regional scale pressure shadow controlled mineralization in the principe orogenic gold deposit central brazil abstract the principe gold deposit situated in the natividade gold district resulted from establishment of the regional transbrasiliano strike slip system during the late neoproterozoic brasiliano event the host rocks however were formed in the paleoproterozoic with sm nd model ages from 2250 to 2500 ma therefore the principe gold deposit is epigenetic the local lithological association is a tonalitic granodioritic suite formed in an island arc environment that later experienced continental collision tectonics leading to the intrusion of the peraluminous principe granite with an age of 2169 42 ma by zircon u pb during the neoproterozoic these units underwent deformational greenschist facies metamorphism and hydrothermal alteration forming metamorphic tectonites inside the principe granite and hydrothermally altered rocks at the northern termination of the granite where the principe gold deposit is located a strong structural control is identified in the deposit with n10 w n20 e trending brittle ductile shear zones that are visible at all scales from thin sections to regional satellite images these shear zones played an important role in the formation of the deposit acting as pathways that promoted a channelized fluid flow to metal precipitation sites hydrothermal alteration processes of different grades occur along these structures mainly characterized by saussuritization biotitization chloritization sericitization carbonatization silicification and sulfidation reactions producing a neoformed mineral assemblage the principe granite acted as a regional scale porphyroclast for migration of the hydrothermal solutions as well as deformation forming two pressure shadows that acted as structural traps for the ore as stress release zones these structures concentrated hydrothermal solutions during seismic fault movement events under a transpressive regime they also changed the physicochemical conditions in the fluid by abruptly reducing the pressure and increasing the fluid rock interaction rate producing a structural framework characterized by a pervasively interconnected system of discontinuous and anastomosed quartz carbonate sulfide gold veins fieldwork petrographic analysis and mineral chemistry characterization suggest that the fluid had an aqueous carbonic nature and low salinity values thermometric studies suggest that gold mineralization occurred between 250 c and 400 c stable isotopes of s c and o indicate a metamorphic source for the fluid whole rock geochemistry and microprobe studies highlight hydrothermal alteration processes involving fe ca mg k na au and ag metasomatism the principe gold deposit belongs to the orogenic class but it is distinguished from other orogenic type occurrences in the natividade gold district and from most orogenic deposits of the world for not being located along a shear zone instead it is situated within a regional scale auriferous pressure shadow that was brought about by a short lived pressure drop during the brasiliano cycle

influence of thermal and mechanical cracks on permeability and elastic wave velocities in a basalt from mt etna volcano subjected to elevated pressure abstract we report simultaneous laboratory measurements of seismic velocities and fluid permeability on lava flow basalt from etna italy results were obtained for dry and saturated samples deformed under triaxial compression during each test the effective pressure was first increased up to 190 mpa to investigate the effect of pre existing crack closure on seismic properties then the effective pressure was unloaded down to 20 mpa a pressure which mirrors the stress field acting under a lava pile of approximately 1 5 2 km thick and deviatoric stress was increased until failure of the specimens using an effective medium model the measured elastic wave velocities were inverted in terms of two crack densities i the crack density of the pre existing thermal cracks and v the crack density of the stress induced cracks in addition a link was established between elastic properties elastic wave velocities vp and vs and permeability using a statistical permeability model our results show that the velocities increase with increasing hydrostatic pressure up to 190 mpa due to the closure of the pre existing thermal cracks this is interpreted by a decrease of the crack density i from 1 to 0 2 the effect of pre existing cracks closure is also highlighted by the permeability evolution which decreases of more than two orders of magnitude under deviatoric loading the velocities signature is interpreted in the first stage of the loading by the closure of the pre existing thermal cracks however with increasing deviatoric loading newly formed vertical cracks nucleate and propagate this is clearly seen from the velocity signature and its interpretation in term of crack density from the location of the acoustic emission sources and from microstructural observations this competition between pre existing cracks closure and propagation of vertical cracks is also seen from the permeability evolution and our study shows that mechanically induced cracks has lesser influence on permeability change than pre existing thermal cracks

major types characteristics and geodynamic mechanism of upper paleozoic copper deposits in northern xinjiang northwestern china abstract syn and post orogenic cu mineralization in the northern xinjiang paleozoic accretionary and collisional orogenic belt in northwestern china is of great economic interest about 40 cu bearing deposits have been discovered in the area making it one of the most important metallogenic belts in china according to their host rocks these deposits can be classified into four principal types 1 volcanic hosted massive sulfide cu pb zn deposits 2 porphyry cu mo au deposits 3 magmatic cu ni sulfide deposits and 4 cu mo au ag skarn deposits tectonically the development of these upper paleozoic deposits was closely associated with subduction and collision of the ancient asian ocean between the siberian block and the tarim craton an important metallogenic epoch involving formation of cu pb zn polymetallic deposits formed during southwestern rollback and associated slab detachment during devonian time 400 370 ma in southern altay southwestern direct rollback and associated slab detachment occurred during the devonian 400 370 ma in response to later collision at the accreted continetal margin xiao w j windley b f badarch g sun s li j l qin k z wang z h 2004 palaeozoic accretionary and convergent tectonics of the southern altaids implications for the lateral growth of central asia journal of the geological society of london 161 339 342 during which the ashele cu pb zn and keketale pb zn deposits formed subduction led to the accretion of the junggar ocean arc system in the middle devonian in the lower to middle carboniferous north dipping subduction beneath the dananhu arc triggered the emplacement of granitic porphyries in the tousuquan and dananhu island arc belt in the east tianshan leading to the formation of the tuwu and yandong porphyry cu mo au ag deposits in the upper carboniferous to lower permian large mafic ultramafic complexes were emplaced during closure of the ancient tianshan ocean resulting in the formation of several magmatic cu ni sulfide deposits including the kalatongke cu ni deposits in north junggar and cu ni sulfide deposits in the huangshan jing erquan area of east tianshan mountains also associated with this extensional event were emplacement of voluminous anatectic granitoids and eruption of volcanic rocks which led to formation of skarn cu mo suoerkuduk cu mo deposit and cu ag deposits weiquan cu ag deposit the tectonic settings geological features and temporal and spatial distribution of these different types of cu deposits reflect to a great extent the accretionary and collisional tectonics that occurred between the siberian block and tarim block

