near real time radar interferometry of the mw 7 1 hector mine earthquake the hector mine earthquake mw 7 1 16 oc tober 1999 ruptured 45 km of previously mapped and un mapped faults in the mojave desert the ers 2 satellite imagedthemojavedeserton15septemberandagain on20 october just 4 days after the earthquake using a newly developed ground station we acquired both passes and were able to form an interferogram within 20 hours of the second overflight estimates of slip along the main rupture are 1 2 meters greater than slip derived from geological mapping the gradient of the interferometric phase reveals an inter esting pattern of triggered slip on adjacent faults as well as a 30 mm deep sink hole along interstate 40

structural and p t evolution of a major cross fold in the central zone of the limpopo high grade terrain south africa the central zone cz of the limpopo complex of southern africa is characterized by a complex deformational pattern dominated by two types of fold geometries large sheath folds and cross folds the sheath folds are steeply ssw plunging closed structures whereas the cross folds are north south oriented with near horizontal fold axes in the area south of messina this complexly folded terrain grades continuously towards the south into a crustal scale ene wsw trending ductile shear zone with moderate dip towards the wsw all sheath folds document consistent top to the ne thrust movement of high grade material the timing of this shear deformational event d and thus of the gneissic fabric s is constrained at 2 6 ga by the syntectonic emplacement throughout the cz of precursors to quartzo feldspathic gneisses singelele type gneisses cross folds deform the s fabric and are characterized by a near vertical axial planar cleavage s recent single phase pb pb dating of garnet from a metapelitic gneiss with an s fabric from one of the largest cross folds in the cz constrains the timing of the deformational d and metamorphic m event at 2 0 ga mineral chemistry for metapelites from this cross fold shows a single peak on an n mg histogram for garnet reflecting a single phase of mineral growth metapelites from this cross fold also preserve evidence for only one well developed reaction texture grt sil qtz crd this reaction is accompanied by the simultaneously operating reaction grt fsp h o bt sil qtz both these divariant reactions belong to the univariant kfmash equilibrium crd grt fsp h o bt sil qtz the progress of the two divariant retrograde reactions leads to the consumption of grt and fsp k feldspar or never occurs with both cordierite and garnet microprobe profiling coupled with calculated isopleths for bt grt and crd in divariant equilibria define a decompression cooling p t path that reflects a single m high grade metamorphic event during the evolution of the cross fold this decompression cooling p t path traverses from 780 c 5 7 kbar to 600 c 3 3 kbar

the 1997 umbria marche italy earthquake sequence a first look at the main shocks and aftershocks a long sequence of earthquakes six with magnitudes between 5 and 6 struck central italy starting on september 26 1997 causing severe damages and loss of human lives the seismogenic structure consists of a nw se elongated fault zone extending for about 40 km the focal mechanisms of the largest shocks reveal normal faulting with ne sw extension perpendicular to the trend of the apennines consistently with the quaternary tectonic setting of the internal sector of the belt and with previous earthquakes in adjacent regions preliminary data on the main shocks and aftershocks show that extension in this region of the apennines is accomplished by normal faults dipping at low angle 40 to the southwest and confined in the upper 8 km of the crust these normal faults might have reactivated thrust planes of the pliocene compressional tectonics the aftershock distribution and the damage patterns also suggest that the three main shocks ruptured distinct 5 to 15 km long fault segments adjacent and slightly offset from one another

exploitation of high density dinsar data points of the umbria marche italy 1997 seismic sequence for fault characteristics 1 high spatial resolution dinsar data for the umbria marche 1997 seismic sequence are exploited by relaxing constraints derived from datasets of different nature such as seismologically derived fault dimensions dinsar data are thus inverted for a realistic slip distribution over the faults in terms of depth distribution and roughness which allows us to relocate the main faults and to minimize the misfit between the vertical displacement pattern derived from dinsar and model predictions our analysis reveals that slip affected not only the shallowest part of the fault system but also its deepest part rupturing the whole seismogenic layer of the crust down to 10 km reaching slip values up to 30 cm at the base of the seismogenic layer misfit is reduced by a factor of two with respect to previous analyses based on a smaller number of digitized fringe points

structural geological and metamorphic significance of the kaapvaal craton limpopo belt contact abstract the hout river shear zone forms the terrane boundary between the granite greenstone terrane of the kaapvaal craton cratonic terrane and the high grade granulite terrane high grade gneiss province of the limpopo belt this structure is superimposed onto a thin skinned northward verging thrust system which exercises a significant control on the distribution of the ene wsw trending greenstone belts the hout river shear zone however dips steeply to the north and flattens out toward the south this structure was responsible for the emplacement of hot granulites against and over the cooler granite greenstone terrane and strongly influenced the metamorphic evolution of the area the shear zone acted as a conduit for infiltrating co2 rich h2o bearing fluids into still hot crust producing a retrograde isograd and associated zone of rehydration in the granulitic hanging wall of the structure retrogressed granulites in the hanging wall are characterized by fine grained kyanite as part of the retrograde assemblages while the greenstones in the footwall are characterized by coarse grained prograde kyanite the terrane boundary appears to be in thermal equlibrium with the lithologies in both the footwall and hanging wall so that tectonically mixed prograde greenstones and retrogressed granulites in and adjacent to the shear zone are apparently at a similar metamorphic grade the granulites appear to have had a hot iron effect on the cooler footwall rocks over which they have been displaced

archaean cratonization and deformation in the northern superior province canada an evaluation of plate tectonic versus vertical tectonic models abstract the archaean minto block northeastern superior province is dominated by tonalite trondhjemite enderbite pyroxene tonalite granodiorite and granite with subordinate mafic rocks and supracrustal belts the plutons have been interpreted as the batholithic roots of andean type plate margins and intra oceanic arcs existing horizontal tectonic models propose that penetrative recrystallization and transposition of older fabrics during terrane assembly at 2 77 and 2 69 ga produced a n nw tectonic grain in the douglas harbour domain northeastern minto block tonalite and trondhjemite dominate the faribault thury complex 2 87 2 73 ga and enderbite constitutes 50 100 km scale ovoid massifs troie and qimussinguat complexes 2 74 2 73 ga magmatic muscovite and epidote in tonalite trondhjemite have corroded edges against quartz plagioclase suggesting resorption during ascent of crystal charged magma foliation maps and air photo interpretation show the common development of 2 10 km scale ovoid structures throughout the douglas harbour domain outcrop and thin section scale structures imply that many plutons experienced a phase of syn magmatic deformation typically followed by high temperature sub magmatic overprints thermobarometric data for plutons indicate near solidus recrystallization at 4 6 kbar pressures the common preservation of syn magmatic fabrics in plutons of different ages seems incompatible with the origin of these fabrics through superimposed regional orogenesis the broad uniformity of intrusion ages and lithologies throughout the minto block and the rarity of shallowly dipping planar fabrics also seem inconsistent with accretion of disparate older terranes each of which should preserve distinct histories a possible alternative explanation for these features is provided by vertical tectonic models whereby buoyant felsic magmas ascended as crystal slurries while dense supracrustal rocks and solidified felsic intrusions emplaced into them subsided as cold fingers 10 20 km scale instabilities shear between upwelling and downwelling limbs would have concentrated in the weak intrusions generating steeply plunging syn magmatic fabrics and producing ductile overprints in solidified rocks

the structural framework of the southern margin of the limpopo belt south africa abstract the southern marginal zone is characterized by two prominent regional structural features i massive crustal wedges 20 km 50 km containing large oval shaped closed fold structures which are related to an early d 1 phase of deformation and which are bounded by ii major ductile shear zones that strike in a general e w direction the hout river shear zone forms the southern boundary of the southern marginal zone where granulites are juxtaposed against lower grade granite greenstones of the kaapvaal craton this fault system also acted as the sole thrust for the other high grade shear zones in the southern marginal zone and played a major role in the development of the zone of retrogression and the establishment of the orthoamphibole isograd in the southern marginal zone the hout river shear zone and related faults within the southern marginal zone clearly post date d 1 and a period of peak metamorphism m 1 they are composite structures showing dominantly reverse sense displacements and are responsible for the emplacement of the granulite terrane over and onto the kaapvaal craton in contrast to these older structures are the reactivated shear zones these structures clearly cross cut and displace the high grade shear zones in the southern marginal zone as well as the retrograde orthoamphibole isograd the fact that the hout river and related shear zones are in metamorphic equilibrium with the surrounding wall rocks suggests their age is that of the metamorphism i e 2670 ma barton and van reenen 1992

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

the 1997 umbria marche italy earthquake sequence relationship between ground deformation and seismogenic structure a field survey performed during the 1997 umbria marche earthquake sequence led us to recognize ground and pavement ruptures associated with the three largest shocks mw 5 7 the ruptures are concentrated in narrow bands that in part are on and near previously mapped high angle normal faults the geometry of the ground deformation is consistent with the ne trending extension indicated by cmt focal solutions of the mainshocks the distribution of aftershocks suggests that the three mainshocks occurred on 40 sw dipping normal faults geological investigations modelling of expected coseismic elevation changes and seismic data suggest that the surface deformation is not the direct result of primary rupture of faults at depth

