shallow creep on the haiyuan fault gansu china revealed by sar interferometry interferometric synthetic aperture radar data are used to map the interseismic velocity field along the haiyuan fault system hfs at the north eastern boundary of the tibetan plateau two m 8 earthquakes ruptured the hfs in 1920 and 1927 but its 260 km long central section known as the tianzhu seismic gap remains unbroken since 1000 years the envisat sar data spanning the 2003 2009 period cover about 200 300 km2 along three descending and two ascending tracks interferograms are processed using an adapted version of roi pac the signal due to stratified atmospheric phase delay is empirically corrected together with orbital residuals mean line of sight velocity maps are computed using a constrained time series analysis after selection of interferograms with low atmospheric noise these maps show a dominant left lateral motion across the hfs and reveal a narrow 35 km long zone of high velocity gradient across the fault in between the tianzhu gap and the 1920 rupture we model the observed velocity field using a discretized fault creeping at shallow depth and a least squares inversion the inferred shallow slip rate distribution reveals aseismic slip in between two fully locked segments the average creep rate is 5 mm yr 1 comparable in magnitude with the estimated loading rate at depth suggesting no strain accumulation on this segment the modeled creep rate locally exceeds the long term rate reaching 8 mm yr 1 suggesting transient creep episodes the present study emphasizes the need for continuous monitoring of the surface velocity in the vicinity of major seismic gaps in terms of seismic hazard assessment

sedimentation from buoyant muddy plumes in the presence of interface mixing an experimental study a series of flume experiments were conducted to study the sediment removal rates characterized by an effective settling velocity from buoyant muddy plumes overriding clear saltwater at steady state conditions under different richardson numbers and initial suspended sediment concentrations the experiments were all carried out in the subcritical regime leading to cusps style instabilities at the interface of the two fluids flocculation in the experiments was not suppressed yet flocs remained small while in the plume layer data from the experiments allowed for calculation of the individual floc settling velocity ws f and the overall effective settling velocity ws eff i e that velocity needed to predict the downward flux with cws eff results showed that ws eff was greater than the floc settling velocity in all runs ws eff was found to increase with plume velocity and interface mixing but not with plume concentration the difference between the effective and floc settling velocities was therefore attributed to turbulent diffusion brought on by mixing at the interface and not to convective sedimentation or leaking the turbulence enhanced settling velocity ws t was found to be a strong function of the richardson number and conceptual and empirical equations are presented to predict ws t as a function of the plume surface velocity ups and richardson number ri this analysis showed that ws t upsri 2 in the runs with low richardson number ws t was approximately equal to the floc settling velocity leading to an overall doubling of the effective settling velocity relative to that of the individual particles this article is protected by copyright all rights reserved

holocene rate of slip and tentative recurrence interval for large earthquakes on the san andreas fault cajon pass southern california abstract detailed mapping of the san andreas fault zone where it crosses cajon creek southern california has revealed a number of late quaternary deposits and geomorphological features offset by the fault radiocarbon dates from alluvial and swamp deposits provide a detailed chronology with which to characterize the activity of the san andreas fault four independent determinations of the slip rate on the san andreas fault yield an average rate of 24 5 3 5 mm yr for the past 14 400 years the similarity of the four values which span different intervals of time from 5900 to 14 400 years ago suggest that the slip rate has been constant during this period the slip rate confirms that the san andreas fault is accumulating slip faster than any other fault in the plate boundary throughout california also the sum of the slip rates on the san andreas 24 5 mm yr and the san jacinto 10 mm yr faults south of their junction is the same as the san andreas north of their junction 35 mm yr an excavation provided evidence for at least two and up to four earthquakes that caused rupture on the fault between 1290 and 1805 a d and tentative evidence for six earthquakes in about the last 1000 years both lines of evidence imply an average recurrence interval for large earthquakes of about 1 to 2 centuries combined with the historic record this investigation indicates that the last major earthquake at cajon creek was probably at the beginning or middle of the 18th century while the record at cajon creek may suggest that the next major earthquake on the san andreas fault is overdue the data can be interpreted to indicate that the recurrence interval for earthquakes on the san andreas south of the 1857 rupture is 3 to 4 centuries and that the anticipated event should not be expected until the next century

