slip system domains 2 kinematic aspects of fabric development in polycrystalline aggregates abstract in the first paper of the present series cobbold and gapais 1986 we develop theoretical models of plane strain domainal deformation by slip along inextensible and indestructible fibres for such extreme mechanical conditions we show that deformation is largely controlled by kinematic factors we use our models to explain domainal patterns of natural slip systems including bedding and foliation planes faults ductile shear zones and lattice planes the present paper focusses on kinematic aspects of fabric development in polycrystalline aggregates a three dimensional kinematic model is developed it reveals that common quartz fabrics may develop domainally by reorientation and selection of inextensible slip directions a axes or slip planes with initially random orientation stable orientations of slip directions are close to both surfaces of no finite extension and orientations of large amount of shear we explain 1 1 common patterns of quartz a and c axis fabrics e g small circles and crossed girdles 2 2 characteristic differences between fabric patterns according to the shape of the finite strain ellipsoid 3 3 development of asymmetric fabrics during non coaxial deformation histories this last process involves selective destruction or replacement of certain orientation domains so that a preferred orientation of slip lines develops close to the bulk shear direction rotation recrystallization is shown to be an efficient natural selection mechanism the models also account for many microstructural features found in oriented polycrystalline rocks especially 1 1 alternating band like or kink like domains of twinned preferred orientations 2 2 individual grains or clusters of grains with retort like shapes and extensive recrystallisation at boundaries 3 3 small scale shear bands formed by strain partitioning and shear localization

the tectonothermal evolution of the cadomian belt of northern brittany france a neoproterozoic volcanic arc abstract the neoproterozoic cadomian belt northern brittany france results from the accretion of crustal blocks that record distinctive p t deformation paths in addition abundant gabbro dioritic to granitic intrusions during and after deformation influence the thermal pattern and are used as time markers as a whole the deformation history of the cadomian belt is characterised by a migration in time of the active zones which become younger towards the southeast relics of eocadomian rocks reveal that arc development took place at about 660 640 ma abundant calc alkaline magmatism intruding strongly deformed palaeoproterozoic orthogneisses characterise the northernmost unit of the cadomian belt i e the tregor unit which cooled before 600 ma the lanvollon basin a short lived intra arc rift containing abundant mafic and felsic volcanics followed by greywackes opened at about 600 580 ma the subsequent tectonothermal history of the cadomian belt is divided into two major episodes the first episode is related to the shortening of the intra arc rift and its southwestward thrusting over the guingamp unit this led to crustal thickening inducing partial melting in the guingamp unit exhumation of the latter rocks is accommodated by late extensional shearing along the boundary between the saint brieuc and guingamp units cooling of the saint brieuc unit is dated at about 570 560 ma the second episode is dominated by sinistral wrenching mainly localised in the eastern part of the cadomian belt at the boundary between the domnonean i e the arc domain and mancellian possibly a fore arc basin domains several shear zones developed during this episode some of them being associated with minor granitic intrusions dated around 550 ma the sinistral shear located southeast of the arc domain is reworking or crosscutting earlier high temperature fabrics within the saint brieuc unit in addition the vertical component of this shearing episode contributes significantly to the exhumation of the saint malo migmatites near the proterozoic cambrian boundary cordierite biotite granitoids intruded at shallow depths the fougeres unit their emplacement outlasting deformation of the sedimentary sequences minor stocks of muscovite leucogranites of cambrian age are possible equivalents of the abundant volcanism in an adjacent nw se trending rift this marks a major change in the kinematic framework with predominance of extension finally minor reactivation of the cadomian structures occurred during the carboniferous associated with the variscan orogeny

the role of hercynian granites in the deformation and metamorphism of brioverian and palaeozoic rocks of central brittany the late proterozoic rocks of central brittany represented essentially by upper brioverian sediments are considered to be a late to post tectonic molasse to the cadomian chain the poly orogenic character cadomian and hercynian of the deformation structures affecting these rocks is noted from the baie de douarnenez to the rennes region however the main syn metamorphic deformation event is clearly of hercynian age furthermore we show that this event and the associated metamorphism are directly related to the emplacement of the hercynian leucogranites the syntectonic nature of the leucogranites with respect to the deformation of their envelope is therefore affirmed and the concept of a brioverian basement in the mechanical sense of the term and contrasted with a palaeozoic cover must be abandoned

glacial tunnel valleys in the eastern goldfields of western australia cut below the late paleozoic pilbara ice sheet abstract open cut gold mines near kalgoorlie in the eastern goldfields region of western australia expose a late paleozoic carboniferous permian network of glacially eroded valleys filled with tillite and shale valleys are incised into archean and proterozoic strata of the low relief western australian shield and buried by tertiary and quaternary strata subsurface data identify a poorly integrated network of narrow 200 m wide deeply incised 80 m and steep sided channels that connect broader sub basins up to 3 km wide lowermost infill strata within valleys consist of bouldery diamictites containing abundant striated clasts of far travelled lithologies and are identified as tillites deposited by a late paleozoic ice sheet pilbara ice sheet that covered the west australian shield tillites are blanketed by shales containing early permian palynomorphs the form and sedimentary infill of the buried valley network is comparable to subglacially cut tunnel valleys that formed below the wet based margins of pleistocene continental ice sheets and a similar origin is proposed for those at kalgoorlie the significance of this finding is that hitherto little was known of the late paleozoic gondwanan ice sheet that grew on the western australian shield and which contributed substantial volumes of sediment to adjacent sedimentary basins the preservation of a relict late paleozoic glacial topography near kalgoorlie indicates that post permian erosion of the region was minimal and cannot be reconciled with denudation models which propose uniform post permian uplift and deep stripping across the shield

namurian uplift in australia and south america triggered the main gondwanan glaciation the permo carboniferous glacigenic sediment at the base of the gondwanan basins reflects the culmination1 2 of the glacial episode that started in australia and southern south america in the namurian after two local episodes in northern south america and adjacent africa in the visean and latest devonian3 fig 1 here we show that the start of each episode was associated with orogenic uplift of the bordering regions northern south america and adjacent africa in the latest devonian and visean and southern south america and eastern and central australia in the namurian all areas except southern south america in the namurian were at mid and not high latitudes thus we show that whereas the first order control of glaciation was the configuration of the continents and oceans during the closing of palaeo tethys orogenesis provided a second order control by the accumulation of ice about bordering uplifts during the three glacial episodes

