eclogites and eclogites in the western gneiss region norwegian caledonides the western gneiss region wgr marks the outcrop of a composite terrane consisting of variably re worked proterozoic basement and parautochthonous or autochthonous cover units the wgr exhibits a gross structural petrographic and thermobarometric zonation from southeast to northwest reflecting an increasing intensity of scandian late palaeozoic

the role of a keystone fault in triggering the complex el mayor cucapah earthquake rupture large earthquakes can rupture several faults analysis of seismic data from the 2010 el mayor cucapah earthquake in california suggests that multiple faults were pinned to a keystone fault whose rupture triggered cascading slip the 2010 mw 7 2 el mayor cucapah earthquake in baja california mexico activated slip on multiple faults of diverse orientations1 2 which is commonly the case for large earthquakes3 4 5 6 the critical stress level for fault failure depends on fault orientation and is lowest for optimally oriented faults positioned approximately 30 to the greatest principal compressive stress7 yet misoriented faults whose positioning is not conducive to rupture are also common8 9 here we use stress inversions of surface displacement and seismic data to show that the el mayor cucapah earthquake initiated on a fault that owing to its orientation was among those that required the greatest stress for failure although other optimally oriented faults must have reached critical stress earlier in the interseismic period coulomb stress modelling shows that slip on these faults was initially muted because they were pinned held in place by misoriented faults that helped regulate their slip in this way faults of diverse orientations could be maintained at critical stress without destabilizing the network we propose that regional stress build up continues until a misoriented keystone fault reaches its threshold and its failure then spreads spontaneously across the network in a large earthquake our keystone fault hypothesis explains seismogenic failure of severely misoriented faults such as the san andreas fault and the entire class of low angle normal faults

paleostress adjacent to the alpine fault of new zealand fault vein and styolite data from the doctors dome area doctors dome 75 km north of christchurch new zealand is an early pleistocene to recent structure being deformed along the southeast edge of the pacific australian plate boundary paleostress in the area has been determined in basement rocks of the mesozoic meta graywacke torlesse supergroup which lies unconformably beneath cretaceous and younger cover rocks pre late cretaceous multiple folding and bedding plane faulting produced a complex low grade metasedimentary basement with predominantly steeply plunging fold hinges and largely isotropic overall behavior with respect to later deformation probable late cretaceous wnw ese shortening and nne wsw extension of the basement produced widespread laumontite calcite and silica veins widespread but sparse slickensided minor fault surfaces are probably related to the same stress system during the late cenozoic dome stage basement was uplifted rotated and severely thrust along some of the range fronts to produce local high concentrations of small slickensided surfaces in the frontal areas inversion of basement fault data for the area indicates a general northwest compression with two peaks one wnw ese parallel to the shortening suggested by the older vein system and the other parallel to southeast northwest stylolite columns in the cover rocks this direction is approximately parallel to regional indicators of contemporary deformation in and adjacent to the alpine fault zone and suggests that the stress field affecting these rocks has not changed significantly since the late pliocene early pleistocene like the san andreas system this compression is at a high angle to the strike of the zone as a whole but is compatible with the direction of plate convergence and motion of the major faults between the overlapping ends of the alpine fault and the hikurangi subduction zone the alpine fault may become subhorizontal at middle lower crustal levels partially decoupling the crust from underlying structures and thus allowing oblique motion to be transferred directly onto the fault from the subduction complex while aiding the change from subduction to continental collision

u pb monazite ages in amphibolite to granulite facies orthogneiss reflect hydrous mineral breakdown reactions sveconorwegian province of sw norway in the rogaland vest agder terrain of the sveconorwegian province of sw norway two main sveconorwegian metamorphic phases are reported a phase of regional metamorphism linked to orogenic thickening m1 and a phase of low pressure thermal metamorphism associated with the intrusion of the 931 2 ma anorthosite charnockite rogaland igneous complex m2 phase m1 reached granulite facies to the west of the terrane and m2 culminated locally at 800 850 c with the formation of dry osumilite bearing mineral associations monazite and titanite u pb geochronology was conducted on 17 amphibolite to granulite facies orthogneiss samples mainly from a suite of 1050 2 8 ma calc alkaline augen gneisses the feda suite in these rocks prograde negatively discordant monazite crystallized during breakdown of allanite and titanite in upper amphibolite facies at 1012 1006 ma in the feda suite and other charnockitic gneisses concordant to slightly discordant monazite at 1024 997 ma probably reflects breakdown of biotite during granulite facies m1 metamorphism a spread of monazite ages down to 970 ma in biotite hornblende samples possibly corresponds to the waning stage of this first event in the feda suite a well defined monazite growth episode at 930 925 ma in the amphibolite facies domain corresponds to major clinopyroxene formation at the expense of hornblende during m2 growth or resetting of monazite was extremely limited during this phase in the granulite facies domain up to the direct vicinity of the anorthosite complex the m2 event was shortly followed by cooling through ca 610 c as indicated by tightly grouped u pb ages of accessory titanite and titanite relict inclusions at 918 2 ma over the entire region a last generation of u poor monazite formed during regional cooling below 610 c in hornblende rich samples at 912 904 ma this study suggests 1 that monazite formed during the prograde path of high grade metamorphism may be preserved 2 that monazite ages reflect primary or secondary growth of monazite linked to metamorphic reactions involving redistribution of rees and th and or fluid mobilisation 3 that the u pb system in monazite is not affected by thermal events up to 800 850 c provided that conditions were dry during metamorphism

record of plate boundary metamorphism during gondwana breakup from lu hf garnet geochronology of the alpine schist new zealand

mechanical validation of the three dimensional intersection geometry between the puente hills blind thrust system and the whittier fault los angeles california the sensitivity of fault interaction to alternative kinematically plausible intersection geometries of the puente hills blind thrust system and the whittier fault is modeled under geodetically constrained horizontal contraction comparisons of modeled slip rates to available geologic rates 1 suggest that the coyote hills seg ment of the puente hills system extends to the base of the seismogenic crust and 2 give slight preference for extension of the active whittier fault to the base of the seismogenic crust rather than limiting active slip to the hanging wall of the coyote hills fault furthermore analysis of strain energy density demonstrates that the pre ferred model has the greatest mechanical efficiency this correlation of fit to geologic slip rates and mechanical efficiency supports the effectiveness of this method for evaluating among alternative geometries in the absence of geologically constrained slip rates the methodology implemented in this study may be effectively used in future studies of deformation within fault systems model generated slip rates along the puente hills faults show significant strike slip implying that seismic hazard of these faults may be underestimated by consid ering reverse slip rates alone contraction at 036 may not be appropriate in the puente hills region because of resulting sinistral slip on the whittier fault which disagrees with paleoseisimc observations however whittier strike slip rates fit pa leoseismic rates under 006 5 contraction because strike slip rates are more sensitive to contraction direction than fault intersection geometry contraction direction should be further constrained in order to accurately assess seismic hazard on these faults

highly variable coastal deformation in the 2016 mw7 8 kaikōura earthquake reflects rupture complexity along a transpressional plate boundary abstract coseismic coastal deformation is often used to understand slip on offshore faults in large earthquakes but in the 2016 m w 7 8 kaik ura earthquake multiple faults ruptured across and sub parallel to the coastline along 110 km of coastline a rich dataset of coastal deformation comprising airborne lidar differencing field surveying and satellite geodesy reveals highly variable vertical displacements ranging from 2 5 to 6 5 m these inform a refined slip model for the kaik ura earthquake which incorporates changes to the slip on offshore faults and inclusion of an offshore reverse crustal fault that accounts for broad low amplitude uplift centered on kaik ura peninsula the exceptional detail afforded by differential lidar and the high variability in coastal deformation combine to form the highest resolution and most complex record of coseismic coastal deformation yet documented this should prompt reassessment of coastal paleoseismic records that may not have considered multi fault ruptures and high complexity deformation fields

earthquake size as a function of fault slip rate abstract estimates of the potential size of earthquakes on mapped active faults are generally based on regressions of earthquake magnitude m w versus length l of fault rupture for historical earthqukes the fault slip rate s has been ignored in formal prediction equations but more accurate predictions of future earthquake magnitudes on mapped faults may be obtained when it is included a least squares regression for a data set of 43 earthquakes occurring on faults for which slip rates are reported shows m w 5 12 1 16 log l 0 20 log s where l is in units of km and s is in units of mm yr the result indicates that the largest earthquakes will occur on the slowest slipping faults if the rupture length is held constant

rayleigh fractionation of heavy rare earths and yttrium during metamorphic garnet growth we present laser ablation microprobe inductively coupled mass spectrometry analyses of y yb er dy and gd in garnet crystals from high grade metamorphic and migmatitic rocks from the sierras pampeanas of argentina these rocks contain large garnet porphyroblasts 4 mm that are compositionally zoned rare earth element concentrations in the rims are typically one order of magnitude lower than those in the cores a notable feature of this zonation is the inversion of yb er and yb dy ratios from 1 in the cores to 1 in the rims we show quantitatively that the spatial distribution of these trace elements in garnet can be most simply and effectively explained as arising from rayleigh fractionation during garnet growth we also analyzed a small garnet crystal 2 mm representative of a garnet population that is associated with migmatitic leucosomes this crystal displays uniformly low concentrations of all trace elements that are virtually identical in both absolute and relative magnitudes to those in the rims of the larger garnet porphyroblasts the small crystals and perhaps part of the porphyroblast rims are likely to be peritectic products of incongruent melting reactions we argue that melts formed from garnet bearing sources may generally be unable to equilibrate with metamorphic garnet cores and may thus be more strongly depleted in heavy rare earth elements and y than modeling based on bulk source rock abundances of these elements would indicate

surface slip and off fault deformation patterns in the 2013 mw 7 7 balochistan pakistan earthquake implications for controls on the distribution of near surface coseismic slip comparison of 398 fault offsets measured by visual analysis of worldview high resolution satellite imagery with deformation maps produced by cosi corr subpixel image correlation of landsat 8 and spot5 imagery reveals significant complexity and distributed deformation along the 2013 mw 7 7 balochistan pakistan earthquake average slip along the main trace of the fault was 4 2 m with local maximum offsets up to 11 4 m comparison of slip measured from offset geomorphic features which record localized slip along the main strand of the fault to the total displacement across the entire width of the surface deformation zone from cosi corr reveals 45 off fault deformation while previous studies have shown that the structural maturity of the fault exerts a primary control on the total percentage of off fault surface deformation large along strike variations in the percentage of strain localization observed in the 2013 rupture imply the influence of important secondary controls one such possible secondary control is the type of near surface material through which the rupture propagated we therefore compared the percentage off fault deformation to the type of material bedrock old alluvium and young alluvium at the surface and the distance of the fault to the nearest bedrock outcrop a proxy for sediment thickness along this hybrid strike slip reverse slip fault we find significantly more off fault deformation in younger and or thicker sediments accounting for and predicting such off fault deformation patterns has important implications for the interpretation of geologic slip rates especially for their use in probabilistic seismic hazard assessments the behavior of near surface materials during coseismic deformation and the future development of microzonation protocols for the built environment

