chronology of deformation within the turbidite dominated lachlan orogen implications for the tectonic evolution of eastern australia and gondwana ar ar data from fabric forming white mica in slates syntectonic quartz veins and granitic mylonites constrain the timing of metamorphism deformation and exhumation in the lachlan orogen australia these data also help define the tectonic evolution of the tasmanides during paleozoic time the lachlan orogen formed by the progressive accretion of a thick turbidite fan sequence and volcanic terrains to gondwana during the closing of a small marginal ocean or back arc basin this tectonic setting was similar to the present western and southwestern pacific region accretion of the lachlan orogen to gondwana occurred by closing of the basin system by subduction accretion processes and some translation the process is typified in the western lachlan orogen by a major eastward migrating deformation involving chevron folding and faulting over an eastward propagating decollement melange zone and is recorded by ar ar mica ages ranging from 455 ma in the western part to 390 ma in the eastern part in the central lachlan orogen deformation migrated southwestward from 440 430 to 405 ma away from the high temperature wagga omeo metamorphic complex where deformation metamorphism occurred between 440 and 400 ma in the north 400 ma mica ages record deformation and inversion of structures in the cobar basin in the eastern lachlan orogen ar ar mica dates range from 450 to 340 ma ages of 455 445 ma are yielded by the narooma accretionary complex 405 390 ma ages are found along the major thrust faults bounding high grade metamorphic complexes and 360 340 ma cooling ages are found in the inverted extensional basins e g hill end and related structural zones the ar ar results also document periods of reactivation on early formed structures during later deformation elsewhere in the orogen

crustal shear zones and thrust belts their geometry and continuity in central africa the precambrian orogenic belts of africa are often defined by ductile shear zones which developed in response to large displacements and which mark orogenic fronts between mobile and stable parts of the crust they are thought to represent the major crustal reflectors seen by seismic reflection profiling in younger orogenic belts these orogenic fronts are connected by shear zones that transfer displacement or accommodate different displacements between orogenic segments smaller shears within an orogenic belt occur as a result of differential movements these shear zones are seen to pass from flat lying to steep structures and may have a thrust or strike slip sense they compare with the staircase trajectories characteristic of foreland thrust belts in common with thrust belts the geometry of the shear zones can be used to estimate displacement direction as can regional extensional fabrics developed in the associated high strain tectonites central africa has been previously described as a complex network of late proterozoic mobile belts the recognition of similar displacements and time equivalence in these belts allows their reinterpretation in terms of a linked thrust and strike slip shear zone system an example is the damaran lufilian zambezi and ukingan system these orogenic belts share a similar displacement picture and broad time equivalence and were apparently linked in a lower crustal shear zone of continental dimensions this shear zone system appears to have developed under a single tectonic framework

silurian to mid devonian basin development of the melbourne zone lachlan fold belt southeastern australia abstract the melbourne zone comprises early ordovician to early devonian marine turbidites which pass conformably upward into a mid devonian fluviatile succession there are four pulses of silurian to mid devonian deep marine sandstone dominated sedimentation early silurian late llandovery late silurian ludlow earliest devonian lochkovian and late early devonian emsian two dispersal patterns have been defined using more than 1100 palaeocurrent measurements mainly from sole marks and cross laminations in graded beds together with sandstone compositions the older pattern of silurian to earliest devonian age contains the lowest three sandstone pulses palaeocurrents and provenance define a wedge of southwesterly derived sediment of largely cratonic provenance thinning eastward this older dispersal pattern is part of an early ordovician to earliest devonian east facing passive continental margin succession palaeocurrents and provenance in the emsian sandstone pulse comprise three patterns 1 west to southwesterly directed palaeocurrents associated with fine to coarse grained locally conglomeratic lithic sandstones containing a high proportion of volcanic detritus 2 east to northeasterly directed palaeocurrents associated with fine to medium grained quartz lithic sandstones 3 north to northwesterly and south to southeasterly directed palaeocurrents associated with fine to medium grained sandstones of variable lithic composition the palaeocurrent and provenance pattern defines a nnw elongate basin with a tectonically active eastern margin and is similar to the coeval mathinna basin of northeastern tasmania both basins are part of the same system of wrench basins which developed along the western side of the wagga omeo metamorphic belt during the earliest devonian to middle devonian the change in tectonic setting in the earliest devonian appears to have occurred during an interval of significant dextral translation of the eastern lachlan fold belt towards the sse along the governor and associated fault zones

