a 2 5 g a reworked sialic crust rb sr ages and isotopic geochemistry of late archaean volcanic and plutonic rocks from e finland in east central finland archaean terrains present three main lithologic units a gneissic basement emplaced from 2 86 g a to 2 62 g a b greenstone belt 2 65 g a and c calc alkaline magmatism 2 50 g a to 2 40 g a twenty three rocks of the calc alkaline suite have been chosen for geochronologic and rb sr isotopic studies these rocks are subdivided into three groups 1 acid volcanics from luoma 2 augen gneiss from arola and 3 post kinematik pink leucogranite from arola the 2 50 0 10 g a age of the luoma volcanics indicates that they represent the upper part of a greenstone belt composed of a single sequence of volcanic rocks the ages initial 87sr 86sr isr and major element compositions of the augen gneisses of arola and suomussalmi indicate that these rocks are the plutonic equivalents of the luoma acid volcanics the arola pink leucogranite marks the terminal phase of archaean magmatic activity from 2 86 g a to 2 41 g a this was followed by at least 0 40 g a of quiescence the isr and major element compositions suggest that the genesis of the calc alkaline magmatic rocks involved crustal materials but all their geochemical features cannot be explained without the participation of mafic greenstone belt materials the first crustal components had low i and low k2o na2o ratios while the younger ones calc alkaline magmas had medium to high isr and high k2o na2o ratios thus the petrogenetic processes have changed with time from ensimatic to ensialic implying major reworking of preexisting crustal materials this evolution leads to the accretion of the continental crust from the mantle

global marine gravity from retracked geosat and ers 1 altimetry ridge segmentation versus spreading rate 1 three approaches are used to reduce the error in the satellite derived marine gravity anomalies first we have retracked the raw waveforms from the ers 1 and geosat gm missions resulting in improvements in range precision of 40 and 27 respectively second we have used the recently published egm2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean third we have used a biharmonic spline interpolation method to construct residual vertical deflection grids comparisons between shipboard gravity and the global gravity grid show errors ranging from 2 0 mgal in the gulf of mexico to 4 0 mgal in areas with rugged seafloor topography the largest errors of up to 20 mgal occur on the crests of narrow large seamounts the global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate for rates less than about 60 mm a the typical ridge segment is 50 80 km long while it increases dramatically at higher rates 100 1000 km this transition spreading rate of 60 mm a also marks the transition from axial valley to axial high we speculate that a single mechanism controls both transitions candidates include both lithospheric and asthenospheric processes

a review of gold mineralization styles in finland a wide range of styles of gold mineralization has been recognized in finland including orogenic metamorphosed epithermal skarn or epigenetic ironstone hosted intrusion related nonskarn massive sulfide hosted paleoplacer and placer deposits gold production in the past was principally as a byproduct from the mining of paleoproterozoic base metal massive sulfide deposits this situation has changed during the last decade with the closure of some base metal mines and the commencement of production from recently discovered gold only deposits gold mineralization occurred during distinct episodes of crustal evolution in finland several late archean greenstone belts in the karelian craton in eastern and northern finland contain orogenic gold deposits dated at about 2 75 to 2 70 ga suggesting a coherent and pervasive tectonic and metallogenic event in the paleoproterozoic low grade the main accretionary stage of the svecofennian orogeny in finland culminated with metamorphism and deformation between 1 89 and 1 86 ga during that time intrusion related au cu mineralization took place in both syntectonic porphyry stocks and their wall rocks in and close to the archean proterozoic margin orogenic gold mineralization took place at or slightly after the metamorphic peak throughout the svecofennian domain possibly also overprinting massive sulfide and intrusion related occurrences it is notable that the largest orogenic deposits are located within discrete plutons rather than hosted by supracrustal sequences this may be a consequence of the rheological contrasts between plutons and the supracrustal lithologies the paleoproterozoic lapland domain in the northern part of the country records a protracted and complicated evolution involving multiple episodes of rifting magmatism sedimentation and alteration culminating at around 1 9 ga with the collision of the karelian craton the svecofennian fold belt to the south and the kola craton to the north these deformational events led to orogenic gold mineralization throughout the proterozoic greenstone belts of northern finland at about 1 89 to 1 86 ga during and soon after the peak of metamorphism and deformation skarnlike or epigenetic ironstone hosted deposits were also formed during the orogeny in the western and southwestern parts of the lapland domain probably somewhat later at around 1 86 ga the most favorable sites for mineralization are regionally extensive zones of early albitization that predate gold mineralization the deposition of molasselike sediments during the terminal stages of the svecofennian orogeny and weathering of both orogenic and syngenetic sulfide mineralization also prior to 1 8 ga produced placer accumulations now paleoplacers in the conglomerates of the uppermost formation of the central lapland greenstone belt placer deposits of controversial origin and provenance have also been worked for many years in the glaciofluvial sediments of northernmost finland the areas with greatest potential for the discovery of new orogenic gold deposits in finland are the late archean and paleoproterozoic greenstone belts in eastern finland and lapland respectively some fe cu au skarns or epigenetic ironstone hosted deposits have been mined in the past and there may be potential for the discovery of larger iron oxide copper gold systems in the western central lapland greenstone belt for intrusion related nonskarn mineralization the most promising areas are close to the raahe ladoga suture and the potential for additional metamorphosed and deformed epithermal mineralization exists in the tampere schist belt the significant number of gold occurrences already known in these areas highlights the potential for new discoveries

source of metals and age constraints for epigenetic gold deposits in the skellefte and pohjanmaa districts central part of the fennoscandian shield the lead isotopic compositions of galena in early proterozoic gold deposits have been determined for three districts in northern sweden and central finland the deposits are hosted by a variety of 1870 1890 ma svecofennian host rocks including the volcanosedimentary succession within the skellefte district island arc in sweden as well as i type tonalites at jorn sweden and pohjanmaa finland the deposits are epigenetic in relation to these svecofennian rocks and are part of a goldbearing metallogenetic belt which can be followed for 600 km parallel to the southwestern margin of the archaean domain in spite of these epigenetic relationships the lead isotopic data indicate that the deposits are not dramatically younger than the 1870 1890 ma svecofennian host rocks probably not exceeding 10 20 million years two principal lead sources were activated when the gold deposits were formed the most significant source is represented by the i type tonalites which constitute a relatively primitive 9 3 and widely distributed source in the entire metallogenic belt in addition the volcanic components in the westernmost part of the skellefte district constitute an extremely primitive 9 0 source which only locally was an important contributor to the epigenetic deposits in this metallogenetic belt the significantly different lead isotopic composition estimated for these sources indicates that the volcanic rocks in the western part of the skellefte district were not comagmatic with the i type tonalites recognized at jorn and central finland

basin centered asperities in great subduction zone earthquakes a link between slip subsidence and subduction erosion 1 published areas of high coseismic slip or asperities for 29 of the largest circum pacific megathrust earthquakes are compared to forearc structure revealed by satellite free air gravity bathymetry and seismic profiling on average 71 of an earthquake s seismic moment and 79 of its asperity area occur beneath the prominent gravity low outlining the deep sea terrace 57 of an earthquake s asperity area on average occurs beneath the forearc basins that lie within the deep sea terrace in sw japan slip in the 1923 1944 1946 and 1968 earthquakes was largely centered beneath five forearc basins whose landward edge overlies the 350 c isotherm on the plate boundary the inferred downdip limit of the locked zone basin centered coseismic slip also occurred along the aleutian mexico peru and chile subduction zones but was ambiguous for the great 1964 alaska earthquake beneath intrabasin structural highs seismic slip tends to be lower possibly due to higher temperatures and fluid pressures kilometers of late cenozoic subsidence and crustal thinning above some of the source zones are indicated by seismic profiling and drilling and are thought to be caused by basal subduction erosion the deep sea terraces and basins may evolve not just by growth of the outer arc high but also by interseismic subsidence not recovered during earthquakes basin centered asperities could indicate a link between subsidence subduction erosion and seismogenesis whatever the cause forearc basins may be useful indicators of long term seismic moment release the source zone for cascadia s 1700 a d earthquake contains five large basin centered gravity lows that may indicate potential asperities at depth the gravity gradient marking the inferred downdip limit to large coseismic slip lies offshore except in northwestern washington where the low extends landward beneath the coast transverse gravity highs between the basins suggest that the margin is seismically segmented and could produce a variety of large earthquakes

sm nd and u pb dating of early proterozoic mafic felsic volcanism in northernmost sweden a sm nd mineral isochron of 1932 45 ma on a kiruna greenstone is defined by greenschist facies metamorphic minerals apparently older than the regional svecokarelian metamorphism 1880 ma however this age agrees within error with u pb zircon ages of 1909 1617 ma on quartz bearing prophyries which overlie but are in part intercalated with basic volcanics if these basic volcanics following previous studies are considered to be contemporary with the kiruna greenstones the present data suggest that eruption of both basic and acid volcanics and associated hydrothermal metamorphism took place over a short time interval close to 1 9 ga the greenstone sample is depleted in light rare earths and has high initial 145nd 144nd indicating a source in which such depletion has existed for a long time in contrast an albite diabase sample with a somewhat younger mineral age 1 80 0 08 ga is light rare earth enriched and has a correspondingly low initial nd isotopic composition

the mw 8 1 2014 iquique chile seismic sequence a tale of foreshocks and aftershocks egu2009 11040 schurr b asch g rosenau m wang r oncken o barrientos s salazar p villotte j p 2012 the 2007m7 7 tocopillanorthernchile earthquake sequence implications for along strike and downdip rupture segmentation and megathrust frictional behaviour j geophys res 117 b05305 doi 10 1029 2011jb009030 schurr b et al 2014 gradual unlocking of the plate boundary controlled the initiation of the 2014 iquique earthquake nature 512 7514 299