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

viscoelastic relaxation and long lasting after slip following the 1997 umbria marche central italy earthquakes summary we combine global positioning system gps measurements with forward modelling of vis coelastic relaxation and after slip to study the post seismic deformation of the 1997 umbria marche central apennines moderate shallow earthquake sequence campaign gps mea surements spanning the time period 1999 2003 are depicting a clear post seismic deformation signal our results favour a normal faulting rupture model where most of the slip is located in the lower part of the seismogenic upper crust consistent with the rupture models obtained from the inversion of strong motion data the preferred rheological model obtained from viscoelastic relaxation modelling consists of an elastic upper crust underlain by a transition zone with a viscosity of 10 18 pa s while the rheology of deeper layers is not relevant for the observed time span shallow fault creep and after slip at the base of the seismogenic upper crust are the first order processes behind the observed post seismic deformation the deep after slip below the fault zone at about 8 km depth acting as a basal shear through localized time dependent deformation identifies a rheological discontinuity decoupling the seismogenic upper crust from the low viscosity transition zone

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

structural development and petrofabrics of eclogite facies shear zones bergen arcs western norway implications for deep crustal deformational processes caledonian eclogite facies shear zones developed from grenvillian garnet granulite facies anorthosites and gabbros in the bergen arcs of western norway allow direct investigation of the relations between macroscopic structures and crystallographic preferred orientation cpo in lower continental crust field relations on the island of holsnoy show that the eclogites formed locally from granulite facies rocks by progressive development of 1 eclogite adjacent to fractures 2 eclogite in discrete shear zones 2 m thick 3 eclogite breccia consisting of 80 well foliated eclogite that wraps around rotated granulite blocks and 4 anastomosing subparallel eclogite facies shear zones 30 100 m thick continuous over distances 1 km within the granulite terrane these shear zones deformed under eclogite facies conditions at an estimated temperature of 670 50 c and a minimum pressure of 1460 mpa which corresponds to depths of 55 km in the continental crust detailed investigation of the major shear zones shows the development of a strong foliation defined by the shape preferred orientation of omphacite and by alternating segregations of omphacite garnet rich and kyanite zoisite rich layers a consistent lineation throughout the shear zones is defined by elongate aggregates of garnet and omphacite the cpo of omphacite determined from five axis universal stage measurements shows a strong b axis maximum normal to foliation and a c axis girdle within the foliation plane with weak maxima parallel to the lineation direction these patterns are consistent with deformation of omphacite by slip parallel to 001 and suggest glide along 010 the lineation and cpo data reveal a consistent sense of shear zone movement although the displacement was small localized faulting of high grade rocks accompanied by fluid infiltration can be an important mode of failure in the lower continental crust field relations show that granulite facies rocks can exist in a metastable state under eclogite facies conditions and imply that the lower crust can host differing metamorphic facies at the same depth deformation of granulite and partial conversion to eclogite such as is exposed on holsnoy island may be an orogenic scale process in the lowermost crust of collisional orogens

petrologic constraints on imbrication metamorphism and uplift in the sw tauern window eastern alps the pressure temperature time deformation pttd history of two tectonic units in the southwest tauern window austria italy is evaluated from p t paths of metamorphism and uplift geochronologic data and observations on fabric development petrologic data indicate burial of the lower schieferhulle lsh to depths of 35 km and the adjacent upper schieferhulle ush to only 24 28 km the units are now separated by only 2 km of section metamorphism was postkinematic in the lsh and synkinematic in the ush correlation of p t path reversals calculated from zoned garnets in the two units however indicates that juxtaposition of the lsh and ush occurred prior to metamorphism temperature time and depth time diagrams for both units show increasing cooling rates and decreasing uplift rates as the rocks approached the surface both the petrologic data and the depth time profiles for the lsh and ush point to a history of differential uplift in the early stages of decompression textural features indicate that the lsh behaved as an essentially rigid body during uplift whereas the ush experienced extensive ductile shearing the pttd data for the lsh and ush are incorporated into a model for continental collision in the eastern alps initial tectonic uplift of the lsh was accompanied by ductile thinning of the ush and overlying austroalpine units final uplift and erosion affected all of the units en masse

geochronology of the hout river shear zone and the metamorphism in the southern marginal zone of the limpopo belt southern africa abstract in this paper monazite u pb and zircon evaporation dates stepleaching pb pb results on garnet staurolite and kyanite and hornblende ar ar data are presented which constrain the timing of granulite facies metamorphism in the southern marginal zone of the limpopo belt and its thrusting onto the kaapvaal craton the southern marginal zone of the limpopo belt is considered to be a lower crustal equivalent of the northern kaapvaal craton granulite exhumation is associated with southward thrusting along the hout river shear zone which is a set of thrust and strike slip shear zones zircon ages for the matok intrusive complex which was emplaced within the zone during this thrusting charno enderbites 2671 4 ma granodiorites between 2667 and 2664 ma have previously been interpreted as evidence for rapid exhumation of the southern marginal zone within only 7 ma we have obtained a u pb date of 2691 7 ma for monazite from the bandelierkop quarry in the southern marginal zone interpreted as the age of high grade metamorphism a single zircon evaporation pb pb date of 2643 1 ma from a leucosome band at the same locality may indicate longer lasting metamorphism or decompression melting during exhumation anatexis of metapelitic xenoliths within the matok intrusive complex was dated at 2663 4 ma by u pb on monazite indistinguishable from existing zircon ages for this complex pb pb step leaching dates obtained on synkinematically grown garnet 2691 20 ma staurolite 2712 37 ma and kyanite 2672 51 ma from the khavagari hills in the giyani greenstone belt in the immediate footwall of the hout river shear zone indicate that early thrusting was contemporaneous with peak metamorphism in the southern marginal zone ar ar dating and geochemistry on syntectonic hornblende separates from the same shear zone system yielded disturbed spectra and indicated multiple populations probably reflecting repeated or continuous tectonic activity of the hout river shear zone up to about 2600 ma

predictive mapping of prospectivity for orogenic gold giyani greenstone belt south africa we present a mineral systems approach to predictive mapping of orogenic gold prospectivity in the giyani greenstone belt ggb by using layers of spatial evidence representing district scale processes that are critical to orogenic gold mineralization namely a source of metals fluids b active pathways c drivers of fluid flow and d metal deposition to demonstrate that the quality of a predictive map of mineral prospectivity is a function of the quality of the maps used as sources of spatial evidence we created two sets of prospectivity maps one using an old lithologic map and another using an updated lithological map as two separate sources of spatial evidence for source of metals fluids drivers of fluid flow and metal deposition we also demonstrate the importance of using spatially coherent or geologically consistent deposit occurrences in data driven predictive mapping of mineral prospectivity the best predictive orogenic gold prospectivity map obtained in this study is the one that made use of spatial evidence from the updated lithological map and spatially coherent orogenic gold occurrences this map predicts 20 of the ggb to be prospective for orogenic gold with 89 goodness of fit between spatially coherent inactive orogenic gold mines and individual layers of spatial evidence and 89 prediction rate against spatially coherent orogenic gold prospects in comparison the predictive gold prospectivity map obtained by using spatial evidence from the old lithological map and all gold occurrences has 80 goodness of fit but only 63 prediction rate these results mean that the prospectivity map based on spatially coherent gold occurrences and spatial evidence from the updated lithological map predicts exploration targets better i e 28 smaller prospective areas with 9 stronger fit to training gold mines and 26 higher prediction rate with respect to validation gold prospects than the prospectivity map based on all known gold occurrences and spatial evidence from the old lithological map

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

coseismic and postseismic displacements related with the 1997 earthquake sequence in umbria marche central italy we study the coseismic and postseismic displacements related with the 1997 umbria marche earthquake sequence by means of leveling lines along a deformed aqueduct located in the epicentral area comparing the 1960 and 10 1997 measurements we obtain 0 49 0 10 m of coseismic displacement distributed along 3 km across the normal fault zone modeling of the coseismic surface dislocation is obtained from a combination of low angle 38 faults at depth and high angle 80 upper fault branches the best fit model indicates that the upper branches stop at 0 4 km below the ground surface and have 60 of slip with respect to the lower faults the postseismic displacement measured during 1998 is 0 18 m and represents 36 of the apparent coseismic deformation moderate earthquakes in the apennines and related surface deformation may thus result from curved faults that reflect the brittle elastic properties of the uppermost crustal structures

post peak fluid mediated modification of granulite facies zircon and monazite in the trivandrum block southern india the quarry at kottavattom in the trivandrum block of southern india contains spectacular examples of fluid assisted alteration of high grade metamorphic rocks garnet biotite gneiss has undergone a change in mineral assemblage to form submetre scale orthopyroxene bearing patches later retrogressed to form an amphibole bearing lithology these patches often referred to as arrested or incipient charnockite crosscut the original metamorphic foliation and are typically attributed to passage of a low ah2o fluid through the rock whilst this conversion is recognised as a late stage process little detailed chronological work exists to link it temporally to metamorphism in the region zircon and monazite analysed from kottavattom not only record metamorphism in the trivandrum block but also show internal lobate textures crosscutting the original zoning consistent with fluid aided coupled dissolution reprecipitation during formation of the orthopyroxene bearing patches high grade metamorphism at the quarry occurred between the formation of metamorphic monazite at 585 ma and the growth of metamorphic zircon at 523 ma the fluid assisted alteration of the garnet biotite gneiss is poorly recorded by altered zircon with only minimal resetting of the u pb system whereas monazite has in some cases undergone complete u pb resetting and records an age for fluid infiltration at 495 ma the fluid event therefore places the formation of the altered patches at least 25 myr after the zircon crystallisation in the garnet biotite gneiss the most likely fluid composition causing the modification and u pb resetting of zircon and monazite is locally derived hypersaline brine

