a physical basis for the frictional melting of some rock forming minerals abstract under conditions of coseismic slip 0 1 2 0 m s 1 within the upper crust differences in the shear yield strengths fracture toughnesses melting points and to a lesser extent thermal conductivities of rock forming minerals result in a hierarchy of friction melting susceptibilities in many so called pseudotachylytes it is observed that phyllosilicates and amphiboles are preferentially consumed to form the melt phase whilst quartz and feldspar tend to survive as clasts this can be explained in terms of the disequilibrium flash melting of those mineral phases possessing the lower shear yield strengths fracture toughnesses and thermal conductivities rather than by eutectic melting that would otherwise generate equilibrium minimum melts indicative of igneous processes at high strain rates typical of coseismic faulting the mechanical behaviour of minerals is primarily controlled by their fracture toughnesses with progressive comminution during slip leading to fusion the friction melting dependence on the mechanical properties of minerals indicates that there may be an important relationship between wall rock lithology and earthquake magnitude if frictional melting results in fault lubrication

seismic slip in the lower crust inferred from granulite related pseudotachylyte in the woodroffe thrust central australia pseudotachylytes generated in granulite facies rocks are found in the woodroffe thrust central australia petrologic evidence and structural and textural features show that these pseudotachylytes contain typical melting origin features including injection occurrence rounded and embayed clasts and microlites within the fine grained matrix which formed contemporaneously with the wall granulite facies rocks under conditions of 8 kbar and 650 700 c these granulite related pseudotachylyte g pt veins are overprinted in subsequent deformation stages by three other types of pseudotachylytes including mylonite related m pt and ultramylonite related um pt pseudotachylytes that are then transcut by cataclasite related pseudotachylytes c pt the overprinting occurred following uplift of the lower crust where the g pt veins formed through the brittle plastic transition zone where the m pt and um pt veins occurred within the brittle dominated regime of the c pt generation zone in the upper crust the coexistence of multiple generations of large voluminous c pt m pt um pt and g pt veins indicates that numerous large earthquakes accompanying distinct seismic slip which produced the pseudotachylytes occurred over an extended period of seismicity and various depths of the crust within the woodroffe thrust zone the spatial distribution and structural features of the multiple stage pseudotachylytes suggest that coseismic slipping caused by large earthquakes which nucleated in the brittle dominated seismogenic zone propagated downward through the brittle plastic transition zone into the plastic dominated granulite facies depth from the upper to lower crust

stable carbon and oxygen isotopes in sphagnum fuscum peat from subarctic canada implications for palaeoclimate studies stable carbon and oxygen isotope ratios in single plant components in sphagnum peat have a good potential to reveal environmental changes in peat archives two peat profiles covering the past 600

oxygen isotope signatures from land snail helix melanostoma shells and body fluid proxies for reconstructing mediterranean and north african rainfall abstract in this paper we show that oxygen isotope ratios from the shell carbonate of the land snail helix melanostoma reflect local rainfall parameters stable oxygen isotopes were measured in the body fluid 18 o body and shells 18 o shell of live collected h melanostoma along a north south transect across the gebel akhdar in northeast libya 18 o body ranged between 8 1 and 13 0 whilst 18 o shell ranged between 1 0 and 2 8 to investigate the relationship between snail oxygen isotope composition and climate these measurements were correlated with ambient air temperature relative humidity rainfall amount and the 18 o composition of rainwater 18 o rain strong and significant correlations were found between 18 o shell and 18 o rain and between 18 o shell and rainfall amount r 2 0 79 and 0 85 respectively suggesting that h melanostoma shells can be used as a proxy for past rainfall conditions when combined in multiple linear regressions 18 o rain and rainfall amount explained 90 of the variance in 18 o shell r 2 0 90 simple and multiple linear regressions were used to develop predictive models for these climate parameters as h melanostoma shells are commonly found in mediterranean and north african archaeological and geological deposits the predictive equations developed in this study hold great potential for reconstructing pleistocene to holocene rainfall and aridity patterns in the gebel akhdar and for assessing the relationship between environmental changes and human behavioural changes

seismic and aseismic weakening effects in transtension field and microstructural observations on the mechanics and architecture of a large fault zone in se tibet

evidence for warmer interglacials in east antarctic ice cores reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotopic ratios and temperature are stable in space and time sime et al analyse three 340 000 year old ice cores from east antarctica and use an isotope enabled general circulation model to show that instead the relationship is nonlinear during warm periods the ratios are less sensitive to temperature so previous estimates of interglacial temperatures are likely to be about 3 c too low this is consistent with peak antarctic interglacial temperatures at least 6 c higher than today this work suggests that there are serious deficiencies in our understanding of climates that are warmer than today s reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotope ratios and temperature are stable in space and time three east antarctic ice core records are now analysed alongside input from general circulation models to reveal that during warmer interglacial periods the isotope ratios are less sensitive to temperature than during colder interglacials consequently previous estimates of interglacial temperatures are probably too cold stable isotope ratios of oxygen and hydrogen in the antarctic ice core record have revolutionized our understanding of pleistocene climate variations and have allowed reconstructions of antarctic temperature over the past 800 000 years 800 kyr refs 1 2 the relationship between the d h ratio of mean annual precipitation and mean annual surface air temperature is said to be uniform 10 over east antarctica3 and constant with time 20 refs 3 5 in the absence of strong independent temperature proxy evidence allowing us to calibrate individual ice cores prior general circulation model gcm studies have supported the assumption of constant uniform conversion for climates cooler than that of the present day3 5 here we analyse the three available 340 kyr east antarctic ice core records alongside input from gcm modelling we show that for warmer interglacial periods the relationship between temperature and the isotopic signature varies among ice core sites and that therefore the conversions must be nonlinear for at least some sites model results indicate that the isotopic composition of east antarctic ice is less sensitive to temperature changes during warmer climates we conclude that previous temperature estimates from interglacial climates are likely to be too low the available evidence is consistent with a peak antarctic interglacial temperature that was at least 6 k higher than that of the present day approximately double the widely quoted 3 1 5 k refs 5 6

order or chaos origin and mode of emplacement of breccias in floors of large impact structures abstract breccias in the crater floor of large impact structures are pseudotachylites sensu largo authigenic monomict and polymict clastic matrix breccias so called footwall breccias and impact melt breccias pseudotachylite bodies in the center of large impact structures e g vredefort dome south africa appear to have a random distribution and orientation but most dip steeply or vertically large bodies of pseudotachylite in the more distal sectors of the 200 km diameter sudbury structure have been interpreted as ring and terrace collapse features in the vredefort dome networks of randomly distributed pseudotachylite veins accompany large mother lode pseudotachylite dikes in general pseudotachylites in the floors of central parts of impact craters may form through explosive transfer of thermal shock energy in a process that could be termed flash replacement melting whereas pseudotachylites at large distances from the centers of large impact structure are believed to have formed through friction leading to partial or complete melting similar to the formation of tectonic pseudotachylites in smaller structures e g ries and slate islands clastic matrix breccias instead of pseudotachylites occur as the most common breccias in the crater floors they have a chaotic distribution pattern their dips are commonly also steep to vertical melt breccia dikes in the target rocks of the crater floor are associated with melt sheets that fill the lower part of the excavation cavity at vredefort erosion has removed the coherent melt sheet but melt breccia dikes vredefort granophyre in the crater floor are preserved they are characterized by a remarkably homogeneous chemical composition and are believed to represent the initial undifferentiated impact melt near the vredefort collar the granophyre forms more or less concentric dikes in the more central parts of the dome their orientation is more random but in places may be controlled by the archean fabric of the crater basement the offset dikes of the sudbury structure are associated with the sudbury igneous complex that represents in total or in part a differentiated impact melt sheet the dikes in many aspects are similar to vredefort granophyres but their interpretation as undifferentiated bulk melt is problematic on geochemical and structural grounds chemically these dikes are not homogeneous and in places they contain massive sulfide deposits that are unlikely components of an undifferentiated impact melt differentiation and precipitation of massive sulfides are slow processes compared with the presumably high energy and fast emplacement of a supposedly undifferentiated melt pseudotachylites of the central impact crater apparently are mainly produced in the compression phase of the impact process whereas clastic matrix breccias form during the uplift and crater modification phases impact melt breccia dikes contain pseudotachylite bearing inclusions and cut across pseudotachylite bodies such impact melt breccia dikes were probably emplaced during uplift and crater modification