relative source locations of continuous tremor before and after the subplinian events at shinmoe dake in 2011 volcano monitoring systems are not always ready to resolve signals at the onset of eruptive activity this study makes use of stations installed later to calibrate the performance of the stations that had been operated before the eruption seven stations recorded continuous volcanic tremor before and during the subplinian eruptions of shinmoe dake japan in 2011 we estimated the source locations of the tremor using the amplitude distribution the stability of the analysis was obtained by careful selection of time windows in which signals from a single source are dominated the site effects and the regional attenuation factor were evaluated using tremor recorded after the major eruptions by a dense seismic array and a good number of stations a tremor source changed its depth beneath the crater for one week before the major eruption rising from a depth of a few kilometer to the water layer three times each of which occurred following shallow inflation and minor eruptions it is interpreted as migration of gas probably with magma which further transported heat to the water layer and triggered the subplinian eruptions

possible source dichotomy of contemporaneous post collisional barren i type versus tin bearing a type granites lying on opposite sides of the south tien shan suture abstract two granitoid complexes in the eastern kyrgyz tien shan situated north and south of the southern tien shan suture were studied the suture formed as a result of the closure of the turkestan ocean and collision of the tarim microcontinent in the south with the middle tien shan in the north the timing of collision is still disputed the deformed calc alkaline terektinsky complex situated immediately north of the suture represents one of the largest shear zone related intrusions in the tien shan 130 5 15 km in size small stocks of evolved a type granites of the inylchek complex hosting economic tin mineralization were emplaced immediately south of the suture opposite the terektinsky complex two samples from the terektinsky complex and 3 samples from three a type stocks were collected for u pb zircon shrimp ii geochronology the ages at 2 level obtained for the terektinsky complex north of the suture 294 5 ma and 291 5 ma and ages of the small granite bodies south of the suture 299 4 ma 295 4 ma 289 6 ma tashkoro inylchek and maida adir intrusions respectively are nearly identical within error limits they show that the southern tien shan suture in the eastern kyrgyz tien shan had already formed by 295 ma and had evolved into a transcrustal mega shear zone controlling emplacement of granitoids geochemical distinction between the two magmatic systems is based on 10 original bulk and trace analyses of rocks from this study and on a large dataset extracted from previously published research and unpublished reports geochemically the rocks of the terektinsky complex comprise calc alkaline high potassium i type series while the granites of the inylchek complex are typical a type granites with an elevated alumina saturation index and higher boron contents compared to a standard a type rapakivi granite contrasting metallogenic features of the two granitoid complexes south and north of the southern tien shan suture are defined by their sources a fertile fore arc complex and or passive margin sediments of tarim to the south and barren metamorphic precambrian basement of the middle tien shan to the north

deglacial and postglacial sedimentary architecture in a deeply incised paleovalley paleofjord the pennsylvanian late carboniferous jejenes formation san juan argentina quebrada de las lajas near san juan argentina preserves an early pennsylvanian deglacial postglacial succession in a highly confined paleofjord setting the sedimentary succession records four distinct stages in the evolution of the valley fill stage 1 is represented by the deposits of subglacial diamictites ice contact deltas and related deep water lacustrine environments including several subaqueous channels stage 2 records a glacio eustatic marine transgression and a slow down of the clastic supply into the paleofjord stage 3 records a sandy confined turbidite environment stage 4 consists of a coarse grained delta which represents a significant rejuvenation of the sedimentary system in the paleofjord the transition from stage 1 to stage 2 was abrupt and basinwide and has proven to be a good regional correlation marker in this paleovalley the glacio eustatic rise probably caused floating and consequent rapid melting of the valley glacier this resulted in a paleovalley wide turbidite event that is up to 5 m thick and indicates an overall waning character the rapid sediment emplacement in this event and resulting loading of the paleovalley sediments may have helped cause widespread mass transport events at the stage 1 2 boundary all stages show evidence of mass transport related deposits but stage 1 records the most widespread mass transport with a large spectrum of processes represented including coherently slumped material rafted blocks and completely mixed debris flow deposits these mass transport deposits range from a few meters to over 50 m thick and up to hundreds of meters wide and long most of the large mass transport deposits in the lower part of the fjord fill occurred at the transition to stage 2 implicating a rise in relative sea level as a possible trigger for the slope failures additionally stage 3 deposits were affected by several thrust sense dislocations that have large offsets relative to the scale of the sedimentary succession tens to over 50 m vertically and hundreds of meters laterally strata associated with the dislocations exhibit growth indicating very early movement and they are interpreted as the frontal ramp zones of mass transport deposits the abundance and size of mass transport deposits in stages 1 and 3 helped control sediment pathways throughout the paleofjord

