present day kinematics of the mediterranean a comprehensive overview of gps results i combine recently published gps results to derive a geodetic horizontal velocity field consistent at the scale of the mediterranean and the surrounding alpine belts the velocity field is then used to discuss the boundary conditions around each major deforming area in the mediterranean to describe the main patterns of motion and deformation to critically review the existing kinematics models and to finally point out the main unresolved kinematics questions strain rate in europe north of the alpines belt is dominated by the signature of the glacial isostatic adjustment and tectonic strain remains below the current accuracy of gps results in the western mediterranean deformation is restricted to the betics the alboran and the morrocan rif with west to southwestward motion with respect to iberia which is part of stable europe shortening consistent with the relative nubia eurasia plate motion is found throughout the maghrebides but the distribution of deformation in northern africa remains largely unknown the central mediterranean is dominated by the counter clockwise rotation of the adriatic the junction between the southern adriatic domain and nubia has yet to be firmly established the deformation over a wide area east of the maghrebides in tunisia and the gulf of sirte in libya still remains to be quantified in the eastern mediterranean the velocity field is dominated by a general anti clockwise rotation and a general trend towards the hellenic trench with velocity magnitude increasing with decreasing distances from the trench this trend is observed not only in the aegean and anatolia but also in the southern balkans geodetic results emphasize that the convergence of the nubia and arabia plates towards eurasia directly controls the deformation across only very few segments along the plate boundary zone additional processes are therefore required to explain the observed velocity field and deformation pattern

rupture directivity of the 2011 mw 5 2 lorca earthquake spain 1 on may 11th 2011 a rather small earthquake caused nine fatalities in the city of lorca se spain we analyze seismograms from a dense network to characterize the source of this earthquake we estimate an oblique reverse faulting mechanism moment magnitude of 5 2 and a shallow hypocenter 4 6 km at only 5 5 km epicentral distance from the city center double difference relocations yield a 5 km long ne sw trending distribution of aftershocks sw of the mainshock suggesting a sw propagating rupture along the alhama de murcia fault we use the mw 4 6 foreshock and an mw 3 9 aftershock as empirical greens functions to estimate apparent source time functions observing a clear directivity effect we model apparent durations with a unilateral and asymmetric bilateral rupture in both cases obtaining rupture directivity of n220 e towards lorca in addition to the near epicenter and shallow depth directivity may have contributed to the significant impact

fault generated mountain fronts in southeast spain geomorphologic assessment of tectonic and seismic activity abstract tectonic activity of se spain is evaluated through the application of a general morphometric analysis over 17 different mountain fronts the selected fronts are distributed along the two most prominent crustal scale structures of the mediterranean sector of spain the eastern betic shear zone ebsz and the valencia trough geomorphic indexes used in this study are mountain front sinuosity index smf and valley floor width ratio vf this work is largely based on the smf vf regression analysis of the studied fronts together with previous available data from sw usa the development of mountain fronts in both different lithologies and tectonic contexts enabled characteristic morphometric signatures for different activity scenarios tectonic activity classes to be obtained this study thus indicates that variations of mountain front geomorphology triggered by different styles of faulting can be detected by morphometric analysis it is demonstrated that discrete uplift rates of 0 15 0 08 m ka are sufficient to keep relatively low smf values down to 1 4 in active fronts class 1 taking into account the reported uplift rates and preliminary palaeoseismic data for some of the class 1 studied fronts recurrence periods for surface rupture events can be theoretically bracketed for se spain recurrence periods for class 1 fronts could theoretically range between 10 000 and 12 500 years for maximum slip conditions and 1750 and 2600 years for minimum slip conditions inactive fronts class 3 develop under uplift rates down to 0 03 m ka and tested recurrence intervals for rupture events range between 25 000 and 50 000 years class 2 fronts of intermediate characteristics and activity display uplift rates between 0 07 and 0 03 m ka

the palaeontology and dating of the weybourne crag an important marker horizon in the early pleistocene of the southern north sea basin abstract in the north sea basin the marine bivalve macoma balthica first appears within the early pleistocene weybourne crag which forms an important biostratigraphical datum here we review the fossil assemblages from sites of this age prompted by new discoveries from sidestrand norfolk uk the molluscan assemblages from this horizon are dominated by intertidal species with some colder deeper water taxa and a few temperate non marine species a high boreal low arctic marine environment with reduced salinities is indicated an extensive assemblage of small mammals dominated by voles includes two species mimomys hordijki and ungaromys dehmi previously unknown from the british pleistocene the assemblage can be assigned to tesakov s mammal biozone mnr1 mn17 middle villafranchian which according to current estimates corresponds to a date of 2 2 2 1 ma mis 84 79 it matches another assemblage from 61 m to 65 m in the zuurland 2 borehole in the netherlands and is similar to that from the dutch tiglian type site at tegelen although this has more temperate elements a late tiglian age is consistent with the co occurrence of the marine bivalves macoma balthica mya arenaria and the freshwater gastropod viviparus glacialis in the zuurland 2 borehole and in a north sea borehole bgs 52 02 472 a macoma balthica mya arenaria concurrent range zone is defined for this assemblage which can be traced across the north sea basin amino acid dating provides strong independent support for these correlations and indicates that the baventian cold stage post dates the bramertonian norwich crag it also confirms that early pleistocene molluscan assemblages with m balthica are younger than those without it the correlation of this marine marker horizon with mammal biozone mnr1 provides a secure link between continental and marine sequences during the early pleistocene it also provides a basis for dating events in the pre glacial fluvial drainage history and linking it to the east european mammal zonation

tephrochronological dating of varved interglacial lake deposits from pianico sellere southern alps italy to around 400 ka the sediment record from the pianico palaeolake in the southern alps is continuously varved spans more than 15 500 years and represents a key archive for interglacial climate variability at seasonal resolution the stratigraphic position of the pianico interglacial has been controversial in the past the identification of two volcanic ash layers and their microscopic analysis provides distinct marker layers for tephrochronological dating of these interglacial deposits in addition to micro facies analyses reconstructing depositional processes of both tephra layers within the lake environment their mineralogical and geochemical composition has been determined through major element electron probe micro analysis on glass shards comparison with published tephra data traced the volcanic source regions of the pianico tephras to the campanian volcanic complex of roccamonfina italy and probably the puy de sancy volcano in the french massif central available dating of near vent deposits from the roccamonfina volcano provides a robust tephrochronological anchor point at around 400 ka for the pianico interglacial these deposits correlate with marine oxygen isotope stage mis 11 and thus are younger than early to middle pleistocene previously suggested by k ar dating and older than the last interglacial as inferred from macrofloral remains and the geo logical setting copyright 2006 john wiley sons ltd

applicability of critical wedge theories to foreland belts applying critical wedge theories to foreland belts in contrast to accretionary wedges of poorly indurated sediments results in basic problems of physics one key distinction between these tectonic regimes is the enormous difference in elastic strain energy that can be stored during deformation another key distinction is that most styles of fault slip occurring in the upper continental crust involve changes of momentum in contrast with the stable sliding invoked in critical wedge theories consequently the mechanics of deformation are fundamentally different for foreland belts as compared with accretionary wedges of sediment

