sills associated with the bushveld complex south africa an estimate of the parental magma composition abstract four distinct ages of sills intrude the floor rocks under the bushveld complex the first is a metadolerite and pre dates the bushveld complex the middle two are generally related to the complex itself one has quench textured olivine and orthopyroxene crystals and chemically equates to the parental magma of the bushveld complex the second suite is a hypersthene microgabbro representative of the second major injection of magma into the complex the last is doleritic and does not obviously correlate with any portion of the layered sequence the sills genetically related to the complex display several features 1 lack of chilled margins coarse grain size ability to melt country rock xenoliths extreme heterogeneity 2 atypical of normal sills but explicable in their present context

the paleomagnetism of single silicate crystals recording geomagnetic field strength during mixed polarity intervals superchrons and inner core growth 1 the basic features of the geomagnetic reversal chronology of the last 160 million years are well established the relationship between this history and other features of the field however has been elusive the determination of past field strength paleointensity is especially challenging commonly accepted results have come from analyses of bulk samples of lava historic lavas have been shown to faithfully record the past field strength when analyzed using the thellier double heating method data from older lavas however tend to show effects of in situ and laboratory induced alteration here we review an alternative approach single plagioclase crystals can contain minute magnetic inclusions 50 350 nm in size that are potential high fidelity field recorders thellier experiments using plagioclase feldspars from an historic lava on hawaii provide a benchmark for the method rock magnetic data from older lavas indicate that the feldspars are less susceptible to experimental alteration than bulk samples this resistance is likely related to the lack of clays in addition magnetic minerals are sheltered by the encasing silicate matrix from natural alteration that can otherwise transform the well defined thermoremanent magnetization into an irresolute chemical remanent magnetization if there is a relationship between geomagnetic reversal frequency and paleointensity it should be best expressed during superchrons intervals with few or no reversals thellier data sets based on single plagioclase crystals from lavas erupted during the cretaceous normal polarity superchron 83 120 million years ago suggest a strong 12 1022 am2 stable field consistent with an inverse relationship between reversal frequency and paleointensity superchrons may represent times when the pattern of core mantle boundary heat flux allows the geodynamo to operate at peak efficiency as suggested in some numerical models thellier data from single plagioclase crystals formed during times of moderate 10 reversals million years reversal occurrence suggest a weaker and more variable field these paleointensity data together with a consideration of paleomagnetic directions suggest that geomagnetic reversals field morphology secular variation and intensity are related the linkages over tens of millions of years imply a lower mantle control on the geodynamo on even longer timescales the magnetization held by plagioclase and other silicate crystals can be used to investigate the proterozoic and archean geomagnetic field during the onset of growth of the solid inner core data from plagioclase crystals separated from mafic dikes together with directional data from whole rocks indicate a dipole dominated field similar to that of the modern 2 5 2 7 billion years ago older archean rocks are of great interest for paleomagnetic and paleointensity investigations because they may record a time when the compositionally driven convection of the modern dynamo may not have been operating and a solid inner core did not play its current role in controlling the geometry of outer core flow most rocks of this age have been affected by low grade metamorphism investigations using single silicate grains provide arguably our best hope of seeing through secondary geologic events and reading the early history of the geodynamo absolute paleointensity measurements of the oldest rocks on the planet will require the further development of methods to investigate silicate crystals with exsolved magnetic minerals that address the uncertainties posed by thermocrystallization remanent magnetization anisotropy and slow cooling fortunately prior work in rock magnetism together with advances in analytical equipment and techniques provides a solid foundation from which these frontier issues can be approached

planetary waves and variability of the semidiurnal tide in the mesosphere and lower thermosphere over esrange 68 n 21 e during winter 1 the main features of the planetary waves and the variability of the semidiurnal tide with planetary wave periods observed by meteor radar over esrange 68 n 21 e have been investigated the interval of 39 months covering continuous measurements from october 1999 to december 2002 has been examined the planetary waves most frequently observed by meteor radar measurements in the mesosphere and lower thermosphere 80 100 km over esrange are 5 8 to 10 16 and 23 day waves the quasi 2 day wave is excluded in this study they are strongly amplified in the winter some differences between high and middle latitude planetary waves notwithstanding the 5 10 and 16 day waves are most probably related to the well known normal mode there are some reasons to believe that the vertically upward propagating 23 day wave could be generated by solar forcing the variability of the semidiurnal tide with periods of planetary waves has been thoroughly studied as well it is found that in the winter when the planetary waves are significantly amplified a very strong periodic variability of the semidiurnal tide is observed as well this result indicates that the most probable mechanism responsible for the periodic tidal variability during winter is in situ nonlinear coupling between tides and planetary waves two winter periods have been examined 1999 2000 and 2001 2002 in order to find strong evidence supporting this suggestion the validity of the frequency phase and vertical wavenumber wavelength relationship between the prime the planetary wave and semidiurnal tide and secondary waves has been established the novel aspect of this work is that we show for the first time that the calculated vertical structures vertical wavelengths of the sum and difference secondary waves which have very close periods are actually very different

a middle miocene relative paleointensity record from the equatorial pacific abstract we present a high resolution magnetostratigraphy and relative paleointensity rpi record derived from the upper 85 m of iodp site u1336 an equatorial pacific early to middle miocene succession recovered during expedition 320 321 the magnetostratigraphy is well resolved with reversals typically located to within a few centimeters resulting in a well constrained age model the lowest normal polarity interval from 85 to 74 87 m is interpreted as the later part of chron c6n 18 614 19 599 ma thirty three other magnetozones occur from 74 87 to 0 85 m which are interpreted to represent the continuous sequence of chrons onset of chron c5er 18 748 ma to the end of chron c5an 1n 12 014 ma we identify three putative previously unrecognized subchrons within chron c5cn 1n chron 5bn 1r and c5abn sedimentation rates vary from about 7 to 15 m myr with a mean of about 10 m myr we observe rapid apparent changes in the sedimentation rate at geomagnetic reversals between 16 and 19 ma that indicate a calibration error in geomagnetic polarity timescale atnts2004 the remanence is carried mainly by non interacting particles of fine grained magnetite which have forc distributions characteristic of biogenic magnetite given the relative homogeneity of the remanence carriers throughout the 85 m thick succession and the fidelity with which the remanence is recorded we have constructed a relative paleointensity rpi record that provides new insights into middle miocene geomagnetic field behavior the rpi record indicates a gradual decline in field strength between 18 5 ma and 14 5 ma and indicates no discernible link between rpi and either chron duration or polarity state

filling the bushveld complex magma chamber lateral expansion roof and floor interaction magmatic unconformities and the formation of giant chromitite pge and ti v magnetitite deposits his mind was like a soup dish wide and shallow irving stone on william jennings bryan a compilation of the sr isotopic stratigraphy of the bushveld complex shows that the evolution of the magma chamber occurred in two major stages during the lower open system integration stage lower critical and lower main zone there were numerous influxes of magma of contrasting isotopic composition with concomitant mixing crystallisation and deposition of cumulates larger influxes correspond to the boundaries of the zones and sub zones and are marked by sustained isotopic shifts major changes in mineral assemblages and development of unconformities during the upper closed system differentiation stage upper main zone and upper zone there were no major magma additions other than that which initiated the upper zone and the thick magma layers evolved by fractional crystallisation the lower and lower critical zones are restricted to a belt that runs from steelpoort and burgersfort in the northeast to rustenburg and northam in the west and an outlier of the lower and lower critical zone up to the lg4 chromitite layer in the far western extension north of zeerust it is only in these areas that thick harzburgite and pyroxenite layers are developed and where chromitites of the lower critical zone occur these chromitites include the economically important c 1 m thick lg6 and mg1 layers exposed around both the eastern and western lobes of the bushveld complex the upper critical zone has a greater lateral extent than the lower critical zone and overlies but also onlaps the floor rocks to the south of the steelpoort area the source of the magmas also appears to have been towards the south as the mg chromitite layers degrade and thin northward whereas the lg layers are very well represented in the north and degrade southward sr and os isotope data indicate that the major chromitite layers including the lg6 mg1 and ug2 originated in a similar way extremely abrupt and stratigraphically restricted increases in the sr isotope ratio imply that there was massive contamination of intruding melt which hit the roof of the chamber and incorporated floating granophyric liquid which forced the precipitation of chromite kruger 1999 kinnaird et al 2002 therefore each chromitite layer represents the point at which the magma chamber expanded and eroded and deformed its floor nevertheless this was achieved by in situ contamination by roof rock melt of the intruding critical zone liquids that had an orthopyroxenitic to noritic lineage the main zone is present in the eastern and western lobes of the bushveld complex where it overlies the critical zone and onlaps the floor rocks to the south and the north where it is also the basal zone in the northern lobe the new magma first intruded the northern lobe north of the thabazimbi murchison lineament interacted with the floor rocks incorporated sulphur and precipitated the platreef along the floor rock contact before flowing south into the main chamber this exceptionally large influx of new magma then eroded an unconformity on the critical zone cumulate pile and initiated the main zone in the main chamber by precipitating the merensky reef on the unconformity the upper zone magma flowed into the chamber from the southern bethal lobe as well as the tml this gigantic influx eroded the main zone rocks and caused very large scale unconformable relationships clearly evident as the gap areas in the western bushveld complex the base of this influx which is also coincident with the pyroxenite marker and a troctolitic layer in the northern lobe is the petrological and stratigraphic base of the upper zone sr isotope data show that all the pge rich ores including chromitites are related to influxes of magma and are thus related to the expansion and filling of the magma chamber dominantly by lateral expansion with associated transgressive disconformities onto the floor rocks coincident with major zone changes these positions in the stratigraphy are marked by abrupt changes in lithology and erosional features over which succeeding lithologies are draped the outcrop patterns and the concordance of geochemical isotopic and mineralogical stratigraphy indicate that during crystallisation the bushveld complex was a wide and shallow lobate sill like sheet and the rock strata and mineral deposits are quasi continuous over the whole intrusion