deep crustal shear zones high grade tectonites and associated metasomatic alteration in the limpopo belt south africa implications for deep crustal processes large thrust sheets of complexly folded d 1 migmatitic granulites bounded by a regional system of anastomosing ductile shear zones d 2 characterize the southern marginal zone of the limpopo belt tectonites within these shear zones are subdivided into primary straight gneisses with preserved textures that can unambiguously be referred to the d 2 exhumation stage annealed straight gneisses that recrystallized during post d 2 cooling and classic mylonites that post date the limpopo orogeny primary straight gneisses within these shear zones contain textural and mineralogical features that suggest they developed by a shear related process of grain size reduction and fabric formation due to decreasing pressure and temperature under granulite facies conditions this process is evident from the synkinematic replacement of garnet by cordierite and hypersthene symplectites the resultant asymmetric sigmoidal corona textures enhance the shear fabric in contrast pelitic granulite

applying insar technique to accurately relocate the epicentre for the 1999 ms 5 6 kuqa earthquake in xinjiang province china summary the 1999 m s 5 6 kuqa earthquake occurred in a seismically active belt between the tianshan mountain and the traim basin because of the sparse seismic network and complex crustal structure it is very difficult to accurately locate the epicentre for this event using seismic waves the epicentres located by different research groups vary over a spatial range of 20 40 km interferometric synthetic aperture radar insar is a geodetic technique with fine spatial resolution good precision and wide coverage an interferometric map of the epicentral region constrains the epicentre of this event the arid climate and sparsely vegetation in the kuqa region provide excellent conditions for insar studies in this paper we firstly construct a interferogram to map the coseismic deformation field due to the 1999 kuqa earthquake using a coseismic interferometric pair of radar images acquired by the esa ers 2 satellite then we develop a new geocoding method and apply it to the interferogram next we infer the geometry of the seismogenic fault according to its focal mechanism and tectonic setting to model the interferogram we assume a dislocation buried in a uniform elastic half space finally we infer the epicentre of this earthquake to be located at 82 80 e 41 92 n which is close to the results of the national earthquake information center of usgs and china earthquake administration the epicentre location inferred from insar falls in the six level isoseismal contour described by xinjiang earthquake administration using the field investigations

role of fluids in the exhumation of the southern marginal zone of the limpopo complex south africa abstract the limpopo complex lc of southern africa displays structural metamorphic and geochronological evidence for a complex exhumation controlled evolutionary history that followed after burial and attainment of peak metamorphic conditions p 9 kbar t 900 c in the root zone central zone cz of the orogen before 2 72 ga the southern marginal zone smz of the lc in addition provides evidence for thrust controlled emplacement of a hot granulite facies nappe onto the adjacent low grade granite greenstone terrane of the northern kaapvaal craton nkvc in the interval 2 69 2 62 ga a tectono metamorphic scenario in which initial near vertical channeling exhumation at 2 69 ga was transferred into horizontal channeling thrusting at 2 67 2 64 ga is interpreted to have commenced with in situ partial melting of crustal rocks in the root zone of the orogen cz this resulted in formation of melt weakened crust migmatized gneisses that with continuous shortening led to vertical transfer of lower crustal material accompanied by fluid fluxed decompression melting that resulted in production of large volumes of leucocratic granitic material this material detached to form buoyant diapirs that accompanied the emplacement at 2 65 ga of mega sheath folds at the middle crustal level throughout the entire cz of the lc this early stage of near vertical exhumation is reflected i by the fact that linear elements of sheath folds and shear zones plunge consistently at steep angles to the sw throughout the entire cz and ii by decompression cooling dc segments of p t paths constructed for metapelitic rocks dc paths in the far northern part of the smz that are associated with the steep north dipping portion of the hout river shear zone hrsz traversed from p 8 5 kbar t 850 c to p 6 5 kbar t 720 c early near vertical exhumation transferred into horizontal channel flow that controlled emplacement at the middle crustal level of the granulite facies nappe smz horizontal channeling thrusting is recorded in metapelitic granulite by near isobaric cooling p 6 kbar t 700 550 c segments of earlier dc p t paths that are associated with the shallow north dipping portion of the hrsz devolitilization of underthrusted greenschist due to thrusting hot granulite over cool greenschist released large volumes of high temperature aqueous fluids from the underthrusted rocks that constantly infiltrated the overriding granulite during southwards migration of the nappe immiscible co 2 rich and brine fluids thus derived persistently infiltrated into and reacted with cooling granulite and triggered the main pulse of anatexis at p 7 5 kbar t 750 c similar fluids established a regional retrograde isograd and associated zone of 4500 km 2 retrograde hydrated granulite at p 6 kbar t 600 630 c located in the hanging wall of the shallow north dipping hrsz that bounds the smz in the south shear zone hosted metasomatic alteration including formation of lode gold deposits occurred at t 600 630 c p 6 kbar in the zone of rehydrated granulite and at higher p t conditions in the granulite zone the granulite facies smz of the lc thus preserves clear evidence for a direct link between persistent fluid flux and fluid rock interaction as an integral component of a conveyor like tectonic mechanism driven by vertical tectonics that operated from the core region of the orogen cz this mechanism explains the important link between the thrust controlled emplacement of the smz onto the nkvc and deep crustal fluid flow

the september 26 1997 colfiorito italy earthquakes modeled coseismic surface displacement from sar interferometry and gps the largest events of the 1997 umbria marche seismic sequence were the two september 26 earthquakes of mw 5 7 00 33 gmt and mw 6 0 09 40 gmt which caused severe damage and ground cracks in a wide area around the epicenters we created an ers sar differential interferogram where nine fringes are visible in and around the colfiorito basin corresponding to 25 cm of coseismic surface displacement gps data show a maximum horizontal displacement of 14 1 8 cm and a maximum subsidence of 24 3 cm we used these geodetic data and the seismological parameters to estimate geometry and slip distribution on the fault planes modeled fault depths and maximum slip amplitudes are 6 5 km and 47 cm for the first event and 7 km and 72 cm for the second one in good agreement with those derived from the seismological data

p t conditions of decompression of the limpopo high grade terrane record from shear zones the southern marginal zone of the late archean limpopo belt of southern africa is an example of a high grade gneiss terrane in which both upper and lower crustal deformational processes can be studied this marginal zone consists of large thrust sheets of complexly folded low strain gneisses bound by an imbricate system of kilometre wide deep crustal shear zones characterized by the presence of high strain gneisses primary straight gneisses these shear zones developed during the decompression stage of this high grade terrane low and high strain gneisses both contain similar reaction textures that formed under different kinematic conditions during decompression evidence for the early m1 d1 metamorphic phase 2690 ma is rarely preserved in low strain gneisses as a uniform orientation of relict al rich orthopyroxene in the matrix and quartz and plagioclase inclusions in the cores of early m1 mg rich garnet porphyroblasts this rare fabric formed at 820 c and 7 5 kbar the retrograde m2 d2 metamorphic fabric 2630 2670 ma is well developed in high strain gneisses from deep crustal shear zones and is microscopically recognized by the presence of reaction textures that formed synkinematically during shear deformation m2 sigmoid shaped reaction textures with oriented cordierite orthopyroxene symplectites formed after the early m1 mg rich garnet porphyroblasts and syn decompression m2 pencil shaped garnet with oriented inclusions of sillimanite and quartz formed after cordierite under conditions of near isobaric cooling at 750 630 c and 6 5 kbar the symplectites and pencil shaped garnet are oriented parallel to the shear fabric and in the stretching direction low strain gneisses from thrust sheets show similar m2 decompression cooling and near isobaric cooling reaction textures that formed within the same p t range but under low strain conditions as shown by their pseudo idioblastic shapes that reflect the contours of completely replaced m1 garnet and randomly oriented cordierite orthopyroxene symplectites the presence of similar reaction textures reflecting low strain conditions in gneisses from thrust sheets and high strain conditions in primary straight gneisses suggests that most of the strain during decompression was partitioned into the bounding shear zones a younger m3 d3 mylonitic fabric 2637 ma in unhydrated mylonites is characterized by brittle deformation of garnet porphyroclasts and ductile deformation of the quartz plagioclase biotite matrix developed at 600 c as the result of post decompression shearing under epidote amphibolite facies conditions

