experimental reactions of amphibolite with boron bearing aqueous fluids at 200 mpa implications for tourmaline stability and partial melting in mafic rocks reactions between hornblende plagioclase amphibolite and acidic and alkaline b bearing aqueous fluids have been investigated by experiments at 475 600 c and 200 mpa at 600 c hornblende calcic plagioclase react to form tourmaline danburite clinopyroxene quartz in acidic fluids containing 0 5 1 0 wt b2o3 tourmaline is precipitated directly from acidic fluids and the reaction is driven by neutralization of fluids by na ca derived from the breakdown of reactant solids the concentration of b2o3 in fluids needed to stabilize tourmaline increases as ph increases above approximately 6 0 and tourmaline is unstable in alkaline fluids ph approximately 6 5 7 0 regardless of b concentration in addition to acid base relations tourmaline stability is favored by comparatively higher activity coefficients for al species in acidic fluids the concentrations of al and si in fluid increase with alkalinity with the eventual production of felsic borosilicate melts through partial melting of the plagioclase component of the amphibolite in seeded experiments tourmaline also contributes components to melt partial melting is evident in the range 500 525 c at 200 mpa in experiments with 8wt b2o3 in fluid as na2b4o7 the experimental results are applied primarily to metasomatic reactions between mafic rocks and borate fluids derived from granitic magmas but tourmaline stability and partial melting in mafic regional metamorphic systems are also discussed briefly

behavior of the southernmost san andreas fault during the past 300 years surficial creep occurs at low rates along the coachella valley segment of the san andreas fault which has not produced a large earthquake during the period of historical record geodetic data indicate however that the crust adjacent to this segment of the san andreas fault is accumulating strain at a high rate furthermore neotectonic and paleoseismic data indicate that the fault does produce very large earthquakes every two to three centuries in view of its long term behavior the occurrence of creep along the surficial trace of the fault in the coachella valley is of particular interest along two short reaches of the san andreas fault in the coachella valley measurements of offset geological deposits and man made structures and from alignment arrays and creep meters show that slip rates of 2 4 mm yr near indio and near the salton sea have persisted for the past three centuries this slow aseismic surficial creep is not a transient precursor to seismic failure of this segment of the fault we suggest that the coachella valley segment of the san andreas fault creeps in its upper few kilometers this behavior may be due to tectonically induced high pore pressures in the coarse sediments that abut the fault

changes in tourmaline composition during magmatic and hydrothermal processes leading to tin ore deposition the cornubian batholith sw england abstract to investigate the potential of tourmaline as a geochemical monitor a comprehensive dataset on major minor and trace element concentrations as well as fe3 fe ratios of tourmaline is presented the dataset includes samples from five plutonic complexes related to diverse magmatic to hydrothermal stages of the cornubian batholith sw england tourmaline composition found in barren and cassiterite bearing samples include all three primary tourmaline groups and tourmaline species with the general endmembers schorl dravite elbaite uvite feruvite foitite and mg foitite based on textures and compositions it is possible to distinguish not only between late magmatic and hydrothermal tourmaline but also between several formation stages hence tourmaline monitors late magmatic processes and the partitioning of elements during exsolution of an aqueous phase for example in hydrothermal tourmaline sn is strongly enriched while ti cr v and sc are depleted compared to late magmatic tourmaline of the same sample several tourmaline generations that precipitated from magmatic fluids can be distinguished with differing major and minor elements and ree patterns depending on the composition of the melt from which they were expelled from strongly zoned tourmaline allows for unraveling the hydrothermal history of a distinct location including ore precipitation the precipitation of sno2 in the study area was probably caused by mixing between acidic reduced sn bearing magmatic fluids and oxidized meteoric fluids which is in agreement with london and manning 1995 and williamson et al 2000 hence the ability of tourmaline composition to monitor changes in sn concentration and redox conditions in hydrothermal fluids has potential as an exploration tool

boron isotope fractionation between tourmaline and fluid an experimental re investigation the fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700 c at 200 mpa and at 500 c 500 mpa tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess in one series of experiments b fluid b tour was 9 after the run in another series it was 0 1 all experiments produced tourmaline as the sole boron bearing solid along with traces of quartz and talc powder xrd and rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline 11b always preferentially fractionated into the fluid for experiments where b fluid b tour was 9 a consistent temperature dependent boron isotope fractionation curve resulted approximated by 11b tour fluid 4 20 1 000 t k 3 52 r2 0 77 and valid from 400 to 700 c no pressure dependence was observed the fractionation 2 7 0 5 at 400 c and 0 8 0 5 at 700 c is much lower than that previously presented by palmer et al 1992 experiments where b fluid b tour was 0 1 showed a significant larger apparent fractionation of up to 4 7 in one of these runs the isotopic composition of handpicked tourmaline crystals of different size varied by 1 3 this is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline thus indicating larger fractionation than observed at equilibrium the effect is eliminated or minimized in experiments with very high boron excess in the fluid we therefore suggest that values given by the above relation represent the true equilibrium fractionations

archean magmatic hydrothermal fluid evolution in the quadrilatero ferrifero se brazil documented by b isotopes la mc icpms in tourmaline abstract in the archean quadrilatero ferrifero district se brazil tourmaline occurs as a major constituent in a leucogranitic intrusion and numerous pegmatitic aplitic veins within magmatic basement complexes as well as in quartzo feldspathic veins in quartz tourmaline rocks tourmalinites and as disseminated grains in the surrounding greenstone belt metasediments the chemical and boron isotope composition of these tourmalines was analysed by electron microprobe and la mc icp ms to determine the origin of the fluids involved and to shed light on the hydrothermal evolution of the region the tourmalines exhibit an overall decrease in fe fe mg ratio and a net increase in cr up to 0 75 wt from tourmaline hosted in the leucogranite the quartzo feldspathic veins the tourmalinites to the disseminated grains in the schists these variations mirror the bulk composition of the host schists and illustrate a strong protolith control on tourmaline major element composition the full range of tourmaline 11b is from 27 1 to 9 2 with a major cluster between 12 and 19 which includes the magmatic tourmaline in the leucogranite 15 2 to 12 5 most of these isotope compositions can be reconciled with a model involving tourmaline growth from late stage exsolved magmatic fluids percolating through the magmatic basement and into the nearby metasediments this model agrees well with the trends of major element compositions as well as with the critical observation that tourmaline occurrence is restricted to the vicinity of the basement complexes 11b values lower than 19 in our dataset are beyond the reach of isotope fractionation during magmatic fluid exsolution and temperature decrease and suggest the presence of a distinct fluid component we propose that an isotopically light fluid was released from mica breakdown in the country rocks during local upper amphibolite facies metamorphism in the dome border shear zone