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

influences of large scale convection and moisture source on monthly precipitation isotope ratios observed in thailand southeast asia abstract many paleoclimatic records in southeast asia rely on rainfall isotope ratios as proxies for past hydroclimatic variability however the physical processes controlling modern rainfall isotopic behaviors in the region is poorly constrained here we combined isotopic measurements at six sites across thailand with an isotope incorporated atmospheric circulation model isogsm and the hybrid single particle lagrangian integrated trajectory hysplit model to investigate the factors that govern the variability of precipitation isotope ratios in this region results show that rainfall isotope ratios are both correlated with local rainfall amount and regional outgoing longwave radiation suggesting that rainfall isotope ratios in this region are controlled not only by local rain amount amount effect but also by large scale convection as a transition zone between the indian monsoon and the western north pacific monsoon the spatial difference of observed precipitation isotope among different sites are associated with moisture source these results highlight the importance of regional processes in determining rainfall isotope ratios in the tropics and provide constraints on the interpretation of paleo precipitation isotope records in the context of regional climate dynamics

preservation of primary stable isotope signatures of peat forming plants during early decomposition observation along an altitudinal transect abstract the preservation of the primary stable isotope compositions of peat forming plants in peat was tested along a short

selective melting processes as inferred from experimentally generated pseudotachylytes abstract high speed friction experiments have been conducted on gabbros and granites to better constrain the process of frictional melting during seismogenic fault motion experiments were done on cylindrical specimens of 25 mm in diameter under a normal stress of 1 0 1 5 mpa and at slip rates up to 2 m s using a rotary shear high speed frictional testing machine the experimentally generated pseudotachylytes consist of a fused glassy matrix with abundant vesicles and angular or sub angular to rounded fragments these locally occur as injected network veins in the fractured rock x ray diffraction analysis has revealed the presence of as much as 40 70 wt glass the mineral contents of clasts in the experimental pseudotachylyte in granite as determined by x ray diffraction analysis indicate that quartz is the most resistant to melting biotite the least and feldspar is intermediate thus the sio2 depletion in natural pseudotachylyte glass is likely to be due to the selective melting of constituent materials during frictional melting

microstructural and chemical changes associated with cataclasis and frictional melting at shallow crustal levels the cataclasite pseudotachylyte connection in pelitic schists of the nason terrane of washington state pseudotachylyte can be demonstrated to have developed subsequent to the formation of foliation parallel cataclasite zones numerous microstructural lines of evidence point to a genetic link between pseudotachylyte and cataclasite and chemical evidence indicates that cataclasis played an important role in controlling pseudotachylyte chemistry besides optical and textural differences between the cataclasite and pseudotachylyte which may occur together there is unambiguous evidence of a melt origin for the pseudotachylyte while such evidence within the cataclasite is absent tem evidence indicates that glass is present in at least some of the veins as demonstrated by a lack of electron diffraction microlites present in the glass lack dislocations high temperature microlites of a mineralogy and composition not present in the host schist occur in various habits which depend on the distance from the vein margin also present are assimilation textures apparently quenched sulfide droplets and vesicles and amygdules in a pseudotachylyte vein studied in detail five microstructural domains occur these include vein margin cataclasite a transitional dark pseudotachylyte vein interior glass opaque and sulfide rich blebs and translucent haloes surrounding some of the blebs the cryptocrystalline cataclasite matrix grades into the dark pseudotachylyte which optically grades into the glass after adjustment for silica the host schist and cataclasite matrix are chemically very similar the dark pseudotachylyte and glass with the exception of na2o and cao are chemically quite similar to the cataclasite matrix the main difference may be the result of the segregation of the opaque plagioclase blebs thus the pseudotachylyte chemistry is strongly dependent upon the chemistry of the material comprising the cataclasite matrix which in turn is dependent on mineral susceptibility to incorporation into the cataclasite matrix fluids infiltrated along the cataclasite zones prior to pseudotachylyte generation as recorded by hydration reactions sulfide veining na2o loss and fluid inclusions this demonstrates that pseudotachylytes can form under fluid rich conditions as opposed to the commonly assumed dry conditions

magnetic fabric of araguainha complex impact structure central brazil implications for deformation mechanisms and central uplift formation article i nfo the weakening mechanisms involved in the collapse of complex impact craters are controversial the ara guainha impact crater in brazil exposes a complex structure of 40 km in diameter and is an excellent object to address this issue its core is dominated by granite in addition to microstructural observations magnetic studies reveal its internal fabric acquired during the collapse phase all granite samples exhibit impact related planar deformation features pdfs and planar fractures pfs which were overprinted by cataclasis cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure fracture planes are systematically decorated by tiny grains b10 m of magnetite and hematite and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility ams and anhysteretic remanence aar are perfectly coaxial in all studied sites therefore we could track the orientation of deformation features which are decorated by iron oxides using the ams and aar the magnetic fabrics show a regular pattern at the borders of the cen tral peak with orientations consistent with the fabric of sediments at the crater s inner collar and complex in the center of the structure both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex im pact structures the widespread occurrence of cataclasis in the central peak and its orientations revealed by magnetic studies indicate that acoustic fluidization likely operates at all scales including the mineral scales the cataclastic flow made possible by acoustic fluidization results in an apparent plastic deformation at the macroscopic scale in the core

can oxygen stable isotopes be used to track precipitation moisture source in vascular plant dominated peatlands a b s t r a c t variations in the isotopic composition of precipitation are determined by fractionation processes which occur during temperature and humidity dependent phase changes associated with evaporation and condensation oxygen stable isotope ratios have therefore been frequently used as a source of palaeoclimate data from a variety of proxy archives which integrate this signal over time applications from ombrotrophic peatlands where the source water used in cellulose synthesis is derived solely from precipitation have been mostly limited to northern hemisphere sphagnum dominated bogs with few in the southern hemisphere or in peatlands dominated by vascular plants new zealand nz provides an ideal location to undertake empirical research into oxygen isotope fractionation in vascular peatlands because single taxon analysis can be easily carried out in particular using the preserved root matrix of the restionaceous wire rush empodisma spp that forms deep holocene peat deposits throughout the country furthermore large gradients are observed in the mean isotopic composition of precipitation across nz caused primarily by the relative influence of different climate modes here we test whether 18o of empodisma cellulose from ombrotrophic restiad peatlands in nz can provide a methodology