crustal lineaments and shear zones in africa their relationship to plate movements abstract many of the major lineaments in southern africa are major ductile shear zones with large displacement occurring within though often bounding orogenic belts an example is the boundary to the limpopo belt in botswana and zimbabwe however some of these shear zones only record slight displacement when considered on a crustal scale they are merely planes recording differential movement on much larger flat to gently dipping shear zones where the boundary to the orogenic belt is a low angle thrust zone these different types of shear zones are clearly shown in the pan african belt of zambia where large ene trending lineaments have been recorded recent work has shown the northern group of shears to be large lateral ramps for example the rocks of the copper belt are part of an ene verging thrust package the southern boundary of which is a major oblique to lateral ramp in southern zambia shears are more analogous to major transform faults they form as tear faults separating zones of different thrust vergence a possible plate tectonic model is given for this part of africa showing the different relative plate movement vectors estimated from the geometry of the pan african shear zones

genetic significance of fluid inclusions in the csa cu pb zn deposit cobar australia csa mine exploits a cobar type cu pb zn au ag deposit within a cleaved and metamorphosed portion of the cobar supergroup central new south wales the deposit comprises systems of lenses that encompass veins disseminations and semi massive to massive cu pb zn ores the systems and contained lenses truncate bedding are approximately coplanar with regional cleavage and similarly oriented shear zones and plunge parallel to the elongation lineation systems have extreme vertical continuity 1000 m short strike length 400 m and narrow width 100 m exhibit vertical and lateral ore type variation and have alteration haloes models of ore formation include classical hydrothermalism structurally controlled remobilisation and polymodal concepts syntectonic emplacement now holds sway fluid inclusions were examined from quartz sulphide veins adjacent to now extracted ore from coexisting quartz sulphide within ore and from vughs in barren quartz veins lack of early primary inclusions precluded direct determination of fluids associated with d2 d3 ore and vein emplacement similarly decrepitation by near isobaric heating of the two oldest secondary populations precluded direct determination of fluid phases immediately following d2 d3 ore and vein emplacement post decrepitation outflow late d3 to early post d3 is recorded by monophase ch4 inclusions entrained outflow of deeply circulated meteoric fluid modified the ch4 system modification is recorded by h2o ch4 and h2o trace ch4 secondary populations and by an h2o trace ch4 primary population the contractional tectonics d2 d3 of ore emplacement was superseded by relaxational tectonics d4p that facilitated meteoric water penetration and return flow under d2 prograde metamorphism entrapment temperatures tt and pressures pt for pre decrepitation secondary inclusions are estimated as tt 300 330 c and pt 1 5 2 kbar plith the lithostatic pressure decrepitation accompanied peak metamorphism t 350 380 c in mid to late d3 while in late d3 to early post d3 essentially monophase ch4 secondary inclusions were entrapped at tt 350 c and pt 1 5 2 kbar plith subsequently abundant ch4 and entrained meteoric water were entrapped as h2o ch4 secondaries under slowly decreasing temperature tt 330 350 c and constant pressure pt 1 5 2 kbar finally with increasingly dominant meteoric outflow h2o trace ch4 populations record decreasing temperatures tt 300 to 350 down to 275 300 c at pressures of phydrostatic pt 1 kbar plith 1 5 kbar the populations of inclusions provide insight into fluid types flow regimes and p t conditions during parts of the deposit s evolution they indirectly support the role of basin derived ch4 fluids in ore formation but provide no insight into a basement sourced ore forming fluid they fully support post ore involvement of meteoric water the poorly constrained entrapment history is believed to span 10 ma from 395 to 385 ma

ages of deformation from k ar and 40ar 39ar dating of white micas a structural and isotopic dating study of white micas from mylonites in the ruby gap duplex off central australia shows that mylonitic deformation occurred during the paleozoic alice springs orogeny deformation of the white micas took place under greenschist facies conditions in the approximate temperature range 250 350 c two distinct populations of white mica have been found 1 porphyroclasts of original muscovite and 2 neocrystallized phengites that define the fabric associated with deformation 40ar 39ar age spectra of neocrystallized phengites yield plateau like spectra of paleozoic age in contrast 40ar 39ar age spectra of muscovite porphyroclasts exhibit proterozoic apparent ages indicating that white micas were not open to significant argon diffusion during formation of the ruby gap duplex we conclude that the ages measured on neocrystallized phengites record the cessation of ductile deformation and migration of tectonic activity toward the internal zones of the thrust system