reversed determination of the reaction phlogopite quartz enstatite potassium feldspar h 2 o in the ranges 750 875 degrees c and 2 12 kbar at low h 2 o activity with concentrated kcl solutions the reaction of phlogopite plus quartz to enstatite potassium feldspar and aqueous fluid in the system kmash kcl was reversed at 2 12 kbar and 750 875 degrees c and at low h 2 o activities by reversal of the h 2 o content of concentrated kcl solutions equilibrated with product and reactant assemblages synthetic 1m phlogopite kmg 3 alsi 3 o 10 oh 2 and enstatite mgsio 3 maintained end member stoichiometry throughout and the potassium feldspar kalsi 3 o 8 was a high sanidine based on unit cell refinements the broad p t xh 2 o and narrow reversal ranges of this investigation were possible because of the low and well defined h 2 o activity yet powerful fluxing action of concentrated kcl solutions solubility experiments on quartz and potassium feldspar in our p t xh 2 o range showed that fluid phase solution of silicate constituents was too small to have affected the h 2 o activity in the experiments the new determinations are more definitive than previous work done at very low pressures with pure h 2 o or in co 2 h 2 o mixtures they establish the standard free energy of the reaction in the experimental range with an uncertainty of about 1 kj and indicate that the synthetic phlogopite has maximal al si disorder under our experimental conditions the standard enthalpy of reaction at 298 k is 106 54 or 2 0 kj 2sigma based on our reversals a value 6 kj less positive than that currently used by many workers in calculations of biotite stability and h 2 o activity in the petrogenesis of high grade metamorphic rocks the lower thermal stability that we find for phlogopite requires revision in estimates of h 2 o activity of granulite facies metamorphism typical values for the natural assemblage orthopyroxene biotite garnet potassium feldspar plagioclase quartz at deep crustal metamorphic conditions 750 850 degrees c 5 10 kbar are alpha h2o 0 4 0 6 compared with values of 0 15 0 30 which would have been estimated with previously available data on phlogopite stability an important consequence of the expanded h 2 o activity range of granulites is that alkali chloride solutions of only moderate concentration xh 2 o 0 5 0 7 which are the values observed in actual fluid inclusions in many kinds of igneous and metamorphic rocks are a feasible alternative to the vapor absent conditions considered necessary by many workers based on previous low estimates of h 2 o participation of concentrated brines in deep crust upper mantle metamorphic processes enables alkali metasomatism and other kinds of chemical transport in an aqueous fluid without large scale melting of the crust

reaction history of garnet sapphirine granulites and conditions of archaean high pressure granulite facies metamorphism in the central limpopo mobile belt zimbabwe sequential reaction textures in archaean garnet corundum sapphirine granulites from the central zone of the limpopo belt document a progression from early coarse grained high pressure p 9 5 kbar granulite facies assemblages m1 to late low pressure p 6 kbar granulite facies sub assemblages m2 the stable m1 assemblage was garnet 57 pyrope mg mg fe 62 sapphirine corundum gedrite phlogopite rutile late m1 boron free kornerupine grew at the expense of garnet and corundum and coexisted with garnet sapphirine and gedrite partial or complete breakdown of coarse garnet and kornerupine during m2 resulted in the development of pseudomorphs and coronas consisting of fine grained symplectic intergrowths of cordierite gedrite and sapphirine later spinel the majority of reaction textures can be explained in terms of a stable reaction sequence and a model time sequence of mineral facies can be constructed when compared with a qualitative petrogenetic grid of fe mg discontinuous reactions in the fmash multisystem sapphirine garnet corundum spinel cordierite gedrite kornerupine the facies sequence indicates decompression at essentially constant t assuming constant a h2o exhumation of m1 corundum inclusions during m2 breakdown of kornerupine resulted in production of metastable spinel by a disequilibrium reaction with gedrite a second disequilibrium reaction of the spinel with cordierite produced sapphirine the operation of such reaction while pressure was decreasing the opposite dp from that implied by the texture if assumed to be the product of an equilibrium reaction has serious implications for the use of reaction textures in the construction of p t vectors garnet biotite thermometry on garnet interiors and phlogopite inclusions in corundum yields temperatures of ca 850 c for the m1 stage a minimum late m1 pressure of ca 7 kbar is indicated by the former association of kornerupine and corundum relict m1 kyanites reported by other workers indicate a minumum early m1 pressure of 9 5 kbar implying metamorphism at depths of at least 33 km probably 38km the high pressure granulite facies metamorphism was followed by an almost isothermal pressure decrease of 5 kbar indicative of rapid uplift the p t path is interpreted as the product of a single metamorphic cycle which probably took place in response to tectonic thickening of the crust such a process contrasts with the extensional origin recently proposed for isobarically cooled granulite facies terranes

manaslu leucogranite a collision signature of the himalaya a model for its genesis and emplacement the manaslu pluton is one of 10 leucogranites that formed in the overthrusted higher himalaya after the indo eurasian collision field and analytical data indicate that the underlying migmatites of the tibetan slab may be where the leucogranitic melts were generated the himalayan crustal thrusting of a hot slab over a rather cold volcano sedimentary pile le fort 1975a provides the necessary release of fluids these fluids cross the main central thrust mct induce the partial anatexis of the overheated tibetan slab and produce a leucogranitic magma the emplacement of the magma at first is located along the main disharmonic plane above the mct between the infrastructure and the superstructure there it generates a convective hydrothermal system extending very far laterally according to the stratification of permeabilities progressive emplacement of the granite proceeds as the convected fluids including the fluids released by the saturated magma dissolve the mainly calcareous host rocks of tibetan sedimentaries a frozen image of this caving out progression is given by the extensive network of granitic dikes outside the pluton the two quite independant fluid cycles of the generation and of the emplacement were triggered or guided by the tectonics due to collision this two fold model dominated by fluid activity may be of importance for other leucogranites and granites

constraints regarding gold deposition in episyenites the permian episyenites associated with the villalcampo shear zone central western spain the villalcampo shear zone around 307 ma shows second order shear zones 420 390 c with gold ore bodies hosted by episyenites which consist of albite episyenites albitites and albite kfs episyenites both types with different contents in sulphides and gold mass transfer modelling supports higher fluid rock ratios in albitites than in albite kfs episyenites the study of worldwide barren and gold bearing episyenites reveals abundant sulphides in the latter as a distinguishing feature the electrochemical processes at the surface of sulphide would have enhanced gold precipitation sulphides working as a gold trap a complex fluid history occurred in gold ore bodies hosted by episyenites although in essence it was similar to quartz sealed faults hosting late variscan gold deposits a an early fluid equilibrated with the metamorphic pile with sulphides or with a metamorphic fingerprint resulted in a sulphide deposition and b a shallower fluid reservoir of meteoric origin provided gold deposition in contrast to earlier claims regarding episyenite fluid flow a down temperature and probably an upwards fluid flow are proposed for the episyenitization process also in keeping with the early stages of fluid flow in quartz sealed faults fluid inclusions in albite confirm that the striking coupled quartz leaching albitization processes occurred around 400 c and 60 mpa crosscutting the retrograde solubility field of silica and yielding a vuggy rock initially albite and later quartz and sulphide filled the vugs from the same or a very similar fluid uraninites deposited during the albitization and probably the onset of the sulphide deposition afforded the same age 270 12 ma as other spanish episyenites confirming a synchronous and a regional scale process and ruling out a relationship with the granite cooling history 324 11 ma

subsidence monitoring using sar interferometry reduction of the atmospheric effects using stochastic filtering 1 the atmospheric effects represent one of the major limits of sar interferometry as a quantitative technique to monitor subsidences in this work which focuses on subsidences of small spatial extent a procedure to reduce these effects is described the atmospheric component of the interferometric phase is estimated adopting a filtering and prediction procedure which exploits the phase over stable areas identified in the vicinity of the analysed subsidence area the procedure was validated on a suitable test site located in north eastern spain furthermore it was employed in the study of a small scale subsidence where the interferometric results were validated using precise geodetic observations

strain and displacement in the harts range detachment zone a structural study of the bruna gneiss from the western margin of the entia dome central australia abstract a detailed structural and strain study has been carried out on the bruna granitic gneiss and its bounding thrusts from the western margin of the entia dome in the eastern harts ranges the zone containing the bruna gneiss has been described recently as comprising the harts range detachment zone hrdz a major low angle lithospheric detachment along which both major extensional and contractional movements have occurred the bruna gneiss contains a ductile fabric which varies from an augen streaky foliation through a ribbon gneiss to protomylonite and mylonite in what is predominantly a granitic gneiss conformably overlying the bruna gneiss is a distinctive dark coloured megacrystic gneiss layer which intruded independently from the bulk of the bruna gneiss and followed a different subsequent strain history principal stretch lineations are consistently north plunging or horizontal n s except where folded the bruna gneiss fabrics are complexly folded about axes in an asymmetric manner which suggests interruption of ductile slip and crumpling of the fabrics followed by continuing slip on other discrete surfaces and shear zones strain measurements of elongated feldspars and aggregates indicate moderate to high strains with predominantly plane strain symmetries strain is partitioned into planar parallel zones and suggests dominant heterogeneous simple shear as the main non coaxial flow mechanism flattening strains occur near the bases of two major zones and constrictional strains occur within some zones a strain integration profile across the detachment zone produces total displacements of only a few kilometres suggesting that much of the overall indicated displacement is partitioned into the discrete bounding thrusts asymmetric augen pressure shadows and shear bands provide kinematic indicators in the bruna gneiss most show reverse sense displacement of the overlying harts range cover in a southerly direction over the entia gneiss basement opposite extensional sense movements occur in some zones and especially at the margins of the detachment zone

