esr dating of fault movement using various defect centres in quartz the case in the western south fossa magna japan the dates of movements of the itoigawa shizuoka tectonic line i s t l and minobu fault in the western south fossa magna have been obtained by esr dating measurements were made on various lattice defects of the ohc ge al and e centres in quartz grains of fault clay and quartz veins intruded at the time of movement all the dates obtained from these centres in quartz grains from two localities of the i s t l and iwo localities of the minobu fault fall in the range of 0 30 0 55 ma this suggests that all the centres were annihilated completely and that the obtained age can be admitted as the actual data of the latest fault movement meanwhile esr dates of quartz vein and fault clay in other localities locations 3 6 7 are divided into 0 30 0 55 ma and 1 5 2 0 ma which suggest incomplete resetting the dates of 0 30 0 55 and 1 5 2 0 ma might correspond to the clino unconformities observed in plio pleistocene sequence of this region

a new method for the estimation of cooling and denudation rates using paramagnetic centers in quartz a case study on the eldzhurtinskiy granite caucasus we present a new method for the assessment of the most recent cooling and denudation rates using paramagnetic centers in quartz measured by electron spin resonance esr spectroscopy these centers have a relatively low thermal stability for cooling rates of 40 o and 1000oc myr effective closure temperatures vary between 55 o and 82oc ti center and 49 o and 64 oc a1 center respectively samples were collected from two cores that were drilled into the eldzhurtinskiy granite which has an emplacement age of 2 ma as measured by u pb analyses of zircons one 1500 rn core was taken from a drill hole into the dome of the granite a second core of 4000 rn from a drill hole at the base of the baksan valley our results yield cooling rates of between 160 and 250oc myr for the upper core and between 570 o and 600oc myr for the lower core the corresponding denudation rates are 2 5 upper core and 5 5mm a lower core the shape of the temperature profile of the lower core indicates recent erosion when fitting the temperature data with a two dimensional heat transfer model we obtain a net denudation rate of 10 mm a and cooling rates in the range of 500oc myr thus confirming the cooling rates estimated by esr however the esr denudation rates underestimate the erosion rate of the baksan valley because the geothermal gradient is not equilibrated between the surface and the depth of the annihilation temperatures 950 and 1800 rn for the a1 and ti centers respectively we conclude that esr measurements of paramagnetic centers in quartz will allow the recon struction of landscape dynamics for the past 10 1000 kyr and that in conjunction with u pb fission track and ar ar analyses it will be possible to develop dynamic models for quaternary tectonic movements

variations of methane induced pyrite formation in the accretionary wedge sediments offshore southwestern taiwan abstract the accretionary wedge of offshore southwestern taiwan contains abundant deposits of gas hydrate beneath the sea floor high concentrations of methane in pore waters are observed at several locations with little data concerning historical methane venting available to understand temporal variation of methane venting in sediments over geologic time a 23 m long calypso piston core md05 2911 was collected on the flank of the yung an ridge pore water sulfate dissolved sulfide dissolved iron methane sedimentary pyrite acid volatile sulfide reactive iron organic carbon and nitrogen as well as carbonate 13 c were analyzed three zones with markedly different pyrite concentration were found at the study site unit i sediments 20 mbsf were characterized with a high amount of pyrite 251 380 mol g and a 13 c depleted carbonate unit ii sediments 15 20 mbsf with a low pyrite 15 43 mol g and a high content of iron oxide mineral and unit iii sediments the oscillation records of pyrite concentrations are controlled by temporal variations of methane flux with an abundant supply of methane to unit i and iii anaerobic methane oxidation and associated sulfate reduction favor diagenetic conditions conducive for significant pyrite formation no aom signal was found in unit ii characterized by typical organically limited normal marine sediments with little pyrite formation the aom induced pyrite formation near the smi generates a marked pyrite signature rendering such formation of pyrite as a useful proxy in identifying methane flux oscillation in a methane flux fluctuate environment

composition and exhalation flux of gases from mud volcanoes in taiwan many mud volcanoes are distributed along the tectonic sutures in southern taiwan and can be divided into five zones based on their relative positions in different tectonic domains most active mud volcanoes are exhaling methane dominated gases nevertheless some gases show unusual carbon dioxide dominated and or nitrogen excess compositions this implies that there are multiple sources for the gas compositions of mud volcanoes in taiwan

tide modulated gas emissions and tremors off sw taiwan abstract the continental margin off sw taiwan is in an incipient stage of orogeny and contains numerous active mud diapirs and mud volcanoes gas emissions out of the seabed off sw taiwan are revealed by acoustic images from 38 khz echo sounders or sub bottom profilers however the mechanism for gas emissions is still poorly understood in this study we show that the gas emissions out of the seabed and the associated tremors off sw taiwan are strongly correlated with the ocean tides especially with the diurnal and semidiurnal constituents particularly for each tidal day the strong gas emissions expulsions and long duration tremors occur mainly during both the rising periods to the higher high tides and the falling periods to the lower low tides both the gas emissions and tremor activities are generally quiescent near the tidal datum on average the daily intensity of gas emissions and the magnitude of tremors are positively proportional to the daily tidal range a larger slope site implies a greater concentration of gas in the shallow sediments most of the individual tremors and long duration tremors observed off sw taiwan occur as results of the strong gas expulsions out of the gas bearing seabed the high frequency components of the induced tremors quickly decay and are followed by horizontal low frequency 7 hz harmonic oscillations of the seabed long duration tremors may enhance seafloor instability and increase the potential for submarine landslides

esr studies for absolute dating of fault movements the principle of absolute dating of fault movements is based on the initialization or resetting of some clock system by faulting in the case of esr dating heating is more effective in resetting esr signals than fracturing according to a computer simulation of resetting by shear heating during faulting the esr signals can never be completely reset at depths of less than 100 200 m below the surface of the earth therefore esr samples must be collected from depth by coring or tunnelling or from outcrop with consideration of the rate of exhumation of the fault outcrop in general unpaired electrons trapped at lattice defects in crystals can diffuse much more easily than atoms hence samples for other dating methods which are based on the diffusion of atoms should be collected at even greater depth on the other hand if no esr signal is observed from unfractured quartz in the wall rocks one may directly determine the age of the fault movement using esr signals in the fractured quartz whose precursors were formed by faulting the age obtained t should then satisfy the following relationship t b t t e where t b and t e are the ages of the beginning and end of the fault movements and it may show the time of a fault movement

esr isochron dating of the nojima fault gouge southwest japan using icp ms an approach to fluid flow events in the fault zone

pge enrichment in chromitite layers and the merensky reef of the western bushveld complex a re os and rb sr isotope study abstract four poikilitic pyroxenites of the bastard unit all being relatively low in osmium concentrations define a re os isochron age of 2043 11 ma with initial 187os 188os 0 151 which is in accordance with the normally cited crystallization age of the bushveld complex the isochron fit demonstrates an excellent radiogenic os isotopic homogeneity of this portion of the complex at the time of crystallization and excludes any later disturbance of the re os isotope system initial 187os 188os ratios of platinum group element pge enriched sulfides and whole rocks of the directly underlying merensky reef are highly radiogenic and variable with values between 0 168 and 0 181 separates of chromite grains and interstitial phases of critical zone chromitite layers show initial 187os 188os signatures ranging from the near chondritic mantle values of lower group chromitites i e 0 120 to 0 137 for middle group chromitites and to 0 150 for the upper group 2 chromitite layer osmium concentrations of interstitial phases exceed those of the associated chromite in all layers by up to 30 fold showing the presence of highly pge enriched interstitial sulfides equal or very similar initial 187os 188os signatures of the interstitial minerals and the cumulus chromite grains together with their coupled increasing and decreasing trends in this ratio clearly demonstrate that interstitial sulfides and associated cumulus chromite of the different chromitite layers scavenged their osmium from the same or similar sources therefore a pge enrichment of the interstitial sulfides by a primary magmatic process such as precipitation of immiscible sulfide droplets during magma mixing appears more likely than a scenario involving fluid or melt transport of pge into these layers such a primary magmatic pge enrichment process is also preferred for the formation of the merensky reef