spatial and temporal variability of ground surface temperature and active layer thickness at the margin of maritime antarctica signy island a calm grid with a data logger system to monitor the active layer thermal regime was established on signy island 60 43 s 45 38 wat 80 m a s l in december 2005 the active layer at each of the 36 nodes of the grid was monitored measuring the ground temperature at least at 4 different depths between 0 02 and 0 4 m at the end of the summer season in addition within the grid we selected four sites closely spaced in a ray of 25 m three of which with the same topographical characteristics north facing aspect but different vegetation coverage one bare ground bg1 and two sites with different vegetation andreaea sp and sanionia uncinata and the fourth bg2 it is as bg1 a bare ground but with south facing aspect in particular 4 thermistors were located at depths of 0 02 0 3 0 6 and 0 9 m at bg2 and at the andreaea sp site 9 thermistors at 0 02 0 3 0 6 1 1 2 1 4 1 6 2 and 2 5 mat bg1 and at 0 02 and 0 6 mof depth at sanionia site generally with the same aspect a thick vegetation cover as in sanionia site provides a greater insulative effect than a thinner vegetation cover as in andreaea site or bare ground bg1 because vegetation both shades and insulates the ground resulting in a reduction in summer heat flux ground surface temperature gst was colder and more buffered in spring and summer under the vegetated ground than in bg1 although the coldest gst and lowest thawing degree days tdd were recorded at bg2 and related to its southern aspect our data confirm that air temperature is the main driver of gst as already reported both in the arctic and antarctic we also found that the effect of air temperature changes seasonally being drastically reduced in winter and to a lesser extent in fall and spring when there is generally thin snow cover b30 cm during the summer when snow cover is usually absent the air temperature is the dominant driver although incoming radiation also had an effect on the northern exposed bare ground and to a lesser extent on the vegetated and southerly exposed bare ground the active layer ranges between 81 and 185 cm on the 4 continuously monitored sites and considering the sites with the same aspect it is thicker under bare ground between 10 up to more than 100 than under vegetated ground confirming previous observations in the arctic and antarctic however at our sites climate forcing has no effect on the active layer thickness enhancing the role of soil properties including the periods of high moisture content and lateral flow of water the lack of a statistically significant regressions between gst and active layer thickness could be due to the limited study period four years and or to the variationwith timeof changes in soil characteristics such as soilmoisture and the possible occurrence of non conductive heat transfer processes including the lateral flow of water further data are required to understand the role of moisture and possible ground water circulation within the active layer to explain the unexpected strong dichotomy between the gst regime and active layer thickness

340 years of atmospheric circulation characteristics reconstructed from an eastern antarctic peninsula ice core 1 precipitation delivery mechanisms for dolleman island di located off the east coast of the antarctic peninsula are investigated using reanalysis and back trajectory data the southern annular mode sam and enso are both shown to influence precipitation delivery and event size precipitation delivery variability is compared against the interannual variation of chemical data from two di ice cores nitrate concentration in the cores is strongly linked with the ratio of easterly to westerly back trajectories arriving at di as described by a cross peninsula index cpi defined in this paper this cpi is used subsequently to reconstruct the atmospheric circulation characteristics for the 340 year ice core record the analysis highlights a period of increased easterlies during 1720 1780 and an increase in westerlies for 1950 1980 the latter concomitant with a positive sam trend and western peninsula warming the reconstruction also reveals periods when polynyas may have been present in the weddell sea

deformation mechanisms in granitic rocks at shallow crustal levels abstract microstructural observations of naturally faulted granitic gneisses show that feldspar grains are weaker than quartz grains at temperatures below 325 c and at depths of less than 8 10 km feldspar grains sustained most of the deformation by grain scale faulting slip along cleavage controlled fractures and cataclasis fracture of feldspar grains within fault zones promoted their alteration to kaolinite quartz grains also deformed by fracturing and often healed to form quartz porphyroclasts and mosaics in a comminuted matrix of feldspar and kaolinite syntectonic alteration of the feldspar grains may have weakened the fault zones over time and resulted in foliated textures within the fault zones this study of naturally deformed rocks confirms published experimental results on the behavior of granitic rocks at low temperatures and pressures and taken together these data show that the theology of the upper 10 km of the crust is greatly influenced by cataclastic processes in feldspar

cataclastic rocks of the san gabriel fault an expression of deformation at deeper crustal levels in the san andreas fault zone the san gabriel fault a deeply eroded late oligocene to middle pliocene precursor to the san andreas was chosen for petrologic study to provide information regarding intrafault material representative of deeper crustal levels cataclastic rocks exposed along the present trace of the san andreas in this area are exclusively a variety of fault gouge that is essentially a rock flour with a quartz feldspar biotite chlorite amphibole epidote and fe ti oxide mineralogy representing the milled down equivalent of the original rock anderson and osborne 1979 anderson et al 1980 likewise fault gouge and associated breccia are common along the san gabriel fault but only where the zone of cataclasis is several tens of meters wide at several localities the zone is extremely narrow several centimeters and the cataclastic rock type is cataclasite a dark aphanitic and highly comminuted and indurated rock the cataclastic rocks along the san gabriel fault exhibit more comminution than that observed for gouge along the san andreas the average grain diameter for the san andreas gouge ranges from 0 01 to 0 06 mm for the san gabriel cataclastic rocks it ranges from 0 0001 to 0 007 mm whereas the san andreas gouge remains particulate to the smallest grain size the ultra fine grain matrix of the san gabriel cataclasite is composed of a mosaic of equidimensional interlocking grains the cataclastic rocks along the san gabriel fault also show more mineralogiec changes compared to gouge from the san andreas fault at the expense of biotite amphibole and feldspar there is some growth of new albite chlorite sericite laumontite analcime mordenite and calcite the highest grade of metamorphism is laumontite chlorite zone zeolite facies mineral assemblages and constrained uplift rates allow temperature and depth estimates of 200 30 c and 2 5 km thus suggesting an approximate geothermal gradient of 50 c km such elevated temperatures imply a moderate to high stress regime for the san andreas which is consistent with experimental rock failure studies moreover these results suggest that the previously observed lack of heat flow coaxial with the fault zone may be the result of dissipation rather than low stress much of the mineralogy of the cataclastic rocks is still relict from the earlier igneous or metamorphic history of the protolith porphyroclasts even in the most deformed rocks consist of relict plagioclase oligoclase to andesine alkali feldspar quartz biotite amphibole epidote allanite and fe ti oxides ilmenite and magnetite we have found no significant development of any clay minerals illite kaolinite or montmorillonite for many sites the compositions of these minerals directly correspond to the mineral compositions in rock types on one or both sides of the fault whole rock major and trace element chemistry coupled with mineral compositions show that mixing within the zone of cataclasis is not uniform and that originally micaceous foliated or physically more heterogeneous rock units may contribute a disproportionally large amount to the resultant intrafault material as previously found for the gouge along the san andreas chemical mobility is not a major factor in the formation of cataclastic rocks of the san gabriel fault we see only minor changes for si and alkalies however there is a marked mobility of li which is a probable result of the alteration and formation of new mica minerals the gouge of the san andreas and san gabriel faults probably formed by cataclastic flow there is some indication presently not well constrained that the fine grained matrix of the cataclasite of from the san gabriel fault formed in response to superplastic flow

injection veins of crushing originated pseudotachylyte and fault gouge formed during seismic faulting this paper describes the injection veins of crushing originated pseudotachylyte and fault gouge formed along the iida matsukawa fault in granitic cataclasite southern nagano prefecture central japan the pseudotachylyte which shows a dense and aphanitic appearances and fault gouge occur as simple veins fault vein along the main fault plane and as complex network veins injection vein in the neighboring cataclasite locally the injection veins of pseudotachylyte and fault gouge can be traced back to the fault veins powder x ray diffraction patterns and petrological analysis indicate that both of the pseudotachylyte and fault gouge consist entirely of fine grained angular clasts and that the pseudotachylytes and fault gouges have a similar x ray diffraction patterns with that of the host granite the similarity of chemical compositions and distribution patterns of grain size also show that the injection veins of pseudotachylyte and fault gouge have the same source material as that of fault veins field occurrences and petrological characteristics strongly suggest that the injection veins of pseudotachylyte and fault gouge formed during seismic faulting by a rapid intrusion and fluidization of crushed fine grained materials generated in the shear zone in a gas solid fluid system

