law for the distance between successive earthquakes 1 discovery of a new law for the three dimensional spatial distance between the foci of successive earthquakes is reported analyzing the seismic data taken between 1984 and 2001 in southern californian it is found that the cumulative distribution of the distances follows the modified zipf mandelbrot law showing complexity of geometry of the events

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

earliest paleoproterozoic supracrustal rocks in the north china craton recognized from the daqingshan area of the khondalite belt constraints on craton evolution abstract the upper wulashan subgroup at daqingshan in the khondalite belt of the western block of the north china craton contains an early paleoproterozoic 2 5 2 45 ga supracrustal sequence incorporating banded iron formations which we refer to as the daqingshan supracrustal rocks they contain rounded to elliptical zircon grains that commonly show core rim or core mantle rim structures and precise shrimp u pb dating of these domains allows the discrimination of a series of tectono thermal events that straddle the archean proterozoic boundary detrital zircon cores with oscillatory zoning have formation ages ranging from 2 55 to 2 50 ga indicating derivation from late neoarchean magmatic rocks as a result of exhumation and erosion these became incorporated in earliest paleoproterozoic sediments that were deposited between 2 50 and 2 45 ga and then underwent high grade metamorphism at 2 45 2 40 ga this event variously recrystallized the cores into two main domains a dark inner domain and a gray outer domain as imaged in cathodoluminescence the gray domains commonly show sector zoning and have th u ratios of 0 1 0 5 a feature commonly noted in zircons recrystallized under high grade metamorphic conditions metamorphic mantles are generally more homogeneous in structure and have lower th u ratios commonly

petrology phase equilibria and monazite geochronology of granulite facies metapelites from deep drill cores in the ordos block of the north china craton abstract among the various precambrian crustal blocks in the north china craton ncc the geology and evolution of the ordos block remain largely enigmatic due to paucity of outcrop here we investigate granulite facies metapelites obtained from deep penetrating drill holes in the ordos block and report petrology calculated phase equilibria and in situ monazite la icp ms geochronology the rocks we studied are two samples of cordierite bearing garnet sillimanite biotite metapelitic gneisses and one graphite bearing two mica granitic gneiss the peak metamorphic age from la icp ms dating of monazite in all three samples is in the range of 1930 1940 ma the u pb th chemical ages through epma dating reveals that monazite occurring as inclusions in garnet are older than those in the matrix calculated metamorphic phase diagrams for the cordierite bearing metapelite suggest peak p t conditions ca 7 9 kbar and 775 825 c followed by decompression and evolution along a clockwise p t path our petrologic and age data are consistent with those reported from the khondalite belt in the inner mongolia suture zone in the northern part of the ordos block suggesting that these granulite facies metasediments represent the largest paleoproterozoic accretionary belt in the ncc

a seismic source zone model for the seismic hazard assessment of the italian territory abstract we designed a new seismic source model for italy to be used as an input for country wide probabilistic seismic hazard assessment psha in the frame of the compilation of a new national reference map we started off by reviewing existing models available for italy and for other european countries then discussed the main open issues in the current practice of seismogenic zoning the new model termed zs9 is largely based on data collected in the past 10 years including historical earthquakes and instrumental seismicity active faults and their seismogenic potential and seismotectonic evidence from recent earthquakes this information allowed us to propose new interpretations for poorly understood areas where the new data are in conflict with assumptions made in designing the previous and widely used model zs4 zs9 is made out of 36 zones where earthquakes with m w 5 are expected it also assumes that earthquakes with m w up to 5 may occur anywhere outside the seismogenic zones although the associated probability is rather low special care was taken to ensure that each zone sampled a large enough number of earthquakes so that we could compute reliable earthquake production rates although it was drawn following criteria that are standard practice in psha zs9 is also innovative in that every zone is characterised also by its mean seismogenic depth the depth of the crustal volume that will presumably release future earthquakes and predominant focal mechanism their most likely rupture mechanism these properties were determined using instrumental data and only in a limited number of cases we resorted to geologic constraints and expert judgment to cope with lack of data or conflicting indications these attributes allow zs9 to be used with more accurate regionalized depth dependent attenuation relations and are ultimately expected to increase significantly the reliability of seismic hazard estimates

combined effects of tectonics and glacial isostatic adjustment on intraplate deformation in central and northern europe applications to geodetic baseline analyses 6 1 we use a suite of spherical thin sheet finite element model calculations to investigate 7 the pattern of horizontal tectonic deformation within europe the calculations incorporate 8 the effects of africa eurasia convergence atlantic ridge push forces and changes 9 in the lithospheric strength of the east european and mediterranean subdomains these 10 predictions are compared to the deformation computed for the same region using a 11 spherically symmetric self gravitating viscoelastic earth model of glacial isostatic 12 adjustment the radial viscosity profile and ice history input into the gia model are taken 13 from a model that best fits three dimensional crustal velocities estimated from the 14 bifrost fennoscandian gps network the comparison of the tectonic and gia signals 15 includes predictions of both crustal velocity maps and baseline length changes associated 16 with sites within the permanent itrf2000 and bifrost gps networks our baseline 17 analysis includes reference sites in northern and central europe that are representative of 18 sites at the center edge and periphery of the gia induced deformation baseline length 19 change predictions associated with all three reference sites are significantly impacted 20 by both tectonic and gia effects albeit with distinct geometric sensitivities in this regard 21 several of our tectonic models yield baseline rates from vaas onsala and potsdam to sites 22 below 55 n which are consistent with observed trends we find that a best fit to the 23 itrf2000 data set is obtained by simultaneously considering the effects of gia plus 24 tectonics where the latter is modeled with a relatively weak mediterranean subdomain in 25 this case the tectonic model contributes to the observed shortening between onsala 26 potsdam and sites to the south without corrupting the extension observed for baselines 27 extending from these reference sites and sites to the north this extension is well reconciled 28 by the gia process alone index terms 1208 geodesy and gravity crustal movements 29 intraplate 8110 3210 mathematical geophysics modeling 8110 tectonophysics continental tectonics 30 general 0905 9335 information related to geographic region europe keywords tectonics gia 31 intraplate deformation

contribution of structural analysis to understanding the geodynamic evolution of the calabrian arc southern italy abstract a marked curvature of crustal structures characterizes the calabrian arc in southern italy the overall deformation of the arc seems mostly controlled by the sangineto shear zone to the north and by the mt kumeta alcantara shear zone to the south which both separate different crustal sectors other important fault systems cut the iblean foreland scicli ragusa fault zone and many others dissect the crystalline units of central calabria neotectonic structural analyses have been carried out in order to recognize the character of the plio pleistocene tectonic phases and their bearing on the present configuration of the arc after the middle miocene extensional phase an early middle pliocene compressional phase is detectable in many parts of the arc right and left lateral displacements respectively characterize the mt kumeta alcantara and sangineto shear zones and right lateral movements are also detectable within the scicli ragusa fault system finally the pleistocene tensional regime seems to have been controlled mainly by uplift the structural and neotectonic data allow us to propose a model of the recent evolution of the arc which was bent mainly as a result of opposed wrench faulting along the sangineto and mt kumeta alcantara shear zones

the dynamics of back arc extension an experimental approach to the opening of the tyrrhenian sea the e w opening tyrrhenian sea developed after the cretaceous palaeogene alpine collision nearly perpendicular to the motion of the african plate as a back arc of the adria ionian westward subduction three driving mechanisms have been proposed to explain the dynamic evolution of the tyrrhenian apennine system 1 the northward indentation of the african plate 2 the retreating subduction of the adria ionian lithosphere and 3 the gravitational collapse of the alpine post collisional wedge in order to define the relative contribution of each of these mechanisms in the neogene dynamic of the tyrrhenian apennine system we performed 3 d laboratory experiments in which we simulated a retreating subduction process in a compressional regime oriented perpendicularly to the direction of subduction in this framework we also tested the influence of the gravitational collapse of the overriding plate experiments were constructed using dry sand and silicone putties to simulate brittle upper crust and ductile lower crust upper mantle respectively these layers floated on a high density low viscosity glucose syrup which simulated the asthenosphere the main conclusion of our experiments is that large scale continental extension similar to that observed in the tyrrhenian area could be reproduced perpendicular to the shortening direction induced by the indentation of the african plate in this framework extensional processes are indeed possible if the trench retreat velocity is higher than the rate of shortening induced by the advancing african plate our experimental results indicate that this high trench retreat velocity could be explained by the coexistence of the gravitational collapse of the post alpine wedge with a slab pull process linked to the retreating subduction of the adria ionian plate while the first mechanism is predominant in the northern tyrrhenian area the second one seems to be important in the latest stage of extension and oceanic accretion of the southern tyrrhenian area

resetting monazite ages during fluid related alteration abstract fluid related coupled dissolution reprecipitation processes can modify the composition of monazite and other orthophosphate minerals at temperatures well below diffusional closure temperatures it is critical to evaluate the effects of alteration processes on th u pb dates especially because incomplete removal of pb during alteration could lead to spurious dates either older or younger than the actual age of the monazite formation experimental alteration of monazite at 450 mpa and 450 c has resulted in the production of altered domains in the vicinity of the grain rim as well as in the vicinity of inclusions and microfractures without any obvious structural control within grains the composition of the altered domains is relatively constant from domain to domain and from grain to grain thorium was reduced from ca 7 wt tho 2 to ca 2 wt uranium and pb were almost entirely removed from the altered domains while unaltered areas of the monazite grains as well as the original monazite grains before the experiment yield very consistent dates of ca 350 ma dates from the altered domains are consistently near zero the implication is that fluid aided alteration of monazite for the conditions of this experiment has resulted in a near complete resetting of the monazite age at temperatures well below the closure temperature because alteration textures in monazite are relatively common in nature careful analysis of such textures offers a means of recognizing and potentially dating fluid rock interactions

origin and role of major strike slip transfers during plate collision in the central mediterranean variations in the crustal structure along the northern african plate margin have caused different modes of collision with eurasia lateral density variations along the central mediterranean collision zone are expressed in a change of the angle of the downbending african plate and lead to the formation of strike slip transfers in these transition zones that are roughly perpendicular to the trend of the collisional zone in some cases these transfer zones are developed into hinge faults while in others they can be developed into transform faults this process governs the segmentation of the collision zone in the central mediterranean region south of the maghrebian thrust belt in tunisia and sicily through the calabrian arc to the northeastern hellenic arc extending further to the cyprian arc and to the taurus zagros chain