40ar 39ar dating of white micas from an alpine high pressure metamorphic belt on naxos greece the resetting of the argon isotopic system overprinting of white micas from high pressure low to medium temperature m1 metamorphic assemblages in pelitic schists on naxos during subsequent thermal dome m2 metamorphism ranges from minor in the southeast of the island to complete recrystallization in the amphibolite facies rocks near the migmatites in the centre of the dome the original m1 minerals are phengites si4 6 7 7 0 and the overprinting minerals are muscovites si4 6 0 6 45 40ar 39ar step heating analyses of white mica separates from rocks in the area where phengite and muscovite occur together yield complex age spectra characterized by low apparent ages in the first and the last stages of gas release and high apparent ages in between these upward convex age spectra are shown to be caused by mixing of two generations of micas each of which has a different age spectrum and argon release pattern seemingly good plateaus in some age spectra from white micas of the area must be interpreted as providing meaningless intermediate ages further the upward convex age spectra have been used to trace the isotopic signature of phengites toward increasing m2 metamorphic grade and suggest that as long as phengites can be observed in the rocks upward convex age spectra occur on naxos crystallization of muscovite at the expense of phengite appears to be the main mechanism of resetting argon isotopic ages in white micas however there is also good evidence for argon loss by volume diffusion from phengites simple diffusion calculations suggest that the m2 metamorphism was caused by a shortlived heat source

precise dating of low temperature deformation strain fringe analysis by 40ar 39ar laser microprobe pyritized graptolites from the welsh basin united kingdom slate belt acted as rigid bodies during cleavage formation and epizonal white micas formed within the resulting strain shadows orthogonal to the principal stress orientation although the quantities of mica are small they are a pure synkinematic mineral and have been dated by ar 40 ar 39 infrared laser microprobe as a means to dating cleavage four samples of strain fringe mica from different hand samples yielded ages ranging from 394 4 3 1 to 397 8 1 8 ma 2sigma with a mean age of 396 1 1 4 ma 2sigma by focusing on minerals that are unequivocally synkinematic this technique provides a novel solution to the problems of isotopically dating slaty cleavage previous studies have predominantly relied on dating whole rock slate samples or separated illite grains by ar 40 ar 39 techniques problems encountered included 1 separating the effects of isotopic contamination by detrital phases 2 ar 39 loss during the irradiation of illite mineral separates and 3 thermally induced ar 40 loss in nature from fine grained minerals by circumventing these problems this new method provides the first unequivocal and high precision age data for acadian deformation in the well characterized welsh basin slate belt with such precision the method may afford geologists the opportunity to track tectonic fronts across orogens and assess the rates of accretion processes in areas that are peripheral to sites of continent continent collision

late palaeozoic deformation in central africa a result of distant collision seismic reflection profiles from the cuvette centrale central basin of zaire show that a major contractional deformation affected a part of central africa during the late permian and early triassic periods at the same time other regions of central africa experienced extensional and strike slip deformation and associated rift formation the coexistence of such varied styles of tectonic activity over a large continental area resembles the cenozoic tectonics of central asia and northwest europe the intracontinental deformation seen in these latter areas is attributed to collisional processes at a distant continental margin1 3 by analogy we argue here that deformation of central africa in the late palaeozoic period was a direct result of collisional processes some distance away at the southern margin of gondwana

40ar 39ar age constraints on deformation and mineralization rosebery zn pb cu and mount lyell cu deposits tasmania australia the 40ar 39ar dating of alteration muscovite from the rosebery zn pb cu and mount lyell cu deposits tasmania australia has determined a succession of deformation events which occurred from 400 378 ma and comprises the devonian tabberabberan orogeny the dates from rosebery range from 400 390 ma are a minimum age for mineralization indicate the time of deformation and provide a maximum age limit for granitoid emplacement in the vicinity of the deposit the ages from the mount lyell field range from 400 378 ma are a minimum for mineralization and date cleavage development the north lyell cu mineralization which was probably broadly coeval with deformation may have formed at 400 ma all pre devonian alteration micas in the rosebery and mount lyell areas have been recrystallized or reset the tabberabberan deformation in western tasmania was broadly contemporaneous with widespread crustal shortening in southeastern australia as established from the dating of alteration minerals associated with deformation related precious and base metal deposits

polyphase late paleozoic tectonothermal evolution of the southwestern meguma terrane nova scotia evidence from 40ar 39ar mineral ages 40ar 39ar incremental release ages of hornblende muscovite and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late paleozoic tectonothermal evolution for the southwestern meguma terrane regional d1 folding with cleavage formation under greenschist lower amphibolite facies m1 metamorphic conditions occurred at ca 400 410 ma and was followed by emplacement of a series of granitic stocks ranging in age between ca 375 and 315 ma these were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade these are locally superposed on m1 regional metamorphic assemblages and result in a complex isograd pattern 40ar 39ar mineral ages suggest episodes of contact metamorphism occurred at 1 360 375 ma possibly related to emplacement of the south mountain batholith or temporal equivalents 2 350 356 ma around the port mouton pluton and northeastern shelburne pluton 3 ca 315 325 ma near the wedgeport pluton and in

