formulation of a fault governing law at high sliding speeds inferences from dynamic rupture models understanding the behavior of natural faults at cosesimic slip velocities v 1 10 m s or more has become a challenging achievement for experimentalists and modelers of earthquake instabilities the rate and state dependent friction laws originally obtained in slow slip rate conditions have been widely adopted in dynamic rupture models by assuming their validity well above the experimental range of observations in this paper we consider a modification at high speeds in which the steady state friction becomes independent of v above a transitional value vt our results show that this modification has dramatic effects on the dynamic propagation as long as vt decreases the breakdown stress drop decreases as well as the slip weakening distance and the fracture energy density moreover we found that the subshear regime is favored as vt decreases we found that for the strength parameter s greater than 1 482 the supershear rupture propagation is inhibited finally we demonstrate that the exponential weakening often observed in laboratory experiments can be theoretically explained in the framework of the rate and state laws

the critical slip distance for seismic faulting experimentally based friction laws1 2 have been found to predict virtually the entire range of observed behaviour of natural faults3 4 these laws contain a critical slip distance l which plays a key role in determining the degree of fault instability the size of the zone of earthquake nucleation the frictional breakdown width and the proportion of pre and post seismic slip to co seismic slip in laboratory measurements l is found to be about 10 5m but modelling results show that it must be about 10 2m if natural earthquake behaviour is to be simulated the discovery that fault surfaces are fractal over the scale range 10 5 105 refs 5 6 even for faults with large net slip has confused the problem of scaling this parameter from laboratory experiments to natural faults because fractal surfaces have no characteristic length here i show that geometrically unmated fractal surfaces when in contact under a normal load develop a characteristic length in their contact because long wavelength apertures close under load whereas short wavelength apertures may remain open this critical distance may be identified with l and calculations based on fault topography data show that at seismogenic depths it will be in the range anticipated from the earthquake modelling studies

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

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

influence of oxygen fugacity on mineral compositions in peralkaline melts the katzenbuckel volcano southwest germany the igneous rocks of the katzenbuckel southwest germany represent a unique and unusual alkaline to peralkaline association within the european volcanic province the magmatic activity can be subdivided into two main phases phase i comprises the main rock bodies of phonolite and nepheline syenite which were later intruded by different peralkaline dyke rocks tinguaites and alkali feldspar syenite dykes of phase ii the dyke assemblage was accompanied by magnetite and apatite veins and was followed by a late stage pneumatolytic activity causing autometasomatic alterations as is typical for alkaline to peralkaline igneous rocks early mafic minerals of phase i rocks comprise olivine augite and fe ti oxides which are substituted in the course of fractionation by na amphibole and na pyroxene for the early magmatic stage calculated temperatures range between 880 and 780 8c with low silica activities 0 4 to 0 6 but high relative oxygen fugacities between 0 5 and 1 9 log units above the fmq buffer even higher oxygen fugacities above the hm buffer are indicated for the autometasomatic alteration which occurred at temperatures between 585 and 780 8c and resulted in the formation of pseudobrookite and hematite the unusually high oxygen fugacities even during the early magmatic stage are recorded by the major element compositions of the mafic minerals forsterite content in olivine between 68 and 78 mol up to 6 2 wt zro2 and 8 5 wt tio2 in clinopyroxene the unusual mineral assemblages pseudobrookite freudenbergite and by the enrichment of fe 3 in the felsic

emerald deposits and occurrences a review abstract emerald the green gem variety of beryl is the third most valuable gemstone after diamond and ruby although it is difficult to obtain accurate statistics colombia supplies most an estimated 60 worth more than 500 000 000 per year of the world s emeralds however there is speculation that the emerald mines in colombia are becoming depleted brazil currently accounts for approximately 10 of world emerald production emeralds have also been mined in afghanistan australia austria bulgaria china india madagascar namibia nigeria pakistan south africa spain tanzania the united states and zimbabwe because it is difficult to obtain accurate analyses of beryllium most published analyses of beryl are renormalized on the basis of 18 oxygen and 3 be atoms per formula unit the color of emerald is due to trace amounts of chromium and or vanadium replacing aluminum at the y site in most cases the cr content is much greater than that of v to achieve charge balance the substitution of divalent cations at the y site is coupled with the substitution of a monovalent cation for a vacancy at a channel site beryl is relatively rare because there is very little be in the upper continental crust unusual geologic and geochemical conditions are required for be and cr and or v to meet in the classic model be bearing pegmatites interact with cr bearing ultrama c or ma c rocks however in the colombian deposits there is no evidence of magmatic activity and it has been demonstrated that circulation processes within the host black shales were sufficient to form emerald in addition researchers are recognizing that regional metamorphism and tectonometamorphic processes such as shear zone formation may play a signi cant role in certain emerald deposits a number of genetic classification schemes have been proposed for emerald deposits most are ambiguous when it comes to understanding the mechanisms and conditions that lead to the formation of an emerald deposit studies of individual emerald deposits show that in most cases a combination of mechanisms magmatic hydrothermal and metamorphic were needed to bring be into contact with the chromophores this suggests the need for a more flexible classification scheme based on mode of formation stable isotopes can be used to estimate the contribution of each mechanism in the formation of a particular deposit such estimates could perhaps be more precisely defined using trace element data which should reflect the mode of formation emerald may be identified in the field by color hardness and form it will tend to show up in stream sediment samples but because its specific gravity is relatively low it will not concentrate in the heavy mineral fraction in colombia structural geology the sodium content of stream sediment samples and the lithium sodium and lead contents of soil samples have all been used to find emerald occurrences exploration for gem beryl could result in the discovery of new occurrences of non gem beryl or other be minerals that could become new sources of be and be oxide future efforts should go towards creating a comprehensive data base of emerald compositions including trace elements determination of the role of metamorphism in the formation of some emerald deposits improved classification schemes and more effective exploration guidelines

sharpening the tomographic image of the subducting slab below sumatra the andaman islands and burma summary taking advantage of the increased ray coverage due to seismicity following the 2004 december and 2005 march great earthquakes an improved iterative regional global tomographic method was applied to the sumatra andaman and adjacent regions to better constrain the 3 d mantle velocity heterogeneity in the region velocity and hypocentral parameters were iteratively perturbed to sharpen the image of the subducted slab several iterations were performed and the effects of source mislocation were considered in the iterative process an issue usually neglected in global tomography we find that source relocation between iterations increases the amplitudes of slab anomalies and sharpens the definition of slab geometry beyond what can be achieved by a fixed source iterative inversion alone in addition extensive restoration tests of synthetic data were conducted that emphasize enhancements obtained by our iterative process these tests show significant increases in amplitude and decreased smearing of synthetic slab features thus when applied to the real data similar enhancements are inferred in the resulting model which better illustrates the complex slab geometry in the upper mantle and transition zone regions along the sumatra andaman and burma subduction zones

khmaralite a new beryllium bearing mineral related to sapphirine a superstructure resulting from partial ordering of be al and si on tetrahedral sites khmaralite ca sub 0 04 mg sub 5 46 fe super 3 sub 0 12 fe super 2 sub 1 87 al sub 14 26 be sub 1 43 b sub 0 02 si sub 4 80 o 40 is a new mineral closely related to sapphirine from khmara bay enderby land antarctica it occurs in a pegmatite metamorphosed at t or 820 degrees c p or 10 kbar the minerals surinamite musgravite and sillimanite associated with khmaralite at casey bay saturate it in beo and thus its beo content could be close to the maximum possible optically khmaralite is biaxial at lambda 589 nm alpha 1 725 2 beta 1 740 2 gamma 1 741 2 2v meas 34 4 1 8 degrees v r strong and beta