la mc icpms and shrimp u pb dating of complex zircons from quaternary tephras from the french massif central magma residence time and geochemical implications abstract analyses of zircon grains from the queureuilh quaternary tephras pumice provide new information about their pre eruptive history u pb dating was performed in situ using two methods shrimp and la mc icpms equipped with a multi ion counting system both methods provided reliable 207pb 206pb and 206pb 238u ratios as well as u and th abundances required for u pb concordia intercept age determination after initial 230th disequilibrium correction the new la mc icpms method was validated by dating a reference zircon 61 308b and zircons from a phonolitic lava dated independently with the two techniques a time resolution of about 20 kyr for 1 ma zircon crystals was achieved for both methods the clear euhedral zircon population from queureuilh tephras is quite complex from several points of view 1 some grains are reddish or yellowish while others are colorless 2 the u and th composition changes by more than an order of magnitude and th u is generally high 1 2 3 there are three discrete ages recorded at 2 35 0 04 1 017 0 008 and 0 640 0 010 ma from the previously determined 40ar 39ar age at 0 571 0 060 ma duffell h 1999 contribution geochronologique a la stratigraphie volcanique du massif des monts dore par la methode 40ar 39ar d e a univ clermont ferrand 56 p the discontinuous zircon age populations the color of the grains and their composition we favor the following model as explanation the oldest less numerous group of reddish zircons represents xenocrystic grains resulting from assimilation of the local material during magma ascent a primitive magma chamber perhaps deep in crustal level was formed at 1 0 ma the related magma previously characterized by high th u ratio 2 2 1 1 underwent rejuvenation during ascent to a new chamber at shallow depth and or during injection of more mafic magmas during this stage at 0 64 ma the colorless zircon grains of lower th u ratio 1 3 0 5 crystallized this last stage defined the magma residence time of 70 kyr prior to eruption dated by the 40ar 39ar method however if the primitive magma is considered the magma residence time as a whole from this first stage reached 446 kyr in the light of the complex history of such magmas which commonly involves recycling of zircon grains that precipitated tens to hundreds of kyr earlier than eruptions the use of zr concentration in geochemical modeling of whole rock compositional data can be problematic

plio pleistocene climate evolution trends and transitions in glacial cycle dynamics abstract we describe the evolution of climate system dynamics by examining the climate response to changes in obliquity and precession over the last 5 3 myr in particular we examine changes in the shape of glacial cycles and the power of obliquity and precession response in benthic 18 o when the exponential trend in 18 o variance is removed its spectral power exhibits strong proportional responses to amplitude modulations in orbital forcing over most of the plio pleistocene precession responses correlate with modulations in forcing for the last 5 myr but 41 kyr response is sensitive to obliquity modulation only before 1 4 myr where responses are sensitive to modulations in forcing we demonstrate that glacial cycles are orbitally forced rather than being self sustained or paced by orbital changes the shapes of glacial cycles have several nonlinear properties which may be indicative of glacial interglacial differences in climate sensitivity or response time the saw tooth asymmetry of glacial cycles first appears shortly after the onset of major northern hemisphere glaciation and the relative duration of interglacial stages decreases at 1 4 myr collectively trends in the shape of glacial cycles and the sensitivity of 18 o to obliquity and precession are suggestive of major transitions in climate dynamics at approximately 2 5 and 1 4 myr but show no significant change associated with the appearance of strong 100 kyr cycles during the mid pleistocene transition

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

neogene basin inversion and recent slip rate distribution of the northern termination of the alhama de murcia fault eastern betic shear zone se spain the alhama de murcia fault is one of the main active structures of the eastern betic shear zone se spain characterized by the presence along its trace of neogene basins developed under early to late miocene extensional tectonics a dominant nnw sse shortening direction is active from late miocene driven by the present day plate convergence we present the structural analysis of the northeastern section of this fault where reliable estimations of slip rates were unknown due to the lack of geomorphological evidence of recent activity the recent tectonic evolution and reactivation of the northeastern section is closely related to the fortuna basin development and tectonic inversion we approach the structural analysis through the interpretation of seismic reflection profiles well data fieldwork and 3d geological modeling we estimated a maximum long term slip rate of 0 32 0 18 0 13 mm yr in the librilla sector last 4 8 7 6 ma based on cross section restorations and assuming current motion trends from gps data according to the results from the cross sections restored along the section and a vertical displacement analysis based on a 3d model the slip rate distribution shows a decrease of activity toward the northeastern tip of the studied fault section this supports a transference of deformation between the alhama de murcia fault and the carrascoy fault which seems to absorb part of the shortening during the plio quaternary explaining the lower relief created by the activity of the northeastern section the slip rates obtained have important implications in seismic hazard assessments and in the distribution of deformation along the region

relationships between fault geometry slip rate variability and earthquake recurrence in extensional settings field observations and modelling indicate that elastic interaction between active faults can lead to variations in earthquake recurrence intervals measured on timescales of 102 104 yr fault geometry strongly influences the nature of the interaction between adjacent structures as it controls the spatial redistribution of stress when rupture occurs in this paper we use a previously published numerical model for elastic interaction between spontaneously growing faults to investigate the relationships between fault geometry fault slip rate variations and the statistics of earthquake recurrence these relationships develop and become systematic as a long term consequence of stress redistribution in individual rupture events even though on short timescales earthquake activity appears to be stochastic we characterize fault behaviour using the coefficient of variation cv of earthquake recurrence intervals and introduce a new measure slip rate variability srv that takes into account the size and time ordering of slip events cv generally increases when the strain is partitioned on more than one fault but the relationship between long term fault slip rate srmean and cv is poorly defined in contrast srv increases systematically where faulting is more distributed and srmean is lower to first order srv is inversely proportional to srmean we also extract earthquake recurrence statistics and compare these to previously published probability density functions used in earthquake forecasting the histograms of earthquake recurrence vary systematically as a function of fault geometry and are best characterized by a weibull distribution with fitting parameters that vary from site to site along the fault array we explain these phenomena in terms of a time varying geometrical control on stress loading of individual faults arising from the history of elastic interactions and compare our results with published data on srv and earthquake recurrence along normal faults in new zealand and in the italian apennines our results suggest that palaeoseismic data should be collected and analysed with structural geometry in mind and that information on srv cv and srmean should be integrated with data from earthquake catalogues when evaluating seismic hazard