mesozoic evolution of the tisza mega unit the south eastern part of the basement of the pannonian basin is made up of variscan crystalline complexes and early mesozoic formations showing striking affinity with the corresponding formations in the southern margin of the european plate this large composite structural unit which is actually an exotic terrane of european plate origin has been named the tisza mega unit based upon relevant data of the pre tertiary basement of southern hungary the reconstruction of the position of the tisza terrane in the early alpine evolutionary stages the process of its separation and break off from the european plate and results of its eo alpine deformations are summarised in the present paper in the variscan and early alpine evolutionary stages the area of the later tisza mega unit was located at the margin of the european plate during variscan orogeny terrane accretion led to intensive deformation and metamorphism in this belt this was followed by transpressional tectonics and the development of molasse basins in the late and post variscan stages and passive margin evolution after the neotethys opening in the middle triassic the separation of the tisza mega unit began with incipient continental rifting along the axis of the later ligurian penninic vahic oceanic branch in the late triassic the end of terrigenous material deposition in the most external zones and a coeval change in fossil assemblage point to the separation of the tisza block from the european plate in the early bathonian significant rotation of the tisza mega unit and coeval paroxysm of alkaline rift type basalt volcanism took place in the early cretaceous in the mid cretaceous due to the northward motion of the adria block and the related closure of the westernmost neotethys basin the extensional regime changed to a compressional one leading to onset of the nappe stacking and low grade regional metamorphism within the tisza microplate in the foreland of the nappe systems flexural basins came into existence that are characterised by flysch type sedimentation in the early tertiary the north eastward motion of the alcapa and tisza dacia blocks led to the formation of the present day heterogeneous basement of the pannonian basin

early permian to middle jurassic rifting and sedimentation in east africa and madagascar pre drift sediments of madagascar early permian middle jurassic have been studied palynologically these studies resulted in a more precise dating of individual stratigraphic units and the recognition of minor and major breaks in the succession palynostratigraphic and physical evidence of unconformities have been used to subdivide the pre drift sediments into depositional cycles and to infer rifting events a comparison with equivalent strata of mozambique tanzania kenya ethiopia and somalia shows a general correspondence and provides additional information for the construction of a generalized framework for the east african madagascan region which demonstrates the relationships between rifting and sedimentation and elucidates the prehistory of the break up of gondwana into a western and eastern fragment during the middle jurassic the predrift succession of east africa madagascar can be subdivided into two major sequences a karoo sequence cycles 1 5 asselian early smithian and a transitional sequence cycles 6 9 ladinian early bajocian the two sequences are separeted by a late scythian to anisian hiatus which indicates extensive uplift and erosion before a major rifting event initiated the resumption of sedimentation in the ladinian this middle triassic event marks the transition from the intracratonic rift stage to the pericratonic basin stage and correlates with a significant event in the pangaean history the transition from final coalescence to initial dispersal the onset of the southward drift of madagascar is believed to have occurred about 60 ma later near the aalenian bajocian boundary contemporaneous with or immediately after the deposition of syntectonic sediments of cycle 9

u pb la icp ms dating of apatite in mafic rocks evidence for a major magmatic event at the devonian carboniferous boundary in the armorican massif france apatite is a ubiquitous accessory mineral found in most magmatic rocks and is often the only u bearing mineral available to date mafic rocks because primary zircon and or baddeleyite are not present in this paper u pb la icp ms dating of apatite was applied to seven different dike and sill samples of dolerite from the variscan belt of brittany armorican massif western france these dolerites which are characterized by a within plate tholeiite geochemical signature are organized in several dense swarms across the belt their geochemical compositions are homogeneous although they intrude a large geographical area subdivided into several domains each characterized by different tectonic metamorphic settings their emplacement ages were so far poorly constrained due to the difficulty to date these mafic rocks using either the 40ar 39ar or the u pb methods on classical minerals like mica plagioclase or zircon although the closure temperature of apatite is lower than the emplacement temperature of the magma physical models show that the time needed to solidify and cool these mafic dikes and sills below the apatite closure temperature is basically of the order of 100 years or less consequently the u pb dates obtained on apatite can be interpreted as the emplacement ages for these mafic intrusions our results demonstrate that in all cases the apatite grains do carry enough radiogenic pb to be dated by in situ u pb analyses and yield a 207pb corrected mean age of 363 4 5 8 ma these results reveal the existence of a major and short lived magmatic event in the variscan belt of brittany during the devonian carboniferous transition a feature further highlighted by field evidence beyond the geological implications of these results u pb la icp ms dating of apatite appears to represent an ideal tool to date small size mafic intrusions

geological deformations in the pannonian basin during the neotectonic phase new insights from the latest regional mapping in hungary abstract the present paper introduces the new 1 500 000 scale map of young geological deformations in hungary including all important deformation structures faults and folds related to the neotectonic evolutionary phase the new map is based on the interpretation of nearly 2900 2d seismic profiles and 70 3d seismic volumes as well as on the critical evaluation of the results of published neotectonic studies an important novelty of the map is that not only the near surface manifestations of the neotectonic faulting but also their roots in the underlying pre pannonian substratum are displayed allowing correlation between various reactivated fault segments of longer fault zones and aiding the better understanding of the regional structural context the new map provides a significantly more accurate definition actual position extension and geometry of the neotectonic structures and provide more details compared to previous regional studies the prevailing e ne w sw striking neotectonic fault pattern clearly reflects the control of identically oriented pre pannonian fault systems during the neotectonic deformations markedly different orientations in the neotectonic structures indicate important differences in the overall orientation of the underlying fault systems these observations demonstrate that neotectonic activity is predominantly due to the reactivation of pre existing predominantly synrift structures all over the pannonian basin as also indicated by previous studies despite experiencing the largest middle to late miocene extension and the formation of the deepest depocenters in the whole pannonian basin se hungary practically lacks any observable neotectonic activity which is a striking but still poorly understood feature detailed 3d seismic analysis of fault segment geometries indicates a consistent regional pattern sinistral shear along e ne w sw oriented and dextral shear along w nw e se oriented fault zones respectively these observations together with the e w trending contractional transpressional structures folds reverse faults imbricates occurring in western and southern hungary indicate a dominantly strike slip stress regime with a laterally slightly rotating from n s to nne ssw maximum horizontal stress axis 1 during the neotectonic phase lateral displacement along major root zones amounts to a maximum of 2 3 km during the neotectonic phase