the life cycle of the northern hemisphere sudden stratospheric warmings motivated by recent evidence of strong stratospheric tropospheric coupling during the northern hemisphere winter this study examines the evolution of the atmospheric flow and wave fluxes at levels throughout the stratosphere and troposphere during the composite life cycle of a sudden stratospheric warming the composite comprises 39 major and minor warming events using 44 years of ncep ncar reanalysis data the incipient stage of the life cycle is characterized by preconditioning of the stratospheric zonal flow and anomalous quasistationary wavenumber 1 forcing in both the stratosphere and troposphere as the life cycle intensifies planetary wave driving gives rise to weakening of the stratospheric polar vortex and downward propagation of the attendant easterly wind and positive temperature anomalies when these anomalies reach the tropopause the life cycle is marked by momentum flux and mean meridional circulation anomalies at tropospheric levels that are consistent with the negative phase of the northern hemisphere annular mode the anomalous momentum fluxes are largest over the atlantic half of the hemisphere and are associated primarily with waves of wavenumber 3 and higher

the shaw method of palaeointensity determinations and its application to recent volcanic rocks summary our new version together with previous versions of the shaw method has been compared by applying them to recent volcanic samples for which we have well determined palaeointensity values although the earlier modifications to the shaw method give a linear portion to the nrm trm diagram of all the specimens about half of the calculated palaeointensities deviate by more than 20 per cent from the expected values this may be caused by alteration of the magnetic minerals during the laboratory heating or by chemical alteration prior to the laboratory experiments the new modification uses a double heating of samples above the curie temperature in the laboratory after heating the specimen twice in the same field the measured intensity from the second heating is compared with the laboratory field intensity if the difference is larger than the experimental error then we assume that the anhysteretic remanent magnetization arm correction is not applicable and the sample is therefore rejected this technique provides a powerful criterion with which to select samples using this selection technique palaeointensities are generally within 10 per cent difference of the expected values with a success rate of about 40 per cent

paleomagnetic and rock magnetic studies of the sakurajima 1914 and 1946 andesitic lavas from japan a comparison of the ltd dht shaw and thellier paleointensity methods abstract paleomagnetic and rock magnetic measurements have been made on samples from the 1914 and 1946 sakurajima andesitic lava flows in order to investigate the suitability of andesite to record both paleodirection and paleointensity the lava flows were split in to three sites each of which consists of two or three sub sites a range of rock magnetic experiments have been made on multiple samples per flow and the samples can be split into two broad rock magnetic categories i and ii paleodirection was determined by stepwise thermal demagnetization and the mean direction determined from both flows is very close to that expected from igrf 10 paleointensity was determined using the ltd dht shaw technique and the thellier method on sister samples of the same cores sixty four out of 72 ltd dht shaw paleointensity experiments were successful and there are no differences between the sub sites seventy out of 71 thellier paleointensity experiments were successful however for sub sites in two out of the three sites there are large differences between the mean paleointensities when all paleointensities are normalized to the expected value from igrf 10 the mean is 0 98 0 11 for the ltd dht shaw method and 1 12 0 13 for the thellier method these means are statistically distinguishable and this is related to the different rock magnetic properties of the samples if only category i samples are considered the ltd dht shaw mean is 1 05 0 07 compared with the thellier mean of 1 08 0 08 in contrast there is a much larger spread in the means determined from category ii samples 0 94 0 11 from the ltd dht shaw experiments and 1 15 0 15 from the thellier experiments this spread could be caused by magnetic interactions between magnetic domains assuming high temperature oxidation of titanomagnetite grains during natural cooling we suggest a scenario that can qualitatively explain the difference between the ltd dht shaw and thellier paleointensity results

geomagnetic field intensity during the last 5 myr ltd dht shaw palaeointensities from volcanic rocks of the society islands french polynesia summary on the basis of the thellier palaeointensities reported so far it has been thought that the time averaged virtual dipole moment vdm and virtual axial dipole moment vadm for the last few million years are almost the same as the present geomagnetic dipole moment 8 1022 a m2 this estimate has been called into question however because recent studies have revealed that the thellier method occasionally overestimates palaeointensities by as much as twice the true values in contrast a recently developed palaeointensity technique namely the double heating technique of the shaw method combined with low temperature demagnetization the ltd dht shaw method can yield expected field intensities from samples which give unreliable palaeointensities using the thellier method therefore we have measured absolute palaeointensities from 0 5 4 6 ma volcanic rocks from the society islands french polynesia mainly using the ltd dht shaw method as a result 195 out of 361 samples passed the selection criteria some of which are compared with additional results obtained with coe s version of the thellier method in the thellier experiments 18 out of 40 samples passed the criteria giving palaeointensities both consistent and inconsistent with the ltd dht shaw results these samples are characterized mostly by two segmented arai diagrams if we take the ltd dht shaw palaeointensities 24 reliable site means are available and give a mean vadm of 3 64 2 10 1022 a m2 this is nearly half of the mean of the 0 5 ma thellier data selected from the latest palaeointensity database 7 46 3 10 1022 a m2 n 458 as well as the present dipole moment the ltd dht shaw palaeointensities newly determined in this study suggest that the present day field is so strong that it may not be typical of the past geomagnetic field

oligocene miocene relative geomagnetic paleointensity correlated from the equatorial pacific iodp site u1334 and odp site 1218 to the south atlantic odp site 1090 abstract late oligocene to early miocene relative paleointensity rpi proxies can be correlated from the equatorial pacific iodp site u1334 and odp site 1218 to the south atlantic odp site 1090 age models are constrained by magnetic polarity stratigraphy through correlation to a common geomagnetic polarity timescale the rpi records do not contain significant power at specific orbital frequencies and hence there is no significant coherency between rpi proxies and the normalizers used to construct the proxies although orbital power is present in some normalizers there is no obvious control on rpi proxies from mean sedimentation rate within polarity chrons magnetic grain size proxies or magnetic concentration parameters the salient test is whether the equatorial pacific records can be correlated one to another and to the records from the south atlantic all records are dominated by rpi minima at polarity reversals as expected although the comparison within polarity chrons is compelling enough to conclude that the intensity of the earth s axial dipole is being recorded this is supported by the fit of rpi data from sites u1334 and 1218 after correlation of the two sites using diverse core scanning data rather than polarity reversals alone we do not see a consistent relationship between polarity chron duration and mean rpi and no consistent skewness saw tooth pattern for rpi within polarity chrons stacks of rpi records for 17 5 26 5 ma include long term changes in rpi on myr timescales that are superimposed on rpi minima associated with polarity reversals and shorter term variations in rpi with an apparent pacing of 50 kyr the equatorial pacific to south atlantic correlations indicate that rpi can be used as a global stratigraphic tool in pre quaternary sediments with typical pelagic sedimentation rates of a few cm kyr

cumulative deformation and original geometry of the bushveld complex abstract a structural review and re interpretation of the bushveld complex based on 254 georeferenced maps from research technical reports and geophysical surveys suggests that its current geometry differs markedly from its original geometry broadly n s flattening left lateral transpressional shearing along an interconnected fault network steepening of cumulate layering and 10 km of uplift to the north of the northern margin of the complex s main chamber were accompanied by an eastward verging escape structure burgersfort bulge and syn cooling gap areas on its western limb southward verging deformation was transmitted from the villa nora fragment via thrusting in the rooiberg area generating 50 70 km of southward displacement uplift and erosional loss of the northern limb s western portion a string of anomalous occurrences of bushveld complex units and dense areas outlined by unconstrained gravity isoshells suggest a further 170 km southward displacement through the center of the main chamber the southern limb underwent predominantly right lateral ductile offset from the western limb along the crocodile river and rustenburg faults expressed by an in line series of nnw trending magnetic highs to the south of their mapped terminations left lateral shearing and progressive splaying of a nne trending dyke swarm to the west of an inflection point provides strain markers for this offset and 35 anticlockwise rotation of the burgersfort bulge and central parts of the main chamber although recent work suggests that the complex cooled within 1 myr late intrusion syn cooling sse wards movement of its deeper ductile central parts within at least 5 10 myr after its initial intrusion the transvaalide fold and thrust event and the expulsion of fluids to form the high ti igneous suite hitis and related bodies appear to have closely post dated the complex s intrusion removal of the effects of cumulative strain produces a more equant complex shortly after its intrusion occupying an orthogonal network of normal faults and perpendicular strike slip transverse faults

vertical coupling from the lower atmosphere to the ionosphere observations inferred from indian mst radar gps radiosonde ionosonde magnetometer olr noaa and saber timed instrument over gadanki

a reliable absolute palaeointensity determination obtained from a non ideal recorder reliable measurements of the intensity of the palaeomagnetic field are notoriously difficult to obtain the approach generally taken is to produce multiple estimates per rock unit and assume that those which meet certain minimum standards of technical quality will combine to produce an accurate mean however here using results produced from a package of 20th century basaltic lava flows from mount etna in sicily we demonstrate that this approach can fail in this case the application of typical sets of selection criteria actually introduces bias into the mean determination that we measure we demonstrate that this is caused by two types of non ideal behaviour acting in combination the first is a result of the multidomain grains that the samples contain and the second is caused by differences in the natural and laboratory cooling rates we discuss means of avoiding these sources of error in future palaeointensity studies performed on ancient rocks we also develop a new more general reliability criterion which is effective here and which we argue should be applied wherever possible in future palaeointensity studies in conjunction with standard criteria it requires two distinct types of materials which both produce some good quality palaeointensity measurements and uses their range of overlap to constrain the true palaeointensity both the application of this criterion and general reliability considerations require that future palaeointensity studies should measure many samples per cooling unit and that these should be as diverse in terms of their rock magnetic properties and cooling histories as possible