the alhama de murcia fault se spain a seismogenic fault in a diffuse plate boundary seismotectonic implications for the ibero magrebian region received 20 december 2002 revised 15 september 2003 accepted 26 september 2003 published 2 january 2004 1 the shortening between the african and the iberian plates is absorbed by a number of faults distributed over a very wide zone with very low slip rates and long periods of seismic loading thus a seismotectonic map based only on faults associated with seismicity or with expressive geomorphic features is incomplete it is possible to characterize seismogenic faults using paleoseismology first paleoseismological results based on trenching analysis in the eastern betics lorca totana segment of the alhama de murcia fault are presented the main paleoseismic parameters of this fault segment are 1 a minimum of two to three mw 6 5 7 earthquakes in the last 27 kyr shortly before 1650 a d between 830 and 2130 b c and shortly before 16 7 ka respectively with a mean recurrence period of 14 kyr and a very short elapsed time and 2 a net slip rate of 0 07 0 6 mm yr during the last 30 kyr these results were extrapolated to the rest of the known active faults in the eastern betics and were added to the slip rates of the active faults at the african margin the total slip rate of the transect which crosses de alhama de murcia fault in spain and reaches the cheliff basin algeria would represent 21 82 of the total shortening between africa and eurasia estimated from plate motion models and seismic moment summation a number of factors could account for this discrepancy 1 hidden seismogenic faults in the emerged areas 2 absence of correlation between current and late pleistocene slip rates 3 extensive small faults that are undetected and that absorb a significant amount of the deformation and 4 possible overestimation of the convergence rates index terms 7221 seismology paleoseismology 7230 seismology seismicity and seismotectonics 7215 seismology earthquake parameters 8150 tectonophysics plate boundary general 3040 keywords eastern betics alhama de murcia fault paleoseismology trenching seismotectonics plate boundary

an exceptionally long paleoseismic record of a slow moving fault the alhama de murcia fault eastern betic shear zone spain most catastrophic earthquakes occur along fast moving faults although some of them are triggered by slow moving ones long paleoseismic histories are infrequent in the latter faults here an exceptionally long paleoseismic record more than 300 k y of a slow moving structure is presented for the southern tip of the alhama de murcia fault eastern betic shear zone which is characterized by morphological expression of current tectonic activity and by a lack of historical seismicity at its tip the fault divides into a splay with two main faults bounding the gonar fault system at this area the condensed sedimentation and the distribution of the deformation in several structures provided us with more opportunities to obtain a complete paleoseismic record than at other segments of the fault the tectonic deformation of the system was studied by an integrated structural geomorphological and paleoseismological approach stratigraphic and tectonic features at six paleoseismic trenches indicate that old alluvial units have been repeatedly folded and thrusted over younger ones along the different traces of the structure the correlation of the event timing inferred for each of these trenches and the application of an improved protocol for the infrared stimulated luminescence irsl dating of k feldspar allowed us to constrain a paleoseismic record as old as 325 ka we identified a minimum of six possible paleoearthquakes of m w 6 7 and a maximum mean recurrence interval of 29 k y this provides compelling evidence for the underestimation of the seismic hazard in the region

neogene and quaternary ignimbrites in the area of arequipa southern peru stratigraphical and petrological correlations abstract this study focuses on the correlation of four newly identified rhyolitic ignimbrites located around arequipa which were previously described as a single ignimbrite sheet 1 the rio chili ignimbrite ca 13 33 ma crops out in the rio chili canyon and consists of a cooling unit of non welded to partially welded massive crystal rich lapilli tuff this ignimbrite represents the base of the neogene ignimbrite succession in the arequipa area and may be stratigraphically equivalent to the 14 13 ma huaylillas ignimbrites in southern peru 2 the second voluminous 20 km3 and widespread la joya ignimbrite sheet ca 4 87 ma filled the arequipa depression its probable source is now buried underneath the chachani volcanic complex the la joya ignimbrite covers both the arequipa batholith toward the rio vitor piedmont and also part of the altiplano to the east and north of the chachani complex 3 the arequipa airport ignimbrite aai sheet ca 1 6 ma 18 km3 the third and latest infill of the arequipa basin consists of a lower white columnar jointed massive lapilli tuff indurated by vapor phase recrystallization and is overlain by an upper pink lithic rich non welded massive lapilli tuff the source of this ignimbrite is also buried underneath the chachani complex as indicated by anisotropy of magnetic susceptibility measurements and component lithology 4 the yura non welded pumice flow deposits ca 1 02 ma 1 5 km3 are restricted to the northern and western flanks of the chachani complex and may correlate with tuffs of the capillune formation on the altiplano all ignimbrites are high k calc alkaline to alkaline rhyolites which contain variable amounts of plagioclase biotite quartz sanidine and fe ti oxides the modal composition of mineral phases and chemistry of amphiboles and biotites are useful for distinguishing the ignimbrites specific geochemical fingerprints such as sr y rb ba cs ree and sr isotopes were effective discriminator elements magmatic differentiation crustal residence time and contamination and source melting processes are discussed in order to explain compositional variations the older la joya ignimbrite and rio chili ignimbrite reflect initial wetter crustal melts closer to granite composition whereas with time the younger arequipa airport ignimbrite and yura tuffs initial melts are slightly less evolved and dryer due to more extensive crustal melting the voluminous 40 km3 neogene ignimbrites of the arequipa area were produced by three major explosive volcanic pulses in the central volcanic zone of southern peru whose genetic relation with tectonic uplift and crustal thickening of the andean cordillera are still a matter of debate

direct dating of plio quaternary pumices by 40ar 39ar step heating and single grain laser fusion methods the example of the monts dore massif massif central france abstract k feldspars separated from plio quaternary pumice flows of the monts dore massif massif central france give 40 ar 39 ar saddle shaped age spectra laser probe analysis of hand picked single grains gives ages in agreement with those of overlying and underlying lava flows previously dated by the conventional k ar method the laser probe ages are lower than the minimum ages measured on the populations of grains by the step heating method as previously suggested by lo bello and co workers for the pumice flow of neschers belonging to the same volcanic massif the saddle shaped age spectra are ascribed to the different ar release patterns of two populations of k feldspars 1 young sanidine phenocrysts of the pumices and 2 old k feldspars plucked from the hercynian basement during the explosive eruption measurements of both the granitic rocks from surrounding areas and the granitic xenoliths included in pumices give ages around 330 ma and show that most of the xenocrysts included in the pumices did not lose significant amounts of argon during the eruption with the 40 ar 39 ar step heating method we were able to detect contamination of quaternary k feldspars by hercynian k feldspars as low as 0 25 because pumice flows of the monts dore massif crop out over large areas these new ages will be useful for establishing a precise stratigraphy of the european plio quaternary

incorporating and reporting uncertainties in fault slip rates 1 quantitative slip rate estimates are essential to understanding crustal deformation processes and assessing seismic hazard computing slip rates requires two fundamental ingredients estimates of the age of an offset landforrn or deposit and displacement along the fault of interest because both of these measures contain uncertainty slip rates are inherently uncertain methods to compute and report slip rates have not been standardized and therefore slip rate data are presented inconsistently and are frequently ambiguous in particular slip rate uncertainty is often insufficiently characterized we present a rigorous probabilistic approach to computing and reporting intermediate to long term fault slip rates additionally we have developed freely available software that provides standard age and displacement uncertainty models we demonstrate the method using recent observations from the neodani and death valley fish lake valley fault zones and we compare slip rates determined using this approach with previously published results

growth of the south pyrenean orogenic wedge a six step reconstruction of the south pyrenean foreland fold and thrust belt in spain delineates the topographic slope basal dtcollement angie internal deformation and thrust front advance from the early eocene until the end of contractional deformation in the late oligocene style of thrust front advance dip of the basal dtcollement slope of the upper surface and internal deformation are decoupled and not simply related internal deformation increased decreased and maintained surface slope angle at different stages from the onset to the cessation of deformation the basal dtcollement angle decreased overall suggesting translation of the thrust belt onto stronger crust with time taper angle of the pyrenean thrust wedge was fundamentally controlled by the flexural rigidity of the lower plate the relative rate of creation of structural relief in the rear versus the front of the wedge the extent of deposition of eroded material within the deforming wedge and the taper of the pretectonic stratigraphic wedge