orogenic gold in the new lycksele storuman ore province northern sweden the palaeoproterozoic faboliden deposit abstract southwest of the well known skellefte district northern sweden a new gold ore province the so called gold line is presently being explored during the past decade a number of gold occurrences have been discovered in this area the largest known gold occurrence is the faboliden deposit late to post orogenic ca 1 81 to 1 77 ga revsund granite constitutes the main rock type in the faboliden area and surrounds a narrow belt of mineralized metagreywackes and metavolcanic rocks the supracrustal rocks are strongly deformed within a roughly n s trending subvertical shear zone the mineralization constitutes a 30 to 50 m wide n s striking steeply dipping zone the mineralization is commonly hosted by arsenopyrite bearing quartz veins within the supracrustal rocks the quartz veins parallel the main foliation in the shear zone gold is closely associated with arsenopyrite lollingite and stibnite and found in fractures and as intergrowths in the arsenopyrite lollingite gold is also seen as free grains in the silicate matrix of the host rock the proximal alteration zone displays positive correlation with ca s as ag sb sn w pb bi cd se and hg whereas k and na show a slightly negative correlation the hydrothermal mineral assemblage in the proximal alteration zone is diopside calcic amphibole biotite and minor andalusite and tourmaline this type of assemblage is commonly recognized in hypozonal orogenic gold deposits worldwide garnet biotite geothermometry indicates amphibolite facies in the faboliden area the ductile fabric that hosts the mineralization is also found in the margin of the surrounding revsund granitoid it is therefore suggested that at least the final stages of the gold mineralization are syn to late kinematic and the minimum age for the mineralization is thus constrained at ca 1 80 ga revsund age

the mejillonia suspect terrane northern chile late triassic fast burial and metamorphism of sediments in a magmatic arc environment extending into the early jurassic the mejillonia terrane named after the mejillones peninsula northern chile has been traditionally considered an early paleozoic block of metamorphic and igneous rocks displaced along the northern andean margin in the mesozoic however u pb shrimp zircon dating of metasedimentary and igneous rocks shows that the sedimentary protoliths were triassic and that metamorphism and magmatism took place in the late triassic norian field evidence combined with zircon dating detrital and metamorphic further suggests that the sedimentary protoliths were buried deformed foliated and folded and metamorphosed very rapidly probably within few million years at ca 210 ma the metasedimentary wedge was then uplifted and intruded by a late arc related tonalite body morro mejillones at 208 2 ma only a short time after the peak of metamorphism the mejillones metamorphic and igneous basement represents an accretionary wedge or marginal basin that underwent contractional deformation and metamorphism at the end of a late permian to late triassic anorogenic episode that is well known in chile and argentina renewal of subduction along the pre andean continental margin in the late triassic and the development of new subduction related magmatism are probably represented by the early jurassic bolfin punta tetas magmatic arc in the southern part of the peninsula for which an age of 184 1 ma was determined we suggest retaining the classification of mejillonia as a tectonostratigraphic terrane albeit in this new context

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

structure and tectonics of the erosional convergent margin off antofagasta north chile 23 30 s subduction erosion has dominated the evolution of the north chile convergent continental margin since at least the mesozoic we investigate the structure of the antofagasta 23 s sector of this margin along a transect using coincident wide angle and near vertical seismic profiling and gravity data a 2 d velocity field of the overriding and subducting plates was obtained using joint refraction and reflection travel time tomography a velocity derived density distribution was used to model marine gravity data and substantiate the velocity model the gravity and velocity models imply that the overriding plate is mainly made of arc type igneous basement the upper plate is constructed of two main rock bodies separated by a subhorizontal layer defined by a velocity inversion the top coincident with a reflection in near vertical seismic images the seismic boundary is interpreted as a detachment separating an upper extended domain with large scale normal faulting from a lower domain apparently undergoing a different type of deformation velocity derived porosity indicates that the front of the margin is probably fluid saturated and disaggregated by fracturation as a consequence of frontal subduction erosion fluids carried into the subduction channel within slope debris filling underthrusting grabens reduce basal friction and probably induce hydrofracturing and basal erosion along the underside of the overriding plate at depths greater than 20 km porosity and density values imply that most fluids have been exhausted and the lower part of the upper plate is structurally coherent and little fractured the change in physical properties leads to increased mechanical coupling along the plate boundary and occurs at the updip limit of the distribution of aftershocks of the 1995 antofagasta earthquake m w 8 0 defining the seismogenic zone

rise of the central andean coast by earthquakes straddling the moho coastlines above subduction zones often uplift over geological timescales analysis of landscape evolution and seismicity at the central andean margin suggests that earthquakes on the deep plate interface help build up coastal topography

fluid inclusion characteristics of auriferous quartz veins in archean and paleoproterozoic greenstone belts of eastern and southern finland fluid inclusions in auriferous quartz veins in five deposits in the archean 2 9 2 7 ga and paleoproterozoic 2 0 1 75 ga greenstone belts of eastern and southwestern finland have been characterized on the basis of their composition reconstructed isochores and decrepitation behavior the dominant fluids associated with gold mineralization are h2o co2 ch4 halite archean and h2o co2 ch4 or h2o ch4 paleoproterozoic in composition phase ratios were generally uniform h2o co2 in the archean but were variable in the paleoproterozoic in the archean au sulfide quartz veins the mineralizing fluids contain less ch4 30 mol and have higher salinities up to 39 wt nacl equiv than the corresponding fluids in the paleoproterozoic au sulfide quartz veins up to 38 mol ch4 and below 13 wt nacl equiv additionally the estimated pressure temperature conditions for gold mineralization differ markedly between the two domains mineralization occurred in a pressure temperature range of 300 to 500 c at 2 to 3 5 kbars in the archean domain and 200 to 300 c at 1 to 2 kbars in the paleoproterozoic domain decrepigrams for the archean and paleoproterozoic auriferous quartz veins show different characteristics and permit classification of the different fluid inclusion populations on a regional scale

gold in the volcanogenic mercury rich sulfide deposit langsele skellefte ore district northern sweden the mineralogy of gold from a volcanogenic sulfide deposit in northern sweden langsele was studied the enrichment of gold and silver in massive ore occurs associated with an intrusive metadolerite vein which can be traced across the ore the emplacement of this vein mobilized the precious metals together with galena and pb sb sulfosalts into fractures and low pressure zones a high mercury content at l ngsele average 250 ppm has influenced the gold mineralogy thus gold occurs as au ag amalgam native gold and rarely as aurostibite ausb2 the results of microprobe analyses of amalgam cluster around au0 45ag0 45hg0 10 the composition of ternary amalgam is discussed in connection with the synthetic au ag hg system furthermore native gold was found myrmekitically integrown with stibnite which has been interpreted as a breakdown product of aurostibite at low temperature

on the age of the kiruna greenstones northern sweden abstract three types of zircons from an albite diabase sill within the kiruna greenstone group have been investigated to determine their age and order of crystallization the youngest pink and transparent zircons probably crystallized in late fissures and in association with a thermal event the intermediate white zircon populations could not be readily dated because of significant lead loss the lead 207 206 ages of both the pink and white zircons agree roughly with that of the sm nd isochron about 1 93 ga on secondary minerals from a kiruna greenstone skiold and cliff the oldest brown zircons indicate an age of about 2 2 ga and probably reflect the initial crystallization of the rock the formation of the early proterozoic greenstones in the kiruna area thus commenced about 2 2 ga ago or earlier these results are consistent with the proposed chronostratigraphy of the jatulian formations in finland e g simonen merilainen a time interval of at least 0 3 ga is assumed for the volcano sedimentary period which pre dates the svecokarelian orogeny of the kiruna area

re os dating of low level highly radiogenic llhr sulfides the harnas gold deposit southwest sweden records continental scale tectonic events to obtain geologically meaningful and precise results on low level sulfides that are highly radiogenic blank corrections that account for the extreme difference in the os isotope composition of sample and blank are necessary and the resulting data is best plotted in 187 re 187 os space much like the approach used for molybdenites we here introduce the acronym llhr as a means of characterizing low level and highly radiogenic sulfides use of the traditional 187 re 188 os vs 187 os 188 os plot for llhr sulfides leads to large analytical uncertainties and highly correlated errors as 188 os is poorly determined and can generally be accounted for by the blank we now recognize that llhr sulfides such as those encountered at the harnas au deposit are a common occurrence and characteristic of many crustally affiliated ore systems the harnas au deposit in southwest sweden is located in the mjosa vanern mineral belt that transects from northwest to southeast the prominent geologic fabric of the sveconorwegian province including the mylonite zone the deposit is hosted in a strongly sheared and locally brecciated sulfide bearing quartz vein that crosscuts the foliation of orthogneisses belonging to the 1600 maa mal granitoid suite a 187 re 187 os isochron of 973 34 ma 2 for samples of pyrite and chalcopyrite from outcrops of the harnas alma and silvergruvan veins was obtained the harnas and subsidiary alma veins are au bearing whereas the silvergruvan 2 5 km to the southeast is not of the au bearing type four replicate analyses of an additional pyrite sample from the harnas vein yield a model age of 616 40 ma 95 c l in all samples re and 187 os concentrations are extremely low 0 35 to 7 1 and 0 005 to 0 074 ppb respectively and total common os 0 002 0 028 ppb is less than half the calculated radiogenic 187 os two samples of galena from the harnas vein yielded blank level re and os neither the 973 nor 616 ma time of mineralization is related to development of the mylonite zone at 920 ma or intrusion of the anorogenic bohus blomskog granites at 920 to 900 ma previously proposed sources for generating mjosa vanern mineral belt ore fluids an age of 973 ma for harnas alma silvergruvan suggests that sulfide deposition was associated with the waning stages 0 97 0 90 ga of the sveconorwegian grenvillian orogeny 1 15 0 90 ga postdating metamorphism and deformation that produced a regionally overthickened crust in the northern part of the sveconorwegian province the vein systems for these and numerous other small deposits in the mjosa vanern mineral belt could have resulted from regional exhumation in the late sveconorwegian with associated extension and the development of fracture systems at cooler middle to upper crustal levels in the southern part of the sveconorwegian province dominated by granulitic facies rocks no mineralization is present perhaps due only to increased exhumation and erosion that has exposed deeper crustal levels the late sveconorwegian age 973 ma records the main period of sulfide deposition for the harnas alma silvergruvan vein systems and indicates the robustness of the chronometer within tectonically complex terranes the late neoproterozoic age 616 ma records a later time of pyrite deposition probably associated with shearing and reopening of the harnas vein system because the au mineralization at harnas has been described as associated with shearing and occurring in fracture fillings in early pyrite we suggest that part or all of the au mineralization could have been introduced at 616 ma during reactivation of the vein system the 616 ma age for pyrite suggests a previously unrecognized and much younger mineralizing episode in the harnas region most likely reflecting continental scale extension and the late neoproterozoic opening of the iapetus ocean

