strain partitioning in the transition area between oblique subduction and continental collision hikurangi margin new zealand spatial differences in late quaternary structural style and deformation rates indicate a complex pattern of strain partitioning within the transition area from oblique subduction beneath southern north island to oblique continental collision in northern south island new zealand the late quaternary structure of the offshore southern hikurangi margin is determined here using seismic reflection profiles mr1 side scan sonar swath images em12dual multibeam swath bathymetry and backscatter images and sediment core and dredge samples where oblique 50 subduction of the oceanic hikurangi plateau is occurring beneath southern wairarapa region the steep dissected upper margin consists of a wedge of rocks that are being deformed by strike slip and reverse faults beneath the lower margin an accretionary wedge of quaternary age has developed rapidly by frontal accretion of a thick succession of turbidites on the pacific plate estimates of late quaternary geological strain rates have been made on two margin perpendicular transects across southern north island and the offshore margin to budget the predicted nuvel 1a plate motion more than 33 55 of the total plate motion is expressed in the offshore part of the upper plate above the subduction detachment in the central hikurangi margin between 40 s and 41 s this offshore deformation could potentially include margin parallel fault slip of up to 14 15 mm yr across the upper plate strain is partitioned into zones of folding and thrust faulting and possibly more than one zone of strike slip faulting but the partitioning may be incomplete with oblique slip thrusting an important component of the deformation the wide distribution of deformation within the upper plate partially reflects strong coupling between the subducting oceanic plateau and the leading edge of the overriding plate this coupling increases toward the southwest where the continental part of the subduction zone beneath marlborough may now be inactive or very strongly coupled toward the southwest the transpressive deformation style of the upper wairarapa margin continues into the upper marlborough margin and onshore into the strike slip marlborough fault system of northern south island in contrast the accretionary wedge narrows to the southwest and terminates in southeastern cook strait approximately above the transition from subducted oceanic crust to subducted continental crust of the pacific plate farther southwest beneath the lower marlborough margin low strain folding and thrust faulting is occurring but the style of deformation is not typical of the accretionary wedge this shortening results either from a small amount of subduction slip beneath marlborough and or from contractional strain partitioned to the southeast of the continental transpression zone whereas the initial onset of continental collision occurs in marlborough the surface expression of deformation of the pacific plate occurs south of 42 30 s normal faulting of the northwestern margin of the continental chatham rise possibly reflects flexural extension of the pacific plate crust at the southern end of the subduction zone whereas folding and thrust faulting of the north canterbury coastal region results from nw se contraction of the delaminated upper crust entering the southern alps collision zone

ar ar dating of k feldspar in low grade metamorphic rocks example of an exhumed mesozoic accretionary wedge and forearc south island new zealand 1 new 40ar 39ar ages from detrital k feldspars and metamorphic white micas from the eastern province terranes of new zealand have been used to investigate the thermo tectonic history of different parts of an exhumed mesozoic forearc basin and accretionary wedge k feldspars from barely metamorphosed sedimentary host rocks mainly record detrital source area ages whereas those from zeolite and prehnite pumpellyite facies host rocks have textures and argon age spectra that indicate recrystallization during regional low temperature metamorphism the results contribute to a model that genetically links thermo tectonic events across the accretionary wedge and forearc basin elements of the convergent margin and into the median batholith arc probably by the early cretaceous and possibly by the middle jurassic thus even though multidiffusion domain mdd models cannot be used to make inference on cooling histories in such situations the k feldspar argon thermochronometer can provide useful information on the timing of geological events in sub greenschist facies rocks

authigenic potassium feldspar a tracer for the timing of palaeofluid flow in carbonate rocks northern calcareous alps austria

five thousand years of surface ruptures on the wellington fault new zealand implications for recurrence and fault segmentation new paleoseismic studies have been undertaken on the wellington hutt valley w hv segment of the wellington fault to characterize its late holocene record of surface rupturing earthquakes trenches and radiocarbon dates from te kopahou and te marua have provided evidence and improved timing for the four most recent earthquake ruptures these events have been recognized on the basis of upward terminating faults coseismic deposition progressive displacement and faulting of colluviums at te kopahou colluvial and scree deposition resulting from surface rupture and strong earthquake shaking buries old ground surfaces associated with peat and or soil development at te marua the timing of the two youngest events has been refined by bracketing the ages of the youngest faulted and unfaulted alluvial terraces of the hutt river assuming that the w hv segment acts as a rupture segment along its length the approximate timings of these faulting events is as follows the most recent faulting event event i occurred between 110 and 310 cal yr b p a d 1640 1840 the penultimate faulting event event ii between 790 and 930 cal yr b p event iii occurred between 1835 and 2340 cal yr b p and event iv between 2460 and 4900 yr b p the minimum and maximum earthquake recurrence intervals derived from the four youngest events are 715 and 1575 yr respectively with a median value of 1145 yr revisions of the earthquake timing recurrence interval data and recently the single event displacement and slip rate collectively reduce the seismic hazard for the w hv segment of the wellington fault a four event paleoearthquake record from the pahiatua section of the wellington fault is statistically similar to that from the w hv segment this has significant implications with respect to the rupture length and magnitude or clustering of future surface rupturing earthquakes on the wellington fault

structure and paleoearthquake records of active submarine faults cook strait new zealand implications for fault interactions stress loading and seismic hazard 1 a new interpretation of active faulting in central cook strait new zealand reveals tectonic structures associated with the spatial transition from subduction to continental transform faulting marine seismic reflection profiles and multibeam bathymetric data indicate that there are no throughgoing crustal faults connecting the north island dextral fault belt and the marlborough fault system in south island the major faults terminate offshore associated with 5 20 km wide step overs and a change in regional fault strike this structure implies that propagation of strike slip earthquake ruptures across the strait is not probable faulted sedimentary sequences in the wairau basin marlborough shelf correlated to glacioeustatic sea level cycles provide a stratigraphic framework for fault analysis a high resolution study of the postglacial 20 ka vertical displacement history of the cloudy and vernon faults reveals up to six and five paleoearthquakes since 18 ka respectively these long timescale records indicate variable recurrence intervals and possibly variable stress drop thus conforming to the variable slip model of earthquake behavior integration of these data with other submarine and terrestrial paleoearthquake records indicates the presence of clustered earthquake sequences involving multiple faults different sequences do not always involve the same faults it appears that earthquake clustering is driven by fault interactions that lead to specific loading conditions favoring the triggering of earthquakes on major faults in relatively short time intervals present day regional coulomb stress distribution has been calculated in two scenarios considered to represent minimum and maximum loading conditions the models incorporating secular tectonic loading and stress changes associated with major crustal earthquakes indicate high stress loading in a large part of central cook strait these conditions may favor the triggering of future damaging earthquakes in this region

coseismic strike slip at a point during the last four earthquakes on the wellington fault near wellington new zealand 1 we analyze progressively displaced late quaternary 12 ka fluvial terraces along the wellington fault near wellington new zealand optically stimulated luminescence dating indicates that degradational terraces were produced at a rate of about one terrace per 1000 years similar to the rate of earthquake surface rupturing along the hutt river near te marua we measured the strike slip of 15 terrace risers and paleochannels on the lowest 8 of these terraces of holocene age the river after earthquakes was generally capable of smoothing its faulted riverbanks the dextral offsets appear to fall into several groupings that record slip accumulation during the last four earthquakes we calculate a mean single event slip of 5 0 0 24 m 95 confidence with an rms scatter 1 of slips about the mean of 1 5 m the coefficient of variation cv of single event slip is thus 0 30 this cv is slightly less than a recently compiled global average for point measurements on strike slip faults suggesting that the southernmost wellington fault has behaved in a more nearly characteristic way we speculate that recent large earthquake ruptures have been bounded on their southern end by the wellington fault s offshore fault termination and perhaps on their northern end by a 2 km wide releasing step over such persistent sources of rupture arrest might have led to a relative uniformity of rupture dimensions and slip amounts we infer a late holocene dextral slip rate of 4 5 0 4 mm yr 1 and 8 2 mm yr and a mean earthquake recurrence interval of 610 1100 years

a high resolution record of multiple diagenetic events ultraviolet laser microprobe ar ar analysis of zoned k feldspar overgrowths abstract high spatial resolution uv laser ar ar analyses were performed in situ on k feldspar overgrowths from sandstone hosted pb zn bodies from central sweden two different populations of ages were detected precambrian cambrian 528 10 to 567 8 ma and late silurian 403 6 to 453 8 ma these were both detected in single pore spaces with the older population adjacent to the detrital feldspar whilst the younger population was always distal to the detrital grain this younging of authigenic k feldspar ages with distance from the detrital grain margin is discussed in terms of disturbance to the argon system within an authigenic overgrowth that is of a single age a the overgrowths are precambrian cambrian in age and the late silurian population might be an artefact of argon loss due to partial resetting b the overgrowths are late silurian and the precambrian cambrian population might have resulted from excess argon uptake and c the overgrowths are late silurian but the precambrian cambrian population is an experimental artefact arising from the analysis of overlapping detrital authigenic feldspars diffusion modelling shows that the partial resetting scenario is a very unlikely cause for the observed age variation because it requires a very particular arrangement of sub grain sizes excess argon was not detected in either the k feldspar or quartz the data are best interpreted as the ages of two discrete diagenetic events an early burial diagenesis and a later tectonically induced fluid flow event relating to the collapse of the caledonian orogen further the use of 38arcl 39ark as a proxy for cl k ratio highlights the physical boundaries between feldspar populations where all other petrographic sem and cl analyses have failed to do so this study shows that high spatial resolution uv laserprobe ar ar analysis is a powerful tool for extracting age information from complex hydrothermal minerals as a means to investigating fluid flow events

seismicity within the actively deforming eastern sierras pampeanas argentina summary the eastern sierras pampeanas of central argentina have been interpreted by previous studies to represent the easternmost expression of continental deformation resulting from the flat slab subduction of the nazca plate beneath the south american plate yet the seismic activity and deformation of this area as well as its relationship to subduction more than 700 km to the west are poorly understood using seismic data recorded by the eastern sierras pampeanas broadband seismic array between 2008 august and 2009 august we identified and located 445 local crustal earthquakes most with magnitudes of 2 5 or less we employed a double difference location method to clarify the hypocentral distribution of local seismicity and to define zones of both clustered and diffuse seismicity the relocated events define active structures in the region including a horizontal zone of seismicity between 15 and 25 km depth a prominent west dipping structure beneath the central ranges and a vertical structure along the eastern margin of the study area overall seismicity in this region during the study period is constrained to the upper 25 km of the crust and is mostly concentrated along minor structures and not along the major range bounding faults focal mechanism solutions from the nine clearest events show mainly normal deformation with an oblique component and e w oriented p axes that likely result from shortening along structures with oblique orientations to the direction of plate convergence this is the first seismic study to document that the eastern sierras pampeanas are actively deforming in response to compression from the convergent margin