paleoproterozoic amphibolite facies retrogression and exhumation of archean metapelitic granulites in the southern marginal zone of the limpopo belt south africa abstract granulite facies terrains that have undergone extensive retrogression provide insights into the recycling of volatiles in the crust during orogenesis the timing of retrogression is key to understanding the geodynamic circumstances of such events this study has investigated amphibolite facies retrogression of melt depleted granulite facies metapelites from the south marginal zone smz of the limpopo belt the granulites formed via incongruent partial melting reactions that consumed biotite and produced garnet and rutile as prominent peritectic products at 2 7 ga under conditions of 11 kbar and 875 c peak metamorphic garnet is replaced by cordierite orthopyroxene symplectites with cordierite subsequently partially replaced by fine grained intergrowths of amphibolite facies assemblages including rutile zr in rutile thermometry yielded a temperature range of 731 846 c for the granulite facies rutiles and 629 690 c for rutile in the retrograde assemblage all rutile generations yielded a youngest u pb age of 2 1 ga some granulite facies rutiles record older dates 2 55 2 25 ga which are non systematic with regard to crystal size and represent non reset relicts of metamorphic recrystallization during a potentially complex history of amphibolite facies metamorphism between 2 7 and 2 2 ga the youngest 2 1 ga rutile u pb age represents the time of final exhumation related cooling of the rocks following a discrete paleoproterozoic amphibolite facies retrograde event coexisting orthoamphiboles in the peak metamorphic assemblage indicate a maximum peak temperature of 625 c the lack of age size correlation and intragrain age zoning in rutile suggest fast cooling following the amphibolite facies retrograde event which is inferred to be not much older u pb dating of zircon from the same rocks confirms that the metapelites underwent granulite facies metamorphism at 2695 35 ma thus the metapelites of the smz record both an archean granulite facies event and a polymetamorphic paleoproterozoic amphibolite facies history that culminated in a mid amphibolite facies peak inducing partial retrogression of the granulites the paleoproterozoic amphibolite facies event is tentatively correlated with mantle melting documented between 2 3 and 2 1 ga to produce mafic and intermediate volcanic rocks in the pretoria group on the kaapvaal craton

ductile thrusting at mid crustal level southwestern grenville province the northwestern boundary zone of the central metasedimentary belt grenville province in the haliburton area ontario is a stack of alternating tonalitic and syenitic crystalline thrust sheets transported toward the northwest on out of sequence upper amphibolite facies ductile thrust zones during the grenvillian orogeny at 1060 ma approximately 100 ma after the initiation of thrusting in the underlying central gneiss belt kinematics of the deformation are complex predominant northwestward thrusting was at least partly coeval with subordinate northeastward thrusting late synmetamorphic extensional shears cut both thrusts and thrust sheets minor late thrusting on discrete ductile shear zones postdates the extensional structures belts of mechanically weak pelite appear to have localised the thrust sheets highly mobile marble behaved as a relatively low viscosity fluid during transport able to intrude and erode more competent wall rock

himalayan tibetan analogies for the evolution of the zimbabwe craton and limpopo belt abstract the limpopo orogeny which lasted from 2700 to 2600 ma was characterised by nnw sse directed shortening this resulted in both crustal thickening accommodated by folding and nnw directed thrusting and associated crustal extrusion whereby a number of crustal blocks including the central zone of the limpopo belt was displaced to the west southwest along wsw ene trending shear zones this was part of a regionally distributed phase of orogenic deformation which affected the adjoining kaapvaal and zimbabwe cratons from the witwatersrand basin in the south to the harare greenstone belt in the north this deformation which migrated northwards with time postdated an earlier phase of crustal accretion during which the archaean crustal unit now marked by the kaapvaal and zimbabwe cratons and the limpopo belt grew towards the north northwest shortening of this unit during the limpopo orogeny may be regarded as the last stage of the crustal accretion process this tectonic process of continental growth by accretion followed by crustal shortening with associated crustal extrusion has many features in common with tibetan tectonics from the mesozoic to the present

analysis of ground deformation detected using the sbas dinsar technique in umbria central italy ground deformation affecting the umbria region central italy in the 9 year period from 1992 to 2000 was investigated through multi temporal differential synthetic aperture radar interferometry dinsar for the purpose the small baseline subset sbas technique was adopted which allows studying the temporal evolution of the detected deformation at two spatial scales a low resolution regional scale and a full resolution local scale for the analysis sar data acquired by the european remote sensing ers 1 2 satellites along ascending and descending orbits were used the detected deformation was analysed to investigate its relevance to geophysical geomorphologic and human induced processes that may result in hazardous conditions to the population of umbria low resolution deformation data were used to i determine the amount of displacement caused by the umbria marche earthquake sequence from september 1997 to april 1998 in the foligno area ii determine the number and percentage of the known landslides that can be monitored by the dinsar technology in the investigated area and iii identify and measure subsidence induced by exploitation of a confined aquifer in the valle umbra results indicate that earthquakes moved through the foligno area westwards up to 3 9 cm and with an uplift reaching 1 7 cm intersection in a gis of the low resolution deformation maps with a detailed landslide inventory map allowed the determination that the portion of landslides that can be monitored by the sbas dinsar technique in umbria ranges from 2 7 to 3 4 and the percentage of the total landslide area ranges from 10 4 to 12 8 in the valle umbra a dependency was found between the time and the amount of detected ground deformation and the record of water withdrawal the full resolution deformation data were used to investigate the movement of the ivancich landslide in the assisi municipality joint analysis of the spatial and the temporal characteristics of the ground displacement allowed the formulation of a hypothesis on the landslide geometry and deformation pattern

the development of orientated symplectites during deformation orientated symplectites have been observed in deformed granulite facies metabasic rocks from the ivrea verbano zone in northern italy the area underwent lower crustal extension accommodated by movement on localized high t shear zones in areas of relatively low strain such as at the margins of shear zones symplectites of orthopyroxene plagioclase and spinel have formed the symplectites are vermiform and orientated parallel to the main foliation and in the regional stretching direction the reaction was synkinematic with the deformation and only developed in potentially dilatant grain boundaries in the rock it was presumably inhibited in grain boundaries subjected to higher normal stress due to the relatively large volume increase involved in the reaction the observations support the interpretation that the deformation was related to regional extension under high t granulite facies conditions the symplectites forming as a result of decreasing pressure

raman spectroscopic characterization of h2o in co2 rich fluid inclusions in granulite facies metamorphic rocks abstract water h2o has been identified during raman analyses at 150 200 c of fluid inclusions from granulites that were previously thought to contain pure co2 at room temperature h2o in a co2 rich fluid inclusion forms an optically unresolvable liquid wetting the inclusion walls during heating the h2o phase evaporates into the co2 phase to produce a homogeneous h2o co2 fluid throughout the inclusion volume and the h2o raman peak at 3640 cm 1 is clearly resolvable at elevated temperatures to test and confirm the method synthetic h2o co2 fi of known composition 87 5 mol and 95 mol co2 were also analyzed previously studied granulite samples from the adirondack mountains usa and from the kerala khondalite belt sittampundi complex and sevitturangampatti india were tested for the presence of h2o in co2 rich fluid inclusions traces of h2o were found in co2 rich fluid inclusions in quartz crystals from the adirondacks and from the kerala khondalite belt h2o was not detected in co2 rich secondary fluid inclusions in garnet from the sittampundi complex and from sevitturangampatti rather hydrogarnet was detected along the walls of inclusions in garnet as evidenced by a peak at 3661 cm 1 the hydrogarnet is interpreted to be a step daughter phase that formed by reaction of the h2o in the fluid inclusion with the garnet host during retrogression these observations confirm the presence of an h2o bearing co2 rich fluid at some time during granulite petrogenesis but do not resolve the question of whether these co2 rich fluids were trapped at peak metamorphic conditions or during retrogression or whether the fluid inclusions have reequilibrated following entrapment

metamorphic p t profiles from the zimbabwe craton to the limpopo belt zimbabwe abstract metamorphic p t profiles in the eastern and western parts of the limpopo belt zimbabwe were examined on the basis of mineralogic and petrologic data from areas which include the southernmost zimbabwe craton the northern marginal zone and the central zone the zimbabwe craton consists of a granite greenstone terrane of 2900 ma to 3600 ma old the northern marginal zone represents a high grade equivalent of the granite greenstone lithologies the central zone has suffered granulite facies metamorphism during the late archean metamorphic temperature of the zimbabwe craton adjacent to the northern boundary of the limpopo belt is calculated to be 650 680 c for amphibolite and 710 720 c for quartzofeldspathic gneiss in the eastern part these temperatures are slightly lower than that calculated from the same assemblages in the northern marginal zone and central zone peak metamorphic conditions in the eastern part of the northern marginal zone are estimated at about 740 790 c and 7 5 7 9 kbar from the assemblage garnet core orthopyroxene plagioclase quartz in pelitic gneiss these conditions were followed by a retrograde event of about 630 660 c and 3 8 4 5 kbar which were calculated from the assemblage garnet rim cordierite sillimanite quartz in the same rock the p t path is very similar to the retrograde path from the southern marginal zone it implies that both the northern marginal zone and southern marginal zone may have shared a similar metamorphic evolution garnet bearing mafic gneiss in the central zone indicates somewhat higher p t conditions than those in the northern marginal zone central zone metamorphic conditions are estimated at 790 890 c and 11 0 13 3 kbar for garnet clinopyroxene plagioclase quartz assemblages and 750 870 c and 7 6 8 8 kbar for garnet hornblende plagioclase quartz assemblages the difference of p t conditions between the northern marginal zone and central zone may be related to movement along the pre triangle shear zone the northern marginal zone appears to have been displaced along the shear zone relative to the central zone during uplift carrying the deeper crust to the surface

