ultracataclasite structure and friction processes of the punchbowl fault san andreas system california abstract the punchbowl fault is an exhumed 40 km displacement fault of the san andreas system in the devil s punchbowl the fault contains a continuous ultracataclasite layer along which the punchbowl formation sandstone and an igneous and metamorphic basement complex are juxtaposed the fabric of the ultracataclasite layer and surrounding rock indicate that nearly all of the fault displacement occurred in the layer by analogy with nearby active faults we assume that the punchbowl fault was seismogenic and that the ultracataclasite structure records the passage of numerous earthquake ruptures we have mapped the ultracataclasite layer at 1 1 and 1 10 to determine the mode of failure and to constrain the processes of seismic slip on the basis of color cohesion fracture and vein fabric and porphyroclast lithology two main types of ultracataclasite are distinguished in the layer an olive black ultracataclasite in contact with the basement and a dark yellowish brown ultracataclasite in contact with the sandstone the two are juxtaposed along a continuous contact that is often coincident with a single continuous nearly planar prominent fracture surface pfs that extends the length of the ultracataclasite layer in all exposures no significant mixing of the brown and black ultracataclasites occurred by offset on anastomosing shear surfaces that cut the contact or by mobilization and injection of one ultracataclasite into the other the ultracataclasites are cohesive throughout except for thin accumulations of less cohesive reworked ultracataclasite along the pfs structural relations suggest that 1 the black and brown ultracataclasite were derived from the basement and sandstone respectively 2 the black and brown ultracataclasites were juxtaposed along the pfs 3 the subsequent final several kilometers of slip on the punchbowl fault occurred along the pfs and 4 earthquake ruptures followed the pfs without significant branching or jumping to other locations in the ultracataclasite by comparison with rock friction experiments the slip localization along the pfs in the ultracataclasite implies rate weakening behavior with a critical slip distance similar to laboratory values and thus relatively small nucleation and breakdown dimensions for earthquake ruptures of the various mechanisms proposed to explain the low strength of the san andreas and to produce dynamic weakening of faults those that require or assume extreme localization of slip are most compatible with our observations

origin of mesozoic and tertiary granite in the western united states and implications for pre mesozoic crustal structure 2 nd and sr isotopic studies of unmineralized and cu and mo mineralized granite in the precambrian craton in the cordilleran region of the western united states mesozoic and tertiary peraluminous granitic rocks display regional variations in initial 143nd 144nd end end 10 to 12 in southern arizona 17 to 19 in the northern great basin ngb and 30 in the northern rocky mountains initial 87sr 86sr values are between 0 710 and 0 721 and show no regional pattern metaluminous granitic rocks have a wider range of end values extending from values similar to those of the peraluminous granites to much higher values the 87sr 86sr values are mostly fairly low between 0 705 and 0 710 except in the ngb where values as high as 0 7157 are observed no systematic differences between the end or 87sr 86sr values of cu or mo mineralized and unmineralized granite were discerned except for cu mineralized granite in eastern nevada and mo mineralized granite in colorado which have end values higher 0 and lower 10 0 respectively than unmineralized granite in the same region comparison to end values of exposed precambrian rock suggests that the peraluminous granite and the mo granite in colorado were derived exclusively from felsic precambrian basement rocks and that the regional variations in the end values reflect the regional variation in the average crustal age the nd data confirm that the precambrian basement underlying the ngb and eastern california is isotopically distinct from precambrian crust in the remainder of the western united states the similarity between the end values of peraluminous granite and precambrian crust also suggests that the high 147sm 144nd 0 13 and the low total light rare earth element lree abundances characteristic of peraluminous granite in southern arizona were imposed during the chemical evolution of the magmas metaluminous granite are interpreted to have formed via mixing of mantle derived magma and large proportions of low 87sr 86sr granulite facies lower crust except in the eastern ngb where the mantle magmas mixed with a lower crustal source with a significantly higher 87sr 86sr ratio ree abundance patterns for metaluminous granite in the ngb are characterized by extreme lree enrichment which supports the proposed origin for these rocks by mantle crust mixing or by remelting of the lower crust alone no systematic difference exists between the sources of cu or mo mineralized and unmineralized metaluminous granite but the data suggest that the cu sources are in the mantle and the mo sources are in preexisting crust overall the nd data indicate that continental interior granite in the western united states was primarily derived from preexisting crust and although changes in the thermal structure of the continental mantle may have triggered magma formation the resulting granites do not represent significant juvenile additions to the continental crust

scaling of the critical slip distance for seismic faulting with shear strain in fault zones theoretical and experimentally based laws for seismic faulting contain a critical slip distance1 5 dc which is the slip over which strength breaks down during earthquake nucleation on an earthquake generating fault this distance plays a key role in determining the rupture nucleation dimension6 the amount of premonitory and post seismic slip7 10 and the maximum seismic ground acceleration1 11 in laboratory friction experiments d c has been related to the size of surface contact junctions2 5 12 thus the discrepancy between laboratory measurements of dc 10 5m and values obtained from modelling earthquakes 10 2m has been attributed to differences in roughness between laboratory surfaces and natural faults5 this interpretation predicts a dependence of dc on the particle size of fault gouge2 breccia and wear material but not on shear strain here we present experimental results showing that dc scales with shear strain in simulated fault gouge our data suggest a new physical interpretation for the critical slip distance in which dc is controlled by the thickness of the zone of localized shear strain as gouge zones of mature faults are commonly 102 103 m thick12 17 whereas laboratory gouge layers are 1 10 mm thick our data offer an alternative interpretation of the discrepancy between laboratory and field based estimates of dc

continental tectonics and continental kinetics abstract we present a model of continental growth which combines the results of geochemical studies and tectonic ideas about the evolution of continents through geological time the process of continental growth is mainly controlled by surface phenomena continental material is extracted from the mantle along subduction zones at the periphery of oceans and is destroyed in collision zones where it is remobilized and made available for subduction we derive an equation for s the portion of the earth s surface occupied by continents which reads as follows ds dt a 1 s b s coefficients a and b depend on the geometry of plates on their number and on their velocities we assume that they decrease exponentially with time with the same time scale this model satisfies both geochemical and tectonic constraints and allows the integration of several current observations in a single framework

experimental interaction of hydrothermal na cl solution with fracture surfaces of geothermal reservoir sandstone of the upper rhine graben abstract the upper rhine graben urg is a tertiary rift structure in central europe offering favorable conditions for geothermal energy utilization relatively high heat flow combines with sufficiently high permeability of the hydrothermal reservoirs one of the target stratigraphic levels is the lower triassic sandstone formation buntsandstein where hot water resources at temperatures up to 250 c can be utilized extensional neotectonics and hydraulic stimulation form new fracture surfaces in the reservoir rocks enhanced geothermal system egs the exposed fresh rock fracture surface reacts with the highly saline reservoir brines na cl up to 200 g l 1 with consequences for the permeability of the reservoir in order to better understand the dynamic evolution of fault systems caused by fluid rock interaction we conducted batch type experiments in a stirred autoclave system and reacted arkosic sandstone with synthetic 2 molal na cl solution at temperatures of 200 c and 260 c after 45 55 days reaction time altered rock samples were compared with the starting material and the geochemical mineralogical processes were deduced with the help of xrd sem methods and emp measurements fluid compositions were examined by icp ms icp oes and ic the arkosic sandstones show a surprisingly high reactivity during the experiments quartz grain surfaces show deep dissolution features and all reaction fluids were saturated with respects to quartz illite and kaolinite from the primary sandstone cementation completely dissolved from the sample surface perfectly euhedral crystals of metastable analcime formed during the experiment as separate crystals on quartz as groups or clusters and as surface covering mats the overall net transfer process dissolves quartz illite kaolinite k feldspar and precipitates analcime chlorite albite the process is accompanied by a total volume increase of the solids of 20 30 vol k feldspar dissolution is hampered by albitization rims shielding k feldspar and efficiently preventing an equilibration of the na k exchange with the fluid the experiments show changes on the rock surface leading to an increase of the aperture of a single fracture during the early phases of reaction and later to a decrease as the fluid rock reaction progresses alteration of the fracture surface also generates loose fragments and altered minerals this fine material may efficiently reduce the fracture aperture at narrow points along the fracture

dynamic rupture processes inferred from laboratory microearthquakes we report macroscopic stick slip events in saw cut westerly granite samples deformed under controlled upper crustal stress conditions in the laboratory experiments were conducted under triaxial loading 1 2 3 at confining pressures 3 ranging from 10 to 100 mpa a high frequency acoustic monitoring array recorded particle acceleration during macroscopic stick slip events allowing us to estimate rupture speed in addition we record the stress drop dynamically and we show that the dynamic stress drop measured locally close to the fault plane is almost total in the breakdown zone for normal stress 75 mpa while the friction f recovers to values of f 0 4 within only a few hundred microseconds enhanced dynamic weakening is observed to be linked to the melting of asperities which can be well explained by flash heating theory in agreement with our post mortem microstructural analysis relationships between initial state of stress rupture velocities stress drop and energy budget suggest that at high normal stress leading to supershear rupture velocities the rupture processes are more dissipative our observations question the current dichotomy between the fracture energy and the frictional energy in terms of rupture processes a power law scaling of the fracture energy with final slip is observed over eight orders of magnitude in slip from a few microns to tens of meters

late mesozoic intrusive complexes in the coastal area of fujian se china the significance of the gabbro diorite granite association abstract the pingtan and daiqianshan igneous complexes southeastern china are typical of calc alkaline series developed at active continental margins these two complexes are dominated by granites or gabbros with minor diorites and granodiorites and these rock types closely coexisted both temporally and spatially the major and trace element signatures of gabbros indicate they were crystallised from high aluminium basaltic magmas which were generated from metasomatised upper mantle the typical metaluminous calc alkaline composition trace element patterns and sr nd isotopes indicate the granites in the complexes are i type granites which may have been generated from the deeper crust by a thermal contribution from the mantle field relationships petrography and geochemistry favour a mechanical mingling together with a limited chemical mixing between high aluminium basaltic magma and granitic magma resulting in the formation of diorites or granodiorites the essentially bimodal character of these complexes reflects the general character of back arc extensional magmatism which was induced by the subduction of the pacific plate beneath the eurasian continent in late mesozoic time