three dimensional p wave velocity structure beneath the indonesian region abstract we present the p wave seismic tomography image of the mantle to a depth of 1200 km beneath the indonesian region the artb inversion method is applied to a dataset of 118 203 p wave travel times of local and teleseismic events taken from isc bulletins although the resolution is sufficient for detailed discussion in only a limited part of the study region the results clarify the general tectonic framework in this region and indicate a possible remnant seismic slab in the lower mantle structures beneath the philippine islands and the molucca sea region are well resolved and high velocity zones corresponding to the slabs of the molucca sea and philippine sea plates are well delineated seismic zones beneath the manila negros and cotabato trenches are characterized by high velocity anomalies although shallow structures were not resolved the molucca sea collision zone and volcanic zones of the sangihe and philippine arcs are dominated by low velocity anomalies the philippine sea slab subducts beneath the philippine islands at least to a depth of 200 km and may reach depths of 450 km the southern end of the slab extends at least to about 6 n near southern mindanao in the south the two opposing subducting slabs of the molucca sea plate are clearly defined by the two opposing high velocity zones the eastward dipping slab can be traced about 400 km beneath the halmahera arc and may extend as far north as about 5 n unfortunately resolution is not sufficient to reveal detailed structures at the boundary region between the halmahera and philippine sea slabs the westward dipping slab may subduct to the lower mantle although its extent at depth is not well resolved this slab trends n s from about 10 n in the philippine islands to northern sulawesi a ne sw trending high velocity zone is found in the lower mantle beneath the molucca sea region this high velocity zone may represent a remnant of the former subduction zone which formed the sulawesi arc during the miocene the blocks along the sunda and banda arcs are less well resolved than those in the philippine islands and the molucca sea region nevertheless overall structures can be inferred the bowl shaped distribution of the seismicity of the banda arc is clearly defined by a horseshoe shaped high velocity zone the tomographic image shows that the indian oceanic slab subducts to a depth deeper than 300 km i e deeper than its seismicity beneath andaman islands and sumatra and may be discontinuous in northern sumatra along southern sumatra java and the islands to the east the slab appears to be continuous and can be traced down to at least a depth of the deepest seismicity where it appears to penetrate into the lower mantle

joint seismic tomography for bulk sound and shear wave speed in the earth s mantle high quality p and s travel times are now available from careful reprocessing of data reported to international agencies a restricted data set has been extracted for which comparable ray coverage is achieved for p and s and used for a joint inversion to produce a three dimensional model for shear and bulk sound velocities represented in terms of 2 2 cells and 18 layers in depth through the mantle about 106 times for each of p and s are combined to produce 312 549 summary rays for each wave type linearizing about the ak135 reference model 583 200 coupled tomographic equations are solved using an iterative partitioned scheme clear high resolution images are obtained for both bulk sound speed and shear wavespeed the bulk and shear moduli have differing sensitivity to temperature and mineral composition and so the images of the two velocity distributions help to constrain the nature of the processes which produce the variations different heterogeneity regimes can be recognised in the upper mantle the transition zone most of the lower mantle and the lowermost mantle in the upper mantle many features can be explained by thermal effects but in some orogenic zones e g western north america the opposite sense of the bulk sound and shear wave speed variation requires compositional effects or volatiles to outweigh any thermal effects in the lower mantle pronounced narrow structures which may represent remnant subduction are most marked in shear the level of large scale variations in bulk sound speed compared to shear diminishes with depth in the lower mantle reaching a minimum near 2000 km below this depth the variability of both wave speeds increases near the core mantle boundary the variations of the two wave speeds show little concordance suggesting the presence of widespread chemical heterogeneity

gahnite chrysoberyl and beryl co occurrence as accessory minerals in a highly evolved peraluminous pluton the belvis de monroy leucogranite caceres spain abstract gahnite znal 2 o 4 chrysoberyl beal 2 o 4 and beryl be 3 al 2 si 6 o 18 have been found as accessory minerals in the external highly fractionated leucogranitic unit within the hercynian reversely zoned belvis de monroy pluton westernmost part of the montes de toledo batholith caceres spain the highly felsic sio 2 72 wt and peraluminous acnk 1 2 character of this leucogranite together with the high content of some incompatible elements f li b and p seems to be a primary consequence of fractional crystallization in a magmatic closed system the high be contents and zn fe total ratio 0 01 are relevant factors which have favoured the precipitation of these minerals moreover the si al p b and f activities might be high favouring the magmatic crystallization of such exotic mineral phases together with be rich cordierite f rich micas sillimanite and al rich phosphates in fact the interplay between the silica and alumina activities likely controls the stabilization and the preferential crystallization of gahnite chrysoberyl or beryl chrysoberyl assemblages in mm sized microdomains the p t crystallization conditions are constrained by the muscovite and sillimanite stability fields and the minimum granite al 2 o 3 saturated solidus and have been estimated at temperatures between 670 and 700 c and pressures between 1 and 2 kbar

complexity of seismicity due to highly rate dependent friction we study a simple antiplane fault of finite length embedded in a homogeneous isotropic elastic solid in order to understand the origin of seismic source heterogeneity in the presence of nonlinear rate dependent friction all the mechanical properties of the medium and friction are assumed to be homogeneous starting from a heterogeneous initial stress distribution we apply a slowly increasing uniform stress load far from the fault and we simulate the seismicity for more than 20 000 events in some cases the style of seismicity produced by this model is determined by a control parameter which measures the degree of rate dependence of friction for classical friction models with rate independent friction no complexity appears and seismicity is perfectly periodic for weakly rate dependent friction seismicity becomes slightly nonperiodic but most events are still characteristic earthquakes when friction is highly rate dependent seismicity is completely irregular and ruptures of all sizes occur inside the fault highly rate dependent friction destabilizes the healing process producing premature healing of slip and partial stress drop premature healing causes rupture to take the form of narrow propagating slip episodes the so called heaton s 1990 pulses partial stress drop produces large variations in the state of stress which in turn produce earthquakes of different sizes we make the conjecture that all models in which static stress drop is only a fraction of the dynamic stress drop produce stress heterogeneity

the mechanics of lubricated faults insights from 3 d numerical models 1 the weakening mechanisms occurring during an earthquake failure are of prominent importance in determining the resulting energy release and the seismic waves excitation in this paper we consider the fully dynamic response of a seismogenic structure where lubrication processes take place in particular we numerically model the spontaneous propagation of a 3 d rupture in a fault zone where the frictional resistance is controlled by the properties of a low viscosity slurry formed by gouge particles and fluids this model allows for the description of the fault motion in the extreme case of vanishing effective normal stress by considering a viscous fault response and therefore without the need to invoke in the framework of coulomb friction the generation of the tensile mode of fracture we explore the effects of the parameters controlling the resulting governing law for such a lubricated fault the viscosity of the slurry the roughness of the fault surfaces and the thickness of the slurry film our results indicate that lubricated faults produce a nearly complete stress drop i e a very low residual friction coefficient 0 01 a high fracture energy density eg few 10s of mj m2 and significant slip velocities vpeak few 10s of m s the resulting values of the equivalent characteristic slip weakening distance d0eq 0 1 0 8 m depending on the adopted parameters are compatible with the seismological inferences moreover in the framework of our model we found that supershear ruptures are highly favored in the case of enlarging gap height we can have the healing of slip or even the inhibition of the rupture quantitative comparisons with different weakening mechanisms previously proposed in the literature such as the exponential weakening and the frictional melting are also discussed