record in metamorphic tourmalines of subduction zone devolatilization and boron cycling boron concentrations and isotope compositions of fluids and lavas from subduction zone settings show great potential for elucidating mass flux at earth s modern convergent margins however the fluid mineral melt behaviorof b and its two stable isotopes remains relatively poorly understood boron isotope analyses of tourmaline in metasedimentary rocks subducted to 15 90 km depths 1 demonstrate the ability of this mineral to retain information regarding prograde devolatilization history in even highly retrograded rocks and 2 indicate the importance of tourmaline in affecting whole rock b loss and b isotope evolution during subduction zone metamorphism the b lost from micas during metamorphism of subducting sedimentary rocks and altered oceanic crust is isotopically more enriched in 1 1 b than the b retained in the micas beneath forearcs and volcanic arcs the b from micas is either removed from the subduction zone rocks via metamorphic fluids or sequestered by growing tourmaline in which the b can be entrained to even greater depths here we demonstrate that these metamorphic fluids could contribute to the relatively high 811b signatures observed in most arc lavas and the across arc trends of decreasing 1 1 b observed in several arcs

leveling precision and bench mark motions pinon flat observatory california the reliability of relative vertical motions detected by levelings of bench marks installed at pinyon flat is highly dependent on the kinds of bench marks installed for monitoring purposes the most stable marks are the end monuments for two 535 m long fluid tiltmeters nine direct measurements of average slope between tiltmeter end monuments agree to within a standard deviation about the mean of 0 2 mm 0 4 rads comparable to the slope measured by the tiltmeters themselves motions of class b steel rod marks are random with standard deviations ranging from 0 5 to 3 2 mm averaging 1 0 mm the motions of nearly all rod marks decreased greatly in the fourth year evidently because of a time dependent establishment of stability in the decomposed granite fundament other kinds of bench marks are stable between 0 5 and 0 8 mm tectonic tilt is not revealed in 15 levelings of the array in 4 years consistent with the tiltmeters but the random bench mark motions dominate the errors in the estimated tilt

tourmaline in a low grade clastic metasedimentary rock an example of the petrogenetic potential of tourmaline detrital tourmaline grains and their associated tourmaline overgrowths provide a means to unravel the provenance and petrogenetic history of low grade clastic metasedimentary rocks evidence derives from tourmaline grains found in a lithic wacke metamorphosed to chlorite zone conditions the detrital tourmaline cores are diagnostic indicators of the source rocks of the sediment whereas the overgrowths record both diagenetic and metamorphic reactions in the rock tourmaline grains consist of a detrital core surrounded by asymmetric overgrowths comprised of inner and outer rims abrupt chemical discontinuities between each of these zones implies that volume diffusion within tourmaline was minor under the conditions of formation compositions of the detrital cores vary widely yet can be correlated with source rock types that are consistent with lithic fragments recognizable in the metawacke at either the analogous or antilogous pole inner rim compositions proximal to the detrital cores converge despite the substrate tourmaline composition indicating an approach to chemical equilibrium however significant dufferences in al and x site vacancies at the expense of mg na and ti between the analogous and antilogous poles of the inner rims demonstrate the presence of significant amounts of compositional polarity outer rim compositions at either pole also converge but compositional polarity between the analogous and antilogous poles persists the presence of the inner and outer rims separated by a compositional discontinuity suggests punctuated evolution of the overgrowth this implies that boron was sporadically available during diagenesis and metamorphism based on boron contents of minerals this may correspond to a mechanism such as boron release due to polytypic change of illite or consumption of illite and or muscovite as such tourmaline growth stages may serve as a monitor of chemical reactions in low grade metamorphic rocks

disequilibrium partitioning of oxygen isotopes associated with sector zoning in quartz fractionation of oxygen isotopes during crystal growth is commonly assumed to be an equilibrium process we present evidence here that large variations in delta 18 o values in a zoned vein quartz crystal are the result of disequilibrium partitioning between fluid and crystal within a single crystal vith well developed concentric and sector zoning delta 18 o values determined with laser extraction techniques on milligram to submilligram sized samples range from 4 7 parts per thousand to 7 3 parts per thousand core to rim variations within single growth sectors fluctuate by 2 6 parts per thousand whereas differences between adjacent sectors along the same growth zone can exceed 2 0 parts per thousand in contrast fluid inclusion homogenization temperatures and salinities are relatively constant and show no effect of grow th or sector zoning differences in delta 18 o values between sectors along the same growth zone cannot result from variations in the oxygen isotope composition of the fluid and strongly suggest disequilibrium partitioning of oxygen isotopes between fluid and the growing crystal the cause of this disequilibrium is believed to be due to differences in surface structure and or growth mechanisms between nonequivalent faces

fault slip in southern california measurements of slip on major faults in southern california have been performed over the past 18 yr using principally theodolite alignment arrays and tautwire extensometers they provide geodetic control within a few hundred meters of the fault traces which complements measurements made by other techniques at larger distances approximately constant slip rates of from 0 5 to 5 mm yr over periods of several years have been found for the southwestern portion of the garlock fault the banning and san andreas faults in the coachella valley the coyote creek fault the superstition hills fault and an unnamed fault 20 km west of el centro these slip rates are typically an order of magnitude below displacement rates that have been geodetically measured between points at greater distances from the fault traces exponentially decaying postseismic slip in the horizontal and vertical directions due to the 1979 imperial valley earthquake has been measured it is similar in magnitude to the coseismic displacements analysis of seismic activity adjacent to slipping faults has shown that accumulated seismic moment is insufficient to explain either the constant or the decaying postseismic slip thus the mechanism of motion may differ from that of slipping faults in central california which move at rates close to the plate motion and are accompanied by sufficient seismic moment seismic activity removed from the slipping faults in southern california may be driving their relatively aseismic motion