zeolites in fissures of granites and gneisses of the central alps six different ca zeolite minerals are widespread in various assemblages in late fissures and fractures in granites and gneisses of the swiss alps the zeolites formed as a result of water rock interaction at relatively low temperatures 250 c in the continental upper crust the zeolites typically overgrow earlier minerals of the fissure assemblages but zeolites also occur as monomineralic fissure fillings they represent the youngest fissure minerals formed during uplift and exhumation of the alpine orogen a systematic study of zeolite samples showed that the majority of finds originate from three regions particularity rich in zeolite bearing fissures i in the central and eastern part of the aar and gotthard massifs 2 gibelsbach fiesch in a fissure breccia located at the boundary of aar massif and permian sedimentary rocks and 3 in penninic gneisses of the simano nappe at arvigo val calanca rail and road tunnel construction across the aar and gotthard massif provided excellent data on zeolite frequency in alpine fissures it was found that 32 gotthard neat rail base tunnel amsteg section and 18 gotthard road tunnel of all studied fissures are filled with zeolites the number of different zeolites is limited to six species laumontite stilbite and scolecite are abundant and common whereas heulandite chabazite and epistilbite occur occasionally calcium is the dominant extra framework cation with minor k and na heulandite and chabazite contain sr up to 29 and 10 mol extra framework cations respectively na and k contents in zeolites tend to increase during growth as a result of changes in fluid composition and or temperature the k enrichment of stilbite found in surface outcrops compared to subsurface samples may indicate late stage cation exchange with surface water texture data relative age sequences derived from fissure assemblages and equilibrium calculations show that the ca dominated zeolites precipitated from fluid with decreasing temperature in the order old to young hot to cold scolecite laumontite heulandite chabazite and stilbite the necessary components for zeolite formation are derived from dissolving primary granite and gneiss minerals the nature of these minerals depends among other factors on the metamorphic history of the host rock zeolites in the aar massif derived from the dissolution of epidote secondary calcite and albite that were originally formed during alpine greenschist metamorphism from primary granite and gneiss assemblages zeolite fissures occur in areas of h2o dominated fluids this is consistent with equilibrium calculations that predict a low co2 tolerance of zeolite assemblages particularly at low temperature

structural evolution of the rieserferner pluton in the framework of the oligo miocene tectonics of the eastern alps abstract the structural evolution of the oligocene rieserferner pluton eastern alps developed during pluton cooling and exhumation includes localized deformation structures consisting of i steeply dipping joints leucocratic dykes and quartz feldspar veins and related ductile shear zones formed at 600 c ii shallowly dipping joints with associated epidote and quartz veins and related ductile shear zones 450 c iii steeply dipping mafic dykes and calcite white mica bearing brittle ductile faults 300 c iv steeply dipping pseudotachylyte bearing faults

ubiquitous weakening of faults due to thermal pressurization faults weaken during earthquakes analysis of the amount of energy released during earthquakes globally suggests that heat induced pressurization of pore fluids can weaken faults during earthquakes of all sizes laboratory simulations of earthquakes show that at high slip rates faults can weaken significantly aiding rupture1 2 3 various mechanisms such as thermal pressurization and flash heating have been proposed to cause this weakening during laboratory experiments1 4 5 6 yet the processes that aid fault slip in nature remain unknown measurements of seismic radiation during an earthquake can be used to estimate the frictional work associated with fault weakening known as an event s fracture energy7 8 9 here we compile new and existing8 9 measurements of fracture energy for earthquakes globally that vary in size from borehole microseismicity to great earthquakes we observe a distinct transition in how fracture energy scales with event size which implies that faults weaken differently during small and large earthquakes and earthquakes are not self similar we use an elastodynamic numerical model of earthquake rupture to explore possible mechanisms we find that thermal pressurization of pore fluid by the rapid shear heating of fault gouge can account for the observed scaling of fracture energy in small and large earthquakes over seven orders of fault slip magnitude we conclude that thermal pressurization is a widespread and prominent process for fault weakening

off fault damage and acoustic emission distributions during the evolution of structurally complex faults over series of stick slip events variations in fault structure for example surface roughness and deformation zone width influence the location and dynamics of large earthquakes as well as the distribution of small seismic events in nature changes in fault roughness and seismicity characteristics can rarely be studied simultaneously so that little is known about their interaction and evolution here we investigate the connection between fault structure and near fault distributions of seismic events over series of stick slip cycles in the laboratory we conducted a set of experiments on rough faults that developed from incipient fracture surfaces we monitored stress and seismic activity which occurred in the form of acoustic emissions aes we determined ae density distributions as a function of fault normal distance based on high accuracy hypocentre locations during subsequent interslip periods the characteristics of these distributions were closely connected to different structural units of the faults that is the fault core off fault and background damage zone the core deformation zone was characterized by consistently high seismic activity whereas the off fault damage zone displayed a power law decay of seismic activity with increasing distance from the fault core the exponents of the power law distributed off fault activity increased with successive stick slip events so that later interslip periods showed a more rapid spatial decay of seismic activity from the fault the increase in exponents was strongest during the first one to three interslip periods and reached approximately constant values thereafter the relatively rapid spatial decay of ae events during later interslip periods is likely an expression of decreasing fault zone complexity and roughness our results indicate a close relationship between fault structure stress and seismic off fault activity a more extensive mapping of seismic off fault activity decay has the potential to significantly advance the understanding of fault zone properties including variations in fault roughness and stress

zircon u th pb and whole rock rb sr age patterns of lower mesozoic igneous rocks in the santa rita mountains southeast arizona implications for mesozoic magmatism and tectonics in the southern cordillera volcanic and plutonic rocks and associated sediments in the santa rita mountains southeast arizona represent one of the most complete mesozoic sections in the cordillera zircon from the lower member of the mt wrightson formation the oldest of the dated units has lost radiogenic lead and contains a component of older zircon accordingly only an imprecise maximum age of 220 ma could be obtained for an andesite from near the middle of this unit the lower member is intruded by the piper gulch granodiorite which gave a concordant zircon u th pb age of 188 2 2 ma complex isotopic systematics of zircon from dacite in the middle member of the mt wrightson formation allow its age to lie between 172 and 190 ma because the piper gulch is interpreted to also cut the base of the middle member a hiatus of no longer than 30 m y is likely to separate the lower and middle members this stratigraphic break marks the change from early predominantly basaltic and andesitic volcanism to later dacitic to rhyolitic lavas and tuffs the silty to conglomeratic red beds and minor volcanic rocks of the gardner canyon formation for which we obtained a nearly concordant u th pb age of 200 5 ma on an abraded fraction of zircon may identify a rift dominated tectonic regime and mark the transition to felsic volcanism a second cycle of andesite and rhyolitic volcanism and sedimentation represented by the temporal and bathtub formations was dated at 151 5 2 ma by the whole rock rb sr isotopic method compared to previous age estimates our results suggest an earlier initiation of arc magmatism in this part of the cordillera apparently by the late triassic this area was already an uplifted continental arc margin analogous to the present day andes shedding volcanic material to what is now the colorado plateau the volcanic rocks we dated fall within the range of ages measured for cobbles of similar lithology from the upper triassic chinle formation in the colorado plateau therefore it is not necessary to invoke the tectonic removal of an early mesozoic arc terrane along the proposed mojave sonora megashear

photo acoustic study of subshear and supershear ruptures in the laboratory abstract we report supershear ruptures observed in spontaneously nucleating laboratory microearthquakes and describe the signature of the associated mach wavefront radiation transducers detect the wavefield both close and at a distance from the fault the rupture velocities are inferred from either photoelastic high speed imaging or using the acoustic recordings both methods yield compatible estimates of sufficient accuracy to discriminate between sub shear and supershear ruptures the acoustic records allow to characterize the mach wavefront radiated from the supershear rupture front in particular its amplitude and decay velocity functions recovered by integrating high frequency accelerometer signals in the case of supershear ruptures consist in a double pulse function a first pulse traveling at supershear velocity followed by a second pulse traveling at the rayleigh wave velocity conversely the sub shear event is characterized by a single pulse finally we perform numerical simulations of our experiment using a prescribed supershear rupture velocity the synthetic waveforms obtained from these simulations including the mach wave amplitude and phase yield a satisfactory fit to the experimental results

a robust calibration technique for acoustic emission systems based on momentum transfer from a ball drop we describe a technique to estimate the seismic moment of acoustic emissions and other extremely small seismic events unlike previous calibration tech niques it does not require modeling of the wave propagation sensor response or signal conditioning rather this technique calibrates the recording system as a whole and uses a ball impact as a reference source or empirical green s function to correctly apply this technique we develop mathematical expressions that link the seismic mo ment m0 of internal seismic sources i e earthquakes and acoustic emissions to the impulse or change in momentum p of externally applied seismic sources i e me teor impacts or in this case ball impact we find that at low frequencies moment and impulse are linked by a constant which we call the force moment rate scale factor c f mm0 p this constant is equal to twice the speed of sound in the material from which the seismic sources were generated next we demonstrate the calibration technique on two different experimental rock mechanics facilities the first example is a saw cut cylindrical granite sample that is loaded in a triaxial apparatus at 40 mpa confining pressure the second example is a 2 m long fault cut in a granite sample and deformed in a large biaxial apparatus at lower stress levels using the empirical cali bration technique we are able to determine absolute source parameters including the seismic moment corner frequency stress drop and radiated energy of these magnitude 2 5 to 7 seismic events

groundwater chemistry and water rock interactions at stripa groundwaters from near surface to a depth of 1232 m in the stripa granite have been sampled and analyzed for major and trace constituents the groundwater composition consists of two general types a typical recharge water of ca hco3 type 700 m depth of high ph 8 10 that reaches a maximum of 1250 mg l in total dissolved solids tds intermediate depths show mixtures of the two types that are highly fracture dependent rather than depth dependent any borehole can vary significantly and erratically in tds for either a horizontal or vertical direction the general transition from ca hco3 type to na ca cl type correlates with the depth profile for hydraulic conductivity that drops from 10 8 m s to 10 11 m s or lower thermomechanical stress from heater experiments clearly shows an effect on the groundwater composition that could be caused by changing flow paths leakage of fluid inclusions or both dissolution and precipitation of calcite fluorite and barite aluminosilicate hydrolysis and addition of a saline source possibly fluid inclusion leakage play the major roles in defining the groundwater composition the low permeability of the stripa granite has produced a groundwater composition that appears intermediate between the dilute shallow groundwaters typical of recharge in a crystalline rock terrain and the saline waters and brines typical of cratonic shield areas at depth

