structural evolution and medium temperature thermochronology of central madagascar implications for gondwana amalgamation madagascar occupied an important place in the amalgamation of gondwana and preserves a record of several neoproterozoic events that are linked to orogenesis of the east african orogen in this study we integrate remote sensing field data and thermochronology to unravel complex deformation in the ikalamavony and itremo domains of central madagascar the deformation sequence comprises a gneissic foliation s1 followed by south to sw directed tight to isoclinal recumbent folding d2 these are overprinted by north trending upright folds that formed during an approximately east west shortening event d3 together these produced type 1 and type 2 fold interference patterns throughout the itremo and ikalamavony domains we show that the itremo and ikalamavony domains were deformed together in the same orogenic system which we interpret as the c 630 ma collision of azania with africa along the vohibory suture in southwestern madagascar in eastern madagascar deformation is syn to post 550 ma and probably formed in response to final closure of the mozambique ocean along the betsimisaraka suture that amalgamated madagascar with the dharwar craton of india apatite u pb and novel laser ablation triple quadrupole inductively coupled plasma mass spectrometry la qqq icp ms muscovite and biotite rb sr thermochronology indicates that much of central madagascar cooled through c 500 c at c 500 ma supplementary material a detailed geological map of central madagascar supplementary a detailed methods and geo and thermochronology results supplementary b isotopic data for geo and thermochronology supplementary c and landsat images and structural interpretation examples supplementary d are available at https doi org 10 6084 m9 figshare c 4840575

paleo to mesoarchean ttg accretion and continental growth in the western dharwar craton southern india constraints from shrimp u pb zircon geochronology whole rock geochemistry and nd sr isotopes a multidisciplinary study involving field petrographic shrimp u pb zircon titanite ages whole rock geochemical and nd sr isotope data is presented for the peninsular gneisses and associated plutons forming core of the dharwar craton two major periods 3350 3280 ma and 3230 3200 ma of crustal growth through ttg accretion sub contemporaneous with greenstone volcanism are documented elemental and nd sr isotope data suggest that the ttgs originated by low and high pressure melting of heterogeneous mafic sources thickened island arc or oceanic plateau crust at different depths among the early accreted ttgs magmatic protoliths of low al gneisses formed by low pressure 10 12 kbar melting of a depleted mafic source at shallow levels island arc type crust with plagioclase amphibole ilmenite in the residue whilst high al gneisses were probably produced by high pressure melting 14 18 kbar of a chondritic or a less depleted mafic source with garnet amphibole pyroxene ilmenite in the residue base of island arc crust or thickened oceanic plateau the 3230 3200 ma trondhjemitic plutons marking the second accretion event derived by higher pressure 14 16 kbar melting of a mafic source island arc type crust with garnet plagiocalse hornblende ilmenite with a minor involvement of previously accreted ttgs this plutonism was coeval with a major phase of crustal scale diapiric overturn that had a major imprint on crustal reworking a later magmatic episode at ca 3100 ma produced granitic plutons derived from crustal melting and leucocratic gneisses derived from a depleted mafic source in the lower crust documentation of depleted shallow and deep mantle reservoirs during 3350 3280 ma magmatism implies massive differentiation of the mantle during an earlier episode of crust formation around 3800 600 ma as substantiated by nd model ages and published pb isotope data as well as u pb detrital zircon ages with in situ hf isotope data

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

shrimp zircon and titanite u pb ages lu hf isotope signatures and geochemical constraints for 2 56 ga granitic magmatism in western dharwar craton southern india evidence for short lived neoarchean episodic crustal growth abstract shrimp u pb zircon and titanite age data for granites adjacent to the gadag greenstone belt ggb in the western dharwar craton wdc india establish the occurrence of voluminous 2 56 ga granitic magmatism and indicate the development and evolution of the ggb over a time span of 70 m y these new data show that the ggb has an evolutionary history distinct from the chitradurga greenstone belt cgb to the south which was previously considered to be linked to that of the ggb based on the continuity of lithological associations whole rock geochemical data indicate granites marginal to the ggb are potassic were derived from intracrustal melting of an arc crust without the involvement of mantle and demonstrates the prevalence of horizontal tectonics in the evolution of dharwar craton lu hf zircon studies indicate that these rocks were derived from a heterogeneous arc crust with distinct crustal histories on either side of the ggb the voluminous 2 56 ga granitic magmatism surrounding the ggb in the wdc in addition to the known 2 61 and 2 56 2 52 ga felsic magmatism supports a number of short lived episodic crustal growth events within the dharwar craton during the neoarchean over a period of 100 m y short lived episodic crustal growth during the archean typically within the time scale of few million years marks the distinction with long lived modern style subduction processes these variations are often attributed to hotter archean mantle and prevailing geodynamic regime

coupled u pb and rb sr laser ablation geochronology trace archean to proterozoic crustal evolution in the dharwar craton india abstract the western dharwar craton wdc and the karwar block kb in southern peninsular india provide important windows to earth s early crustal evolution and continental growth as these domains likely represent fragments of the first landmass or supercontinent on our planet here we employ for the first time a coupled laser ablation zircon u pb dating and in situ rb sr dating of micas biotite muscovite and feldspars to evaluate the meso to neoarchean crustal evolution and proterozoic magmatism metamorphism in the karwar block this novel approach based on integrated geochronological results show that the wdc and kb experienced i a major mesoarchean continental growth event c 3 2 to 2 9 ga ii younger neoarchean and paleoproterozoic magmatism migmatization syn and post tectonic granite formation events at c 2 8 2 6 ga and 2 2 ga respectively and iii mesoproterozoic metamorphism thermal imprint as young as 1 2 ga the zircon ehf t values exhibit a range from 0 4 to 9 8 in amphibolite hornblende gneiss and trondhjemite 3 28 3 08 ga as well as the 6 1 to 9 7 range for 2 96 ga old zircons in porphyritic granite which suggests juvenile source for the magmatism that constructed this crustal block overall this study illustrates the benefits of using coupled zircon u pb and in situ rb sr mica and feldspar dating approaches as the former u pb provides robust constraints or a baseline age for initial crystallization of crustal sequences whereas the latter rb sr is sensitive to younger magmatic and metamorphic events thus the integration of these two laser ablation icp ms based geochronometers applied to crustal evolution studies has the potential to provide more comprehensive insights into continental growth in the early earth and later magmatic and metamorphic history of the region

shear fracture pattern and microstructural evolution in transpressional fault zones from field and laboratory studies abstract zones of transpressional shear deformation accommodate strike slip and oblique slip displacements field work in a transpressive shear zone and transpressional analogue clay box modelling show that a p oriented foliation and associated p shears are preferentially developed over the more common r 1 riedel shears the carboneras fault system cfs in se spain is a left lateral transpressional shear zone with an internal geometry characterized by first order y oriented faults and widespread p oriented second order faults the mesoscopic to microscopic gouge fabric reflects the regional architecture of the shear zone being dominated by a pervasive poriented foliation and discrete y and p shears friction experiments carried out to investigate the textural evolution of gouge fabrics showed four textural stages of fabric development from foliation formation to extreme shear localization resulting in cross gouge failure transpression clay box models favoured the formation of secondary p oriented shear fractures and p oriented shear lenses further deformation caused differential shear lens rotation and shear lens orientations closer to the mean displacement direction our field studies and laboratory analogue experiments indicate that shear zones dominated by p shears are diagnostic of a transpressional deformation regime

