modeling of the transport and deposition of tungsten in the scheelite bearing calc silicate gneisses of the montagne noire france scheelite bearing calc silicate gneisses csg oceur in the montagne noire within a series of dominant micaschists detailed petrographical and mineralogical studies reveal three successive stages of metamorphism and hydrothermal alteration 1 stage 1 a regional metamorphism at 550 c and 4 5 kb where no mineralization is formed 2 stage 2a a hydrothermal alteration at 500 to 450 c and 4 to 3 kb which is characterized by an intense sericitization of feldpars and deposition of sn in sn bearing cale silicates and 3 stage 2b a hydrothermal alteration characterized by the crystallization of idocrasegrossular in csg with concomittant precipitation of scheelite tungsten was transported through the micaschist environment and deposited as scheelite only in the csg of stage 2b at relatively low pressures to characterize the mechanism of tungsten transport tungsten speciation at high p t and scheelite solubility in aqueous solations buffered by the csg and by the micaschists assemblages were calculated it was found that h2wo 0 4 hwo 4 and wo 2 4 are the dominant tungsten aqueous species in h2o nacl one molal solutions at 500 c and 2 4 kb calculations also indicate that scheelite deposition is controlled by decreasing pressure and increasing activity of aqueous calcium in this system this is consistent with the petrographical and mineralogical observations the consequences of the presence of volatiles n2 ch4 co2 in the regional fluids were examined by determining the effect of n2 on tungsten speciation and scheelite solubility the addition of n2 up to 10 mol to the mineralizing fluids results in a marked increase in h2wo 0 4 and hwo 4 concentrations relative to wo 2 4 and in a large decrease of scheelite solubility this mechanism favours scheelite precipitation and accounts for the commonly observed association of w and sn deposits with graphitic series generating mixed volatiles fluids

paragonite hornblende assemblages and their petrological significance an example from the austroalpine schneeberg complex southern tyrol italy paragonite bearing amphibolites occur interbedded with a garbenschist micaschist sequence in the austroalpine schneeberg complex southern tyrol the mineral assemblage mainly comprises paragonite mg hornblende tschermakite quartz plagioclase biotite ankerite ti phase garnet muscovite equilibrium p t conditions for this assemblage are 550 600 c and 8 10 kbar estimated from garnet amphibole plagioclase ilmenite rutile and si contents of phengitic muscovites in the vicinity of amphibole paragonite is replaced by symplectitic chlorite plagioclase margarite biotite assemblages muscovite in the vicinity of amphibole reacts to form plagioclase biotite margarite symplectites the reaction of white mica hornblende is the result of decompression during uplift of the schneeberg complex the breakdown of paragonite hornblende is a water consuming reaction and therefore it is controlled by the availability of fluid on the retrogressive p t path paragonite hornblende is a high temperature equivalent of the common blueschist assemblage paragonite glaucophane in ca bearing systems and represents restricted p t conditions just below omphacite stability in a mafic bulk system while paragonite glaucophane breakdown to chlorite albite marks the blueschist greenschist transition the paragonite hornblende breakdown observed in schneeberg complex rocks is indicative of a transition from epidote amphibolite facies to greenschist facies conditions at a flatter p t gradient of the metamorphic path compared to subduction zone environments ar ar dating of paragonite yields an age of 84 5 1 ma corroborating an eoalpine high pressure metamorphic event within the austroalpine unit west of the tauern window eclogites that occur in the otztal crystalline basement south of the schneeberg complex are thought to be associated with this eoalpine metamorphic event

earthquake activity related to seismic cycles in a model for a heterogeneous strike slip fault we investigate the evolution of seismicity within large earthquake cycles in a model of a discrete strike slip fault in elastic solid the model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of regions around the fault static kinetic friction and dislocation creep along the fault and 3d elastic stress transfer the fault consists of brittle parts which fail during earthquakes and undergo small creep deformation between events and aseismic creep cells which are characterized by high ongoing creep motion this mixture of brittle and creep cells is found to generate realistic aftershock sequences which follow the modified omori law and scale with the mainshock size furthermore we find that the distribution of interevent times of the simulated earthquakes is in good agreement with observations the temporal occurrence however is magnitude dependent in particular the small events are clustered in time whereas the largest earthquakes occur quasiperiodically averaging the seismicity before several large earthquakes we observe an increase of activity and a broadening scaling range of magnitudes when the time of the next mainshock is approached these results are characteristics of a critical point behavior the presence of critical point dynamics is further supported by the evolution of the stress field in the model which is compatible with the observation of accelerating moment release in natural fault systems

phase relationships and fluid inclusions characteristics of the metamorphosed stratiform sulfide deposit matchless namibia silicate assemblages in the wallrocks of the metamorphosed stratiform sulfide deposit matchless damara orogen namibia yield temperatures between 550 and 625 c and pressure of 6 8 kbar highest density fluid inclusions containing either pure co2 or co2 ch4 n2 mixtures display isochors which extrapolate through these metamorphic peak conditions a second group of inclusions with the same fluid compositions exhibit isochors conforming to lower pressures i e 3 kbar as deduced from sphalerite barometer at the same temperatures from these observations we deduce an isothermal uplift path after peak of amphibolite facies metamorphism

stress slip and earthquakes in models of complex single fault systems incorporating brittle and creep deformations numerical simulations of slip evolution along a cellular vertical strike slip fault in an elastic half space are performed for several models representing discrete fault systems embedded in three dimensional elastic continua the geometry and imposed boundary conditions correspond approximately to the central san andreas fault the simulations incorporate brittle and creep deformations in series the net fault zone deformation rate is the sum of creep rate and frictional slip rate brittle fault properties are given by various distributions of earthquake stress drops on failing segments numerical cells the assumed distributions represent two idealized situations corresponding to different extreme states along an evolutionary path of a fault 1 a strongly disordered state characterized by a wide range of size scales representing immature fault zones and extended spatial domains and 2 a relatively regular state having a narrow range of size scales representing mature highly slipped faults the assumed creep properties are identical in all cases these are prescribed in terms of coefficients characterizing a power law dependency of creep slip rate on stress the combined brittle creep process and employed parameters lead to an overall pine tree stress depth profile with a brittle ductile transition depth of about 12 5 km and variable stress along strike profiles with brittle creep transition around 65 km nw of the 1857 rupture the spatial patterns of simulated hypocenters are statistically similar to observed data the results indicate that the range of size scales characterizing strong fault zone heterogeneities has important manifestations on the seismic response of a fault system a narrow range of size scales leads to frequency size statistics of earthquakes resembling the characteristic earthquake distribution and quasi periodic temporal distribution of large events as in the seismic gap hypothesis on the other hand a wide range of size scales leads to gutenberg richter power law frequency size statistics and random or clustered temporal distribution of large events the simulations demonstrate that treatment of the various observed forms of frequency size and temporal statistics of earthquakes can be unified through the concept of range of size scales characterizing fault zone heterogeneities this has a clear physical interpretation in terms of structural properties of a given fault zone or broad lithospheric domain and is supported by observed earthquake and fault data in some simulated cases the frequency size statistics of small earthquakes fall sharply below the self similar gutenberg richter line the results indicate that small earthquakes prepare the fault for the occurrence of a large event by smoothing during gradual tectonic loading the long wavelength components of stress on the fault this is done through short wavelength stress roughening associated with the numerous ruptures of the small events the above pattern of smoothing roughening of long short wavelengths of stress on the fault is reversed during large scale ruptures of the big events

the earthquake prediction experiment at parkfield california since 1985 a focused earthquake prediction experiment has been in progress along the san andreas fault near the town of parkfield in central california parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years the most recent a magnitude 6 event in 1966 the probability of another moderate earthquake soon appears high but studies assigning it a 95 chance of occurring before 1993 now appear to have been over simplified the identification of a parkfield fault segment was initially based on geometric features in the surface trace of the san andreas fault but more recent microearthquake studies have demonstrated that those features do not extend to seismogenic depths on the other hand geodetic measurements are consistent with the existence of a locked patch on the fault beneath parkfield that has presently accumulated a slip deficit equal to the slip in the 1966 earthquake a magnitude 4 7 earthquake in october 1992 brought the parkfield experiment to its highest level of alert with a 72 hour public warning that there was a 37 chance of a magnitude 6 event however this warning proved to be a false alarm most data collected at parkfield indicate that strain is accumulating at a constant rate on this part of the san andreas fault but some interesting departures from this behavior have been recorded here we outline the scientific arguments bearing on when the next parkfield earthquake is likely to occur and summarize geophysical observations to date

recalibration of mutually consistent garnet biotite and garnet cordierite geothermometers abstract garnet biotite and garnet cordierite geothermometers have been consistently calibrated using the results of fe 2 mg cation exchange experiments and utilizing recently evaluated nonideal mixing properties of garnet nonideal mixing parameters of biotite including fe mg al vi and ti and of cordierite involving fe and mg are evaluated in terms of iterative multiple least square regressions of the experimental results assuming the presence of ferric fe in biotite in relation to the coexisting fe oxide phases case a and assuming the absence of ferric fe in biotite case b two formulae of garnet biotite thermometer have been derived the garnet cordierite geothermometer was constructed using margules parameters of garnet adopted in the garnet biotite geothermometers the newly calibrated garnet biotite and garnet cordierite thermometers clearly show improved conformity in the calculated temperatures the thermometers give temperatures that are consistent with each other using natural garnet biotite cordierite assemblages within 50 c the effects of ferric fe in biotite on garnet biotite thermometry have been evaluated comparing the two calibrations of the thermometer the effects are significant it is clarified that taking ferric fe content in biotite into account leads to less dispersion of thermometric results

seasonal and universal time distribution of patches in the northern and southern polar caps ion density measurements from the dynamics explorer 2 and defense meteorological satellite program f8 and f9 satellites are used to examine hemispherical differences in the occurrence patterns of polar ionization patches as a function of season universal time ut and interplanetary magnetic field imf when bz 0 the greatest frequency of patch occurrence in the northern hemisphere is in the winter in the 1000 2200 ut range this time corresponds to the interval when the northern magnetic pole and hence the cusp lies the farthermost toward the dayside this fact is often used to explain the creation of patches in terms of the entrainment of dayside plasma into the cusp by high latitude convection in the southern hemisphere we see that the occurrence frequencies peak at over twice the northern hemisphere values in the same general ut region 1000 2300 ut however the southern hemisphere cusp is most dayward at approximately 0300 ut a time of minimum patch formation examination of the relationship of the terminator to the polar cap boundaries in each hemisphere leads to a simple explanation in terms of the differing offset of the magnetic poles and the ionospheric convection pattern from the geographic poles

