self destructive sulfide segregation systems and the formation of high grade magmatic ore deposits the metal concentrations of sulfide liquids depend upon the mass of silicate magma that they are able to process for metals some high grade magmatic ni cu pge deposits and many magmatic platinum group element pge ni cu deposits demand very high magma sulfide ratios that seem improbable in the light of physical and kinetic constraints recent models for some high grade deposits invoke multistage upgrading processes in which an early formed sulfide liquid reacts with multiple later batches of silicate magma quantitative models of this open system process demonstrate that it is indeed more efficient than a closed system however it is likely that most later magmas in such a system will be sulfur undersaturated and will thus partly redissolve preexisting sulfide liquids further increasing metal concentrations in the remaining sulfide liquids this combined process is termed multistage dissolution upgrading and quantitative models show that it could reduce the mass of silicate magma that must be processed by as much as two orders of magnitude furthermore if sulfide liquids are extensively dissolved during enrichment their base metal concentrations will generally stabilize at a limiting value whereas their pge concentrations will generally increase without limit this divergence could account for unusually high pge concentrations and high pge base metal ratios in many pge dominated deposits the multistage dissolution upgrading model is tested using reasonable degrees of dissolution in the context of natural deposits in the noril sk area and the bushveld intrusion the models reproduce the observed sulfide compositions significantly better than previous models and are also consistent with other aspects of the geology of these deposits thus dynamic sulfide forming magmatic systems may be intrinsically self destructive but this apparently undesirable attribute could play an important role in forming high grade deposits however dissolution could lead to the complete destruction of sulfide liquids and the return of all metals to later magma batches in this case no sulfide deposit would remain but metal depletion signatures indicating sulfide liquid segregation would be preserved in rocks that crystallized from early magmas caution is therefore advised in the use of magmatic depletion signatures to infer overall mineral potential or to estimate the possible sizes of undiscovered magmatic sulfide deposits

seismic evidence for an earthquake nucleation phase near source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event this phase was observed for the 30 earthquakes having moment magnitudes 2 6 to 8 1 and the size and duration of this phase scale with the eventual size of the earthquake during the nucleation phase moment release was irregular and appears to have been confined to a limited region of the fault it was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone these observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake

dynamic inversion of the 2015 jujuy earthquake and similarity with other intraslab events fondo nacional de desarrollo cientifico y tecnologico fondecyt of comision nacional de investigacion cientifica y tecnologica conicyt chile 11130230 programa riesgo sismico universidad de chile conicyt pcha magisternacional 2014 22140434

changes in sulfides and platinum group minerals with the degree of alteration in the roby twilight and high grade zones of the lac des iles complex ontario canada the lac des iles complex hosts pd deposits with unusually high pd pt and pd ir ratios these high ratios have been attributed to the introduction of pd by late magmatic hydrothermal fluids the presence of hydrous silicates and low temperature sulfide mineral assemblages has been advanced as evidence for fluid overprint this idea has been investigated by documenting the change in silicate sulfide and platinum group mineralogy and texture in samples from the deposit ranging from fresh gabbronorite to extensively altered chlorite actinolite schist in addition whole rock analysis combined with laser ablation analysis of the sulfides was used to determine which phase controlled each of the pge in fresh gabbronorite the sulfide assemblage is igneous pyrrhotite pentlandite chalcopyrite and pd is present mainly in pentlandite and kotulskite pdte inclusions associated with the sulfide minerals all other pge except pt are present in solid solution in pyrrhotite and pentlandite platinum is present as sperrylite ptas2 and montcheite ptte2 inclusions associated with the sulfide minerals these observations suggest that the pge in the fresh gabbronorite were all collected by magmatic sulfide liquid in the chlorite actinolite schist the sulfide assemblage is a low temperature assemblage consisting of chalcopyrite pyrite millerite a minor amount of palladium is present in millerite but most is present as bismuth rich kotulskite and pd arsenides both of which are associated with hydrous silicate all other pge except pt are hosted by pyrite a minor amount of pt is present in pyrite but most is found as sperrylite and montcheite associated with hydrous silicate minerals the pyrite could have formed by fe loss from pyrrhotite resulting in the pyrite inheriting os ir ru and rh and fe loss from pentlandite to form millerite resulting in the millerite inheriting some pd the pge concentrations of the whole rock show there is no direct correlation between the sulfide assemblage the degree of alteration of the silicate minerals and ore grade thus although fluids have clearly altered the sulfide silicate and platinum group mineralogy and their textures it is not clear that these fluids have changed the pge content of the rocks

high mgo lavas from the keweenawan midcontinent rift near mamainse point ontario detailed study of the basal 500 m of the keweenawan mamainse point volcanics in ontario canada has revealed that the section is dominated by basaltic to picritic lavas with up to 23 wt mgo two stratigraphic suites with distinct chemical characteristics are separated by four flows of high tio 2 ferrobasalt containing large and abundant plagioclase spherulites the focus of this study is on the lower suite that contains the most mgo rich compositions and that generally has lower tio 2 content although most of the flows are olivine phyric the olivine phenocrysts are skeletal suggesting in situ crystallization from magmas with high normative olivine content furthermore the compositional variation of the lavas does not fall along an olivine only control line taken together the data indicate that the compositional variation of the lavas represents fractionation of high mgo liquids rather than accumulation of olivine in basaltic liquids most of the fractionation apparently involved crystallization of olivine clinopyroxene and cr spinel but later fractionation involved olivine clinopyroxene and plagioclase the occurrence of picritic lavas low in the overall volcanic section is similar to relations in other flood basalt provinces and should eventually yield important tectonic and magmatic constraints for the development of the keweenawan midcontinent rift of north america

identification of high frequency pulses from earthquake asperities along chilean subduction zone using strong motion the chilean subduction zone is one of the most active of the world with m 8 or larger interplate thrust earthquakes occurring every 10 years or so on the average the identification and characterization of pulses propagated from dominant asperities that control the rupture of these earthquakes is an important problem for seismology and especially for seismic hazard assessment since it can reduce the earthquake destructiveness potential a number of studies of large chilean earthquakes have revealed that the source time functions of these events are composed of a number of distinct energy arrivals in this paper we identify and characterize the high frequency pulses of dominant asperities using near source strong motion records two very well recorded interplate earthquakes the 1985 central chile ms 7 8 and the 2007 tocopilla mw 7 7 are considered in particular the 2007 tocopilla earthquake was recorded by a network with absolute time and continuos recording from the study of these strong motion data it is possible to identify the arrival of large pulses coming from different dominant asperities the recognition of the key role of dominant asperities in seismic hazard assessment can reduce overestimations due to scattering of attenuation formulas that consider epicentral distance or shortest distance to the fault rather than the asperity distance the location and number of dominant asperities their shape the amplitude and arrival time of pulses can be one of the principal factors influencing chilean seismic hazard assessment and seismic design the high frequency pulses identified in this paper have permitted us to extend the range of frequency in which the 1985 central chile and 2007 tocopilla earthquakes were studied this should allow in the future the introduction of this seismological result in the seismic design of earthquake engineering

source of the 1730 chilean earthquake from historical records implications for the future tsunami hazard on the coast of metropolitan chile historical records of an earthquake that occurred in 1730 affecting metropolitan chile provide essential clues on the source characteristics for the future earthquakes in the region the earthquake and tsunami of 1730 have been recognized as the largest to occur in metropolitan chile since the beginning of written history the earthquake destroyed buildings along 1000 km of the coast and produced a large tsunami that caused damage as far as japan here its source characteristics are inferred by comparing local tsunami inundations computed from hypothetical earthquakes with varying magnitude and depth with those inferred from historical observations it is found that a 600 800 km long rupture involving average slip amounts of 10 14 m mw 9 1 9 3 best explains the observed tsunami heights and inundations this large earthquake magnitude is supported by the 1730 tsunami heights inferred in japan the inundation results combined with local uplift reports suggest a southward increase of the slip depth along the rupture zone of the 1730 earthquake while shallow slip on the area to the north of the 2010 earthquake rupture zone is required to explain the reported inundation only deeper slip at this area can explain the coastal uplift reports since the later earthquakes of the region involved little or no slip at shallow depths the near future earthquakes on metropolitan chile could release the shallow slip accumulated since 1730 and thus lead to strong tsunami excitation moderate shaking from a shallow earthquake could delay tsunami evacuation for the most populated coastal region of chile 250 250

distance of movement of coarse particles in gravel bed streams distributions of distance of bedload particle movement were examined in two gravel bed streams using several hundred magnetically tagged cobbles and pebbles the compound poisson model of einstein hubbell sayre and a simple gamma function model were compared with observed distributions of moved particles and of all particles both models fit the data reasonably well for small mean displacements but notable misfits occurred in an event with large mean displacement when mean particle travel distance approaches the scale of bar spacing trapping in the bars interrupts particle progress and the dispersion process the data remain very noisy so definitive discrimination of suitable models will require trials with more than 103 particles

intense foreshocks and a slow slip event preceded the 2014 iquique mw 8 1 earthquake the subduction zone in northern chile is a well identified seismic gap that last ruptured in 1877 the moment magnitude mw 8 1 iquique earthquake of 1 april 2014 broke a highly coupled portion of this gap to understand the seismicity preceding this event we studied the location and mechanisms of the foreshocks and computed global positioning system gps time series at stations located on shore seismicity off the coast of iquique started to increase in january 2014 after 16 march several mw 6 events occurred near the low coupled zone these events migrated northward for 50 kilometers until the 1 april earthquake occurred on 16 march on shore continuous gps stations detected a westward motion that we model as a slow slip event situated in the same area where the mainshock occurred

on the mechanisms for low sulfide high platinum group element and high sulfide low platinum group element mineralization in the eastern gabbro coldwell complex canada evidence from textural associations s se values and platinum group element concentrations of base metal sulfides

a re evaluation of the great aleutian and chilean earthquakes of 1906 august 17 summary we investigate two great earthquakes that occurred in the aleutian islands and chile within 30 min of each other on 1906 august 17 based on a collection of seismograms compiled shortly after the events by scientists at strasbourg the method of preliminary determination of focal mechanisms pdfm is applied to 14 mantle waves from seven stations in order to resolve the moment tensors of the two shocks it is complemented by examination of body wave polarities at japanese stations to lift the remaining indeterminacy in focal mechanism the chilean earthquake occurring second is a regular subduction event whose moment 2 8 1028 dyn cm is revised downwards from previous estimates except kanamori s suggesting that its rupture did not involve more than 200 km of fault the aleutian earthquake occurring first has a larger moment 3 8 1028 dyn cm but features mantle wave radiation patterns and body wave polarities incompatible with both underthrusting at the aleutian subduction zone and tensional buckling at the outer rise rather we suggest that it is an intraplate somewhat deeper 50 km earthquake this is supported by tentative relocation of available arrival times north of it the origin of the earthquake may be related to the presence of the bowers ridge north of the amchitka pass in the epicentral area finally hydrodynamic simulations using our source mechanisms support the observation that the chilean event was the source of the reported transpacific tsunami the report of a 3 5 m wave at maui constitutes a misassociation as its timing is shown to be non causal for both events