palaeointensity study of the oshima 1986 lava in japan implications for the reliability of the thellier and ltd dht shaw methods abstract we have performed a palaeointensity study of the oshima 1986 lava in order to examine the reliability of the thellier and ltd dht shaw methods with special reference to high temperature oxidation states of magnetic grains coe s version of the thellier method was applied to fifteen specimens from five block samples the palaeointensities determined by this thellier method ranged from 44 8 to 59 0 t with an average of 51 0 4 1 t n 15 they are systematically higher than the expected intensity 45 5 t from the dgrf 1985 since the in situ magnetic survey at the sampling site indicates no strong local magnetic anomaly these high palaeointensities are overestimation probably due to some rock magnetic property and or some thermal alteration during the experiments microscopic observations show that the samples where some titanomagnetites surrounding vesicles were classified with intermediate oxidation indices of iii v gave 10 30 higher palaeointensity values therefore the erroneously high thellier palaeointensities have a relation to the high temperature oxidation state for eight of the fifteen specimens used in the thellier experiments the applied dc field was perpendicular to the primary nrm component for quantitative evaluation of laboratory induced chemical remanent magnetisation crm directional changes of nrm thermally demagnetised during the thellier experiments indicate that most of the samples more or less acquired crm due to laboratory heating suggesting that some magnetic phase with high blocking temperatures was produced for the specimens of intermediate oxidation level the crm appears to have been gradually acquired at relatively low temperatures 400 c it would appear to be difficult to detect this gradual thermal alteration with the standard ptrm check weak field susceptibility measurements and hysteresis parameter changes we also applied the double heating technique of the shaw method combined with low temperature demagnetisation ltd dht shaw method to seven specimens from the same block samples the palaeointensities determined by the ltd dht shaw method yielded an average of 46 4 4 7 t n 6 which agrees with the expected intensity indicating no dependence on the high temperature oxidation states

long term variations in palaeointensity we compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass the basaltic glass data more than double the number of reliable thellie

rock magnetic artifacts on long term relative paleointensity variations in sediments 1 long term changes of geomagnetic field intensity including possible dependence on lengths of polarity intervals provide fundamentally important information for understanding the geodynamo a positive correlation between paleointensity and polarity interval length was previously suggested from an oligocene ca 23 34 ma relative paleointensity record at deep sea drilling program site 522 in the atlantic ocean which is the only continuous paleointensity data set published so far for this age interval we have conducted a paleomagnetic study of eocene to oligocene sediments at three sites in the eastern equatorial pacific ocean our objectives include revisiting the issue of the paleointensity polarity length correlation magnetic properties of the sediments meet the frequently used criteria for reliable relative paleointensity estimation although short wavelength normalized remanence intensity fluctuations associated with polarity boundaries and possible geomagnetic excursions agree among the three sites long term changes are inconsistent apparent positive correlation between normalized intensity and polarity length was observed but the normalized intensity has an obvious anti correlation with the ratio of anhysteretic remanent magnetization arm to isothermal remanent magnetization irm which is mainly controlled by the relative abundance of biogenic and terrigenous magnetic minerals furthermore the normalized intensity correlates with sedimentation rate these facts indicate a lithological contamination on the normalized intensity records the dependence on arm irm and sedimentation rate is also evident at site 522 it is inferred that variations in sedimentation rate and the relative abundance of biogenic magnetite on depositional remanent magnetization acquisition efficiency may not be well compensated by the normalization it is therefore premature to conclude that stronger geomagnetic fields were recorded during longer polarity intervals from currently available normalized intensity records

signatures of low latitude high latitude coupling in the tropical mlt region during sudden stratospheric warming 1 the present paper analyses the variations of daytime mesopause temperature over an equatorial station during polar stratospheric sudden warming ssw events indicating a possible dynamical coupling between the two regions through the intensification of planetary wave activity the amplified wave signatures of quasi 16 day period have been seen in the equatorial mesopause temperature emt and polar stratospheric temperature at 10 hpa during the course of the ssw the emt measurements were made from trivandrum 8 5 n 76 5 e an equatorial station in india and the stratospheric temperatures were obtained from ncep ncar reanalysis this investigation reveals 1 an overall enhancement and amplified wave activity in the emt prior to the ssw and 2 propagation of a wave disturbance from equatorial stratosphere to north pole in about a month these results are new and reveal some newer aspects of the ssw and its equatorial effects

reliable absolute palaeointensities independent of magnetic domain state knowledge of palaeointensity variation is required for determining the full vector variation of the geomagnetic field as a function of geological time this provides essential constraints for numerical geodynamo models to date most palaeointensity determination methods are laborious characterised by rather low success rates and demand substantial processing time the rocks under investigation must obey stringent criteria to yield faithful palaeointensities the magnetic particles must be single domain the natural remanent magnetisation must be a thermoremanent magnetisation and during the successive heating steps in the laboratory no chemical alteration should occur here we describe a new method that allows all magnetic domain states to be processed i e it does not require single domain particles the method makes use of the linearity of partial thermoremanent magnetisation ptrm with the applied laboratory field multiple specimens are used so that every sample is exposed only once to a laboratory field warranting that all samples experienced the same magnetic history through the limited number of thermal steps alteration effects are reduced as well the laboratory ptrm and natural remanent magnetisation nrm of the specimens are oriented parallel to minimise the effects of high temperature tails that affect multidomain minerals the ptrm acquisition temperature is selected below the temperature at which chemical alteration sets in and above the temperature trajectory where secondary viscous nrm components occur the procedure requires a lower number of steps than any other palaeointensity method reducing significantly the total time needed per rock unit we propose to name the new protocol multispecimen parallel differential ptrm method i t provides the correct answer to 5 for artificial samples and natural rocks containing multidomain magnetic particles that were given a laboratory trm of known intensity application to the paricutin september december 1943 lava flow three sites 7 specimens per site yields a weighted mean of 45 9 1 25 t within uncertainty margin of the expected value of 45 0 t

petrology and mineralisation of the southern platreef northern limb of the bushveld complex south africa the platreef the putative local analogue of the merensky reef forms the floor to the mafic succession in the northern limb of the bushveld complex we define the platreef as the lithologically variable unit dominated by pyroxenite which is irregularly mineralised with pge cu and ni between the transvaal metasedimentary footwall or archaean basement and the overlying main zone gabbronorite we define the mineralisation around calcsilicate xenoliths within the main zone in the far north of the limb as a platreef style mineralisation the platreef ss has a strike extent of 30 km whereas platreef style mineralisation occurs over a strike length of 110 km the platreef varies from 400 m thick in the s to 30 modal in some intersections these are dominated by pyrrhotite with lesser pentlandite and chalcopyrite minor pyrite and traces of a wide compositional range of sulphides in the southern sector mineralised zones have cu grades of 0 1 0 25 and ni 0 15 0 36 massive sulphides are localised commonly but not exclusively towards the contact with footwall metasedimentary rocks magmatic sulphides are disseminated or net textured ranging from a few microns to 2 cm grains of pyrrhotite and pentlandite with chalcopyrite and minor pyrite much of the sulphide is associated with intergranular plagioclase or quartz feldspar symplectites along the margins of rounded cumulus orthopyroxenes the pges in the southern sector occur as tellurides bismuthides arsenides antimonides bismuthoantimonides and complex bismuthotellurides pgm are rarely included in the sulphides but occur as micron sized satellite grains around interstitial sulphides and within alteration assemblages in serpentinised zones the pt pd ratio 1 and pge grade may be decoupled from s and base metal abundance

paleointensity study of the middle cretaceous iritono granite in northeast japan implication for high field intensity of the cretaceous normal superchron abstract paleointensity of the cretaceous normal superchron cns has been studied using the middle cretaceous iritono granite of the abukuma massif in northeast japan our previous study wakabayashi k tsunakawa h mochizuki n yamamoto y takigami y 2006 paleomagnetism of the middle cretaceous iritono granite in the abukuma region northeast japan tectonophysics 421 161 171 indicates that the iritono granite retains a stable and primary component of high blocking temperatures and high coercivities which is characterized by the shallow inclination and carried mainly by single domain magnetite applying coe s version of the thellier method and the ltd dht shaw method we have obtained 16 successful results with an average of 58 4 7 3 t however an effect of long cooling time of the granite on the paleointensity measurement should be taken into account an estimate of cooling time to acquire the primary component ranges in 4 10 4 to 1 4 10 7 years from a thermal diffusion model of the granite body and the difference between 40 ar 39 ar biotite age of 101 9 0 2 1 ma and u pb zircon age of 115 7 1 9 1 ma from single domain theory thermoremanent magnetization trm of the iritono granite samples in nature is estimated to be about 1 5 times as strong as the laboratory trm applying this correction factor the corrected paleointensity is 39 0 4 9 t and the virtual dipole moment vdm is calculated to be 9 1 1 1 10 22 a m 2 this vdm can be interpreted as representative of the middle cns geomagnetic field since the individual granite samples with long cooling time can average out the paleosecular variation the obtained vdm is a few times higher than mean vdms averaged for 0 5 ma 3 6 10 22 a m 2 and 0 160 ma 4 8 10 22 a m 2 except for the cns by previous studies this suggests that the geomagnetic field intensity was high in the middle cns

long term trends in paleointensity the contribution of dsdp odp submarine basaltic glass collections abstract the deep sea drilling project and the ocean drilling program have been collecting fresh appearing submarine basaltic glass from the world s oceans for over three decades this glass has proved nearly ideal for estimating paleointensity variations of the earth s magnetic field we compile here data for 726 paleointensity experiments from six publications on paleointensity using dsdp odp glass we also include new data for an additional 225 specimens these were obtained through the so called izzi paleointensity experiment of tauxe l staudigel h 2004 strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite geochem geophys geosyst 5 2 q02h06 doi 10 1029 2003gc000635 whereby infield zerofield steps are alternated with the zerofield infield steps to enhance quality assessment of the resulting data the entire collection of data from 951 experiments was prepared for uploading to the magic data base http earthref org including original measurements interpretations and useful metadata excellent results were obtained throughout the depth 1400 mbsf and age 0 160 ma range sampled dsdp odp glass data are compared with published paleointensity data meeting minimal acceptance criteria from the time interval 1 160 ma paleolatitudes were estimated for all cooling units in a self consistent manner for use in calculating virtual axial dipole moments we conclude 1 there is about a 20 difference in mean values between the sbg and the lava flow data 48 36 and 57 29 zam2 respectively the difference is caused by the fact that there are more higher values in the lava flow data than in the sbg data set rather than a difference in the minimum values lava flows cooling over a periods of days to months can account for the discrepancy 2 the positive relationship between polarity interval length and average paleofield intensity first hypothesized by cox a v 1968 lengths of geomagnetic polarity intervals j geophys res 73 3247 3260 is supported by data compiled here the brunhes data for which we have only a minimum estimate for polarity interval length are consistent with a long polarity interval suggesting that instead of racing toward reversal hulot g eymin c langlais b mandea m olsen n 2002 small scale structure of the geodynamo inferred from oersted and magsat satellite data nature 416 620 623 we could instead be in the midst of a long stable polarity interval 3 because the average value appears to be a function of polarity interval length it is probably not useful to calculate a mean value nonetheless it appears that most of the time apart from the brunhes and the longest polarity intervals the average dipole moment is substantially less than the present day value as suggested by juarez t tauxe l gee j s pick t 1998 the intensity of the earth s magnetic field over the past 160 million years nature 394 878 881