scaling relations of earthquakes and aseismic deformation in a damage rheology model summary we perform analytical and numerical studies of scaling relations of earthquakes and partition of elastic strain energy between seismic and aseismic components using a thermodynamically based continuum damage model brittle instabilities occur in the model at critical damage level associated with loss of convexity of the strain energy function a new procedure is developed for calculating stress drop and plastic strain in regions sustaining brittle instabilities the formulation connects the damage rheology parameters with dynamic friction of simpler frameworks and the plastic strain accumulation is governed by a procedure that is equivalent to drucker prager plasticity the numerical simulations use variable boundary forces proportional to the slip deficit between the assumed far field plate motion and displacement of the boundary nodes these boundary conditions account for the evolution of elastic properties and plastic strain in the model region 3 d simulations of earthquakes in a model with a large strike slip fault produce scaling relations between the scalar seismic potency rupture area and stress drop values that are in good agreement with observations and other theoretical studies the area and potency of the simulated earthquakes generally follow a linear log log relation with a slope of 2 3 and are associated with stress drop values between 1 and 10 mpa a parameter space study shows that the area potency scaling is shifted to higher stress drops in simulations with parameters corresponding to lower dynamic friction more efficient healing and higher degree of seismic coupling

effect of grossular on garnet biotite fe mg exchange reactions evidence from garnet with mixed growth and diffusion zoning garnets that exhibit mixed growth and diffusion zoning are used to evaluate the effect of grossular content on garnet fe mg exchange reactions these garnets from the uppermost amphibolite facies to granulite facies gneiss of the wissahickon group southeastern pennsylvania show variation in grossular content 0 035 xca 0 14 but nearly constant mg xmg xmg xfe and xmn through the interior indicating re equilibration of garnet and matrix minerals with respect to iron magnesium and manganese mg is not correlated with calcium content evidence that the effect of calcium on garnet fe mg exchange reactions is small or is offset by other interactions in almandine rich garnets in either case the data presented here indicate that correction for calcium content of garnets in the application of garnet biotite geothermometry to high grade metapelites is unnecessary and may lead to an overestimate of peak temperature

geophysical properties of the lower crustal granulites from the qinling orogenic belt china abstract the lower continental crust plays a crucial role in continental evolution and mountain building it is widely accepted that the lower crust is dominated by granulites mafic or felsic in the present paper our studies are presented on the geophysical properties of granulites from two adjacent tectonic units the late archean taihau complex along the southern margin of the north china craton in lushan and the early proterozoid dahe formation in the qinling orogen in tongbai eastern henan province china the results indicate that the granulites from the two units were formed within the p t regime of the lower crust but in distinct environments

geothermobarometry in albite garnet orthogneisses a case study from the gran paradiso nappe western alps abstract the aim of this paper is to estimate syntectonic p t conditions within albite and garnet bearing orthogneisses these rocks are generally characterized by the assemblage quartz albite biotite phengite cafe garnet epidote titanite garnet contains up to 55 mole per cent of grossular k feldspar is a relict magmatic phase p t conditions are estimated using several independent methods first it is shown that exchange reactions based on the fe mg partitioning between garnet and biotite or garnet and phengite cannot be used to estimate temperatures in these rocks due to the high grossular content of garnet second maximum and minimum pressures are constrained respectively by the occurrence of albite instead of jadeite quartz and by the assemblage phengite biotite quartz third phase equilibria in albite and garnet bearing metagranites are modelled in the system k 2 o cao feo al 2 o 3 sio 2 h 2 o equilibrium curves are calculated for the observed phase compositions uncertainties in p t estimates mainly result from the choice of appropriate non ideal solution models for the garnet an application is developed for granites from the gran paradiso nappe western alps these granites show an heterogeneous deformation of alpine age expressed by mylonitic shear zones cutting across weakly deformed domains estimated p t conditions for the synkinematic assemblages are 10 16 kbar at 550 50 c

a global comparison of o upward flows at 850 km and outflow rates at 6000 km during nonstorm times 1 there has been recent progress in understanding the sources and consequences of energetic o in the ring current and other regions of the magnetosphere various energization mechanisms that depend on geomagnetic activity altitude magnetic local time and relative position within the auroral oval acting on o have been proposed our understanding of the altitude and magnetic local time variation of these processes has not proceeded as rapidly however contemporary magnetosphere models now include species dependent dynamics these models will benefit from improved spatial and altitudinal knowledge of o energization processes here we present a global view of o upward flows observed at dmsp 850 km compared to outflow rates observed by polar 5000 7000 km during nonstorm times in the framework of dynamic auroral boundary coordinates this study considers observational proxies for heating and energization mechanisms and shows that these proxies set useful boundaries on their efficacy this study indicates that during nonstorm times 1 energization between 850 km and 5000 7000 km is predominantly transverse 2 the efficiency of ion energization is often not focused at the boundaries of the auroral zone and 3 auroral zone acceleration above dmsp is relatively more important in the cusp than at midnight

granulite facies spinel cordierite assemblages from the kerala khondalite belt southern india abstract granulite facies metapelites at koliacode in the kerala khondalite belt show compositional bands of cordierite spinel sillimanite and biotite alternating with quartz feldspar rich bands reaction textures involving cordierite and garnet show evidence for decompression mineral phase equilibria computations provide temperatures of ca 700 750c and pressures of 4 5 5 0 kbar spinel in these rocks is remarkably enriched in zn zno up to 9 4 wt the metamorphic p t conditions and mineral reactions indicate that the terrain underwent rapid and near isothermal decompression

investigating the southern daytime midlatitude trough s relation with the daytime weddell sea anomaly during equinoxes a detailed study with statistical investigations was conducted on the morning topside ionosphere for the 1996 1997 equinoctial period utilizing defense meteorological satellite program data and coupled thermosphere ionosphere plasmasphere wind simulations highly structured plasma densities including a daytime weddell sea anomaly wsa about 0900 lt over the southeastern pacific and localized high latitude plasma enhancements about 0800 lt in the australian sector were tracked poleward and equatorward winds respectively were strongest there high resolution regional surface maps and field aligned profiles tracked their thermal structures o and h composition vertical drifts v m s and horizontal plasma flows f i cms a daytime heavy ion ni o stagnation trough 54 5 4 5 s geomagnetic appeared equatorward of both the wsa 60 0 4 0 s center 185 310 e geographic and these enhancements 62 0 3 5 s 30 180 e meanwhile the plasmapause developed poleward of the wsa and equatorward of these enhancements plasma convection became significantly increased by enhanced electron temperatures nearby upflows underlying localized plasma enhancements upflow velocities modeled as about 694 5 m s shows close similarities to the actual direct measurements of about 700 m s both slow and enhanced plasma convections promoted stagnation events and trough formation however regular trough features became significantly altered by the development of a downward dipping poleward wall in the wsa region and by the absence of regular trough walls in the region of localized plasma enhancements statistically the trough and localized plasma enhancement locations varied linearly with magnetic activity and showed an equatorward movement with increasing activity a rate of 0 026 0 002 s nt for the trough and 0 067 0 003 s nt for the localized plasma enhancements were modeled this higher approximately two times rate of movement indicates the localized plasma enhancements more responsiveness copyright 2010 by the american geophysical union

a systematic spatiotemporal test of the critical point hypothesis for large earthquakes 1 the critical point hypothesis for large earthquakes predicts two different precursory phenomena in space and time an accelerating moment release and the growth of the spatial correlation length the objective of this work is to investigate both methods with respect to their predictive power a systematic statistical test based on appropriate random earthquake catalogs allows to quantify the correlations of a precursory pattern with the subsequent mainshock activity the analysis of target earthquakes in california since 1960 with magnitudes m mcut reveals that these correlations increase systematically with growing mcut and correlations at greater than 95 confidence are observed for mcut 6 5 in the case of the spatial correlation length in particular the seismicity patterns are found to be significantly correlated with each of the largest earthquakes m 7 0 individually the acceleration of the moment release has a similar trend but is less significant

effect of grossular content in garnet on the partitioning of fe and mg between garnet and biotite in contrast to ferry 1980 x ca values in garnet even lower than 0 1 have a significant effect on the calculated equilibrium temperature using the experimental calibration of the fe and mg paritioning between garnet and biotite garnet compositions and mg fe distribution coefficients from samples of the eoalpine staurolite in zone in the southern otztal are related by the quadratic regression equation ink d 1 7500 0 0226 2 978 0 5317 x ca gt 5 906 2 359 x ca gt 2 temperatures derived by the ferry and spear 1978 calibration using chemistry corrected k d values are petrologically realistic analysis of our data supports non ideal mixing of grossular with almandine pyrope solid solution the derived excess mixing energies are quite small for the almandine pyrope solution w femg 133 cal mole and about 2775 cal mole for the difference between pyrope grossular and almandine grossular solutions w mgca w feca at metamorphic conditions of 570 c and 5 000 bar the mixing parameters proposed by ganguly and saxena 1984 are not confirmed by our data as they would result in significantly lower temperatures

metamorphic evolution of a subduction complex south shetland islands antarctica a subduction complex composed of ocean floor material mixed with arc derived metasediments crops out in the elephant island group and at smith island south shetland islands antarctica with metamorphic ages of 120 80 ma and 58 47 ma respectively seven metamorphic zones i vii mapped on elephant island delineate a gradual increase in metamorphic grade from the pumpellyite actinolite facies through the crossite epidote blueschist facies to the lower amphibolite facies geothermometry in garnet amphibole and garnet biotite pairs yields temperatures of about 350 c in zone iii to about 525 c in zone vii pressures were estimated on the basis of si content in white mica al2o3 content in alkali amphibole nam4 aliv in sodic calcic and calcic amphibole alvi si in calcic amphibole and jadeite content in clinopyroxene mean values vary from about 6 7 5 kbar in zone ii to about 5 kbar in zone vii results from the other islands of the elephant island group are comparable to those from the main island smith island yielded slightly higher pressures up to 8 kbar with temperatures estimated between 300 and 350 c zoned minerals and other textural indications locally enable inference of p t t trajectories all with a clockwise evolution a reconstruction in space and time of these p t t paths allows an estimate of the thermal structure in the upper crust during the two ductile deformation phases d1 d2 that affected the area this thermal structure is in good agreement with the one expected for a subduction zone the arrival and collision of thickened oceanic crust may have caused the accretion and preservation of the subduction complex in this model d1 represents the subduction movements expressed by the first vector of the clockwise p t t path d2 reflects the collision corresponding to the second vector with increasing temperature and decreasing pressure and d3 corresponds to isostatic uplift accompanied by erosion under circumstances of decreasing temperature and pressure