fluid induced earthquakes with variable stress drop the static stress drop of an earthquake which quantifies the ratio of seismic slip to the size of the rupture is almost constant over several orders of magnitudes although variations are often observed it is difficult however to attribute these variations either to a well defined phenomenon or simply to measurement uncertainty in this study we analyze the static stress drop of earthquakes that occurred during a water circulation test in the soultz sous forets france geothermal reservoir in 2010 during this circulation test 411 earthquakes were recorded the largest event having a magnitude md2 3 we show that several earthquakes in the reservoir can be combined into groups of closely located similar repeating waveforms we infer that the amplitudes and hence magnitudes vary between the repeaters although the waveforms and spectra are both similar in shape we measure similar corner frequencies for these events despite their different magnitudes suggesting a similar rupture size our results imply that events at the same location may exhibit stress drop variations by as much as a factor of 300 we interpret that this variation in stress drop is caused by fluid pressure at the interface reducing the normal stress we also hypothesize that the observed variations reflect a transition from stable to unstable slip on the imaged asperities

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

the early andean magmatic province eamp 40ar 39ar dating on mesozoic volcanic and plutonic rocks from the coastal cordillera northern chile abstract the early andean magmatic province eamp consists of about 150 000 km 3 of volcanic and plutonic units in the coastal cordillera of northern chile and southern peru and represents a major magmatic mesozoic event in the world for which the precise age of the thick volcanic series was unknown thirty 40 ar 39 ar analyses were carried out on primary mineral phases of volcanic and plutonic rocks from northern chile 18 30 24 s reliable plateau and mini plateau ages were obtained on plagioclase amphibole and biotite from volcanic and plutonic rocks despite widespread strong alteration degree in the arica tocopilla and antofagasta 700 km apart regions the ages obtained on lava flows constrain the volcanic activity between 164 and 150 ma and no n s migration of volcanism is observed the uppermost lava flows of the volcanic sequence at the type locality of the la negra formation extruded at ca 153 150 ma suggesting the end of the volcanic activity of the arc at that time the oldest volcanic activity occurred probably at ca 175 170 ma in the iquique area although no plateau age could be obtained the plutonic bodies of the same regions were dated between ca 160 and 142 ma indicating that they were partly contemporaneous with the volcanic activity at least one volcanic pulse around 160 ma is evidenced over the entire investigated reach of the eamp according to the ages found in arica tocopilla michilla and mantos blancos regions the episodic emplacement of huge amounts of subduction related volcanism is observed throughout the whole andean history and particularly during the jurassic southern peru northern chile and southern argentina these events probably correspond to periodic extensional geodynamic episodes as a consequence of particular subduction conditions such as change of obliquity of the convergence change in the subduction angle slab roll back effect or lower convergence rate that remain to be precisely defined

coulomb theory applied to accretionary and nonaccretionary wedges possible causes for tectonic erosion and or frontal accretion based on observations from both modem convergent margins and sandbox modeling we examine the possible conditions favoring frontal accretion and or frontal and basal tectonic erosion mean characteristic parameters t t and are used to discuss the mechanical stability of 28 transects across the frontal part of convergent margins where the coulomb theory is applicable natural observations reveal that typical accretionary wedges are characterized by low tapers with smooth surface slope and subducting plate low convergence rates and thick trench sediment while nonaccretionary wedges display large tapers with irregular surface slopes and rough subducting plate high convergence rates and almost no trench fill sandbox experiments were performed to illustrate the effects of seamounts ridges in the subduction zone on the deformation of an accretionary wedge these experiments show that a wedge of sand is first trapped and pushed in front of the seamount which acts as a moving bulldozer this is followed by a tunnelling effect of the subducting seamount through the frontal wedge material which results in considerable sand reworking at an advanced subduction stage the d6collement jumps back from a high level in the wedge to its former basal position we conclude that a high trench sedimentation rate relative to the convergence rate leads to frontal accretion in contrast several conditions may favor tectonic erosion of the upper plate first oceanic features such as grabens seamounts or ridges may trap upper plate material during their subduction process second destabilization of the upper plate material by internal fluid overpressuring causing hydrofracturing is probably another important mechanism

andean structural control on interseismic coupling in the north chile subduction zone segmentation can influence the extent of earthquake rupture and event magnitude large megathrust earthquakes result from total rupture of relatively continuous segments of the subduction interface segmentation is attributed to variations in the frictional properties of the seismogenic zone or to topographic features on the down going plate structures in the overriding plate may also influence segmentation but their importance has been dismissed here we investigate the links between interface segmentation at the north chile seismic gap and a crustal scale fault structure in the overriding plate that forms a coastal scarp of about 1 km in height we use satellite interferometric synthetic aperture radar insar and global positioning system gps data to measure interseismic surface deformation between 2003 and 2009 and compare the deformation with rupture extent during well documented earthquakes from these data we infer the degree of coupling and segmentation at depth we find that along a 500 km long segment the base of the strongly coupled seismogenic zone correlates with the line of the surface coastal scarp and follows the outline of the mejillones peninsula this correlation implies that large scale structures in the overriding plate can influence the frictional properties of the seismogenic zone at depth we therefore suggest that the occurrence of megathrust earthquakes in northern chile is controlled by the surface structures that build andean topography

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

gradual unlocking of plate boundary controlled initiation of the 2014 iquique earthquake a long foreshock series unlocked the south american plate boundary until eventually initiating the m 8 1 iquique chile earthquake two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure on 1 april 2014 northern chile was struck by a magnitude 8 1 earthquake following a protracted series of foreshocks the integrated plate boundary observatory chile monitored the entire sequence of events providing unprecedented resolution of the build up to the main event and its rupture evolution here we show that the iquique earthquake broke a central fraction of the so called northern chile seismic gap the last major segment of the south american plate boundary that had not ruptured in the past century1 2 since july 2013 three seismic clusters each lasting a few weeks hit this part of the plate boundary with earthquakes of increasing peak magnitudes starting with the second cluster geodetic observations show surface displacements that can be associated with slip on the plate interface these seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion leading up to this earthquake the b value of the foreshocks gradually decreased during the years before the earthquake reversing its trend a few days before the iquique earthquake the mainshock finally nucleated at the northern end of the foreshock area which skirted a locked patch and ruptured mainly downdip towards higher locking peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch we conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure distinguishing the iquique earthquake from most great earthquakes finally only one third of the gap was broken and the remaining locked segments now pose a significant increased seismic hazard with the potential to host an earthquake with a magnitude of 8 5

metallogeny of gold in the precambrian of northern europe fennoscandian gold deposits have been successfully explored in a wide range of precambrian geological environments in sweden and finland during the last two decades under explored areas still exist at other sites in the fennoscandian shield particularly in russia and norway and there is a high potential for future new discoveries of economic gold in northern europe careful geological documentation of a number of previously productive gold deposits such as haveri and saattopora finland boliden adelfors and enasen sweden and eidsvoll and bidjovagge norway is now available in the literature kutemajarvi pahtavaaraa and suurikuusikko finland and bjorkdal akerberg harnas and pahtohavare sweden represent a new generation of gold mines and recent research on these enables an improved base for formulating regional and local metallogenetic models younging trends from northeast to southwest characterize both the crust and ore forming regional patterns in the fennoscandian shield orogenic or mesothermal gold deposits are found in a wide range of host rocks and are closely linked to either the paleoproterozoic svecokarelian or the neoproterozoic sveconorwegian orogeny unlike these shear zone related deposits significant amounts of gold were concentrated in volcanogenic massive sulfide vms deposits by magmatic hydrothermal processes in conjunction with formation of paleoproterozoic svecofennian juvenile crust hundreds of gold deposits of a variety of ages and genetic styles are therefore now known in the precambrian of northern europe of which some are economic others subeconomic and still others only of scientific interest one hundred representative deposits in sweden norway finland and russia are discussed in this review literature references are provided for each of them and detailed maps show the location of each deposit or prospect listed data on tonnage and grades for the most recent exploration targets as well as the economically and historically most significant deposits show that they were formed during the entire precambrian yield of gold in the fennoscandian shield is so far confined to proterozoic deposits but the potential to find economically viable gold deposits in the russian parts of the archean greenstone belts should not be underestimated