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

the brittle plastic transition in experimentally deformed quartz aggregates deformation experiments have been conducted to provide constraints on the processes responsible for the brittle plastic transition in quartz aggregates a correlation between mechanical behavior and distinctive microstructural characteristics indicates that the brittle plastic transition in nonporous quartzite involves at least three transitions in deformation mechanism that occur with increasing temperature and or pressure first there is a transition from cataclastic faulting to semibrittle faulting microstructural observations indicate that this transition occurs due to the activation of dislocations in addition faulting is more stable in the semibrittle faulting regime due to the blunting of the stresses at the advancing fault tip by dislocation glide second there is a transition from semibrittle faulting to semibrittle flow this transition corresponds to a change from localized to distributed deformation microstructural observations indicate that microcracks nucleate in response to stress concentrations at dislocation pileups in the semibrittle flow regime we conclude that the transition to semibrittle flow occurs when the stress intensity at crack tips is insufficient to allow propagation across grain boundaries third there is a transition from semibrittle flow to dislocation creep microstructural observations suggest that this transition occurs as a result of an increase in grain boundary mobility with increasing temperature in addition microstructural observations indicate that a transition from dominantly mode i axial to mode ii shear microcracking occurs with an increase in confining pressure from 0 4 to 0 8 gpa regardless of temperature the differential stresses supported by the experimentally deformed samples are higher than those expected under geologic conditions however a comparison of the experimentally produced microstructures to those reported from natural fault zones suggests that similar processes are operative in the laboratory and in the earth the results of this study provide further evidence to indicate that the brittle plastic transition in the continental crust occurs over a relatively wide range of conditions

a review of the inferred geodynamic evolution of the dharwar craton over the ca 3 5 2 5 ga period and possible implications for global tectonics the geological history and evolution of the dharwar craton from ca 3 5 2 5 ga is reviewed and briefly compared with a second craton kaapvaal to allow some speculation on the nature of global tec

geochemical and numerical constraints on neoarchean plate tectonics this paper discusses early neoarchean 2 8 2 7 ga plate tectonics by integrating knowledge from new geochemical observations and numerical models based on a geochemical dataset of 295 granitoid samples from the karelian and kola cratons of the fennoscandian shield we divide neoarchean juvenile extracted from oceanic crust or mantle granitoids into three groups 1 low hree heavy rare earth elements ttgs tonalite trondhjemite granodiorite high sio2 low mg low hree higher sr lower ybn and higher nb ta 2 high hree ttgs slightly lower range of sio2 larger range of mgo contents and higher cr and ni contents high hree lower sr higher ybn and lower nb ta and 3 high ba sr sanukitoids medium hree high mg and high k ba sr the main difference between the low and high hree groups lies in their pressure sensitive element contents which indicates high pressure melting conditions for the low hree group and low pressure conditions for the high hree group a possible tectonic scenario for the genesis of the two groups is an incipient hot subduction underneath a thick oceanic plateau protocrust melting in the lower part of thick basaltic oceanic crust could produce ttgs of the low hree type whereas low pressure melting of subducting slab and possible interactions with the mantle wedge at shallow depths would be capable of generating high hree ttgs the third group of archean high ba sr sanukitoids was formed after the ttgs their low sio2 and high mg k ba sr contents suggest an origin by melting in an enriched metasomatized mantle source probably as a result of a slab breakoff following a continental collision or attempted subduction of a thick oceanic plateau ttg protocontinent such hypothesis is supported by numerical modeling results that suggest an increased occurrence of slab breakoff in the archean which locally increased temperatures within the mantle wedge more frequent breakoff resulted because subducting plates were weaker due to rheologically thinner lithosphere and a thicker basaltic crust and tensile stresses within the subducting plate were larger due to a thick crust that transforms from buoyant basalt to dense eclogite

the main variscan deformation event in the pyrenees new data from the structural study of the bielsa granite abstract a structural and magnetic fabric study of the bielsa granite axial zone of the pyrenees provides new data indicating that this pluton was emplaced during the main variscan event recognized in the pyrenees we argue that the later post triassic deformation was localized along mylonitic bands reactivating earlier variscan shear bands the bielsa granite intrudes cambro ordovician metasediments at its northern border and the pluton is unconformably overlain by sediments triassic in age to the south and east the main structures in the igneous body are magmatic foliations and lineations defined by feldspar phenocrysts and biotite and dextral shear bands with dominant wnw ese trends the wnw ese striking magmatic foliations have variable dips and the magmatic lineation a subhorizontal wnw ese trend the zonation of low field magnetic susceptibility coarsely related to mineral content indicates a layer arrangement of rock types with more basic compositions at the northern border the magnetic ellipsoids are prolate along a wnw ese central band and oblate at the pluton borders where flattening is more important all these data allow us to interpret the bielsa intrusion as being caused by coeval nne shortening and dextral shear the presence of shear bands indicates that strain localization under dextral transpression continued during late variscan times

deformation mechanisms in granitic rocks at shallow crustal levels abstract microstructural observations of naturally faulted granitic gneisses show that feldspar grains are weaker than quartz grains at temperatures below 325 c and at depths of less than 8 10 km feldspar grains sustained most of the deformation by grain scale faulting slip along cleavage controlled fractures and cataclasis fracture of feldspar grains within fault zones promoted their alteration to kaolinite quartz grains also deformed by fracturing and often healed to form quartz porphyroclasts and mosaics in a comminuted matrix of feldspar and kaolinite syntectonic alteration of the feldspar grains may have weakened the fault zones over time and resulted in foliated textures within the fault zones this study of naturally deformed rocks confirms published experimental results on the behavior of granitic rocks at low temperatures and pressures and taken together these data show that the theology of the upper 10 km of the crust is greatly influenced by cataclastic processes in feldspar

source inversion of w phase speeding up seismic tsunami warning w phase is a long period phase arriving before s wave it can be interpreted as superposition of the fundamental first second and third overtones of spheroidal modes or rayleigh waves and has a group velocity from 4 5 to 9 km s 1 over a period range of 100 1000 s the amplitude of long period waves better represents the tsunami potential of an earthquake because of the fast group velocity of w phase most of w phase energy is contained within a short time window after the arrival of the p wave at a distance of 50 w phase energy is contained within 23 min after the origin time which is the distinct advantage of using w phase for rapid tsunami warning purposes we use a time domain deconvolution method to extract w phases from the broad band records of global seismic networks the bandwidth of w phase is approximately from 0 001 to 0 01 hz and we bandpass filter the data from 0 001 to 0 005 hz in most cases having extracted w phase from the vertical component records we perform a linear inversion using a point source to determine mw and the source mechanism for several large earthquakes including the 2004 sumatra andaman earthquake the 2005 nias earthquake the 2006 kuril is earthquake and the 2007 sumatra earthquake w phase inversion yields reliable solutions and holds promise of the use of w phase for rapid assessment of tsunami potential

alteration and mass transfer in cataclasites and mylonites in 6 6 km of granitic crust at the siljan impact structure central sweden granitic rocks deformed by cataclasis and mylonitization on macro a few meters and micro thin section scales are found at depths down to 6 6km in the siljan impact structure in central sweden granites near fault planes exhibit 1 fracturing kinking fragmentation and recrystallization of feldspars into pure k and na endmember varieties 2 fragmentation polygonization and development of undulose extinction in quartz and 3 kinking appearance of wavy extinction and alteration of biotite chlorite amphibole and alteration of ilmenite and magnetite whole rock chemical analyses of deformed and undeformed rocks show that deformed rocks are enriched in sio2 by about 5 wt and depleted in other oxides by variable percentages apart from rb and co the concentrations of other trace elements including ba sr zn zr pb cd cu cr ni v u th la and li are lower in deformed relative to undeformed rocks mass balance calculations for a 1000 cm3 model granite which were based on modal mineralogy whole rock chemistry and mineral analyses suggest that the break down of primary biotite chlorite and amphibole in deformed zones released elements to circulating fluids these calculations also indicate liberation of water and a doubling of porosity from 1 to 2 during the deformation episodes later precipitation of minerals in shear and tension fractures reduced this porosity within the upper 2000 m of the gravberg 1 well the formation of fracture filling minerals smectite calcite hematite chlorite and albite is impact related and was favored by active circulation of meteoric water fracture filling minerals in the upper 2000 m of the borehole formed at temperatures of 70 to 200 c between depths of 2000 and 3500 m fracture filling mineral assemblages dominated by fe mg chlorite sphene and epidote suggest formation temperatures in the range of 150 to 300 c occurrence of pumpellyite and prehnite in some altered biotite and chlorite of the deformed zones between 3500 and 5500 m suggest preimpact metamorphism and formation temperature above 150 c below 5500 m the mineral assemblages in the fractures are dominated by quartz sphene epidote and some muscovite and chlorite indicating a temperature range between 300 and 450 c one of the possible origins for the ch4 and h2 gases detected in the gravberg 1 well is a combination of hydrogen ions released by decomposition of hydrated silicates biotite chlorite hornblende with carbon the presence of iron in the deformed granitic rocks prevented the resulting ch4 from being oxidized