slip rate on the wellington fault new zealand during the late quaternary evidence for variable slip during the holocene we investigate fault offset fluvial terraces at two sites along the hutt river near wellington new zealand to determine horizontal slip rates for the southern part of the wellington fault for the last 100 ka using photogrammetric analysis of historic aerial photos we measured the original displacements of terrace risers at emerald hill which have been modified by urban development fourteen sediment samples from this site and from another location dry creek were analyzed using optically stimulated luminescence osl methods yielding ages of between 10 ka and 100 ka from our displacement age relations we estimate an average slip rate of graphic 1 2 during the last 100 ka however slip on the wellington fault has not been steady throughout this time during the holocene there was a phase of heightened ground rupture activity between 10 and 8 ka when an incremental dextral displacement of 32 m accrued this was followed by a period of relative quiescence between 8 and 4 5 ka with 5 m of displacement during this time another period of heightened activity followed resulting in a further 20 m of slip during the last 4 5 ka our inference of variable slip during the holocene accords with independent evidence from paleoseismological studies at other sites along the wellington fault slip on the wellington fault and its variability through time may be influenced by activity on neighboring faults online material part i optically stimulated luminescence osl dating technical report and results part 2 stratigraphic logs 1 embed inline graphic 1 gif

a revised local magnitude ml scale for new zealand earthquakes in this study a new local magnitude m l scale is developed for new zealand and adjacent offshore regions seiscomp3 sc3 has been in use for earthquake analysis in new zealand since september 2012 with the original richter 1935 log a attenuation relationship for calculating m l the attenuation characteristics of new zealand differ significantly from southern california where m l was originally defined and therefore result in m l that is consistently high when compared with moment magnitude m w using m w from 528 regional moment tensor solutions along with peak observed amplitudes a new log a curve is derived along with station correction factors that define a revised m l scale for new zealand earthquakes that is more consistent with m w the new log a curve is similar to the original richter 1935 definition at hypocentral distances of 100 200 km but differs significantly at closer and farther distances the new m l is more consistent with m w across new zealand including crustal earthquakes and earthquakes below the crust the california institute of technology caltech u s geological survey seismic processer cusp system was used for earthquake analysis prior to sc3 and previous studies have derived regression relationships relating cusp m l with m w after applying the regression relationships to cusp m l we found very good agreement between cusp m l and the new sc3 m l which is important for developing a consistent m l between different catalogs online material table of station corrections for the new zealand seismograph network

applicability of the gutenberg richter relation for major active faults in new zealandapplicability of the gutenberg richter relation for major active faults in new zealand

the surface rupture and slip distribution of the 17 august 1999 izmit earthquake m 7 4 north anatolian fault the 17 august 1999 izmit earthquake occurred on the northern strand of the north anatolian fault zone the earthquake is associated with a 145 km long surface rupture that extends from southwest of duzce in the east to west of hersek delta in the west detailed mapping of the surface rupture shows that it consists of five segments separated by releasing step overs herein named the hersek karamursel golcuk izmit sapanca lake sapanca akyazi and karadere segments from west to east respectively the hersek segment which cuts the tip of a large delta plain in the western end of the rupture zone has an orientation of n80 the n70 80 e trending karamursel golcuk segment extends along the linear southern coasts of the izmit gulf between karamursel and golcuk and produced the 470 cm maximum displacement in golcuk the northwest southeast striking golcuk normal fault between the karamursel golcuk and izmit sapanca segments has 2 3 m maximum vertical displacement the maximum dextral offset along the izmit sapanca lake segment was measured to be about 3 5 m and its trend varies between n80 e and east west the sapanca akyazi segment trends n75 85 w and expresses a maximum displacement of 5 2 m the karadere segment trends n65 e and produced up to 1 5 m maximum displacement the karadere and sapanca akyazi segments form fan shape or splaying ruptures near their eastern ends where the displacement also diminished

quaternary temporal stability of a regional strike slip and rift fault intersection abstract intersecting strike slip and normal fault systems form either two or three plate configurations in circumstances where they intersect to form a triple junction internal block deformation produces a quasi stable 3 d configuration permitting maintenance of both the regional geometry and kinematics of the intersection this paper examines the temporal stability of such a triple junction in new zealand over a range of timescales from individual earthquakes to millions of years and discusses the factors that impact its stability using seismic reflection gravity drill hole and outcrop data the accumulation of vertical displacements is examined both on individual faults and across the intersection zone between the strike slip north island fault system nifs and the taupo rift fault throws and throw rates for the nifs and taupo rift suggest that despite a three fold increase in throw rates in both fault systems at about 0 3 ma which may have modified the orientation of the slip vectors and therefore the contemporary kinematics of the triple junction the intersection of the two fault systems has functioned coherently for the last 0 6 1 5 myr accumulating vertical displacements interdependently since the early stages of rifting the apparent arrest of a large magnitude earthquake on the rift bounding fault adjacent to the intersection suggests that the short term dynamic behaviour of the system is relatively complex compared to the more coherent long term kinematics

microstructural constraints on complex thermal histories of refractory cai like objects in an amoeboid olivine aggregate from the alha77307 co3 0 chondrite abstract we have carried out a fib tem study of refractory cai like objects in one aoa from the alha77307 co3 0 chondrite the cai like objects in the aoa consist of a zoned sequence with a spinel rich core through an intergrowth layer of spinel and al ti rich diopside to a diopside rim the spinel rich core consists of polycrystalline aggregates of spinel and minor melilite showing equilibrated grain boundary textures the intergrowth layer contains fine grained diopside and spinel with minor anorthite with highly curved and embayed grain boundaries the diopside rim consists of polycrystalline aggregates of diopside the compositions of pyroxene change significantly outward from al ti rich diopside in contact with the spinel rich core to al ti poor diopside next to the surrounding olivine of the aoa overall microstructural and chemical characteristics suggest that the spinel rich core formed under equilibrium conditions whereas the intergrowth layer is the result of reactions that occurred under conditions that departed significantly from equilibrium the remarkable changes in formation conditions of the cai like objects may have been achieved by transport and injection of refractory objects into a region of a partially condensed ca ti saturated gas which reacted with spinel and melilite to form al ti rich diopside crystallographically oriented tio2 nanoparticles decorate the grain boundaries between spinel grains and between spinel and al ti rich diopside grains during the disequilibrium back reaction of spinel with a partially condensed ca ti saturated gas metastable tio2 nanoparticles may have condensed by an epitaxial nucleation mechanism and grown on the surface of spinel these tio2 nanoparticles are disordered intergrowths of the two tio2 polymorphs anatase and rutile these nanoparticles are inferred to have nucleated as anatase that underwent partial transformation into rutile the local presence of the tio2 nanoparticles and intergrowth of anatase and rutile imply that the disequilibrium back reaction of spinel with the gas occurred on a short timescale i e minutes to hours at maximum

a chlorine disinfectant for excess argon released from k felsspar during step heating abstract the release of excess 40 ar 40 ar e from virtually all alkali feldspars at low temperatures 40 ar 39 ar step heating experiments obscures potentially valuable age and thermal history information we report a method that takes advantage of the differential release of 40 ar e between contiguous isothermal heating steps due to the decrepitation of fluid inclusions and which permits derivation of a correction for the contaminating argon differences in age and cl k between successive temperature pairs commonly yield a single well correlated array on a 40 ar k versus cl k plot that identifies the cl correlated composition of 40 ar e 40 ar e cl affecting that sample eighteen of the twenty k feldspar samples we have measured yield a single 40 ar e cl component that varies from 1 1 10 3 to 4 2 10 6 making possible recovery of otherwise unobtainable thermochronological information the upper bound on the 40 ar e cl distribution of 10 3 may reflect ar saturation of pore fluids or the maximum duration between deuteric alteration and cooling below ar closure in k feldspar

faulting and extension rate over the last 20 000 years in the offshore whakatane graben new zealand continental shelf oblique rifting in the offshore taupo volcanic zone new zealand is expressed in widely distributed active normal faulting in the 20 km wide whakatane graben active faults are identified along seafloor scarps and displacements of the post last glacial transgressive ravinement surface 400 faults we derive an extension rate at seismogenic depths 6 10 km across the graben of 13 6 mm yr by summing surface measurements assuming an average crustal fault dip of 45 15o and correcting for the discrepancies between surface and deep crustal extension estimates structural and kinematic data implies an extension direction 20o oblique to the rift axis resulting in up to 4 6 2 1 mm yr of dextral motion parallel to the rift axis the strike slip motion is accommodated by dip slip displacements on oblique faults in the centre of the graben and oblique slip faulting along the rift margins pure dip slip in the graben centre represents 50 of the total slip with the rangitaiki fault accommodating 25 of the total extension in the graben

using synthetic seismicity to evaluate seismic hazard in the wellington region new zealand summary a computer synthetic seismicity program for the wellington region has been implemented and used to infer the effect of the 1848 awatere and 1855 wairarapa mega earthquakes on the timing of the next characteristic magnitude 7 35 or more earthquake on the wellington hutt valley section of the wellington fault we find that on average over several hundred cases a wellington fault event is delayed by 259 years the synthetic catalogue of 500 000 events magnitude 5 5 or more also gives the average recurrence time of characteristic wellington fault events 960 yr and their coefficient of variation 0 40 there is also a strong retarding effect on moderate magnitude wellington fault events magnitude 6 5 7 3 sensitivity tests indicate that these results are robust the synthetic model contains 58 known major faults and 3000 randomly placed small faults to reproduce the rate and spatial distribution of background seismicity observed recently from the synthetic catalogue it is possible to determine the average recurrence rate for all major faults also there is strong evidence of the short term 10 yr temporal clustering of large events throughout the region a factor that contributes to a highly variable moment release rate over time spans of a few hundred years

neoproterozoic to early palaeozoic events in the sierra de san luis implications for the famatinian geodynamics in the eastern sierras pampeanas argentina the application of the sensitive high resolution ion microprobe shrimp u pb dating technique to zircon and monazites of different rock types of the sierra de san luis provides an important insight into the provenance and timing of deposition of the sedimentary precursors as well as the metamorphic and igneous history of the various basement domains additional constraints on the famatinian metamorphic episode are provided by pb pb stepwise leaching experiments on one staurolite and two garnet separates the results indicate that the sedimentary precursors of the conlara metamorphic complex have a maximum age of c 590 ma whereas the pringles metamorphic complex metasediments appear to be sourced from the pampean orogen in the early cambrian folded xenoliths within the c 496 ma el penon pluton suggest that the host conlara metamorphic complex underwent a pampean compression from a 208 pb 232 th monazite age of 478 ma for a migmatite from the nogoli metamorphic complex the structural evolution of this basement complex appears to be entirely post pampean onset of the famatinian high grade metamorphism between c 500 ma and c 450 ma follows a period of crustal extension on the western outboard of gondwana and might not be related directly to a mid ordovician accretion of the cuyania terrane