evidence for protracted prograde metamorphism followed by rapid exhumation of the zermatt saas fee ophiolite major and trace element zoning in garnet in combination with rb sr sm nd and lu hf geochronology provide evidence for a protracted garnet growth history for the zermatt saas fee zsf ophiolite western alps four new lu hf ages from pfulwe c 52 46 ma and one from chamois c 52 ma are very similar to a previously published lu hf age from lago di cignana overall the similarity of geochronological and garnet zoning patterns suggests that these three localities had a similar prograde tectonic history commensurate with their similar structural position near the top of the zsf samples from the lower part of the zsf at saas fee and st jacques however produced much younger lu hf ages c 41 38 ma neither differences in whole rock geochemistry which might produce distinct garnet growth histories nor rare earth element zoning in garnet can account for the age differences in the two suites this suggests a much later prograde history for the lower part of the zsf supporting the idea that it was subducted diachronously such a model is consistent with changes in subduction vectors based on plate tectonic reconstructions where early oblique subduction which produced long prograde garnet growth changed to more orthogonal subduction which corresponds to shorter prograde garnet growth six new rb sr phengite ages range from c 42 to 39 ma and in combination with previously published rb sr ages constrain the timing of the transition from eclogite to upper greenschist facies p t conditions the proximity of the zsf in the saas fee region to the underlying continental monte rosa unit and the similarity of peak metamorphic ages suggest these two units were linked for part of their tectonic history this in turn indicates that the monte rosa may have been partly responsible for rapid exhumation of the zsf unit

dependency of near field ground motions on the structural maturity of the ruptured faults little work has been undertaken to examine the role of specific long term fault properties on earthquake ground motions here we empirically examine the influence of the structural maturity of faults on the strong ground motions generated by the rupture of these faults and we compare the influence of fault maturity to that of other source properties slip mode and blind versus surface rupturing we analyze the near field ground motions recorded at rock sites for 28 large mw 5 6 7 8 crustal earthquakes of various slip modes the structural maturity of the faults broken by those earthquakes is classified into three classes mature intermediate and immature based on the combined knowledge of the age slip rate cumulative slip and length of the faults we compare the recorded ground motions to the empirical prediction equation of boore et al 1997 at all frequencies earthquakes on immature faults produce ground motions 1 5 times larger than those generated by earthquakes on mature faults the fault maturity appears to be associated with larger differences in ground motion amplitude than the style of faulting factor of 1 35 between reverse and strike slip earthquakes and the surface rupture occurrence factor of 1 2 between blind and surface rupturing earthquakes however the slip mode and the fault maturity are dependent parameters and we suggest that the effect of slip mode may only be apparent actually resulting from the maturity control we conclude that the structural maturity of faults is an important parameter that should be considered in seismic hazard assessment

lu hf geochronology of mississippian high pressure metamorphism in the acatlan complex southern mexico abstract since the first discovery of eclogite in the acatlan complex in southern mexico the age of the high pressure metamorphism has been a matter of debate several attempts to date high pressure metamorphic rocks of the acatlan complex have been made using the u pb and 40 ar 39 ar methods the resulting dates however do not correspond unambiguously to the time of eclogite facies metamorphism in this study the age of high pressure metamorphism in the acatlan complex has been determined by lu hf garnet whole rock geochronology this paper presents four high precision 4 to 7 point garnet whole rock isochrons of amphibolitized eclogite from the piaxtla suite and the asis lithodeme in the acatlan complex the four dates agree within uncertainties yielding a weighted mean of 352 5 1 6 ma which we interpret to be the age of eclogite facies metamorphism in the piaxtla suite and the asis lithodeme marking active subduction in the acatlan complex in the carboniferous mississippian high pressure metamorphism in turn might be related to the closure of the rheic ocean and the assembly of pangea

initiation of crustal scale thrusts triggered by metamorphic reactions at depth insights from a comparison between the himalayas and scandinavian caledonides active eclogitization has recently been inferred at depth beneath the himalaya from geophysical observations and the mechanical consequences of eclogitization can be observed in the field in the eroded and extended nappe stack of the scandinavian caledonides there proterozoic metastable granulites and igneous protoliths underwent partial eclogitization during the collision of baltica with laurentia the reaction began in pseudotachylites and veins and eventually formed a connected network of eclogite facies shear zones that localized deformation and weakened the lower crust of baltica during the collision with laurentia all these features can be compared with the seismic activity of the indian lower crust its strength loss beneath the himalayan ranges and its delayed density increase regarding its penetration in the eclogite facies the caledonian bergen arc eclogites and the himalayan ama drime eclogites are both derived from continental crust in both cases these eclogites were formed contemporaneously with the activation of the main thrusts responsible for the construction of the orogenic wedges the main central thrust in the himalayas and the main thrust below the jotun nappe complex in the caledonides the similarities in these two orogens which compare both in size and structure highlight the importance of eclogitization at depth as a mechanism for weakening of the lower crust and for decoupling of the crust and lithospheric mantle in collision zones

zircon geochronology and ca 400 ma exhumation of norwegian ultrahigh pressure rocks an ion microprobe and chemical abrasion study understanding the formation and exhumation of the remarkable ultrahigh pressure uhp rocks of the western gneiss region norway hinges on precise determination of the time of eclogite recrystallization we conducted detailed thermal ionization mass spectrometry chemical abrasion analysis and sensitive high resolution ion microprobe analysis of zircons from four ultrahigh and high pressure hp rocks ion microprobe analyses from the flatraket eclogite yielded a broad range of apparently concordant caledonian ages suggesting long term growth in contrast higher precision thermal ionization mass spectrometry analysis of zircon subject to combined thermal annealing and multi step chemical abrasion yielded moderate pb loss from the first lowest temperature abrasion step possible minor pb loss or minor growth at 400 ma from the second step and a 407 404 ma cluster of slightly discordant 206pb 238u ages most likely free from pb loss from the remaining abrasion steps we interpret the latter to reflect zircon crystallization at 405 400 ma with minor discordance from inherited cores zircon crystallization occurred at eclogite facies possibly post peak conditions based on compositions of garnet inclusions in zircon as well as nearly flat hree profiles and lack of eu anomalies in zircon fractions subjected to chemical abrasion these ages are significantly younger than the 425 ma age often cited for western norway eclogite recrystallization implying faster rates of exhumation 2 5 8 5 km myr and coeval formation of eclogites across the uhp portion of the western gneiss region

eclogites and polyphase p t cycling in the caledonian uppermost allochthon in troms northern norway eclogites in the tromso area northern norway are intimately associated with meta supracrustals within the uppermost allochthon of the scandinavian caledonides the tromso nappe complex the whole sequence which includes pelitic to semipelitic schists and gneisses marbles and calc silicate rocks quartzofeldspathic gneisses metabasites and ultramafites has undergone three main deformational metamorphic events d1 m1 d2 m2 and d3 m3 detailed structural microtextural and mineral chemical studies have made it possible to construct separate p t paths for these three events chemically zoned late syn to post d1 garnets with inclusions of bt pl and qtz in ky bearing metapelites indicate a prograde evolution from 636 c 12 48 kbar to c 720 c 14 15 kbar this latter result is in agreement with grt cpx geothermometry and grt cpx pl qtz geobarometry on eclogites and trondhjemitic to dioritic gneisses maximum pressures at c 675 c probably reached 17 18 kbar based on cpx pl qtz inclusions in eclogitic garnets and grt ky pl qtz and jd ab qtz in trondhjemitic gneisses post d1 pre d2 decompressional breakdown of the high p assemblages indicates a substantial drop in pressure at this stage inclusions and chemical zoning in syn to post d2 garnets from metapelites record a second episode of prograde metamorphism from 552 c 7 95 kbar passing through a maximum pressure of 10 64 kbar at 644 c with final equilibration at c 665 c 9 10 kbar the corresponding apparently co facial paragenesis grt cpx pl qtz in metabasites yields c 635 c 8 10 kbar in the metapelites post d3 grt in apparent equilibrium with bt phe and pl yield c 630 c 9 kbar the d1 m1 and d2 m2 episodes are exclusively recorded in the tromso nappe complex and must thus pre date the emplacement of this allochthonous unit on top of the underlying lyngen nappe while the d3 m3 episode is common for the two units a previously published sm nd mineral isochron grt cpx am on a partly retrograded and recrystallized ecologite of 598 107 ma represents either the timing of formation of the eclogites or the post eclogite pre d2 decompression stage while a rb sr whole rock isochron of an apparently post d1 pre d2 granite of 433 11 ma is consistent with a k ar age of post d1 pre d2 amphiboles from a retrograded eclogite of 437 16 ma which most likely record cooling below the 475 500 c isotherm after the m3 metamorphism

early carboniferous unroofing in western norway a tale of alkali feldspar thermochronology abstract 40ar 39ar thermochronologic data from an extensional detachment zone in western norway document punctuated late paleozoic through mesozoic tectonothermal activity diffusion and thermal modeling of alkali feldspars sampled in a profile through the detachment replicate laboratory argon release patterns when feldspars comprise three or four diffusion domains with differing activation energies that represent high intermediate and low closure temperatures these domains correspond to distinct changes in late paleozoic cooling rates 1 slow cooling at 0 4 2 2 c m yr from ca 380 360 ma 2 rapid cooling at 15 c m yr in late devonian early carboniferous time 360 340 ma 3 slow cooling at 0 4 1 7 c m yr after ca 340 ma with partial argon loss in permian and late jurassic early cretaceous times the early carboniferous rapid cooling event recorded by the feldspars links the western norway margin to contemporaneous unconformities regional extension basin inversion and igneous activit

microsampling lu hf geochronology on mm sized garnet in eclogites constrains early garnet growth and timing of tectonometamorphism in the north qilian orogenic belt

geochronology of fluid induced eclogite and amphibolite facies metamorphic reactions in a subduction collision system bergen arcs norway rb sr multimineral isochron data for metamorphic veins allow to date separate increments of the mineral reaction history of polymetamorphic terranes granulite facies rocks of the lindas nappe bergen arcs norway were subducted and exhumed during the caledonian orogeny the rocks show petrographic evidence for two distinct events of local fluid infiltration and vein formation along fractures and shear zones the first occurred at eclogite facies 15 21 kbar 650 750 c and a later one at amphibolite facies conditions 8 10 kbar 600 c the presence of fluids enabled local metamorphic equilibration only near fluid pathways in fluid absent domains preexisting assemblages were metastably preserved this resulted in a heterogeneity of metamorphic signatures on meter to m scales well preserved granulite facies rocks preserve their proterozoic rb sr mineral ages as does the u pb system of zircon in most lithologies six rb sr multimineral isochron ages for eclogite facies veins and their immediate wallrocks date the fluid induced eclogitization at 429 9 3 5 ma 2 weighted average mswd 0 39 an eclogite facies vein has yielded metamorphic zircon with concordant u pb ages of 429 3 ma identical to the u pb age of 427 4 0 9 ma for zircon xenocrysts in an amphibolite facies vein seven rb sr mineral isochron ages date amphibolite facies fluid infiltration at 414 2 2 8 ma mswd 1 5 an age value testifying to residence of the rocks in the deep orogenic crust at temperatures 600 c for nearly 15 ma the new data show that rb sr mineral isochron ages effectively date fluid induced re crystallization events rather than stages of cooling the direct link between isotopic ages and distinct petrographic equilibrium assemblages aids to constrain the evolution of rocks in the p t reaction time space which is essential for understanding exhumation histories and the internal dynamics of orogens in general