multi stage zeolite facies mineralization in the hvalfjordur area iceland the hvalfjordur area 30 km north of iceland s capital reykjavik belongs to the sequence of late tertiary to early quaternary flood basalts with minor intercalations of hyaloclastites and rhyolites the basalts are affected by progressive low temperature metamorphism caused by the burial of the lava succession and higher heat flow from nearby central volcanoes low grade zeolite facies metamorphism of basaltic lavas in the hvalfjordur area results in two distinct mineral parageneses that can be correlated to events in the burial and hydrothermal history of the lava pile stage ia represents syn eruptive near surface alteration in which celadonite and silica were precipitated along primary pores during regional burial metamorphism stage ib hydrolysis of olivine and glass led to the formation of mixed layer chlorite smectite clays the chlorite content of stage ib phyllosilicate vesicle rims increases with increasing burial depth and temperature stage ii occurred after the burial and is marked by zeolite mineralization caused by higher heat flow from the laxarvogur and hvalfjordur central volcanoes altogether 11 different zeolites were found in the hvalfjordur area analcime chabazite epistilbite heulandite laumontite levyne mesolite stilbite stellerite thomsonite and yugawaralite in total three separate depth and temperature controlled zeolite zones occur in the hvalfjordur area

very low grade metamorphism of the taveyanne greywacke glarus alps switzerland detailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic eocene oligocene taveyanne greywacke of the glarus alps eastern switzerland presented data indicate an increase of metamorphic grade from zeolite facies to prehnite pumpellyite and pumpellyite actinolite facies low grade outcrops contain laumontite minor corrensite and pumpellyite assemblage type 1 whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite type 2 prehnite pumpellyite al white mica type 3 a single outcrop shows pumpellyite actinolite facies type 4 from the zeolite to prehnite pumpellyite pumpellyite actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain 1 mm in type 1 to a few millimetres in type 2 and to a whole thin section in type 3 metamorphic p t conditions were determined by a combination of chlorite thermometry fluid inclusion and vitrinite reflectance data peak temperatures range from 170 190d c for zeolite facies to 270 310d c for prehnite pumpellyite and pumpellyite actinolite facies for the higher temperature range pressures of 2 3 kbar are derived indicating a geothermal gradient of 24 32d c km 1 the well constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed the best correspondence to the temperatures determined here is for the cathelineau calibration in addition in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites

tectono magmatic evolution of the west philippine mariana region and the origin of boninites re examination of published data on the tectomagmatic evolution of the west philippine mariana region indicate that arc magmatism and back arc extensional pulses are not synchronous but are largely asynchronous arc volcanism ceases within a few million years of the development of a back arc basin and recommences oceanward on a new arc during the final stages in the development of the back arc basin following karig s model we believe that ascent beneath the arc axial chain of a line of diapirs of morb source mantle interferes with processes of arc magma generation and arc magmatism wanes partial melting of the diapirs produces voluminous morb type tholeiites which split the arc and form the crust of a widening back arc basin we show for both the west philippine mariana region and occurrences of boninite like lavas in ophiolites that boninites appear to be erupted after arc magmatism and immediately before eruption of morb type lavas passage of a diapir of hot morb source mantle through refractory sub arc peridotite which has been enriched in lile and h2o will result in limited partial melting of the hydrous peridotite and the restricted production of boninitic magmas these are more likely to erupt modified or only slightly modified by crystal fractionation through the thin forearc crust continued ascent of the morb source mantle diapir will result in it partially melting to yield morb tholeiites which erupt shortly after and in considerably more voluminous amounts than the boninites finally we suggest that forearcs regions are likely to be incorporated into foldbelts and that boninite or low ti lava bearing ophiolites may characterize such regions

a hot spring in granite of the western tianshan china the western tianshan range is a major cenozoic orogenic belt in central asia exposing predominantly paleozoic rocks including granite ongoing deformation is reflected by very rugged topography with peaks over 7000 m high active tectonic deformation is tied to an e w trending fracture and fault system that sections the mountain chain into geologically diverse blocks that extend parallel to the orogen in the muzhaerte valley upwelling hot water follows such a fault system in the muza granite about 20 l min 1 na so4 cl water with a temperature of 55 c having a total mineralization of about 1 g l 1 discharge from the hot spring the water is used in a local spa that is frequented by the people of the upper ili river area its waters are used for balneological purposes and the spa serves as a therapeutic institution the major element composition of the hot water is dominated by na and by so4 and cl ca is a minor component dissolved silica 1 04 mmol l 1 corresponds to a quartz saturation temperature of 116 c and a corresponding depth of the source of the water of about 4600 m this temperature is consistent with na k and na li geothermometry the water is saturated with respect to fluorite and contains 7 5 mg l 1 f as a consequence of the low ca concentration the water is undersaturated with respect to the primary minerals of the reservoir granite at reservoir temperature causing continued irreversible dissolution of granite the waters are oversaturated with respect to ca zeolite minerals such as stilbite and mesolite and it is expected that zeolites precipitate in the fracture pore space and in alteration zones replacing primary granite the stable isotope composition of o and h supports a meteoric origin of the water the cl br mass ratio of 1500 suggests that the salinity results from halite dissolution salts leached from powders of muza granite show the same cl br signature as the hot spring water sodium chloride is stored in fluid and solid inclusions in the granite which have been introduced to quartz by ductile shearing and faulting related to ongoing orogenesis the hot water remobilizes the salt that is continuously liberated by the tectonic deformation water granite interaction contributes a thenardite component na2so4 to the major element composition by albite dissolution in h2so4 the water rock interaction along faults and fractures transforms and alters muza granite to a low temperature epigranite

hornblende k ar ages and the climax of tertiary metamorphism in the lepontine alps south central switzerland an old problem reassessed abstract twenty five new k ar ages for amphiboles from the tertiary barrovian type metamorphic terrain of the central alps were determined these results lead to the conclusion that the meso alpine metamorphism reached its peak condition and maximum expanse about 26 3 m y ago along a profile of increasing grade of alpine metamorphism in both basement and cover rocks the following observations can be made 1 pre alpine hornblendes in the zone of greenschist facies show ages ranging from 639 to 152 m y the implied open system behavior may be related to the observed mineralogical instability of these hornblendes during the alpine overprint in contrast two greenschist facies hornblendes which grew in pennine mesozoic rocks during the alpine metamorphism yield ages of 23 2 and 29 3 m y 2 on both sides of the boundary marking the first occurrence of alpine staurolite pre or early alpine hornblende k ar ages are not fully reset unless the rocks were completely recrystallized for one rock specimen which clearly exhibits two generations of hornblende an age two times greater was obtained for the smaller crystals oriented parallel to the foliation than for the structurally younger hornblende porphyroblasts which overgrew the preexisting texture 3 in the high grade area of alpine metamorphism only young alpine ages between 23 and 28 m y were found for hornblendes which grew syn to postkinematically with respect to the last penetrative deformation one amphibolitic inclusion not affected by this deformation yielded a significantly older hornblende age of 32 1 m y these results suggest that temperature controlled ar diffusion is not the main factor governing the k ar system of metamorphic hornblendes we conclude that these hornblende ages should not be interpreted as cooling ages from a structurally ill defined earlier event instead they indicate that the high grade metamorphism responsible for the well known isograd pattern in the lepontine area persisted until some 23 m y ago

the pre atlantic hf isotope evolution of the east laurentian continental margin insights from zircon in basement rocks and glacial tillites from northern new jersey and southeastern new york abstract this paper presents laser ablation u pb age and hf isotope data for zircons from basement rocks and glacial deposits in northern new jersey and southeastern new york the purpose is to understand the eastern laurentian continental margin s hf isotope record in relation to its geologic evolution prior to the opening of the atlantic ocean the basement samples encompass a meso to neoproterozoic continental margin arc an anatectic magmatic suite as well as a late ordovician alkaline igneous suite emplaced during post orogenic melting of the lithospheric mantle additional samples were collected from terminal moraines of two quaternary continental ice sheets across the entire dataset zircons with ages corresponding to the timing of continental margin arc magmatism 1 4 ga to 1 2 ga have positive e hf initial values that define the more radiogenic end of a crustal evolution array this array progresses towards more unradiogenic e hf initial values along a series of low 176 lu 177 hf 0 022 to 0 005 trajectories during subsequent anatectic magmatism 1 2 ga to 1 0 ga and later metamorphic and metasomatic re working 1 0 ga to 0 8 ga of the continental margin arc crust in contrast nearly chondritic e hf initial values from the late ordovician alkaline magmas indicate that the laurentian margin was underlain by a re fertilized mantle source such a source may have developed by subduction enrichment of the mantle wedge beneath the continental margin during the mesoproterozoic additionally preliminary data from a metasedimentary unit of unknown provenance hints at the possibility that some of the sediments occupying this portion of the laurentian margin prior to the ordovician were sourced from crust older than 1 9 ga

properties of seismic fault zone waves and their utility for imaging low velocity structures a two dimensional solution for the scalar wave equation in a model of two vertical layers between two quarter spaces is used to study properties of seismic waves in a laterally heterogeneous low velocity structure the waves referred to as seismic fault zone waves include head waves internal fault zone reflections and trapped waves the analysis aims to clarify the dependency of the waves on media velocities media attenuation coefficients layer widths and source receiver geometry additional calculations with extreme low velocity layers provide examples that may be relevant for volcanic and geothermal domains the interference patterns controlling seismic fault zone waves change with the number of internal reflections in the low velocity structure this number increases with propagation distance along the structure decreases with fault zone width and increases for given length scales with the velocity contrast the relative lateral position of the source within the low velocity layer modifies die length scales associated with internal reflections and influences the resulting interference pattern low values of q affect considerably the dominant period and overall duration of the waves thus there are significant tradeoffs between propagation distance along the structure fault zone width velocity contrast source location within the fault zone and q the lateral and depth receiver coordinates determine the particular point where the interference pattern is sampled and observed motion is a strong function of both coordinates the zone connecting sources generating fault zone waves and observation points with appreciable wave amplitude can be over an order of magnitude larger than the fault zone width calculations for cases with layer p wave velocity of 200 m s 1 modeling a vertical dike or crack with fluid and gas show conspicuous persisting oscillations the results resemble aspects of seismic data in volcanic domains if these waves exist in observed records their explicit recognition and modeling will help to separate source and structural effects and aid in the interpretation of volcano seismology signals although the tradeoffs in parameters governing seismic fault zone waves are significant each variable has its own signature and the parameters may be constrained by additional geophysical data simultaneous modeling of many waveforms with an appropriate solution can resolve the various parameters and provide a high resolution structural image