mechanism for postliquefaction water film generation in layered sand soil investigations at two sites demonstrate that layered structure or stratification in sand deposits is prevalent not only in reclaimed ground but also in natural alluvial ground one dimensional liquefaction tests in a lucite tube are then carried out for models of several types of layered sand indicating that water films will develop under most circumstances beneath or within less permeable sublayers a basic mechanism for the water film generation is discussed based on the measurements of soil settlement and excess pore pressure the development of the water film and the associated soil settlement are numerically simulated by a simple sedimentation analysis and a rational explanation of the test results is found thus a significant involvement of water films in liquefied sand deposits and their basic mechanism are clarified it is highly probable that water films are involved as a part of a sliding surface and play a significant role in a seismically induced flow failure in loose and layered sand deposits during liquefaction

earthquake response and sliding displacement of submarine sensitive clay slopes abstract many submarine landslides occur through marine sensitive clay layers and the strain softening behavior plays a key role the changing soil properties induced by various disturbances will have marked impact on earthquake performance of submarine clay slopes in the present study undrained triaxial compression tests on reconsolidated samples of a soft sensitive marine clay were conducted and a soil disturbance dependent simple constitutive model is proposed for describing post peak nonlinear strain softening behavior of sensitive clays based on experimental results and then is implemented in quiver code to perform one dimensional seismic response analysis of mild infinite slopes to address the relative importance of soil disturbance effect on the site response and sliding displacement of submerged slopes during seismic loading detailed laboratory test descriptions and results of a soft sensitive marine clay model formulations and comprehensive computational efforts are presented parametric study of site response analysis focusing on the effects of soil disturbance degree and depth on generic clay grounds with varying sloping angles subjected to harmonic and earthquake loadings are performed the predicted acceleration amplification maximum shear strains and permanent displacements provide insight of earthquake performance of submarine sensitive clay slopes the main findings are drawn based on several key concepts first undisturbed sensitive clay is typically stiffer and stronger than disturbed clay consolidated at the same stress level and hence unless strain softening is triggered structured sensitive clay will perform better than insensitive clay of the same residual strength second post peak softening at shallow depth will lead to strain localization on a thin layer which is the main cause of sudden change of upward wave propagation characteristics and large permanent displacement at seabed surface of mild submarine clay slope thirdly soil disturbance degrees and depths have very marked effects on seismic response and displacement performance of sensitive clay slopes and such effect will be further enhanced by slope angle or earthquake intensity which should be cautiously treated in engineering design

tectonic evolution of the south tianshan orogen and adjacent regions nw china geochemical and age constraints of granitoid rocks geochemical and geochronological evidence was obtained from granitoids of the south tianshan orogen and adjacent regions which consist of three individual tectonic domains the kazakhstan yili plate the central tianshan terrane and the tarim plate from north to south the central tianshan terrane is structurally bounded by the early paleozoic nikolaev line north nalati fault and late paleozoic atbashy inyl chek south nalati qawabulak fault zones against the kazakhstan yili and tarim plates respectively the meta aluminous to weakly peraluminous granitic rocks which are exposed along the kekesu river and the bikai river across the central tianshan terrane have a tholeiitic calc alkaline or high potassium calc alkaline composition i type geochemical trace element characteristics and the y versus rb nb or y versus nb discrimination diagrams favor a continental arc setting for these granitoid rocks shrimp u pb and la icp ms u pb zircon age data indicate that the magmatism started at about 480 ma continued from 460 to 330 ma and ended at about 275 ma the earlier magmatism 470 ma is considered to be the result of a simultaneous southward and northward subduction of the terskey ocean beneath the northern margin of the tarim plate and the kazakhstan yili plate respectively the later magmatism 460 330 ma is related to the northward subduction of the south tianshan ocean beneath the southern margin of the kazakhstan yili central tianshan plate the dataset presented here in conjunction with previously published data support a late paleozoic tectonic evolution of the south tianshan orogen not a triassic one as recently suggested by shrimp u pb zircon dating for eclogites

seismic triggering of submarine slides in soft cohesive soil deposits abstract the geological profile of many submerged slopes on the continental shelf consists of normally to lightly overconsolidated clays with depths ranging from a few meters to hundreds of meters for these soils earthquake loading can generate significant excess pore water pressures at depth which can bring the slope to a state of instability during the event or at a later time as a result of pore pressure redistribution within the soil profile seismic triggering mechanisms of landslide initiation for these soils are analyzed with the use of a new simplified model for clays which predicts realistic variations of the stress strain strength relationships as well as pore pressure generation during dynamic loading in simple shear the proposed model is implemented in a finite element program to analyze the seismic response of submarine slopes these analyses provide an assessment of the critical depth and estimated displacements of the mobilized materials and thus are important components for the estimation of submarine landslide induced tsunamis