solubility and stability of beryl in granitic melts beryllium contents of granitic melts at saturation in beryl or chrysoberyl phenakite or quartz have been determined by forward and reverse direction experiments at 650 850 degrees c and 200 mpa using natural beryl or the compositionally equivalent mixture of phenakite alumina quartz added to metaluminous haplogranite peraluminous haplogranite and macusanite a peraluminous li b f and p enriched rhyolite obsidian from macusani peru chrysoberyl coexists with beryl or quartz in moderately to strongly peraluminous systems asi approximately or 1 05 the assemblage phenakite beryl chrysoberyl is stable in silica undersaturated bulk composition the beo content of the melts which ranged between 0 03 0 40 wt varies principally with temperature the solubility of beryl falls with decreasing t and with the activity product of beryl alpha beo 3 alpha al2o3 alpha sio2 6 beryllia contents are lowest in strongly peraluminous and quartz saturated haplogranite melts however the highest beo content measured in glass products occurs for the strongly peraluminous macusanite at 850 degrees c 4016 ppm we infer that the greater solubility of beryl in macusanite melt results from melt speciation reactions involving li f b and p for all bulk compositions studied the beo content of melt projects to a narrow range of similar values at low t near the solidus of haplogranite thus metaluminous to peraluminous granitic magmas with and without common volatile and fluxing components will if cooled to subsolidus temperatures have similarly low beo requirements for beryl saturation the small beo content of melt near the solidus of haplogranite results in a minor 10 degrees c depression of the freezing point compared to be free haplogranite melt the mean melt composition at the beryl saturated granite minimum shifts slightly toward quartz beryl is common in peraluminous granitic rocks in part because lower beo contents are required to saturate these melts in beryl and possibly because these melts acquire higher beo contents by mica melting reactions at their sources beryl is also a common constituent of border facies assemblages in granitic pegmatite dikes regardless of their asi values this early crystallization of beryl results from the low beo content required to saturate any granitic melt in beryl at the low t environments in which pegmatite dikes solidify

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

slip dependent friction law and nucleation processes in earthquake rupture abstract matsu ura m kataoka h and shibazaki b 1992 slip dependent friction law and nucleation processes in earthquake rupture in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 135 148 we developed a physical model that interprets slip strengthening and slip weakening processes in brittle shear fracture by considering the microscopic interaction between statistically self similar fault surfaces our model successfully describes general features of the constitutive behaviour observed in laboratory experiments of stick slip with the progress of fault slip frictional stress first increases rapidly up to a peak value and then decreases gradually to a constant level the first slip strengthening process can be explained by the increase of frictional resistance in transition from the in phase contact to the random phase contact of fault surfaces the latter slip weakening process can be explained by the decrease of frictional resistance due to the abrasion of surface asperities the trade off between these two processes determines the peak stress and the critical displacement over which the slip weakening proceeds we examined the nucleation process proceeding in a seismogenic zone with the increase of external shear stress through numerical simulations in our model the seismogenic zone is represented by a broad weak zone with a locally strong part asperity on a fault plane the basic equations governing the nucleation process are the equation of equilibrium and the constitutive relation between frictional stress and fault slip we obtained the following results the nucleation process first proceeds quasi statically at the weak portions with the increase of external shear stress then if the constitutive relation at the asperity has a high and narrow peak of stress brittle dynamic rupture occurs in a limited area around the asperity when the constitutive relation has a low and broad peak the dynamic rupture of the asperity does not occur the process is completely aseismic when the peak of stress is high and broad the dynamic rupture of the asperity leads to the catastrophic rupture which extends over the whole region from these results it is concluded that diversity in the nucleation process can be ascribed to difference in the variation of constitutive behaviour along the fault

geochemical and petrogenetic features of mineralization in rare element granitic pegmatites in the light of current research abstract tremendous expansion of high technology applications of rare metals and specialty minerals requires periodic reassessment of their geological sources keeping in mind the long range technological potential of all hi tech materials available from a given type of deposit granitic pegmatites are a classic example of diversified sources li rb cs be ga sc y ree sn nb ta u th zr hf optical quartz and fluorite high purity feldpar petatite and refractory spodumene ceramic amblygonite e tc such rare element pegmatites can be subdivided into three principal families lct pegmatites with li rb cs be ga sn ta nb b p f nyf pegmatites with nb ta ti y ree zr th and u f pegmatites with a mixed geochemical signature the less evolved members of the lct family produce mainly only be nb ta and sn but exotic types with be ta nb f b p with li rb and cs and are also known so far no differences ini mineralization styles have been observed between the spodumene petalite and amblygonite subtypes of the complex type except the mineralogy of their substantial li contents however extensive divergence in k rb cs fractionation is observed violating the classic criteria for for example pollucite potential and economic ga concentration is recognized the lepidolite subtype is commonly enriched in y and h ree albitespodumene pegmatites have largely simple li sn nb ta be mineralization but a suprisingly broad range of alkali fractionation levels the not so common albite type seems to be typically enriched in sn nb ta ti the nyf family is much less abundant a general subdivision of these pegmatites is not yet available except for the recognition of sporadic lree enriched and much more widespread y hree enriched subtypes scandium is an element recognized recently as much more abundant than previously thought internal evolution of individual pegmatites is better understood today in terms of london s model of crystallization from highly hydrous but homogeneous melts experimental evidence does not support the jahns and burnham proposal of early separation of a fluid phase peraluminous fertile s granites generating lct pegmatites are derived by partial melting of upper middle crustal rocks undergoing their first anatexis and the pegmatites commonly show regional zoning metaluminous granites yeilding poorly zoned groups of nyf pegmatites are largely of the a type generated by second melting of short lived depleted lower crustal protoliths however a juvenile igneous or fluid component may be involved mixed nyf lct granite pegmatite suites may originate in several ways peraluminous lct sequences were traditionally regarded as orogenic in contrast to anorogenic nyf systems tectonic correlation with geochemistry is now considered secondary to the control by source lithologies it is the understanding of the association of pegmatite types with their geological setting and petrogenetic affiliation which assists in the search for selected hi tech materials

coherence of mach fronts during heterogeneous supershear earthquake rupture propagation simulations and comparison with observations 1 we study how heterogeneous rupture propagation affects the coherence of shear and rayleigh mach wavefronts radiated by supershear earthquakes we address this question using numerical simulations of ruptures on a planar vertical strike slip fault embedded in a three dimensional homogeneous linear elastic half space ruptures propagate spontaneously in accordance with a linear slip weakening friction law through both homogeneous and heterogeneous initial shear stress fields in the 3 d homogeneous case rupture fronts are curved owing to interactions with the free surface and the finite fault width however this curvature does not greatly diminish the coherence of mach fronts relative to cases in which the rupture front is constrained to be straight as studied by dunham and bhat 2008a introducing heterogeneity in the initial shear stress distribution causes ruptures to propagate at speeds that locally fluctuate above and below the shear wave speed calculations of the fourier amplitude spectra fas of ground velocity time histories corroborate the kinematic results of bizzarri and spudich 2008a 1 the ground motion of a supershear rupture is richer in high frequency with respect to a subshear one 2 when a mach pulse is present its high frequency content overwhelms that arising from stress heterogeneity present numerical experiments indicate that a mach pulse causes approximately an 1 7 high frequency falloff in the fas of ground displacement moreover within the context of the employed representation of heterogeneities and over the range of parameter space that is accessible with current computational resources our simulations suggest that while heterogeneities reduce peak ground velocity and diminish the coherence of the mach fronts ground motion at stations experiencing mach pulses should be richer in high frequencies compared to stations without mach pulses in contrast to the foregoing theoretical results we find no average elevation of 5 damped absolute response spectral accelerations sa in the period band 0 05 0 4 s observed at stations that presumably experienced mach pulses during the 1979 imperial valley 1999 kocaeli and 2002 denali fault earthquakes compared to sa observed at non mach pulse stations in the same earthquakes a 20 amplification of short period sa is seen only at a few of the imperial valley stations closest to the fault this lack of elevated sa suggests that either mach pulses in real earthquakes are even more incoherent that in our simulations or that mach pulses are vulnerable to attenuation through nonlinear soil response in any case this result might imply that current engineering models of high frequency earthquake ground motions do not need to be modified by more than 20 close to the fault to account for mach pulses provided that the existing data are adequately representative of ground motions from supershear earthquakes