fault controlled carboniferous a type magmatism in the proto andean foreland sierras pampeanas argentina geochemical constraints and petrogenesis abstract the intrusion of granitoids into the eastern sierras pampeanas in the early carboniferous took place after a long period of mainly compressional deformation that included the famatinian ordovician and achalian devonian orogenies these granitoids occur as small scattered plutons emplaced in a dominant extensional setting within older metamorphic and igneous rocks and many of them are arranged along a reactivated large shear zone a set of 46 samples from different granitic rocks huaco granitic complex san blas pluton and the la chinchilla stock from the sierra de velasco zapata granitic complex from sierra de zapata and the los arboles pluton from sierra de fiambala display high and restricted sio 2 contents between 69 2 and 76 4 wt on both feo feo mgo vs sio 2 and na 2 o k 2 o cao vs sio 2 plots the samples plot in the ferroan and alkaline calcic to calco alkaline fields feo feo mgo 0 88 1 0 na 2 o k 2 o cao 6 3 8 3 thus showing an a type granitoid signature the high concentrations for the high field strength elements hsfe such as y nb ga ta u th etc and flat ree patterns showing significant negative eu anomalies are also typical features of a type granites our petrogenetic model supports progressive fractional crystallization with dominant fractionation of feldspar and a source mineral assemblage enriched in plagioclase biotites have distinctive compositions with high feo mgo ratios 7 8 61 5 f 360 5610 ppm and cl 120 1050 ppm the feo mgo ratios together with the f and cl content of igneous biotites seem to reflect the nature of their parental host magmas and may be useful in identifying a type granitoids the isotopic data rb sr and sm nd confirm that the a type granites represent variable mixtures of asthenospheric mantle and continental crust and different mixtures lead to different subtypes of a type granite illustrating the lack of consensus about a type magma origin we conclude that prominent shear zones play an important role in providing suitable conduits for ascending asthenospheric material and heat influx in the crust a hypothesis that is in accord with other recent work on a type granites

the 40ar 39ar laser analysis of k feldspar constraints on the uplift history of the grenville province in ontario and new york 1 a comprehensive geochronologic database describes a period of late extension across the metasedimentary belt mb of the grenville province in northeastern north america because extension continued through much of the young unroofing history of the region these data do not bracket the timing of final extension across all shear zones and do not constrain the timing of final juxtaposition of terranes analysis of k feldspar in the mb by the 40ar 39ar method can give information on the very latest perturbations in the area since k feldspars have multiple low closure temperatures ranging from about 150 to 300 c these multiple diffusion domains require temperature time modeling to fully interpret argon release spectra this modeling requires precise knowledge of the temperature of degassing of each step which usually requires the use of a resistance furnace for sample analysis we establish a first order relationship between laser power and temperature which can be used for multidiffusion domain modeling of k feldspars comparison of samples analyzed by both methods reveals virtually no difference between the systems supporting the validity of k feldspar analyses by laser step heating our data suggest that using the laser for k feldspars can give results that are geologically reasonable precise and easier to collect in this case these data are then applied to the cooling history of the north american grenville province our k feldspar analyses show that the latest extensional motion along shear zones in the mb is after 900 ma and the region is uplifting as a uniform block by 780 ma

the famatina complex nw argentina back docking of an island arc or terrane accretion early palaeozoic geodynamics at the western gondwana margin

argon diffusion in plagioclase and implications for thermochronometry a case study from the bushveld complex south africa plagioclase is not only the most abundant mineral in the earth s crust but is present in almost all terrestrial tectonic settings and is widespread in most extraterrestrial material applying the k ar system to this common mineral would provide a powerful tool for quantifying thermal histories in a wide variety of settings nonetheless plagioclase has rarely been used for thermochronometry largely due to difficulties in simultaneously acquiring precise geochronologic data and quantifying argon diffusion kinetics from a mineral with low k concentration here we describe an analytical technique that generates high precision 40 ar 39 ar data and quantifies ar diffusion kinetics of low k minerals we present results of five diffusion experiments conducted on single crystals of plagioclase from the bushveld complex south africa the observed diffusion kinetics yield internally consistent thermochronological constraints indicating that plagioclase is a reliable thermochronometer individual grains have activation energies of 155 178 kj mol and ln d0 a 2 varies between 3 5 and 6 5 these diffusion parameters correspond to closure temperatures of 225 300 c for a 10 c ma cooling rate age spectra generally conform to single domain diffusive loss profiles suggesting that grain scale diffusion dominates argon transport in this fairly simple plagioclase conjointly examining several single grain analyses enables us to distinguish episodic reheating from slow cooling and indicates that the bushveld complex cooled rapidly and monotonically from magmatic temperature to 300 c over 3 ma followed by protracted cooling to ambient crustal temperatures of 150 200 c over 600 ma 2009 elsevier ltd all rights reserved

resetting errorchrons and the meaning of canonical cai initial 26al 27al values abstract the difference between the precise mc icpms analyses of bulk calcium aluminum rich inclusion cai fragments e g jacobsen et al 2008 and supra canonical values obtained by micro analytical techniques e g laser ablation mc icpms young et al 2005 and sims taylor et al 2005 at face value seems to be problematic and therefore leads many to dismiss claims of the solar system 26al 27al 0 greater than 5 10 5 as spurious here we use mass balance calculations to quantify the importance of open system isotopic exchange during cai evolution and show that in situ supra canonical in situ canonical and bulk canonical measurements can all exist for an individual cai the calculations describe mechanisms of isotopic exchange that may have occurred early 100 s ka and late 1 5 ma in the solar nebula and much later 10 s ma on parent body planetesimals a range of possible modal mineralogies is modeled in order to populate the compositional space defined by in situ and bulk cai measurements in support of these simulated data we describe in situ measurements of 27al 24mg 25mg 24mg and 26mg 24mg obtained by la mc icpms comprising core to rim traverses across three cv3 cais the cais exhibit distinctive mg isotopic zoning profiles and varying abundances of daughter products of the short lived nuclide 26al that are consistent with varying amounts of open system isotope exchange

cosmochemical consequences of particle trajectories during fu orionis outbursts by the early sun abstract the solar nebula is thought to have undergone a number of episodes of fu orionis outbursts during its early evolution we present here the first calculations of the trajectories of particles in a marginally gravitationally unstable solar nebula during an fu orionis outburst which show that 0 1 10 cm sized particles traverse radial distances of 10 au or more inward and outward in less than 200 yrs exposing the particles to temperatures from 60 k to 1500 k such trajectories can thus account for the discovery of refractory particles in comets refractory particles should acquire wark lovering like rims as they leave the highest temperature regions of the disk and these rims should have significant variations in their stable oxygen isotope ratios particles are likely to be heavily modified or destroyed if they pass within 1 au of the sun and so are only likely to survive if they formed in the final few fu orionis outbursts or were transported to the outer reaches of the solar system calcium aluminum rich inclusions cais from primitive meteorites are the oldest known solar system objects and have a very narrow age range most cais may have formed at the end of the fu orionis outbursts phase with an age range reflecting the period between the last few outbursts

a plate boundary earthquake record from a wetland adjacent to the alpine fault in new zealand refines hazard estimates abstract discovery and investigation of millennial scale geological records of past large earthquakes improve understanding of earthquake frequency recurrence behaviour and likelihood of future rupture of major active faults here we present a 2000 year long seven event earthquake record from john o groats wetland adjacent to the alpine fault in new zealand one of the most active strike slip faults in the world we linked this record with the 7000 year long 22 event earthquake record from hokuri creek 20 km along strike to the north to refine estimates of earthquake frequency and recurrence behaviour for the south westland section of the plate boundary fault eight cores from john o groats wetland revealed a sequence that alternated between organic dominated and clastic dominated sediment packages transitions from a thick organic unit to a thick clastic unit that were sharp involved a significant change in depositional environment and were basin wide were interpreted as evidence of past surface rupturing earthquakes radiocarbon dates of short lived organic fractions either side of these transitions were modelled to provide estimates for earthquake ages of the seven events recognised at the john o groats site three post date the most recent event at hokuri creek two match events at hokuri creek and two events at john o groats occurred in a long interval during which the hokuri creek site may not have been recording earthquakes clearly the preferred john o groats hokuri creek earthquake record consists of 27 events since 6000 bc for which we calculate a mean recurrence interval of 291 23 years shorter than previously estimated for the south westland section of the fault and shorter than the current interseismic period the revised 50 year conditional probability of a surface rupturing earthquake on this fault section is 29 the coefficient of variation is estimated at 0 41 we suggest the low recurrence variability is likely to be a feature of other strike slip plate boundary faults similar to the alpine fault

cooling of a late syn orogenic pluton evidence from laser k feldspar modelling of the carion granite madagascar since the late 1980s it has been hypothesized that the wide range of apparent argon ages seen within single k feldspar samples might be due to a distribution of diffusion domain sizes within the mineral to test and apply this idea an analytical technique that combines conventional laboratory degassing experiments resistance heating with numerical inversion procedures has been developed to extract cooling history information from feldspars a key part of the method involves careful control of temperature in the laboratory to constrain the diffusion parameters of the feldspar samples in our study we have k feldspar data from single crystals that mimic the types of data seen in classic resistance heater fusion experiments our step heating data are based on using a continuous argon ion laser with no direct control on temperature however with only a single added free parameter in the model we show that it is possible to analyze this data in the multi domain style and make some simple inferences on the nature of the cooling history of the carion pluton in central madagascar the carion granitic pluton in central madagascar was intruded into warm continental crust following orogenic events related to the final amalgamation of gondwana u pb shrimp dating of the pluton yields an emplacement age of 532 1 5 2 ma followed by relatively slow cooling as constrained by 40ar 39ar ages on hornblende biotite and k feldspar four hornblende samples yielded a mean 40ar 39ar age of 512 7 2 6 ma a biotite sample yielded an age of 478 9 1 0 ma and modeled k feldspar ages show cooling from 350 c at 466 ma to 100 c by 410 ma collectively the data suggest that the pluton cooled from 850 c at 532 1 5 2 u pb zircon ma to 500 c at 512 7 2 6 ma 40ar 39ar hornblende or approximately 18 c ma slowing to 4 c ma between 512 ma and 478 ma and finally to about 3 c ma between 478 and 410 ma

26 al 26 mg and 207 pb 206 pb systematics of allende cais canonical solar initial 26 al 27 al ratio reinstated abstract the precise knowledge of the initial 26 al 27 al ratio 26 al 27 al 0 is crucial if we are to use the very first solid objects formed in our solar system calcium aluminum rich inclusions cais as the time zero age anchor and guide future work with other short lived radio chronometers in the early solar system as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation new high precision multi collector inductively coupled plasma mass spectrometry mc icp ms measurements of 27 al 24 mg ratios and mg isotopic compositions of nine whole rock cais six mineralogically characterized fragments and three micro drilled inclusions from the cv carbonaceous chondrite allende yield a well defined 26 al 26 mg fossil isochron with an 26 al 27 al 0 of 5 23 0 13 10 5 internal mineral isochrons obtained for three of these cais a44a ajef and a43 are consistent with the whole rock cai isochron the mineral isochron of ajef with 26 al 27 al 0 4 96 0 25 10 5 anchored to our precisely determined absolute 207 pb 206 pb age of 4567 60 0 36 ma for the same mineral separates reinstate the canonical 26 al 27 al 0 of 5 10 5 for the early solar system the uncertainty in 26 al 27 al 0 corresponds to a maximum time span of 20 ka thousand years suggesting that the allende cai formation events were culminated within this time span although all allende cais studied experienced multistage formation history including melting and evaporation in the solar nebula and post crystallization alteration likely on the asteroidal parent body the 26 al 26 mg and u pb isotopic systematics of the mineral separates and bulk cais behaved largely as closed system since their formation our data do not support the supra canonical 26 al 27 al ratio of individual minerals or their mixtures in cv cais suggesting that the supra canonical 26 al 27 al ratio in the cv cais may have resulted from post crystallization inter mineral redistribution of mg isotopes within an individual inclusion this redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk cai and bulk mineral data obtained by mc icp ms the radiogenic 208 pb 206 pb ratio obtained as a by product from the pb pb age dating is used to estimate time integrated 232 th 238 u ratio value of cais limited variations among the minerals within a single cai contrasted by much larger variations among the bulk cais suggest th u fractionation occurred prior to crystallization of igneous cais if interpreted as primordial heterogeneity the value can be used to calculate the mean age of the interstellar dust from which the cais condensed