the variscan structural and metamorphic evolution of the eastern southalpine basement the basement of the southern alps northern italy belongs to the southernmost part of the european variscan mountain belt in contrast to other areas of the alps the post variscan metamorphic and tectonic overprint is weak and therefore permits the unravelling of the variscan tectonometamorphic evolution of this region overprinting criteria and the mapping of the penetrative structural elements s2 and l2 allow three deformational events to be distinguished major variscan deformation d2 in the southern alps commenced in the carboniferous and lasted until the end of the late carboniferous tectonic movement during d2 was north directed and was accompanied and followed by greenschist facies metamorphism peak metamorphic conditions reached 450 550 c and 5 6 5 kbar in the brixen area and decreased in a southeasterly direction tectonic movement during d2 followed subduction of the plankogel terrane and collision of the noric terrane northernmost part of gondwana with laurasia and is interpreted to result from late orogenic extensional collapse of the variscan mountain chain extensional deformation caused exhumation of the basement rocks as evidenced by greenschist facies basement pebbles which show no substantial retrograde overprint in late carboniferous early permian conglomerates

quantitative modeling of the lithosphere dynamics earthquakes and seismic hazard abstract understanding of lithosphere dynamics tectonic stress localization earthquake occurrences and seismic hazards has significantly advanced during the last decades meanwhile despite the major advancements in geophysical sciences yet we do not see a decline in earthquake disaster impacts and losses although earthquake disasters are mainly associated with significant vulnerability of society comprehensive seismic hazards assessments and earthquake forecasting could contribute to preventive measures aimed to reduce impacts of earthquakes modeling of lithosphere dynamics and earthquake simulations coupled with a seismic hazard analysis can provide a better assessment of potential ground shaking due to earthquakes here we present a block and fault dynamics bafd model which simulates earthquakes due to lithosphere dynamics and allows for studying the influence of fault network properties and regional movements on seismic patterns the model s performance is analyzed in terms of reproduction of basic features of the observed seismicity such as the frequency magnitude relationship clustering of earthquakes occurrences of large events fault slip rates and earthquake mechanisms several studies related to the application of the bafd model to the following earthquake prone regions are reviewed the southeastern carpathians caucasus the western india tibet himalaya and the sunda arc we examine then a new approach to seismic hazard analysis which is based on instrumentally recorded historical and bafd simulated earthquakes and analyze how earthquake modeling can assist in hazard assessment finally we discuss perspectives in modeling of earthquake occurrences and improvements in hazard assessment

empirical garnet muscovite geothermometry in low grade metapelites selwyn range canadian rockies partitioning of fe and mg between garnet and phengitic muscovite was calibrated as a geothermometer by green hellman 1982 using experimental data at 25 30 kbar when the thermometer is applied to pelites regionally metamorphosed at pressures of between 3 and 7 kbar it yields temperatures much higher than those from the garnet biotite thermometer a new empirical calibration is proposed for use with such rocks with particular application where garnet occurs at lower grades than biotite the new calibration is where k is given by in k in kd and xii are mole fractions in the garnets the calibration was derived from comparison with the garnet biotite thermometer of ferry spear 1978 assuming no pressure dependence for the partitioning between garnet and muscovite no ferric iron partitioning ideal mixing in muscovite and the garnet mixing model of ganguly saxena 1984 modified for a non linear ca effect this latter garnet mixing model was selected because it gave the geologically most reasonable results it has not proved possible to distinguish a pressure effect from a ferric iron effect despite the simplifying assumptions used to derive the calibration it yields temperatures generally within 15 c of those given by the garnet biotite thermometer and has been used to supply thermometric data in a low grade region of the canadian rockies

contrasting p t paths in the eastern himalaya nepal inverted isograds in a paired metamorphic mountain belt petrology and phase equilibria of rocks from two profiles in eastern d f matrix assemblages are overprinted by decompression reaction textures and in zones f and g progress into the sillimanite field nepal from the lesser himalayan sequences across the main central thrust zone and into the greater himalayan sequences the two terranes were brought into juxtaposition during formation of sillimanite biotite gedrite foliation seams s3 formed at reveal a paired metamorphic mountain belt pmmb composed of two thrust bound metamorphic terranes of contrasting metamorphic conditions of 674 33 c and 5 7 1 1 kbar the contrasting average geothermal gradients and p t paths of these two metastyle at the higher structural level the greater himalayan sequences experienced high t moderate p metamorphism with an anmorphic terranes suggest they make up a pmmb the upperplate position of the greater himalayan sequences produced an ticlockwise p t path low p inclusion assemblages of quartz hercynitic spinel sillimanite have been overgrown by peak anticlockwise p t path with the high average geothermal gradient being possibly due to high radiogenic element content in this terrane metamorphic garnet cordierite sillimanite assemblages that equilibrated at 837 59 c and 6 7 1 0 kbar matrix in contrast the lower plate lesser himalayan sequences were deeply buried metamorphosed in a clockwise p t path and display minerals are overprinted by numerous metamorphic reaction textures that document isobaric cooling and re equilibrated samples preserve inverted isograds as a result of progressive ductile overthrusting of the hot greater himalayan sequences during prograde metamorphism evidence of cooling to 600 45 c at 5 7 1 1 kbar below the main central thrust the lesser himalayan sequences are a continuous though inverted barrovian sequence of high p moderate t metamorphic rocks metamorphic zones upwards from the

comparison of garnet biotite calcite graphite and calcite dolomite thermometry in the grenville orogen ontario canada the elzevir terrane of the grenville orogen in southern ontario contains metapelites and abundant graphitic marbles that were regionally metamorphosed from the upper greenschist to upper amphibolite facies comparative thermometry was undertaken with widely used calibrations for the systems garnet biotite calcite dolomite and calcite graphite temperatures that are obtained from matrix biotites paired with prograde garnet near rim analyses are usually consistent with those determined using calcite graphite thermometry however calcite graphite thermometry occasionally yields low temperatures due to lack of equilibration of anomalously light graphite application of calcite graphite and garnet biotite systems may yield temperatures up to 70 c higher than calcite dolomite in amphibolite facies rocks calcite dolomite temperatures most closely approach those from calcite graphite and garnet biotite when the samples contain a single generation of dolomite and calcite grains contain no visible dolomite exsolution lamellae however some of these samples yield temperatures considerably lower than temperatures calculated from calcite graphite and garnet biotite thermometry indicating that the calcite dolomite thermometer may have been partially reset during retrogression estimated peak metamorphic temperatures of regional metamorphism between madoc upper greenschist facies and bancroft upper amphibolite facies range from 500 to 650 c these results place the chlorite staurolite isograd at 540 c the kyanite sillimanite isograd at 590 c and the sillimanite k feldspar isograd at 650 c although each thermometer may have an absolute uncertainty of as much as 50 c the 50 to 60 c temperature differences between the isograds are probably accurate to 10 to 20 c an incomplete picture of the thermal gradients can result from the application of only one thermometer in a given area simultaneous application of several systems allows one to recognize and overcome the inherent limitations of each thermometer

p t t deformation paths recorded by kinzigites during diapirism in the western variscan belt golfe du morbihan southern brittany france the high grade metamorphic rocks of southern brittany underwent a complex tectonic evolution under various p t conditions high p high t related to stacking of nappes during palaeozoic continentcontinent collision the east to west thrusting observed in the whole belt is strongly perturbed by vertical movements attributed to the ascent of anatectic granites in the high t area the field reconstruction of subvertical closed elliptical structures in gneisses and migmatites associated with the subhorizontal doubly radial pattern of stretching lineation in the mica schists suggests the existence of an elliptical diapiric body buried at depth beneath the present erosion level deformation is associated with a complex p t evolution partly recorded in aluminous gneisses kinzigites e g morbihanites a chronology of successive episodes of mineral growth at different compositions is established by detailed studies of the mineral microstructure relationships in x z sections using the deformation partitioning concept low and high strain zones several thermometric and barometric calibrations are applied to mineral pairs either in contact or not in contact but in equivalent microstructiiral positions with respect to the deformation history this methodology provides a continuous microstructural control of p t variations through time and leads to three p t t d paths constructed from numerous successive p t estimations path 1 is a clockwise retrograde path preserved in low strain zones which records general exhumation movements after crustal thickening paths 2 and 3 are clockwise prograde retrograde paths from high strain zones they are interpreted and discussed in the light of models of crustal anatexis and upward movement of magma diapirism deformation and p t effects induced by diapirism can be distinguished from the general deformation metamorphic history of a belt and would seem to be produced during a late stage of its history the present microstructural petrological approach to defining successive mineral equilibria in relation to progressive deformation steps provides a far more accurate evaluation of the metamorphic evolution than is possible by standard thermobarometry

evolving towards a critical point a review of accelerating seismic moment energy release prior to large and great earthquakes there is growing evidence that some proportion of large and great earthquakes are preceded by a period of accelerating seismic activity of moderate sized earthquakes these moderate earthquakes occur during the years to decades prior to the occurrence of the large or great event and over a region larger than its rupture zone the size of the region in which these moderate earthquakes occur scales with the size of the ensuing mainshock at least in continental regions a number of numerical simulation studies of faults and fault systems also exhibit similar behavior the combined observational and simulation evidence suggests that the period of increased moment release in moderate earthquakes signals the establishment of long wavelength correlations in the regional stress field the central hypothesis in the critical point model for regional seismicity is that it is only during these time periods that a region of the earth s crust is truly in or near a self organized critical soc state such that small earthquakes are capable of cascading into much larger events the occurrence of a large or great earthquake appears to dissipate a sufficient proportion of the accumulated regional strain to destroy these long wavelength stress correlations and bring the region out of a soc state continued tectonic strain accumulation and stress transfer during smaller earthquakes eventually re establishes the long wavelength stress correlations that allow for the occurrence of larger events these increases in activity occur over longer periods and larger regions than quiescence which is usually observed within the rupture zone of a coming large event the two phenomena appear to have different physical bases and are not incompatible with one another

high pressure micro inclusions and development of an inverted metamorphic gradient in the santiago schists ordenes complex nw iberian massif spain evidence of subduction and syncollisional decompression the santiago schists are located in the basal unit of the ordenes complex one of the allochthonous complexes outcropping in the inner part of the hercynian belt in the north west of the iberian peninsula their tectonothermal evolution is characterized by the development of an eo hercynian metamorphic episode c 374 ma of high p low to intermediate t the mineral assemblage of the high p episode is preserved as a very thin si s1 foliation included in albite porphyroblasts being composed of albite garnet i white mica 1 chlorite 1 epidote quartz rutile ilmenite the equilibrium conditions for this mineral assemblage have been estimated by means of different thermobarometers at 495 10 c and 14 7 0 7 kbar probably minimum pressure the later evolution syn d2 of the schists defines a decompressive and slightly prograde p t path which reached its thermal peak at c 525 10 c and 7 kbar decompression of the unit occurred contemporaneously with an inversion of the metamorphic gradient so that the zones of garnet ii biotite with an upper subzone with chloritoid and staurolite developed from bottom to top of the formation the estimated p t path for the santiago schists suggests that the basal unit probably a fragment of the gondwana continental margin was uplifted immediately after its subduction at the beginning of the hercynian orogeny it also suggests that the greater part of the unroofing history of the unit took place in a context of ductile extension probably related to the continued subduction of the gondwana continental margin and the contemporaneous development of compensatory extension above it the inverted metamorphic gradient seems related to conductive heat transferred from a zone of the mantle wedge above the subducted continental margin when it came into contact with the upper parts of the schists along a detachment probably of extensional character the general metamorphic evolution of the santiago schists with the development of high p assemblages with garnet prior to decompressive and prograde parageneses with biotite is unusual in the context of the european hercynian belt and shows a close similarity to the tectonothermal evolution of several high p low to intermediate t circum pacific belts