dual megathrust slip behaviors of the 2014 iquique earthquake sequence the transition between seismic rupture and aseismic creep is of central interest to better understand the mechanics of subduction processes a mw 8 2 earthquake occurred on april 1st 2014 in the iquique seismic gap of northern chile this event was preceded by a long foreshock sequence including a 2 week long migration of seismicity initiated by a mw 6 7 earthquake repeating earthquakes were found among the foreshock sequence that migrated towards the mainshock hypocenter suggesting a large scale slow slip event on the megathrust preceding the mainshock the variations of the recurrence times of the repeating earthquakes highlight the diverse seismic and aseismic slip behaviors on different megathrust segments the repeaters that were active only before the mainshock recurred more often and were distributed in areas of substantial coseismic slip while repeaters that occurred both before and after the mainshock were in the area complementary to the mainshock rupture the spatiotemporal distribution of the repeating earthquakes illustrates the essential role of propagating aseismic slip leading up to the mainshock and illuminates the distribution of postseismic afterslip various finite fault models indicate that the largest coseismic slip generally occurred down dip from the foreshock activity and the mainshock hypocenter source imaging by teleseismic back projection indicates an initial down dip propagation stage followed by a rupture expansion stage in the first stage the finite fault models show an emergent onset of moment rate at low frequency 0 5 hz 0 5 hz this indicates frequency dependent manifestations of seismic radiation in the low stress foreshock region in the second stage the rupture expands in rich bursts along the rim of a semi elliptical region with episodes of re ruptures suggesting delayed failure of asperities the high frequency rupture remains within an area of local high trench parallel gravity anomaly tpga suggesting the presence of subducting seamounts that promote high frequency generation our results highlight the complexity of the interactions between large scale aseismic slow slip and dynamic ruptures of megathrust earthquakes

deformation of accretionary wedges in response to seamount subduction insights from sandbox experiments sandbox experiments using a two dimensional and a three dimensional approach are used to study the deformation of margins in response to seamount subduction successive mechanisms of deformation are activated during the subduction of conical seamounts first reactivation of the frontal thrusts and compaction of the accretionary wedge is observed then back thrusting and conjugate strike slip faulting develops above the leading slope of the subducted seamount the basal d6collement is deflected upward in the wake of the subducting high and a large shadow zone develops behind the seamount trailing slope consequently frontal accretion is inhibited and part of the frontal margin is dragged into the subduction zone when the main d6collement returns to its basal level in the wake of the seamount the margin records a rapid subsidence and a new accretionary wedge develops closing the margin reentrant the sediments underthrusted in the wake of the seamount into the shadow zone are underplated beneath the rear part of the accretionary wedge substantial shortening and thickening of the deformable seaward termination of the upper plate basement associated with basal erosion is observed seamount subduction induces significant material transfer within the accretionary wedge favors large tectonic erosion of the frontal margin and thickening of the rear part of the margin the subduction and underplating of relatively undeformed water ladden sediments associated with fluid expulsion along the fractures affecting the margin could modify the fluid pressure along the basal ddcollement consequently significant variations of the effective basal friction and local mechanical coupling between the two plates could be expected around the subducting seamount

structure and tectonics of the central chilean margin 31 33 s implications for subduction erosion and shallow crustal seismicity the pre and current collision of the juan fernandez ridge with the central chilean margin at 31 33 s is characterized by large scale crustal thinning and long term subsidence of the submarine forearc caused by subduction erosion processes here we study the structure of the central chilean margin in the ridge trench collision zone by using wide angle and multichannel seismic data the transition from the upper to middle continental slope is defined by a trenchward dipping normal scarp with variable offsets of 500 2000 m height beneath the scarp the 2 d velocity depth models show a prominent lateral velocity contrast of 1 s 1 that propagates deep into the continental crust defining a major lateral seismic discontinuity the discontinuity is interpreted as the lithological contact between the subsided collapsed outermost forearc composed of eroded and highly fractured volcanic rocks and the seaward part of the uplifted coastal cordillera made of less fractured metamorphic igneous rocks extensional faults are abundant in the collapsed outermost forearc however landward of the continental slope scarp both extensional and compressional structures are observed along the uplifted continental shelf that forms part of the coastal cordillera particularly at the landward flank of the valparaiso forearc basin 32 33 5 s shallow crustal seismicity has been recorded in 2008 2009 forming a dense cluster of thrust events of mw 4 5 the estimated hypocentres spatially correlate with the location of the fault scarp and they highlight the upper part of the seismic crustal discontinuity

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

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

deep seismic structure of the tonga subduction zone implications for mantle hydration tectonic erosion and arc magmatism we present the first detailed 2d seismic tomographic image of the trench outer rise fore and back arc of the tonga subduction zone the study area is located approximately 100 km north of the collision between the louisville hot spot track and the overriding indo australian plate where 80 ma old oceanic pacific plate subducts at the tonga trench in the outer rise region the upper oceanic plate is pervasively fractured and most likely hydrated as demonstrated by extensional bending related faults anomalously large horst and graben structures and a reduction of both crustal and mantle velocities the 2d velocity model presented shows uppermost mantle velocities of 7 3 km s 10 lower than typical for mantle peridotite 30 mantle serpentinization in the model tonga arc crust ranges between 7 and 20 km in thickness and velocities are typical of arc type igneous basement with uppermost and lowermost crustal velocities of 3 5 and 7 1 km s respectively beneath the inner trench slope however the presence of a low velocity zone 4 0 5 5 km s suggests that the outer fore arc is probably fluid saturated metamorphosed and disaggregated by fracturing as a consequence of frontal and basal erosion tectonic erosion has most likely been accelerated by the subduction of the louisville ridge causing crustal thinning and subsidence of the outer fore arc extension in the outer fore arc is evidenced by 1 trenchward dipping normal faults and 2 the presence of a giant scarp 2 km offset and several hundred kilometers long indicating gravitational collapse of the outermost fore arc block in addition the contact between the subducting slab and the overriding arc crust is only 20 km wide and the mantle wedge is characterized by low velocities of 7 5 km s suggesting upper mantle serpentinization or the presence of melts frozen in the mantle

crustal extensional faulting triggered by the 2010 chilean earthquake the pichilemu seismic sequence 1 we report a sequence of crustal quakes that began after the mw 8 8 thrust subduction maule earthquake that affected the central chile margin on 27 february 2010 this activity lasted by several months having the most important events on 11 march 2010 mw 6 9 and mw 7 0 with normal focal mechanisms seismicity shows a rupture oriented along a nw striking and sw dipping normal fault from the surface down to the interplate contact seismicity can be correlated with neotectonics extensional structures similarly oriented in the region which have coexisted with nne ssw reverse faults since the late pliocene even though both have older periods of activity since the paleozoic this crustal rupture would have been triggered by the high coulomb stress change produced by the maule earthquake enhanced by likely fluid presence along weakened zones of the forearc crust as evidenced by high vp vs ratio the occurrence of relevant neotectonic activity in coincidence with short term deformation suggests a relationship with long term tectonic features of this region which would have been acting as a barrier during the interseismic period increasing the strain accumulation and triggering contractional faulting in the crust as well as producing high slip patches during great subduction ruptures favoring triggering of crustal extensional faulting crustal faulting in pichilemu suggests that this kind of events should be considered in seismic hazard analysis despite the absence of historical crustal seismic activity before the maule earthquake

continuing megathrust earthquake potential in chile after the 2014 iquique earthquake the 2014 iquique event was not the earthquake that had been expected to fill the regional seismic gap given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure the seismic gap theory1 identifies regions of elevated hazard based on a lack of recent seismicity in comparison with other portions of a fault it has successfully explained past earthquakes see for example ref 2 and is useful for qualitatively describing where large earthquakes might occur a large earthquake had been expected in the subduction zone adjacent to northern chile3 4 5 6 which had not ruptured in a megathrust earthquake since a m 8 8 event in 1877 on 1 april 2014 a m 8 2 earthquake occurred within this seismic gap here we present an assessment of the seismotectonics of the march april 2014 iquique sequence including analyses of earthquake relocations moment tensors finite fault models moment deficit calculations and cumulative coulomb stress transfer this ensemble of information allows us to place the sequence within the context of regional seismicity and to identify areas of remaining and or elevated hazard our results constrain the size and spatial extent of rupture and indicate that this was not the earthquake that had been anticipated significant sections of the northern chile subduction zone have not ruptured in almost 150 years so it is likely that future megathrust earthquakes will occur to the south and potentially to the north of the 2014 iquique sequence

multi chronometric ages and origin of archaean tonalitic gneisses in finnish lapland a case for long crustal residence time the tojottamanselka gneisses of the koitelainen region northern finland have been dated by the sm nd and the common pb methods the sm nd data of seven samples from a small area 100 m 100 m define an isochron oft 3 06 0 12 2 ga with correspondingind 0 50848 9 2 orend t 3 7 1 8 this age is in good agreement with the zircon u pb discordia age 3 1 ga reported by kroner et al 1981 and is interpreted as the time of magmatic emplacement the distinctly negativeend t value is found for the first time for archean tonalitic gneisses and implies derivation of these magmas by remelting of continental material with a long 200 500 ma crustal residence time a few samples on the other hand possessend t values close to zero hence they are thought to be derived by partial melting of basaltic sources with nearchondritic ree distribution patterns