geodynamic controls on tertiary arc magmatism in ecuador constraints from u pb zircon geochronology of oligocene miocene intrusions and regional age distribution trends abstract we obtained u pb zircon ages of late tertiary intrusions in the northern andes to provide robust time calibration points for the intrusive geochronologic framework of ecuador which is mostly based on k ar data magmatism associated with intrusion emplacement ranges from 31 to 7 ma with ages mainly pooling in the late oligocene early miocene where both k ar and u pb data exist for a given intrusive system ages obtained by the different methods are usually concordant within 1 4 m y suggesting that k ar ages are accurate indicators for the timing of tertiary arc magmatism on a regional multi m y scale except for a single sample the investigated intrusions completely lack externally inherited zircons in agreement with dominantly zircon poor oceanic crustal basement domains spatio temporal distribution trends of tertiary arc magmatism inferred from screened u pb k ar and zircon fission track geochronologic data allow tracking of the progressive along arc broadening of a flat slab segment below southernmost ecuador in the mid to late miocene and of moderate slab shallowing in northern central ecuador in the late miocene these regional arc migration patterns correlate in time with the subduction of the buoyant inca plateau and the carnegie ridge seamount chain the temporal distribution of tertiary ecuadorian arc magmatism indicates a late oligocene early miocene arc magmatic flare up event comprising widespread ignimbrite eruption and batholith construction initiation of the flare up event coincides in time with accelerating less oblique farallon nazca south america plate convergence suggesting a positive feedback between convergence rates asthenospheric melt production mantle crust melt flux and upper crustal arc magmatic productivity in ecuador

exhumation and preservation of porphyry cu au deposits at oyu tolgoi south gobi region mongolia field relationships and u pb data zircon are used to constrain the timing of tectonomagmatic events that occurred shortly after the formation of late devonian 372 ma porphyry cu au deposits at oyu tolgoi mongolia in the two northernmost of the several discrete porphyry centers hugo dummett deposits upper devonian rocks positioned stratigraphically above copper gold mineralization preserve a record of uplift exhumation and subsequent burial shortly after mineralization strongly altered and mineralized quartz monzodiorite and volcanic rocks at hugo dummett are overlain by an unmineralized dacite sequence 369 2 ma the basal breccia and conglomerate of the dacite sequence contain mineralized porphyry clasts derived from erosion of the porphyry deposits two zircon grains recovered from one of these mineralized porphyry clasts yielded chemical abrasion thermal ionization mass spectrometry ca tims 206 pb 238 u dates of 374 0 1 9 and 371 4 1 6 ma which are consistent with previously published ages for mineralized intrusions this implies that oyu tolgoi or other nearby porphyry deposits were exhumed shortly after the main mineralization event weakly mineralized granodiorite dikes intruded the postmineralization dacite sequence as well as devonian sedimentary and volcaniclastic rocks that structurally overlie the dacite a weighted mean 206 pb 238 u age of 370 6 0 5 ma for this rock is based on the three youngest grains analyzed by the ca tims technique mswd 1 14 burial of the cu au deposits at oyu tolgoi soon after their exhumation was critical to their preservation exhumation and subsequent burial occurred at 371 ma during a short time frame within the overlapping u pb zircon ages for the quartz monzodiorite mineralized porphyry clast unmineralized dacite sequence and granodiorite unit

uniform slip rate along the kunlun fault implications for seismic behaviour and large scale tectonics a long term slip rate is derived from concordant 10 be 26 al and 14 c dating of cumulativeoffse ts along much of the length of the kunlun fault values at 6 sites indi cateuniform slip 11 5 2 0 mm yr since 40 kyr bp this relatively high slip rate corresponds to a first order discon tinuity in the asian crustal velocity field m 8a nd m 7 5 earthquakes on 2 segments of the fault recur with charac teristic slip 10 2ma nd 4 4 0 4m ev e ry 850 and 420 yrs respectively