timing of eclogite facies metamorphism in the southernmost scandinavian caledonides by lu hf and sm nd geochronology the scandinavian caledonides contain several non cogenetic eclogite bearing terranes that were metamorphosed before the main orogenic stage in scandian time 430 395 ma although petrological and geochronological data from these terranes have provided essential information on the geodynamic history of the caledonian orogenic cycle the general picture is still patchy to refine existing geodynamic models we have dated the eclogite occurrence in the jaeren nappe sw norway by lu hf and sm nd geochronology five out of the six studied samples provide a weighted mean lu hf age of 469 9 1 2 ma 2 one sample provided a significantly younger age of 457 9 2 4 ma garnet from the younger sample grew exclusively at eclogite facies conditions in contrast garnet from the other samples comprises prograde cores and peak metamorphic rims age estimates that take lu contributions of each zone into account provide an age of 471 0 0 9 ma for the cores and suggest a ca 455 ma age for the rims which is identical to the bulk garnet age of the younger sample the same pattern is indicated by sm nd ages although these are relatively imprecise and reflect isotopic disturbance during thermal overprinting upon exhumation the data define a new high pressure age population for the scandinavian caledonides which allows more detailed insight into the subduction history that affected the baltoscandian margin before scandian continental collision furthermore this study highlights the potential complexities involved in garnet geochronology and shows the strength of lu hf dating for unraveling the geochronological record of hp rocks

diffusion limited ree uptake by eclogite garnets and its consequences for lu hf and sm nd geochronology garnets from the zermatt saas fee eclogites contain narrow central peaks for lu yb tm er and at least one additional small peak towards the rim the ree sm eu gd tb dy are depleted in the cores but show one prominent peak close to the rim these patterns cannot be modeled using rayleigh fractionation accompanied by mineral breakdown reactions instead the patterns are well explained using a transient matrix diffusion model where ree uptake is limited by diffusion in the matrix surrounding the porphyroblast observed profiles are well matched if a roughly linear radius growth rate is used the secondary peaks in the garnet profiles are interpreted to reflect thermally activated diffusion due to temperature increase during prograde metamorphism the model predicts anomalously low 176lu 177hf and 147sm 144nd ratios in garnets where growth rates are fast compared to diffusion of the ree and these results have important implications for lu hf and sm nd geochronology using garnet

geometry of eclogite facies structural features implications for production and exhumation of ultrahigh pressure and high pressure rocks western gneiss region norway 1 well preserved eclogite facies structural features in metamorphosed gabbro and diorite gneiss in baltica crust formed at a minimum depth of 60 70 km during the scandian orogeny allow direct inferences to be made regarding the geometry of folds kinematics and original structural orientations related to production and exhumation of high pressure rocks folds associated with eclogite facies fabrics are isoclinal to tubular with axes parallel to the trend of a stretching lineation strain estimates and l s or l s fabrics indicate that these structures were formed in a constrictional strain field locally they are well preserved in eclogite facies mylonite zones at least 40 m thick that cut proterozoic gabbro and adjacent gneiss where steeply dipping they show a north side up shear sense across a younger northeast trending shallowly plunging amphibolite facies anticlinorium formed in a constrictional noncoaxial strain field where original structural facing direction can be inferred small circle rotation of the eclogite facies lineation about the anticline axis indicates that the relative motion vector of baltica with respect to overlying imbricated crust and laurentia was oriented 320 in a present day reference frame this result is identical to the orientation of the relative motion vector estimated from paleomagnetic plate reconstructions and consistent with late silurian to early devonian oblique sinistral convergence between baltica and laurentia results of this study indicate that coherent baltica crust at 60 70 km depth experienced subvertical and horizontal shortening while extending toward the foreland during tops southeast thrusting parallel to plate motion high pressure rocks were progressively imbricated and stacked along eclogite facies mylonite zones with the deforming zone separating coherent baltica crust from imbricated basement above the constrictional strains under eclogite facies conditions are interpreted to have resulted from stretching associated with sinking of the cool dense mantle lithosphere

high localization of primary slip zones in large earthquakes from paleoseismic trenches observations and implications for earthquake physics 1 paleoseismic exposures excavated across relatively straight sections of major faults in southern california display a high degree of localization at depths of only a few meters below the surface in some cases the width of the slip zone in events with multimeter displacement is on the order of 1 2 mm to a cm which is the resolution of the observations repetitive slip events in the same zone increase the observed width of the faulting as expressed at trench depths but the superposed slip again tends to be highly localized these observations are probably representative of 80 of the length of the faults studied based on these results combined with the expected tendency for narrower slip zone with depth observations from exhumed faults and high localization of seismicity along large faults we hypothesize that the majority of slip carried by large faults occurs in very narrow zones if correct the emerging integrated view of high slip localization during earthquake ruptures places important constraints on many issues of earthquake dynamics

early history of earth s crust mantle system inferred from hafnium isotopes in chondrites the 176lu to 176hf decay series has been widely used to understand the nature of earth s early crust mantle system1 2 3 4 5 6 the interpretation however of lu hf isotope data requires accurate knowledge of the radioactive decay constant of 176lu as well as bulk earth reference parameters a recent calibration of the value calls for the presence of highly unradiogenic hafnium in terrestrial zircons with ages greater than 3 9 gyr implying widespread continental crust extraction from an isotopically enriched mantle source more than 4 3 gyr ago7 but does not provide evidence for a complementary depleted mantle reservoir here we report lu hf isotope measurements of different solar system objects including chondrites and basaltic eucrites the chondrites define a lu hf isochron with an initial 176hf 177hf ratio of 0 279628 0 000047 corresponding to 1 983 0 033 10 11 yr 1 using an age of 4 56 gyr for the chondrite forming event this value indicates that earth s oldest minerals were derived from melts of a mantle source with a time integrated history of depletion rather than enrichment7 the depletion event must have occurred no later than 320 myr after planetary accretion consistent with timing inferred from extinct radionuclides8 9 10

strain distribution across the australian pacific plate boundary in the central south island new zealand from 1992 gps and earlier terrestrial observations as part of a geodetic experiment aimed at understanding the deformation associated with the australian pacific plate boundary in the south island of new zealand in 1992 we reoccupied using global positioning system gps techniques a first order triangulation and trilateration network established in 1978 between christchurch on the east coast and hokitika on the west the network crosses the south island a few tens of kilometers southwest of the region where the plate boundary changes from a single throughgoing oblique slip fault the alpine fault to a series of subparallel strike slip faults the marlborough faults the gps data have been analyzed as daily network solutions with about 12 stations in each solution rms repeatabilities for stations with multiple occupations are 4 mm 8 mm and 15 mm in the north east and vertical components respectively the observed strain across the network is consistent with the entire nuvel ia pacific australia plate velocity being accommodated on land across this part of the south island shear strain rates derived from the gps and terrestrial data show that the highest strain rate 0 4 rad yr occurs in the region of the southern alps and alpine fault this rate is about two thirds of the rate predicted from the nuvel ia plate velocity model assuming that all the plate boundary deformation occurs across this region implying that about two thirds of the plate motion is accommodated in the vicinity of the alpine fault significant shear strain rates greater than 0 2 rad yr are also observed farther east particularly in the region of the porters pass amberley fault zone demonstrating that this zone accommodates a significant part of the plate boundary deformation using dislocation modeling we show that the variation in fault parallel shear strain rates across the alpine fault is reasonably consistent with a nonoptimized dislocation model involving a 50 dipping fault that is presently locked to a depth of 12 km one explanation for this observation is that the upper 12 km of the crust in this area is storing most of the right lateral shear component of the relative plate motion as elastic energy that will be released in a future major earthquake the variation in the other component of shear strain which may be interpreted as fault normal relative contraction is not explained by a simple dislocation model implying that the normal component of plate motion is taken up in other ways

polyphase zircon in ultrahigh temperature granulites rogaland sw norway constraints for pb diffusion in zircon shrimp u pb ages have been obtained for zircon in granitic gneisses from the aureole of the rogaland anorthosite norite intrusive complex both from the ultrahigh temperature uht 900 c pigeonite in zone and from outside the hypersthene in isograd magmatic and metamorphic segments of composite zircon were characterised on the basis of electron backscattered electron and cathodoluminescence images plus trace element analysis a sample from outside the uht zone has magmatic cores with an age of 1034 7 ma 2 n 8 and 1052 5 ma 1 n 1 overgrown by m1 metamorphic rims giving ages between 1020 7 and 1007 5 ma in contrast samples from the uht zone exhibit four major age groups 1 magmatic cores yielding ages over 1500 ma 2 magmatic cores giving ages of 1034 13 ma 2 n 4 and 1056 10 ma 1 n 1 3 metamorphic overgrowths ranging in age between 1017 6 ma and 992 7 ma 1 corresponding to the regional m1 sveconorwegian granulite facies metamorphism and 4 overgrowths corresponding to m2 uht contact metamorphism giving values of 922 14 ma 2 n 6 recrystallized areas in zircon from both areas define a further age group at 974 13 ma 2 n 4 this study presents the first evidence from rogaland for new growth of zircon resulting from uht contact metamorphism more importantly it shows the survival of magmatic and regional metamorphic zircon relics in rocks that experienced a thermal overprint of c 950 c for at least 1 myr magmatic and different metamorphic zones in the same zircon are sharply bounded and preserve original crystallization age information a result inconsistent with some experimental data on pb diffusion in zircon which predict measurable pb diffusion under such conditions the implication is that resetting of zircon ages by diffusion during m2 was negligible in these dry granulite facies rocks imaging and th u y systematics indicate that the main processes affecting zircon were dissolution reprecipitation in a closed system and solid state recrystallization during and soon after m1

a regionally evolving transpressional duplex along the northern margin of the altyn tagh fault new kinematic and timing constraints from the sanweishan and nanjieshan china

the margins of avalonia during cambrian and earliest ordovician times avalonia was an area forming an integral part of the huge gondwanan continent probably along the northern margin of amazonia until in early ordovician late arenig or llanvirn time it split off from gondwana leaving a widening rheic ocean to its south today its southern margin with gondwana extends northeast from east of cape cod massachusetts through nova scotia north of the meguma terrane and thence below sea level to the south of newfoundland on the eastern side of the present atlantic the southern margin may separate southwest portugal from the rest of the iberian peninsula it can be traced eastwards with more certainty from the south cornwall nappes to a line separating the northern phyllite belt on the southern margin of the rhenohercynian terrane and the mid german crystalline high there is no certain evidence of avalonian crust to the northeast of the elbe line the northern margin of avalonia extends westwards from south of denmark to the british isles where it merges with the iapetus ocean suture between scotland and england traced westwards it crosses ireland and reappears in northern newfoundland to the east of new world island where it may follow the trace of the dog bay line and the cape ray fault recent work suggests that the northern margin of avalonia may clip the northern tip of cape breton island in nova scotia and then enter the north american mainland at the bay of chaleur it may then be traced from north and west of the popelogan and bronson hill arcs to long island sound near newhaven connecticut the cambrian to devonian faunas reflect the history of avalonia initially they were purely gondwanan but as ordovician time proceeded more genera crossed firstly the tornquist ocean as it narrowed between avalonia and baltica to close in latest ordovician and early silurian times and secondly the iapetus ocean so that by the early silurian most of the benthic shelly faunas apart from the ostracods were the same round the adjacent margins of all three palaeocontinents

calcium diffusivity in alumino silicate garnets an experimental and atem study concentration gradients in calcium are common in metamorphic or magmatic garnets and can be used to determine the timescales of geological processes however the kinetics of ca diffusion in garnet is poorly constrained and experimental studies have to date yielded widely varying diffusion coefficients in this paper we describe a new method for generating diffusion profiles in garnet we incorporated polished and compositionally homogeneous garnet seeds in a finely ground powder of clinopyroxene and garnet during the experiments 1 3 gpa 1 050 1 250 c and o2 the graphite o2 buffer the mineral powder partially melted recrystallized and formed a 10 50 m wide overgrowth zone of compositionally distinct garnet around the seeds long duration experiments generated measurable relaxation profiles at these seed overgrowth interfaces we performed analytical transmission electron microscope traverses across the interfaces in each experiment thirteen usable compositional profiles were obtained with characteristic distances of diffusion ranging from 300 to 1 000 nm from these profiles ca fe mg interdiffusion coefficients were retrieved using an analytical solution for the diffusion equation and the data were cast in an arrhenius relation linear regression of the data yields an activation energy q ca fe mg equal to 188 48 kj mol 1 and a frequency factor d 0 equal to 6 6 10 14 m2 s 1 within the compositional range studied the composition of garnet has no major effect on the ca fe mg interdiffusion coefficient the very slow diffusion rate of ca is in agreement with natural observations indicating that ca diffuses more slowly than fe and mg the ca diffusion coefficients derived from this study are not model dependent and can be used to determine the durations of geological events from ca relaxation profiles in natural garnets

