a frictional law for volcanic ash gouge abstract volcanic provinces are structurally active regions undergoing continual deformation along faults within such fault structures volcanic ash gouge containing both crystalline and glassy material may act as a potential fault plane lubricant here we investigate the frictional properties of volcanic ash gouges with varying glass fractions using a rotary shear apparatus at a range of slip rates 1 3 1300 mm s and axial stresses 0 5 2 5 mpa we show that the frictional behaviour of volcanic ash is in agreement with byerlee s friction law at low slip velocities irrespective of glass content the results reveal a common non linear reduction of the friction coefficient with slip velocity and yield a frictional law for fault zones containing volcanic ash gouge textural analysis reveals that strain localisation and the development of shear bands are more prominent at higher slip velocities 10 mm s the textures observed here are similar to those recorded in ash gouge at the surface of extrusive spines at mount st helens usa we use the rate weakening component of the frictional law to estimate shear stress resistance reductions associated with episodic seismogenic slip events that accompany magma ascent pulses we conclude that the internal structure of volcanic ash gouge may act as a kinematic marker of exogenic dome growth

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

deformation fabrics and strain localization mechanisms in graphitic carbon bearing rocks from the ailaoshan red river strike slip fault zone abstract graphitic carbon bearing rocks generally occur in low to high grade metamorphic units in many brittle faults graphitic carbon is often associated with gouge or low grade metamorphic rocks whereas in ductile faults graphitic carbon commonly occurs in marble schist or gneiss carbonaceous material gradually transforms from an amorphous into an ordered crystalline structure by increasing thermal metamorphism the degree of graphitization is believed to be a reliable indicator of peak temperature conditions in the metamorphic rock in this contribution based on detailed field observations the variably deformed and metamorphosed graphitic gneisses to phyllites located within the footwall and hangingwall unit of the cenozoic ailaoshan red river strike slip shear zone are studied according to lithological features and temperatures determined by raman spectra of carbonaceous material these graphitic rocks and deformation fabrics are divided into three types type i is represented by medium grade metamorphism and strongly deformed rocks with an average temperature of 509 c and a maximum temperature of 604 c type ii is affected by low grade metamorphism and deformed rocks with an average temperature of 420 c type iii is affected by lower grade metamorphism and occurs in weakly deformed undeformed rocks with an average temperature of 350 c slip localized micro shear zones and laterally continuous or discontinuous slip planes constituted by graphitic carbon aggregates are developed in types i and ii the electron back scattered diffraction ebsd lattice preferred orientation lpo patterns of graphitic carbon grains were firstly observed in comparison with lpo patterns of quartz and switch from basal rhomb to prism slip systems which indicate increasing deformation temperatures comparison of quartz and graphite lpos indicates that graphite lpos show higher temperature conditions according to the graphitic slip planes micro shear zones with grain size reduction and mylonitic foliation constituted by graphitic carbon minerals we also propose that the development of fine grained amorphous carbon plays an important role in rheological weakening of the whole rock during progressive ductile shearing

structural and geochronological constraints on the tectonic evolution of the dulong song chay tectonic dome in yunnan province sw china abstract the dulong song chay tectonic dome lies on the border of china se yunnan province and northern vietnam and consists of two tectonic and lithologic units a core complex and a cover sequence separated by an extensional detachment fault these two units are overlain unconformably by late triassic strata the core complex is composed of gneiss schist and amphibolite shrimp zircon u pb dating results for the orthogneiss yield an age of 799 10 ma which is considered to be the crystallization age of its igneous protolith formed in an arc related environment a granitic intrusion within the core complex occurred with an age of 436 402 ma which probably formed during partial closure of paleotethys within the core complex metamorphic grades change sharply from upper greenschist low amphibolite facies in the core to low greenschist facies in the cover sequence there are two arrays of foliation within the core complex detachment fault and the cover sequence s 1 and s 2 the pervasive s 1 is the axial plane of intrafolial s 0 folds d 1 deformation related to this foliation is characterized by extensional structures the strata were structurally thinned or selectively removed along the detachment faults indicating exhumation of the dulong song chay tectonic dome the major extension occurred at 237 ma determined by shrimp zircon u pb and 39 ar 40 ar isotopic dating techniques regionally simultaneous tectonic extension was associated with pre indosinian collision between the south china and indochina blocks the s 2 foliation appears as the axial plane of nw striking s 1 buckling folds formed during a compressional regime of d 2 d 2 is associated with collision between the south china and indochina blocks along the jinshajiang ailao shan suture zone and represents the indosinian deformation the dulong granites intruded the dulong song chay dome at 144 2 140 2 and 116 10 ma based on 39 ar 40 ar measurement on muscovite and biotite the dome was later overprinted by a conjugate strike slip fault and related thrust fault which formed a vortex structure contemporaneously with late cenozoic sinistral movement on the ailao shan red river fault

coseismic extension recorded within the damage zone of the vado di ferruccio thrust fault central apennines italy abstract recent high resolution hypocentral localisation along active fault systems in the central apennines illuminates the activation of seismogenic volumes dipping at low angle here we report field and microstructural evidence of seismogenic extensional faults localized within pre existing thrust fault zones the vado di ferruccio thrust fault vftf is a narrow fault zone

vitrinite reflectance and raman spectra of carbonaceous material as indicators of frictional heating on faults constraints from friction experiments abstract vitrinite reflectance r o and raman spectra of carbonaceous material rscm are both widely used as indicators of the maximum attained temperatures in sedimentary and metamorphic rocks however the potential of these methods to estimate temperature increases associated with fault slip has not been closely studied to examine this issue friction experiments were conducted on a mixture of powdered clay rich fault material and carbonaceous material cm at slip rates of 0 15 mm s and 1 3 m s in nitrogen n 2 gas with or without distilled water after the experiments we measured r o and rscm and compared to those in starting material the results indicate that when fault material suffers rapid heating at 500 c in 9 s at 1 3 m s r o and the intensity ratio of d1 and d2 raman bands of cm i d2 i d1 markedly increase comminution with very small temperature rise in 32 min at 0 15 mm s is responsible for very limited changes in r o and i d2 i d1 our results demonstrate that r o and rscm could be useful for the detection of frictional heating on faults when the power density is 0 52 mw m 2 however the conventionally used r o and rscm geothermometers are inadequate for the estimation of peak temperature during seismic fault slip the reaction kinetics incorporating the effects of rapid heating at high slip rates and studies of the original microtexture and composition of cm are required to establish a reliable thermometer for frictional heating on faults

the correlation between mid latitude trough and the plasmapause 1 we use simultaneous global observations of the mid latitude trough and the plasmapause to experimentally prove a long standing conjecture of magnetosphere ionosphere coupling namely the mid latitude trough and plasmapause are on the same field line global ionospheric maps gim generated using ground based gps receivers are used to detect the globally extended mid latitude trough while global image euv pictures are used to estimate the plasmapause position observations during the equinox and solstices and during quiet and disturbed periods are analyzed in addition positions of the mid latitude trough are calculated using a simple empirical model the two independent observations mid latitude trough and plasmapause positions and an empirical model have been compared on a global scale and found to be in excellent agreement

frictional properties of natural gouges from longmenshan fault zone ruptured during the wenchuan mw7 9 earthquake abstract we investigated the properties of frictional sliding of natural gouges collected from longmenshan fault zone which ruptured during the wenchuan mw7 9 earthquake based on xrd analysis five gouge samples of different mineralogical assemblies and mineral contents are chosen for frictional sliding experiments with initial confining pressure of 50 mpa and at different temperatures from 25 c to 150 c to obtain the rate dependence of friction shearing rates are stepped up and down in the range of 0 0488 to 6 1 m s while the friction coefficient of most gouge samples decreases with the clay content following a general trend consistent with previous studies the organic matter bearing sample px 3 shows a much lower value than the prediction by the general trend indicating further strength reduction due to the 9 organic matter included we also found a significant effect of temperature on the sliding behavior of organic matter bearing and carbonate rich gouges when temperature increases to 150 c the px 3 sample with organic matter exhibits unstable oscillation that indicates velocity weakening frictional sliding behavior in contrast to the velocity strengthening behavior at lower temperatures the velocity dependence of carbonate rich samples px 1 px 2 with more than 50 wt carbonates is also sensitive to temperature and shearing rates and both samples have smaller velocity dependence of friction a b at higher temperatures the a b value of the px 2 sample with 80 carbonates even decreases to the velocity neutral point at 150 c and slow shearing rates based on the rate and state friction framework fast slip nucleation is possible for faults associated with the organic matter bearing gouge at 150 c whereas triggered seismic slips are possible in faults that include the carbonate rich samples which have a small a b value at 150 c the temperature dependent sliding behavior of carbonate dominant and organic matter bearing gouges probably provides a new clue to the problem of transition from shallow aseismic zone to seismic zone in subduction interfaces of the oceanic plate

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

weak faults rotten cores earthquakes are triggered when crustal deformation produces displacements along fault zones the rock in these zones is found to be weaker than adjacent material but what are the mechanisms of this loss of strength in his perspective holdsworth 1 discusses how recent studies of exposed ancient fault zones combined with laboratory analyses are revealing that rock properties at the grain scale can determine the large scale behavior of crustal deformation 1 http www sciencemag org cgi content full 303 5655 181