granites and early proterozoic crustal evolution in sweden evidence from smnd upb and o isotope systematics abstract u pb zircon and whole rock rb sr sm nd and o isotope results are reported for granitoids from three proterozoic provinces in sweden that represent different crustal environments the radiometric ages span the period 1 89 1 65 ga and record events ranging from original igneous crystallisation to late metamorphic resetting these events occurred at different times in the crustal segments the o isotope ratios identify different crustal source materials for the granitoids the sm nd results indicate that the major crustal source components common to most of the granitoids formed shortly before 1 9 ga close in time to the formation of the earliest granitoids contributions from recycled archaean basement are minimal the geographically widespread occurrence of such crustal sources indicates that the period around 2 ga was of great importance for the growth of new continental crust in sweden

origin of continental crust of 1 9 1 7 ga age nd isotopes in the svecofennian orogenic terrains of sweden initial nd isotopic ratios are reported for 57 samples representing all crustal components in the central and southern parts of the 1 9 1 7 ga old svecofennian orogenic terrains of sweden and the 1 8 1 7 ga old transscandinavian granite porphyry belt transscandinavian igneous belt u pb zircon ages are determined where the magmatic ages were not sufficiently constrained the nd isotopic results show that there are no archaean crustal blocks within the studied 1 9 1 7 ga old crustal segment this is consistent with results from finland the main input of recycled archaean crust to the svecofennian was in the form of sediments which are concentrated in the central svecofennian subprovince of north central sweden this is consistent with the vicinity of this subprovince to the archaean craton of the baltic shield these turbidite sediments contain up to 40 archaean material but s type granitoids associated with them have a smaller archaean component around 20 most of the quantitatively predominant i type granitoids and volcanics as well as all the basaltic rocks studied have nd from 1 to 3 and consist of 90 material newly derived from the mantle 1 9 1 7 ga ago we argue that the archaean material was introduced in the form of sediments but we cannot distinguish between pelagic sediments delivered on subducting oceanic crust and turbidite accumulations like the ones seen in north central sweden in either case an overall 15 archaean contribution for the swedish svecofennian was reasonably well homogenized with mantle derived magmatic products for this to occur an active near surface tectonic environment such as a complex of subduction zones must have been necessary

control of high oceanic features and subduction channel on earthquake ruptures along the chile peru subduction zone we discuss the earthquake rupture behavior along the chile peru subduction zone in terms of the buoyancy of the subducting high oceanic features hof s and the effect of the interplay between hof and subduction channel thickness on the degree of interplate coupling we show a strong relation between subduction of hof s and earthquake rupture segments along the chile peru margin elucidating how these subducting features play a key role in seismic segmentation within this context the extra increase of normal stress at the subduction interface is strongly controlled by the buoyancy of hof s which is likely caused by crustal thickening and mantle serpentinization beneath hotspot ridges and fracture zones respectively buoyancy of hof s provide an increase in normal stress estimated to be as high as 10 50 mpa this significant increase of normal stress will enhance seismic coupling across the subduction interface and hence will affect the seismicity in particular several large earthquakes mw 7 5 have occurred in regions characterized by subduction of hof s including fracture zones e g nazca challenger and mocha hotspot ridges e g nazca iquique and juan fernandez and the active nazca antarctic spreading center for instance the giant 1960 earthquake mw 9 5 is coincident with the linear projections of the mocha fracture zone and the buoyant chile rise while the active seismic gap of north chile spatially correlates with the subduction of the iquique ridge further comparison of rupture characteristics of large underthrusting earthquakes and the locations of subducting features provide evidence that hof s control earthquake rupture acting as both asperities and barriers this dual behavior can be partially controlled by the subduction channel thickness a thick subduction channel smooths the degree of coupling caused by the subducted hof which allows lateral earthquake rupture propagation this may explain why the 1960 rupture propagates through six major fracture zones and ceased near the mocha fracture zone in the north and at the chile rise in the south regions characterized by a thin subduction channel in addition the thin subduction channel north of the juan fernandez ridge reflects a heterogeneous frictional behavior of the subduction interface which appears to be mainly controlled by the subduction of hof s

testing mechanisms of subduction zone segmentation and seismogenesis with slip distributions from recent andean earthquakes abstract a long standing goal of subduction zone earthquake studies is to determine whether or not there are physical processes that control seismogenesis and the along strike segmentation of the megathrust studies of individual earthquakes and global compilations of earthquakes find favorable comparison between coseismic interplate slip distributions and several different long lived forearc characteristics such as bathymetry coastline morphology crustal structure and interplate frictional properties but no single explanation seems to govern the location and slip distribution of all earthquakes one possible reason for the lack of a unifying explanation is that the inferred earthquake parameters most importantly the slip distribution calculated in some areas were inaccurate blurring correlation between earthquake and physical parameters in this paper we seek to test this possibility by comparing accurate slip distributions constrained by multiple datasets along several segments of a single subduction zone with the various physical properties that have been proposed to control or correlate with seismogenesis we examine the rupture area and slip distribution of 6 recent and historical large mw 7 earthquakes on the peru northern chile subduction zone this analysis includes a new slip distribution of the 14 november 2007 mw 7 7 earthquake offshore tocopilla chile constrained by teleseismic body wave and insar data in studying the 6 events we find that no single mechanism can explain the location or extent of rupture of all earthquakes but analysis of the forearc gravity field and its gradients shows correlation with many of the observed slip patterns as suggested by previous studies additionally large scale morphological features including the nazca ridge arica bend mejillones peninsula and transverse crustal fault systems serve as boundaries between distinct earthquake segments

an early proterozoic ophiolite the jormua mafic ultramafic complex northeastern finland abstract the 1 96 ga old jormua complex comprises a fault bounded unit 2 5 20 km in the centre of the kainuu schist belt at the eastern margin of the early proterozoic svecokarelides the complex was dismembered and metamorphosed to lower amphibolite facies during the svecokarelian orogeny in the intact complex the basal unit was formed by serpentinites the middle unit of mafic dykes and the uppermost extrusive unit of basaltic pillow lavas gabbroic rocks are present as intrusive bodies in the serpentinites and narrow interdyke screens within the dyke unit trondhjemitic rocks occur as minor segregations in the gabbroic rocks or as cross cutting narrow dykes in the mafic dyke unit the dyke unit is locally composed exclusively of subparallel metabasalt and metadolerite dykes in places interdyke metagabbro and serpentinite screens are abundant well preserved chilled margins are common and many dykes are split and intruded by younger dykes the chemical composition of the serpentinites indicates derivation from harzburgitic dunitic mantle peridotites the gabbroic rocks which represent obvious tholeiitic cumulates show extreme differentiation similar to gabbros of the high ti ophiolites and gabbros dredged from present midocean ridges in chemistry the trondhjemitic rocks are close to granitic rocks from mid ocean ridges and high ti ophiolites the similar chemical composition of the dykes and lavas of the complex indicates that they are cogenetic both being tholeiitic metabasalts with chondrite normalized ree patterns ranging from slightly lree depleted to slightly lree enriched ones compared with modern rocks the jormua metabasalts most closely resemble transitional midocean ridge basalts it is suggested that the jormua complex and related mafic ultramafic bodies in eastern finland originated as divergent margin ophiolites concomitantly with the break up of the archaean craton in the extensional stage of the svecokarelian orogeny which culminated in the opening of a major ocean after 1 97 ga the tectonic emplacement of these ophiolites into their present locations occurred in connection with thrusting during the compressional stage of the orogeny about 1 9 ga ago

revisiting the north chile seismic gap segmentation using gps derived interseismic coupling no major earthquake occurred in north chile since the 1877 m w 8 6 subduction earthquake that produced a huge tsunami however geodetic measurements conducted over the last decade in this area show that the upper plate is actually deforming which reveals some degree of locking on the subduction interface this accumulation of elastic deformation is likely to be released in a future earthquake because of the long elapsed time since 1877 and the rapid accumulation of deformation thought to be 6 7 cm yr many consider this area is a mature seismic gap where a major earthquake is due and seismic hazard is high we present a new global positioning system gps velocity field acquired between 2008 and 2012 that describes in some detail the interseismic deformation between 18 s and 24 s we invert for coupling distribution on the nazca south america subduction interface using elastic modelling our measurements require that at these latitudes 10 to 12 mm yr 1 i e 15 per cent of the whole convergence rate are accommodated by the clockwise rotation of an andean block bounded to the east by the subandean fold and thrust belt this reduces the accumulation rate on the subduction interface to 56 mm yr 1 in this area coupling variations on the subduction interface both along strike and along dip are described we find that the north chile seismic gap is segmented in at least two highly locked segments bounded by narrow areas of weak coupling this coupling segmentation is consistent with our knowledge of the historical ruptures and of the instrumental seismicity of the region intersegment zones iquique mejillones correlate with high background seismic rate and local tectonic complexities on the upper or downgoing plates the rupture of either the paranal or the loa segment alone could easily produce a mw 8 0 8 3 rupture and we propose that the loa segment from 22 5 s to 20 8 s may be the one that ruptured in 1877

subducted seamounts and recent earthquakes beneath the central cascadia forearc bathymetry and magnetic anomalies indicate that a seamount on the juan de fuca plate has been subducted beneath the central cascadia accretionary complex and is now located 45 km landward of the deformation front passage of this seamount through the accretionary complex has resulted in a pattern of uplift followed by subsidence that has had a profound influence on slope morphology gas hydrate stability and sedimentation based on potential field data and a new three dimensional seismic velocity model we infer that this is the most recent of several seamounts subducted over the past several million years beneath this segment of cascadia more deeply subducted seamounts may be responsible for recent earthquake activity on the plate boundary in this region and for along strike variations in the thickness of the subduction channel which may affect coupling across the plate boundary