11 million years of oligocene geomagnetic field behaviour summary an 11 million year long record of the oligocene geomagnetic field has been obtained from pelagic sediments of dsdp hole 522 an average sample spacing of 4 cm yielded approximately one specimen per 4 to 8 kyr the rock magnetics are remarkably consistent across the entire interval previous work demonstrated a magnetic mineralogy dominated by magnetically stable magnetite the natural remanent magnetism nrm carries an oligocene polarity timescale that is in excellent agreement with the oligocene reversal record as determined from marine magnetic anomalies mmas including many of the so called crypto chrons normalized nrm intensities from the undisturbed portions of the record yield a time series of variations with features consistent with a number of other palaeointensity time series derived from both sedimentary and lava sequences these features include consistent major decreases in palaeointensity dips at reversal boundaries and occasional dips between reversal boundaries that could correspond to lineated tiny wiggles in the mma records the data set suggests that the overall field strength was 40 per cent higher in the first half of the oligocene when the average reversal frequency was 1 6 myr l than in the second half when the reversal frequency was 4myr there is also a weak dependence of average field strength on length of polarity interval finally in the three cores suited to spectral analysis of coherent polarity and relative intensity independent of lithological contamination there is a persistent ca 30 50 ka periodicity in the variations of the relative intensity suggesting that the geomagnetic field pulses at about this frequency not only during the brunhes as demonstrated by tauxe shackleton 1994 but in the oligocene as well

morphology of ionospheric f2 region variability associated with sudden stratospheric warmings the effect of sudden stratospheric warming ssw on the f2 region ionosphere has been extensively analyzed for the major event of year 2009 apart from a few reports on other major and minor events morphology of ionospheric responses during ssw can be better comprehended by analyzing such warming events under different solar geomagnetic and meteorological conditions we investigate the features of f2 region variability following the ssw events of 2010 2011 2012 2013 2014 2015 and 2016 using ionosonde data from the asian region covering a broad latitudinal range from 26 6 n to 45 1 n we find perceptible ionospheric variations in electron densities during these warming events which is accompanied by a large variation of 117 within enhancements as compared to a meagre variation of 11 within depressions during these events we also examine six months data at these latitudes and longitudes and find that the maximum and minimum variation in f2 layer critical frequency is observed during each ssw period the influence of quasi stationary 16 day planetary waves is seen during these ssw events further a recently proposed parameter ssw integrated strength by vieira et al 2017 to characterize ssw event with respect to ionosphere is also examined it is seen that it does not fit well for these seven ssw events at these latitudes and longitudes

toward an optimal geomagnetic field intensity determination technique 1 paleointensity determinations based on double heating techniques in field zero field cooling zero field in field cooling and two in field steps with opposite laboratory fields are generally considered to be functionally interchangeable producing equally reliable paleointensity estimates to investigate this premise we have developed a simple mathematical model we find that both the zero field first and in field first methods have a strong angular dependence on the laboratory field parallel orthogonal and anti parallel while the two in field steps method is independent of the direction of the laboratory produced field contrary to common practice each method yields quite different outcomes if the condition of reciprocity of blocking and unblocking temperatures is not met even with marginal 10 tails of partial thermoremanence our calculations suggest that the zero field first method with the laboratory produced field anti parallel to the natural remanence nrm is the most robust paleointensity determination technique when the intensity of the lab induced field is smaller than ancient field however the zero field first method with the laboratory field parallel to the nrm is the optimum approach when the intensity of the lab induced field is larger than the ancient field by far the best approach however is to alternatethe infield zerofield iz steps with zerofield infield zi steps

the role of fluid pressure in the formation of bedding parallel thrust hosted gold deposits sabie pilgrim s rest goldfield eastern transvaal abstract shallowly dipping thrust hosted gold veins occur within the paleoproterozoic transvaal supergroup rocks in the eastern transvaal of south africa internally the veins record episodic events of fluid infiltration and subsequent mineral deposition within discrete local scale thrust faults evidence also exists for subvertical dilation within the individual veins and textures which record open space filling are preserved the probable depth of formation suggests lithostatic pressures in excess of 2 2 kbar and the vein textures indicate numerous reactivation events associated with individual thrust faults occurring in a terrain characterised by low levels of preserved strain fault reactivation may have occurred under conditions of low differential stress in the presence of high pressure fluids with p fluid approaching or exceeding lithostatic levels

fine scale study of a thick stratospheric ozone lamina at the edge of the southern subtropical barrier a large scale transport event resulting in a thick ozone lamina originating from midlatitudes is observed in the tropical stratosphere over reunion island 55 e 21 s this isentropic transport was detected from stratospheric balloon borne ozone measurements that showed the occurrence of the lamina and was investigated using different tools based on ertel s potential vorticity epv analyses an original software dybal using surface coordinate and the equivalent length of epv contours as diagnostic tools in conjunction with high resolution outputs from an epv advection model mimosa allows us to specify the origin of the lamina the results indicate that a broad layer of stratospheric air was isentropically advected from midlatitudes across the southern edge of tropical reservoir and reached reunion island on 12 july 2000 in addition eliassen palm s flux vectors calculated from ecmwf analysis show that planetary wave activity was quite large during that time period with wave breaking occurring around 30 km and could have driven that exchange in contrast with analyses of filamentation events based on model and satellite data the present study focuses on a fine scale vertical survey from in situ measurements the filament reported in this paper is characterized by a large vertical extension and is located around the maximum of ozone concentration in the tropical stratosphere 600 k the analysis of such events poorly documented in the tropics could complement satellite studies and contribute to a better determination of the transport between the tropics and the midlatitudes

properties of the quasi 16 day wave derived from eos mls observations 1 this paper describes the use of eos microwave limb sounder mls data to observe the field of traveling planetary waves with quasi 16 day periods this study utilizes mls v2 2 temperature and geopotential data between 1 january 2005 and 31 december 2008 in the range 316 hpa to 0 001 hpa approximately 8 to 97 km to examine these waves analysis demonstrates that the quasi 16 day wavefield is made up of a number of components with westward and eastward propagating s 1 and s 2 waves generally dominant in the northern hemisphere the westward and eastward propagating s 1 waves have similar magnitudes and are larger than the other modes while in the southern hemisphere the eastward propagating s 1 and s 2 waves are larger than the westward propagating wave modes all of the modes examined display strong seasonal patterns in the temperature amplitude significant variability in the wave activity from year to year and the presence of strong pulse like patterns in the activity all of the modes also display large median temperature amplitudes poleward of 40 degrees in both hemispheres our analysis also demonstrates that the variability in winter from year to year is larger in the northern hemisphere than the southern hemisphere detailed study also suggests that the exclusion of waves from regions of negative refractive index squared likely forms much of the seasonal pattern observed thus regions of strong westward wind speeds effectively exclude vertically propagating waves as expected from theory the reflection and absorption of waves associated with critical lines is also likely to explain the frequent occurrence of standing wave patterns in the eos mls temperature observations this study highlights the potential of mls observations for observing waves from the upper troposphere to the lower mesosphere

a comparison of thermal and microwave palaeomagnetic techniques using lava containing laboratory induced remanence summary a series of laboratory experiments has been carried out using lava from hawaii and australia containing laboratory induced remanence to compare thermal and microwave palaeomagnetic techniques three samples of hawaiian lava containing a known laboratory induced thermal remanence trm were subjected to microwave palaeointensity experiments using the liverpool 8 2 ghz microwave system conventional modified thellier palaeointensity experiments were carried out on the same three lava samples this time containing a known microwave induced thermoremanent magnetisation tmrm both palaeointensity techniques produced the correct intensity value demonstrating the equivalence of trm and tmrm no indications of alteration during the experiment were evident during the microwave experiments whereas alteration was pronounced after heating to 350 c in the thellier experiments demonstrating that alteration during microwave palaeointensity analysis is reduced when compared to thermal techniques in a second set of experiments six samples three hawaiian and three australian lava samples were given a laboratory induced full trm and a secondary perpendicular partial trm ptrm at lower temperatures sister samples were then demagnetised using thermal and microwave methods analysis of the orthogonal vector plots ovps revealed little difference in separating the two components for five out of the six samples for one sample microwave demagnetisation did not clearly distinguish between the two components with the primary component not being resolved until 74 per cent of the moment had been demagnetised compared to just 4 per cent with thermal demagnetisation for this one sample it appears that the microwave unblocking spectra is not equivalent to the thermal unblocking spectra probably due to a combination of microwave demagnetisation processes occurring comparison of the intensity of magnetisation plots during demagnetisation shows that the relationship between temperature and microwave power appears more logarithmic than linear this study demonstrates the validity of the microwave palaeointensity technique and as long as the primary component of magnetisation can be isolated from multicomponent remanence then the microwave palaeointensity technique can be applied