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

crystallographic controls on the frictional behavior of dry and water saturated sheet structure minerals 1 we compare the frictional strengths of 17 sheet structure mineral powders measured under dry and water saturated conditions to identify the factors that cause many of them to be relatively weak the dry coefficient of friction ranges upward from 0 2 for graphite leveling off at 0 8 for margarite clintonite gibbsite kaolinite and lizardite the values of dry correlate directly with calculated 001 interlayer bond strengths of the minerals this correlation occurs because shear becomes localized along boundary and riedel shears and the platy minerals in them rotate into alignment with the shear planes for those gouges with dry 0 8 shear occurs by breaking the interlayer bonds to form new cleavage surfaces where dry 0 8 consistent with byerlee s law the interlayer bonds are sufficiently strong that other frictional processes dominate the transition in dry friction mechanisms corresponds to calculated surface energies of 2 3 j m2 adding water causes to decrease for every mineral tested except graphite if the minerals are separated into groups with similar crystal structures wet increases with increasing interlayer bond strength within each group this relationship also holds for the swelling clay montmorillonite whose water saturated strength is consistent with the strengths of nonswelling clays of similar crystal structure water in the saturated gouges forms thin structured films between the plate surfaces the polar water molecules are bonded to the plate surfaces in proportion to the mineral s surface energy and wet reflects the stresses required to shear through the water films

on the role of phyllosilicates on fault lubrication insight from micro and nanostructural investigations on talc friction experiments 1 exposures of mature faults at the earth s surface show that in the shallow crust some of co seismic slip occurs within a narrow phyllosilicate rich gouge material mechanical behavior of phyllosilicates sheared at seismic slip velocities remains a complex issue as suggested by the experimental and theoretical studies reported so far talc represents a simple case for common phyllosilicates in natural faults and therefore we chose talc as an analogue to better understand the mechanical behavior of clay rich mature crustal faults we present a series of high velocity friction experiments conducted on talc at 1 31 m s 1 and normal stresses of 0 3 1 8 mpa for wet and dry conditions at 1 mpa normal stress both wet and dry experiments show a slip weakening behavior however with a higher decreasing rate in wet conditions dynamic shear stress evolves from a peak value of 0 24 0 52 mpa down to a residual state value of 0 08 0 18 mpa in wet conditions and from a peak value of 0 46 1 17 mpa down to a residual state value of 0 12 0 62 mpa in dry conditions based on a detailed microstructural analysis down to the nanoscale we propose thermal pressurization as a possible slip weakening mechanism for wet conditions on the contrary in dry conditions the long lasting weakening is interpreted to be due to a combination of i progressive disappearance of geometrical incompatibilities ii solid lubrication of talc lamellae and iii powder lubrication by nanometric aggregates we conclude that initial gouge humid conditions and inherited fabric from past sliding may have large influence on the slip weakening for subsequent slip

experimental frictional heating of coal gouge at seismic slip rates evidence for devolatilization and thermal pressurization of gouge fluids high velocity 1 m s friction experiments on bituminous coal gouge display several earthquake related phenomena including devolatilization by frictional heating gas pressurization and slip weakening stage i is characterized by sample shortening and reduction in the coefficient of friction from 1 to 0 6 stage ii is characterized by high frequency 5 hz oscillations in stress and strain records and by gas emissions stage iii is marked by rapid weakening 0 1 to 0 35 and sample shortening together with continued gas emissions stage iv produces stable stress records and continued weakness 0 2 but without gas emission stage i shortening is due to compaction of the gouge and the weakening is attributed to mechanical or thermal effects stage ii behavior is interpreted as due to coal gasification and fluctuations in fluid pressure resulting in high frequency stick slip type behavior dramatic reduction in shear stress in stage iii is attributed to gas pressurization by pore collapse and corresponds to a frictional instability analogous to nucleation of an earthquake microstructural observations indicate the deformation was brittle during stages i and ii but ductile during stages iii and iv time dependent finite element frictional heat models indicate the center of the samples became hot 900 c during stage ii whereas the edge of samples remained relatively cold 300 c vitrinite reflectance of coal samples shows an increase in reflectance from 0 5 to 0 8 over the displacement interval 20 40 m 20 40 s indicating that the reflectance responds to frictional heating on a short time scale the energy expended per unit area in these low stress large displacement experiments is similar to that of higher stress 50 mpa short displacement 1 m earthquakes 107 j m2

textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone alpine fault new zealand graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization we examine processes of graphitic carbon emplacement and deformation in the active alpine fault zone new zealand by analysing samples obtained from deep fault drilling project dfdp boreholes optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain raman spectroscopy allowed interpretation of the degree of graphite crystallinity which reflects both thermal and mechanical processes in the amphibolite facies alpine schist highly crystalline graphite indicating peak metamorphic temperatures up to 640 c occurs mainly on grain boundaries within quartzo feldspathic domains the subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions 500 600 c resulting in clustered in protomylonites and foliation aligned graphite in mylonites in cataclasites derived from the mylonitized schists graphite is most abundant 50 as opposed to 10 elsewhere and has two different habits inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon tectonic hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences the increasing abundance of graphite towards the fault zone core may be a significant source of strain localization allowing fault weakening

extreme dynamic weakening of faults during dehydration by coseismic shear heating the dynamic strength of seismogenic faults has a critical effect on earthquake slip instability and seismic energy release high velocity friction experiments on simulated faults in serpentinite at earthquake slip conditions show a decrease in friction coefficient from 0 6 to 0 15 as the slip velocity reaches 1 1 m s at normal stresses up to 24 5 mpa the extraordinary reduction in fault strength is attributed to flash heating at asperity contacts of gouge particles formed during sliding the rapid heating at asperities causes serpentine dehydration in impermeable fault zones in nature serpentine dehydration and subsequent fluid pressurization due to coseismic frictional heating may promote further weakening this dynamic fault weakening mechanism may explain the lack of pronounced heat flow in major crustal faults such as the san andreas

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

frictional strength and wear rate of carbonate faults during high velocity steady state sliding article history we ran an extensive series of shear experiments to test the effect of shear velocity and normal stress on wear rate and frictional strength the experiments were conducted on three types of carbonate samples with a rotary shear apparatus on solid ring shaped rock samples that slipped for displacements up to tens of meters at slip velocity of v 0 002 0 96 m s and normal stress n 0 25 6 9m pa the analysis reveals that during steady state stage the values of wear rate and frictional strength depend on both slip velocity and normal stress the wear rates at low slip velocity show linear relations to the normal stress archard s model however at high velocity v 0 5m s the wear rates are independent of the normal stress and may vanish at the highest velocity and normal stress of the present experiments the steady state friction coefficient correlates best with the experimental power density shear stress slip velocity we recognized three friction regimes high 0 8a t low power density low 0 3 at high power density and a transition regime of fast drop of friction coefficient as the power density increases from 0 03 to 0 3 mw m 2 runs of low power density high friction displayed fault surfaces covered with fine grained gouge whereas runs of high power density low friction displayed shiny smooth fault surfaces we interpret the observed intensity variations of wear rate and frictional strength as indicating a brittle to ductile transition associated with frictional heating

paleomagnetic study of permian and mesozoic sedimentary rocks from northern thailand supports the extrusion model for indochina abstract the mode of deformation of southeast asia resulting from the indian collision is still controversial is convergence between stable india and siberia absorbed principally by crustal shortening and thickening and minor strike slip faulting or by a mechanism of extrusion involving crustal thickening and lateral escape of blocks along major strike slip zones in order to test these models we have carried out a paleomagnetic study of sedimentary rocks of jurassic to cretaceous age on the khorat plateau in thailand a large discrepancy between the poles of indochina presented in this paper and a compilation of south china block pole positions both at the triassic jurassic and the jurassic cretaceous boundary imply some 1500 800 km of post middle cretaceous left lateral slip along the red river and xian shui he fault zones and approximately 14 7 of clockwise rotation for the indochina block relative to the south china block such relative motions are in agreement with a model of lateral extrusion of indochina during the india asia collision additional data of permian upper triassic and lower jurassic age collected in indochina indicate a post late permian remagnetization for the upper permian limestones a comparison of these data with those from yunnan south china the north china block and the south china block shows that these blocks have probably been in contact at least since the late triassic

storm enhanced plasma density and polar tongue of ionization development during the 15 may 2005 superstorm we investigate the ionosphere s global response to the 15 may 2005 superstorm in terms of storm evolution and ionospheric electrodynamics our aim is to study the global distribution of plasma and the resultant large scale ionospheric features including the equatorial ionization anomaly eia storm enhanced density sed and polar tongue of ionization toi we have combined multi instrument ionospheric data solar and terrestrial magnetic data and polar convection maps results reveal the prompt penetration of the interplanetary electric field to the polar region and then to the equator with a dusk to dawn polarity during the initial phase and with a dawn to dusk polarity during the main phase this drove during the initial phase a weak eastward equatorial electrojet eej in the american sector at nighttime and a weak westward eej in the indian australian sector at daytime during the main phase these eejs intensified and changed polarities sed and polar toi development was observed prior to and during the initial phase at evening premidnight hours over north america and during the main phase in the south at afternoon evening hours in the australian sector during the main phase and early in the recovery phase the eia sed structure was well formed in the asian longitude sector then polar toi development was absent in the north because of the long distance from the magnetic pole but was supported in the south because of the closeness of daytime cusp and magnetic pole thus the eia sed toi structure developed twice but each time in a different longitude sector and with different characteristics