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

on the deterministic description of earthquakes 1 the quantitative estimate of earthquake damage due to ground shaking is of pivotal importance in geosciences and its knowledge should hopefully lead to the formulation of improved strategies for seismic hazard assessment numerical models of the processes occurring during seismogenic faulting represent a powerful tool to explore realistic scenarios that are often far from being fully reproduced in laboratory experiments because of intrinsic technical limitations in this paper we discuss the prominent role of the fault governing model which describes the behavior of the fault traction during a dynamic slip failure and accounts for the different and potentially competing chemical and physical dissipative mechanisms we show in a comprehensive sketch the large number of constitutive models adopted in dynamic modeling of seismic events and we emphasize their prominent features limitations and specific advantages in a quantitative comparison we show through numerical simulations that spontaneous dynamic ruptures obeying the idealized linear slip weakening sw equation and a more elaborated rate and state dependent friction law produce very similar results in terms of rupture times peaks slip velocity developed slip and stress drops provided that the frictional parameters are adequately comparable and more importantly that the fracture energy density is the same our numerical experiments also illustrate that the different models predict fault slip velocity time histories characterized by a similar frequency content a feeble predominance of high frequencies in the sw case emerges in the frequency ranges 0 3 1 and 11 50 hz these simulations clearly indicate that even forgiving the frequency band limitation it would be very difficult virtually impossible to discriminate between two different but energetically identical constitutive models on the basis of the seismograms recorded after a natural earthquake

imaging changes in morphology geometry and physical properties of the subducting pacific plate along the izu bonin mariana arc abstract recent studies on slab structure in the northwest pacific have imaged variable geometries of the subducted oceanic lithosphere along the plate margin tomographic images show portions of the subducted pacific plate penetrate vertically into the lower mantle below the mariana arc whereas below the izu bonin arc the slab appears to be lain down horizontally on top of the 670 km discontinuity using new technology to grid and visualize regional seismic tomography data even more detail about the structure of the subducting plates can be extracted from the three dimensional images we investigate the morphology and geometry of the subducting pacific plate as it changes between horizontal to nearly vertical using p wave tomographic images the most profound result from these new models is the presence of a distinct change of seismic property in the downgoing pacific slab beneath the izu bonin arc at a depth of 350 400 km the position of this anomaly corresponds to a region north and west of the ogasawara plateau we propose the change in morphology and physical property of the slab is related to the distortion of the pacific plate geometry as its shape converts from near horizontal to vertical together with the subduction of the ogasawara plateau

mineralogical constraints on the magmatic hydrothermal evolution of rare elements deposits in the bailongshan granitic pegmatites xinjiang nw china abstract the bailongshan pegmatite district in south xinjiang province nw china is a newly discovered area of rare element pegmatites it is a superlarge li rb reserve that includes an estimated 3 45 million tons of li2o and 176 000 tons of rb2o on the basis of a detailed characterization of textures and minerals in the bailongshan 2 and 5 pegmatites six zones are identified a saccharoidal albite zone zone i a graphic pegmatite zone zone ii a blocky microcline zone zone iii a muscovite quartz zone zone iv a cleavelandite spodumene zone zone v and a quartz spodumene zone zone vi the detailed mineralogical characteristic is performed by epma for illustrating both the existent state of rare elements and the magmatic hydrothermal evolution of the bailongshan pegmatite lithium be rb nb ta and sn are major economic rare elements which are concentrated in zones v and vi the rare elements are hosted by minerals including spodumene montebrasite eucryptite lepidolite beryl rb enriched k feldspar columbite group minerals cassiterite and tourmaline which formed from the fractional crystallization of pegmatitic magma the bailongshan pegmatites show lower degrees of fractional crystallization than many other li cs ta lct family pegmatites worldwide as evidenced by the relatively low nb ta zr hf and k rb fractional degree in the carrier minerals in zones v and vi the primary minerals record intense interaction with hydrothermal fluids which caused the alteration of spodumene and mica the development of cs or na enriched veinlets in beryl and the formation of mn and ta enriched veinlets coupled with micropores within columbite group minerals the hydrothermal fluids were composed predominantly of li f cs and ta which conformed to the evolved trend of pegmatitic melt these late hydrothermal fluids exsolved from the magma as it differentiated and may have the benefit with rare elements metallogeny

earthquake triggering by static and dynamic stress changes 1 in this study we aim to understand the effect of static and dynamic stress changes in promoting earthquake failures on secondary faults toward this goal we solve the equation of motion of a spring slider dynamic system including inertia and using rate and state dependent constitutive laws we separately investigate the dynamic response of this fault analog system to a sudden stress change represented either as a stress step or as a stress pulse which are used to model permanent static and transient dynamic stress perturbations the induced earthquake failure does not occur immediately at the application of the coseismic stress change but it is delayed in time we define this time interval as the triggering delay for a given stress perturbation we analyze the dependence of triggering delays on different system conditions and constitutive parameters our results clearly show that the effects of static and dynamic stress changes are quite different while a static stress change is able to advance as well as to delay an induced instability depending on its sign a dynamic stress pulse is only able to promote a nearly instantaneous failure provided its amplitude is positive and large enough with respect to the direct effect of friction in other words dynamic stress changes can only cause nearly instantaneous failures without any relevant triggering delay these results should be considered in interpreting the seismicity rate changes caused by large earthquakes at least as long as seismic events are interpreted as sliding instabilities obeying rate and state dependent friction laws

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

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

what can physical source models tell us about the recurrence time of earthquakes abstract earthquake prediction no matter what the timescale has been and continues to be a contentious subject and it is indubitably a prominent challenge for modern seismology and earthquake physics indeed few natural events can have the catastrophic consequences of earthquakes earthquakes today account for about 60 of natural fatalities a physical description of an earthquake represents an amenable approach to the prediction but it suffers of some limitations basically due to the notorious ignorance about the initial state of a given fault and about the physical law controlling its traction evolution independent on those intrinsic epistemic limitations the concept of the earthquake recurrence based upon the idea of the cyclic or characteristic earthquake has been often invoked to describe and thus to predict subsequent instability events on a seismogenic structure in this paper by using the simplest analog fault model the one degree of freedom mass spring system we quantitatively show that the concepts of the recurrence time and the earthquake cycle have limitations even making them meaningless we will discuss in a compendious synopsis all the possible physical mechanisms which can dramatically affect the recurrence time our conclusions emphasize again that the competing mechanisms potentially occurring during faulting even in the simplest and idealized condition of an isolated fault can significantly complicate the regular cyclicity of earthquakes predicted by the analog fault system these conclusions can contribute to the debate about the role of the physical modeling of earthquakes in the contest of seismic hazard assessment

stress in the indo australian plate cloetingh s and wortel r 1986 stress in the ind austr ian plate in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 49 67 we modelled the state of stress in the indo australian plate in order to investigate quantitatively variations observed in tectonic style the numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere estimates are presented for the average net resistive forces at the himalayan collision zone the suction force acting on the overriding indo australian plate segment at the tonga kermadec trench and the drag at the base of the lithosphere our modelhng shows a concen ation of compressive stresses of the order of 3 5 lcbar in the ninetyeast ridge area the effects of the compressive resistance associated with himalayan collision and subduction of young lithosphere off the northern part of the sunda arc are focused in this region the stress field as calculated gives a consistent explanation for the observed concentration of seismic activity stein and okal 1978 and significant deformation in the oceanic crust weissel et al 1980 mcadoo and sandwell 1985 in the area the calculated stress field in the area adjacent to the southeast and central india ridges is characterized by tension parallel to the spreading axis this explains the concentration of near ridge normal faulting seismicity with t axes subparaile1 to the spreading ridge in the indian ocean as recently observed by bergman et al 1984 and wiens and stein 1984 the regional stress field along the strike of the sunda arc varies from compression seaward of and parallel to the sumatra trench segment to tension perpendicular to the java flores segment this explains the selective occurrence of well developed grabens seaward off the java flores segment of the trench observed by hilde 1983 our modelling shows that the observed rotation of the stress field denham et al 1979 in the australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down going slab in each of these the state of compression in west and central australia is induced by the action of resistive forces at the himalayan and banda arc collision zones the joint occurrence of high levels of compression in the plate s interior and normal faulting seismicity in the near ridge areas is a transient feature unique to the present dynamic situation of the indo australian plate