limited latitudinal mantle plume motion for the louisville hotspot hotspots that form above upwelling plumes of hot material from the deep mantle typically leave narrow trails of volcanic seamounts as a tectonic plate moves over their location these seamount trails are excellent recorders of earth s deep processes and allow us to untangle ancient mantle plume motions during ascent it is likely that mantle plumes are pushed away from their vertical upwelling trajectories by mantle convection forces it has been proposed that a large scale lateral displacement termed the mantle wind existed in the pacific between about 80 and 50 million years ago and shifted the hawaiian mantle plume southwards by about 15 of latitude here we use 40ar 39ar age dating and palaeomagnetic inclination data from four seamounts associated with the louisville hotspot in the south pacific ocean to show that this hotspot has been relatively stable in terms of its location specifically the louisville hotspot the southern hemisphere counterpart of hawai i has remained within 3 5 of its present day latitude of about 51 s between 70 and 50 million years ago although we cannot exclude a more significant southward motion before that time we suggest that the louisville and hawaiian hotspots are moving independently and not as part of a large scale mantle wind in the pacific

aura microwave limb sounder observations of dynamics and transport during the record breaking 2009 arctic stratospheric major warming a major stratospheric sudden warming ssw in january 2009 was the strongest and most prolonged on record aura microwave limb sounder mls observations are used to provide an overview of dynamics and transport during the 2009 ssw and to compare with the intense long lasting ssw in january 2006 the arctic polar vortex split during the 2009 ssw whereas the 2006 ssw was a vortex displacement event winds reversed to easterly more rapidly and reverted to westerly more slowly in 2009 than in 2006 more mixing of trace gases out of the vortex during the decay of the vortex fragments and less before the fulfillment of major ssw criteria was seen in 2009 than in 2006 persistent well defined fragments of vortex and anticyclone air were more prevalent in 2009 the 2009 ssw had a more profound impact on the lower stratosphere than any previously observed ssw with no significant recovery of the vortex in that region the stratopause breakdown and subsequent reformation at very high altitude accompanied by enhanced descent into a rapidly strengthening upper stratospheric vortex were similar in 2009 and 2006 many differences between 2006 and 2009 appear to be related to the different character of the ssws in the two years

midlatitude ionospheric responses to the 2013 ssw under high solar activity ionospheric responses to sudden stratospheric warming ssw are not well understood particularly in the midlatitudes and under high solar conditions during the 2013 ssw ionospheric disturbances were observed in eight locations on the meridional chain from 30 5 degrees n to 42 8 degrees n in northern china the midlatitude ionosphere responded strongly to the ssw despite being under high solar flux the f 2 layer maximum electric density increased by more than 80 and the peak height was elevated more than 60km well set and organized semidiurnal variations were recorded in early and middle january during the ssw in eight observation locations the expected f o f 2 decrease in the afternoon hours was not clearly discernible however nighttime enhancements occurred frequently the time period spectra of the average f o f 2 and zonal winds and meridional winds at altitudes of 86 95km presented quasi 16day planetary wave like oscillations during the warming event the coupling between the atmosphere and ionosphere may be strengthened by the quasi 16day waves the amplified diurnal semidiurnal and terdiurnal tides in f o f 2 were also recorded during the warming in good agreement with earlier observations importantly the variations in the semidiurnal tides included a 16day periodic component indicating that the modulated semidiurnal tides may transmit these 16day planetary wave like oscillations to the f region through wind dynamo although the pw tide interaction theory is not novel it is of significance in the midlatitude ionospheric response to ssw

flexural slip structures in the bushveld complex south africa this paper investigates structures in the layered critical zone of the bushveld complex in south africa that have detrimentally affected mining operations the common structures are layer parallel faults with reverse dip slip and ramp faults with curved slip planes and prominent striations geometric variations include duplex ramps contained within floor and roof layer parallel faults and linking ramps connecting separate layer parallel faults hidden in the footwall and hangingwall the orientations geometries displacements and shear senses of the layer parallel faults and ramp faults are interpreted to be flexural slip structures formed during bending of the originally horizontal bushveld complex into a basin fold geometry during crustal loading

a statistical analysis of the propagating quasi 16 day waves at high latitudes and their response to sudden stratospheric warmings from 2005 to 2018

paleointensity of the geomagnetic field in the late cretaceous and earliest paleogene obtained from drill cores of the louisville seamount trail information on the strength of the geomagnetic field is important for understanding the behavior of the geodynamo polarity reversal frequency increases toward the late cenozoic since the end of the cretaceous normal superchron accumulating reliable paleointensity data in this time interval is still desired for elucidating the possibility of a link between reversal frequency and paleointensity we conducted a paleointensity study on 288 samples from four seamounts from 74 to 50 ma in age that constitutes the louisville seamount trail based on thermomagnetic curves and scanning electron microscopy we first excluded 134 samples that showed evidence for low temperature oxidation we then applied the tsunakawa shaw method with low temperature demagnetization and double heating after rejecting some samples that do not preserve stable primary remanence and 52 successful results were obtained an average virtual axial dipole moment vadm of 3 75 1 52 1022 am2 was obtained at site u1372 on canopus seamount 74 ma based on 16 independent measurements sites u1373 and u1374 on rigil seamount 70 ma yielded a mean of 3 79 1 40 n 16 and site u1376 on burton seamount 65 ma yielded a mean of 3 70 1 37 n 8 these vadms are similar to the long term average of the last 200 myr by tauxe et al 2013 and the mean of the last 5 myr by yamamoto and tsunakawa 2005 the volcanic sequence drilled at site u1372 probably belongs to chron c33n of 5 59 myr long whereas others belong to shorter chrons our results support no discernible relationship between polarity length and paleointensity

responses of quasi 2 day waves in the mlt region to the 2013 ssw revealed by a meteor radar chain we present an analysis of the responses of quasi 2 day waves qtdws to the 2013 sudden stratosphere warming ssw in the mesosphere and lower thermosphere mlt region the study is based on data collected by a meteor radar chain along the 120 e meridian in the northern hemisphere which consists of four stations at mohe 52 5 n 122 3 e beijing 40 3 n 116 2 e wuhan 30 5 n 114 6 e and sanya 18 3 n 109 6 e it is the first time that an enhancement of the qtdw in the neutral wind during the 2013 ssw is observed in the midlatitudes in the northern hemisphere during the ssw the amplification of the qtdw in the low latitudes is the most prominent and the direction of the mean zonal wind shows clear reversion from eastward to westward the consistent variations of the qtdws and the mean neutral wind at the four stations are very likely associated with the ssw

a major stratospheric sudden warming event in january 2009 abstract the major stratospheric sudden warming ssw event of january 2009 is analyzed using the japan meteorological agency jma climate data assimilation system jcdas this ssw event is characterized by the extraordinary predominance of the planetary scale wave of zonal wavenumber 2 wave 2 the total amount of the upward eliassen palm ep flux for wave 2 was the strongest since the winter of 1978 79 it is found that the remarkable development of the upper troposphere ridge over alaska played important roles in the ssw in january 2009 during the first development stage the ridge excited wave packets upward as well as eastward over around alaska the eastward propagating packets intensified a trough over eastern siberia which led to the development of the planetary wave over eastern siberia during the second development stage the results of this study indicate that the pronounced wave 2 pattern observed in the stratosphere was brought about by accumulative effects of rather localized propagati

connectivity between the western and eastern limbs of the bushveld complex abstract the mafic layered rocks of the bushveld complex are 6 8 km thick and crop out over an area of 65 000 km 2 previous interpretations of the bouguer gravity anomalies suggested that the intrusion consisted of two totally separate bodies however the mafic sequences in these arcuate western and eastern limbs are remarkably similar with at least six petrologically distinctive layers and sequences being recognisable in both limbs such similarity of sequences in two totally discrete bodies 200 300 km apart is petrologically implausible and it is suggested that they formed within a single lopolithic intrusion all previous bouguer gravity models failed to consider the isostatic response of the crust to emplacement of this huge mass of mafic magma isostatic adjustment as a result of this intrusion would have caused the base of the crust to be depressed by as much as 6 km with this revised whole crustal model it becomes possible to construct a gravity model consistent with observed data which includes a 6 km thick sequence of mafic rocks connecting the western and eastern limbs of the bushveld complex the exact depth at which the mafic rocks of the bushveld complex lie in the centre of the structure cannot be constrained by the gravity data such a first order model is an approximation because there have been subsequent deformation and structural readjustments in the crust some of them probably related to the emplacement of the bushveld complex specifically the observed geometry of the rocks around the crocodile river dennilton marble hall and malope domes suggests that major upwarping of the crust occurred on a variety of scales triggered by emplacement of the bushveld complex

a paleointensity technique for multidomain igneous rocks 1 we developed a paleointensity technique to account for concave up arai diagrams due to multidomain md contributions to determine unbiased paleointensities for 24 trial samples from site ga x in pleistocene lavas from floreana island galapagos archipelago the main magnetization carrier is fine grained low titanium magnetite of variable grain size we used a comprehensive back zero forth bzf heating technique by adding an additional zero field heating between the thellier two opposite in field heating steps in order to estimate paleointensities in various standard protocols and provide internal self consistency checks after the first bzf experiment we gave each sample a total thermal remanent magnetization ttrm by cooling from the curie point in the presence of a low 15 t laboratory applied field then we repeated the bzf protocol with the laboratory applied ttrm as a synthetic natural remanent magnetization nrm using the same laboratory applied field and temperature steps to obtain the synthetic arai signatures which should only represent the domain state dependent properties of the samples we corrected the original arai diagrams from the first bzf experiment by using the arai signatures from the repeated bzf experiment which neutralizes the typical md concave up effect eleven samples meet the arai diagram post selection criteria and provide qualified paleointensity estimates with a mean value for site ga x of 4 23 1 29 t consistent with an excursional geomagnetic field direction reported for this site