synthetic seismicity models for the wellington region new zealand implications for the temporal distribution of large events our previous synthetic seismicity model for multiple interacting faults in a three dimensional half space has been extended and applied to the wellington region new zealand generating long catalogs of earthquakes for studying the effects of elastic interactions on the temporal distribution of large events the region is one of oblique plate convergence with the interface between the subducting and overlying plates at an average depth of 22 km faults included besides the subduction thrust are segments of the four major arc parallel strike slip faults overlying the plate interface we have used 40 different models with geometric and mechanical parameters chosen at random within reasonable ranges to generate catalogs of 200 000 years duration each for comparison each model was rerun with the elastic interactions suppressed considering events of magnitude 7 2 or more characteristic events in the sense that they rupture most of a fault plane the number of short 250 years the relative numbers are again mostly higher experiments with simple models indicate that this pattern requires both interfault enhancement and inhibition of large events mutual enhancement occurs most often between the subduction thrust and the overlying strike slip faults and between the two segments of the wellington fault that almost join end to end mutual inhibition mostly occurs between the subparallel strike slip faults

exhumation and uplift of the sierras pampeanas preliminary implications from k ar fault gouge dating and low t thermochronology in the sierra de comechingones argentina the sierras pampeanas in central and north western argentina constitute a distinct morphotectonic feature between 27 s and 33 s the last stage of uplift and deformation in this area are interpreted to be closely related to the andean flat slab subduction of the nazca plate beneath the south american plate k ar fault gouge dating and low temperature thermochronology along two transects within the sierra de comechingones reveal a minimum age for the onset of brittle deformation about 340 ma very low exhumation rates since late paleozoic time as well as a total exhumation of about 2 3 km since the late cretaceous new ar ar ages 7 54 1 91 ma of volcanic rocks from the san luis volcanic belt support the eastward propagation of the flat slab magmatic front confirming the onset of flat slab related deformation in this region at 11 2 ma although low temperature thermochronology does not clearly constrain the signal of the andean uplift it is understood that the current structural relief related to the comechingones range has been achieved after the exhumation of both fault walls circa 80 70 ma

a crystal chemical basis for pb retention and fission track annealing systematics in u bearing minerals with implications for geochronology this study develops an empirical crystal chemical framework for systematizing the kinetics of pb loss and fission track annealing in u bearing minerals ionic porosity z the fraction of a mineral s unit cell volume not occupied by ions potentially accounts for kinetic behavior by monitoring mean metal oxygen bond length strength various tests of a general kinetics porosity relationship are presented based upon diverse mineral data including 1 pb diffusion parameters 2 measured closure temperatures tc for fission track annealing and 3 retentivities of both pb and fission tracks from apparent age data every kinetic parameter including tc and mineral age for both the u pb and fission track systems is inversely correlated with z within the sub assemblage zircon z 29 titanite 34 and apatite 38 assuming a diffusional closure model pb isotopic transport phenomena are described by a tc z scale calibrated with field based tc data for titanite 680 20 c and apatite 500 c extrapolation of this scale yields tc estimates for the following minerals staurolite tc 1060 c z 25 garnet 1010 c 26 5 zircon 900 c monazite xenotime and epidote 750 c 32 and ca clinopyroxene 670 30 c 34 1 depending on composition these empirical results imply that a u pb pb date for staurolite or garnet records the time of mineral growth not post growth isotopic closure as also concluded in recent field studies because z systematizes fission track annealing this recrystallization process like volume diffusion must also be rate limited by the strength of chemical bonds the extent to which other recrystallization processes are likewise rate limited is important to u pb geochronology because they potentially compete with diffusion as mechanisms for pb isotopic resetting in nature

40ar39ar analysis of perthite microtextures and fluid inclusions in alkali feldspars from the klokken syenite south greenland laser probe andin vacuo crushing have been used to apply the40ar39ar technique to microtexturally well characterised pristine and turbid alkali feldspar from the 1166 ma klokken syenite individual crystals are several millimetres in size but sem and tem studies reveal complex microstructures which define a range of sub grain sizes over three orders of magnitude from 100 m in pristine areas with fine scale cryptoperthite down to 200 nm in turbid areas with coarsened perthites and numerous micropores laser probe40ar39ar measurements of turbid feldspar gave low apparent ages indicating significant40ar loss 40 average which can be accounted for by sustained heating of the small sub grains 1 m for 1166 ma at low temperature 150 c pristine feldspar gives high apparent ages indicating the presence of excess40ar this component was readily lost from the feldspar by laboratory heating at low temperature 600 c and was also released by crushing which indicates that it was released from fluid inclusions during crushing release of excess40ar is correlated with cl release and the40ar cl ratio of the fluid is similar to that of mantle fluids turbid feldspar also released a fluid during crushing but the40ar cl ratio was lower probably as a result of evolution of the original fluid during boiling anomalously high apparent ages are often a feature of low temperature ar release in stepped heating age spectra of feldspars the presence of excess40ar in fluid inclusions may substantially affect the lower temperature release in feldspar stepped heating spectra the character of the microtextures in the host feldspar provides information on the temperature of fluid trapping because inclusions formed above the coherent alkali feldspar solvus have little or no effect on the exsolution textures whereas fluids trapped at low temperatures are associated with major structural rearrangements leading to development of patch perthite

cenozoic plate kinematics subduction and magmatism south american andes revised plate reconstructions and enlarged isotopic age data sets strongly support three mechanisms for controlling the configuration and associated volcanism and tectonism of the andean subduction zone these include age of subducted plate convergence rate and interaction with hotspot traces from 50 to 25 ma in the andes the age of oceanic plate subducted progressively decreased apparently resulting in a9gradual decrease in subduction angle and consequent eastward shift in the loci of magmatic activity a major reorganization of plate motions at 25 ma resulted in an increased convergence rate normal to the chilean andes and was accompanied by subsequent broadening of the locus of magmatic activity into adjacent portions of bolivia and argentina convergence rates changed only slightly across the peruvian margin and no clear effect on subsequent magmatism is indicated interaction of the andean subduction zone with the juan fernandez and easter nazca hotspot traces apparently resulted in lower angle subduction and consequent gaps in magmatic activity as predicted continuations of the traces correspond with regions lacking dated volcanic rocks the current gaps in igneous activity correspond with contemporary subduction of the two traces and this association apparently occurred in the past as well

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

oblique back arc rifting of taupo volcanic zone new zealand taupo volcanic zone tvz is a back arc rift innorth island new zealand its geometry andkinematics are investigated using shaded reliefimages field examination of faults and offset streamchannels the results show that tvz trends nne is 250 km long by hikurangi margin in the north island of new zealand 20 km wide and consists of fivesegments extension is principally manifest as steeplydipping 60 90 normal faults parallel to tvz these in the last 300 kyr have experienced acomponent of dextral shear tvz is therefore anoblique back arc rift the dextral shear is 37 of thetotal displacement which for previously estimatedspreadingrates 7mm yr correspondsto 2 6mm yr thisvalueissimilartopreviousestimatesofthedextralshear from the back arc to the forearc domains in thenorthisland distributeddextralshearacrosstvzthussuggests that strain partitioning across the plateboundary at latitudes of tvz is less significant thanpreviously thought

transpressional rupture of an unmapped fault during the 2010 haiti earthquake the enriquillo plantain garden strike slip fault accommodates the relative motion between the north american and caribbean plates and was thought to have ruptured during the 2010 haiti earthquake satellite data instead indicate that a blind thrust fault possibly related to the haitian fold thrust belt was responsible and caused some contractional deformation on 12 january 2010 a mw 7 0 earthquake struck the port au prince region of haiti the disaster killed more than 200 000 people and caused an estimated 8 billion in damages about 100 of the country s gross domestic product1 the earthquake was initially thought to have ruptured the enriquillo plantain garden fault of the southern peninsula of haiti which is one of two main strike slip faults inferred to accommodate the 2 cm yr 1 relative motion between the caribbean and north american plates2 3 here we use global positioning system and radar interferometry measurements of ground motion to show that the earthquake involved a combination of horizontal and contractional slip causing transpressional motion this result is consistent with the long term pattern of strain accumulation in hispaniola the unexpected contractional deformation caused by the earthquake and by the pattern of strain accumulation indicates present activity on faults other than the enriquillo plantain garden fault we show that the earthquake instead ruptured an unmapped north dipping fault called the leog ne fault the leog ne fault lies subparallel to but is different from the enriquillo plantain garden fault we suggest that the 2010 earthquake may have activated the southernmost front of the haitian fold and thrust belt4 as it abuts against the enriquillo plantain garden fault as the enriquillo plantain garden fault did not release any significant accumulated elastic strain it remains a significant seismic threat for haiti and for port au prince in particular

deriving a long paleoseismic record from a shallow water holocene basin next to the alpine fault new zealand a sedimentary sequence that was highly sensitive to fault rupture driven changes in water level and sediment supply has been used to extract a continuous record of 22 large earthquakes on the alpine fault the fastest slipping fault in new zealand at hokuri creek in south westland an 18 m thickness of holocene sediments accumulated against the alpine fault scarp from ca a d 800 to 6000 b c we used geomorphological mapping sedimentology and paleoenvironmental reconstruction to investigate the relationship between these sediments and alpine fault rupture we found that repeated fault rupture is the most convincing mechanism for explaining all the features of the alternating peat and silt sedimentary sequence climate has contributed to sedimentation but is unlikely to be the driver of these cyclical changes in sediment type and paleoenvironment other nontectonic causes for the sedimentary alternations do not produce the incremental increase in basin accommodation space necessary to maintain the shallow water environment for 6800 yr our detailed documentation of this near fault sedimentary basin sequence highlights the advantages of extracting paleoearthquake records from such sites the continuity of sedimentation abundance of dateable material and pristine preservation of older events