integrated 3d geophysical and geological modelling of the hercynian suture zone in the champtoceaux area south brittany france this paper combines geological knowledge and geophysical imagery at the crustal scale to model the 3d geometry of a segment of the hercynian suture zone of western europe in the champtoceaux area brittany france the champtoceaux complex consists of a stack of metamorphic nappes of gneisses and micaschists with eclogite bearing units the exhumation of the complex during early carboniferous times was accompanied by deformation during regional dextral strike slip associated with a major hercynian shear zone the south armorican shear zone sasz dextral shearing produced a km scale antiformal structure with a steeply dipping axial plane and a steeply eastward plunging axis armor 2 deep seismic profile shows that the regional structure was cut by a set of faults with northward thrusting components based on the seismic constraint direct 2d crustal scale modelling was performed throughout the champtoceaux fold on seven radial gravity profiles also using geological data and density measurements from field and drill hole samples the 3d integration of the cross sections the digitised geological map and the structural information foliation dips insure the geometrical and topological consistency of all sources of data the 2d information is interpolated to the whole 3d space using a geostatistical analysis finally the 3d gravity contribution of the resulting model is computed taking into account densities for each modelled geological body and compared to the bouguer anomaly the final 3d model is thus compatible with the seismic and gravity data as well as with geological data main geological results derived from the modelling are i the overall 3d geometry of the south dipping thrust system interpreted on the seismic profile emphasises northward thrusting and folding of the champtoceaux complex which was coeval with strike slip along the south armorican shear zone ii the gravity modelling suggests the presence of a relatively dense body below the champtoceaux complex that could be interpreted as a result of relative uplift of midcrustal material during thrusting along the e w trending wrench thrust system iii the northern limb of the champtoceaux anticline is a relatively shallow feature and iv vigneux synkinematic granitic body is a laccolith sheared and rooted along the southern branch of the sasz and spreads away from the strike slip zone within weak country rocks d 2004 elsevier b v all rights reserved

role of unconformity bounded units in the stratigraphy of the continental record a case study from the late miocene of the western pannonian basin hungary

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

strike slip tectonics in the pannonian basin based on seismic surveys at lake balaton strike slip tectonics has been the dominant style of deformation during the neotectonic pliocene and quaternary evolution of the pannonian basin main faults are exposed in the island mountains of the basin but strike slip tectonic features can be best studied in the basin fill by seismic data lake balaton offers the opportunity to carry out high to ultra high resolution seismo acoustic surveys to image stratigraphic and tectonic features in the central part of the pannonian basin several campaigns in the lake using different acquisition techniques have resulted in more than 2000 km seismo acoustic profiles with a range of resolutions and penetration depths interpretation of faults and folds shows a few kilometers wide shear zone below the lake in late miocene pliocene strata this zone can be identified as the continuation of the balatonf line known onshore to the east of the lake mapping revealed a set of duplex structures and highlighted the importance of this shear zone in the formation of lake balaton comparison of our results to analogue clay models suggests that the observed shear zone is sinistral and the horizontal displacement is on the order of hundreds of meters looking at 3d industrial seismic data to the south of the lake we suggest that the first order balaton line which represents the continuation of periadriatic line is also sinistral and characterized by small horizontal displacement of about 1 0 1 5 km during pliocene and quaternary times this indicates a 0 2 0 3 mm year average slip rate which is compatible with recent gps measurements

analogue modelling of intraplate strike slip tectonics a review and new experimental results abstract intraplate strike slip zones commonly display intricate 3 d geometries with rapid changes in structural style along strike and with depth strike slip deformation typically results in complex vertical and horizontal sections that can be difficult to interpret coherently physical modelling of strike slip fault systems is a powerful and graphic tool to help in providing a unified picture of the evolution of strike slip zones with considerable spatial and temporal detail a large number of experimental studies have investigated different aspects of strike slip tectonics using materials such as dry sand wet clay or silicone the choice of analogue material and experimental design exerts a strong control on the structures that form in the model here we present a review of different experimental setups used to investigate intraplate strike slip tectonics from the classical riedel experiment to more sophisticated setups using brittle and viscous analogue materials we review our current understanding from models of distributed shear transtension transpression pull apart basins formed in releasing stepovers and popups formed in restraining stepovers in addition we present the results of two new experimental series that investigated 1 the effect of crustal weak zones on strike slip fault zone segmentation and 2 strike slip and transpressional reactivation of extensional basins

mathematical removal of regional ductile strains in central brittany evidence for wrench tectonics abstract hercynian deformation in central brittany is responsible for folding of paleozoic and earlier sediments with concurrent development of cleavage essentially e w and vertical and stretching lineation essentially horizontal in the past the regional motion was inferred to be a n s shortening more recent studies emphasize e w transcurrent motions associated with major crustal faults values and orientations of ductile strain at 29 localities in central brittany show that the regional deformation is basically a horizontal plane strain with local three dimensional perturbations we first remove the perturbations rendering the problem two dimensional then a selected domain is divided into an array of finite elements parallel to strain trajectories using strain values extant at element centroids each element is unstrained independently of its neighbours resulting gaps and overlaps are minimized using a least squares technique which allows elements to translate and rotate rigidly thus we obtain the configuration of the domain in the undeformed state to within an unknown but constant rigid rotation the domain has undergone a heterogeneous dextral simple shear with vertical shearing plane striking n125 and horizontal shear direction a band of low strain running through guer is flanked by two zones of more intense strain the banding is approximately parallel to a major transcurrent fault in the area the south armorican shear zone

an outline of neotectonic structures and morphotectonics of the western and central pannonian basin abstract neotectonic deformation in the western and central part of the pannonian basin was investigated by means of surface and subsurface structural analyses and geomorphologic observations the applied methodology includes the study of outcrops industrial seismic profiles digital elevation models topographic maps and borehole data observations suggest that most of the neotectonic structures in the pannonian basin are related to the inverse reactivation of earlier faults formed mainly during the miocene syn and post rift phases typical structures are folds blind reverse faults and transpressional strike slip faults although normal or oblique normal faults are also present these structures significantly controlled the evolution of landforms and the drainage pattern by inducing surface upwarping and river deflections our analyses do not support the postulated tectonic origin of some landforms particularly that of the radial valley system in the western pannonian basin the most important neotectonic strike slip faults are trending to east northeast and have dextral to sinistral kinematics in the south western and central eastern part of the studied area respectively the suggested along strike change of kinematics within the same shear zones is in agreement with the fan shaped recent stress trajectories and with the present day motion of crustal blocks derived from gps data

modeling late paleozoic glaciation late paleozoic glaciation on gondwana is associated with changes in geography solar luminosity and estimated co sub 2 levels to assess the relative importance of these boundary conditions the authors conducted a suite of climate model simulations for the periods before during and after peak mid carboniferous approximately 300 ma glaciation 340 300 and 255 and 225 ma respectively orbital insolation values favorable for glaciation and interglaciation were used for each time interval results indicate that changes in geography cause significant changes in snow area but the temporal trend is not consistent with the geologic record for glaciation combined co sub 2 plus geography changes yield the best agreement with observations in addition interglacial orbital configurations result in almost ice free conditions for the glacial interval at 300 ma at a time of low co sub 2 the large simulated glacial interglacial snowline fluctuations for permian carboniferous time may explain cyclothem fluctuations at these times overall results support the importance of the co sub 2 paradigm but also indicate that a fuller understanding of past climate change requires consideration of paleogeographic luminosity and orbital insolation changes