european mediterranean regional centroid moment tensors 1997 2000 the mediterranean region is seismically very active and undergoing rapid deformation earthquakes as strong as m 6 are present but relatively rare on the other hand moderate magnitude seismicity 4 5 m 5 5 is widespread and often damaging an improved knowedge of moderate magnitude earthquakes can contribute significantly to a better understanding of active tectonics in the region harvard centroid moment tensors cmt today represent the most widely used reference for reliable source mechanisms but modelling seismic sources with the cmt technique for earthquakes with magnitude less than m 5 5 5 is quite difficult since 1997 we are using an extension of the standard cmt algorithm to compute regional centroid moment tensors rcmt for moderate magnitude earthquakes mw as low as 4 0 analyzing intermediate period surface waves from regional and teleseismic seismograms we routinely apply the algorithm to european mediterranean seismicity to produce a catalog of seismic moment tensors for events with magnitude between 4 5 and 5 5 which generally are not included in the harvard cmt catalog in this paper we show the results for earthquakes that occurred between 1997 and 2000 consisting of 252 solutions and we discuss the characteristics of the catalog and the areas where these new data are most relevant

preservation of old prograde metamorphic u th pb ages in unshielded monazite from the high pressure paragneisses of the variscan ulten zone italy abstract three samples of garnet kyanite paragneiss from the variscan ulten zone northern italy were studied in detail for u th pb monazite dating monazite in these gneisses is abundant shows highly variable grain size and occupies different textural positions within the matrix as inclusion in garnet and kyanite within apatite aggregates monazite shows different deformation features as a function of the textural position enclosed shielded monazite is generally more fractured than matrix unshielded monazite the integration of textural information with deformation features and in situ u th pb analyses by la icp ms indicates that there is no direct correlation between textural site and monazite ages old ages of 351 343 ma determined on portions of large matrix unshielded monazite and on rare domains of monazite shielded by garnet have been related to a prograde stage of the variscan metamorphic evolution of the ulten zone ages of 330 326 ma which are related to the thermal peak are recorded by small matrix monazite external domains of large matrix monazite and by domains of fractured monazite enclosed in garnet and kyanite large old unshielded grains formed as blasts during the prograde metamorphic history and survived the peak metamorphism during which crystallisation re crystallisation partially occurred

space geodetic constraints on glacial isostatic adjustment in fennoscandia analysis of global positioning system gps data demonstrates that ongoing three dimensional crustal deformation in fennoscandia is dominated by glacial isostatic adjustment our comparison of these gps observations with numerical predictions yields an earth model that satis es independent geologic constraints and bounds both the average viscosity in the upper mantle 5 x 10 20 to 1 x 10 21 pascal seconds and the elastic thickness of the lithosphere 90 to 170 kilometers we combined gps derived radial motions with fennoscandian tide gauge records to estimate a regional sea surface rise of 2 1 0 3 mm year furthermore ongoing horizontal tectonic motions greater than 1 mm year are ruled out on the basis of the gps derived three dimensional crustal velocity field

paleoproterozoic accretionary orogenesis in the north china craton a shrimp zircon study abstract the inner mongolia suture zone imsz and the trans north china orogen tnco incorporate the major paleoproterozoic accretionary orogens in the north china craton ncc with the jiao liao ji belt jljb representing the third one here we investigate the paleoproterozoic tectonics of the imsz and tnco through zircon shrimp geochronology on a representative suite of rocks comprising metasediments and arc magmatic rocks shrimp analysis of zircons with textures indicating extreme recrystallization under ultrahigh temperature uht conditions from the metapelites at heling er in the southern domain of the imsz reveals a single population with a weighted mean 207 pb 206 pb age of 1913 17 ma the zircons in another uht granulite from this locality yield a weighted mean 207 pb 206 pb age of 1910 18 ma these data correlate with the ca 1 92 ga age reported from zircons in sapphirine bearing uht granulites further north and confirm the regional extent of the paleoproterozoic uht metamorphism within the imsz zircons in a charnockite from the southern margin of the khondalite belt fringing the uht granulites in the imsz show two distinct age groups an older population with a magmatic paragenesis and a weighted mean 207 pb 206 pb age of 1932 24 ma and a younger group of metamorphic zircons with an age of 1858 26 ma we also report zircon ages from charnockites in two localities around xing he in the huangtuyao belt belonging to the huai an complex within the westernmost domain of the tnco at the junction with the imsz the charnockite from first locality carries two distinct zircon populations with the older group yielding a weighted mean 207 pb 206 pb age of 2477 2 ma and the younger population showing an age of 1807 38 ma the internal structure as revealed from cl images and the overall high th u values up to 2 42 of the older zircons suggest their magmatic affinity whereas the younger group with extremely low th u 0 02 0 09 is of metamorphic origin zircons from the charnockite in the second locality also define two distinct age clusters with a dominant older magmatic group having a weighted mean 207 pb 206 pb age of 2147 11 ma and a minor younger group with an age of 1958 25 ma the range of ages from 2477 to 2147 ma from magmatic zircons in the charnockites from the eastern periphery of the imsz within the western margin of the tnco in combination with similar ages reported in recent studies from zircons in magmatic complexes within the imsz suggest a prolonged history of subduction related arc magmatism and accretionary tectonics analogous to those in some of the phanerozoic belts such as the central asian orogenic belt and the western pacific subsequent progressive collision and suturing of the continental blocks were accompanied by the exhumation of high pressure hp and uht metamorphic rocks the available data from the imsz and tnco suggest long lived convergent margins associated with the southward subduction of the yinshan block and westward subduction of the eastern block in a double sided subduction realm prior to the final amalgamation of the ncc and its incorporation within the columbia supercontinent in the late paleoproterozoic

thermobarometric modelling of zircon and monazite growth in melt bearing systems examples using model metapelitic and metapsammitic granulites u pb age data collected from zircon and monazite are used to draw fundamental inferences about tectonic processes in the earth despite the emphasis placed on zircon and monazite ages the understanding of how to relate the timing of growth of zircon and monazite to an evolving rock system remains in its infancy in addition few studies have presented large datasets of geochronological data from zircon and monazite occurring in the same metamorphic rock sample such information is crucial for understanding the growth of zircon relative to monazite in a systematic and predictive manner as per this study the data that exist support the generally held conception that zircon ages tend to be older than monazite ages within the same rock here experimental data for zircon and monazite saturation in melt bearing rocks are integrated with phase diagram calculations the calculations constrain the dissolution and growth behaviour of zircon and monazite with respect to evolving pressure temperature and silicate mineral assemblages in high grade melt bearing metasedimentary rocks several key results emerge from this modelling first that in aluminous metapelitic rocks i e garnet cordierite sillimanite assemblages zircon ages are older than monazite ages in the same rock second that the growth rate of accessory minerals is nonlinear and much higher at and near saturation than at lower temperatures and third that the difference in zircon and monazite ages from the same rock may be ascribed to differences in the temperature s at which zircon and monazite grow rather than differences in closure temperature systematics using our methodology the cooling rate of granulites from the reynolds range central australia have been constrained at 4 c myr 1 this study serves as a first pass template on which further research in applying the technique to a field study can be based

spatiotemporal variations of seismic quiescence prior to the 2011 m 9 0 tohoku earthquake revealed by an improved region time length algorithm the region time length rtl algorithm which takes into account the epicenter time and magnitude of earthquakes is an effective technique in detecting seismic quiescence in order to reduce the possible ambiguity due to the selection of model parameters in the rtl algorithm we propose an improved technique of searching for the optimal model parameters as a case study we investigated the spatiotemporal variations of seismic quiescence prior to the m 9 0 tohoku earthquake by applying the improved rtl algorithm to the declustered and complete earthquake catalog of the japan meteorological agency jma the temporal variation of the rtl parameter at the epicenter indicated that a seismic quiescence occurred between 2006 and 2008 the spatial distribution showed the consistent time window of the appearance of anomalous quiescence near the epicenter the significance of the seismic quiescence anomaly was supported by the close investigations of model parameter effects and the stochastic test based on randomized earthquake catalogs

a non extensive statistical physics view in the spatiotemporal properties of the 2003 mw6 2 lefkada ionian island greece aftershock sequence investigation of the spatiotemporal properties of the 2003 lefkada seismic sequence is performed through non extensive statistical physics information on highly accurate aftershock source parameters became feasible from the recordings of a portable digital seismological network that was installed and operated in the study area during the evolution of the seismic sequence thus the spatiotemporal distribution of aftershocks onto the main and neighboring fault segments was investigated in detail enabling the recognition of four distinctive seismicity clusters separated by less active patches the aftershock spatiotemporal properties are studied here using the ideas of non extensive statistical physics nesp the cumulative distribution functions of the inter event times and the inter event distances are presented using the data set in each seismicity cluster and the analysis results in values for the statistical thermodynamic qt and qd parameters for each cluster where qt varies from 1 16 to 1 47 and qd from 0 42 to 0 77 for the inter event times and distances distributions respectively these values confirm the complexity and non additivity of the spatiotemporal evolution of seismicity and the applicability of the nesp approach in investigating aftershocks sequence the temporal pattern is discussed using the closely connected to nesp approach of superstatistics which is based on a superposition of ordinary local equilibrium statistical mechanics the result indicates that the temporal evolution of the lefkada aftershock sequence in clusters a b and c is governed by very low number of degrees of freedom while d is a less organized seismicity structure with a much higher number of degrees of freedom

mantle viscosity inferences from joint inversions of pleistocene deglaciatio induced changes in geopotential with a new slr analysis and polar wander joint inversions of post glacial rebound induced secular changes in low degree harmonics of the geopotential and true polar wander tpw systematically indicate that the upper mantle viscosity has a value that is considerably smaller than 10 21 pas the lower mantle viscosity is about one order of magnitude larger than the upper mantle viscosity discrepancies in the viscosity profiles inferred from even and odd zonals are likely an indication of recent unmodeled glacial forcings and or insufficient precision in the evaluation of the mass loss from pleistocene ice sheets the influence of systematic errors in slr data reduction due to thermal drag on the lageos satellites for the uneven zonals of the geopotential is avoided by making use of the starlette and stella satellites to recover the uneven zonals and by considering lumped coefficients for these uneven terms

la icp ms u pb zircon ages of the qianlishan complex constrains on the evolution of the khondalite belt in the western block of the north china craton abstract the qianlishan complex is located in the westernmost part of the khondalite belt a continent continent collisional belt along which the yinshan block in the north and the ordos block in the south amalgamated to form the western block which then collided with the eastern block along the trans north china orogen to form the north china craton the complex is dominated by high grade supracrustal rocks and minor s type granites of which the supracrustals consist of graphite bearing sillimanite garnet gneiss garnet quartzite felsic paragneiss calc silicate rock and marble cl images reveal the existence of detrital and metamorphic zircons in major rocks of the qianlishan complex in most cases detrital zircons occur as either single grains with oscillatory zoning or oscillatory zoning cores typical of igneous origin which are surrounded by metamorphic overgrowth rims that are structureless high bright and low in th u ratio detrital zircons from the qianlishan complex yield nearly concordant 207 pb 206 pb ages ranging from 2 3 to 2 0 ga suggesting that the protoliths of the high grade supracrustal rocks in the qianlishan complex were deposited at some time after 2 0 ga metamorphic zircons yield two age populations with one at 1 95 ga and another at 1 92 ga of which the former is interpreted as the timing of the collision between the yinshan and ordos blocks to form the western block whereas the later is considered to be the age of subsequent post orogenic extensional event minor s type granites were emplaced at 1 88 ga as a result of partial melting of supracrustals at the stage of the exhumation of the qianlishan complex these new zircon ages combined with structural and metamorphic considerations enable resolution of the tectonothermal events involving the collision between the yinshan and ordos blocks to form the western block followed by the post collisional extension and subsequent exhumation of the khondalite belt