nearfield interseismic vertical strain on the central garlock fault southern california 1984 1991 repeated precise leveling of fault crossing arrays at two sites on the central and western parts of the garlock fault discloses minor height changes of a few centimeters across the fault in seven years during that time the seismicity of the fault has been very low relative to other parts of california although other investigators have measured a millimeter or two of horizontal displacement per year near each of the leveling arrays the vertical changes measured in this study probably result from nontectonic differential subsidence across the fault due to the effects of the 1985 1991 drought in southern california the vertical displacement at cameron could turn out to be tectonic but at the koehn lake site the subsidence may be related to nearby pumping of groundwater the changes and rates of heights reported here should not be extrapolated in time or space because of the relatively short period of observations and because these sites measure only minuscule parts of the 250 km long fault

trace element systematics of tourmaline in pegmatitic and hydrothermal systems from the variscan schwarzwald germany the importance of major element composition sector zoning and fluid or melt composition article an extensive data set on the compositional variation of tourmaline from granitic pegmatites from migmatitic gneisses and from various types of hydrothermal veins from the schwarzwald germany is provided the investigated tourmalines are members of the alkali and x vacant groups representing mostly dravite schorl solid solutions with some analyses belonging to the foitite mg foitite series oxygen isotope data on quartz tourmaline pairs indicate formation temperatures between 550 and 350 c for most of the quartz tourmaline veins most of the tourmalines show strong sector zonation fractionating certain major e g na mg minor e g ti ca and trace elements e g sr pb ree among the different crystallographic sectors of the crystals we conclude that comparison of tourmaline compositions for petrogenetic interpretations must be based on the concentrations in the neutral a sector in order to eliminate the effects of intra crystalline fractionation most trace element contents vary over several orders of magnitude with median concentrations generally be tween 0 1 and 10 g g the highest concentrations are found for zn v sr sc sn and li median concentrations of several tens to hundreds of g g whereas very low median concentrations b0 1 g g were found for u th bi tl and cs the concentration of several trace elements e g sr ree co correlates with the major element composition of the tourmaline which implies potential crystal chemical effects on their incorporation conse quently the general assumption that tourmaline is a passive monitor for the chemical compositions of the melts or fluids from which it crystallizes has to be questioned nevertheless our study demonstrates that the trace element composition of tourmaline allows to distinguish between geochemically distinct fluid sources and the trace element composition of tourmaline may therefore be used to unravel the chemical complexity of granite related hydrothermal systems

tourmaline geochemistry and δ11b variations as a guide to fluid rock interaction in the habachtal emerald deposit tauern window austria tourmalines from the habachtal emerald deposit in the eastern alps formed together with emerald in a ductile shear zone during blackwall metasomatism between pelitic country rocks and a serpentinite body electron microprobe and secondary ion mass spectrometric sims analyses provide a record of chemical and b isotope variations in tourmalines which represent an idealized profile from metapelites into the blackwall sequence of biotite and chlorite schists tourmaline is intermediate schorl dravite in the country rock and become increasingly dravitic in the blackwall zones while f and cr contents increase and al drops metasomatic tourmaline from blackwall zones is typically zoned optically and chemically with rim compositions rich in mg ti ca and f compared with the cores the total range in 11b values is 13 8 to 5 1 and the within sample variations are typically 3 5 both of these ranges are beyond the reach of closed system fractionation at the estimated 500 550 c conditions of formation and at least two boron components with contrasting isotopic composition are indicated a key observation from tourmaline core analyses is a systematic shift in 11b from the country rock 14 to 10 to the inner blackwall zones 9 to 5 we suggest that two separate fluids were channeled and partially mixed in the habachtal shear zone during blackwall alteration and tourmaline emerald mineralization a regional metamorphic fluid carried isotopically light boron as observed in the metapelite country rocks the other fluid is derived from the serpentinite association and has isotopically heavier boron typical for morb or altered oceanic crust

surficial offsets on the central and eastern garlock fault associated with prehistoric earthquakes geomorphic features offset along the central and eastern garlock fault record the amount of surface slip associated with prehistoric earthquakes along the easternmost 90 km of the fault the smallest offsets cluster around 2 3 m of left lateral slip apparently associated with the most recent earthquake on this portion of the fault larger offsets along this part of the fault especially in pilot knob valley cluster around values consistent with 2 4 m of slip in each of the past several events farther west south of el paso mountains offset geomorphic features suggest that each of the past two earthquakes on this stretch of the garlock fault was produced by about 7 m of slip whereas the third event back was produced by about 4 m of slip vertical displacements of geomorphic features range from 0 to 30 of the left lateral offsets within pilot knob valley along the southern side of the slate range vertical displacements are consistently up on the northern side whereas within the avawatz mountains both north and south side up vertical displacements are present on the basis of the geomorphic offsets the geometry of the garlock fault and the precedents set by historical strike slip earthquakes elsewhere a number of different rupture patterns are plausible these range from rupture of the entire garlock fault in a single event with a maximum magnitude of about mw 7 8 to separate rupture of the western segment and of the central and eastern segments combined with approximate magnitudes mw 1 1 and mw 7 5 respectively to separate rupture of even shorter segments producing earthquakes of magnitudes mw 6 6 to mw 7 5 in conjunction with available slip rates for the garlock fault the geomorphic offsets suggest that average recurrence intervals are probably within the range of 600 1200 years south of el paso mountains about 200 750 years in searles valley about 200 1300 years in pilot knob valley and about 200 3000 years near leach lake and in the avawatz mountains