effect of degradation on seismic response of israeli continental slope constitutive models of soil behavior under cyclic loading that incorporate masing rules are often used to perform seismic site response analyses these analyses often ignore the effect of cyclic degradation of stiffness and strength on the seismic response of horizontal soft clay strata the authors recently proposed a normalized form of the shear stress strain relationship for undrained cyclic simple shear of soft clay cyclic degradation is considered via a single fatigue parameter the mean effective stress used in normalization of stresses and strains cyclic degradation of the small strain shear modulus though is neglected the normalized model is combined with an effective stress model for simple shear loading and boundary conditions developed within the framework of bounding surface kinematic and isotropic hardening plasticity to produce a model that is suitable for site response analysis this paper demonstrates the use of this model in one dimensional propagation analysis to compare the expected response in a soft clay profile to that response that would be estimated without accounting for cyclic degradation by neglecting cyclic degradation underestimation of velocities and accelerations developed in the profile are apparent

triassic mineralization with cretaceous overprint in the dahu au mo deposit xiaoqinling gold province constraints from shrimp monazite u th pb geochronology abstract the xiaoqinling terrane in central china is the second largest gold producing area in china previous application of age constraints has yielded ages for the gold mineralization ranging from paleoproterozoic through triassic indosinian to jurassic and cretaceous yanshanian shrimp u th pb dating of hydrothermal monazite in a mo mineralized quartz vein from the dahu au mo deposit in the northern xiaoqinling terrane identifies two mineralization episodes hydrothermal monazite intergrown with molybdenite yields an initial precipitation age of 216 5 ma which is identical to but more precise than the molybdenite re os isochron age of 218 41 ma a younger generation of monazite is distinguished by data falling on a mixing array it is inferred that the younger monazite was formed at the expense of the older ones during the yanshanian probably during a single event that occurred at 125 ma combining these results with available geochronological data and geological evidence we conclude that molybdenum mineralization accompanied by monazite deposition took place in the indosinian followed by a yanshanian tectono hydrothermal event that resulted in large scale gold mineralization in the xiaoqinling terrane our observation demonstrates that monazite is sensitive to hydrothermal overprint and thus is useful for dating fluid infiltration event

analysis of submarine landsliding in the rupture area of the 27 february 2010 maule earthquake central chile the comparison of bathymetric datasets compiled before and after the mw 8 8 maule earthquake of the 27 february 2010 offshore central chile proves that no new submarine landslides on a size scale detectable with hull mounted bathymetric echosounders features of a horizontal size of 1 km formed as a direct consequence of the ground shaking gravity coring around a pre existing slide feature offshore concepcion biobio slide however documents that 1 a number of events occurred as retrogressive failures of the biobio slide wall the youngest of which is 700 1000 years old and that 2 a very recent small scale slide structure resulted from non destructive imbricate stacking of a thin sediment layer pore water geochemical data show that this event post dates the maule earthquake suggesting that it was triggered by one of the numerous aftershocks the absence of larger failures and the presence of a small slide let us propose that in contrast to apparent logic frequent violent earthquakes at convergent margins do not necessarily pose a particular tsunami risk by landslides the frequent shaking might even limit the slide volume and therefore their tsunami hazard as instead of rare and large slides frequent smaller slides are induced

galicia bank sediment transport activity in response to continuous sedimentary instability dynamics a geotechnical perspective the sedimentary instability dynamics occurring over time throughout the isolated galicia bank atlantic ocean nw iberian peninsula have been studied using a sedimentological and geotechnical approach featuring a quantitative assessment of slope stability under different scenarios including earthquake activity the erosion of the scarps in the galicia bank includes the continuous development of small instabilities evacuated along gullies and channels or deposited on slopes these deposits may be subsequently mobilized evolving into new sedimentary gravity flows e g turbidity flow the studied sediments consist mostly of poorly to very poorly sorted sands and silts transported by turbidity currents and occasionally by debris flow processes the sediments in the study area identified as normally consolidated and located on gently sloping areas gradients less than 5 may become unstable if low magnitude seismic events occur pga 10 without any trigger other than oversteepening in contrast overconsolidated sediments may remain stable under static conditions and may become unstable on slope gradients 10 when earthquakes occur with the maximum peak ground acceleration pga 0 34 the sedimentological and geotechnical models presented herein are complementary approaches that can be utilized to understand the long term sedimentary instability dynamics observed within the study area such results are critical for better understanding sedimentary models of the dismantling processes of deep seamounts located far away from continental sedimentary inputs