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

restoration of basins driven by extension and salt tectonics example from the cotiella basin in the central pyrenees the structure of the cotiella basin consists of four well differentiated salt floored sub basins which contain more than 6 km of halokinetic growth strata and have been interpreted to be formed by gravity driven extensional faults and diapirism during the middle coniacian early santonian the subsequent pyrenean orogeny late santonian to miocene inverted the extensional basins and squeezed the diapirs leaving little trace of the original salt volume although both the extensional and the salt related features of the cotiella basin were preserved this paper provides new insights into the evolution of the cotiella basin by establishing a correlation between sub basins by means of structural restorations the workflow followed and the assumptions made during the restoration of the inversion and especially of the extensional structures are outlined in detail

plio pleistocene ice volume antarctic climate and the global δ18o record we propose that from 3 to 1 million years ago ice volume changes occurred in both the northern and southern hemispheres each controlled by local summer insolation because earth9s orbital precession is out of phase between hemispheres 23 000 year changes in ice volume in each hemisphere cancel out in globally integrated proxies such as ocean 18 o or sea level leaving the in phase obliquity 41 000 years component of insolation to dominate those records only a modest ice mass change in antarctica is required to effectively cancel out a much larger northern ice volume signal at the mid pleistocene transition we propose that marine based ice sheet margins replaced terrestrial ice margins around the perimeter of east antarctica resulting in a shift to in phase behavior of northern and southern ice sheets as well as the strengthening of 23 000 year cyclicity in the marine 18 o record

segmentation and growth of an obliquely reactivated normal fault abstract detailed kinematic analysis of a large 1800 m maximum displacement reactivated normal fault in the taranaki basin new zealand has been conducted using high quality 3d seismic data the parihaka fault is approximately north south striking in basement where it accrued late cretaceous to early eocene displacements in response to east west extension and was obliquely reactivated by nw se extension in the pliocene reactivation resulted in upward propagation newly formed segmentation and up dip clockwise rotation of the fault surface by up to 20 from the strike of the basement fault fault segmentation and map view soft linkage by relay zones in post miocene strata was synchronous with the formation of antithetic faults in late miocene strata at bends in the fault surface fault segment lengths antithetic faults and relay zone dimensions were formed geologically instantaneously during initial reactivation of the main fault at 3 7 3 4 ma i e within the first 10 of faulting rapid formation of pliocene fault segments is followed by displacement accumulation without an increase in fault segment length until eventual relay breaching when continued ramp rotation is unsustainable this evolutionary history is consistent with a model in which arrays of fault segments are from inception components of a single coherent structure

half graben structures balanced models of extensional fault bend folds one common structural style in extensional regimes is a half graben bounded on one side by a master normal fault and on the other side by a domain of beds dipping toward the master fault this geometry is modeled as being caused by a bend in the master fault the hanging wall beds dipping toward the master fault are bounded by axial surfaces formed as the hanging wall moves past the bend resulting in an extensional fault bend fold the footwall beds remain undeformed and unrotated the major assumptions used in the derivation are that the geometry is area balanced and that the axial surfaces in the hanging wall have dips equal and opposite to the dip of the master fault above the bend important consequences of the model include a relationship between master fault dip above and below a bend and the amount of hanging wall dip the horizontal width of the dipping beds in the hanging wall is twice the heave on the master fault above the bend the asymmetry of the axial surfaces in the hanging wall requires that the rotated beds be strained hanging wall beds dipping toward the master fault are predicted for a fault bend wherein the dip decreases downward hanging wall beds dipping away from the master fault are predicted for a bend wherein the dip increases downward the model fits measurements taken from a published ramp and flat clay model by e cloos and is used to develop a balanced and restorable cross section of the schell creek fault a basin and range structure in nevada

tephro chronostratigraphy of the lacustrine interglacial record of pianico italian southern alps identifying the volcanic sources using radiogenic isotopes and trace elements abstract the chronostratigraphic position of the pianico carbonate sequence oroebic alps italy remains controversial notwithstanding that it is one of the best preserved records of an alpine interglacial two distal tephra were discovered in the sequence the lowermost t21d is a rhyolitic tephra dated by k ar at 779 13 ka different from the uppermost phonolitic tephra t32 with an assigned age of 393 12 ka the volcanic source of t32 was recently interpreted as being the brown leucitic tuff of the roccamonfina volcano southern italy new trace element and nd and sr isotopic composition of t32 and of 420 200 ka volcanic products of the roccamonfina clearly indicate that this volcano is not the source of t32 but that it likely originated from the northern roman magmatic province the products of the initial explosive activity of sabatini mts dated ca 780 800 ka isotopically match t32 and are proposed as its source this indicates that the previously inferred age of 400 ka for t32 is erroneous new isotopic and geochemical data of t21d confirm it as being associated with the first pyroclastic eruptions 790 710 ka of the puy de sancy volcano french massif central the early middle pleistocene k ar ages obtained previously for t21d together with the isotopic attribution of volcanic sources to both tephra layers presented here confirm pianico as one of the best interglacial sequences of cromerian age in the western alps

marine to non marine sedimentation in the upper miocene evaporites of the eastern betics se spain sedimentological and geochemical evidence abstract several neogene basins in the eastern betics contain a record of thick upper miocene evaporites the inner basins those located distal to the mediterranean coast include evaporite units ranging from the late tortonian to the early messinian whereas the marginal basins those located in the vicinity of the mediterranean coast include evaporite units corresponding to the late messinian that are linked to the salinity crisis the sedimentological and geochemical comparison of the evaporites in the inner and marginal basins enable us to show their differences in the modes of deposition under local structural controls and differentiated palaeogeography in the inner basins of the murcia alicante region a number of evaporite units have been differentiated whose gypsum lithofacies have 1 variable strontium contents with mean values primary gypsum between 1121 and 2380 ppm 2 isotopic compositions of sulphur 34 s ranging from those characteristic of the tertiary marine water 20 3 to 25 5 to those characteristic of the triassic sulphates 8 0 to 16 0 the latter suggesting recycling of the sulphate anion in meteoric waters intermediate values 17 4 to 19 6 are attributed to mixed mother brines and 3 strontium ratios 87 sr 86 sr comprised between 0 70804 and 0 70888 these values range from those of the tertiary marine water to those exceeding the triassic sulphates suggesting additional continental contributions from country rocks and hydrothermal solutions the comparison between the sulphur and strontium isotopic compositions of the sulphates together with the study of the biota present in the marls associated with the gypsum allows us to distinguish between marine continental and mixed units in the marginal basins of the eastern betics where single evaporite units characterized by selenitic gypsum prevail 1 the strontium contents are more homogeneous with mean values primary gypsum between 493 and 625 ppm 2 the isotopic compositions of oxygen 18 o and sulphur 34 s are comprised between 12 2 and 14 8 and between 22 0 and 23 5 respectively and 3 the strontium ratios 87 sr 86 sr vary from 0 70890 to 0 70895 all these isotopic values reveal a marine origin and the lack of contribution of significant continental water during the late messinian evaporite deposition in the betic strait these characteristics are similar to those of the lower evaporite