source parameters of small earthquakes recorded at 2 5 km depth cajon pass southern california implications for earthquake scaling a 2 5 km deep triaxial seismometer at cajon pass in southern california has recorded several hundred earthquakes ml4 0 occurring within the san andreas fault system at 2 5 km seismic background noise is below amplifier sensitivity and the 2 250 hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs compared with downhole recorded motion seismic amplitudes at the surface are amplified below 10 hz and severely attenuated above 30 hz we estimate that qs is at least 1000 for wave motion at 2 5 km and below and qp is over 2000 the range of source dimensions in the downhole recorded catalog is 10 m to 70 m ml 2 0 mo 108 nm to ml 2 7 mo 1013 nm the plot of log source radius vs log moment has a straight line trend compatible with earthquake scaling at constant stress drop inferred stress drops are scattered between 1 and 500 bars there is no evidence in the catalog for the proposed minimum source dimension at 100 m when the cajon pass borehole catalog containing some of the smallest recorded natural earthquakes is combined with 800 larger events from previous studies the moment radius trend suggests that natural earthquakes are self similar over a magnitude range m 2 to 8 we suggest that inferences of minimum source dimension are more likely due to bias in bandlimited individual catalogs than to properties of the seismic crust

structure and evolution of lithospheric slab beneath the sunda arc indonesia tomographic imaging reveals seismic anomalies beneath the sunda island arc indonesia that suggest that the lithospheric slab penetrates to a depth of at least 1500 kilometers the sunda slab forms the eastern end of a deep anomaly associated with the past subduction of the plate underlying the mesozoic tethys ocean in accord with previous studies the lithospheric slab was imaged as a continuous feature from the surface to the lower mantle below java with a local deflection where the slab continues into the lower mantle the deep slab seems to be detached from the upper mantle slab beneath sumatra this complex slab structure is related to the tertiary evolution of southeastern asia and the indian ocean region

chemical and paragenetic data on gadolinite group minerals from baveno and cuasso al monte southern alps italy a chemical and paragenetic study was performed on gadolinite group minerals occurring in miarolitic pink granite and granophyric leucogranite of the subvolcanic hercynian plutons at baveno and cuasso al monte southern alps italy in the localities investigated gadolinite group minerals are hosted in massive pegmatite in aplite and in miarolitic cavities having different degrees of evolution the petrological relations indicate that progressive crystallization has occurred from magmatic through to hydrothermal conditions at baveno ce rich gadolinite y with ree y formed during the primitive stages of pegmatite crystallization gadolinite y with ree y gadolinite y with ree y formed during intermediate stages of evolution and hingganite y is dominant in highly evolved miarolitic cavities together with several rare element phases the chemical differences observed in the gadolinites from the two localities may indicate a different parental magma composition and reflect a difference in the crystallization processes in contrast to baveno the crystallization at cuasso al monte occurred under open system conditions which prevented the formation of a zeolite datolite bearing stage and generated a typical medium to low temperature hydrothermal mineral assemblage consisting of quartz fluorite barite sulfides and carbonates the large variations in the y dy ratio observed in the studied samples may be due to a change in the fluorine abundance in hydrothermal fluids related to paragenetic effects and mixing processes this work reports paragenetic and chemical data obtained on gadolinite group minerals found in the miarolitic nyfpegmatites the granite and the granophyre of both the baveno and cuasso al monte localities these minerals are recognized in pegmatitic systems as crystallizing from primitive magmatic conditions through to highly evolved hydrothermal conditions which show extensive changes in their compositions particularly during the latest stages of evolution of the miarolitic cavities our results show that the gadolinite group minerals may be of petrological interest in the characterization of the pegmatitic pneumatolitic and hydrothermal stages of granite plutons geologic setting

a constitutive scaling law and a unified comprehension for frictional slip failure shear fracture of intact rock and earthquake rupture 1 it is widely recognized that some of the physical quantities inherent in a rupture are scale dependent and the scale dependence is one of the most no facts and features of rupture phenomena the paper addresses how such scale dependent shear rupture of a broad range from laboratory scale frictional slip failure and shear fracture of intact rock to field scale rupture as an earthquake source can be unified by a single constitutive law noting that the earthquake rupture is a mixed process between frictional slip failure and the shear fracture of intact rock it is concluded that the constitutive law for the earthquake rupture be formulated as a unifying law that governs both frictional slip failure and shear fracture of intact rock it is demonstrated that the slip dependent constitutive law is such a unifying law and a constitutive scaling law is derived from laboratory data on both frictional slip failure and shear fracture of intact rock this constitutive scaling law enables one to provide a consistent and unified comprehension for scale dependent physical quantities inherent in the rupture over a broad range from small scale frictional slip failure and shear fracture in the laboratory to large scale earthquake rupture in the field

formation and evolution of the hogtuva beryllium deposit norway metagranite in the hogtuva tectonic window nordland norway hosts several spatially restricted be mineralisations with phenakite as the main ore mineral geochronology of magmatic zircon zircon i indicates crystallisation of phenakite bearing and beryl free metaluminous granite at 1787 57 ma and of phenakite and beryl beryl i bearing peraluminous aplites and pegmatites at 1710 59 ma crystallisation of texturally distinct zircon zircon ii cogenetic with fluorite in peraluminous aplites and pegmatites occurred at 434 14 ma during caledonian metamorphism in be mineralised and barren metagranite breakdown of phenakite post dates growth of zircon ii and resulted in the crystallisation of metamorphic hogtuvaite ca2 text fe 3 2 text fe 3 3 si4bealo20 in metaluminous metagranite and metamorphic beryl beryl ii in peraluminous metamorphosed aplites and pegmatites qualitative and quantitative assessment of mineral reactions implies that be has not been mobilised to significant degrees during metamorphism in spite of the presence of a fluorine rich fluid and that phenakite underwent in situ metamorphic reactions hogtuvaite crystallised as a metamorphic phase at the expense of phenakite the anorthite component in albitic plagioclase magnetite and possibly clinopyroxene in peraluminous environments the breakdown of phenakite to metamorphic beryl ii is accompanied by the formation of albite a decreasing activity ratio of a k h in the metamorphic fluid results in the reaction of k feldspar and phenakite to beryl ii further decrease in a k h finally results in complete transformation of the remaining k feldspar into albite the metamorphic breakdown of phenakite in the distinct be mineralisation types at hogtuva is probably controlled by changes in the activities of na k and h in the coexisting metamorphic fluid

stress breakdown time and slip weakening distance inferred from slip velocity functions on earthquake faults we estimate the critical slip weakening distance on earthquake faults by using a new approach which is independent of the estimate of fracture energy or radiated seismic energy the approach is to find a physically based relation between the breakdown time of shear stress tb the time of peak slip velocity tpv and the slip weakening distance dc from the time histories of shear stress slip and slip velocity at each point on the fault which can be obtained from dynamic rupture calculations using a simple slip weakening friction law numerical calculations are carried out for a dynamic shear crack propagating either spontaneously or at a fixed rupture velocity on a vertical fault located in a 3d half space and a more realistic horizontally layered structure with finite difference schemes the results show that tpv is well correlated with tb for faults even with a heterogeneous stress drop dis tribution except at locations near strong barriers and the fault edges we also inves tigate this relation for different types of slip weakening behavior we have applied the method to two recent strike slip earthquakes in western japan the 2000 tottori and the 1995 kobe events we integrated the slip velocity functions on the vertical fault obtained from kinematic waveform inversion of strong motion and teleseismic records from the arrival time of rupture tr to the time of the peak slip velocity tpv and we then corrected the slip obtained at tpv for the errors expected from the dynamic calculations it was found that the slip weakening dis tance d c estimated in the frequency window between 0 05 and 0 5 hz ranges between 40 and 90 cm on the two earthquake faults however if we consider the limited frequency resolution of the observed waveforms probable time errors in the slip velocity functions obtained from kinematic inversion and the uncertainty of the slip weakening behavior the above estimates may be those located between the minimum resolvable limit and the upper bound of their real values the estimated dc values do not necessarily seem to indicate larger values in the shallower part and smaller values in the deeper part of the fault but rather a spatially heterogeneous distribution that appears to be dependent on the local maximum slip this possible dependence might be interpreted by the frictional properties of the fault such as the degree of roughness or the thickness of gouge layers in addition to stress heterogeneities

