting pre existing joints the gole larghe fault strikes n105 5 and is dextral the fault rocks are cataclasites and widespread centimetre thick pseudotachylytes the passo cercen fault strikes on average n130 and is formed by multiple fault horizons fault segments striking n105 n130 are mainly dextral whereas faults striking n135 n140 are mainly sinistral microstructural mineralogical and geochemical investigations show that the fault rocks are cataclasites associated with thick epidote k feldspar quartz veins and rare millimetre thick pseudotachylytes field evidence suggests that in both fault zones the direction of the maximum horizontal stress 1 was n135 the gole larghe fault strikes at about 30 to 1 and is favourably oriented for reactivation by contrast the passo cercen fault strikes at low angles to 1 and is unfavourably oriented for reactivation therefore requiring the development of high pore pressures as suggested by the occurrence of extensive epidote veining and hydraulic breccias it is proposed that frictional melting in the passo cercen fault zone was inhibited by the development of high pore pressures and low effective normal stresses

origin of hydrous fluids at seismogenic depth constraints from natural and experimental fault rocks abstract fluids control the mechanical behavior of fault zones during the seismic cycle we used geochemical mineralogical microstructural hydrogen isotope compositions and fourier transform infrared ftir investigations to characterize the origin of hydrous fluids involved in ductile and brittle shear zones at the bottom of the seismogenic crust natural samples were collected from exhumed mylonitic shear zones and cataclasite pseudotachylyte bearing faults in the northern adamello italian southern alps which were active at 9 11 km depth pseudotachylytes solidified coseismic friction induced melts testify to ancient seismogenic behavior of the faults natural pseudotachylytes were compared with artificial pseudotachylytes produced in high velocity friction experiments simulating seismic slip mylonites have mineralogical elemental and hydrogen isotope compositions 80 d 78 similar to the host tonalite 77 d 73 within the analytical error of 5 cataclasites have instead mineralogical chlorite epidote k feldspar no biotite major and trace elements enrichment in k2o ba rb depletion in cao na2o sio2 and hydrogen isotope 69 d 60 compositions suggesting interactions with a crustal metamorphic fluid pseudotachylytes are composed of high temperature minerals plagioclase biotite dmisteinbergite cordierite and scapolite and have elemental compositions resulting from mixing of tonalite and cataclasite pseudotachylytes have complex microstructures including i microlitic domains with well crystallized micrometric biotite which have hydrogen isotope composition 81 d 59 similar to cataclasites and tonalite and ii cryptocrystalline domains with poorly crystallized biotite which have very high water content release water upon heating at t 50 c and have low d value 93 the hydrogen isotope composition of bulk samples is dominated by the composition of cryptocrystalline domains 103 d 88 where most of the water is hosted their hydrogen isotope composition is compatible with adsorption of present day rainfall water d 95 artificial pseudotachylytes have the same hydrogen isotope compositions of the starting tonalite 76 d 74 or cataclasite 68 d 62 with a slight decrease of the d values in some samples 85 d 81 the first ingression of a crustal metamorphic fluid occurred in cataclastic faults natural pseudotachylytes when not contaminated by present day rainfall water have a hydrogen isotope composition similar to tonalite and cataclasite as reproduced in dry high velocity friction experiments the fluids dissolved in coseismic melts are most likely derived from the breakdown of hydrous minerals of cataclasite and tonalite undergone melting and we could not identify the infiltration of an external fluid during earthquakes

climatically versus tectonically forced erosion in the alps thermochronometric constraints from the adamello complex southern alps italy abstract we apply u th sm he dating and fission track thermochronometry of apatites to the adamello complex located in the southern european alps our goal is to constrain exhumation rates since the miocene in particular to determine whether the increase in sedimentation documented in the foreland basins since 5 ma is recorded in cooling rates of the southern alps thermochronometry provides a cooling rate for rocks which can be converted to an exhumation rate through thermal modeling thereby quantifying the amount of rock exhumed at different time scales apatite fission track and u th sm he analyses all record miocene ages we find no evidence for an increase in exhumation rate during the plio pleistocene the results of our exhumation rate estimates and tectono geomorphic modeling suggest that unroofing during thrust propagation of the southern alps in the late miocene drove most of the exhumation while changes in relief mainly associated with plio pleistocene climate change likely did not affect the adamello complex the findings from this study combined with other studies highlight that there appears to be a gradient across the alps with more intensive plio pleistocene erosion in the western and central alps compared to the eastern and southern alps

frictional melt and seismic slip 1 frictional melt is implied in a variety of processes such as seismic slip ice skating and meteorite combustion a steady state can be reached when melt is continuously produced and extruded from the sliding interface as shown recently in a number of laboratory rock friction experiments a thin low viscosity high temperature melt layer is formed resulting in low shear resistance a theoretical solution describing the coupling of shear heating thermal diffusion and extrusion is obtained without imposing a priori the melt thickness the steady state shear traction can be approximated at high slip rates by the theoretical form ss n1 4 a under a normal stress n slip rate v radius of contact area r a is a dimensional normalizing factor and w is a characteristic rate although the model offers a rather simplified view of a complex process the predictions are compatible with experimental observations in particular we consider laboratory simulations of seismic slip on earthquake faults a series of high velocity rotary shear experiments on rocks performed for n in the range 1 20 mpa and slip rates in the range 0 5 2 m s 1 is confronted to the theoretical model the behavior is reasonably well reproduced though the effect of radiation loss taking place in the experiment somewhat alters the data the scaling of friction with n r and v in the presence of melt suggests that extrapolation of laboratory measures to real earth is a highly nonlinear nontrivial exercise