geochemistry of hydrothermal tourmaline from iocg occurrences in the great bear magmatic zone implications for fluid source s and fluid composition evolution abstract tourmaline crystallized during iron oxide and alkali calcic alteration and iocg mineralization in the great bear magmatic zone canada within the samples analyzed tourmaline occurs as small crystals in the groundmass of hydrothermal breccias southern breccia and contact lake or as large prismatic crystals in quartz ore mineralogy veins contact lake devries lake and nico the tourmaline from these localities is predominantly shorlitic in composition with minor dravitic uvitic and feruvitic components the boron isotopic composition ranges from 15 to 5 with the majority of values between 15 and 10 the lack of variation among samples supports a common fluid source across the belt for the metasomatic hydrothermal systems these results are isotopically similar to global magmatic and non marine evaporitic reservoirs and lighter than seawater and marine sedimentary rocks the 11b results support a single fluid iocg deposit model for the systems studied wherein metasomatic hydrothermal fluids derived by magmatism ascend and evolve over time through fluid rock interactions

detrital metamorphic and metasomatic tourmaline in high pressure metasediments from syros greece intra grain boron isotope patterns determined by secondary ion mass spectrometry the boron isotopic composition of zoned tourmaline in two metasediments from the island of syros determined by secondary ion mass spectrometry sims reflects the sedimentary and metamorphic record of the rocks tourmaline from a silicate bearing marble contains small 20 m detrital cores with highly variable 11b values 10 7 to 3 6 pointing to a heterogeneous protolith derived from multiple sources the sedimentary b isotopic record survived the entire metamorphic cycle with peak temperatures of 500 c prograde to peak metamorphic rims are homogeneous and similar among all analysed grains 11b 0 9 the varying 11b values of detrital cores in the siliceous marble demonstrate that in situ b isotope analysis of tourmaline by sims is a potentially powerful tool for provenance studies not only in sediments but also in metasediments a meta tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin 11b 3 3 and prograde to peak metamorphic overgrowth zones 1 6 fe rich rims formed during influx of b bearing fluids under retrograde conditions show strongly increasing 11b values up to 7 7 towards the margins of the grains the 11b values of metamorphic tourmaline from syros formed in mixed terrigenous marine sediments reflect the b signal blended from these two different sources and was probably not altered by dehydration during subduction

boron isotope geochemistry of metasedimentary rocks and tourmalines in a subduction zone metamorphic suite abstract in order to understand the behavior of boron b and its isotope fractionation during subduction zone metamorphism b contents and isotopic compositions together with major element compositions were determined for metasedimentary rocks and tourmalines from the sambagawa metamorphic belt central shikoku japan no systematic changes in whole rock b content and isotope composition of the metasediments were observed among the different metamorphic grades indicating the lack of a bulk fluid rock b isotope fractionation as a result of devolatilization both modal abundance and grain size of tourmaline increase with increasing metamorphic grade in contrast b contents in muscovite and chlorite decrease with increasing metamorphic grade these observations combined with mass balance calculations of b suggest the formation of tourmaline during progressive metamorphism from metamorphic fluids containing b mainly derived from muscovite and subordinately from chlorite without allowing significant net removal of b from the metasedimentary rocks tourmalines in the higher grade metasedimentary rocks have zonal structure of b isotope and major element composition with decreasing 11 b and increasing mg mg fe from the inner rim core to the outer rim the change of mg mg fe in the tourmalines with increasing grade is paralleled by similar variation in chlorite these observations suggest that the growing tourmalines record the progressive evolution of the b isotopic composition of the metamorphic fluid in the outermost rims preserving the isotope signature of peak metamorphic p t fluid conditions based on the above observations the 11 b of the tourmaline is thought to have been nearly identical to that of the metamorphic fluid resulting in the apparent b isotopic fractionation factor between metamorphic fluid and whole rock 11 b 10 b fluid 11 b 10 b whole rock which decreases from 1 007 0 003 to 1 001 0 003 from chlorite to biotite zone metamorphism such results together with the formation of tourmaline from and sequestering of b in metamorphic fluids may lead to less b isotopic fractionation as a result of subduction zone devolatilization than noted in suites containing less tourmaline this therefore makes it possible to transport b isotopic signatures which ultimately reflect earth s surface materials to the deep mantle perhaps resulting in mantle b isotope anomalies near convergent margins

tourmaline at diagenetic to low grade metamorphic conditions its petrologic applicability article i nfo tourmaline developed under low temperature conditions b 300 c typically has distinctive morphological and chemical characteristics that reveal significant information about the environments in which they crys tallize under diagenetic conditions tourmaline can develop as overgrowths on detrital tourmaline cores or as new authigenic crystals tourmaline as monopolar crystal overgrowths is found in sandstones shales conglomerates dolostones and limestones nucleating exclusively at the positive end of the c axis cpole on the detrital grain a feature related to the mineral s polar nature these overgrowths tend to have compo sitions dominated by x site vacant tourmaline species e g foitite and can be linked to growth in aqueous environments low in na with other chemical characteristics related to the host rocks as temperature in creases tourmaline overgrowths develop at both the cpole andc pole but continue to exhibit a signif icant degree of morphological and chemical asymmetries these differences at either pole diminish as a function of increasing temperature such that it can be used as an intramineral geothermometer authigenic tourmalines without detrital tourmaline nuclei are found in many sedimentary or weakly meta morphosed metasedimentary rocks as well as fluid dominated geothermal systems here tourmalines are commonly foititic but have mg fe contents influenced by the host rock composition low temperature tour malines developed in hypersaline environments e g salt domes have distinct chemical characteristics high na fe 3 and w o and follow a trend between oxy dravite and povondraite o p trend this composi tional trend can be used as a guide to indicate tourmaline development within low temperature hypersaline environments and appears to be diagnostic of an oxidizing environment with high na in the fluid and high sa linity with the resulting reduction of the activity of h2o the o p trend is retained in some meta evaporite de posits that are relatively high grade and is found in tourmaline from some types of economically important metal deposits although tourmalines in low temperature environments are largely overlooked they have po tential to be a useful indicator of the chemical and thermal environments in a regime largely absent of such indicators