identification of a suspected quaternary fault in eastern korea proposal for a paleoseismic research procedure for the mapping of active faults in korea abstract in terms of seismic hazard in the korean peninsula the occurrence of destructive earthquakes has long been overlooked because of no serious modern instrumental seismicity and lack of historical earthquake records of large earthquakes in recent years although the importance and uses of paleoseismological studies has significantly increased in seismic hazard assessments of critical facilities there is still a huge lack of paleoseismological data to improve our knowledge for korean active tectonics and relevant seismic hazards in this study we identified and characterized a suspected quaternary fault in the eastern part of the korea peninsula based on lineament analyses field observations and trench surveys we focus on a prominent lineament around the northern part of the previously reported but not sufficiently studied maeup fault firstly a potential fault lineament is recognized by geomorphic expressions in a mountainous area from satellite and digital elevation model dem generated images then fault related geomorphic and hydrologic features such as disconnected drainages sag ponds and asymmetric water leaking out on an artificial ditch were observed along the lineament in the field studies finally the existence of the fault is confirmed by an exposure of a 2 5 m wide fault core in trench surveys the internal structures of the fault core i e slip surfaces slickenlines and s c fabrics indicate that the fault evolved via a series of slip events under a variety of tectonic settings probably leading up to the current stress regime sustained during quaternary thus our results suggest that the newly identified fault could be a quaternary fault and hence it is necessary to perform more paleoseismic investigations around the study region this case study emphasizes the importance of the careful interpretation of tectonic landforms and fault zone structures in the study of active faults and proposes a suitable research procedure for the identification of active faults in korea

tidal modulation of seismic noise and volcanic tremor 1 we present seismic data from fogo volcano cape verde republic that document a tidal control on the amplitude of seismic noise and volcanic tremor the effect is detectable in the raw data by simple eye inspection we identified the main periodicity in the noise modulation which coincides with the tidal component m2 the signal duration of 40 days together with a sampling rate of 1440 samples per day seismic r m s time series allowed the resolution of m2 from the neighbor solar frequencies that are often related to environmental effects spectral analysis shows that the modulation affects selectively the frequency range 2 0 hz 3 0 hz which we interpret as volcanic tremor white noise from 1 5 hz to 7 hz is also modulated comparison with meteorological data reinforces the conclusion that the effect is not due to environmental parameters

criteria for complete zeroing of esr signals during faulting of the san gabriel fault zone southern california in using electron spin resonance esr to date the time of the last movement on a fault it is essential to demonstrate that the esr signal was fully zeroed at the time of faulting if the signal was not completely reset then the esr age obtained will be too great we have refined the criteria for complete zeroing of esr signals at the time of fault movement samples of fault rocks were collected from surface outcrops of the san gabriel fault zone in the little tujunga region near los angeles southern california using quartz grains of 250 m the estimated ages for either e or ohc signals in all fault rock samples analyzed decrease with grain size down to a plateau value for particles smaller than some critical grain size in some cases the al signal in the smallest grains yields the same age as the plateau age of either the e or ohc signal plateau ages of reactivated younger gouges were indeed smaller than those of the older fault host rocks within the plateau region different grain size fractions show different radiation sensitivity for a single esr signal but all converge to the same de equivalent dose value this indicates that the complete resetting probably occurred during fault movement the depth of fault rocks during fault movement can be estimated from uplift rates and the esr ages the estimated uplift rates was about 0 3 cm yr for the holocene and 0 03 cm yr for the late pleistocene menges et al 1979 the estimated plateau esr ages ranged from 1200 to 135 ka the depths at the time of the last fault movements in the little tujunga region were in the range of 68 360 m the measured maximum horizontal stresses at this depth in southern california range from 5 to 10 mpa for a depth of 70 m the calculated vertical stress is 1 16 mpa and measured maximum horizontal stress is about 5 mpa the angle between the strike of the san gabriel fault and the direction of maximum horizontal stress is about 85 using above values calculated shear stress on the fault is about 0 67 mpa and the normal stress to the fault is about 5 mpa if we assume mean displacements of 4 cm m 4 to 1 m m 7 these conditions were sufficient to reset esr signals in quartz below critical grain size at the time of fault activity

internal tides recorded at ocean bottom off the coast of southeast taiwan an ocean bottom experiment consisting of an array of four ocean bottom seismometers obs was conducted off the coast of southeast taiwan during may july 2011 we develop comprehensive analyses of the space time kinematics of the tidal signals recorded in the compact high sensitivity temperature loggers chtl and the obs geophones at the ocean bottom with depths ranging from 1254 to 1610 m the evidence suggests that internal tides are responsible for the recorded signals baroclinic internal waves mainly the m2 tide are generated by barotropic tidal currents in the luzon strait the internal tides exhibit gradual phase changing and irregularly fluctuating strength leaving signatures in the chtl as ambient temperature variations signifying low mode wave motions within the stratified water layers and in obs geophones as intermittent tremor agitations signifying high mode turbulent flows on the seafloor the m2 internal tides across our array are found to propagate in the northeast direction at speeds ranging from 1 to 2 m s 1 furthermore the internal tides are identified at the ocean bottom based on an operational hydrodynamic hindcast forecast model the simulations show good agreement with the observed temperature variation on the seafloor and substantiate the vertical velocity and displacement of the water parcel driven by the internal tides the joint detection of the temperature and tremor signals provides further information about the interactions of internal tides with the seafloor topography and the associated energy dissipation our results elucidate the space time ubiquity of the internal tides at the ocean bottom which is an important interface of dynamic oceanography

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

a reply to comments by w m buhay on increase of radiation sensitivity of esr centers by faulting and criteria of fault dates buhay 1 confined his discussion on my paper 2 to two esr centers the ohc and ai centers however because not only ohc and a1 centers but also ge and e centers are the main lattice defect centers in quartz his discussion should have been on all the esr centers in quartz in my paper 2 i regarded the increase of radiation sensitivity of esr centers as a phenomenon of major importance and this was based on experimental results the experiments may be divided broadly into 1 uniaxial compression and 2 thermal annealing tests 1 uniaxial compression test under uniaxial compression of about 1 kbar for 540 min at room temperature the rates of increase of the signal intensities of the ohc ge and ai centers remain almost unchanged against artificial irradiation however i have not denied the increase of radiation sensitivity of these centers under greater normal stress as mentioned recently by fukuchi 3 the bond between oxygen and silicon ions in quartz is cut with the formation of dislocations or subgrain boundaries at the time of deformation and consequently silicon and oxygen vacancies which are the precursors of the ohc and e centers are formed s i o and si seeing as the formation of dislocations depends on temperature confining pressure differential stress strain rate and so on these precursors may be formed even under a confining pressure of about 1 kbar if the temperature is higher or the strain rate is lower in addition vacancies and interstitials which play important roles in the diffusion of atoms and the consequent increase of radiation sensitivity can also be formed along dislocations or subgrain boundaries this discussion was presented in the paper 2 as lattice defects can be caused by fracturing more fracturing or plastic deformation of quartz grains may be necessary to increase the radiation sensitivities of esr centers in contrast the signal intensity at the e center increased with gamma irradiation after the fracturing fig 4b in 2 this is thought to be due to the formation of oxygen vacancies by fracturing although it is clear from the paper that the radiation sensitivity of esr centers depends on the degree of cataclastic deformation of quartz why did buhay neglect the fact that the radiation sensitivity of e center increased in order to clarify the mechanism of the increase of radiation sensitivity by fracturing more detailed experiments are necessary and such experiments should be the next step i therefore believe that buhay should have discussed these problems on the basis of his own i e new experimental data 2 thermal annealing test i carried out isothermal annealing experiments on the esr centers in quartz at several temperatures and investigated the change of radiation sensitivity the radiation sensitivities of the ohc and ge center increased by heating and this has been reconfirmed with other natural quartz samples if buhay refutes these experimental observations he should show results to support his claim secondly buhay believed that once the effect of temperature was removed the majority of the