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

closure of the africa eurasia north america plate motion circuit and tectonics of the gloria fault we examine the closure of the current plate motion circuit between the african north american and eurasian plates to test whether these plates are rigid and whether the gloria fault is an active transform fault we also investigate the possible existence of microplates that have been previously proposed to lie along these plate boundaries and compare the predicted direction of motion along the african eurasian plate boundary in the mediterranean with the direction of slip observed in earthquakes from marine geophysical data we obtain 13 transform fault azimuths and 40 3 m y average spreading rates 34 of which are determined from comparison of synthetic magnetic anomaly profiles to 140 observed profiles slip vectors from 32 earthquake focal mechanisms further describe plate motion detailed magnetic surveys north of iceland provide 11 rates in a region where prior plate motion models had few data magnetic profiles north of the azores triple junction record a rate of 24 mm yr 4 mm yr slower than used by prior models gloria and sea beam surveys accurately measure the azimuths of seven transform faults our plate motion model fits six of the seven within 2 two transform faults surveyed by gloria side scan sonar lie near famous area transform faults a and b and give azimuths 13 clockwise of them because recent studies show that short offset transforms such as transforms a and b are in many places oblique to the direction of plate motion we exclude azimuths from transforms with less than 35 km offset the best fitting and closure enforced vectors fit the data well except for a small systematic misfit to the slip vectors on right lateral slipping transforms slip vectors tend to be a few degrees clockwise of plate motion and mapped fault azimuths whereas on left lateral slipping transforms slip vectors tend to be a few degrees counterclockwise of plate motion and mapped fault azimuths we search the long eurasia north america boundary for evidence of an additional plate but find no systematic misfits to the data in particular if a spitsbergen plate exists and moves relative to eurasia its motion is less than 3 mm yr an africa eurasia euler vector determined by adding the eurasia north america and africa north america euler vectors is consistent with the gloria fault trend and with slip vectors from eastern azores gibraltar ridge focal mechanisms a small circle centered at the africa eurasia closure enforced pole fits the trace of the gloria fault the model in which closure was enforced predicts 4 mm yr slip across the azores gibraltar ridge and west northwest convergence near gibraltar 45 more oblique than suggested by a recent model based on compressive axes of focal mechanisms moreover our model predicts directions of plate motion that agree well with northwest trending slip vectors from thrust earthquakes between gibraltar and sicily because closure enforced vectors fit the data nearly as well as the best fitting vectors we conclude that the data are consistent with a rigid plate model and with the gloria fault being a transform fault

examining the interior of llaima volcano with receiver functions abstract llaima volcano in chile is one of the largest and most active volcanoes in the southern andes with over 50 eruptions since the 1600s after years of persistent degassing llaima most recently erupted in a series of violent strombolian eruptions in 2007 2009 this period had few precursory signals which highlights the need to obtain accurate magma storage information while petrologic advancements have been made in understanding magma degassing and crystallization trends a comprehensive seismic study has yet to be completed here we present results of a receiver function survey utilizing a dense seismic array surrounding llaima volcano application of h stacking and common conversion point stacking techniques reveals a new moho estimate and two structural anomalies beneath llaima volcano we interpret a low velocity zone between 8 and 13 km depth as a newly imaged magma body

pyroclastic chronology of the sancy stratovolcano mont dore french massif central new high precision 40ar 39ar constraints abstract the sancy 16 km2 is the youngest of the two stratovolcanoes that constitute the mont dore massif massif central france the restricted number of high precision radio isotopic ages currently limits our knowledge of the pyroclastic chronology of this edifice which is the source of many tephra layers detected in middle pleistocene sequences in southeast europe to improve our knowledge of the building phases of this stratovolcano we collected thirteen pyroclastic units covering the entire proximal record we present 40ar 39ar single grain laser dating performed in the facility hosted at the lsce gif sur yvette france the 40ar 39ar ages range from 1101 11 ka to 392 7 ka 1 external four pyroclastic cycles lasting on average 100 ka were identified c i to c iv c i corresponds to the earlier explosive phase between 1101 ka and 1000 ka and starts about 100 ka earlier than previously thought the second pyroclastic cycle c ii is the main pyroclastic episode spanning from 818 to 685 ka this cycle is constituted of a minimum of 8 major pyroclastic eruptions and includes a major event that corresponds to a large plinian eruption at 719 10 ka 1 external and recorded as a 1 4 m thick layer 60 km south east of the sancy volcano the link between this large eruption and formation of a caldera stays however hypothetical the third pyroclastic cycle c iii found in the northeastern part of the sancy mont dore valley spanned from 642 to 537 ka finally the youngest pyroclastic cycle c iv starts at 392 ka and probably ends around 280 ka the age versus geographic location of each pyroclastic cycle indicates three preferential directions of channeling of the pyroclastic events and or collapse of the volcanic edifice northwest to west c i southeast c ii and finally north to northeast c iii and iv the new high precision 40ar 39ar age for the queureuilh bas pyroclastic unit 642 9 ka is identical within error with the u pb age obtained by cocherie et al 2009 geochimica et cosmochimica acta 73 1095 1108 and suggests a short residence time of the magma in a shallow short lived small magmatic chamber finally the source of the t21d tephra layer found in the pianico sellere varved sequence northern italy is not the rivaux pumice flow as proposed by brauer et al 2007 journal of quaternary science 22 85 96 and neither one of the c ii pyroclastic units as suggested by roulleau et al 2009 quaternary international 204 31 43 accordingly the source for the t21d layer has yet to be found at sancy or elsewhere

arsenic and thioarsenic species in the hot springs of the rehai magmatic geothermal system tengchong volcanic region china abstract rehai is the sole geothermal area in mainland china that discharges both acidic and alkaline hot springs with phs ranging from 1 4 to 10 0 the hot springs in rehai are also characterized by a wide range of arsenic concentrations with the highest being 1 35 mg l analysis of the arsenic geochemistry indicates that the alkaline and neutral hot springs in rehai have high arsenic concentrations the alkaline hot springs represent arsenic rich boiled reservoir fluids and the neutral hot springs represent mixtures of these reservoir fluids with non thermal waters and or condensed steam the enrichment of arsenic in the deep reservoir fluids also called primary fluids is primarily attributable to the leaching of reservoir rocks at high temperatures but a possible arsenic contribution from magmatic fluids cannot be ruled out the acidic springs in contrast have much lower arsenic concentrations because they are a mixture of non thermal oxygenated waters and condensed steam both of which are depleted in arsenic in addition to arsenite and arsenate mono di and tri thioarsenates have been detected in the rehai geothermal waters the arsenic speciation in the rehai hot springs is primarily linked to the formation processes of the various secondary fluids at the surface and their sulfide concentrations in addition the speciation is also affected by the ph values and the redox potentials of the waters compared to the springs along secondary e w trending faults the chloride rich springs along the main n s trending faults are generally much less affected by mixing with non thermal waters and or condensed steam they are also more enriched in sulfide and thioarsenates consequently represent a greater proportion of the total arsenic this is the first study to report the thioarsenic geochemistry of hot springs in china