on the occurrence and boron isotopic composition of tourmaline in ultra high pressure metamorphic rocks abstract the extensive p t stability and the high chemical variability of tourmaline tur together with its common occurrence in metasediments proves its high potential for petrological and isotope geochemical studies on fluid rock interaction in subduction and collision related rocks this paper reviews the occurrence major element chemistry and boron isotopic composition of tur in high and ultrahigh pressure metamorphic uhpm rocks in addition it presents a new discovery of coesite bearing tur schorl from the erzgebirge germany as well as tur dravite related to the retrograde history of coesite and diamond bearing rocks from the erzgebirge and the kokchetav massif kazakhstan the scarce data on worldwide occurrences of u hpm tur reveal a high occupation of the crystallographic x site dominated by na and the possible presence of excess b with little further distinctiveness in its major element composition when compared with tur from medium grade rocks high k 2 o contents in tur are probably not related to uhp growth or equilibration the b isotopic composition of u hpm tur ranges in 11 b from 16 to 1 with many samples in or below the range of continental crust in contrast tur formed during retrograde fluid influx typically shows high 11 b values up to 28 suggesting heavy b fluids infiltrating the exhuming u hpm units coesite inclusions in tur characterized by raman spectroscopy are regarded as the best indicator for its uhp stability supplementary material analytical methods tourmaline compositions and boron isotope values are available at http www geolsoc org uk sup18354

modern ground failure in the garlock fault zone fremont valley california modern ground failures ranging from renewed displacement on 2 5 km long fault scarps to 1 km long tension cracks occur in fremont valley california most of the failures formed along pre existing holocene fault scarps that are part of the tectonically active garlock fault system the failures began to form in the 1960s and currently affect an area of 17 km 2 that is coincident with ground water level decline induced by pumping for crop irrigation several observations indicate that these failures were caused by water level decline rather than natural tectonism first modern ground failure began after water level started to decline and was restricted to the area affected by decline land subsidence was associated with this decline and appears to be caused by aquifer compaction second geodetic monitoring from 1977 to 1982 of faults near the center of the cone of depression demonstrated that fault creep occurred during periods of seasonal water level decline and stopped during periods of seasonal water level recovery by contrast faults near the margin of the cone of depression where water levels declined at a constant rate moved at a steady rate third surface strain fields near failures suggest that subsurface fault associated deformation was restricted to aquifer level depths and fourth seasonal rebound of the land surface across one fault was caused by elastic expansion of the aquifer system that was induced by large seasonal water level recovery

magmatic hydrothermal fluids and volatile metals in the spirit lake pluton and margaret cu mo porphyry system sw washington usa the halogen bearing minerals tourmaline amphibole and biotite formed during magmatic hydrothermal processes associated with the late stage cooling of the spirit lake granitoid pluton mt st helens wa and with the younger sulphide mineralised rocks of the margaret cu mo porphyry deposit located entirely within the pluton major and trace element discrimination suggests that one tourmaline population crystallised from fractionated late stage melt pockets in granodiorite monzogranitic dykes of the pluton these coarse euhedral oscillatory and complexly sector zoned uvite tourmalines span a limited range in mg mg fe mg space 0 4 0 7 apfu and show the highest ti ca f nb and ta contents and low x site vacancies 0 6 apfu lower ca and f contents and the highest li as and hree contents 80 ppm li 1200 ppm as this population appears to record direct rapid crystallisation from magmatic meteoric fluid s bearing the signature of the breakdown of primary feldspars and pyroxenes with fluid exsolution from fractionated melt patches likely triggered by the formation of the previous generation of tourmaline mineralised porphyry deposit tourmaline compositions from the stockwork span a much larger range in mg space 0 05 0 9 apfu and are almost entirely ca free x sites of these schorl tourmalines are dominated by na or vacancies and the y sites are strongly fe enriched the highest mn and zn concentrations 4000 and 1000 ppm respectively potentially reflect the composition of mineralising fluids during ore deposition a number of boron isotopic analyses yield predominantly heavy boron but 11b values range from 5 2 to 6 2 and average 1 4 whilst most plutonic tourmalines conform to reported a and c sector element partitioning models those from the mineralised porphyry show large and variable sector fractionation differences suggesting that external controls may also be important wider evidence for late stage pervasive metasomatism by halogen bearing exsolved fluid s is provided by the high mg 70 secondary amphiboles and biotites from within the spirit lake pluton where the amphiboles are clear replacement products of primary pyroxenes fluid halogen fugacity ratios calculated from the biotite compositions overlap with other global mineralised porphyry systems despite not being immediately associated with sulphide ores the evidence suggests complex fluid processes and the coincidental development of the mineralised porphyry system within the pluton heat fluids and metals were therefore likely supplied by a later phase of magmatism unrelated to the consolidation of the main spirit lake granitoid these new constraints on magmatic hydrothermal fluid signatures have wider applicability to potentially tracing proximal barren and mineralised processes and for distinguishing between formation mechanisms for primary and secondary halogen bearing minerals

hourglass sector zoning in metamorphic tourmaline and resultant major and trace element fractionation a new type of sector zoning with an hourglass shape has been identified in metamorphic tourmalines that formed under a wide variety of physical and chemical conditions the two sectors in the c direction are not equivalent due to asymmetry in the crystal structure of tourmaline along the c axis the c sector is characterized by low concentrations of ti ca mg and na although al is high and has a pale commonly blue or pale green color conversely the c sector is low in mg and al and high in ca fe and ti the latter two causing the dark brown color of this sector the a sector has intermediate characteristics and probably approximates a sector free tourmaline thin sectioning of these sector zoned tourmalines perpendicular to the c axis can produce three types of apparent radial zoning patterns blue green cores dark brown cores or no distinct cores these apparent cores will further vary in relative diameter depending on the sectioning level furthermore core boundaries can be straight or ragged depending on whether the relative growth speeds for the different faces was constant or variable these textures have been used to argue for a prograde or detrital origin of tourmaline cores however sector zoning is a more appealing explanation for most of these textures and can further explain the textural resemblance among metamorphic tourmalines from highly variable bulk rock composition metamorphic history and mineral paragenesis the sector zoning that is described here develops by preferential uptake of elements on the r growth plane resulting from a combined effect of differences in surface charge and morphology of this plane in the c and c directions this leads to the preferential incorporation of more positively charged elements in the c direction and a preference for a vacant x site in the c direction because the compositional differences among the sectors are pronounced in both major and trace elements and in the same order of magnitude as growth zoning variability the presence of sector zoning must be established and taken into account when making inferences from tourmaline chemistry