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

pseudotachylyte controversy fact or friction high speed slip experiments performed on westerly granite using friction welding apparatus reveal that comminution is an essential precursor to melting by friction observations of slip surfaces via analytical scanning electron microscopy sem document the following sequence of events occurring in 2 s with increasing velocity up to 2 m s fracture progressive comminution surface melting of mineral fragments fragment to fragment adhesion and finally production of a fragment laden melt supported suspension explosive dehydration and melting of the epidote group mineral allanite indicates that temperatures of at least 1000 c were realized at the interface this is corroborated by calculation of the temperature rise for the known operating conditions contrary to earlier proposals these results show that comminution and frictional melting are complementary and not mutually exclusive processes depending on the velocity shear stress displacement relations prevailing during frictional slip rocks produced in seismogenic zones can be predominantly comminuted wall rock or fragment melt mixes pseudotachylytes

sudbury breccia at whitefish falls ontario evidence for an impact origin sudbury breccias are unusual clast matrix rock bodies formed in abundance around the sudbury igneous complex the most obvious manifestation of a major impact event at sudbury at whitefish falls 70 km southwest of sudbury similar breccias consisting of clasts of argillite and amphibolite dyke enclosed in a fine grained matrix of host rock are developed in metamorphosed argillites of the huronian supergroup pre brecciation brittle textures in the host argillite and breccia clasts such as layer parallel foliation offset by cataclastic fractures suggest that the host rock was entirely competent prior to brecciation one composite penetrative foliation and its associated ductile folding were also formed in the argillite host prior to brecciation post brecciation ductile deformation produced a regionally dominant east west trending foliation and two late stage folding events and indicate a syn penokean age of brecciation the breccias at whitefish falls are enriched in ferromagnesian minerals compare

the effect of refreezing on the isotopic composition of melting snowpack the isotopic composition of solid and liquid portions of natural melting snowpack is investigated in detail by the separating of liquid water from snow grains at different depths of the snowpack the slope of the d 18o line for the liquid phase is found to be lower than for the solid phase this is proved to be due to the isotopic fractionation occurring in the melt freeze mass exchange within the snowpack melting of the snowpack has no clear impact on the d 18o line for the solid phase but the slope of the d 18o line for the liquid shows an overall slight decrease in the melting period when the snowpack is refrozen the refreezing process would inevitably cause the slope of the solid phase to decrease because of the discrepancy between the slopes of the two phases thus the slope of the solid would become lower and lower as the diurnal melt freeze episodes cycle throughout the melting season this effect is then demonstrated by looking into the isotopic composition changes of glacier firn the extent of the effect depends on the snowpack properties and environmental conditions the slope changes also result in a decreasing trend in deuterium excess copyright 2007 john wiley sons ltd

the destiny of a clast within a molten pseudotachylyte vein pseudotachylytes are important markers that can indicate the thermal state during a coseismic slip failure and provide indirect information about the level of stress and sliding velocities attained during that time window on the other hand survivor fragmented clasts embedded in the quenched material are also very impor tant in that they provide information about the energy spent to create new fracture surfaces in this paper i study the temperature evolution of clasts subjected to the heat dissipated by a just formed molten pseudotachylyte pt vein in particular i find the analytical solutions for the temperature evolution within the pt vein the surrounding undamaged host rock and inside a clast according to the proposed model the numerical results show that the clasts tend to preferentially melt in the inner part of the pt vein i e they are completely assimilated by the pt in contrast some clasts can survive far from the pt vein center my solutions although based upon a simplified model can provide a theoretical framework to predict the maximum size of the survived clasts at a given distance from the pt center the distribution of these survivor clasts follows a power law relation in terms of their radius and its features generally agree with field and laboratory observations

extreme frictional processes in the volcanic conduit of mount st helens usa during the 2004 2008 eruption abstract the 2004 2008 eruption of mount st helens saw the extrusion of seven high viscosity spines and formation of discrete shear zones along the conduit margin at spine 7 this shear zone consists of four structurally distinct layers the outer surface gouge l1 crosscuts a dark banded layer l2 which grades into a moderately sheared layer l3 and undeformed rock l4 inside the spine field observations porosity measurements geochemistry mineralogy microstructure crystal size and shape distribution kinetic properties and magnetic analyses chart the evolution of deformation processes and products throughout the eruption gouge formation was concomitant with characteristic microseismic drumbeats at depths 0 5 1 km in addition the seismic record shows two larger earthquakes with similar seismic signatures in august 2006 which we conclude represent larger slip amounts along the conduit margin of spine 7 extensive slip resulted in frictional heating on the order of several hundreds of degrees melting the highly viscous crystalline ascending magma plug and forming a pseudotachylyte high ambient temperatures in the conduit resulted in near equilibrium melting and slow recrystallisation thus impeding the development of signature pseudotachylyte characteristics and hindering identification thus frictional melting and recrystallisation in ascending magma plugs may be a common but unidentified phenomena at composite volcanoes worldwide

rock record and magnetic response to large earthquakes within wenchuan earthquake fault scientific drilling cores fault related pseudotachylytes are often considered to be produced by large seismic events to investigate the rock record and magnetic response to large earthquakes within cores from the wenchuan earthquake fault scientific drilling borehole 2 wfsd 2 we carried out microstructural geochemical and rock magnetic analyses of representative cores based on microstructural observations and powder x ray diffraction analyses we found 21 layers of melt origin pseudotachylytes from 579 62 to 599 31 m depth in the cores the presence of early formed pseudotachylyte fragments in the new layer suggests that seismic faulting processes exploited the same fault strand more than once pseudotachylyte veins have higher values of magnetic susceptibility relative to wall rocks rock magnetic results indicate that the magnetic minerals within the pseudotachylyte veins are magnetite with varying amounts of paramagnetic minerals magnetic hysteresis loops show that a reduction of the grain size of ferromagnetic minerals is not a plausible explanation for the higher magnetic susceptibility values in pseudotachylyte veins rock magnetic analyses indicate that frictional heating 500 c occurred in the pseudotachylyte veins during large earthquakes the resulting high temperatures induced thermal decomposition of paramagnetic minerals forming magnetite and contributing to the higher magnetic susceptibility values different generations of pseudotachylytes and numerous high magnetic susceptibility zones together demonstrate that ancient powerful earthquakes may have occurred repeatedly in the longmen shan thrust belt

changes in antarctic temperature wind and precipitation in response to the antarctic oscillation output of a 14 year integration with a high resolution 55 km 55 km regional atmospheric climate model is used to study the response of antarctic near surface climate to the antarctic oscillation aao the periodical strengthening and weakening of the circumpolar vortex in the southern hemisphere in spite of the relatively short record wind temperature and precipitation show widespread and significant aao related signals when the vortex is strong high aao index northwesterly flow anomalies cause warming over the antarctic peninsula ap and adjacent regions in west antarctica and the weddell sea in contrast cooling occurs in east antarctica the eastern ross ice shelf and parts of marie byrd land most of the annual temperature signal stems from the months march august the spatial distribution of the precipitation response to changes in the aao does not mirror temperature changes but is in first order determined by the direction of flow anomalies with respect to the antarctic topography when the vortex is strong high aao index the western ap becomes wetter while the ross ice shelf parts of west antarctica and the lambert glacier basin east antarctica become drier