tectonic history of granitic bodies in the south fossa magna region central japan new evidence from fission track analysis of zircon abstract a fission track ft analysis of zircons has been performed to clarify tectonic history of the tertiary granitic bodies in the northern part of the izu bonin arc and the south fossa magna region of central japan a total of 30 ft ages was obtained from the kaikoma tsuburai ashigawa tokuwa and tanzawa granitic bodies confined ft lengths were also measured on 11 zircon samples from the granitic rocks to obtain more information on the thermal history of the region the ft ages and confined ft length data from the kaikoma indicate that this granitic body cooled below the isotherm of zircon 240 c at 9 4 0 4 ma 2 the tsuburai ashigawa tokuwa and tanzawa granitic bodies which have a similar lithology and tectonic setting lie from northwest to southeast respectively the ft ages for these bodies are 15 0 0 6ma for the tsuburai 11 9 0 4 ma for the ashigawa 12 5 1 4 ma for the tokuwa which is comparable with the ft age of the ashigawa 7 1 2 0 ma for the tanzawa which is the youngest the data indicate a differential uplift of the granitic bodies in the south fossa magna region in general the ft ages become younger as one proceeds southeastwards approaching the izu bonin arc the ft age data provide constraints on the tectonic effects of the collision of the izu bonin arc with the central honshu of the japan arc

mud volcanism by repeated roof collapse 3d architecture and evolution of a mud volcano cluster offshore nigeria abstract using 3d seismic data we document the subsurface architecture of a cluster of 3 mud volcanoes located on the upper continental slope offshore nigeria in a background of gently dipping stratified sediments the subsurface of the cluster contains 8 seismic sequences made of one subcircular syncline 1 3 km in diameter and adjoining unstratified units synclines flatten out upward through intercalation of unstratified concave up lenses between stratified units and are eventually filled by a convex up unstratified lens onlapped by background sediments the lower boundary of each sequence is a 0 5 1 5 km deep bowl shaped unconformity across which high dip strata rest above truncated low dip series we interpret each seismic sequence as a mud volcano system mvs sourced from a connected region and evolving through episodes of roof collapse three are associated with the surface mud volcanoes and another 4 to fossil ones mud volcano systems are dynamic features that record the evolution of 1 the material extruded from one single connected source region depletion zone as it grows downwards and stepwise becomes depleted 2 the basal unconformity which joins strata originally separated by material evacuated in the remobilization process by analogy with salt tectonics we propose to call it a mud weld 3 the conduits and 4 the successive collapsed roofs of the depletion zone the evolution of each mud volcano system in this interpretation records progressive growth of the depletion zone by downbuilding punctuated by episodes of roof collapse and extrusion the geometry and evolution of this type of mvs can be interpreted in the light of analogue models of magmatic caldera development in early stages the thin roof experiences downsagging while remobilized material is extruded through an axial pipe like conduit in later stages the thickened roof undergoes piston like subsidence and mud extrusion occurs along the peripheral fault

studies on a new esr signal r signal of fault gouges for fault dating abstract a new esr signal designated r is used for the esr fault dating the r signal is masked by the e signal at commonly used microwave powers typically 1 mw but is clearly distinguished from it at higher microwave powers the r signal of quartz grains of the youngest fault gouge of the atotsugawa fault a major active fault in central japan was the most intense and increased remarkably by artificial gamma ray irradiation while source rocks have no r signal it indicates that precursors of paramagnetic centres associated with the r signal are produced during or after faulting and that the r signal increases later our experiments reveal that heating prior to artificial irradiation is ineffective for the production of the precursors and the precursors is made by another mechanism probably mechanical fracturing at faulting if so the d e value by the r signal means the equivalent dose of natural radiation which a sample received after faulting therefore the r signal might directly give the age of the most recent fault movement

non volcanic tremor resulting from the combined effect of earth tides and slow slip events swarms of non volcanic tremor in southeastern japan are associated with slow slip events and tend to occur with a periodicity of 12 or 24 h this periodicity can be reproduced by a combination of stresses due to earth tides and transient stress changes caused by slow slip events non volcanic tremors may therefore be useful for understanding stress relaxation at the subduction zone interface slow slip events1 are accompanied by swarms of non volcanic tremor2 3 along the subduction zone of the philippine sea plate in southwest japan the swarms often occur with a periodicity of about 12 or 24 h refs 4 5 these episodic events are considered to be a manifestation of stress relaxation at the subducting plate interface1 6 7 here we analyse seismic data to record the locations and durations of non volcanic tremor swarms that occurred in may 2005 and february 2006 we evaluate the magnitude of stress changes produced by slow slip events as well as the effective normal stress on the plate interface where slow slip events occur we find that the observed periodicity in tremor occurrence originates from a combined effect of the periodic stress due to earth tides and the transient stress due to slow slip events our calculations show that non volcanic tremor is sensitive to stress change this phenomenon can therefore be effective in monitoring the process of stress relaxation at subducting plate interfaces

cooperite and braggite from the bushveld complex implications for the miscibility gap and identification analyses of the pt pd ni sulphides cooperite braggite and vysotskite reported from worldwide occurrences seem to imply a continuum of compositions between vysotskite and cooperite with no obvious miscibility gap this is contrary to the experimentally confirmed miscibility gap between cooperite and braggite and the established compositional gap between co existing cooperite and braggite from the merensky reef although the only unambiguous way of distinguishing between cooperite and braggite is to obtain structural information through x ray diffraction or equivalent techniques most identification of pt pd ni sulphides is based on microanalytical techniques due to the small grain size of most platinum group minerals ni contents also have to be considered because a classification based on the pt pd ratio alone can be very misleading naming of pt pd ni sulphide compositions with high pt contents based on qualitative or semi quantitative analyses should be avoided natural pt pd ni sulphides which project into the compositional gap established by experimental work cannot be named without supporting structural information compositions of grains which plot inside the gap are considered to be metastable and to result from the loss of pd through interaction with hydrothermal fluids

mud volcanoes the most important pathway for degassing deeply buried sediments abstract this paper discusses the nature of the phenomenon of mud volcanism with respect to degassing of deeply buried sediments mud volcanoes are defined as geological structures and their main elements are described based on the nature of activity mud volcanoes are grouped in to three main types and the relationship between each type and corresponding morphological expression is discussed the presented up to date data of the world geographical distribution of mud volcanoes show that they approximate to 1800 individuals a detail overview of geological environments in which they occur helps to deduce some necessary conditions for mud volcano formation the basic mechanisms of mud volcano formation are discussed specifically the fluid pressure hypothesis and some triggering events are identified the most common investigation approach and some criteria for recognizing of a submarine mud volcano on side scan sonar records and seismic sections are given mud volcanism in the mediterranean ridge an accretionary complex and black sea abyssal plane a back ark basin with tectonic regime of extension are described as case studies to show variety in morphology and common factors in development of mud volcanoes the manifestation of continuous gas migration through mud volcanoes is clarified and the attempt made to quantify the gas release shows that mud volcanoes are one of the significant natural sources of atmospheric methane emitting a total amount of about 10 3 to 12 6 tg annually

origin of phlogopite orthopyroxene inclusions in chromites from the merensky reef of the bushveld complex south africa about 30 of the chromite grains of variable sizes in a chromitite seam at the base of the merensky reef of the bushveld complex on the farm vlakfontein contain abundant composite mineral inclusions the inclusions are polygonal to circular with radial cracks that protrude into the enclosing chromite they vary from a few microns to several millimeters in diameter and are concentrated in the cores and mantles of chromite crystals electron backscattered patterns indicate that the host chromites are single crystals and not amalgamations of multiple grains na phlogopite and orthopyroxene are most abundant in the inclusions edenitic hornblende k phlogopite oligoclase and quartz are less abundant cl rich apatite rutile zircon and chalcopyrite are present at trace levels na phlogopite is unique to the inclusions it has not been found elsewhere in the bushveld complex other minerals in the inclusions are also present in the matrix of the chromitite seam but their compositions are different the mg mg fe2 ratios of orthopyroxene in the inclusions are slightly higher than those of orthopyroxene in the matrix k phlogopite in the inclusions contains more na than in the matrix the average compositions of the inclusions are characterized by high mgo 26 wt na2o 2 4 wt and h2o 2 6 wt and low cao 1 1 wt and feo 4 4 wt the 18o value of the trapped melt estimated by analysis of inclusion rich and inclusion poor chromites is 7 this value is consistent with the previous estimates for the bushveld magma and with the 18o values of silicate minerals throughout the reef the textural features and peculiar chemical compositions are consistent with entrapment of orthopyroxene with variable amounts of volatile rich melts during chromite crystallization the volatile rich melts are thought to have resulted from variable degrees of mixing between the magma on the floor of the chamber and na k rich fluids expelled from the underlying crystal pile the addition of fluid to the magma is thought to have caused dissolution of orthpyroxene leaving the system saturated only in chromite both oxygen and hydrogen isotopic values are consistent with the involvement of a magmatic fluid in the process of fluid addition and orthopyroxene dissolution most of the cr and al in the inclusions was contributed through wall dissolution of the host chromite dissolution of minor rutile trapped along with orthopyroxene provided most of the ti in the inclusions the na and k rich hydrous silicate minerals in the inclusions were formed during cooling by reaction between pyroxene and the trapped volatile rich melts