thermal alteration of pyrite to pyrrhotite during earthquakes new evidence of seismic slip in the rock record seismic slip zones convey important information on earthquake energy dissipation and rupture processes however geological records of earthquakes along exhumed faults remain scarce they can be traced with a variety of methods that establish the frictional heating of seismic slip although each has certain assets and disadvantages here we describe a mineral magnetic method to identify seismic slip along with its peak temperature through examination of magnetic mineral assemblages within a fault zone in deep sea sediments cored from the japan trench one of the seismically most active regions around japan during the integrated ocean drilling program expedition 343 the japan trench fast drilling project fault zone sediments and adjacent host sediments were analyzed mineral magnetically supplemented by scanning electron microscope observations with associated energy dispersive x ray spectroscopy analyses the presence of the magnetic mineral pyrrhotite appears to be restricted to three fault zones occurring at 697 720 and 801 m below sea floor in the frontal prism sediments while it is absent in the adjacent host sediments elevated temperatures and coseismic hot fluids as a consequence of frictional heating during earthquake rupture induced partial reaction of preexisting pyrite to pyrrhotite the presence of pyrrhotite in combination with pyrite to pyrrhotite reaction kinetics constrains the peak temperature to between 640 and 800 c the integrated mineral magnetic microscopic and kinetic approach adopted here is a useful tool to identify seismic slip along faults without frictional melt and establish the associated maximum temperature

ar ar and fission track ages in the song chay massif early triassic and cenozoic tectonics in northern vietnam the song chay massif is the northeasternmost metamorphic complex in vietnam to the east of the red river shear zone it shows a large antiformal structure involving orthogneisses and migmatites overlain on its northern flank by muscovite bearing marbles an e w striking fault bounds the dome to the south kinematic indicators along a s n section reveal top to the n shear sense along the interface between the orthogneissic core and the overlying metasediments radiometric ages were obtained by the 40ar 39ar method using purified mica separates across the dome ages range from 236 ma at the southern edge to 160 ma in the core attesting to a strong imprint in the early triassic time a clear difference is seen between these mesozoic ages and the eocene to miocene ages from 40 to 24 ma that obtained in the nearby red river shear zone using the same method these data show that the song chay massif was already high in the crust when the high temperature deformation of the red river shear zone took place the final exhumation of the song chay orthogneiss constrained by fission track analysis on samples along the same transect occurred during the early miocene and could be interpreted as the consequence of a first normal sense of motion along the fault which bounds the massif to the south timing is similar to that of exhumation in the red river shear zone

the origin and hydrothermal mobilization of carbonaceous matter associated with paleoproterozoic orogenic type gold deposits of west africa abstract the chemical and physical properties of carbonaceous matter cm were studied in paleoproterozoic metasediment hosted orogenic type gold deposits in burkina faso the inata deposit in mali the syama deposit and in ghana the obuashi and bogoso deposits two types of cm occur in all the studied deposits metamorphosed and hydrothermal metamorphosed cm prevails in all the deposits hydrothermal cm occurs in small veinlets in hydrothermally altered rocks and in quartz veins or forms irregular accumulations parallel or sub parallel to c type cleavage within the shear zones the origin of hydrothermal cm which occurs in paragenesis with au bearing arsenopyrite or pyrite seems to have been due to supersaturation of hydrothermal fluids with carbon at the deeper or middle crustal levels the isotopic composition of carbon in bulk cm 33 1 to 26 2 vpdb indicates its biogenic origin the isotopic composition of carbon in hydrothermal carbonates ranges from 14 5 to 4 4 vpdb which suggest mixing of carbon derived from a deep seated source with carbon derived from an organic source the interaction of hydrothermal fluids with metamorphosed cm could be one of the causes of the reduction of hydrothermal fluids and formation of the respective mineralization the optical properties and raman spectra of the metamorphosed cm particles in the individual studied mineral deposits differ considerably the temperatures calculated on the basis of the raman spectra of metamorphosed cm vary between 280 and 440 c depending on the thermometer used and correspond to temperatures of metamorphism of upper sub grenschist and greenschist facies the temperatures calculated for hydrothermal cm at the individual deposits are only slightly lower compared to the metamorphosed cm at the same deposits which indicates approximately the same temperature of the metamorphic and hydrothermal processes

coal maturation by frictional heat during rapid fault slip 1 the detection of frictional heating effects along faults provides key insight into the dynamics of earthquakes and faulting thermal maturity of organic matter has been considered a possible fault thermometer that records the frictional heat signature of ancient earthquakes however whether or not organic matter can mature on the order of seconds typical earthquake rise time remains uncertain here we present the results of experiments aimed at revealing coal maturation by frictional heat generated at slip velocities representative of natural earthquakes of up to 1 3 m s our results show that coal can mature coseismically in 11 seconds at temperatures induced by frictional heat ranging from 26 to 266 c even with a temperature rise to only 28 7 c over 15 m displacement in 3 2 hours coal can slightly mature within a shear localized zone the commonly used kinetic model of vitrinite maturation cannot predict the experimental results a kinetic model involving the effect of flash temperature at grain contacts and mechanochemical effects on reaction kinetics is necessary to better estimate heat generation along a fault

carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan abstract carbonaceous material in pelitic schists of the sanbagawa metamorphic belt in central shikoku japan was separated from the host rocks and its x ray diffraction and chemical composition were studied its crystal structure and chemistry change continously with increasing metamorphic grade and approach those of well ordered graphite near the biotite isograd as graphitization is a rate process the temperature of complete graphitization differs from one metamorphic terrain to another as a function of the duration of metamorphism in an individual metamorphic terraan however the degree of graphitization is a useful indicator of relative metamorphic temperature in lower grade rocks

microstructures in landslides in northwest china implications for creeping displacements abstract microstructures mineralogical composition and texture of selected landslide samples from three landslides in the southern part of the gansu province china were examined with optical microscopy transmission electron microscopy tem x ray diffraction xrd and synchrotron x ray diffraction measurements common sheet silicates are chlorite illite muscovite kaolinite pyrophyllite and dickite other minerals are quartz calcite dolomite and albite in one sample graphite and amorphous carbon were detected by tem edx analyses and tem high angle annular dark field images the occurrence of graphite and pyrophyllite with very low friction coefficients in the gouge material of the suoertou and xieliupo landslides is particularly significant for reducing the frictional strength of the landslides it is proposed that the landslides underwent comparable deformation processes as fault zones the low friction coefficients provide strong evidence that slow moving landsliding is controlled by the presence of weak minerals in addition tem observations document that grain size reduction in clayey slip zone material was produced mainly by mechanical abrasion for calcite and quartz grain size reduction was attributed to both pressure solution and cataclasis therefore besides landslide composition the occurrence of ultrafine grained slip zone material may also contribute to weakening processes of landslides tem images of slip zone samples show both locally aligned clay particles as well as kinked and folded sheet silicates which are widely disseminated in the whole matrix small newly formed clay particles have random orientations based on synchrotron x ray diffraction measurements the degree of preferred orientation of constituent sheet silicates in local shear zones of the suoertou and duang he ba landslide is strong this work is the first reported observation of well oriented clay fabrics in landslides

shear induced graphitization of carbonaceous materials during seismic fault motion experiments and possible implications for fault mechanics abstract carbonaceous materials often concentrate in fault zones developed in pelitic rocks among carbonaceous minerals graphite is known as a lubricant and possibly plays a key role in frictional properties of the fault graphite reported from slip localized zones suggests that graphitization can occur during seismogenic fault motion thus we performed friction experiments on amorphous carbon and graphite to investigate how graphite forms in association with fault motion and how these carbonaceous minerals affect frictional properties of faults experiments were done at normal stresses of 0 5 2 8 mpa and slip rates of 50 m s to 1 3 m s in atmospheres of air and n 2 gas using rotary shear apparatuses xrd and tem analyses revealed that graphitization can indeed occur during seismogenic fault motion perhaps due to large shear strain short lived flash heating and stress concentration at asperity contacts even at low temperatures and pressures under anoxic environments we found large differences in steady state friction coefficient ss between graphite ss 0 1 and amorphous carbon ss 0 54 at low slip rate but amorphous carbon exhibits marked velocity weakening at slip rate above 10 mm s and its steady state friction reduces to the same level as that of graphite at a slip rate of 1 3 m s faults with amorphous carbon are not weak at low slip rates but they can become dynamically weak to foster fault motion during the generation of large earthquakes enriched graphite in fault zones can lubricate at all slip rates even at great depths and should receive more attention

the altitude extension of the mid latitude trough and its correlation with plasmapause position 1 tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density in an altitude versus geographic latitude grid at a specified longitudinal sector the method which involves monitoring the total electron content tec of the ionosphere using signals transmitted from the global positioning system gps has the ability to reveal the detailed structure of the ionosphere including the mid latitude trough the tomographic reconstruction of ionospheric electron density structures are performed at different specific longitudinal sectors both in the northern and southern hemisphere at the same time the plasmapause position is estimated from image euv images and mapped onto tomographic images the simultaneous location of the altitude extension of the mid latitude trough and the plasmapause position are essentially co located