la icp ms u pb zircon timescale constraints of the pleistocene latest magmatic activity in the sancy stratovolcano french massif central abstract it has been demonstrated for several years that the u pb zircon system can provide useful dating information for understanding the time evolution of the volcanic systems in addition in situ techniques were successfully used for determining the formation age of young pliocene and pleistocene volcanic rocks and to record the spatial and temporal distribution and the lifetime evolution of the magma chambers generally in the case of large volcanic domains here we show that it is possible to obtain a precision at the percent level on zircon from a short size and late volcanic event from the sancy stratovolcano french massif central la icp ms dating of pleistocene magmatic zircons allow to distinguish the timescale of these late magmatic events within the complex volcanic activity of this large stratovolcano a syenite xenolith enclosed into a trachyte pumice flow were dated at 277 6 3 2 ka and 260 1 3 6 ka respectively whereas an earlier trachyandesite dome was emplaced at 284 4 4 2 ka these different ages allow to propose a minimum evolution time of about 24 8 kyrs for a differentiated magma chamber which corresponds to a short lifetime associated with low magma volumes the duration of this discrete volcanic event should be compared to the hundreds of thousands of years reported for the large volcanic systems interestingly the zircon crystals from the pumices were embedded into a thin layer of glass of trachytic composition demonstrating that these zircons crystallized into the melt only a short time before eruption

historical seismicity of the mont dore volcanic province auvergne france unraveled by a regional lacustrine investigation new insights about lake sensitivity to earthquakes lake sediments are relevant natural seismographs over long time scale however because tectonic events are not systematically recorded in lake sediments one forthcoming challenge for paleoseismology is to better assess lake sensitivity to earthquakes to this end a limnogeological investigation including hydroacoustic mapping techniques core sampling and multi proxy sediment analyses has been conducted within four small volcanic lakes located in the mont dore province auvergne france an area with a moderate seismo tectonic activity results show the existence of several gravity reworking processes in the lakes over the last millennium around ad 1300 the occurrence of synchronous events in lakes pavin chauvet montcineyre and guery 100 km 2 area highlights an undocumented earthquake as a common trigger for slope failures in disconnected basins at regional scale the record of this tectonic event may have been favored by human induced increase in sediment load chauvet and montcineyre and or after an abrupt lake level drop pavin affecting the sediment stability in addition synchronous turbidites and mass wasting deposits mwd recorded in lakes pavin and guery provide evidence for a seismic activity during the xix th century potential triggers are historical earthquakes that occurred either in the mont dore area or in the southern part of the limagne fault at this time despite moderate seismic activity in this intraplate volcanic domain these results highlight the role of tectonics as a major trigger in the sedimentary processes dominating these lacustrine infills within the diversity of studied sites it appears that lake sensitivity to earthquakes was not constant over time this sensitivity can be expressed as a combination of external factors namely earthquake magnitude and lake epicenter distance and internal factors such as lake morphology nature of sediment lake level fluctuations and human induced changes in catchment sedimentary load

a discrete element model for orogenesis and accretionary wedge growth 1 we develop a two dimensional discrete element model to investigate the evolution of doubly vergent orogenic and accretionary wedges this generates the localization of deformation across persistent structures as emergent phenomena unlike many continuum models that require predefined weaknesses to localize strain the model is used to study how deformation processes evolve for two different boundary conditions drawing strong comparisons with previous sandbox analogues and computational approaches the deformational history of the modeled wedges is characterized by three stages defined by an evolution in the mechanisms available to accommodate shortening the first stage develops a strong retrovergent thrust that initiates at the subduction point the second stage shows a change in vergence of deformation as thin skinned thrusting propagates into material carried on the subducting plate thus evolving a folded and thrusted prowedge finally a second shallower retrowedge develops in the overriding plate through accretion this final stage is not present in all sand analogue modeling approaches and defines a difference in the deformation style thresholds in geometry and size regulate the localization and style of deformation and hence the progression through the three stages the wedges produced show periodicity in the modes of accretion to maintain a geometric form with deformation localizing across structures that are internally reactivated thus prowedges and retrowedges are seen to oscillate about constant taper angles

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

underthrusting accretion cycle work budget as revealed by the boundary element method 1 sandbox models of accretionary wedges have demonstrated that fault systems grow episodically via cycles of alternating wedge thickening which is accommodated by slip along faults within the wedge underthrusting and wedge lengthening which is accommodated by growth of new faults at the wedge toe accretion the transition between these two modes of deformation is controlled by the interplay of work against gravity frictional heating the work of deformation around faults and the work of fault propagation and seismic acoustic energy using numerical mechanical models based on the boundary element method we have simulated the deformation observed in sandbox experiments providing a mechanical analysis of the underthrusting accretion transition our results show that the total work done by the contracting wedge increases during the underthrusting stage up to a critical value when the propagation of a new frontal thrust significantly reduces the work required for further deformation the numerical models also predict the location of the maximum shear along the basal decollement during underthrusting as well as the energetically most viable position and vergence for the nucleation of a new thrust these locations do not coincide and the match of the energetically most favorable position with the experimental results suggests that the new thrust ramps develop first ahead and then link down and backward to the propagating basal decollement the shear localization producing a new thrust ramp will occur where the energy spent by the deforming wedge is minimized due to an optimal combination of gravitational frictional internal and propagation work terms

evidence for a post 3 16 ma change in nubia eurasia north america plate motions we combine updated gps velocities from the nubian nu eurasian eu and north american na plates with 500 new 3 16 myr average seafloor spreading rates and nine transform fault azimuths from the northern atlantic and arctic basin seafloor spreading centers to estimate and test for changes in the relative motion between these plates the numerous new seafloor spreading rates and gps velocities improve our ability to detect recent changes in the relative motions of these plates the angular velocity vector that best fits the eu na gps velocities lies significantly north of the 3 ma average pole in accord with previously published geologic evidence that the eu na pole has migrated northward since v3 ma although we also find evidence for a significant post 3 ma change in nu na motion it is less compelling because the nubian plate gps velocity field is sparse and nu na seafloor spreading rates appear to have remained steady within the 1 mm yr 31 uncertainties if we systematically decrease the seafloor spreading rates to correct for outward displacement of seafloor spreading magnetic lineations the nu eu pole derived from gps site velocities lies more than 30 angular degrees south of the tightly constrained 3 ma average estimate and predicts significantly slower and more oblique present day nu eu convergence in the mediterranean both models for nu eu motion pass a key test for their accuracy namely they correctly predict strike slip motion along the well mapped gloria fault east of the azores the change to more oblique nu eu motion may reflect increasing difficulty in maintaining margin normal convergence within this continent continent collision zone 8 2003 published by elsevier b v