formation of archean 3600 2500 ma continental crust in the dharwar craton southern india abstract the generation preservation and destruction of continental crust on earth is of wide interest in understanding the formation of continents cratons and supercontinents as well as related mineral deposits in this contribution we integrate the available field petrographic geochronologic elemental nd hf pb isotope data for greenstones ttg gneisses sanukitoids and anatectic granites from the dharwar craton southern india this review allows us to evaluate the accretionary processes of juvenile crust mechanisms of continental growth and secular evolution of geodynamic processes through the 3600 2500 ma window hence providing important insights into building of continents in the early earth the dharwar craton formed by assembly of micro blocks with independent thermal records and accretionary histories the craton can be divided into three crustal blocks western central and eastern separated by major shear zones the western block contains some of the oldest basement rocks with two generations of volcano sedimentary greenstone sequences and discrete potassic plutons whereas the central block consist of older migmatitic ttgs abundant younger transitional ttgs remnants of ancient high grade supracrustal rocks linear volcanic dominated greenstone belts voluminous calc alkaline granitoids of sanukitoid affinity and anatectic granites in contrast the eastern block comprises younger transitional ttgs abundant diatexites thin volcanic sedimentary greenstone belts and calc alkaline plutons published geochronologic data show five major periods of felsic crust formation at ca 3450 3300 ma 3230 3150 ma 3000 2960 ma 2700 2600 ma and 2560 2520 ma which are sub contemporaneous with the episodes of greenstone volcanism u pb ages of inherited zircons in ttgs as well as detrital zircons together with nd pb hf isotope data reveal continental records of 3800 3600 ma the u pb zircon data suggest at least four major reworking events during ca 3200 ma 3000 ma 2620 2600 ma and 2530 2500 ma corresponding to lower crustal melting and spatially linked high grade metamorphic events the ttgs are sub divided into the older 3450 3000 ma ttgs and the younger 2700 2600 ma transitional ttgs the older ttgs can be further sub divided into low al and high al groups elemental and isotopic data suggest that the low al type formed by melting of oceanic island arc crust within plagioclase stability field in contrast the elemental and isotopic features for the high al group suggest derivation of their magmatic precursor by melting of oceanic arc crust at deeper levels 55 65 km with variable garnet and ilmenite in residue the transitional ttgs likely formed by melting of composite sources involving both enriched oceanic arc crust and sub arc mantle with minor contamination of ancient crustal components the geochemical and isotopic compositions of granitoids with sanukitoid affinity suggest derivation from enriched mantle reservoirs finally anatectic granites were produced by reworking of crustal sources with different histories in the light of the data reviewed in this contribution we propose the following scenario for the tectonic evolution of the dharwar craton during 3450 3000 ma ttgs sources oceanic arc crust formed by melting of down going slabs and subsequent melting of such newly formed crust at different depths resulted in ttg magmas on the contrary by 2700 ma the depth of slab melting increased melting of slab at greater depth alongside the detritus results in enriched melts partly modified the overlying mantle wedge subsequent melting of such newly formed enriched oceanic arc crust and surrounding arc mantle generated the magmatic precursor to transitional ttgs finally at ca 2600 2560 ma eventual breakoff of down going slab caused mantle upwelling which induced low degree 10 15 melting of overlying enriched mantle at different depths thereby generating the sanukitoid magmas which upon emplacement into the crust caused high temperature metamorphism reworking and final cratonization the crustal accretion patterns in the dharwar craton share similarities with those in other archean cratons such as the bundelkhand craton in central india pilbara yilgarn craton in western australia southern africa swaziland and limpopo belt north china craton tanzania craton antongil craton ne madagascar

neoarchean microblock amalgamation in southern india evidence from the nallamalai suture zone abstract a collage of crustal blocks ranging in age from mesoarchean to neoarchean accreted to the southern margin of the dharwar craton in peninsular india preserve distinct evolutionary history but share a common metamorphic record during archean proterozoic transition here we investigate the tectonic boundary between two of these microblocks the shevaroy block to the west and the madras block to east termed as the nallamalai suture zone nlsz we present integrated field petrological geochemical and zircon u pb and lu hf data from a suite of meta igneous and metasedimentary units along the nlsz and its flanks zircon grains from the meta monzogranite hornblende biotite gneiss amphibolite granodiorite diorite charnockite bif banded iron formation and bmq from this area show magmatic emplacement ages clustering around 2 50 to 2 56 ga except for the meta monzogranite showing ages up to 3 2 ga correlating with long lived convergent margin magmatism through multiple slab melting episodes all the rocks show tightly constrained early paleoproterozoic ca 2 46 2 48 ga metamorphic ages including the metamorphic zircon in the bifs marking the timing of collision of the two continental blocks with consumption of the intervening oceanic lithosphere the ehf t values of magmatic zircon grains from the different rock types range from 4 1 to 5 7 and together with t dm c hf model ages of 2672 3247 ma a dominantly juvenile crust growth is indicated which initiated around 3 3 ga and continued to 2 7 ga followed by crustal reworking in a continental arc towards the end of neoarchean the geochemical data suggest that tholeiitic to calc alkaline parental melts for the mafic intermediate felsic suite were generated by low degree partial melting of a peridotitic mantle wedge metasomatized by subduction derived fluids and sediments and continuous slab melting ensued by intracrustal fractional crystallization of melts with reworking of older continental crust the bif and bmq samples display positive eu anomalies negative to negligible ce anomalies and superchondritic y ho ratios suggesting their formation in an oceanic realm proximal to an active continental margin setting the magmatic and tectonic attributes are consistent with eastward oceanic subduction and ocean closure along the nlsz which is defined here as the trace of a suture welding the shevaroy and madras blocks we envisage that multiple subduction and amalgamation of several microblocks occurred in the dharwar craton and its southern domains amalgamating several microblocks during the archean paleoproterozoic transition

earthquake source parameters and stress distribution in the adak island region of the central aleutian islands alaska source parameters have been systematically determined for all earthquakes with mw 5 that occurred between 172 w and 179 w longitude in the adak island region of the central aleutian islands during 1977 march 1987 we relocate the events using a plate velocity model developed for the region and use two alternative methods of depth determination the first method uses arrival times of direct and prominent reflected phases primarily pwp the second method uses broadband p wave displacement seismograms in an inversion for source depth the analysis of these events provides a well constrained data set for the study of stress release along an active subduction zone three earthquakes which occurred seaward of the trench axis are located just below the crust mantle interface and show extension nearly perpendicular to the trench axis seven events occurred in the wadati benioff zone sixty four events are located in the main thrust zone and except for five unusual events are characterized by thrust mechanisms with one nodal plane dipping north at a shallow angle in cross section the thrust zone appears as a thin 10 15 km thickness interplate region which extends from 15 to 50 km depth a 10 15 average discrepancy between observed slip vector azimuths and the predicted relative motion direction between the pacific and north american plates exists for these events the observed slip vectors are oriented more normal to the trench than is predicted by plate motions five earthquakes which occurred as aftershocks to the may 7 1986 earthquake mw 8 0 in the crust of the overriding plate have strike slip mechanisms consistent with right lateral motion on arc parallel fault planes observations of slip vectors along the whole aleutian arc show a similar trend to that observed in the adak island region the largest differences 30 between observed and predicted slip azimuths occur around 175 e we propose a model of plate interaction in which a portion of the along arc motion occurs along a weak strike slip shear zone in the upper plate near the volcanic line the slip azimuths in the main thrust zone fit this model well if the amount of transcurrent slip occurring in the upper plate is 60 of the arc parallel relative plate motion a consequence of the model is along arc extension of the overriding plate between the accretionary wedge and the volcanic line especially in the western part of the aleutian arc calculations based on a tectonic model by geist et al 1988 for the formation of arc summit basins through block rotation and translation suggest that along arc extension has been significant since late miocene or early pliocene