thrust controlled gold mineralisation at the elandshoogte mine sabie pilgrim s rest goldfield south africa stratiform quartz sulphide gold veins locally termed reefs are hosted within the proterozoic transvaal sequence sedimentary succession in the sabie pilgrim s rest goldfield eastern transvaal these deposits have produced about 180 tonnes of gold and share many characteristics with those of telfer western australia detailed examination of the elandshoogte mine shows that gold deposition occurred in two stages both linked to bedding parallel thrust faulting within the sedimentary pile deformation being concentrated within incompetent shale beds interlayered within more competent units the majority of gold was introduced in the second stage of mineralisation and occurs within fractures in early formed sulphide minerals deposition of competent quartz veins accompanying early sulphide and gold mineralisation resulted in a change in deformation style within the reef zone from early shearing in shales to later duplex faulting of the quartz reef fluids accompanying faulting are implied to have transported gold and a magmatic source of mineralisation is suggested

the flexural slip mechanism abstract detailed field studies of turbiditic sequences from south georgia south atlantic north devon england and cardigan bay wales show that flexural slip occurs on discrete movement horizons between rock packets in which the beds have welded contacts stair stepping displacements of sedimentary dykes and of early quartz veins show that the movement horizons generally have a decimetre to metre spacing and are marked by bedding parallel quartz veins these veins are from 1 mm to several cm thick and can be used to identify movement horizons in the absence of displaced markers they consist of several sheets of quartz fibres which each carry a slickenfibre lineation and which together preserve a record of the displacements on an individual surface complex slickenfibre patterns and departures from ideal behaviour in which slip occurs orthogonal to the fold hinge probably result from changes in slip vector on the limbs of growing non cylindrical folds movement horizons show many of the features associated with large scale thrusting such as ramps duplexes and imbricate structures and the shear sense given by fibre steps on these surfaces and by duplexes within stratigraphically restricted packages changes across fold hinges chevron folds are thought to develop mainly by flexural flow in the early stages with flexural slip becoming dominant later as the beds become lithified new slip surfaces are generated as the dip of the fold limbs increases

response of the stratosphere to interannual variability of tropospheric planetary waves a primitive equation global model of the middle atmosphere is used to investigate the response of the extratropical stratosphere to different levels of wave forcing from steady perturbations of the geopotential height near the tropopause the response of the stratosphere is compared to that in quasi geostrophic beta plane models used in previous studies the primitive equation model exhibits three flow regimes under perpetual january conditions strong westerly steady flow for small wave amplitude forcing strong westerly but unsteady flow for moderate wave amplitude forcing and oscillations between easterly and westerly flow for large wave amplitude forcing the regimes for low and high forcing are analogous to solutions of the simpler holton mass hm quasi geostrophic model the moderate forcing regime does not occur in the hm model and it is attributed to instability of the strongly sheared flow generated by planetary waves in the upper stratosphere we also show how the observed patterns of interannual variability in the winter stratosphere can be explained in terms of these three flow regimes in the northern hemisphere the flow often enters the high forcing regime where variations in conditions in the early winter flow or quasi steady upper tropospheric planetary wave amplitudes make similar contributions to the interannual variability in the stratospheric circulation for the southern hemisphere we suggest that the flow alternates between the low and moderate forcing regimes through year to year changes in the amplitude of quasi steady waves near the tropopause this mechanism produces large enough changes to explain the interannual variability in the southern stratosphere

a new look at stratospheric sudden warmings part iii polar vortex evolution and vertical structure the evolution of the arctic polar vortex during observed major midwinter stratospheric sudden warmings ssws is investigated for the period 1957 2002 using 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 ertel s potential vorticity pv and temperature fields timelag composites of vertically weighted pv calculated relative to the ssw onset time are derived for both vortex displacement ssws and vortex splitting ssws by averaging over the 15 recorded displacement and 13 splitting events the evolving vertical structure of the polar vortex during a typical ssw of each type is clearly illustrated by plotting an isosurface of the composite pv field and is shown to be very close to that observed during representative individual events results are verified by comparison with an elliptical diagnostic vortex moment technique for both types of ssw little variation is found between individual events in the orientation of the developing vortex relative to the underlying topography that is the location of the vortex during ssws of each type is largely fixed in relation to the earth s surface during each type of ssw the vortex is found to have a distinctive vertical structure vortex splitting events are typically barotropic with the vortex split occurring near simultaneously over a large altitude range 20 40 km in the majority of cases of the two daughter vortices formed it is the siberian vortex that dominates over its canadian counterpart in contrast displacement events are characterized by a very clear baroclinic structure the vortex tilts significantly westward with height so that the top and bottom of the vortex are separated by nearly 1808 longitude before the upper vortex is sheared away and destroyed

detecting multidomain magnetic grains in thellier palaeointensity experiments the thellier technique is the most commonly used method for absolute palaeointensity studies it is based on thellier s laws stating that partial thermoremanent magnetisations ptrms are independent and additive which however only are true for non interacting single domain sd grains for multidomain md grains individual ptrms are not independent and thellier palaeointensity experiments on rocks with a significant proportion of md grains may therefore lead to erroneous palaeofield estimates by introducing a ptrm tail check in the coe version of the thellier technique j geophys res 72 1967 3247 we present a simple method to detect and discard such rocks the usefulness of the ptrm tail check is exemplified by thellier palaeointensity experiments performed on two palaeomagnetic sample collections with different magnetomineralogy miocene baked sediments from french massif central are shown to be ideal for thellier studies with the remanent magnetisation residing in thermally stable sd grains for palaeocene eocene basaltic lavas from faeroe islands 64 of otherwise acceptable palaeointensity estimates are discarded due to the failure of ptrm tail checks indicating the presence of significant concentrations of md grains 2001 elsevier science b v all rights reserved

analysis of 11 myr of geomagnetic intensity variation we have conducted a detailed exploratory analysis of an 11 million year long almost continuous record of relative geomagnetic paleointensity from a sediment core acquired on deep sea drilling project leg 73 at site 522 in the south atlantic we assess the quality of the paleointensity record using spectral methods and conclude that the relative intensity record is minimally influenced by climate variations isothermal remanence is shown to be the most effective normalizer for these data although both susceptibility and anhysteretic remanence are also adequate statistical analysis shows that the paleointensity variations follow a gamma distribution and are compatible with predictions from modified paleosccular variation models and global absolute paleointensity data when subdivided by polarity interval the variability in paleointensity is proportional to the average and further the average is weakly correlated with interval length spectral estimates for times from 28 77 until 22 74 ma when the reversal rate is about 4 myr 1 are compatible with a poisson model in which the spectrum of intensity variations is dominated by the reversal process in the frequency range 1 50 myr 1 in contrast between 34 7 and 29 4 ma when the reversal rate is about 1 6 myr 1 the spectra indicate a different secular variation regime the magnetic field is stronger and more variable and a strong peak in the spectrum occurs at about 8 myr 1 this peak may be a reflection of the same signal as recorded by the small variations known as tiny wiggles seen in marine magnetic anomaly profiles

quasi 16 day oscillation in the mesosphere and lower thermosphere a quasi 16 day wave in the mesosphere and lower thermosphere is investigated through analyses of radar data during january february 1979 and through numerical simulations for various background wind conditions previous workers have examined about 19 days of tropospheric and stratospheric data during january 10 28 1979 and present conflicting evidence as to whether a large westward propagating wavenumber 1 oscillation observed during this period can be identified in terms of the second symmetric rossby normal mode of zonal wavenumber 1 commonly referred to as the 16 day wave in the present work we have applied spectral analysis techniques to meridional and zonal winds near 95 km altitude obtained from radar measurements over obninsk russia 54 n 38 e and saskatoon canada 52 n 107 w these data reveal oscillations of the order of 10 m s 1 with a period near 16 days as well as waves with periods near 5 and 10 days these periodicities all correspond to expected resonant frequencies of atmospheric disturbances associated with westward propagating free rossby modes of zonal wavenumber 1 numerical simulations are performed which demonstrate that the 95 km measurements of the 16 day wave are consistent with upward extension of the oscillation determined from the tropospheric and stratospheric data noteworthy features of the model in terms of its applicability in the mesosphere lower thermosphere regime are explicit inclusion of eddy and molecular diffusion of heat and momentum and realistic distributions of mean winds especially between 80 and 100 km the latter include a westerly wind regime above the summer easterly mesospheric jet thus providing a ducting channel enabling interhemispheric penetration of the winter planetary wave disturbance this serves to explain the appearance of a quasi 16 day wave recently reported in the high latitude summer mesopause williams and avery 1992 however the efficiency of this interhemispheric coupling may be reduced by gravity wave stress no significant penetration of the 16 day oscillation above about 100 km is predicted by the model reported signatures of a 16 day periodicity in ionospheric data therefore require modulation of tidal or gravity wave accessibility to the thermosphere or perhaps in situ excitation

two day wave structure and mean flow interactions observed by radar and high resolution doppler imager data obtained with four mf and meteor radars at equatorial and subtropical sites and with the high resolution doppler imager hrdi instrument aboard the uars satellite were used to examine the structure wave mean flow interactions and potential sources of the 2 day wave in the middle atmosphere during three southern hemisphere summers the three wave events were highly transient having typical durations of 20 to 30 days and exhibiting modulation at shorter periods temporal variations were found to exhibit good correlations between radar and hrdi data radar and hrdi data were used to estimate those components of the eliassen palm flux that could be assessed with these data meridional fluxes of momentum and heat were computed using hrdi data and agree reasonably with the momentum fluxes computed from radar data at discrete locations these fluxes were found to exhibit consistent latitudinal structures each year suggesting systematic wave excitation and wave mean flow interactions meridional momentum flux gradients were seen to be anticorrelated with zonal wind accelerations in a manner consistent with wave forcing of the large scale circulation the apparent wave mean flow interactions suggest that the 2 day wave could be a transient response to baroclinic instability of the summer hemisphere mesospheric jet a calculation of the meridional gradient of quasi geostrophic potential vorticity using hrdi winds and the cospar international reference atmosphere cira 1986 temperatures exhibits a region of instability in the lower and middle mesosphere extending into subtropical latitudes and provides additional evidence of a possible source of this motion via baroclinic instability of the summer hemisphere jet structure