frictional melt homogenisation during fault slip geochemical textural and rheological fingerprints abstract volcanic environments often represent structurally active settings where strain localisation can promote faulting frictional deformation and subsequent melting along fault planes such frictional melting is thermodynamically a disequilibrium process initiated by selective melting of individual mineral phases and softening of volcanic glass at its glass transition as a response to rapid frictional heating the formation of a thin melt layer on a fault plane surface can drastically accelerate or terminate slip during fault motion a comprehensive understanding of the physical and chemical properties of the frictional melt is required for a full assessment of slip mechanisms as frictional rheology depends on the contributions from selectively melted mineral and glass phases as well as the physical effects of restite fragments suspended in the frictional melt here we experimentally investigate the impact of host rock mineralogy on the compositional and textural evolution of a frictional melt during slip high velocity rotary shear hvr experiments were performed under controlled volcanically relevant coseismic conditions 1 m s 1 slip rate and 1 mpa normal stress using three intermediate dome lavas with contrasting mineral assemblages sampled from volcanic systems where fault friction is evident 1 an amphibole bearing andesite soufriere hills volcano montserrat 2 an amphibole poor dacite santiaguito dome complex guatemala and 3 an amphibole free andesite volcan de colima mexico for each sample five hvr experiments were terminated at different stages of frictional melt evolution namely 1 at the onset of melting 2 upon formation of a steady state melt layer and 3 after 5 m 4 10 m and 5 15 m of slip at steady state conditions progressive mixing and homogenisation of selective single phase melts within the frictional melt layer through double diffusion convection demonstrates the control of melt composition on slip behaviour amphiboles melted preferentially leading to consistently lower shear stress 1 mpa less than amphibole poor samples and pronounced shear weakening during the frictional melting of amphibole bearing lavas the results highlight the implications of mineral assemblages on fault slip including conduit flow processes which may influence the style of eruptions and run out distances of rapid granular flows

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

brittle to ductile transition due to large strains along the white rock thrust wind river mountains wyoming abstract the deformed foreland of the rocky mountain cordilleras is characterized by major reverse faults that bring precambrian basement rocks to the surface the white rock thrust in the wind river mountains of wyoming is one such fault that developed at fairly shallow levels in the crust detailed study of grain size variations and textures within the fault zone provide a framework for discussion of the mechanics of movement along the fault textural criteria are suggested for distinguishing between dominantly brittle and dominantly ductile deformation a transition from brittle fracturing to ductile deformation is seen with increasing strain and resultant decrease in grain size along the fault zone diffusional creep in the final stages of deformation leads to strain softening and may allow large strains to take place along narrow zones at low deviatoric stresses this may be one way of obtaining large displacements along major faults at shallow levels in the crust

amorphous material formed by the mechanochemical effect in natural pseudotachylyte of crushing origin a case study of the iida matsukawa fault nagano prefecture central japan abstract pseudotachylytes from the iida matsukawa fault central japan iida pseudotachylytes are described down to the nanometer scale using high resolution electron microscopy scanning electron microscopy analyses of chemical compositions and mercury intrusion porosimetry the pseudotachylyte matrix chiefly consists of nanoscale particles and elongated submicron fragments with biotite composition amorphous material of several tens of nanometers in size is also observed despite the absence of melt textures lattice fringe images reveal that the amorphous phase coexists with lattice distortion in deformed biotite fragments that are several hundreds of nanometers in size the presence of these submicrostructures indicates that the amorphous material formed by mechanical stress during the comminution process that is via the mechanochemical effect we conclude that amorphous material does not always provide evidence of the rapid cooling of melt in pseudotachylyte the amorphous materials present in the iida pseudotachylyte resulted from the mechanochemical effect due to both shear stress and normal stress during the comminution process that accompanied fault motion

roundness of clasts in pseudotachylytes and cataclastic rocks as an indicator of frictional melting abstract we examine the roundness rd of clasts derived from fault rocks and discuss its possible application as an indicator for fracturing and chipping or frictional melting the roundness of quartz and feldspathic clasts derived from four frictional melting originated pseudotachylytes and one crushing without melting originated pseudotachylyte as well as three cataclastic rocks was measured between 230 and 270 clasts 10 m in size were measured for each sample the analyses show that rd is lower than 0 4 in all the clasts included in the cataclastic rocks and crushing originated pseudotachylyte whereas it varies from 0 1 to 1 0 and 35 90 of clasts have a roundness 0 4 in the melting originated pseudotachylyte it is suggested that the clasts having a roundness 0 4 were rounded by frictional melting rather than by fracturing or chipping in pseudotachylytes and that the roundness of clasts may be used as a special index of disintegration attributed to attrition and melting

oxygen isotopes in cellulose from modern and quaternary intertropical peatbogs implications for palaeohydrology abstract cellulose 18o values were measured in modern peatbog plants in recent peats and in mountain peatbog cores from burundi in a study of the hydrologic control of the frsol 18o 16o ratio in intertropical peat cellulose modern plants and waters were collected under various altitudes 800 2500 m a s l with mean annual relative humidity ranging from 0 72 to 0 82 the water 18o values i vary between 4 and 2 5 the cellulose water enrichment is of 25 3 0 5 for aquatic plants of 24 6 emergent plant species the scatter in the cellulose 18o values in vary between 4 and 2 5 the cellulose water enrichment is cellulose 18o values of emergent plantss tend to decrease with increasing elevation 0 6 to 0 07 per 100 m and relative humidity 0 5 to 0 1 per mean emergent plant 18o values are approximated within 0 6 by available cellulose 18o models relating cellulose 18o to the relative humidity h and the environmental water 18o except in a large swampy system peats were subsampled in core ka 2 kashiru burundi 3 28 s 29 34 e 890 cm long 2240 m a s l altitude and for control in the topmost 50 cm of core ku 2 kuruyangwe 3 35 s 29 41 e 2020 m a s l altitude similar 18o vaues 26 to 28 5 were found in the topmost 50 cm of both cores they compare well with the mean 18o for modern emergent plants at kashiru ams 14c dating showed that core ka 2 spans the last 30 ka celluloses are mainly derived from emergent plants and yield 18o values ranging from 19 to 29 with the highest values between 2 1 and 0 ka and the lowest values 19 to 23 5 between 6 and 4 5 ka for the period between 6 and 4 5 ka the models yield a decrease in in of 4 to 2 5 relative to present for an h increase of 6 to 11 before 11 7 ka the models yield a in value close to the present value for an h increase of 6

long term climate variability in continental subarctic canada a 6200 year record derived from stable isotopes in peat the rapid warming of arctic regions during recent decades has been recorded by instrumental monitoring but the natural climate variability in the past is still sparsely reconstructed across many a

glassy pseudotachylyte veins from the fuyun fault zone northwest china glassy pseudotachylytes occur in granitic mylonites from the fuyun fault zone northwest china powder x ray diffraction data indicate that the fine grained matrices of the fuyun pseudotachylytes vary from almost crystalline to complete glass a few to 90 wt glass powder x ray diffraction patterns also indicate that clasts in the glass type pseudotachylyte veins mostly consist of quartz grains microlites displaying quenched or rapid cooling textures vesicles and amygdules flow structures and rounded fragments are also common in the fuyun pseudotachylytes the average bulk chemical compositions of these pseudotachylytes are similar to those of the host rocks but the glass matrix has a low sio2 component which is 5 15 wt lower than that of the host rocks the pseudotachylytes contain 2 3 wt water h2o using experimental data which relate the solubility of water to pressure approximately 400 bars lithostatic pressure corresponding to approximately 1 5 km depth of pseudotachylyte formation is estimated a minimum temperature estimate of 1450 c can be estimated due to the presence of the pure sio2 glass the x ray diffraction and chemical data indicate that the fuyun pseudotachylytes formed during seismic faulting at shallow depths by selective melting under water saturated conditions rather than by total melting or by crushing of the host rocks along fault surfaces

