correlations between surface chlorophyll and sea surface height in the tropical pacific during the 1997 1999 el nino southern oscillation event correlations between sea viewing wide field of view sensor seawifs surface chlorophyll and topex sea surface height ssh are examined in the tropical pacific 30 s 30 n using empirical orthogonal function eof analysis both separately and jointly on the two fields this analysis is done on data from september 1997 the start of data from the seawifs satellite through december 1999 a time period dominated by the el nino southern oscillation four distinct biological responses are observed the dominant response is a symmetric off equatorial chlorophyll increase during la nina that extends between 2 and 18 latitude from the eastern pacific to the date line the chlorophyll mode is tightly correlated to ssh suggesting that the chlorophyll increase is a result of the shoaling thermocline which increases the surface nutrient supply the better known equatorial decrease in chlorophyll during el nino is seen in a separate eof mode using acoustic doppler current profiler data from the tropical atmosphere ocean triton array it is shown that the cessation of the el nino equatorial chlorophyll minimum is tied to the recommencement of the iron rich equatorial undercurrent which occurs several months prior to the termination of the el nino there is an off equatorial bloom during the peak of the el nino between 120 w 180 w and 8 n 15 n this bloom occurs within the area covered by the previously mentioned la nina bloom but it is more localized and its fluctuations appear correlated with changes in the north equatorial counter current the shoaling thermocline in the western warm pool during el nino results in a chlorophyll bloom that extends from the philippines to 155 e between 0 n and 15 n this bloom terminates in unison with the end of the el nino when elevated ssh is reestablished in the western basin

the lower eastern layered series of rhum the lower eastern layered series lels comprises approximately units 1 5 of previous workers remapping has revealed considerable along strike lithological variation in the units of the lels it is suggested on the basis of field and geochemical evidence that two layers formerly regarded as conformable intrusive sheets of fine grained olivine gabbro may be evolved alii valite layers rather than later intrusions xenolith suites in these layers and elsewhere indicate a component derived from the roof or walls of the magma chamber cryptic variation is more extensive in the lels than in other parts of rhum olivine forsterite content varies from 85 6 to 70 and clinopyroxene mg 100 mg fe varies from 88 to 74 postcumulus effects and subsolidus re equilibration have altered the initial compositions of the mineral phases the data are consistent with a model of repeated replenishment by picritic magma although the replenishing liquids may have been slightly less magnesian than those subsequently available during the formation of the upper els

deformation textures and mechanical behavior of a hydrated amorphous silica formed along an experimentally produced fault in chert 1 we conducted a series of friction experiments on chert at intermediate to high slip velocities v 0 87 104 mm s and at low normal stress n 1 5 mpa to better understand the process of fault weakening by silica gel formation as identified in previous friction experiments on quartz rocks fault weakening in chert samples occurred in association with the formation of a 0 1 mm thick fault gouge layer that contains a thin foliated layer of fine grained material and a cataclastically fragmented zone characterized by clast matrix texture mft ir and xrd analyses reveal that the fault gouge consists of a mixture of hydrated amorphous silica and quartz grains the mechanical behavior of the fault gouge at a small magnitude of strain 0 008 as examined independently of the friction experiments using a rheometer is characterized by a negative dependence of shear stress on strain rate with a notable hysteresis behavior

postcumulus processes in layered intrusions during the postcumulus stage of solidification in layered intrusions fluid dynamic phenomena play an important role in developing the textural and chemical characteristics of the cumulate rocks one mechanism of adcumulus growth involves crystallization at the top of the cumulate pile where crystals are in direct contact with the magma reservoir convection in the chamber can enable adcumulus growth to occur to form a completely solid contact between cumulate and magma another important process may involve compositional convection in which light differentiated melt released by intercumulus crystallization is continually replaced by denser melt from the overlying magma reservoir this process favours adcumulus growth and can allow adcumulus growth within the pore space of the cumulate pile calculations indicate that this process could reduce residual porosities to a few percent in large layered intrusions but could not form pure monomineralic rocks intercumulus melt may also be replaced by more primitive melt during episodes of magma chamber replenishment dense magma emplaced over a cumulate pile containing lower density differentiated melt may sink several metres into the underlying pile in the form of fingers reactions between melt and matrix may lead to changes in mineral compositions mineral textures and whole rock isotope compositions another important mechanism for forming adcumulate rocks is compaction in which the imbalance of the hydrostatic and lithostatic pressures in the cumulate pile causes the crystalline matrix to deform and intercumulus melt to be expelled for cumulate layers from 10 to 1000 metres in thickness compaction can reduce porosities to very low values 1 and form monomineralic rocks the characteristic time scale for such compaction is theoretically short compared to the time required to solidify a large layered intrusion during compaction changes of mineral compositions and texture may occur as moving melts interact with the surrounding matrix both compaction and compositional convection can be interrupted by solidification in the pore spaces compositional convection will only occur if the rayleigh number is larger than 40 if the residual melt becomes lower in density and the convective velocity exceeds the solidification velocity measured by the rate of crystal accumulation in the chamber orthocumulates are thus more likely to form in rapidly cooled intrusions where residual melt is frozen into the pore spaces before it can be expelled by compaction or replaced by convection

silica diagenesis ii general mechanisms abstract amorphous silica phases opal a precipitate in nature due to the formation of dense colloids in supersaturated alkaline aqueous solutions with low relative concentrations of other ions opal a dissolves and yields solutions of still relatively high silica content in pore waters containing abundant cations open framework polymers form which flocculate to yield opal ct opal ct becomes increasingly ordered primarily due to preferential growth of cristobalite relative to tridymite and crystal size increase opal ct dissolves to yield pore waters of low silica concentration which allows slow growth of quartz crystals from monomeric solution the quartz crystals then slowly increase in size and crystallinity carbonates appear to enhance opal ct formation possibly due to the activity of positively charged hydroxyl complexes hence polymerization in relatively pure systems is involved in opal a formation and polymerization in impure systems is involved in opal ct formation and slow growth from monomeric low silica concentration solutions is involved in precipitation of quartz in sedimentary realms

porous sidewall and sloping floor crystallization experiments using a reactive mush implications for the self channelization of residual melts in cumulates abstract tank crystallization experiments with aqueous solutions were used to explore interactions between a buoyant residual fluid and a porous cumulate at a sloping floor and a vertical wall the fluid flow path in a non reactive mush glass beads was used as a control for a vertical non reactive mush the rise of the buoyant solute depleted fluid was confined within it fluid flow paths were curved in the case of a sloping mushy floor with the upper part of the mush being principally a plume discharge zone and the lower part being a recharge zone more realistic reactive mushes were created by supercooling a nh 4 cl solution cooling against a vertical surface produced an initial mat of dendrites that were subsequently overgrown by a vertically grooved dendrite structure the grooves contained upwardly flowing residual melt while the ridges extended beyond the buoyant boundary layer into the thermally convecting solute rich part of the tank with time the grooves were covered over by a dendrite mat but remained as open channels within the mush focussing and accelerating the upflow of residual melt a buoyant boundary layer on the outside of the mush was not observed in the experiment with a sloping floor a thin mat of homogeneous mush was succeeded by a more organized deposit characterized by chimneys residual melt escaped as plumes through the chimneys chimneys formed because buoyant residual melt dissolved the mush as it rose and warmed chimney spacing increased and the number of chimneys decreased as the mush thickened dissection of the mush showed that individual chimney channels were inclined upslope so that melt residual from crystallization at the foot of the slope emerged from chimneys near the top of the slope formation of channels in cumulates would greatly increase fractionation efficiency by increasing the effective volume from which residual melts could be extracted and by increasing the rate at which residual melts could be transferred to the upper part of the chamber

a closer look at the central pacific el nino and warm pool migration events from 1982 to 2011 national science foundation nsf 11 582 nasa physical oceanography program epscor noaa sea grant

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

interannual variability of the south pacific convergence zone and implications for tropical cyclone genesis the interannual variability of the south pacific convergence zone spcz and its influence on tropical cyclone tc genesis in the south pacific are investigated using observations and era40 reanalysis over the 1979 2002 period in austral summer the spcz displays four typical structures at interannual timescales the first three are characterized by a diagonal orientation of the spcz and account for 85 of the summer seasons one is close to climatology and the other two exhibit a 3 northward or southward departure from the spcz climatological position in contrast the fourth one that only encompasses three austral summer seasons the extreme 1982 1983 and 1997 1998 el nino events and the moderate 1991 1992 el nino event displays very peculiar behaviour where the spcz largely departs from its climatological position and is zonally oriented variability of the western central pacific equatorial sea surface temperature sst is shown to modulate moisture transport south of the equator thereby strongly constraining the location of the spcz the spcz location is also shown to strongly modulate the atmospheric circulation variability in the south pacific with specific patterns for each class however independently of its wide year to year excursions the spcz is always collocated with the zero relative vorticity at low levels while the maximum vorticity axis lies 6 to the south of the spcz position this coherent atmospheric organisation in the spcz region is shown to constrain tropical cyclogenesis to occur preferentially within 10 south of the spcz location as this region combines all the large scale atmospheric conditions that favour the breeding of tcs this analysis also reveals that cyclogenesis in the central pacific in the vicinity of french polynesia only occurs when the spcz displays a zonal orientation while this observation was previously attributed to el nino years in general different characteristics of el nino southern oscillation enso related pacific equatorial warming are shown to impact differently on the spcz position suggesting that for regional scales such as the south pacific the spcz classification is more appropriate than a simple enso index to characterize tc interannual variability these findings suggest that forecasting the strength of el nino through sst variations in the eastern pacific may not be sufficient to accurately predict cyclogenesis in the south pacific especially east of the dateline