determination of the friction law parameters of the mw 6 7 michilla earthquake in northern chile by dynamic inversion 1 we perform a full dynamic inversion at low frequencies of the 16 december 2007 mw 6 7 northern chile earthquake that we model as a simple elliptical patch we use two different stress friction end member models asperities and barriers finding similar results the inversions are performed for strong motion data filtered between 0 02 and 0 5 hz eleven geometrical and stress and friction parameters are inverted using the neighbourhood algorithm the optimum solutions have relative errors lower than 0 21 the earthquake rupture has duration of less than 5 s and propagates at sub shear speed the rupture area is similar to that of the aftershock distribution and the seismic moment is 0 95 10 19 nm we derive the friction law parameters from the models situated close to the optimum solution using a monte carlo technique the results show a strong trade off between applied stress and frictional resistance we find that the distribution of friction models collapses into a finite zone of the space of moment and non dimensional parameter k we conclude that it is possible to determine the friction law from near field seismograms but there is a strong trade off between friction and initial stress

coastal evidence for holocene subduction zone earthquakes and tsunamis in central chile abstract the 500 year historical record of seismicity along the central chile coast 30 34 s is characterized by a series of m 8 0 8 5 earthquakes followed by low tsunamis 10 m but the frequency of such large events is unknown we extend the seismic history of central chile through a study of a lowland stratigraphic sequence along the metropolitan coast north of valparaiso 33 s at this site higher relative sea level during the mid holocene created a tidal marsh and the accommodation space necessary for sediment that preserves earthquake and tsunami evidence within this 2600 yr long sequence we traced six laterally continuous sand beds probably deposited by high tsunamis plant remains that underlie the sand beds were radiocarbon dated to 6200 5600 5000 4400 3800 and 3700 cal yr bp sediment properties and diatom assemblages of the sand beds for example anomalous marine planktonic diatoms and upward fining of silt sized diatom valves point to a marine sediment source and high energy deposition grain size analysis shows a strong similarity between inferred tsunami deposits and modern coastal sediment upward fining sequences characteristic of suspension deposition are present in five of the six sand beds despite the lack of significant lithologic changes between the sedimentary units under and overlying tsunami deposits we infer that the increase in freshwater siliceous microfossils in overlying units records coseismic uplift concurrent with the deposition of five of the sand beds during our mid holocene window of evidence preservation the mean recurrence interval of earthquakes and tsunamis is 500 years our findings imply that the frequency of historical earthquakes in central chile is not representative of the greatest earthquakes and tsunamis that the central chilean subduction zone has produced

genesis of the marathon cu platinum group element deposit port coldwell alkalic complex ontario a midcontinent rift related magmatic sulfide deposit the marathon copper and platinum group element pge deposit is hosted by the two duck lake intrusion located at the eastern margin of the port coldwell alkalic complex northwestern ontario the two duck lake intrusion is subdivided into an upper layered zone and a lower unlayered zone that consists of olivine gabbro and pegmatite with trace amounts of granophyre the sulfides are hosted in the lower zone which is referred to here as two duck lake gabbro petrography mineral chemistry and geochemical data imply that two duck lake gabbro crystallized in situ from a plagioclase crystal mush there is no geochemical evidence for metasomatic alteration of the gabbro the sulfides are disseminated in gabbro and pegmatite and consist of approximately equal proportions of chalcopyrite and pyrrhotite and minor amounts of pentlandite and pyrite samples of two duck lake gabbro exhibit a significant correlation between sulfur and ni ir rh pt pd au and cu further the pd ir and pd ni ratios increase with increasing concentrations of rh pt pd au and cu consequently bulk sulfide compositions are best explained by the separation of a sulfide liquid from a gabbroic magma this origin is contrary to that proposed by previous workers they presented detailed petrographic and mineral chemical data that imply inter action of cl bearing hydrous fluids and sulfides at low temperatures in the light of our study we interpret these observations to indicate that elements migrated over very short distances and that bulk sulfides were not enriched with cu and pge as previously proposed a model for the genesis of the marathon deposit is proposed many characteristics of the marathon deposit bear a striking resemblance to observations reported in disseminated sulfide deposits at the base of the duluth complex minnesota the features include mineral textures abundances and compositions crystallization paths for the host gabbroic bodies silicate sulfide associations trace element trends and chalcophile element fractionation trends the similarities imply that the marathon deposit and deposits in the duluth complex formed by analogous processes

the 1985 central chile earthquake a repeat of previous great earthquakes in the region a great earthquake surface wave magnitude 7 8 occurred along the coast of central chile on 3 march 1985 causing heavy damage to coastal towns intense foreshock activity near the epicenter of the main shock occurred for 11 days before the earthquake the aftershocks of the 1985 earthquake define a rupture area of 170 by 110 square kilometers the earthquake was forecast on the basis of the nearly constant repeat time 83 9 years of great earthquakes in this region an analysis of previous earthquakes suggests that the rupture lengths of great shocks in the region vary by a factor of about 3 the nearly constant repeat time and variable rupture lengths cannot be reconciled with time or slip predictable models of earthquake recurrence the great earthquakes in the region seem to involve a variable rupture mode and yet for unknown reasons remain periodic historical data suggest that the region south of the 1985 rupture zone should now be considered a gap of high seismic potential that may rupture in a great earthquake in the next few tens of years

modelling fluid flow in complex natural fault zones implications for natural and human induced earthquake nucleation abstract pore fluid overpressures in active fault systems can drive fluid flow and cause fault weakening and seismicity in return deformation accommodated by different modes of failure e g brittle vs ductile also affects fault zone permeability and hence fluid flow and pore fluid pressure distribution current numerical simulation techniques model how fluid flow controls fault reactivation and associated seismicity however the control exerted by pore fluid pressure on the transition from slow aseismic fault sliding to fast seismic sliding during the earthquake nucleation phase is still poorly understood here we model overpressured supercritical co2 fluid flow in natural faults where non linear complex feedback between fluid flow fluid pressure and fault deformation controls the length of the nucleation phase of an earthquake and the duration of the interseismic period the model setup is an analogue for recent seismic source events in the northern apennines of italy e g m w 6 0 1997 98 colfiorito and m w 6 5 2016 norcia earthquakes our modelling results of darcy fluid flow show that the duration of the nucleation phase can be reduced by orders of magnitude when realistic models of fault zone architecture and pore pressure and deformation dependent permeability are considered in particular earthquake nucleation phase duration can drop from more than 10 years to a few days minutes while the seismic moment can decrease by a factor of 6 notably the moment of aseismic slip m 0 10 9 n m obtained during the nucleation phase modelled in our study is of the same order as the detection limit of local strain measurements using strain meters these findings have significant implications for earthquake early warning systems as the duration and moment of the nucleation phase will affect the likelihood of timely precursory signal detection interestingly aseismic slip has been measured up to a few months before some recent large earthquakes although in a different tectonic context than the model developed here rekindling interest in the nucleation phase of earthquakes in addition our results have important implications for short and long term earthquake forecasting as crustal fluid migration during the interseismic period may control fault strength and earthquake recurrence intervals

insights into the extreme pge enrichment of the w horizon marathon cu pd deposit coldwell alkaline complex canada platinum group mineralogy compositions and genetic implications the w horizon marathon cu pd deposit in the mesoproterozoic midcontinent rift is one of the highest grade pge repositories in magmatic ore deposits world wide the textural relationships and compositions of diverse platinum group mineral pgm and sulfide assemblages in the extremely enriched ores 100 ppm pd pt au over 2 m of the w horizon have been investigated in mineral concentrates with 10 000 pgm grains and in situ using scanning electron microprobe and microprobe analyses here we show from ore samples with concentrations up to 23 1 pd ppm 8 9 pt ppm 1 4 au ppm and 0 73 rh ppm the diversity of minerals n 52 including several significant unknown minerals and three new mineral species marathonite pd25ge9 mcdonald et al 2016 palladogermanide pd2ge ima 2016 086 mcdonald et al 2017 kravtsovite pdag2s ima no 2016 092 vymazalova et al 2017 the pgm are distributed as pg sulfides 52 vol arsenides 34 vol intermetallics of au ag pd cu and pd ge 10 vol and bismuthides and tellurides 4 vol the discovery of abundant 330 grains large unknown sulfide minerals with rh allows us to present analyses three significant potentially new minerals wuk 1 wuk 2 wuk 3 that are all clearly enriched in rh averaging 4 2 8 5 and 28 21 wt rh respectively several examples of paragenetic sequences and mineral chemical changes for enrichment of cu pd and rh with time are revealed in the pgm and base metal sulfides we suggest this enhanced metal enrichment formed in response to increasing fo2 causing the oxidation of fe2 to fe3 and to a lesser extent s phase relations in the ag pd s rh ni fe s pd ge au pd cu ag pd ag te systems help constrain the crystallization temperatures of the majority of ore minerals in the w horizon at 500 c or moderate to high subsolidus temperatures 400 600 c local transport by aqueous fluids becomes evident as minerals recrystallize down to 300 c the pge enriched w horizon ores exhibit a complex post magmatic history dominated by the effects of oxidation during cooling of a cu pge enriched magma source from a deep reservoir

parental magmas of the nain plutonic suite anorthosites and mafic cumulates a trace element modelling approach equilibrium melt trace element contents are calculated from proterozoic nain plutonic suite nps mafic and anorthositic cumulates and from plagioclase and orthopyroxene megacrysts assumed trapped melt fractions tmf 20 generally eliminate all minor phases in most mafic cumulate rocks reducing them to mixtures of feldspar pyroxene and olivine which would represent the high temperature cumulus assemblage in anorthosites tmf 15 generally reduce the mode to a feldspar only assemblage all model melts have trace element profiles enriched in highly incompatible elements relative to normal mid ocean ridge basalt nmorb commonly with negative nb and th anomalies most mafic cumulates yield similar profiles with constant incompatible element ratios and can be linked through fractional crystallization high k la subtypes probably represent crust contaminated facies mafic cumulates are inferred to belong to a tholeiitic differentiation series variably contaminated by upper and lower crustal components and probably related to coeval tholeiitic basaltic dyke swarms and lavas in labrador model melts from anorthosites and megacrysts have normalized trace element profiles with steeper slopes than those calculated from mafic cumulates indicating that mafic cumulates and anorthosites did not crystallize from the same melts orthopyroxene megacrysts yield model melts that are more enriched than typical anorthositic model melts precluding an origin from parental melts jotunites have lower k rb ba y yb and higher la ce than model residues from fractionation of anorthositic model melts suggesting they are not cosanguineous with them but provide reasonable fits to evolved mafic cumulate model melts incompatible element profiles of anorthositic model melts closely resemble those of crustal melts such as tonalites with steep y yb lu segments that suggest residual garnet in the source inversion models yield protoliths similar to depleted lower crustal granulite xenoliths with aluminous compositions suggesting that the incompatible trace element budget of the anorthosites are derived from remobilization of the lower crust the similarity of the highly incompatible trace elements and lile between anorthositic and mafic cumulate model melts suggests that the basalts parental to the mafic cumulates locally assimilated considerable quantities of the same crust that yielded the anorthosites the reaction between underplating basalt and aluminous lower crust would have forced crystallization of abundant plagioclase and remobilization of these hybrid plagioclase rich mushes then produced the anorthosite massifs

the role of fluids in the formation of platinum group minerals duluth complex minnesota mineralogic textural and chemical evidence several new occurrences of platinum group minerals pgm including sperrylite ptas 2 taimyrite pd cu 3 sn froodite pdbi 2 michenerite pdbite and moncheite pt bi 2 te 3 are recorded from drill core samples of the basal troctolites of the duluth complex the first documentation of a vanadium chromium hercynite v 2 o 3 ranging from 5 14 5 23 wt in graphite rich samples of the mineralized zone of the duluth complex is also reported the pgm are associated predominantly with serpentinized olivine and secondary magnetite or with altered calcic plagioclase approximately an 75 prehnite actinolite hornblende and chlorite the pd bismutho tellurides are associated with parkerite ni 3 bi 2 s 2 tellurobismuthite bi 2 te 3 bismuthinite bi 2 s 3 hessite ag 2 te native gold and clausthalite pb s se with low temperature sulfides like valleriite 2 fe cu s 3 mg fe oh 2 violarite feni 2 s 4 heazlewoodite ni 3 s 2 and in some instances graphite these associations especially the occurrence of the pgm in altered silicates suggest that the pgm reported in this study were transported and deposited during a late magmatic hydrothermal event which could be related to the introduction of volatiles from the metasedimentary virginia formation and the biwabik iron formation the high cl contents of the serpentine biotite apatite and graphite as well as the high an contents of the plagioclase in contact with the sulfides and pgm further suggest that chloride complexing was a possible mechanism for the transport and deposition of the pgm during the hydrothermal event the occurrence of high vanadium chromium hercynite is also consistent with this interpretation