paleoclimatic implications of the relationship between oxygen isotope ratios of moss cellulose and source water in wetlands of lake superior abstract groundwater dominated wetlands contain abundant peat deposits but few studies have addressed the potential of using the oxygen isotopic composition 18 o of fen peat cellulose to evaluate past changes in climate here we investigated the relationship between 18 o values of pond water and those of moss cellulose from species inhabiting different micro environments in three different swales near lake superior united states isotope results over two growing seasons indicate a negligible effect of evaporation on the studied fens and the strong control of groundwater on the isotopic composition of swale water isotopic values for groundwater show a small seasonal variability and their low values suggest the influence of snowmelt our results show a consistent offset of 27 1 between average swale water 18 o and cellulose 18 o values for hollow sphagnum species reflecting the fractionation associated with cellulose biosynthesis when sphagnum species from hummocks are included the offset shows a larger variability 27 3 pointing to evaporative effects affecting hummock species this evaporative effect is more pronounced in emerged mosses which show the largest difference 30 relative to their source water the smaller variability associated with hollow species points to the possibility of performing species specific analyses from peat cellulose for improved paleoclimatic reconstructions

himalayan cross faults affect thrust sheet geometry an example from the munsiari thrust sheet near the gish transverse fault zone frontal darjiling himalaya india abstract the munsiari thrust mt sheet is a dominant thrust sheet in the himalaya and forms the frontal ridge in the gorubathan recess of the darjiling himalaya the geometry of the mt sheet in the recess was poorly constrained thereby inhibiting the understanding of how the geometry and kinematics of the sheet varied from the nepal to the bhutan himalaya we present new structural data and infer the deformation mechanisms and the geometry of the mt sheet in the gorubathan recess in the darjiling himalaya to fill this knowledge gap the mt sheet was dominated by large scale overturned antiforms and synforms the entire mt sheet was later folded to a north easterly plunging synformal fold with ne sw axial trend due to the effect of a himalayan cross fault in the region named the gish transverse fault a new brittle out of sequence and neotectonically active phaparkheti thrust was recognized in the mt sheet deformation microstructures indicate that the temperature of deformation in the mt fault zone and the sheet was 500 c to 700 c and 400 c respectively our approach of first mapping major and minor structures and then integrating these studies with deformation microstructure and tectonic geomorphology data resulted in an improved understanding of the structural characteristics of the mt sheet in the darjiling himalaya our study also suggests that there is considerable variation in the geometry and kinematics of frontal thrust sheets along the himalayan arc that must be studied systematically in the context of himalayan salients and recesses

differing source water inputs moderated by evaporative enrichment determine the contrasting δ18ocellulose signals in maritime antarctic moss peat banks 1 oxygen isotope palaeoclimate records preserved in moss tissue cellulose are complicated by environmental influences on the relationships between source water inputs and evaporative conditions we carried out stable isotope analyses of precipitation collected from the maritime antarctic and cellulose extracted from co located chorisodontium aciphyllum dominated moss peat bank deposits accumulated since 1870 a d analyses of stable oxygen and hydrogen isotope composition of summer precipitation on signy island 60 7 s 45 6 w established a local meteoric water line lmwl similar to both the global mwl and other lmwls and almost identical to the hadam3 isotope enabled global circulation model output the oxygen isotopic composition of cellulose 18oc revealed little temporal variation between four moss peat banks on signy island since 1870 however 18oc followed two patterns with sites a and d consistently 3 enriched relative to 18oc values from sites b and c the growing moss surfaces at sites a and d are likely to have been hydrated by isotopically heavier summer precipitation whilst at sites b and c the moss banks are regularly saturated by the isotopically depleted snow melt streams laboratory experiments revealed that evaporative enrichment of c aciphyllum moss leaf water by 5 occurred rapidly following saturation ecologically equivalent to post rainfall or snow melt periods in addition to the recognized source water cellulose fractionation extent of 27 3 such a shift would account for the 32 difference measured between 18o of signy island precipitation and cellulose

an argument against the crush origin of pseudotachylytes based on the analysis of clast size distribution abstract the origin of pseudotachylytes has been controversial since wenk cast doubt on the melt origin of the matrix of pseudotachylytes in 1978 the matrix of this rock is so fine grained that the crush origin of pseudotachylytes revived by wenk cannot easily be denied this paper presents a new line of argument based on the size analysis of clasts contained in pseudotachylytes in felsic granulite from the musgrave range central australia these clasts are definitely crush products produced during the pseudotachylyte generation their sizes as measured on photomicrographs of thin sections obey the size distribution n n r d where n is the cumulative number of clasts with sizes greater than r d is the fractal dimension and n is a constant that depends on the number of measurements d was found to be 1 5 0 05 for the size ranges of 10 2000 m if the matrix of the pseudotachylytes consists mostly of ultrafine crush products they must have formed simultaneously with those coarse crush products the proportion of fine products relative to the coarse clasts can be estimated assuming that a similar size distribution also holds for the fine products the estimated area occupied by fine products in a thin section is of the order of only several percent whereas the measured area of the matix is about 60 thus the major part of the matrix of the pseudotachylytes cannot be regarded as crush products it is also shown that the number of clasts smaller than about 5 m becomes very small perhaps as a result of nearly complete dissolution of fine clasts in a melt however if the ultrafine grained matrix of the pseudotachylytes had formed by crushing during seismogenic fault motion the grain size refinement during the crushing should have occurred jumping the size range of at least 1 5 m this is quite unreasonable and disproves the crush origin for the matrix of pseudotachylytes

frictional fusion due to coseismic landsliding during the 1999 chi chi taiwan ml 7 3 earthquake fused materials pseudotachylytes generated from landsliding during the 1999 chi chi taiwan ml7 3 earthquake are found on the glide plane in mio pliocene interbedded shale and siltstone the pseudotachylytes occur as thin layers on the glide plane and as veins injected into cracks in the host rocks which are a few mm to 1 cm in thickness typical melting textures within the pseudotachylyte include vesicles glassy matrices flow structures and rounded and embayed clast shapes powder x ray diffraction analysis has revealed a glass content of up to 50 wt within the pseudotachylyte physical conditions of pseudotachylyte formation are estimated to have been 1 5 mpa corresponding to ca 40 m depth at a temperature of at least 1100 1600 c the geological and petrological data suggests that these pseudotachylytes formed by frictional melting generated from coseismic landsliding during the chi chi earthquake

stable carbon and oxygen isotopes in sub fossil sphagnum assessment of their applicability for palaeoclimatology abstract to investigate the potential of stable isotopes of sphagnum peat deposits for palaeoclimate research and to inform sampling strategies we present results from a study of selected sphagnum plant constituents we report a combined stable carbon and oxygen isotope record of cellulose separately extracted from sphagnum branches and stem sections manually sampled from a 4000 year old peat deposited in a small dry maar crater located in the westeifel volcanic field germany we have determined the species composition of each individual sample of sphagnum branches to address the sensitivity of the stable isotope records to potential changes in sphagnum assemblages the youngest approximately 3000 years old peat section consists of scarcely decomposed sphagnum plant material from the bog s surface to a depth of 60 cm the predominant species is sphagnum magellanicum between 60 and 550 cm the peat predominantly consists of sphagnum capillifolium var rubellum at greater depths the decomposition status increases species identification is however solely achievable if the record under examination consists of moderately decomposed peat the stable carbon and oxygen isotope values of cellulose from sphagnum stem sections are significantly lighter than those of the branches both isotopic offsets between the different plant compounds exhibit a strong degree of correlation are statistically highly significant and observable down core the stable carbon isotope offset averages to 1 5 however presumably decreases with increasing age of the plant material in contrast the averaged oxygen isotope offset of 0 9 is consistent in time our results imply that if no differentiation into sphagnum branches and stem sections prior to stable isotope analyses is possible erroneous interpretations of the isotope records are likely since down core changes in the ratio of branches to stem sections in the peat profile are most likely this also implies that the removal of all non sphagnum plants or plant fragments is insufficient to retrieve stable isotope signals from peat deposits exclusively reflecting palaeo environmental conditions even isotopic records from bulk sphagnum cellulose comprise of two different signals firstly an environmental signal based on the plant response to external controls this signal is however masked by a second plant physiological signal originating from the isotopic offset between branches and stem sections