evidence of dmisteinbergite hexagonal form of caal2si2o8 in pseudotachylyte a tool to constrain the thermal history of a seismic event the determination of the maximum temperature achieved by friction melt tmelt in pseudotachylytebearing faults is crucial to estimate earthquake source parameters e g earthquake energy budgets coseismic fault strength on a geological basis here we investigated the mineralogy of a pseudotachylyte from the gole larghe fault italian alps by using x ray powder diffraction micro raman spectroscopy and eds equipped field emission scanning electron microscopy in particular we report the presence of the hexagonal polymorph of caal2si2o8 dmisteinbergite in a pseudotachylyte published experimental work shows dmisteinbergite can crystallize at 1200 1400 c by rapid quenching therefore the presence of dmisteinbergite in pseudotachylyte could be a reliable geothermometer for friction melts for which tmelt has only as yet been estimated

development of interconnected talc networks and weakening of continental low angle normal faults fault zones that slip when oriented at large angles to the maximum compressive stress i e weak faults represent a significant mechanical problem here we document fault weakening induced by dissolution of dolomite and subsequent precipitation of calcite abundant talc along a low angle normal fault within the fault core talc forms an interconnected foliated network that deforms by frictional sliding along 50 200 nm thick talc lamellae the low frictional strength of talc combined with dissolution precipitation creep can explain slip on low angle normal faults in addition the stable sliding behavior of talc is consistent with the absence of strong earthquakes along such structures the development of phyllosilicates such as talc by fluid assisted processes within fault zones cutting mg rich carbonate sequences may be widespread leading to profound and long term fault weakness

rare earth and trace element mobility in mid crustal shear zones insights from the mont blanc massif western alps the behaviour of rare earth elements ree during fluid rock interaction in mid crustal shear zones has received little attention despite their potential for mass balance calculation and isotopic tracing during deformation in this study several cases of large ree mobility during alpine fluid driven shear zone development in the pre alpine granitic basement of the mont blanc massif are considered on a regional scale the undeformed granite compositions range within 5 wt sio2 70 5 75 3 wt and magmatic chemical variations are of the order of 10 20 ascribed to minor effects of crystal fractionation major and trace element mobility observed in shear zones largely exceeds these initial variations shear zones developed a range of mineral assemblages as a result of shearing at mid crustal depths at not vert similar0 5 gpa 400 c five main shear zone assemblages involve muscovite chlorite epidote actinolite and calcite respectively as major phases in most cases selective enrichments of light or heavy ree and y ta hf are observed ree mobility is unrelated to deformation style cataclastic mylonitic the intensity of strain and to the shear zone s major metamorphic mineral assemblages instead the changes in ree concentrations are ascribed to the alteration of pre existing magmatic ree bearing minerals during deformation related fluid rock interaction and to the syntectonic precipitation of metamorphic ree bearing minerals mainly monazite bastnasite aeschynite and tombarthite minor proportions 2 of these accessory phases with grain sizes mostly 20 m account for enrichments of up to 5 1 compared to the initial granite whole rock ree budget the stability of the ree phases appears to be largely dependent on the altering fluid composition ree mobility is ascribed to changes in ph and to the availability of co32 po42 and so42 ligands in the fluid such processes are likely to influence the mobility of ree y hf and ta in shear zones

energy partitioning during seismic slip in pseudotachylyte bearing faults gole larghe fault adamello italy thedeterminationoftheearthquakeenergybudgetremainsachallengingissueforearthscientists asunderstandingthepartitioningofenergyisa keytowardsthe understandingthe physicsofearthquakes here weestimatethe partitionofthe mechanical workdensity intoheatandsurfaceenergy energyrequiredtocreatenewfracturesurface duringseismicsliponalocationalongafault earthquakeenergypartitioningisdeterminedfromfield and microstructural analyses of a fault segment decorated by pseudotachylyte solidified friction induced melt produced during seismic slip exhumed from a depth of 10 km typical for earthquake hypocenters in the continental crust frictional heat per unit fault area estimated from the thickness of pseudotachylytes is 27 mj m 2 surface energy estimated from microcrack density inside clast i e cracked grains entrapped in the pseudotachylyte and in the fault wall rock ranges between 0 10 and 0 85 mj m 2 our estimates for the studied fault segment suggest that 97 99 of the energy was dissipated as heat during seismic slip we conclude that at 10 km depth less than 3 of the total mechanical work density is adsorbed as surface energy on the fault plane during earthquake rupture 2008 elsevier b v all rights reserved

water loss and the origin of thick ultramylonites hydrolytic weakening has been suggested as a major process facilitating strain localization in line with many studies that found a positive correlation between water content and intensity of deformation we examine the role of water in the unusually thick ultramylonite of the el pichao shear zone northwestern argentina we used fourier transform infrared spectroscopy to measure water content in quartz and feldspar comparing ultramylonitic rocks to mylonites and weakly deformed rocks quartz and feldspar in ultramylonites contained half the water of weakly deformed rocks contrary to findings in previous studies we propose that the kilometer thick ultramylonite formed in three stages 1 localized deformation and recrystallization caused release of intracrystalline water to grain boundaries which promoted grain boundary sliding forming the ultramylonite 2 high pressure in the shear zone continuously expelled intercrystalline water to the surroundings drying the boundaries and leading to strain hardening and 3 water migrated to less deformed rocks causing hydrolytic weakening repeating the cycle and widening the ultramylonite