raman spectra of carbonaceous materials in a fault zone in the longmenshan thrust belt china comparisons with those of sedimentary and metamorphic rocks abstract we analyzed micro raman spectra of carbonaceous materials cm in natural and experimentally deformed fault rocks from longmenshan fault zone that caused the 2008 wenchuan earthquake to characterize degree of disordering of cm in a fault zone raman spectral parameters for 12 samples from a fault zone in shenxigou sichuan china all show low grade structures with no graphite low crystallinity and 13c values 24 to 25 suggest that cm in fault zone originated from host rocks late triassic xujiahe formation full width at half maximum values of main spectral bands d1 and d2 and relative intensities of two subbands d3 and d4 of cm were variable with sample locations however raman parameters of measured fault rocks fall on established trends of graphitization in sedimentary and metamorphic rocks an empirical geothermometer gives temperatures of 160 230 c for fault rocks in shenxigou and these temperatures were lower for highly sheared gouge than those for less deformed fault breccia at inner parts of the fault zone the lower temperature and less crystallinity of cm in gouge might have been caused by the mechanical destruction of cm by severe shearing deformation or may be due to mixing of host rocks on the footwall cm in gouge deformed in high velocity experiments exhibits slight changes towards graphitization characterized by reduction of d3 and d4 intensities thus low crystallinity of cm in natural gouge cannot be explained by our experimental results graphite formation during seismic fault motion is extremely local or did not occur in the study area and the cm crystallinity from shallow to deep fault zones may be predicted as a first approximation from the graphitization trend in sedimentary and metamorphic rocks if that case graphite may lower the friction of shear zones at temperatures above 300 c deeper than the lower part of seismogenic zone

multiradar observations of the polar tongue of ionization 1 we present a global view of large scale ionospheric disturbances during the main phase of a major geomagnetic storm we find that the low latitude auroral and polar latitude regions are coupled by processes that redistribute thermal plasma throughout the system for the large geomagnetic storm on 20 november 2003 we examine data from the high latitude incoherent scatter radars at millstone hill sondrestrom and eiscat tromso with superdarn hf radar observations of the high latitude convection pattern and dmsp observations of in situ plasma parameters in the topside ionosphere we combine these with north polar maps of stormtime plumes of enhanced total electron content tec derived from a network of gps receivers the polar tongue of ionization toi is seen to be a continuous stream of dense cold plasma entrained in the global convection pattern the dayside source of the toi is the plume of storm enhanced density sed transported from low latitudes in the postnoon sector by the subauroral disturbance electric field convection carries this material through the dayside cusp and across the polar cap to the nightside where the auroral f region is significantly enhanced by the sed material the three incoherent scatter radars provided full altitude profiles of plasma density temperatures and vertical velocity as the toi plume crossed their different positions under the cusp in the center of the polar cap and at the midnight oval polar cap boundary greatly elevated f peak density 1 5e12 m 3 and low electron and ion temperatures 2500 k at the f peak altitude characterize the sed toi plasma observed at all points along its high latitude trajectory for this event sed toi f region tec 150 1000 km was 50 tecu both in the cusp and in the center of the polar cap large upward directed fluxes of o 1 e14 m 2 s 1 were observed in the topside ionosphere

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

geochemistry of shear zone hosted uranium mineralisation at the zadni chodov uranium deposit bohemian massif abstract samples from the zadni chodov uranium deposit of the bohemian massif were analysed using optical and chemical methods organic matter and brannerite were studied in detail to estimate conditions that prevailed in association with uranium enriched shear zones four major events are known in the high grade metasediments the pre ore stage is associated with the formation of shear zones during the uranium ore deposition stage temperatures ranged from 122 c to 258 c and coffinite and brannerite appeared two generations of post ore stage minerals are distinguishable a detailed study of a brannerite mineral grain revealed variations in its interior and surroundings but these are related to the composition of brannerite which is not a nominal mineral si and al are presented as chlorites but the main mineral phases are mixtures of anatase oxidized brannerite with non stoichiometric uranium oxide and carbonaceous matter carbonaceous matter in the samples studied appeared as a mixture of substances of different composition origin and age optical and structural characteristics showed variations in three coexisting types of metamorphosed carbonaceous matter including fine grained and larger lamella shaped particles that represent anthracite meta anthracite and semi graphite stages lamellas of crystalline graphite and pyrobitumen corresponding to impsonite the structure of organic particles was not affected by uranium minerals which is an interesting difference from changes that minerals undergo in for example coal biomarkers compounds used in assessing sources of organic matter were present in extracts but they were not a remnant of the original shear zone organic material they are likely products from a later impact probably of tertiary and younger sediments

formation of polar ionospheric tongue of ionization during minor geomagnetic disturbed conditions previous investigations of ionospheric storm enhanced density sed and tongue of ionization toi focused mostly on the behavior of toi during intense geomagnetic storms little attention has been paid to the spatial and temporal variations of toi during weak to moderate geomagnetic disturbed conditions in this paper we investigate the source and development of toi during a moderate geomagnetic storm on 14 october 2012 multi instrumental observations including gps total electron content tec defense meteorological satellite program dmsp in situ measured total ion concentration and ion drift velocity superdarn measured polar ion convection patterns and electron density profiles from the poker flat incoherent scatter radar pfisr have been utilized in the current analysis gps tec maps show salient toi structures persisting for about 5 h over high latitudes of north america on 14 october 2012 in the later recovery phase of the storm when the magnitudes of imf by and bz were less than 5 nt the pfisr electron density profiles indicate that the extra ionization for tec enhancements mainly occurred in the topside ionosphere with no obvious changes in the bottomside ionosphere and vertical plasma drifts additionally there were no signatures of penetration electric fields in the equatorial electrojet data and upward ion drifts at high latitudes at the same time strong subauroral polarization streams with ion drift speeds exceeding 2 5 km s carried sunward fluxes and migrated toward lower latitudes for about 5 based on the dmsp cross track drift measurements based on those measurements we postulate that the combined effects of initial build up of ionization at midlatitudes through daytime production of ionization and equatorward or less poleward than normal daytime neutral wind reducing downward diffusion along the inclined filed lines and an expanded polar ion convection pattern and its associated horizontal plasma transport are important in the formation of the toi

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

the occurrence of ionospheric signatures of plasmaspheric plumes over different longitudinal sectors 1 plasmaspheric plumes have ionospheric signatures and are observed as storm enhanced density sed in global positioning system gps total electron content tec these ionospheric signatures have been primarily observed over the american sector and in a few limited examples over the european sector this study examines the longitudinal occurrence frequency of plasmaspheric plumes we analyzed all images from the imager for magnetopause to aurora global exploration image extreme ultraviolet imager euv databases for the first half of 2001 and identified a total of 31 distinct plume intervals observed during different storm events out of the total image euv plumes that we identified 12 were projected over north america 10 over asia and the remaining 9 were over europe and the atlantic ocean using ground based gps tec from mit s madrigal database we searched for corresponding sed tec plumes at different longitudinal sector and found 12 ionospheric sed plume signatures over north america 4 over europe and 2 over asia this indicates that the observation probability of an ionospheric sed plume when a plasmaspheric plume is seen is 100 in the american sector 50 in the european sector and 20 in the asian sector this could be due to the fact that the plumes may be either positioned beyond the limit of the ground based gps field of view which happens mainly when there is less plasmaspheric erosion or are too weak to be detected by the sparse number of gps receivers over asia the in situ plasma densities from the available coincident defense metrological satellite program dmsp satellites were also used to study the characteristics of sed tec plume at dmsp orbiting altitude i e 870 km the topographic explorer topex altimeter tec also is used to identify the conjugate sed plume signature over the southern hemisphere

carbon forming reactions under a reducing atmosphere during seismic fault slip graphite is a well known solid lubricant and can be as important as clay minerals in reducing the frictional strength of faults some natural fault zones contain carbonaceous material cm even where host rocks do not contain it and seismic fault motion can promote the graphitization of low grade cm thus the origin of cm in fault zones is an important issue in fault mechanics previous high velocity friction experiments have revealed various chemical reactions in fault zones during seismic fault motion but most experiments have been conducted in an atmosphere under oxic conditions here we report experimental results on carrara marble free of cm conducted under n2 or h2 atmospheres at a slip rate of 1 3 m s and normal stresses of 2 0 3 1 mpa a small amount of blackish material formed in generated gouge only under reducing conditions with the h2 atmosphere and raman spectroscopic analysis revealed the presence of cm amorphous carbon in the material the cm is attributable to 1 the generation and pyrolitic dissociation of ch4 and or 2 a reduction reaction of emitted co2 due to calcite decomposition we confirmed the formation of ch4 using gas chromatography the cm produced in experiments resembles cm in the nojima fault japan gouge in terms of raman spectra the granitic host rock of this fault is free of cm and calcite is precipitated close to the cm therefore the cm probably formed through processes similar to those simulated in our experiments future research should investigate the amount and origin of cm in natural fault zones

generation of amorphous carbon and crystallographic texture during low temperature subseismic slip in calcite fault gouge identification of the nano scale to micro scale mechanochemical processes occurring during fault slip is of fundamental importance to understand earthquake nucleation and propagation here we explore the micromechanical processes occurring during fault nucleation and slip at subseismic rates 3 10 6 m s 1 in carbonate rocks we experimentally sheared calcite rich travertine blocks at simulated upper crustal conditions producing a nano grained fault gouge strain in the gouge is accommodated by cataclastic comminution of calcite grains and concurrent crystal plastic deformation through twinning and dislocation glide producing a crystallographic preferred orientation cpo continued wear of fine grained gouge particles results in the mechanical decomposition of calcite and production of amorphous carbon we show that cpo and the production of amorphous carbon previously attributed to frictional heating and weakening during seismic slip can be produced at low temperature during stable slip at subseismic rates without slip weakening