undulatory silver rich polymetallic veins of the castrovirreyna district central peru fault growth and mineralization in a perturbed local stress field strongly undulatory silver veins of the castrovirreyna district central peru formed in a dilatant anastamosing low displacement left lateral fault system during late miocene east west directed compression the steeply dipping veins have multiple orders of undulations as seen in map view and underground mines expose strong dip reversals kinematic indicators from the east northeast to west northwest striking veins record mainly left lateral slip and lesser oblique reverse slip these striation data considered along with vein intersection angles and map patterns indicate that the veins did not form as a simple conjugate fracture set the preferred interpretation is that the curved fracture growth and complex slip distributions developed because of local stress field modifications by the propagating faults and dilating vein segments during regional east west directed compression variably oriented fault striations compound displacement profiles and multiple scales of vein curvature are all characteristics of stress interaction between subparallel veins veins possessing these features may be expected to host oreshoots with a complex geometry that depends not only on local accommodation space produced at dilant jogs but also on the proximity to other veins and changing slip directions

the long precursory phase of most large interplate earthquakes many earthquakes are preceded by foreshocks however the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown here we use seismic catalogues from the best instrumented areas of the north pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011 of magnitude larger than 6 5 and at depths shallower than 50 km the data set comprises 31 earthquakes at plate boundaries and 31 in plate interiors we find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes most large earthquakes at plate interfaces in the north pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock in contrast foreshocks are much less frequent in intraplate settings we suggest that at plate boundaries the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake this relatively long precursory phase could help mitigate earthquake risk at plate boundaries

closing of the midcontinent rift a far field effect of grenvillian compression the midcontinent rift formed in the laurentian supercontinent between 1109 and 1094 ma soon after rifting stresses changed from extensional to compressional and the central graben of the rift was partly inverted by thrusting on original extensional faults thrusting culminated at about 1060 ma but may have begun as early as 1080 ma on the southwest trending arm of the rift the crust was shortened about 30 km on the southeast trending arm strike slip motion was dominant the rift developed adjacent to the tectonically active grenville province and its rapid evolution from an extensional to a compressional feature at ca 1080 ma was coincident with renewal of northwest directed thrusting in the grenvllle probably caused by continent continent collision a zone of weak lithosphere created by rifting became the locus for deformation within the otherwise strong continental lithosphere stresses transmitted from the grenville province utilized this weak zone to close and invert the rift

timing of surficial process changes down a mojave desert piedmont abstract we measured 10 be and 26 al in 29 sediment samples to infer the history and millennial scale rates of change down a low gradient piedmont a common but enigmatic landform that dominates the mojave desert nuclide data suggest that a large volume of sediment was deposited on the proximal east range road piedmont in fort irwin california 75 500 yr ago since then this material has been stable or eroding slowly in contrast on the distal piedmont 3 5 km from the upland source basins soil stratigraphy suggests that there have been alternating periods of surface stability erosion and deposition over the last 70 000 yr nuclide data from samples amalgamated along cross piedmont transects suggest that long term average down gradient sediment speeds range from 9 cm yr 1 near the uplands to 22 cm yr 1 6 km down piedmont these speeds are similar to 10 be estimated sediment speeds down three other piedmonts in the mojave desert suggesting that piedmont surface morphologies dominated by shallow migrating channels have similar sediment transport rates the timing of surface process change down the east range road piedmont is determined by a combination of sediment available in the source basins sediment transport rates and the size of the piedmont

re and os concentrations in arc basalts the roles of volatility and source region fo2 variations olivine and spinel compositions major elements including ferric and ferrous iron s re and os contents have been measured for a suite of primitive most 6 wt mgo basalts from the trans mexican volcanic belt tmvb including the western mexican volcanic belt the michoacan guanajuato volcanic field sierra chichinautzin pico de orizaba region palma sola san martin tuxtlas and the eastern alkaline province eap sulfur contents at sulfide saturation were calculated to determine whether the measured s contents are representative of sulfide saturated liquids most of the samples have s contents much lower than expected for sulfide saturation a few have higher contents than calculated perhaps due to the presence of sulfate in the measured total sulfur i e more oxidized samples comparison of the tmvb samples along with previously analyzed morb oib babb and arc samples reveals a continuum of re and os contents that is best explained by variation in oxygen fugacity and thus sulfide stability in the source region high re and os magmatic suites are best explained by derivation by melting of oxidized mantle where sulfide is no longer stable and re and os behave incompatibly whereas low re and os magmatic suites are derived from melting of relatively reduced mantle where sulfide is stable and re and os behave compatibly intermediate examples abound and arc magmas span a wide range of re and os concentrations due to variation of fo2 in the source during genesis of arc magmas low re magmatic suites are furthermore potentially affected by volatility which can lower re by a factor of 3 5

scour fill and burial depth of coarse material in gravel bed streams scour fill and burial depths of coarse particles were examined in two ephemeral streams using magnetically tagged particles and scour chains the burial depth varied within a bedform and from one bedform to another the maximum burial depth was recorded in bars but differences in the mean burial depth in the pools bar and thalweg were insignificant mean burial depth was three to six times the median size of material on bar surfaces and ten to thirty times that in the pools and thalweg more than eighty per cent of the tagged particles which were located on or close to the bed surface moved in each event although previously buried particles were moved by flood events others which were initially exposed remained stationary on the surface or were buried in situ the data indicate that the mean burial depth was intermediate between the mean depths of scour and fill deeply buried particles probably reflect the development of scour holes during flood flows aggradation and degradation changed the recorded burial depth relative to the local bed surface of stationary tracer particles these observations indicate that scour and fill processes during a flow event are sporadic and change with water discharge

interseismic coupling megathrust earthquakes and seismic swarms along the chilean subduction zone 38 18 s the recent expansion of dense gps networks over plate boundaries allows for remarkably precise mapping of interseismic coupling along active faults the interseismic coupling coefficient is related to the ratio between slipping velocity on the fault during the interseismic period and the long term plates velocity but the interpretation of coupling in terms of mechanical behavior of the fault is still unclear here we investigate the link between coupling and seismicity over the chilean subduction zone that ruptured three times in the last 5 years with major earthquakes maule mw 8 8 in 2010 iquique mw 8 1 in 2014 and illapel mw 8 4 in 2015 we combine recent gps data acquired over the margin 38 18 s with older data to get the first nearly continuous picture of the interseismic coupling variations on the subduction interface here we show that at least six low coupling zones lcz areas where coupling is low relatively to the neighboring highly coupled segments can be identified we also find that for the three most recent mw 8 events co seismic asperities correlate well with highly coupled segments while lczs behaved as barriers and stopped the ruptures the relation between coupling and background seismicity in the interseismic period before the events is less clear however we note that swarm sequences are prone to occur in intermediate coupling areas at the transition between lcz and neighboring segments and that the background seismicity tends to concentrate on the downdip part of the seismogenic locked zone thus highly coupled segments usually exhibit low background seismicity in this overall context the metropolitan segment that partly ruptured during the 2015 illapel earthquake appears as an outlier since both coupling and background seismicity were high before the rupture raising the issue of the remaining seismic hazard in this very densely populated area

kinematic and dynamic inversion of the 2008 northern iwate earthquake we perform kinematic and dynamic inversion of the 24 july 2008 m w 6 8 northern iwate intermediate depth earthquake in japan using strong motion records from the k net and kik net networks the rupture of this moderate magnitude earthquake is modeled as a simple elliptical patch the optimal solutions are found comparing observed and synthetic records using an l 2 norm and the neighborhood algorithm to search for the best solution followed by an exploration of solution space with a monte carlo technique the geometry of the rupture rupture velocity and slip distribution are estimated by kinematic inversion the rupture geometry stress and friction parameters are obtained by dynamic inversion both approaches converge to very similar source models with semiminor axes of 4 km maximum slip of about 4 m and large stress drops in the 30 45 mpa range rupture duration was less than 3 s because of very high sub rayleigh rupture propagation speeds energy release rate for the best models was in the range 23 36 mj m2 a rather large value for events of this size for both kinematic and dynamic inversion we found families of solutions that fit the strong motion data within a certain error confirming the strong trade off among inverted parameters finally we demonstrate that dynamic inversion solutions are controlled by the dynamic similarity parameter and by seismic moment m these two parameters define a region of model space where dynamically similar models fit the observations with approximately the same misfit online material figures that compare observed and synthetic waveforms for all available stations and comparison of fourier spectrum of observed and synthetic seismograms

reexamination of the magnitudes for the 1906 and 1922 chilean earthquakes using japanese tsunami amplitudes implications for source depth constraints far field tsunami records from the japanese tide gauge network allow the reexamination of the moment magnitudes mw for the 1906 and 1922 chilean earthquakes which to date rely on limited information mainly from seismological observations alone tide gauges along the japanese coast provide extensive records of tsunamis triggered by six great mw 8 chilean earthquakes with instrumentally determined moment magnitudes these tsunami records are used to explore the dependence of tsunami amplitudes in japan on the parent earthquake magnitude of chilean origin using the resulting regression parameters together with tide gauge amplitudes measured in japan we estimate apparent moment magnitudes of mw 8 0 8 2 and mw 8 5 8 6 for the 1906 central and 1922 north central chile earthquakes the large discrepancy of the 1906 magnitude estimated from the tsunami observed in japan as compared with those previously determined from seismic waves ms 8 4 suggests a deeper than average source with reduced tsunami excitation a deep dislocation along the chilean megathrust would favor uplift of the coast rather than beneath the sea giving rise to a smaller tsunami and producing effects consistent with those observed in 1906 the 1922 magnitude inferred from far field tsunami amplitudes appear to better explain the large extent of damage and the destructive tsunami that were locally observed following the earthquake than the lower seismic magnitudes ms 8 3 that were likely affected by the well known saturation effects thus a repeat of the large 1922 earthquake poses seismic and tsunami hazards in a region identified as a mature seismic gap