complex multifault rupture during the 2016 mw 7 8 kaikōura earthquake new zealand the 2016 moment magnitude m w 7 8 kaik ura earthquake was one of the largest ever to hit new zealand hamling et al show with a new slip model that it was an incredibly complex event unlike most earthquakes multiple faults ruptured to generate the ground shaking a remarkable 12 faults ruptured overall with the rupture jumping between faults located up to 15 km away from each other the earthquake should motivate rethinking of certain seismic hazard models which do not presently allow for this unusual complex rupture pattern science this issue p eaam7194 1 1 lookup doi 10 1126 science aam7194

lu hf geochronology on cm sized garnets using microsampling new constraints on garnet growth rates and duration of metamorphism during continental collision menderes massif turkey abstract this study shows lu hf geochronology of zoned garnet crystals contained in mica schists from the southern menderes massif turkey selected samples are four 3 5 cm large garnet megacrysts of which several consecutive garnet shells have been sampled with a micro saw and analyzed for dating the results are used to extract growth rates of garnet and also to improve the time constraint for alpine aged overprint of the pan african basement in the menderes massif lu hf ages of the sampled garnet shells are determined by two point garnet only isochrons using the garnets lu depleted rim compositions this yields a consistent decrease of age information from core to rim segments of individual garnet crystals and the calculated isochron ages propose a time frame of growth between 42 6 1 9 and 34 8 3 1 ma major element profiles in the investigated garnets characterize zoning patterns indicative of prograde conditions rayleigh fractionated bell shaped mn and decreasing fe fe mg are recorded by the garnets core to rim compositions therefore the obtained lu hf ages record timing of early prograde growth for the cores of the garnets two of the large garnet crystals also yield isochron ages of 58 83 0 69 and 50 16 0 84 ma in their innermost cores which appear to record an early nucleation event this view however is not in concordance with the observed major element profiles of these garnets and therefore is interpreted with caution termination of the garnet growth period is determined through the calculation of radial growth rates based on the size of the garnets and the lu hf ages obtained for consecutive shells extrapolation of these rates potentially constrains the total duration for garnet growth terminating at 31 6 ma comparison of the growth rates calculated for individual crystals shows a variety of slow and fast growing garnets and similar results have been previously obtained with the rb sr and sm nd isotope systems the new data provides a precise age determination for prograde barrovian metamorphism in the southern menderes massif which so far was placed between 63 and 27 ma on the basis of mica rb sr and ar ar dating this study provides new constraints crucial to the understanding of the tectonic evolution of southwest anatolia and the aegean realm as it yields a shorter outline for alpine aged continental collision

a geometric model to estimate slip rates from terrace rotation above an offshore listric thrust fault kaikōura new zealand abstract the kaik ura peninsula lies at the transition from subduction to continental collision at the southern end of the hikurangi subduction system this study uses a 2012 lidar survey over the kaik ura peninsula to re map a flight of four uplifted late pleistocene marine terraces at high resolution the lidar shows that the terraces are being progressively tilted landwards in a manner consistent with listric thrust faulting offshore the fault known as the kaik ura peninsula fault dips shallowly at c 30 to the northwest at depth and probably truncates the seaward segment of the hope fault in the footwall of the jordan thrust geometric analysis of the tilt using ages based on previous dating and a regional sea level curve suggests that slip rates on the kaik ura peninsula fault have ranged between 2 3 1 5 mm yr and 4 1 1 3 mm yr over the late pleistocene the elevations of late holocene fringing beaches track regional sea level changes apart from a departure indicating a single uplift event penultimate earthquake in the late 18th to earliest 19th century 1702 1838 ce followed by uplift in the 2016 kaik ura earthquake the slip rate calculated from beach uplift including the kaik ura earthquake is consistent with longer term rates the accumulation of the slip over only c 220 years following 2000 years of quiescence suggests that the offshore thrust and associated faults exhibit clustered behavior possibly as a result of keystone faulting

metamorphic zircon formation at the transition from gabbro to eclogite in trollheimen surnadalen norwegian caledonides a transition from gabbro to eclogite has been investigated at vinddoldalen in south central norway with the aim to link reaction textures to metamorphic zircon growth and to obtain a direct u pb zircon age of the metamorphic process in the different rocks of the transition zone zircon occurs as i igneous prismatic grains ii metamorphic polycrystalline rims and pseudomorphs after baddeleyite and iii as tiny 10 mu m bead like zircon grains textural relations suggest that type ii zircon formed by breakdown of baddeleyite in the presence of silica whereas fe ti oxides were the main zr source for the type iii zircon subsolidus liberation of zr and formation of bead zircon took place by oxyexsolution of titanomagnetite during fluid assisted metamorphism and by resorption of fe ti oxide in rock domains that were completely recrystallized to eclogite sims secondary ion mass spectrometry and tims thermal ionization mass spectrometry dating provides comparable u pb ages of magmatic zircon and baddeleyite baddeleyite tims yielded an age of 1457 11 ma for the gabbro emplacement bead type metamorphic zircon from eclogite gave 425 10 ma tims dating the metamorphic transition from gabbro to eclogite in the upper basement of the lower allochthon in the south central scandinavian caledonides less

coseismic rupture and preliminary slip estimates for the papatea fault and its role in the 2016 mw 7 8 kaikōura new zealand earthquake coseismic rupture of the 19 km long north striking and west dipping sinistral reverse papatea fault and nearby structures and uplift translation of the papatea block are two of the exceptional components of the 14 november 2016 mw 7 8 kaik ura earthquake the dual stranded papatea fault comprising main sinistral reverse and western dip slip strands ruptured onshore and offshore from south of waipapa bay to george stream in the north bounding the eastern side of the papatea block fault rupture mapping was aided by the acquisition of multibeam bathymetry light detection and ranging lidar topography and other imagery as well as differential lidar d lidar from along the coast and clarence river valley on land vertical throw and sinistral offset on the papatea fault was assessed across an aperture of 100 m using uncorrected d lidar and field data to develop preliminary slip distributions the maximum up to the west throw on the main strand is 9 5 0 5 m and the mean throw across the papatea fault is 4 5 0 3 m the maximum sinistral offset measured near the coast on the main strand is 6 1 0 5 m from these data and considering fault dip we calculate a maximum net slip of 11 5 2 m and an average net slip of 6 4 0 2 m for the papatea fault surface rupture in 2016 large sinistral reverse displacement on the papatea fault is consistent with uplift and southward escape of the papatea block as observed from interferometric synthetic aperture radar insar and optical image correlation datasets the throw and net slip are exceedingly high for the length of the papatea fault such large movements likely only occur during multifault kaik ura type earthquakes that conceivably have recurrence times of 5000 12 000 yrs the role of the papatea fault in the kaik ura earthquake has significant implications for characterizing complex fault sources in seismic hazard models

trace element zoning in a metamorphic garnet trace element zoning has been measured in an amphibolite garnet from the tauern window austria by using an ion microprobe humps in the zoning profiles of na sc v y and the heavy rare earth elements mark a period of open system behavior these humps correspond to a part of the major element zoning profile that is interpreted as a p t reversal the source of the mass excesses of these elements remains ambiguous they were derived either on a thin section scale by the breakdown of trace element enriched refractory minerals or externally from unusual trace element enriched fluids p t paths determined from garnet zoning may require modification if open system behavior is important during garnet growth

characteristics of the fault related rocks fault zones and the principal slip zone in the wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 abstract scientific drilling in active faults after a large earthquake is ideal to study earthquake mechanisms the wenchuan earthquake fault scientific drilling project wfsd is an extremely rapid response to the 2008 ms 8 0 wenchuan earthquake which happened along the longmenshan fault eastern margin of the tibetan plateau in order to better understand the fault mechanism and the physical and chemical characteristics of the rocks the wfsd project will eventually drill 5 boreholes along the two main faults this paper focuses on the first hole wfsd 1 which started just 178 days after the earthquake down to a final depth of 1201 15 m petrological and structural analyses of the cores allowed the identification of fault related rocks in the yingxiu beichuan fault fault gouge cataclasite and fault breccia and the principle slip zone psz location of the wenchuan earthquake was determined we found 12 fault zones in the entire core profile with at least 10 including the yingxiu beichuan fault zone with a multiple cores structure and minimum width of 100 m the co seismic slip plane of the wenchuan earthquake at depth corresponding to the yingxiu beichuan fault zone at the outcrop as well as its psz was expected to be located at the bottom of the fault zone at 759 m depth instead it was found at 590 m depth with 1 cm wide fresh fault gouge as determined by logging data such as temperature natural gamma ray p wave velocity and resistivity combined with the fresh appearance magnetic susceptibility and microstructure of the gouge the wenchuan earthquake slip plane has a dip angle of 65 showing the high angle thrust feature the distribution of fault gouge with several meters thick the location of the wenchuan earthquake s psz and the thickness of fresh gouge all imply a correlation between the width of the fault zone and the number of seismic events

mechanical fault interaction within the los angeles basin a two dimensional analysis using mechanical efficiency 1 mechanical models examine deformation within eight different structural cross sections proposed by davis et al 1989 and shaw and suppe 1996 along a northeast southwest transect across the los angeles basin california horizontal contraction of the models constrained by geodetic measurements yields varying dip slip rates along frictionally sliding faults within the different cross sections mechanical efficiency analysis using effective stiffness and strain energy density assesses the overall fault system deformation as well as the partitioning of work between fault slip and host rock strain the cross section interpreted by shaw and suppe 1996 has the best fit to paleoseismically determined slip rates and the greatest mechanical efficiency greatest proportion of work toward fault slip however this model produces excessive reverse slip along the newport inglewood fault a modified fault configuration with a wedge or blind puente hills thrust fault rather than a ramp detachment configuration better matches the paleoseismic data with slightly lower mechanical efficiency slip rates in the mechanical models based on interpretations of shaw and suppe 1996 have much closer match to the geologically determined rates than those estimated from kinematic models this difference is due to 1 differing time spans of slip rate estimates and 2 deformable rather than rigid host rock in the mechanical models the mechanical efficiency analysis provides quantitative indicators of overall fault system deformation including the cumulative effect of interaction between individual faults assessment of effective stiffness and strain energy density furthers our understanding of two dimensional fault interactions in the los angeles basin and offers great potential for future applications

fault structure control on fault slip and ground motion during the 1999 rupture of the chelungpu fault taiwan the chelungpu fault taiwan ruptured in a mw 7 6 earthquake on 21 september 1999 producing a 90 km long surface rupture analysis of core from two holes drilled through the fault zone combined with geologic mapping and detailed investigation from three outcrops define the fault geometry and physical properties of the chelungpu fault in its northern and southern regions in the northern region the fault dips 45 60 east parallel to bedding in both the hanging wall and footwall and consists of a narrow 1 20 cm core of dark gray sheared clay gouge the gouge is located at the base of a 30 to 50 m zone of increased fracture density confined asymmetrically to the hanging wall microstructural analysis of the fault gouge in dicates the presence of extremely narrow clay zones 50 300 lm thick that are interpreted as the fault rupture surfaces few shear indicators are observed outside of the fault gouge implying that slip was localized within the gouge zone slip localization along a bed parallel surface resulted in a narrow gouge zone that pro duced less high frequency ground motion and larger displacements average 8 m during the earthquake than in the southern region displacement in the southern region averaged only 2 m but ground shaking consisted of large amounts of high frequency ground motion the fault in the southern region dips 20 30 at the surface and consists of a wide 20 70 m thick zone of sheared foliated shale with numerous gouge zones these data demonstrate a potential correlation between fault structure i e gouge width geometry and earthquake characteristics such as displacement and ground motion i e acceleration