stochastic model of heterogeneity in earthquake slip spatial distributions summary finite fault source inversions reveal the spatial complexity of earthquake slip or pre stress distribution over the fault surface the basic assumption of this study is that a stochastic model can reproduce the variability in amplitude and the long range correlation of the spatial slip distribution in this paper we compute the stochastic model for the source models of four earthquakes the 1979 imperial valley the 1989 loma prieta the 1994 northridge and 1995 hyogo ken nanbu kobe for each earthquake except imperial valley we consider both the dip and strike slip distributions in each case we use a 1 d stochastic model for the four earthquakes we show that the average power spectra of the raw that is non interpolated data follow a power law behaviour with scaling exponents that range from 0 78 to 1 71 for the four earthquakes we have found that a non gaussian probability law that is the levy law is better suited to reproduce the main features of the spatial variability embedded in the slip amplitude distribution including the presence and frequency of large fluctuations since asperities are usually defined as regions with large slip values on the fault the stochastic model will allow predicting and modelling the spatial distribution of the asperities over the fault surface the values of the levy parameters differ from one earthquake to the other assuming an isotropic spatial distribution of heterogeneity for the dip and the strike slip of he northridge earthquake we also compute a 2 d stochastic model the main conclusions reached in the 1 d analysis remain appropriate for the 2 d model the results obtained for the four earthquakes suggest that some features of the slip spatial complexity are universal and can be modelled accordingly if this is proven correct this will imply that the spatial variability and the long range correlation of the slip or pre stress spatial distribution can be described with the help of five parameters a scaling exponent controlling the spatial correlation and the four parameters of the levy distribution constraining the spatial variability

evidence from neodymium isotopes for mantle contributions to phanerozoic crustal genesis in the canadian cordillera sm nd and rb sr isotopic studies of several phanerozoic orogenic belts have shown that much of the crust in these belts is composed of reworked pre existing continental crust in contrast isotopic data collected from two of the largest terranes in the canadian cordilleran orogenic belt the alexander and stikine terranes show that these tectonic fragments are composed of mantle derived continental crust in many respects the style and rate of crustal accretion of these and related terranes appear similar to those of some proterozoic crustal regions

brittle structural facies analysis a diagnostic method to unravel and date multiple slip events of long lived faults abstract regional scale faults typically experience complex long lasting histories commonly recording evidence of multiple reactivation events therefore they contain multiscalar structural domains characterised by varying microstructures mineralogical compositions and kinematics these domains result from differential strain partitioning during the recorded faulting stages and as a result can preserve the isotopic and kinematic signature of the different slip periods their detailed structural analysis integrated with k ar dating of the fault rock assemblage can help to identify these commonly tightly juxtaposed although not coeval domains which we refer herein to as brittle structural facies bsf bsf analysis is pivotal i to understand the structural heterogeneity of fault zones ii the diachronic formation of geometrically and kinematically complex fault cores and iii to reconstruct faults evolution in time and through space following this approach this study relies on meso and microstructural analysis chemical characterisation and k ar dating to unravel the evolution of the laerdal gjende fault lgf southwestern norway the lgf is a multiply reactivated top to the nw extensional fault with a 1 m thick poorly consolidated core we recognised sampled and characterised five bsf i indurated dark reddish gouge ii poorly consolidated cataclasite iii weakly foliated greenish gouge iv clay rich gouge and v a few mm thick clay smear decorating the principal slip surface samples were separated into five grain size fractions from

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

fault zone trapped seismic waves two instances of fault zone trapped seismic waves have been observed at an active normal fault in crystalline rock near oroville in northern california trapped waves were excited with a surface source and recorded at five near fault borehole depths with an oriented three component borehole seismic sonde at parkfield california a borehole seismometer at middle mountain recorded at least two instances of the fundamental and first higher mode seismic waves of the san andreas fault zone at oroville recorded particle motions indicate the presence of both love and rayleigh normal modes the love wave dispersion relation derived for an idealized wave guide with velocity structure determined by body wave travel time inversion yields seismograms of the fundamental mode that are consistent with the observed love wave amplitude and frequency applying a similar velocity model to the parkfield observations we obtain a good fit to the trapped wavefield amplitude frequency dispersion and mode time separation for an asymmetric san andreas fault zone structure a high velocity half space to the southwest a low velocity fault zone a transition zone containing the borehole seismometer and an intermediate velocity half space to the northeast in the parkfield borehole seismic data set the locations depth and offset normal to fault plane of natural seismic events which do or do not excite trapped waves are roughly consistent with our model of the low velocity zone we conclude that it is feasible to obtain near surface borehole records of fault zone trapped waves because trapped modes are excited only by events close to the fault zone proper thereby fixing these events in space relative to the fault a wider investigation of possible trapped mode waveforms recorded by a borehole seismic network could lead to a much refined body wave tomographic velocity model of the fault and to a weighting of events as a function of offset from the fault plane it is an open question whether near surface sensors exist in a stable enough seismic environment to use trapped modes as an earth monitoring device

hydrothermal alteration and zeolitization of the fohberg phonolite kaiserstuhl volcanic complex germany the subvolcanic fohberg phonolite kaiserstuhl volcanic complex germany is an economic zeolite deposit formed by hydrothermal alteration of primary magmatic minerals it is mined due to the high 40 wt zeolite content which accounts for the remarkable zeolitic physicochemical properties of the ground rock new mineralogical and geochemical studies are carried out a to evaluate the manifestation of hydrothermal alteration and b to constrain the physical and chemical properties of the fluids which promoted hydrothermal replacement the alkaline intrusion is characterized by the primary mineralogy feldspathoid minerals k feldspar aegirine augite wollastonite and andradite the rare earth elements phase gotzenite is formed during the late stage magmatic crystallization fluid induced re equilibration of feldspathoid minerals and wollastonite caused breakdown to a set of secondary phases feldspathoid minerals are totally replaced by various zeolite species calcite and barite wollastonite breakdown results in the formation of various zeolites calcite pectolite sepiolite and quartz zeolites are formed during subsolidus hydrothermal alteration 150 c under alkaline conditions a sequence of ca na dominated zeolite species gonnardite thomsonite mesolite is followed by natrolite the sequence reflects an increase in log a text na a text h and decrease in log a text ca 2 a text h 2 of the precipitating fluid low radiogenic 87sr 86sr values indicate a local origin of the elements necessary for secondary mineral formation from primary igneous phases in addition fractures cut the intrusive body which contain zeolites followed by calcite and a variety of other silicates carbonates and sulfates as younger generations stable isotope analysis of late fracture calcite indicates very late circulation of meteoric fluids and mobilization of organic matter from surrounding sedimentary units

crust mantle interaction in continental arcs inferences from the mesozoic arc in the southwestern united states arc magmas ranging in composition from basaltic andesites to rhyolites and intrusive equivalents were emplaced into the western margin of the north american craton starting in late triassic time giving way to rift0related sedimentation in the late jurassic the region of this study cuts across proterozoic basements of contrasting nd model ages 1 7 1 8 ga average nd 11 in eastern arizona and 2 0 to 2 3 ga average nd 18 in western arizona and eastern california bennett and depaolo 1987 the mesozoic rocks have initial nd of 3 4 to 6 4 in the eastern part of the study area and 7 1 to 9 2 in the western part all of the rocks have elevated 87sr 87sr initial ratios 0 706 trends in initial nd values of mesozoic arc rocks are directly correlated with the nd model ages of the basement through which they passed simple two component mixing calculations indicate that recycled continental crust in the arc magmas represents on average about 65 a minimum of 35 mantle input into continental arc magmas as recent as the mesozoic represents a significant contribution to the growth of the continental crust in the absence of a return flow of continental material into the mantle of similar magnitude in a detailed study in the santa rita mountains arizona there is a pattern of increase of nd with time early basaltic andesites have more negative nd than later felsic rocks a correlated pattern of depletion with time is also observed with trace element and major element data we attribute this either to progressive hybridization of the lower crust by repeated injection of mantle magmas or the progressive thinning of the continental crust during prolonged arc magmatism the present data do not allow distinction between the two models progressive decrease in crustal contribution to arc magmas with time may be an important feature of continental arc evolution hybridization of the lower crust due to repeated injection of mantle melts during arc magmatism may help contribute to small scale heterogeneities in lower crust inferred from seismic and xenolith data similarly whether there is a well defined moho or sharp crust mantle boundary in any given segment of the continental crust may in part depend on the extent of crust modification as a result of continental arc magmatism

seismic radiation from an sh line source in a laterally heterogeneous planar fault zone a solution to the class of problems in which an sh line source is operating in a medium consisting of two quarter spaces with an arbitrary number of semi infinite vertical layers in between is given in a frequency wavenumber domain the general result is applied to a model with a single vertical layer and synthetic seismograms are calculated for a source specified as an sh line dislocation at the interface between the vertical layer and the faster quarter space the numerical examples demonstrate that moderate fault normal material heterogeneity can have significant effects on the seismic response of a medium the overall distribution of travel times amplitudes and motion polarities in the presence of fault zone material heterogeneity is different from a corresponding distribution in a homogeneous half space the effects are most prominent near the fault zone where head waves surface waves and trapped modes result in waveform complexities large amplifications over an order of magnitude in the fault zone itself and first motion polarities which are reversed from homogeneous medium predictions the results imply that material heterogeneity should be included in fault zone models which are used for the interpretation of observed seismic data and theoretical calculations of near fault responses such models can be utilized to obtain important fault zone and earthquake source parameters

preslip and cascade processes initiating laboratory stick slip recent modeling studies have explored whether earthquakes begin with a large aseismic nucleation process or initiate dynamically from the rapid growth of a smaller instability in a cascade up process to explore such a case in the laboratory we study the initiation of dynamic rupture stick slip of a smooth saw cut fault in a 76 mm diameter cylindrical granite laboratory sample at 40 120 mpa confining pressure we use a high dynamic range recording system to directly compare the seismic waves radiated during the stick slip event to those radiated from tiny m 6 discrete seismic events commonly known as acoustic emissions aes that occur in the seconds prior to each large stick slip the seismic moments focal mechanisms locations and timing of the aes all contribute to our understanding of their mechanics and provide us with information about the stick slip nucleation process in a sequence of 10 stick slips the first few microseconds of the signals recorded from stick slip instabilities are nearly indistinguishable from those of premonitory aes in this sense it appears that each stick slip begins as an ae event that rapidly 20 s grows about 2 orders of magnitude in linear dimension and ruptures the entire 150 mm length of the simulated fault we also measure accelerating fault slip in the final seconds before stick slip we estimate that this slip is at least 98 aseismic and that it both weakens the fault and produces aes that will eventually cascade up to initiate the larger dynamic rupture