thermal history of low metamorphic grade paleoproterozoic sedimentary rocks of the penokean orogen lake superior region evidence for a widespread 1786 ma overprint based on xenotime geochronology abstract paleoproterozoic strata in northern michigan wisconsin and minnesota were deposited between 2 3 and 1 75 ga within the rifted margin and subsequent foreland basin of the penokean orogen these strata show evidence for multiple regional metamorphic events previously attributed entirely to the penokean orogeny 1875 1835 ma metasandstones from the marquette range supergroup and the animikie mille lacs and north range groups were sampled at multiple localities across minnesota wisconsin and michigan for metamorphic xenotime suitable for in situ shrimp u pb geochronology all samples are from the northern penokean foreland basin where the metamorphic grade is greenschist to sub greenschist and the strata are virtually undeformed xenotime u pb ages in these samples have a bimodal population with means of 1786 4 ma n 32 and 1861 10 ma n 9 xenotime of both ages are contained in metasandstones from the basal chocolay group in michigan and wisconsin and the mille lacs group and north range groups in minnesota the older age records a regional low temperature thermal event that is slightly older than the overlying menominee group in michigan and the animikie group in minnesota and ontario this 1861 ma event coincides with regional uplift that led to the formation of the unconformity between the menominee group and the overlying baraga group in michigan hence xenotime growth must have occurred at shallow burial depths younger units from the menominee and baraga groups in michigan and the animikie group in minnesota record only the 1786 ma event a dominant 1800 1790 ma metamorphic monazite population that overprints penokean interval monazite has been documented within amphibolite to granulite facies rocks immediately north of the niagara fault zone within the vicinity of gneiss domes and granitic plutons in contrast the 1786 ma xenotime ages are from low grade virtually undeformed rocks 50 150 km from the high grade zones and thus do not appear to reflect a local thermal imprint rather the geographic extent of the 1786 ma xenotime growth event suggests that it reflects a basin wide subtle thermal pulse it is proposed that the xenotime ages record widespread subtle heating triggered by renewed subduction along the orogen due to yavapai interval convergence the 1800 1700 ma yavapai terrane forms an accretionary belt throughout the central and southwestern u s and truncates the southern part of the penokean orogen in central wisconsin and southeastern minnesota about 200 km south of the sample sites alternatively an 1800 1765 ma interval of gravitational collapse of overthickened crust of the penokean orogen immediately north of the niagara fault zone may have driven a northward flow of hydrothermal fluids which subtly but pervasively altered the northern parts of the penokean foreland and resulted in xenotime growth

late quaternary history of the chemehuevi mountain piedmont mojave desert deciphered using 10be and 26al we used the cosmogenic nuclides 10 be and 26 al as cosmic ray dosim eters to track sediment movement across the incised chemehuevi mountain piedmont surface the piedmont extends 12 km from highland source basins to an ephemeral wash at the toe of the piedmont nuclide activity in sediment from steep source basins and from the bedrock pediment allows us to estimate rates of sediment generation and thus the rate at which sediment is supplied to the piedmont from weathering rock analysis of amalgamated sediment samples collected along 4 km long transects spaced at 1 km intervals from the mountain front provide context for understanding nuclide activity in sediment samples collected from two soil pits and demonstrate that sediment steadily moves down the channel network samples from the two soil pits allow for estimates of sediment deposition rates and thus further illuminate piedmont history model results suggest that the chemehuevi mountains are eroding about 40 mm ky 1 whereas the mountain proximal bedrock pediment and the interpiedmont saw tooth range are eroding more slowly 10 to 21 mm ky 1 and 9 5 mm ky 1 respectively cosmogenic nuclide profiles in two soil pits suggest a complex history of deposition at rates between 19 to 39 mm ky 1 and stability over the past 60 ky a change in process from sediment deposition to sediment transport occurred distally on the piedmont approximately 8 ky ago while the mid piedmont piedmont surface has been stable since the mid holocene the incised chemehuevi mountain piedmont is changing at rates similar to planar and uniformly active piedmonts such as those adjacent to the iron and granite mountains all three piedmonts have average sediment grain velocities of decimeters per year long term source basin erosion rates between 35 to 40 mm ky depositional hiatuses around the pleistocene holocene climatic transition from moister to drier conditions and pleistocene deposition rates of 18 to 39 mm ky such similarity in piedmont behavior despite clear differences in morphology and appearance might suggest large scale geologic and climatic controls on the generation transport and deposition of sediment in the mojave desert

stone movement on hillslopes in the mojave desert california a 16 year record previous research has shown that either hydraulic action or creep may be the dominant process transporting coarse debris down hillslopes in the american southwest this study analyses the movement over 16 years of painted stones on two hillslopes in the central mojave desert to ascertain which of these two processes dominate in this region the distance moved m is found to be directly related to length of overland flow x and hillslope gradient s and inversely related to particle size d the fact that m is more highly correlated with x than with s suggests that hydraulic action rather than creep is the dominant process it is concluded that this is probably the case over most of the mojave and sonoran deserts on slopes up to at least 24 and that it is only at higher elevations where winters are more severe that creep may become dominant

applications of the combined portable xrf benchtop sem methodology to pge exploration abstract portable xrf pxrf and benchtop scanning electron microscopes equipped with energy dispersive systems bsem eds are two real time analytical techniques that can be combined to collect on site lithogeochemical and mineral chemical results at dramatically reduced cost and time compared to traditional analytical methods the coldwell complex northwestern ontario is used as a case study on how the combination of these techniques can be applied to mineral exploration our results show that whole rock ba v ti cu s determined by pxrf and plagioclase olivine and clinopyroxene compositions measured by bsem eds can be applied to exploration for pge deposits cu s ratios for disseminated sulfides are a proxy for metal tenor which can be applied as a vector towards higher grade mineralization potential magma recharge zones are identified by inspecting down hole variations in plagioclase olivine and clinopyroxene compositions fluctuating down hole variations in these parameters are interpreted to reflect episodic magma recharge whether rocks contain pge mineralization can initially be assessed by documenting the variability of mineral chemistry i e the greater variability of mineral chemistry could be used to vector higher grade pge mineralization particularly if the mineralization is conduit related lastly geochemical mapping of the igneous stratigraphy enables identification of favorable hosts for mineralization down hole whole rock variations in ba and v ti from pxrf and mineral chemical profiles from bsem eds are used to discriminate the mineralized marathon series from the barren layered series throughout the coldwell complex whole rock ba and v ti from pxrf and mineral chemical results from bsem eds could prove useful in other settings of the midcontinent rift e g the duluth complex eagle and eagle east intrusions tamarack intrusive complex and the sonju lake intrusion and elsewhere e g the stillwater complex to identify mineralized host rock types an additional important application is a rapid interpretation of petrogenesis down hole variations in olivine clinopyroxene mg fe exchange coefficients determined by bsem eds analyses show that olivine clinopyroxene pairs in the marathon series units particularly for those within pge mineralized zones have compositions that are closer to chemical equilibrium constant compared to units of the barren layered series highly variable and thus could be a tool for interpreting petrogenetic processes active in the magma chamber or during the mineralization forming event

pgm facies variations for cu pge deposits in the coldwell alkaline complex ontario canada abstract accurate characterization of the platinum group mineral pgm assemblages for cu ni pge deposits are typically constrained by sample size and the difficulty of finding statistically significant numbers of grains which is expected given the low concentrations of platinum group elements 75 m can account for large fractions of total mass despite these limitations an accurate survey of pgm from different deposit types would have significant value towards developing deposit models and respective exploration strategies in this study we present results for a comprehensive evaluation of pgm at four copper pge occurrences hosted within separate but co genetic gabbro or troctolite intrusions in the coldwell alkaline complex and confirm that accurate surveys are possible with sufficient sample material and efficient pgm concentration methods the pgm concentration methods used include 1 hydroseparation of sieved size fractions of pulverized material and 2 panning of grain separates produced by electric pulse disaggregation of drill core specimens a favourable comparison of the results has verified the reliability of each method and added confidence that the pgm assemblages identified at three of the four locations are fully characterized precious metal mineral pmm assemblages are determined for the main zone and w horizon at the marathon deposit and the main zones at each of the geordie lake deposit and area 41 occurrence a total of 10 824 pmm grains pge and au ag and 68 mineral species including 16 unknown minerals were identified of which 768 grains and 31 species occur at the main zone 523 grains and 41 species at area 41 9485 grains and 43 species at w horizon and 56 grains and 12 species at geordie lake the pmm are grouped as follows pd ge pge s as pt fe alloy pd cu pb au pd ni s pd pt sn pt as pd as pd pt sb as pd pt bi te and au ag all of the deposits were found to contain similar proportions of pd pt sb as pd pt bi te and au ag minerals but the w horizon and area 41 are distinguished from the marathon main zone and geordie lake deposits by the presence of minerals in the pge s as pt fe alloy pd cu pb au and pd ge groups taken together the pmm assemblages for deposits in the coldwell exhibit a strong correlation to pge enrichment relative to the range for mantle cu pd values 1000 10 000 and there is no relationship between the abundances of pd pt bi te and pd pt sb as minerals that are commonly associated with hydrous phases and the intensity of hydrothermal alteration thus minerals found only at the w horizon and area 41 where significant pge upgrading has occurred including pt fe alloys rustenburgite marathonite palladogermanide unknown rh ni fe sulfide au pd cu alloy braggite coldwellite laurite zvyagintsevite laflammeite and unknown phases pd 5 as 2 pd 3 as pd 3 as pb bi might be considered as index minerals for pge enriched types of mineralization in the coldwell

cosmogenically enabled sediment budgeting we used 10 be and 26 al to constrain the millennial scale sedi ment and nuclide budget for a common long studied but poorly understood landform in arid regions the desert piedmont we sampled the chemehuevi mountain piedmont a complex multi surfaced landform in the mojave desert western united states the nuclide data indicate that sediment is produced more rapidly 1 1 3 10 5 kg yr 21 km 22 in steep mountain source basins than on the low gradient pediment 4 0 3 10 4 kg yr 21 km 22 or the intra piedmont mountain range 2 5 3 10 4 kg yr 21 km 22 however the bulk of the sediment in transport is derived from erosion of the large abandoned alluvial surface 3 9 3 10 4 kg yr 21 km 22 the combination of mass and nuclide budgeting suggests that sediment transport speeds decrease downslope from tens of meters per year in confined channels on the proximal pediment to decimeters per year in unconfined distributaries on distal wash surfaces the sed iment and nuclide budgeting approach we use is particularly valu able in arid regions where geomorphically significant events are infrequent and dating control is poor thus confounding traditional sediment budgeting techniques

nickel copper occurrences in the belleterre angliers belt of the pontiac subprovince and the use of cu pd ratios in interpreting platinum group element distributions within the belleterre angliers greenstone belt of the pontiac subprovince there are a number of ni cu sulfide occurrences associated with synvolcanic gabbros the stratigraphy and geochemistry of the belt suggest that it is a rifted island arc and that the gabbros which contain the ni cu sulfides were derived from the mantle plume that rifted the island arc the conditions under which the sulfides formed may be modeled either by recalculating the sulfide compositions to 100 percent sulfide or by using the cu pd ratios both approaches suggest that most of the sulfide occurrences formed from an enriched morb magma with r factors of 200 to 1 000 one of the occurrences la force is depleted in platinum group elements pge relative to cu and this depletion may be the result of the removal of sulfides from the magma prior to emplacement at this stratigraphic level the advantage of using the cu pd ratio rather than recalculating to 100 percent sulfide is that it is not necessary to have s analyses to model the conditions of formation of the sulfides further the cu pd ratio may be used as a prospecting tool rocks with ratios greater than mantle values formed from magmas depleted in pd possibly due to removal of sulfide from the magma this implies the potential for a pge bearing sulfide deposit at stratigraphically lower levels such an approach has been applied to pge targets in the eastern abitibi subprovince samples from four ni cu occurrences with cu pd ratios close to mantle ratios have the potential to produce pge as a by product samples from seven ni cu sulfide occurrences and the layered intrusions lac dore bell river and cummings complex have cu pd ratios much greater than mantle ratios indicating that these intrusions and sulfides are not good targets for pge at this stratigraphic level although there may be pge rich sulfides present at depth