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

cataclastic flow and semi brittle deformation of anorthosite abstract a series of experiments on dry bushveldt anorthosite an 75 350 m grain size 5 impurities is carried out at 25 700 c 500 1500 mpa pressures and 10 5 s 1 strain rate the strength of the bushveldt anorthosite remains pressure sensitive throughout the applied p t range while weakening occurs with increased temperature at a given pressure a transition from stick slip to stable sliding occurs at 200 300 c and pressures of 1500 mpa reduction in strength at 200 300 c localized cataclastic flow and lack of microscopic evidence of crystal plastic deformation raises the possibility that the transition may be coincident with the propagation of a critical number of randomly distributed thermal cracks uniform ductile flow occurs only at temperatures of 600 and 700 c and 1000 1500 mpa pressures coincident with the development of mechanical twinning patchy and banded undulatory extinction and is likely to be due to semi brittle deformation under these conditions the deformation remains distributed to strains as high as 44

description and kinematics of the se loreto basin fault array baja california sur mexico a positive field test of oblique rift models abstract we present the results of mapping and kinematic analysis on an 18 km2 array of normal and oblique slip faults in the se loreto basin near loreto baja california sur mexico the fault array developed on the western margin of the gulf of california in late pliocene time during the early part of the modern stage of oblique rifting of the gulf the se loreto fault array is an antithetic transfer zone between two large e dipping normal faults the fault array is coherent and formed in one episode the dominant n to nne striking faults primarily dip w and display nearly pure normal slip more ne striking faults show normal sinistral slip and nw striking faults have dextral normal to dextral slip n to nw striking faults have steeper dips and a greater component of dextral slip with more northwesterly strike bulk extension based on strain analysis of faults with striae is oriented nearly e w with little plunge and consistent throughout the fault array the kinematic analysis of the se loreto fault array provides a well constrained test of oblique rift models our results support previous modeling of homogeneous extension in oblique rifted margins when both instantaneous and finite strain are considered positive field tests of analytical and experimental models such as this one indicate that such models may be robust predictors of the obliquity of rifting in ancient mountain belts where brittle fault arrays are preserved but plate motions are unknown

u pb and hf isotope records in detrital and magmatic zircon from eastern and western dharwar craton southern india evidence for coeval archaean crustal evolution abstract u pb and lu hf isotopic records in detrital and magmatic zircons from the eastern and the western dharwar craton edc and wdc suggest presence of 3 4 ga crustal components in both the blocks magmatic zircon from the western block has ages ranging between 3 1 and 3 2 ga while those from the eastern block show a bi modal age distribution with records of 3 0 3 2 ga protolith components as well as 2 7 and 2 5 ga metamorphic overgrowths detrital and magmatic zircons from granitoid conglomerate clasts of the western dharwar block show initial hf values consistent with models for the early archaean mantle suggesting their juvenile character lower hf values in younger as well as detrital zircons from eastern dharwar block reflect importance of reworking of 3 2 ga crust the combined u pb and hf isotope study strengthens suggestions for contemporaneous crust formation processes in both the western and eastern parts of the dharwar craton

introduction to global tsunami science past and future volume ii twenty two papers on the study of tsunamis are included in volume ii of the pageoph topical issue global tsunami science past and future volume i of this topical issue was published as pageoph vol 173 no 12 2016 eds e l geist h m fritz a b rabinovich and y tanioka three papers in volume ii focus on details of the 2011 and 2016 tsunami generating earthquakes offshore of tohoku japan the next six papers describe important case studies and observations of recent and historical events four papers related to tsunami hazard assessment are followed by three papers on tsunami hydrodynamics and numerical modelling three papers discuss problems of tsunami warning and real time forecasting the final set of three papers importantly investigates tsunamis generated by non seismic sources volcanic explosions landslides and meteorological disturbances collectively this volume highlights contemporary trends in global tsunami research both fundamental and applied toward hazard assessment and mitigation

mylonite development in the hercynian basement of sardinia italy abstract plastic deformation predominates over large areas in the hercynian basement of sardinia during lower carboniferous continental shortening mylonitization associated with ubiquitous top to south southwest thrusting decreases from internal central sardinia to foreland areas southern sardinia in the barbagia unit mylonites completely obliterate all the previous structures in the meana sardo unit plastic deformation strongly overprints early folds and in the gerrei unit mylonites are found only below the meana sardo thrust a thick shear zone the baccu locci mylonite zone develops between the gerrei and riu gruppa units inferences from deformation mechanisms in quartz mylonites suggest a temperature during deformation below 400 c along thrusts throughout the study area overprinting relationships between foliations deformation of annealed microstructures and porphyroblasts with inclusion patterns indicate that crystal growth occurred after early thrusting events and before the main nappe emplacement phase microstructural investigations in the baccu locci mylonites record two changes in the main deformation mechanism operating during progressive mylonitization in the early stages of deformation most of the strain is accommodated by dislocation creep in a fine grained quartz matrix at higher strain dynamic recrystallization fully affects larger quartz crystals producing pure quartz layers where plastic deformation and strain localize ongoing deformation together with syntectonic breakdown of feldspar producing mica leads to mineral changes grain size reduction and reaction softening with strain localization in the fine matrix again dynamically deformed quartz is boudinaged in the later stages of mylonitization significant fluid infiltration during deformation can account for some of the large ore bodies hosted in the baccu locci mylonites

improvements of precision and accuracy in in situ hf isotope microanalysis of zircon using the laser ablation mc icpms technique abstract we have developed a new analytical technique for precise and accurate in situ hf isotope ratio measurements for zircons by means of laser ablation multiple collector inductively coupled plasma mass spectrometry la mc icpms newly designed sample cell and n 2 mixing technique provided higher elemental sensitivity with smoother signal intensity profiles in order to improve the accuracy of the hf isotope ratio analysis previously reported correction methods for isobaric interferences on 176 hf by 176 yb and 176 lu were rigorously evaluated and we found that the use of independent mass bias factors for hf and yb in the isobaric interference correction resulted in more reliable hf isotopic data in order to test the reliability of the hf isotopic data from 35 m diameter ablation pits that are smaller than the typical size of most zircon grains lu hf isotopes for three zircons harvard 91500 antarctic zircon pma7 and acasta zircon ay199 were measured the present 176 hf 177 hf isotope ratio of 0 282321 46 2 s d and initial 176 hf 177 hf isotope ratio of 0 282315 47 2 s d were obtained for zircon standard 91500 the resulting present 176 hf 177 hf isotope ratio shows an excellent agreement with the previously reported data our in situ isotopic data revealed that the lu hf ratio varied significantly within the 91500 grain 176 lu 177 hf 0 000130 0 000345 suggesting the existence of slight isotopic heterogeneity in present 176 hf 177 hf approximately 15 ppm for antarctic zircon pma7 despite the smaller size of the single grain 50 100 m wide 80 300 m long and the presence of various mineral inclusions resulting analytical precision for the initial 176 hf 177 hf ratio was 128 ppm 0 281208 36 2 s d for acasta zircon ay199 despite the high yb hf 0 05 and lu hf 0 01 isotope ratios with the early archean crystallization age 3 74 ga resulting analytical precision for the initial 176 hf 177 hf ratio was 187 ppm 0 280160 52 2 s d these results demonstrate clearly that in situ hf isotope ratio microanalysis developed here has the potential to become a significant tool for zircon lu hf isotopic study