the concentrations of the noble metals in southern african flood type basalts and morb implications for petrogenesis and magmatic sulphide exploration concentrations of the platinum group elements have been determined in several suites of southern african flood type basalts and mid ocean ridge basalt morb covering some 3 ga of geologic evolution and including the etendeka karoo soutpansberg machadodorp hekpoort ventersdorp and dominion magmas the magmas cover a compositional range from 3 7 to 18 7 mgo 26 720 ppm ni 16 250 ppm cu and 1 255 ppb total platinum group elements pge the younger basalts etendeka karoo tend to be depleted in pge relative to cu while most of the older basalts hekpoort machadodorp ventersdorp dominion show no pge depletion relative to cu further the younger basalts tend to have lower average pt pd ratios than the older basalts and the morbs have lower average pt pd than the continental basalts within the broad groupings of old and young basalts this may reflect 1 a decreasing degree of mantle melting through geologic time and 2 source heterogeneity in that the morbs are derived from predominantly asthenospheric mantle whereas the continental basalts also contain a lithospheric mantle component enriched in pt in addition to these factors some pge fractionation also occurred during differentiation of the magmas with pd showing incompatible behaviour and the other pge variably compatible behaviour the examined southern african flood type basalts and morb appear to offer limited prospects for magmatic sulfide ores largely because they show little evidence for significant chalcophile metal depletion that could be the result of sulphide extraction during ascent and crystallization

the merensky reef at winnaarshoek eastern bushveld complex a primary magmatic hypothesis based on a wide reef facies the merensky reef on the winnaarshoek property in the central sector of the eastern limb of the bushveld complex belongs to what may be described as a wide reef facies in which platinum group element pge mineralization is largely contained within a relatively thick succession of medium grained nonpegmatoidal feldspathic orthopyroxenite bounded top and bottom by thin chromite stringers the wide reef merensky reef facies at winnaarshoek presents the opportunity to study subtle processes which could potentially be obscured or obliterated in the thinner reef facies found in many areas of the western limb especially in places where the reef zone contains a component of pegmatoidal orthopyroxenite at winnaarshoek a pegmatoidal feldspathic orthopyroxenite is developed below the lower chromite stringer and a second pegmatoidal orthopyroxenite is intermittently developed several centimeters above the upper chromite stringer in contrast to most occurrences in the western limb however both these pegmatoidal orthopyroxenites are only sporadically mineralized if at all in addition rather than being at the base of a feldspathic orthopyroxenite unit as is the case throughout most of the western limb the merensky reef at winnaarshoek occurs toward the top of a sequence of feldspathic orthopyroxenite despite the gross relative uniformity of the merensky reef on a property wide scale at winnaarshoek we demonstrate using underground channel samples that individual intersections spaced a matter of meters apart commonly display remarkable variations in grade distribution our study is based primarily on whole rock and mineral chemical profiles from drill cores through three separate and distinctive subfacies of essentially normal i e nonpothole reef one of the drill core intersections represents typical reef in which pge mineralization forms an upper reef extending from the upper chromitite stringer approximately 1 m into the underlying feldspathic pyroxenite and a much thinner lower reef centered on the lower chromitite stringer the other two drill core intersections represent extremes in terms of the vertical distribution of the pge one having mineralization confined to the immediate vicinity of the two chromitite stringers while the other is richly mineralized throughout the reef zone peaks in pge concentrations in all three intersections are coincident with the most primitive compositions of orthopyroxene plagioclase and chromite the dominant rock forming minerals whereas the cumulate layers below major pge peaks are the most evolved as indicated by mineral compositions and elevated whole rock incompatible element concentrations furthermore the lowest grade merensky reef intersection has the most chemically evolved footwall whereas the richest intersection has a relatively primitive footwall we consider the origin of the merensky reef in the context of its position as the culmination of a sequence of several pge mineralized chromite bearing layers in the upper critical zone and suggest that the regular upward variations in the chemistry of the chromitite from one layer to the next and the overall cyclicity are indicative of complex magma replenishment and mixing processes in the chamber we apply a model of lateral streaming of magma with chromite crystallization and consequent sulfide and platinum group mineral pgm precipitation resulting from magma mixing specifically the merensky reef cannot be properly interpreted outside the context of the sequence of successive events that evolved throughout the development of the upper critical zone genetic models also need to account for lateral facies variations in the reef

how was taiwan created abstract since the beginning of formation of proto taiwan during late miocene 9 ma the subducting philippine ph sea plate moved continuously through time in the n307 direction at a 5 6 cm year velocity with respect to eurasia eu tearing the eurasian plate strain states within the eu crust are different on each side of the western ph sea plate boundary extensional in the okinawa trough and northeastern taiwan versus contractional for the rest of taiwan island the b feature corresponds to the boundary between the continental and oceanic parts of the subducting eurasian plate and lies in the prolongation of the ocean continent boundary of the northern south china sea strain rates in the philippines to northern taiwan accretionary prism are similar on each side of b contractional though with different strain directions perhaps in relation with the change of nature of the eu slab across b consequently in the process of taiwan mountain building the deformation style was probably not changing continuously from the manila to the ryukyu subduction zones the luzon intra oceanic arc only formed south of b above the subducting eurasian oceanic lithosphere north of b the luzon arc collided with eu simultaneously with the eastward subduction of a portion of eu continental lithosphere beneath the luzon arc in its northern portion the lower part of the luzon arc was subducting beneath eurasia while the upper part accreted against the ryukyu forearc among the consequences of such a simple geodynamic model i the notion of continuum from subduction to collision might be questioned ii traces of the miocene volcanic arc were never found in the southwestern ryukyu arc we suggest that the portion of eu continental lithosphere which has subducted beneath the coastal range might include the miocene ryukyu arc volcanoes formed west of 126 e longitude and which are missing today iii the 150 km wide oceanic domain located south of b between the luzon arc and the manila trench above the subducting oceanic eu plate south china sea was progressively incorporated into the eu plate north of b

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

the role of magma mixing in the genesis of pge mineralization in the bushveld complex thermodynamic calculations and new interpretations the elegant magma mixing model for the formation of the platinum group elements pge mineralization associated with chromite and sulfide in the bushveld complex proposed by naldrett and von gruenewaldt 1989 has recently been questioned by cawthorn 1999 based on his own calculation cawthorn concluded that the concave upward sulfur solubility curve of a fractionated basaltic magma which is central to the model does not exist cawthorn 1999 pointed out that both the hanging wall and footwall sequences of the merensky reef formed from sulfide undersaturated magmas instead of sulfide saturated magmas as predicted by the model cawthorn argued that there is a mass balance problem with the model if these rocks did not contribute pge to the sulfides in the reef our thermodynamic calculations indicate that the concave upward curve of s solubility though different in detail from the original is very much in evidence our calculations also indicate that the content of s dissolved in the residual magma may fall below the s solubility curve when the rate of s increase in the magma due to the removal of silicate cumulates is less than the rate of increase in its s solubility due to the change in its temperature and composition during fractional crystallization mixing of such fractionated and yet sulfide undersaturated magma with appropriate amounts of a primitive magma is still capable of achieving sulfide oversaturation in the hybrid once the immiscible sulfides settle out of the magma the content of s dissolved in the hybrid may fall below its solubility curve again during further crystallization thus no sulfide segregation is expected in the rocks crystallized subsequently r factor assessment needs to consider the consequence of sulfide suspension in magma small quantities of sulfide droplets formed during the normal course of fractional crystallization may remain suspended in magma until the next replenishment and in this case they can be redissolved in the hybrid when the proportion of a new input is large enough because there is no early sulfide liquid segregation both the residual and new magmas will not be depleted in pge and are equally important for contributing pge to the sulfide liquid segregated during a subsequent magma mixing event