tectonic versus glacial isostatic deformation in europe 1 tectonic deformation induced by the alpine collision and glacial isostatic adjustment gia in europe are modelled by means of a finite element scheme and viscoelastic normal modes techniques in order to compare the resulting deformation patterns with the itrf2000 international terrestrial reference frame geodetic dataset due to the alpine collision and to the flow from the equatorial mantle to the deglaciated regions in the northern hemisphere both tectonics and gia contribute to the observed widespread shortening with tectonics playing a major role in the southern part of the modelled domain from potsdam to the alpine front and gia affecting the shortening in proximity of the region subject to post glacial rebound since the stiff baltic shield causes a counterclockwise rotation of the collision velocity away from the shield itself and the gia induced velocities are directed outward from the deglaciated region both tectonics and gia contribute to the observed east west baseline extension of 0 8 1 1 mm yr at the latitude of onsa

p wave deep velocity structure of the southern tyrrhenian subduction zone from nonlinear teleseismic traveltime tomography a new 3 d model for the p wave velocity structure of the southern tyrrhenian subduction zone stsz is determined from nonlinear inversion of relative arrival times of teleseismic events the data used in the imaging are the travel time residuals of both direct p and pk p df and secondary pp sp pcp pkp bc phases computed with respect to the global 1 d velocity model ak135 2308 teleseismic waveforms were collected for this study from 109 events recorded by the italian national seismic network rsnc during 1988 1998 the velocity perturbation field is reconstructed gradually by means an iterative sequence of linearized inversions incorporating a 3 d minimum travel time ray tracing the tomographic images reveal a broad high velocity zone dominating the pattern of lateral variations beneath the southern tyrrhenian sea and calabria this fast structure extends laterally for a maximum of 350 km from northern sicily to southern campania and vertically for at least 400 km from the uppermost mantle down to 500 km depth below 350 km the geometry of the depicted slab is characterized by horizontal deflection of the subducting lithosphere towards the central tyrrhenian basin

electron microprobe dating of monazite because monazite is extremely rich in u and th radiogenic pb pb accumulates very quickly and reaches in about 100 ma a level where it is possible to analyse it with the electron probe assuming that common pb is negligible and that partial loss of pb has not occurred the simultaneous measurement of u th and pb allows to obtain a geologically meaningful age from a single electron probe analysis here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method a specific statistical method to deal with the large number of data which can be obtained on a single sample is described and several guidelines illustrated by examples are suggested to optimize the method electron probe measurements carried out on samples of known age from 200 ma to 3 1 ga yield ages that always fall inside the confidence interval of the isotopically determined age demonstrating that this method is reliable the younger age limit is approximately 100 ma although it can be younger in some favourable cases in old monazites extremely high pb contents have been found up to 5 wt indicating that monazite can tolerate high radiation doses without experiencing lead loss the final precision on the age for a normal monazite is 30 50 ma for a total counting time of 600 s a complete dating procedure can be completed in less than 1 h first results indicate that old ages can be preserved in monazite either in small relict cores in crystals or by the coexistence of several generations of monazites in a sample this method has all the advantages of the electron probe it is non destructive has an excellent spatial resolution monazites as small as 5 i m can be dated and because it is possible to work on normal polished thin sections the petrographical position of the dated crystal is known this method offers a large number of geologists access to an in situ dating technique at moderate cost

gps derived strain rate field within the boundary zones of the eurasian african and arabian plates we use the gps velocity field 1988 1998 for eastern mediterranean and asia minor to determine the crustal deformation strain rate field in an area bounded by 35 n and 43 n and 20 e and 48 e we calculate the normal and shear strain rate components associated with the major faults and compare these qualitatively with seismological data uncertainties in the calculation of the strain rates reach 50 nstrain yr 1 in sparsely observed parts of anatolia whereas we estimate errors 20 nstrain yr 1 in the aegean and marmara regions the largest compressional strain rate components in the eastern part of the study area occur along the greater caucasus mountain front reaching 70 nstrain yr 1 1 nstrain yr 1 0 0317 10 15 s 1 the north anatolian fault zone is the clearest feature in the shear strain rate field it is expressed as a pronounced dextral strike slip fault zone reaching rates of up to 170 nstrain yr 1 this holds true also for the izmit area where the august 17 1999 earthquake occurred central anatolia is almost strain free whereas extension prevails in western anatolia the principal axes of extension vary around the n s direction with strain rates of up to 85 nstrain yr 1 these extensional areas coincide with graben features and normal faulting earthquakes the central and southwestern aegean sea is strain free with values far below 40 nstrain yr 1 the seismic cluster around the dodekanissa islands southeastern aegean sea coincides with nw se oriented extension attaining strain rates of up to 90 nstrain yr 1 this area of extension also exhibits recent active volcanism the entire hellenic arc shows compressional strain rates perpendicular to the arc the pliny strabo troughs along the eastern segment of the arc show left lateral shear strain rates reaching 80 nstrain yr 1 significant extension is found in central greece with a nne ssw oriented maximum of 120 nstrain yr 1 centered around the gulf of corinthos the kephalonia fault zone in nw greece is a distinct dextral fault zone separating apulia from the rapidly moving aegean microplate right lateral shear strain rates reach 150 nstrain yr 1

active tectonics and gps data analysis of the maghrebian thrust belt and africa eurasia plate convergence in tunisia abstract the atlas mountains of tunisia belong to the seismically active zone of the africa nubia eurasia plate boundary in the central western mediterranean we study the eastern section of the maghrebian thrust belt using a subset 6 days from each of 5 years 2014 to 2018 of permanent survey mode gps data and active tectonics wnw to nnw trending velocities express crustal motion and geodetic strain fields from the sahara platform to the tell atlas consistent with african plate convergence to the south the velocities and trajectories indicate nearly wnw ese trending right lateral motion of the sahara fault related atlas fold belt with respect to the sahara platform farther north and northeast the significant decrease in velocities between the eastern platform sahel central atlas and tell atlas and the clockwise rotation mark the nnw trending shortening deformation associated with local ene wsw extension visible in the quaternary grabens the velocity field and strain distribution associated with the active e w to wnw ese trending right lateral faulting and ne sw fault related folds illustrate the transpression tectonics and support the identification of four tectonic domains north of the africa nubia platform in tunisia the transpression reduces northward when reaching the central and tell atlas these results change our perception of the africa eurasia plate boundary previously located along the western mediterranean coastline

analysis of italian seismicity by using a nonextensive approach abstract using the ingv national institute of geophysics and volcanology seismic catalogue nonextensive analysis of the instrumental seismicity of italy was performed the time span of the analyzed catalogue is from april 16 2005 to march 31 2009 and only events with magnitude ml 1 9 were considered the analysis of the spatial variation of the nonextensive parameters q and a was performed by means of scanning the italian territory by a 1 1 spatial window with a shift of 0 2 in longitude and latitude the nonextensive parameters were estimated by means of the levenberg marquadt nonlinear least square fitting method and the obtained results were checked for stability with the variation of a0 and q0 the initial values of the parameters in the fitting procedure it was found that the q value is relatively low in areas in which the strongest events mw 5 5 during the last 40 years occurred this finding could suggest that different earthquake triggering mechanisms govern the italian seismicity stick slip like where q is relatively low and fragment asperity interaction type where q is relatively high of course new analyses from different areas are needed in order to test such findings

late neoarchean paleoproterozoic arc continent accretion along the khondalite belt western block north china craton insights from granitoid rocks of the daqingshan wulashan area abstract late neoarchean early paleoproterozoic granitoid rocks are widely exposed in the daqingshan wulashan area in the central segment of the khondalite belt kb western block north china craton ncc and are characterized by widespread evidence of ductile deformation and anatexis to improve our understanding of the formation and evolution of the kb in this study we analyzed zircon u pb ages zircon lu hf isotopes and whole rock geochemistry of the granitoid rocks la icp ms u pb analysis of zircons from eight representative granitoid samples indicates the granitoid rocks were emplaced at ca 2 45 and ca 2 50 ga and underwent multi stage metamorphism at ca 1 90 1 95 2 45 and 2 50 ga zircon lu hf isotopic analysis shows that the granitoids have positive zircon ehf t values with an average of 4 36 and two stage depleted mantle zircon hf model ages tdm2 clustering around 2 7 3 0 ga indicative of a juvenile crustal source that formed at ca 2 7 3 0 ga furthermore whole rock geochemical analysis of 34 granitoid samples reveal them to be magnesian low to high k calcic to calc alkalic and metaluminous to weakly peraluminous alumina saturation index asi 0 74 1 17 they are characterized by high total rare earth element ree contents 57 45 346 96 ppm enrichment in light ree and depletion in heavy ree with la yb n ratios of 8 33 224 16 they have weak eu anomalies eu eu 0 37 2 53 average 1 08 high sr contents 300 ppm and relatively low y and yb concentrations average 10 55 and 0 96 ppm respectively primitive mantle normalized trace element diagrams show that the granitoid samples are depleted in high field strength elements nb ta u and ti and enriched in large ion lithophile elements ba k rb and sr in general the samples have geochemical characteristics consistent with cordilleran i type granitoids which form in subduction related magmatic arcs therefore our results together with the occurrence of synchronous mafic rocks and other available geological data indicate the kb contains multiple magmatic arcs and underwent long term deposition and multi phase metamorphism analogous to phanerozoic accretionary orogens such as the cordilleran orogen consequently we infer that the kb underwent long term arc continent accretion along the southern margin of the yinshan block during the late neoarchean paleoproterozoic and late stage continent continent collision between the yinshan and ordos blocks at ca 1 90 1 95 ga

a nonextensive statistical physics analysis of the 1995 kobe japan earthquake this paper presents an analysis of the distribution of earthquake magnitudes for the period 1990 1998 in a broad area surrounding the epicenter of the 1995 kobe earthquake the frequency magnitude distribution analysis is performed in a nonextensive statistical physics context the nonextensive parameter q m which is related to the frequency magnitude distribution reflects the existence of long range correlations and is used as an index of the physical state of the studied area examination of the possible variations of q m values is performed during the period 1990 1998 a significant increase of q m occurs some months before the strong earthquake on april 9 1994 indicating the start of a preparation phase prior to the kobe earthquake it should be noted that this increase coincides with the occurrence of six seismic events each of these events had a magnitude m 4 1 the evolution of seismicity along with the increase of q m indicate the system s transition away from equilibrium and its preparation for energy release it seems that the variations of q m values reflect rather well the physical evolution towards the 1995 kobe earthquake