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

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

non pegmatitic deposits of beryllium mineralogy geology phase equilibria and origin non pegmatitic occurrences of be minerals constitute a diverse set of geologic environments of considerable mineralogical and petrological interest they currently provide the majority of the world s be ore and emeralds and they contain the greatest resource of these commodities of the approximately 100 be minerals known see chapter 1 by grew appendix a most occur in hydrothermal deposits or non pegmatitic igneous rocks where their distribution varies systematically with the setting and origin table 1 fig 1 view this table table 1 beryllium minerals in non pegmatitic deposits formulas use and occurrence 1 figure 1 chemography of the principal solid phases in the beo al2o3 sio2 h2o f2o 1 bash system with the projected positions of helvite group and alkali be silicates also shown are generalized fields for some of the major types natural of occurrences cf table 1 fig 4 see text for discussion beryllium minerals are best known from geologic systems associated with felsic magmatism they also occur in a variety of settings that lack evident igneous associations environments range from the surface to the deep crust and host rocks range from feldspathic to carbonate to ultramafic in composition genetically related igneous rocks are felsic and share low calcium and high f contents but are diverse in composition setting and origin compositions range from strongly peraluminous to peralkaline and can be silica undersaturated beryllium minerals also occur in metamorphic and basinal environments and are redistributed by surface processes table 2 summarizes the types and significance of major groups of occurrences by their lithologic associations figure 2 shows the global distribution of some important examples and regional belts for most types at least one example has been described in some detail and can be used to help evaluate general patterns however

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

seismic tomography with p and s data reveals lateral variations in the rigidity of deep slabs abstract regional seismic tomography of the northwest pacific island arcs using p and s wave arrival time data with similar path coverage reveals an oceanic lithospheric slab deflected in the mantle transition zone beneath the izu bonin region in good agreement with the results of earlier tomographic and other seismic studies in the region the s wave images however do not show clearly the deflection of the slab this implies that the stagnant lithospheric slab in the transition zone is more likely a bulk sound structure which is strongly supported by our results from joint inversions for bulk sound and shear wavespeeds for the izu bonin region where trench migration has been reported the properties of the deflected slab lying on top of the 660 km discontinuity show strong bulk sound and weak shear signatures in contrast to the descending slab itself there is an indication in the shear images that a component of the former oceanic lithosphere is penetrating into the top of the lower mantle suggesting that a slab split has occurred

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

be minerals synthesis stability and occurrence in metamorphic rocks a major interest in beryllium minerals which are rock forming constituents in certain metamorphic hydrothermal and igneous environments comes from their use as ore materials for be as single crystal material for special optical purposes and as gemstones beryl ideally al2be3si6o18 bertrandite be4si2o7 oh 2 and phenakite be2sio4 are mined and processed as ores of be beryl and chrysoberyl are used as maser and laser crystals and bromellite beo has outstanding properties such as exceptionally high electrical conductivity and speed of sound propagation in combination with great strength and chemical resistance be minerals find wide use as gemstones emerald and alexandrite are among the most highly prized for all these reasons a large amount of experimental work has been reported on the synthesis of these minerals the interest in be minerals for petrology comes from the fact that be can be a minor component in several rock forming silicates such as sapphirine margarite and cordierite and can have an important influence on the phase relations of these minerals the study of the behavior of be and be minerals may give an important insight in the history of magmatic and metamorphic rocks one of the key questions for the natural occurrences is the problem of enrichment of be so that either be minerals can be formed or that common rock forming minerals such as cordierite contain an appreciable amount of be we start with a review of experimental work about synthesis of be minerals in various simplified systems their phase equilibria and their compositional variation thermodynamic data and calorimetric work are reviewed by barton and young this volume in the second part we review the geological setting and mineralogical characteristics of be mineralizations in regional metamorphic terrains and on hydrothermal be occurrences metamorphosed be rich pegmatites leucogranites and

emerald mineralisation in colombia fluid chemistry and the role of brine mixing emerald mineralisation in colombia is located in two distinct zones along the borders of the eastern cordillera some 80 km apart mineralisation in the western zone has been dated at ca 35 ma whereas in the eastern zone it is 30 ma older crush leach analysis of the electrolyte chemistry of fluid inclusions contained in emerald quartz calcite dolomite and fluorite from both zones demonstrates that in each region brines associated with emerald mineralisation range between two extremes with many samples yielding intermediate compositions fluid 1 found mainly in emerald hosted fluid inclusions is dominated by nacl with high cl br ratios indicating that the salinity was derived by dissolution of halite most probably from the local salt beds fluid 2 found notably in quartz hosted fluid inclusions is of similar salinity but contains less na and significant concentrations of ca k fe cl and other cations it has lower cl br ratios more comparable with formation waters but is inferred to have obtained part of its salinity by halite dissolution bivariate plots of almost all cations have linear or sublinear trends regardless of the mineral hosting the inclusions or the locality from which the samples originated demonstrating that mixing of the two saline fluids has occurred because the same two fluids occur in both eastern and western zones despite the difference in space and time it is inferred that fluid compositions were rock controlled by similar interactions with evaporites and black shales in both instances it is proposed that beryllium was transported as be f complexes in the nacl fluid and was precipitated as emerald after mixing with the calcic brine caused precipitation of fluorite and parisite

spatial and temporal evolution of the subducting pacific plate structure along the western pacific margin 1 tomographic images of the subducting pacific plate beneath the izu bonin mariana arc illustrate a progression of geometries from shallow dipping to vertical from north to south along the arc recent advances in technology and inversion techniques have improved resolution of slab structure beneath the western pacific island arcs but reasons for the variation in geometry and morphology are still poorly understood by comparing high resolution tomographic images of the western pacific and updated paleogeographic reconstructions we are able to link the spatiotemporal evolution of the subducting pacific plate back to the mid miocene we have reconstructed tectonic motions along the kurile japan izu bonin mariana arc system and the ryukyu arc to provide an independent additional interpretation of the subducting pacific plate using the most current plate motion data we then investigate the plausibility of our model and three other proposed models based on the interpreted slab structure from tomographic images the new reconstruction agrees with the basic characteristics of former trench retreat models but illustrates the importance of the collision of the ogasawara plateau with the trench in the mid miocene and its subsequent effect on the slab structure at depth and the impact of other aseismic ridge collisions along the plate boundary the combination of evidence in changed physical properties imaged with tomography and the current interpreted slab morphology can be analyzed with the past plate motions to understand subduction zone processes