andersonian wrench faulting in a regional stress field during the 2010 2011 canterbury new zealand earthquake sequence the initial mw7 1 darfield earthquake sequence was centred west of christchurch city in the south island of new zealand but aftershocks including a highly destructive mw6 3 event eventually extended eastwards across the city to the coast the mainshock gave rise to right lateral strike slip of up to 5 m along the segmented rupture trace of a subvertical fault trending 085 58 across the canterbury plains for c 30 km in agreement with teleseismic focal mechan isms near field data however suggest that the mainshock was composite initiating with reverse slip north of the surface rupture stress determinations for the central south island show maximum compressive stress s1 to be horizontal and oriented 115 58 the principal dextral rupture there fore lies at c 3 08 to regional s1 the classic andersonian orientation for a low displacement wrench fault an aftershock lineament trending c 1458 possibly represents a conjugate left lateral strike slip structure this stress field is also consistent with predominantly reverse slip reactivation of nne ne faults along the southern alps range front the main strike slip fault appears to have a low cumulative displacement and may represent either a fairly newly formed fault in the regional stress field or an existing subvertical fault that happens to be optimally oriented for frictional reactivation

earthquake scaling fault segmentation and structural maturity abstract slip and length measurements on earthquakes suggest large stress drop variability we analyze an extended set of slip length measurements for large earthquakes m 6 to seek for the possible origin s of this apparent variability we propose that such variability arises from earthquakes breaking a variable number of major fault segments that number depends on the strength of the inter segment zones which itself depends on the structural maturity of the faults we propose new d max l parameterizations based on that idea of multiple segment ruptures in such parameterizations each broken segment roughly scales as a crack while the total multi segment rupture does not stress drop on individual segments is roughly constant only varying between 3 5 to 9 mpa the slight variation that is still observed depends on fault structural maturity more mature faults have lower stress drops than immature ones the new d max l functions that we propose reduce uncertainties with respect to available relationships they thus provide a more solid basis to estimate seismic hazard by integrating fault properties revealed by geological studies

u pb ages of ophiolites and arc related plutons of the norwegian caledonides implications for the development of iapetus u pb zircon ages are reported for four ophiolites and three crosscutting arc related plutons from the norwegian caledonides plagiogranite differentiated from gabbro of the karmoy ophiolite is dated at 493 7 4 ma whereas arc related trondhjemite cutting this ophiolite crystallized at 485 2 ma a crosscutting clinopyroxene phyric gabbro intrusion is dated at 470 9 5 ma by near concordant magmatic titanite sphene and discordant u rich 2903 6677 ppm zircon lower intercepts of 247 68 and 191 70 ma defined by the plagiogranite and clinopyroxene phyric gabbro best fit lines may reflect a real low t alteration rift related event

sm nd dating of seve eclogites norrbotten sweden evidence for early caledonian 505 ma subduction the seve nappes consist of long transported thrust sheets belonging to the upper allochthon within the scandinavian caledonides eclogites from two different megalenses within the seve nappe complex in norrbotten northern sweden have been dated with the sm nd method the two eclogite bearing megalenses have been subjected to different pressure and temperature conditions during the high pressure metamorphism garnet omphacite whole rock from ts2 within the tsakkok lens give an age of 505 18 ma 2 i 0 512231 0 000024 mswd 0 10 garnet and whole rock from ts5 and whole rock ts3 also fall on the above isochron the composite isochron gives an age of 503 18 ma 2 these results are interpreted to date the peak of the high pressure metamorphism 500 630 c and 12 15 kbars for the tsakkok lens the eclogites in the vaimok lens at grapesvarre were subjected to higher pressure and temperature conditions and more extensive reequilibration during the early cooling stages retrograde breakdown reactions accompanied by retrograde zoning of relict garnet seems to be associated with disturbance of the sm nd isotopic systems in contrast a sample with unzoned garnet and well preserved high pressure mineralogy from grapesvarre gives a sm nd garnet omphacite age of 503 14 ma 2 i 0 512010 0 000038 2 the ages for the seve eclogites are significantly older than the sm nd eclogite dates from the western gneiss region of norway wgr suggesting the existence of at least two eclogite forming events in the caledonide orogen the younger event has been related to the main continent continent collision stage of the caledonian orogeny while the older event that led to the production of the norrbotten eclogites must have taken place several hundred kilometres to the north and in a different tectonic setting more oceanward to the wgr it appears that the older event ca 505 ma was restricted to the subduction of dyke intruded sedimentary cover rocks which are thought to represent the rifted edge of the baltic continent

fault trace complexity cumulative slip and the shape of the magnitude frequency distribution for strike slip faults a global survey summary we examine whether the shape of the magnitude frequency distribution for strike slip faults is described by the gutenburg richter relationship log n a bm or by the characteristic earthquake model by analysing a data set of faults from california mexico japan new zealand china and turkey for faults within regional seismic networks curves of the form log n yrpl a bm where n yr is the number of events per year equal to magnitude m are fit to the instrumental record of seismicity and geological data are used to estimate independently the size and recurrence rate of the largest expected earthquakes that would rupture the total length of the fault extrapolation of instrumentally derived curves to larger magnitudes agrees with geological estimates of the recurrence rate of the largest earthquakes for only four of the 22 faults if uncertainties in curve slope are considered and significantly underestimates the geological recurrence rates in the remaining cases also if we predict the seismicity of the faults as a function of fault length and slip rate and the predicted seismicity is distributed in accord with the gutenburg richter relationship we find the predicted recurrence rate to be greater than the observed recurrence rates of smaller earthquakes along most faults if individual fault zones satisfy the gutenburg richter relationship over the long term our observations imply that during the recurrence interval of the largest expected earthquakes the recurrence of lesser sized events is not steady but rather strongly clustered in time however if the instrumental records provide an estimate of the long term rate of small to moderate earthquakes along the faults our observations imply that the faults generally exhibit a magnitude frequency distribution consistent with the characteristic earthquake model also we observe that the geometrical complexity of strike slip faults is a decreasing function of cumulative strike slip offset the four faults we observe to be consistent with the gutenburgrichter relationship are among those characterized by the least amount of cumulative slip and greatest fault trace complexity we therefore suggest that the ratio of the recurrence rate of small to large earthquakes along a fault zone may decrease as slip accumulates and the fault becomes smoother

surface rupture of the hundalee fault during the 2016 mw 7 8 kaikōura earthquake the hundalee fault is one of at least 20 faults that ruptured during the 2016 m w mw 7 8 kaik ura earthquake in the northeast of the south island of new zealand here we document a 12 km onshore section of the hundalee fault that exhibited surface rupture from this event to the northeast of our observations the fault crosses the coast and independent seabed surveys show that the 2016 rupture continued at least 2 km offshore no surface rupture was observed across the southwestern section of the hundalee fault which crosses hilly vegetated terrain and poorly consolidated valley floor sediment however previous interferometric synthetic aperture radar insar analyses suggest that a 9 km long section of the fault did rupture hence the minimum length of the 2016 rupture along the hundalee fault is 23 km field measurements indicate oblique dextral reverse slip along northeast trending hundalee fault sections and reverse sinistral slip along north to north northeast trending sections this is consistent with the regional principal horizontal shortening direction maximum vertical and horizontal offset measurements are 2 5 0 5 2 5 0 5 and 3 7 0 5 m 3 7 0 5 m respectively the discontinuous and irregular surface ruptures we observed are characteristic of a structurally immature fault yet previous geological mapping indicates that the hundalee fault is a regionally significant fault with 1 km 1 km late cenozoic throw furthermore a 60 m wide sequence of fault rocks exposed by the rupture indicates that slip has localized into 10 cm thick 10 cm thick gouge zones as anticipated for a mature fault therefore a discrepancy exists between geological evidence of the hundalee fault being a structurally mature fault and the characteristics of the 2016 rupture we speculate that this signifies that the 2016 rupture was imposed on the hundalee fault by movement across an inefficient multifault network rather than independent rupture of the hundalee fault itself

protolith ages and exhumation histories of ultra high pressure rocks across the western gneiss region norway the timing of protolith formation ultrahigh pressure uhp subduction and subsequent exhumation for the ultrahigh pressure to high pressure units across the eastern part of the western gneiss region norway were assessed using u pb zircon th pb monazite and 40 ar 39 ar white mica ages u pb zircon ages from eclogites demonstrate that oceanic and continental allochthons were emplaced onto the baltica basement before the entire mass was subducted to ultra high pressure eclogites within the allochthons across the entire western gneiss region are caledonian and show a degree of zircon re crystallization that increases with peak pressure permitting the interpretation that the entire region underwent synchronous subduction 40 ar 39 ar white mica ages of 399 ma indicate that the eastern part of the western gneiss region had been exhumed to shallow crustal levels while uhp metamorphism was ongoing farther west indicating a westward dip to the slab the 40 ar 39 ar white mica ages also show a clear east to west gradient across the entire western gneiss region indicating that the western gneiss region rose diachronously to crustal levels from east to west between 399 and 390 ma

how well do surface slip measurements track slip at depth in large strike slip earthquakes the importance of fault structural maturity in controlling on fault slip versus off fault surface deformation abstract comparisons of observed surface displacements with geodetically inferred slip at depth in six large m w 7 1 strike slip earthquakes reveal a correlation between the structural maturity of the fault and the ratio of deep slip to surface slip that occurs on localized zones of surface rupture specifically structurally immature faults 25 km of total displacement manifest only 50 60 of total slip on narrow fault surface traces versus 85 95 for structurally mature faults 85 km total slip the same pattern holds when structurally simple parts of a surface rupture are analyzed separately from parts that exhibit obvious structural complexity e g discontinuous or multiple traces or significant dip slip these results imply that geologic measurements of surface slip along structurally immature faults are likely to significantly underestimate the true slip at depth in large earthquakes this observation has implications for a number of important problems including determination of fault slip rates which are based on surface offsets earthquake probability assessments which are based on geologic fault slip rates comparisons of geologic and geodetic rate data in the search for strain transients the structural evolution of fault zones estimation of paleo earthquake magnitudes based on geomorphic offsets analyses of the relative importance of faulting vs distributed deformation in accommodating relative plate motions in continental crust the design and construction of infrastructure built near active faults and possibly for the prediction of strong ground motions which may at least partially depend on the degree of slip localization to the surface