chemical and oxygen isotope composition of natural and artificial pseudotachylyte role of water during frictional fusion abstract pseudotachylyte samples from the long ridge fault north carolina the homestake shear zone colorado the fort foster fault maine and experimentally produced frictional melt were analyzed for major elements and o isotopes using an electron microprobe and laser microprobe respectively the pseudotachylytes display a 18o range of 5 9 10 7 standard mean ocean water smow and are both isotopically lighter and heavier than their respective host rocks in general the isotopic composition of bulk pseudotachylyte pt in the absence of water rock interaction can be modeled as 18 o bulk pt x frag 18 o frag x min 18 o min where xfrag refers to the volume fraction of unmelted mineral fragments and xmin refers to the volume fraction of minerals that undergo melting mineral melt isotopic fractionation is considered to be small and less than 1 the majority of pseudotachylyte isotopic compositions can be explained as a disequilibrium partial melt of the protolith rock comprising melted feldspar and micas plus a small proportion 10 of unmelted quartz clasts in contrast the long ridge fault samples are substantially depleted in 18o by up to 4 relative to their host rock which is best explained by closed system water rock interaction of a pore fluid at 100 c with a melt at 1000 c and a water rock weight ratio of 0 2 this fluid is also inferred to have caused oxidation of the pseudotachylyte melts producing the hematite characteristic of this location

thermosphere density response to the 20 21 november 2003 solar and geomagnetic storm from champ and grace accelerometer data 1 densities in the 400 500 km height region inferred from accelerometer measurements on the champ and grace satellites are utilized to study the response to the isolated and severe geomagnetic storm of 20 21 november 2003 the champ and grace satellites provide data at approximate local times of 1110 2310 and 1430 0230 hours respectively in a global sense density increases of order 300 800 occur during this storm with relatively little time delay at high latitudes and with about 4 hour delay at the equator significant latitudinal asymmetries in the response are discussed in the context of neutral wind patterns and enhanced summer versus winter joule heating rates at high latitudes comparisons with the nrlmsise 00 empirical model densities during this period show marked differences in amplitude of the response as well as latitudinal and temporal structures evidence for a tight coupling between solar wind and neutral density variability is found for the high latitude summer hemisphere near noon in that densities near 410 km are very responsive to increases in solar wind dynamic pressure even during periods when both bz and by are near zero or positive filtering of the data reveals regional scale 1000 2000 km density anomalies that are common between the champ and grace measurements during the geomagnetic disturbance alternating regions of density enhancements 50 and depressions 50 exist between the pole and low to middle latitudes that have the appearance of a standing wave pattern during magnetically quiet intervals before and after the storm daytime density depressions 4 8 are seen that track the magnetic equator while density enhancements 10 track the latitudes of the ionospheric appleton anomaly peaks large scale 1000 km wave like structures are also prevalent during both day and night during the magnetic disturbance and extend throughout both hemispheres consistent with the concept that these are associated with the so called direct gravity waves forced in the auroral regions and propagating far from the source substantial variability is also present at medium scales 300 500 km but these structures are confined mainly to middle to high latitudes in accord with theoretical expectations grace a and grace b data are used in a feasibility study of the detection of small scale wave activity by taking advantage of the 30 s separation of the satellites in the same orbital plane despite the large amount of maneuvers which are not always recorded this first analysis is promising amplitude variations of order 10 20 and wave speeds of 1000 1500 m s 1 are observed

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

hemispheric asymmetry of subauroral ion drifts statistical results a large database of more than 18 000 subauroral ion drift said events from dmsp observations from 1987 to 2012 is used to systematically investigate the features of said said occurs mostly at 62 60 magnetic latitude mlat and 22 15 22 45 magnetic local time mlt for geomagnetically quiet conditions and at 58 56 mlat and 22 15 22 45 mlt for geomagnetically disturbed conditions in the north hemisphere nh south hemisphere sh respectively significant north south asymmetries in said occurrence shape and geomagnetic activity variations are found in this statistical study the latitudinal width of a said is larger in the nh than in the sh an interesting finding of this work is that the said occurrence probability peaks have an 180 difference in longitude between the two hemispheres in the geographic coordinates for both geomagnetically quiet and disturbed conditions the said width peaks in almost the same geomagnetic meridian zone with a geomagnetic longitude of 80 120 in both hemispheres significant hemispheric asymmetries and spike signatures with sharp dips are found in all the latitudinal profiles of the horizontal velocities of saids the said is highly correlated to geomagnetic activity indicating that the location and evolution of the said might be influenced by global geomagnetic activity auroral dynamics and the dynamics of ring currents

high latitude plasma outflow as measured by the dmsp spacecraft 1 we have examined the vertical ion flux in the topside high latitude ionosphere from measurements of the vertical ion drift and ion number density made by the dmsp f13 satellite we found that the average vertical flux over the entire high latitude region near 800 km altitude is quite small this suggests that most of the vertical ion flux is associated with a large scale breathing of the upper ionosphere in the polar cap the vertical ion flux is uniformly downward at all locations however in the auroral zone the ion flux is highly structured and a net upward flux is produced only by spatially and temporally confined events containing upward fluxes in excess of 1010 cm 2 s 1 that have no downward counterparts

bubble collapse structure a microstructural record of fluids bubble formation and collapse and mineralization in pseudotachylyte abstracta complex microstructural feature has been discovered within centimeter scale pseudotachylyte veins and is here termed bubble collapse structure bcs three first order features of bcss are 1 a central quartz dominated monocrystal or polycrystal 2 a light colored reaction halo and 3 a generally radial but commonly curving pattern of opaque seams and or elliptical quartz amygdules two populations of bubbles were principally responsible for forming bcss one was a population of millimeter scale bubbles and the second involved much more numerous small bubbles mean diameter m the first population likely formed from liquid water interstitial to the precursory cataclasite or from melting of hydrous minerals whereas the second population formed by diffusional growth bcss began forming as the pseudotachylyte melt cooled and the pressure inside the bubbles decreased as the large bubbles flattened into oblate ellipsoids parallel to the vein margins melt flowed toward each collapsing bu