seismicity of the garlock fault california the garlock fault is a 265 km long left slip fault striking northeastward from the san andreas fault in southern california relocations of earthquakes that occurred from 1932 to 1981 on and near this major fault were made using the master event technique the spatial distribution of seismicity along the fault is different west and east of its midpoint near rand where the largest en echelon offset and a marked change in strike occur these two segments also display distinct geologic features and different seismic and aseismic behavior the 150 km long segment west of rand has shown continuous low seismic activity during the past 50 yr well documented aseismic creep and has a relatively complex fault trace in contrast the 155 km long segment east of rand has very few small earthquakes no demonstrable creep and a simpler fault trace p wave first motion studies substantiate predominantly left slip motion along the garlock fault overall energy release during this 50 yr period gives a seismic moment rate of 2 75 10 21 dyne cm yr much lower than that inferred from holocene geologic offsets thus indicating that the garlock fault currently represents a temporal seismic gap and that the potential exists for large earthquakes if behavior of the garlock fault is similar to that of the san andreas the western segment of the fault can be compared with the central creeping segment of the san andreas and the eastern segment with those segments broken by the 1857 and 1906 earthquakes thus larger events might be expected on the eastern segment than on the western segment or if the entire fault breaks during a single event larger displacements toward the east

boron sulphur and copper isotope systematics in the orogenic gold deposits of the archaean hattu schist belt eastern finland abstract the hattu schist belt is located in the western part of the archaean karelian domain of the fennoscandian shield the orogenic gold deposits with au bi te geochemical signatures are hosted by ne sw n s and nw se oriented shear zones that deform 2 76 2 73 ga volcanic and sedimentary sequences as well as 2 75 2 72 ga tonalite granodiorite intrusions and diverse felsic porphyry dykes mo w mineralization is also present in some tonalite intrusions both separate from and associated with au mineralization somewhat younger unmineralized leucogranite intrusions 2 70 ga also intrude the belt lower amphibolite facies peak metamorphism at 3 5 kbar pressures and at 500 600 c temperatures affected the belt at around 2 70 ga and post date hydrothermal alteration and ore formation in this study we investigated the potential influence of magmatic hydrothermal processes on the formation of orogenic gold deposits on the basis of multiple stable isotope b s cu studies of tourmaline and sulphide minerals by application of in situ sims and la icp ms analytical techniques crystal chemistry of tourmaline from a mo w mineralization hosted by a tonalite intrusion in the hattu schist belt is characterized by fe3 al3 substitution indicating relatively oxidizing conditions of hydrothermal processes the range of 11b data for this kind of tourmaline is from 17 2 to 12 2 the hydrothermal tourmaline from felsic porphyry dyke swith gold mineralization has similar crystal chemistry e g dravite povondraite compositional trend with fe3 al3 substitution and 11b values between 19 0 and 9 6 the uvite foitite compositional trend and 11b values between 24 1 and 13 6 characterize metasomatic hydrothermal tourmaline from the metasediment hosted gold deposits composition of hydrothermal vein filling and disseminated tourmaline from the gold bearing shear zones in metavolcanic rocks is transitional between the felsic intrusion and metasedimentary rock hosted hydrothermal tourmaline but the range of average boron isotope data is essentially identical with that of the metasediment hosted tourmaline rock forming magmatic tourmaline from leucogranite has 11b values between 14 5 and 10 8 and the major element composition is similar to that of the metasediment hosted tourmaline the range of 34svcdt values measured in pyrite chalcopyrite and pyrrhotite is from 9 1 to 8 5 which falls within the typical range of sulphur isotope data for archaean orogenic gold deposits in the hattu schist belt positive 34svcdt values characterize metasediment hosted gold ores with sulphide parageneses dominated by pyrrhotite and arsenopyrite the 34svcdt values are both positive and negative in ore mineral parageneses within felsic intrusive rocks in which variable amounts of pyrrhotite are associated with pyrite purely negative values were only recorded from the pyrite dominated gold mineralization within metavolcanic units therefore the shift of 34svcdt values to the negative values reflects precipitation of sulphide minerals from relatively oxidizing fluids the range of measured 65cunbs978 values from chalcopyrite is from 1 11 to 1 19 positive values are common for mineralization in felsic intrusive rocks and negative values are more typical for deposits confined to metasedimentary rocks positive and negative 65cunbs978 values occur in the ores hosted by metavolcanic rocks there is no correlation between sulphur and copper isotope data obtained in the same chalcopyrite grains evaluation of sulphur and boron isotope data together and comparisons with other archaean orogenic gold provinces supports the hypothesis that the metasedimentary rocks were the major sources of sulphur and boron in the orogenic gold deposits in the hattu schist belt variations in major element and boron isotope compositions in tourmaline as well as in the 34svcdt values in sulphide minerals are attributed to localized involvement of magmatic fluids in the hydrothermal processes the results of copper isotope studies indicate that local sources of copper in orogenic gold deposits may potentially be recognized if the original distinct signatures of the sources have not been homogenized by widespread interaction of fluids with a large variety of rocks and provided that local chemical variations have been too small to trigger changes in the oxidation state of copper during hydrothermal processes