rb sr record of fluid rock interaction in eclogites the marun keu complex polar urals russia abstract rb sr internal mineral isochrons in the eclogite facies marun keu metamorphic complex polar urals russia date periods of fluid rock interaction and record the metamorphic reaction history the marun keu complex consists of late proterozoic to early ordovician mostly igneous rocks that experienced a subduction related non pervasive eclogite facies metamorphism followed by a local decompression related amphibolite facies overprint during the uralian orogeny field observations show that metamorphic reactions as well as ductile deformation are controlled by local availability of a free fluid phase isotopic data reveals that availability of fluids similarly exerts control on isotope distribution from a relic gabbro which has never been infiltrated by free fluids a premetamorphic rb sr age of 467 39 ma was obtained rb sr isochron ages for 14 samples of eclogite and amphibolite facies assemblages sampled from within or close to metamorphic fluid veins range from 352 5 ma to 360 3 ma a sm nd isochron for a metagranite yields an age of 354 4 ma taken together the ages for both prograde and retrograde metamorphic assemblages overlap within analytical uncertainty and yield an average value of 355 5 1 4 ma indicating that the metamorphic evolution and incipient exhumation of the marun keu complex proceeded rapidly the results demonstrate that assemblages preserve their rb sr isotopic signatures as long as they remain devoid of free fluids and that only fluid rock interaction may cause sr isotope redistribution in addition the data suggest local fluid rock equilibrium low fluid rock ratios with overall fluid deficiency and limited fluid mobility at depth however some fluids must have been mobile on the km scale since they can be traced into the suprasubduction zone mantle wedge metasomatic veins in the rai iz ophiolite yield a rb sr mineral isochron age of 373 1 5 4 ma they are interpreted as evidence for suprasubduction zone metasomatism in an oceanic setting prior to subduction of the east european margin and associated formation of eclogites in the marun keu complex we propose that rb sr mineral isochron ages provide hygrochronological rather than thermochronological constraints they define the cooling history only in combination with zircon and apatite fission track data the straightforward interpretation of rb sr mineral ages as cooling ages is obsolete

creep of garnet in eclogite mechanisms and implications abstract the rheological properties of subducting rocks represent a fundamental parameter in the dynamics of subduction zones making robust predictions about these properties and the general strength evolution of subducting plates is hampered by a relatively restricted understanding of the mechanisms by which rocks deform at high and ultrahigh pressure this uncertainty is relates to the discrepancy between experimental and field based observations of eclogite deformation and in particular the role of garnet to further investigate this important aspect we performed a textural and micro structural investigation applying optical microscopy element mapping and electron backscatter diffraction on deformed garnet polycrystals from an eclogite mylonite the results were compared to those from a study of undeformed polycrystals that formed from a supercooled frictional melt at hp conditions the mylonites polycrystals are flattened parallel to the main high pressure foliation in the rock and individual grains were shortened by an average 15 although dislocation creep is commonly presumed to dominate garnet straining in eclogites no record of this mechanism was found instead the garnet grains have dissolution surfaces indicative of deformation by intergranular pressure solution the observations provide compelling evidence for the role of fluids and syn tectonic porosity in the weakening of garnet a supposedly rigid eclogite component such weakening represents a crucial step in the fundamental feedback loop between fluid ingress metamorphism and near instantaneous competence loss in rocks undergoing deep subduction

evolution and progressive geomorphic manifestation of surface faulting a comparison of the wairau and awatere faults south island new zealand reply field mapping and lidar analysis of surface faulting patterns expressed in flights of geologically similar fluvial terraces at the well known branch river and saxton river sites along the wairau alpine and awatere strike slip faults south island new zealand reveal that fault related deformation patterns expressed in the topography at these sites are markedly less structurally complex along the higher displacement hundreds of kilometers structurally mature wairau fault than along the awatere fault 13 20 km total slip these differences which are generally representative of the surface traces of these faults provide direct evidence that surface faulting becomes structurally simpler with increasing cumulative fault offset we also examine the degree to which off fault deformation ofd is expressed in the landscape at the saxton river site along the less structurally mature awatere fault significantly greater amounts of ofd are discernible as a wide damage zone 460 m fault perpendicular width in older ca 15 ka more displaced 64 74 m fluvial terraces than in younger ca 1 7 ka less displaced 55 m terraces no ofd is discernible in the lidar data on the least displaced 35 m terraces from this we infer that ofd becomes progressively more geomorphically apparent with accumulating displacement these observations imply that 1 the processes that accommodate ofd are active during each earthquake but may not be evident in deposits that have experienced relatively small displacements 2 structures accommodating ofd will become progressively geomorphically clearer with increasing displacement 3 geomorphic measurements of overall fault zone width taken in deposits that have experienced small displacements will be underestimates and 4 fault slip rates based on geomorphic surface offsets will be underestimates for immature faults if based solely on measurements along the high strain fault core

surface rupture of multiple crustal faults in the 2016 mw 7 8 kaikōura new zealand earthquake multiple 20 20 crustal faults ruptured to the ground surface and seafloor in the 14 november 2016 m w mw 7 8 kaik ura earthquake and many have been documented in detail providing an opportunity to understand the factors controlling multifault ruptures including the role of the subduction interface we present a summary of the surface ruptures as well as previous knowledge including paleoseismic data and use these data and a 3d geological model to calculate cumulative geological moment magnitudes m g w mwg and seismic moments for comparison with those from geophysical datasets the earthquake ruptured faults with a wide range of orientations sense of movement slip rates and recurrence intervals and crossed a tectonic domain boundary the hope fault the maximum net surface displacement was 12 m 12 m on the kekerengu and the papatea faults and average displacements for the major faults were 0 7 1 5 m south of the hope fault and 5 5 6 4 m to the north m g w mwg using two different methods are m g w mwg 7 7 0 3 0 2 7 7 0 2 0 3 and the seismic moment is 33 67 of geophysical datasets however these are minimum values and a best estimate m g w mwg incorporating probable larger slip at depth a 20 km seismogenic depth and likely listric geometry is m g w mwg 7 8 0 2 7 8 0 2 suggests 32 32 of the moment may be attributed to slip on the subduction interface and or a midcrustal detachment likely factors contributing to multifault rupture in the kaik ura earthquake include 1 the presence of the subduction interface 2 physical linkages between faults 3 rupture of geologically immature faults in the south and 4 inherited geological structure the estimated recurrence interval for the kaik ura earthquake is 5 000 10 000 yrs 5 000 10 000 yrs and so it is a relatively rare event nevertheless these findings support the need for continued advances in seismic hazard modeling to ensure that they incorporate multifault ruptures that cross tectonic domain boundaries

3 2ga eolian deposits from the moodies group barberton greenstone belt south africa implications for the origin of first cycle quartz sandstones abstract the 3 2 ga moodies group in barberton greenstone belt south africa contains the oldest recognized evidence for eolian processes on earth these eolian facies indicate that significant wind regimes existed in the archean atmosphere eolian deposits are developed in the lower moodies group in the central part of the belt and consist of stacked inversely graded strata ranging in thickness from 2 to 10 mm individual strata consist of fine to medium grained quartz sandstone at the base that passes vertically into very coarse to coarse grained quartz sandstone strata make up cross bed sets up to 3 5 m thick sets of wind ripple strata are either tabular tangential or in the form of broad troughs this type of inversely graded stratification is the product of wind ripple migration the coarse grain size of the sediment combined with the low angle of inclination of the strata is best interpreted as the product of sand sheet or dune plinth preservation based on the geometry of eolian set boundaries dunes were probably simple barchan form the tens of meters thick eolian deposits are underlain by braided stream deposits composed of subfeldspathic pebbly sandstones the vertical change from braided stream subfeldspathic sandstones to eolian quartz arenites highlights the underappreciated capacity of eolian processes to generate first cycle quartz sandstones on landscapes pre dating the advent of land vegetation

burial rates during prograde metamorphism of an ultra high pressure terrane an example from lago di cignana western alps italy abstract estimation of burial rates and duration of prograde metamorphism of ultra high pressure uhp rocks t 590 630 c p 2 7 2 9 gpa of the zermatt saas ophiolite from lago di cignana italy may be made through combined lu hf and sm nd garnet geochronology in conjunction with petrologic estimates of the prograde p t path we report a lu hf garnet omphacite whole rock isochron age of 48 8 2 1 ma from the uhp locality at lago di cignana which stands in contrast to the sm nd age of 40 6 2 6 ma amato et al earth planet sci lett 171 1999 425 438 obtained from the same sample and mineral material the sm nd and lu hf ages as well as other ages determined on metamorphic garnet zircon and white mica amato et al earth planet sci lett 171 1999 425 438 mayer et al eur union geosci 10 1999 abstr 809 rubatto et al contrib mineral petrol 132 1998 269 287 dal piaz et al int j earth sci 90 2001 668 684 from lago di cignana and elsewhere in the zermatt saas ophiolite lie within a range of 50 38 ma which we interpret to encompass the duration of prograde metamorphism and possibly the duration of garnet growth the difference in measured sm nd and lu hf ages from cignana can be accounted for by expected core to rim variations in lu hf sm and nd the measured yttrium content in garnet which may be a proxy for lu is highest in garnet core and lowest in the mineral rim generally following a profile that is predicted by rayleigh fractionation preferential enrichment of lu in the core produces a lu hf age that is weighted toward the older garnet core sm nd ages as predicted by rayleigh fractionation of sm and nd during garnet growth however reflect later grown garnet as compared to lu hf ages the difference in sm nd and lu hf ages from a single sample should therefore be a minimum estimate for the duration of garnet growth and prograde metamorphism so long as sm nd and lu hf blocking temperatures were not exceeded for a long period of time based on the 12 myr duration of prograde garnet growth estimated in this study burial rates for rocks at lago di cignana were on the order of 0 23 0 47 cm yr these values correlate with continuous shortening rates of 0 4 1 4 cm yr between the european plate and the african adriatic promontory between 50 and 38 ma which is on the order of that calculated for plate velocities from plate reconstructions suggesting that the zermatt saas ophiolite may have remained well coupled to the down going slab to uhp conditions

a 2000 yr paleoearthquake record along the conway segment of the hope fault implications for patterns of earthquake occurrence in northern south island and southern north island new zealand paleoseismic trenches excavated at two sites reveal ages of late holocene earthquakes along the conway segment of the hope fault the fastest slipping fault within the marlborough fault system in northern south island new zealand at the green burn east gbe site a fault perpendicular trench exposed gravel colluvial wedges fissure fills and upward fault terminations associated with five paleo surface ruptures radiocarbon age constraints indicate that these five earthquakes occurred after 36 b c e with the four most recent surface ruptures occurring during a relatively brief period 550 yr between about 1290 c e and the beginning of the historical earthquake record about 1840 c e additional trenches at the green burn west gbw site 1 4 km west of gbe reveal four likely coseismically generated landslides that occurred at approximately the same times as the four most recent gbe paleoearthquakes independently overlapping with age ranges of events gb1 gb2 and gb3 from gbe combining age constraints from both trench sites indicates that the most recent event gb1 occurred between 1731 and 1840 c e the penultimate event gb2 occurred between 1657 and 1797 c e gb3 occurred between 1495 and 1611 c e gb4 occurred between 1290 and 1420 c e and gb5 occurred between 36 b c e and 1275 c e these new data facilitate comparisons with similar paleoearthquake records from other faults within the alpine hope jordan kekerengu needles wairarapa al hp jkn wr fault system of throughgoing fast slip rate 10 mm yr reverse dextral faults that accommodate a majority of pacific australia relative plate boundary motion these comparisons indicate that combinations of the faults of the al hp jkn wr system may commonly rupture within relatively brief 100 year long sequences but that full wall to wall rupture sequences involving all faults in the system are rare over the span of our paleoearthquake data rather the data suggest that the al hp jkn wr system may commonly rupture in subsequences that do not involve the entire system and potentially at least sometimes in isolated events