fault plane processes and mesoscopic structure of a strong type seismogenic fault in tonalites adamello batholith southern alps abstract the gole larghe fault is an exhumed paleoseismic fault crosscutting the adamello tonalites italian southern alps ambient conditions of faulting were 9 11 km in depth and 250 300 c in the study area the fault accommodates 1100 m of dextral strike slip over a fault thickness of 550 m displacement is partitioned into three hierarchically different sets of discrete subparallel cataclastic horizons faults1 2 3 fault displacement is in the range of few centimeters faults3 to a maximum of a few tens of meters in major faults1 faults1 2 nucleated on pre existing joints whereas faults3 are newly generated fractures produced during slip along faults1 2 each fault within the gole larghe fault records the same evolution with development of indurated cataclasites precursory to pseudotachylyte production pseudotachylytes are usually generated at the host rock cataclasite boundary and within cataclasites the mean clast size decreases getting closer to pseudotachylyte fault veins pseudotachylytes and cataclasites have a similar chemical composition which is enriched in loss on ignition k rb ba u and fe3 compared to host rock we envision two models for the evolution of the gole larghe fault in both models synkinematic fluid rock interaction along a fault causes fault hardening by precipitation of abundant k feldspar epidote and minor chlorite in the cataclasite matrix conducive to final production of pseudotachylyte in the first model induration occurs progressively by differential precipitation related to fabric evolution in cataclasites in the second model induration occurs abruptly dependent on the development of full connectivity within the fault network and to fluid reservoir whatever the model the gole larghe fault represents a strong fault where hardening processes resulted in a low displacement fault thickness ratio and contrast with many mature weak faults where localized repeated seismic slip along the same weak horizons yields high displacement fault thickness ratios

fluid history related to the early eocene middle miocene convergent system of the northern apennines italy constraints from structural and isotopic studies 1 the late eocene middle miocene erosive plate boundary between the european and the adriatic plates is exhumed in the northern apennines of italy the fossil fault zone is 500 m thick and the outcropping portion exposes the first 5 km of its depth at this plate boundary basal and frontal tectonic erosion incorporated unlithified fluid rich sediments into the fault zone the deformation and nature of the material along the plate boundary define a fossil subduction channel here we couple a detailed structural analysis of the apennine subduction channel focusing in particular on calcite veins with a stable isotope analysis to characterize the fluid regime along an active subduction channel the 13c and 18o composition of calcite vein and host rock samples within the fault zone indicates that there is a deep metamorphic source of fluids migrating upward along the subduction channel in addition to locally derived fluid components dewatering of subducting turbidites contributes significantly only in the shallowest part of the channel structural observations indicate fluid flow along and across the subduction channel at deep levels fluid flow is associated with discrete deformation events on shear faults offset by dilational jogs filled with implosion breccias at intermediate levels deformation is still cyclic and associated with repeated crack and seal events at the shallowest levels deformation occurred while portions of the subducting material were still unlithified here the deformation was quasicontinuous without associated vein development both isotope and structural analyses indicate that this erosive subduction channel behaved as a weak fault with a vertical maximum principal stress

modeling of the global distribution of ionospheric electric fields based on realistic maps of field aligned currents 1 a new approach for modeling the global distribution of ionospheric electric potentials utilizing high precision maps of facs derived from measurements by the orsted and champ satellites as input to a comprehensive numerical scheme is presented the boundary conditions provide a correct treatment of the asymmetry of conductivity and sources of electric potential between the northern and southern hemispheres on the basis of numerical simulation the basic convection patterns developed simultaneously in both hemispheres for equinox and summer winter solstices are obtained a rather complicated dependence of the convection patterns on season linked with the sign of imf by is found in particular the combinations of by 0 summer and by 0 winter the model predicts that the summer cross polar potentials are smaller than the winter potentials the value of the ratio depends on the combination of season imf by sign the ratio is found to be greater for the combination of by 0 southern summer and by 0 northern summer under northward imf conditions at middle latitudes the main features of the mlt profile of the westward and equatorward electric field components are reproduced the model predicts that during solstice the equatorward component of the midlatitude electric field is negative at all local times for by 0 citation lukianova r and f christiansen 2006 modeling of the global distribution of ionospheric electric fields based on realistic maps of field aligned currents j geophys res 111 a03213 doi 10 1029 2005ja011465

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

dependencies of high latitude plasma convection consideration of interplanetary magnetic field seasonal and universal time factors in statistical patterns 1 the database of the nine radars of the super dual auroral radar network superdarn in the northern hemisphere has been analyzed for information on factors that influence the convection of plasma in the high latitude ionosphere the velocity measurements were collected over the period 1998 2002 the data were first used to derive a new statistical model of convection that improves upon the earlier one radar model of ruohoniemi and greenwald 1996 in its specification of the dependence of the convection pattern on the magnitude and direction of the imf in the gsm y z plane we then derived average patterns for secondary sortings by season year and radar such dependencies as emerged were most clearly seen by contrasting the results for by and by the seasonal effect in the convection pattern is found to have similarities to that of the sign of by in particular the combination of by summer by winter reinforces the tendency of the by sign factor to sculpt the dusk and dawn cells into more round crescent crescent round shapes and to shift the crescent cell across the midnight mlt meridian however these combinations are associated with lower estimates of the total cross polar cap potential drop pc while the nonreinforcing combinations produce elevated pc especially by summer there is an overall tendency for pc to increase from winter to summer although the pure seasonal effect on the potential drop is weaker than that of the by sign season factor we did not find pronounced differences among the patterns derived for the 5 individual years which spanned the most recent interval of solar cycle maximum sorting by radar we found few differences among the patterns for by but for by variations emerged that are consistent with a possible dependence on universal time ut the impacts of season and ut on convection in the high latitude ionosphere thus depends on the imf especially the sign of by we speculate that variability in the ionospheric conductivity has a greater effect on magnetosphere ionosphere coupling under by conditions