an advanced slip model for the umbria marche earthquake sequence coseismic displacements observed by sar interferometry and model inversion summary we report an improved slip model for the 1997 september october umbria marche earthquake sequence in central italy the model is based on coseismic displacements estimated by differential synthetic aperture radar dinsar interferometry using an advanced inverse modelling approach that enables the characteristics of the sar data especially their dense spatial sampling to be fully exploited the paper first looks at dinsar analysis using the simplest configuration that is a single image pair that temporally covers the earthquake sequence yet given that this dinsar configuration is often used for coseismic studies and the limited availability of sar data we duly consider the limitations of the dinsar results and discuss the rigorous dinsar procedure carried out highlighting key errors associated with such observations we then focus on the inversion of the estimated dinsar displacements and on our advanced heterogeneous slip model for this earthquake sequence s main shocks emphasizing its most significant features

the significance of rb sr ages of biotite and phlogopite for the thermal history of the central and southern marginal zones of the limpopo belt of southern africa and the adjacent portions of the kaapvaal craton abstract generally rb sr biotite and phlogopite ages range from 2050 ma to 1950 ma between the murchison thabazimbi and triangle tuli sabi shear zones of southern africa in the rocks comprising the central and southern marginal zones of the limpopo belt and adjacent portions of the kaapvaal craton in some shear zones however similar ages ocurr as young as 800 ma in contrast within the kaapvaal craton south of the murchison thabazimbi shear zone rb sr biotite ages range between 3150 ma and 2100 ma and show no regular distribution in all cases the ages are interpreted to indicate the time elapsed since the biotite last cooled below its closure temperature approximately 320 c the regular pattern of 2050 ma to 1950 ma rb sr biotite ages north of the murchison thabazimbi shear zone suggests that the present erosional surface approximates a paleo isothermal surface this surface was exposed by uplift and erosion which was completed by 1900 ma to 1800 ma ago when the sedimentary and volcanic rocks of the soutpansberg group were deposited the regional uplift was accommodated by motion on the murchison thabazimbi and triangle tuli sabi shear zones and probably was related to tectonism associated with the emplacement of the anorogenic bushveld and phalaborwa complexes other anorogenic granitic magmatism accompanied uplift the depth represented by the paleo isothermal surface and the magnitude of the uplift that exhumed it cannot be constrained precisely it is suggested however that the majority of the 10 to 15 km by which crust in this area is thinner than that of the adjacent cratons is the manifestation of this uplift

shear zones of the limpopo belt and adjacent granitoid greenstone terranes implications for late archaean collision tectonics in southern africa abstract granulite metamorphism in the 2 65 ga limpopo belt of southern africa is related to crustal thickening due to late archaean collision tectonics the central zone of the belt is a major thrust sheet of distinctive lithological structural and isotopic character separated from adjacent terranes by crustal scale shear zones and the northern and southern marginal zones are up thrust deep level granulite facies terranes of the adjacent cratons geometrically the marginal zones are mirror images and the limpopo belt is essentially symmetrical in n s section conventionally regarded as a n s collisional orogeny the gross structural and lithological differences between the central zone and the marginal zones kinematic data from shear zones and geophysical data showing the three dimensional geometry of the central zone are here used to suggest that the direction of emplacement of the central zone was also the collision direction this was from northeast to southwest with the upthrust outwardly directed marginal zones developing in mechanical response to this collision

effects of geological complexities on coseismic displacement hints from 2d numerical modelling by means of a 2d finite element procedure we tested how heterogeneities at the scale of seismogenic fault affect the displacement we defined one or more slip distributions for two typical normal faulting earthquakes in the central apennines computed the displacement occurred within different structures including lateral heterogeneities and compared the different displacement profiles to isolate the effect of the crustal structure to understand at what magnitude the heterogeneities affect the observation significantly we compared the predicted coseismic displacement with gps and dinsar data for the colfiorito 1997 earthquake we find that heterogeneities significantly affect the observable horizontal coseismic displacement for the larger magnitudes whereas for smaller quakes they affect horizontal displacement close to the fault trace only

fluid inclusions in rocks from the amphibolite facies gneiss to charnockite progression in southern karnataka india direct evidence concerning the fluids of granulite metamorphism fluid inclusion studies of rocks from the late archaean amphibolite facies to granulite facies transition zone of southern india provide support for the hypothesis that co2 rich h2o poor fluids were a major factor in the origin of the high grade terrain charnockites closely associated leucogranites and quartzo feldspathic veins contain vast numbers of large co2 rich inclusions in planar arrays in quartz and feldspar whereas amphibole bearing gray gneisses of essentially the same compositions as adjacent charnockites in mixed facies quarries contain no large fluid inclusions inclusions in the northernmost incipient charnockites as at kabbal karnataka occasionally contain about 25 mol of immiscible h2o lining cavity walls whereas inclusions from the charnockite massif terrane farther south do not have visibile h2o microthermometry of co2 inclusions shows that miscible ch4 and n2 must be small probably less than 10mol combined densities of co2 increase steadily from north to south across the transitional terrane entrapment pressures calculated from the co2 equation of state range from 5 kbar in the north to 7 5 kbar in the south at the mineralogically inferred average metamorphic temperature of 750 c in quantitative agreement with mineralogic geobarometry this agreement leads to the inference that the fluid inclusions were trapped at or near peak metamorphic conditions calculations on the stability of the charnockite assemblage biotite orthopyroxene k feldspar quartz show that an associated fluid phase must have less than 0 35 h2o activity at the inferred p and t conditions which agrees with the petrographic observations high tio2 content of biotite stabilizes it to lower h2o activities and the steady increase of biotite tio2 southward in the area suggests progressive decrease of ah2o with increasing grade oxygen fugacities calculated from orthopyroxene magnetite quartz are considerably higher than the graphite co2 o2 buffer which explains the absence of graphite in the charnockites the present study quantifies the nature of the vapours in the southern india granulite metamorphism it remains to be determined whether co2 flushing of the crust can by itself create large terranes of largeion lithophile depleted granulites or whether removal of h2o bearing anatectic melts is essential

geologic history of the central zone of the limpopo complex the west alldays area abstract new field structural petrologic and age data show that tectonic styles and metamorphic histories in the west alldays area of the central zone of the limpopo complex southern africa can be linked to neo archean and paleoproterozoic high grade granulite facies tectonometamorphic events the styles comprise 1 a regionally developed high grade s2 gneissic fabric that evolved into a regional d2 system of sheath folds mapped as circular to oval shaped structures with lineations plunging steeply to the wsw and 2 a system of mainly n s trending and north verging d3 shear zones characterized by high grade tectonites straight gneisses with well developed s3 gneissic fabrics in the west alldays area the superimposition of d3 onto the regional d2 fold pattern produced the kilometer scale n s trending baklykraal shear zone which before this study was mapped as the baklykraal fold and interpreted as part of the regional d2 fold pattern in the central zone the paleoproterozoic high

characteristics of a kilometer scale high strain zone in the lower continental crust mt hay block central australia abstract a granulite facies high strain zone was studied on capricorn ridge part of the mt hay block granulites in the arunta inlier central australia deformation occurred in these primarily mafic composition granulites at lower crustal conditions 8 kb 800 c at 1740 1690 ma pervasive and consistently oriented foliation striking ssw and dipping steeply and lineations pitching steeply eastward occur within the shear zone the high strain zone is recognized by the presence of sl tectonites parallelism of grain shape fabrics and lithologic boundaries transposition of lithologic boundaries into parallelism with the foliation and the local occurrence of sheath like folds field based fabric mapping uses compositional foliation intensity as a proxy for finite strain to document strain variations within the capricorn ridge high strain zone there is no observed microstructural grain size reduction that corresponds to these strain variations fabric intensity increases from the centers of the major lithologic units towards the contacts 100 m scale strain localization within capricorn ridge occurs adjacent to major lithologic contacts indicating competency contrast during lower crustal deformation

evolution of ptygmatic folds in migmatites from the type area s finland abstract it is proposed that ptygmatic folds in migmatites form during leucosome melanosome differentiation volume loss by depletion of quartz and feldspar takes place in the interlimb domains of folds leaving a residual melanosome buckling leucosomes increase in volume due to this process and are protected from substantial thinning concurrent with tectonic segregation albeit at a lower rate the leucosome expands by replacing the melanosome this process is induced by fluid activity at the leucosome boundary as suggested by the occurrence of secondary offshoot veinlets segregation and growth causes the most typical aspect of ptygmatic folds preservation of an overall buckle shape during the stage when the folds become isoclinal and devoid of interlimb matrix