isotopic and geochemical investigation of unit 10 from the eastern layered series of the rhum intrusion northwest scotland sr and nd isotopic compositions together with whole rock sr and nd abundances and olivine compositions are presented for cumulates from unit 10 of the eastern layered series of the rhum intrusion northwest scotland the results show an nd sr isotopic correlation consistent with contamination by high 87 sr 86 sr low 143 nd 144 nd crust there is a strong correlation between the degree of contamination sr and nd whole rock abundance and fe enrichment in cumulus olivine the allivalites are the most contaminated while the basal peridotites are uncontaminated this suggests that the cumulates crystallized from a primitive uncontaminated magma and the allivalites from an evolved contaminated magma subsequently movement of contaminated feldspathic intercumulus liquid has perturbed the isotopic trace element and olivine composition of the upper peridotites

flow and deformation of viscous silica oversaturated dispersions in low grade faults abstract cryptocrystalline silica veins occur along shear faults and in dilatational cracks in low grade cataclasites derived from leucocratic granitoids the silica minerals occur as radiate bladed quartz and as spherulitic and sheaf like clusters of neocrystallites that nucleated on crush fragments in a matrix of opaline and chalcedony this texture is indicative of rapid crystallization from a viscous oversaturated fluid the veins are clast loaded and typically demonstrate a banding defined by variation in the amount and size of feldspar crush fragments three types of veins are distinguished that differ in relative timing of viscous fluid flow deformation and crystallization type 1 veins are dilatational cracks in which static settling and crystallization took place an undisturbed planar layering is found which has no fixed orientation with respect to the vein wall this banding is commonly associated with a layering defined by periodic variations in hematite precipitates type 2 veins show a gradual decrease in grain size of the crush fragments from one vein wall to the other this banding shows pinch and swell structures micro boudinage and folding suggestive of flow type 3 veins occur in shear faults and demonstrate a banding which is asymmetric with respect to the vein walls apart from pinch and swell structures and folds the foliation shows sigmoidal deflection similar to that in shear bands in ductile mylonites it is proposed that the cryptocrystalline fragment loaded veins are formed by solidification of a silica sol or hydrogel that was formed by quenching of a hot fragment bearing solution during brittle failure the effect of a viscous fluid in fault rock is discussed in terms of rheology and of seismic periodicity

western pacific coastal sources of iron manganese and aluminum to the equatorial undercurrent 1 we present results from the first zonal transect of iron aluminum and manganese conducted from the western source region of the equatorial undercurrent euc to the central equatorial pacific trace metals were elevated along the slope of papua new guinea and within the new guinea coastal undercurrent ngcu which is the primary southern hemisphere entry path of water to the euc subsurface maxima in total acid soluble iron aluminum and manganese were evident in the euc these maxima were generally greatest in the western equatorial pacific and decreased in magnitude eastward maxima in iron and aluminum persisted to 140 w maxima in manganese extended to 175 w iron and manganese maxima were deeper 25 75 m than aluminum maxima and located in the lower euc which undergoes less interior ocean mixing than shallower waters the depth of the aluminum subsurface maxima correlated strongly r 0 88 with the depth of the euc velocity maximum surface waters were enriched in aluminum and manganese offshore of papua new guinea surface metal concentrations decreased eastward throughout the western warm pool up to the longitude 180 w of the salinity front detrital sediment input from either direct riverine input or sediment resuspension appeared to be the primary mechanism of supplying metals to the ngcu we estimated eastward fluxes of metals in the euc and found greatest fluxes in the western equatorial pacific between 160 e and 165 e except for aluminum fluxes of aluminum and to a lesser extent manganese increased concurrently with water volume transport in the central equatorial pacific iron transport in the euc remained constant east of the dateline apparently due to the combined effects of dilution by meridional entrainment and scavenging iron was mobilized in a highly active western boundary current region and transported eastward in the lower euc

estimates of horizontal divergence and vertical velocity in the equatorial pacific abstract horizontal divergence and vertical velocity in the surface mixed layer of the equatorial pacific between 90 and 150 w are estimated from current measurements obtained from trajectories of freely drifting buoys during 1979 1990 the 12 year averaged horizontal divergence is predominantly meridional and has a maximum magnitude of 3 4 10 6 s 1 in a 20 km wide latitude band cantered on the equator using the equation of continuity this divergence corresponds to an upwelling velocity of 1 5 2 10 4 m s 1 at 50 m depth the seasonal variations of equatorial divergence are in good agreement with the local zonal wind stress

chlorophyll bloom in the western pacific at the end of the 1997 1998 el nino the role of the kiribati islands 1 during the transition between el nino and la nina conditions in 1998 a dramatic bloom occurred near the equator around 170 e with chlorophyll concentrations reaching more than 0 8 mg m 3 in may previous studies attributed this bloom to a wind driven upwelling and to the shoaling of the equatorial undercurrent euc but they did not explain its particular location near the kiribati islands by combining simulations with observations we determined that these islands were able to locally disrupt the physical dynamics and the nutrient fields to the extent that they were directly responsible for the location and the amazing strength of the bloom our results suggest that an island mass effect was responsible for generating the bloom while the barrier formed by the islands increased euc shoaling to the west of them which explained the bloom peak

the relationship between slickenside surfaces in fine grained quartz and the seismic cycle abstract well polished or reflective fault surfaces with or without linear striae indicating the sliding direction are commonly referred to as slickensides this study examines the development of slickensides which are now exposed along the surface trace of a large seismically active normal fault zone in dixie valley nevada u s a geologic and mineralogic constraints indicate the slickenside surfaces formed at depths of less than 2 km and temperatures less than 270 c the slickenside surface material is composed of greater than 98 quartz with less than 2 kaolinite and iron oxide transmission electron microscope tem observations reveal that the slickenside surface material has an extremely fine yet variable grain size 0 01 1 m and an unusual nonequilibrium texture characterized by irregular grain boundaries and low dislocation density angular fragments in the cataclasite to either side of the slickensides provide clear evidence of cataclasis crystallographic preferred orientation in the slickenside surface material indicates that non brittle continuous deformation occurred within 0 1 10 mm of the fault surfaces in many areas non brittle continuous deformation must have alternated with cataclasis because some fragments in the cataclasite have strong preferred orientations we suggest that in the dixie valley slickensides continuous deformation and the development of crystallographic preferred orientations occurred at relatively low strain rates during the interseismic period while cataclasis occurred at higher strain rates associated with seismic events the wide range of strain rates occurring within a fault zone during the earthquake cycle may be an essential element in the formation of fine grained glassy slickensides both at dixie valley nevada and many other areas

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

signature of coseismic decarbonation in dolomitic fault rocks of the naukluft thrust namibia unequivocal geological signatures of seismic slip are rare exceptionally so in carbonate hosted faults where carbonate minerals dissociate at temperatures lower than those required for producing a friction melt this thermal dissociation leads to significant fault weakening by increased fluid pressure and or nanoparticle lubrication preventing further heating of the fault surface pseudotachylyte is therefore unlikely to form in carbonate hosted faults and other evidence for seismic slip must be identified we studied the lower cambrian naukluft thrust which crops out in central namibia it contains a cataclastic dolomite fault rock referred to as gritty dolomite which we interpret as a signature of coseismic carbonate dissociation and subsequent fluid rock interactions the fault was active at ambient temperatures below 2001c gritty dolomite contains rounded low aspect ratio dolomite clasts with a uniform fe rich dolomite coating euhedral to subhedral magnetite quartz and k feldspar in a fine grained massive to laminated carbonate matrix of particulate dolomite and crystalline calcite cement the fault rock texture combined with evidence of injectites of gritty dolomite into the wallrock indicates the cataclasite deformed as a fluidized granular flow at seismic slip velocities frictional heating caused dissociation of dolomite to co 2 and ca fe and mg oxides this release of co2 decreased the ph of the pore fluid in the fault causing dissolution and rounding of dolomite clasts within an inertial grain flow and precipitation of carbonate coatings and euhedral silicates and oxides during subsequent cooling and co2 escape examples of similar rocks having some if not all of these characteristics have been described from other carbonate hosted faults the geological setting of the naukluft thrust is unique in spatial extent and quality of exposure allowing us to eliminate alternative hypotheses for sources of co2 to drive fluidization

fault slip distribution and fault roughness summary we present analysis of the spatial correlations of seismological slip maps and fault topography roughness illuminating their identical self affine exponent though the complexity of the coseismic spatial slip distribution can be intuitively associated with geometrical or stress heterogeneities along the fault surface this has never been demonstrated based on new measurements of fault surface topography and on statistical analyses of kinematic inversions of slip maps we propose a model which quantitatively characterizes the link between slip distribution and fault surface roughness our approach can be divided into two complementary steps i using a numerical computation we estimate the influence of fault roughness on the frictional strength pre stress we model a fault as a rough interface where elastic asperities are squeezed the hurst exponent h characterizing the self affinity of the frictional strength field approaches h h 1 where h is the roughness exponent of the fault surface in the direction of slip ii using a quasi static model of fault propagation which includes the effect of long range elastic interactions and spatial correlations in the frictional strength the spatial slip correlation is observed to scale as hs h 1 where hs represents the hurst exponent of the slip distribution under the assumption that the origin of the spatial fluctuations in frictional strength along faults is the elastic squeeze of fault asperities we show that self affine geometrical properties of fault surface roughness control slip correlations and that hs h given that h 0 6 for a wide range of faults various accumulated displacement host rock and slip movement we predict that hs 0 6 even if our quasi static fault model is more relevant for creeping faults the spatial slip correlations observed are consistent with those of seismological slip maps a consequence is that the self affinity property of slip roughness may be explained by fault geometry without considering dynamical effects produced during an earthquake