40 ar 39 ar dating of cleavage formation in tuffs during anchizonal metamorphism 40ar 39ar incremental release analyses were carried out on whole rock and constituent white mica illite rich size fractions 0 63 1 to 6 3 20 m within two very low grade penetratively cleaved metatuffs of contrasting anchizonal metamorphic grade northeastern rheinisches schiefergebirge federal republic of germany one sample from the upper anchizone displays internally concordant 40ar 39ar spectra with plateau ages ranging between ca 316 and 325 ma these are similar to conventional k ar ages determined for the whole rock and size fractions together the isotopic results suggest that cleavage formed at ca 320 ma during a concomitant very low grade metamorphism this is consistent with biostratigraphic controls which suggest that metamorphism and cleavage formation occurred during the westphalian

reflection and transmission characteristics at the edge of shore fast sea ice the reflection and transmission of ocean waves at a sea ice boundary is reconsidered the sea ice is modelled as a continuous thin elastic plate of uniform thickness floating on water of arbitrary constant depth unlike earlier solutions matching of potentials between the free surface domain and the ice covered domain is done at all depths previous solutions were incompletely matched as the potentials in each domain were deficient in the present solution a number of the infinity of evanescent modes which were hitherto ignored are included in the solution and allow matching to be carried out by minimization of an integrated error term from surface to seafloor reflection and transmission are found to be markedly influenced by the inclusion of these modes suggesting that conclusions based on the incomplete potentials may be substantially in error

calcium in regolith carbonates of central and southern australia its source and implications for the global carbon cycle abstract the widespread regolith carbonates of the australian continent are a potential sink for co 2 we have used sr isotopes to investigate the source of the ca in regolith carbonates that cover approximately 1 6 10 6 km 2 of inland australia 87 sr 86 sr ratios for nearly all the carbonates were in the range 0 7094 to 0 7211 the results show that only about 10 of the ca in regolith carbonates is derived from weathered bedrock with the remaining component being derived from an external marine source the exceptions are the most northerly samples with a range of 0 7270 to 0 7374 in which bedrock content may be as high as 30 the likely ca source areas are sedimentary carbonates located on the continental shelf and calcareous aeolianites that surround much of the southern and western australian coastline winds passing over these carbonates continually rework and transport the material over the australian continent where it has settled and formed the regolith carbonates we see today the impact of this process is that despite the immense area covered australian regolith carbonates do not capture any additional co 2 instead the carbonate is simply being remobilised from one pool marine to another terrestrial

exsolution in hornblende and its consequences for 40ar39ar age spectra and closure temperature abstract step heating studies of hornblende and biotite which coexist in an amphibolite near north walpole vermont reveal dramatically different 40 ar 39 ar age spectra the biotite mg 59 is characterized by a plateau over 98 percent 39ar release at 343 5 ma in strong contrast to the amphibole which exhibits both a complex age spectrum and a k ar age significantly younger than the biotite the amphibole release pattern contains three complete age cycles which range between extremes of 199 ma and 408 ma interestingly the k ca ratio calculated from reactor produced isotopes also varies with ar release but follows a trend which is antipathetic to the 40 ar 39 ar age pattern detailed microstructural examination including transmission electron microscopy tem reveals a complex exsolution structure that is consistent with both the complexity of the release pattern as well as the low degree of radiogenic 40ar 40ar retentivity in the amphibole this result underscores the variability of closure temperature tc for 40ar in metamorphic amphiboles and should warn against accepting a single universal value of tc

weathering indices as climate proxies a step forward based on congo and sw african river muds abstract despite the influence of other geological and geomorphological factors chemical weathering at the earth s surface is strongly controlled by climate thus a measure of weathering intensity determined from soils or sediments should provide information about the climatic conditions associated with their formation available geochemical and mineralogical data on modern fluvial and marine muds from different regions of southern africa and its atlantic continental margin are used to review the links between sediment composition and climatic properties together with the possible causes of variance although river muds may not be generated exclusively in a single sedimentary cycle and erosion and weathering processes do not necessarily take place in a spatially homogeneous way significant relationships between mineralogical and geochemical signatures of river mud and rainfall in the corresponding catchment area were recognised our study shows that the composition of clay is strongly influenced by climatically driven weathering whilst coarser mud fractions tend to be more affected by provenance grain size hydraulic sorting and recycling in the marine environment the climatic signal may be lost even in clay because of hydraulic fractionation authigenic mineral growth and mixing with foreign particles given the ubiquitous character of fluvial muds and the easy and non expensive methods available for separating and analysing clay fractions their geochemical fingerprints represent a most precious source of information concerning climate any geochemical parameter used as a regional proxy of climate however still requires that the diversity of geological geomorphological and biological factors that affect its value are cautiously considered