basin inversion and contractional reactivation of inherited normal faults a review based on previous and new experimental models abstract compressional inversion of former extensional sedimentary basins is a particularly common phenomenon given that passive margins share the same destiny of being subsequently incorporated into fold and thrust belts during basin inversion pre existing faults may concentrate stress and localise future thrust ramps or may be reactivated recording reversal of movement from extension to reverse this process has attracted attention largely because of its economic implications related to petroleum and ore deposit prospects and seismic hazard assessment since more than two decades analogue modelling has been used to indentify and or test a number of parameters relevant for the inversion process this paper aims therefore to offer a reasoned review of the analogue modelling work done on the subject coupling such previous results with those of a new experimental series inspired to the northern apennines stratigraphy and evolution past models have explored the role of main factors governing fault reactivation susceptibility such as fluid pressure fault weakness fault steepness angle of shortening and sediment loading the new models have addressed the role played by geometry and strength of a basal ductile layer during inversion two sets of sand silicone models were first extended orthogonally at different velocities to produce dissimilar pre inversion internal geometries and then shortened coaxially at different velocities to vary the brittle ductile coupling the experimental results confirm the selectiveness of fault inversion and reveal strong similarities with structural styles of tectonic inversion reported from the northern apennines and various areas worldwide the preferred geological model inferred from this modelling involves contribution of 1 syn inversion rotation of pre existing faults to shallower dip and 2 rotation of principal stress axes which could explain the invariable reactivation of only one of the two oppositely dipping graben bounding faults these factors would thus interact with the other well established parameters controlling the fault reactivation process

the betic segment of the lithospheric trans alboran shear zone during the late miocene abstract the betic sinistral transcurrent shear zone betic cordilleras crosses the southeastern part of spain the study of the geodynamics of this area is approached from tectonic sedimentary magmatic and geophysical data large strike slip movements tectono sedimentary processes and magmatic events are seen at the boundary between two different lithospheric slabs they are located in a thinned compartment with a high geothermal gradient the large scale movements vertical and horizontal and the intensity of magmatic activity are the expression of the mechanical behaviour of this hot and thin crust all the geological events from the late miocene to recent are integrated in a crustal scale cross section which shows that the betic sinistral transcurrent shear zone widely affects the lithosphere it appears that subduction zones are not the only geodynamic context in which calc alkaline magmatism occurs

basin inversion and fault reactivation in laboratory experiments abstract a series of analogue models have been performed to get insights into the relationships between the reactivation of pre existing normal faults and the orientation of a successive compressive stress field the models were deformed in two phases 1 a first extension phase h 3 generating a graben and 2 a successive compressive phase with the orientation of the shortening direction h 1 trending between 0 and 90 obliquity angle to the faults bounding the graben the deepening of this graben was accompanied by syn tectonic sedimentation that included a basal ductile layer simulating salt in nature overlain by a brittle sand pack the experimental results suggest that the development of compressive structures is strongly controlled by the pre existing normal faults and by the obliquity angle the experiments have invariably shown that the extensional faults were reactivated during shortening whatever the value of the angle whereas strike slip reactivation of major normal faults is favoured by low obliquity angles mostly dip slip reactivation of pre existing structures is instead promoted for high obliquity angles the analysis of model results highlights the important role played by a ductile layer at the base of the basin fill and the obliquity angle in controlling both strain partitioning and brittle ductile decoupling

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

mode of extensional tectonics in the southeastern betics se spain implications for the tectonic evolution of the peri alboran orogenic system the gibraltar arc which closes the westernmost part of the mediterranean basin is a miocene a type subduction arc formed by the continental collision of various pre miocene terranes in the major zone of collision between the iberian and african cratons the hanging wall block known as the alboran domain has undergone more than 300 km migration from a more easterly position where it was the continuation of the alpine cretaceous paleogene orogen contemporaneous with thin skinned thrusting in the footwall the alboran domain underwent two episodes of nearly orthogonal extension in which extensional systems developed with directions of extension varying from a nnw sse system orthogonal to the belt axis in the late burdigalian langhian to a wsw directed orogen parallel one in the serravallian the superposition of these two systems resulted in a chocolate tablet megastructure this extensional pattern is not satisfactorily explained in previously proposed models for the evolution of the arc orthogonal extension is plausible in a process of the gravitational collapse of an overthickened crust nevertheless orogen parallel extension is more difficult to explain in this context we advocate that the wsw directed low angle normal faults formed during large scale extension in connection with important westward arc migration the driving force of extension in a general context of convergence is controversial and varies between a convective removal model and a delamination model constraints on both the timing and the kinematics of extension as presented in this paper seem to support the contribution of both mechanisms convective removal may have started the process but continued n s convergence could have resulted in westward tectonic escape and asymmetric lateral inflow of asthenospheric material accompanying lithospheric delamination

distinguishing volcanic debris avalanche deposits from their reworked products the perrier sequence french massif central debris avalanches associated with volcanic sector collapse are usually high volume high mobility phenomena debris avalanche deposit remobilisation by cohesive debris flows and landslides is common so they can share textural characteristics such as hummocks and jigsaw cracks distinguishing original deposits from reworked products is critical for geological understanding and hazard assessment because of their different origin frequency and environmental impact we present a methodology based on field evidence to differentiate such epiclastic breccias basal contact mapping constrained by accurate altitude and location data allows the reconstruction of deposit stratigraphy and geometry lithological analysis helps to distinguish the different units incorporation structures kinematic indicators and component mingling textures are used to characterise erosion and transport mechanisms we apply this method to the enigmatic sequence at perrier french massif central where four units u1 u4 have been interpreted either as debris flow or debris avalanche deposits the sequence results from activity on the monts dore volcano about 2 ma ago the epiclastic units are matrix supported with an almost flat top u2 and u3 have clear debris flow deposit affinities such as rounded clasts and intact blocks no jigsaw cracks u1 and u4 have jigsaw cracked blocks with matrix injection and stretched sediment blocks u1 lacks large blocks 10 m wide and has a homogenous matrix with an upward increase of trapped air vesicle content and size this unit is interpreted as a cohesive debris flow deposit spawned from a debris avalanche upstream in contrast u4 has large mega blocks up to 40 m wide sharp contacts between mixed facies zones with different colours and numerous jigsaw fit blocks open jigsaw cracks filled by monogenic intra clast matrix mega blocks are concentrated near the deposit base and are spatially associated with major substratum erosion this deposit has a debris avalanche distal facies with local debris flow affinities due to partial water saturation we also identify two landslide deposits l1 and l2 resulting from recent reworking that has produced a similar facies to u1 and u4 these are distinguishable from the original deposits as they contain blocks of mixed u1 u4 facies a distinctly less consolidated and more porous matrix and a fresh hummocky topography this work shows how to differentiate epiclastic deposits with similar characteristics but different origins in doing so we improve understanding of present and past instability of the monts dore and identify present landslide hazards at perrier