multi scale strainfield analysis using geostatistics investigating the rheological behavior of the hot variscan crust of the pyrenees axial zone the present study provides a quantitative way to analyze and interpolate strainfields from ductile fabric field measurements using geostatistics based on variogram analysis and kriging interpolations the developed methodology allows computing automatic cleavage and lineation trajectory maps at different scales from a same field structural dataset for the example provided by the hot variscan crust of the pyrenees the analysis of cleavage stretching lineations orientation and kinematic data document pure shear conditions recorded during convergence strain was vertically partitioned between an upper crust submitted to homogeneous thickening responding to n s orogen normal shortening and a hot and partially molten mid lower crust affected by horizontal longitudinal orogen parallel flow the emplacement of plutons and gneiss domes generated heterogeneities in the upper crust and induced strain localization into steep anastomosed transpressional shear zones flanking those structures the results show that geostatistics applied to structural geology are powerful tools for retrieving tectonic regimes of large orogenic segments by identifying and quantifying perturbations in the strainfields induced by protracted and potentially complex tectonic histories the variogram analysis also gives first order clues to evaluate whether the considered structural domains underwent single continuous ductile or polyphased brittle ductile deformation

antimony deposits in the variscan armorican belt a link with mafic intrusives the variscan armorican belt was the world leading producer of antimony at the beginning of the twentieth century however geological controls on the deposits remain unconstrained here we illustrate the field setting of mineralisations and perform a statistical analysis using geographical information system software geophysical and geological data the analysis shows that sb deposits are spatially correlated with high density and magnetic zones this may reflect the presence of mafic ultramafic bodies at depth a suggestion that is further supported by numerous occurrences of doleritic dykes throughout the region future antimony prospecting should focus on the high density and high magnetic zones which comprise about 18 of the armorican massif links between sb deposits and mafic intrusions are recognised elsewhere in the west european variscan belt emphasising that these may be key for antimony prospecting in deformation belts

lower crustal extension across the northern carnarvon basin australia evidence for an eastward dipping detachment asymmetry and strain partitioning along conjugate margins are often explained in terms of detachment faults nevertheless cogent evidence for their existence remains limited furthermore even when inferred detachment faults are imaged seismically it is difficult to demonstrate that differential displacement has occurred across these surfaces we present tectonic and stratigraphic evidence from the northern carnarvon basin northwest australia that documents the existence of an intracrustal eastward dipping detachment by integrating sequence stratigraphy with kinematic and isostatic models of basin development we conclude that the northern carnarvon basin was formed as a consequence of four extension events 1 a broadly distributed late permian event 2 a predominantly localized rhaetian event responsible for the inception of the barrow and dampier subbasins 3 a localized callovian fault reactivation within the barrow dampier subbasins and 4 a tithonian valanginian event that generated large post valanginian regional subsidence across the northern carnarvon basin with only minor accompanying brittle deformation and erosional truncation the regional distribution and amplitude of the post valanginian subsidence are not consistent with the minor amounts of tithonian valanginian brittle upper crustal extension observed on the margin large portions of the platform were emergent or at very shallow water depths prior to the tithonian valanginian extension to match the distribution and magnitude of the post valanginian thermal type subsidence requires significant lower crustal and mantle extension across the northern carnarvon basin such a distribution of extension implies the existence of an eastward dipping intracrustal detachment having a ramp flat ramp geometry that effectively thinned the lower crust and lithospheric mantle the detachment breached the surface close to the position of the continent ocean boundary west of the exmouth plateau the flat component of the detachment occurred at midcrustal depths 15 km across the plateau and ramped beneath the australian continent lower crustal ductile extension provides a viable mechanism to generate large regional subsidence with little attendant brittle deformation which may explain the paradox that both sides of many conjugate margins appear to be the upper plate

tertiary paleomagnetic results and structural analysis from the transdanubian range hungary rotational disintegration of the alcapa unit abstract we carried out an integrated paleomagnetic and structural study in the transdanubian range western and central hungary as a result the tertiary tectonic history of this area can be characterized by three events of counterclockwise ccw rotation and four or five phases of brittle deformation the change of the orientation of stress axes between phases is mainly apparent and reflects the rotation of the faults predating a particular rotation event the first two rotation events r1 and r2 were probably governed by the rollback mechanism of the subducting european plate we suggest that these rotations were taking place from 18 17 and 16 14 5 ma respectively i e simultaneously with the rotations of the north hungarian paleogene basin and the main part of the western carpathians however the angle of both rotations was less in the transdanubian range due to increasing distance from the subduction front the differential rotation was accommodated by extensional faulting by formation of a graben system on the other hand the youngest rotation event r3 seems to be connected to the renewed rotation of the adriatic plate around 5 ma our combined data set strongly supports earlier conclusions namely that the different subunits of the eastern alpine western carpathian northern pannonian unit alcapa did not form a rigid unit although they moved in similar manner

subaqueous mass flow origin for lower permian diamictites and associated facies of the grant group barbwire terrace canning basin western australia the intracratonic canning basin is western australia s largest sedimentary basin 400 000 km2 and has experienced repeated episodes of phanerozoic extension and subsidence resulting in deposition of a number of first order megasequences a major phase of basin extension and sedimentation grant group occurred in the late carboniferous early permian when australia lay at high palaeolatitudes facies analysis of 5000 m of drill core from 25 continuously cored wells in grant group strata on the fault bounded barbwire terrace in the northern canning basin identified three facies associations fas these record the predominance of fault generated subaqueous mass flow and sediment reworking the lowest association fa i up to 355 m thick rests unconformably on tilted older strata and consists of coarse grained subaqueously deposited sediment gravity flow facies these include fault generated breccias massive and graded sandstones and conglomerates deposited by turbidity currents and diamictites generated by mixing of different textural populations during downslope remobilization fa i is overlain abruptly by relatively fine grained deposits of fa ii up to 140 m thick which consist of laminated to thin bedded mudstone and sandstone turbidites recording an abrupt increase in relative water depths in turn these facies coarsen upwards and are transitional into shallow water swaley cross stratified and rippled sandstones of fa iii up to 125 m thick the overall stratigraphic succession probably records an initial phase of faulting and accommodation of coarse sediment fa i a subsequent phase of rapid subsidence increasing water depths and sediment underfilling fa ii and finally a regressive phase of shoreface progradation the occurrence of rare striated clasts in fa i suggests reworking of glacial sediment but no direct glacial influence on sedimentation can be identified