paleoseismicity along the southern kuril trench deduced from submarine fan turbidites abstract large m 8 damaging interplate earthquakes occur frequently in the eastern hokkaido region northern japan where the pacific plate is subducting rapidly beneath the okhotsk north american plate at approximately 8 cm yr 1 with the aim of estimating the long term recurrence intervals of earthquakes in this region seven sediment cores were obtained from a submarine fan located on the forearc slope along the southern kuril trench japan the cores contain a number of turbidites some of which can be correlated among the cores on the basis of the analysis of lithology chronology and the composition of sand grains foraminiferal assemblages and the composition of sand grains indicate that the upper middle slope 1000 m water depth is the source of the turbidites the deep sea origin of the turbidites is consistent with the hypothesis that they were derived from slope failures initiated by strong shaking associated with earthquake events the recurrence intervals of turbidite deposition are 113 439 yr for events that occurred over the past 7 kyr the short intervals are recorded in the cores obtained from levees on the middle fan although many large earthquakes 150 cm s 2 of peak ground acceleration at the inferred slump sources occurred during the 19th and 20th centuries the pilot core from the upper fan contains only three turbidites located stratigraphically above layers of 17th century volcanic ash the results of 210pbex and 137cs dating combined with simulations of the ground accelerations of historical earthquakes enable correlation of the three turbidites with known historical earthquakes the 1952 tokachi oki and the 1961 and 1973 nemuro oki earthquakes the turbidites within the sampled cores potentially record about half of the large earthquakes known to have occurred over the interval covered by the cores the fact that any single core records only a portion of the known seismic events suggests that the recurrence interval of earthquakes in this region is less than 113 yr during holocene

assessment of source probabilities for potential tsunamis affecting the u s atlantic coast abstract estimating the likelihood of tsunamis occurring along the u s atlantic coast critically depends on knowledge of tsunami source probability we review available information on both earthquake and landslide probabilities from potential sources that could generate local and transoceanic tsunamis estimating source probability includes defining both size and recurrence distributions for earthquakes and landslides for the former distribution source sizes are often distributed according to a truncated or tapered power law relationship for the latter distribution sources are often assumed to occur in time according to a poisson process simplifying the way tsunami probabilities from individual sources can be aggregated for the u s atlantic coast earthquake tsunami sources primarily occur at transoceanic distances along plate boundary faults probabilities for these sources are constrained from previous statistical studies of global seismicity for similar plate boundary types in contrast there is presently little information constraining landslide probabilities that may generate local tsunamis though there is significant uncertainty in tsunami source probabilities for the atlantic results from this study yield a comparative analysis of tsunami source recurrence rates that can form the basis for future probabilistic analyses

intrusion hosted mineralization in the charters towers goldfield north queensland new isotopic and fluid inclusion constraints on the timing and origin of the auriferous veins auriferous quartz sulfide veins of the charters towers goldfield are mainly hosted in oxidized i type granitoids of the ravenswood batholith k ar and ar ar isotope age data of hydrothermal muscovite from alteration envelopes of veins at charters towers and the hadleigh castle mine 40 km east of charters towers are indistinguishable within error suggesting broadly synchronous gold deposition between 410 and 404 ma and across a significant segment of the ravenswood batholith published geochronological data indicate that several granitoid bodies were emplaced into the ravenswood batholith at the time of gold mineralization despite their association in space and time with igneous rocks the gold deposits lack an obvious causative intrusion moreover published lead isotope studies indicate that the lead in the ore was not acquired from any of the exposed intrusions a distal origin of the ore forming fluids also may be inferred from nitrogen isotope values of hydrothermal sericite suggesting wall rock interaction with metamorphic fluids or fluids that were in equilibrium with metamorphic rocks during the paragenetic stage of pyrite and arsenopyrite deposition stage ii veins of the charters towers goldfield contain three different types of fluid inclusions which are distinguishable by petrography and microthermometry this study is the first to report saline fluid inclusions in sphalerite 18 9 28 3 wt nacl equiv and vein quartz 20 9 24 7 wt nacl equiv trapped during the stage of gold deposition stage iii the range of temperatures and salinities particularly of the saline inclusions in sphalerite could indicate mixing between hotter more saline fluids e g deep seated magmatic and cooler more dilute solutions e g modified meteoric as the cause of gold deposition the geological and geochemical data are not compatible with derivation of fluids metals and ligands from individual plutons similarity of host rocks ore element associations alteration assemblages structural controls and tectonic settings strongly suggest that the auriferous veins of the charters towers goldfield belong to a group of granitoid hosted lode gold deposits that are generally classified as orogenic