basement control on the deformation of cover basins an example from the cobar district in the lachlan fold belt australia abstract early carboniferous deformation of ensialic early devonian to early carboniferous sedimentary basins in the cobar district was controlled by movement on reactivated basement faults two cover zones each with different structures reflect differences in basement geometry particularly the frequency and orientation of pre existing faults zone 1 a high strain zone on the eastern edge of the deformed basins has a vertical cleavage and down dip lineation characteristic of slate belts zone 2 a low strain zone to the west bears the imprint of wrench tectonics at least in the early part of the history of its deformation the boundary between zones 1 and 2 is a sharply defined cleavage front and is localized along a major fault in zone 2 nw trending f 1 folds developed initially as a response to left lateral movement on wnw trending basement faults later f 1 folds trending west suggest rotation of the direction of local maximum principal stress perhaps as resistance to sliding of basement blocks developed further rotation of this local stress direction led to the formation of ne trending f 2 folds and to left lateral movement on bounding n and nne trending faults in zone 1 deformation was more intense and controlled by high angle reverse movement with some left lateral displacement on n and nw trending basement faults leading to d 1 folding cleavage formation and vertical extension in the cover shortening was both oblique and parallel to the eastern margin of the basin at an early stage of deformation before cleavage formation zone 1 may have been locally coupled to zone 2 subzone boundaries defined by abrupt changes in strike of s 1 and f 1 in zone 1 probably represent reactivated faults which acted as hinge lines separating areas deforming in response to different directions of shortening except for possible folds contributing to abrupt changes in strike of d 1 structures regional d 2 structures are absent from zone 1 this contrasts with the well developed f 2 folds in zone 2

nd and sr isotopic signatures of metasedimentary rocks around the south pacific margin and implications for their provenance an nd sr isotope database including c 200 new analyses is presented for palaeozoic and mesozoic metasedimentary successions extending through southeastern australia new zealand west antarctica and the antarctic peninsula to southern south america combining with u pb detrital zircon age data this enables characterization of new zealand terranes especially within the eastern province where there is a progression from westernmost terranes of both volcanic volcaniclastic and accretionary origin with primitive sediment sources to easternmost terranes with mature continental sediment inputs in southern south america west antarctica and the antarctica peninsula similar accretionary complexes have nd model ages principally reflecting mixing of sedimentary material from multiple sources both mature and juvenile a mature gondwana continental provenance dominates in sedimentary basins inboard of the active margin especially in the palaeozoic western province new zealand interior west antarctica and nw argentina and contributes significantly to pre mesozoic sedimentary rocks of patagonia east of the andes along the gondwanaland margin nd systematics for younger late palaeozoic to early mesozoic accretionary complex metasediments reflect younger source inputs notably in the scotia metamorphic complex many of the accretionary complex deposits must involve significant crustal reworking there is no apparent south american equivalent of the primitive provenance of the westernmost accretionary terranes of new zealand

excess argon 40are uptake during slate formation a 40ar 39ar uv laserprobe study of muscovite strain fringes from the palaeozoic welsh basin uk syn kinematic pure muscovite strain fringes grew around pyritized graptolites in response to the early devonian acadian closure and uplift of the peri gondwanan welsh basin they record ar isotope information on the timing of low temperature deformation and the mudrock to slate transition here we have applied three different 40ar 39ar laserprobe dating methods to strain fringes from the central welsh basin to test for variations in age and to explore the technical limitations of the method infrared laserprobe step heating analyses yielded only occasional plateau ages varying between ca 403 ma and 422 ma and strong evidence for discordance in the ar system likewise ages from infrared laserprobe total fusion analysis are scattered and range from ca 390 ma to 651 ma by contrast ultraviolet laserprobe intra fringe age profiles revealed a complex pattern of ages across individual strain fringes this is the highest spatial resolution technique available and the resulting age profiles consistently showed an oscillatory pattern comprising troughs or baseline ages that are all within error of ca 397 ma and peaks or apparent ages ranging up to ca 550 ma these apparent ages we interpret as the results of repeated periodic assimilation of excess 40ar 40are during deformation and the mudrock to slate transition here basinal fluids carrying 40are are driven through bulk mudrock during contractional phases of the acadian orogen and 40are is taken up by muscovite strain fringes the concentration of 40are varies with metamorphic grade and is inversely proportional to the temperature of metamorphism and we suggest is controlled by the solubility of ar in water which has potentially quite severe implications for 40ar 39ar dating of k bearing minerals in any mudrock these results provide a first record of ar isotope information in strain fringes and a first record of orogenically driven fluid flow through bulk deforming mudrock they also demonstrate how the high spatial resolution ultraviolet laserprobe 40ar 39ar method can access ar isotope information that is obscured by lower spatial resolution laser analysis or bulk sampling methods