relationship between plagioclase crystallization and cooling rate in basaltic melts rock textures commonly preserve a record of the near surface crystallization history of volcanic rocks under conditions of simple cooling without convection or mixing textures will reflect sample cooling rate the temperature at which crystallization was initiated and the distribution of mineral phase precipitation across the crystallization interval compilation of plagioclase size and number density data on natural dike sill and lava lake and experimental samples suggests that 1 growth and nucleation rates of plagioclase in natural basaltic samples are a predictable function of cooling rate and 2 the observed crystallization rate dependence on cooling rate is similar to that observed in experiments initiated at subliquidus temperatures comparison of natural and experimental samples thus suggests that most basalts crystallize under conditions of heterogeneous nucleation with the number density of preexisting nucleii partially controlling textural responses to cooling rate changes time scales of crystallization and cooling in magmatic systems are intimately linked through a balance between heat removal from the system and heat evolved through crystallization evaluation of textural data in the context of recent numerical models of crystallization in simple one and two component systems provides new insight into regularities in the crystallization behavior of basaltic magmas for example the rate of change in crystal size and number density as dictated by mass balance has been used as a measure of the relative importance of time scales of crystallization and cooling in numerical models of crystallizing systems in natural samples plagioclase size scales with the length scale of cooling such that a logarithmic plot of grain size as a function of normalized distance across the dike has a slope that appears approximately independent of dike width solidification time comparison with available textural data for other phenocryst phases suggests that the same may be true for pyroxene and magnetite crystallization with each phase having a characteristic slope probably controlled by the thermodynamic properties of the crystallizing phase measured crystal size distributions are unimodal and show maximum frequencies in the smaller size classes distributions broaden and the grain size at peak frequency increases with increasing crystallization times decreasing cooling rates in contrast partially crystallized makaopuhi lava lake samples have crystal size distributions that decrease exponentially with increasing crystal size measured size distributions in dikes can be explained by late stage modification of makaopuhi type distributions through loss of small crystals possibly the consequence of growth without nucleation finally this compilation of the textural response of basaltic magmas to changes in cooling rate suggests that empirical calibrations of crystallization rate dependence on cooling rate from natural samples provide a reasonable model for plagioclase crystallization in near surface basaltic systems predicted growth rates will be slow and relatively constant 10 10 10 11 cm s for crystallization times expected in most shallow volcanic systems 1000 years

role of poleward moving auroral forms in the dawn dusk auroral precipitation asymmetries induced by imf by 1 in a case study we document the detailed spatial temporal structure of the aurora in the 0900 1500 magnetic local time mlt sector during an interval of steady southeast imf orientation emphasis is placed on ground based observations of structure that is often averaged out in large statistical studies a central feature is the phenomenon of poleward moving auroral forms pmafs an ionospheric manifestation of pulsed magnetopause reconnection in the form of flux transfer events ftes whose evolution in both prenoon and postnoon mlts can be monitored under similar interplanetary conditions differences in auroral precipitation associated with pmafs about the noon meridian related to imf by are documented while the prenoon pmafs develop in three stages spanning a latitude range of 500 km the highest latitude stage is absent in postnoon pmafs for by 0 which after the initial intensification progressively fade we suggest that this auroral precipitation asymmetry is closely related to the different field aligned current configuration in pmafs prenoon and pmafs postnoon and the underlying plasma convection pattern we detail the association between the high latitude component of pmafs in the prenoon sector by 0 and a channel of plasma convection located in the dawnside convection cell the latter convection channel located in the regime of old open flux represents an aspect of the svalgaard mansurov effect which is not included in the traditional description the auroral and plasma convection data are placed in the context of recent work on solar wind magnetosphere interconnection topology for a southward pointing imf with a strong by component

near simultaneous polar and dmsp measurements of topside ionospheric field aligned flows at high latitudes near simultaneous observations of topside 0 parallel flows are presented for four periods of measurement by polar and dmsp satellites during april 1996 the polar measurements are from southern perigee measurements near 5000 km altitude while the dmsp measurements were from 840 km altitude these observations provide a view of wide spread upward downward ionospheric o flows over the broad polar region along extended and multiple distinct satellite tracks in general the velocities are upward toward expected cleft and auroral latitudes typically about a 2 10 km s at 5000 km altitude and 0 2 km s at 840 km altitudes at the highest polar cap latitudes downward velocities are more frequent at both altitudes but especially at the lower 840 km altitude the downward velocities were typically a few hundred d s at 840 altitude and 0 1 km s at 5000 km altitude in some instances apparently downward velocities were observed at 840 km altitudes while upward 0 flows were observed at 5000 km altitude on the same flux tube the o density were characteristically 1 10 o cu cm at 5000 km altitude and 10 exp 3 10 exp 40 o cu cm at 840 km altitude while the o flux were characteristically 1 10 exp 5 10 exp 7 o sq cm sec at 5000 km altitudes and characteristically 10 exp 7 10 exp 9 o sq cm sec at 840 km altitude we have also examined the dual altitude parameter measurements for a polar cap field line the polar and dmsp measurements approximately 30 minutes apart and compared them with results from a transport simulation in which a flux tube was subjected to a brief pulse of soft electron precipitation and topside transverse ion heating the simulated density and velocity altitude profiles for 5 minutes later generally matched the observations except that the observed downward velocities 500 600 m s at 840 km altitude were much larger than those simulated