highly siderophile and strongly chalcophile elements in magmatic ore deposits an ore deposit by definition must be economically viable that is to say it must contain sufficient material at high enough grade to make it possible to mine and process it at a profit bates and jackson 1987 this requires the elements to be collected and concentrated by some phase and for them to be deposited close to the surface of the earth at the oxygen fugacities found in the crust native fe is not normally stable and thus the highly siderophile elements defined as ru rh pd re os ir pt and au cannot behave as siderophile elements except in rare cases such as on disko island klock et al 1986 where the magma is sufficiently reduced for native fe to be present however if mafic magmas become saturated in a base metal sulfide liquid the highly siderophile elements behave as highly chalcophile elements table 1 thus these elements are generally found in association with base metal sulfide minerals which crystallized from a magmatic sulfide liquid namely pyrrhotite pentlandite chalcopyrite cubanite pyrite an exception to this is au although au is strongly chalcophile and is produced as a by product from many platinum group element pge deposits table 2 most primary au deposits consist of native au groves et al 1998 these will not be discussed in this chapter there are many pge deposits i e accumulations of pge minerals and base metal sulfides containing pge bates and jackson 1987 around the world but most of these do not constitute pge ore deposits because they are either too small or their grade is too low or other political or infrastructure factors prevent the economic exploitation of the deposit bates and jackson 1987 for the purpose of this work we have defined pge ore deposits as those which have significant production 2 of the annual world

deep transient slow slip detected by survey gps in the region of atacama chile we detected a long term transient deformation signal between 2014 and 2016 in the atacama region chile using survey global positioning system gps observations over an 150 km along strike region survey gps measurements in 2014 and 2016 deviate significantly from the interseismic trend estimated using previous observations this deviation from steady state deformation is spatially coherent and reveals a horizontal westward diverging motion of several centimeters along with a significant uplift it is confirmed by continuous measurements of recently installed gps stations we discard instrumental hydrological oceanic or atmospheric loading effects and show that the transient is likely due to deep slow slip in the transition zone of the subduction interface 40 to 60 km depth in addition daily observations recorded by a continuous gps station operating between 2002 and 2015 highlight similar transient signals in 2005 and 2009 suggesting a recurrent pattern

cu isotope systematics of conduit type cu pge mineralization in the eastern gabbro coldwell complex canada chalcopyrite from the cu pge sulfide deposits in the eastern gabbro coldwell complex canada exhibit a 2 variation in 65cu in the marathon deposit the 65cu of chalcopyrite increases from the lower footwall zone 1 49 to 0 75 to the main zone 1 04 to 0 08 to the upper w horizon 0 35 to 1 07 in the northern deposits chalcopyrite at four dams and sally have 65cu that range from 0 08 to 0 47 and 0 59 to 0 05 respectively notably samples from the marathon deposit with lower chalcopyrite 65cu values tend to have higher s se and cu pd ratios integrated geological and geochemical evidence suggests that secondary hydrothermal alteration and redox processes are unlikely to have been the primary causes of the observed cu isotope variation numerical modeling of 65cu cu pd s se of mineralization in the eastern gabbro illustrates three key aspects of cu isotope behavior in magmatic ni cu pge systems first r factors less than 10 000 can exhibit significant control on the 65cu of sulfides second sulfide liquid silicate melt fractionation factors for cu 65cusul sil greater than 0 5 are applicable to ni cu pge systems third sulfide segregation exhibits no measurable control on the 65cu of sulfides at degrees of fractionation typical of ni cu pge systems 0 3 in the marathon deposit the range of 65cu s se cu pd is attributed to the addition of archean sedimentary cu to a pool of sulfide liquid located at depth followed by progressive dilution of the contaminated 65cu s se signature and decrease in cu pd ratio by influxes of uncontaminated pulses of magma i e increasing r factor some of which had cu isotope compositions heavier than the mantle variably contaminated and enriched with respect to pd sulfides from this pool were entrained by magma pulses and emplaced to form the marathon deposit this contribution demonstrates that cu isotopes can fractionate at high temperatures and when combined with other geochemical proxies can be valuable in characterizing magmatic post magmatic processes in ni cu pge sulfide deposits and for identifying pge rich sulfide deposits

the effect of trapped liquid crystallization on cumulus mineral compositions in layered intrusions a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates the calculation assumes local equilibrium between phases and that the system remains chemically closed during crystallization of the trapped liquid the latter assumption is held to be valid on a scale of tens to hundreds of centimeters it is not necessary to know the composition of the trapped liquid as the calculation only requires an estimate of feo content and trapping temperature the change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the trapped liquid shift its magnitude depends on the modal proportions of cumulus phases and the initial porosity and is only weakly dependent on initial phase compositions trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization crystallization of 30 trapped liquid gives rise to shifts of up to 10 mol percent in mg number of olivine or pyroxene the size of the shift becomes greater when the initial cumulus assemblage has a lower total feo mgo content and vice versa as a result of the relationship between trapped liquid shift and cumulus mode mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals for example in a cyclic unit grading from a pyroxenitic base to an anorthositic top crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle as has been observed in the upper critical zone of the bushveld complex

nucleation of stick slip instability within a large scale experimental fault effects of stress heterogeneities due to loading and gouge layer compaction geodetic observations and large scale laboratory experiments show that seismic instability is preceded by slow slip within a finite nucleation zone in laboratory experiments rupture nucleation is studied mostly using bare rock interfaces whereas upper crustal faults are typically filled with gouge to investigate effects of gouge on rupture nucleation we performed a biaxial shearing experiment on a 350 mm long saw cut fault filled with gypsum gouge at room temperature and a minimum horizontal stress 2 0 3 5 mpa the gouge layer was sandwiched between polymethylmethacrylate pmma plates for reference also a fault without gouge was deformed strain gauges and digital image correlation were used to monitor the deformation field along the fault zone margins stick slip behavior occurred on both the gouge filled fault and the pmma fault nucleation of instability on the pmma fault persistently occurred from one location 2 3 to 3 4 along the fault adjacent to a slow slip zone at the fault end but nucleation on the gouge filled fault was more variable nucleating at the ends and or at approximately 2 3 along the fault with precursory slip occurring over a large fraction of the fault nucleation correlated to regions of high average fault stress ratio n which was more variable for the gouge filled fault due to small length scale variations in normal stress caused by heterogeneous gouge compaction rupture velocities and slip rates were lower for the gouge filled fault than for the bare pmma fault stick slip persisted when 2 was lowered and the nucleation zone length increased expanding from the center to the sample ends before transitioning into instability

multiband array detection and location of seismic sources recorded by dense seismic networks we present a new methodology for detection and space time location of seismic sources based on multiscale frequency selective coherence of the wave field recorded by dense large scale seismic networks and local antennas the method is designed to enhance coherence of the signal statistical features across the array of sensors and consists of three steps signal processing space time imaging and detection and location the first step provides for each station a simplified representation of seismic signal by extracting multiscale non stationary statistical characteristics through multiband higher order statistics or envelopes this signal processing scheme is designed to account for a priori unknown transients potentially associated with a variety of sources e g earthquakes tremors and to prepare data for a better performance in posterior steps following space time imaging is carried through 3 d spatial mapping and summation of station pair time delay estimate functions this step produces time series of 3 d spatial images representing the likelihood that each pixel makes part of a source detection and location is performed in the final step by extracting the local maxima from the 3 d spatial images we demonstrate the efficiency of the method in detecting and locating seismic sources associated with low signal to noise ratio on an example of the aftershock earthquake records from local stations of international maule aftershock deployment in central chile the performance and potential of the method to detect locate and characterize the energy release associated with possibly mixed seismic radiation from earthquakes and low frequency tectonic tremors is further tested on continuous data from southwestern japan

the eagle and east eagle sulfide ore bearing mafic ultramafic intrusions in the midcontinent rift system upper michigan geochronology and petrologic evolution 1 the eagle and east eagle intrusions are small subvertical dike like mafic ultramafic bodies that cut proterozoic sedimentary strata in the baraga basin in northern michigan the eagle intrusion hosts a newly discovered magmatic ni cu pge deposit the nearby east eagle intrusion also contains sulfide mineralization but the extent of this mineralization has yet to be determined by further drilling both intrusions contain olivine bearing rocks such as feldspathic peridotite melatroctolite and olivine melagabbro sulfide accumulations range from disseminated at both eagle and east eagle to semimassive and massive at eagle u pb baddeleyite dating gives a crystallization age of 1107 2 5 7 ma for the eagle intrusion coeval with eruption of picritic basalts at the base of the volcanic succession in the midcontinent rift system mrs the fo contents of olivine cores in the eagle and east eagle intrusions vary between 75 and 85 mol higher than those of olivine in larger layered intrusions in the mrs such as the duluth complex the feo mgo ratios and al2o3 contents of the parental magmas for the eagle and east eagle intrusions inferred from olivine and spinel compositions are similar to those of picritic basalts in the base of the mrs volcanic succession these petrochemical data suggest that the eagle and east eagle intrusions are the intrusive equivalents of high mgo basalts that erupted in the early stages of continental magmatism associated with the development of the rift variations in mineral compositions and incompatible trace element ratios suggest that at least three major pulses of magmas were involved in the formation of low sulfide rocks in the eagle intrusion lower fo contents of olivine associated with semimassive sulfides as compared to that of olivine in low sulfide rocks suggest that the magma associated with the semimassive sulfide was more fractionated than the parental magmas of the low sulfide rocks in the eagle intrusion accumulation of suspended olivine crystals and sulfide droplets from ascending magmas as they passed through wide parts of the conduits at eagle and east eagle played a critical role in the genesis of olivine rich rocks and sulfide ores in the intrusions the eagle ni cu pge deposit typifies the conduit style of magmatic sulfide deposition that is associated with continental basaltic magmatism

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

earthquake nucleation size evidence of loading rate dependence in laboratory faults recent gps observations of major earthquakes such as the 2014 chile megathrust show a slow pre slip phase releasing a significant portion of the total moment ruiz et al 2014 despite advances from theoretical stability analysis rubin ampuero 2005 ruina 1983 and modeling kaneko carpenter nielsen 2017 it is not fully understood what controls the prevalence and the amount of slip in the nucleation process here we present laboratory observations of slow slip preceding dynamic rupture where we observe a dependence of nucleation size and position on the loading rate laboratory equivalent of tectonic loading rate the setup is composed of two polycarbonate plates under direct shear with a 30 centimeters long slip interface the results of our laboratory experiments are in agreement with the pre slip model outlined by ellsworth and beroza 1995 and observed in laboratory experiments latour schubnel nielsen madariaga vinciguerra 2013 nielsen taddeucci vinciguerra 2010 ohnaka kuwahara 1990 which show a slow slip followed by an acceleration up to dynamic rupture velocity however further complexity arises from the effect of 1 rate of shear loading and 2 inhomogeneities on the fault surface in particular we show that when the loading rate is increased from 10 2 mpa s 1 to 6 mpa s 1 the nucleation length can shrink by a factor of three and the rupture nucleates consistently on higher shear stress areas the nucleation lengths measured fall within the range of the theoretical limits lb and l derived by rubin and ampuero 2005 for rate and state friction laws

imaging of seismogenic asperities of the 2016 ml 6 0 amatrice central italy earthquake through dynamic rupture simulations numerical simulations are carried out for the dynamic rupture and wave propagation process of the 24th august 2016 ml 6 0 amatrice italy earthquake using a boundary domain method bdm a hybrid method of boundary integral equation and finite difference methods dynamic rupture parameters of two seismogenic asperities are searched by iterative search through the comparison of the near field ground motions the preferred models indicate two asperities aligned at around 4 5 km depth and separated from each other as well as from the initial rupture point this requires a few supplementary patches connecting them and that are less energetic than the asperities the asperities are characterized by a radius of 2 3 km in the south first to rupture and of 2 4 km in the north second to rupture and the corresponding fracture energies of the asperities are 25 35 0 63 1012 j and 38 05 7 91 1012 j respectively these values are consistent with the scaling relation extrapolated from various analyses of large earthquakes although the parameter space of the search is limited due to the numerical performance of the dynamic rupture simulation the proposed simple characterization of the earthquakes source confirms the scaling relation in fracture energy of the seismogenic asperities which is essential for constructing mechanical earthquake source models

determination of bedload transport using naturally magnetic tracers first experiences at squaw creek gallatin county montana pebbles and cobbles constitute an important part of the sediment discharge of many streams data on the movement of this coarse bedload is important to a variety of studies including analysis of total sediment yield resevoir filling rates bridge erosion and trout spawning habitat despite the importance of knowledge regarding coarse bedload transport measurement remains difficult and unreliable a new detector has been constructed which records the movement of naturally magnetic pebbles and cobbles the detector was installed at a log sill in the bed of squaw creek gallatin county montana to evaluate the detector under natural conditions during a flood in may 1981 the detector recorded the passage of magnetic particles larger than 32 mm extrapolation of the data allows estimation of total bedload transport based on the composition of an unvegetated gravel bar upstream of the detector and on measurements of turbidity during the flood bedload accounted for approximately 66 of the solid material leaving the drainage basin since many coarse bed streams probably contain material as magnetic as the andesitic rocks in squaw creek the procedure should be widely applicable