coeval formation of cataclasite and pseudotachylyte in a miocene forearc granodiorite southern kyushu japan abstract cataclastic rocks and pseudotachylytes are exposed along the uchinoura shear zone a normal fault zone cutting the middle miocene 14 ma osumi granodiorite in southern kyushu japan cataclastic rocks include non foliated clast supported to matrix supported cataclasite and foliated clast supported cataclastic granodiorite in these rocks fracturing and comminution played a major role but dissolution and recrystallization of quartz and plastic deformation of quartz and biotite were also active processes especially in foliated granodiorite two types of pseudotachylyte are distinguished a foliated type characterized by a planar arrangement of clasts and microlites and a spherulitic type characterized by clasts surrounded by microlite overgrowths both types are of melt origin as attested by the presence of microlites and rounded or embayed clasts and by the scarcity of biotite clasts unlike spherulitic type pseudotachylyte which solidified without being deformed the foliated type pseudotachylyte underwent flow before complete solidification this deformation is thought to reflect post seismic strain accommodation immediately following the main slip episode kinematic indicators which consist of riedel type secondary fractures branching on primary fractures shear bands offsetting the foliation of foliated granodiorite or asymmetrical porphyroclast systems within pseudotachylyte veins show that all fault rocks were generated during n s to nw se directed extensional deformation pseudotachylyte is closely associated both in time and space with cataclastic rocks thus indicating that the behaviour of the uchinoura fault zone alternated between comminution and frictional melting given the slow strain rates which characterize dissolution and recrystallization processes detected in cataclasites the juxtaposition of pseudotachylytes and foliated cataclasites provides an example of aseismic and seismic displacements within the same shear zone

fracturing mode analysis and relative age dating of faults by surface textures of quartz grains from fault gouges abstract surface textures of quartz grains taken from about 250 samples of fault gouges in faults ranging in length from several metres to several tens of metres with the faults extending several tens to several hundreds of kilometres in length are examined by means of the scanning electron microscope and are categorized into four groups from i to iv based on the smoothness of the surface degree of undulation and development of cavities as mentioned in a previous paper based on surface features of quartz grains from faults the geological age of movement of which is known the groups i to iv are tentatively related to the age of formation of quartz grains and the period of formation of surface textures this correlation makes it clear that quartz grain surface textures are an important clue to dating a relative age of faulting river patterns striations granular fracture surfaces and dimple like textures are observed to appear on less corroded surfaces of quartz grains from fault gouges fractographic analysis of these surfaces of quartz grains should be a clue to revealing the mode of fracture of the fault movement which released the quartz grains into the fault gouge

numerical modelling and analysis of temperature controlled density currents in tomales bay california abstract the coastal region adjacent to tomales bay california is dominated by wind driven upwelling during spring and summer and the cold upwelled water is moved towards tomales bay entering the estuary with the flood tide if the tidal excursion is 6 km and the cold water subducts beneath the warmer less dense estuarine water a temperature controlled density current may form and intrude towards the head of the estuary as a thermally stratified bottom layer the numerical modelling was aimed at determining the capability of the delft3d flow model to reproduce the cold ocean water intrusion events the response development and progression of these intrusions to differing physical scenarios and the comparative importance of the parameters to the intrusions the numerical model successfully reproduced the density intrusions and showed that the persistence and break down of the density intrusions were affected by a number of physical parameters to varying degrees the sensitivity analysis showed that density intrusion formation is controlled by tidal conditions and ocean water temperature the strength and persistence of the developed density intrusions are influenced by wind insolation and estuary depth fresh water inflow at the head of the estuary had no impact on the density intrusions three dimensional numerical modelling is thus a valuable tool in understanding the estuary and its functioning

melt origin of fault generated pseudotachylytes demonstrated by textures a petrographic and electron microprobe study of fault generated pseudotachylytes from the outer hebrides thrust zone scotland demonstrates that the textures have resulted from the primary crystallization of a clast laden melt rather than the devitrification of a glass or by crushing and cataclasis the observations are consistent with these pseudotachylytes having formed by frictional fusion followed by rapid quenching implying faulting at shallow crustal depths

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

holocene climate variability revealed by oxygen isotope analysis of sphagnum cellulose from walton moss northern england abstract stable isotope analyses of sphagnum alpha cellulose precipitation and bog water from three sites across northwestern europe raheenmore ireland walton moss northern england and dosenmoor northern germany over a total period of 26 months were used to investigate the nature of the climatic signal recorded by sphagnum moss the 18o values of modern alpha cellulose tracked precipitation more closely than bog water with a mean isotopic fractionation factor cellulose precipitation of 1 0274 0 001 1 27 sub samples of isolated sphagnum alpha cellulose were subsequently analysed from core wlm22 walton moss northern england yielding a sphagnum specific isotope record spanning the last 4300 years the palaeo record calibrated using the modern data provides evidence for large amplitude variations in the estimated oxygen isotope composition of precipitation during the mid to late holocene estimates of palaeotemperature change derived from statistical relationships between modern surface air temperatures and 18oprecipitation values for the british isles give unrealistically large variation in comparison to proxies from other archives we conclude that use of such relationships to calibrate mid latitude palaeo data must be undertaken with caution the 18o record from sphagnum cellulose was highly correlated with a palaeoecologically derived index of bog surface wetness bsw suggesting a common climatic driver

the origin of present day antarctic precipitation from surface snow deuterium excess data the deuterium excess d is defined as a linear combination of the d h and 18 o 16 o ratios in natural waters we present an interpretation of deuterium excess data in surface antarctic snow using an isotopic model to derive information on the origin of present day antarctic precipitation the data come from near the coast d47 adelie land and from inland south pole 1000 km from the sea the one dimensional isotopic model belongs to the rayleigh family but fully accounts for mixed cloud processes between 0 c and 30 c modeling d in polar snowfalls meets the problem of a large sensitivity to the saturation conditions prevailing at snow formation therefore we decided to tune the saturation in the model in order to yield realistic mean d values but we use the seasonal phase of d versus which is less sensitive to the saturation conditions as an independent validation of the model predictions both inland and near the coast our model can simulate the observed phase between d and in snow with moisture of subtropical origin 40 20 s although we do not treat specifically storm precipitation near the coast this study indicates that the observed phase between d and brings up a new validation of isotopic models it supports a distant vapor source for large scale precipitation delivered to the antarctic continent