high velocity frictional behavior and microstructure evolution of fault gouge obtained from nojima fault southwest japan abstract high velocity experiments on fault gouge taken from the nojima fault that slipped during the 1995 kobe earthquake were conducted to investigate physical mechanism associated with the slip weakening behavior with increasing slip the friction values of the gouge sheared at 0 62 mpa normal stress and 1 03 m s slip velocity decrease exponentially from a peak value of more than 0 6 to a steady state value of 0 2 the textures of the gouge are characterized by grain comminution oblique and parallel shear planes and localized deformation zone with strongly preferred orientation in the friction weakening stage and folding and fluttering structures at the steady state friction stage numerical modeling based on the temperature measurements close to the gouge layer shows that the temperature inside the gauge layer did not exceed 400 c during the experiments in a slide hold slide test a full strength recovery of the fault gouge was observed only after 12 s slip pause and the slip weakening curves are the same between the two successive slips the steady state coefficient of friction decreased from 0 8 to about 0 2 when the slip velocity increased from 0 006 m s to 1 03 m s this high velocity weakening feature was observed in a synthetic quartz gouge as well as in the nojima gouge although it is unclear which mechanism causes the weakening among thermal pressurization silica gel lubrication flash heating moisture draining and so on the present experimental results suggest that the high velocity weakening is related to the high heat production rate finally the flow structures observed in the samples deformed up to the final steady state stages have never been reported in previous slow rate experiments and could be a key structure characteristic of high velocity frictional sliding

the 40ar 39ar dating of biotite in ore veins and zircon u pb dating of porphyrtic granite dyke in the nanyangtian tungsten deposit in se yunnan china abstract the nanyangtian tungsten deposit is located in the laojunshan sn w polymetallic metallogenic province in se yunnan china tectonically it is located in the conjunction of the cathaysia and indochina blocks the orebodies primarily hosted within the stratiform like skarn and marble in the paleoproterozoic nanyangtian formation three ore forming stages have been identified based on mineral assemblages and on the intercalated relationships between the veins they include skarn scheelite stage quartz scheelite vein stage and carbonate scheelite vein stage in this paper we present 40ar 39ar laser incremental heating analyses of hydrothermal biotite intergrowth with scheelite from quartz scheelite vein with two yielded well defined 40ar 39ar plateau ages of 97 49 0 97 ma and 99 48 0 97 ma and two isochronal ages of 97 01 1 39 ma and 99 58 0 98 ma respectively representing the age of second mineralization stage of the nanyangtian tungsten deposit the ages are well consistent with the emplacement age of the laojunshan granite 96 ma to 117 ma u pb geochronological data for magmatic zircons separated from porphyritic granite dyke in the mine pit indicate that the granite body was emplaced in the post ore stage 89 88 0 53 ma integrated with previously high resolution diagenetic and metallogenic geochronological data two significant magmatic mineralization events are presented in se yunnan china and north vietnam the first event took place from 97 ma to 124 ma which is closely related to the tungsten mineralization the second event occurred from 75 ma to 95 ma which is closely related to the sn cu ag zn mineralization according to the exhibited data we preliminarily conclude that the late cretaceous magmatic mineralization activity in se yunnan and north vietnam is the product of post collision of the cathaysia and indochina blocks and should have formed under a same geodynamic setting

structural doming tectonics intracontinental deformation of the sw margin of the yangtze block china the southwest margin of the yangtze block underwent multiple tectonic events including the collision between the yangtze and the south china plate caledonian folding and uplift of south china subduction of the western pacific plate and cenozoic continental escape during the indo asia collision the structural framework and tectonic evolution of the area are currently unclear through field petrologic and structural studies microstructures within the deformed units and estimates of the temperature of deformation we constrain the conditions of deformation and further classify at least four stage deformation the first stage involved northeastward thrusting that produced folds mylonites and dynamically recrystallized quartz and calcite electron backscatter diffraction data indicate that deformation during this event occurred at 400 c corresponding to a depth of 10 km the second stage of deformation involved uplift extension and the generation of a domal structure during the third event high angle normal faults formed within the cover sequence that surrounds the dome the fourth stage of deformation occurred in the cenozoic and involved motion along sinistral and dextral strike slip faults which cut structures that formed during the previous stages of deformation the first deformation event was related to triassic n s collision with the indochina block the second and third stages resulted from far field compression related to westward subduction of the paleo pacific plate and the fourth event was related to displacement along the ailaoshan red river strike slip fault the dome in the study area represents a transitional structure between a metamorphic core complex and a gneissic dome which we refer to as structural doming

a group of papers on fluid inclusion research applied to ore deposits an introduction the group of six papers and one scientific contribution that follow this brief introduction illustrate the application of fluid inclusion research to ore deposits a field pioneered by edwin woods roedder july 30 1919 august 1 2006 fig 1 who contributed nearly 400 published works during a career that spanned more than three quarters of a century his first paper was published in 1935 roedder 1935 on the topic of black sulfur at hillborn new york his final posthumous publication in 2008 was as a coauthor on the thermal history of yucca mountain nevada whelan et al 2008 many readers of this journal will know that ed roedder was the leader in the field of fluid and melt inclusions roedder 1984b but some may not realize that he also made significant contributions in other areas including experimental petrology of the k2o feo al2o3 sio2 system roedder 1951 the geologic storage of radioactive waste roedder 1957 and lunar petrology roedder and weiblen 1970 ed s most significant contributions were related to the critical role that fluids and related processes play in ore formation a large number of his publications were related to mineral deposits and ore genesis with 25 of these published in economic geology between 1962 roedder 1962 and 1989 anderson et al 1989 a compilation and summary of much of ed s work up until the early 1980s is included in his well known publication fluid inclusions roedder 1984b a complete listing of ed roedder s publications is available at the edwin woods roedder memorial virtual library at the following location some lithium salts exhibit high solubilities in aqueous solutions leading to high concentrations in continental brines postmagmatic hydrothermal systems and rare element pegmatites despite lithium being a trace element in

modeling subauroral polarization streams equatorward of the plasmapause footprints pinter b thom s d balthazor r vo h bailey g j modeling subauroral polarization streams equatorward of the plasmapause footprints journal of geophysical research volume 111 issue a10 citeid a10306 rae2008

reduction in bet surface area of nojima fault gouge with seismic slip and its implication for the fracture energy of earthquakes abstract a common view concerning the energetics of seismogenic fault motion is that at least part of the fracture energy is consumed in grain crushing in the fault zone and that this part may be estimated by grain size analysis of fault rocks we address this problem by conducting room dry friction experiments on nojima fault gouge at subseismic to seismic slip rates 0 009 1 31 m s and at normal stresses up to 3 64 mpa and by measuring the bet surface area of the gouge before and after the experiments where it cuts granite the nojima fault zone has bet surface area of about 65 10 6 m 2 per unit fault area 1 m 2 clayey and granular fault gouges composed mainly of quartz plagioclase kaolinite and smectite were collected from a granitic fault zone at a new outcrop in funaki awaji island southwest japan both clayey and granular gouges exhibit dramatic weakening at high slip rates specific bet surface areas of clayey and granular gouges decreased with increasing slip rate from 46 0 and 15 4 m 2 g before deformation to about 20 and 5 m 2 g after deformation 55 70 reduction respectively microstructural observations revealed that grain welding within the slip zones at high slip rates reduced grain surface area the energetics of seismic fault motion should be examined with broader views taking into account grain crushing grain welding decomposition and frictional melting

dynamic response of ionospheric plasma density to the geomagnetic storm of 22 23 june 2015 on 21 22 june 2015 three consecutive interplanetary shocks slammed into the earth s magnetosphere immediately after the third shock at 18 36 ut on 22 june marked by an exceptional sudden storm commencement with an amplitude of delta sym h similar to 106 nt a major geomagnetic storm commenced in the present study a multi instrument approach comprising observations data analysis and modeling is used to examine the global ionospheric response results show that enhanced storm time processes produced major total electron content tec variations at different latitudes longitudes and phases of the storm a closer inspection of the tec observations reveals strong longitudinal and hemispherical asymmetry in addition multiple equatorward and poleward propagating traveling ionospheric disturbances tids were detected in the tec data equatorward propagating tids are consistent with vertical neutral winds simulated from thermosphere ionosphere electrodynamics general circulation model however poleward tids were not reproduced in the model we find that a combination of driving processes including enhanced high latitude injection prompt penetration electric fields disturbance dynamo effect neutral winds and composition changes were acting at different stages of the storm

dynamic weakening of smectite bearing faults at intermediate velocities implications for subduction zone earthquakes the hydrous clay mineral smectite which is pervasive in sediments on subducting oceanic plates is thought to weaken and stabilize subduction thrust faults however these frictional properties of smectite alone cannot explain the large coseismic slip in the vicinity of a trench here we performed friction experiments to demonstrate the rate dependence of friction at slip rates from 30 m s to 1 3 m s for water saturated smectite quartz mixtures with various smectite contents so as to shed light on the frictional response of smectite bearing faults at intermediate to high slip rates at slip rates of 30 to 150 m s the friction coefficients decreased gradually from 0 5 0 6 to 0 1 with an increase in smectite content from 20 to 50 wt in contrast at slip rates higher than 1 3 mm s friction exhibited marked slip weakening resulting in low friction coefficients of 0 1 0 05 even for low smectite contents roughly 30 wt drastic slip weakening occurred at smectite contents of 10 30 wt at slip rates of 10 mm s which is 1 to 2 orders of magnitude lower than the slip rate at which slip weakening was observed in previous experiments on various rock types the intermediate velocity weakening could be attributed to a rise in pore pressure caused by both shear enhanced compaction and microscopic thermal pressurization of pore fluids this process could weaken the fault even below seismic slip rates leading to an acceleration of fault motion and potentially facilitating large coseismic slip and a stress drop in the vicinity of a trench