boron isotope systematics of tourmaline formation in the sullivan pb zn ag deposit british columbia canada abstract we report here the results of 54 boron isotope analyses of tourmaline associated with the giant sullivan pb zn ag deposit in southeastern british columbia canada the 11 b values range from 11 1 to 2 9 which is almost as great as the range found worldwide in tourmalines from 33 massive sulfide deposits and tourmalinites in dominantly clastic metasedimentary terranes the major control on the overall 11 b values of the sullivan tourmalinites is the boron source potential controls over the large range of the data also include 1 differences in formation temperatures of the tourmalinites 2 different stages of tourmaline formation 3 variations in the proportions of dissolved boron incorporated into the tourmaline rayleigh fractionation 4 seawater entrainment and 5 post depositional metamorphism the boron isotope data at sullivan are consistent with boron derivation from leaching of footwall clastic sediments however the great abundance of tourmaline in the sullivan deposit suggests that the local clastic sediments were not the sole source of boron and we argue that non marine evaporites buried deep below the orebody are the most viable source of this additional boron it is likely that some of the variation in tourmaline 11 b values reflect mixing of boron from these two sources comparison of the potential effects of these controls with geologic and other geochemical evidence suggests that major causes for the wide range of 11 b values measured at sullivan are seawater entrainment and rayleigh fractionation although in places post depositional alteration and thermal metamorphism were important in determining 11 b values of some of the recrystallized tourmalinites

studies of multibaseline spaceborne interferometric synthetic aperture radars the authors have utilized a set of seasat synthetic aperture radar sar data that were obtained in nearly repeat ground track orbits to demonstrate the performance of spaceborne interferometric sar insar systems an assessment of the topography measurement capability is presented a phase measurement error model is described and compared with the data obtained at various baseline separations and signal to noise ratios finally the implications of these results on future spaceborne insar design are discussed

dynamics of fault creep observations along the surface traces of active faults in california and elsewhere indicate that tectonic displacement can occur as seismic slip or as aseismic fault creep fault creep occurs as secular displacement and as displacement episodes called creep events which last a few hours to days and include from a millimeter or less to a few tens of millimeters of displacement instrumental measurements of displacement versus time during creep events show that many events have a characteristic simple form including a steep beginning followed by a gradual decay in the rate of displacement some creep events display small amounts of precursory slip and many seem to be composed of several discrete simple events propagation of creep events along the san andreas calaveras and imperial faults in california has been inferred from the nearly simultaneous observation of creep events at nearby creepmeters and from kinematic modeling of continuous measurements of strain during creep events fault creep can be viewed as arising from the interplay of three factors stress applied to the fault from external sources stress caused by the geometry and distribution of displacement on the fault arising from the elastic response of the surrounding medium to the displacements within the anelastic fault zone itself and the constitutive relations characterizing the resistance to slip on the fault analytic solutions are presented for a simple rectangular dislocation quasi static model of nonpropagating fault creep assuming viscous and quasi plastic power law creep fault zone rheology and for a multi element composed of several rectangular or striplike dislocation surfaces quasi static model assuming a viscous rheology viscous rheology implies solutions composed of exponentials that decay with time the simple one element quasi plastic model is in agreement with the form of creep events observed at melendy ranch california a matrix formulation is presented to calculate dislocation stresses on a fault zone in a half space or plate the formulation involves the division of the dislocation surface into strips or rectangles and the use of published solutions to calculate the stress resulting from displacement on each individual element results from the matrix method agree with analytic results for equilibrium displacements on stress free cracks the matrix formulation is then used as the basis for a numerical method to simulate one and two dimensional propagating creep assuming a quasi plastic rheology on the fault zone results from this method agree reasonably well with observations of afterslip from the 1966 parkfield 1975 oroville and 1979 imperial valley california earthquakes and of a propagating creep event observed along the southern calaveras fault central california during july 1977 this method of analysis and the assumption that creep at each point on the fault zone follows a power law rheology after the applied stress reaches a spatially varying yield stress can explain the secular and episodic nature of fault creep afterslip the simple shape of some individual events and the multiple composite shape of others and the propagation of creep events on the southern calaveras fault observations of propagating creep indicate a yield stress near zero at the surface and throughout much of the fault zone however they also indicate the presence of a zone at a depth of about 0 5 km and about 5 km long with a yield stress of about 15 bars 1 5 mpa the methods of solution presented here should be applicable to many problems in the dynamics of faulting

topographic mapping from interferometric synthetic aperture radar observations interferometric synthetic aperture radar observations provide a means for obtaining high resolution topographic terrain maps from data acquired simultaneously at two slightly displaced antennas calculation of the three dimensional coordinates of all the points in a radar image can be made from the combination of along track slant range and interferometer fringe measurements thus the result compensates for the layover exhibited by conventional radar maps and removes the false targets generated by multiple signal paths to a given object in the scene we have derived a topographic map of a portion of the san francisco bay area utilizing data that were recorded by a radar system mounted on a nasa cv990 aircraft and processed by a general purpose digital computer this map displays the height above sea level of a region approximately 11 km by 10 km in size sampled on an 11 m pixel grid uncertainties in the estimated height result from imprecise knowledge of the observational geometry radar bandwidth limitations and finite signal to noise ratios for our system each factor contributed approximately 3 4 m to a relative rms error of about 6 m additional global errors of the order of 10 m can result from inaccurate monitoring of aircraft attitude the statistical variation of the height measurements from the ocean portion of the map which we can presume to be quite flat is 2 10 m rms which is consistent with the theoretical estimate comparison of our results with u s geological survey contour maps indicates a high degree of correlation between the two sets of altitude data

evolution of compositional polarity and zoning in tourmaline during prograde metamorphism of sedimentary rocks in the swiss central alps the compositional evolution of tourmaline from diagenetic to lower amphibolite facies conditions was investigated in two metasedimentary units redbed and black shale formations along a traverse across the central alps with increasing metamorphism three distinct rim zones grew around detrital tourmaline cores simultaneously with the development of prismatic neoblasts detrital cores and all successive rim zones are preserved in the amphibolite facies rocks as indicated by whole rock data the b required for tourmaline growth was released from illite and muscovite and was not introduced from external sources the studied samples of tourmaline exhibit compositional polarity i e their compositions are different at the opposite ends of the c axis the compositional difference between the two poles can be expressed by the substitutions na mg 0 al and 2al ti mg with the positive pole always richer in al and having more x site vacancies both chemical and optical polar effects are most pronounced in the internal rim zones and become less prominent toward the external zones the systematic prograde compositional trends are depicted in a vector space for li poor tourmaline at low grade conditions the tourmaline composition is clearly controlled by the host rock composition but with increasing metamorphic grade the compositions of tourmaline from a variety of rocks converge the data show that in the central alps increasing metamorphic grade is reflected by increases in ca ca na and mg mg feh a decrease in fe3 and an increase in the occupancy of the x site of tourmaline