26al 26mg isotope systematics of the first solids in the early solar system high precision bulk aluminum magnesium isotope measurements of calcium aluminum rich inclusions cais from cv carbonaceous chondrites in several laboratories define a bulk 26al 26mg isochron with an inferred initial 26al 27al ratio of approximately 5 25 10 5 named the canonical ratio nonigneous cv cais yield well defined internal 26al 26mg isochrons consistent with the canonical value these observations indicate that the canonical 26al 27al ratio records initial al mg fractionation by evaporation and condensation in the cv cai forming region the internal isochrons of igneous cv cais show a range of inferred initial 26al 27al ratios 4 2 5 2 10 5 indicating that cai melting continued for at least 0 2 ma after formation of their precursors a similar range of initial 26al 27al ratios is also obtained from the internal isochrons of many cais igneous and nonigneous in other groups of carbonaceous chondrites some cais and refractory grains corundum and hibonite from unmetamorphosed or weakly metamorphosed chondrites including cvs are significantly depleted in 26al at least some of these refractory objects may have formed prior to injection of 26al into the protosolar molecular cloud and its subsequent homogenization in the protoplanetary disk bulk aluminum and magnesium isotope measurements of various types of chondrites plot along the bulk cv cai isochron suggesting homogeneous distribution of 26al and magnesium isotopes in the protoplanetary disk after an epoch of cai formation the inferred initial 26al 27al ratios of chondrules indicate that most chondrules formed 1 3 ma after cais with the canonical 26al 27al ratio

fault gouge analyses k ar illite dating clay mineralogy and tectonic significance a study from the sierras pampeanas argentina we introduce a method for the detailed interpretation of k ar illite fine fraction ages of fault gouges from non sedimentary host rocks ages are cross evaluated with several independent parameters e g illite crystallinity illite polytype quantification grain size mineralogical observations k ar muscovite and biotite host rock cooling ages as well as low temperature thermochronological data aft ahe zhe this interpretation approach is applied to a regional study in order to constrain the deformation path of the eastern sierras pampeanas in nw argentina in the course of this study a large number of gouge bearing fault zones were systematically sampled and analysed obtained k ar illite fine fraction ages range from devonian to cretaceous times documenting a long lasting brittle fault activity in this region ages 320 ma are synchronous with a period of intra carboniferous compressional tectonism whereas permo triassic ages are contemporaneous to a flat slab subduction episode of the farallon plate beneath the south american plate middle to late permian and early triassic ages as well as early jurassic to middle cretaceous ages correlate with extensional tectonics in this region additionally k ar illite ages reveal a propagation of brittle deformation from north to south in the sierras de cordoba and san luis data integrity and consistency with other chronometers and geological evidence show that the here suggested interpretation is valid and can provide a powerful tool to evaluate cooling and deformation histories despite of that we could show that the reliability of fault gouge data strongly depends on the regional cooling

surface rupture earthquakes over the last 1000 years in the wellington region new zealand and implications for ground shaking hazard the wellington region is cut by five active right lateral strike slip faults wairarapa wellington ohariu shepherds gully pukerua and wairau faults that have average recurrence intervals of meter scale surface rupture that range from 500 years to 5000 years and lateral slip rates that range from 1 to 10 mm yr only the wairarapa fault has ruptured since european settlement since circa a d 1840 paleoseismological studies on these faults have allowed the compilation of a complete record of surface rupture events over the past 1000 years in the wellington region within this time period there does not appear to be any temporal clustering of surface rupture events on adjacent faults the m 8 a d 1855 wairarapa earthquake did not trigger rupture on any other fault in the region the most recent surface faulting event on the wellington fault 290 440 cal years b p cal years are calendar years before a d 1950 does not coincide with rupture of any other onland fault and over 300 years separate the timing of the second most recent rupture on the wellington fault 660 720 cal years b p and the most recent rupture of the ohariu fault 1060 1140 cal years b p the most recent rupture of the shepherds gully pukerua fault is probably older than that of the ohariu fault the apparent nonclustering of surface rupture earthquakes in the wellington region has been documented only for the on land strike slip faults there are other possible seismogenic sources in the region and thus important issues remain to be addressed regarding the history of large earthquakes in the wellington region 1 the seismogenic potential and earthquake recurrence interval of the subduction thrust beneath wellington is not known 2 the timing of rupture events on the offshore portion of the wairau fault is not known and 3 paleoseismic data are not available for the section of the wellington fault north of the wellington hutt valley segment estimates of earthquake hazard in the wellington region for all return times greater than 50 years that incorporate paleoseismicity data are between one and two modified mercalli mm intensity units higher than the hazard based solely on the historical seismicity catalog and the hazard is spatially more variable using a deterministic attenuation model the level of shaking hazard approaches near maximum values within a return time of 500 years largely reflecting the recurrence interval 500 770 years of surface rupture earthquakes on the wellington fault inclusion of a plausible model for magnitude 8 subduction zone earthquakes does not affect the level of mm intensity in wellington region at return times greater than 500 years but does make a small contribution to the hazard at return times between 50 and 500 years

evidence for past subduction earthquakes at a plate boundary with widespread upper plate faulting southern hikurangi margin new zealand abstract at the southern hikurangi margin new zealand we use salt marsh stratigraphy sedimentology micropaleontology and radiocarbon dating to document evidence of two earthquakes producing coseismic subsidence and in one case a tsunami over the past 1000 yrs the earthquake at 520 470 yrs before present b p produced 0 25 0 1 m of subsidence at big lagoon the earthquake at 880 800 yrs b p produced 0 45 0 1 m of subsidence at big lagoon and was accompanied by a tsunami that inundated 360 m inland with a probable height of 3 3 m distinguishing the effects of upper plate faulting from plate interface earthquakes is a significant challenge at this margin we use correlation with regional upper plate paleoearthquake chronologies and elastic dislocation modeling to determine that the most likely cause of the subsidence and tsunami events is subduction interface rupture although the older event may have been a synchronous subduction interface and upper plate fault rupture the southern hikurangi margin has had no significant m 6 5 documented subduction interface earthquakes in historic times and previous assumptions that this margin segment is prone to rupture in large to great earthquakes were based on seismic and geodetic evidence of strong contemporary plate coupling this is the first geologic evidence to confirm that the southern hikurangi margin ruptures in large earthquakes the relatively short time interval between the two subduction earthquakes 350 yrs is shorter than in current seismic hazard models online material historical accounts description of vertical deformation core names foraminifera census and abundance diatom census modern analog samples map of cores collected stratigraphic correlation diagram for all cores and detailed core logs

stratigraphic architecture and fault offsets of alluvial terraces at te marua wellington fault new zealand revealed by pseudo 3d gpr investigation 1 past earthquake slips on faults are commonly determined by measuring morphological offsets at current ground surface because those offsets might not always be well preserved we examine whether the first 10 m below ground surface contains relevant information to complement them we focus on the te marua site new zealand where 11 alluvial terraces have been dextrally offset by the wellington fault we investigated the site using pseudo 3d ground penetrating radar and also produced a high resolution digital elevation model dem of the zone to constrain the surface slip record the gpr data reveal additional information 1 they image the 3d stratigraphic architecture of the seven youngest terraces and show that they are strath terraces carved into graywacke bedrock each strath surface is overlain by 3 5 m of horizontally bedded gravel sheets including two pronounced and traceable reflectors 2 thanks to the multilayer architecture terrace risers and channels are imaged at three depths and their lateral offsets can be measured three to four times constraining respective offsets and their uncertainties more reliably and 3 the offsets are better preserved in the subsurface than at the ground surface likely due to subsequent erosion deposition on the latter from surface and subsurface data we infer that te marua has recorded six cumulative offsets of 2 9 7 6 18 23 2 26 and 31 m 1 2 m large earthquakes on southern wellington fault might produce 3 5 m of slip slightly less than previously proposed pseudo 3d gpr thus provides a novel paleoseismological tool to complement and refine surface investigations

ar ar dating of authigenic k feldspar quantitative modelling of radiogenic argon loss through subgrain boundary networks we have analysed two distinct generations of authigenic k feldspar in fucoid bed sandstones from an t sron and skiag bridge nw highlands scotland which have experienced post growth heating to levels in excess of the predicted ar closure temperature authigenic k feldspars show microtextural similarities to patch perthites that is subgrains separated by dislocation rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon the two generations of authigenic k feldspar in the fucoid bed sandstones can be distinguished by different microtextural zones bulk mineral compositions fluid inclusion populations and inferred temperatures and chemistries of parent fluids ar ar age data obtained using high resolution ultraviolet laser ablation show that the first cementing generation is ordovician and the second cementing generation is silurian modelling of ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono thermal thrust model assuming transient heating of the fucoid beds is inconsistent with observed data removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed ar ar ages for both generations of cement alternatively ar diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the fucoid bed palaeothermal maxima and determined ar ar age ages for the two generations of k feldspar cement based on this alternate explanation we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic k feldspars explaining the apparent robustness of authigenic k feldspar with respect to ar retention

oxygen isotopic variations in the outer margins and wark lovering rims of refractory inclusions abstract oxygen isotopic variations across the outer margins and wark lovering wl rims of a diverse suite of six coarse grained types a and b refractory inclusions from both oxidized and reduced cv3 chondrites suggest that cais originated from a 16 o rich protosolar gas reservoir and were later exposed to both relatively 17 18 o rich and 16 o rich reservoirs the o isotope profiles of cais can be explained by changes in the composition of gas near the protosun or the migration of cais through a heterogeneous nebula variability within the inclusion interiors appears to have been set prior to wl rim growth modeling the isotopic zoning profiles as diffusion gradients between inclusion interiors and edges establishes a range of permissible time temperature combinations for their exposure in the nebula at mean temperatures of 1400 k models that match the isotope gradients in the inclusions yield timescales ranging from 5 10 3 to 3 10 5 years assuming cais originated with a relatively 16 o rich protosolar isotopic composition differences among the melilite interiors and the isotopic gradients in their margins imply the existence of a number of isotopically distinct reservoirs evidence at the edges of some cais for subsequent isotopic exchange may relate to the beginning of rim formation in the wl rim layers surrounding the interiors spinel is relatively 16 o rich but subtly distinct among different cais melilite is often relatively 16 o poor but rare relatively 16 o rich grains also exist pyroxene generally exhibits intermediate o isotope compositions and isotopic zoning olivine in both wl and accretionary rims when present is isotopically heterogeneous the extreme isotopic heterogeneity among and within individual wl rim layers and in particular the observed trends of outward 16 o enrichments suggest that rims surrounding cais contained in cv3 chondrites like the inclusions themselves formed from a number of isotopically distinct gas reservoirs collectively these results support numerical protoplanetary disk models in which cais were transported between several distinct nebular reservoirs multiple times prior to accretion onto a parent body

astrophysics of cai formation as revealed by silicon isotope la mc icpms of an igneous cai silicon isotope ratios of a typical cai from the leoville carbonaceous chondrite obtained in situ by laser ablation mc icpms together with existing 25 mg 24 mg data reveal a detailed picture of the astrophysical setting of cai melting and subsequent heating models for the chemical and isotopic effects of evaporation of the molten cai are used to produce a univariant relationship between ph2 and time during melting the result shows that this cai was molten for a cumulative time of no more than 70 days and probably less than 15 days depending on temperature the object could have been molten for an integrated time of just a few hours if isotope ratio zoning was eliminated after melting by high subsolidus temperatures e g n1300 k for 500 yr in all cases subsolidus heating sufficient to produce diffusion limited isotope fractionation at the margin of the solidified cai is required these stable isotope data point to a two stage history for this igneous cai involving melting for a cumulative timescale of hours to months followed by subsolidus heating for years to hundreds of years the thermobarometric history deduced from combining si and mg isotope ratio data implicates thermal processing in the disk perhaps by passage through shockwaves following melting this study underscores the direct link between the meaning of stable isotope ratio zoning or lack thereof and the inferred astrophysical setting of melting and subsequent processing of cais 2007 elsevier b v all rights reserved

late holocene faulting in the southeast sierras pampeanas of argentina the seismic history of extra andean south america is poorly documented between lat 26 s and 33 s about 375 km east of the fold and thrust belt that marks the present orogenic front the block faulted crystalline basement uplifts of the sierras pampeanas in argentina reveal extensive quaternary reverse faulting 14c dates of 1080 70 and 1310 40 yr b p have been determined on organic material from colluvium on the footwall of the east dipping los molinos branch of the comechingones fault they indicate at least 2 1 m of slip probably coseismic during the past 1300 yr in an area for which no significant deformation has been reported in association with historical earthquakes