effects of sample preparation on the microstructural signatures of faulting in clay bearing fault gouge abstract clay rich fault gouge in the principal slip zones of faults stores abundant water within pores and between clay interlayers during the preparation of thin sections and rock chips for microstructural observations fault gouge samples are commonly air dried at room temperature or in an oven however during the drying process remnant liquid water between gouge grains produces an inter particle adhesion force liquid bridge force which rearranges the grain to grain structure likely resulting in a disturbance of the original fabric for this study we prepared gouge samples from the itozawa fault northeastern japan using a t butyl alcohol freeze drying method that mitigates drying induced fabric disturbance we then compared the microstructure of our samples with those prepared using the conventional air drying method the freeze dried samples preserve a smooth fault plane clearly defined nanoparticles and well developed shear sense indicators including slickenlines and riedel shear planes in contrast the air dried samples underwent shrinkage during drying which distorted the geometry of the fault plane these air dried samples lack nanoparticles and display only a weak shear fabric we conclude that microstructural observations on samples prepared using the t butyl alcohol freeze drying method compared with conventional air drying could preserve more evidence for the retrieval of fault information including the kinematics slip stability and dynamic weakening mechanism of a fault

the role of graphite layers in gravitational deformation of pelitic schist abstract deep seated landslides in pelitic schists are common in many countries but are poorly investigated and understood in this study we present the first detailed examination and modelling of landslide mechanisms in these materials we found that pelitic schist commonly contains black graphite rich layers on a scale of millimeter to centimeter thickness that are typically weaker than neighboring layers by examining microscopic textures in borehole samples obtained from landslide masses of pelitic schist we find that ductile gravitational shearing commonly occurs within these weaker layers accompanied by brittle fracture in the surrounding layers to investigate these mechanisms we have performed high precision direct shear tests using a novel back pressured shearbox on artificial rock samples both with and without graphite layers placed between pre cut shear surfaces the tests used normal stresses up to 800 kpa equivalent to 32 m depth of burial we found that the coefficients of friction for samples with graphite layers embedded in the artificial rock samples 0 30 representing an angle of internal friction of 16 7 were much lower than those without graphite layers on the pre cut surface 0 85 the shear strength of the artificial rocks with embedded layers of graphite decreased abruptly with increasing areal extent of the graphite layer along the shear surface from which it can be inferred that the continuity of a graphite layer in natural pelitic schist has a considerable effect on shear resistance these results suggest that even comparatively low dip angles of schistosity in pelitic schist could initiate microscopic slip along the graphite rich layers

reconstruction of seismic faulting by high velocity friction experiments an example of the 1995 kobe earthquake 1 high velocity friction experiments on a fault gouge collected from the nojima fault activated during the 1995 kobe earthquake showed that the friction coefficient decreased from 0 63 to 0 18 over a slip weakening distance dc at high slip rates of 1 m s the dramatic drop in friction coefficient of more than 0 3 is consistent with that for the kobe earthquake estimated from seismological observations experimentally determined dc becomes 5 m at a higher normal stress of 1 85 mpa close to the order of magnitude of seismologically determined dc of 0 5 to 1 m the difference in dc is not significant because the fracture energy consumed during frictional slip is the same order of 106 n m for both cases here we show that frictional behavior of a fault during an earthquake can be predicted by conducting high velocity friction experiments

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

ionospheric signatures of a plasmaspheric plume over europe 1 previously ionospheric signatures of plasmaspheric plumes were reported only at the north american longitude sector this led to the hypothesis that the geomagnetic field configuration at those longitudes played a vital role in the observation of plasmaspheric plume signatures only over the american continent combining ground based gps total electron content tec eiscat incoherent scattering radar isr and dmsp f15 ion drift meter observations we have observed greatly elevated density over the european continent during storm recovery phase on 12 september 2005 the tec seen over europe has a tongue of enhanced ionization extending to higher latitudes which is identical to the plasmaspheric plume signatures that have been often observed over north america therefore our observations clearly demonstrate that ionospheric signatures of plasmaspheric plumes are not limited to the north american sector and suggest that they may be observed at any longitude as long as a dense array of instruments are available to identify these signatures citation yizengaw e m b moldwin and d a galvan 2006 ionospheric signatures of a plasmaspheric plume over europe geophys res lett 33 l17103 doi 10 1029 2006gl026597

long lived plasmaspheric drainage plumes where does the plasma come from long lived weeks plasmaspheric drainage plumes are explored the long lived plumes occur during long lived high speed stream driven storms spacecraft in geosynchronous orbit see the plumes as dense plasmaspheric plasma advecting sunward toward the dayside magnetopause the older plumes have the same densities and local time widths as younger plumes and like younger plumes they are lumpy in density and they reside in a spatial gap in the electron plasma sheet in sort of a drainage corridor magnetospheric convection simulations indicate that drainage from a filled outer plasmasphere can only supply a plume for 1 5 2 days the question arises for long lived plumes and for any plume older than about 2 days where is the plasma coming from three candidate sources appear promising 1 substorm disruption of the nightside plasmasphere which may transport plasmaspheric plasma outward onto open drift orbits 2 radial transport of plasmaspheric plasma in velocity shear driven instabilities near the duskside plasmapause and 3 an anomalously high upflux of cold ionospheric protons from the tongue of ionization in the dayside ionosphere which may directly supply ionospheric plasma into the plume in the first two cases the plume is drainage of plasma from the magnetosphere in the third case it is not where the plasma in long lived plumes is coming from is a quandary to fix this dilemma further work and probably full scale simulations are needed

the occurrence of graphite bearing fault rocks in the atotsugawa fault system japan origins and implications for fault creep abstract graphite in fault zones has received little attention even though it is a well known solid lubricant that could affect frictional properties of faults dramatically this paper reports the presence of abundant graphite in fault zones of the atotsugawa fault system central japan mesoscopic and microscopic observations of fault rocks revealed two processes of carbon enrichment in fault zones one is a pressure solution process or diffusive mass transfer in general which removes water soluble minerals such as quartz and carbonates from rocks resulting in the enrichment of insoluble minerals including carbon the other process is precipitation of graphite from a high temperature carbon rich fluid forming graphite filling fractures within cataclasitic fault zones the two processes have led to the concentration up to 12 wt of graphite in the atotsugawa fault zones compared to 0 to 3 wt of carbonaceous materials in the host rocks this concentration is high enough for graphite to affect frictional properties at wide range of slip rates the presence of graphite may provide an explanation for the low resistivity the patterns of microearthquakes and fault creep along the western part of the atotsugawa fault system graphite should receive more attention as a weakening and stabilizing agent of faults

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

pressure temperature and fluid conditions during emerald precipitation southeastern yukon canada fluid inclusion and stable isotope evidence abstract the crown emerald veins are somewhat enigmatic displaying characteristics that are common to emerald deposits of tectonic hydrothermal origin and of igneous origin the veins cut the fire lake mafic meta volcanic rocks occurring within 600 m of an outcrop of cretaceous s type granite field work and vein petrography are consistent with a polythermal origin for the veins the primary vein mineralogy is quartz and tourmaline with variable sized alteration haloes consisting of tourmaline quartz muscovite chlorite and emerald the veins weather a buff brown colour due to jarosite scheelite and minor lepidocrocite which were precipitated during the waning stages of vein formation microthermometic studies of primary fluid inclusions within emerald growth zones are consistent with emerald precipitation from h 2 o co 2 ch 4 n 2 h 2 s bearing saline brines the estimated fluid composition is approximately 0 9391 mol h 2 o 0 0473 mol co 2 0 0077 mol ch 4 and 0 0059 mol nacl 2 wt nacl eq fluid inclusion and stable isotope studies are consistent with vein formation in the temperature range 365 498 c with corresponding pressures along fluid inclusion isochore paths ranging from 700 to 2250 bars these data correlate with a very slow uplift rate for the region of 0 02 0 07 mm year emerald deposits are generally formed when geological conditions bring together cr v and be cr and v are presumed to have been derived locally from the mafic and ultramafic rocks during hydrothermal alteration the be is most likely derived from the nearby cretaceous granite intrusion

oxygen isotope systematics of emerald relevance for its origin and geological significance oxygen isotopic composition of emerald from 62 occurrences and deposits in the world reveals a wide range in 18o smow between 6 2 and 24 7 the 18o values for each deposit are restricted and can be used to determine the origin of emerald from the world s most important producers the 18o value of emerald appears to be a fingerprint of its origin especially for gems of exceptional quality from colombia eastern emerald zone 18o 16 8 0 1 western emerald zone 18o 21 2 0 5 afghanistan 18o 13 5 0 1 pakistan swat mingora districts 18o 15 7 0 1 brazil santa terezinha de goias 18o 12 2 0 1 quadrilatero ferrifero 18o 6 9 0 4 and zimbabwe sandawana 18o 7 5 0 5 furthermore the 18o composition of emerald appears to be a good marker of its geological environment because the data suggest that host rock buffering of fluid 18o is considerable during fluid rock interaction