a ductile to brittle shear zone hosted cu mineralization geological geochronological geochemical and fluid inclusion studies of the lingyun cu deposit southern tianshan nw china abstract the lingyun cu deposit is located at the northern margin of the south tianshan accretionary complex nw china in the lingyun mine area the rocks are cut by a nw trending yanxingshan ductile to brittle shear zone all orebodies are hosted in crystal tuff the sulfide mineralization in the lingyun cu deposit can be divided into early e and late l paragenetic stages the e stage is characteristic of fault controlled sulfide assemblages chalcopyrite bornite chalcocite quartz veins in the foliation fabric of the crystal tuff with albite sericite epidote biotite assemblages in the l stage the assemblages of ankerite chalcopyrite bornite chalcocite are present in veinlets that cut the e stage assemblages the sulfide assemblages in the lingyun deposit are characterized by striations in the metamorphosed crystal tuff ribbon like silicate minerals in the crystal tuff share common deformation features with the sulfide assemblages the host rock of the lingyun cu deposit yields a concordia age of ca 405 ma indicating that the aerbishibulake formation formed during southward subduction of the south tianshan ocean beneath the tarim block moreover crystal tuff samples show well developed negative sr anomaly and positive rb th u nd and p anomalies which are common in arc related volcanic rocks the ca 297 ma re os isochron age yielded by sulfides is much younger than the host rock which implies that the lingyun cu deposit is a typical epigenetic deposit both similar ree fractionated patterns between sulfide ores and crystal tuff and the high initial 187 os 188 os ratio 18 54 0 67 indicate significant crustal materials input the 40 ar 39 ar plateau age of ca 292 ma from the ribbon like sericite in crystal tuff is coeval with the mineralization occurrence in the lingyun cu deposit by contrast diorite dikes that crosscut the crystal tuff formed at ca 221 ma which is much younger than the sulfide mineralization thus the mineralization in the lingyun deposit is likely to have been generated by shear zone activity rather than the intrusion of diorite dikes three types of fluid inclusions have been identified in the lingyun cu deposit aqueous w type mixed aqueous carbonic m type and pure carbonic c type inclusions these three types of fluid inclusions are all found in the e stage quartz whereas only the w type fluid inclusions have been observed in l stage ankerite fluid inclusions from the e stage commonly contain co 2 and h 2 o locally with n 2 with low salinity which are common in orogenic deposits by contrast l stage fluid inclusions show low co 2 concentrations and salinity indicating a significant inflow of meteoric water given the regional geology ore geology coeval ore forming and deformation and fluid inclusion features the lingyun cu deposit may be associated with the orogenic class of mineral systems

influence of weak layers on seismic stability of submarine slopes abstract instability of submarine slopes and the risk posed by submarine slides are a concern in offshore activities related to energy communications food production and tourism in particular much of the offshore infrastructure needed for the extraction and transportation of hydrocarbons in deep waters are located on the continental slope with significant exposure to the risk posed by a submarine landslide recent studies of the triggering mechanisms of a submarine landslide show that the combination of a predisposition factor like a weak layer within the soil profile together with a short duration trigger such as an earthquake is one of the most likely scenarios for slide initiation in this paper the influence of a weak layer on the stability of a submarine slope before during and after a strong earthquake event is examined the slope under study is located in the southern part of the gulf of mexico on the continental slope in a water depth of 500 m the slope stability assessments in the study include static slope stability using the limit equilibrium method and the finite element method pseudo static analyses using the limit equilibrium method as well as 1 d and 2 d non linear dynamic analyses using the finite element method the earthquake induced shear strains within the soil deposit are a key parameter in the slope stability assessment therefore the dynamic analyses focused on estimating the maximum and permanent shear strains within the soil profile given the complexity of the problem the decrease of the soil strength during and after the earthquake loading was estimated through a decoupled approach based on the calculated shear strains and results of advanced laboratory tests the results of the study show quantitatively the important role of a weak layer in the initiation of a submarine landslide under a strong earthquake

explanation of temporal clustering of tsunami sources using the epidemic type aftershock sequence model temporal clustering of tsunami sources is examined in terms of a branching process model it previously was observed that there are more short interevent times between consecutive tsunami sources than expected from a stationary poisson process the epidemic type aftershock sequence etas branching process model is fitted to tsunami catalog events using the earthquake magnitude of the causative event from the centennial and global centroid moment tensor cmt catalogs and tsunami sizes above a completeness level as a mark to indicate that a tsunami was generated the etas parameters are estimated using the maximum likelihood method the interevent distribution associated with the etas model provides a better fit to the data than the poisson model or other temporal clustering models when tsunamigenic conditions magnitude threshold submarine location dip slip mechanism are applied to the global cmt catalog etas parameters are obtained that are consistent with those estimated from the tsunami catalog in particular the dip slip condition appears to result in a near zero magnitude effect for triggered tsunami sources the overall consistency between results from the tsunami catalog and that from the earthquake catalog under tsunamigenic conditions indicates that etas models based on seismicity can provide the structure for understanding patterns of tsunami source occurrence the fractional rate of triggered tsunami sources on a global basis is approximately 14 online material figures of residual analysis for tsunami and earthquake catalogs

acoustic emission and velocities associated with the formation of compaction bands in sandstone received 31 may 2005 revised 2 may 2006 accepted 22 june 2006 published 7 october 2006 1 a series of laboratory experiments has been conducted in which three dimensional 3 d locations of acoustic emissions ae were recorded and used to analyze the development of compaction bands in bleurswiller sandstone which has a porosity of 25 results were obtained for saturated samples deformed under triaxial compression at three different confining pressures 60 80 and 100 mpa a pore pressure of 10 mpa and room temperature we recorded acoustic emissions compressional and shear wave velocities and porosity reduction under hydrostatic condition and under triaxial loading conditions at a constant axial strain rate our results show that seismic velocities and their amplitude increased during hydrostatic pressure build up and during initial axial loading during shear enhanced compaction axial and radial velocities decreased progressively indicating an increase of stress induced damage in the rock in experiments performed at confining pressures of 80 and 100 mpa during triaxial loading acoustic emissions were localized in clusters during progressive loading ae clusters grow horizontally perpendicular to the maximum principal stress direction indicating formation of compaction bands throughout the specimens microstructural analysis of deformed specimens confirmed a spatial correspondence of ae clusters and compaction bands for the experiment performed at a confining pressure of 60 mpa ae locations and microstructural observations show symmetric compaction bands inclined to the cylinder axis of the specimen in agreement with predictions from recent theoretical models