tephrochronology of the mont dore volcanic massif massif central france new 40ar 39ar constraints on the late pliocene and early pleistocene activity the mont dore massif 500 km2 the youngest stratovolcano of the french massif central consists of two volcanic edifices the guery and the sancy to improve our knowledge of the oldest explosive stages of the mont dore massif we studied 40ar 39ar dated through single grain laser and step heating experiments 11 pyroclastic units from the guery stratovolcano we demonstrate that the explosive history of the guery can be divided into four cycles of explosive eruption activity between 3 09 and 1 46 ma g i to g iv we have also ascertained that deposits associated with the 3 1 3 0 ma rhyolitic activity which includes the 5 km3 grande nappe ignimbrite are not recorded in the central part of the mont dore massif all the pyroclastites found in the left bank of the dordogne river belong to a later explosive phase 2 86 2 58 ma g ii and were channelled down into valleys or topographic lows where they are currently nested this later activity also gave rise to most of the volcanic products in the perrier plateau 30 km east of the mont dore massif three quarters of the volcano sedimentary sequence up to 100 m thick was emplaced within less than 20 ky associated with several flank collapses in the northeastern part of the guery the age of the fournet flora 2 69 0 01 ma found within an ash bed belonging to g ii suggests that temperate forests already existed in the french massif central before the pliocene pleistocene boundary the guery s third explosive eruption activity cycle g iii lasted between 2 36 and 1 91 ma it encompassed the guery lake and morangie pumice and ash deposits as well as seven other important events recorded as centimetric ash beds some 60 to 100 km southeast of the massif in the velay region we propose a general tephrochronology for the mont dore stratovolcano covering the last 3 1 my this chronology is based on 44 40ar 39ar dated events belonging to eight explosive eruption cycles each lasting between 100 and 200 ky the occurrence of only one pumice deposit in the 800 ky period between 1 9 and 1 1 ma suggests that volcanic explosive activity was strongly reduced or quiescent

40ar 39ar dating on tephra of the velay maars france implications for the late pleistocene proxy climatic record abstract pollen contents and magnetic records of the pleistocene sedimentary sequences cored in the praclaux and lac du bouchet maars velay region french massif central demonstrated that they have high potential as detailed climatic and environmental archives tephra layers interbedded in these sequences have been studied in order to perform isotopic dating first petrographic studies and 40 ar 39 ar ages have shown that these tephra layers are the witness of the same eruption from the sancy volcano centre located 100 km to the north according to fourteen 40 ar 39 ar ages carried out on sanidine and biotite grains this eruption occurred 275 5 ka ago this result allows to construct a time scale for a composite high resolution record of the climate covering the last 300 000 years and to establish an absolute chronology for the palaeoclimatic events recorded in these sequences these tephra layers are interbedded in organic layers deposited during an interstadial stage called the amargiers interstadial which according to its age can be considered as equivalent to isotopic stage 9a moreover the geographical extension of the tephra and its well constrained age give to this tephra the interest of a chronostratigraphic marker for upper quaternary sequences in southeastern france

spatial and temporal variations in growth rates along active normal fault systems an example from the lazio abruzzo apennines central italy abstract the geometry kinematics and rates of active extension in lazio abruzzo italian apennines have been measured in order to gain a better understanding of the spatial and temporal variations in fault growth rates and seismic hazards associated with active normal fault systems we present fault map traces throws throw rates and slip directions for 17 parallel en echelon or end on active normal faults whose 20 40 km lengths combine to form a soft linked fault array ca 155 km in length and ca 55 km across strike throw rates derived from observations of faulted late glacial features and holocene soils show that both maximum throw rates and throw rate gradients are greater on centrally located faults along the strike of the array total throws and throw gradients show similar spatial variations but with weaker relationships with distance along strike when summed across strike throw rates are increasingly high towards the centre of the array relative to summed throws we interpret the above to suggest that throw rates have changed in the recent past ca 0 7 ma from spatially random fault growth rates initiating at 2 5 3 3 ma to growth rates that are greater on centrally located faults we interpret this as evidence for fault interaction producing throw rate variations that drive throw profile readjustment on these crustal scale soft linked faults the results are used to discuss seismic hazards in the region which are quantified in a second paper in this issue

tectonic and seismic implications of an intersegment rupture the damaging may 11th 2011 mw 5 2 lorca spain earthquake on may 11th 2011 a mw 5 2 earthquake stroke the city of lorca in the se spain this event caused 9 fatalities 300 injuries and serious damage on the city and the surrounding areas the lorca earthquake occurred in the vicinity of a region bounding two well known segments of a large active fault the alhama de murcia fault amf the lorca earthquake offers a unique opportunity to study how strain is accommodated in an intersegment region of a large strike slip fault we map recent tectonic structures in the epicentral region and we use radar interferometry to analyze the coseismic deformation combining these data with seismological observations of lorca seismic sequence we first model the source of the earthquake then we analyze the influence of our preferred model in the adjacent segments by coulomb failure stress modeling the proposed earthquake source model suggests that this event ruptured an area of 4 3 km within the complex structure that limits the gonar lorca and lorca totana segments of the amf the induced static stress change on the adjacent segments of the fault represents a seismic cycle advance equivalent to 200 to 1000 years of tectonic loading

alder creek sanidine acs 2 a quaternary 40ar 39ar dating standard tied to the cobb mountain geomagnetic event accurate 40ar 39ar dating of quaternary and holocene samples requires a standard neutron fluence monitor of appropriate age this standard should be isotopically homogenous at the scale of analysis and should be well intercalibrated with other standards several such standards have been proposed including sanidine from the 1 19 ma alder creek rhyolite acs turrin et al 1994 turrin b d donnely nolan j m hearn b c jr 1994 40ar 39ar ages from the rhyolite of alder creek california age of the cobb mountain normal polarity subchron revisited geology 22 251 254 this sanidine is satisfactorily homogeneous well intercalibrated with fish canyon sanidine fcs renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 and is linked to the astronomically calibrated magnetic polarity time scale since the alder creek rhyolite lava is the type occurrence of the cobb mountain event cm we collected 408 kg of this rock from which we anticipate being able to extract more than 8 kg of 425 m sanidine crystals analyses of sanidine phenocryts from the acs 2 from three separate irradiations and two distinct grain sizes yield ages ranging from 1 190 0 004 to 1 194 0 003 ma1 with a weighted mean age of 1 193 0 001 ma mswd 0 74 n 225 based on fcs 28 02 ma renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 the value of the intercalibration factor renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 is rfcsacs 2 0 04229 0 00012 n 8 identical with that of the original acs measurements 0 04229 0 00012 renne et al 1998 renne p r swisher c c deino a l karner d b owens t l depaolo d j 1998 intercalibration of standards absolute ages and uncertainties in 40ar 39ar dating chem geol 145 117 152 the age of acs 2 is in agreement with the recent astronomical calibration of the cm event 1 215 to 1 190 ma channell j e t mazaud a sullivan p turner s raymo m e 2002 geomagnetic excursions and paleointensities in the matuyama chron at ocean drilling program sites 983 and 984 iceland basin j geophys res 107 6 10 1029 2001jb000491 the apparent absence of xenocrysts and excess argon suggests that multigrain analyses are feasible and therefore the amount of material can be tailored to experimental requirements aliquots from various grain sizes will be available upon request zircon is also potentially available which may be of interest to u th he researchers