valid garnet biotite gb geothermometry and garnet aluminum silicate plagioclase quartz gasp geobarometry in metapelitic rocks abstract at present there are many calibrations of both the garnet biotite gb thermometer and the garnet aluminum silicate plagioclase quartz gasp barometer that may confuse geologists in choosing a reliable thermometer and or barometer to test the accuracy of the gb thermometers we have applied the various gb thermometers to reproduce the experimental data and data from natural metapelitic rocks of various prograde sequences inverted metamorphic zones and thermal contact aureoles we have concluded that the four gb thermometers perchuk l l lavrent eva i v 1983 experimental investigation of exchange equilibria in the system cordierite garnet biotite in saxena s k ed kinetics and equilibrium in mineral reactions springer verlag new york berlin heidelberg pp 199 239 kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 model 6av kaneko y miyano t 2004 recalibration of mutually consistent garnet biotite and garnet cordierite geothermometers lithos 73 255 269 model b are the most valid and reliable of this kind of thermometer more specifically we prefer the holdaway holdaway m j 2000 application of new experimental and garnet margules data to the garnet biotite geothermometer american mineralogist 85 881 892 and the kleemann and reinhardt kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 calibrations due to their small errors in reproducing the experimental temperatures and good accuracy in successfully discerning the systematic temperature changes of the different sequences in addition after applying the gasp barometer to 335 natural metapelitic samples containing one kind of aluminosilicate and 33 natural metapelitic samples containing two kinds of aluminosilicate as well as to rocks in limited geographic areas and thermal contact aureoles we propose that the calibrations of holdaway holdaway m j 2001 recalibration of the gasp geobarometer in light of recent garnet and plagioclase activity models and versions of the garnet biotite geothermometer american mineralogist 86 1117 1129 and newton and haselton newton r c haselton h t 1981 thermodynamics of the garnet plagioclase al2sio5 quartz geobarometer in newton r c navrotsky a wood b j eds thermodynamics of minerals and melts new york springer verlag 131 147 based on kleemann and reinhardt s kleemann u reinhardt j 1994 garnet biotite thermometry revised the effect of alvi and ti in biotite european journal of mineralogy 6 925 941 thermometer are the most valid gasp barometers other gb thermometers and gasp barometers are not recommended

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

earthquakes as self organized critical phenomena a cellular automation model with threshold elements previously proposed by bak et al 1988 which generates 1 f noise and self organizes into a critical state is studied as a model for earthquake occurrence the model explains some of fractal features of earthquakes such as the power law distribution of the size of the earthquake the model is modified so that every earthquake may trigger aftershocks the modified trigger model explains other fractal features of earthquakes such as the power law decay of aftershock frequency and the power law decay of aftershock frequency and the power law correlation of the hypocenter distribution

thermal gradients in the sri lankan granulite terrane a garnet biotite thermometric approach thermal zoning of the highland complex sri lanka has been delineated using the fe2 mg distribution coefficient between garnet and biotite from garnet biotite gneiss samples collected with wide geographical distribution in order to minimize the potential for retrograde fe mg exchange and maximize the potential for retaining peak equilibrium kd garnet biotite and temperature garnet and biotite included within feldspar and quartz without other mineral inclusions have been selected the calculated results indicate four distinct temperature contours with kd values varying from 1 84 to 6 38 and temperature varying from 996 to 591 c from the present results it is possible to divide the highland complex into two major metamorphic zones a high temperature area in the central region and a low temperature area in the south western and north eastern region in conjunction with the metamorphic pressure variations estimated from the granulites of the highland complex in previous studies it is shown that the high and low temperature areas are complemented by a high pressure region towards the eastern side and a low pressure region towards the western side of this complex this thermal dome is interpreted to be an artifact of the different crustal levels exhumed following pan african metamorphism

trace element partitioning between coexisting biotite and muscovite from metamorphic rocks western labrador structural compositional and thermal controls coexisting biotite and muscovite in ten metapelitic and quartzofeldspathic rocks from western labrador have been analyzed by electron microprobe for major and minor elements and by a laser ablation microprobe coupled to icp ms lam icp ms for selected trace elements li sc v cr mn co ni cu zn rb sr y zr nb cs ba ree hf and ta the samples have experienced a single prograde grenvillian metamorphism ranging from 490 to 680 c and from 7 to 12 kbar the trace element compositions of coexisting micas in the metamorphic rocks are used to assess the effects of crystal structure major element composition and temperature on the partitioning of each element between biotite and muscovite overall trace element distributions are systematic across the range of metamorphic grade and bulk composition suggesting that chemical equilibrium was approached most distribution coefficients biotite muscovite show good agreement with published data however distribution coefficients for co and sr are significantly different from previous determinations probably because of contamination associated with older data obtained by bulk analysis techniques the sequence of distribution coefficients is governed mainly by the ionic radii and charges of substituting cations compared to the optimum ionic radius of each crystallographic site in the micas in particular distribution coefficients exhibit the sequence cr3 0 615 a v3 0 64 a sc3 0 745 a in vi sites and ba2 1 61 a sr2 1 44 a and cs 1 88 a k 1 64 a rb 1 72 a na 1 39 a in xii sites the distributions of li sc sr and ba appear to be thermally sensitive but are also controlled by major element compositions of micas v and zr partitioning is dependent on t and may be used to cross check thermometry calculations where the latter suffer from retrograde re equilibration and or high concentrations of fe3 the ranges and dependence of distribution coefficients on major element compositions provide important constraints on the values that can be used in geochemical modeling

metamorphic geology and regional geothermobarometry of a grenvillian massif the long range inlier newfoundland abstract geothermobarometry of middle proterozoic amphibolite to granulite facies gneiss of the long range inlier reveals a southwestward increase in metamorphic temperature from 600 650 c to nearly 800 c at a pressure between 5 and 8 kbar throughout the massif a steep d p d t slope of 14 bars c 1 determined using the garnet orthopyroxene plagioclase quartz thermobarometer indicates fairly rapid uplift of the inlier and or records the effects of a late grenvillian 970 ma tectonothermal overprint grenvillian granitoid rocks and a mafic pluton of unknown age have narrow thermal aureoles and intruded the gneiss complex following regional high grade metamorphism metamorphic conditions of the adjacent grenville province span those determined for the long range inlier available data suggest that both areas were uplifted from moderate crustal levels during the middle to late proterozoic and indicate negligible differential uplift of the inlier relative to the grenville province during paleozoic orogenies

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

the seismic cycle at subduction thrusts 2 dynamic implications of geodynamic simulations validated with laboratory models 1 the physics governing the seismic cycle at seismically active subduction zones remains poorly understood due to restricted direct observations in time and space to investigate subduction zone dynamics and associated interplate seismicity we validate a continuum visco elasto plastic numerical model with a new laboratory approach paper 1 the analogous laboratory setup includes a visco elastic gelatin wedge underthrusted by a rigid plate with defined velocity weakening and strengthening regions our geodynamic simulation approach includes velocity weakening friction to spontaneously generate a series of fast frictional instabilities that correspond to analog earthquakes a match between numerical and laboratory source parameters is obtained when velocity strengthening is applied in the aseismic regions to stabilize the rupture spontaneous evolution of absolute stresses leads to nucleation by coalescence of neighboring patches mainly occurring at evolving asperities near the seismogenic zone limits consequently a crack or occasionally even pulse like rupture propagates toward the opposite side of the seismogenic zone by increasing stresses ahead of its rupture front until it arrests on a barrier the resulting surface displacements qualitatively agree with geodetic observations and show landward and from near the downdip limit upward interseismic motions these are rebound and reversed coseismically this slip increases adjacent stresses which are relaxed postseismically by afterslip and thereby produce persistent seaward motions the wide range of observed physical phenomena including back propagation and repeated slip and the agreement with laboratory results demonstrate that visco elasto plastic geodynamic models with rate dependent friction form a new tool that can greatly contribute to our understanding of the seismic cycle at subduction zones

field occurrences and petrology of eclogites from the dabie mountains anhui central china four distinct types of eclogites are recognized according to their field occurrences and mineral parageneses in a gneiss terrane of the dabie mountains a collision zone between the sino korean and yangtze cratons in central china some eclogites contain coesite and its quartz pseudomorphs enclosed in garnet and omphacite type i eclogites occur as layers in serpentinites and contain garnet clinopyroxene orthopyroxene phengite rutile and coesite pseudomorph type ii eclogites occur as lenticular bodies inside serpentinites and contain garnet clinopyroxene quartz rutile and edenitic hornblende type iii eclogites occur as blocks of 2 cm to 20 m in size in a matrix of hornblende gneiss and biotite gneiss and type iv eclogites occur as thin layers interbedded with amphibolites p t estimates for these different eclogites indicate that they were formed under different physical conditions all the eclogites were affected by later regional metamorphism for which the p t conditions are estimated this paper provides an introduction to the abundant eclogites from central china which have not been reported previously in western literature specifically the mode of field occurrence petrography mineral chemistry and formation conditions of the four types of eclogites are described the paper is thus designed to establish a petrological framework for future detailed studies of the eclogites and their country rocks in an ancient zone of collision

eclogite meso and microfabrics implications for the burial and exhumation history of eclogites in the tauern window eastern alps from p t d paths abstract the eclogite zone of the central southern tauern window comprises eclogites and associated high pressure metasediments that are intercalated between penninic basement units in the foot wall and an imbricate stack in the hanging wall this nappe stack consists of continental basement units cover sequences of a distal continental slope and the main part of the ophiolitic glockner nappe textures and microfabrics of eclogites from the central southern tauern window allow the establishment of the eclogitic and post eclogitic deformation histories from burial by subduction to subsequent exhumation the metamorphic evolution of the eclogites is documented by 1 initial greenschist to blueschist facies 2 eclogite facies at ca 550 630 c and 20 kbar 3 a second blueschist facies overprint ca 450 c 10 15 kbar and 4 exhumation to pressures of ca 6 7 kbar at 500 550 c upper greenschist to lower amphibolite facies an eclogitic penetrative foliation s 1 and s dipping stretching lineation l 1 formed during the final stages of subduction of the eclogite bearing unit the p t evolution of the eclogites during d 1 documents the final increment of the prograde p t path later blueschist facies metamorphism is contemporaneous to top to the n emplacement of the eclogite bearing unit onto continental basement units within a subduction zone we discuss two models of eclogite emplacement most probably emplacement is achieved by a thrust along the base of the eclogite bearing unit alternatively the p t path of the eclogite facies rocks suggests an emplacement model similar to corner flow subsequent to eclogite and nappe emplacement the nappe stack is entirely affected by a penetrative deformation d 2 that resulted in the development of a mylonitic foliation s 2 and an e w oriented stretching lineation l 2 within lower amphibolite to upper greenschist facies this deformation is related to a crustal scale detachment zone that formed during the exhumation of the penninic units