on the pseudomorphing of melt filled pores during the crystallization of migmatites pseudomorphs of melt filled pores recognized by their generally cuspate shape are used as diagnostic for the former presence of partial melt they are commonly observed in migmatites from the mid to deep crust although they occur in the smaller pores in migmatites from shallower levels 1 2 kbar the pseudomorphing of meltfilled pores is controlled by the kinetics of nucleation and is a consequence of the greater supersaturation required for nucleation in a small pore compared with a larger one we examine three migmatites in detail a contact metamorphosed cherty band from an iron formation an archaean regional granulite from an accretionary prism and an amphibolite facies sample from the roots of an archaean mountain chain the greater undercooling required for nucleation in progressively smaller pores is recorded by the composition of plagioclase pseudomorphs a study of dihedral angles at the corners of pseudomorphed pores demonstrates that melt solid textural equilibrium was probably attained only in the contact aureole the regional granulite preserves an almost unmodified reaction controlled melt distribution with little evidence for either melt solid textural equilibration or solid solid re equilibration whereas the reactioncontrolled melt distribution in the regional amphibolite facies example has been modified by a partial approach to solid solid textural equilibrium it is not clear whether the differences in dihedral angle population are due to differences in uplift and exhumation rates or due to the presence of h2o on grain boundaries

th u pb monazite geochronology of the luliang and wutai complexes constraints on the tectonothermal evolution of the trans north china orogen abstract recent lithological metamorphic and geochronological studies show that the basement of the north china craton ncc formed by collision of two discrete archean to paleoproterozoic blocks eastern and western blocks along a paleoproterozoic orogen named the trans north china orogen however the timing of the collision is controversial and post collisional exhumation has not been precisely dated this study applies the electron microprobe th u pb monazite dating technique to determine the ages of the peak metamorphic event and subsequent exhumation of the low to medium grade luliang and wutai complexes in the trans north china orogen electron microprobe th u pb monazite data for the luliang complex reveal five tho 2 pbo age ranges 1 1940 1938 ma 2 1880 1847 ma 3 1795 1755 ma 4 1720 1703 ma and 5 1648 ma of these age ranges the first four have also been recorded in the wutai complex which yields tho 2 pbo ages of 1 1930 ma 2 1838 1822 ma 3 1793 ma and 4 1719 ma the oldest age range of 1940 1930 ma is interpreted to record the widespread emplacement of mafic dikes in rocks of the luliang and wutai complexes the age range of 1882 1822 ma is in accord with the shrimp u pb ages of metamorphic zircons and mineral sm nd and 40 ar 39 ar ages obtained for other complexes in the orogen and is interpreted as the age of the major metamorphic event caused by amalgamation between the eastern and the western blocks the age range of 1795 1755 ma is consistent with emplacement of large scale unmetamorphosed mafic swarms at 1800 1765 ma interpreted as the time of post orogenic extension the 1720 1703 ma and 1648 ma ages are considered to date later multiple stages of hydrothermal alteration since monazites with such young ages only occur along fractures in older monazite grains and at the rims these new monazite tho 2 pbo ages support the tectonic model for the evolution of the north china craton that envisages discrete eastern and western blocks colliding along the trans north china orogen at 1 85 ga and then undergoing post collisional extension in the period 1795 1755 ma

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

on postglacial geoid subsidence over the equatorial oceans we develop two new spectral formalisms for the gravitationally self consistent solution of the sea level equation which governs the redistribution of glacial meltwater on a visco elastic earth the first is a purely spectral technique based on an extension of theory outlined by dahlen 1976 for determining the equilibrium oceanic tide on an elastic planet using this technique with a feasible spherical harmonic truncation level l 30 we can obtain convergence in the computed sea level variations within the degree range l 10 we also develop a second pseudospectral technique however which permits the construction of gravitationally self consistent solutions to much higher degree and order l 100 the pseudospectral formalism is employed here to develop a comprehensive physical explanation for the global pattern of present day sea level variations due to ongoing glacial isostatic adjustment in particular we focus upon a mechanism which we term equatorial ocean syphoning that acts to draw water toward the oceanic portion of the collapsing peripheral bulge that encircles previously glaciated regions the collapse of the forebulge induces a flow of water which is required to maintain hydrostatic equilibrium the syphoning mechanism dominates the relative sea level rsl variation in oceans in the far field of the ice sheets that is beyond the peripheral bulge during periods such as the interglacial of the past 4000 years during which the volume of the ice sheets has not apparently changed appreciably while at the same time isostatic adjustment persists the rsl change in the near field is in contrast dominated by the local vertical displacement of the solid surface finally comparison of gravitationally self consistent predictions of rsl change in the far field with the observational data at small pacific island sites has provided an upper bound of 1 to 2 m for the eustatic sea level rise produced by any recent last 3000 years melting of the antarctic ice sheet

a non extensive statistics of the fault population at the valles marineris extensional province mars a non extensive statistical physics approach is formulated and tested for the fault length distribution in the valles marineris extensional province mars the approach is composed of the following parts 1 the tsallis entropy 5 defined as s q k b 1 sigma w i 1 p i q q 1 2 maximization of the tsallis entropy under appropriate constraints 3 derivation of the cumulative distribution function cdf of the fault length population in testing the model a non extensive q parameter equal to 1 10 for independent non interacting faults and q 1 75 for linked faults are estimated the latter supports the conclusion that the fault system in the valles marineris extensional province mars is a sub extensive one and verifies with statistical physics terms the geological criteria introduced by schultz 2000 to classify the faults in independent and linked respectively c 2011 elsevier b v all rights reserved

structural analysis and miocene to present tectonic evolution of a lithospheric scale transcurrent lineament the sciacca fault sicilian channel central mediterranean sea abstract seismo stratigraphic and structural analysis of a large number of multichannel seismic reflection profiles acquired in the northern part of the sicilian channel allowed a 3 d reconstruction of a regional ns trending transfer zone which displays a transcurrent tectonic regime and that is of broad relevance for its seismotectonic and geodynamic implications it is constituted of two major transcurrent faults delimiting a 30 km wide mostly undeformed basin the western fault capo granitola does not show clear evidence of present day tectonic activity and toward the south it is connected with the volcanic area of the graham bank the eastern fault sciacca is structurally more complex showing active deformation at the sea floor particularly evident along the nerita bank the sciacca fault is constituted of a master and splay faults compatible with a right lateral kinematics sciacca fault is superimposed on an inherited weakness zone a mesozoic carbonate ramp which borders to the east a 2 5 km thick plio quaternary basin and that was reactivated during the pliocene a set of scaled claybox analogue models was carried out in order to better understand the tectonic processes that led to the structural setting displayed by seismic data tectonic structures and uplift subsidence patterns generated by the models are compatible with the 3 d model obtained from seismic reflection profiles the best fit between the tectonic setting deriving from the interpretation of seismic profiles and the analogue models was obtained considering a right lateral movement for the sciacca fault nevertheless the stress field in the study area derived from gps measurements does not support the present day modelled right lateral kinematics along the sciacca fault moreover seismic events along this fault show focal mechanisms with a left lateral component we ascribe the slip change along the sciacca fault from a right lateral transcurrent regime to the present day left lateral kinematics to a change of principal horizontal stress direction starting from late pliocene

statistical significance of minimum of the order parameter fluctuations of seismicity before major earthquakes in japan in a previous publication the seismicity of japan from 1 january 1984 to 11 march 2011 the time of the m9 tohoku earthquake occurrence has been analyzed in a time domain called natural time chi the order parameter of seismicity in this time domain is the variance of chi weighted for normalized energy of each earthquake it was found that the fluctuations of the order parameter of seismicity exhibit 15 distinct minima deeper than a certain threshold 1 to around 3 months before the occurrence of large earthquakes that occurred in japan during 1984 2011 six out of 15 of these minima were followed by all the shallow earthquakes of magnitude 7 6 or larger during the whole period studied here we show that the probability to achieve the latter result by chance is of the order of 10 5 this conclusion is strengthened by employing also the receiver operating characteristics technique

modern tectonic regime in the tyrrhenian area observations and models summary the rapid opening since 10 ma of the tyrrhenian sea in a context of convergence between eurasia and africa remains a puzzling geodynamic problem one of the most plausible scenarios proposed by malinverno ryan 1986 attributes extension to southward and eastward migration of the trench resulting from subduction of the african adriatic lithosphere below the european lithosphere at present subduction only continues along the calabrian arc a compilation of recent strain and stress indicators by rebai philip taboada 1992 indicates that an extensional regime still prevails in the tyrrhenian sea whereas compression dominates north and south of this area in an earlier paper bassi sabadini 1994 used a numerical model to demonstrate the necessity of a trench suction force acting along the subduction trench to produce the present extension in the tyrrhenian domain this study however did not discuss in detail the tectonic regime in the different areas composing the domain nor the match between the observations and the model in this paper we first review the constraints provided by the observations compiled by rebaiet al 1992 and by more recent measurements we then investigate how much of the observed tectonic regime can be understood in terms of plate interaction forces using thin plate models bird 1989 the geometry and heterogeneous lithospheric properties of the models are constrained by observations the best constrained boundary conditions are held constant the remaining are regarded as parameters that we tune in order to fit the observations our results indicate that the present day tectonic regime in the tyrrhenian area can be explained as a consequence of trench retreat associated with the subduction of ionian oceanic lithosphere under the calabrian arc combined with a rotation of the apennines possibly related to a rotation of the adriatic microplate this study supports therefore the model of malinverno ryan 1986 and suggests moreover that rotation of the apennines is an ongoing process which is supported by seismological and geodetic data but remains to be understood in terms of geodynamics a discrepancy between observations and models is observed in western sicily which can be attributed to modelling limitations the weak extensional activity of the corsica sardinia block however is not explained by this model

u pb and hf isotopic study of detrital zircons from the luliang khondalite north china craton and their tectonic implications two types of metasedimentary rocks occur in the trans north china orogen of the north china craton one type consists of highly metamorphosed supracrustal rocks with protoliths of mature cratonic shale called khondalites as found in the luliang complex rocks of the other type are also highly metamorphosed but less mature as represented by the wanzi supracrustal assemblage in the fuping complex u pb isotopic data for detrital zircons from khondalites show a provenance dominated by 1 9 2 1 ga palaeoproterozoic rocks these detrital zircons display a wide range of e hf values from 16 0 to 9 2 and give hf isotopic model ages mostly around 2 3 ga the high positive e hf values approach those for the depleted mantle at 2 1 ga highlighting a juvenile crustal growth event in palaeoproterozoic times hf isotopic data also imply that c 2 6 ga old crustal material was involved in the palaeoproterozoic magmatic event these data are similar to those for the khondalitic rocks from the interior of the western block of the north china craton suggesting a common provenance in contrast other metasedimentary rocks in the trans north china orogen such as the wanzi supracrustal assemblage in the fuping complex have a source region with both palaeoproterozoic and archaean rocks their detrital zircon hf isotopic data indicate reworking of old crustal material and a lack of significant juvenile palaeoproterozoic magmatic input these rocks are similar to the coevally deposited meta sedimentary rocks in the interior of the eastern block we propose that the luliang khondalites were deposited on the eastern margin of the western block in a passive continental margin environment and were thrust eastward later during collision with the eastern block other metasedimentary rocks in the trans north china orogen were deposited on the western margin of the eastern block in a continental arc environment our data support the eastward subduction model for the palaeoproterozoic tectonic evolution of the north china craton