large trench parallel gravity variations predict seismogenic behavior in subduction zones we demonstrate that great earthquakes occur predominantly in regions with a strongly negative trench parallel gravity anomaly tpga whereas regions with strongly positive tpga are relatively aseismic these observations suggest that over time scales up to at least 1 million years spatial variations of seismogenic behavior within a given subduction zone are stationary and linked to the geological structure of the fore arc the correlations we observe are consistent with a model in which spatial variations in frictional properties on the plate interface control trench parellel variations in fore arc topography gravity and seismogenic behavior

the geology and genesis of the proterozoic massive sulfide deposit at garpenberg central sweden the garpenberg deposit of central sweden is a metamorphosed strata bound zn pb cu ag sulfide deposit intercalated in an early proterozoic supracrustal sequence of felsic metavolcanics and subordinate metasedimentary rocks which have been folded metamorphosed and intruded by synorogenic granitoids the magmatism is calc alkaline and most of the volcanic activity occurred as explosive submarine volcanism the garpenberg deposit is emplaced at the contact between metasedimentary and metavolcanic rocks and consists of 32 lens shaped orebodies stratiform zn pb cu mineralization is underlain by cu bearing stockwork ore with an extensive alteration zone of quartz phlogopite rocks with minor chlorite cordierite garnet staurolite and andalusite chemically the altered zone is enriched in magnesium iron ore metals manganese and volatiles and is depleted in sodium and calcium the proposed volcanogenic origin related to calc alkaline magmatism is supported by the morphology wall rock alteration and ore mineralogy the similarity of the garpenberg deposit to the archean massive sulfide deposits of canada and the kuroko deposits of japan supports this theory but also reveals possible differences between the compositions of precambrian and phanerozoic seawater dissimilarities in the metal ratios cu pb zn of the different deposits and their associated lithologies suggest differences in their tectonic setting the garpenberg deposit is thought to have formed in an active continental margin setting rather than in an island arc

seismic imaging of a convergent continental margin and plateau in the central andes andean continental research project 1996 ancorp 96 1 a 400 km long seismic reflection profile andean continental research project 1996 ancorp 96 and integrated geophysical experiments wide angle seismology passive seismology gravity and magnetotelluric depth sounding across the central andes 21 s observed subduction of the nazca plate under the south american continent an east dipping reflector nazca reflector is linked to the down going oceanic crust and shows increasing downdip intensity before gradual breakdown below 80 km we interpret parts of the nazca reflector as a fluid trap located at the front of recent hydration and shearing of the mantle the fluids being supplied by dehydration of the oceanic plate patches of bright quebrada blanca bright spot to more diffuse reflectivity underlie the plateau domain at 15 30 km depth this reflectivity is associated with a low velocity zone p to s wave conversions the upper limits of high conductivity and high vp vs ratios and to the occurrence of neogene volcanic rocks at surface we interpret this feature as evidence of widespread partial melting of the plateau crust causing decoupling of the upper and lower crust during neogene shortening and plateau growth the imaging properties of the continental moho beneath the andes indicate a broad transitional character of the crust mantle boundary owing to active processes like hydration of mantle rocks in the cooler parts of the plate margin system magmatic underplating and intraplating under and into the lowermost crust mechanical instability at moho etc hence all first order features appear to be related to fluid assisted processes in a subduction setting

abrupt change in the dip of the subducting plate beneath north chile no large tsunamigenic earthquake has occurred in north chile since 1877 and the region has been largely recognized as a mature seismic gap1 2 3 4 5 6 7 8 9 at the southern end of the seismic gap the 2007 mw 7 7 tocopilla earthquake ruptured the deeper seismogenic interface whereas the coupled upper interface remained unbroken4 6 7 seismological studies onshore show a gently varying dip of 20 to 30 of the downgoing nazca plate3 6 which extends from the trench down to depths of 40 50 km here we study the lithospheric structure of the subduction zone of north chile at about 22 s using wide angle seismic refraction and reflection data from land and sea complemented by hypocentre data recorded during the 2007 tocopilla aftershocks7 our data document an abrupt increase in the dip of the subducting plate from less than 10 to about 22 at a depth of approximately 20 km the distribution of the 2007 aftershocks indicates that the change in dip acted as a barrier for the propagation of the 2007 earthquake towards the trench which in turn indicates that the subduction megathrust is not only segmented along the trench but also in the direction of the dip we propose that large magnitude tsunamigenic earthquakes must cross the barrier and rupture the entire seismogenic zone

a fluid inclusion and stable isotope study of the proterozoic bidjovagge au cu deposit finnmark northern norway the bidjovagge au cu deposit northern norway hosted within a shear zone in the early proterozoic kautokeino greenstone belt is more base metal rich than archaean mesothermal gold deposits an early phase of gold and copper mineralization is hosted by sheared albitic felsites within an alteration and oxidation zone to graphitic schists along with a series of syenodiorite dikes fluid inclusions related to gold mineralization comprise varying amounts of h2o co2 ch4 and salt having salinities between 30 to 45 wt nacl equivalent zonation of the fluid inclusions exists with ch4 predominantly in the ore zone microthermometric data indicate that fluid trapping occurred between 300 to 375 c and 2 to 4 kbars carbon isotope data display a trend from 0 7 in the footwall to 4 6 within the ore zone fluid inclusion and carbon isotope data suggest that redox reactions between the fluid and the graphitic schists resulted in gold precipitation from chloride complexes

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

the iquique earthquake sequence of april 2014 bayesian modeling accounting for prediction uncertainty the subduction zone in northern chile is a well identified seismic gap that last ruptured in 1877 on 1 april 2014 this region was struck by a large earthquake following a two week long series of foreshocks this study combines a wide range of observations including geodetic tsunami and seismic data to produce a reliable kinematic slip model of the mw 8 1 main shock and a static slip model of the mw 7 7 aftershock we use a novel bayesian modeling approach that accounts for uncertainty in the green s functions both static and dynamic while avoiding nonphysical regularization the results reveal a sharp slip zone more compact than previously thought located downdip of the foreshock sequence and updip of high frequency sources inferred by back projection analysis both the main shock and the mw 7 7 aftershock did not rupture to the trench and left most of the seismic gap unbroken leaving the possibility of a future large earthquake in the region

do subducting seamounts generate or stop large earthquakes seamount subduction is a common process in subduction zone tectonics contradicting a widely held expectation that subducting seamounts generate large earthquakes seamounts subduct largely aseismically producing numerous small earthquakes on rare occasions when they do produce relatively large events the ruptures tend to be complex suggesting multiple rupture patches or faults we explain that the seismogenic behavior of these seamounts is controlled by the development and evolution of an adjacent fracture network during subduction and cannot be described using the frictional behavior of a single fault the complex structure and heterogeneous stresses of this network provide a favorable condition for aseismic creep and small earthquakes but an unfavorable condition for the generation and propagation of large ruptures

tectonic styles of early proterozoic ore deposition in the fennoscandian shield the early proterozoic metallogenic events of the fennoscandian shield are connected with two major stages of crustal evolution the karelian continental development 2 5 2 1 ga and the svecofennian orogeny 2 0 1 75 ga the karelian continental development was dominated by deposition of terrestrial sediments and tholeiitic volcanism on archaean crust a tensional regime probably associated with a mantle plume and partial melting of the upper mantle culminated in the generation of an ene wsw trending rift zone which was intruded by tholeiitic magma 2 44 ga ago some 15 layered igneous bodies hosting cr pge ni cu and fe v ti deposits are known in the kemi suhanko and koillismaa belts these mafic ultramafic bodies originally formed either several lopoliths or one single layered igneous complex with a minimum length of 260 km nw se and nnw sse trending dolerite dykes intruded the rifted and attenuated archaean crust 2 25 2 0 ga ago preceding ocean opening the coeval ne sw trending dolerite dykes in the northern part of the shield are interpreted as manifestation of an aulacogen the failed arm of a triple armed rift system oceanic crust is preserved in 1 96 ga old ophiolite complexes the cu co zn ni and cr contents of the outokumpu type deposits derive from hydrothermal leaching of oceanic crust and were discharged together with chemogenic cherts and carbonates from ascending hydrothermal fluids on the seafloor above fissure vents in the northern part of the shield rifting and probably ocean opening resulted in the formation of the layered tholeiitic sedimentary complex of the petsenga ni cu district intruded by mineralized mafic ultramafic magma the age of this event is poorly constrained the basin was subsequently closed and continental collision of the kola suture was accompanied by southward obduction of the lapland granulite belt on the archaean crust during the svecofennian orogeny the divergent continental margin was converted into an active margin early subduction of oceanic crust produced oceanic island arcs intruded by 1 93 1 9 ga old tonalites and trondhjemites subsequent subduction of oceanic crust generated 1 9 1 87 ga old continental island arcs associated with massive sulphide cu zn pb ag au deposits the island arcs were accreted to the archaean crust in a concave belt containing the ore districts of kiruna skellefte vihanti pyhasalmi aijala orijarvi and bergslagen bimodal volcanic suites with felsic calc alkaline and mafic tholeiitic volcanites are attributed to rifting of the overriding plate above subduction zones ni cu deposits in synorogenic 1 9 1 87 ga old mafic ultramafic intrusions occur in linear fault controlled belts at the margin of the archaean crust the generation of ni bearing tholeiitic to komatiitic magma is explained by partial melting of the mantle wedge above the early subduction zone magma differentiation and magma upwelling along transcurrent faults on the continental margin sulphur was probably assimilated from the supracrustal wall rocks 1 89 1 87 ga old early svecofennian granitoids are associated with porphyry type cu mo au deposits widespread late svecofennian s type 1 84 1 75 ga granitic magmatism generated minor mo u w sn and ree deposits emphasis is laid on the importance of geotectonic models as a basis for further exploration in the fennoscandian shield