mineralogical changes and distribution of heavy metals caused by the weathering of hydrothermally altered pyrite rich andesite the weathering of pyrite rich andesite in the southeastern part of korea has led to acid rock drainage creating severe environmental problems in the region in this study the mineral compositions and geochemical mobility of heavy metals in the bedrock in addition to the weathering products are investigated samples of bedrock and weathering products were collected from two sites in the yangsan area site 2 shows considerably more weathering than site 1 due to the longer duration of weathering the mineral compositions show that the bedrock at site 2 was more heavily altered by hydrothermal activity the weathering products at site 2 contain jarosite and goethite with lower ph values than site 1 in which the samples are buffered by calcite this indicates that the mineral compositions and ph values of the weathering products at the two sites are influenced by the primary mineral compositions of the bedrock and the duration of weathering with the exception of pb the concentrations of heavy metals at site 1 are higher than those at site 2 probably due to higher concentrations in the bedrock moreover the labile and acid soluble fractions which can be more readily released into the environment are higher at site 1 mainly due to the shorter duration of weathering accordingly the weathering process at site 1 carries more potential hazards to the environment than that at site 2 however chemical weathering is locally impeded by calcite buffering at site 1 although the concentrations of heavy metals at site 2 are lower than those at site 1 they are being continuously released due to the lower ph and longer and more and extensive weathering

source regions of granites and their links to tectonic environment examples from the western united states this review in honor of ilmari haapala s retirement reflects on lessons learned from studies of three granitic systems in western north america 1 mesoproterozoic samples from west texas and east new mexico 2 laramide granitic systems associated with porphyry copper deposits in arizona and 3 granites of the colorado mineral belt the studies elucidate relationships amongst tectonic setting source material and magma chemistry mesoproterozoic basement samples are from two different felsic suites with distinct elemental and isotopic compositions the first suite the plutonic province is dominantly magnesian calc alkalic to alkali calcic and metaluminous it has low k2o na2o and rb sr and nd model ages of 1 56 to 1 40 ga the second suite the panhandle igneous complex is magnesian metaluminous alkalic and is part of the mesoproterozoic belt of magmatism that extends from finland to southwestern united states samples from the panhandle igneous complex demonstrate three episodes of magmatism the first pulse was intrusion of quartz monzonite at 1380 to 1370 ma the second was comagmatic epizonal granite and rhyolite at 1360 to 1350 ma both of these rock types are high k to slightly ultra high k the third pulse at 1338 to 1330 ma was intrusion of ultra high k quartz syenite nd model ages 1 94 to 1 52 ga are distinct from those of the plutonic province and systematically older than crystallization ages implying a substantial crustal input to the magmas at the sierrita porphyry copper deposit in the mazatzal province of southeastern arizona trace element sr and nd isotopic compositions were determined for a suite of andesitic and rhyolitic rocks 67 ma intruded by granodiorite and granite isotopic composition and chemical evolution are well correlated throughout the suite andesite has the least negative initial end 4 3 and lowest 87sr 86sri 0 7069 it is also the oldest and chemically most primitive having low concentrations of rb sio2 and high concentrations of transition elements these parameters change through the system to the youngest unit granite which has the most negative end 8 5 the highest 87sr 86sri 0 7092 and is chemically most evolved correlation between chemical and nd isotopic evolution probably resulted from a continuous process of progressive assimilation in which mafic magmas invade and incorporate continental crust deposits in arizona with end values more negative than the 8 5 of sierrita lie in the older yavapai province in the northwestern part of the state the difference in the most negative epsilon nd implies that nd isotopic signature is sensitive to the age of the precambrian domain the granites from the colorado mineral belt were emplaced during the transition from laramide convergence to mid tertiary extension three different groups of granites are recognized the first is laramide and was formed during assimilation fractional crystallization involving lower crustal mafic source materials the second and third groups are mid tertiary and represent intracrustal melting of heterogeneous sources this change in source regions and melt regimes in transition from convergence to extension is fundamental to the mesozoic and cenozoic evolution of western north america

fluid regimes during late stages of a continental collision physical chemical and stable isotope measurements of fluid inclusions in fissure quartz from a geotraverse through the central alps switzerland fluid evolution during neo alpine metamorphism during late stages of the continental collision between europe and africa was studied by analyzing fluid inclusions in alpine fissure quartz collected in forty nine localities along a geotraverse through the central alps switzerland the methods employed include microthermometry micro raman spectroscopy k na thermometry and stable isotope analysis early fluid inclusions provide evidence of close to peak metamorphic temperatures of the late tertiary or neo alpine metamorphic event fluid composition evolved along the geotraverse from north to south as follows higher hydrocarbons were dominant in the low and medium grade diagenetic zones methane was the main volatile in the high grade diagenetic and low grade anchizone water dominated in the highgrade anchizone and low grade epizone with co2 10 mol in the high grade epizone and in the mesozone higher hydrocarbons and ch4 were the products of kerogen maturation and cracking of preexisting petroleum large water supplies originated from the dehydration of cooler metasedimentary rocks that were overthrust by crystalline basements of the lepontines aar and gotthard massifs carbon isotope analyses suggest that the co2 component was derived from oxidation of graphitic matter especially in the vicinity of sulfate bearing metasediments and from decarbonation reactions in the aar and gotthard massifs as well as in the helvetic axen nappe and its underlying north helvetic flysch high fluid pressures prevailed and favored nappe transport by contrast in the southern lepontine area very low early fluid pressures were probably related to dry rocks and scarce metasediments and to high geothermal gradients that resulted from intense uplift and erosion between 26 and 18 ma retrograde fluid evolution was recorded by a succession of fluid inclusion populations in each alpine fissure it was controlled by uplift and cooling and characterized by decreasing contents of volatiles and an increase in 18o of host quartz tectonic activity led to episodic pressure drops of at least 0 5 to 2 kbar and promoted fluid unmixing channelized flow and rapid growth of skeletal quartz channelized rather than pervasive fluid migration at temperatures 450 c and under conditions of brittle deformation is documented by episodic increases in salinity and by fluid flushing through the massifs there is stable isotope evidence for involvement of meteoric water only in late crystallizing quartz formation of alpine fissures and fissure minerals was the result of a unique coincidence of late continental collision 450 c fluid expulsion from overthrust metasediments uplift and erosion

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

nd isotope evidence for crust mantle interaction in the generation of a type granitoid suites in labrador canada early proterozoic a type granite suites in labrador northeastern canada have initial nd isotopic compositions that lie between those of a depleted mantle reservoir and the local basement rocks one of these a type granite suites consists of a linear array of discrete plutons that crosses the boundary between an archean craton and an adjoining early proterozoic crustal block the nd of these granites at formation t 1720 ma changes from 8 to 4 across this boundary reflecting changes in the nature and antiquity of the continental crust however in both domains the granites cannot be derived entirely by anatexis of the local basement rocks and apparently require significant amounts of juvenile mantle derived material a type granites have been widely interpreted as anatectic derivatives of lower crustal rocks that were depleted by previous melt extraction the nd isotopic data suggest that these labrador examples were instead mixtures of mantle derived magmas and overlying lower crustal rocks and that new material may have been the volumetrically dominant component 50 90 in most cases as an alternative to the prevalent residual source model it is proposed that the distinctive geochemical characteristics of these a type granites are a function of the high liquidus temperatures and primitive mg rich character of subcrustal magma fluxes in post orogenic and anorogenic environments where such magmas are emplaced into stabilized continental crust further nd isotope studies of other a type granite suites are required to ascertain if models invoking crust mantle interaction are more widely applicable

slip pulse rupture behavior on a 2 m granite fault we describe observations of dynamic rupture events that spontaneously arise on meter scale laboratory earthquake experiments while low frequency slip of the granite sample occurs in a relatively uniform and crack like manner instruments capable of detecting high frequency motions show that some parts of the fault slip abruptly velocity 100 mm s 1 acceleration 20 km s 2 while the majority of the fault slips more slowly abruptly slipping regions propagate along the fault at nearly the shear wave speed we propose that the dramatic reduction in frictional strength implied by this pulse like rupture behavior has a common mechanism to the weakening reported in high velocity friction experiments performed on rotary machines the slip pulses can also be identified as migrating sources of high frequency seismic waves as observations from large earthquakes show similar propagating high frequency sources the pulses described here may have relevance to the mechanics of larger earthquakes

constraining long term fault activity in the brittle domain through in situ dating of hydrothermal monazite sims th pb dating of hydrothermal fissure vein monazite ce has the unique potential to date multiple tectonic events under low grade metamorphic brittle ductile conditions over large time frames monazites ce from brittle fault systems in the eastern alps allow us to constrain their cretaceous activity over 20 ma within single crystals recording all major tectonic events eo alpine formation of the fluid filled fissure veins occurred 90 ma ago at 352 19 c and 342 42 mpa this corresponds to peak conditions during regional metamorphism of the cretaceous collisional nappe stacking several stages of dissolution reprecipitation recrystallization record fault activity between 84 and 70 ma corresponding fluid inclusions indicate conditions of 229 10 c and 143 20 mpa this correlates with the formation of sedimentary basins during post orogenic extension associated with strike slip movements the results strengthen the hypothesis that many large fault systems in the eastern alps developed during the cretaceous orogeny and became reactivated during neogene alpine tectonics

petrology and geochemistry of boninite series volcanic rocks from the mariana trench boninite series volcanic rocks have been recovered from three dredge hauls on the inner slope of the mariana trench these hauls included olivine boninites boninites boninitic andesites and boninitic dacites as well as island arc tholeiitic basalts and andesites the boninite series volcanics range from 52 to 68 sio2 and are characterized by very low abundances of high field strength cations and heavy rare earth elements boninites and olivine boninites have phenocrysts of olivine and orthopyroxene the andesites phenocrysts of orthopyroxene and clinopyroxene and the dacites orthopyroxene clinopyroxene and plagioclase most of the major and trace element variation in the series from boninite to boninitic dacite can be modelled by fractionation of olivine orthopyroxene clinopyroxene and plagioclase in the proportions 2 5 4 1 2 leaving 47 residual liquid the fractionation must be in part open system reverse zoned phenocrysts resorbed olivine and plagioclase xenocrysts and bulk rock compositions which cannot be fit by simple closed system crystallization indicate some magma mixing and phenocryst accumulation two boninitic magma stems can be identified with similar high field strength element abundances but different amounts of ca na al and light rare earth elements there is also evidence for a magma stem transitional in chemistry from the boninites to arc tholeiites the compositions of these boninites are consistent with hypotheses for boninite formation by partial melting of a depleted mantle mixed with an incompatible element enriched fluid the mariana forearc boninite series lacks a strong iron enrichment but produces andesites with lower ti al and y zr and higher mg ni and cr than typical calcalkaline arc andesites and dacites boninites in the mariana system were erupted only in the earliest phases of subduction zone activity