correction to a thin viscous sheet model for continental deformation summary the governing equation derived by england mckenzie for the deformation of a thin viscous shell contains an error we give the correct derivation here and correct those figures where the change makes a visible difference the correct results differ quantitatively from those of england mckenzie but their conclusions are not affected

metallogeny and craton destruction records from the north china craton abstract the link between metallogeny and craton destruction in the north china craton ncc remains poorly understood particularly the mechanisms within the interior of the craton in this overview we summarize the major stages in the history of formation and evolution of the ncc the spatio temporal distribution and types of major ore species as well as mantle contribution to the metallogeny in an attempt to evaluate the geodynamic settings of metallogeny and the mechanisms of formation of the ore deposits the early precambrian history of the ncc witnessed the amalgamation of micro blocks and construction of the fundamental tectonic architecture of the craton by 2 5 ga the boundaries of these micro blocks and the margins of the ncc remained as weak zones and were the principal locales along which inhomogeneous destruction of the craton occurred during later tectonothermal events these zones record the formation of orogeny related gold copper iron and titanium during the early to middle paleoproterozoic with ages ranging from 2 5 to 1 8 ma the early ordovician kimberlite and diamond mineralization at ca 480 ma the late carboniferous and early to middle permian calc alkaline i type granitoids and gold deposits of 324 300 ma and the triassic alkaline rocks and gold silver polymetallic deposits occurring along these zones and the margins of the blocks correlate with rising mantle plume southward subduction of the siberian plate and northward subduction of the yangtze plate respectively the voluminous jurassic granitoids and cretaceous intrusives carrying gold molybdenum copper lead and zinc deposits are also localized along the weak zones and block margins the concentration of most of these deposits in the eastern part of the ncc invokes correlation with lithosphere thinning associated with the westward subduction of the pacific plate although magmatism and mineralization have been recorded along the margins and few places within the interior of the ncc in the jurassic their peak occurred in the cretaceous in the eastern part of the ncc marking large scale destruction of the craton at this time the junctions of the boundaries between the micro continental blocks are characterized by extensive inhomogeneous thinning we propose that these junctions are probably for future mineral exploration targeting in the ncc

new gps constraints on the africa eurasia plate boundary zone in southern italy 1 southern italy is a key area for understanding the tectonic processes in the africa eurasia collision zone we analyze new gps measurements carried out between 1994 and 2001 the results are presented in terms of time series trajectories and velocities of crustal motion as well as a geodetic strain rate field while central italy corsica sardinia and the tyrrhenian sea move like the eurasian plate the overall motion of the sicily rift zone region matches african plate motion unexpected are the north northwest directed motions of northeastern sicily and the eolian islands most striking on the deformation field are a north south oriented compression along the northern sicilian coast compression between apulia and northwestern greece as well as extension in the sicily rift zone and the interior of sicily

shrimp u pb zircon geochronology of palaeoproterozoic metasedimentary rocks in the north china craton evidence for a major late palaeoproterozoic tectonothermal event abstract although metasedimentary successions are widely distributed across the north china craton those of palaeoproterozoic age are restricted to three orogenic belts namely the trans north china orogen the khondalite belt and the jiao liao ji belt prior to this work some of those successions were considered to be archaean in age the palaeoproterozoic metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 0 to 2 1 ga with the majority recording an age between 2 3 and 2 0 ga this latter group define a series of magmatic events that occurred between formation of the archaean basement and deposition of the metasedimentary rock protoliths the metasedimentary rocks occur as two associations older volcano sedimentary units that formed between 2 37 and 2 0 ma and younger sedimentary units that formed mainly between 2 0 and 1 88 ga all these rock associations were then subjected to metamorphism during the late palaeoproterozoic 1 88 and 1 85 ga tectonothermal event named the luliang movement in early chinese literature which was a continent continent collision that led to the amalgamation of the north china craton

th u pb monazite ages from al mg rich metapelites rauer group east antarctica the age of high temperature granulite facies metamorphism 800 850 c in the rauer group prydz bay east antarctica is relevant for establishing the metamorphic and temporal architecture of the prydz bay mobile belt monazites within al mg rich granulite facies metapelites give an overall tanh estimated pan african age of 511 4 ma 2r using in situ electron microprobe based th u pb chronology consistent with existing u pb zircon geochronology from the rauer group and prydz bay monazite occurs primarily within cordierite bearing coronae and symplectic min eral reaction textures and also within biotite pan african granulite facies metamorphism is preferred as responsible for the development of the cordierite bearing microstructures and probably peak coarse grained assemblages constrained using an integrated geologic geochronologic and metamorphic framework thus pan african granulite facies metamorphism affected the rauer group within the prydz bay mobile belt moreover integrated monazite geochronology may be used to decipher the temporal metamorphic histories of potentially complex high temperature terrains

crustal velocity field of western europe from permanent gps array solutions 1996 2001 we derive a new geodetic velocity field for western europe and the western mediterranean by rigorously combining 1 a selection of 36 itrf2000 sites 2 a solution from a subset of sites of the european permanent gps network euref epn 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy of the order of i mm yr 1 or better its analysis shows that central europe defined as east of the rhine graben and north of the alps and the carpathians behaves rigidly at a 0 4 mm yr 1 level and defines a stable europe reference frame in that reference frame we find no significant motion at sites located west of the rhine graben and on the iberian peninsula which sets an upper bound of 0 6 mm yr 1 on horizontal motion across the rhine graben and the pyrenees we find that the current strain pattern in the western alps combines e w extension and right lateral shear we confirm a counterclockwise rotation of the adriatic microplate which appears to control the strain pattern along its boundaries in the friuli area the alps and the apennines our results also suggest that the africa eurasia plate motion in the western mediterranean may be 40 50 per cent slower that the nuvel1a plate motion model and rotated 20 30 counterclockwise

tectonothermal history of the basement rocks in the western zone of the north china craton and its tectonic implications the basement of the north china craton can be divided into the eastern central and western zones based on lithological structural metamorphic and geochronological data the western zone comprises two different petrotectonic units archaean tonalitic trondhjemitic granodioritic ttg grey gneisses and metamorphic mafic rocks and palaeoproterozoic khondalite series the former is characterized by isobaric cooling ibc type anticlockwise p t paths in the north northwestern part of the zone and near isothermal decompression itd type clockwise p t paths in the eastern part adjacent to the central zone on the other hand the tectonothermal evolution of palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling defining clockwise p t paths the archaean ttg gneisses and associated mafic rocks with anticlockwise metamorphic p t paths reflects an origin related to underplating and intrusion of mantle derived magmas which may be derived from mantle plumes they represent a late archaean continental block in the western part of the north china craton the palaeoproterozoic khondalite series rocks represent passive continental margin deposits they were metamorphosed and deformed in the late palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the north china craton the itd type clockwise p t t paths of the palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the north china craton at c 1800 ma

microprobe monazite geochronology putting absolute time into microstructural analysis abstract high resolution compositional mapping and dating of monazite on the electron microprobe is a powerful addition to microstructural analysis and an increasingly important tool for tectonic analysis microprobe monazite geochronology can be an efficient reconnaissance tool for evaluating metamorphic and deformational age domains but more importantly its in situ nature and high spatial resolution offer an entirely new level of structurally and texturally specific geochronologic data that can be used to put absolute time constraints on p t d paths constrain the rates of metamorphic and deformational processes and provide new links between metamorphism and deformation microprobe geochronology is particularly applicable to three persistent microstructural microtextural problem areas 1 constraining the chronology of metamorphic assemblages 2 constraining the timing of deformational fabrics and 3 interpreting other geochronological results although some monazite generations can be directly tied to metamorphism or deformation at present the most common constraints rely on monazite inclusion relations in porphyroblasts that in turn can be tied to the deformation and or metamorphic history microprobe mapping and dating allow geochronology to be incorporated into the routine microstructural analytical process resulting in a new level of integration of time t into p t d histories

average strain rate in the italian crust inferred from a permanent gps network ii strain rate versus seismicity and structural geology summary high quality weekly solutions for the coordinates of 45 permanent gps stations spanning 1 6 years and covering the alpine mediterranean area are used to estimate a horizontal velocity field aligned with the itrf2000 velocity datum after subtracting model velocities for the eurasian plate we show that the residual velocity field north of the apennines in the adriatic dinaric region describes a nne trending tectonic flow with a negative velocity gradient from 6 mm yr 1 ne of the apennines to virtually zero ne of the dinarids in the calabria region we observe a divergent pattern with nnw orientation which turns to west as one moves north towards tuscany very small residual velocities are observed for stations in the sardinia corsica block spain southern france and north of the alps this regional pattern of velocities defines areas of intraplate strain on the basis of good station coverage and of a strain rate value above a threshold we define five provinces calabria central apennines both in the extensional regime and north adriatic eastern alps and south adriatic under compression we show that the orientations of the principal strain rate axes agree with the stress pattern that is inferred from local seismicity a comparison of the geodetically determined strain rate with the strain rate associated with the seismic moment of earthquakes in the past 30 yr shows that each province may differ considerably from the others in the amount of seismic moment that is accommodated by surface strain for example the umbria seismic sequence of 1997 seems to have released a seismic moment that was not exceptionally large but concentrated over a short time interval so that the equivalent coseismic strain rate was larger than the value observed geodetically on average depending on the assumptions on the seismogenic volume and time span 70 100 per cent of the surface strain seems to be accommodated by the release of seismic moment in the upper italian crust

africa eurasia kinematics main constraints and uncertainties abstract it is widely believed that the africa eurasian relative motion in the mediterranean region is oriented se nw to s n this result has been deduced from the analysis of north atlantic kinematic data by assuming that eurasia is a unique coherent plate from the north atlantic ridges to the pacific trenches however this assumption cannot easily account for the not negligible tectonic activity inside and around western europe rhine graben system pyrenees and off shore portugal this paper shows that if one allows western europe to move independently from main eurasia the kinematic indicators in the north atlantic do not exclude other kinematic solutions which are significantly different from those currently accepted in particular it is demonstrated that a ssw nne to sw ne trending africa eurasia convergence beside allowing plausible explanations of major post tortonian deformation events in the central mediterranean region can fit north atlantic data within experimental errors