kinematical and rheological evolution of a crustal scale ductile thrust zone central metasedimentary belt grenville orogen ontario reply the central metasedimentary belt boundary thrust zone is a 10 km thick 200 km long stack of crystalline thrust sheets enclosed by an anastomosing network of ductile thrust zones formed at mid

fluid control of charnockitization abstract the reactions bt qtz opx kfs h2o bt1 qtz k2o or bt2 n h2o mg ts opx otz k2o or en pl1 k2o pl2 or na2o and prg en qtz k2o or ed recorded in unique rock textures and mineral compositions from gneissic complexes of some granulite facies terrains have been studied it is shown that chemical potentials of the perfectly mobile co2 h2o and k2o in a metamorphic fluid govern the charnockitization process along the retrograde p t paths typical of granulite facies rocks the sensors indicating the contribution of thermodynamic parameters to the process are discussed in many complexes charnockitization took place at a aflh2o similar to or even higher than that for initial gneisses the origin of arrested charnockites in the precambrian gneissic complexes is considered to be co2 1bh2o fluid gneiss interaction which causes migration of the majority of the basic components mgo feo cao tio2 etc from initial metamorphic rocks toward a transition zone the scale of the migration depends strongly on the intensity of the interaction the migration of the elements from a given rock volume propagates the shift of its bulk composition toward the charnockite kfs qtz fs eutectic and subsequent melting this model may explain the existence of zoned metabasite enderbite charnockite complexes of precambrian granulite facies terrains the arrested charnockites are a small scale model for the formation of these complexes

fluids in granulites since the discovery of co2 fluid inclusions in granulites the role of fluids in the formation of these rocks has been widely studied owing to the complexity of the tectono metamorphic history of granulite terrains fluid inclusion data alone are not sufficient they need to be integrated with geochemical and mineralogical studies done on the same rock samples a clear understanding of the tectono metamorphic history of granulite terranes is also indispensable the widespread occurrence of co2 and the later discovered high salinity aqueous fluid inclusions support the idea that the lower crust underwent fluid flow and that both carbonic and brine fluids played a role in its formation both low h2o activity fluids play a similar role in destabilizing hydrous mineral phases furthermore experimental studies have shown that brine fluids have a much larger geochemical effect on granulites than initially expected these fluids are far more mobile in the lower crust compared with co2 and also have the capability for dissolving numerous minerals as in the example of the limpopo complex fluid inclusions and many metasomatic features observed in granulite terranes can thus be explained only by large scale movement of high salinity aqueous fluids and to a lesser extent co2 implying that lower crustal granulites are not as dry as previously assumed similar brines and co2 rich fluids are also found in mantle material most likely derived from deeply subducted supracrustal protoliths

kinematics of ductile shearing from outcrop to crustal scale in the monte rosa nappe western alps significant ductile deformation has produced widespread mylonitic structures in the basement orthogneisses and the mesozoic cover quartzites and marbles of the monte rosa nappe in the inner part of the western alps we summarize here the results of a detailed microstructural study at several scales of observation in the northern part of the nappe and discuss the kinematic significance and compatibility of such results most of the observed deformations can be accounted for by progressive wnw vergent shearing during and after the late eocene within a ductile shear zone of crustal scale the displacement of the hanging wall may have been in excess of several tens of kilometers however some ese vergent shear criteria cannot be reconciled with this general picture and suggest that local backthrusting occurred later near the toe of the monte rosa nappe

melt origin of fault generated pseudotachylytes demonstrated by textures a petrographic and electron microprobe study of fault generated pseudotachylytes from the outer hebrides thrust zone scotland demonstrates that the textures have resulted from the primary crystallization of a clast laden melt rather than the devitrification of a glass or by crushing and cataclasis the observations are consistent with these pseudotachylytes having formed by frictional fusion followed by rapid quenching implying faulting at shallow crustal depths

structure of the nagavali shear zone eastern ghats mobile belt india correlation in the east gondwana reconstruction abstract interpretation of satellite data in combination with regional field traverses delineating the major structural features such as the nagavali and vamsadhara shear zones and associated fold patterns provides a synoptic picture of the regional tectonic framework of the central part of the eastern ghats mobile belt the complex geology of the study area can broadly be grouped into three distinct deformational events d1 fabrics represented by near flat lying gneissic foliations paralleling the lithological banding are best preserved in low strain domains and are related to middle to late archaean thrusting 3000 2600 ma the second deformational event d2 is characterized by the development of shear zones and associated mylonitic fabrics and magmatism probably during 1450 850 ma the pan african thermal 500 550 ma overprint is restricted to shear zones in the form of reworking regionally the central part of the eastern ghats mobile belt can be divided into five distinct structural domains based on structural geometry of folds foliations and lineations a three dimensional block diagram of the nagavali and vamsadhara shear zones involving fold thrust tectonics associated with westward thrusting is presented here a correlation of pan african shear zones in adjacent continents wrapping around the archaean dharwar craton in the reconstruction of rodinia and east gondwana supercontinent suggests an east west convergence

constraints on the composition of fluids involved in retrograde anthophyllite formation in the limpopo belt south africa abstract orthoamphibole occurs widely in the metapelitic gneisses and other lithologies within the southern marginal zone of the limpopo belt in southern africa petrographic relations indicate that the orthoamphibole formed as a retrogressive replacement of the granulite facies minerals cordierite and orthopyroxene the existence of a discrete retrograde orthoamphibole isograd that can be mapped for over 150 km has led previous workers to suggest that the orthoamphibole formed as a result of equilibrium high temperature reactions which occurred in response to regional influx of fluids at the close of the limpopo orogeny 2670 ma ago however in order to substantiate this interpretation it is necessary to show from phase equilibrium analysis that the metapelitic minerals and their retrograde products comprise assemblages stable at elevated pressure and temperatures rather than disequilibrium assemblages formed at unspecified lower temperatures by monotropic reactions some of the properties of the infiltrating fluids may in turn be specified if the alteration products represent equilibrium assemblages it is shown that the presence of anthophyllite and the absence of talc in two analysed metapelites from the retrograde isograd require an associated vapour phase to have been relatively low in water ah2o 0 7 and temperatures to have been below 620 c when the anthophyllite developed from the orthopyroxene the fast kinetics of formation of talc and the relatively sluggish kinetics of formation of anthophyllite in experimental systems make it highly unlikely that the orthoamphibole could have formed metastably at low temperatures and high water activities a more general phase equilibrium analysis based on the coexistence of cordierite garnet biotite enstatite plagioclase and quartz with retrograde anthophyllite and kyanite indicates that this assemblage was in equilibrium at temperatures between 450 to 650 c for pressures of 5 to 7 kbars and water activities between 0 6 and 0 1 the temperatures pressure and water activities are highly correlated and lower pressures and water activities are required for equilibrium at lower temperatures the reduced water activities calculated require that a substantial quantity of another volatile be present in the vapour phase in the absence of stable scapolite or carbonates this volatile cannot be confirmed to be co2 the required infiltration of late orogenic fluids with reduced water activities is apparently a major feature of the limpopo event and may have parallels in other large precambrian high grade terrains in as much as orthoamphibole replacing orthopyroxene is a commonly observed mineral assemblage

evolution of regional metamorphism in the cape smith thrust belt northern quebec canada interaction of tectonic and thermal processes syn metamorphic re imbrication of the internal part of thrust belts can result in distinct pressure temperature time deformation p t t d pathways for different structural metamorphic domains in the early proterozoic cape smith thrust belt canada an external piggyback sequence thrusting domain is characterized by thermal peak metamorphism occurring after deformation in contrast thermal peak metamorphism in an internal domain occurred during re imbrication by out of sequence thrusting the interactions of tectonic and thermal processes have been studied using three methods i qualitative evaluation of the timing between mineral growth and deformation ii analytical p t paths from growth zoned garnet porphyroblasts and iii numerical modelling of vertical heat conduction derived p t t d pathways suggest that uplift in the external domain resulted in part from erosion and isostatic unloading in contrast paths for the internal domain indicate that the out of sequence portion of the thrust belt may have experienced faster unroofing relative to the external domain this is attributed to thickening by out of sequence thrusting and possibly to extensional faulting at now eroded higher structural levels observations on the timing of metamorphism coupled with numerical modelling suggest that the thermal peak metamorphism documented in the external domain is a consequence of the emplacement of the out of sequence thrusts stack in the internal portion of the thrust belt

constraints on the form of the p t loop in the southern marginal zone of the limpopo belt south africa abstract a generalised clockwise p t path consisting of a prograde portion a high grade isothermal decompression portion and an essentially isobaric cooling portion has been suggested for the metamorphic evolution of the southern marginal zone previous studies have concluded that the high grade decompression path started in the kyanite stability field peak metamorphic mineral compositions have been reset during the equilibrium decompression event and hydration during the cooling dominated isobaric portion occurred in the kyanite stability field the present petrographic study from the bandelierkop quarry a locality in the granulite zone of the southern marginal zone identified a series of sequential anatectic reactions which record a period of prograde heating from approximately 700 c to 850 c during this period pressure is constrained to within the sillimanite stability field by the production and preservation of prograde generations of sillimanite the maximum temperature melting event is closely followed by two divariant reactions ga qz sil cord and ga qz cord hy which occur in response to a period of general isothermal decompression a subsequent cooling dominated rehydration period is indicated by a crystallisation hydration reaction cord ksp melt bi ky qz which occurred at a minimum temperature of approximately 640 c and pressure greater than 6 5 kbar the present data confirms the clockwise form of the loop and also supports the previously suggested flat slope of the retrograde cooling portion additional mineral chemistry data relating to the second decompression reaction indicate that the zonation profiles of cordierite and garnet as well as the growth of small quantities of garnet after the reaction are in strong support of the suggested p t path the present mineral compositions in the southern marginal zone reflect a near total re equilibration during the high grade cooling dominated portion of the p t path and as a result reflect p t conditions considerably lower than those of the peak metamorphism