the viscous brittle transition of crystal bearing silicic melt direct observation of magma rupture and healing magmas may fl ow or break depending on their deformation rate the transition between such viscous and brittle behavior controls the style of volcanic eruptions while the brittle failure of silicate melts is reasonably well characterized the effect of crystals on the viscous brittle transition has not yet been constrained here we examine the effect of suspended crystals on the mechanical failure of magmas using torsion experiments performed at temperatures 600 900 c strain rates 10 4 10 1 s 1 and confi ning pressures 200 300 mpa relevant for volcanic systems we present a relationship that predicts the critical stress and associated strain rate at which magmas fail as a function of crystal fraction furthermore the results demonstrate that the viscous to brittle transition occurs at lower stresses and strain rates when crystals are present the fractures formed during brittle failure of crystal bearing magma originate in the melt phase which enables gas to escape and hence to reduce gas overpressure these degassing pathways heal on relatively short time scales owing to the high confi ning pressure at depth highlighting the possibility that coherent lavas may actually be the healed remains of partially degassed magma parcels that have undergone many cycles of fracturing and healing

re os pyrite and u pb zircon geochronology from the taldybulak levoberezhny gold deposit insight for cambrian metallogeny of the kyrgyz northern tien shan abstract the taldybulak levoberezhny gold deposit located in the eastern part of the kyrgyz northern tien shan is hosted in highly deformed precambrian schist and gneisses that have undergone intense quartz carbonate fuchsite and tourmaline alterations gold mineralization is ultimately subdivided into two stages based on the observation of alteration assemblages orebody geometries and the occurrences of au bearing minerals negative thermal ionization mass spectrometry re os isotopic analyses of five au rich pyrite samples from the early stage yielded an isochron age of 511 18 ma zircon sensitive high resolution ion microprobe u pb dating of a diorite dike sample postdating the late stage mineralization yielded a wide range of ages from 3055 to 291 ma while a weighted mean 206 pb 238 u age of 414 6 6 8 ma is believed to represent the age of dike intrusion and the upper limit on the timing of the late stage quartz tourmaline gold formation the pyrite 187 os 188 os initial ratio of 0 132 0 011 together with os values varying from 0 to 14 indicate a major mantle component for the source of os and by inference ore metals which may be linked to the ophiolite suite of the kopurelisai complex in the taldybulak levoberezhny area considering the geodynamic setting of the kyrgyz northern tien shan during the early paleozoic we suggest that cambrian mineralization of the taldybulak levoberezhny deposit can be attributed to a subduction related setting probably associated with the earliest accretion of the northern tien shan

sediment gravity flows triggered by remotely generated earthquake waves recent great earthquakes and tsunamis around the world have heightened awareness of the inevitability of similar events occurring within the cascadia subduction zone of the pacific northwest we analyzed seafloor temperature pressure and seismic signals and of video stills of sediment enveloped instruments recorded during the 2011 2015 cascadia initiative experiment and seafloor morphology our results led us to suggest that thick accretionary prism sediments amplified and extended seismic wave durations from the april 11 2012 mw8 6 indian ocean earthquake located more than 13 500 km away these waves triggered a sequence of small slope failures on the cascadia margin that led to sediment gravity flows culminating in turbidity currents previous studies have related the triggering of sediment laden gravity flows and turbidite deposition to local earthquakes but this is the first study in which the originating seismic event is extremely distant 10 000 km the possibility of remotely triggered slope failures that generate sediment laden gravity flows should be considered in inferences of recurrence intervals of past great cascadia earthquakes from turbidite sequences future similar studies may provide new understanding of submarine slope failures and turbidity currents and the hazards they pose to seafloor infrastructure and tsunami generation in regions both with and without local earthquakes

cascadia onshore offshore site response submarine sediment mobilization and earthquake recurrence local geologic structure and topography may modify arriving seismic waves this inherent variation in shaking or site response may affect the distribution of slope failures and redistribution of submarine sediments i used seafloor seismic data from the 2011 to 2015 cascadia initiative and permanent onshore seismic networks to derive estimates of site response denoted sn in low and high frequency 0 02 1 and 1 10 hz passbands for three shaking metrics peak velocity and acceleration and energy density sn varies similarly throughout cascadia and changes primarily in the direction of convergence roughly east west in the two passbands sn patterns offshore are nearly opposite and range over an order of magnitude or more across cascadia sn patterns broadly may be attributed to sediment resonance and attenuation this and an abrupt step in the east west trend of sn suggest that changes in topography and structure at the edge of the continental margin significantly impact shaking these patterns also correlate with gravity lows diagnostic of marginal basins and methane plumes channeled within shelf bounding faults offshore sn exceeds that onshore in both passbands and the steepest slopes and shelf coincide with the relatively greatest and smallest sn estimates at low and high frequencies respectively these results should be considered in submarine shaking triggered slope stability failure studies significant north south sn variations are not apparent but sparse sampling does not permit rejection of the hypothesis that the southerly decrease in intervals between shaking triggered turbidites and great earthquakes inferred by goldfinger et al 2012 2013 2016 and priest et al 2017 is due to inherently stronger shaking southward

seismicity preceding volcanic eruptions new experimental insights a variety of seismic signals representing different physical mechanisms precedes volcanic eruptions the most meaningful signals are high and low frequency earthquakes and volcanic tremor that have tentatively been related to fracturing and magma transport in the volcanic edifice we provide experimental support for this association by reproducing magma migration while recording seismic signals opening fractures emit high frequency acoustic events while the switch to low frequency and harmonic tremor accompanies the flow of the melt in the fractures discerning between these seismic signals in nature can significantly refine volcanic hazard evaluation