natural fracture propping and earthquake induced oil migration in fractured basement reservoirs the geological processes that create fluid storage capacity and connectivity in global fractured basement reservoirs are poorly understood compared to conventional hydrocarbon plays hosting potentially multibillion barrels of oil the upfaulted precambrian basement of the rona ridge offshore west of shetland uk gives key insights into how such reservoirs form oil presence is everywhere associated with sub millimeter to meterthickness mineralized fracture systems cutting both basement and local preseal cover sequences mineral textures and fluid inclusion geothermometry suggest a low temperature 90 220 c near surface hydrothermal system as does the preservation of clastic sediments in the same fractures these fills act as permanent props holding fractures open forming long term fissures in the basement that permit oil ingress and storage calcite fill u pb dating constrains the onset of mineralization and contemporaneous oil charge to the late cretaceous the additional preservation of oil stained injected sediment slurries and silica gels along basement faults suggests that rift related seismogenic faulting initiated lateral oil migration from jurassic source rocks into the adjacent upfaulted ridge subsidence below sea level in the latest cretaceous sealed the ridge with shales and buoyancy driven migration of oil into the preexisting propped fracture systems continued long after the cessation of rifting these new observations provide an explanation for the viability of sub unconformity fractured basement reservoirs worldwide and have wider implications for subsurface fluid migration processes generally

the unique 2009 2010 el nino event a fast phase transition of warm pool el nino to la nina 1 the latest el nino event in 2009 2010 which is classified as warm pool el nino holds a unique ground in that it marks the strongest warming signal in the central pacific but rapidly decays to strong la nina the strong eastward propagating cold anomaly at the subsurface level is found to be a key factor and two possible mechanisms are suggested that resulted in the fast phase transition of the 2009 2010 event 1 the anomalously warm indian ocean induces a surface easterly over the western edge of the pacific which generates the forced kelvin waves 2 the record breaking high sea surface temperature in the central pacific excites a strong rossby response that is to be reflected as an upwelling kelvin wave at the western boundary the strong subsurface anomaly then propagates eastward and results in an unusually fast phase transition of the 2009 2010 warm pool el nino event

twentieth century enso characteristics in the ipcc database in this paper we assess and compare to observations the spatial characteristics of the twentieth century enso sst variability simulated by 23 models of the ipcc ar4 cmip3 database the analysis is confined to the sst anomalies along the equatorial pacific and is based on the use of a non linear neural classification algorithm the self organizing maps systematic biases include a larger than observed proportion for modelled enso maximum variability occurring in the western pacific no clear relationship is found between this bias and the characteristics of the modelled mean state bias in the equatorial pacific this bias is mainly related to a misrepresentation of both el nino and la nina termination phases for most of the models in contrast the onset phase is quite well simulated modelled el nino and la nina peak phases display an asymmetric bias whereas the main bias of the modelled el nino peak is to exhibit a maximum in the western pacific the simulated la nina bias mainly occurs in the central pacific in addition some models are able to capture the observed el nino peak characteristics while none of them realistically simulate la nina peaks it also arises that the models closest to the observations score unevenly in reproducing the different phases preventing an accurate classification of the models quality to reproduce the overall enso like variability

characteristics of the convergence zone at the eastern edge of the pacific warm pool 1 the characteristics of the convergence zone at the eastern edge of the equatorial pacific warm pool are studied using a compilation of in situ current and salinity measurements during the period 1992 2001 the displacement of the convergence zone is observed for the first time as far west as 140 e in the far western pacific mainly during la nina periods and near 140 w in the central pacific during the 1997 98 el nino the convergence zone may be associated with a salinity front dividing the fresh waters of the warm pool from the salty waters upwelled in the central equatorial pacific despite a zonal displacement ranging over about one fifth of the equatorial circumference of the earth the characteristics of the main parameters involved in the air sea interactions are nearly constant on each side of the convergence zone salinity front these results suggest that coupled models used for el nino research and forecasting should be able to reproduce these important features

a whirling ecosystem in the equatorial atlantic 1 the equatorial pacific and atlantic oceans exhibit remarkable meridional undulations in temperature and chlorophyll fronts visible from space over thousands of kilometers and often referred to as tropical instability waves here we present new observations of an ecosystem ranging through three trophic levels phytoplankton zooplankton and small pelagic fish whirling within a tropical vortex of the atlantic ocean and associated with such undulations cold nutrient and biologically rich equatorial waters are advected northward and downward to form sharp fronts visible in all tracers and trophic levels the equatorward recirculation experiences upwelling at depth with the pycnocline and ecosystem progressively moving toward the surface to reconnect with the equatorial water mass the observations thus indicate that it is a fully three dimensional circulation that dominates the distribution of physical and biological tracers in the presence of tropical instabilities and maintains the cusp like shapes of temperature and chlorophyll observed from space

elastohydrodynamic lubrication of faults the heat flow paradox provides evidence that a dynamic weakening mechanism may be important in understanding fault friction and rupture we present here a specific model for dynamic velocity weakening that uses the mechanics of well studied industrial bearings to explain fault zone processes an elevated fluid pressure is generated in a thin film of viscous fluid that is sheared between nearly parallel surface this lubrication pressure supports part of the load therefore reducing the normal stress and associated friction across the gap the pressure also elastically deforms the wall rock the model is parameterized using the sommerfeld number which is a measure of the lubrication pressure normalized by the lithostatic load for typical values of the material properties slip distance and velocity the sommerfeld number suggests that lubrication is an important process if the lubrication length scales as the slip distance in an earthquake the frictional stress during dynamically lubricated large earthquakes is 30 less than the friction with only hydrostatic pore pressure elastohydrodynamic lubrication also predicts a decrease in high frequency 1 hz radiation above a critical slip distance of a few meters this prediction is well matched by the strong motion data from the 1999 taiwan earthquake the observed 2 orders of magnitude variation in scaled radiated energy between small m w 6 is also predicted by the lubrication model

basaltic replenishment of the rhum magma chamber evidence from unit 14 a detailed geochemical and lithological profile through unit 14 of the rhum eastern layered series is presented and interpreted to trace the evolution of this cyclic peridotite troctolite unit the lower 15 5 m of the unit are peridotite which has an abrupt contact with the upper 35 5 m of troctolite numerous thin subsidiary peridotites occur within the troctolite variation in the modes whole rock 87 sr 86 sr ratios and ni and fo in olivine provide most information about the evolution of the unit discontinuities in these parameters divide the unit into six subunits i the lower peridotite ii the middle main peridotite iii the upper main peridotite and lowermost troctolite iv the middle troctolite v the upper troctolite and vi the disturbed troctolite these subunits are interpreted as the result of magma replenishment by picritic and by basaltic magmas field evidence suggests that the subsidiary peridotites are later sills intruded into solid or semi consolidated troctolite the olivine fo and ni values are similar to those of surrounding troctolite suggesting either re equilibration with or assimilation of the troctolite comparison with unit 10 shows that the unit 14 resident basaltic liquid was more mafic than that of unit 10 this factor along with the basaltic replenishment can explain many of the differences in geochemical and lithological variation between the two units

colloidal gold and silica in mesothermal vein systems some of the textural features of mesothermal gold quartz veins may be best explained by the initial precipitation of amorphous silica gel colloid which subsequently crystallizes to quartz this can occur in brittle ductile shear zones where a significant fluid pressure drop occurs during stick slip failure such a process rapidly supersaturates the hydrothermal fluid with respect to amorphous silica which precipitates instead of quartz owing to favorable kinetics depressurization also commonly leads to fluid unmixing and destabilization of soluble gold complexes however the presence of colloidal silica can stabilize gold colloid allowing further transport of particulate gold in suspension in the hydrothermal fluid silica gel would be highly unstable under mesothermal conditions and would undergo rapid syneresis and crystallization to form quartz solid impurities would tend to be expelled toward grain boundaries this model can account for the primary anhedral aggregate textures typical of mesothermal quartz veins the concentration of gold along grain boundaries and the formation of discrete gold nuggets and the rare occurrence of low order silica polymorphs and relict spheroidal structures the transport of gold in colloidal form may be one reason for the frequently consistent bulk grade distribution in gold quartz vein systems over many hundreds of metres in some cases kilometres of depth in addition the formation of charged colloidal particles may help to explain the attraction of gold grains to specific mineral surfaces

fluidization of granular material in a subduction thrust at seismogenic depths abstract subduction thrusts exhumed from seismogenic depths may record the dynamic slip processes during subduction zone earthquakes the thrust faults in the shimanto accretionary complex of southwest japan imbricate the melange derived from sedimentary rocks and basalt which represent a duplex underplating associated with the downward step of the subduction thrust at seismogenic depths 4 6 km in depth temperature 130 150 c one well exposed duplex fault zone consists mainly of foliated cataclasites and ultracataclasites derived from basalt the fault zone structure suggests slip localization along the 2 20 cm thick ultracataclasite layer at the boundary between different lithologies the common features observed along the ultracataclasite layer are the injection of granular material into the melange without the sorting of fine grained particles along with a small detection probability of the fragmented counterparts in the injected materials which suggests a rapid injection of fluidized granular material during faulting the ultracataclasite layer is marked by fluid related processes as indicated by the alteration and precipitation of amorphous silica gel along the ultracataclasite and the concentration of veins near the ultracataclasite the fluidization during localized slip under fluid infiltrated conditions could be due to thermal pressurization which causes the fluid pressure to approach lithostatic values the injection of fluidized granular material may result from hydraulic fracturing in response to an increase in the fluid pressure associated with thermal pressurization the plate boundary subduction thrust could be lubricated when the granular material fluidizes due to thermal pressurization during earthquakes