characteristics and occurrence of bedding parallel slip surfaces and laminated veins in chevron folds from the bendigo castlemaine goldfields implications for flexural slip folding the occurrence of bedding slip planes and associated slip striated laminated quartz veins in the bendigo castlemaine goldfields southeastern australia was investigated bedding slip planes are concentrated in thin siltstone layers data from surface stratigraphic sections on the limbs of five major anticlines gave a mean slip plane spacing of 8 9 m n 96 and a mean laminated vein thickness of 19 mm most laminated veins are 20 mm thick and discontinuous along strike and around fold hinges thicker veins are correspondingly more continuous and are traceable around fold hinges the mean thickness of laminated veins from individual fold limbs increases with increasing mean spacing of slip planes on each limb suggesting a sympathetic relationship between vein thickness and net slip however there is no such correlation between individual vein thickness and spacing these relations are explained using a model for the progressive generation of bedding slip planes via shear failure at competent incompetent layer interfaces as a result of shear strain rate incompatibilities between competent and incompetent beds during fold limb steepening the model predicts flexural slip activity continuing well into the stage of homogeneous flattening of the folds and gives rise to a population of slip planes dominated by those with low net slip

flexural slip folding in the meguma group nova scotia canada abstract flexural slip folding has been established for two anticlines in the meguma group nova scotia flexural slip postdates the main acadian episode of flexural flow fold growth and represents a late brittle ductile reactivation of the fold belt flexural slip structures are dominated by bedding parallel movement horizons but include a linked system of frontal and lateral ramps and conjugate movement horizons slip amount calculated from displacement of discordant quartz veins combined with vein spacing indicates an average local shear strain of approximately 0 5 however because flexural slip occurred when the fold limbs were steep the shear strain accounts for a small change in limb dip 4 8 variation of slip amount with spacing of movement horizons suggests progressive flexural slip was accommodated by continuous initiation of new movement horizons as well as continuing slip on existing movement horizons the presence of quartz veins along flexural slip structures together with evidence for ductile deformation coeval with flexural slip suggests that slip episodes were fluid assisted and intermittent separated by periods of ductile deformation and build up of fluid pressure flexural slip veins in the ovens anticline are auriferous and a flexural slip model may be appropriate for other similar meguma gold deposits thrust sheets up to 10 m thick occurring on a fold limb are interpreted to have originated in flat box fold hinges and to have been placed onto the steep limbs of the chevron folds during the flexural slip episode thrusting may have assisted the transformation of a box fold into a chevron

a chronostratigraphic framework for the north central kaapvaal craton the bushveld complex and the vredefort structure abstract sufficient geochronological data are available pertaining to the north central part of the kaapvaal craton to construct a chronostratigraphic framework for the rock units involved in the vredefort event from the basement rocks at 3170 ma to the waterberg soutpansberg groups deposited between 2025 and 1425 ma the resulting framework forms a convenient chronological guide to the geological evolution of this area and the timing of events such as that at vredefort the basement on which the supracrustal rocks were deposited stabilised from 3170 to 3060 ma but metamorphism and metasomatism of these rocks occurred up to 2800 m y ago in different parts of the craton the first unit of the wits triad the volcaniclastic dominion group was deposited at 3060 ma on the stabilising basement this was followed by the dominantly clastic witwatersrand supergroup and the overlying ventersdorp supergroup the dominantly volcanic ventersdorp rocks are 2700 m y old and form the last unit of the wits triad a considerable time gap of 200 300 ma separates the triad from the lowermost units of the overlying transvaal sequence the age of these volcanic and clastic protobasinal rocks is poorly constrained between 2500 and 2300 ma they may in fact represent eroded remnants of a more extensive depositional cycle the mainly clastic sedimentary part of the transvaal sequence pretoria group has been dated at 2224 ma the upper part of the transvaal sequence rooiberg group is only constrained by the age of the intrusive bushveld complex the bushveld basic layered rocks are well dated at 2060 ma as are the subsequent granites at 2050 ma the vredefort event which post dates the bushveld complex is reasonably well constrained by the age of the bronzite granophyre at 2000 ma deposition of the waterberg and soutpansberg groups which post date the bushveld complex is poorly constrained between the age of the bushveld granites and younger alkaline intrusives at 1425 ma but these sediments and volcanics were probably formed between 2025 and 1752 ma the waterberg group may therefore contain debris from the vredefort structure

the intensity of the earth s magnetic field over the past 160 million years in contrast to our detailed knowledge of the directional behaviour of the earth s magnetic field during geological and historical times1 2 data constraining the past intensity of the field remain relatively scarce this is mainly due to the difficulty in obtaining reliable palaeointensity measurements a problem that is intrinsic to the geological materials which record the earth s magnetic field although the palaeointensity database has grown modestly over recent years3 4 5 these data are restricted to a few geographical locations and more than one third of the data record the field over only the past 5 myr the most recent database5 covering the time interval from 5 to 160 myr contains only about 100 palaeointensity measurements here we present 21 new data points from the interval 5 160 myr obtained from submarine basalt glasses collected from locations throughout the world s oceans whereas previous estimates for the average dipole moment were comparable to that of the earth s present field6 the new data suggest an average dipole moment of 4 2 2 3 1022 a m2 or approximately half the present magnetic field intensity this lower average value should provide an important constraint for future efforts to model the convective processes in the earth s core which have been responsible for generating the magnetic field

microwave archaeointensities from peruvian ceramics summary accurate determination of the strength of the ancient geomagnetic field is limited by mineralogical alteration that may occur when samples are heated to produce a thermoremanent magnetization thellier thellier 1959 shaw 1974 by using direct microwave excitation of the magnetic grains we have been able to form a thermoremanent magnetization without significantly heating the bulk sample thus avoiding thermal alteration walton et al 1993 incorporation of this new microwave heating technique with the conventional thellier palaeointensity method has dramatically reduced the scatter of archaeointensity results from peruvian ceramics and clearly defined how the field strength has varied in peru over the past 2000 years the new microwave technique will therefore enhance the feasibility of archaeointensity dating and provide accurate field strength data for geomagnetic modelling

validity of the ltd dht shaw and thellier palaeointensity methods a case study of the kilauea 1970 lava the double heating technique of the shaw method with low temperature demagnetisation ltd dht shaw method for determination of geomagnetic palaeointensity is applied to samples exhibiting high temperature oxidation states from the kilauea 1970 lava hawaii island results are obtained for 11 of the 12 specimens prepared from five block samples yielding an average palaeointensity of 38 2 2 8 t n 11 1 this value is consistent with the expected value determined from dgrf 1970 35 8t and does not appear to be significantly dependent on the high temperature oxidation state coe s version of the thellier method was also applied to nine specimens prepared from the same block samples and successful results were obtained for seven specimens giving an average palaeointensity of 43 2 8 4 t n 7 although this average is statistically consistent with the expected value the results include erroneously high palaeointensities 52 1 and 55 4 t for specimens from one block sample of intermediate high temperature oxidation state the present results therefore reinforce the broader applicability of the ltd dht shaw method for samples with high temperature oxidation states compared with coe s version of the thellier method it is also shown that the samples yielding overestimated thellier palaeointensities tend to fall close to the mixing line between single domain and or pseudo single domain and multidomain components on the day plot this relationship may be useful as a pre selection technique for application of the thellier method 2004 elsevier b v all rights reserved

geochemical evolution of the rooiberg silicic lavas in the loskop dam area southeastern bushveld the rooiberg felsite is the voluminous volcanic precursor to the plutonic episodes of bushveld magmatism in the area north of the loskop dam a 3 520 m thickness of felsite is dominated by flows of dacitic and rhyodacitic lava occasional silicic andesites are developed near the base whereas true rhyolites become overwhelmingly dominant toward the top of the sequence nine major stratigraphic units of lava are present these are usually separated by and sometimes include volumetrically minor pyroclastic and sedimentary deposits whole rock chemical data on 165 lava samples embracing the entire stratigraphy suggest that nonuniform alteration processes have been most effective in the upper units nevertheless field petrographic and chemical criteria enable identification of three felsite magma types a high mg type mgo 1 7 containing low zr and y contents is present only within the lowermost 1 400 m of section a low mg type mgo 2 asymp 1 p 2 o 5 asymp 0 35 type which only occurs in the lower part of the succession the high mg lavas exhibit a systematic eruptive progression from more to less evolved compositions apparently reflecting continuous tapping of successively deeper levels of a normally zoned magma chamber during the early volcanism the low mg lavas were erupted intermittently with the high mg types probably from a separate and much larger chamber pronounced differentiation of this magma is only evident in the youngest volcanic units where several element profiles display conspicuous steplike variations across the prominent ash flow horizons the steps reflect upward enrichments in nb zr and y and corresponding incremental depletions in ti p and sc such trends imply the existence of a discontinuous but reversed compositional zonation in the evolved low mg chamber the high fe ti p lavas were also erupted from the low mg chamber this may indicate the development of an early type of chemical stratification that was markedly different from the compositional layering in the evolved system

geomagnetic palaeointensities during the cretaceous normal superchron measured using submarine basaltic glass high quality palaeointensity data have been obtained from thellier thellier experiments on recent and cretaceous submarine basaltic glasses whereas the recent samples faithfully yield today s geomagnetic intensity at the site the palaeointensities for the beginning and end of the cretaceous normal superchron are only 45 and 25 respectively of today s value the data thus extend the mesozoic dipole low into the cretaceous superchron and confirm that submarine basaltic glass is an excellent material for palaeointensity studies