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

early paleozoic tectonic evolution of the chinese south tianshan orogen constraints from shrimp zircon u pb geochronology and geochemistry of basaltic and dioritic rocks from xiate nw china traditionally the chinese south tianshan has been regarded as a late paleozoic orogenic belt however little is known about the early paleozoic tectonic architecture of the region this paper presents the first evidence of cambrian ordovician morb type basalts and adakitic diorites on the southern margin of the yili plate in china basalts from xiate in southwestern tianshan show a typical transitional t morb and ferrobasalt composition which indicate a formation at a propagating spreading ridge the basalts give a weighted mean 206pb 238u crystallization age of 516 3 7 4 ma by shrimp u pb zircon dating and have experienced contact metamorphism due to the intrusion of a dioritic pluton the dioritic pluton has a weighted mean 206pb 238u crystallization age of 470 12 ma and geochemical characteristics resembling that of adakitic rocks the pluton is considered to have been formed by partial melting of garnet amphibolites from thickened lower crust in arc or continental collision settings the basalts and diorites are considered to outline the eastern extension of the early paleozoic suture zone the nikolaev line which stretches east west for hundreds of kilometers between the northern tianshan and central tianshan terranes of kyrgyzstan our findings substantiate that the yili and central tianshan plates were separated by the early paleozoic terskey ocean the terskey ocean probably closed during the early stage of the late ordovician lomize et al in geotectonics 31 6 463 482 1997 resulting in the final amalgamation of the yili and central tianshan plates consequently an early paleozoic suture zone is documented in the chinese tianshan region which is most likely represented by the north nalati fault

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

late magmatic healed fractures in granitoids and their influence on subsequent solid state deformation abstract late magmatic fractures developed during final stages of magma crystallization are recorded in many granitoid plutons by planar trails of magmatic biotite and or leucocratic veins but have not been previously described such biotite rich trails with lengths of a few centimetres to several tens of centimetres widths of a few millimetres and a variable orientation are ubiquitous in meta granitoids of the neves area tauern window eastern alps italy these pre alpine granitoids were metamorphosed to upper amphibolite facies and deformed during the alpine orogeny allowing the effect of planar healed magmatic fractures on the nucleation of subsequent solid state ductile shear zones to be directly assessed numerical models considering power law viscous materials predict that planar arrays of a weaker mineral e g biotite oriented at around 45 to the shortening direction should nucleate and localize viscous deformation however no discernible localization on the natural small scale biotite trails is observed even when they delineate planes that were well oriented for shear reactivation in contrast heterogeneous shear zones nucleated on larger scale 1 10 m long planar compositional or structural boundaries such as joints dykes quartz veins alteration layers surrounding veins and zones of magma mingling outlined by densely packed clusters of basic enclaves irrespective of their orientation relative to the imposed shortening direction clearly some crucial aspect is missing from purely viscous numerical models we propose that this missing aspect is the observed interplay between fracture and flow with new fractures developing and localizing shear at bulk strains too low for discernible localization to occur on the pre existing healed magmatic fractures natural granitoids have a truly elasto plasto viscous rheology even at low differential stress as in the neves example and for high grade metamorphic conditions considered as typical of wet ductile middle crust

laboratory simulation of volcano seismicity the physical processes generating seismicity within volcanic edifices are highly complex and not fully understood we report results from a laboratory experiment in which basalt from mount etna volcano italy was deformed and fractured the experiment was monitored with an array of transducers around the sample to permit full waveform capture location and analysis of microseismic events rapid post failure decompression of the water filled pore volume and damage zone triggered many low frequency events analogous to volcanic long period seismicity the low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample these events exhibited a weak component of shear double couple slip consistent with fluid driven events occurring beneath active volcanoes

mass wasting on the submarine lomonosov ridge central arctic ocean a total of seven arcuate transverse troughs 5 6 km wide 7 9 km long and 150 200 m deep are present on both sides of the crest of the central part of lomonosov ridge arctic ocean the troughs occur within a restricted ridge length of ca 65 km trough morphology and disrupted piecewise continuous sub bottom reflections down to a common stratigraphic horizon below the troughs indicate lateral spread of progressively disintegrating sediment blocks above a glide plane lomonosov ridge is aseismic but the spatially restricted mass waste occurrences suggest sediment instability induced by earthquake loading another possibility is a pressure wave from a possible impact of an extraterrestrial object on alpha ridge about 500 km away the slide event s is likely to be pre late pleistocene as sediment deposition within one of the slide scars appears continuous over the last c 600 ka 2007 elsevier b v all rights reserved