sedimentary mechanisms and underlying tectonic structures of the northwestern mediterranean margin as revealed by comprehensive bathymetric and seismic surveys abstract the tectonic structures lithological contrasts and sedimentary processes of the northwestern mediterranean margin are revealed by a comprehensive survey including recently acquired seabeam and seismic profiling data mass wasting by gravity flow processes occurs over this entire area gravity slides are concentrated on the thick plio quaternary formations located in the interchannel areas they can lead to surprisingly steep walls and contribute to the widening of the canyons the contrasts between these superficial formations and the underlying neogene formations are morphologically well expressed the slide products sometimes directly observed as voluminous erratic blocks can seal the deep sea channels and cause their migrations areal extent of these slides can be very large especially with respect to the small size of the basin however the turbidity currents are the main gravity flow processes leading to the construction during the quaternary glacial epochs of the rhone deep sea fan and other sedimentary ridges they are responsible for the formation of particular bedforms such as circular depressions into the valley floors or sediment waves on the interchannel areas the wide extent of the gravity flow processes can be explained by the particular geological setting of this margin which is a mountainous borderland with steep slopes and rapid deposition of undercompacted sediments the general instability is favored by recent tectonic movements linked with the alpine setting and especially in the deepest areas by the lubricating effects of the underlying messinian salt layer under the loading effect of the sedimentary cover this salt layer crops out around the rhone deep sea fan as a peripheral belt of diapirs having shapes controlled by deep tectonic structures

earthquake induced gravitational potential energy change in the active taiwan orogenic belt summary the philippine sea plate is converging against the eurasian plate near taiwan at a velocity of 7 8 cm yr 1 this has caused the taiwan orogenesis and induced abundant earthquakes in this study we examine the corresponding change of gravitational potential energy gpe using 757 earthquakes from the earthquake catalogue of the broadband array in taiwan for seismology bats from 1995 july to 2003 december our results show that the variation of

remarks on esr dating of fault movements laboratory experiments and detailed investigations of natural fault gouge indicate that it is in principle possible to date the last movement of a fault by esr this paper gives a brief introduction to esr dating and outlines the specific problems that have to be addressed before esr can be established as a reliable technique for the dating of fault movements

earthquake relocation in the ligurian sea western mediterranean geological interpretation abstract relocated epicenters are computed with a model based on complex local structure i e oceanic floor in the central ligurian basin and thinned continental margins by superposing these relocated earthquakes on a basement bathymetric map the structural relations are clearly demonstrated compressive stress towards the west northwest is confirmed in the northern ligurian basin by focal mechanism study according to our results most of the earthquakes appear to be shallow and linked to rejuvenation of older distensive and strike slip structures on margins as in the basin by a compressional motion

current challenges to esr dating abstract electron spin resonance dating is applicable to a wide range of materials found at quaternary sites and which can generally be assured to exhibit zero signals at the time to be dated t 0 local inhomogeneity in external dose rates may contribute to dispersion in apparent dates but average dates may still be good estimates of site ages testing of u uptake models by u series measurements shows that both early and continuous uptake can occur possibly even in the same site problems of signal lifetime determination and diagenesis are reviewed

resetting experiment of e centres by natural faulting the case of the nojima earthquake fault in japan abstract the resetting state of e centres in quartz in fault clay gouge has been examined using the nojima earthquake fault that moved during the southern hyogo prefecture earthquake in 1995 as a result the e centres have never been reset by this faulting event furthermore there is no regular tendency among the d e values obtained from the grain samples and the plateau region of the esr ages does not exist in the case of the nojima fault therefore it is not possible to judge the complete resetting of esr signals by natural faulting on the other hand the increase of radiation sensitivity of the e centres may be ascribed to the formation of the precursors by rays emitted from the radioactive elements adhered around the grain samples since the adherence of the radioactive elements may begin with fracturing the quartz grains by faulting the esr ages obtained from the unsaturated e centres with high radiation sensitivity may give the age of beginning of the fault movements the esr ages obtained from these unsaturated e centres of the nojima fault 0 88 0 3 ma 1 51 0 51 ma or 1 07 0 36 ma 1 75 0 59 ma are consistent with the geological age estimate of the beginning of the fault movements

esr dating of north anatolian turkey and nojima japan faults abstract electron spin resonance esr ages were obtained on al e and oh centres in quartz extracted from fault gouge from the north anatolian fault naf in turkey and the nojima fault nf in japan the data were used to test two contradictory criteria which have been used for the recognition of complete signal resetting during the fault movement the grain size plateau and the isochron models the grain size plateau method predicts decreasing ages with decreasing gain sizes because the fine grains are more intensely stressed during the faulting process for those grains that were completely reset a plateau of constant age is obtained and esr ages derived from centres with different stress sensitivity converge the isochron method is based on the fact that newly formed fracture surfaces are exposed to external alpha and beta radiation thus smaller grains ought to accumulate larger dose values the plot of grain size versus external dose rate yields an isochron which gives the age of the fracturing process it was found that most samples yielded smaller doses with decreasing grain sizes thus confirming the underlying principles of the grain size plateau method however only one sample yielded an extended plateau over a wider particle size range and converging ages for the different centres the e centre of the sample from the nf yielded the only result that indicated that the isochron method might work the results derived from the e centre of the other samples may have been interferred with by the so called counterfeit e signal which may render those results unreliable the esr ages obtained on the naf burdigalian to pliocene agree with those derived from geological estimates sample b which gave the extended plateaux and an age estimate of 2 54 0 58 ma indicates the time when faulting began the youngest age of 0 59 0 1 ma may indicate the last major faulting episode of the naf the minimum age of 1 56 0 22 ma obtained on the sample from the nf coincides with the commencement of the uplift of awaji island at about 1 2 ma ago which was caused by movements of the nf as well as a range of other fault systems in the area

the distribution of chalcophile and platinum group elements in the ug 2 chromitite layer of the bushveld complex a ug 2 chromitite sample contains two sequences in which the concentrations of cu ni s pt pd rh ru and ir conform to a process of fractionation according to the rayleigh law both of these sequences are followed by others in which the trends are almost horizontal from the sequences that conform to the rayleigh law one can calculate the relations between the possible thicknesses of the magma column that gave rise to the ug 2 layer the bulk distribution coefficients and the original concentrations of the elements involved it appears that the elements were withdrawn from a surprisingly thin layer of magma between the first and the second cycles certain elements have been depleted and others enriched which indicates a heave of new magma rather than the recirculation of old partly depleted magma by a process like convective overturn the fact that s and the chalcophile elements cu and ni were concentrated in the same way and at the same time as the platinum group elements shows that the same collector was probably involved therefore sulfide could not have acted as a collector for the platinum group elements it is thought that chromite or a precursor of chromite was involved in some way with the collection process

cold seep systems in the south china sea an overview abstract three decades after the discovery of cold seep systems various sites of hydrocarbon seepage have been found in the south china sea scs over the past decade these sites have become model systems for understanding the variability of hydrocarbon seepage and associated biogeochemical processes in this review we describe the cold seep systems of the scs with an emphasis on seafloor manifestations fluid sources biogeochemical processes and macroecology seafloor features associated with seeps include mud volcanoes pockmarks and carbonate deposits a common characteristic of cold seeps is the occurrence of authigenic i e in situ precipitated carbonate minerals these carbonates commonly exhibit low 13c and high 18o values suggesting the incorporation of methane derived carbon and oxygen derived from gas hydrate water biogeochemical processes such as sulfate driven anaerobic oxidation of methane sd aom the key process at seeps have been studied in detail with the aim of establishing geochemical proxies to trace these processes into the geological past we also detail the features characterizing seep ecosystems understanding the impact of decomposing methane hydrate on the marine carbon budget remains challenging and requires additional seafloor observations as well as models predicting how gas hydrate responds to changing conditions such as temperature increase sea level rise and episodic mass wasting