tectonic models for early cretaceous rifting in southeastern arizona the early cretaceous tectonic setting of southeastern arizona was one of northeast southwest extensiomal deformation characterized by differential vertical movements along northwest trending normal faults local fault block uplifts created a basin and range type paleogeography that included local clastic filled basins and mountain ranges rimmed by alluvial fans the glance conglomerate the basal formation of the lower cretaceous bisbee group represents the proximal parts of these syntectonic alluvial fans this extensional back arc tectonic setting is strikingly different from the compressional setting found behind the continental margin magmatic arc farther to the north sevier orogeny possible explanations for this profound difference in back arc tectonic style include propagation of an aulacogen from the gulf of mexico to southeastern arizona variable dip subduction along the continental margin magmatic arc and an apparent anticlockwise rotation of the north american plate relative to the continental margin arc

crustal melting by ponding of mafic magmas a numerical model abstract we examine the possibility that an abating period of mantle related volcanic activity at continental margins triggers the production of crustal derived melts a vertical zone permeated by rising mafic melts is established below the volcanic arc if long lasting mantle derived magmatism occurs this situation can be assumed to exist at continental arcs we propose that mafic magmas release heat and water into the crustal environment if subsequent magma ascent is stopped due to establishment of a density barrier this process enhances intracrustal partial melting using a finite element program we simulate in a 2d model area the time dependent change of the crustal thermal structure the spatial distribution of potential melting zones and their degree of partial melting within the crust is computed the amount of generated melt able to segregate is calculated and compared with volume estimates given by field investigation and geochemical constraints in a natural test case we chose the altiplano puna volcanic complex apvc which is part of the central andes as an example where the process may have happened and show from simple approximations that the model can explain the volumes of crustal melts represented by the felsic volcanics in this region although the model parameters and assumptions used are specific to this geologic context the proposed model is generally applicable to any arc setting

the origin of the cretaceous gabbros in the fujian coastal region of se china implications for deformation accompanied magmatism the cretaceous gabbros in the fujian coastal region southeastern china experienced different magmatic and tectonic processes associated with deformation of the changle nanao shear zone group 1 gabbros 115 ma show marked lile e g sr ba and k and lree enrichment and hfse e g ta nb zr and hf depletion strongly suggesting an island arc affinity the parental magma of group 1 gabbros arguably derived from an arc related source mantle modified by previous subduction rose into and interacted with the coexisting syntectonic granitic magma generated during the main stage of shear zone deformation and produced the gabbro diorite granite complexes group 2 and 3 gabbros 106 95 ma possibly formed by coupling of the subduction modified source mantle with part of undepleted mantle e g nb enrichment in an extensional environment at the end of deformation their parental magmas did not undergo significant magma mixing but produced a cumulate nature all the three groups of gabbros were contaminated by crustal material during the processes of intrusion and emplacement

euclidean and fractal models for the description of rock surface roughness accurate description of the topography of rock surfaces is essential because surface roughness affects frictional strength the flow of fluids in joints and fractures the seismic behavior of faults and the formation of gouge and breccia in fault zones real rock surfaces can be described using self similar and self affine fractal models of surface roughness if a surface is self similar a small portion of the surface when magnified isotropically will appear statistically identical to the entire surface if a surface is self affine a magnified portion of the surface will only appear statistically identical to the entire surface if different magnifications are used for the directions parallel and perpendicular to the surface at least two parameters are required to describe a fractal model one parameter typically describes how roughness changes with scale while the other specifies the variance or surface slope at a reference scale the divider method and the spectral method are in common use to determine the best fit fractal model from surface profile data power spectra from self similar surfaces have slopes of 3 on log log plots of power spectral density versus spatial frequency while spectra from self affine surfaces have slopes other than 3 power spectra can be interpreted with greater facility if dimensionless amplitude to wavelength ratios are contoured on plots of power spectral density versus frequency the topography of many natural rock surfaces including both fractures and faults is approximately self similar within the 6 5 order of magnitude wide wavelength band of 10 m to 40 m within smaller wavelength bands natural rock surfaces may exhibit self affine behavior

plate tectonics model for proterozoic continental accretion in the southwestern united states proterozoic crustal provinces in the southwestern united states decrease in age south from the archean wyoming province supracrustal rocks define three major age provinces from north to south 1 72 to 1 80 1 65 to 1 72 and 1 1 to 1 2 b y successions within each province are similar and define two assemblages a bimodal volcanic assemblage commonly overlain by a quartzite shale assemblage precambrian granitic plutons intrude all three provinces geochemical and sr isotope data indicate a variably depleted upper mantle source for basalts and a short lived these observations can be explained by a plate tectonics model involving successive marginal basin closures and andean type orogenies associated with southward migrating arcs the net result is to accrete 1 300 km of continental crust to the southwestern margin of north america between 1 8 and 1 1 b y ago

rapid uplift and crustal growth in extensional environments an isotopic study from the death valley region california the willow spring diorite in the black mountains of the central death valley extended terrain yields a u pb zircon age of 11 6 plus minus 0 2 ma sup 40 ar sup 39 ar analyses of hornblende and u pb analyses of sphene from this sample give ages of about 10 ma indicating that the batholith remained above about 500 c for about 1 5 m y after crystallization geologic relations indicate that the diorite was exposed to erosion by about 5 ma bracketing the evolution of the diorite within the time between onset of extension and uplift of the black mountain crustal block initial sup 87 sr sup 86 sr ratios range from 0 7060 mafic diorite to 0 7083 felsic diorite in samples collected from an area 200 x 100 m these data combined with structural and petrologic evidence suggest that the batholith represents a rare view of a mid crustal zone of mixing between mantle derived magma and crustal material often suggested to exist on the basis of observations of intermediate volcanic rocks the black mountains may therefore expose a cross section through a continental rift magmatic system from partially contaminated mafic to intermediate intrusive rocks in the deep crust up to their volcanic equivalents the relatively low initial sup 87 sr sup 86 srmore and high epsilon sub nd minus 1 4 of the diorite which is within proterozoic basement with epsilon sub nd approximately minus 18 is consistent with significant amounts of mantle input in continental rifts inferred from geophysical data and measurement of he isotopic ratios such additions to the crust in continental rights may represent a significant process of crustal growth furthermore the emplacement of igneous bodies with a large mantle component may help reconcile the large crustal pull apart in the basin and range in excess of 140 km with the fact that the crust still has as normal thickness of about 30 35 km less

dynamic stress variations due to shear faults in a plane layered medium summary a complete set of expressions is presented for the computation of elastic dynamic stress in plane layered media we use a discrete wavenumber reflectivity method to compute the stress field radiated by arbitrary moment tensor sources the expressions derived here represent an interesting tool for both the observational and theoretical analysis of dynamic stress changes associated with earthquake phenomena dynamic stress changes associated with a strike slip fault having unilateral rupture are shown this modelling which is similar to the 1992 landers california earthquake illustrates the effects of distance directivity and depth on transient stress changes

a chemical and isotopic study of the laramide granitic belt of northwestern mexico identification of the southern edge of the north american precambrian basement along the laramide belt of northwestern mexico granitic rocks of similar bulk composition show isotopic and trace element signatures that help to delineate the position of the southern edge of the north american precambrian basement in the northern part the laramide plutons the northern granites intruded proterozoic crystalline rocks and a thick late proterozoic through paleozoic miogeoclinal cover of north american affinity in the central part the granitic bodies the central granites were emplaced into a sequence of paleozoic eugeoclinal rocks overlain by late triassic clastic units the southern part of the belt the southern granites intruded a less known crust characterized by middle to late mesozoic island arc related volcanic and sedimentary rocks of the guerrero terrane data from a suite of metaluminous to slightly peraluminous calc alkalic granitic rocks along the belt display north to south geochemical and isotopic variations which could correlate with the type of intruded basement the northern and central granites are characterized by strongly fractionated light rare earth element ree enriched patterns which display generally pronounced negative europium anomalies whereas the southern granites have lower total ree enrichments and much flatter chondrite normalized slopes displaying almost no europium anomalies isotopic results also suggest regional variations as shown by the following initial sr and end ranges 0 7070 to 0 7089 and24 2 to25 4 respectively for the northern granites 0 7060 to 0 7079 and23 4 to25 1 for the central granites and 0 7026 to 0 7062 and20 9 to 14 2 for the southern granites on the basis of their isotopic similarities the proterozoic mafic to intermediate lower crust revealed by xenoliths from young volcanic flows in southern arizona and northern mexico is interpreted as a reasonable parental source for the northern and central granites however mantle derived melts are not excluded the more primitive southern granites are interpreted to come from a source that lacked proterozoic basement instead they were probably derived by mixing of juvenile mantle melts with partial melts of the lower parts of the guerrero terrane in general the north to south compositional variations of the laramide granitic rocks of northwestern mexico reflect the crustal structure underneath the batholiths the sr and nd data indicate that the edge of the north american precambrian basement extends approximately southeastward from the coastal batholith of central sonora then about 200 km south of hermosillo in southern sonora the edge bends eastward and continues to the east beneath the sierra madre occidental volcanic province

the geology of the mccoy mountains formation southeastern california and southwestern arizona the mccoy mountains formation is a 7 3 km thick metasedimentary sequence exposed in at least 6 mountain ranges in southeastern california and southwestern arizona the siliciclastic mccoy mountains formation is deposited on and interbedded at its base with a jurassic volcanic terrane and is intruded by undeformed upper cretaceous plutons it has been assigned a cretaceous paleocene age on the basis of fossil angiosperm wood found within the upper third of the sequence presently known exposures of mccoy mountains formation define a west northwest trending basin 140 km long by 25 km wide which was filled from the north by predominantly alluvial processes the mccoy mountains formation is divided into six members each containing distinctive stratigraphy and sedimentary petrology sandstone consists of quartz feldspar and lithics and each member has a different composition the source evolved from volcanic sedimentary to plutonic sedimentary composition with time much thinner laterally equivalent clastic sequences are now known on the craton adjacent to the basin s northern margin the mccoy mountains formation is homoclinal and south dipping and its uppermost strata are deformed into a north verging overturned syncline with sympathetic south dipping cleavage northern exposures of mccoy mountains formation and underlying jurassic volcanic terrane contain a north dipping cleavage and south verging overturned folds sympathetic to the cleavages and folding are north and south bounding faults which limit mccoy mountains formation exposures and place the north american craton north side and the mojave sonora complex or tujunga terrane south side onto mccoy basin rocks structural analysis and paleomagnetic data strongly suggest that the thrusting over and folding of the mccoy basin rocks took place in late jurassic time as a single event the fault along the southwestern margin of the mccoy basin is thus apparently a jurassic terrane boundary and may be a northern extension of the jurassic mojave sonora megashear if true proposed early tertiary accretion of the tujunga terrane must have occurred farther to the southwest