the tsunami induced by the 2003 zemmouri earthquake mw 6 9 algeria modelling and results summary a strong tsunami with sea disturbances observed along the algerian coast but with significant damage mainly in the balearic islands spain harbours affected the western mediterranean following the 2003 zemmouri earthquake m w 6 9 algeria an average regional uplift of 0 55 m was measured along the shoreline in the epicentral area field observations main shock and aftershocks characteristics are consistent with thrust along a 55 km long rupture trending ne sw dipping se the seismotectonic parameters indicate a hypocentre 7 8 km deep and a possible fault break between 5 and 15 km offshore several tide gauges located in the western mediterranean coast indicated an average of 0 4 m of sea level change with a maximum of 2 m in the balearic islands we generated high resolution bathymetry grids from the algerian coasts to the balearic islands coasts in order to test different seismic sources with different fault rupture location strike and dip and model the tsunami initiation and propagation for the modelling we employed the crank nicolson numerical schema with a finite difference method and the okada elastic dislocation theory for the fault rupture we also highlight the different factors responsible for waves amplification around the balearic coast the best fit between synthetic and real data tide gauges gps levelling and coastal uplift as compared to run up values are obtained for a thrust rupture comparable with the earthquake fault inferred from seismotectonic studies and located within 15 km offshore an analysis of t waves reinforces the earthquake rupture origin for the tsunami this study presents the results and modelling of a major tsunami recorded in the western mediterranean sea

structural characteristics of granitic plutons emplaced during weak regional deformation examples from late carboniferous plutons morocco abstract strain patterns have been investigated around shallow crustal granitic plutons emplaced during weak regional deformation in the western moroccan hercynian belt the plutons are distributed along reactivated deep faults and display elliptical shapes which are consistently oriented with respect to the regional strain field pluton age orientation and ellipticity can be correlated with strain history ductile deformation and contact metamorphism are mainly located in the thermally softened aureoles finite strain gradients towards plutons are accompanied by the development of superimposed microstructures finite strain trajectories and variations of strain ellipsoid shapes exhibit perturbations of the regional strain field around plutons structures internal to the plutons are continuous with regional structures foliation development in granitoids records a decrease in temperature during syntectonic pluton cooling geometry and kinematics of deformation reflect the influence of both regional deformation and pluton intrusion

global seismicity of 2003 centroid moment tensor solutions for 1087 earthquakes abstract centroid moment tensor cmt solutions are presented for 1087 earthquakes that occurred during 2003 the solutions are obtained using the method of dziewonski et al dziewonski a m chou t a woodward j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 and applying corrections for aspherical earth structure as represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging vol 19 plenum press new york pp 785 797 the model of inelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of inelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms the focal mechanisms of the largest or otherwise significant earthquakes of 2003 are reviewed

grain size reduction of feldspars by fracturing and neocrystallization in a low grade granitic mylonite and its rheological effect abstract feldspar grain size reduction occurred due to the fracturing of plagioclase and k feldspar myrmekite formation and neocrystallization of albitic plagioclase along shear fractures of k feldspar porphyroclasts in the leucocratic granitic rocks from the yecheon shear zone of south korea that was deformed under a middle greenschist facies condition the neocrystallization of albitic plagioclase was induced by strain energy adjacent to the shear fractures and by chemical free energy due to the compositional disequilibrium between infiltrating na rich fluid and host k feldspar with increasing deformation from protomylonite to mylonite alternating layers of feldspar quartz and muscovite developed the fine grained feldspar rich layers were deformed dominantly by granular flow while quartz ribbons were deformed by dislocation creep with layer development and a more distributed strain in the mylonite lower stresses in the quartz rich layers resulted in a larger size of dynamically recrystallized quartz grains than that of the protomylonite

multi stage crustal growth and neoarchean geodynamics in the eastern dharwar craton southern india abstract the dharwar craton is a composite archean cratonic collage that preserves important records of crustal evolution on the early earth here we present results from a multidisciplinary study involving field investigations petrology zircon shrimp u pb geochronology with in situ hf isotope analyses and whole rock geochemistry including nd isotope data on migmatitic ttg tonalite trondhjemite granodiorite gneisses dark grey banded gneisses calc alkaline and anatectic granitoids together with synplutonic mafic dykes along a wide northwest southeast corridor forming a wide time window in the central and eastern blocks of the dharwar craton the dark grey banded gneisses are transitional between ttgs and calc alkaline granitoids and are referred to as transitional ttgs whereas the calc alkaline granitoids show sanukitoid affinity our zircon u pb data together with published results reveal four major periods of crustal growth ca 3360 3200 ma 3000 2960 ma 2700 2600 ma and 2570 2520 ma in this region the first two periods correspond to ttg generation and accretion that is confined to the western part of the corridor whereas widespread 2670 2600 ma transitional ttg together with a major outburst of 2570 2520 ma juvenile calc alkaline magmatism of sanukitoid affinity contributed to peak continental growth the transitional ttgs were preceded by greenstone volcanism between 2746 ma and 2700 ma whereas the calc alkaline magmatism was contemporaneous with 2570 2545 ma felsic volcanism the terminal stage of all four major accretion events was marked by thermal events reflected by amphibolite to granulite facies metamorphism at ca 3200 ma 2960 ma 2620 ma and 2520 ma elemental ratios la yb n sr y nb ta hf sm and hf nd isotope data suggest that the magmatic protoliths of the ttgs emplaced at different time periods formed by melting of thickened oceanic arc crust at different depths with plagioclase amphibole garnet titanite ilmenite in the source residue whereas the elemental ba sr la yb n sr y nb ta hf sm and hf nd isotope data ehf t 0 67 to 5 61 end t 0 52 to 4 23 of the transitional ttgs suggest that their protoliths formed by melting of composite sources involving mantle and overlying arc crust with amphibole garnet clinopyroxene plagioclase ilmenite in the residue the highly incompatible and compatible element contents ree k ba sr mg ni cr together with hf and nd isotope data ehf t 4 5 to 3 2 end t 1 93 to 1 26 of the sanukitoids and synplutonic dykes suggest their derivation from enriched mantle reservoirs with minor crustal contamination field elemental and isotope data ehf t 4 3 to 15 0 end t 0 5 to 7 0 of the anatectic granites suggest their derivation through reworking of ancient as well as newly formed juvenile crust secular increase in incompatible as well as compatible element contents in the transitional ttgs to sanukitoids imply progressive enrichment of neoarchean mantle reservoirs possibly through melting of continent derived detritus in a subduction zone setting resulting in the establishment of a sizable continental mass by 2700 ma which in turn is linked to the evolving earth the neoarchean geodynamic evolution is attributed to westward convergence of hot oceanic lithosphere with continued convergence resulted in the assembly of micro blocks with eventual slab break off leading to asthenosphere upwelling caused extensive mantle melting and hot juvenile magma additions to the crust this led to lateral flow of hot ductile crust and 3d mass distribution and formation of an orogenic plateaux with subdued topography as indicated by strain fabric data and strong seismic reflectivity along an e w crustal profile in the central and eastern blocks of the dharwar craton