increase of radiation sensitivity of esr centres by faulting and criteria of fault dates abstract the esr spectra and ages of the fractured rocks along the itoigawa shizuoka tectonic line a major fault in japan were measured the esr signal intensities tend to become larger with decreasing distance from the fault boundary because the radiation sensitivities of the esr centres have increased by faulting according to fracturing and heating experiments when the radiation sensitivities of esr centres have visibly increased the signals may have been almost completely reset by faulting as a result of the increase of radiation sensitivity the error range of the td values for incompletely reset esr signals is comparatively large whereas it is smaller in the case of completely reset signals therefore by assessing the error range of td values we can determine whether esr signals were completely reset at the time of faulting

timing of recent out of sequence active deformation in the frontal himalayan wedge insights from the darjiling sub himalaya india recent studies of india eurasia convergence suggest that the entire convergence in the himalayan wedge is almost exclusively accommodated along its basal detachment fault main himalayan thrust mht and its near surface equivalent main frontal thrust mft using direct dating of fault zone gouge and strath terrace deposits we conclude the following 1 the present mountain front in the darjiling sub himalaya was emplaced by ca 40 ka 2 out of sequence deformation on surface breaking faults north of the mft in the darjiling sub himalaya began ca 20 ka and has probably continued since 3 the tista river responded to the ca 20 ka deformation by migrating 150 m eastward average rate 13 mm yr 1 and by incising 48 m vertically average rate 4 4 mm yr 1 creating unpaired disjointed strath terraces between 11 3 1 3 ka and 1 4 0 3 ka out of sequence surface breaking faults in the himalaya indicate partial accommodation of active convergence within the himalayan wedge using the results from the bhuj earthquake of 2001 we suggest that active deformation along the out of sequence faults is a potential seismic hazard in the himalaya and himalayan seismic hazard models must account for this we also propose a conceptual model for active deformation in the himalaya

correlation between chromite composition and pge mineralization in the critical zone of the western bushveld complex detailed mineralogical investigations of chromite in the lower and critical zones in the northwestern sector of the bushveld complex have revealed significant compositional variations with regard to modal proportions host rock lithology and stratigraphic height superimposed on these variations are long range systematic trends in the composition of chromite in the massive layers these long range trends are closely linked with the evolution of the silicate cumulates the massive chromitite layers are divided into two types type 1 comprises the chromitites hosted entirely within ultramafic cumulates while type 2 chromitites are within cyclic units in which plagioclase cumulates occur the types are also distinguishable by their respective contents of platinum group elements pges and distribution patterns thereof viz the ratios between ru os ir and pt pd rh or relative element proportions both of which display a systematic change with height in accordance with chromite composition the relation between silicate geochemistry chromite composition and pge tenor leads to the development of a model explaining the formation of pge mineralized sulphide poor chromitite layers in the critical zone of the bushveld complex

turbidites and megaturbidites from the herodotus abyssal plain eastern mediterranean unrelated to seismic events abstract a transect of 9 piston and gravity cores was taken across the southeast flank of the mediterranean ridge the transect extends from the abyssal plain to a location 290 m shallower than the abyssal plain and 50 km north of the edge of the ridge each core contains two or more turbiditic layers which belong to two discrete types here called a and b type a essentially consists of black plastic clays rich in smectite with silt fraction of terrigenous nature source area is the nile cone and age is middle or late pleistocene type b turbidites are pale brown to whitish in color coarse grained carbonate rich and bioclastic in composition with shallow water fossils dominant they are poor in smectite and the silt fraction is very rich in carbonates calcite and aragonite the source area is the north african shelf south of the abyssal plain a megabed belonging to type b turbidites is correlatable from core to core with a thickness in excess of 10 m in the abyssal plain and an estimated volume of 10 km 3 its stratigraphic position in the latest pleistocene suggests that its origin is related to a sudden collapse of bioclastic sediments accumulated in a canyon head during a low sea level stand the source areas of the two discrete turbidite types belong to the essentially aseismic north african continental margin although they are presently recorded on the tectonically active mediterranean ridge no seismic events are required to account for the presence of either type of turbidite

potential distribution of methane hydrate beneath the european continental margins gridded datasets have been constructed for the physical parameters controlling the formation of gas hydrate simultaneous solutions to the gas hydrate phase and pressure temperature equations were obtained for each node of these grids the results show sub bottom depths of potential methane hydrate bsrs these are presented as colour contoured grids for the thickness of the hydrate stability zone for the european margins the chart proposes that if gas hydrates exist over these areas then this is the potential depth to the bsr this depth is generally greater along the continental margins and also increases with increasing age of the margin shallowing of the bsr can be seen over areas of thinned continental crust and plateaus the geological factors controlling gas hydrate formation determine areas of likely occurrence so the apparent paucity of identified hydrate layer bsrs off the european margins particularly in the mediterranean is most notable

evidence for late quaternary brittle deformation and back thrusting within the indus suture zone ladakh himalaya abstract although the tectonic evolution of the southern himalaya has been extensively studied relatively few studies have focused on potential neotectonic activity in the most hinterland part of himalaya north of the region that separates the southern edge of the tibetan plateau from the peaks of the higher himalayan range here we use a combination of new structural and geomorphic field data optically stimulated luminescence osl chronology as well as previously published seismicity and denudation rate dataset to suggest that the trans himalaya within the region of the indus suture zone isz is neotectonically active based on fault gouge tilted paleolake deposits and the chronology of deformed fluvial gravels constrained by osl dating the present study provides evidence for the tectonic activity along the isz between 78 and 58 ka the occurrence of two earthquakes of mw 4 0 and the focal mechanism solution of a shallow focus earthquake mw 3 0 depth 8 km near the town of upshi shows a pure thrust mechanism we suggest that this earthquake was likely associated with the upshi bazgo thrust a major structure which separates the mid miocene indus molasse from the cretaceous ladakh batholith it is envisaged that the fault and fold systems in the ladakh region such as the upshi bazgo thrust originated due to 1 acceleration in the northward movement of indian plate relative to the eurasian plate and 2 post collisional shortening parallel to plate convergence on account of this the eocene to miocene post collisional sedimentary sequences such as the indus molasse rode over the now extinct ladakh arc as it acted as a rigid body and formed a system of backthrusts which are neotectonically active

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

correlation of tremor activity with tidal stress in the northern cascadia subduction zone 1 we analyze hourly data from five tremor episodes in the northern cascadia subduction zone over the period 2003 2005 provided by the tremor activity monitoring system tams all five tremor episodes correspond to slow slip events observed by gps fourier decomposition is used to separate the hourly tremor counts for each episode into long period 0 2 2 cpd components the tidal component of the observations is compared with theoretical stress variations at depths of 20 30 and 40 km with 40 km being the depth of the interpreted subduction thrust interface the stress variations are predicted by a 2 d ocean tide loading model combined with estimates of stress variations from earth tides we find that the shear stress in the thrust direction and the compressive normal stress on shallow dipping surfaces correlates with the data significantly better than the confining stress over the range of depths investigated the relative amplitudes of tidal shear stress and compressive normal stress result in positive coulomb stress favoring slip peak tremor activity occurs at times of maximum tidal shear stress in the thrust direction which would assist slow slip and would suggest that tidal tremor and slip are colocated the response of the tremor to tidal shear stress is roughly proportional to the mean activity level controlled by tectonic conditions of stress and pore pressure a significant nontidal daily variation in tremor activity of unknown origin is identified

deposition of megabeds megaturbidites and sea level change in a proximal part of the eocene miocene flysch of central dalmatia croatia some carbonate megabeds of the proximal part of the dalmatian eocene miocene flysch basin eastern adriatic sea are underlain and overlain by conglomeratic fan deltas whereas thinner bedded turbidites interfinger with fan delta conglomerates fan deltas and interfingering turbidites are interpreted as having been deposited during lowstand s and early sea level rise s whereas deposition of megabeds is attributed to periods of accelerated sea level rises that aborted growth of fan deltas attribution of megabeds to periods of sea level rise is based on the following observations 1 they overlie some conglomeratic fan deltas 2 skeletal and lithic debris in megabeds originated by subaerial weathering of older sediments and 3 their large thickness indicates considerable primary accumulation 0f debris and low frequency of hows sea level changes inferred from mega beds are different from those related to thinner classical turbidites and distinction of the two is important for sequence stratigraphy in deep marine sediments