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

time constraints on the tectonic evolution of the eastern sierras pampeanas central argentina the application of the shrimp u pb dating technique to zircon and monazite of different rock types of the sierras de cordoba provides an important insight into the metamorphic history of the basement domains additional constraints on the pampean metamorphic episode were gained by pb pb stepwise leaching pbsl experiments on two titanite and garnet separates results indicate that the metamorphic history recorded by crd free gneisses m2 started in the latest neoproterozoic earliest cambrian 553 and 543 ma followed by the m4 metamorphism at 530 ma that is documented in the diatexites zircon ages of 492 ma in the san carlos massif correlate partly with rather low th u ratios 0 1 suggesting their growth by metamorphic fluids this age is even younger than the pbsl titanite ages of 506 ma it is suggested that the fluid alteration relates to the beginning of the famatinien metamorphic cycle in the neighbouring sierra de san luis and has not affected the titanite ages the ptt evolution can be correlated with the plate tectonic processes responsible for the formation of the pampean orogene i e the accretion of the pampean basement to the rio de la plata craton m2 and the later collision of the western pampean basement with the pampean basement

structural evolution of a composite middle to lower crustal section the sierra de pie de palo northwest argentina 1 the sierra de pie de palo of northwest argentina preserves middle to lower crustal metamorphic rocks that were penetratively deformed during ordovician accretion of the precordillera terrane to the gondwana margin new structural petrologic and geochronologic data from a 40 km structural transect reveals that the sierra de pie de palo preserves a middle to lower crustal ductile thrust complex consisting of individual structural units and not an intact ophiolite and cover sequence top to the west thrusting occurred intermittently on discrete ductile shear zones from 515 to 417 ma and generally propagated toward the foreland with progressive deformation ordovician crustal shortening and peak metamorphic temperatures in the central portion of the sierra de pie de palo were synchronous with retro arc shortening and magmatic flare up within the famatina arc accretion of the precordillera terrane resulted in the end of arc flare up and the onset of synconvergent extension by 439 ma continued synextensional to postextensional convergence was accommodated along progressively lower grade shear zones following terrane accretion and the establishment of a new plate margin west of the precordillera terrane the results support models of cordilleran orogens that link voluminous arc magmatism to periods of regional shortening the deformation metamorphic and magmatic history within the sierra de pie de palo is consistent with models placing the region adjacent to the famatina margin in the middle cambrian and not as basement to the precordillera terrane

magmatic evidence for neogene lithospheric evolution of the central andean flat slab between 30 s and 32 s abstract geochemical data from andean miocene magmas erupted through the now volcanically inactive flat slab between 30 s to 32 s coupled with geological and geophysical data illuminate details on magmatic and continental lithospheric evolution over a progressively shallowing subduction zone pb sr and nd isotopic and trace element data show that main cordilleran precordilleran and pampean magmas were contaminated in both the mantle and crust and that the nature of the contaminants varied in time and space reflecting tectonic events contaminants included both enriched high lil element high sr and pb and low nd isotopic ratios and depleted low lile element low sr and pb and high nd isotopic ratios types in the western region main cordilleran earlier miocene lavas had contaminants with less enriched signatures than later miocene lavas progressive enrichment is attributed to a increasing amounts of sediment and tectonically eroded crust being subducted into the mantle wedge and b contamination in a thickening main cordilleran lower crust whose composition was progressively enriched this enrichment occurred through addition of upper crust by an intracrustal mixing process driven by a propagating wedge tip associated with westward wedging heating and deformation of crust from beneath the shortening precordillera thrust belt to the east further east magmas erupted through back arc crust have more depleted signatures those erupted in the central part through the evolving precordilleran thrust belt were contaminated by an older thinner grenville 1100 ma basement whose depleted signature is unique among central andean terranes late miocene pocho lavas erupted further east in conjunction with uplift of the sierras pampeanas show enrichment through time arguably these magmas could contain a component mechanically removed from the base of the thinning continental lithosphere to the west and progressively incorporated into the convecting asthenosphere first order mass balance calculations comparing the lithospheric geometry proposed for 20 ma with that today suggests that 60 of the lithosphere within 600 km of the trench at 20 ma has been lost this lithospheric loss is required to accommodate simultaneous shallowing of the oceanic slab and thickening and shortening of the crust continental lithosphere recycled into the asthenosphere could contribute to the sources of the enriched em1 and em2 mantle components in oceanic island basalts

microstructures and formation history of melilite rich calcium aluminum rich inclusions from the alha77307 co3 0 chondrite abstract we have studied four melilite rich calcium aluminum rich inclusions cais from the allan hills a77307 co3 0 chondrite using transmission electron microscopy with the focused ion beam sample preparation technique this type of cai represents one of the dominant types of refractory inclusions in co3 chondrites individual melilite rich cais 04 07 record complex formational histories involving high temperature gas solid condensation that occurred under both equilibrium and disequilibrium conditions cai 04 contains two texturally and compositionally distinct occurrences of perovskite fine grained perovskite within a melilite rich core and aggregates of perovskite grains that surround the core the perovskite in the core was probably involved in a disequilibrium reaction with early equilibrium condensates e g melilite and spinel and a nebular gas to form al ti rich diopside followed by a later condensation of the perovskite aggregates under equilibrium conditions cai 05 has a compact melilite rich core surrounded by a porous mantle and likely formed by at least two different condensation events under equilibrium and disequilibrium conditions in cai 06 complex intergrowth layers of spinel and diopside surrounding a melilite rich core indicate disequilibrium reaction of spinel and melilite with a nebular gas to form al ti rich diopside following core formation by equilibrium condensation cai 07 is dominated by melilite with a narrow compositional range and equilibrated textures suggesting its formation by equilibrium condensation over a limited temperature range collectively we infer that the melilite rich inclusions formed by a generalized sequence of high temperature gas solid condensation that involved 1 formation of cai cores by aggregation of primary equilibrium condensates i e perovskite spinel and melilite 2 back reactions of the primary core minerals with a nebular gas under disequilibrium conditions forming diopside that evolves in composition from al ti rich at the interface with the inclusion core to al ti poor on the exterior of the inclusions the change in formation conditions may have been achieved by transport and injection of the core materials into a region of a partially condensed gas that still contained refractory elements in the gas phase

oblique collision in the northeastern caribbean from gps measurements and geological observations 1 previous caribbean gps studies have shown that the rigid interior of the caribbean plate is moving east northeastward 070 at a rate of 18 20 3 mm yr relative to north america this direction implies maximum oblique convergence between the island of hispaniola on the caribbean plate and the 22 27 km thick crust of the bahama carbonate platform on the adjacent north america plate we present a tectonic interpretation of a 15 site gps network which spans the hispaniola bahama oblique collision zone and includes stable plate interior sites on both the north america and caribbean plates measurements span the time period of 1994 1999 in a north america reference frame gps velocities in puerto rico st croix and the lesser antilles indicate that these areas move as a single block in an east northeast direction 070 at a rate of 19 20 mm yr consistent with the movement of the rigid interior of the caribbean plate gps velocities at six sites in central and eastern hispaniola dominican republic show drastically different behavior with more eastwardly strikes 080 and much slower rates 4 17 mm yr than areas of the stable caribbean plate the boundary between the relatively slower moving hispaniola collisional zone and the relatively faster moving uncollided puerto rico virgin islands area is the mona passage where late neogene rifting occurs in a broad zone elastic modeling favors strain partitioning with oblique slip on the outer low angle submarine thrust faults north hispaniola muertos and strike slip on the inner subvertical subaerial strike slip faults septentrional enriquillo

motion and rigidity of the pacific plate and implications for plate boundary deformation 1 using up to 11 years of data from a global network of global positioning system gps stations including 12 stations well distributed across the pacific plate we derive present day euler vectors for the pacific plate more precisely than has previously been possible from space geodetic data after rejecting on statistical grounds the velocity of one station on each of the pacific and north american plates we find that the quality of fit of the horizontal velocities of 11 pacific plate pa stations to the best fitting pa euler vector is similar to the fit of 11 australian plate au velocities to the au euler vector and 20 better than the fit of nine north american plate na velocities to the na euler vector the velocities of stations on the pacific and australian plates each fit a rigid plate model with an rms residual of 0 4 mm yr while the north american velocities fit a rigid plate model with an rms velocity of 0 6 mm yr our best fitting pa au relative euler vector is located 170 km southeast of the nuvel 1a pole but is not significantly different at the 95 confidence level it is also close 70 km in position and 3 in rate to a pole derived from transform faults identified from satellite altimetry suggesting that the vector has not changed significantly over the past 3 myr our relative euler vector is also consistent with all known geological and geodetic evidence concerning the au pa plate boundary through new zealand the gps sites offshore of southern california are presently moving 4 5 1 mm yr relative to predicted pacific velocity with their residual velocities in approximately the opposite direction to pa na relative motion likewise the easternmost sites in south island new zealand are moving 3 1 mm yr relative to predicted pacific velocity with the residuals in approximately the opposite direction to pa au relative motion these velocity residuals are in the same sense as predicted by elastic strain accumulation on known plate boundary faults but are of a significantly higher magnitude in both southern california and new zealand implying that the plate boundary zones in both regions are wider than previously believed index terms 1206 geodesy and gravity crustal movements interplate 8155 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8158 tectonophysics evolution of the earth plate motions present and recent 3040 8159 tectonophysics evolution of the earth rheology crust and lithosphere keywords pacific plate motion plate rigidity plate boundary deformation

exhumation history of the andean broken foreland revisited the andean broken foreland in west central argentina located 400 800 km from the peru chile trench is associated with flat subduction linked to collision of the oceanic juan fernandez ridge while the conditions associated with flat subduction would be expected to produce increases in rock uplift and exhumation where thrusting and dynamic forces work together a prevalence of pre cenozoic apatite fission track aft cooling ages suggests that there is no such link the lack of cenozoic cooling ages is at odds with structural reconstructions and basin studies along the foreland that show several kilometers of exhumation this paradox can be reconciled by taking into account the thermal effects of flat subduction that removed the mantle wedge and a significant source of heat flow into the crust reinterpretation of published aft exhumation data 320 ages using more realistic lower geothermal gradient values allows for substantial exhumation and explains the lack of cenozoic exhumation ages across the foreland region

links between topography erosion rheological heterogeneity and deformation in contractional settings insights from the central andes abstract orogenic structure in the central andes 15 s 34 s systematically varies with mean annual precipitation suggesting that erosional processes may be coupled to tectonic processes we explore the range of possible interactions between deformation erosional processes changing geodynamic conditions and preexisting geologic structures to assess the relative importance of each our review and synthesis indicates that the pre orogenic geologic history and changing geodynamic conditions leave a lasting imprint on the modern structure of the mountain belt in contrast changes in precipitation that result from regional scale atmospheric and oceanic circulation interact with local topography to control the climatic zoning across the central andes changes in erosion which likely correspond to changes in climate rock uplift rate and the exposure of different lithologies may in turn affect the tectonic development of the region at the scale of each morphotectonic province in this view geologic and geodynamic factors set the stage for the nature and strength of coupling between erosional processes tectonic deformation and mountain belt structure in the different parts of the central andes