semi brittle flow of granitoid fault rocks in experiments field studies and seismic data show that semi brittle flow of fault rocks probably is the dominant deformation mechanism at the base of the seismogenic zone at the so called frictional viscous transition to understand the physical and chemical processes accommodating semi brittle flow we have performed an experimental study on synthetic granitoid fault rocks exploring a broad parameter space temperature t 300 400 500 and 600 c confining pressure pc 300 500 1000 and 1500 mpa shear strain rate 10 3 10 4 10 5 and 10 6 s 1 to finite shear strains 0 5 the experiments have been carried out using a granular material with grain size smaller than 200 m with a little h2o added 0 2wt only two experiments performed at the fastest strain rates and lowest temperatures have failed abruptly right after reaching peak strength 1400 mpa all other samples reach high shear stresses 570 1600 mpa then weaken slightly by 10 190 mpa and continue to deform at a more or less steady state stress level clear temperature dependence and a weak strain rate dependence of the peak as well as steady state stress levels is observed in order to express this relationship the strain rate stress sensitivity has been fit with a stress exponent assuming n and yields high stress exponents n 10 140 which decrease with increasing temperature the microstructures show widespread comminution strain partitioning and localization into slip zones containing at first nanocrystalline and partly amorphous material later during continued deformation fully amorphous material in slip zones despite the mechanical steady state conditions the fabrics in the slip zones and outside continue to evolve and do not reach a steady state microstructure below 5 within the slip zones the fault rock material progressively transforms from a crystalline solid to an amorphous material we present and interpret the experimental results both in terms of sliding friction and viscous flow and we discuss the possible effect that the formation of nanocrystalline and amorphous layers may have on earthquake nucleation

equatorial wave sequence associated with warm pool displacements during the 1986 1989 el nino la nina in the pacific equatorial band the zonal displacement of the eastern edge of the warm pool subject to insignificant seasonal variations is dominated by strong interannual variations almost in phase with the southern oscillation index over the 1971 1973 el nino la nina period gill 1983 suggested that such displacement was caused solely by horizontal advection by zonal current anomaly basin wide geosat derived zonal surface current anomalies are available during the 1986 1989 period and they agree quite well with observed equatorial currents in the western and central pacific within the 4on 4 s equatorial band the cumulative contribution of first baroclinic kelvin and first symmetric m 1 rossby modes to surface zonal equatorial current anomalies account for most of the geosat derived current variability from these geosat derived currents it is demonstrated that the eastward westward displacement of the eastern edge of the warm pool was primarily due to horizontal advection by zonal current anomalies during the 1986 1987 el nino 1988 1989 la nina as a corollary the el nino la nina warm cold sea surface temperature sst anomaly in the central western pacific was the result of anomalous zonal advection the 1986 1989 displacement of the warm pool appeared as a low frequency movement resulting from high frequency forcing i e a succession of local wind forcing and its remote kelvin and m 1 rossby wave responses in the equatorial waveguide in the central western pacific a in 1 downwelling rossby wave issued from the eastern pacific shifted the displacement from eastward to westward and therefore seems to have been the cause for el nino to turn to la nina in boreal fall 1987 in the eastern pacific the simultaneous occurrence of free propagating downwelling upwelling kelvin waves with the seasonal sst warming cooling appeared necessary for the development of local el nino la nina sst anomaly over most of the equatorial pacific slow migration of sst anomalies clearly showed up distinct during el nino and la nina these zonal migrations appeared to result from the delayed association of two phenomena the zonal advection in the central western pacific and the arrival of downwelling upwelling kelvin waves into the eastern pacific synchronous with the seasonal sst warming cooling albeit different in terms of equatorial wave action as compared to the delayed action oscillator theory our results suggest that zonal advection and wave dynamics were both important for the generation and migration of el nino southern oscillation sst anomalies in 1986 1989 finally our observational results about warm pool displacements equatorial wave sequence the shift from el nino to la nina and the slow sst migrations are presented in a schematic form involving sequential ocean atmosphere coupling which appears continuously over the november 1986 to a

macrorhythmically layered gabbronorites in the windimurra gabbroid complex western australia abstract plagioclase orthopyroxene augite cumulates gabbronorites in the 3 5 km thick wagoo hills section show strong rhythmic modal layering over about 200 m of section layers of mafic gabbronorite mgn 1 10 m thick alternate with leucogabbronorite lgn 10 5 m thick with sharp contacts mgn are adcumulates with 65 70 plagioclase cores an68 reverse zoning 20 orthopyroxene mg69 15 augite mg78 and whole rock mg number 65 in contrast lgn are mesocumulates more orthocumulate character with 80 90 plagioclase cores an75 normal zoning 6 augite mg71 4 orthopyroxene mg62 and whole rock compositions have mg numbers ca 54 and higher concentrations of incompatible elements e g k p and lower concentrations of compatible elements and pge than in mgn lgn contain minor interstitial postcumulus quartz hornblende fe ti oxides apatite and 5 25 hydrous alteration products unlike mgn the cause of the presumed cumulus stage differences in pyroxene plagioclase modal ratio noncotectic proportions in lgn and sharp mgn lgn mgn contacts is not clear but could result from rhythmic variations in supercooling and nucleation the postcumulus differences postcumulus mineralogy normal zoned plagioclase more fe rich pyroxenes and higher incompatibles in lgn are interpreted in terms of an in situ crystallisation compositional convection model cumulus mineral assemblages in mgn have a higher fractionation density and their in situ crystallisation released a buoyant residual liquid which was continuously displaced by fresher magma resulting in only 0 5 residual liquid trapped with the mush adcumulate formation in contrast in situ crystallisation of a plagioclase rich cumulus assemblage lower fractionation density in lgn resulted in a denser stagnant residual liquid 10 15 of which was trapped in the crystal mush producing normal zoning in plagioclase 6 8 atom fe shift in pyroxene compositions and higher incompatible element concentrations and h 2 o the latter resulting in selective alteration of lgn as a result mgn had higher solidus t and acted like seals or aquicludes whereas lgn had lower solidus t and were sinks or aquifers for incompatibles and volatiles

upper equatorial pacific ocean current and salinity variability during the 1996 1998 el nino la nina cycle the recent el nino la nina cycle exhibited striking patterns of current and salinity variability in the upper equatorial pacific ocean this evolution is described from mid 1996 through 1998 using a remarkable data set of 35 meridional conductivity temperature depth ctd acoustic doppler current profiler adcp sections along with buoy data the sections nominally from 8 s to 8 n between 165 e and 95 w were occupied over the course of 27 months a wide range of current variability was sampled with currents that appeared or disappeared some time during the cycle including an equatorially trapped eastward surface current the equatorial undercurrent the northern branch of the south equatorial current and the north equatorial countercurrent basin wide interannual changes in upper ocean and pycnocline zonal transports were as large as 64 32 106 m3 s 1 changes in the salinity structure included a deep and fresh mixed layer in the central equatorial pacific that built up during the el nino and was then disrupted by upwelled salty water with the onset of la nina a very fresh mixed layer observed in the eastern equatorial pacific late in the el nino and a reduction in the strength of the meridional equatorial salinity gradient within the pycnocline to one third of the usual value during the el nino finally the zonal transports above the thermocline from 5 s to 5 n were well correlated with the rate of change of warm water volume west of the individual ctd adcp sections

tectonic processes in papua new guinea and past productivity in the eastern equatorial pacific ocean phytoplankton growth in the eastern equatorial pacific ocean today accounts for about half of the new production the fraction of primary production fuelled by externally supplied nutrients in the global ocean the recent demonstration that an inadequate supply of iron limits primary production in this region1 supports earlier speculation that in the past fluctuations in the atmospheric deposition of iron bearing dust may have driven large changes in productivity2 but we argue here that only small 2 nm increases in the iron concentration in source waters of the upwelling equatorial undercurrent are needed to fuel intense diatom production across the entire eastern equatorial pacific ocean episodic increases in iron concentrations of this magnitude or larger were probably frequent in the past because a large component of the undercurrent originates in the convergent island arc region of papua new guinea which has experienced intensive volcanic erosional and seismic activity over the past 16 million years cycles of plankton productivity recorded in eastern equatorial pacific sediments may therefore reflect the influence of tectonic processes in the papua new guinea region superimposed on the effects of global climate forcing