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

trace element signature and u pb geochronology of eclogite facies zircon bergen arcs caledonides of w norway secondary ion mass spectrometry sims u pb and trace element data are reported for zircon to address the controversial geochronology of eclogite facies metamorphism in the lindas nappe bergen arcs caledonides of w norway caledonian eclogite facies overprint in the nappe was controlled by fracturing and introduction of fluid in the proterozoic sveconorwegian granulite facies meta anorthosite norite protolith zircon grains in one massive eclogite display a core rim structure sveconorwegian cores have trace element signatures identical with those of zircon in the granulite protolith i e 0 31 th u 0 89 heavy rare earth element hree enrichment and negative eu anomaly weakly zoned to euhedral oscillatory zoned caledonian rims are characterized by th u 0 13 low lree content minimum normalized abundance for pr or nd variable enrichment in hree and no eu anomaly a decrease of ree towards the outermost rim especially hree is documented this signature reflects co precipitation of zircon with garnet and clinozoisite in a feldspar absent assemblage and consequently links zircon to the eclogite facies overprint the rims provide a mean 206pb 238u crystallization age of 423 4 ma this age reflects eclogite forming reactions and fluid rock interaction this age indicates that eclogite facies overprint in the lindas nappe took place at the onset of the scandian silurian collision between laurentia and baltica

slow exhumation of uhp terranes titanite and rutile ages of the western gneiss region norway abstract u pb ages of titanite and rutile were obtained from the central western gneiss region norway to assess the style and timing of exhumation and cooling of the western gneiss uhp terrane approximately half of the titanite ages are concordant the majority of which yield a limited age range from 393 to 390 ma the other titanite data are discordant and define discordia arrays with upper intercept ages of either 938 ma or 1 6 ga and a lower intercept of 389 ma concordant rutile analyses range from 385 to 392 ma both titanite and rutile ages young wnw toward the core of the orogen and are 4 ma older than 40 ar 39 ar muscovite ages corresponding to a cooling rate of 90 c ma a well defined boundary between concordant and discordant titanite ages in combination with the wnw increasing p t gradient and the similarity between muscovite cooling ages in the east and eclogite ages in the west suggests that the wgr remained coherent throughout its exhumation history and was progressively unroofed from east to west a 390 2 0 8 ma titanite in the soroyane uhp domain indicates that exhumation occurred at a vertical rate of 7 mm yr for 12 ma these rates are slower than estimates from smaller uhp terranes but similar to other large uhp terranes suggesting that there may be fundamental differences in the mechanisms controlling the evolution of large uhp terranes that undergo protracted subduction and exhumation and smaller uhp terranes that undergo rapid subduction and exhumation

the tectonic significance of pre scandian 40ar 39ar phengite cooling ages in the caledonides of western norway pre silurian continental margin deposits in western norway non conformably overlying allochthonous continental orthogneisses retain ordovician 40 ar 39 ar cooling ages for phengites implying either rapid cooling immediately after a late ordovician orogenic event or less likely a slow cooling following an early ordovician or older orogeny the dalsfjord suite hoyvik group basement cover pair are probably a lateral equivalent to late proterozoic sandstones sparagmites covering the jotun nappe gneisses of the middle allochthon in central south norway the hoyvik group underwent polyphase deformation greenschist facies metamorphism t max 40 ar loss probably occurred during subsequent scandian deformation and late to post orogenic extension the hoyvik group rocks were unroofed before the wenlock time 423 428 ma and cooled through the temperature for argon retention in phengite at c 447 4 ma indicating a maximum cooling rate between 14 and 22c ma 1 through ashgill and llandovery times before being subjected to low grade metamorphism during the scandian orogeny rapid pre scandian cooling combined with peak metamorphic conditions of 450c or less may indicate that the dalsfjord hoyvik basement cover pair were avected by an orogenic event during the late ordovician caradoc time the data also suggest that the caledonian margin of baltica may have experienced a more protracted tectonism during the caledonian cycle than previously models focusing on early caledonian and tremadoc or older ophiolite obduction and the scandian continental collision between baltica and laurentia

combined lu hf and sm nd geochronology of the marianske lazně complex new constraints on the timing of eclogite and granulite facies metamorphism abstract lu hf and sm nd garnet whole rock geochronology combined with petrographic observations minero chemical variations thermodynamic modelling and structural data was used to constrain the p t t d evolution of eclogites from the marianske lazn complex bohemian massif boudins of mostly isotropic eclogite with relict steep eclogite facies fabric are affected by steep migmatitic foliation which is followed on a regional scale by the development of almost pervasive predominantly se dipping extensional foliation the structural succession shows continuous transition from eclogite to garnetiferous migmatitic amphibolite and to amphibolite migmatite a least retrogressed sample of eclogite shows clusters of fine grained inclusion poor garnet omphacite relicts surrounded by a fine grained clinopyroxene plagioclase symplectite with minor amphibole biotite plagioclase intergrowths after white mica kyanite with plagioclase spinel coronas and accessory rutile rare potassic white mica occurs as inclusions in omphacite a more retrogressed eclogite with no omphacite or kyanite relicts contains inclusion poor garnet surrounded by amphibole plagioclase corona in a matrix dominated by plagioclase amphibole symplectite with minor clinopyroxene in places the symplectite is overgrown by coarse grained amphibole peak p t conditions inferred from combined conventional thermobarometry and phase equilibria modelling and based on inclusions of white mica up to 3 33 si p f u matrix omphacite jd33 36 and garnet core alm33 38prp38 42grs22 25sps1 compositions are 25 kbar at 650 750 c a ht overprint occurred at 14 18 kbar and 800 c based on coexisting clinopyroxene jd18 24 plagioclase an18 35 and amphibole na b lu hf and sm nd garnet geochronology has been applied to both samples an older age c 390 ma obtained by the lu hf method is interpreted as the timing of hp metamorphism while c 15 ma younger ages were obtained by the sm nd method as temperatures for the ht overprint exceed the empirically and experimentally determined closure temperature of the sm nd system the sm nd ages are interpreted to date cooling following the ht overprint combined together contrasting eclogite and amphibolite facies migmatite fabrics the mineral textures calculated p t conditions and distinct lu hf and sm nd ages provide a complete p t t d path characterised by rapid 15 ma transition from hp subduction crustal thickening to extensional ht shearing this unconventional exhumation path does not fit to models of monocyclic exhumation in a subduction channel proposed for the munchberg and zev devonian hp units to the west in contrast the post peak extensional low angle shearing shortly after subduction and collision resembles more the geodynamic model typical for the iberian subduction system both in time scales and sequence of tectonic events

ordovician continental margin terranes in the lachlan orogen australia implications for tectonics in an accretionary orogen along the east gondwana margin 1 four continental margin turbidite black shale terranes of the lachlan orogen in the southern tasmanides of eastern australia formed in two major systems along the east gondwana margin and constrain the ordovician assembly of this accretionary orogen key features are the dissimilar stratigraphies of the adjacent bendigo and melbourne terranes in the western system the dissimilar stratigraphies of the adjacent melbourne and albury bega terranes that reflect juxtaposition of the two systems during the middle devonian and the presence of the albury bega terrane both west and east of the macquarie arc in the eastern system that also includes the ocean floor narooma terrane and igneous ocean crust terrane s repetition of the albury bega terrane either side of the arc requires either rifting or orogen parallel strike slip duplication of a once contiguous package terrane interactions began in the earliest gisbornian with early docking uplift deformation and exchange of detritus amalgamation occurred in the earliest silurian benambran orogeny with accretion in the middle devonian over 40 myr discrete turbidite terranes aligned along the gondwana margin in two systems were converted into a very wide orogen characterized by the along strike juxtaposition of superficially similar terranes

tectonic evolution of the grenville orogen in the central appalachians abstract remnants of the grenville orogeny a globally pervasive tectonothermal event resulting from the amalgamation of the supercontinent rodinia between ca 1 3 and 1 0 ga are exposed throughout eastern north america for ca 3000 km from labrador to alabama although tectonic models for the development of the grenville have historically been based on observations from the large and well exposed canadian grenville province recent investigations suggest that initial continental collision occurred proximal to the appalachian blue ridge mesoproterozoic rocks within this portion of the orogen are exposed within a series of allochthonous terranes that were extensively reworked during paleozoic orogenesis to better understand the tectonic history of this critical region we utilized garnet and monazite geochronology to reconstruct the metamorphic history of eleven samples of ortho and paragneiss from the appalachian blue ridge province the resultant dates together with new results from trace element thermobarometry define a prolonged record of high temperature metamorphism coincident with the timing of continent continent collision as recognized in the northern portion of the orogen initial garnet and monazite growth commenced between 1100 and 1065 ma with peak granulite facies conditions 750 900 c 0 55 0 85 gpa occurring from 1050 to 1010 ma burial and heating of the paragneisses progressed rapidly with peak metamorphism occurring 20 30 myr after deposition of the sedimentary protoliths local hydrothermal alteration followed peak metamorphism and occurred at 1000 990 ma with later cooling through 660 c between 980 and 935 ma 3 2 c myr the metamorphic history outlined here together with insights from previous studies is consistent with formation of the blue ridge rocks within a continental suture zone that had an orogenic architecture comparable to that of the himalayan tibetan orogen

models of garnet differential geochronology abstract rayleigh distillation models are developed to describe theoretical growth zoning of lu hf rb sr sm and nd in typical garnet crystals from metapelites and metabasites effects of diffusion limited transport within the matrix and intracrystalline diffusion are also considered qualitatively theoretical zoning profiles show strong depletions of lu in garnet rims compared to cores but virtually invariant hf rb sr sm and nd profiles generally consistent with natural profiles for lu and hf and previously published models theoretical isochron diagrams for lu hf exhibit distinctive arcuate distributions and high mswds consistent both with himalayan data and with expectations that garnet growth durations exceed chronologic resolution by as much as an order of magnitude predicted isochron diagrams for sm nd and rb sr exhibit vertical arrays for garnet and high mswds that are generally lower than for lu hf in metapelites inherent chronologic resolution for bulk separates is best for lu hf in metapelites and rb sr but analytical considerations favor rb sr or sm nd for chronologic zoning studies diffusion limited transport in the rock matrix strongly influences zoning profiles but does not change the main trends on isochron diagrams intracrystalline diffusion will initially rotate lu hf isochrons to steeper slopes giving older apparent ages the natural himalayan data indicate growth of garnet in one rock from the greater himalayan sequence at 34 ma consistent with previously measured monazite ages from the same rock data from another himalayan rock suggest polymetamorphism that includes a paleozoic component