ductile extensional shear zones in the lower crust of a passive margin we describe and interpret an unpublished set of ion geophysical seismic reflection profile showing strong organized seismic reflectors at the base of the continental crust of the uruguayan volcanic rifted margin we distinguish two main groups of reflectors in the lowermost continental crust a first group at depths ranging from 32 km below the continent to 16 km in the continent ocean transition comprises reflectors continuous over tens of kilometers peculiarly visible near the mantle crust boundary a second group of reflectors dipping toward the ese oceanward is widely distributed in the lower crust these reflectors are slightly curved and tend to merge and become sub parallel with the first group of reflectors together they draw the pattern of thick shallow dipping top to the continent shear zones affecting the lower continental crust such sense of shear is also consistent with the continentward dip of the normal faults that control the deposition of the thick syn tectonic volcanic formations sdr a major portion of the continental crust behaved in a ductile manner and recorded a component of top to the continent penetrative simple shear during rifting indicative of a lateral movement between the upper crust and the mantle

deglaciation sequences in the permo carboniferous karoo and kalahari basins of southern africa a tool in the analysis of cyclic glaciomarine basin fills the late westphalian to artinskian glaciomarine deposits of the karoo and kalahari basins of southern africa consist of massive and stratified diamictite mudrock with ice rafted material sandstone silty rhythmite shale and subordinate conglomerate forming a cyclic succession recognizable across both basins a complete cycle comprises a resistant basal unit of apparently massive diamictite overlain by softer bedded stratified diamictite sandstone and mudrock with a total thickness of as much as 350 m four major cycles are observed each separated by bounding surfaces lateral facies changes are present in some cycles the massive diamictites formed as aprons and fans in front of the ice grounding line whereas the stratified diamictites represent more distal debris flow fans the sandstones originated in different environments as turbidite sands small subaqueous outwash channel sands and delta front sands the rhythmites and mudrock represent blanket deposits derived from turbid meltwater plumes cycles represent deglaciation sequences which formed during ice retreat phases caused by eustatic changes in the karoo and kalahari basins evidence for shorter term fluctuation of the ice margin is present within the major advance retreat cycles hardly any sediment was deposited during lowstand ice sheet expansion whereas a deglaciation sequence was laid down during a sea level rise and ice margin retreat with the volume of meltwater and sediment input depending on temporary stillstands of the ice margin during the retreat phase the duration of the cycles is between 9 and 11 ma suggesting major global tectono eustatic events smaller cycles probably linked to orbital forcing were superimposed on the longer term events a sequence stratigraphic approach using the stacking of deglaciation sequences with the ice margin advance phases forming bounding surfaces can be a tool in the framework analysis of ancient glaciomarine basin fills

tectonic implications of the gps velocity field in the northern adriatic region 1 continuous and episodic gps observations between 1991 and 2004 show that adria moves independently of both stable eurasia and nubia adria moves nne at 3 4 5 mm yr increasing from n to s relative to eurasia and may be fragmenting along the gargano dubrovnik seismic zone the observed 2 3 mm yr of n s adria eurasia convergence is taken up by contraction across a narrow 70 km zone in the eastern alps and concomitant extrusion of the alpine north pannonian unit the adria central dinarides boundary is a broader collisional zone with intense 1 1 5 mm yr shortening near shore and 2 mm yr spread across the dinarides the remaining 1 2 mm yr motion e of the alps and ne of the dinarides is absorbed by the inverted contracting pannonian basin leaving no significant deformation above 0 5 mm yr in the western and northern carpathians and european platform

synkinematic mafic ultramafic sheeted intrusions emplacement mechanism and strain restoration of the permian huangshan ni cu ore belt eastern tianshan nw china abstract whilst petrology geochemistry and metal content of small mafic ultramafic ni cu bearing complexes have been extensively studied their structural controls and emplacement mechanisms are still poorly documented this study addresses the last two points with the huangshan ni cu ore belt chinese eastern tianshan as a case study the huangshan intrusions are early permian a period when the tianshan orogenic belt recorded major right lateral wrench tectonics characterized by crustal scale shear zones detailed mapping petro structural analysis and strain rate calculation within and around the intrusions allow us to establish that the huangshan ni cu bearing mafic ultramafic complexes are not layered intrusions instead they emplaced by injection of several mafic ultramafic magma batches within kilometre scale tension gashes generated by permian dextral shearing and should be considered as synkinematic sheeted intrusions finite strain analysis across the huangshan kangguer shear zone provides rather high shear strain rates 4 5 considering the location and alignment of the ni cu bearing mafic ultramafic bodies along regional shear zones throughout eastern tianshan it appears that wrench tectonics most likely controlled and focussed the intrusion of parent magmas as a consequence rifting related to post orogenic extension is not required to account for permian magmatic features of the tianshan belt finally the huangshan ni cu bearing mafic ultramafic intrusions are neither parts of an ophiolitic suture nor of a dunite cored alaskan type ore deposit as postulated in some previous studies in the light of these new results we believe that structural controls and emplacement mechanisms of many ni cu sulphides deposits hosted by small intrusions particularly funnel shaped ones should be re evaluated from a structural and geophysical point of view

tuffs tectonism and glacially related sea level changes carboniferous permian southern namibia abstract the carboniferous permian glacigene dwyka group in southern africa has been widely regarded as amagmatic only in the higher parts of the permian and subsequent younger strata has evidence of magmatism been recognised particularly in the form of pyroclastic fallout ash beds the source of these tuffs has been suggested to be patagonia and west antarctica forming part of an extensive volcanic arc which lay some 1500 to 2000 km to the south and west in their pre break up gondwana positions rhyolitic dacitic and basaltic andesitic tuff beds within the glaciomarine sediments of the dwyka group in namibia reveal new evidence for an early onset of proximal bimodal volcanic activity in southern africa contemporaneous tectonism is recorded by type 1 unconformities and systematic thickness changes across nw se trending extensional normal faults we suggest that this tectonomagmatic period marks initial extensional events in southern namibia and the carboniferous permian volcanic trend appears to coincide with the position of the eventual namibian continental margin significantly the stratigraphic positions of the tuff beds show a distinct association with enclosing marine transgressive depositional sequences most of them coincide with sharply defined flooding surfaces within relatively thick shaly successions reflecting their multiple transgressive nature widening the study context to the latest early permian in southern africa the main karoo basin of southern africa exhibits a similar coincidence of marine transgressions and extrusion of volcanics the relationship between tuff beds and transgressive depositional sequences is not only the result of enhanced preservational potential during transgression but of a genetic coupling between magmatism extensional tectonics and basin subsidence the latter accelerating a rise in relative sea level this interaction is significant not only for understanding potential controls on relative sea level change but also for understanding the early geodynamic evolution of the southern south atlantic continental margin