surface rupture and slip distribution along the lenglongling fault in the ne tibetan plateau implications for faulting behavior abstract the lenglongling fault lllf is located in the western section of the tianzhu seismic gap along the qilian haiyuan fault zone in the ne tibetan plateau between the 1920 m8 5 haiyuan and the 1927 m8 0 gulang earthquakes there is little information about the paleoseismic history of the lllf and understanding the faulting history of the lllf is important for determining the seismic hazards of both the fault and the seismic gap using uav based photogrammetry high resolution satellite imagery and field investigations we mapped the surface trace of the fault in detail and measured 192 left lateral offsets of geomorphic markers along the fault trace a binned cumulative offset probability density copd distribution was calculated to analyze single event and multi event cumulative offsets as a result we find that the lllf has fresh scarps along the entire 120 km length indicating that the most recent event might have ruptured the full segment of the fault the coseismic offset of the most recent event changes along the fault trace and has an asymmetrical bell shaped distribution the maximum offset was 7 m located in the middle eastern section of the fault and the offset decreases progressively towards both ends the minimum offset located at the western end was 3 0 m and the average coseismic offset was 4 8 m the cumulative offsets of the four most recent paleoearthquakes are multiples of the coseismic offset of the most recent event and show similar slip distributions indicating that the fault ruptures with a characteristic slip the fault slip distribution estimated recurrence interval and estimated moment magnitude imply that the lllf releases accumulated strain energy mainly by repeatedly producing mw 7 5 7 8 earthquakes every 1000 200 years we also show that the binned copd technique performs well to separate single event and multi event cumulative offsets

subduction zones an introduction to comparative subductology abstract the subduction model for trench arc back arc systems was deduced more or less as a logical consequence of sea floor spreading many features in these systems such as thrust type inter plate earthquakes and deep earthquakes along wadati benioff zones are readily explained by the subduction model but other features such as extensional spreading and high heat flow in back arc regions and arc volcanism are difficult to explain an approach to solve these problems may be to recognize the existence of the two basically different modes of subduction one chilean type causing a compressional stress regime in the arc and back arc regions the other mariana type causing a tensional stress regime implications of the two types of the mode of subduction for some tectonic problems such as vertical movement and sediment accretion at trenches are discussed with special reference to the results of recent dsdp active margin drilling in discussing the possible causes of the two modes it is suggested that the large scale thermal and stress regimes in the back arc areas may not be the direct products of simple subduction but of some additional factors involving much greater energy such as mantle flow associated with the motion of major plates finally the possible great importance of various types of collision accretion and erosion at subduction zones is emphasized

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

late paleozoic to triassic evolution of the gondwana margin evidence from chilean frontal cordilleran batholiths 28 s to 31 s upper paleozoic to triassic chilean granitoids in the andean frontal cordillera between 28 s and 31 s record crustal and mantle conditions at the gondwana margin during the final assembly and initial breakup of the pangea supercontinent this period overlaps the end of paleozoic terrane accretion and precedes andean subduction integration of new trace element and isotopic data with other information on the granitoids and the regional geology leads to a tectonic model that has implications for other parts of the gondwana margin in the model the carboniferous to early permian is a period of oblique convergence associated elqui complex granitoids are diverse those in the guanta and montosa units are predominantly related to subduction processes whereas those in the cochiguas and el volcan units are dominated by melting of the subduction complex and older crust progressive oblique collision of the last pre pangea terrane equis along the margin resulted in crustal thickening associated with shortening deformation of foreland basinal sedimentary rocks and uplift of the elqui complex subsequent gravitational collapse of the inactive slab and lithospheric delamination resulted in the production of large amounts of basalt which intruded and melted the crust producing the post collisional ingaguas complex the los carricitos granitoids formed in thickened crust whereas the chollay el colorado and el leon units formed in thinner crust the ingaguas complex is part of the choiyoi granite rhyolite province whose formation similar to that of other gondwana silicic provinces was probably accentuated by anomalously hot upper mantle associated with the pangea supercontinent