pb diffusion in monazite a combined rbs sims study abstract we report measurements of pb diffusion in both synthetic cepo4 and natural monazites run under dry 1 atm conditions powdered mixtures of prereacted cepo4 and pbzro3 were used as the source of pb diffusant for in diffusion experiments conducted in sealed pt capsules for durations ranging from a few hours to several weeks following the diffusion anneals pb concentration profiles were measured with rutherford backscattering spectroscopy rbs and supplemented by measurements with secondary ion mass spectrometry sims in order to evaluate potential compositional effects upon pb diffusivity and simulate diffusional pb loss that might occur in natural systems we also conducted out diffusion experiments on pb bearing natural monazites in these experiments monazite grains were surrounded by a synthetic zircon powder to act as a sink monazites from these experiments were analyzed with sims over the temperature range 1100 to 1350 c the arrhenius relation determined for in diffusion experiments on synthetic monazite is given by d 0 94 exp 592 39 kj mol 1 rt m 2 s 1 diffusivities for synthetic and natural monazites are similar as are results of measurements made on the same samples using both rbs and sims the activation energy for pb diffusion we determined is more than three times that for natural monazite reported previously with pb diffusivities at

u pb and hf isotopic study of detrital zircons from the wulashan khondalites constraints on the evolution of the ordos terrane western block of the north china craton abstract detrital zircons from the wulashan khondalites in the ordos terrane western block of the north china craton give u pb ages between 1 84 and 2 32 ga showing that their provenance was dominated by paleoproterozoic rocks much younger than those exposed in the eastern block these zircons have oscillatory growth zoning and possess e hf values between 8 and 9 suggesting derivation of their precursor magmas from old crust and juvenile materials from the mantle the lowest e hf values of zircons with different ages give a line that intersects the depleted mantle line at about 2 6 ga in a e hf vs time diagram this may imply that the precursor magma source in the deep level of the crust was largely separated from the mantle 2 6 ga ago and therefore 2 6 ga may be an important crustal formation period for the terrane one khondalite sample has detrital zircons with a single age population at 2 0 ga and positive e hf values from 1 to 9 clearly recording the significant addition of juvenile materials at 2 0 ga in the source region this may inspire us to seek whether there was a connection between a mantle superevent and the formation of columbia supercontinent data of this study exclusively demonstrate that the ordos terrane was developed independently from the eastern block until assembly of the columbia supercontinent therefore tectonic models involving that the whole north china craton was cratonized 2 5 ga ago should be dismissed

the precambrian khondalite belt in the daqingshan area north china craton evidence for multiple metamorphic events in the palaeoproterozoic era high grade pelitic metasedimentary rocks khondalites are widely distributed in the northwestern part of the north china craton and were named the khondalite belt prior to the application of zircon geochronology a stratigraphic division of the supracrustal rocks into several groups was established using interpretative field geology we report here shrimp u pb zircon ages and hf isotope data on metamorphosed sedimentary and magmatic rocks at daqingshan a typical area of the khondalite belt the main conclusions are as follows 1 the early precambrian supracrustal rocks belong to three sequences a 2 56 2 51 ga supracrustal unit the previous sanggan group a 2 51 2 45 ga supracrustal unit a portion of the previous upper wulashan group and a 2 0 1 95 ga supracrustal unit including the previous lower wulashan group a portion of original upper wulashan group and the original meidaizhao group the units thus do not represent a true stratigraphy 2 strong tectono thermal events occurred during the late neoarchaean to late palaeoproterozoic with four episodes recognized 2 6 2 5 2 45 2 37 2 3 2 0 and 1 95 1 85 ga with the latest event being consistent with the assembly of the palaeoproterozoic supercontinent columbia 3 during the late neoarchaean to late palaeoproterozoic 2 55 2 5 2 37 and 2 06 ga juvenile mantle derived material was added to the crust

metamorphism of diverse basement gneisses of the ordos basin record of multistage paleoproterozoic orogenesis and constraints on the evolution of the western north china craton abstract although it remains deeply hidden and largely enigmatic the basement of the ordos basin has played a pivotal role in the evolution of the western part of north china craton diverse gneiss samples collected from boreholes advanced into the deep basement of the ordos basin are investigated by integrating petrography phase equilibria modeling and geochronology the results reveal the basement gneisses have different protoliths with ages extending from the late archean to the paleoproterozoic medium to low pressure metamorphism from amphibolite to granulite facies 4 7 7 3 kbar and 740 810 c is constrained for the basement gneisses using phase equilibrium modeling in the mnnckfmashto system evidence is provided of metamorphic monazite growing later than zircon in the same basement gneisses and multi stage paleoproterozoic orogenesis is delineated using metamorphic zircon and monazite ages from the basement gneisses the basement gneisses from most boreholes across the basin are comparable to those in adjoining paleoproterozoic belts in terms of metamorphic and geochronological characteristics the results of the study suggest in combination with previous data that a large area of the basement was involved in the paleoproterozoic orogenis the northern part of the ordos basin basement is closely associated with the khondalite belt

incipient extension along the active convergent margin of nubia in sicily italy cefalu etna seismic zone 1 recent geodetic data are compatible with nne ssw tectonic extension at a rate of 5 mm yr in sicily southern italy within a broader region of net active compression along the nubian plate margin northern africa the structures that accommodate such extensional regime and its cause are still unknown from field structural surveys and seismological analyses the geometry kinematics structural architecture and seismic potential of an extensional seismic zone linking cefalu and mount etna in central eastern sicily are defined the zone includes high angle wnw striking normal and right lateral strike slip faults and subordinate north and nne striking strike slip faults either right or left lateral the occurrence of small discontinuous faults and the absence of related depressions and sedimentary basins suggest that the extensional regime is still in an incipient stage the ongoing seismic activity possibly reactivates preexisting faults instrumentally and historically recorded earthquakes are lower than about 6 in magnitude and destructive events are historically unknown since at least 1300 a d this apparent upper bound of earthquake magnitudes is consistent with the maximum magnitude values estimated from the length of the longest mapped faults and sources of seismic swarms which all together suggest a value between 6 and 6 5 as the maximum expected magnitude that can be proposed at the present stage of investigation for earthquakes in the study area lateral extension on preexisting faults and upwelling of melt mantle material beneath mount etna are considered viable processes to explain at least in part the active extensional tectonics along the cefalu etna seismic zone strike slip seismic faulting beneath mount etna may be part of a previously proposed diffuse transfer zone affecting northeastern sicily and including the tindari fault

p t t evolution of pelitic gneiss from the basement underlying the northwestern ordos basin north china craton and the tectonic implications abstract using petrography phase equilibria modeling and in situ u th pb monazite geochronology we show that pelitic gneiss from close to the bottom of the qitan1 borehole in the northwest of the ordos basin records a four stage metamorphic evolution the m1 m3 stages which were suprasolidus are represented by rutile relicts in the matrix and biotite k feldspar plagioclase sillimanite quartz inclusions in the cores of garnet porphyroblasts m1 inclusion free mantles on garnet with ilmenite partially replacing rutile and biotite k feldspar plagioclase sillimanite quartz in the matrix m2 and the appearance of cordierite in the assemblage biotite k feldspar plagioclase sillimanite ilmenite quartz m3 the final subsolidus mineral assemblage is garnet biotite k feldspar plagioclase sillimanite cordierite ilmenite quartz m4 the p t conditions for the mineral assemblage evolution m1 m4 are constrained by a p t pseudosection constructed in the na 2 o cao k 2 o feo mgo al 2 o 3 sio 2 h 2 o tio 2 o 2 chemical system the p t t path is clockwise involving slight heating during near isothermal decompression from 8 8 kbar at 769 c to 5 5 kbar at 785 c followed by close to isobaric cooling across the solidus two cores of monazite and three unzoned grains that have similar populations of dates yield robust ages of 1 96 1 94 ga interpreted to date the timing of late prograde to peak metamorphism m1 m2 in addition one rim and two unzoned monazite grains with similar populations of dates yield robust ages of 1 90 1 88 ga interpreted to date the timing of post decompression slow cooling across the solidus m3 m4 on the basis of these results the pelitic gneiss is interpreted to have formed by crustal thickening m1 during collision between the yinshan and ordos terranes the latter with the khondalite belt protoliths along its northern margin present co ordinates this collision culminated at ca 1 95 ga and was followed by decompression m2 m3 and slow cooling m4 to ca 1 89 ga during post collisional extension the similarity between the p t t path determined in this study and those from hp mp granulites in the khondalite belt confirms that they experienced a common tectono metamorphic history the p t t path records an evolution from an apparent thermal gradient of 75 c kbar at peak pressure to 150 c kbar after decompression together with the occurrence of mid paleoproterozoic magmatism in the basement of the ordos basin these features indicate that the ordos terrane was the upper plate at a convergent margin with the khondalite belt representing the forearc sediments along its northern edge collision with the yinshan terrane part of the subducting plate led to shallow slab breakoff and the development of a two sided hot collision and formation of a wide plateau like hot orogen similar to those in the numerical models of sizova et al 2014

is the ordos block archean or paleoproterozoic in age implications for the precambrian evolution of the north china craton the ordos block is a large but poorly exposed crustal segment in the western part of the north china craton little is known about its precambrian basement rocks and their evolution because of an extensive cover by younger sedimentary rocks we report shrimp zircon ages and hf in zircon isotopic compositions for five samples recovered from drill holes that penetrated into the ordos basement based on these data two age groups of rocks can be distinguished an early paleoproterozoic group that is represented by one sample from the northern margin of the ordos block and a late or middle late paleoproterozoic group consisting of the remaining four samples the early paleoproterozoic sample contains zircon cores and metamorphic rims with ages of 2 4 ga and 2 28 ga respectively the cores have ehf t values of 8 8 to 6 2 and hf crustal model ages of 2606 to 3221 ma the remaining rocks of late or middle late paleoproterozoic age contain zircons that may also show a core rim structure but with the cores having ages of 2 08 ga and the metamorphic rims recording ages of 1 9 ga the zircon cores have ehf t values of 9 1 to 10 1 and hf crustal model ages of 2039 to 3068 ma combined with data from earlier studies we draw the conclusion that late paleoproterozoic metasedimentary rocks are widespread in the ordos basement there is no evidence from our samples of an archean component and this calls into question the prevailing view that the ordos basement is an archean cratonic block the fact that the ordos basement was involved in a widespread late paleoproterozoic tectono thermal event indicates that most current models for the tectonic evolution of the western portion of the north china craton need to be revised