ocean waves and ice sheets a complete analytical study is presented of the reflection and transmission of surface gravity waves incident on ice covered ocean the ice cover is idealized as a plate of elastic material for which flexural motions are described by the timoshenko mindlin equation a suitable non dimensionalization extracts parameters useful for the characterization of ocean wave and ice sheet interactions and for scaled laboratory studies the scattering problem is simplified using fourier transforms and the wiener hopf technique the solution is eventually written down in terms of some easily evaluated quadratures an important feature of this solution is that the physical conditions at the edge of the ice sheet are explicitly built into the analysis and power flow theorems provide verification of the results asymptotic results for large and small values of the non dimensional parameters are extracted and approximations are given for general parameter values

african stress pattern from formal inversion of focal mechanism data abstract the kinematic models and the associated orientation of extensional stress of the east african rift system have been subjected to much debate since a long time in the past decades the proposed models relied on the interpretation of the overall rift geometry geological fault slip data and the few focal mechanisms available these models generally suffer of a poor time control and an underestimation of the possible changes in the stress field and geodynamic regime with time and space in the recent years there has been a significant increase in the number of focal mechanisms available for the entire rift system and it is now possible to estimate the present day stress field in relative detail based on seismotectonic data alone we compile 347 focal mechanism data from the global harvard cmt catalogue and various other sources and grouped 332 of them in 24 distinct regions boxes on the basis of their geographical proximity kinematic homogeneity and tectonic setting for each box and for the same data set reduced stress tensors have been obtained by formal stress inversion using both the tensor program delvaux sperner 2003 and the slick method michael 1984 1987 both inversion methods show in comparable results in terms of horizontal stress axes orientations and tectonic stress regimes which stem for the robustness of the approach the obtained stress pattern reflects a complex interaction between 1st order effects as different driving forces including plate boundary forces and 2nd and 3rd order effects as gravitational potential of topography intra lithospheric processes and the influence of structural heterogeneities of the rift structures the evidence present in the stress orientations of the 2nd and 3rd order stress pattern as the variations in the horizontal stress axes along the axis of the rift are of particular interest as they were not yet captured or shown in earlier numerical models of the stress field additional sources of tectonic forces in supplement to the gravitational potential energy forces as considered in the earlier models are necessary to explain the observed patterns

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

evidence for a neoproterozoic carbonate ramp on the northern edge of the central african craton relations with late proterozoic intracratonic troughs during late proterozoic times the archaean central african craton was affected by trough faulting which led to the formation of grabens the sangha aulacogen being the main structure of this type in the studied area this transverse basin connects with other basins on the northern and south western borders of the craton during the cryogenian this network of basins was filled with fluvio deltaic and lacustrine periglacial deposits the glacio eustatic transgression in neoproterozoic iii end proterozoic times flooded extensive areas of shelf on the northern edge of the craton leading to the development of carbonate sedimentation in a broad outer shelf environment associated with nearshore barriers and evaporitic lagoons these facies are similar to those developed in the west congolian schisto calcaire shale limestone ramp succession the north central african ramp succession sediment slope contains an example of tidal rhythmites in vertical accretion which occurs beneath the barrier deposits on the subtidal outer shelf mathematical analysis of the bedding pattern yields a period of 29 30 days for the lunar month a result which is in agreement with astrophysical evidence for this epoch i e 650 ma ago major subsidence and seismic activity on this gently sloping platform associated with the proximity of the sangha aulacogen caused the triggering of carbonate turbidites and mass flow deposits the proliferation of microbial mats under euphotic conditions on an extensive shelf led to the build up of a carbonate platform during early neoproterozoic iii times the west congolian and north central african ramps prograded northwards and southwards respectively into the sangha aulacogen the sea at that time was restricted to a long graben like basin while a remaining area of marine sedimentation persisted into the palaeozoic thus the pattern of end proterozoic carbonate sedimentation on the borders of the central african craton can be interpreted in terms of an overall gently sloping ramp model with progradation converging towards the sangha aulacogen

uplift history of a transform continental margin revealed by the stratigraphic record the case of the agulhas transform margin along the southern african plateau the south and southeast coast of southern africa from 28 s to 33 s forms a high elevated transform passive margin bounded to the east by the agulhas falkland fracture zone affz we analysed the stratigraphic record of the outeniqua and durban thekwini basins located on the african side of the affz to determine the evolution of these margins from the rifting stage to present day the goal was to reconstruct the strike slip evolution of the agulhas margin and the uplift of the inland high elevation south african plateau the agulhas transform passive margin results from four successive stages 1 rifting stage from late triassic to early cretaceous 200 134 ma punctuated by three successive rifting episodes related to the gondwana breakup 2 wrench stage 134 131 ma evidenced by strike and dip slip deformations increasing toward the affz 3 active transform margin stage 131 92 ma during which the falkland malvinas plateau drifts away along the affz with an uplift of the northeastern part of the outeniqua basin progressively migrating toward the west 4 thermal subsidence stage 92 0 ma marked by a major change in the configuration of the margin onset of the shelf break passive margin morphology two main periods of uplift were documented during the thermal subsidence stage of the agulhas margin 1 a 92 ma short lived margin scale uplift followed by a second one at 76 ma located along the outeniqua basin and 2 a long lasting uplift from 40 to 15 ma limited to the durban thekwini basin this suggests that the south african plateau is an old upper cretaceous relief 90 70 ma reactivated during late eocene to early miocene times 40 15 ma