factors controlling floc settling velocity along a longitudinal estuarine transect a 147 km longitudinal transect of flocculated cohesive sediment properties in san francisco bay sfb was conducted on june 17th 2008 our aim was to determine the factors that control floc settling velocity along the longitudinal axis of the estuary the inssev lf video system was used to measure floc diameters and settling velocities at 30 stations at a distance of 0 7 m above the estuary bed floc sizes d ranged from 22 m to 639 m and settling velocities ws ranged between 0 04 mm s 1 and 15 8 mm s 1 during the longitudinal transect nearbed turbulent shear stresses throughout the transect duration were within the 0 2 0 5 pa range which typically stimulates flocculation growth the individual d ws floc density plots suggest the suspended sediments encountered throughout sfb were composed of both muddy cohesive sediment and mixed sediments flocs mass weighted population mean settling velocity wsmass ranged from 0 5 mm s 1 to 10 mm s 1 the macrofloc and microfloc demarcation at 160 m sub populations demonstrated parameterised settling velocities which spanned nearly double the range of the sample mean settling velocities wsmean the macroflocs tended to dominate the suspended mass up to 77 of the ambient suspended solid concentration ssc from san pablo bay to carquinez strait the vicinity of the turbidity maximum zone microfloc mass was particularly significant typically 60 100 of the ssc in the northern section of south bay and most of central bay the transect took eleven hours to complete and was not fully synoptic during slack tide larger and faster settling flocs deposited accounting for most of the longitudinal variability the best single predictor of settling velocity was water velocity 39 min prior to sampling not suspended sediment concentration or salinity resuspension and settling lags are likely responsible for the lagged response of settling velocity to water velocity the distribution of individual floc diameters and settling velocities indicates that floc density for a given floc diameter varies greatly a small portion a few percent of suspended sediment mass in sfb is sand sized and inclusion of sand in flocs appears likely fractal theory for cohesive sediment assumes that there is a single primary particle size that flocculates which is not the case for these types of mixed sediment flocs the wide variability in the physical biological and chemical processes which contribute to flocculation within sfb means that spatial floc data is required in order to accurately represent the diverse floc dynamics present in the bay system the importance in determining accurate estimates of floc density has been highlighted by the sfb data as these provide the basis for realistic distributions of floc dry mass and the mass settling flux across a floc population however although video floc sampling devices can produce the various floc property trends observed in sfb good survey practice is still paramount one can see that if the sampling coverage i e data collection frequency is poor this could lead to potential mis interpretations of the data and only limited conclusions may be drawn from such a restricted survey for example a limited survey i e only 3 stations compared to the 10 stations in the full survey in south bay produces an under estimate in both the macrofloc sscmacro distribution by a factor of four and the wsmacro by a factor of two to develop sediment transport numerical models for sfb high quality floc size and settling data are needed to understand and simulate the depositional qualities of both suspended cohesive sediment and mixed sediments in san francisco bay this study has shown that the most pragmatic solution is a physically based approach whereby the detailed flocs d vs ws spectra are parameterised in terms of their macrofloc and microfloc properties this aids in model calibration whilst retaining more of the dynamical aspects of the floc populations all forms of flocculation are dynamically active processes therefore it is important to also include both ssc and turbulence functions together with the floc data

spatial coincidence and similar geochemistry of late triassic and eocene oligocene magmatism in the andes of northern chile evidence from the mmh porphyry type cu mo deposit chuquicamata district the mmh porphyry type copper molybdenum deposit in northern chile is the newest mine in the chuquicamata district one of largest copper concentrations on earth mineralized eocene oligocene porphyry intrusions are hosted by essentially barren triassic granodiorites despite a century of exploitation geologists still have problems in the mine distinguishing the triassic granodiorite from the most important ore carrying eocene porphyries in the district to resolve the problem internally consistent high quality geochemical analyses of the triassic and tertiary intrusives were carried out explaining the confusion they show that the rock units in question are nearly identical in composition and thus respond equally to hydrothermal alteration in detail the only difference in terms of chemical composition is that the main eocene oligocene porphyries carry relatively less fe and ni unexpectedly the mineralized eocene oligocene porphyries have consistently less u and th than other tertiary intrusions in the district a characteristic that may be valuable in exploration the supergiant copper molybdenum deposits in the central andes were formed within a narrow interval between 45 and 31 ma close to 7 of the 200 my duration of andean magmatism which resulted from subduction of oceanic lithosphere under south america since the jurassic although recent work has shown that subduction was active on the margin since paleozoic times pre andean pre jurassic gondwanan magmatism is often described as being very different having involved crustal melting and the generation of massive peraluminous rhyolites and granites this study shows that the indistinguishable late triassic and eocene oligocene intrusions occupy the same narrow ns geographic belt in northern chile if it is accepted that magma character may determine the potential to generate economic cu mo deposits then late triassic volcano plutonic centres in the same location in the south american margin could have contained valuable ore deposits although their preservation will depend on the level attained by pre mid jurassic erosion both late triassic and eocene oligocene magmatic events occurred during the waning stages of vigorous volcano plutonic cycles and both preceded apparent gaps in igneous activity rhaetian and post oligocene abrupt lateral shifts of the volcanic front and radical changes in the character of the magmas generated both late triassic and eocene oligocene intrusions were emplaced along the same narrow strip of crust it is probable that they both exploited the same deep crustal structures the eocene oligocene magmatic front was controlled by an orogen parallel shear system caused by oblique subduction it is possible that late triassic magmatism along the same belt had a similar setting the identified rhaetian gap in subduction and magmatism may have widespread implications