seismoturbidites a new group of resedimented deposits abstract turbidite beds of exceptionally large volume and areal extent occur in both modern and ancient deep water basins these beds which may reach individual volumes in excess of 100 km3 are apparently the product of catastrophic gravity flows triggered by earthquakes along the margins of highly mobile basins most commonly elongate flysch troughs turbidite beds produced by these catastrophic events are generally characterized by very distinctive geometry internal structures and composition and are termed herein seismoturbidites characteristically these sediments lack time persistent features of deep sea fans such as channels and lobes seismoturbidites may occur as scattered intercalations diluted within otherwise normal turbidite sequences thus forming generally excellent markers for basin wide correlations or as closely spaced repetitive units comprising the bulk of the sedimentary fill of certain flysch basins in both cases they may offer a tremendously useful tool for a better understanding of the distribution of paleoseismic zones in time and space

catastrophic wave erosion on the southeastern coast of australia impact of the lanai tsunamis ca 105 ka sand barriers along the coast of southern new south wales dating from the last interglacial have been almost completely destroyed most probably by a catastrophic tsunami evidence for catastrophic wave erosion can also be traced to heights of at least 15 m above present sea level on coastal abrasion ramps these erosional features lie above the range of effective erosion by contemporary storm waves and cannot be attributed to either eustatic fluctuations or local uplift chronological evidence for the timing of the destruction of the last interglacial barriers suggests that tsunamis generated by the submarine slide off lanai in the hawaiian islands 105 ka traveled across the pacific and eroded this coast

applicability of esr dating using multiple centres to fault movement the case of the itoigawa shizuoka tectonic line a major fault in japan abstract no direct method for dating the fault movement has been hitherto established except esr dating whose applicability is disputed however the most serious question in esr dating is whether accumulated esr signals are completely reset at the time of fault movement when the defect centres are partially preserved at the time of previous faulting the date obtained is uncertain we have shown fukuchi et al 1985 1986 however that we can judge correctly whether esr signals were completely reset or not when the esr signal counting is done for multiple esr centres of different stabilities for resetting from the data for completely reset centres actual date of fault movement can be calculated this multiple centre method was tested with samples whose esr signal intensities are judged to be about zero at the time of fault movement the result which confirms the applicability for the fault movement dated back to 100 ka bp is presented in this paper

observations on the micro texture and esr spectra of quartz from fault gouge abstract we have investigated fault gouge samples from a variety of sites in eastern china with esr optical and scanning electron microscopy sem x ray diffraction and cathodoluminescence the results reveal two different types of quartz a macrocrystalline and a microcrystalline variety the macrocrystalline samples show increasing esr intensities of the e centre with increasing grain size whilst the microcrystalline samples show the opposite trend we also found that the dissolution of quartz grains and secondary quartz precipitation on the surface of the grains is significant in some samples indicating active chemical weathering in these fault zones the occurrence of secondary quartz has serious implications for the reliability of any dating attempt

activation of gas bubble emissions indicated by the upward decreasing lead 210 activity at a submarine mud volcano ty1 offshore southwestern taiwan abstract a submarine mud volcano mv known as ty1 is one of the largest conical structures found offshore southwestern taiwan active gas bubble emissions at the flat crest of the mud volcano disperse sediment particles into the water column changes in the mud volcanism of ty1 were revealed by radiograph and grain size analysis of the sediment cores 210 pb geochronology was applied to the near seafloor sediments to reveal the detailed mud volcanism from the deposition rate in a 58 cm long sediment core taken from the northern margin of the crest known as ty1 n 170 the size and frequency of the mud clasts decrease upward the clasts are smaller than 8 mm above a sediment depth of 34 cm below the sea floor cmbsf sediments between 0 and 19 cmbsf are massive and particles larger than 2 mm are absent an enrichment of coarse silt sized particles in the massive sediment unit and the restricted distribution of the unit suggest that the massive unit was generated by re deposition of sediment particles that were dispersed into the water column by gas bubble emission these characteristics suggest that during the last mud volcanism of ty1 there was a decrease in mud eruption energy and gas bubble emission became the main activity in core ty1 s 440 taken from the southern slope a massive sediment unit enriched with coarse silt sized particles is intercalated between mud breccia structures this suggests repeated mud breccia flows caused by ty1 the excess 210 pb activity present in the massive sediment unit of ty1 n 170 suggests activation of gas bubble emission in the massive unit a decrease in excess 210 pb activity appears upward toward the seafloor the highest value is 3 1 dpm g at 19 8 cmbsf 26 4 g cm 2 in cumulative mass values lower than 1 0 dpm g are distributed 2 8 6 8 cmbsf 3 6 8 8 g cm 2 the upwardly decreasing trend is opposite that of the reference core from which a reasonable areal sedimentation rate was obtained using a constant flux constant sedimentation model the anomalous depth profile at the massive unit indicates an increasing rate of sediment deposition which originated from the activation of gas bubble emission

climatic control of turbidite deposition on the madeira abyssal plain studies of sedimentation in the southwestern part of the madeira abyssal plain have revealed sequences of turbidites correlatable over thousands of square kilometres turbidites are sediments transported by turbidity currents and represent rapidly accumulated sedimentary units1 in this case in the distal part of the flow they are very fine grained and homogeneous occasionally with silty bases individual turbidites are separated by thin pelagic units which alternate from oozes to pelagic clays a stratigraphy for these pelagic units has been produced from combining coccolith distributions and lithological changes which enables comparison to cores containing only pelagic sediments from outside the turbidite province these comparisons show that turbidity currents cause no significant erosion in the area the major turbidites occur between lithological alternations which reflect global climate changes associated with glaciations and related eustatic sea level fluctuations turbidites have been linked with eustacy on previous occasions but only with low stands of sea level2 3 our work shows that turbidites are more likely to occur during regressions and transgressions rather than in the quiet periods between

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

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

contrasting sulphide contents of the bushveld and sudbury igneous complexes the sudbury igneous complex sic contains abundant sulphides especially near the base and hosts one of the world s largest nickel and copper deposits the bushveld complex bc contains relatively little sulphide but hosts the world s largest platinum group element deposits the most recent calculations of the sulphur solubility in magmas that produced the bc are based on the sulphur solubility of mid ocean ridge basalts that have less sio2 than bushveld magmas such a difference may lead to an overestimation of sulphur solubility by as much as 25 the revised sulphur solubility curve presented here for bushveld magmas may also have relevance to the sic in view of its siliceous nature sulphur solubility curves can be used to determine the proportion of sulphide expected in cumulate rocks once sulphur saturation is attained these models are tested using observed sulphide contents in both intrusions the observed decreasing sulphur contents 0 3 0 05 s from the base of the sic upward are broadly consistent with these sulphur solubility curves and are consistent with sulphide saturation through the entire mafic portion in contrast the lower half of the bc contains extremely little sulphur generally 0 02 s except for two thin layers which is not consistent with sustained sulphide saturation at any level previous interpretations of the sulphur content of bushveld rocks have suggested that the lower and critical zones were sulphide saturated but that they had then lost some of the sulphide due to various processes the present sulphide content of the cumulates of the bc is so low that if they had once been saturated over 90 of all the sulphide must have been removed mass balance calculations indicate that these large amounts of displaced sulphur remain unaccounted for in such models instead the observed sulphur contents are in reasonable agreement with that expected in a cumulate sequence forming from a sulphur undersaturated magma whereas the merensky reef and bastard pyroxenite contain minor sulphides the compositions of the immediate hanging wall rocks indicate sulphide undersaturation such an abrupt return to sulphide undersaturation is not consistent with models involving sulphide formation from large volumes of magma one possible explanation for these two observations is that intermittent sulphur degassing occurred through a fractured roof of the bc so that the magma was never continuously sulphur saturated with respect to an immiscible sulphide liquid