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

rare earth diffusion kinetics in garnet experimental studies and applications abstract we determined the diffusion coefficient of sm in almandine garnet as function of temperature at 1 bar and fo 2 corresponding to that of wustite iron buffer and to a limited extent that of a few other selected rare earth elements in almandine and pyrope garnets both garnets were demonstrated to have metastably survived the diffusion annealing at conditions beyond their stability fields the experimental diffusion profiles were analyzed by secondary ion mass spectrometry and in addition by rutherford back scattering spectroscopy for two samples transmission electron microscopic study of an almandine crystal that was diffusion annealed did not reveal any near surface fast diffusion path using reasonable approximations and theoretical analysis of vacancy diffusion the experimental data were used to develop an expression of rare earth element ree diffusion coefficient in garnet as a function of temperature pressure fo 2 ionic radius and matrix composition calculation of the closure temperature for the sm nd decay system in almandine garnet in a metamorphic terrain shows very good agreement with that constrained independently modeling of the ree evolution in melt and residual garnet suggests that for dry melting condition the ree pattern in the melt should commonly conform closely to that expected for equilibrium melting however for much lower solidus temperatures that would prevail in the presence of a h 2 o co 2 fluid the concentration of light ree in the melt could be significantly lower than that under equilibrium melting condition a reported core and rim differences in the ree content of a garnet crystal in a mantle xenolith in kimberlite have been reproduced by assuming that the ree zoning was a consequence of entrapment in a magma derived from an external source for 32 000 yr before the eruption

the transition from subduction to continental collision crustal structure in the north canterbury region new zealand summary the north canterbury region marks the transition from pacific plate subduction to continental collision in the south island of new zealand details of the seismicity structure and tectonics of this region have been revealed by an 11 week microearthquake survey using 24 portable digital seismographs arrival time data from a well recorded subset of microearthquakes have been combined with those from three explosions at the corners of the microearthquake network in a simultaneous inversion for both hypocentres and velocity structure the velocity structure is consistent with the crust in north canterbury being an extension of the converging chatham rise the crust is about 27 km thick and consists of an 11 km thick seismic upper crust and 7 km thick seismic lower crust with the middle part of the crust being relatively aseismic seismic velocities are consistent with the upper and middle crust being composed of greywacke and schist respectively while several lines of evidence suggest that the lower crust is the lower part of the old oceanic crust on which the overlying rocks were originally deposited the distribution of relocated earthquakes deeper than 15 km indicates that the seismic lower crust changes dip markedly near 43 s to the south west it is subhorizontal while to the north east it dips north west at about lo fault plane solutions for these earthquakes also change near 43 s for events to the south p axes trend approximately normal to the plate boundary reflecting continental collision while for events to the north t axes are aligned down the dip of the subducted plate reflecting slab pull while lithospheric subduction is continuous across the transition it is not clear whether the lower crust near 43 s is flexed or

is the earth lazy a review of work minimization in fault evolution abstract the principle of work minimization has been used in various forms to account for the development of active fault systems within a wide range of tectonic settings we review the successes challenges and implications learned from previous applications of work minimization examination of the energy budget provides insight into the competing influences of different processes within fault systems at a variety of scales we present each work budget component with considerations for numerical implementation additionally we demonstrate numerical implementation by solving for the energy budgets and finding the most efficient propagation paths of a joint and several faults consideration of the energy budget captures growth patterns that are consistent with both laboratory observations and theoretical predictions using the energy release rate g unlike using g work minimization is not limited to collinear growth in comparison with predictions using coulomb failure planes work minimization eliminates uncertainty in predicting fault propagation by 1 evaluating the trade off between tensile and shear failure ahead of the fault and 2 avoiding the ambiguity introduced by the two potential coulomb failure planes application of work minimization to faulting demonstrates the effectiveness of this approach in predicting both the orientation and timing of fault propagation

slow subduction of a thick ultrahigh pressure terrane 1 high precision lu hf and sm nd ages reported here cover a large portion of the western gneiss region wgr ultrahigh pressure uhp terrane norway and range from 413 9 3 7 to 397 1 4 8 ma collectively new and existing geochronologic data for eclogites demonstrate that eclogite facies metamorphism occurred over a large area 60 000 km2 for an unexpectedly long period of 20 ma a thermal model using slow subduction 2 4 mm a 1 of a relatively warm and thick slab can reproduce the observed p t t history of the wgr uhp terrane indicating that large uhp terranes with protracted peak or near peak histories probably reflect slow subduction of relatively thick crustal sections

location of largest earthquake slip and fast rupture controlled by along strike change in fault structural maturity due to fault growth earthquake slip distributions are asymmetric along strike but the reasons for the asymmetry are unknown we address this question by establishing empirical relations between earthquake slip profiles and fault properties we analyze the slip distributions of 27 large continental earthquakes in the context of available information on their causative faults in particular on the directions of their long term lengthening we find that the largest slips during each earthquake systematically occurred on that half of the ruptured fault sections most distant from the long term fault propagating tips i e on the most mature half of the broken fault sections meanwhile slip decreased linearly over most of the rupture length in the direction of long term fault propagation i e of decreasing structural maturity along strike we suggest that this earthquake slip asymmetry is governed by along strike changes in fault properties including fault zone compliance and fault strength induced by the evolution of off fault damage fault segmentation and fault planarity with increasing structural maturity we also find higher rupture speeds in more mature rupture sections consistent with predicted effects of low velocity damage zones on rupture dynamics since the direction s of long term fault propagation can be determined from geological evidence it might be possible to anticipate in which direction earthquake slip once nucleated may increase accelerate and possibly lead to a large earthquake our results could thus contribute to earthquake hazard assessment and earthquake early warning

subduction related magmatism of late ordovician age in eastern england deep boreholes show that plutonic and volcanic igneous rocks comprise an important component of the caledonian basement in eastern england the isotopic compositions of these rocks reveal that many of them are of late ordovician age 440 460 ma and their geochemical compositions suggest calc alkaline affinities the intermediate diorite tonalite plutonic rocks are associated with a prominent northwest southeast trending belt of aeromagnetic anomalies extending from derby to st ives hunts which is interpreted to work the plutonic core of a calc alkaline magmatic arc it is inferred that this arc was generated by the subduction of oceanic lithosphere possibly from the tornquist sea in a south or southwest direction beneath the midlands microcraton in late ordovician times the age and geochemical composition of concealed ordovician volcanic rocks in eastern england and hypabyssal intrusions of the midlands minor intrusive suite in central england is compatible with such a hypothesis

preliminary geometry displacement and kinematics of fault ruptures in the epicentral region of the 2016 mw 7 8 kaikōura new zealand earthquake

national seismic hazard model for new zealand 2010 update a team of earthquake geologists seismologists and engineering seis mologists has collectively produced an update of the national probabilistic seismic hazard psh model for new zealand national seismic hazard model or nshm the new nshm supersedes the earlier nshm published in 2002 and used as the hazard basis for the new zealand loadings standard and numerous other end user applica tions the new nshm incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new new zealand based and international scaling relationships for the parameterization of the faults the dis tributed seismicity model has also been updated to include post 1997 seismicity data a new seismicity regionalization and improved methodology for calculation of the seismicity parameters probabilistic seismic hazard maps produced from the new nshm show a similar pattern of hazard to the earlier model at the national scale but there are some significant reductions and increases in hazard at the regional scale the national scale differences between the new and earlier nshm appear less than those seen between much earlier national models indicating that some degree of consis tency has been achieved in the national scale pattern of hazard estimates at least for return periods of 475 years and greater online material table of fault source parameters for the 2010 national seismic hazard model

the kinematics of a transition from subduction to strike slip an example from the central new zealand plate boundary 1 we develop a kinematic model for the transition from subduction beneath the north island new zealand to strike slip in the south island constrained by gps velocities and active fault slip data to interpret these data we use an approach that inverts the kinematic data for poles of rotation of tectonic blocks and the degree of interseismic coupling on faults in the region convergence related to the hikurangi subduction margin becomes very low offshore of the northern south island indicating that in this region the majority of the relative plate motion has been transferred onto faults within the upper plate as suggested by previous studies this result has implications for understanding the likely extent of subduction interface earthquake rupture in central new zealand easterly trending strike slip faults such as the boo boo fault are the key features that facilitate the transfer of strike slip motion from the northern south island faults further north into the southern north island and onto the hikurangi subduction thrust our results also indicate that the transition from rapid forearc rotation adjacent to the hikurangi subduction margin to a strike slip dominated plate boundary with negligible vertical axis rotation in the south island occurs via a crustal scale hinge or kink in the upper plate compatible with paleomagnetic and structural geological data despite the ongoing tectonic evolution of the central new zealand region our study highlights a remarkable consistency between data sets spanning decades gps thousands of years active faulting data and millions of years paleomagnetic data and bedrock structure

early ordovician u pb metamorphic ages of the eclogite bearing seve nappes northern scandinavian caledonides eclogite grade metamorphism of the seve nappe complex snc in norrbotten sweden records the attempted subduction of the baltic continental margin during the early palaeozoic evolution of the iapetus ocean metamorphic titanite sampled from several calcsilicate gneisses of the snc in norrbotten occurs as part of a prograde eclogite facies metamorphic mineral assemblage and yields concordant to nearly concordant u pb ages of 500 475 ma later structural disruption of these rocks occurred during the siluro devonian scandian phase of the caledonide orogeny but the u pb systematics show no evidence of a second generation metamorphic or recrystallized of titanite or of post early ordovician disturbance through pb loss hence the u pb ages are believed to record the time of prograde mineral growth during eclogite facies metamorphism of the snc these results support earlier sm nd and 40ar 39ar studies indicating an early ordovician metamorphic age for the eclogitic norrbotten snc and confirm the early ordovician destruction of at least this segment of the palaeozoic passive margin of baltica these results indicate that the snc in the northern scandinavian caledonides was subducted and metamorphosed to high grade some 50 70 myr prior to the high grade metamorphism of the snc in the central scandinavian caledonides this result requires significantly different early palaeozoic tectonic histories for rocks mapped as snc in the northern caledonides and those in the central caledonides despite a seemingly similar tectonostratigraphic position and broadly similar high grade metamorphism

the tornquist sea and baltica avalonia docking early ordovician late arenig limestones from the sw margin of baltica scania bomholm have multicomponent magnetic signatures but high unblocking components predating folding and the corresponding palaeomagnetic pole latitude 19degreesn longitude 051degreese compares well with arenig reference poles from baltica collectively the arenig poles demonstrate a midsoutherly latitudinal position for baltica then separated from avalonia by the tomquist sea tornquist sea closure and the baltica avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for avalonia and baltica during the mid late ordovician by the caradoc avalonia had drifted to palaeolatitudes compatible with those of sw baltica and subduction beneath eastern avalonia was taking place we propose that explosive vents associated with this subduction and related to andean type magmatism in avalonia were the source for the gigantic mid caradoc c 455 ma ash fall in baltica i e the kinnekulle bentonite avalonia was located south of the subtropical high during most of the ordovician and this would have provided an optimum palaeoposition to supply baltica with large ash falls governed by westerly winds in scama we observe a persistent palaeomagnetic overprint of late ordovician ashgill age pole latitude 4degreess longitude 012degreese the remagnetisation was probably spurred by tectonic derived fluids since burial alone is inadequate to explain this remagnetisation event this is the first record of a late ordovician event in scania but it is comparable with the shelveian event in avalonia low grade metamorphism in the north sea basement of ne germany 440 450 ma and sheds new light on the baltica avalonia docking c 2002 elsevier science b v all rights reserved less

the timing of stabilisation and the exhumation rate for ultra high pressure rocks in the western gneiss region of norway new petrographic evidence and a review of the latest radiometric age data are taken to indicate that formation of the ultra high pressure uhp eclogites within the western gneiss region of norway probably occurred within the 400 410 ma time frame thus this event took place significantly later than the previous widely accepted age of c 425 ma for the timing of the high pressure metamorphism in this part of the scandinavian caledonides garnet growth under uhp coesite stable conditions is recognised as a discrete younger event following on from earlier garnet formed under firstly amphibolite facies then quartz stable eclogite facies conditions currently the best constrained and most precise age specifically for uhp mineral growth is the 402 2 ma u pb age for metamorphic zircon some of which retain coesite inclusions from the hareidland eclogite exhumation must have followed shortly thereafter and based on synoptic pressure temperature and depth time curves must have been very fast our data and those of others indicate an initial fast exhumation to about 35 km depth by about 395 ma at a mean rate of about 10 mm a 1 this rapid exhumation rate may have been driven by the appreciable residual buoyancy of the deeply subducted continental crustal slab due to incomplete eclogitization of the dominant proterozoic orthogneisses during the short lived uhp event subsequent exhumation to 8 10 km depth by about 375 ma occurred at a much slower mean rate of about 1 3 mm a 1 with the late stage extensional collapse of the caledonian orogen playing an increasingly important role especially in the final unroofing of the western gneiss region with some remarkably preserved uhp rocks