nonlinear characteristics of paleoseismicity in china detailed studies of historical seismicity and paleoseismological data for major late quaternary faults in china reveal spatial and temporal patterns in paleoseismic activity associated with these faults analysis of space time distributions of late quaternary faults and consideration of new models for deformation of the asian continent provide a basis for proposing a division of china and surrounding areas into five active tectonic provinces slip rates for active faults are highest in the himalayan collision zone between the indian and eurasian plates and gradually decrease away from the collision zone into the adjacent active tectonic provinces paleoearthquake recurrence intervals in the active tectonic provinces of china reflect seismogenic properties that are closely related to the position of these provinces relative to the converging indian and eurasian plates average recurrence intervals are 2000 years to as little as 310 900 years for active faults in the qinghai tibetan active tectonic province whereas recurrence intervals are 2000 4500 years in the xinjiang active tectonic province and longer than 2000 years to as much as 7250 years in the north china active tectonic province although average recurrence intervals are closely related to the slip rates of late quaternary faults no simple linear relationship exists between recurrence interval and slip rate further analysis of paleoseismicity on major active faults shows that there are temporal variations in recurrence intervals the case studies also indicate that for some provinces faults or fault segments there are three paleoseismic patterns linear logarithmic and stepped in the logarithmic and stepped patterns the earthquake temporal sequence is characterized by active periods earthquake clusters with relatively short recurrence intervals and quiet periods lack of clustering and relatively long recurrence intervals

laboratory investigation of the impact of lateral spreading on buoyancy flux in a river plume abstractthe relationship between lateral spreading and mixing in stratified gravity currents is investigated by comparing laterally confined and unconfined currents in a series of laboratory experiments the vertical turbulent buoyancy flux is determined using a control volume approach with velocity and density fields derived from combined particle image velocimetry piv and planar laser induced fluorescence plif lateral spreading is determined in the unconfined experiments based on plan view imaging using the optical thickness method otm the authors find that lateral spreading dramatically modifies the plume structure the spreading plume layer consists of approximately linear density and velocity profiles that extend to the surface whereas the channelized plume profiles are uniform near the surface lateral spreading decreases the average plume density relative to laterally confined currents with similar inflow conditions however the local turbulent buoyancy flux in the spreading experiments i

quaternary and active faulting observed on the 1985 academia sinica royal society geotraverse of tibet active and recent faulting along the main north south road in tibet is dominated by normal faulting occurring on northerly trending planes and by strike slip faulting both of which reflect an east west extension of the plateau normal faulting is prevalent in the southern half of the plateau but we saw no evidence for any major graben in the northern half strike slip faulting on roughly easterly trending structures is m ore prevalent in the northern half but conjugate faulting with right lateral slip on northwesterly trending planes and left lateral slip on northeasterly trending planes is common in the southern half in two areas we also observed components of thrust faulting apparently in association with young strikeslip faulting our most important results are bounds on the rates of slip on the two main strands of the kunlun strike slip fault system which trends east w est through the kunlun range ground moraine containing boulders of pyroxenite is separated by 30 km from the nearest outcrop of such rock implying that amount of displacement in the last 1 5 to 3 m a therefore the average rate of slip during the quaternary period has been between 10 and 20 mm a with a likely value of 13 mm a abundant fresh tension cracks and mole tracks imply continued slip on the main strand the xidatan tuosuohu maqu fault and the likely occurrence of a major earthquake in the last few hundred years consistent offsets of gullies and dry stream channels of about 10 m may reflect slip of that amount during such an earthquake and possible multiple offsets at one site suggest that slip may occur by large displacements of 10 m during infrequent great earthquakes along the other strand the kunlun pass fault offsets of roughly 50 to 150 m of apparently post glacial valleys and of one glacier and its terminal moraine suggest a holocene rate of slip between 5 and 20 mm a and most likely about 10 mm a on this fault these rapid rates of displacement imply that tibet is being extruded rapidly eastward at a rate com parable to the rate at which india is penetrating into eurasia and therefore that at present a substantial fraction of this penetration is being absorbed by the eastward extrusion of tibet