atmospheric tides in the low latitude e and f regions and their responses to a sudden stratospheric warming event in january 2010 an extensive analysis of atmospheric tides in the low latitude thermosphere and their responses to a major sudden stratospheric warming ssw event 18 23 january 2010 is presented the analysis is based on observational data from the arecibo dual beam incoherent scatter radar important findings of the present study are as follows 1 the diurnal tide with an evanescent phase structure dominates the f region meridional wind field the diurnal tide has a peak amplitude of 45 m s occurring at about 245 km and it is very stable throughout the nine consecutive days observation below 114 km the vertical structures of the diurnal tide in the meridional and zonal components are consistent which resemble the classical solar s 1 s 1 tidal mode 2 the f region semidiurnal tide is much weaker and has larger day to day variability than the diurnal tide in the e region the semidiurnal amplitudes in the meridional and zonal components grow continuously in the altitude ranges from 106 to 121 km and from 100 to 115 km respectively the vertical wavelength of the zonal component is estimated to be 45 km above 100 km which is close to the solar s 2 s 4 and s 2 s 5 tidal modes 3 the semidiurnal and terdiurnal tides respond strongly to the ssw while the impact that the ssw has on the diurnal tide in the meridional wind is limited during the ssw event the amplitudes of the semidiurnal and terdiurnal tides are enhanced in the f region but reduced in the upper e region

flexural slip during visco elastic buckle folding abstract flexural slip is considered as an important mechanism during folding and a general conceptual and qualitative understanding has been provided by various field studies however quantitative evidence of the importance of the flexural slip mechanism during fold evolution is sparse due to the lack of suitable strain markers in this study 2d finite element analysis is used to overcome these disadvantages and to simulate flexural slip during visco elastic buckle folding variations of single and multilayer layer fold configurations are investigated showing that flexural slip is most likely to occur in effective single layer buckle folds where slip occurs between contacts of competent layers based on effective single layer buckle folds the influence of the number of slip surfaces the degree of mechanical coupling based on the friction coefficient and layer thickness on the resulting slip distribution are investigated the results are in agreement with the conceptual flexural slip model and show that slip is initiated sequentially during the deformation history and is maximum along the central slip surface of the fold limb the cumulative amount of slip increases as the number of slip surfaces is increased for a lower degree of mechanical coupling increased slip results in different fold shapes such as box folds during buckling in comparison with laboratory experiments geometrical relationships and field observations the numerical modeling results show similar slip magnitudes it is concluded that flexural slip should represent a significant contribution during buckle folding affecting the resulting fold shape for increased amounts of slip

paleointensity results from the jurassic new constraints from submarine basaltic glasses of odp site 801c 1 tholeiite of the oldest oceanic crust was drilled during odp legs 129 and 185 at hole 801c in the western pacific fresh appearing submarine basaltic glass sbg was recovered from the tholeiites 167 ma which has been shown to be nearly ideal for determining absolute paleointensity paleointensities of the younger off axis alkalic basalts 160 ma overlying the tholeiites had been studied earlier here we report results from the older tholeiitic on axis sequence we subjected a total of 73 specimens from 17 cooling units to absolute paleointensity experiments of these 30 specimens and six cooling unit averages met our strictest reliability criteria yielding an average of 11 9 3 9 t the bulk of evidence suggests a paleolatitude of the site of 14 s with an uncertainty of 10 this translates the intensity to a value for the virtual axial dipole moment of 28 zam2 slightly lower than values determined from the plagioclase crystals in the three cooling units of the younger alkalic basalts overlying the tholeiites tarduno cottrell 2005 our value is low when compared to the long term median value of the field of 42 zam2 our results and those of the published literature therefore support the contention of a low magnetic field strength in the jurassic average of 28 14 zam2 n 138 individual estimates as initially suggested by prevot et al 1990 our interpretation of the body of available data argue for low field strengths for the entire jurassic extending into the early cretaceous

genetic aspects of the granophyric rocks of the bushveld complex this study of the granophyric rocks of the bushveld complex was undertaken in order to distinguish the different types of granophyre and to determine their probable origin aspects of the granophyre and associated rock types that were studied include their field relations geochemistry and rb sr isotope chemistry thermal modeling of causal mechanisms was also carried out the results obtained demonstrate that a number of genetically different types of granophyre exist in the bushveld complex two types the diepkloof granophyre and the zwartbank pseudogranophyre were formed by metamorphic processes related to the intrusion of the bushveld basic rocks a third type the stavoren granophyre was formed by magmatic processes it is also concluded that the stavoren granophyre is genetically related to the volcanic pre bushveld rooiberg group and forms the shallow intrusive equivalent thereof

transfer of displacement from multiple slip zones to a major detachment in an extensional regime example from the dead sea rift israel fabric development and block rotation related to flexural slip were examined in sedimentary strata draped over a basement normal fault at the western margin of the dead sea rift in southern israel in addition to documenting differences in deformation style as a function of lithology this study focuses on the progressive development of flexural slip horizons and fabric development in extensional settings deformation in the intercalated shale siltstone carbonate and gypsum beds of the turonian ora formation is dominated by extension bedding plane slip and block rotation which occur at different scales and magnitudes throughout the approximately 12 m section extension appears as boudinage in carbonate beds and fibrous sigmoidal gypsum veins in shale whereas strong foliation highly deformed gypsum veins and asymmetric folds characterize slip and adjacent drag zones magnitude of extension in individual beds is directly related to relative magnitude of adjacent bedding plane slip horizons implying a common origin initial flexural slip was lithologically controlled with displacement occurring along numerous narrow zones throughout shale and siltstone horizons continued top to the west bedding plane slip however led to antithetic block rotation within competent beds which in turn resulted in the termination of slip along zones abutting block bounding faults as block size increased during progressive development of flexural slip so did the spacing between active slip zones therefore rigid block rotation within subhorizontal simple shear zones provided the mechanism for concentrating flexural slip along several major detachments during extension of the ora formation above a basin bounding normal fault

planetary waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003 2004 1 the vertical coupling of the stratosphere mesosphere system through quasi stationary and traveling planetary waves during the major sudden stratospheric warming ssw in the arctic winter of 2003 2004 has been studied using three types of data the uk met office ukmo assimilated data set was used to examine the features of the global scale planetary disturbances present in the winter stratosphere of the northern hemisphere sounding the atmosphere using broadband emission radiometry saber satellite measurements were used as well for extracting the stationary planetary waves in the zonal and meridional winds of the stratosphere and mesosphere radar measurements at eight stations four of them situated at high latitudes 63 69n and the other four at midlatitudes 52 55n were used to determine planetary waves in the mesosphere lower thermosphere mlt the basic results show that prior to the ssw the stratospheremesosphere system was dominated by an upward and westward propagating 16 day wave detected simultaneously in the ukmo and mlt zonal and meridional wind data after the onset of the ssw longer period 22 24 days oscillations were observed in the zonal and meridional mlt winds these likely include the upward propagation of stationary planetary waves from below and in situ generation of disturbances by the dissipation and breaking of gravity waves filtered by stratospheric winds citation pancheva d et al 2008 planetary waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003 2004 j geophys res 113 d12105 doi 10 1029 2007jd009011

palaeointensity study of the hawaiian 1960 lava implications for possible causes of erroneously high intensities summary it is known that the hawaiian 1960 lava sometimes yields higher palaeointensities than the igrf 36 2 t in order to clarify the causes we have performed a comprehensive investigation of palaeointensity measurements on 19 cores from the lava according to various rock magnetic analyses they are classified into three groups with degrees of the deuteric oxidation in coe s version of the thellier method a significantly larger mean palaeointensity of 49 0 9 6 t n 17 was observed similar to previous studies these palaeointensities showed a dependence on the oxidation indices which can be explained by thermochemical remanent magnetization tcrm acquisition during the natural cooling stage of the lava although it is generally difficult to distinguish the tcrm from thermoremanent magnetization trm a lowtemperature demagnetization ltd treatment on nrm and trm in the thellier experiment seems to allow us to detect the influence of the tcrm on nrm another possible tool for tcrm detection is the double heating technique dht of the shaw method combined with ltd ltd dht shaw method it gave a better average of 39 4 7 9 t n 9 though the success rate was much lower most of the inappropriate results were screened by a combination of the double heating test the arm correction and the ltd treatment if two outliers are further excluded the average is improved to be 35 7 3 3 t n 7 which agrees well with the expected intensity the results of both methods emphasize the importance of taking and measuring samples from the parts of various oxidation degrees in a lava flow

morphology and geometry of duplexes formed during flexural slip folding abstract bedding parallel slip on the limbs of chevron style folds during flexural slip folding results occasionally in the formation of small scale duplexes the duplexes described here from upper carboniferous turbidites in sw england generally range in thickness from 0 3 to 30 cm and are up to 2 4 m long they have smooth nearly flat roofs and both the internal thrusts and the slickenfibres on them are commonly oblique to the mean transport direction as indicated by slickenfibres on the floor and roof thrusts the morphology of the duplexes suggests that they developed between active floor and roof thrusts and they show a characteristic lack of hangingwall anticlines on the link thrusts their shear sense always corresponds to that required by flexural slip and the total bedding parallel displacement across each is commensurate with that predicted by the flexural slip model all thrust surfaces in the duplexes are marked by quartz fibre veins a feature which distinguishes them from soft sediment and other pre folding duplexes and carry slickenfibres whose mean orientation and complex variations in slip direction on different fibre sheets on the same slip surface are identical to those on flexural slip movement horizons from the same fold limb the duplexes form either as a result of resistance to thrust propagation by local facies or bed thickness changes or develop as transfer structures between the tips of movement horizons propagating along adjacent slip surfaces late stage duplexes develop from imbricated fibre veins and also form on slip surfaces oblique to the axial planes of major folds