deflation acting on pantelleria island sicily channel inferred through geodetic data abstract pantelleria is a volcanic island situated at the centre of the sicily channel continental rift since 1980 the island has been monitored by geodetic techniques electro optical distance measurements edm and levelling and gravimetry after more than 10 years the edm network was re measured in 1995 and successively it has been improved and measured also with global position system gps techniques it has therefore been possible to carry out a long term analysis 1980 1996 of the deformation pattern the levelling in the 1980 1996 period revealed a marked lowering of the central southern part of the island with respect to the northern sector the horizontal edm measurements all prove to be in contraction and suggest that a deflation is ongoing in the central southern part the effects of areal contraction and lowering are interpreted as being due to the volcanic field which appears to predominate over possible stretching induced by the sicily channel dynamics we modelled the horizontal and vertical changes accumulated over 16 years using a 3d ellipsoidal depressuring model which indicates a ca 5 km deep source located under the area within the most recent caldera this model could explain a short term tens of years acting deflation we also propose an interpretive framework in the case where the deflation is acting over a long period thousands of years in this case the deflation is interpreted as readjustment following the loss of mass occurring with recent volcanism 18 3 kyr

temperatures of granulite facies metamorphism constraints from experimental phase equilibria and thermobarometry corrected for retrograde exchange this study assesses temperatures of formation of common granulites by combining experimental constraints on the p t stability of granulite facies mineral associations with a garnet orthopyroxene grt opx thermobarometry scheme based on al solubility in opx corrected for late fe mg exchange we applied this scheme to 414 granulites of mafic intermediate and aluminous bulk compositions our findings suggest that granulites are much hotter than traditionally assumed and that the p t conditions of the amphibolite granulite transition portrayed in current petrology textbooks are significant underestimates by over 100 c for aluminous and intermediate granulites mean corrected temperatures based on our method are 890 17 and 841 11 c respectively uncertainties reported as 95 confidence limits on the mean consistent with minimum temperatures for orthopyroxene production by fluid absent partial melting in these bulk compositions in contrast mean temperatures based on grt opx fe mg exchange equilibria using the same thermodynamic data are 732 22 and 723 11 c respectively well below the minimum temperatures for opx stability for mafic granulites the mean corrected temperature using our method is 816 12 c similar to the mean temperature of 793 13 c from fe mg exchange reasons for the differences between the mafic granulites and aluminous intermediate granulites are unclear but may be due to the lower al concentrations in opx in the mafic rocks and possible deficiencies in the thermodynamic modelling of these low concentrations we discuss a number of well known granulite terrains in the context of our findings including the adirondacks the acadian granulites of new england the incipient charnockites of southern india and sri lanka and the kerala khondalite belt our findings carry implications for thermotectonic models of granulite formation a computer program to perform our thermobarometry calculations rclc is available from the journal of petrology website at http www petrology oupjournals org or from the authors at http www geo ucalgary ca pattison drm pattison rclc htm

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

single zircon grains record two paleoproterozoic collisional events in the north china craton abstract the western block of the north china craton consists of the yinshan block in the north and the ordos block in the south which were amalgamated along the east west trending khondalite belt at 1 95 ga the western block then collided with the eastern block to form the coherent basement of the north china craton along the north south trending trans north china orogen at 1 85 ga the huaian complex a high grade terrrane located at the conjunction of the khondalite belt and trans north china orogen records metamorphic events associated with both collisions the complex consists of lithologies from both the khondalite belt and trans north china orogen of which the former consist of graphite garnet sillimanite gneiss garnet quartzite felsic paragneiss calc silicate rock and marble together called the khondalite series zircons in the graphite garnet sillimanite gneiss can be divided into three types 1 spherical grains without internal structures 2 grains with a core and rim structure and 3 grains with a dark core surrounded by double rims except for the dark core in type 3 all other types of zircon domains are structureless and highly luminescent with very low th u ratios typical of a metamorphic origin analyses on the cores of type 2 and the inner rims of type 3 from two samples yield upper intercept ages of 1946 26 and 1947 22 ma similar to previously determined metamorphic ages from the khondalite belt and thus interpreted as the time of collision between the yinshan and ordos blocks analyses on type 1 zircons rims of type 2 and the outer rims of type 3 from the same two samples give ages of 1850 15 and 1857 16 ma interpreted as the time of collision between the eastern and western blocks thus zircons in the graphite garnet sillimanite gneiss of the huaian complex record both of the paleoproterozoic collisional events in the north china craton

a non extensive approach in investigating the seismicity of l aquila area central italy struck by the 6 april 2009 earthquake ml 5 8 terra nova 00 1 7 2009 abstract using the non extensive statistics the analysis of the magnitude distribution of the 2005 2009 seismicity of l aquila area central italy struck by a strong earthquake ml 5 8 on 6 april 2009 1 32 utc was performed this was the strongest event of the sequence the analysis of the frequency magnitude distribution of three time intervals 1 from 16 april 2005 to 30 march 2009 2 from 30 march 2009 to 6 april 2009 and 3 from 6 april 2009 to 1 july 2009 reveals that the non extensivity parameter q increases in the seismic interval 2 before the occurrence of the strongest l aquila event indicating an increase in the degree of out of equilibrium state before the occurrence of the strongest event

structure and deformation processes in the strait of sicily rift zone abstract the strait of sicily rift zone ssrz is a young tectonic feature early pliocenerecent cutting across the pelagian sea it is characterized by a thin continental type crust which progressively thickens towards the african continental margin and beneath the sicilian chain geophysical data available for the whole area show that extensional faulting is active in many places along structures trending roughly nnw sse but that the dominant mode of deformation at a regional scale can be best described in terms of strike slip tectonics strike slip faults trending nw se are seismically documented west of the island of pantelleria in the eastern sector of the malta graben and along the southern border of the medina graben similar features have also been mapped on land in malta and pantelleria kinematic analysis of these structures suggest that the ssrz cannot be considered as a classical intracontinental rift because the deformation does not appear to be dominated by a generalized thermal instability but rather by compressive stresses in a transcurrent tectonic regime therefore an alternative model which accounts for the activation of large scale right lateral strike slip faults seems to be more suitable within this main dextral shear zone the progressive development of pull apart basins could be responsible for the incipient separation of the sicilian microplate from the african continent and for the thinning of the crust and the associated volcanic activity of the northwestern sector of the ssrz

crustal motion along the eurasia nubia plate boundary in the calabrian arc and sicily and active extension in the messina straits from gps measurements 1 we investigate crustal deformation along the eurasia nubia plate boundary in calabria and sicily revealed by the gps velocity field obtained by the combination of continuous site velocities with previous results from episodic campaigns we recognize two distinct crustal domains characterized by different motions and styles of deformation convergence in sicily is taken up by crustal shortening along the former tyrrhenian back arc passive margin in agreement with seismological data and geological evidence of recent cessation of deformation along the plio pleistocene subduction front the analysis of the gps data and the consistency between earthquake slip vectors and convergence direction suggest that eu nu convergence in sicily does not require intermediate crustal blocks significant eurasia 3 mm yr to nne and nubia fixed 5 mm yr to ese residual velocities in calabria suggest instead the presence of an intermediate crustal block which can be interpreted as a forearc sliver or as an independent ionian block according to the first hypothesis subduction is still active in the ionian wedge although we find no evidence for active back arc spreading in the tyrrhenian sea the n115 e oriented sicily calabria gps relative motion is consistent with the extension observed during the 1908 mw 7 1 messina earthquake we suggest that up to 3 mm yr 80 of this estimated relative motion between sicily and the calabrian arc may be taken up in the messina straits

a spectral formalism for computing three dimensional deformations due to surface loads 2 present day glacial isostatic adjustment using a spherically symmetric self gravitating linear viscoelastic earth model we predict present day three dimensional surface deformation rates and baseline evolutions arising as a consequence of the late pleistocene glacial cycles in general we use realistic models for the space time geometry of the final late pleistocene deglaciation event and incorporate a gravitationally self consistent ocean meltwater redistribution the predictions of horizontal velocity presented herein differ significantly in both their amplitude and their spatial variation from those presented in an earlier analysis of others which adopted simplified models of both the late pleistocene ice history and the earth rheology an important characteristic of our predicted velocity fields is that the melting of the laurentide ice sheet over canada is capable of contributing appreciably to the adjustment in europe the sensitivity of the predictions to variations in mantle rheology is investigated by considering a number of different earth models and by computing appropriate frechet kernels these calculations suggest that the sensitivity of the deformations to the earth s rheology is significant and strongly dependent on the location of the site relative to the ancient ice sheet the effects on the predictions of three dimensional deformation rates of altering the ice history or adopting approximate models for the ocean meltwater redistribution have also been considered and found to be important the former especially so finally for a suite of earth models we provide predictions of the velocity of a number of baselines in north america and europe we find that in general both radial and tangential motions contribute significantly to baseline length changes and that these contributions are a strong function of the earth model we have furthermore found a set of earth models which together with the ice 3g deglaciation chronology produce predictions of baseline length changes that are consistent with very long baseline interferometry measurements of baselines within europe

an effective geochemical method to identify provenance from sources with similar geology a case study from ordos basin china abstract rare earth elements as the most resistant elements have been widely used to determine sediment provenance however yin mountains and qinling orogen the two main source terrains of the ordos basin both dominated by felsic rocks and experienced passive continental margin settings and active margin setting from the middle proterozoic to the tertiary without strongly contrasting geological settings rees distribution pattern alone and these related discrimination diagrams are inadequate to distinguish both nevertheless the rees abundance of mudstones solely supplied by each source terrain vary distinctly moreover the total rees contents of shales with the same provenance increase roughly with increasing cia indices mudstones supplied by yin mountains are significantly more enriched in rees average 309 4 ppm but yield lower cia indices average 79 6 while those sourced from qinling orogen yield lower rees content average 135 6 ppm but higher cia value average 90 1 considering the particular situation we combine cia with the total ree content rees to provide new insights into sediment provenance identification and effectively distinguish the two source regions in ordos basin