water rock interaction and hydrothermal mineral equilibria in the tendaho geothermal system abstract the tendaho geothermal system occurs within a nw se trending rift basin filled with quaternary volcanics mainly basalts and fluvio lacustrine sediments three deep td 1 td 2 and td 3 and one shallow td 4 geothermal wells have been drilled the waters of productive wells td 1 td 2 and td 4 are typical na cl geothermal waters with reservoir temperature ranging between 220 and 270 c chemical analysis of core samples altered basalts shows increased ca fe mg al content owing to the dissolution of plagioclase and femics and the precipitation of wairakite laumontite epidote garnet calcite and clay minerals and decreased na k si and ti owing mostly to the dissolution of glass matrix petrographic study of cuttings and core samples shows 1 evidence of an early stage of calcite zeolite wairakite or laumontite and quartz crystallization while calcite underwent different stages of dissolution precipitation possibly due to abrupt changes in ph and co 2 partial pressure 2 that epidote garnet prehnite pyroxene and amphibole crystallization occurred after wairakite or laumontite chlorite is the main layered silicate in the basaltic rocks in wells td 1 and td 2 temperatures beyond the stability of smectite and chlorite smectite c s interlayers must have been reached the smectites and c s interlayers in association with chlorite in well td 3 indicate that this well has had a more complex thermal history with variable temperatures the smectites occur at temperatures above 120 c which is considered to be the threshold for the transformation of smectite to illite no evidence of disequilibrium conditions of smectites has been found at reservoir temperatures currently present at tendaho fluid inclusion data indicate heating in the well td 1 and thermal conditions similar to the ones measured in the deepest part of well td 2 while the uppermost part of this latter has undergone cooling intense cooling has affected well td 3 drilled far from the upflow zone of the field probably in an area characterized by self sealing cooling and very low permeability

mass transfer and porosity evolution during low temperature water rock interaction in gneisses of the simano nappe arvigo val calanca swiss alps late alpine fissures and fractures in amphibolite facies basement gneisses at arvigo val calanca swiss alps show distinct cm sized reaction selvages parallel to the fracture walls that composed of subgreenschist facies assemblages produced by the interaction of water present in the fracture porosity with the old high grade gneiss assemblages the process of selvage or reaction vein formation occurred in the brittle deformation regime and at temperatures characteristic of first the prehnite pumpellyite facies and then later of the zeolite facies the vein formation occurred during uplift and cooling at very late stages of the alpine orogeny the reaction veins are composed of a selvage of altered gneiss on both sides of the central fracture and a central zone with fissure minerals that have been growing in the open fracture pore space the central zone of the arvigo veins contains an early assemblage with epidote prehnite and chlorite and a late succession sequence of various species of zeolite the veins of the arvigo quarry are convincing evidence that fracture fluids in gneiss and granite have the potential to precipitate ca zeolite this is an important find because many fluids recovered from deep continental drill holes and from geothermal energy exploration are found to be oversaturated in respect to a number of ca zeolite species vein formation during late uplift and cooling of the alps occurred at continuously decreasing t and at hydrostatic pressure 1 coexisting prehnite epidote records temperatures of 330 380 c 2 chlorite formation at temperature of 333 32 c and 3 formation of zeolites 250 c in the selvages the prime reaction is the replacement of plagioclase by albite along a sharp reaction front that separates the selvage from unaltered gneiss in addition to albitisation chloritisation of biotite is the second important reaction in the alteration process the reactions release components for the formation of ca al silicates the water rock interaction is associated with a depletion of al si ca fe and k in the altered wall rock the overall reaction is associated with an increase in porosity of up to 14 2 2 2 in the selvage zone altered wall rock caused by the volume decrease during albitisation and the removal of biotite the propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution reprecipitation mechanism zeolite formation is tied to the plagioclase alteration reaction in the rock matrix which releases components for zeolite formation to a co2 poor aqueous liquid

origin of zeolite cements in the miocene sandstones north tejon oil fields california zeolite cement zoning from heulandite via heulandite laumontite to laumontite is found in miocene volcaniclastic sandstones at the north tejon oil field southern san joaquin basin california the zeolite transition occurs at the depth range from 2703 2743 m present temperature range 90 92 degrees c heulandite and minor smectite forms together from the dissolution of volcanic glass during early diagenesis at depths shallower than 2743 m early laumontite forms directly at the expense of heulandite by a reaction of the form 1250 cc 1470 cc ca sub 3 75 al sub 7 5 si sub 28 5 o 72 24h 2 o 3 35ca super 2 6 7al oh 4 super 7 1caal 2 si 4 o 12 4h 2 o 9h 2 o heulandite laumontite this reaction is based on the volumetrical relation between both zeolites and the absence of quartz cements during the zeolite transition the sources of the ca and al appear to be partial dissolution of plagioclase and smectite occurring prior to the above reaction and incorporation of residual smectite coatings at that reaction time active albitization and late laumontite formation begin to occur in the laumontite bearing sandstones at depths greater than 2743 m present temperatures greater than 94 degrees c this albitization reaction accompanying the late laumontite is as follows 100 cc 70 cc 62 cc na sub 0 7 ca sub 0 3 al sub 1 3 si sub 2 7 o 8 0 6h 4 sio 4 0 7naalsi 3 o 8 0 3caal 2 si 4 o 12 4h 2 o plagioclase albite lumontite clay mineral transitions from smectite via mixed layer clay minerals c s or i s to chlorite or illite probably produced the h 4 sio 4 necessary for the above reaction in addition to the albitization the source of late laumontite was derived in part from a mass transfer from outside during the late laumontite formation calcite locally forms and acts as an additional sink for ca immediately adjacent to deformed biotite flakes

on relating apparent stress to the stress causing earthquake fault slip apparent stress a is defined as where is the average shear stress loading the fault plane to cause slip and is the seismic efficiency defined as ea w where ea is the energy radiated seismically and w is the total energy released by the earthquake the results of a recent study in which apparent stresses of mining induced earthquakes were compared to those measured for laboratory stick slip friction events led to the hypothesis that this hypothesis is tested here against a substantially augmented data set of earthquakes for which can be estimated mostly from in situ stress measurements for comparison with a the expanded data set which includes earthquakes artificially triggered at a depth of 9 km in the german kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb borehole and natural tectonic earthquakes covers a broad range of hypocentral depths rock types pore pressures and tectonic settings nonetheless over 14 orders of magnitude in seismic moment apparent stresses exhibit distinct upper bounds defined by a maximum seismic efficiency of 0 06 consistent with the hypothesis proposed before this behavior of a and can be expressed in terms of two parameters measured for stick slip friction events in the laboratory the ratio of the static to the dynamic coefficient of friction and the fault slip overshoot typical values for these two parameters yield seismic efficiencies of 0 06 in contrast to efficiencies for laboratory events for which is always near 0 06 those for earthquakes tend to be less than this bounding value because ea for earthquakes is usually underestimated due to factors such as band limited recording thus upper bounds on appear to be controlled by just a few fundamental aspects of frictional stick slip behavior that are common to shallow earthquakes everywhere estimates of from measurements of a for suites of earthquakes using are found to be comparable in magnitude to estimates of shear stress on the basis of extrapolating in situ stress data to seismogenic depths

measurements of frictional heating in granite a large 150 150 40 cm granite sample sawn diagonally in half to simulate a fault was deformed in a biaxial rock press at normal stress up to 6 41 mpa displacements and local shear stress were monitored along the fault 200 40 cm temperature transients as large as 10 m c were recorded following stick slip events at distances of 0 2 to 1 0 cm from the fault and were related to stress displacement and total work the temperature measurements were used to calculate the heat generated on the fault during slip frictional heating was found to be 94 2 of the total work expended in each event implying a seismic efficiency of 4 8 when water was injected onto the fault both fractional stress drop and static frictional stress increased the efficiency of frictional heating was not lowered by the presence of water heat generated during deformation of a 0 15 cm thick layer of simulated gouge was also measured for sliding rates from 0 09 to 9 1 m s in these gouge experiments temperature rises were less than 0 1 c and were proportional to sliding rate

geochemistry of late cretaceous granitoids from northeastern washington implication for genesis of two mica cordilleran granites mesozoic two mica granites and i type granodiorites from northeastern washington have initial sup 87 sr sup 86 sr ratios around 0 7100 similar to many other cordilleran granitoids metapelite and calcsilicate country rocks equivalent to the belt supergroup have measured sup 87 sr sup 86 sr ratios in the range of 0 91 to 0 98 unlike many of their cordilleran counterparts the northeastern washington two mica granites are enriched in u rb and other incompatible elements and therefore cannot have been derived from depleted lower crust sedimentary sources both the two mica granites and the i type granodiorites have similar rare earth element and trace element enrichment patterns trace elements modeling shows that it is feasible to derive the two mica granites by 60 partial melting of a granodiorite like source the close association of cordilleran metamorphic core complexes and older i type granodiorites with two mica granites supports this model

cretaceous age of the upper part of the mccoy mountains formation southeastern california and southwestern arizona and its tectonic significance reconciliation of paleobotanical and paleomagnetic evidence the upper part of the 7 km thick mccoy mountains formation in southeastern california contains fossil angiosperm wood that closely resembles the genus paraphyllanthoxylon which is known only from strata of late early cretaceous and younger age this wood in conjunction with geologic field relations supports previous interpretations that the upper part of the mccoy mountains formation is of late early cretaceous and or late cretaceous age in contrast to a more recent interpretation that the entire formation is of jurassic age alternatives are therefore needed to the recent hypothesis that deposition deformation and metamorphism of the mccoy mountains formation were related to movement on the jurassic mojave sonora megashear

can observations of earthquake scaling constrain slip weakening summary we use observations of earthquake source parameters over a wide magnitude range m w 0 7 to place constraints on constitutive fault weakening the data suggest a scale dependence of apparent stress and stress drop both may increase slightly with earthquake size we show that this scale dependence need not imply any difference in fault zone properties for different sized earthquakes we select 30 earthquakes well recorded at 2 5 km depth at cajon pass california we use individual and empirical green s function spectral analysis to improve the resolution of source parameters including static stress drop and total slip s we also measure radiated energy e s w ecompare the cajon pass results with those from larger california earthquakes including aftershocks of the 1994 northridge earthquake and confirm the results of abercrombie 1995 e s m 0 where rigidity and both e s m 0 and increase as m 0 and s increases uncertainties remain large due to model assumptions and variations between possible models and earthquake scale independence is possible within the resolution assuming that the average trends are real we define a quantity g 2 es m 0 s 2w hich is the total energy dissipation in friction and fracture minus 1 s w here 1 is the final static stress if 1 d the dynamic shear strength during the last increments of seismic slip then g g the fracture energy in a slip weakening interpretation of dissipation