tectonometamorphic evolution of the bohemian massif evidence from high pressure metamorphic rocks the variscan orogenic belt of which the bohemian massif is a part is typically recognized for its characteristic low pressure high temperature metamorphism and a large volume of granites however there are also bodies of high pressure rocks eclogites garnet peridotites and high pressure granulites which are small in size but widely distributed throughtout the massif initially the high pressure rocks were considered to be relicts of a much older orogenic event but the increasing data derived from isotopic and geochronological investigations show that many of these rocks have palaeozoic protoliths metamorphic ages from the high pressure rocks define no single event instead a number of discrete clusters of ages are found between about 430 ma and the time of the dominant low pressure event at around 320 330 ma

on the internal geometry of mylonite zones mylonite zones are generally characterized by abrupt and very large strain transitions which commonly result in excessively anastomosing schistosities on a wide range of scales when compared with nonmylonitic foliations this geometry is very susceptible to remodification during progressive mylonitization resulting in unusual and complex fold lineation and foliation geometries and interrelationships open folds of the mylonitic foliation with axes parallel to the stretching lineation in the surrounding mylonite cannot have formed by the rotation of fold axes through a large angle within their axial planes as has been usually proposed for isoclinal and sheath folds in mylonitic zones open folds initiate with axes parallel or close to the stretching lineation due to the geometric effects of folding a mylonitic foliation which anastomoses around an ellipsoidal pod of less deformed material this initial geometry also allows the generation of fold axes curved within their axial plane through 1800 about the stretching lineation at the time of nucleation successive mylonitic foliations develop during this folding and refolding process with boundaries that truncate and isolate earlier fold hinges and portions of fold limbs as a consequence stretching and intersection lineations can vary from plane to plane through the mylonite zone although careful examination often reveals a weak overprinting stretching lineation parallel to the bulk movement direction for the whole zone fold asymmetry in mylonite zones is a potential indicator of shear sense across a zone if the fold axes lie at an angle to the bulk stretching lineation direction in such circumstances however a single asymmetry projected onto a plane perpendicular to the mylonitic foliation and containing the bulk stretching lineation can indicate either sense of shear depending on a variety of factors these include whether the foliation folded is primary or mylonitic and in the latter case whether the mylonite zone formed with a steep dip and horizontal stretching lineation or in some other orientation the most satisfactory sense of shear indicator is the asymmetry of s and c planes

superheated friction induced melts in zoned pseudotachylytes within the adamello tonalites italian southern alps pseudotachylytes and cataclasites are present along a strike slip fault zone in the tonalites of the adamello intrusion italian southern alps ambient conditions during faulting were 0 25 0 3 gpa and 250 300 c pseudotachylyte veins thicker than 6 mm are zoned and consist of two symmetric microlitic domains towards the vein walls and a central spherulitic domain the thickness of the microlitic domains x increases linearly with the half total thickness a of the pseudotachylyte vein commonly 2 cm according to the relation x 0 29 0 12 a the spherulitic and microlitic domains have similar chemical composition but the microlitic domain has a lower amount of plagioclase clasts a numerical model explains zoning as the result of the different cooling rates and clast melt interactions at the center and periphery of thick veins zoning is compatible with the injection of a single pulse of superheated friction induced melt tmelt 1450 c melt temperatures estimated by the clast matrix ratio o hara 2001 are considerably lower 316 577 c it is suggested that the difference in the temperature estimates reflects a more complex slip history than a single seismic slip event along the fault during production of cataclasites pseudotachylytes

a variable slip fault model for the 1908 messina straits italy earthquake by inversion of levelling data summary a variable slip fault model is presented for the 1908 december 28 messina italy earthquake it has been obtained by inversion of levelling data using a gradient method fault location and mechanism are consistent with an approximately n s orientation and normal faulting on a low angle plane dipping 39 with about 45 of strike slip component the main difference from a homogeneous slip model is represented by a higher slip area up to 3 m located close to the city of reggio calabria it is interpretable as a major asperity which is related to the main fracture episode this is in agreement with some macroseismic evidence and the same structure could be responsible for the nearby recent seismic activity the area which effectively slipped is all confined within the messina straits this result differs from the homogeneous slip model recently proposed by capuano et al 1988

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

evolution of stretching lineations in granulite hosted ductile shear zones eastern ghats province india role of temperature strain rate and pre existing stretching lineations abstract shear zone kinematics are interpreted from sections x z parallel to the stretching lineation x direction and perpendicular to the mylonitic foliation x y the stretching lineation is a product of finite strain defined by minerals or mineral aggregates that deform plastically in quartzofeldspathic rocks deformed below 600 c rheological contrasts between quartz and feldspar are amplified and the mesoscopic stretching lineation in the shears may be indistinct in outcrop as quartz ribbons anastomose around relatively competent feldspar clasts in high strain rate zones rheological contrasts between these minerals are reduced and a stretching lineation suitable for kinematic interpretation develops in late amphibolite and greenschist facies shear zones transecting pre lineated quartzofeldspathic granulites of the eastern ghats province india the stretching lineation represents the resultant of pre existing stretch and superposed increments of later shearing until the stretch accumulated in the x direction of the later deformation exceeds the earlier finite stretch the pre existing stretching lineation progressively rotates towards the later x direction with decreasing aspect ratio these intermediate lineation orientations have no kinematic relevance to either earlier or later deformations this example highlights the importance of temperature strain rate and orientation of pre existing stretching lineations in the appearance and kinematic interpretation of stretching lineations in ductile shear zones

p t conditions mechanism and timing of the localized melting of metapelites from the petronella shear zone and relationships with granite intrusions in the southern marginal zone of the limpopo belt south africa

slip distribution of the 1997 umbria marche earthquake sequence joint inversion of gps and synthetic aperture radar interferometry data 1 in september october 1997 a seismic sequence struck the southern part of the umbria marche region in central italy the three largest earthquakes took place on 26 september 0033 ut mw 5 7 09 40 gu mw 6 0 near colfiorito and on 14 october mw 5 6 near sellano we present a slip model for the main sequence over two separate fault planes we use previously published global positioning system gps and differential interferometric synthetic aperture radar dinsar data as well as new dinsar data covering the sellano event as input to a simulated annealing solution for the distribution of fault slip the combination of both types of geodetic data as well as the combination of sar interferograms from both ascending and descending satellite tracks allows us to make a more complete geodetically based assessment of the fault slip for these earthquakes for the solutions presented here we required the slip distribution to match the observed surface displacements while maintaining a total scalar seismic moment approximately equal to the seismologically inferred moments for this sequence we find the slip was concentrated in a zone at 4 5 5 km depth with a shallower tail extending to near the surface at the northern end of the colfiorito sequence for both the second colfiorito event and the sellano event individual patches were calculated with maximum slip of 2 m implying stress drops as high as 20 mpa coulomb stress calculations show that the coseismic slip distribution for the colfiorito events facilitated slip of the adjacent sellano earthquake

abruzzo italy earthquakes of april 2009 heterogeneous fault slip models and stress transfer from accurate inversion of envisat insar data abstract the seismic sequence that occurred in the abruzzo apennines near l aquila italy in april 2009 caused extensive damage and a large number of casualties more than 300 the earthquake struck an area in the italian apennines chain where several faults belonging to adjacent seismotectonic domains create a complex tectonic regime resulting from the interaction among regional stress buildup local stress changes caused by individual earthquakes and viscous elastic stress relaxation understanding such complex interaction in the apennines can lead to a large step forward in the seismic risk mitigation in italy the abruzzo earthquake has been very well recorded by interferometric synthetic aperture radar insar data much better than the first italian earthquake ever recorded by satellites namely the 1997 umbria marche earthquake envisat environmental satellite data for the abruzzo earthquake are in fact very clear and allow an accurate reconstruction of the faulting mechanism we present here an accurate inversion of vertical deformation data obtained by envisat images aimed to give a detailed reconstruction of the fault geometry and slip distribution the resulting fault models are then used to compute by a suitable theoretical model based on the elastic dislocation theory the stress changes induced on the neighboring faults the correlation of the subsequent mainshocks and aftershocks of the abruzzo sequence with the volumes undergoing increasing coulomb stress clearly evidence the triggering effect of coseismic stress changes on further seismicity moreover this analysis put in evidence which seismotectonic domains have been more heavily charged by stress released by the abruzzo mainshocks the most important faults significantly charged by the abruzzo sequence belong to the sulmona and avezzano tectonic domains taking into account the average regional stress buildup in the area the positive coulomb stress changes caused by this earthquake can be seen as anticipating the next earthquakes in the neighboring domains of 15 20 yr