microblock amalgamation in the north china craton evidence from neoarchaean magmatic suite in the western margin of the jiaoliao block abstract the archaean earth is considered to have been characterized by microcontinents that formed dominantly through the accretion of oceanic arcs and plateaus the north china craton ncc provides a typical case where at least seven ancient microcontinental nuclei with distinct lithological features and independent tectonic histories were amalgamated into the cratonic framework at the end of the archaean here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks the jiaoliao block that forms part of the composite eastern block of the ncc we present petrological geochemical and zircon u pb geochronological data from the taipingzhai charnockite suite and associated amphibolites metagabbros and orthogneisses from the qianxi complex geochemically the rocks show a wide range of sio 2 charnockite suite 52 57 75 50 wt metagabbro 43 71 wt amphibolite 50 24 wt garnet bearing biotite 63 73 wt and mgo charnockite suite 0 89 5 01 wt metagabbro 3 99 wt amphibolite 6 23 wt garnet bearing biotite 2 08 wt the composition of the felsic units straddle from diorite through syeno diorite to granite with both alkalic and subalkalic affinity with dominantly magnesian composition and arc related features their immobile trace element relationships suggest calc alkaline affinity they show positive pb ba la nd and gd and negative nb ta sr th and ti anomalies with slightly negative anomalies of ce and y attesting to arc related features in tectonic classification diagrams the rocks plot in the vag syn colg field or the vag area suggesting subduction related origin the dominant population of zircons in all these rocks displays magmatic crystallization features including high th u values with core rims textures indicating subsequent thermal events the zircon u pb data yield upper intercept ages of 2587 10 ma to 2543 17 ma and 207 pb 206 pb mean ages of 2578 7 3 ma to 2536 8 ma for the charnockite suite marking the timing of emplacement of the arc magmas the overgrowth rims as well as discrete neoformed grains are interpreted as dating subsequent metamorphism and yield 207 pb 206 pb ages between 2533 ma to 2490 ma zircons in the metagabbro preserve upper intercept ages of 2556 20 ma representing the crystallization age of this rock the younger ages of 2449 58 ma upper intercept age and 1845 25 ma 207 pb 206 pb spot age are interpreted to represent subsequent multiple thermal events in this area zircons in the amphibolite preserve the 207 pb 206 pb mean age of 2539 9 ma representing the crystallization age of this rock the garnet bearing biotite gneiss shows an upper intercept age of 2562 10 ma mswd 0 66 n 36 and the 207 pb 206 pb mean age of 2561 9 ma mswd 0 63 n 33 which is taken to represent the crystallization age of this rock some inherited zircons are also identified with 207 pb 206 pb ages of 2664 26 ma and 2628 26 ma zircon lu hf data show dominantly positive ehf t values and combined with crustal residence ages the results suggest mesoarchean to neoarchean juvenile crust formation in the ncc we interpret the data presented here to represent a phase of major late neoarchaean arc magmatism along the western margin of the jiaoliao block related to the birth of microcontinental nuclei within the ncc our data suggest that the western and eastern blocks might not have existed as discrete crustal blocks and that the construction of the ncc is a result of the assembly of several microblocks or terranes at the end of archaean similar archean cratonic nuclei in other regions of the world might have formed part of a primitive supercontinent in the early earth

seismic potential of southern italy abstract to improve estimates of the long term average seismic potential of the slowly straining south central mediterranean plate boundary zone we integrate constraints on tectonic style and deformation rates from geodetic and geologic data with the traditional constraints from seismicity catalogs we express seismic potential long term average earthquake recurrence rates as a function of magnitude in the form of truncated gutenberg richter distributions for seven seismotectonic source zones seismic coupling seems to be large or even complete in most zones an exception is the southern tyrrhenian thrust zone where most of the african european convergence is accommodated here aseismic deformation is estimated to range from at least 25 along the western part to almost 100 aseismic slip around the aeolian islands even so seismic potential of this zone has previously been significantly underestimated due to the low levels of recorded past seismicity by contrast the series of 19 m6 7 earthquakes that hit calabria in the 18th and 19th century released tectonic strain rates accumulated over time spans up to several times the catalog duration and seismic potential is revised downward the southern tyrrhenian thrust zone and the extensional calabrian faults as well as the northeastern sicilian transtensional zone between them which includes the messina straits where a destructive m7 event occurred in 1908 all have a similar seismic potential with minimum recurrence times of m 6 5 of 150 220 years this potential is lower than that of the southern apennines m 6 5 recurring every 60 to 140 years but higher than that of southeastern sicily minimum m 6 5 recurrence times of 400 years the high seismicity levels recorded in southeastern sicily indicate some clustering and are most compatible with a tectonic scenario where the ionian deforms internally and motions at the calabrian trench are small the estimated seismic potential for the calabrian trench and central and western sicily are the lowest minimum m 6 5 recurrence times of 550 800 years most zones are probably capable of generating earthquakes up to magnitudes 7 7 5 with the exception of central and western sicily where maximum events sizes most likely do not exceed 7

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

the signatures of tectonics and glacial isostatic adjustment revealed by the strain rate in europe summary tectonics and glacial isostatic adjustment gia are simultaneously taken into account in order to quantitatively define their role in crustal deformation in europe a spherical finiteelement model based on the thin viscous shell approach and suitable for predicting tectonic deformation and a spherical stratified viscoelastic earth model based on the normal mode approach to quantifying the effects of gia are used to predict intraplate deformation in europe model predictions are compared with the geodetic strain rate obtained from itrf2000 velocity solutions our results confirm that both geophysical processes influence intraplate deformation in europe with tectonics playing the leading role south of potsdam and gia being the only mechanism north of onsala both geophysical processes affect the deformation at intermediate latitudes where the contributions to the deformation coming from tectonics and gia are of the same magnitude and the combined tectonic plus gia model succeeds in reproducing the eigendirections of the local predominantly ssw nne directed compression the stiffening in the east european platform is crucial for shielding the northeastern regions from the compressional effects of africa eurasia convergence and to allow se nw directed extension in fennoscandia driven by gia

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

ground deformation of the southern sector of the aeolian islands volcanic arc from geodetic data abstract the deformation pattern and the dynamics of the southern sector of the aeolian archipelago are investigated a study on the ground deformation measured over the last 20 years in the trilateration geodetic network between the islands of vulcano and lipari has been conducted analysis of the relative displacements and the uniform strain tensor parameters as well as the comparison between areal dilatation and the vertical variations deduced by precise levelling allow distinguishing different phases associated both with the regional dynamics and the local volcanic context of the area these phases however appear to be closely interrelated the analysis of the deformation pattern allows to constrain the predominance of a roughly e w trending extension and a n s contraction at a regional scale this regime is consistent with right lateral movements along a nw se striking fault system

geodetic strain in peninsular italy between 1875 and 2001 1 we determine geodetic strain in peninsular italy by the gps reoccupation of the first order triangulation network of italy installed from 1860 the uncertainties in the original measurements about 3 ppm and the time span between the two observations imply that tectonic signals larger than about 0 03 ppm yr are resolvable along the apenninic belt where the largest earthquakes are concentrated the geodetic deformation has a clear and consistent strain pattern between adjacent regions well above the uncertainties and shows a pervasive ne sw extension along the tyrrhenian and adriatic coasts the geodetic signal is not homogeneous and is comparable with the uncertainty in the original measurements seismic deformation calculated over the same time interval agrees well with estimated extensional direction but the magnitudes of geodetic and seismic strain differ suggesting that in part of the apennines significant strain accumulation over the past 130 years may not have been released in earthquakes

discovery of neoarchean suprasubduction zone ophiolite suite from yishui complex in the north china craton abstract the archean tectonic realm of the north china craton ncc is considered in recent models as a collage of several microblocks which were amalgamated along zones of ocean closure during late neoarchean here we report the finding of a dismembered ophiolite suite from the southern margin of the jiaoliao microblock in the interior of the unified eastern block of the ncc the suite is composed of lherzolite pyroxenite noritic and hornblende gabbro and hornblendite intruded by veins and sheets of leuco granite together with transposed layers and bands of metavolcanics and amphibolites banded iron formation bif and diabase dykes in the adjacent locations the yishui complex corresponds well with a dismembered suprasubduction zone ophiolite suite clinopyroxene in the pyroxenite and gabbroic rocks is mg rich and range in composition from augite to diopside among orthopyroxenes those in lherzolite show the highest xmg of 0 84 0 85 plagioclase in hornblende gabbro shows high anorthite content an50 64 calcic amphiboles in the gabbroic rocks range in composition from ferropargasite to ferro edenite edenite and pargasite spinel inclusions in lherzolite are cr rich magnesiospinel geochemically the mafic rocks from yishui complex show subalkaline basaltic source whereas the granitoids show volcanic arc affinity the hornblende gabbro and gabbro lherzolite and hornblendite show compositional similarity to e morb and n morb respectively the lherzolite and hornblendite possess arc related ultramafic cumulate nature with overall features straddling the fields of iat and iat morb the geochemical features are consistent with evolution in a suprasubduction regime with no significant crustal contamination the majority of zircon grains in the yishui suite exhibit magmatic texture and high th u ratios zircon grains from hornblendite define 207pb 206pb upper intercept age of 2538 30 ma zircons from the granite show ages of 2538 16 ma and 2503 21 ma and those from the gabbros yield ages of 2503 16 ma and 2495 10 ma the well defined major age peak at 2500 ma is broadly coeval with neoarchean ages reported from the microblocks in the north china craton the zircon lu hf data from the yishui suite display ehf t values between 2 5 and 5 0 with corresponding model ages suggesting magma derivation from neoarchean juvenile sources together with limited reworked paleo mesoarchean crustal components our study is the first report of neoarchean suprasubduction type ophiolites from a locality far from the margins of the major crustal blocks and suture zones in the ncc and strengthens the concept that the craton is a mosaic of several microblocks with intervening oceans that closed along multiple subduction zones we envisage that the amalgamation between the xuhuai and the jiaoliao microblocks resulted in the accretion of the yishui suprasubduction zone ophiolitic assemblages onto the southern margin of the jiaoliao microblock the neoarchean microblock amalgamation in the north china craton provides new insights into continental growth in the early earth and confirms that modern style plate tectonics might have been initiated early in the history of our planet

on the post 25 ma geodynamic evolution of the western mediterranean during the neogene and quaternary western mediterranean geodynamics were dominated by the eastward migration of the apenninic arc and associated back arc basins the migration was controlled by retreat of the apenninic slab and was associated with boudinage of the lithosphere in the back arc area palaeo reconstruction of the kinematics of the arc suggests about 775 km of migration from the late oligocene to present along a transect from the gulf of lions to calabria a maximum of 135 km of n s converge occurred between africa and europe during the same time span the western mediterranean was thus mainly shaped by the migration of the slab related to west directed subduction it is hypothesized that minor n s convergence deformed the arc but was not the cause of its formation 1998 elsevier science b v all rights reserved

indenter growth in analogue models of alpine type deformation a series of analogue experiments were carried out to simulate continental convergence as seen in a profile through the central alps a rigid indenter representing the adriatic plate was driven laterally into a sand pack representing the brittle upper crust of europe detached and thickening above its subducting ductile lower crust the rigid indenter advanced at the same steady rate in each experiment but the dip of its front face was steepened in 15 increments from 15 to 90 where the rigid indenter face dipped at 45 or less a sand wedge rose and was bound by a series of forekinks that nucleated at the toe of the indenter where the face of the rigid indenter dipped 60 or more the wedge was defined by a single forekink and one or more backkinks that nucleated from a point advancing in front of the indenter toe we interpret these results as indicating that slices of the sand pack and rising wedge are transferred across kink bands to build an effective indenter with a frontal dip closer to that dictated by the changing shear strength of the sand pile which thickens vertically as it shortens laterally one of our models with a rigid indenter dipping 75 simulates most of the major structures shown in recent syntheses of surface geology and deep seismic data in the central alps without the isostatic lithospheric depression this model accounts for the late collisional stage oligocene to present complex strain and metamorphic histories in the core of the orogenic wedge the rapid rise and extrusion of small pips of alpine eclogites and the current passivity of the insubric line it also emphasizes that lateral extension along gently dipping thrusts orogen normal horizontal escape is confined to the extruded portion of the rising wedge