tidally controlled gas bubble emissions a comprehensive study using long term monitoring data from the neptune cabled observatory offshore vancouver island long term monitoring over one year revealed high temporal variability of gas emissions at a cold seep in 1250 m water depth offshore vancouver island british columbia data from the north east pacific time series underwater networked experiment observatory operated by ocean networks canada were used the site is equipped with a 260 khz imagenex sonar collecting hourly data conductivity temperature depth sensors bottom pressure recorders current meter and an ocean bottom seismograph this enables correlation of the data and analyzing trigger mechanisms and regulating criteria of gas discharge activity three periods of gas emission activity were observed a short activity phases of few hours lasting several months b alternating activity and inactivity of up to several day long phases each and c a period of several weeks of permanent activity these periods can neither be explained by oceanographic conditions nor initiated by earthquakes however we found a clear correlation of gas emission with bottom pressure changes controlled by tides gas bubbles start emanating during decreasing tidal pressure tidally induced pressure changes also influence the subbottom fluid system by shifting the methane solubility resulting in exsolution of gas during falling tides these pressure changes affect the equilibrium of forces allowing free gas in sediments to emanate into the water column at decreased hydrostatic load we propose a model for the fluid system at the seep fueled by a constant sub surface methane flux and a frequent tidally controlled discharge of gas bubbles into the ocean transferable to other gas emission sites in the world s oceans

direct esr dating of fault gouge using clay minerals and the assessment of fault activity abstract the esr dating method has been applied to the fault gouge of the nojima fault the outcrop of which arose due to the southern hyogo prefecture earthquake on january 17th 1995 and to the fault gouge of the median tectonic line mtl which is a major active fault in japan without considering the resetting of esr signals the esr ages obtained for clay minerals in the fault gouges are considered to indicate the age of the beginning of the fault movements at the outcrop assuming no radon loss and the general values of water content and ray efficiency the esr ages of the fault gouges of the nojima fault and mtl are estimated as 0 55 1 16 and 6 76 9 28 ma respectively the esr age of the nojima fault is consistent with the age of the beginning of the rokko movements in the kinki districts estimated geologically on the other hand the esr age obtained from the mtl is younger than the k ar age about 11 ma which is presumably overestimated due to the existence of the source minerals in the k ar dating sample since it is geologically known that the mtl at the outcrop had moved until the late pleistocene holocene the fault movement of the mtl at this outcrop probably began at 6 76 9 28 ma b p after the intrusion of the felsitic dyke 12 16 ma which is the source rock of the fault gouge into the fault boundary the esr dating of clay minerals in the fault gouge may be effective for assessing fault activity if no quaternary deposit exists at the outcrop the younger the esr age of the fault gouge is the higher the fault activity is if not indurated and the freshest clay gouge can be collected at the outcrop the esr age of the most recent movement may be obtained from the clay gouge

the bushveld complex south africa formation of platinum palladium chrome and vanadium rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large relatively slowly cooling subsiding magma chamber platinum group element pge deposits in the bushveld complex and other layered intrusions form when large incompletely solidified magma chambers undergo central subsidence in response to crustal loading resulting in slumping of semi consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides oxides olivine and pyroxene and less dense layers enriched in plagioclase the most economic pge cr and v reefs form in large multiple replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification the depth of emplacement has to be relatively shallow as otherwise ductile crust would not be able to flex and collapse in smaller intrusions cooling rates are faster subsidence is less pronounced and where it occurs the cumulate may be largely solidified resulting in insignificant mush mobility and mineral sorting layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower but the reefs can be relatively thicker an additional factor controlling the pge cr and v prospectivity of intrusions is their location within cratons intra cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large layered igneous bodies furthermore intrusions sited within cratons are more readily preserved because cratons are underlain by thick buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust

giant submarine landslides submarine landslides can generate enormous turbidity currents that carry that carry 500 km3or more of sediment down to the oceans abyssal plains the slides can cause tsunamis and may release large amounts of methane to the air

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

character of the ug2 chromitite and host rocks and petrogenesis of its pegmatoidal footwall northeastern bushveld complex the ug2 chromitite and its immediate footwall have been mapped at the centimeter scale in a characteristic section exposed in a wall in the middelpunt mine northeast bushveld complex in this region the ug2 chromitite and its coarse grained footwall rocks are underlain and overlain by plagioclase pyroxenite the ug2 chromitite itself is a massive 70 cm thick layer composed of 75 to 90 percent chromite with plagioclase as the dominant interstitial mineral immediately beneath the chromitite is the so called mixed layer a previously undescribed but distinct mappable layer 50 to 70 cm thick consisting of chromite bearing pegmatoidal pyroxenite and chromitite intimately mixed at scales of centimeters to decimeters the mixture is chaotic with no megascopic fabric and contains in bulk about 15 percent chromite the contact between the mixed layer and overlying chromitite is well defined but sinuous at scales of centimeters to decimeters based on observations of drill core and outcrop the mixed layer appears to exist throughout the central sector of the eastern bushveld and may be ubiquitous throughout the entire complex the mixed layer usually rests directly on the ug2 pegmatoid which is a well known and widespread pegmatoidal plagioclase pyroxenite the pegmatoid is much coarser grained than the underlying pyroxenite but the two lithologic units are similar in terms of mineral modes and compositions the contact between them is irregular at scales of decimeters to meters with vertical fingers of pegmatoid extending into the pyroxenite the mixed layer and ug2 pegmatoid contain rare lenses of massive anorthosite encased by continuous centimeter thick rims of chromitite a model is proposed to account for the footwall sequence of the ug2 chromitite in this model the ug2 pegmatoid formed when hydrous interstitial melt percolated up through the partially molten crystal pile accumulated beneath the preexisting compacted massive chromitite and metasomatized and partially melted the pyroxenite protolith which upon cooling recrystallized to a coarse grained rock on the basis of published experiments illustrating the effect of water on melting in mafic systems it is shown how the hydrous melt was able to penetrate the pyroxene bearing assemblages below the chromitite but unable to partially melt the chromitite itself which in consequence remained relatively impermeable the anorthosite lenses in the pegmatoid mark local areas of relatively high degrees of hydration partial melting with the anorthosite representing the crystalline residue the mixed layer formed by gradual collapse of the base of the ug2 chromitite into the less dense relatively fluid footwall the mixed layer and ug2 pegmatoid are diagnostic of the ug2 chromitite and the three lithologic units should be considered a single petrologic unit

platinum group elements in silicate rocks of the lower critical and main zones at union section western bushveld complex concentration patterns of platinum group elements pge in the lower critical and main zones of the bushveld complex are modelled by a process of metal collection by segregating sulphide melt followed by fractional crystallization of monosulphide solid solution mss separation of os ir ru rh enriched mss cumulate ore and pt pd enriched residual sulphide melt is inferred to have occurred by upward percolation of interstitial silicate melt entraining sulphide melt whereas mss crystals are entrapped by early crystallizing chromite this process resulted in os ir ru rh enrichment of the chromitites and an upward increasing trend of pt pd os ir ru crystallization of platinum group minerals pgm from s undersaturated sulphide melt or from coalescing noble metal clusters are alternative possibilities to explain the observed pge patterns but remain difficult to model at present remobilization of pt and pd by percolating late magmatic hydrous fluids could have resulted in metal enrichment of pre existing magmatic sulphides but this model is not supported by the metal budget of the reefs and the field data there is no evidence for solid substitution of pge into oxides and silicates

esr dating of fault gouge the effect of grain size abstract esr signals of quartz grains in fault gouge have been partially or completely reset by movements on the fault which allows the dating of the last fault movement in order to better understand the zeroing process we have studied the variation in esr signal ad and age in various grain sizes since it can be expected that larger grains will be less affected by stress than smaller grains we propose that a plateau of constant lower age for the smallest grains indicates total resetting this is confirmed in gouge from a fault in california only such samples should be used for dating

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults

the ug2 merensky reef interval of the bushveld complex northwest of pretoria northwest of pretoria the ug2 merensky reef interval overlies a critical zone lower zone sequence that contains numerous large blocks of floor material nevertheless individual layers can be correlated with equivalent units at crocodile river mine the rustenburg impala union and amandelbult sections concentrations of platinum group elements in two borehole intersections of the ug2 chromitite are 4 ppm over 1 2 m and 2 4 ppm over 2 2 m therefore bulk pge levels appear to be only moderately lower than those at western platinum mine this renders models explaining pge enrichment by upward percolating melt or fluids problematic the merensky reef although containing sulphides is only weakly mineralized with pge 0 6 ppm the ug2 pyroxenite is separated from the ug2 chromitite by a 15 m noritic layer the introduction of feldspathic cumulates between two units that elsewhere directly overly each other may be explained by the more evolved composition of resident magma in those parts of the chamber distally located with regard to a major feeder zone at union section it also suggests that the ug2 unit is a multiple rather than a single cyclic unit