evidence from gps measurements for contemporary interplate coupling on the southern hikurangi subduction thrust and for partitioning of strain in the upper plate the spatial extent and strength of contemporary coupling between the pacific and australian plates on the hikurangi subduction interface beneath the wellington region of new zealand are not well known consequently the potential for the plate interface to produce great thrust earthquakes or to load the major wellington and wairarapa faults in the overlying plate is also unknown to address these issues a gps network across the southern north island has been partially or wholly surveyed six times between 1992 and 1999 and yields well determined relative velocities between 82 points the relative velocity of the east coast with respect to the west coast across the 80 km width of the southern end of the north island is 14 mm yr 1 at an azimuth of 258 this is about one third of and closely parallel to the nuvel 1a relative velocity of the pacific with respect to the australian plate 39 4 mm yr 1 at 261 strain rate solutions indicate partitioning of contemporary strain with a 35 change in principal axis orientations across the network using elastic dislocation theory an inversion of the observed point velocities and their full variance covariance matrix determines the variation with depth of contemporary coupling at the subduction interface if uniform coupling is assumed then 100 coupling occurs from very shallow depths down to 29 1 km however if variable coupling is assumed it reaches 100 at depths between 16 and 24 km at greater depths there is a transition zone at least 20 km wide down to a depth of at least 40 km over which contemporary coupling diminishes to zero these depth ranges correlate moderately well with low angle thrust focal mechanisms recently obtained by other workers and indicate that the downdip width of the interface over which a great thrust earthquake could occur exceeds 100 km elastic dislocation models also explain the observed partitioning of strain with coulomb stress calculations indicating that the wairarapa fault is being loaded at seismogenic depths

the capilla del monte pluton sierras de cordoba argentina the easternmost early carboniferous magmatism in the pre andean sw gondwana margin new geochronological geochemical and isotopic data are reported for the capilla del monte two mica granite pluton in the northeastern sierras de cordoba an early carboniferous age is established by a u pb zircon concordia 336 3 ma and a rb sr whole rock isochron 337 2 ma zircon saturation geothermometry indicates relatively high temperatures 735 800 c the granites have high average sio2 74 2 na2o k2o 7 8 and high field strength elements high k2o na2o 1 7 and feo mgo ratios 5 1 with low cao content 0 71 ree patterns with marked negative eu anomalies eu eu 0 14 0 56 indicate crystal fractionation dominantly of plagioclase and k feldspar from a peraluminous magma enriched in f isotope data 87sr 86srinitial 0 7086 e nd336 5 5 to 4 4 with t dm 1 5 ga zircon e hf336 0 8 to 6 1 mean t dm 1 5 ga suggest a mesoproterozoic continental source albeit with some younger or more juvenile material indicated by the hf data the pluton is the easternmost member of a carboniferous a type magmatic suite which shows an increase in juvenile input toward the west in this part of the pre andean margin the petrological and geochemical data strongly suggest a similar intraplate geodynamic setting to that of the nearby but much larger late devonian achala batholith although hf isotope signatures of zircon suggest a more uniformly crustal origin for the latter further studies are required to understand whether these bodies represent two independent magmatic episodes or more continuous activity

magnetic anomaly interpretation across the southern central andes 32 34 s the role of the juan fernandez ridge in the late tertiary evolution of the margin marine and terrestrial magnetic surveys have been integrated to study the tectonic structure of the convergent margin of chile between 32 34 s three magnetic domains have been identified oceanic continental margin and subaerial the oceanic domain has seafloor spreading anomalies 16 37 ma to 18 39 5 ma disturbed by anomalies of the juan fernandez hot spot chain in the continental margin the most prominent fabric are e w anomalies in the upper slope corresponding to onshore e w anomalies of large intrusive bodies onshore a n s lineament of short wavelength anomalies defines the roots of a cretaceous volcanic arc a resembling lineament offshore indicates a submerged older volcanic arc and that continental basement extends to 50 km landward of the trench absolute cenozoic plate motion for nazca and south american plates and dating of the juan fernandez chain provide a kinematic model of ridge continent collision the reconstruction indicates rapid southward migration of the collision point along 1400 km of the margin from 20 to 11 ma 20 cm yr 1 from 11 ma to present the collison point has migrated at a slower rate along 375 km of the margin 3 5 cm yr 1 the predicted location of the subducted portion of the juan fernandez chain coincides with the south edge of the southward migrating flat slab segment of the subducted lithosphere and with a cluster of deep earthquakes indicating a causal relationship in the last 10 myr the ridge has separated a sediment starved trench to the north where subduction erosion may dominate from a sediment filled trench to the south where recent sediment accretion dominates these observations indicate that subduction of the juan fernandez chain plays a major role in arc forearc tectonics

polymetallic pb zn cu ag au vein type deposits in brittle ductile transtensional shear zones eastern sierras pampeanas argentina age constraints and significance for the late paleozoic tectonic evolution and metallogenesis abstract this paper discusses new structural kinematic and geochronological data from polymetallic pb zn cu ag au vein type deposits hosted in the metamorphic basement of the southern sierras de cordoba a carboniferous age was established for the hydrothermal event between 329 and 315 ma late mississippian early pennsylvanian by the k ar fine fraction dating method of sericitic alteration related to metallic ore deposition in the las guindas and oro districts the obtained ages postdate the spatially associated devonian magmatism and overlap the a type early carboniferous magmatism defined for the eastern sierras pampeanas the presence of non exhumed granitic bodies at shallow depths possibly related to mineralization is supported by available geophysical and field evidence the strain fabric and 3 d kinematic analyses constitute first kinematic data for the carboniferous basement of the southern sierras pampeanas demonstrating that mineralization was controlled by nnw and ene trending brittle ductile transtensional shear zones that overprint the earlier high strain deformation fabrics of the basement transtensional deformation has accommodated large amounts of strike slip movements and subordinated extensional components the calculated kinematic axes indicate a coherent kinematic pattern of the mineralized systems in the two studied districts with a maximum extension direction oriented nne to ne and maximum shortening direction oriented wnw to nw this deformation regime active during mineralization point to a non compressive setting at the late mississippian early pennsylvanian boundary in line with other regional evidence we propose a distinctive carboniferous deformational phase in the eastern sierras pampeanas dominated by transtension this period would have occurred after the transition with the devonian compressional transpressional orogenic regime

late paleozoic deformation and exhumation in the sierras pampeanas argentina 40 ar 39 ar feldspar dating constraints systematic 40ar 39ar feldspar data obtained from the sierras pampeanas are presented filling the gap between available high 300 c and low temperature 150 c thermochronological data results show silurian devonian exhumation related to the late stages of the famatinian ocloyic orogeny for the sierra de pocho and the sierra de pie de palo regions whereas the sierras de san luis and the sierra de comechingones regions record exhumation during the carboniferous comparison between new and available data points to a carboniferous tectonic event in the sierras pampeanas which represents a key period to constrain the early evolution of the proto andean margin of gondwana this event was probably transtensional and played a major role during the evolution of the paganzo basin as well as during the emplacement of alkaline magmatism in the retroarc

early carboniferous sub to mid alkaline magmatism in the eastern sierras pampeanas nw argentina a record of crustal growth by the incorporation of mantle derived material in an extensional setting a recently discovered granitic intrusion at cerro la gloria in western sierra de famatina nw argentina is representative of sub to mid alkaline carboniferous magmatism in the region the main rock type consists of microcline quartz and plagioclase with amphibole magnetite ilmenite biotite epidote zircon allanite and sphene as accessory minerals we report a u pb zircon shrimp age for the pluton of 349 3 ma mswd 1 1 i e tournaisian whole rock chemical composition and nd isotope analyses are compatible with an origin by melting of older mafic material in the lower crust endt between 0 58 and 0 46 and tdm values of about 1 1 ga the pluton is intruded by penecontemporaneous to late alkaline mafic dykes that are classified as back arc basalts coeval early carboniferous a type granites occur farther east in the sierras pampeanas probably generated during lithospheric stretching overall the early carboniferous granitic rocks show a west to east mineralogical and isotopic zonation indicating that magma genesis involved a greater contribution of juvenile material of mantle character to the west based on the observed patterns of geochronology geochemistry and field relationships we suggest that a type magma genesis in the eastern sierras pampeanas was linked to an andean type margin where the lithospheric mantle played a role in its generation

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

high precision u pb calibration of carboniferous glaciation and climate history paganzo group nw argentina the duration and geographic extent of carboniferous glacial events in southern gondwana remain poorly constrained despite recent evidence for a more dynamic glacial history than previously considered we report 10 high precision 2 0 1 u pb ages for the permian carboniferous paganzo group nw argentina that redefi ne the chronostratigraphy of the late paleozoic paganzo and rio blanco basins and signifi cantly refi ne the timing of glacial events and climate shifts in the western region of southern gondwana radiometric calibration of the paganzo group indicates three pulses of carboniferous glaciation in the mid visean the late serpukhovian to earliest bashkirian and between the latest bashkirian to early moscovian an abrupt shift in depositional style from high sinuosity single storied fl uvial deposits and clay rich paleosols to low sinuosity multi storied feldspathic fluvial deposits inter calated with eolianites and calcic paleosols is constrained to the latest moscovian and earliest kasimovian these constraints indicate a relatively abrupt climate shift from humid subhumid to nonseasonal semiarid regional climate conditions that occurred signifi cantly earlier than previously inferred early permian this period of high latitude aridity was contemporaneous with a shift to dryland depositional environments and a major vegetation regime shift documented throughout the pangean paleotropics in the pennsylvanian

geochronology of shear zones a review abstract shear zones play a major role in the deformation of the crust at a variety of scales as expressions of strain localization during orogeny and rifting and also as reactivated structures they influence the geometry and evolution of orogenic belts and rifts crustal rheology magma ascent and emplacement and fluid flow consequently assessing the timing of shear zone activity is crucial to reconstruct the tectonometamorphic evolution of the lithosphere the interpretation of thermochronologic data from shear zones is however not straightforward in the first place closure temperatures depend on a number of factors grain size cooling rate mineral composition and pressure among others on the other hand deformation related processes such as dynamic recrystallization neocrystallization and fluid circulation seem to be crucial for isotopic systems and thus the obtained ages cannot be solely interpreted as a function of temperature in sheared rocks for this reason geochronologic data from shear zones might not only record cooling below closure temperature conditions but may also be affected by neo or recrystallization fluid assisted deformation and inheritance of the protolith age s in order to robustly reconstruct p t e t paths of long term crustal scale shear zones structural microstructural and petrologic data from mylonites need to be integrated with ages from different thermochronometric systems in addition geochronologic data from associated intrusions and adjacent blocks can provide further irreplaceable constraints on the timing of deformation and its regional implications one of the most challenging aspects that future lines of investigation should analyze is the quantitative evaluation of so far poorly explored aspects of isotopic diffusion particularly the coupling with deformation processes based on natural theoretical and experimental data future works should also investigate the role of strain partitioning and localization processes in order to constrain the timing of deformation in different parts of a shear zone or in different branches of anastomosing shear zone networks