life in the sublittoral zone of long lived lake pannon paleontological analysis of the upper miocene szak formation hungary life and depositional environments in the sublittoral zone of lake pannon a large brackish paratethyan lake from the late miocene were reconstructed from fossils and facies of the szak formation this formation is exposed in several roughly coeval 9 4 8 9 ma outcrops located along strike of the paleo shelf break in northwestern hungary the silty argillaceous marl of the formation was deposited below storm wave base at 20 30 to 80 90 m water depth the abundance of benthic organisms indicates that the bottom water was usually well oxygenated interstitial dysoxia however may have occurred immediately below the sediment water interface as evidenced by occasional preservation of trace fossils such as diplocraterion the fauna comprised endemic mollusks including brackish cockles of the subfamily lymnocardiinae dreissenid mussels congeria and highly adapted uniquely large sized deep water pulmonate snails planorbids and lymnaeids ostracods were dominated by endemic species and in some cases endemic genera of candonids leptocytherids cypridids and loxoconchids fish remnants include a sciaenid otolith and the oldest skeletal occurrence of perca in europe the phytoplankton comprised exclusively endemic coccolithophorids mostly endemic dinoflagellates prevailingly spiniferites and cosmopolitan green algae the late miocene fauna and flora of lake pannon were in many ways similar to the modern caspian biota and in particular cases can be regarded as its precursor

late paleozoic faunal climatic and geographic changes in the baoshan block as a gondwana derived continental fragment in southwest china abstract the carboniferous and permian of the baoshan block consist of three major depositional sequences a lower carboniferous carbonate sequence a lower permian siliciclastic sequence and a middle permian carbonate sequence these three sequences were interrupted by two major regressive events first the namurian uplift ranging in age from serpukovian to gzhelian and second the post sakmarian regression occurring probably at artinskian time in the baoshan block although the precise time interval of the latter event is still unclear the baoshan block is characterized by warm water highly diverse and abundant faunas during the early carboniferous by cold water and low diversity faunas during the early permian and by possibly warm water but low diversity faunas during the middle permian the sweetognathus bucaramangus conodont fauna constrains the upper boundary of the diamictite bearing siliciclastic deposits dingjiazhai formation to the sakmarian to early artinskian as well as the eruption of the rifting basalts woniusi formation to at least the post early artinskian paleozoogeographically affiliation of the faunas in the baoshan block changed from eurasian in the early carboniferous to peri gondwanan in the early permian and to marginal cathaysian cimmerian in the middle permian cimmerian blocks have more or less comparable geohistory to one another in the carboniferous and permian during the middle permian the eastern cimmerian blocks such as sibumasu s s baoshan and tengchong are not far from the palaeoequator but apparently more distant than the western cimmerian blocks based on the presence or absence of some index taxa such as the fusulinaceans eopolydiexodina and neoschwagerina and the corals thomasiphyllum and wentzellophyllum persicum

tectonic and lithological constraints on the evolution of the karoo graben of northern malawi east africa the results of a lithostratigraphic tectonic and kinematic study of the karoo deposits of northern malawi are reported the objective of the lithostratigraphic study is to correlate the deposits of the karoo basins of northern malawi with the well known deposits of southern tanzania thus establishing a stratigraphic framework through which the timing of faulting can be constrained the kinematic analysis of faulting constrains the opening direction for the karoo graben in this area and provides basic data to discuss the karoo graben development within the regional tectonic framework of south eastern africa the studied adults are defined by moderately to steeply dipping cataclastic zones with a width of up to 15 m and are characterized by an array of slickensided fault surfaces with different orientations and slip directions in this study small faults offset 10 m but generally not exceeding 30 40 m have been distinguished methods used to analyse the kinematic data include the pressure tension pt method which estimates the principal axes for the bulk brittle strain and the internal rotation axis ira method which estimates the axis of bulk internal rotation and the overall sense of slip at the faults a mass balance calculation reveals a volume increase of up to 16 during cataclastic deformation in the fault zones the pt method shows an approximately east trending extension direction for faults that occur only in the latest carboniferous and early permian strata whereas the fault kinematics from faults that cut middle permian to early triassic rocks is characterized by a ese to se trending extension direction the small faults yield essentially the same kinematic results as the meso scale faults in a transport parallel cross sectional view the principal extension axes are at an acute angle of approximately 60 to the major fault planes given the moderate fault density the relatively high angle between the orientation of the principal extension axis and the fault planes suggest only a moderate amount of horizontal extension across the karoo graben of northern malawi riedel structures in the fault zones formed within two conjugate sets of localized shear zones slip on one set was top to the w nw and on the other top to the e se the two conjugate sets of riedel structures have an acute angle about the regional shortening axes implying that no pronounced rotation of the strain axes occurred the internal rotation axes for the riedel structures reveal a largely bimodal distribution and inferred weakly monoclinic to orthorhombic symmetry therefore the overall deformation during karoo rifting in northern malawi is interpreted to be close to a coaxial deformation with a limited amount of horizontal extension p

subduction mega shear systems and late palaeozoic basin development in the african segment of gondwana basins within the african sector of gondwana contain a late palaeozoic to early mesozoic gondwana sequence unconformably overlying precambrian basement in the interior and mid palaeozoic strata along the palaeo pacific margin small sea board pacific basins form an exception in having a carboniferous to early permian fill overlying devonian metasediments and intrusives the late palaeozoic geographic and tectonic changes in the region followed four well defined consecutive events which can also be traced outside the study area during the late devonian to early carboniferous period up to 330 ma accretion of microplates along the patagonian margin of gondwana resulted in the evolution of the pacific basins thermal uplift of the gondwana crust and extensive erosion causing a break in the stratigraphic record characterised the period between 300 and 330 ma at the end of this period the gondwana ice sheet was well established over the uplands the period 260 300 ma evidenced the release of the gondwana heat and thermal subsidence caused widespread basin formation late carboniferous transpressive strike slip basins e g sierra australes colorado karoo falklands ellsworth central transantarctic mountains in which thick glacial deposits accumulated formed inboard of the palaeo pacific margin in the continental interior the formation of zambesi type rift and extensional strike slip basins were controlled by large mega shear systems whereas rare intracratonic thermal subsidence basins formed locally in the late permian the tectonic regime changed to compressional largely due to northwest directed subduction along the palaeo pacific margin the orogenic cycle between 240 and 260 ma resulted in the formation of the gondwana fold belt and overall north south crustal shortening with strike slip motions and regional uplift within the interior the gondwana fold belt developed along a probable weak crustal zone wedged in between the cratons and an overthickened marginal crustal belt subject to dextral transpressive motions associated with the orogenic cycle was the formation of mega shear systems one of which falklands east africa tethys shear split the supercontinent in the permo triassic into a west and an east gondwana by a slight clockwise rotation of east gondwana a supradetachment basin formed along the tethyan margin and northward displacement of madagascar west falkland and the gondwana fold belt occurred relative to a southward motion of africa