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

coeval formation of cataclasite and pseudotachylyte in a miocene forearc granodiorite southern kyushu japan abstract cataclastic rocks and pseudotachylytes are exposed along the uchinoura shear zone a normal fault zone cutting the middle miocene 14 ma osumi granodiorite in southern kyushu japan cataclastic rocks include non foliated clast supported to matrix supported cataclasite and foliated clast supported cataclastic granodiorite in these rocks fracturing and comminution played a major role but dissolution and recrystallization of quartz and plastic deformation of quartz and biotite were also active processes especially in foliated granodiorite two types of pseudotachylyte are distinguished a foliated type characterized by a planar arrangement of clasts and microlites and a spherulitic type characterized by clasts surrounded by microlite overgrowths both types are of melt origin as attested by the presence of microlites and rounded or embayed clasts and by the scarcity of biotite clasts unlike spherulitic type pseudotachylyte which solidified without being deformed the foliated type pseudotachylyte underwent flow before complete solidification this deformation is thought to reflect post seismic strain accommodation immediately following the main slip episode kinematic indicators which consist of riedel type secondary fractures branching on primary fractures shear bands offsetting the foliation of foliated granodiorite or asymmetrical porphyroclast systems within pseudotachylyte veins show that all fault rocks were generated during n s to nw se directed extensional deformation pseudotachylyte is closely associated both in time and space with cataclastic rocks thus indicating that the behaviour of the uchinoura fault zone alternated between comminution and frictional melting given the slow strain rates which characterize dissolution and recrystallization processes detected in cataclasites the juxtaposition of pseudotachylytes and foliated cataclasites provides an example of aseismic and seismic displacements within the same shear zone

zircon u pb age hf isotope and geochemistry of carboniferous intrusions from the langshan area inner mongolia petrogenesis and tectonic implications abstract late paleozoic was a critical period for the tectonic evolution of the northern margin of the alxa north china craton but the evolutionary history is not well constrained the carboniferous intrusions in the langshan area in the western part of the northern margin of the alxa north china craton are mainly composed of tonalite quartz diorite olivine gabbro and pyroxene peridotite zircon la icp ms u pb dating indicates that the langshan carboniferous intrusions were emplaced at ca 338 324 ma the quartz diorites are characterized by high amounts of compatible trace elements cr ni and v and high mg values which may suggest a significant mantle source the positive pb and negative nb ta ti anomalies the variable ehf t 6 9 to 2 0 values and the old hf model ages 1218 1783 ma imply some involvement of ancient continental materials in its petrogenesis the tonalite has relatively high sr y ratios low mg yb and y contents features of adakite like rocks negative ehf t values 9 8 to 0 1 and older hf model ages 1344 1953 ma which suggest significant involvement of ancient crust materials and mantle derived basaltic component in its petrogenesis the high mg values high cr and ni contents and low zr and hf contents of the mafic ultramafic rocks show evidence of a mantle source and the relatively low zircon ehf t values 5 9 to 3 2 might point to an enriched mantle the trace element characteristics indicate the influence of subducted sediments and slab derived fluids in the tectonic discrimination diagrams all the rocks plot in subduction related environment such as volcanic arc and continental arc considering the regional geology we suggest that the carboniferous intrusions in the langshan area were likely emplaced during the late stage of the southward subduction of the paleo asian ocean plate which formed a continental arc along the northern margin of the alxa north china craton

fluid inclusions in pseudotachylytes from the nojima fault japan pseudotachylytes i e rocks formed by frictional melting have been observed in the nojima fault that was penetrated by the hirabayashi borehole drilled 1 year after the 1995 hyogo ken nanbu kobe earthquake these rocks display millimeter scale banding defined by different pseudotachylyte layers the nature of unmolten crystal fragments k feldspar albite calcite and or quartz allows us to infer a minimum melting temperature of 1200 c the glass has a 8 3 volatile content and a higher cao content than that of the parent granodiorite thus suggesting that pseudotachylyte formation occurred in an already altered calcite bearing and hydrated fault zone fluid inclusions have been observed in the glass and are filled with a dense low salinity 4 3 1 2 wt eq nacl co2 h2o fluid characterized by steep isochoric curves the intersection between the isochores and the measured 24 c km geothermal gradient indicates a minimum 15 km depth for the pseudotachylyte formation such a depth suggests that an important uplift has brought the studied pseudotachylytes to their present position and that these pseudotachylytes are probably pre miocene in age the calculated thermal evolution of a typical millimeter scale pseudotachylyte layer indicates that cooling does not last more than a few seconds this indicates that related seismic processes such as deceleration of fault movement and healing of the fault were both very rapid the geometry and thermal budget of the millimeter thick pseudotachylytes suggest that seismic events of magnitude 6 to 7 are responsible for their formation

longitudinal modulation of electron and mass densities at middle and auroral latitudes effect of geomagnetic field strength in this study the effect of a reduction in magnetic field strength on the longitudinal modulation of electron density ne and mass density is investigated we study conditions during the september equinox and june and december solstices at middle and auroral latitudes in both northern and southern hemispheres the global ionosphere thermosphere model was employed for the theoretical study simulations were performed with a realistic international geomagnetic reference field igrf model and an igrf model reduced in strength by 50 the reduction in field strength increased the longitudinal variations in ne by 2 34 in the nighttime sector but reduced the variation by 7 20 in the daytime sector at mid latitudes in both hemispheres conversely at auroral latitudes ne was reduced by 2 32 at all local times the changes during equinoxes are larger than those for the solstices the differences with local time in the response of ne to a reduction in magnetic field strength were mainly due to changes in the oxygen molecular nitrogen o n2 ratio in the northern hemisphere whereas the differences were due to the combined effects of vertical winds and changes in the o n2 ratio in the southern hemisphere both vertical winds and horizontal e b convection eliminated ne at high latitudes got enhanced at both middle and auroral latitudes which was related to the enhanced joule heating effect when the magnetic field was reduced