postcumulus modification of magnetite grains in the upper zone of the bushveld complex south africa abstract a detailed electron microprobe study has been made of magnetite grains from magnetitite layer 1 of the upper zone of the bushveld complex in order to establish if there is any evidence for postcumulus processes having affected magnetite compositions representative composition profiles obtained from detailed step traverses are presented for touching magnetite grains and where magnetite is in contact with either ilmenite or plagioclase magnetite grains in all textural settings are compositionally heterogeneous touching magnetite grains display systematic compositional zonations the rims of grains show a marked decrease in al and mg towards the grain boundary the cores are characterised by a distinctive peak and trough pattern for these elements these variations can be related to the positions of exsolved phases exsolutions in the cores are either pleonaste or an fe 3 bearing al mg spinel whereas those at the grain boundaries are generally more al rich and include corundum similar exsolution related compositional variations for mg and al were found in magnetites in contact with ilmenite and plagioclase a model has been developed which illustrates the possible sequence of postcumulus events during the interval between accumulation of the magnetite and the cessation of subsolidus reactions the essential feature of the model is the delicate interplay between depletion of the host magnetite by corundum pleonaste and the fe 3 bearing al mg spinel exsolutions and diffusion of al and mg into the depleted areas from the surrounding magnetite data for cr contents in magnetites show that although this particular trace element is apparently resistant to redistribution by exsolution processes it is affected by subsolidus re equilibration between magnetite and ilmenite or magnetite and intercumulus liquid

effects of h2o on phase relations during crystallization of gabbros in the kap edvard holm complex east greenland in the kap edvard holm complex of east greenland layered monly results in the formation of discordant igneous bodies within crystallizing cumulus sequences in some olivine gabbros host numerous small discordant bodies of ultramafic cases partially molten cumulates appear to have reacted rock and magnetite gabbro that formed by late magmatic metasomatic with liquids or fluids that originated within the cumulus replacement of partially solidified gabbroic cumulates similar repile resulting in resorption of cumulus minerals crysplacive rocks are also present as large semi conformable sheet like tallization of intrusive or replacive bodies and rebodies within the layered gabbro sequence replacive bodies of all distribution of mass within the intrusion e g robins sizes are spatially associated with xenoliths of metabasaltic lava 1982 butcher 1985 butcher et al 1985 helz 1987 the small bodies cluster around xenoliths and the large bodies host irvine 1987 boudreau 1988 mcbirney sonnenthal swarms of xenoliths the replacive bodies are inferred to have formed 1990 larsen brooks 1994 scoon mitchell 1994 by reaction of gabbroic cumulates with pore liquids that were mathez 1995 meurer et al 1997 boudreau 1999 in enriched in h2o by degassing or dehydration melting of the other cases partially molten cumulates are inferred to metabasalts as these liquids migrated through the cumulus pile have reacted with externally derived magmas that inthey resorbed plagioclase and produced ultramafic bodies where the truded the cumulus pile resulting in the development liquids came to rest they reacted with gabbroic cumulates to produce of discordant replacive bodies via the reaction of the bodies of magnetite rich gabbro the most evolved pore liquids cumulates with intruding magmas e g morse et al 1987 segregated to form hornblende rich pegmatitic dikes of roughly dacitic bedard et al 1988 tegner wilson 1993 tegner composition suggesting that hydration and possibly oxidation of the robins 1996 because cumulus rocks preserve records magma shifted the liquid line of descent from a tholeiitic trend toward of magmatic fractionation and replenishment in large a calc alkaline trend these inferences imply that contamination of mafic intrusions recognizing and understanding postmagmas by dehydration of hydrothermally altered crustal rocks may cumulus processes such as these can provide insights significantly influence the evolution of mafic magma systems into the evolution of mafic magma chambers and the differentiation of basaltic magmas within the crust near the western margin of the kap edvard holm

sea surface chlorophyll signature in the tropical pacific during eastern and central pacific enso events 1 recent analyses of physical measurements show the existence of a central pacific type of el nino cpen with a sea surface temperature warming pattern distinct from that of the classical eastern pacific el nino epen in this study we analyze the surface chlorophyll signature of el nino southern oscillation enso using monthly maps of satellite derived chlorophyll anomalies between september 1997 and december 2010 we identify five typical enso structures the first structure describes the lonely 1997 1998 epen of the period the second and third represent la nina the fourth illustrates intermediate conditions and the fifth characterizes cpen during the 1997 1998 epen a large eastward shift of the oligotrophic warm pool and a reduction of equatorial upwelling result in negative chlorophyll anomalies east of 170 e between 10 s and 10 n during the four cpen events a reduced eastward shift yields negative chlorophyll anomalies in the equatorial band within about 160 e and 160 w only westward surface current in the central basin limits the expansion of the anomaly core negative chlorophyll anomalies that extend eastward from the equatorial anomaly core probably result from reduced upward iron fluxes linked to the deepening of the equatorial undercurrent during la nina the westward expansion of the equatorial upwelling results in positive chlorophyll anomalies west of the date line away from the equatorial band advection of oligotrophic warm pool waters by enhanced eastward countercurrents drives negative anomalies within 8 10 n and toward the marquesas islands during cpen while reduced countercurrents lead to positive chlorophyll anomaly during la nina

mineral precipitation as a mechanism of fault core growth abstract faults vary in structural style from simple planes to complex systems composed of fault cores and damage zones increased fault complexity results from the interaction of mechanical and chemical processes including fracture growth shear and linkage and mineral dissolution and precipitation although water rock interaction is traditionally associated with fault rock weakening and shear localization we investigate processes of fault core widening by water rock interactions that resulted in quartz precipitation we combine field and petrographic observations with prior mechanical characterization to assess the impact of alteration and cementation on fault architecture at the dixie comstock epithermal gold deposit nevada usa mineralized portions of the fault contain strong thick silicified fault cores and wide weak damage zones with evidence for widening of the core through entrainment of damage zone material and repeated cycles of embrittlement dilation and cementation we present a model of fault zone evolution in which the hydrothermal regimes favoring either alteration weakening or precipitation strengthening result in distinct fault zone architecture and mechanical and flow properties of fault systems alteration weakening favors localization of the fault into thinner clay rich low permeability fault cores precipitation strengthening promotes thick strong and low permeability fault cores with mineralization embrittlement enhancing transient permeability following coseismic failure

implications of changing el nino patterns for biological dynamics in the equatorial pacific ocean 1 el nino events are known to strongly affect biological production and ecosystem structure in the tropical pacific understanding and predicting biological processes in this area are hampered because the existing in situ observing system focuses primarily on physical measurements and does not observe key biological parameters the only high spatial and temporal resolution biology related observations are from the global array of ocean color satellites which provide an estimate of surface chlorophyll concentrations only since the 1990s an apparent shift of the el nino maximum sea surface temperature sst warm anomaly from the eastern to the central equatorial pacific has frequently been observed satellite observations show significant changes in chlorophyll a chl a new production np and total primary production pp in the equatorial pacific associated with these new central pacific cp el nino events also called el nino modoki relative to eastern pacific el ninos during cp el ninos np chl a and pp in the central basin are depressed relative to ep el ninos and lower values of chl a and pp coincide spatially with higher sst in the central pacific while surface chl a and integrated np and pp over the entire equatorial band decrease during both cp and ep el ninos the magnitude of this decrease seems to depend more on the intensity than type of event the changing spatial patterns have significant implications for equatorial biological dynamics if as has been suggested cp el ninos increase in frequency in the future citation turk d c s meinen d antoine m j mcphaden and m r lewis 2011 implications of changing el nino patterns for biological dynamicsinthe equatorial pacificocean geophys res lett 38 l23603 doi 10 1029 2011gl049674

contrasting the flavors of el nino southern oscillation using sea surface salinity observations 1 the recent detection of a central pacific type of el nino has added a new dimension to the el nino southern oscillation climatic puzzle sea surface salinity sss observations collected during 1977 2008 in the tropical pacific are used to contrast the three eastern pacific ep 1982 1983 1991 1992 1997 1998 and seven central pacific cp 1977 1978 1986 1988 1990 1991 1992 1995 2002 2003 2004 2005 2006 2007 types of el nino events as well as the six ep 1985 1986 1988 1989 1995 1996 1999 2001 2005 2006 2007 2008 and two cp 1983 1984 1998 1999 types of la nina events the ep el nino events result in large 30 longitude eastward displacements of the eastern edge of the low salinity warm pool waters in the equatorial band a resulting well marked sss freshening 1 near the dateline and a sss increase 1 below the mean position of the south pacific convergence zone spcz the cp el nino events are characterized by smaller 50 eastward displacements of the eastern edge a 15 longitude westward shift of the equatorial sss freshening and a comparatively reduced 50 sss increase in the spcz a qualitative analysis indicates that changes in zonal currents and precipitation can account for the observed contrasted signature in sss eastward current anomalies appear over most of the equatorial band during ep el nino events in contrast there is a tendency for zonal current convergence slightly west of the dateline during cp el nino events consistent with the confinement of the warm fresh pool in the western central equatorial basin the related quasi inexistent northeastward migration of the spcz and associated heavy precipitation regime

the unit 12 allivalite eastern layered intrusion isle of rum a textural and geochemical study of an open system magma chamber the eastern layered intrusion of the rum central complex nw scotland comprises 16 macro units broadly defined by a basal peridotite body overlain by gabbros and troctolites the local term for the upper plagioclase bearing cumulates is allivalite the unit 12 allivalite contains five subsidiary peridotite horizons each continuous on the kilometre scale field textural and geochemical evidence points to the unit 12 allivalite forming by progressive accumulation of crystals from up to seven separate magma batches varying from picrite to basalt the thickness of the magma lens in the sill like chamber was as low as 30 m during a significant part of the development of the unit 12 allivalite and evidence supports one eruption from the chamber during its accumulation