eoarchean to mesoarchean crustal evolution in the dharwar craton india evidence from detrital zircon u pb and hf isotopes abstract the formation and evolution of continental crust in the early earth are of fundamental importance in understanding the emergence of continents their assembly into supercontinents and evolution of life and environment the dharwar craton in southern india is among the major archean cratons of the world where recent studies have shown that the craton formation involved the assembly of several micro continents during meso to neoarchean through subduction accretion collision processes here we report u pb hf isotope data from detrital zircons in a suite of metasediments including quartz mica schist fuchsite quartzite and metapelite from the southern domain of the chitradurga suture zone that marks the boundary between the western and central dharwar craton morphology and internal structure of the zircon grains suggest that the dominant population was derived from proximal granitic felsic sources zircon u pb data are grouped into paleo mesoarchean and neoarchean to paleoproterozoic with peaks at 3227 ma and 2575 ma the age spectra of detrital zircon grains in combination with the lu hf isotopic analyses indicate sediment provenance from magmatic sources with model ages in the range of ca 3 67 to 2 75 ga a transition from dominantly juvenile to a mixture of juvenile and recycled crustal components indicate progressive crustal maturity the results from this study suggest major crustal growth events during ca 3 2 ga and 2 6 ga in dharwar our study provides insights into continental emergence weathering and detrital input through river drainage systems into the trench during eoarchean to mesoarchean

petrography chemistry and isotopic ages of peninsular gneiss dharwar acid volcanic rocks and the chitradurga granite with special reference to the late archean evolution of the karnataka craton southern india abstract new petrographic major and trace element and isotopic age data are presented for four suites of rocks from the low to medium grade part of the south indian archaean craton in central karnataka two suites are from the peninsular gneiss basement to the late archaean dharwar supergroup the third is a suite of dharwar potassic rhyolites and the fourth is from the chitradurga granite which has intrusive contacts with the dharwar supergroup the chikmagalur granite granodiorite which with its host gneisses forms part of the basement peninsular gneiss to the dharwar supergroup in the bababudan basin yields rb sr and pb pb whole rock isochron dates of 3080 110 ma and 3175 45 ma respectively an initial 87 sr 86 sr ratio of 0 7013 0 0009 and a 1 value 238 u 204 pb of 7 98 host tonalitic gneisses to the chikmagalur granite give an rb sr whole rock isochron date of 3060 160 ma with an initial 87 sr 86 sr ratio of 0 7015 0 0004 and a pb pb whole rock isochron date of 3190 100 ma with a model 1 value of 8 00 a suite of granites and granodioritic tonalitic gneisses chitradurga granitic rocks and gneisses forming part of the peninsular gneiss basement to the dharwar supergroup west of the chitradurga belt yields rb sr and pb pb whole rock isochron dates of 2970 100 ma and 3028 28 ma respectively with an initial 87 sr 86 sr ratio of 0 7035 0 0013 and a model 1 value of 7 62 the suite of dharwar acid volcanic rocks from north of honnali defines a poorly fitted 207 pb 206 pb linear array mswd 15 8 which gives an apparent age of 2565 28 ma and a model 1 value of 7 46 the poor fit of this isochron shows that a closed system was not maintained a conclusion supported by high k abundances which are attributed to a syn or post magmatic ion exchange process the chitradurga granite which intrudes the older rocks of the dharwar supergroup in the chitradurga belt yields a well fitted pb pb whole rock isochron date of 2605 18 ma with a model 1 value of 7 68 the u pb relations in these suites from karnataka are in marked contrast with the commonly severe u depletion and consequently unradiogenic pb isotopic compositions observed in deeply eroded high grade archaean gneiss terranes such as those bordering the north atlantic this contrast indicates that the cratonic rocks in central karnataka represent a relatively high level in the original archaean continental crust

earthquake near field and w phase observations at teleseismic distances near field phases can be observed on individual broadband seismograms at teleseismic distances from great earthquakes even at distances of 20 30 such phases can have amplitudes of several tenths of a mm while previous studies have identified near field phases in vertical component data i show that such phases can be much more easily observed using the transverse component although observed effects agree well with complete waveform calculations using point moment tensor sources they do not satisfy some of the assumptions commonly made in seismic data analysis it is therefore suggested that care be taken in the analysis of very broadband seismograms which may contain these effects recent w phase observations are shown to be a case in point

very fast characterization of focal mechanism parameters through w phase centroid inversion in the context of tsunami warning most of the tsunami potential seismic sources in the neam region are in a magnitude range of 6 5 le m w le 7 5 e g the tsunami triggered by the boumerdes earthquake of 2003 with m w 6 9 the centre d alerte aux tsunamis cenalt in operation since 2012 as the french national tsunami warning centre ntwc and candidate tsunami service provider ctsp has to issue warning messages within 15 min of earthquake origin time these warnings are based on the seismic source parameters m w magnitude focal depth and type of fault which are computed by focal mechanisms and centroid inversion methods the w phase method developed by kanamori and rivera allows quick computation of seismic source parameters due to the early arrival time between p waves and surface waves and is therefore particularly useful for monitoring we assess the w phase method with 29 events of magnitude m w ge 5 8 for the period 2010 2015 in the neam region results with 10 min of signal length are in good agreement compared to the global centroid moment tensor gcmt catalog

anorthosites from an archean continental arc in the dharwar craton southern india implications for terrane assembly and cratonization abstract anorthositic rocks have attracted attention in terms of their possible role as the primordial crust of our planet and also as markers of archean paleoproterozoic plate tectonic regimes here we investigate the konkanhundi gabbro anorthosite suite from peninsular india adjacent to the major collisional suture between the western and eastern dharwar cratonic blocks the anorthosites display high al2o3 contents with negative correlation against mgo high cao and sr contents and positive eu anomalies indicating plagioclase flotation in the magma chamber the pyroxenite and gabbroic rocks of the suite show high ni cr co contents and geochemical features typical of pyroxene cumulation la icpms u pb analyses of magmatic zircon grains yield weighted mean 207pb 206pb ages of 2601 12 ma for pyroxenite 2616 12 ma for gabbro 2615 13 ma and 2627 14 ma for anorthositic gabbro 2594 16 ma for anorthosite and 2605 27 ma for microgabbro the age data from the different rock types in the anorthosite suite are broadly consistent marking the emplacement time as ca 2 6 ga and providing insights on one of the oldest anorthosite complexes in peninsular india zircon grains in the surrounding ttg gneisses into which the gabbro anorthosite suite was emplaced show weighted mean 207pb 206pb age of 3321 11 ma suggesting mesoarchean basement the zircon grains display high th u values and ree patterns typical of magmatic crystallization with enriched hree positive ce and sm anomalies and negative pr nd eu anomalies zircon lu hf analysis yield negative ehf t values of 4 9 0 7 with t dm c two stage model ages of 3123 3376 ma for pyroxenite 4 5 1 7 and 3192 3366 ma for gabbro 5 3 0 9 and 3034 3410 ma for anorthositic gabbro and 3 9 2 4 and 3221 3311 ma respectively suggesting the incorporation of mesoarchean components within the neoarchean magmatic suite however zircon grains in the ttg gneiss possess more juvenile ehf t values in the range of 0 2 1 3 with t dm c in the range of 3554 3646 ma the zircon hf isotopes and trace element data together with the whole rock geochemical features suggest that the parent magma of the konkanhundi gabbro anorthosite suite was derived from subduction related depleted mantle source that also incorporated continental crustal components the time of emplacement of the gabbro anorthosite complex broadly correlates with widespread arc magmatism and crust production as well recycling in other domains of the dharwar craton we envisage multiple convergence of microblocks during craton assembly at the end of archean in dharwar with the greenstone belts marking zones of paleo ocean closure