precursory seismic activation and critical point phenomena in this paper we relate the behavior of seismicity prior to a characteristic earthquake to the excitation in proximity to a spinodal instability we illustrate the spinodal instability as the upper limit of superheated water prior to a steam explosion we draw an analogy between the steam explosion and a characteristic earthquake and show that the power law activation associated with the spinodal instability is essentially identical to the power law increase in benioff strain observed prior to characteristic earthquakes we find that theory and actual data give very similar results

tectonometamorphic evolution of the chewore inliers partial re equilibration of high grade basement during the pan african orogeny only minor structural reworking during m2 granulite terrane the chewore inliers are isolated outcrops of the zambezi mobile samples within 2 km of the basal thrust margin preserve m1 belt within the mesozoic lower zambezi rift valley in zimbabwe mineral assemblages but these minerals were chemically re equidetailed mapping has recognized four terranes the zambezi librated without recrystallization during m2 at conditions of 5 6 quartzite granulite and ophiolite terranes apart from the 1 5 kbar and 631 100 c granulite terrane samples were ophiolite terrane all are dominated by supracrustal gneisses with totally recrystallized in shear zones at the margin of this terrane concordant granitic orthogneiss units of 1071 8 and 1083 these samples equilibrated at conditions identical to the peak of 8 ma age these terranes experienced low p high t metamorphism m2 at 7 7 1 9 kbar and 590 110 c the re equilibrated m1 terminated by isobaric cooling at 945 34 ma m1 and recrystallized sample sets define two points on the clockwise assemblages of sillimanite spinel garnet garnet orthopyroxene and p t path experienced by the granulite terrane during further two pyroxene mafics are recorded in the granulite terrane and burial and reworking in the pan african orogeny and are consistent conditions of formation were 4 4 1 7 kbar and 800 c m1 with the m2 p t path documented for the other terranes mineral parageneses and associated ductile deformation structures dominate the granulite terrane but m1 mineral parageneses are only preserved as sillimanite spinel inclusions in garnet cores in the other terranes the zambezi quartzite and ophiolite terranes were almost totally recrystallized during reworking in the m2

accelerated seismic release and related aspects of seismicity patterns on earthquake faults observational studies indicate that large earthquakes are sometimes preceded by phases of accelerated seismic release asr characterized by cumulative benioff strain following a power law timeto failure relation with a term tf t m where tr is the failure time of the large event and observed values of m are close to 0 3 we discuss properties of asr and related aspects of seismicity patterns associated with several theoretical frameworks the subcritical crack growth approach developed to describe deformation on a crack prior to the occurrence of dynamic rupture predicts great variability and low asymptotic values of the exponent m that are not compatible with observed asr phases statistical physics studies assuming that system size failures in a deforming region correspond to critical phase transitions predict establishment of long range correlations of dynamic variables and power law statistics before large events using stress and earthquake histories simulated by the model of ben zion 1996 for a discrete fault with quenched heterogeneities in a 3 d elastic half space we show that large model earthquakes are associated with nonrepeating cyclical establishment and destruction of long range stress correlations accompanied by nonstationary cumulative benioff strain release we then analyze results associated with a regional lithospheric model consisting of a seismogenic upper crust governed by the damage rheology of lyakhovsky et al 39 over a viscoelastic substrate we demonstrate analytically for a simplified 1 d case that the employed damage rheology leads to a singular power law equation for strain proportional to t f t 1 3 and a nonsingular power law relation for cumulative benioff strain proportional to t f t 1 3 a simple approximate generalization of the latter for regional cumulative benioff strain is obtained by adding to the result a linear function of time representing a stationary background release to go beyond the analytical expectations we examine results generated by various realizations of the regional lithospheric model producing seismicity following the characteristic frequency size statistics gutenberg richter power law distribution and mode switching activity we find that phases of asr exist only when the seismicity preceding a given large event has broad frequency size statistics in such cases the simulated asr phases can be fitted well by the singular analytical relation with m 1 3 the nonsingular equation with m 0 2 and the generalized version of the latter including a linear term with m 1 3 the obtained good fits with all three relations highlight the difficulty of deriving reliable information on functional forms and parameter values from such data sets the activation process in the simulated asr phases is found to be accommodated both by increasing rates of moderate events and increasing average event size with the former starting a few years earlier than the latter the lack of asr in portions of the seismicity not having broad frequency size statistics may explain why some large earthquakes are preceded by asr and other are not the results suggest that observations of moderate and large events contain two complementary end member predictive signals on the time of future large earthquakes in portions of seismicity following the characteristic earthquake distribution such information exists directly in the associated quasi periodic temporal distribution of large events in portions of seismicity having broad frequency size statistics withrandom or clustered temporal distribution of large events the asr phases have predictive information the extent to which natural seismicity may be understood in terms of these end member cases remains to be clarified continuing studies of evolving stress and other dynamic variables in model calculations combined with advanced analyses of simulated and observed seismicity patterns may lead to improvements in existing forecasting strategies

stormtime measurements of topside ionospheric upflow from defense meteorological satellite program 1 we have examined characteristics of the vertical ion flux of thermal o in the topside high latitude ionosphere before and during a number of geomagnetic storms including the october and november 2003 events using measurements of the vertical ion drift and ion number density made by the dmsp f13 and f15 spacecraft prior to storm onset typical upward fluxes of approximately 108 109 cm 2 s 1 are observed in the auroral zones with somewhat smaller downward fluxes in the polar caps immediately following storm onset upward fluxes reach and sometimes exceed 1010 cm 2 s 1 and are observed with vertical velocities of 500 1500 m s 1 at the same time downward fluxes at the higher latitudes reach unusually high values of 109 cm 2 s 1 separately integrating the upward and downward fluxes over the high latitude region auroral zone and polar cap for each spacecraft pass allows the observation of variations in the total upflow downflow during the progression of a geomagnetic storm a superposed epoch analysis of events from 1995 to 2004 reveals a pattern of sudden onset of upward flux averaging approximately 14 hours with a gradually increasing and more extended period of downward flux lasting about 24 hours the upward fluxes are stronger when the coincident fluctuations in the z component of the imf are larger strong upward flux events during storm times tend to occur when the solar wind velocity is elevated and the solar wind density is high upward flux events can also occur without a coincident geomagnetic storm if the solar wind velocity is above average

tectonic setting of cadomian low pressure metamorphism in the central ossa morena zone iberian massif sw spain abstract the upper proterozoic serie negra a monotonous pre and syntectonic slate greywacke series including volcanic episodes crops out widely in the central area of the ossa morena zone sw iberian massif iberian peninsula this unit was affected by complex late precambrian tectonothermal events the cadomian orogeny during which two phases of deformation d1 and d2 are recognized in the 610 585 ma time span the second deformational episode d2 was the most prominent and was related to progressive low pressure high temperature metamorphism lp ht reaching the highest grade in the lower structural levels where thermal evolution led to extensive migmatization and gave rise to the generation of different kinds of anatectic granitoids in this work we present field petrographic and analytical data dealing with the metamorphic evolution of a cadomian lp ht terrane from the central ossa morena zone iberian massif sw spain whose tectonic setting is unclear so far the tectonic setting proposed herein for cadomian d2 lp ht events is discussed in terms of its relationship to plate convergence or to extensional tectonic regimes modelling of the p t t trajectories undergone by a crust moderately overthickened by the thrusting of thinned sialic crust slices reproduces well the observed p t t aths if moderate or low uplift rate and high geothermal gradients are assumed for the uplift history numerical simulations combined with structural and metamorphic evidence support a compressional tectonic setting as responsible for the observed facies series distribution and deformation metamorphism relationships furthermore the regional geodynamic context coeval high pressure metamorphism in neighboring areas of the ossa morena zone and extensive calc alkaline magmatism is consistent with such a tectonic setting a correlation is tentatively proposed here between compressional cadomian deformations in the ossa morena zone upper proterozoic docking of avalonian terranes in ne america and cadomian orogenesis in the northern armorican massif

la zone tectonique du front de grenville a l est de louvicourt quebec exhumation de la croute archeenne pendant l orogenie grenvillienne the grenville front tectonic zone east of louvicourt in quebec defines a tectonometamorphic domain marked by the grenville front oriented north 50 that is locally crosscut by a north 30 reverse fault the matchi manitou fault these tectonic accidents separate the central parts of the superior province to the northwest from the grenville province to the southeast the archean age high grade polymetamorphic sequences of the grenville province consist of paragneisses and migmatitic quartzofeldspathic gneisses associated to coarse grained anatectic pegmatitic veins the whole containing shreds of two pyroxenes bearing mafic gneisses the metamorphic disequilibrium textures the chemical analyses of the mineral phases and the whole rock chemistry of these sequences indicate that a strong crustal thickening marked by the incorporation of shreds of volcanic rocks in the metasedimentary sequences led to the granulitization of the lithologies and the quartzofeldspathic pegmatitic vein formation by fluid

aftershocks resulting from creeping sections in a heterogeneous fault 1 we show that realistic aftershock sequences with space time characteristics compatible with observations are generated by a model consisting of brittle fault segments separated by creeping zones the dynamics of the brittle regions is governed by static kinetic friction 3d elastic stress transfer and small creep deformation the creeping parts are characterized by high ongoing creep velocities these regions store stress during earthquake failures and then release it in the interseismic periods the resulting postseismic deformation leads to aftershock sequences following the modified omori law the ratio of creep coefficients in the brittle and creeping sections determines the duration of the postseismic transients and the exponent p of the modified omori law

the alpine geodynamic evolution of penninic nappes in the eastern central alps the eastern central alps consist of several pennine nappes with different tectonometamorphic histories the tectonically uppermost units oceanic avers bundnerschiefer continental suretta and tambo nappes oceanic vals bundnerschiefer show cretaceous early tertiary w directed thrusting with associated blueschist facies metamorphism related to subduction of the pennine units beneath the austroalpine continental crust this event caused eclogite facies metamorphism in the underlying continental adula nappe the gross effect was crustal thickening the tectonically lower continental simano nappe is devoid of any imprint from this event in the course of continent continent collision high t metamorphism and n directed movements occurred both affected the whole nappe pile more or less continuously from amphibolite to greenschist facies conditions crustal thinning commenced during the regional temperature peak a final phase is related to differential uplift under retrograde p t conditions further thinning of the crust was accommodated by e to ne directed extensional deformation