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

silica gel in a fault slip surface field evidence for palaeo earthquakes high velocity friction experiments have shown an almost complete loss of strength associated with silica gel formation on slip surfaces the identi cation of frictional silica gel products in palaeo seismic faults is however problematic because there are multiple natural sources of silica gel and recrystallization of gel to quartz complicates preservation the importance of gel formation on natural faults is therefore unknown here we report a structurally distinct and semi continuous 0 5 10 mm thick layer of microcrystalline quartz along a major carbonate hosted fault the olive fault in the naukluft nappe complex namibia the quartz layer is distinguished by ow banding like textures and unusual cathodoluminescence characteristics the layer consists of 2 20 m hexagonal quartz crystals which include distinct crystalline pore bearing micro to nano spheres separated by pore geometries indicative of volumetric contraction and with grain boundaries enriched in aluminium we interpret these features to indicate that the quartz crystals formed from recrystallization and dehydration of a silica gel because it is found in a carbonate hosted fault and crosscuts lithological layering the silica source is not from comminution of local wall rocks rather the gel likely formed from reshear of a quartz coated fault surface or incremental shear slip associated with precipitation of silica driven by co seismic pressure drops this example of fault related silica gel may have formed by a different mechanism than the gels produced in high velocity friction experiments but once formed may have comparable rheological effects

infiltration metasomatism of cumulates by intrusive magma replenishment the wavy horizon isle of rum scotland the eastern layered intrusion of the rum layered suite comprises paired peridotite and allivalite troctolite and gabbro layers forming 16 macro rhythmic units whereas the majority of these macro units are believed to have formed by a process of crystal liquid differentiation involving successive accumulation of crystals from multiple picritic replenishments of the chamber the unit 9 peridotite is interpreted as a layer parallel picrite intrusion closely correlated with this discontinuous peridotite body is a distinctive feature generally known as thewavy horizon which divides the overlying allivalite into a lower troctolite and an upper gabbro along a well defined undulating contact we propose that the wavy horizon is a metasomatic feature formed consequent to the removal of clinopyroxene from an original gabbroic mush foundering of the mush into the picritic sill resulted in the replacement of the original interstitial liquid by one saturated only in olivine plagioclase progressive through flow of this liquid resulted in the stripping out of clinopyroxene from the lower parts of the allivalite we interpret thewavy horizon as a reaction front representing the point at which the invading liquid became saturated in clinopyroxene the distinctive pyroxene enriched zone immediately above thewavy horizon could have formed when mixing of the interstitial liquids on either side of the reaction front formed a supercooled liquid oversaturated in pyroxene as a result of the curvature of the olivine plagioclase clinopyroxene cotectic the presence of many such approximately layer parallel features defined by differences in pyroxene content in the eastern layered intrusion of rum suggests that such an infiltration reaction process was not unique to unit 9

textural immaturity of cumulates as an indicator of magma chamber processes infiltration and crystal accumulation in the rum eastern layered intrusion textural maturity describes the extent to which rocks have approached textural equilibrium for igneous rocks this is a function of the time integrated thermal history in the sub solidus which for cumulate rocks generally translates to the cooling history via the rate of solidification of the accumulating crystal mush the most straightforward way to quantify the textural maturity of orthocumulates sensu lato is to measure the angle subtended at the corners of interstitial grains texturally mature cumulates have angle populations with median values of c 120 whereas texturally immature cumulates have lower medians inherited by the interstitial phase which infills either an impingement texture in the accumulating mush or a texturally equilibrated pore topology textural observations of allivalites from the rum layered suite demonstrate that stratigraphically localized excursions towards textural immaturity are the result of either transient relatively rapid solidification rates perhaps a result of the arrival of cold crystal laden bodies of fluid on the chamber floor or late stage infiltration of fully solidified cumulates by evolved liquids expelled upwards by compaction of underlying horizons these two processes have distinct textural and compositional signatures

crystallization and compositional convection in a porous medium with application to layered igneous intrusions growing crystals can provide a local source of buoyancy by depleting melt of certain chemical components and vigorous convective motions in the fluid can result we report a quantitative experimental study in which saturated aqueous solutions of cuso4 and na2so4 in porous media of either glass balls or cuso4 5h2o crystals were crystallized by cooling from below the crystals growing in the pore space released light chemically depleted solution which had the potential to convect out of the porous medium and be replaced by additional saturated solution from above we explore the physical and chemical effects of compositional convection during the complete solidification of the interstitial solution by varying the permeability of the porous medium the cooling rate and the initial composition of the solution this type of convection can form adcumulate rocks by enabling continuous circulation of melt from the main magma reservoir through the pores of a cumulus pile adcumulus growth can occur by this mechanism as long as the convective velocity in the porous medium is greater than the velocity of the solidification front we scale the experimental results to magmatic conditions and infer that this process should occur commonly in layered igneous intrusions when our porous media had a small permeability compositional convection enabled the adcumulate growth of a completely solid contact between melt and cumulate trapping of dynamically unstable melt beneath this impermeable layer of crystals also occurred in these experiments and may be important geologically small shallowly emplaced intrusions and the cumulate zones at the base of komatiites are probably cooled too rapidly for significant intercumulus convection to occur

tracing papua new guinea imprint on the central equatorial pacific ocean using neodymium isotopic compositions and rare earth element patterns abstract the nd isotopic composition ic and rare earth patterns of hydrodynamic structures of the equatorial pacific ocean were characterized along 140 w the nd ic of antarctic intermediate water aaiw and of the lower layer of the equatorial undercurrent euc at 140 w 13 c water are much more radiogenic at the equator than at their origin in the south equatorial current 12 s revealing that these water masses have been in contact with the highly radiogenic papua new guinea png slope in both cases only a small fraction less than 9 of the sediment deposited on the png slope is required to be exchanged or dissolved to explain these nd ic variations whereas the hydrographic properties of the same water masses remain unchanged this confirms the usefulness of this tracer to identify pathways of water masses these results emphasize the importance of jets in transporting lithogenic material into the subsurface layers of remote areas where aeolian inputs are particularly weak and corroborate the previous results on fe and al maximum in this area m l wells g k vallis e a silver nature 398 1999 601 604 the nd ic of the upper layer of the euc contrasts strongly to that of the subpycnocline layer indicating that the equatorial upwelling only affects the surface waters and is not effective between 120 and 150 m we calculate that the nd imprint of the png input is likely to vanish from this surface layer as it traverses the basin due to the replacement of upwelled waters by non radiogenic ones

deformation and hydrofracture in a subduction thrust at seismogenic depths the rodeo cove thrust zone marin headlands california we have investigated the fabric and the deformational processes of an exhumed subduction zone thrust active at seismogenic depths the rodeo cove thrust zone which outcrops north of the golden gate bridge of san francisco imbricates two basalt chertsandstone sequences belonging to the marin headlands terrane franciscan complex the thrust outcrop is a 200 m thick complex zone that displays a range of stratal disruption from incipient deformation to a broken formation in the central part of the outcrop dominated by basaltic lithologies where zones of concentration of deformation have been mapped disruption is made by variably dense discrete fault systems synthetic to the main thrust r and p fractures these faults are marked by cataclasites with a shaly matrix that shows a scaly foliation defi ned by chlorite and pumpellyite which also constrain the depth of faulting 8 10 km t 200 250 c within the seismogenic zone the central part of the fault also features the densest system of carbonate fi lled veins veins occur in the broken formation matrix and fragments in both cases parallel to the foliation the veins are either folded truncated or pressure solved along the cleavage cementation and hardening of shear surfaces of the fault core may have caused the distribution as opposed to localization of subsequent slip events the fault core may have developed in basaltic rocks because of their inherently high permeability and propensity to transmit overpressure from deeper levels of the subduction zone our analysis has shown that accretionary deformation is strongly controlled by injection of overpressured fl uids occurring through systems of multiple dilatant fractures grossly parallel to the decollement zone the crosscutting relationships between veining and foliation suggest that fl uid injection is cyclic and consequently that large transient variations in permeability and cohesion may occur the repeated injection of veins parallel to the fault zone may be explained by cyclic changes of the stress or by difference in tensional strength parallel to and perpendicular to the foliation both of which would require extremely high fl uid pressure we interpret the features of the rodeo cove thrust zone as evidence of the seismic cycle and hypothesize a compressional stress fi eld in the interseismic phase and an extensional stress fi eld in the immediately postseismic phase

a magmatic heat pump the structures of igneous cumulates can provide valuable clues to inaccessible magmatic processes many mafic layers in the rhum intrusion have finger structures 1 3 that protrude into the overlying felsic rocks these structures are attributable to melting of the overlying olivine feldspar rocks by hot mafic magma emplaced as sills4 the bases of mafic layers contain smooth bottomed olivine cumulates here i show that the heat needed to melt the roof of the layer is carried by rapidly rising light solute released by growth of basal olivine crystals that were deposited by two phase convection compositional convection therefore drives a heat pump transfering heat of fusion from remote growing crystals to those that are melting this action contrasts with cooling under a refractory roof which is conduction limited the heat pumping principle shows why ultramafic magmas may melt their roofs whereas felsic magmas tend to form upper border zones