characterisation of the seismological pattern in a slowly deforming intraplate region central and western france abstract we analyzed the seismicity of central and western france using historical data a compilation of all recorded earthquakes from 1962 to 2002 4574 events relocated and all published focal mechanisms 119 focal solutions the aim is to understand what are the causes of earthquakes and stress accumulation in a slowly deforming intraplate region the distribution of earthquakes and focal mechanisms is first correlated with recognized faults geological structures and tomographic images then in order to better understand the distribution of hypocenters and seek deeper crustal sources for stress accumulation euler solutions are computed from the available bouguer anomaly data the analysis of the obtained pattern for heat flow values provides a better understanding of the concentration of seismicity in some particular zones two different behaviors of this slowly deforming intraplate region are evidenced one is linked to the presence of a hot spot under the massif central the other to reactivation of the hercynian structural heritage our results highlight that several possible sources for earthquake clustering can be invoked in central western france

reconciling plate tectonic reconstructions of alpine tethys with the geological geophysical record of spreading and subduction in the alps article a new reconstruction of alpine tethys combines plate kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution from sea floor spreading through subduction to collision in the alps unlike previous models which relate the fate of alpine tethys solely to relative motions of africa iberia and europe during opening of the atlantic our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record the motions of these microplates adria iberia alcapia alkapecia and tiszia relative to both africa and europe during late cretaceous to cenozoic time involved the subduction of remnant tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces 1 131 84 ma intra oceanic subduction of the ligurian part of alpine tethys attached to iberia coincided with eo alpine orogenesis in the alcapia microplate north of africa these events were triggered primarily by foundering of the older 170 131 ma neotethyan subduction slab along the ne margin of the composite african adriatic plate subduction was linked by a sinistral transform system to e w opening of the valais part of alpine tethys 2 84 35 ma subduction of primarily the piemont and valais parts of alpine tethys which were then attached to the european plate beneath the overriding african and later adriatic plates nw translation of adria with respect to africa was accommodated primarily by slow widening of the ionian sea 3 35 ma recent rollback subduction of the ligurian part of alpine tethys coincided with western alpine orogenesis and involved the formation of the gibraltar and calabrian arcs rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable retreating adriatic and african slabs during slow convergence of africa and europe the upper european iberian plate stretched to accommodate this slab retreat in a very mobile fashion while the continental core of the adriatic microplate acted as a rigid indenter within the alpine collisional zone the subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the alps and apennines as well as beneath parts of the pannonian basin the adriatic sea the ligurian sea and the western mediterranean the predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10 30 indicating that parts of slabs may be superposed within the mantle transition zone and or that some of this subducted lithosphere became seismically transparent

ductile thrusting recorded by the garnet isograd from blueschist facies metapelites of the ile de groix armorican massif france

cadomian tectonics in northern brittany a contribution of 3 d crustal scale modelling abstract both available and newly acquired geological and geophysical data processed in the framework of the armor project have been used to construct a 3 d geometric and geological model of the cadomian domain of northern brittany the major results of the data processing are presented and discussed relative to a composite profile transecting the studied domain and constructed from the surface geology reflection seismics magnetotelluric soundings and gravimetric data they are then extrapolated at regional scale through a series of cross sections compiled from the surface geology and gravimetric data and calibrated onto the composite profile the 3 d crustal scale models were computed according to two procedures the first using a strim matra datavision modeler defines various interfaces through correlation between adjacent cross sections and is well adapted to the 3 d representation of geological structures the second based on voronoi diagrams leads to a volumetric model of the geological units and is a powerful tool for calculating 3 d geophysical responses of the model when the physical properties of the rock units are known the tectonic implications of the computed 3 d crustal scale geometry of the cadomian domain are then discussed in terms of volcanic arc thrusting with special emphasis being placed on the obliquity of the shortening direction by reference to the thrust fault trend finally the data are used to demonstrate the reactivation of some cadomian faults during the deposition of ordovician sandstones and following the emplacement of the paleozoic dolerite dyke swarm of northern brittany

wind erosion under cold climate a pleistocene periglacial mega yardang system in central europe western pannonian basin hungary abstract mega yardangs are known to form under extremely arid warm or in some instances moderate climates here we report on the mega yardang field of the pannonian basin hungary which was uniquely formed under periglacial probably semi arid conditions and discuss its implications on factors controlling yardang formation in general the yardang field is composed of advanced streamlined forms and of less aerodynamic ridges separated by well developed corridors the length of the largest features exceeds 60 km their height varies around 150 m together with ventifacts deflation hollows and wind blown sand areas the yardang field is part of an integrated eolian feature system driven by northerly to northwesterly winds dating of ventifact surfaces with in situ produced cosmogenic nuclides places the onset of significant wind erosion to the early pleistocene 1 5 ma osl dated young loess from which well developed yardangs were sculpted and wind blown sands show that eolian action continued until the early holocene the long temporal range of wind erosion compared to average yardang formation rates and the rarity of advanced yardang forms indicate intermittent and relatively short most probably millennial scale deflation periods since the early holocene the system has been inactive and demonstrates that yardangs can persist in a recognizable form for several millennia even under less arid conditions the main control on yardang formation appears to be the existence of strong unidirectional winds in the pannonian basin facilitated mainly by the channeling effect of topographic lows in the surrounding mountain chains yardangs can form even under semi arid climates however the rarity of these occurrences suggests that this requires a special association of environmental conditions yardang formation is facilitated by homogeneous lithology namely by widespread weakly consolidated sandy sediments the distribution of yardang fields is controlled by vertical neotectonic movements which provided uplifted areas to be sculptured and topographic obstacles that sheltered downwind sediments faulting can be excluded as a controlling factor in mega yardang formation nor is the role of jointing supported