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

geochemical stratigraphy of the keweenawan midcontinent rift volcanic rocks with regional implications for the genesis of associated ni cu co and platinum group element sulfide mineralization the development of the north american midcontinent rift can be understood in the context of a tectonic and magmatic event in which the far field effects of continental drift influenced magmatism produced by a mantle plume we report and interpret new data for samples collected from stratigraphically controlled sequences of basaltic rocks in the osler volcanic group and the mamainse point volcanic group in ontario canada we confirm that the earliest phase of rift development involved primitive melts that produced basalts in the lower formation of the osler volcanic group with fo74 80 olivine 1 490 2 280 ppm ni the earliest basalts are primitive in both the mamainse point volcanic group and osler volcanic group sections with elevated mgo cr and ni these rocks also have high tio2 and high gd yb which are features that indicate low degrees of melting of a garnet bearing lherzolite mantle the central formation a and b basalts of the osler volcanic group that overlie the lower formation lavas record an upward increase and then decrease in the degree of contamination of basaltic rocks with normal ni and platinum group element pge abundance levels that require no sulfide saturation event to accompany contamination the upper formation of the osler volcanic group is characterized by a limited number of pge depleted flows although these basalts are highly fractionated and typically develop textures with stellate to laminated plagioclase feldspar they are usually not significantly contaminated the lower and upper formations of the mamainse point volcanic group show a diversity in geochemistry consistent with contributions from different mantle sources but contamination is restricted to a small number of flows with normal ni and pge abundance levels there is no indication of a regional metal depletion signature on the scale of the nadezhdinsky formation at noril sk but there is evidence that local s saturation events were triggered in the unexposed conduits feeding some of the upper sequence flows in response to fractionation of the magma massive to heavy disseminated ni cu pge sulfide mineralization in the midcontinent rift is hosted by small primitive intrusions that were formed early in the evolution of the rift and are typically associated with transtensional structures in the cratonic blocks adjacent to the main rift examples include the eagle deposit in michigan the tamarack mineralization in minnesota and the current lake complex in ontario the american examples are associated with splays of the great lakes tectonic zone and the canadian example is associated with the quetico fault zone the intrusions share the geochemical fingerprints of the more primitive lowermost volcanic rocks of the midcontinent rift and they are broadly contemporaneous with the development of the lower stratigraphy of the osler volcanic group and mamainse point volcanic group although the low grade but large tonnage cu ni pge deposits of the duluth were formed significantly later than the small primitive intrusions their host rocks share the same lithophile trace element signature as these early intrusions the parental magmas that produced all of these intrusions were derived from deeper mantle depths where garnet was a stable phase than the magmas that produced the central formation basalts and some of the upper formation basalts investigated in this study

the transport of gravel in an ephemeral sandbed river the channel dynamics of an ephemeral sandbed river the metsemotlhaba in southeast botswana were studied over a five year period using tagged magnetic particles of pebble and cobble size scour chains and topographic cross sections with particular emphasis on the three dimensional dispersal of gravels patterns of scour and fill and depth of active layer two major flow events of equivalent magnitude occurred moving the tagged particles in december 1987 a mean distance of 837 m at a mean burial depth of 0 40 m and in march 1991 a mean distance of 263 m at a mean burial depth of 0 39 m the volume of mobile sediment based on scour depth and distance of travel was 2 7 times greater in the december 1987 event in which the mean scour depth was almost twice the mean burial depth of the tagged particles the distribution of distance of movement was asymmetrical in this first flood when the tracer started from a surface location but was monotonic thereafter intervening small to medium events yielded limited tracer movement with a mean burial depth equivalent to depth of scour the tracer moved in the low and transitional flow regimes burial depth distribution followed the gamma model field data confirm that longitudinal transport is independent of particle size and shape and strongly skewed with respect to distance whilst depths of scour in excess of 1 m for high magnitude events suggest that scour values predicted from the empirical equation of leopold et al underestimate by an order of magnitude copyright 1999 john wiley sons ltd

high precision u pb geochronology in the minnesota river valley subprovince and its bearing on the neoarchean to paleoproterozoic evolution of the southern superior province high precision u pb ages have been obtained for high grade gneisses late kinematic to postkinematic granitic plutons and a crosscutting mafic dike of the archean minnesota river valley tectonic subprovince at the southern ramparts of the superior craton of north america the antiquity of the minnesota river valley terranes is confirmed by a high precision u pb zircon age of 3422 2 ma for a tonalitic phase of the morton gneiss voluminous late kinematic monzogranites of the benson ortonville granite and morton sacred heart granite blocks yield identical crystallization ages of 2603 1 ma illustrating the synchrony and rapidity of deep crustal melting and plutonism throughout the minnesota river valley terranes postkinematic 2591 2 ma syenogranites and aplitic dikes in both blocks effectively constrain the final penetrative deformation of the minnesota river valley subprovince monazite growth from 2609 to 2595 ma in granulitic paragneisses of the benson and montevideo blocks is interpreted to record prograde to peak granulite facies metamorphic conditions associated with crustal thickening and magmatism neoarchean metamorphism and plutonism are interpreted to record the timing of collisional accretion and terminal suturing of the mesoarchean continental minnesota river valley terranes to the southern margin of the superior province along the western great lakes tectonic zone subsequent paleoproterozoic rifting of this margin is recorded by voluminous basaltic dike intrusion expressed in the minnesota river valley by major wnw trending tholeiitic diabase dikes dated at 2067 1 ma only slightly younger than the structurally and geochemically similar 2077 4 ma fort frances kenora kabetogama dike swarm of northern minnesota and adjoining canada

the geordie lake intrusion coldwell complex ontario a palladium and tellurium rich disseminated sulfide occurrence derived from an evolved tholeiitic magma the geordie lake intrusion is a small body of sulfide bearing mafic rocks that has intruded contemporaneous syenites of the coldwell alkaline complex northwestern ontario the intrusion consists of alternating layers of troctolite containing dendritic olivines and ophitic gabbros cumulate rocks are absent and the rocks are interpreted to be a series of rapidly cooled intrusions of tholeiitic basaltic magma compositional data are presented for olivine plagioclase alkali feldspar clinopyroxene amphibole magnetite and ilmenite these data together with whole rock major and trace element analyses demonstrate that the geordie lake magma was relatively evolved at the time of emplacement the formation of secondary amphiboles and biotite together with low equilibration temperatures calculated for coexisting fe ti oxides demonstrates that extensive deuteric subsolidus reequilibration has occurred sulfides consist principally of disseminated chalcopyrite associated with minor bornite pyrite millerite cobaltite siegenite sphalerite and galena tellurides hessite melonite altaite and platinum group minerals are associated primarily with disseminated chalcopyrite and are rare in late stage massive chalcopyrite the platinum group minerals are dominantly palladium tellurides and arsenides rare sperrylite is the only platinum mineral present textural relationships suggest that rapid cooling of the magma and crystallization of olivine and magnetite induced the early separation of an immiscible sulfide melt this melt remained as a liquid until the silicate host rocks had cooled to subsolidus temperatures during the final stages of crystallization of the silicate magma the sulfide melt and residual water rich fluids were trapped together within pore spaces crystallization of ti poor magnetite tellurides and platinum group minerals from the sulfide melt occurred at low temperatures 550 degrees c the fugacities of sulfur and tellurium prevailing during crystallization of the sulfide melt are estimated from predominance diagrams pyrrhotite pentlandite and ir os and rh based minerals are absent from the sulfide assemblage the predominance of pd and cu tellurides and sulfides coupled with low pt pt pd and high cu cu ni ratios suggests that the geordie lake platinum group minerals sulfide assemblage crystallized from a relatively evolved sulfide melt associated with an evolved tholeiitic magma

anatomy of the andean subduction zone three dimensional density model upgraded and compared against global scale models summary we present an upgraded version of a previously published 3 d density model of the andean subduction zone between 18 s and 45 s this model consists of 3 d bodies of constant density which geometry is constrained by independent seismic data and is triangulated from vertical cross sections these bodies define the first order morphology and internal structure of the subducted nazca slab and south american plate the new version of the density model results after forward modelling the bouguer anomaly as computed from the most recent version of the earth gravitational model egm2008 the 3 d density model incorporates new seismic information to better constrain the geometry of the subducted slab and continental moho cmh and has a trench parallel resolution doubling the resolution of the previous model as an example of the potential utility of our model we compare the geometry of the subducted slab and cmh against the corresponding global models slab1 0 and crust2 0 respectively this exercise demonstrates that although global models provide a good first order representation of the slab and upper plate crustal geometries they show large discrepancies up to 40 km with our upgraded model for some well constrained areas the geometries of the slab lithosphere asthenosphere boundary below the continent cmh and intracrustal density discontinuity that we present here as supporting information can be used to study andean geodynamic processes from a wide range of quantitative approaches

distinguishing intraplate from megathrust earthquakes using lacustrine turbidites subduction zone seismicity arises from megathrust crustal and intraslab earthquakes and understanding the recurrence patterns of each type is crucial for hazard assessments lake sediments can record earthquakes from all three seismogenic sources here we studied the turbidite record of lo encanado an andean lake located in central chile we show that lo encanado turbidites can be attributed to 1 subaquatic slope failure by earthquake shaking coseismic phase 2 floods or human impact and 3 postseismic catchment response all historical events with shaking intensities vi modified mercalli intensity have triggered coseismic turbidites but only the intraplate earthquakes triggered subaerial slope failures followed by postseismic turbidites we argue that this contrasting result is due to different spectra of seismic waves from these earthquake sources higher frequency accelerations from intraplate earthquakes are hardly attenuated in rocks around the lake whereas lower frequency accelerations from megathrust earthquakes are amplified in soft lake sediments we tested our findings by comparing acceleration response spectra of recent and historical intraslab and megathrust earthquakes along a longitudinal profile results suggest that the location of andean lakes is ideal to distinguish earthquake sources