geodynamic significance of the trm segment in the east african rift w tanzania active tectonics and paleostress in the ufipa plateau and rukwa basin abstract the tanganyika rukwa malawi trm rift segment in western tanzania is a key sector for understanding the opening dynamics of the east african rift system ears in an oblique opening model it is considered as a dextral transfer fault zone that accommodates the general opening of the ears in an nw se direction in an orthogonal opening model it accommodates pure dip slip normal faulting with extension orthogonal to the rift segments and a general e w extension for the entire ears the central part of the trm rift segment is well exposed in the ufipa plateau and rukwa basin within the paleoproterozoic ubende belt it is also one of the most seismically active regions of the ears we investigated the active tectonic architecture and paleostress evolution of the ufipa plateau and adjacent rukwa basin and in order to define their geodynamic role in the development of the ears and highlight their pre rift brittle tectonic history the active fault architecture fault kinematic analysis and paleostress reconstruction show that the recent to active fault systems that control the rift structure develop in a pure extensional setting with extension direction orthogonal to the trend of the trm segment two pre rift brittle events are evidenced an older brittle thrusting is related to the interaction between the bangweulu block and the tanzanian craton during the late pan african early paleozoic it was followed by a transpressional inversion during the early mesozoic this inversion stage is the best expressed in the field and caused dextral strike slip faulting along the fault systems that now control the major rift structures it has been erroneously interpreted as related to the late cenozoic ears which instead is characterized by pure normal faulting our third and last stress stage

on the oblique reflexion and transmission of ocean waves at shore fast sea ice a mathematical model is reported describing the oblique reflexion and penetration of ocean waves into shore fast sea ice the arbitrary depth model allows all velocity potentials occurring in the open water region to be matched precisely to their counterparts in the ice covered region matching is done using a preconditioned conjugate gradient technique which allows the complete solution to be found to a predefined precision the model enables the reflexion and transmission coefficients at the ice edge to be found and examples are reported for ice plates of different thicknesses a critical angle is predicted beyond which no travelling wave penetrates the ice sheet in this case the deflexion of the ice is due only to evanescent modes critical angle curves are provided for various ice thicknesses on deep intermediate and shallow water the strain field which is set up within the ice sheet due to the incoming waves is also discussed principal strains are provided as are the strains normal to the ice edge finally the spreading function within the ice cover and some consequences of this function to unimodal seas with realistic open water spreading functions are reported with the aim of generalizing the work to model the effect of shore fast ice on an incoming directional wave spectrum of specified structure

wallrock alteration at the western system of the csa mine cobar new south wales australia abstract petrological and geochemical characteristics of the sequence from chloritic siltstone through siliceous siltstone to elvan which occurs approaching ore on the hanging wall of the western system in the csa mine cobar indicate its formation by extensive dilational silicification together with minor addition of s and k very close to the ore the manner whereby more chloritic members of this sequence developed from background muscovite rich siltstones remote from mineralization is less clear elvan is not an exhalative chert the distribution of wallrock alteration products and characteristics of the ores do not support suggestions that cobar orebodies are remobilized stratiform deposits alteration preceded epigenetic ore emplacement in the early stages of a regional metamorphic episode which took place soon after early devonian turbidite sedimentation without associated igneous activity mineralization is attributed to diagenetic dewatering or metamorphic dehydration of the sediment pile

tectonic evolution of the cuvette centrale zaire the cuvette centrale central basin of zaire is an infra cambrian to recent basin with up to 9 km of sedimentary section basin subsidence can be largely explained by a postulated late proterozoic failed rift and subsequent thermal relaxation seismic reflection profiles and well data reveal a palaeozoic development of the basin punctuated by two regional deformational episodes one in the early palaeozoic late cambrian and a second in the late palaeozoic late permian triassic both episodes result from ne sw contraction with the late palaeozoic episode being largely a reactivation of the early palaeozoic structures the timing of the two deformations correlates with collisional events at continental margins some distance from the congo basin in the early palaeozoic the deformation appears to be related to the late stages of the west congolian fold and thrust belt and coincides regionally with the pan african event sensu stricto the late palaeozoic deformation coincides with collisional tectonics along the southern margin of gondwana and the generation of the cape and sierra ventana foldbelts it is postulated that in both the early and late palaeozoic africa and gondwana experienced widespread intracontinental deformation generated by distant collisional processes much as central asia is experiencing today