late devonian early carboniferous contraction dominated deformation in central armorica monts d arree brittany france and its relationship with the closure of the rheic ocean abstract in the monts d arree western brittany france a high strain slate belt is well exposed the slate belt is located in the central armorica terrane a low grade middle to upper crustal domain in the armorican massif composed of a cadomian basement and its neoproterozoic and palaeozoic metasedimentary cover sequence the slate belt consists of highly deformed siliciclastic rocks of the pridolian to lochkovian plougastel formation a structural analysis has demonstrated that the slate belt primarily reflects a coaxial contraction dominated deformation history resulting from a top to the nw shearing on top of a weakly dipping decollement it resulted in nw verging folding and a pervasive cleavage development giving rise to a pronounced subvertical mechanical anisotropy only during the later stages of deformation history incipient strain partitioning on this anisotropy lead to the development of punctuated strain heterogeneities consistently reflecting dextral belt parallel strike slip strain the deformation largely occurred prior to the emplacement of the early carboniferous granitoid intrusions in central armorica and can therefore be correlated with the late devonian early carboniferous bretonian tectonometamorphic event the kinematics inferred in the monts d arree moreover are consistent with the top to the nw thrusting and nappe stacking inferred in the leon terrane situated to the northwest of the central armorican terrane these new insights allow linkage of the early variscan contraction dominated deformation in central armorica to the closure of the rheic ocean and the continental collision of the leon microcontinental block with armorica our study also reveals the importance of the bretonian tectonometamorphic event in the entire north western parts of central armorica the main cleavage forming deformation was diachronous and followed by subordinate wrench related deformation

insights into the 1968 1997 dasht e bayaz and zirkuh earthquake sequences eastern iran from calibrated relocations insar and high resolution satellite imagery summary the sequence of seismicity in the dasht e bayaz and zirkuh region of northeastern iran which includes 11 destructive earthquakes within a period of only 30 years forms one of the most outstanding examples of clustered large and intermediate magnitude seismic activity in the world we perform a multiple event relocation analysis with procedures to remove systematic location bias of 169 earthquakes most of which occurred in the period 1968 2008 to better image the distribution of seismicity within this highly active part of iran the geographic locations of the clustered earthquakes were calibrated by the inclusion of phase arrivals from seismic stations at short epicentral distances and also by matching the relative locations of the three largest events in the study to their mapped surface ruptures the two independent calibration methods provide similar results that increase our confidence in the accuracy of the distribution of relocated epicentres these calibrated epicentres combined with the mapping of faults from high resolution satellite imagery and from an insar derived constraint on fault location in one case allow us to associate individual events with specific faults and even with specific segments of faults to better understand the nature of the active tectonics in this region during the past four decades several previous assumptions about the seismicity in this region are confirmed 1 that the 1968 august 30 mw 7 1 dasht e bayaz earthquake nucleated at a prominent segment boundary and left step in the fault trace 2 that the 1968 september 11 mw 5 6 aftershock occurred on the dasht e bayaz fault at the eastern end of the 1968 rupture and 3 that the 1976 november 7 mw 6 0 qayen earthquake probably occurred on the e w left lateral avash fault we show in addition that several significant events including the 1968 september 1 and 4 mw 6 3 and 5 5 ferdows earthquakes the 1979 january 16 mw 6 5 and 1997 june 25 mw 5 9 boznabad events and the 1979 december 7 mw 5 9 kalat e shur earthquake are likely to have ruptured previously unknown faults our improved description of the faulting involved in the 1968 1997 earthquake sequence highlights the importance of rupturing of conjugate left and right lateral faults in closely spaced events or potentially even within a single earthquake as was likely the case at the eastern end of the 1979 november 27 mw 7 1 khuli buniabad main shock the high level of clustered seismic activity probably results from the simultaneous activity on left and right lateral faults an inherently unstable arrangement that must evolve rapidly the combination of high resolution satellite imagery and calibrated earthquake locations is a useful tool for investigating active tectonics even in the absence of detailed field observations

petrogenesis of hercynian leucogranites from the southern armorican massif contribution of ree and isotopic sr nd pb and o geochemical data to the study of source rock characteristics and ages abstract ree geochemistry and isotopic pb sr nd o compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in south brittany ages decrease from 340 ma in the north to 300 ma in the south whereas initial 87 sr 86 sr ratios increase from 0 706 to 0 710 0 717 ree abundances are relatively low la n 20 80 chondrites with a strong enrichment of lree relative to hree la n lu n 13 4 26 6 pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 ma ago 18 o 16 o ratios are high and relatively uniform at 10 7 to 12 8 mean 11 9 u pb studies on zircon indicate the presence of an inherited radiogenic pb component and that the sediment dominated source region had been metamorphosed during the siluro devonian ligerian negativee nd t values imply that the source region had been enriched in lree prior to the melting episode based on the combined data large scale partial melting of crustal material dominantly of sedimentary origin is proposed the model age of the source rocks is not very old 600 700 to 1200 ma the pb and sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites

carboniferous permian palynostratigraphy of west australian marine rift basins resolving tectonic and eustatic controls during gondwanan glaciations abstract the longest interval of cold climate in earth s phanerozoic history spanned some 55 million years from the namurian late carboniferous to the kungurian early permian when glaciation affected much of high latitude gondwana uncertainty surrounds the timing of glaciation s and the frequency of interglacial episodes ice volumes and the location of ice centres this is because the glacial record is preserved predominantly within marine strata deposited in intracontinental rift basins marginal to onshore ice centres on uplifted basement highs the direct stratigraphic record of glaciation is meagre on adjoining basement highs and extremely difficult to date many basins contain broadly similar threefold lithostratigraphic successions of lowermost glaciomarine diamictite facies middle shales and uppermost carbonate and sandstone rich commonly coal bearing deltaic strata in the absence of absolute age control and infrequent presence of macrofossils such deglaciation sequences are widely assumed to be correlative from basin to basin recording gondwanan deglaciation s and a world wide glacioeustatic sea level rise a newly compiled biostratigraphic database for west australia using first appearance datums of spore pollen types allows correlation of late palaeozoic siliciclastic successions between seven basins bonaparte canning carnarvon collie gunbarrel northern and southern perth basins these extend some 3800 km along australia s western continental margin adjacent to the west australian shield all but the gunbarrel basin contain tripartite glacially influenced successions diamictite shale sandstone biostratigraphic data reveal sharp differences in ages and stratigraphic distributions and marked variations in the thickness of coeval units diamictite shale sandstone successions accumulated diachronously from basin to basin recording a dominant tectonic control on subsidence and relative sea level middle shale units are not exact correlatives between basins and thus are unlikely to simply represent widespread climatically controlled glacioeustatic events instead they are argued to record high relative sea levels during times of maximum synrift subsidence this tectonostratigraphic model can be applied to other intracontinental rift basin successions across gondwana