rupture speed and slip velocity what can we learn from simulated earthquakes abstract in this paper we consider a wide catalog of synthetic earthquakes numerically modeled as spontaneous fully dynamic 3 d ruptures on extended faults governed by different friction laws including slip dependent and rate and state dependent equations we analyze the spatial correlations between the peak of fault slip velocity vpeak and the rupture speed vr at which the earthquake spreads over the fault we found that vpeak positively correlates with vr and that the increase of vpeak is roughly quadratic we found that near the transition between sub and supershear regimes vpeak significantly diminishes and then starts to increase again with the square of vr this holds for all the governing models we consider and for both homogeneous and heterogeneous configurations moreover we found that on average vpeak increases with the magnitude of the event vpeak m00 18 our results can be incorporated as constraints in the inverse modeling of faults

an efficient mechanism to avert frictional melts during seismic ruptures abstract we consider the spatio temporal evolution of temperature due to frictional heating caused by the spontaneous propagation of 3 d dynamic seismic ruptures on planar faults in our numerical experiments which characterize typical crustal earthquakes we assume that fault friction is controlled by different linear and nonlinear slip dependent friction laws in this paper we confirm that a necessary condition to prevent melting is to have a nearly complete breakdown stress drop our simulations which employ a nonlinear slip dependent governing equation recently inferred from laboratory experiments by sone and shimamoto 2009 reproduce such a dramatic fault weakening and represent a plausible explanation for the prevention of melting during earthquake ruptures we also demonstrate that low friction alone although necessary is not a sufficient condition to avert melts the linear or classical slip weakening sw law would produce melting even assuming the same lengthscales and frictional levels to avoid melting with linear sw law we have to impose a specific value of the sw distance this reveals the prominent role of the time evolution of traction within the cohesive zone where the stress release is realized and of the value of the fracture energy density

surinamite a high temperature metamorphic beryllosilicate from lewisian sapphirine bearing kyanite orthopyroxene quartz potassium feldspar gneiss at south harris n w scotland the sapphirine like mineral surinamite mg fe 2 3 al fe 3 3 o albesi 3 o 15 occurs at south harris as tiny grains enclosed in kyanite or as tabular grains up to 1 mm long mostly surrounded by si rich cordierite a few surinamite grains enclose orthopyroxene sillimanite and si rich sapphirine ion microprobe analyses gave 3 52 to 3 81 wt beo 0 766 to 0 824 be atoms per formula unit and 2 to 13 ppm b in surinamite excess si suggests the presence of significant beo in cordierite and sapphirine given the anti clockwise p t time path inferred for the south harris rock we suggest that surinamite formed at first by the continuous reaction besial 2 in sapphirine sillimanite orthopyroxene surinamite quartz and subsequently by the discontinuous reaction be depleted sapphirine quartz surinamite orthopyroxene kyanite with increase of p to 12 kbar at 850 900 c surinamite reacted with orthopyroxene kyanite and quartz to form beryllian cordierite during subsequent decrease in p and t the high silica content and peraluminous composition of the surinamite bearing gneiss are consistent with a metasedimentary origin this rock is markedly depleted in th 0 13 ppm u 0 11 ppm y 0 94 ppm and rare earth elements e g ce 7 7 ppm its bulk be content 9 ppm is not excessive the appearance of a discrete be phase in be poor rocks could be due to the absence of potential carriers of be namely muscovite and primary cordierite at high t and low water activity moreover surinamite is indicative of a distinctive metamorphic history in which high temperature rocks recrystallized at higher pressures or are isobarically cooled and consequently scarcity of be in metamorphic systems is not the only factor controlling surinamite formation

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

complex slab subduction beneath northern sumatra 1 new data provided by the 2004 2005 sumatra andaman great earthquake sequences allow us to image with improved detail the p wave velocity structure beneath sumatra and adjacent regions below northern sumatra we find that the slab is folded at depth exhibiting geometry similar to that of the volcanic arc and the trench at the surface we speculate that this fold plays a major role in the segmentation of the sumatra megathrust and may impede rupture propagation in the region north of sumatra significant slab material in the mantle transition zone is imaged for the first time and we infer the presence of a major tear between the upper mantle and transition zone there

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

determination of beryllium and its distribution in rocks of the snw granite of regoufe northern portugal abstract the determination of be by electrothermal atomic absorption spectrometry with zeeman background correction zetaas is compared with the determination by inductively coupled plasma emission spectrometry icpes the samples are decomposed with a hf hcio 4 hno 3 method both methods compare well though the results by zetaas are generally 2 ppm higher than the icpes values especially icpes results are in good agreement with the accepted values for international reference samples zetaas has a lower detection limit than icpes the methods were tested on 55 samples of the regoufe granite northern portugal the average for the regoufe granite is 17 ppm be and the values range from 4 to 57 ppm be the granite may be regarded as be specialised the distribution is compared with those of the elements ti p rb sr cu zn u sn w ta nb f li and cs and with major minerals in the granite feldspars and micas correlations with be were generally low from theoretical considerations and from statistical data it is concluded that be is enriched in the final stages of the magma crystallisation and was mobile in all the major late and post magmatic processes in the granite

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

beryllium in silicic magmas and the origin of beryl bearing pegmatites this chapter addresses the portion of the geochemical cycle of beryllium that entails its transfer through the continental crust by the generation and migration of silicic magmas which will be referred to loosely as granitic but will include all of the textural variants of rocks derived from the granitic bulk compositions within the granite system we will examine the distribution of be between anatectic melts and residual crystals and we will track the accumulation of be in melt via crystal fractionation culminating in the saturation of pegmatite forming melts in the mineral beryl beryl is unquestionably the most common manifestation of be enrichment and the most abundant of the phases that contain essential beryllium see cern this volume to explain the presence of beryl in pegmatites we pose four questions 1 how much be does it take to saturate a granitic pegmatite forming melt in beryl 2 how much be is likely to be incorporated in silicic partial melts at their source 3 consequently how much fractionation of a typical granitic magma must occur to achieve beryl saturation in pegmatitic derivatives or is beryl saturation possible without extended magmatic fractionation 4 and should all granitic magmas be expected to achieve beryl saturation eventually or are there special attributes of the source material or crystalline phases in the magma that predetermine the likelihood of forming beryl in pegmatitic differentiates to address these questions we start with a review of beryl saturation in pegmatites we then examine the likely abundance of be derived by anatexis at the sources of granitic magmas with the two ends of the system bracketed we can then subject be fractionation to conventional modeling methods to ascertain how much fractionation must take place to bring granitic melts to beryl saturation as a review this chapter relies as much as possible on readily available publications

stability of genthelvite zn4 besio4 3s an exercise in chalcophilicity using exchange operators phase relations involving genthelvite are studied on the basis of physical chemical principles and natural occurrences stability diagrams and exchange operators are considered as well as an extended system natural associations and solid state relations it is noted that the extremely high chalcophilicity of zn explains in part why genthelvite is such as rare mineral it is only somewhat more stable than willemite and is therefore restricted to the extremely low s environments provided by alkaline granites and syenites

geochemical evidence for a multistage magmatic genesis of ta sn li mineralization in the granite at beauvoir french massif central the beauvoir rare metal granite at the southern edge of the echassieres granite massif french massif central is mineralized by disseminated ta sn and li the granite body formed from an independent melt which was emplaced soon after the main granite facies of the massif the geochemistry of the beauvoir granite relates it to the phosphorus rich type of ta bearing granites and geochemical and mineralogical data establish its similarity to pegmatite melts the beauvoir granite results built up from two distinct intrusions both intrusions are cogenetic and were emplaced within a short time interval a geochemical study of a deep drill hole bored down to 900 m under the surface to the floor of the granite sheet with selected key zones observed in greater detail has allowed the recreation step by step of a long process leading to the economic concentration of ta sn and li the comparison of major element trace element and isotopic geochemistry with the petrology makes it possible to unravel the numerous processes contributing to the ore formation local events need to be determined before main events can be identified constraints on the interpretation of the ore genesis are provided by a careful observation of data interpretations of these observations are strongly backed up by experimental data e g keppler 1993 the source rock was most likely enriched in sn and w at about 10 ppm precluding a slightly enriched granitic melt by partial melting it is not known whether the melt was already enriched in ta but this is not a prerequisite subsequently deep seated fractional crystallization produced granitic magma similar in composition ta nearly equal 9 m to the adjacent colettes granite and further fractionation processes led to a melt already strongly enriched in ta ca 40 ppm strongly peraluminous and enriched in the depolymerizing elements f and p the viscosity was therefore very low allowing easy ascent during transport small scale fluctuations in the viscosity were amplified by upward movement leading to an f and p rich melt preceding the magma batch this less viscous melt again underwent crystallization while moving through the upper