fluid dynamic and geochemical evolution of cyclic unit 10 rhum eastern layered series lithological major element trace element and sr isotope data from cyclic unit 10 of the rhum eastern layered series are presented the lower 65 metres of the unit are peridotite subdivided on textural and geochemical grounds into a lower homogeneous portion approximately 50 metres thick and an upper heterogeneous portion approximately 15 metres thick the uppermost 16 5 metres of the unit are allivalite there are steep geochemical gradients across the peridotite allivalite boundary in ni content of olivine and whole rock sr isotope composition calculations are presented on the geochemical evolution of a rhum picritic liquid undergoing olivine precipitation both when the olivines remain suspended in the residual liquid as they precipitate and when they are continuously fractionated quenched groundmass and olivine compositions from the rhum dykes and the unit 10 peridotite olivines show good agreement with the suspension model but are inconsistent with the fractionation model the rhum chamber is thought to have been replenished with a picritic liquid from which olivine crystallized while held in suspension however replenishment by a highly olivine phyric basalt is also possible the peridotite probably accumulated rapidly as olivines were dumped out of suspension onto the chamber floor the lower part of the peridotite is a poikilitic adcumulate it is suggested that this formed by convective circulation of melt in the pores of the pile of cumulus olivines in the latter stages of adcumulus growth more fe rich and isotopically contaminated magma entered the top of the cumulus pile causing cumulus olivines to re equilibrate and giving the intercumulus plagioclase a higher sr isotope ratio than lower down the olivines in the allivalite show steep stratigraphic gradients in major element composition but not in their ni content they also show substantial variation in major element composition laterally within the allivalite it is suggested that these features are a consequence of postcumulus re equilibration of olivine with migrating intercumulus magma

impact of shifting patterns of pacific ocean warming on north atlantic tropical cyclones two distinctly different forms of tropical pacific ocean warming are shown to have substantially different impacts on the frequency and tracks of north atlantic tropical cyclones the eastern pacific warming epw is identical to that of the conventional el nino whereas the central pacific warming cpw has maximum temperature anomalies located near the dateline in contrast to epw events cpw episodes are associated with a greater than average frequency and increasing landfall potential along the gulf of mexico coast and central america differences are shown to be associated with the modulation of vertical wind shear in the main development region forced by differential teleconnection patterns emanating from the pacific the cpw is more predictable than the epw potentially increasing the predictability of cyclones on seasonal time scales

magmatic lineations inferred from anisotropy of magnetic susceptibility fabrics in units 8 9 and 10 of the rum eastern layered series nw scotland the eastern layered series of the rum layered suite nw scotland comprises a sequence of sixteen 30 150 m thick cyclic units the upper troctolite olivine gabbro parts of each of these units exhibit small scale modal layering and a pervasive layerparallel mineral lamination that is often associated with soft sediment deformation structures a sporadic macroscopic magmatic lineation measurable on mineral lamination surfaces is also observed in places anisotropy of magnetic susceptibility ams fabrics were studied in three of these cyclic units 8 9 and 10 in the northern part of the eastern layered series magnetic fabrics measured in the troctolites and gabbros yield one dominant trend in which magnetic foliations parallel magmatic layering and magnetic lineations trend nw se and plunge gently magnetic fabrics measured for two detailed traverses through unit 10 on the northern side of hallival also yield one dominant trend similar to that measured elsewhere in the eastern layered series however toward the centre of unit 10 in each traverse magnetic lineations sometimes plunge approximately downdip sw on the magnetic foliation planes the implications of these results are discussed with reference to previous textural and fabric observations on rum a model is suggested in which weak linear arrangements of cumulus olivine and plagioclase crystals are developed due to slumping and soft sediment deformation of unconsolidated crystal mushes during central sagging of the rum layered suite 2007 elsevier b v all rights reserved

western pacific modulation of large phytoplankton blooms in the central and eastern equatorial pacific 1 satellite observations show that large scale phytoplankton blooms increases in chlorophyll occurred in the equatorial pacific in 1998 2003 and 2005 following termination of the three most recent el nino events the occurrence of blooms following successive el nino events cannot be explained by local enhancement of vertical nutrient flux as evidenced by observations of equatorial winds thermocline depth and the depth and strength of the equatorial undercurrent euc which supplies the limiting nutrient iron to the euphotic zone however near the peak of each el nino event late in 1997 2002 and 2004 while the thermocline of the western equatorial pacific was anomalously shallow the flow of the new guinea coastal undercurrent ngcuc which is the primary source of iron enriched waters to the euc intensified and its core shoaled from 200 m to 100 m depth analysis of ngcuc variability using a high resolution terrain following three dimensional ocean circulation model simulation indicates that as the ngcuc shoals and intensifies it develops meanders and eddies that augment coupling of the new guinea shelf and upper slope to the euc we hypothesize that these changes in ngcuc circulation during el nino enhance iron transport from the new guinea margin into the euc and thereby trigger large scale blooms when iron enriched waters subsequently reach the euphotic zone along the equator the threefold to fourfold chlorophyll increases over large regions up to 5 105 km2 must have profound impacts on the equatorial ecosystem and biogeochemical cycles

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

indices of el nino evolution abstract to characterize the nature of el nino southern oscillation enso sea surface temperature sst anomalies in different regions of the pacific have been used an optimal characterization of both the distinct character and the evolution of each el nino or la nina event is suggested that requires at least two indices i sst anomalies in the nino 3 4 region referred to as n3 4 and ii a new index termed here the trans nino index tni which is given by the difference in normalized anomalies of sst between nino 1 2 and nino 4 regions the first index can be thought of as the mean sst throughout the equatorial pacific east of the date line and the second index is the gradient in sst across the same region consequently they are approximately orthogonal tni leads n3 4 by 3 to 12 months prior to the climate shift in 1976 77 and also follows n3 4 but with opposite sign 3 to 12 months later however after 1976 77 the sign of the tni leads and lags are reversed

inferring earthquake physics and chemistry using an integrated field and laboratory approach abstract earthquakes are the result of a combination of 1 physico chemical processes operating in fault zones which allow ruptures to nucleate and rock friction to decrease with increasing slip or slip rate and 2 of the geometrical complexity of fault zones in this review paper we summarize recent experimental findings from high velocity conducted at about 1 m s slip rate or typical seismic slip rates rock friction experiments with an emphasis on potential dynamic weakening mechanisms melt lubrication nanopowder lubrication etc and how these mechanisms might be recognized by means of microstructural and mineralogical studies in exhumed fault zones we discuss how earthquake source parameters coseismic fault strength weakening distances energy budgets etc might be derived from the field and laboratory experiments additionally we discuss what needs to be considered in terms of fault zone geometry and morphology focusing on fault surface roughness in order to develop models of realistic fault surfaces and present theoretical considerations for microphysical modeling of laboratory data at seismic slip rates with an emphasis on the case of melt lubrication all experimental data and in the case of melt lubrication microphysical models indicate that faults must be very weak

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

ocean chlorophyll response to two types of el nino events in an ocean biogeochemical coupled model based on a long term simulation of an ocean biogeochemical coupled model we investigate the biogeochemical response to the two types of el nino events a cold tongue ct el nino and a warm pool wp el nino in which a local maximum of anomalous sea surface temperature sst is located in the eastern and central tropical pacific our model is able to reasonably simulate the characteristics of the biological variables in a way comparable to the observations during the developing period anomalous low chlorophyll appears in the eastern pacific while it appears in the central pacific in the wp el nino the difference in the spatial temporal response of chlorophyll for the two types of el nino events is mainly due to the eastward zonal advection of upper ocean currents which plays a role in bringing nutrient poor water from the western pacific during the decaying period of the wp el nino anomalous high chlorophyll appears concurrently with anomalous low sst in the eastern pacific conversely anomalous high chlorophyll appears in the central pacific prior to the decaying period of the ct el nino in particular the anomalous low sea level from the northwestern pacific shifts to the southern equatorial region during the decaying period of the ct el nino this drives anticyclonic boundary currents which enhance the equatorial undercurrent playing a role in the supply of nutrients to the central equatorial pacific resulting in an increase in chlorophyll concentration in the same region

successive episodes of reactive liquid flow through a layered intrusion unit 9 rum eastern layered intrusion scotland we present a detailed microstructural and geochemical study of reactive liquid flow in unit 9 of the rum eastern layered intrusion scotland unit 9 comprises an underlying lens like body of peridotite overlain by a sequence of troctolite and gabbro termed allivalite with some local and minor anorthosite the troctolite is separated from the overlying gabbro by a distinct sub horizontal undulose horizon the major wavy horizon higher in the stratigraphy is another similar horizon the minor wavy horizon that separates relatively clinopyroxene poor gabbro from an overlying gabbro to the north of the peridotite lens both troctolite and gabbro grade into poikilitic gabbro clinopyroxene habit in the allivalite varies from thin rims around olivine in troctolite to equigranular crystals in gabbro and to oikocrysts in poikilitic gabbro the poikilitic gabbros contain multiple generations of clinopyroxene with cr rich 1 1 wt cr2o3 anhedral cores with moderate ree concentrations core1 overgrown by an anhedral ree depleted second generation with moderate cr 0 7 wt cr2o3 core2 these composite cores are rimmed by cr poor 0 2 wt cr2o3 and ree poor to moderate clinopyroxene we interpret these microstructures as a consequence of two separate episodes of partial melting triggered by the intrusion of hot olivine phyric picrite to form the discontinuous lenses that comprise the unit 9 peridotite loss of clinopyroxene saturated partial melt from the lower part of the allivalite immediately following the early stages of sill intrusion resulted in the formation of clinopyroxene poor gabbro the spatial extent of clinopyroxene loss is marked by the minor wavy horizon a second partial melting event stripped out almost all clinopyroxene from the lowest allivalite to form a troctolite with the major wavy horizon marking the extent of melting during this episode the poikilitic gabbro formed from clinopyroxene saturated melt moving upwards and laterally through the remobilized cumulate pile and precipitating clinopyroxene en route this process called reactive liquid flow is potentially important in open magma chambers

textural record of the seismic cycle strain rate variation in an ancient subduction thrust active faults slip at different rates over the course of the seismic cycle earthquake slip c 1 m s 1 interseismic creep c 10 100 mm year 1 and intermediate rate transients e g afterslip and slow slip events studies of exhumed faults are sometimes able to identify seismic slip surfaces by the presence of frictional melts and slow creep by textures diagnostic of rate limited plastic processes the pasagshak point thrust preserves three distinct fault rock textures which are mutually cross cutting and can be correlated to different strain rates ultrafine grained black fault rocks including pseudotachylyte were formed during seismic slip on layers up to 30 cm thick well organized s c cataclasites 7 31 m thick were formed by slow creep with pressure solution as a dominant rate limiting mechanism these must have formed at strain rates consistent with long term plate boundary motion but solution creep healing acted to reduce porosity of the cataclasites and eventually restricted fluid connectivity such that creep by this mechanism could not continue disorganized non foliated rounded clast cataclasites were formed at shear rates faster than solution creep and are interpreted as representing shear at intermediate strain rates these could have formed during afterslip or delocalization of slip associated with an earthquake rupture