reconstruction of ice sheet changes in the antarctic peninsula since the last glacial maximum this paper compiles and reviews marine and terrestrial data constraining the dimensions and configuration of the antarctic peninsula ice sheet apis from the last glacial maximum lgm through deglaciation to the present day these data are used to reconstruct grounding line retreat in 5 ka time steps from 25 ka bp to present glacial landforms and subglacial tills on the eastern and western antarctic peninsula ap shelf indicate that the apis was grounded to the outer shelf shelf edge at the lgm and contained a series of fast flowing ice streams that drained along cross shelf bathymetric troughs the ice sheet was grounded at the shelf edge until 20 cal ka bp chronological control on retreat is provided by radiocarbon dates on glacimarine sediments from the shelf troughs and on lacustrine and terrestrial organic remains as well as cosmogenic nuclide dates on erratics and ice moulded bedrock retreat in the east was underway by about 18 cal ka bp the earliest dates on recession in the west are from bransfield basin where recession was underway by 17 5 cal ka bp ice streams were active during deglaciation at least until the ice sheet had pulled back to the mid shelf the timing of initial retreat decreased progressively southwards along the western ap shelf the large ice stream in marguerite trough may have remained grounded at the shelf edge until about 14 cal ka bp although terrestrial cosmogenic nuclide ages indicate that thinning had commenced by 18 ka bp between 15 and 10 cal ka bp the apis underwent significant recession along the western ap margin although retreat between individual troughs was asynchronous ice in marguerite trough may have still been grounded on the mid shelf at 10 cal ka bp in the larsen a region the transition from grounded to floating ice was established by 10 7 10 6 cal ka bp the apis had retreated towards its present configuration in the western ap by the mid holocene but on the eastern peninsula may have approached its present configuration several thousand years earlier by the start of the holocene mid to late holocene retreat was diachronous with stillstands re advances and changes in ice shelf configuration being recorded in most places subglacial topography exerted a major control on grounding line retreat with grounding zone wedges and thus by inference slow downs or stillstands in the retreat of the grounding line occurring in some cases on reverse bed slopes

generation and crystallization of an amphibolite shear melt an investigation using radial friction welding apparatus a cylinder of amphibolite comprising the assemblage amphibole clinozoisite albite has been frictionally melted using radial friction welding apparatus this was achieved by rotating a steel ring at 750 rpm and a force of 98 kn for 10 s against a stationary steel casing which housed the rock sample the ring penetrated the casing then proceeded to rotate and compress the sample to 95 of its original volume until it cracked at right angles to its length this generated a whole rock silicate melt which injected the crack and on cooling produced glass crystallites and vesicles melting occurred in two stages an initial low pressure melting event with crystallization to augite fe rich anorthite followed by a high pressure melting event with crystallization to fassaitic clinopyroxene it is estimated that pressures of 0 5 gpa rising to 1 gpa were realized at the ring rock interface under these conditions fassaite superseded augite anorthite crystallization due to the increased solubility of ca tschermak s component in clinopyroxene the high pressure event provides a crude analogue for the frictional melting of basic rock at depths of 15 30 km in a seismogenic fault a situation realized along the slip zone between cold descending lithosphere and overlying mantle during subduction

variations of 18o 16o in plants from temperate peat bogs switzerland implications for paleoclimatic studies despite the great potential of peat bogs as climatic archives to date only few studies have focused on the climatic controls on cellulose isotopic composition in modern bog plants this study attempts to calibrate plant climate relationships by sampling a set of modern plant species both vascular plants and mosses and bog surface waters along an altitude transect in switzerland isotopic analyses of water samples show that the 18o values of surface bog waters follow the trend of precipitation despite significant scatter in the data set detailed sampling of surface waters within one bog shows that 18o values vary widely and are closely related to the micro topography of the bog surface more enriched 18o 16o ratios in water samples collected from small raised hummocks than the ones collected from hollows are documented in both horizontal and vertical profiles a 18o d plot indicates that the process leading to the isotopic enrichment of the uppermost surface waters is evaporation greater above sphagnum covered hummocks than above open pools to investigate the implications of such high variability of source water for plant cellulose 18o values a detailed study of both surface water and cellulose 18o values within one site is conducted the large 18o variability observed in surface waters is found to be considerably smoothed in cellulose by a factor of 5 10 depending on the plant species this indicates that the water used by plant photosynthetic processes reflects the isotopic composition of the average annual precipitation this points to a source water level for plants of a few decimeters where the variations are smaller than at the air water interface the response of the cellulose 18o to the environmental gradient along the altitude transect varies considerably from species to species for most of the species studied the 18o values decrease with altitude following the trends of 18o values in precipitation and in surface water samples some species the cotton sedge eriophorum vaginatum and the moss sphagnum capillifolium show statistically significant 18o relationships to an altitude of 1 8 km and 2 9 km respectively however some other plant species calluna vulgaris vaccinium uliginosum andromeda poliflora carex pauciflora sphagnum cuspidatum and sphagnum magellanicum do not or only partially reflect changes in climatic parameters associated with an altitude increase furthermore changes in relative humidity which are not correlated with altitude are found to explain a large part of the variability in 18o values for the sedge carex pauciflora and the moss sphagnum cuspidatum therefore this study confirms the importance of species specific studies when interpreting 18o 16o ratios of macrofossils along a fossil peat sequence as a record of past climate changes our study allows to extend the mechanistic model that isotopically links source water and cellulose to the physiological specificities of sedges and mosses a comparison of the modeled and calculated net biological fractionation factors for eriophorum vaginatum and sphagnum capillifolium reveals that these two species appear to have a more homogeneous leaf reservoir than trees

chemical heterogeneities of caledonian pseudotachylites in the eidsfjord anorthosite north norway the 1 8 1 7 ga eidsfjord anorthosite complex on langoy vesteralen north norway is thrust over monzonitic gneisses in a 100 m wide fault zone the anorthosite contains abundant pseudotachylite which also overprint ductilely formed ultra mylonites in the monzonitic gneisses 40ar 39ar dating of the pseudotachylites indicates that this deformational event took place during the end of the caledonian orogeny pseudotachylite formation by in situ melting is corroborated by a detailed petrological investigation of chemical and textural criteria identity of host rock mineral compositions and modes with pseudotachylite clasts and calculated modes confirm the common notion that transport over more than a few cm did not occur during pseudotachylite formation because the characteristics of the host rocks are inherited by the pseudotachylite pseudotachylite compositions lie in the range of xrf whole rock analyses of deformed and undeformed host rocks demonstrating that no material was added or lost during pseudotachylitisation the pseudotachylites show strong chemical heterogeneity on a scale of tens of micrometers this compositional variation can be described by an approximately binary mixture of plagioclase with a homogenised mafic component comprising orthopyroxene clinopyroxene and fe ti oxides although the pseudotachylite matrix is not homogenised and locally shows schlieren textures the mafic phase in the anorthositic rocks must have homogenised very well before incorporation into the pseudotachylite different viscosities and mixing properties for the al and the fe rich parts of the pseudotachylite melt are inferred

microlite morphology and chemistry in pseudotachylite from the fuyun fault zone china microlites in pseudotachylite veins from the fuyun fault zone northwest china can be divided into four morphological groups simple skeletal dendritic and spherulitic from the margin to the center of microcrystalline and microlitic pseudotachylite veins the size of single crystals or crystal fibers becomes progressively larger from a few m to as much as 15 m the morphologies of microlites vary from simple shapes such as acicular and globular forms to more complex forms such as skeletal dendritic and coarse spherulitic forms in glassy pseudotachylites only simple and fine spherulitic microlites generally smaller than 5 6 m occur these microlites have a varied mineralogy but are mainly made up of plagioclase an20 70 and alkali feldspar including sanidine and anorthoclase as well as clinopyroxene grossular garnet biotite hornblende and some magnetic minerals the biotite and hornblende microlites have a variable ti content generally higher than that of biotite and hornblende frag