strain patterns within the late variscan granitic dome of velay french massif central the velay granites are intruded as a late variscan dome in the french massif central strain patterns within the velay granites reflect the geometry and kinematics of late carboniferous deformation at the site of final emplacement the internal deformation developed during granitic magmatism is not homogeneously distributed from inner to outer zones increasing deformation is marked by changes from high temperature foliations to s c orthogneisses strain concentration at the margins reflects a strength contrast due to cooling and subsequent magma hardening according to the internal strain field two zones can be distinguished in the velay dome i a central and southern zone where concentric patterns indicate a southward expansion of granites and ii a northern zone where the lateral expansion is limited and combined with top to the north extensional shearing along the mont pilat detachment zone and high temperature wrenching these asymmetric strain patterns relate to the expansion and deformation of granites emplaced below a detachment fault during the uplift of a thickened area post thickening combination of extensional and wrench tectonics is inferred

weakening of deforming granitic rocks with layer development at middle crust abstract in the middle crust deformation of granitic rocks is characterized by crystal plastic deformation of quartz and cataclasis of feldspar for common granitic rocks with textures of framework feldspar and interstice filling quartz brittle strength of feldspar is a close approximation of the bulk rock strength because feldspar forms the load bearing framework with deformation these rocks tend to develop localized high strain zones the high strain zones commonly consist of quartz rich layers and feldspar rich layers we have examined how the strength of granitic rocks changes with the volume fraction of these layers by combining the flow laws developed by handy et al handy m r wissing s b streit l e 1999 frictional viscous flow in mylonite with varied bimineralic composition and its effect on lithospheric strength tectonophysics 303 175 191 our results suggest a dramatic weakening of the bulk rock strength at an early stage of the layer development we also found that formation of muscovite in the layer structures by breakdown of feldspar can result in further weakening in the layer structure the bulk rock strength with mica bearing layers is reduced by a significant amount compared with the mica absent layers our analysis suggests that layer development with syntectonic formation of mica can be a major source of weakening for granitic rocks

the lower crust of the dharwar craton southern india patchwork of archean granulitic domains u pb geochronological major and trace element and isotope geochemical data identify crustal domains of contrasted petrological origins and histories in the lower crust of the dharwar craton all affected by granulite facies metamorphism and deformation in the neoarchean four lower crustal domains have been identified and investigated across the neoarchean amphibolite to granulite facies transition zone 1 in the southern part of the western dharwar craton wdc high grade metamorphism affects rocks formed before 3 0 ga high grade metamorphism is recorded at ca 2 51 ga followed by possible complex cooling and resetting until 2 2 ga 2 the br hills mm hills domain represents the lower crust of the central dharwar province cdp which is here defined as a transitional crust between the old 3 ga wdc and the eastern dharwar province edp not older than 2 7 ga this granulitic domain contains the oldest rocks of the dharwar craton with ttg suites formed at ca 3 4 ga and ca 2 6 ga suites of probable crustal recycling origin both suites are involved in 2513 5ma granulite facies metamorphism 3 the nilgiri granulitic domain is tectonically juxtaposed with the deepest level of the wdc as a consequence of neoarchean dextral slip along the moyar shear zone the massif consists of rocks of orogenic affinities formed between 2 70 and 2 56 ga and overprinted by granulite facies metamorphism at 2518 10 ma 4 the krishnagiri domain exposes the deepest levels of the eastern dharwar craton it is composed of ttg and calc alkaline igneous protoliths formed between 2 55 and 2 53 ga migmatization in the upper part of the domain took place at 2507 6ma and granulite facies overprint in the deepest parts of the domain is constrained at 2516 5 ma the krishnagiri domain was magmatically accreted to the lower crust of both the cdp and edp by interaction with mafic magmatism inducing reworking of the 2 7 2 6 ga or older overlying crust the nilgiri granulites share several temporal and petrological properties with the madras granulites that make the easternmost outcrop of the dharwar craton we tentatively suggest that the nilgiri and madras granulites evolved as parts of a common madras domain in the lower crust of the edp before activation of the moyar shear zone in this sense the nilgiri massif may be considered as an allochtonous unit in a context of neoarchean ultra hot orogeny in south india

w phase source inversion for moderate to large earthquakes 1990 2010 rapid characterization of the earthquake source and of its effects is a growing field of interest until recently it still took several hours to determine the first order attributes of a great earthquake e g m w 7 5 even in a well instrumented region the main limiting factors were data saturation the interference of different phases and the time duration and spatial extent of the source rupture to accelerate centroid moment tensor cmt determinations we have developed a source inversion algorithm based on modelling of the w phase a very long period phase 100 1000 s arriving at the same time as the p wave the purpose of this work is to finely tune and validate the algorithm for large to moderate sized earthquakes using three components of w phase ground motion at teleseismic distances to that end the point source parameters of all m w 6 5 earthquakes that occurred between 1990 and 2010 815 events are determined using federation of digital seismograph networks global seismographic network broad band stations and sts1 global virtual networks of the incorporated research institutions for seismology data management center for each event a preliminary magnitude obtained from w phase amplitudes is used to estimate the initial moment rate function half duration and to define the corner frequencies of the passband filter that will be applied to the waveforms starting from these initial parameters the seismic moment tensor is calculated using a preliminary location as a first approximation of the centroid a full cmt inversion is then conducted for centroid timing and location determination comparisons with harvard and global cmt solutions highlight the robustness of w phase cmt solutions at teleseismic distances the differences in m w rarely exceed 0 2 and the source mechanisms are very similar to one another difficulties arise when a target earthquake is shortly e g within 10 hr preceded by another large earthquake which disturbs the waveforms of the target event to deal with such difficult situations we remove the perturbation caused by earlier disturbing events by subtracting the corresponding synthetics from the data the cmt parameters for the disturbed event can then be retrieved using the residual seismograms we also explore the feasibility of obtaining source parameters of smaller earthquakes in the range 6 0 mw 6 5 results suggest that the w phase inversion can be implemented reliably for the majority of earthquakes of mw 6 or larger

semi brittle deformation within the alpine fault zone new zealand abstract this paper reports the results of an attempt to identify the deformation micromechanisms in the brittle ductile transition zone of the alpine fault new zealand characterization of sequentially developed microstructures was carried out using optical microscopy hvem and stem analysis it was found that the transition zone corresponds to a broad zone of retrogression produced initially by microcracking and fluid infiltration the non catastropic nature of the fracturing indicates that fluid enhanced sub critical cracking is a significant crustal deformation mechanism after the initial phase of retrogression both ductile and brittle processes coexist and cyclically alternate in response to stress cycling the relative importance of macroscopic brittle processes may decrease with time as more ductile minerals especially phyllosilicates develop during continued retrogression

localized ductile shear below the seismogenic zone structural analysis of an exhumed strike slip fault austrian alps 1 the miocene salzachtal ennstal mariazell puchberg semp strike slip fault in austria allows study of the internal structure of a fault zone from the near surface to 30 km depth as it enters the tauern window along the rinderkarsee shear zone the semp fault passes from a dominantly brittle to a dominantly ductile structure the shear zone consists of three 1 to 100 m wide zones of brittle ductile and ductile deformation separated by 500 m wide zones of less deformed rocks the southern shear zone is mylonitic with ductile amphibole and plagioclase weak crystal preferred orientations imply that the main deformation mechanism was dislocation accommodated grain boundary sliding the northern and central shear zones are characterized by discrete millimeter wide shear zones with ductile quartz muscovite and biotite and brittle feldspar shear zone nucleation at the grain scale involved dislocation creep and the transformation of plagioclase to muscovite strain then localized in muscovite rich grain boundary shear zones that linked to form throughgoing shear zones