geologic evidence for multiple slip weakening mechanisms during seismic slip in crystalline rock we examine exhumed seismogenic faults to investigate the mechanisms that may have achieved dynamic fault weakening during ancient ruptures field and microscope observations imply more than one weakening mechanism must have been active during slip events on the faults pseudotachylytes that are continuous over the scale of field exposures are indicative of melt lubrication a fault breccia crosscutting earlier formed cataclasites was mobilized during faulting and possibly represents a pressurized fault rock that resulted from thermal pressurization or elastohydrodynamic lubrication in some faults pseudotachylytes are developed in patches several meters long cataclasites in which there is no evidence for melting are present immediately along strike from the pseudotachylyte patches by considering the energy required for melting we show that the pseudotachylytes must have formed during ruptures larger than the patches implying that the cataclasites also accommodated seismic slip the distribution of fault rock types shows that the frictional response to slip during a single event was spatially variable reworked pseudotachylytes also indicate that coseismic processes change over time at a point on a fault these observations emphasize that macroscopic dynamic fault weakening is a function of multiple coeval processes at microscales to mesoscales detailed observations of the discontinuous pseudotachylytes show that slip zone thickness is the critical parameter that controls active coseismic processes the frictional response of a fault to slip is therefore dependent on the internal structure of faults given the along strike heterogeneity of most mapped fault zones the coexistence of multiple slip weakening mechanisms in a single earthquake will be common

structural aspects of fluid rock interactions in detachment zones metamorphic core complexes and associated detachment faults of the north american cordillera represent gently dipping normal displacement shear zones detachment zones along which hot deeper levels of the crust were transported upward and outward from underneath a brittlely distended upper plate structures that formed during the ductile to brittle evolution of detachment zones can be used to reconstruct the relative magnitudes of fluid pressure and deviatoric stress at different levels within the shear zones mylonitization which occurred along deeper segments of detachment zones below the brittle ductile transition was locally accompanied by tensile failure indicative of low deviatoric stress and high fluid pressure this condition persisted into the earliest phases of brittle deformation after which shear fractures formed due to both a reduction in fluid pressure and an increase in deviatoric stress brittle deformation of upper plate rocks occurred largely under conditions of low fluid pressure structural and geochemical data suggest that normal displacement on detachment zones results in establishment of two fluid systems 1 an upper plate system driven by convection and dominated by meteoric and connate fluids at near hydrostatic pressures and 2 a system within deeper levels of the shear zone where fluids are largely derived from igneous sources and fluid migration is aided by dilatancy pumping the late phases of normal displacement on detachment zones structurally juxtaposed rocks affected by the two fluid systems and locally caused the shear zone rocks to be overprinted by mineralization related to the upper plate fluid system

superposed epoch analysis of the ionospheric convection evolution during substorms imf by dependence we present superposed epoch analyses of the average ionospheric convection response in the northern and southern hemispheres to magnetospheric substorms occurring under different orientations of the interplanetary magnetic field imf observations of the ionospheric convection were provided by the super dual auroral radar network superdarn and substorms were identified using the far ultraviolet fuv instrument on board the imager for magnetopause to aurora global exploration image spacecraft we find that during the substorm growth phase the expected imf by dependent dawn dusk asymmetry is observed over the entire convection pattern but that during the expansion phase this asymmetry is retained only in the polar cap and dayside auroral zone in the nightside auroral zone the convection is reordered according to the local substorm electrodynamics with any remaining dusk dawn asymmetry being more closely related to the magnetic local time of substorm onset itself only weakly governed by imf by owing to the preponderance of substorms occurring just prior to magnetic midnight the substorm asymmetry tends to be an azimuthal extension of the dusk convection cell across the midnight sector a manifestation of the so called harang discontinuity this results in the northern southern hemisphere nightside auroral convection during substorms generally resembling the expected pattern for negative positive imf by when the preexisting convection pattern in the northern southern hemisphere is driven by positive negative imf by the nightside auroral convection changes markedly over the course of the substorm to establish this same harang configuration

superheated friction induced melts in zoned pseudotachylytes within the adamello tonalites italian southern alps pseudotachylytes and cataclasites are present along a strike slip fault zone in the tonalites of the adamello intrusion italian southern alps ambient conditions during faulting were 0 25 0 3 gpa and 250 300 c pseudotachylyte veins thicker than 6 mm are zoned and consist of two symmetric microlitic domains towards the vein walls and a central spherulitic domain the thickness of the microlitic domains x increases linearly with the half total thickness a of the pseudotachylyte vein commonly 2 cm according to the relation x 0 29 0 12 a the spherulitic and microlitic domains have similar chemical composition but the microlitic domain has a lower amount of plagioclase clasts a numerical model explains zoning as the result of the different cooling rates and clast melt interactions at the center and periphery of thick veins zoning is compatible with the injection of a single pulse of superheated friction induced melt tmelt 1450 c melt temperatures estimated by the clast matrix ratio o hara 2001 are considerably lower 316 577 c it is suggested that the difference in the temperature estimates reflects a more complex slip history than a single seismic slip event along the fault during production of cataclasites pseudotachylytes