crustal provenance and cooling of the basement complexes of the sierra de san luis an insight into the tectonic history of the pro to andean margin of gondwana abstract the sierra de san luis constitutes the southernmost tip of the eastern sierras pampeanas its palaeozoic metamorphic basement units define a key location for the understanding of the accretional history along the proto andean margin of gondwana although it is largely accepted that the polyphase accretional history of the sierras pampeanas is preluded by the docking of the pampean terrane followed by the famatinian orogenic cycle that involves subduction along the margin of gondwana and the accretion of the precordillera cuyania terrane and finally ceased with the collision of the chilenia terrane a vast amount of controversial information concerning the timing and mode of collisions as well as the origin of the different involved crustal fragments within the eastern sierras pampeanas is published in this paper those different hypothesis are presented and evaluated under the light of new isotopic data of the sierra de san luis nd systematics of the metasedimentary sequences of the sierra de san luis indicate that the studied sequences were developed on the pampean terrane an amazonian origin of the pampean terrane that was probably detached from the arequipa antofalla craton is proposed furthermore the correlation of two low grade phyllitic belts san luis formation with the widespread puncoviscana formation is not supported by sm nd data it is suggested that the sedimentary precursors of the pringles metamorphic complex and the topping phyllites were sourced on the pampean orogen and accommodated in a newly formed back arc basin during the early famatinian the cooling history of the basement complex is recorded by an extensive amount of k ar muscovite and biotite ages a high variability in muscovite ages is only partly related to different intrusion times of two pegmatoid generations post famatinian to achalian crustal scale mylonite formation 359 ma and a rotational exhumation of the central basement unit are causal for the observed k ar muscovite age pattern in the range from 395 ma to 447 ma therefore the decrease in metamorphic degree from west to east is the result of the erosion level of a crustal profile from the mid lower crust to the upper crust an even higher variability in k ar biotite cooling ages covering the range from 315 ma to 418 ma is related to the slow cooling after the famatinian orogenic cycle or reheating during the achalian orogenic cycle and consequent variable reset of the isotopic system however ages recorded by biotite booklets substantiate the hypothesis of a differential exhumation of the basement of the sierra de san luis

constraints on the formation age of cometary material from the nasa stardust mission we measured the 26 al 26 mg isotope systematics of a 5 m refractory particle coki returned from comet 81p wild 2 in order to relate the time scales of formation of cometary inclusions to their meteoritic counterparts the data show no evidence of radiogenic 26 mg and define an upper limit to the abundance of 26 al at the time of particle formation of 26 al 27 al 5 the absence of 26 al indicates coki formed 1 7 ma after the oldest solar system solids ca al rich inclusions cais the data presented here suggest that high temperature inner solar system material formed was subsequently transferred to the kuiper belt and incorporated into comets several million years following cai formation

u pb th pb and ar ar geochronology from the southern sierras pampeanas argentina implications for the palaeozoic tectonic evolution of the western gondwana margin

active basement uplift of sierra pie de palo northwestern argentina rates and inception from10be cosmogenic nuclide concentrations quaternary tectonic and denudation rates are investigated for an actively growing basement anticline the sierra pie de palo range which belongs to the andean foreland of northwestern argentina 28 s 33 s in this study a detailed morphometric analysis of the topography is combined with in situ produced cosmogenic10be concentrations measured in 1 surface boulders abandoned on alluvial terraces affected by fault activity along the north bounding fault and growth of the basement fold along the southeastern border 2 bedrock outcrops corresponding to an exhumed and folded regional erosion surface and 3 fluvial sediments sampled at the outlets of several watersheds along the eastern and northern borders of the range incision and uplift rates have been estimated at approximately 0 5 and 1 mm yr when integrated on holocene and pleistocene time scales in close agreement with both long term structural and basin evolution data and short term gps derived velocity field analyses cosmogenic derived denudation and uplift rates combined with geomorphic characteristics of watersheds and river channels allows estimating the onset of the uplift at 4 6 ma followed by a more recent period of topographic rejuvenation at roughly 1 2 ma probably synchronous with steepening of the eastern and northern flanks of the anticline

refined exhumation history of the northern sierras pampeanas argentina 1 the sierra de aconquija and cumbres calchaquies in the thick skinned northern sierras pampeanas nw argentina present an ideal setting to investigate the tectonically and erosionally controlled exhumation and uplift history of mountain ranges using thermochronological methods although these ranges are located along strike of one another their spatiotemporal evolution varies significantly integrating modeled cooling histories constrained by k ar ages of muscovite and biotite apatite fission track data as well as u th he measurement of zircon and apatite reveal the structural evolution of these ranges beginning in the late stage of the paleozoic famatinian orogeny following localized rift related exhumation in the central part of the study area and slow erosion elsewhere growth of the modern topography commenced in the cenozoic during andean deformation the main activity occurred during the late miocene with varying magnitudes of rock uplift surface uplift and exhumation in the two mountain ranges the cumbres calchaquies is characterized by a total of 5 7 km of vertical rock uplift around 3 km of crestal surface uplift and a maximum exhumation of 2 4 km since that time the sierra de aconquija experienced 10 13 km of vertical rock uplift 4 5 km of peak surface uplift and 6 8 km of exhumation since around 9 ma much of this exhumation occurred along a previously poorly recognized fault miocene reactivation of cretaceous rift structures may explain along strike variations within these ranges dating of sedimentary samples from adjacent basins supports the evolutionary model developed for the mountain ranges

the las chacras potrerillos batholith pampean ranges argentina structural evidences emplacement and timing of the intrusion within the southern part of the sierra pampeanas the sierra de san luis argentina a series of extensive intrusive bodies are regarded to post date the famatinian cycle but were emplaced during the achalian a period of heterogeneous deformation along crustal scale fault zones the largest of those is the las chacras potrerillos batholith that is situated at the northern end of the transpressive sinistral guzman shear zone this composite pluton exhibits three sub domains that comprise two granitoid sub units each the southern potrerillos stock muscovite bearing red granite and biotite bearing red granite and the central biotite porphyritic granite and giant porphyritic granite and northern domain equigranular granite and porphyritic granite of the las chacras stock the crystallisation ages of the biotite porphyritic granite is around 381 ma u pb on zircons and pb pb on sphene while the host rock was already cooled below 350 c at 420 ma thermal modelling approaches favour a pulsed intrusion with a duration of 1 5 ma the emplacement was followed by rapid cooling below the muscovite cooling temperature biotite cooling ages in different sub units reflect either a long lasting cooling history of approximately 30 ma which is supported by the modelling or a reheating effect at around 350 ma devonian age determinations on the fault rocks and granitoids point to a syn tectonic emplacement of the batholith the pluton is interpreted to be positioned at the crossover of sinistral shear zones the origin of this nne directed extensional setting in a transpressive regime seems to be related to the transfer of displacement along a secondary set of nnw trending sinistral faults the final emplacement is due to a subsequent ballooning of the batholith following the direction of space creation this model is based on the relative timing of the emplacement sequence and macroscopically visible planar fabrics in the field as well as magnetic fabric data our results indicate that the emplacement is syn kinematic with respect to the achalian deformation event

the tectonic significance of k ar illite fine fraction ages from the san luis formation eastern sierras pampeanas argentina the sierra de san luis forms the southern tip of the eastern sierras pampeanas in central argentina two narrow belts of low grade phyllites and quartz arenites i e the san luis formation have accommodated part of the strain related differential exhumation of the medium to high grade metamorphic domains that constitute to the basement complex of the sierra eleven phyllite samples were subjected to the k ar fine fraction dating technique results are interpreted in relation to the kubler index of the illites which indicate epimetamorphic conditions for the majority of the samples obtained ages between 330 and 290 ma cover a period of compressional tectonics in the late mississippian visean serpukhovian boundary followed by the subsidence during the formation of the paganzo basin in the provinces of la rioja and san luis these tectonic movements are coincident with the toco orogeny in northern chile and southern bolivia this suggests that the older k ar ages document the compressional stage and that younger ages record the cooling of the basement during the subsequent extensional uplift of the basement

apatite fission track thermochronology of the sierras pampeanas central western argentina implications for the mechanism of plateau uplift in the andes over much of its length the andean orogen is characterized by a generally east vergent geometry and a progressive eastward cratonward migration of individual arc orogenic elements a departure from this model occurs in the sierras pampeanas region of central western argentina where a terrane of active basement uplifts is currently developing to the east of the main cordillera apatite fission track data from uplifted precambrian and phanerozoic basement rocks of the sierras pampeanas constrain the tectonic development of this terrane and indicate that deformation associated with exhumation may have propagated broadly westward since the late miocene two pre andean cooling events during the carboniferous permian ca 300 280 ma and the early jurassic middle jurassic ca 200 174 ma have been identified the onset of andean deformation is represented by a cooling event during the late paleocene middle eocene this cooling was followed by a period of middle miocene late miocene reheating during foreland basin style sedimentation exhumation and possible westward migration of the exhumation front in the sierras pampeanas commenced during the late miocene pliocene to the east of the dominantly east vergent precordillera fold and thrust belt the apparent convergence of deformation in these two terranes and the progressive closure of miocene pliocene intermontane basins in the sierras pampeanas may reflect the early stages of andean plateau uplift the relative timing of plateau development along strike suggests that lateral thickening of the orogen is progressing southward at least from the latitude of central bolivia ca 20 s furthermore the time space coincidence between basement uplift and flattening of the subducted slab beneath the sierras pampeanas suggests that a relationship exists between westward displacement of the terrane and the dynamics of plate interaction

reciting the layers evidence for past tsunamis at mataora wairau lagoon aotearoa new zealand abstract sedimentary geochemical microfossil and geochronological analyses were carried out on 10 sediment cores across the south eastern corner of mataora wairau lagoon m wl south island aotearoa new zealand this multi proxy approach provides strong evidence for three late holocene palaeotsunamis two previously unreported and a historical tsunami generated by rupture of the wairarapa fault in 1855 ce the main scientific evidence for these events consists of anomalous high energy marine sediment layers that overlie material of contrasting composition these layers coincide with peaks in planktonic and benthic marine to brackish marine diatoms and geochemical signatures indicative of sudden changes in environmental conditions palaeotsunami i maximum date 2095 cal bp and palaeotsunami ii maximum date 915 cal bp previously identified by clark et al 2015 appear to represent large events contemporaneous with major earthquakes inducing tectonic uplift and coseismic subsidence around the cook strait region palaeotsunami ii is close to the date of the earliest settlement of the m wl area by m ori and a traditional narrative that references loss of life following waves over washing the wairau boulder bank given the boulder bank was likely to have been seaward of its current position during events i and ii we surmise that the inundation distances would have been greater than the most landward extent 340 m inferred from the deposits found in this study palaeotsunami iii maximum date 525 cal bp was associated with tectonic subsidence across the study site most likely associated with rupture of the southern hikurangi subduction zone we expect the ongoing refinement of the methods used in this study and the results from future studies of analogue sites and offshore fault systems will improve our understanding of the significant tsunami hazard facing this region

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

the proto andean margin of gondwana an introduction a basic background is presented for the discussion of the early palaeozoic geology of western argentina covered by this book this includes the definition and terminology of orogenic cycles on this part of the gondwana margin represented by the eastern sierras pampeanas the pampean orogeny early cambrian relates to an intense but short lived period of terrane collision predating the rifting of the precordillera terrane from laurentia the famatinian cycle is predominantly represented by intense subductionrelated magmatism of early middle ordovician age developed on the continental margin of gondwana during the rifting and drifting of the precordillera terrane the grenvillian basement of the latter is further exemplified by a new rb sr whole rock isochron age of 1021 12 ma for orthogneisses from the western sierras pampeanas a mid ordovician granite in this area dated at 481 6 ma by u pb ion microprobe data may be related to rifting while the precordillera terrane was still attached to laurentia a divergence of opinion is pointed out between some authors in this book who favour mid ordovician collision of the precordillera with gondwana and others who place it much latter in silurian or devonian times