scardec a new technique for the rapid determination of seismic moment magnitude focal mechanism and source time functions for large earthquakes using body wave deconvolution accurate and fast magnitude determination for large shallow earthquakes is of key importance for post seismic response and tsumami alert purposes when no local real time data are available which is today the case for most subduction earthquakes the first information comes from teleseismic body waves standard body wave methods give accurate magnitudes for earthquakes up to mw 7 7 5 for larger earthquakes the analysis is more complex because of the non validity of the point source approximation and of the interaction between direct and surface reflected phases the latter effect acts as a strong high pass filter which complicates the magnitude determination we here propose an automated deconvolutive approach which does not impose any simplifying assumptions about the rupture process thus being well adapted to large earthquakes we first determine the source duration based on the length of the high frequency 1 3 hz signal content the deconvolution of synthetic double couple point source signals depending on the four earthquake parameters strike dip rake and depth from the windowed real data body wave signals including p pcp pp sh and scs waves gives the apparent source time function stf we search the optimal combination of these four parameters that respects the physical features of any stf causality positivity and stability of the seismic moment at all stations once this combination is retrieved the integration of the stfs gives directly the moment magnitude we apply this new approach referred as the scardec method to most of the major subduction earthquakes in the period 1990 2010 magnitude differences between the global centroid moment tensor cmt and the scardec method may reach 0 2 but values are found consistent if we take into account that the global cmt solutions for large shallow earthquakes suffer from a known trade off between dip and seismic moment we show by modelling long period surface waves of these events that the source parameters retrieved using the scardec method explain the observed surface waves as well as the global cmt parameters thus confirming the existing trade off for some well instrumented earthquakes our results are also supported by independent studies based on local geodetic or strong motion data this study is mainly focused on moment determination however the scardec method also informs us about the focal mechanism and source depth and can be a starting point to study systematically the complexity of the stf

microstructure of deformed biotite defining foliation in cataclasite zones in granite central japan abstract foliated cataclasite occurs along both left lateral faults striking n10 40 w and right lateral faults striking n10 25 e formed in the late cretaceous naegi agematsu granite along and near the atera fault in central japan quartz and feldspars in the cataclasite are angular to subangular in shape biotites which are granular or elongate exhibit kink bands and cleavage separation or cleavage steps and biotite fish arrays of deformed biotite define a p foliation that formed in the fault zones the angle between the p foliation and the 001 biotite cleavage and the ratio w l of apparent width w to length l of deformed biotites are related to the type of biotite microstructure developed in the samples studied there were no values of in the ranges 30 75 and 105 150 the cleavage step microstructure exhibits an angle of less than 30 with w l less than 0 2 kink band and or cleavage separation microstructures have an angle of 75 105 with w l between 0 5 and 1 5 biotite fish have an angle of more than 150 with w l less than 0 2 these data imply that the orientation of cleavage in biotite with respect to the plane of shear strongly controlled the response of biotite to deformation the resulting microstructures provide good kinematic indicators in biotite bearing shear zones and faults

laser ablation rb sr dating by online chemical separation of rb and sr in an oxygen filled reaction cell abstract the rb sr beta decay dating system is one of the most attractive tools in geochronology as rb is sufficiently abundant in common k bearing minerals like biotite muscovite and k feldspar this allows dating of a wide variety of rocks e g volcanic magmatic metamorphic sedimentary and hydrothermal environments without the need of preconcentration as is often required for u pb dating of zircon however this advantage was to date negatively counteracted by the lack of a suitable in situ technique as beta decay systems by nature have isobaric interferences of the daughter isotope by their respective parent isotope a reaction cell sandwiched between two quadrupoles within an inductively coupled plasma mass spectrometer icp ms allows exactly this the online chemical separation of two different elements coupled to a laser ablation la system in situ rb sr dating is therefore possible if a suitable reaction gas within the reaction cell can be found that separates sr from rb we present here a simple procedure in which rb sr ages can be obtained from a suite of individual phases in regular thin sections using the most established reaction gas oxygen o 2 it is possible to react part of the ablated sr to sro while no rbo is formed measurements of feldspars and micas with a spot size of 80 m were calibrated against glass standards nist srm 610 bcr 2g and biotite from la posta california 91 6 ma results are presented for a variety of magmatic rocks with well established thermal records a sample each from the klokken syenodiorite greenland 1161 ma the ulvo alkaligabbro sweden 1256 ma and a pegmatite from the bohus granite sweden 920 ma obtained in situ rb sr isochron ages are accurate 87 sr 86 sr ratios are accurate the methodology outlined in this study has significant implications for rb sr studies due to the high spatial resolution 1 quality of measurements can be better controlled by avoiding alterations and inclusions 2 large sample numbers can be investigated simply by using regular thin sections 3 several mineral generations can be targeted that would not be distinguishable in mineral separates and 4 isotope zonation within single crystals can be revealed this will open the rb sr dating system to new fields of study for example thermochronologic studies can use 87 sr 86 sr and 87 rb 86 sr zonation within crystals to better work out cooling and or reheating paths further applications are in the field of provenance studies and temporal evolution of shear zones

s c cataclasite in granitic rock abstract foliated cataclasites in granitic rocks along the rokko awaji fault zone japan display s c fabrics similar to those of mylonites the s c cataclasites have s surfaces defined by shape preferred orientation of biotite fragments and aggregates of quartz and feldspar fragments and c surfaces defined by microshears all quartz and feldspar fragments show mainly brittle deformational microstructures the biotite fragments however have some fabric characteristics like those observed in s c mylonites such as biotite fish cleavage steps bending and folding these differences in microfabric between biotite quartz and feldspar suggest that there are marked differences in their deformational behavior under the same deformational conditions biotite deformed by a combination of brittle plastic shearing processes and quartz and feldspar were brittlely damaged one of the most significant microstructural differences between s c cataclasites and s c mylonites is the absence of dynamically recrystallized grains in the s c cataclasites the microstructural characteristics and the geological evidence suggest that the s c cataclasites in the rokko awaji fault zone formed at temperatures between 150 and 250 c corresponding to depths of 5 8 km at a continental geothermal gradient of 30 c km before being uplifted and exposed this study of cataclastically deformed rocks shows that the fault zone rheology of the upper 5 10 km of crust is greatly influenced by deformational processes in s c cataclasites

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

rupture process of the april 24 2017 mw 6 9 valparaiso earthquake from the joint inversion of teleseismic body waves and near field data abstract the central chilean margin 32 33 s is characterized by the subduction of the juan fernandez ridge jfr beneath the continental south american plate the jfr corresponds to a hotspot track composed by seamounts typically 3 3 5 km high above the surrounding seafloor with a ridge trench collision zone underlying the prominent valparaiso forearc basin vfb this region has been affected by several large and mega earthquakes where the last event corresponds to a complex seismic sequence that took place at the southern edge of vfb in april 2017 the spatio temporal distribution of the seismic events is characterized by a predominant southeast migration of the seismicity an mw 6 9 earthquake triggered two days after the sequence started and occurred at the northern end of the rupture area of the 1985 mw 8 0 valparaiso earthquake we compute the kinematic rupture process of the 2017 mw 6 9 valparaiso earthquake from the joint inversion of teleseismic body waves and near field data the akaike s bayesian information criterion was used to objectively estimate both the relative weighting between datasets and the weighting of spatial and temporal constraints used as a priori information the coseismic slip is distributed over an area of dimensions 35 10 km2 with a maximum slip of 1 5 m the rupture propagated unilaterally downdip the source duration from the moment rate solution is 20 s with a total seismic moment of 3 05 1019 nm mw 6 9 the analysis of the seismicity shows that most of the events occurred along the plate interface foreshock clustered northern from the mainshock epicenter and the aftershocks occurred to the southeast at a deeper location the inverted regional moment tensors show similar faulting mechanism than the mainshock the seismic sequence started two days before the mainshock and lasted for about two weeks and a migration pattern of the seismicity was observed the rupture of the 2017 mw 6 9 earthquake nucleated where the san antonio seamount belonging to the jfr is subducting and propagated downwards along a zone that presents high interseismic coupling the complex seismic sequence might be explained by an aseismic slip transient in the zone and the influence of the downdip migration of fluids from the accretionary prism along the subduction channel the erosive and tunneling effect left by the sudden slip of the subducting seamount might provide the cavity for downdip migration of fluids and subsequent swarm seismicity