bidjovagge copper gold deposit in finnmark northern norway the bidjovagge copper gold deposit is located 40 km northwest of kautokeino in finnmark northern norway the deposit occurs in the lower proterozoic kautokeino greenstone belt and consists of four ore deposits in albitic felsite and graphitic albitic felsite over a strike length of 2 5 km the orebodies occur on the eastern limb of a north south striking anticline the albitic felsite may represent strongly altered tuffite and diabase or partly metamorphosed chemical sediment the alteration of the metadiabase in the footwall sequence is complex carbonatization is very extensive but there are also zones with biotite scapolite and hematite alteration the main ore is strata bound and occurs as veins breccias and low grade disseminated mineralization of a more stratiform character high gold values are usually related to late quartz carbonate veins containing tellurides and are often associated with weak uranium mineralization the ore minerals of economic significance are chalcopyrite and native gold other common metallic minerals are pyrite and pyrrhotite marcasite magnetite ilmenite hematite tellurides rutile sphalerite galena davidite and pentlandite occur in accessory amounts preliminary isotopic analyses show that the lead isotope composition is markedly radiogenic 206 pb 204 pb 22 2 23 8 the association of ore deposits with albitic felsites is also known to the north in the kvnangen tectonic window where similar copper deposits but with low gold values occur in the bergmark area and to the east near masi in big geluobbal where u v ti rare earth element mineralization has recently been found bidjovagge is similar in its depositional environment to the viscaria deposit in sweden and the pahtavuoma deposit in finland

subducted seafloor relief stops rupture in south american great earthquakes implications for rupture behaviour in the 2010 maule chile earthquake great subduction earthquakes cause destructive surface deformation and ground shaking over hundreds of kilometres their rupture length is limited by the characteristic strength of the subduction plate interface and by lateral variations in its mechanical properties it has been proposed that subduction of topographic features such as ridges and seamounts can affect these properties and stop rupture propagation but the required relief and physical mechanisms of topographic rupture limitation are not well understood here we show that the rupture limits of thirteen historic great earthquakes along the south america nazca plate margin are strongly correlated with subducted topography with relief 1000 m including the juan fernandez ridge the northern limit of rupture in the mw 8 8 maule chile earthquake of 27 february 2010 is located where this ridge subducts analysis of intermediate magnitude earthquakes shows that in most places the subduction of high seafloor relief creates weak aseismic zones at the plate interface which prevent rupture propagation but that the juan fernandez ridge is associated with a locally strong plate interface the maximum rupture length and thus magnitude of great subduction earthquakes is therefore determined by the size and lateral spacing of topographic features where they are present on the subducting plate

invited review paper seismicity along the south american subduction zone review of large earthquakes tsunamis and subduction zone complexity abstract earthquakes along the shallow south american subduction zone exhibit heterogeneous rupture characteristics going back several centuries of the earthquake record in this area this heterogeneity is manifest in several ways such as changes in rupture mode from magnitude 8 events during one century followed by smaller ones in other time periods as well as unusual tsunami events there is also an apparent interaction between earthquake rupture and subducting plate complexity in this region significant complexity exists on the subducting nazca plate including fracture zones and ridges such as the large nazca ridge several large magnitude earthquakes have occurred in the region of ridge subduction but no earthquake rupture has ruptured through these features into adjacent regions suggesting that these subducting features act to segment the margin other features such as fracture zones and variable sediment thickness on the nazca plate appear to influence earthquake behavior over a wide range of magnitude scales upper plate features such as crustal faults also lead to heterogeneous earthquake behavior here i provide an overview of seismicity along the margin since 1850 in the context of the subduction zone structures this includes great earthquakes such as the 1906 ecuador and 1960 chile events i also present results showing increased rupture complexity in moderate magnitude earthquakes that can also be linked to certain nazca plate features

effect of margin curvature on plate deformation in a 3 d numerical model of subduction zones summary the large amount of data acquired along most subduction zones underlines the importance of three dimensions in the subduction mechanism in this work we use a fully 3 d mechanical numerical model to analyse the impact of the plate boundary geometry on the deformation of the upper plate the model consists of two initially horizontal independent plates overlying an inviscid fluid and continuously pushed towards each other the initial geometry of the contact zone between the two plates controls the stress regime and the strain pattern in the upper plate the case with a linear plate boundary and orthogonal convergence is first considered and used as a reference model with this simple model the effects of some important parameters i e the interplate friction and the lithosphere asthenosphere density contrast are investigated finally cases with curved plate boundaries are considered and the results are used to shed light on the importance of the dip direction of the interplate plane for the upper plate strain pattern unnecessary oceanward convexity causes an accumulation of the subducted material beneath the upper plate and induces an important uplift of the convex area on the contrary the material escapes from an oceanward concavity and provokes subsidence in the forearc zone such a behaviour induces preferential zones of weakeness in the overriding plate and may allow for explaining some local stress regime variations along convergent margins

recent paludification of kettle holes on the central isjands of lake bienville northern quebec canada this paper reports on the paludification of kettle holes formed in a proglacial esker complex at lake bienville in northern quebec deep hollows on the central islands of this large subarctic lake c 900 kin2 are highly exposed to northeasterly and southwesterly winds over long fetches and accumulate large amounts of drifting snow c 4 m modifications in local snow distribution associated with holocene vegetation and climate changes contributed to an increased water supply in kettle holes podzolic soils with light patches in the b horizon are attributed to differential water circulation during thawing in coarse textured soils with high moisture supply associated with thicker snow peat started to form over well drained podzolic soils after 600 bp especially c 200 bp when suitable conditions for sphagnum growth established at the front of snowbeds the recent development of patchy podzolic soils and paludification of kettle holes are interpreted as the result of a combination of bioclimatic even

earthquake rupture stalled by a subducting fracture zone we showed that the rupture produced by the great peru earthquake moment magnitude 8 4 on 23 june 2001 propagated for 70 kilometers before encountering a 6000 square kilometer area of fault that acted as a barrier the rupture continued around this barrier which remained unbroken for 30 seconds and then began to break when the main rupture front was 200 kilometers from the epicenter the barrier had relatively low rupture speed slip and aftershock density as compared to its surroundings and the time of the main energy release in the earthquake coincided with the barrier s rupture we associate this barrier with a fracture zone feature on the subducting oceanic plate

density depth model of the continental wedge at the maximum slip segment of the maule mw8 8 megathrust earthquake abstract complexities in the rupture process during a megathrust earthquake can be attributed to the combined effect of inhomogeneous distribution of stress accumulated during the interseismic period and inhomogeneous rheology of the seismogenic contact we modeled the free air gravity field of the southern central chile convergent margin along five 2 d profiles that cross the patch of highest slip during the chilean 2010 megathrust earthquake in order to analyze variability in the density and shape of the continental wedge and its relationship with seismotectonics we also analyzed the bathymetry to derive the long term interplate friction coefficient the results show that the high slip patch during the maule earthquake corresponds to a segment of the margin characterized by 1 low densities in the continental wedge 2 low vertical loading over the inter plate contact 3 a well developed shelf basin and 4 low taper angles consistent with a low effective basal friction coefficient we interpret the correlation between these parameters in terms of the total potential energy change during the earthquake and conclude that if the normal stress or frictional coefficient are low then a large slip does not necessarily imply a large amount of coseismic work heterogeneities in density of the continental basement can therefore be related to complexities in the pattern of coseismic slip and in the aftershock distribution locally a subducted seamount or seaward spur of high density continental crust may be present near the high slip patch

rupture process of the 2014 iquique chile earthquake in relation with the foreshock activity the rupture process of the 2014 iquique chile earthquake is inverted from teleseismic p wave data applying a novel formulation that takes into account the uncertainty of green s function which has been a major error source in waveform inversion the estimated seismic moment is 1 5 1021 nm mw 8 1 associated with a 140 km long and 140 km wide fault rupture along the plate interface the source process is characterized by unilateral rupture propagation during the first 20 s the dynamic rupture front propagated from the hypocenter to the large asperity located about 50 km southward crossing a remarkably active foreshock area at high velocity of about 3 0 km s but small and irregular seismic moment release rate our result may suggest that the 20 s long initial phase was influenced by the stress drop due to the foreshock activity near the main shock hypocenter moreover the 2 week long swarm like foreshock activity migrating roughly at 5 km day toward the main shock hypocenter and possibly associated slow slip contributed to the stress accumulation prior to the mw 8 1 megaquake the main shock initial rupture phase might have triggered the rupture of the large asperity which had large fracture energy