the timing and p t conditions of regional metamorphisni in the central highlands scotland the central highlands of the scottish caledonides are dominated by a sequence of poly deformed metasedimentary rocks largely belonging to the grampian and appin groups of the dalradian supergroup in the northern part of the area these are separated from a suite of variably gneissose to locally migmatitic rocks by a number of prominent mid crustal shear zones the early evolution of the central highlands is interpreted in terms of regional d1 d2 folding and n to nw directed thrusting accompanied by kyanite grade metamorphism p 7 0 8 0 kbar t 500 600 c the later stages of this event were characterized by continued ductile shearing along the pre existing shear zones under sillimanite grade metamorphic conditions p 4 7 5 9 kbar t 585 695 c the exact age of this progressive tectonothermal event remains uncertain however available geochronological data can be interpreted as indicating an entirely precambrian age c 840 800 ma this questions previously held views of an entirely caledonian age for deformation throughout the highlands

cadomian subduction collision and variscan transpression in the badajoz cordoba shear belt southwest spain abstract the tectonothermal evolution of the badajoz cordoba shear belt southwest iberian massif spain involved the build up of a cadomian upper proterozoic lower paleozoic subduction collision orogenic wedge complex made up of five stacked tectonic slices and its deformation under transpression during hercynian late paleozoic intracontinental shearing episodes cadomian metamorphism in the high grade gneissic units of the wedge complex is characterized by peak metamorphic conditions of 720 c 8 kbar for the lowermost tectonic slice higuera de llerena mylonite gneiss and 670 c 10 kbar in the overlying gneissic slice blastomylonitic migmatic gneisses the p t conditions recorded by eclogites structurally overlying the previous gneisses enhance a scheme of inverted metamorphism since these eclogites equilibrated at 685 700 c 15 kbar during peak metamorphic conditions after the high pressure event the highest temperatures attained by the eclogites correspond to a period of nearly isothermal decompression with a drastic decrease in pressure later on the retrogressed eclogites experienced a pressure increase before they began to reequilibrate under progressively lower pandt conditions similar to those recorded by the retrogression of gneisses such a p increase in eclogites might be related to a period of underthrusting below continental crust responsible for the amalgamation of the different tectonic units of the badajoz cordoba shear belt the present results unravel that the models concerned with the geotectonic evolution of the ibero armorican arc and the respective correlations among hercynian and pre hercynian cadomian for our aims terranes across the north atlantic must be reconsidered

contrasting geochemical and sm nd isotopic compositions of archean metasediments from the kongling high grade terrain of the yangtze craton evidence for cratonic evolution and redistribution of ree during crustal anatexis abstract twenty three clastic metasediments from the kongling high grade terrain of the yangtze craton south china were analyzed for major trace and rare earth elements and sm nd isotopic ratios associated dioritic tonalitic trondhjemitic dtt and granitic gneisses as well as amphibolites were also analyzed in order to constrain provenance the results show that the clastic metasediments can be classified into 3 distinct groups in terms of mineralogical geochemical and sm nd isotopic compositions group a is characterized by having no to slight negative eu anomalies eu eu 0 82 1 07 being high in cr 191 396 ppm and ni 68 137 ppm and low in th 3 3 7 8 ppm and ree ree 99 156 ppm these characteristics are similar to those of metasediments from archean greenstone belts in addition the group a metasediments have the value of the chemical index of alteration ciw close to felsic gneisses their sm nd isotopic ree and trace element compositions can be interpreted by mixtures of the dtt gneisses and amphibolites dating of detrital zircons from 2 group a samples by shrimp reveals a major concordant age group of 2 87 3 0 ga which is identical to the age of the trondhjemitic gneiss these results strongly suggest that group a was principally the first cycle erosion product of the local kongling dtt gneiss and amphibolite moreover the higher than amphibolite cr content and slight eu depletion exhibited by some samples from this group infer that ultramafic rocks like komatiite and granite of probably 3 0 3 3 ga in age also played a role group b is characterized by the presence of graphite and shows a more evolved composition similar to post archean shales with a prominent negative eu anomaly eu eu 0 48 0 77 and high ciw on paired cr th vs la co and co th plots group b samples conform to a two end member mixing line of the kongling granitic gneiss and amphibolite however data on nd model age and ciw suggest that the granite component should be younger than the sampled granitic gneiss and derived from a distal source both groups a and b exhibit a clear positive correlation between ciw and tdm and a negative one between ciw and eu eu these correlations point to the crustal evolution of the yangtze craton towards coupled increasing ciw and eu depletion with decreasing age this in turn reflects the change of granitoid magmatism from local na rich dioritic tonalitic trondhjemitic rocks to widespread k feldspar granite the change led to the intracrustal differentiation stabilization and growth of the craton group c is restite and contains abundant sillimanite and garnet and unusually high ilmenite 7 11vol which can be seen to be dehydration melting products of biotite under the microscope this group shows extremely varied ree distributions from lree enriched to depleted and from negative to strong positive eu eu 1 63 eu anomalies compared to groups a and b group c is severely depleted in na2o k2o lree rb and ba whereas tio2 co v sc and hree and y are considerably enriched this is accompanied by anomalous high sm nd 0 21 0 28 147sm 144nd 0 1361 0 1738 and 143nd 144nd 0 511589 0 511958 ratios tdm correlates clearly with sm nd ratio and 2 out of 3 samples give significantly older to unrealistic tdm 3 9 4 9 ga the results document redistribution of ree and an open behavior of the sm nd isotope system during the biotite dehydration melting of metasediments

prograde retrograde p t t deformation path of austroalpine micaschists during variscan continental collision eastern alps a complete prograde p t path defined by 10 calculated p t fields in succession is recognized from metapelites by using geothermobarometry on garnet bearing assemblages with microstructural control overstacking of several tectonic units during an early variscan continental collision explains the complex prograde p t history isostatic uplift and deformation controlled the retrograde p t path deformation with changing character acted continuously during all stages of the evolution of the austroalpine basement complex after the intrusion of caledonian granitoids metapelites and magmatic rocks suffered a shearing deformation d1 d2 which produced sheath folds as well as the main foliation s2 spessartine rich first generation garnets situated in microlithons enclosed by s2 record the onset of shearing under increasing high pressure low temperature conditions 7 kbar 380 c geothermobarometry on second generation garnets which have been rotated during growth indicates isothermal decompression from 9 kbar to 5 kbar 500 c and subsequent recompression heating during continuing shearing this is explained by overthrusting of a tectonic unit unit 2 from ne to sw upon the micaschist unit unit 1 followed by isostatic uplift and further overstocking of a third unit unit 3 the resulting pmax of 12 kbar at 650 c and further increasing temperatures up to 680 c accompanied by decompression have been calculated using a third generation of garnets these high pressure high temperature conditions may explain the occurrence of eclogitic metabasites in adjacent regions staurolite and kyanite first appeared under decreasing pressures at the last stage of prograde p t evolution shortening deformation d3 and simultaneous growth of typical amphibolite facies minerals staurolite 2 kyanite 2 sillimanite andalusite occurred during the retrograde path a final step of variscan evolution was marked by an oppositely directed shearing d4 at t 300 c and p 3 kbar possibly indicating backthrusting or extension apart from acid intrusions no signs of a previous caledonian thermotectonic history were found in the area to the south of the defereggen antholz vals line

mechanism of the spatial distribution and migration of the strong earthquakes in china inferred from numerical simulation abstract strong earthquakes that occurred in the chinese continent are usually characterized by grouped activity long distance jumping migration and different main activity areas formed in different times in the present study a three dimensional 3 d finite element model was set up for the chinese continent involving surface topography major active fault zones and initial stress field to study the mechanism of the long distance jumping migration of main active areas for the strong earthquakes that occurred in the chinese continent a number of numerical simulation experiments have been made by introducing the birth and death of element groups under different boundary loading configurations our results show that 1 in an environment where always exists an initial stress field in the earth s crust the areas where strong earthquakes have occurred taken as a killed element in the model have no longer abilities to concentrate the stress largely enough and can cause the stress adjustment by an order of mpa in a large area which may be one of the main factors affecting the long distance jumping migration of the follow up strong earthquakes and 2 it is hard to accurately predict where the follow up strong earthquakes will occur because it could be affected by many factors such as the loading manner geological structure active fault zones initial stress field or stress field adjustment induced by strong earthquakes but in an active period of earthquakes the major activity area migration of strong earthquakes may be affected largely by the boundary loading configurations these results suggest that it is helpful to predict a trend of the strong earthquake migration by investigating various kinds of boundary loading manners and the relationship between stress field adjustment induced by strong earthquakes and the regions where the strong earthquakes occurred

a synthetic seismicity model for the xianshuihe fault southwestern china simulation using a rate and state dependent friction law summary we performed a numerical simulation of seismic activity along the xianshuihe fault a highly active strike slip fault approximately 350 km long located along the eastern margin area of the tibetan plateau southwestern china historical earthquake data over the last 300 yr indicate repeated periods of seismic activity and migration of large earthquakes along the fault during active seismic periods to understand the characteristics of historical seismicity and to obtain insight into seismic potential we performed a numerical simulation of slip behaviour along the fault using a 2 d elastic plate model the friction on the model fault obeys a laboratory derived rate and state dependent friction law while the long term slip rates along the fault are assumed to be consistent with geologically and geodetically estimated slip rates to simulate segmented rupture behaviour we introduced non uniformity into friction parameters along the fault the simulation results indicate that seismic rupture is arrested in regions with frictional properties that are highly velocity strengthening or large values of characteristic slip distance over which frictional stress evolves in the regions where seismic rupture is arrested post seismic sliding occurs causing time dependent stress transfer along the fault post seismic slip histories in highly velocity strengthening regions are well approximated by logarithmic time functions while those in regions with large characteristic slip distances increase more rapidly in the initial stages of post seismic sliding this difference in post seismic sliding produces the difference in time dependent stress transfer and in consequence the statistical characteristics of earthquake recurrence fault interactions near a fault branch point produce complexity in the simulated earthquake sequence simulated rupture commonly triggers additional rupture in a neighbouring segment with a time delay of several years the simulated seismic activity shows good agreement with observational data with respect to the following statistical features 1 successive seismically active periods are separated by periods of relative quiescence of 100 200 yr duration 2 and the duration of active period is a few tens of years strictly speaking neither the time nor slip predictable models are able to describe the simulated local slip history for each fault segment the ratio of the standard deviation to the average value of the recurrence intervals of simulated earthquakes ranges from 0 05 to 0 22 depending on the fault segment the cumulative distribution function of the recurrence intervals of simulated earthquakes at each segment approximately obeys a brownian passage time distribution or a lognormal distribution which is commonly used in the statistical evaluation of earthquake occurrence