storm time plasma transport at middle and high latitudes associated with the large scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions solar produced f region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector as a result of the offset between the geomagnetic and geographic poles the afternoon sector region of strong sunward convection is shifted to increasingly lower geographic latitude throughout the interval between 12 ut and 24 ut a snowplow effect occurs in which the convection cell continually encounters fresh corotating ionospheric plasma along its equatorward edge producing a latitudinally narrow region of storm enhanced plasma density sed and increased total electron content which is advected toward higher latitudes in the noon sector the millstone hill incoherent scatter radar regularly observes sed as a spatially continuous large scale feature spanning local times between noon and midnight and at latitudes between the polar cap and its mid or low latitude source region for local times away from noon the latitude of most probable sed occurrence moves equatorward by 6 for an increase of 2 in the kp index during strong disturbances the topside sed is observed to be convecting sunward at 750 m s 1 with a flux of 1014 m 2 s 1 this feature accounts for the pronounced enhancement of ionospheric density near dusk at middle latitudes observed during the early stages of magnetic storms called the dusk effect and constitutes a source for the enhanced f region plasma observed in the polar cap during disturbed conditions

fault lubrication and earthquake propagation in thermally unstable rocks experiments performed on dolomite or mg calcite gouges at seismic slip rates v 1 m s and displacements d 1 m show that the frictional coefficient decays exponentially from peak values m p 0 8 in the byerlee9s range to extremely low steady state values ss 0 1 attained over a weakening distance d w microstructural observations show that discontinuous patches of nanoparticles of dolomite and its decomposition products periclase and lime or portlandite were produced in the slip zone during the transient stage d w these observations integrated with co 2 emissions data recorded during the experiments suggest that particle interaction in the slip zone produces flash temperatures that are large enough to activate chemical and physical processes e g decarbonation reactions t 550 c during steady state d d w shear strength is very low and not dependent upon normal stresses suggesting that pressurized fluids co 2 may have been temporarily trapped within the slip zone at this stage a continuous layer of nanoparticles is developed in the slip zone for d d w a slight but abrupt increase in shear strength is observed and interpreted as due to fluids escaping the slip zone at this stage dynamic weakening appears to be controlled by velocity dependent properties of nanoparticles developed in the slip zone experimentally derived seismic source parameter w b i e breakdown work the energy that controls the dynamics of a propagating fracture 1 matches w b values obtained from seismological data of the a d 1997 m6 colfiorito italy earthquakes which nucleated in the same type of rocks tested in this study and 2 suggests similar earthquake scaling relationships as inferred from existing seismological data sets we conclude that dynamic weakening of experimental faults is controlled by multiple slip weakening mechanisms which are activated or inhibited by physicochemical reactions in the slip zone

sources of the nanwenhe song chay granitic complex sw china ne vietnam and its tectonic significance abstract the nanwenhe song chay complex nscc is a large early paleozoic pluton straddling the border between sw china and ne vietnam it is located at the tectonic junction of the yangtze cathaysia and indochina blocks so that the source of the complex is still enigmatic the rocks from the complex are high k calc alkaline and peraluminous s type granite la icp ms u pb dating of zircons from twelve granitic samples in the complex gives crystallization ages in the range of 436 423 ma zircon u pb hf isotopes and geochemical data show that the nanwenhe granites in the northern part of the nscc probably were mainly derived from neoproterozoic metamorphic pelites analogous to those in the xiajiang and danzhou groups in contrast the song chay granites in the southern part of the nscc were probably derived from neoproterozoic metamorphic psammites analogous to those in the fanjingshan and sibao groups in the southwestern yangtze block the granites from the complex contain abundant inherited zircons with a main peak at 836 808 ma and subordinate peaks at 734 ma and 528 665 ma the inherited zircons have age distribution patterns and hf isotopic compositions similar to those for the detrital zircons from neoproterozoic to early paleozoic sedimentary rocks in the southwestern part of the yangtze block but different from those of the cathaysia block and indochina block therefore the basement of the nscc is equivalent to the yangtze block and the complex may represent the westernmost tip of the early paleozoic orogenic belt in the scb we thus assume that the boundaries between the yangtze block and the cathaysia block and between the scb and icb should be located to the southeast and southwest of the nanwenhe song chay area respectively

gouge graphitization and dynamic fault weakening during the 2008 mw 7 9 wenchuan earthquake the longmenshan fault that ruptured during the 2008 mw 7 9 wenchuan china earthquake was drilled to a depth of 1200 m and fault rocks including those in the 2008 earthquake slip zone were recovered at a depth of 575 595 m we report laboratory strength measurements and microstructural observations from samples of slip zone fault rocks at deformation conditions expected for coseismic slip at borehole depths results indicate that the longmenshan fault at this locality is extremely weak at seismic slip rates in situ synchrotron x ray diffraction analysis indicates that graphite was formed along localized slip zones in the experimental products similar to the occurrence of graphite in the natural principal slip zone of the 2008 wenchuan rupture we surmise that graphitization occurred due to frictional heating of carbonaceous minerals because graphitization was associated with strong dynamic weakening in the experiments we further infer that the longmenshan fault was extremely weak at borehole depths during the 2008 wenchuan earthquake and that enrichment of graphite along localized slip zones could be used as an indicator of transient frictional heating during seismic slip in the upper crust

carbon ordering in an aseismic shear zone implications for raman geothermometry and strain tracking abstract determining the burial and strain history of sedimentary rocks is important for understanding crustal behaviour when rocks contain organic carbon increased temperatures at depth can alter the molecular structure of the carbon this change known as carbon ordering can be detected using raman spectroscopy as a result raman spectroscopy is increasingly used to estimate burial depths and associated maximum temperatures in carbon bearing rocks it is known from experiments and natural samples that other factors can affect raman derived maximum temperatures including frictional heating on fault planes and interaction with hot fluids for faulted samples a question remains as to whether it is purely frictional heating that causes carbon ordering or strain or a combination of the two in this study we use a mid crustal shear zone to show that strain related carbon ordering occurs in natural rock samples during aseismic shear strain a traverse across the shear zone whose relative strain we quantify with respect to the surrounding less deformed rock shows a marked decrease in raman d g peak intensity ratios indicating greater carbon ordering within the shear zone we interpret this as evidence for carbon ordering as a result of aseismic shear strain rather than inflated temperatures due to frictional heating commonly associated with seismic strain rates on faults our results have implications for the further development of raman spectroscopy as a geothermometer which may yield erroneous results in strained rock samples and for understanding strain localisation processes in the earth s crust and its associated rheological implications

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

seismic slip record in carbonate bearing fault zones an insight from high velocity friction experiments on siderite gouge pseudotachylyte formed by frictional melting has been the only unequivocal evidence of past seismogenic fault slip we report from high velocity friction experiments on siderite bearing gouge that mineral decomposition due to frictional heating also can leave evidence of paleoseismic events along shallow crustal faults other than pseudotachylyte experiments were conducted room dry on simulated gouge composed of siderite or mixture of siderite calcite and quartz initially at room temperature under normal stresses of 0 6 1 3 mpa and at seismic slip rates of 1 3 2 0 m s in all cases gouge exhibited dramatic slip weakening and siderite was decomposed into nanocrystalline magnetite and co 2 gas as confirmed by co 2 measurement x ray diffraction analyses and transmission electron microscopy the weakening was caused by the low frictional strength of ultrafine decomposition products at seismic slip rates magnetite formation during shearing changed gouge color to black and increased magnetic susceptibility by a few orders of magnitude those changes can be recognized in natural fault zones and black gouge in the chelungpu fault zone in taiwan is perhaps such an example thus our results suggest that thermal decomposition in shallow crustal faults can be an important co seismic process not only for dynamic fault weakening but also for leaving seismic slip records

frictional properties of simulated shale coal fault gouges implications for induced seismicity in source rocks below europe s largest gas field abstract we report 21 frictional sliding experiments performed on simulated fault gouges prepared from shale coal mixtures our aim was to investigate the effects of local coal seam smearing on the frictional properties and induced seismogenic potential of faults cutting the upper carboniferous source rocks underlying the groningen gas reservoir netherlands we used shale siltstone core recovered from beneath the groningen reservoir plus polish bituminous coal of similar age and origin to coals locally present in the groningen source rocks we performed friction experiments in velocity stepping constant velocity slide hold slide shs and slide unload slide sus modes under near in situ conditions of 100 c and 40 mpa effective normal stress employing sliding velocities of 0 1 100 m s and a variety of pore fluids samples with 0 50 vol coal showed friction coefficients 0 45 with minor slip weakening samples with 50 vol coal showed marked slip weakening from peak friction values of 0 47 to 0 3 regardless of experimental conditions presumably reflecting strain localization in weak coal rich shear bands possibly accompanied by changes in coal molecular structure however re sliding experiments sus showed that slip weakening is limited to small initial displacements 2 3 mm and does not occur during slip reactivation at near steady state almost all experiments performed at in situ stress pore water pressure 15 mpa and temperature conditions exhibited stable velocity strengthening behaviour regardless of coal content by contrast under dry and gas saturated ch4 argon conditions or using water at 1 atm 50 50 vol shale coal mixtures showed velocity weakening and even stick slip our results imply that faults in the groningen carboniferous shale siltstone sequence are not prone to induced earthquake nucleation at in situ conditions even when coal bearing or coal enriched by smearing however the mechanisms controlling coal friction remain unclear at the sliding velocities studied and the evolution of coal friction at seismic slip velocities remains unknown