metallogeny of gold in the fennoscandian shield gold occurs in a number of different ore types in the fennoscandian shield ranging in age from late archean to late proterozoic until recently the metal was exploited primarily as a byproduct in volcanogenic massive sulphide deposits but during the 1980s more gold mines have been opened than during any other episode in the mining history of northern europe the occurrence of gold in the fennoscandian shield is reviewed in the context of the major tectonostratigraphic units 1 in the karelian province gold is hosted by greenstone belts of the archean basement complex e g at ilomantsi eastern finland greenstone belts of the nordkalott province which are interpreted as part of an early proterozoic cover sequence contain gold deposits associated with copper bidjovagge saattopora and pahtohavare gold is also associated with cobalt in the metasomatically altered early proterozoic cover in north eastern finland meurastuksenaho and juomasuo 2 in the svecofennian domain the major gold deposits were generated during the emplacement of 1 92 1 87 ga old accretional magmatism these deposits occur in the northeastern part of the svecofennian domain close to the archean proterozoic boundary they comprise two major types a the porphyry type and shear zone gold hosted by tonalite at tallberg laivakangas kopsa and osikonmaki b as a component of volcanogenic massive sulphide deposits e g holmtjarn boliden and pyhasalmi other types are c gold bearing quartz alumina alteration zones formed during the 1 92 1 87 ga magmatic period enasen d gold in massive sulphide and iron ore deposits in bergslagen 3 gold associated with 1 84 1 54 ga granites has been reported from several sites in the shield including quartz veins and contact metasomatic deposits in addition shear zone related gold deposits post dating these granites have been identified in southeastern sweden adelfors 4 in the sveconorwegian domain the gold deposits at bleka eidsvoll glava and hamas are associated with shear zones which developed penecontemporaneously with the intrusion of late 1 0 0 9 ga granites

metal sources in the early proterozoic svecofennian terrain of central sweden pb isotope evidence the lead isotope composition of three cu zn pb sulfide deposits and one au deposit in the early proterozoic svecofennian of central sweden reveals the existence of two distinct lead sources in the region rockliden and enstern contain lead of upper crustal affinity and are isotopically homogeneous lead in these deposits probably originates from archean derived detritus which was well homogenized by sedimentary processes and deposited over large areas as a component in early proterozoic sedimentary and tuffaceous rocks lead isotopic homogeneity within the tjarnberget and enasen deposits is less pronounced and the less radiogenic character of the lead suggests a source of mantle affinity in areas where metasedimentary rocks are absent or contain very little archean derived material the isotopic signature of mantle derived volcanic rocks is reflected in the ore lead this approach is also applicable to other svecofennian deposits together with deposits in west central finland the rockliden deposit constitutes the northern boundary for lead of upper crustal affinity i e archean derived lead in svecofennian sulfide deposits

jorn an early proterozoic intrusive complex in a volcanic arc environment north sweden abstract the jorn complex is an early svecokarelian granitoid suite intruded into a volcanic arc environment on the southern margin of a major proterozoic continental area both the complex and its country rocks have been affected by hydrothermal alteration and low grade regional metamorphism four phases can be distinguished on geological chemical and geophysical criteria in particular a heterogeneous calcic outer zone and a more evolved central diapir the rock types vary from granodiorite to granite and have major and trace element abundances similar to those phanerozoic subduction related granitoids from relatively immature volcanic arcs zircon populations from the different phases are rather heterogeneous but do not show significant differences in u distribution or u pb age between the phases while pooled u pb data 13 points give an upper intercept of 1890 7 8 ma a two stage model assuming an age difference between cores and rims gives a more probable crystallisation age of 1876 2 ma with significant lead loss at 1720 ma and 410 ma epsilon nd values range from 1 8 to 3 2 indicating that the source material for the jorn complex was derived from an lree depleted mantle with a small contribution of older crustal material and had a relatively short crustal residence period metaluminous compositions and oxygen isotope ratios suggest non pelitic sources the jorn complex probably originated as a series of subduction related melts of basic to intermediate composition which underwent varying degrees of subsequent differentiation and secondary alteration

coupled tectonic evolution of andean orogeny and global climate abstract the largest tectonic relief breaking the earth s surface 13 km vertically is at the subduction margin of the andes which generates routinely megathrust earthquakes mw 8 5 and drives the paradigmatic andean orogen here we present key geologic evidence to reassess first order features of geomorphology and tectonics across the central andes where the orogen includes the altiplano plateau and attains its maximum integrated height and width the andean subduction margin has a stepped morphology dominated by the low relief atacama bench which is similar to a giant uplifted terrace slopes gently over a width of 60 100 km from the andes to the pacific and runs over more than 1000 km of coastal length we find that the genesis of stepped morphology at the andean seaboard is due to concomitant development of large west vergent thrusts parallel to the subduction interface and increasing aridity in the atacama desert which keeps an unprecedented large scale record of interplaying tectonics and cenozoic climate change incorporating our results with published geological knowledge demonstrates that andean orogeny is characterized by trench perpendicular bivergent and trench parallel bilateral growth over the past 50 myr associated with positive trench velocity toward the continent trench advance and subduction of a wide slab under south america we hypothesize that a global plate tectonic reorganization involving long lasting viscous mantle flow has probably forced both andean orogeny and global climate cooling since 50 ma in contrast two important stepwise pulses of increasing aridity and trench perpendicular andean growth appear to be results of changes in erosion rates due to global late eocene and middle miocene cooling events

the depositional evolution of the svecofennian supracrustal sequence in finland and sweden abstract on the basis of six new zircon ages from metavolcanic rocks together with other isotopic geophysical and geological data the chronological and tectono stratigraphic evolution of the early proterozoic svecofennian supracrustal rocks in finland and sweden are discussed these data suggest that a nw se displacement from the bothnian bay to lake ladoga and a sinking of the southwestern block was initiated 1950 2000 ma ago accumulation of pelitic sediments and greywackes on the subsiding archaean basement continued until about 1860 ma in south central and northern sweden shallow submarine and subaerial volcanics were extruded 1880 1890 ma ago the thick sedimentary piles and volcanic rocks were subsequently intruded by plutonic rocks forming large batholiths 1860 1890 ma ago

weak interplate coupling by seamounts and repeating m 7 earthquakes subducting seamounts are thought to increase the normal stress between subducting and overriding plates however recent seismic surveys and laboratory experiments suggest that interplate coupling is weak a seismic survey in the japan trench shows that a large seamount is being subducted near a region of repeating earthquakes of magnitude m 7 both observed seismicity and the pattern of rupture propagation during the 1982 m 7 0 event imply that interplate coupling was weak over the seamount a large rupture area with small slip occurred in front of the seamount its northern bound could be determined by a trace of multiple subducted seamounts whereas a subducted seamount itself may not define the rupture area its width may be influenced by that of the seamount

upper plate reverse fault reactivation and the unclamping of the megathrust during the 2014 northern chile earthquake sequence after 137 years without a great earthquake the mw 8 1 pisagua event of 1 april 2014 occurred in the central portion of the southern peru northern chile subduction zone this megathrust earthquake was preceded by more than 2 weeks of foreshock activity migrating 3 5 km day toward the mainshock hypocenter this foreshock sequence was triggered by an mw 6 7 earthquake on a reverse fault in the upper plate that strikes at a high angle to the trench similar to well documented reverse faults onshore these margin oblique reverse faults accommodate north south shortening resulting from subduction across a plate boundary that is curved in map view reverse slip on the crustal fault unclamped the subduction interface precipitating the subsequent megathrust foreshock activity that culminated in the great pisagua earthquake the combination of crustal reverse faults and a curved subduction margin also occurs in cascadia and northeastern japan indicating that there are two additional localities where great megathrust earthquakes may be triggered by upper plate fault activity

petrogenesis of archaean trondhjemites tonalites and granodiorites from eastern finland major and trace element geochemistry

paleogene building of the bolivian orocline tectonic restoration of the central andes in 2 d map view using available information on the magnitude and age of tectonic shortening as well as paleomagnetically determined tectonic rotations we have run a series of 2 d map view restorations of the central andes neogene shortening in the foreland belt induced only slight orogenic curvature of the central andes the constraints on the ages of the large observed fore arc rotations average of 37 counterclockwise in southern peru and 29 clockwise in northern chile indicate that the bolivian orocline formed during the eocene oligocene as a consequence of differential shortening focused in the eastern cordillera to minimize local block rotations along the fore arc the restoration that best fits the central andean rotation pattern requires about 400 km of total paleogene plus neogene shortening near the arica bend this value corresponds to the upper bound of estimates of maximum horizontal shortening for the central andes along strike variations in horizontal shortening in the back arc induced bending of the continental margin block rotations with fore arc along strike extension and or orogen parallel transport of upper crustal material toward the symmetry axis of the orocline

implications of new upb zircon chronology to early proterozoic crustal accretion in northern sweden abstract u pb ages ranging from 1 89 to 1 78 ga are reported for zircon populations formed during major magmatic events in the proterozoic development of northern sweden the studied area includes parts of the continental and the marine svecokarelian domains of the baltic shield the ages record crustal accretion and reactivation off the margin of an exposed archaean craton and show that magmatism was broadly coeval throughout the entire north swedish portion of the svecokarelian province irrespective of regions involved a detailed chronostratigraphy is presented for the skellefte district of northern sweden and comparisons are made with the evolution in other parts of the svecokarelian province two main magmatic phases commencing at 1 89 and 1 79 ga ago are recognized the first represents large scale volcanism and plutonism which in the skellefte district was characterized by the introduction of mainly mantle derived magmas or by magmas formed from rocks with short crustal residence time in the vicinity of the archaean craton some distance to the north the crust generating processes included the mobilization of archaean sources and appear to have continued until c 1 85 ga ago a relatively long period of consolidation and denudation separates this magmatic phase from the one at c 1 79 ga ago the generation of these later migmatite associated granites in the svecokarelian province coincided in time and was possibly associated with those processes which gave rise to the initial plutonism in the neighbouring transscandinavian granite porphyry belt