similar power laws for foreshock and aftershock sequences in a spring block model for earthquakes we introduce a crust relaxation process in a continuous cellular automaton version of the burridge and knopoff 1967 model the most important model parameters are the level of conservation and the ratio of the crust relaxation time to the tectonic reloading time in correspondence with the original spring block model the modified model displays a robust power law distribution of event sizes the principal new result obtained with our model is the spatiotemporal clustering of events exhibiting several characteristics of earthquakes in nature large events are followed by aftershock sequences obeying the omori 1894 law and preceded by localized foreshocks which are initiated after a time period of seismic quiescence while we observe a considerable variability of precursory seismicity we find that the rate of foreshocks increases on average according to a power law with an exponent q which is in good agreement with the exponent p of the omori law in contrast to other events the distribution of foreshock sizes is characterized by a significantly smaller richter b value our model reproduces simultaneously the empirically observed values of the power law exponents the richter b p and q and their variability

aluminous reaction textures in orthoamphibole bearing rocks the pressure temperature evolution of the high grade proterozoic of the bamble sector south norway aluminous reaction textures in orthoamphibole bearing rocks from the froland area bamble south norway record the prograde pressure temperature path of the high grade kongsbergian orogeny c 1600 1500 ma and the low mid amphibolite facies overprint during the sveconorwegian orogeny c 1100 1000 ma the rocks contain anthophyllite gedrite garnet cordierite biotite quartz andalusite kyanite cr rich staurolite tourmaline ilmenite rutile and corundum in a variety of parageneses the p t path is deduced from petrographic observations mineral chemistry and zoning geothermometry and n fmash equilibria the results indicate the sequence of metamorphic stages outlined below a an m1 phase characterized by the presence of strongly deformed andalusite gedrite and tourmaline b an m2 phase with the development of kyanite after andalusite and the growth of staurolite associated with strong na al mg zoning in orthoamphibole indicating an increase in pressure 4 8 kbar and temperature 500 650 c c pressure decrease at high p 6 7 kbar and high t 600 700 c during m3a with the production of cordierite corundum between kyanite staurolite and orthoamphibole and cordierite growth between corundum and orthoamphibole d temperature increase to 740 60 c and 7 kbar static growth of garnet m3b at the metamorphic climax peak t the heat supply necessary to explain the temperature increase between the m3a and m3b phases is correlated with synkinematic enderbitic charnockitic and basic intrusions in the arendal granulite facies terrain e m3b metamorphic conditions were followed by an initial isobaric cooling path early m4 and late stage pressure decrease late m4 early m4 conditions of 6 7 kbar and 550 600 c assuming ph2o ptotal are indicated by a retrograde talc kyanite quartz assemblage in late quartz cordierite veins late m4 conditions of 3 4 kbar and 420 530 c are inferred from a kyanite andalusite chlorite quartz assemblage in vein cordierite the m1 m3 stages are interpreted as being the result of the same metamorphic p t path which was caused by both tectonic and magmatic thickening a prolonged crustal residence time is proposed for the bamble sector before uplift during the later stages of m4 occurred

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

large plasma density enhancements occurring in the northern polar region during the 6 april 2000 superstorm we focus on the ionospheric response of northern high latitude region to the 6 april 2000 superstorm and aim to investigate how the storm enhanced density sed plume plasma became distributed in the regions of auroral zone and polar cap plus to study the resultant ionospheric features and their development multi instrument observational results combined with model generated two cell convection maps permitted identifying the high density plasma s origin and the underlying plasma transportation processes results show the plasma density feature of polar cap enhancement pce 600 103 i cm3 appearing for 7 h during the main phase and characterized by increases reaching up to 6 times of the quiet time values meanwhile strong westward convections 17 500 m s created low plasma densities in a wider region of the dusk cell oppositely small 750 m s but rigorous westward drifts drove the sed plume plasma through the auroral zone wherein plasma densities doubled as the sed plume plasma traveled along the convection streamlines and entered the polar cap a continuous enhancement of the tongue of ionization toi developed under steady convection conditions however convection changes caused slow convections and flow stagnations and thus segmented the toi feature by locally depleting the plasma in the affected regions of the auroral zone and polar cap from the strong correspondence of polar cap potential drop and subauroral polarization stream saps we conclude that the saps e field strength remained strong and under its prolonged influence the sed plume provided a continuous supply of downward flowing high density plasma for the development and maintenance of pces

geothermobarometry in metasediments of the southern grossvenediger area tauern window austria metasediments in the southern grossvenediger area tauern window austria were studied along a cross section through rocks of increasing metamorphic grade from the margin of the tauern window in the south to the base of the upper schieferhulle including the eclogite zone in the north in the southern part of the cross section there is no evidence for a pre late alpine metamorphic history in the form of high pressure relics or pseudomorphs mineral assemblages are characterized by the stability of tremolite calcite biotite calcite and biotite chlorite calcite in the northern part a more complete alpine metamorphic evolution is preserved primary high pressure assemblages are dolomite quartz tremolite zoisite zoisite dolomite quartz phengite i and probably tremolite dolomite phengite i secondary post kinematic assemblages tremolite calcite talc calcite phengite ii chlorite calcite quartz biotite chlorite calcite biotite zoisite calcite formed as a result of the dominant late alpine metamorphic overprint the occurrence of biotite zoisite calcite is confined to the northernmost area and defines a biotite zoisite calcite isograd p t estimates based on standard thermobarometric techniques and on stability relationships of tremolite calcite dolomite quartz and zoisite give consistent results p t conditions of the main tertiary metamorphic overprint were 525 c p 7 5 1 kbar in the northern part of the cross section the southern part was metamorphosed at lower temperatures of 430 470 c the si content of phengites from this area is almost as high as that of phengites from the eclogite zone simax 3 4 pfu pressures 10 kbar at 420 c are suggested by phengite barometry according to massone schreyer 1987 in the absence of high pressure relics or pseudomorphs these phengites which lack late alpine re equilibration are the only record that rocks of the southern part probably also experienced an early non eclogitic high pressure metamorphism

earthquake failure sequences along a cellular fault zone in a three dimensional elastic solid containing asperity and nonasperity regions numerical simulations of earthquake failure sequences along a discrete cellular fault zone are performed for a three dimensional 3 d model representing approximately the central san andreas fault the model consists of an upper crust overlying a lower crust and mantle region together defining an elastic half space with a vertical half plane fault the fault contains a region where slip is calculated on a uniform grid of cells governed by a static kinetic friction law and regions where slip is prescribed so as to represent tectonic loading aseismic fault creep and adjacent great earthquakes the computational region models a 70 km long and 17 5 km deep section of the san andreas fault to the nw of the great 1857 rupture zone different distributions of stress drops on failing computational cells are used to model asperity parkfield asperity and nonasperity fault regions the model is inherently discrete and corresponds to a situation in which a characteristic size of geometric disorder within the fault i e cell size here a few hundreds of meters is much larger than the nucleation size of the order of tens of centimeters to tens of meters based on slip weakening or state evolution slip distances the computational grid is loaded by a constant plate motion imposed at the lower crust upper mantle and creeping fault regions and by a staircase slip history imposed at the 1857 and 1906 rupture zones stress transfer along and outside the fault due to the imposed loadings and failure episodes along the computational grid is calculated using 3 d elastic dislocation theory the resulting displacement field in the computational region is compatible with geodetic and seismological observations only when the asperity and nonasperity regions are characterized by significantly different average stress drops the frequency magnitude statistics of the simulated failure episodes are approximately self similar for small events with b 1 2 the b value of statistics based on rupture area ba is about 1 but are strongly enhanced with respect to self similarity for events larger than a critical size this is interpreted as a direct manifestation of our 3 d elastic stress transfer calculations beyond certain rupture area and potency seismic moment divided by rigidity release values the event is usually unstoppable and it continues to grow to a size limited by a characteristic model dimension this effect is not accounted for by cellular automata and block spring models in which the adopted simplified stress transfer laws fail to scale properly with increasing rupture size the simulations suggest that local maxima in observed frequency magnitude statistics correspond to dimensions of coherent brittle zones such as the width of the seismogenic layer or the length of a fault segment bounded by barriers the analysis indicates that a single cell size representing approximately a single scale of geometric disorder cannot induce self similarity in a 3 d elastic model over a broad range of magnitudes a representation of geometric disorder covering a range of scales may thus be required to generate a wide domain of self similar gutenberg richter statistics our simulations show a great diversity in the mode of failure of the parkfield asperity the earthquakes themselves define an irregular sequence of events the modeling like many other discrete fault models suggests that expectations for periodic parkfield earthquakes and or simple precursory patterns repeating from one event to the other are unrealistic

first tomographic image of ionospheric outflows 1 an image of the dayside low energy ion outflow event that occurred on 16 december 2003 was constructed with ground and space based gps global positioning system total electron content tec data and ion drift meter data from the dmsp defense meteorological satellite program a tomographic reconstruction technique has been applied to the gps tec data obtained from the gps receiver on the low earth orbit leo satellite fedsat the two dimensional tomographic image of the topside ionosphere and plasmasphere reveals a spectacular beam like dayside ion outflow emanating from the cusp region the transverse components of the magnetic field in fedsat s newmag data show the presence of field aligned current fac sheets indicating the existence of low energy electron precipitation in the cusp region the dmsp ion drift data show upward ion drift velocities and upward fluxes of low energy ions and electrons at the orbiting height of the dmsp spacecraft in the cusp region this study presents the first tomographic image of the flux tube structure of ionospheric ion outflows from 0 13 re up to 3 17 re altitude

metamorphism and uplift of alpine schist in the franz josef fox glacier area of the southern alps new zealand geothermometry and geobarometry of 10 garnet oligoclase zone schists in the franz josef fox glacier area southern alps new zealand give temperatures ranging from 415 to 625 c and pressures from 5 2 to 9 2 kbar indicating a t p array of about 50 c kbar and inferred peak temperature conditions over a c 15 km thick section at depths between c 20 and 34 km the present day distribution of the schist samples implies that only about one third of the original crustal section is now exposed the garnet oligoclase zone schists represent the deeper part of a metamorphosed and deformed accretionary complex that was associated with late palaeozoic early mesozoic subduction along the gondwana continental margin partial uplift c 0 2 m ma and erosion of the complex during jurassic cretaceous times rangitata uplift was synchronous with d2 deformation and recrystallization as recorded by the p t array cenozoic kaikoura uplift and exhumation of the schist since c 30 ma to form the southern alps was associated with oblique slip movement on the alpine fault the present day position and steep eastward dip of isograds and d2 structures suggest considerable clockwise rotation during uplift associated with ductile attenuation and tectonic thinning by over two thirds of the original schist sequence largely due to simple shear along schistosity planes as the schist generally shows only incipient greenschist facies retrograde recrystallization an apparently complete although contracted prograde mineral sequence has been preserved by rapid uplift 5 km ma of hot rock and the effects of limited shear heating near the alpine fault