beryllium mineral evolution beryllium is a quintessential upper crustal element being enriched in the upper crust by a factor of 30 relative to primitive mantle 2 1 vs 0 07 ppm most of the 112 minerals with be as an essential element are found in granitic pegmatites and alkalic rocks or in hydrothermal deposits associated with volcanic and shallow level plutonic rocks and skarns because of the extensive differentiation needed to enrich rocks sufficiently in beryllium for beryllium minerals to form these minerals are relative latecomers in the geologic record the oldest known is beryl in pegmatites associated with the sinceni pluton swaziland 3000 ma in general beryllium mineral diversity reflects the diversity in the chemical elements available for incorporation in the minerals and increases with the passage of geologic time furthermore the increase is episodic that is steep increases at specific times are separated by longer time intervals with little or no increase in diversity nonetheless a closer examination of the record suggests that at about 1700 ma the rate of increase in diversity decreases and eventually levels off at 35 species formed in a given 50 ma time interval between 1125 and 475 ma then increases to 39 species at 125 ma except for four spikes before dropping off to 30 species for the last 100 ma these features appear to reflect several trends at work 1 diversifications at 2475 1775 and 525 ma which are associated with highly fractionated rare element granitic pegmatites and with skarns at langban and similar deposits in the bergslagen ore region of central sweden and which are inferred to correspond to the collisional phases of the supercontinents kenorland nuna and gondwana respectively 2 diversification at 1175 ma due to the rich assemblage of beryllium minerals in the ilimaussaq peralkaline complex gardar province west greenland in an extensional environment 3 diversification at 275 ma which is largely attributable to granitic pegmatites appalachian mountains u s a and urals russia and the larvik alkalic complex norway but nonetheless related to continental collision and 4 limited exhumation of environments where beryllium minerals could have formed in the last 100 ma that the maximum diversity of be minerals in any one geologic environment could be finite is suggested by the marked slowing of the increase in the number of species formed in a given 50 ma time interval whereas the drop off at 100 ma could be due to 100 myr being too short a time interval to exhume the deep seated occurrences where many be minerals had formed the relative roles of chance vs necessity in complex evolving systems has been a matter of considerable debate one equally applicable to what extent the temporal distribution of beryllium minerals is a matter of contingency on the one hand the appearance of the most abundant be minerals such as beryl and phenakite early in the history of be mineralization appears to be a deterministic aspect since these minerals only require the abundant cations al and si and crystallize at relatively low concentrations of be in aqueous solution or granitic magmas on the other hand it could be argued that the very existence of most other be minerals as well as the temporal sequence of their appearance is a matter of chance since 55 of the 112 approved be minerals are known from a single locality and many of these phases require an unusual combination of relatively rare elements consequently we cannot exclude the possibility that other equally rare and thus contingent potential be minerals await discovery in as yet unexposed subsurface deposits on earth and we suggest that details of be mineral evolution on other earth like planets could differ significantly from those on earth

temperature variations of constitutive parameters can significantly affect the fault dynamics abstract a rate and state dependent governing law with temperature dependent constitutive parameters is considered on the basis of laboratory inferences we model the whole seismic cycle of a homogeneous fault obeying to such a law by adopting a spring slider dashpot fault analog model we show that the variations of the parameter a accounting for the so called direct effect with the temperature cause the system to enter at high speeds in a conditionally stable regime and also in a velocity strengthening regime although we do not observe the complete cessation of slip we can see a severe reduction of the degree of the instability of the fault in particular the peaks of the sliding velocity are reduced as well as the developed temperature due to frictional sliding and the released stress during each instability event moreover the recurrence times are reduced of a factor of two with respect to a reference configuration where the canonical formulation of rate and state friction with temporally constant parameters is assumed the obtained results can help the interpretation of high velocities laboratory experiments and further illuminate the importance of the temperature in the context of seismic hazard assessment

mineralogy of beryllium in granitic pegmatites beryllium is one of the most widespread rare elements in granitic pegmatites these rocks have been historically the sole industrial source of this metal e g norton et al 1958 and they still contribute a significant proportion of the global output of beryllium ores hand cobbed beryl constitutes a substantial proportion of beryllium ore concentrates in africa asia and south america although non pegmatitic rhyolite related bertrandite ores are virtually the single source in north america petkof 1975 the mineralogy of beryllium in granitic pegmatites is strongly diversified but very imbalanced in terms of numbers of species per mineral class on one hand and of the paragenetic role distribution and abundances on the other only a very few be minerals form at the magmatic stage of pegmatite consolidation with beryl absolutely dominant among them phosphates constitute most of the late subsolidus phases with silicates a close second but the number of the phosphate occurrences is very low and volumes are negligible a few oxide hydroxide and borate minerals complement the spectrum so far no other mineral classes are represented although the occurrence of some arsenates is considered possible part of the reason for the pattern above is the crystal chemical behavior of be one of the classic amphoteric elements which acts as a cation in acidic environments but participates in complex anions under alkaline conditions thus beryllo alumino silicates and beryllo phosphates of alkali and alkaline earth cations are widespread in contrast to silicates or phosphates of beryllium with no other cations or al only be2 is always tetrahedrally coordinated with oxygen beo4 6 or with oxygen and hydroxyl beo3oh 5 the divalent charge on be renders substitutions for other tetrahedrally coordinated oxycomplex forming cations such as si al or p difficult it is possible only by charge balancing via additional alkali or alkaline earth

mineralogy isotope geochemistry and ore genesis of the miocene cuonadong leucogranite related be w sn skarn deposit in southern tibet abstract the himalayan orogenic belt is characterized by widespread leucogranites which are mostly peraluminous with less than 5 mafic minerals previous studies mainly focused on the petrological characteristic genetic mechanism magmatic evolution and tectonic significance of these leucogranites however recently a skarn type be w sn polymetallic deposit which is spatially related to the cuonadong leucogranites of the himalayan leucogranites belt was discovered the orebodies occur in the inner and outer contact zones between the cuonadong leucogranites and their surrounding marble this study focuses on the the characteristics of the skarn mineral assemblages the deposit shows a typical skarn mineral zonation from inside to outside including dark pyroxene garnet skarn zone red garnet zone dark green amphibole specularite zone light green vesuvianite epidote ribbon and vesuvianite chlorite zone zircon u pb dating shows that the ore related leucogranite was emplaced at ca 18 ma geochemically the leucogranite has high sio2 al2o3 na2o k2o and low cao contents belonging to peraluminous granite the cuonadong leucogranite is characterized by right dipping chondrite normalized ree patterns with distinct negative eu anomalies importantly all samples show lanthanide tetrad effect on chondrite normalized ree patterns indicating significant melt fluid interaction has occurred due to strong fractional crystallization additionally the cuonadong leucogranite is enriched in large ion lithophile elements such as rb and relatively depleted in high field strength elements such as nb zr hf suggesting a crustal source region high f and b contents in the magma could have significantly increased the solubility of water in the magma while the magmatic hydrothermal solution enriched in f and b should have remarkably enhanced the metal carrying capacity and increased the permeability of surrounding rocks which in turn effectively facilitated water rock reaction

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km