platinum group elements in sulphide minerals platinum group minerals and whole rocks of the merensky reef bushveld complex south africa implications for the formation of the reef the concentrations of platinum group elements pge co re au and ag have been determined in the base metal sulphide bms of a section of the merensky reef in addition we performed detailed image analysis of the platinum group minerals pgm the aims of the study were to establish 1 whether the bms are the principal host of these elements 2 whether individual elements preferentially partition into a specific bms 3 whether the concentration of the elements varies with stratigraphy or lithology 4 what is the proportion of pge hosted by pgm 5 whether the pgm and the pge found in bms could account for the complete pge budget of the whole rocks in all lithologies most of the pge 65 up to 85 are hosted by pgm essentially pt fe alloy pt pd sulphide pt pd bismuthotelluride lesser amounts of pge occur in solid solution within the bms in most cases the pgm occur at the contact between the bms and silicates or oxides or are included within the bms pentlandite is the principal bms host of all of the pge except pt and contains up to 600 ppm combined pge it is preferentially enriched in pd rh and co pyrrhotite contains rh os ir and ru but excludes both pt and pd chalcopyrite contains very little of the pge but does concentrate ag and cd platinum and au do not partition into any of the bms instead they occur in the form of pgm and electrum in the chromitite layers the whole rock concentrations of all the pge except pd are enriched by a factor of five relative to s ni cu and au this enrichment could be attributed to bms in these layers being richer in pge than the bms in the silicate layers however the pge content in the bms varies only slightly as a function of the stratigraphy the bms in the chromitites contain twice as much pge as the bms in the silicate rocks but this is not sufficient to explain the strong enrichment of pge in the chromitites in the light of our results we propose that the collection of the pge occurred in two steps in the chromitites some pgm formed before sulphide saturation during chromitite layer formation the remaining pge were collected by an immiscible sulphide liquid that percolated downward until it encountered the chromitite layers in the silicate rocks pge were collected by only the sulphide liquid

controls on the t phase energy fluxes recorded on juan fernandez island by continental seismic wave paths and nazca bathymetry conicyt pcha doctorado nacional 2017 21171480 prs programa de riesgo sismico universidad de chile fondecyt 1170430

effects of fo2 fs2 temperature and melt composition on fe ni exchange between olivine and sulfide liquid implications for natural olivine sulfide assemblages the apparent equilibrium constant for the exchange of fe and ni between coexisting olivine and sulfide liquid kd xnis xfes liquid xnisi12o2 xfesi12o2 olivine xi mole fraction has been measured at controlled oxygen and sulfur fugacities fo2 10 8 1 to 10 10 and fs2 10 0 9 to 10 1 7 over the temperature range 1200 to 1385 c with 5 to 37 wt ni and 7 to 18 wt cu in the sulfide liquid at log fo2 of 8 7 0 1 and log fs2 of 0 9 to 1 7 kd is relatively insensitive to sulfur fugacity but comparison with previous results shows that kd increases at very low sulfur fugacities kd values show an increase with the nickel content of the sulfide liquid but this effect is more complex than found previously and is greatest at log fo2 of 8 1 lessens with decreasing fo2 and kd becomes independent of melt ni content at log fo2 9 5 the origin of this variation in kd with fo2 and fs2 is most likely the result of nonideal mixing of fe and ni species in the sulfide liquid such behavior causes activity coefficients to change with either melt oxygen content or metal sulfur ratio effects that are well documented for metal rich sulfide melts application of these experimental results to natural samples shows that the relatively large dispersion that exists in kd values from different olivine sulfide saturated rock suites can be interpreted as arising from variations in fo2 fs2 and the nickel content of the sulfide liquid estimates of fo2 based on kd and sulfide melt composition in natural samples yields a range from fayalite magnetite quartz fmq 1 to fmq 2 or lower which is in good agreement with previous values determined for oceanic basalts that use glass ferric ferrous ratios anomalously high kd values recorded in some suites such as disko island probably reflect low fs2 during sulfide saturation which is consistent with indications of low fo2 for those samples it is concluded that the variation in kd values from natural samples reflects olivine sulfide melt equilibrium at conditions within the t fo2 fs2 range of terrestrial mafic magmas

seismic stereometry reveals preparatory behavior and source kinematics of intermediate size earthquakes although moderate size earthquakes are poorly studied by lack of near fault observations they can provide key information about larger damaging earthquakes here we propose a new approach inspired by double difference relocation that uses high coherency waveforms recorded at neighboring sensors to study the preparation phase and dynamics of moderate size earthquakes we validate this technique by analyzing the 2016 m w 5 2 borrego springs earthquake in southern california and find consistent rupture velocities of 2 km s highlighting two main rupture asperities the analysis of the 2019 ml5 2 le teil earthquake in france reveals slow nucleation at depth that migrates to the surface and propagates northward with a velocity of 2 8 km s highlighting two main rupture events also imaged by insar by providing unprecedented resolution in our observation of the rupture dynamics this approach will be useful in better understanding the preparation phase and rupture of both tectonic and induced earthquakes plain language summary small and moderate size earthquakes are much more numerous yet studied in much less detail than large and damaging earthquakes this is because to study small earthquakes precisely one needs seismometers very close to the rupture which is rarely the case it is still unclear if small and large earthquakes start the same way thus studying more systematically small earthquakes could help to answer this question here we show that we can use two close by seismometers as we would do with 3 d glasses to observe with a stereoscopic effect the evolution of intermediate size earthquakes when they rupture along a fault we can retrieve the direction of rupture the speed at which the fault breaks and the length of the rupture important parameters that help to characterize the earthquakes using this new method we can sometimes also observe the behavior of the fault before the main rupture which will be useful to better understand how earthquakes start

an 8 month slow slip event triggers progressive nucleation of the 2014 chile megathrust the mechanisms leading to large earthquakes are poorly understood and documented here we characterize the long term precursory phase of the april 1st 2014 mw8 1 north chile megathrust we show that a group of coastal gps stations accelerated westward eight months before the mainshock corresponding to a mw6 5 slow slip event on the subduction interface 80 of which was aseismic concurrent interface foreshocks underwent a diminution of their radiation at high frequency as shown by the temporal evolution of fourier spectra and residuals with respect to ground motions predicted by recent subduction models such ground motions change suggests that in response to the slow sliding of the subduction interface seismic ruptures are progressively becoming smoother and or slower the gradual propagation of seismic ruptures beyond seismic asperities into surrounding metastable areas could explain these observations and might be the precursory mechanism eventually leading to the mainshock

the influence of country rock assimilation and silicate to sulfide ratios r factor on the genesis of the dunka road cu ni platinum group element deposit duluth complex minnesota the dunka road deposit is one of several cu ni platinum group element pge sulfide occurrences found along the northwestern margin of the duluth complex where the host troctolitic rocks are in contact with metasedimentary rocks of the animikie group magma contamination through assimilation of sulfidic argillaceous country rocks is generally recognized as having played a key role in the genesis of the mineralization three main types of disseminated sulfide mineralization have been identified within the dunka road deposit i norite hosted sulfides ii troctolite hosted sulfides and iii pge rich sulfide horizons the norite hosted sulfides are found either adjacent to country rock xenoliths or near the basal contact the troctolite hosted sulfides form the bulk of the deposit and occur throughout the lower 250 m of the intrusion the pge rich sulfide horizons are typically localized directly beneath ultramafic layers the composition of the different types of sulfide occurrences is modelled using cuipd ratios it is shown that each type results from the interplay of two main parameters namely the degree of magma contamination and the silicate magma to sulfide melt ratio r factor the norite hosted sulfides formed at low r factors and high degrees of contamination as expressed by their pge depleted nature low seis ratios and elevated content in pyrrhotite and arsenide minerals the troctolite hosted sulfides formed at moderate r factors and small degrees of contamination as shown by their moderate pge content and mantle like seis ratios finally the pge rich sulfide horizons are modelled using elevated r factors from an uncontaminated parental magma which is substantiated by their elevated noble metal content and seis ratios and low pyrrhotite to precious metal sulfide ratio le gite de dunka road est un parmi plusieurs gites de sulfures de cu ni elements du groupe du platine egp trouves le long de la bordure nord ouest du complexe de duluth ou les roches hotes troctolitiques sont en contact avec les roches metasedimentaires du groupe d animikie il est generalement reconnu que la contamination du magma par l assimilation de roches argileuses sulfurees encaissantes a joue un role capital dans la genese de la mineralisation trois types principaux de mineralisation de sulfures dissemines ont ete identifies dans le gite de dunka road i sulfures dans la norite hote ii sulfures dans la troctolite hote et iii horizons de sulfures enrichis en egp les sulfures dans la norite hote apparaissent soit dans les zones adjacentes aux xenolites encaissants ou pres du contact basal les sulfures dans la troctolite hote forment le plus gros du gisement et ils apparaissent dans les 250m inferieurs de l intrusion la localisation typique des horizons de sulfures enrichis en egp se trouve directement sous les couches ultramafiques les rapports cu pd ont ete utilises pour elaborer un modele de la composition des differents types de mineralisation de sulfures il est demontre que chaque type resulte de l interaction de deux parametres dominants a savoir le degre de contamination du magma et le rapport du magma silicate au liquide sulfure facteur r les sulfures dans la norite hote ont ete formes sous des conditions de faibles facteurs r et de fortes contaminations comme en temoignent la teneur appauvrie en egp les faibles rapports se s et les concentrations elevees de la pyrrhotite et des mineraux arsenieux les sulfures dans la troctolite hote ont ete formes sous des conditions de facteurs r moderes et de faibles contaminations comme le revelent leur teneur modere en egp et les rapports se s analogues a ceux du manteau finalement les horizons de sulfures enrichis en egp sont modelises en utilisant des facteurs r eleves et un magma parental non contamine ce qui est appuye par leur forte teneur en elements nobles et les rapports se s eleves et par le rapport faible de la pyrrhotite sur les sulfures de metaux precieux

historical and recent large megathrust earthquakes in chile abstract recent earthquakes in chile 2014 mw 8 2 iquique 2015 mw 8 3 illapel and 2016 mw 7 6 chiloe have put in evidence some problems with the straightforward application of ideas about seismic gaps earthquake periodicity and the general forecast of large megathrust earthquakes in northern chile before the 2014 iquique earthquake 4 large earthquakes were reported in written chronicles 1877 1786 1615 and 1543 in north central chile before the 2015 illapel event 3 large earthquakes 1943 1880 1730 were reported and the 2016 chiloe earthquake occurred in the southern zone of the 1960 valdivia megathrust rupture where other large earthquakes occurred in 1575 1737 and 1837 the periodicity of these events has been proposed as a good long term forecasting however the seismological aspects of historical chilean earthquakes were inferred mainly from old chronicles written before subduction in chile was discovered here we use the original description of earthquakes to re analyze the historical archives our interpretation shows that a priori ideas like seismic gaps and characteristic earthquakes influenced the estimation of magnitude location and rupture area of the older chilean events on the other hand the advance in the characterization of the rheological aspects that controlled the contact between nazca and south american plate and the study of tsunami effects provide better estimations of the location of historical earthquakes along the seismogenic plate interface our re interpretation of historical earthquakes shows a large diversity of earthquakes types there is a major difference between giant earthquakes that break the entire plate interface and those of mw 8 0 that only break a portion of it