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

biological physical coupling in the central equatorial pacific during the onset of the 1997 98 el nino perturbations to phytoplankton biomass associated with the onset of the 1997 98 el nino event are described and explained using physical and bio optical data from moorings in the central equatorial pacific the physical progression of el nino onset is depicted from reversal of the trade winds in the western equatorial pacific through eastward propagation of equatorially trapped kelvin waves and advection of waters from the nutrient poor western equatorial warm pool fluctuations in chlorophyll and quantum yield of fluorescence are tightly coupled to thermocline variations

complex siliceous concretions in the jurassic morrison formation church rock new mexico usa implications of inorganic factors in ichnological interpretations abstract complex concretions in the jurassic morrison formation in new mexico usa were studied to elucidate their enigmatic origin the concretions mostly in the 0 1 2 m height range are characterized by a microcrystalline quartz matrix and many tiny 4 8 mm diameter cylindrical protrusions a common architecture revealed by weathering is a vertical cylindrical concentric casing around a homogenous core concretion morphologies include irregular bodies and larger horizontal cylinders with surficial protrusions sometimes cores and or protrusions are absent micromorphological data and open grain packing indicate concretions formed in unconsolidated sediments light and scanning electron microscopy shows gradational contacts between the siliceous concretions and host sandstones point counts of concretions and host rock show more cement and intergranular volume in the concretions but fewer grains and primary pores most concretions are cemented by microporous microcrystalline quartz chlorite kaolinite and illite smectite x ray fluorescence and instrumental neutron activation analyses indicate that silica was added to form the concretions previous models for the concretions include burrows termite nests and rhizocretion however these interpretations are challenged by geochemical macromorphological and micromorphological data presented in this study infiltration possibly due to hydrothermal activity may have added silica but explanations for several morphological details remain elusive these data imply that inorganic diagenetic factors can be important in ichnological interpretations

origin of pseudotachylites in slow creep experiments we conducted a series of experiments on granitoid cataclasites under mid crustal conditions pc 500 mpa t 300 c and slow displacement rates 10 8 ms 1 d 10 7 ms 1 i e within an order of magnitude of plate tectonic velocities the samples reach high peak strength 1250 1375 mpa then weaken slightly by 40 mpa and continue to deform without any abrupt stress drops up to a of 4 microstructural observations show that at peak strength nanocrystalline mean grain size 34 nm smallest crystalline particles 8 nm to partly amorphous material develops weakening occurs once this material is abundant enough to form through going anastomozing slip zones where the strain partitions during higher strain deformation deformation localizes further and 1 to 2 multiply connected layers of fragment loaded amorphous material develop this material shares many similarities with naturally occurring pseudotachylites however was formed at velocities up to 8 orders of magnitude slower than those calculated for earthquakes 1 ms 1 we conclude that the use of pseudotachylites as indicators for paleoseismic events should be reconsidered

co seismic and or a seismic microstructures of jfast 343 core samples from the japan trench abstract the microstructures mineralogy and chemistry of four representative samples collected from cores extracted from the japan trench during integrated ocean drilling project expedition 343 the japan trench fast drilling project jfast have been studied using optical microscopy tem sem xrf xrd and microprobe analyses the samples provide a transect from relatively undeformed marine sediments in the hanging wall to the undeformed footwall material crossing the thrust interface between the pacific and north american plate where the fault slipped during the march 2011 tohoku oki earthquake our preliminary results suggest that the low strength of jfast fault gouge material is caused by the high amount of clay minerals 60 smectite 14 illite clay minerals in the decollement gouge sample are partly replaced by newly formed manganese oxide which precipitated from hydrothermal fluids dauphine twins were found in quartz grains of the decollement sample suggesting local high stress possible during seismic loading other microstructures cannot be assigned unambiguously to co seismic or a seismic faulting processes the observed scaly clay fabric is consistent with observations in many other plate boundary fault zones significant grain size reduction was found in the fault decollement zone sample but a change in lithology of the fault material cannot be ruled out microstructures typical for a seismic deformation like dissolution precipitation features e g dissolved grain boundaries mineral alteration occur in all jfast core samples but more frequently in the decollement sample

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity

hot on the trail coseismic heating on a localized structure along the muddy mountain fault nevada abstract recent advances in the use of thermal proxies to identify past earthquake slip in exhumed faults have created an extraordinary opportunity to map the geometry of past ruptures in unprecedented detail this approach can reveal along strike differences in the structure and speed of earthquake slip here we present organic thermal maturity data collected along the muddy mountain thrust in nevada to investigate where it was within the fault that earthquake slip occurred and whether this is consistent along strike we observe large changes in thermal maturity which represent temperature rise variations along the fault modeling of thermal maturity measurements yield peak temperatures of 760 1090 c where the principal slip zone psz is narrowest 0 8 mm nearby where the psz is thicker 1 5 mm these temperatures did not exceed 500 c based upon estimates of temperature rise within a submillimeter psz mean frictional work during earthquake slip was 6 3 7 1 mjm 2 these results show that thickness of the active slipping zone can vary at small spatial scales and development of a continuously narrow

peridotite sills and metasomatic gabbros in the eastern layered series of the rhum complex mapping of the eastern layered series els of the rhum ultrabasic complex on the northern flank of hallival shows that peridotite and allivalite troctolite or gabbro layers are laterally discontinuous and vary both in thickness and lithology peridotite generally has sharp upper and lower contacts against the allivalites which sometimes cut across the layering in the allivalite reaction dissolution and hybridization effects between peridotite and allivalite are developed locally some troctolite layers terminate as isolated fingered blocks in peridotite there are many small peridotite bodies which are clearly intrusive into allivalite and have previously been identified as distinct peridotite sheets and plugs they are petrographically almost identical to the major stratiform peridotites and in some cases are apophyses from them we propose that many of the peridotite layers in the els formed as thick sills of picritic magma emplaced into a partly solidified layered troctolite complex the stratiform gabbros of the els are heterogeneous layered rocks that commonly contain relicts of troctolite and anorthosite wavy metre scale contacts between gabbro and troctolite cut across pre existing grain size modal and rhythmic layering with little disruption these metasomatic gabbros mimic the textures grain size and rhythmic layering of their troctolitic protoliths we propose that many of the els gabbros formed as a result of interaction between porous troctolites and a low temperature basaltic melt residual basaltic melt segregated from solidifying peridotite may have caused this metasomatism

silica gel formation during fault slip evidence from the rock record dynamic reduction of fault strength is a key process during earthquake rupture many mechanisms for causing coseismic weakening have been proposed based on theory and laboratory experiments including silica gel lubrication however few have been observed in nature here we report on the fi rst documented occurrence of a natural silica gel coating a fault surface the corona heights fault slickenside in san francisco california is covered by a shiny layer of translucent silica microstructures in this layer show fl ow banding armored clasts and extreme comminution compared to adjacent cataclasites the layer is composed of 100 nm to 1 m grains of quartz hydrous crystalline silica and amorphous silica with 10 100 nm inclusions of fe oxides and ellipsoidal silica colloids kinematic indicators and mixing with adjacent cataclasites suggest the shiny layer was fl uid during fault slip the layer therefore represents a relict silica gel that formed during fault motion and which could have resulted in frictional instability these observations confi rm that the silica gels formed in rock friction experiments do occur in natural faults and therefore that silica gel formation can act as a dynamic weakening mechanism in faults at shallow crustal conditions

natural and experimental evidence of melt lubrication of faults during earthquakes melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake here we estimate the dynamic shear resistance f in the presence of friction induced melts from both exhumed faults and high velocity 1 28 meters per second frictional experiments exhumed faults within granitoids tonalites indicate low f at 10 kilometers in depth friction experiments on tonalite samples show that f depends weakly on normal stress extrapolation of experimental data yields f values consistent with the field estimates and well below the byerlee strength we conclude that friction induced melts can lubricate faults at intermediate crustal depths

enso regimes reinterpreting the canonical and modoki el nino 1 we propose that the first two empirical orthogonal function eof modes of tropical pacific sea surface temperature sst anomalies do not describe different phenomena i e el nino southern oscillation enso and el nino modoki but rather the nonlinear evolution of enso we introduce two new uncorrelated indices e and c based on the leading eofs that respectively account for extreme warm events in the eastern and cold moderate warm events in the central equatorial pacific corresponding to regimes with different evolution recent trends in enso can be described as an increase in the central pacific c variability that is associated with stronger cold events as well as a reduction in the eastern pacific e variability within the cold moderate warm regime consistent with model projections however little can be said observationally with respect to the extreme warm regime