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

deep fluid circulation in alpine shear zones pyrenees france field and oxygen isotope studies a combined field stable isotope and whole rock chemical study was made on late cretaceous to tertiary metasomatic shear zones cutting hercynian gneisses in the aston massif pyrenees france mylonitisation occurred during the early stages of alpine compression under retrograde conditions at 400 450 c and about 10 km depth whole rock 18o values of 11 to 12 in the gneisses was lowered to 5 to 9 in the shear zones with the quartz muscovite 18o 16o fractionations of about 2 to 4 essentially unchanged these 18o 16o systematics together with d muscovite 40 to 50 indicate that large volumes of formation waters or d rich meteoric waters passed through the shear zones during deformation the same fluids also redistributed major elements as shown by the correlation of 18o shift with muscovitisation and albitisation reactions in granitic wall rocks however even though 18o was universally lowered within the shear zones the 18o 16o ratios were not homogenised nor do they correlate in detail with the presence or absence of muscovitisation suggesting that fluid flow was probably fracture controlled and episodic field mapping shows that along the length of a particular shear zone muscovitisation of granite gneiss dies out 150m above the contact with underlying sillimanite gneiss thus muscovitisation and albitisation of granite gneiss in shear zones and their wall rocks probably occurred during re equilibration of acidic chloride rich aqueous fluids that had previously moved upward within the shear zones through underlying sillimanite gneiss extremely high material balance fluid rock ratios 103 are required to explain the extent of muscovitisation along this shear zone implying integrated fluid mass fluxes of about 108 kg m2 this is probably close to the maximum value for other shear zones in the network similar volumes of a more chemically evolved fluid must have passed through the unmuscovitised mylonites showing that the absence of alteration cannot necessarily be used to infer low values of fluid flux for reasonable pressure gradients and time scales of fluid movement effective permeabilities of 10 15 to 10 17 m2 are required such values can be accounted for by short lived widely spaced cracks produced during seismic activity a model is presented in which formation waters were seismically pumped down an underlying shallow southward dipping decollement and then upward through the steeply dipping shear zone network

a new petrogenetic grid for low grade metabasites abstract we have used internally consistent thermodynamic data to present calculated phase equilibria for the system na2o cao mgo al2o3 sio2 h2o ncmash in the range 0 500 c and 0 1 10 kbar involving the phases anorthite glaucophane grossular heulandite jadeite laumontite lawsonite paragonite prehnite pumpellyite stilbite tremolite wairakite zoisite with excess albite clinochlore quartz and pure water average activity terms derived from published mineral chemical data were included for clinochlore glaucophane prehnite pumpellyite tremolite and zoisite the new petrogenetic grid delineates stability fields and parageneses of common index minerals in zeolite prehniteactinolite prehnite pumpellyite pumpellyite actinolite blueschist and greenschist facies metabasites the stability fields of mineral assemblages containing prehnite pumpellyite epidote actinolite albite chlorite quartz were analysed in some detail using activity data calculated from five specific samples for example the prehnite actinolite facies covers a p t field ranging from about 220 to 320 c at pressures below 4 5 kbar the transition from the prehnite actinolite and pumpellyite actinolite to greenschist facies occurs at about 250 300 c at 1 3 kbar and at about 250 350 c at 3 8 kbar p t fields of individual facies overlap considerably due to variations in chemical composition

diagnosing open system magmatic processes using the magma chamber simulator mcs part i major elements and phase equilibria the magma chamber simulator mcs is a thermodynamic tool for modeling the evolution of magmatic systems that are open with respect to assimilation of partial melts or stoped blocks magma recharge mixing and fractional crystallization mcs is available for both pc and mac in the mcs the thermal mass and compositional evolution of a multicomponent multiphase composite system of resident magma wallrock and recharge reservoirs is tracked by rigorous self consistent thermodynamic modeling a recharge assimilation assimilated partial melt or stoped blocks fractional crystallization rnasnfc ntot 30 scenario is computed by minimization or maximization of appropriate thermodynamic potentials using the family of rhyolite and pmelts engines coupled to an excel visual basic interface in mcs during isobaric cooling and crystallization resident magma thermally interacts with wallrock that is in internal thermodynamic equilibrium wallrock partial melt above a user defined percolation threshold is homogenized i e brought in to chemical potential equilibrium with resident magma crystals that form become part of a cumulate reservoir that remains thermally connected but chemically isolated from resident melt up to 30 instances n 30 of magma mixing by recharge and or bulk assimilation of stoped wallrock blocks can occur in a single simulation each recharge magma or stoped block has a unique user defined composition and thermal state recharge magmas and stoped blocks hybridize equilibrate with resident melt yielding a single new melt composition and temperature mcs output includes major and trace element concentrations and isotopic ratios sr nd hf pb os and o as defaults of wallrock recharge magma stoped blocks resident magma melt and cumulates the chemical formulae of equilibrium crystalline phases in the cumulate reservoir wallrock and recharge magmas stoped blocks are also output depending on the selected rhyolite melts engine the composition and properties of a possible supercritical fluid phase h2o and or co2 are also tracked forward modeling of theoretical magma systems and suites of igneous rocks provides quantitative insight into key questions in igneous petrology such as mantle versus crustal contributions to terrestrial magmas the record of magmatism preserved in cumulates and exsolved fluids and the chronology of rasfc processes that may be recorded by crystal populations melt inclusions and whole rocks here we describe the design of the mcs software that focuses on major element compositions and phase equilibria mcs phaseeq case studies that involve fractional crystallization magma recharge mixing and crustal contamination of a depleted basalt that resides in average upper crust illustrate the major element and phase equilibria consequences of these processes and highlight the rich array of data produced by mcs the cases presented here which represent an infinitesimal fraction of possible rasfc processes and bulk compositions show that the records of recharge and or crustal contamination may be subtle and are not necessarily those that would be predicted using conventional intuition and simple mass balance arguments mass and energy constrained thermodynamic tools like the mcs quantify the open system evolution of magmas and provide a systematic understanding of the petrology and geochemistry of open system magmatic processes the trace element and isotope mcs computational tool mcs traces is described in a separate contribution part ii

evidence for fault lubrication during the 1999 chi chi taiwan earthquake mw7 6 the ground motion data of the 1999 chi chi taiwan earthquake exhibit a striking difference in frequency content between the north and south portions of the rupture zone in the north the ground motion is dominated by large low frequency displacements with relatively small high frequency accelerations the pattern is opposite in the south with smaller displacements and larger accelerations we analyze the fault dynamics in light of a fault lubrication mechanism using near field seismograms and a detailed rupture model the fault zone contains viscous material e g gouge in which pressure increases following the reynolds lubrication equation when the displacement exceeds a threshold lubrication pressure becomes high enough to widen the gap thereby reducing the area of asperity contact with less asperity contact the fault slips more smoothly suppressing high frequency radiation

probing the structure of the deep continental crust old buried deformed crystalline rocks apparently make up most of the 40 kilometer thick continental crust this part of the earth is poorly explored and constitutes a major frontier of modern earth science two techniques seismic reflection profiling and drilling which were developed by industry for other purposes offer special potential for such exploration seismic profiling of the deep crust by cocorp the consortium for continental reflection profiling has already produced important information including evidence for extensive thin skinned thrusting of older rocks over a continental margin as the corresponding ocean basin closed deep drilling of crystalline rocks of the continents for scientific purposes is so far relatively unexploited in the united states but is already being carried on elsewhere in general big science is likely to become more important in basic geology as this frontier is explored

secondary ca al silicates in plutonic rocks implications for their cooling history secondary ca al silicates are used to constrain the p t x conditions of the very early post magmatic stage of the intermediate to basic hercynian plutonic complexes of charroux civray nw massif central france and fichtelgebirge ne bavaria germany the secondary ca al silicates hydrogarnet prehnite pumpellyite epidote and laumontite form lenses within unaltered or only slightly chloritized biotite hydrogarnet as the first occurring ca al silicate phase crystallizes at temperatures above 340 c the common paragenesis prehnite pumpellyite post dates hydrogarnet and indicates rather narrow ranges of temperature 200 280 c and pressure 2 3 kbar laumontite is formed at the end of ca al silicate crystallization 180 260 c 1 3 kbar mostly in small fractures in association with prehnite and adularia the observed crystallization sequence of the ca al silicates and their stabilities define a retrograde alteration path for the plutonic rocks the ca al silicate assemblage results from an early pervasive alteration of the plutonic rocks by low xco2 fluids during post magmatic cooling subsolidus cooling starts at about 4 kbar at solidus temperatures as indicated by magmatic epidote stability hornblende barometry and fluid inclusion data and continues under slightly decreasing pressure uplift down to 2 3 kbar at 200 280 c prehnite pumpellyite paragenesis this shows that ca al silicate assemblages may be a unique tool to constrain the p t conditions of the subsolidus cooling of intermediate to basic plutonic bodies

timing of low temperature mineral formation during exhumation and cooling in the central alps switzerland abstract construction of the new gotthard rail base tunnel through the central alps provided a truly unique sample of a fissure assemblage formed during exhumation and cooling of the central alps the base of the tunnel is at 500 m a s l and the overburden at the sampling locality amounts to 2000 m the fissure assemblage apophyllite kf laumontite and quartz occurs within the southern aar granite it formed during exhumation and erosion of the alpine orogen apophyllite and laumontite mark very late fissure minerals in the central swiss alps only followed by stilbite hematite and calcite the data from a combined study of 40 ar 39 ar age dating of apophyllite apatite fission track analysis and the petrology of rock samples from tunnel and the from the mountains above the tunnel reflect the late stages of an aging orogen apatite fission track analysis yields an exhumation rate of 0 46 mm yr a cooling rate of 12 3 c m y and a geothermal gradient of 27 c km at the time of apophyllite formation combining these data with the 40 ar 39 ar plateau age of 2 ma for the formation of apophyllite a minimum formation temperature and depth of 68 c at 2550 m below the present day erosion surface follow at this time the position of the sample location was 550 m below the tunnel level assemblage stabilities and computed temperature time evolution of fissures in the aar massif indicate that laumontite formed between 11 and 2 ma ago at temperatures between 180 and 70 c chemical components for forming laumontite were provided from dissolution of minerals of the alpine greenschist facies variscan granitoid rocks of the aar massif basement systematic variations in the composition of laumontite are an effect of decreasing temperature