quantifying sediment transport on desert piedmonts using 10be and 26al in situ produced 10 be and 26 al measured in 40 sediment samples collected from the iron and granite mountain piedmonts eastern mojave desert provide a unique view of piedmont modification processes and process rates over the 10 3 to 10 5 year time scale cosmogenic nuclide based models suggest that the iron and granite mountains generate 0 11 0 13 and 0 082 0 097 m 3 of sediment per year per meter of rangefront respectively the sediment moves down the piedmont in an active transport layer atl which is 20 to 30 cm thick based on visual observations measurements of depth to a buried b horizon cosmogenic nuclide data and maximum ephemeral channel depths sediment in this layer is well mixed vertically and horizontally on the 10 2 year time scale indicating that the small ephemeral channels which dominate the piedmont surface migrate quickly interpretive models of increasing nuclide activities at depth in two pits suggest steady sediment deposition on the piedmont at rates between 17 21 and 38 45 m ma 1 until the late pleistocene epoch when a discontinuity to markedly lower nuclide activities in the isotopically well mixed active transport layer suggests that deposition stopped a significant change in piedmont behavior nuclide activities in 10 amalgamated surface samples each collected along a different 4 km long transect increase steadily away from the mountain front thus we infer that sediment is uniformly dosed by cosmic rays as it is transported down the iron and granite mountain piedmonts interpretive models suggest that long term average sediment speeds down the iron and granite mountain piedmonts are a few decimeters to a meter per year d 2002 published by elsevier science b v

seismicity controlled by a frictional afterslip during a small magnitude seismic sequence m l 5 on the chihshang fault taiwan we report evidence for frictional afterslip at shallow depths about 5 to 7 km during a small magnitude seismic sequence with ml 5 along the chihshang fault a main active structure of the longitudinal valley in southeast taiwan the afterslip which was recorded by a nearby borehole dilatometer lasted about a month with a cumulative geodetic moment magnitude of 4 8 0 2 the afterslip comprised two stages and controlled the aftershock sequence the first postseismic stage which followed a ml 4 6 earthquake lasted about 6 h and mostly controlled the ruptures of neighboring asperities e g multiplets near the hypocenter then a 4 week duration large afterslip event following a ml 4 9 earthquake controlled the rate of aftershocks during its first 2 days through brittle creep the study presents a rare case of simultaneous seismological and geodetic observations for afterslip following earthquakes with magnitude lower than 5 furthermore the geodetic moment of the postseismic phase is at least equivalent to the coseismic moment of the sequence

nucleation phase and dynamic inversion of the mw 6 9 valparaiso 2017 earthquake in central chile the valparaiso 2017 sequence occurred in the central chile mega thrust an active zone where the last mega earthquake occurred in 1730 intense seismicity started 2 days before the mw 6 9 main shock a slow trench ward movement was observed in the coastal gps antennas and was accompanied by foreshocks and repeater type seismicity to characterize the rupture process of the main shock we perform a dynamic inversion using the strong motion records and an elliptical patch approach we suggest that a slow slip event preceded and triggered the mw 6 9 earthquake which ruptured an elliptical asperity semi axis of 10 km and 5 km with a sub shear rupture stress drop of 11 71 mpa yield stress of 17 21 mpa slip weakening of 0 65 m and kappa value of 1 98 this earthquake could be the beginning of a long term nucleation phase to a major rupture within the highly coupled central chile zone where a mega thrust earthquake like 1730 is expected

isotopic insights into smoothening of abandoned fan surfaces southern california cosmogenic nuclide concentrations measured on abandoned fan surfaces along the mojave section of the san andreas fault suggest that sediment is generated transported and removed from the fans on the order of 30 40 kyr we measured in situ produced cosmogenic 10 be and in some cases 26 al in boulders n 15 surface sediment n 15 and one depth profile n 9 nuclide concentrations in surface sediments and boulders underestimate fan ages suggesting that 10 be accumulation is largely controlled by the geomorphic processes that operate on the surfaces of the fans and not by their ages field observations grain size distribution and cosmogenic nuclide data suggest that over time boulders weather into grus and the bar sediments diffuse into the adjacent swales as fans grow older the relief between bars and swales decreases the sediment transport rate from bars to swales decreases and the surface processes that erode the fan become uniform over the entire fan surface the nuclide data therefore suggest that over time the difference in 10 be concentration between bars and swales increases to a maximum until the topographic relief between bars and swales is minimized resulting in a common surface lowering rate and common 10 be concentrations across the fan during this phase the entire fan is lowered homogeneously at a rate of 10 15 mm kyr 1

residence time and crystallization history of nickeliferous olivine phenocrysts from the northern yatsugatake volcanoes central japan application of a growth and diffusion model in the system mg fe ni abstract the chemical zoning of nickeliferous olivine phenocrysts in calc alkaline andesites from the northern yatsugatake volcanoes central japan is examined by a growth and diffusion model in the system mg fe ni nickeliferous olivine phenocrysts are included in the high alumina basaltic end member magma which forms the mixed calc alkaline andesites in the northern yatsugatake volcanoes the olivine phenocrysts can be divided into three types on the basis of chemical composition zoning profile and occurrence type 1 olivine is rich in ca and mg and the zoning profile of type 1 forms a slightly more fe rich trend than the maximum fractionation trend in the nio versus forsterite content fo diagram the most mg and ni rich and mn poor core of type 1 fo 91 5 mol nio 0 40 wt mno 0 13 wt can be in equilibrium with peridotite in the upper mantle by contrast type 2 olivine is ca poor and rich in fe and ni compared to type 1 the zoning patterns of type 2 are more variable the nio content in fe rich type 2 phenocrysts decreases rapidly from core to rim within a narrow range of fo the maximum nio content of type 2 is 0 53 wt the transitional type olivine has an intermediate composition between type 1 and type 2 and a similar zoning profile as that of type 1 type 1 olivine mainly occurs as isolated phenocrysts while fe rich type 2 occurs as crystal clots the growth and diffusion calculation in the system mg fe ni revealed that the composition of normally zoned olivine is enriched in fe by diffusion without a marked depression in the ni content due to a larger fe mg interdiffusion coefficient than the ni tracer diffusion coefficient in olivine the zoning patterns of both type 1 and type 2 can be reproduced by calculation the residence time of type 1 olivine in the magma is estimated to be less than 10 0 5 1 y at 1150 1050 c whereas the residence time of fe enriched type 2 olivine is from ten to one hundred times longer than that of type 1 the long residence time and occurrence as crystal clots suggest that the fe enriched type 2 olivine phenocrysts were captured and crystallized in the crystal mush at the roof and bottom of a magma chamber

tracer pebble movement along a concave river profile virtual velocity in relation to grain size and shear stress over 1400 tracer pebbles 16 256 mm in diameter were tracked for 2 years in six reaches of allt dubhaig scotland a small gravel bed river along which shear stress and bed surface grain size decrease toward a local base level pebble movement was size selective both within and between reaches within reaches the decrease in mean travel distance with increasing grain size is strongest in the coarse tail of the size distribution particle shape has a minor secondary effect a nondimensional grain velocity averaged over the duration of competent flow is used to compare different size classes and reaches over 90 of its variance is explained by relative grain size and reach shields stress the pattern of size selectivity is consistent with single event tracer results elsewhere bedload trap data from our distal reach and the concept of partial mobility it provides a mechanism for strong downstream fining by selective transport and deposition along rivers in which stress declines toward base level the nondimensional prediction equation for grain velocity may be of use in other rivers but requires testing

geochemistry and mineralogy of platinum group element mineralization in the river valley intrusion ontario canada a model for early stage sulfur saturation and multistage emplacement and the implications for contact type ni cu pge sulfide mineralization the river valley intrusion within the 2 48 ga east bull lake intrusive suite in ontario canada is an example of a mafic igneous intrusion with contact type ni cu pge sulfide mineralization along its base whereas many contact type deposits are thought to form from in situ contamination of the magma by the addition of crustal s during emplacement there are some intrusions including the river valley intrusion which appear to have a much more complex history where the timing of s saturation and thus the critical ore genesis processes may have occurred much earlier prior to emplacement the river valley intrusion is made up of a basal 100 m of unlayered inclusion bearing units overlain by layered cumulates the basal units contain autoliths of gabbroic rocks and inclusions of footwall gneiss and amphibolites all within a gabbroic matrix platinum group element rich magmatic sulfide mineralization occurs throughout both the inclusions and the matrix as blebby and disseminated sulfides the matrix and inclusions can be separated into two distinct textural types hydrothermally altered greenschist assemblages and unaltered metamorphic amphibolite assemblages the platinum group mineral pgm assemblages vary only between textural types and not between inclusions and matrix being dominated tellurides in all rock types the hydrothermally altered rocks however have fewer tellurides and an increased amount of sb and as bearing pgm indicative of minor fluid interaction although the pgm have not been mobilized significantly away from the base metal sulfides precious and base metal geochemistry shows all rock types to have an excellent correlation between all the platinum group elements pge indicating the presence of a single well homogenized pge rich sulfide liquid however au and cu appear to be decoupled from the pge at low concentrations although correlate well with each other which is interpreted to be due to minor fluid redistribution and alteration of sulfide bleb margins the overlying layered units above the mineralized units are not pge depleted trace element data including th yb pm and nb th pm ratios demonstrate that all river valley rocks were formed from crustally contaminated magmas following interaction with local country rocks in a deeper subchamber although some samples have s se ratios indicative of crustal s most have s se ratios lower than the mantle range indicative of s loss we propose a multistage model for the formation of the mineralization in the river valley intrusion with a major contamination event at depth with the addition of s from local crustal rocks inducing sulfide saturation sulfide droplets were then enriched in pge within a conduit system with possible further upgrading of sulfide metal tenors and reduction of s se ratios via partial dissolution of sulfide the pge enriched sulfide liquid then settled in a staging chamber and partially crystallized before a major pulse of magma entrained sulfide liquid eroded blocks of precrystallized and mineralized gabbro and footwall rocks and emplaced an inclusion bearing package as the lower 100 m or so of the river valley intrusion later emplacement of main river valley magma was from an s undersaturated pge fertile magma the river valley intrusion is thus an example whereby contact type mineralization is purely a function of the earliest magma intruded containing preformed sulfide mineralization rather than contamination triggering sulfide saturation in situ in such cases processes at depth determine the generation and subsequent tenor of the mineralization in particular dissolution of the sulfide can upgrade metal tenor but subsequently will reduce s se ratios masking the signature of crustal contamination in addition a multistage emplacement such as this will not necessarily preserve the characteristic increase in cu pd ratios in the overlying cumulates that is often used in exploration for pge deposits in mafic intrusions thus a full understanding of all the field geochemical and mineralogical factors is required to construct genetic models for such deposits and especially in the interpretation of s se and cu pd ratios as an indicator of crustal contamination and the presence of pge mineralization

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

tracking painted pebbles short term rates of sediment movement on four mojave desert piedmont surfaces 1 to quantify short term sediment movement rates across mojave desert piedmonts 1600 painted and numbered pebbles were laid out in paired orthogonal 20 m lines at 4 sites and resurveyed five times over 2 years and revisited 2 years later pebble lines cross shallow 5 15 cm ephemeral channels and adjacent unconsolidated interfluves the latter being the dominant landform at all sites two sites are located on surfaces that have been or are impacted by military training activities including the use of tracked vehicles the two other sites have not been disturbed by human impact three different processes transport pebbles episodic streamflow in ephemeral channels transports a few pebbles long distances decimeters to meters down gradient bioturbation moves many pebbles small distances centimeters in any direction and vehicular disturbance transports pebbles varying distances centimeters to meters in any direction significant down gradient sediment movement occurred dominantly in channels where flowing water was concentrated interfluves were stable surfaces where little transport occurred off road vehicle use is coincident with accelerated pebble movement pebbles moved further and faster down gradient at the disturbed iron mountain and east range road sites mean speeds of 0 18 and 0 34 m yr 1 respectively than at the undisturbed chemehuevi and goldstone sites mean speeds of 0 17 and 0 02 m yr 1 respectively mean pebble movement is highly and negatively correlated with vegetation density short term pebble movement rates are several times lower than long term 103 to 104 year rates suggesting the importance of rare extreme precipitation events for sediment transport such as those of fall and winter 2004