the role of heterogeneities as a tuning parameter of earthquake dynamics we investigate the influence of spatial heterogeneities on various aspects of brittle failure and seismicity in a model of a large strike slip fault the model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of regions around the fault static kinetic friction laws creep with depth dependent coefficients and 3 d elastic stress transfer the dynamic rupture is approximated on a continuous time scale using a finite stress propagation velocity quasidynamic model the model produces a brittle ductile transition at a depth of about 12 5 km realistic hypocenter distributions and other features of seismicity compatible with observations previous work suggested that the range of size scales in the distribution of strength stress heterogeneities acts as a tuning parameter of the dynamics here we test this hypothesis by performing a systematic parameter space study with different forms of heterogeneities in particular we analyze spatial heterogeneities that can be tuned by a single parameter in two distributions 1 high stress drop barriers in near vertical directions and 2 spatial heterogeneities with fractal properties and variable fractal dimension the results indicate that the first form of heterogeneities provides an effective means of tuning the behavior while the second does not in relatively homogeneous cases the fault self organizes to large scale patches and big events are associated with inward failure of individual patches and sequential failures of different patches the frequency size event statistics in such cases are compatible with the characteristic earthquake distribution and large events are quasi periodic in time in strongly heterogeneous or near critical cases the rupture histories are highly discontinuous and consist of complex migration patterns of slip on the fault in such cases the frequency size and temporal statistics follow approximately power law relations

large earthquake hazard of the san jacinto fault zone ca from long record of simulated seismicity assimilating the available instrumental and paleoseismic data we investigate spatio temporal properties of earthquake patterns in the san jacinto fault zone sjfz california between cajon pass and the superstition hill fault using a long record of simulated seismicity constrained by available seismological and geological data the model provides an effective realization of a large segmented strike slip fault zone in a 3d elastic half space with heterogeneous distribution of static friction chosen to represent several clear step overs at the surface the simulated synthetic catalog reproduces well the basic statistical features of the instrumental seismicity recorded at the sjfz area since 1981 the model also produces events larger than those included in the short instrumental record consistent with paleo earthquakes documented at sites along the sjfz for the last 1 400 years the general agreement between the synthetic and observed data allows us to address with the long simulated seismicity questions related to large earthquakes and expected seismic hazard the interaction between m 7 events on different sections of the sjfz is found to be close to random the hazard associated with m 7 events on the sjfz increases significantly if the long record of simulated seismicity is taken into account the model simulations indicate that the recent increased number of observed intermediate sjfz earthquakes is a robust statistical feature heralding the occurrence of m 7 earthquakes the hypocenters of the m 5 events in the simulation results move progressively towards the hypocenter of the upcoming m 7 earthquake

high grade metamorphic rocks and peridotites along the leiza fault western pyrenees spain acid and basic granulites migmatites and lherzolites outcrop along the leiza fault navarra spain in the western extremity of the pyrenean belt the protoliths of the acid granulites have granodioritic composition textural and mineralogical data suggest that the acid granulites evolved from a first syn kinematic medium pressure granulite facies stage garnet biotite i kfsp to a post kinematic granulite facies stage of lower pressure and higher temperature garnet biotite ii cordierite kfsp spinel kinzigites basic granulites were formed from protoliths with composition of tholeiitic to alkaline basalts basic granulites exhibit millimeter size subidiomorphic garnets dispersed through the matrix and smaller coronitic garnets between opaques or orthopyroxenes and plagioclase thermo barometric estimates for the peak of the granulite facies metamorphism are c 800 c and 8 kbar the migmatites presumably represent a shallower level of metamorphism andalusite sillimanite kfsp scapolite in the basic granulites was formed during a post granulitic metamorphic episode the lherzolites have been intensely brecciated and serpentinized which makes difficult the comparison of their evolution with that observed in the other rocks associated with the leiza fault acid and basic granulites migmatites and lherzolites along the leiza fault may be correlated with similar rocks outcropping elsewhere in the north pyrenean zone and along the north pyrenean fault as tectonic slices and massifs by analogy with those rocks the granulitefacies metamorphism observed in the rocks studied must be hercynian in age the leiza fault constitutes therefore the western continuation of the north pyrenean fault and the rocks studied except perhaps the lherzolites may be considered as remnants of an hercynian metamorphic massif dismembered as a consequence of the activity of the fault at the end of the hercynian cycle and during the alpine tectonometamorphic events

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

earthquake rupture as a critical point consequences for telluric precursors abstract earthquakes are related to rupture phenomena in complex statistical systems of cracks we first review some available information suggesting that rupture in earthquakes is a critical point the consequences of this hypothesis on several phenomena are then discussed in particular we focus our attention on a simple theory of electroseismic activity based on mechano electrical transduction effects such as the piezoelectric or the pressure induced polarization effect the neighbourhood of the rupture threshold is characterized by a specific response which could correspond to telluric wave activity observed as precursors of earthquakes

exhumation and tilting of the western metamorphic belt of the coast orogen in southern southeastern alaska the uplift history of the western metamorphic belt in southern southeastern alaska can be traced using emplacement depths and cooling ages of mid cretaceous plutons which intruded the metamorphic belt during the period 101 ma to 89 ma during the period 101 ma to 94 ma the rocks of the metamorphic belt now at the surface were buried to a depth of approximately 30 km pressure data indicate that by 89 ma the western portion of the metamorphic belt was at a shallower crustal level 23 km within the study area while the eastern side remained at a depth of approximately 30 km cooling curves constructed from minerals in mid cretaceous plutonic rocks indicate that the western side of the metamorphic belt cooled earlier than the eastern side an observation consistent with the inferred uplift history southwestward transport of metamorphic belt rocks within the hanging walls of thrust and high angle faults may have provided one mechanism for uplift during mid to late cretaceous time the eastern portion of the western metamorphic belt cooled rapidly at 55 ma probably in response to a period of rapid uplift the coast shear zone an early tertiary high angle fault with west side up displacement bounds the east side of the metamorphic belt we suggest tertiary uplift occurred by tilting of the metamorphic belt due to movement along this fault

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

petrology and fluid inclusions in garnetiferous gneisses and charnockites from weddagala ratnapura district sri lanka fluid inclusions have been studied in garnetiferous gneisses and igneous charnockites from weddagala sri lanka fluid distribution brines in metasediments co 2 in charnockites compares well with other regions notably bamble southern norway for the brines it suggests an ultimate pre metamorphic origin and for co 2 initial entrapment during metamorphic crystallization the fluid density has been completely reset during post metamorphic evolution maximum co 2 densities indicate much lower pressure than those at peak metamorphic conditions recorded by the solid assemblages about 5 vs 8 kbars the evolution of co 2 densities with time suggests a post metamorphic trajectory concave toward the pressure axis adiabatic uplift and local redistribution and reequilibration of co 2 inclusions between 500 and 600 c fluid movements were mostly limited to grain scale millimeter order of magnitude and did not transgress the lithological boundaries

ultrahigh pressure metamorphism in the śnieznik mountains sudetes poland p t constraints and geological implications the petrology and p t conditions of eclogites and associated gneisses from the nieznik mountains sudetes sw poland were investigated to establish an exhumation path for these ultrahigh pressure rocks peak pressure conditions are represented by the assemblage garnet omphacite phengite kyanite coesite rutile post dating this assemblage but still in the eclogite facies garnet with lower grossular content and a first generation of amphibole are formed under lower pressure conditions giving rise to the assemblage garnet omphacite phengite kyanite quartz rutile calcic amphibole i continuing depressurization caused the successive destabilization of omphacite garnet kyanite and phengite in some places the primary eclogite assemblage was completely transformed into amphibolite facies mineral assemblages estimated peak pressures in the nieznik and miedzygorze units lie in the coesite stability field p 27 kbar at temperatures of about 700 800 c and are not significantly different to the zlote un

large earthquake cycles and intermittent criticality on heterogeneous faults due to evolving stress and seismicity 1 we analyze evolving stress and seismicity generated by three realizations of a discrete model of a strike slip fault in a three dimensional 3 d elastic half space using five functions of stress and five functions of seismicity the first model f has realistic dynamic weakening static minus dynamic frictions the second fc has zero critical dynamic weakening and the third sys is constrained to produce only system size events the results for model f show cyclical development saturation and destruction of fluctuations and long range correlations on the fault punctuated by the system size events the development stage involves evolution of stress and seismicity to distributions having broad ranges of scales evolution of response functions toward scale invariant behavior increasing seismicity rate and event sizes and increasing hypocenter diffusion most functions reach asymptotically stable values around 2 3 of the cycle and then fluctuate until one event cascades to become the next large earthquake in model fc the above evolution is replaced by scale invariant statistical fluctuations while in model sys the signals show simple cyclic behavior the results suggest that large earthquake cycles on heterogeneous faults with realistic positive dynamic weakening are associated with intermittent criticality produced by spontaneous evolution of stress heterogeneities toward a critical level of disorder having a broad range of scales the stress evolution and development of large earthquake cycles may be tracked with seismicity functions

nature and composition of the lower continental crust in central spain and the granulite granite linkage inferences from granulitic xenoliths xenolith bearing alkaline ultrabasic dykes were intruded into the of the hercynian basement of the spanish central system in early mesozoic times the suite of lower crustal xenoliths in the dykes divided into three groups felsic peraluminous granulites metapelitic granulites and charnockitic granulites the felsic granulites form 95 of the total volume of the xenoliths whereas the charnockitic and metapelitic granulites are much less abundant 0 01 5 respectively thermobarometric calculations based on mineral paragenesis indicate equilibration conditions around 850 950 c 7 11 kbar thus the xenoliths represent lower continental crustal material superimposed on this high t high p assemblage is a high t low p paragenesis represented mainly by kelyphitic coronas reflecting re equilibration during transport in the clearly restitic mineral assemblages with up to 50 garnet and 37 sillimanite major and trace element modelling supports the idea that the late hercynian peraluminous granites of central spain represent liquids in equilibrium with restitic material of similar composition to the studied lower crustal xenoliths 87sr 86sr and end of the felsic xenoliths calculated at an average hercynian age of 300 ma are in the range 0 706 0 712 and 1 4 to 8 2 respectively these values match the isotopic composition of the outcropping late hercynian granites the sr isotopic composition of the xenoliths is lower than that of the outcropping mid crustal lithologies orthogneisses pelites a major contribution from the lower crust to the source of hercynian granites greatly reduces the necessity of invoking a large mantle contribution in models of granite petrogenesis the felsic nature of the lower continental crust in central spain contrasts with the more mafic lower crustal composition estimated in other european hercynian areas suggesting a non underplated crust in this region of the hercynian orogenic belt