geodetic evidence for aseismic reverse creep across the teton fault teton range wyoming the valley block hanging wall of the central segment of the teton fault rose 8 plus minus 0 7 mm during 1988 and 1989 relative to the mountain block west of the fault a displacement opposite to that expected on a normal fault the height change is based on first order leveling data over a 21 2 km long fault crossing line of 42 permanent bench marks established and initially surveyed in 1988 and resurveyed in 1989 the rapid height change took place across a 1 200 m wide zone coincident with the steep escarpment at the base of the range front including the surface trace of the east dipping teton fault a major active range front normal fault bounding the east side of the teton range at the northeastern edge of the basin and range province the total stratigraphic offset across the fault as much as 9 km accumulated over the last 7 to 9 million years quaternary fault scarps up to 52 m in height cut pinedale about 14 000 yr glacial and younger fluvial alluvial deposits indicating that the teton fault has been the locus of several large scarp forming earthquakes in the past 14 000 years and it exhibits up to 25 m of latest quarternary displacement where crossedmore by the level line although the relative uplift of the hanging wall may be local and unique to the teton fault this unexpected observation of aseismic reverse creep may have a variety of tectonic and non tectonic causes including hydrologic effects aseismic fault creep or tilt and pre seismic dilation less

boron isotope and light element sector zoning in tourmaline implications for the formation of b isotopic signatures hourglass sector zoning in metamorphic tourmaline is known to effectively fractionate the major and trace elements between different sectors producing three distinct compositions at the growth surface here we show that the light elements li be h and b as well as the 11 b signature are also affected by sector zoning the sector enrichment in elements is controlled by a dual process of initial preference due to growth surface charge and morphology followed by consecutive charge balance controlled enrichment the light elements especially b and h appear to act as charge balance cations in this mechanism with a preferred b 3 for si 4 and o 2 for oh substitution in the c sector a lighter 11 b signature d c c 1 8f0 6x accompanies this increase in b iv in the c sector in line with the lighter signatures for b iv compared to b iii in minerals however it exceeds this theoretical fractionation by a factor of 10 although we have not identified a definite process that is responsible for this fractionation it may be related to local variations in host medium along the growth surface resulting from preferred uptake of elements these observations show that 11 b signatures in tourmaline are not an independent measure of its host environment but also a function of mineral composition and the 3 dimensional zoning variations herein 2007 elsevier b v all rights reserved

terrain height measurement accuracy of interferometric synthetic aperture radars presents a simple expression for the accuracy with which an interferometer synthetic aperture radar ifsar can measure terrain elevation the expression derived analytically and confirmed by monte carlo simulation accounts for thermal noise resolution cell size terrain slope and roughness volume scattering above the terrain radar terrain geometry interferometer baseline and radar frequency this paper takes a glint approach to assessing the impact of scatterers distributed in angle the results show that there is a residual uncertainty in the height of a pixel due to its angular extent even when the signal to noise ratio is very large the analysis identifies an optimum range resolution for minimizing the height uncertainty for a particular terrain slope

late magmatic immiscibility during batholith formation assessment of b isotopes and trace elements in tourmaline from the land s end granite sw england quartz tourmaline orbicules are unevenly distributed in the roof segment of the land s end granite sw england this study shows that the orbicules formed from an immiscible hydrous borosilicate melt produced during the late stages of crystallization and differentiates tourmaline formed by dominantly magmatic and dominantly hydrothermal processes trace elements and boron isotope fractionation can be tracked in tourmaline and create a timeline for crystallization tourmaline from the granite matrix has higher v cr and mg content and is isotopically heavier than the later crystallizing inner orbicule tourmaline overgrowths of blue tourmaline occurring together with quartz showing hydrothermal cathodoluminescence textures crystallized from an aqueous fluid during the very last crystallization and are significantly higher in sr and sn and isotopically heavier tourmaline associated with sn mineralization is also high in sr and sn but has boron isotopic compositions close to that of the magmatic tourmaline and is not formed by the same fluids responsible for the blue overgrowths the ore forming fluids precipitating tourmaline and cassiterite are likely derived from the same magma source as the granite but exsolved deeper in the magma chamber and at a later stage than orbicule formation tourmaline from massive quartz tourmaline rocks is concentrically zoned with major and trace element compositions indicating crystallization from a similar melt as for the orbicules but shows a more evolved signature

lateral offsets and revised dates of large prehistoric earthquakes at pallett creek southern california recent excavation and new radiocarbon dates of sediments at pallett creek are the basis for new conclusions regarding the late holocene history of the san andreas fault systematic dissection of a 50 m long 15 m wide 5 m deep volume of earth centered on the fault enables documentation in three dimensions of fault patterns lateral offsets and vertical deformation associated with large earthquakes of the past the excavations expose evidence for 12 earthquakes that occurred between about 260 and 1857 a d with an average recurrence interval of about 145 years prehistoric slip events that occurred in 1720 50 1550 70 1350 50 1080 65 and 845 75 a d have lateral offsets that are comparable to those of the most recent great earthquake of 1857 thus all of these events represent earthquakes of large magnitude the lateral offsets of two other events in 935 85 and 1015 100 a d are an order of magnitude smaller and may be interpreted in several ways with regard to the size of these events the new data constrain the average recurrence interval for large earthquakes at this site to between 145 and 200 years but suggest a monotonic decrease in individual intervals to below this range during the past 900 years on the basis of these data the probability of a large earthquake with surficial fault rupture at this site is between 0 2 and 5 during 1984 and 7 and 60 by the year 2000