ionospheric signatures of plasmaspheric tails 1 we make direct comparisons between gps maps of total electron content tec over the north american continent millstone hill radar observations of storm enhanced density and low and high altitude satellite measurements of the perturbation of the outer plasmasphere during the march 31 2001 geomagnetic storm we find that storm enhanced density sed and plumes of greatly elevated tec are associated with the erosion of the outer plasmasphere by strong sub auroral polarization electric fields the sed tec plumes identified at low altitude map closely onto the magnetospheric determination of the boundaries of the plasmapause and plasmaspheric tail determined by euv imaging from the image spacecraft characteristics of the sed tec plumes tails for the march 31 2001 event are tec 100 tecu f region sunward velocity 1000 m s sunward flux 5 1024 ions s 1 total transport to dayside magnetopause merging region 3 hr event 5 1028 ions

flash heating and local fluid pressurization lead to rapid weakening in water saturated fault gouges coseismic fault displacement is quite large at shallow depths in some earthquakes and it implies that fault gouges and sediments have extremely low dynamic friction during seismic slip however the dynamic weakening mechanisms of gouges under wet conditions are still not well constrained here we present direct evidence for the occurrence of flash heating and local fluid pressurization in water saturated gouges by performing low to high velocity v 10 m s to 1 m s friction experiments in a pressure vessel under conditions specially designed to suppress weakening effects of bulk thermal and compaction induced pressurization the tested gouges exhibit transition from velocity strengthening to drastic velocity weakening as slip rates increase strong dynamic weakening starts to occur at v 0 04 m s at the initiation of sliding 0 1 m which is much more efficient than previously reported in terms of the weakening velocity and distance furthermore the onset of weakening is always accompanied by an instantaneous dilatancy 10 25 m which is much larger than that observed in dry tests and in contrast with gradual changes displayed in the wet tests without dynamic weakening numerical modeling integrated with microstructural observation reveals that bulk thermal pressurization cannot explain the experimental results while flash weakening triggered by vaporization of water layers on around asperity contacts and the resultant local fluid pressurization may be responsible for the observed rapid weakening concomitant with instantaneous dilatancy given high efficiency of such weakening process fluid infiltrated faults could be weakened more rapidly than previously recognized during seismic slip

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

conditions for early cretaceous emerald formation at dyakou china fluid inclusion ar ar and stable isotope studies the dyakou emerald occurrence is located in malipo county in the province of yunnan southern china the occurrence lies in the northern part of the laojunshan song chay metamorphic core complex which is exposed in an area of approximately 2 000 km2 and extends across the border between china and vietnam emerald mineralization is hosted by pegmatite and associated quartz veins that intrude deformed proterozoic biotite muscovite granofels and schist hydrogen and oxygen isotope results from the emerald channel waters and emerald respectively are consistent with an igneous fluid source the 18o fractionation between emerald and quartz yields vein temperatures of 365 to 420 c fluid inclusions indicate that the emerald precipitated from saline brines ranging from almost pure water to 10 5 mass percent nacl equiv fluid inclusion isochores intersected with 18o data yield pressures changing along the geothermal gradient from 1 500 to 3 300 bars ar ar geochronology of biotite and muscovite from the emerald veins yields consistent ages of 124 1 ma these constraints combined with field observations indicate that the dyakou emerald deposit is consistent with the igneous related model for emerald formation

strain induced amorphization of graphite in fault zones of the hidaka metamorphic belt hokkaido japan abstract we report here on two distinct processes of deformation affecting graphite in fault zones of the hidaka metamorphic belt hokkaido japan one process involves the micrometer scale delamination mmd in the stacking of graphite and the other is the nanometer scale delamination nmd in the stacking plus pulverization p of carbon sheets to less than 10 nm graphite in mylonites mainly glide along the 002 planes and they exhibit layer separation kink banding and bending structures produced by mmd processes whereas nmd p processes induce a significant size reduction and amorphization of the graphitic structures in cataclasites ultracataclasites and pseudotachylytes the strain induced amorphization of graphite as inferred from xrd and micro raman spectroscopy corresponds well with nano to micro scale deformation structures observed under the hrtem suggesting a systematic increase of edge planes by interlayer delamination and pulverization of carbon sheets in addition the carbon isotopic compositions of the graphite in fault rocks have negative 13 c signatures indicating a sedimentary organic origin such graphite has a tendency to accumulate within the shear bands our data suggest that the graphitic structures record information on both the peak metamorphic temperatures and the deformation processes and they show the progressive amorphization with increasing brittle deformation

extreme enhancement in total electron content after sunset on 8 november 2004 and its connection with storm enhanced density 1 after sunset on 8 november 2004 the ionospheric total electron content tec was observed to have anomalously increased following a severe daytime positive tec storm at longitudes of japan the observation was made using a dense gps receiver network and covered a geographic latitudinal range of 27 to 45 n there was a greater increase in tec at higher latitudes in the evening and the tec reached 90 tec units at 45 n 40 n magnetic latitude at 1145 ut 2045 lt the tec enhancement exhibited features significantly different from those of positive tec storms normally observed at japan s longitudes these features are interpreted as low latitude signatures of a storm enhanced density sed previously seds were reported only at longitudes of america and this led to the hypothesis that geomagnetic field configurations at these longitudes play a role in their formation the present observations indicate that seds can be observed at other longitudes

long and complex thermal history of the song chay metamorphic dome northern vietnam by multi system geochronology multi system geochronology was used to unravel the long and complex thermal history of the song chay range northern vietnam a high grade granitic and metamorphic dome in the vicinity of the cenozoic ailao shan red river fault zone it was considered to be proterozoic south china basement but its geological history was basically unknown scattered field observations suggest three episodes of high temperature deformation firstly at the time of granite emplacement secondly a decollement with top to the north shear and thirdly anticlinal doming of the foliations formed during the two first stages p t estimates suggest that metamorphism coeval with the second deformation phase culminated at 580 ca nd 4 5 kbar 16 km depth multi system geochronology is applied to a two micas granite sample slightly deformed within the decollement u pb dating of zircon yields an age of 428 5m a 2s interpreted as the time of granite crystallization within the south china caledonian belt rb sr on white micas and biotite yields ages of 206 10 ma and 176 5 3 ma respectively 2s whereas 39ar 40 ar ages of the same minerals are 210 9a nd 190 8m a 2s these ages suggest an upper triassic episode of rapid cooling interpreted as due to doming a few million years after the end of movement on the decollement the k feldspar irregular 39ar 40ar age spectrum can to the first order be explained by a cooling history with two episodes of rapid cooling one at 140 ma and a second around 41 to 25 ma apatite fission tracks central age 33 6 3 6 ma 1s confirms a tertiary rapid cooling event interpreted as the final exhumation of the song chay dome 2000 elsevier science b v all rights reserved

mechanisms of fault mirror formation and fault healing in carbonate rocks abstract the development of smooth mirror like surfaces provides insight into the mechanical behaviour of crustal faults during the seismic cycle to determine the thermo chemical mechanisms of fault mirror formation we investigated carbonate fault systems in seismically active areas of central greece using multi scale electron microscopy combined with raman and electron energy loss spectroscopy we show that fault mirror surfaces do not always develop from nanogranular volumes the microstructural observations indicate that decarbonation is the transformation process that leads to the formation of smooth surface coatings in the faults studied here piercement structures on top of the fault surfaces indicate calcite decarbonation producing co2 and lime cao lime subsequently reacts to portlandite ca oh 2 under hydrous conditions nanoscale imaging and electron diffraction reveal a thin coating of a non crystalline material sporadically mixed with nano clay forming a complex composite material that smooths the slip surface spectroscopic analyses reveal that the thin coating is non crystalline carbon we suggest that ordering hybridisation of amorphous carbon led to the formation of partly hybridised amorphous carbon but did not reach full graphitisation calcite nanograins 100 nm and new nanograins formed by back reaction secondary nanograins

equilibria within the mineral assemblage quartz muscovite biotite garnet plagioclase and implications for the mixing properties of octahedrally coordinated cations in muscovite and biotite interaction parameters derived using empirical calibration methods indicate strong non ideality in the mixing of octahedrally coordinated cations in muscovite and biotite the data set used for calibration comprises mineral compositions from 49 samples containing quartz muscovite biotite garnet plagioclase and al2sio5 kyanite or sillimanite pressures and temperatures in the data set were determined through the simultaneous application of geothermometry based on the garnet biotite femg1 exchange equilibrium and geobarometry based on the anorthite breakdown equilibrium two equilibria yielded simple expressions from which binary interaction parameters for octahedrally coordinated cations in biotite could be directly determined a four component fe2 mg al ti regular symmetric mixing model was assumed for biotite one equilibrium yielded a simple expression from which an interaction parameter for the mixing of the mgal celadonite component in muscovite could be directly determined two sets of calculations were performed utilizing different calibrations of the garnet biotite geothermometer and the anothite breakdown geobarometer and different garnet activity models both placed samples within or near the stability field of the al2sio5 phase present in each sample and both yielded similar values for the interaction parameters within narrow uncertainties indicating that the values are insensitive to differences in the underlying methods using the derived interaction parameters activity models were formulated for the annite phlogopite eastonite and siderophyllite components of biotite and for the mgal celadonite component of muscovite these were utilized for the empirical calibration of 45 fluid independent equilibria involving unique combinations of phase components from the mineral assemblage garnet plagioclase biotite muscovite quartz forty three of the equilibria may be applied as geobarometers to equilibrium assemblages of quartz muscovite biotite garnet plagioclase when care is taken to insure that applications are restricted to valid compositional ranges for these the calibrations yielded multiple correlation coefficients ranging from 0 953 to 0 998 and standard deviations of the residuals ranging from 597 to 118 bars