the elura ag pb zn mine in australia ore genesis in a slate belt by syndeformational metasomatism along hydrothermal fluid conduits the ag pb zn ore deposit at the elura mine new south wales australia is situated in a devonian slate belt and essentially consists of two vertically elongated ellipsoidal bodies of massive sulfide these are located above a zone of subeconomic vein mineralization from the boundary of each orebody toward its core the host sediment is progressively incorporated as inclusions in a deformed matrix of massive sulfide but continuity of bedding attitudes is retained across separate inclusions preserved bedding patterns and the sulfide deformation show that each orebody formed by metasomatism in the hinge of a developing anticline the two anticlines are doubly plunging structures with superposed smaller folds in which four generations of fold axial plane cleavages s 1 s 4 represent polyphase deformation d 1 d 4 the sulfide distribution in bedding parallel outliers of the orebodies is controlled by the s 2 cleavage but the style of d 2 folding within such horizons has been influenced by the presence of sulfide also there are mesoscopic replicas of the orebodies with a shape and orientation that reflect the vertically elongated d 2 strain ellipsoid most replicas lie across hinges of d 2 folds but locally their presence has affected the fold pattern these and other complex relationships are explained as a consequence of relatively rapid metasomatism by sulfide during d 2 deformation synkinematic syn d 2 porphyroblasts of siderite mark an alteration halo around the ore alteration patterns indicate a coeval origin for the ore and its halo which is further marked by vein hosted breccias within a swarm of tension veins crack seal microstructures in the latter indicate repeated microcracking during vertical stretching of the dome and basin folds at lithostatic pore fluid pressures structural relationships between the crack seal veins and breccia veins are complex but suggest periodic release of the overpressured fluids by brecciation of sediment the drops in fluid pressure triggered metasomatism by carbonates and sulfides in the two largest fold domes the brecciation is attributed to dome collapse following dilational rupture due to faulting in a system defined by shear zones and domains of bedding disruption

copper and gold rich deposits in deformed turbidites at cobar australia their structural control and hydrothermal origin the cobar mining field new south wales consists of three types of deposits copper gold rich ones 0 to 18 km south of cobar central the peak and coronation queen bee areas copper lead zinc rich ones 10 km north of cobar c s a mine and silver lead zinc rich ones 40 km north of cobar elura mine all deposits are hosted by folded and cleaved early devonian thin bedded turbidites and lie oblique to bedding previous ideas of ore genesis have varied from epigenetic by early workers to remobilized syngenetic by more recent ones the copper gold deposits discussed here are structurally controlled and lie in zones of silicification on or adjacent to major faults with the exception of minor massive lead zinc mineralization mineralization occurs in veins generally in quartz veins and as disseminations in silicified rock in the central area deposits mineralized veins are north northwest trending steeply east dipping northwest trending steeply east dipping and subhorizontal the steep north plunging shape of the orebodies reflects maximum dilation at the intersection of the north northwest trending and northwest trending sets of veins surface veins around deposits of the central area have been grouped into six geometric sets with formation taking place over a prolonged history during the d 1 deformation of the surrounding sediments this implies that the vein style mineralization is epigenetic in origin and that it resulted from precipitation from hydrothermal fluids circulating through major faults and adjacent fractures connected to those faults

isotopic dating of basin inversion the palaeozoic cobar basin lachlan orogen australia abstract the age of inversion of the early devonian cobar basin is poorly defined by field geological data which have to be extrapolated from the coeval shelf west of the basin in order to better constrain the age of deformation a whole rock isotopic dating program was undertaken and yields the following results rb sr isotopic dates predate the depositional age giving a regional isochron of 442 4 ma three k ar dates from zone 1 are mutually indistinguishable 402 8 402 8 405 8 ma suggesting a mid to late early devonian age of cleavage formation four whole rock 40ar 39ar spectra from the high strain zone 1 give intermediate temperature plateaux ranging from ca 389 ma to 404 ma in the lower strain zone 2 total gas ages from three samples range from ca 401 ma to ca 423 ma an approximate intermediate temperature plateau for one sample indicates an age ca 405 ma the other sample yields a good plateau of ca 437 ma these data are interpreted as reflecting a low grade cleavage forming inversion event which took place at ca 395 400 ma isotopic data from zone 1 suggest near complete rejuvenation of detrital phases during the 395 400 ma event in contrast the older zone 2 rb sr ages and some of the 40ar 39ar ages reflect at least in part basement provenance ages preserved within detrital micas and feldspars which did not undergo complete rejuvenation because of lower deformational strain and or temperature of metamorphism the intense 395 400 ma late early devonian inversion event in zones 1 and 2 of the former cobar basin largely bypassed the southwestern part of the basin and the adjacent shelf to the west these only underwent minor block faulting and uplift at this time but were more strongly deformed along with the overlying fluviatile mulga downs group in the carboniferous