rough faults distributed weakening and off fault deformation 1 we report systematic spatial variations in fault rocks along nonplanar strike slip faults cross cutting the lake edison granodiorite sierra nevada california sierran wavy fault and lobbia outcrops of the adamello batholith in the italian alps lobbia wavy fault in the case of the sierran fault pseudotachylyte formed at contractional fault bends where it is found as thin 1 2 mm fault parallel veins epidote and chlorite developed in the same seismic context as the pseudotachylyte and are especially abundant in extensional fault bends we argue that the presence of fluids as illustrated by this example does not necessarily preclude the development of frictional melt in the case of the lobbia fault pseudotachylyte thickness varies along the length of the fault but the pseudotachylyte veins thicken and pool in extensional bends we conduct a quantitative analysis of fault roughness microcrack distribution stress and friction along the lobbia fault numerical modeling results show that opening in extensional bends and localized thermal weakening in contractional bends counteract resistance encountered by fault waviness resulting in an overall weaker fault than suggested by the corresponding static friction coefficient the models also predict static stress redistribution around bends in the faults which is consistent with distribution of microcracks indicating significant elastic and inelastic strain energy is dissipated into the wall rocks due to nonplanar fault geometry together these observations suggest that damage and energy dissipation occurs along the entire nonplanar fault during slip rather than being confined to the region close to the dynamically propagating crack tip

isotopic composition of precipitation in italy a first overall map abstract composite monthly samples of atmospheric precipitation were collected over different periods of time ranging from one to seven years at 77 different locations throughout italy these samples were measured for their oxygen and hydrogen isotopic composition to obtain basic information for hydrological and meteorological studies in this area on the basis of the results obtained a first map of the isotopic composition of precipitations in italy has been drawn up the main features of this map are the following 1 no isotopic latitudinal gradient has been found along the tyrrhenian coast from sicily to the italian french border despite the considerable range of latitude 2 a minor latitudinal gradient is found in the southeasternmost section of the country apulia partially favored by the local morphology 3 a marked shadow effect of the apennines is apparent along the southern section of the po valley and along the central section of the adriatic coast 4 the contribution of water vapor from the northernmost section of the adriatic sea affects the eastern and central sections of the po plain 5 the shadow effect of the alps is considerably smaller than expected 6 the isotopic vertical gradients calculated in nine different areas and based on groups of two to five different stations vary but are essentially close to about 0 2 100 m 7 when mean monthly temperature values were available their relationship with the isotopic composition of precipitation was found to be on average very poor 8 the relationship between mean 18o and mean d calculated for the collection locations shows shifts of both the slope and the deuterium excess when compared to the global meteoric water line these shifts are different for northern central and southern italy 9 in a few cases anomalously low monthly values suggest the existence of pronounced amount effects

instantaneous healing of micro fractures during coseismic slip evidence from microstructure and ti in quartz geochemistry within an exhumed pseudotachylyte bearing fault in tonalite abstract exhumed faults within the tonalitic adamello pluton southern alps were seismic at depth as indicated by the presence of pseudotachylytes solidified friction induced melts during cooling of tonalite early formed joints were first exploited by localized ductile shear zones associated with deposition of quartz veins at 500 c and later by pseudotachylyte bearing cataclastic faults at 250 300 c ambient temperature adjacent to pseudotachylytes quartz of the host tonalite shows pervasive thin 1 10 m wide healed micro fractures and ultra fine 1 2 m grain size recrystallized aggregates along micro shear zones under cathodoluminescence cl the healed micro fractures have a darker gray shade than the host magmatic quartz that reflects a change in ti concentrations ti as indicated by nanosims measurements ti vary from 35 55 ppm in the cl lighter host quartz to 10 13 ppm along the cl darker healed micro fractures these ti were inherited by the ultra fine recrystallized aggregates that overprinted both the magmatic quartz and the healed micro fractures during the high temperature transient related to frictional seismic slip based on ti in quartz thermometry we infer that micro fracture healing occurred at higher temperatures than the ambient temperatures of faulting 250 300 c at 0 2 gpa for which ti

interhemispheric asymmetry of the high latitude ionospheric convection on 11 12 may 1999 1 ionospheric convection over the southern polar cap on 11 12 may 1999 has been studied by using the syowa east and south hf radar data and the dmsp ion driftmeter data when the solar wind density was very low and geomagnetic activity was low the overall convection pattern is consistent with the previous results by ohtani et al 2000 however the syowa radars and the dmsp satellites observed very high 1500 m s westward plasma flows at dusk directed from the nightside toward the dayside only in the southern dark hemisphere the high speed flow was observed continuously across the fields of view of both radars from 1530 ut on 11 may to 0200 ut on 12 may when the solar wind density was close to minimum comparison with the dmsp particle and auroral image data shows that the westward flow regions were located in the middle of the auroral precipitation area the strong asymmetry of the convection between the two hemispheres indicates the importance of the presence absence of solar illumination for the absence presence of the strong and localized ionospheric flows

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

stable isotopic evidence for large scale seawater infiltration in a regional metamorphic terrane the trois seigneurs massif pyrenees france oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a hercynian metamorphic sequence in the trois seigneurs massif pyrenees france indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous 18o values the extent of homogenization is shown by the similarity of 18o values in metacarbonates metapelites and granitic rocks 11 to 13 and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies these values contrast with the 18o values of metapelites of lower metamorphic grade 18o about 15 homogenization was caused by a pervasive influx of hydrous fluid mass balance calculations imply that the fluid influx was so large that its source was probably high level groundwaters or connate formation water hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at d 25 to 30 suggesting a seawater origin many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water rich fluid the composition of which was externally buffered deep penetration of surface waters in such environments has been hitherto unrecognized and may be a key factor in promoting major anatexis of the continental crust at shallow depth three types of granitoid are exposed in the area the leucogranites and the biotite granite quartz diorite are both mainly derived from fusion of local paleozoic pelitic metasediment because all these rocks have similar whole rock 18o values 11 to 13 the post metamorphic biotite granodiorite has a distinctly different 18o 9 5 to 10 0 and was probably derived from a deeper level in the crust rare mafic xenoliths within the deeper parts of the biotite granite quartz diorite also have different 18o 8 0 to 8 5 and possibly represent input of mantle derived magma which may have provided a heat source for the metamorphism