in situ observations of floc settling velocities in glacier bay alaska abstract in situ floc settling velocities and diameters of particles ranging in size from 0 63 to 5 05 mm equivalent circular diameter were measured under a buoyant discharge plume by deploying a bottom tripod mounted floc camera assembly fca in tarr inlet glacier bay alaska these observations were used to estimate floc effective densities three results emerge from this work first fits of settling velocity and effective density to diameter are consistent with expressions published for other environments suggesting that common controls on floc size and settling velocity operate across diverse marine environments second the raw data show considerable scatter with upper and lower 95 prediction intervals on settling velocity and excess density differing by about a factor of 7 analysis of sources of error suggests that the variability is caused by differences in component grain composition among flocs and turbulent stirring within the stilling box third bin averaged effective densities and settling velocities are highly correlated with diameter thus while it is not possible based on diameter to predict accurately the settling velocity of a single floc it is possible to estimate the mean settling velocity of a population of like sized flocs

active faulting and tectonics of the ningxia hui autonomous region china strike slip thrust and normal faulting all seem to play an active role in the tectonics of ningxia in the southernmost part of the region a major left lateral strike slip fault enters the region from the neighboring gansu province to the west and trends about s65 e this fault is very clear on landsat imagery and on aerial photos and the portion in eastern gansu and ningxia broke in the haiyuan earthquake of december 16 1920 displacements of 5 10 m caused by that earthquake are clear in numerous localities and accord with a revised value of the seismic moment of 1 2 1021n m the eastern end of the haiyuan fault terminates in a narrow south trending fold and thrust zone several other similar north to northwest trending fold and thrust belts are present in the area about 50 200 km northeast of the haiyuan fault and divide it into small apparently relatively undeformed blocks 10 40 km in dimensions the geometry of the structures in the fold and thrust zones and the apparently shallow depths at the time of deformation suggest that current deformation is similar to that that occurred in the fold and thrust belt of the idaho wyoming rocky mountains north of this area both the helan shan a horst and the yinchuan graben are bounded by clear active northerly trending normal faults in some cases with right lateral strike slip components the overall deformation hence seems to include dominant components of east west left lateral strike slip movement northeast southwest crustal shortening and northwest southeast extension we interpret the extension as a response to a northeast directed force applied to the ordos block and both this northeast directed force and the left lateral slip on the haiyuan fault to the eastward displacement of material on the northeast edge of the tibetan plateau with respect to eurasia north of it

offsets of late quaternary morphology rate of slip and recurrence of large earthquakes on the chang ma fault gansu china the chang ma fault in the western qilian shan gansu province shows evidence of consistent left lateral displacements despite a complex en echelon geometry we have measured short and long term offsets on two n70 80 e striking segments of the fault along the southern edge of the ta quen kou basin where it cuts late quaternary terraces transverse ridges and drainage channels to analyze the offsets of such structures at one site in the eastern part of the basin we ran topographic profiles parallel and perpendicular to the fault over a distance of about 5 km spectral analysis and comparison of longitudinal profiles north and south of the fault allowed us to separate horizontal offsets of structures of different wavelengths apparent on air photos and satellite images transverse profiles were used to determine the vertical throw whose variations appear to result from changes in the fault strike small horizontal offsets of ridge crests and valley slopes are about 55 m along the n70 e striking segment of the fault this displacement corresponds to an uplift of the northern block of about 27 m implying that the fault dips about 73 to the south the measurements also constrain horizontal projection of the slip vector to about n78 e a larger horizontal offset 500 m of morphological swells of longer wavelength 1 6 km is visible on the longitudinal profiles assuming that periglacial erosion has reshaped the surface of the lateral slopes and tops of ridges during the wurm glacial period the smallest offsets of adjacent ridge crests may postdate the begining of the holocene yielding an average rate of left lateral slip on the fault of 5 5 2 2 mm yr in the last 10 2 kyr in the western part of the ta quen kou basin a somewhat slower rate of holocene slip 4 6 4 mm yr is obtained measurement of the horizontal displacement due to the 1932 earthquake there 6 2 0 6 m would imply that the recurrence interval for similar earthquakes at this second site is 1350 540 years

global climate perturbations during the permo triassic mass extinctions recorded by continental tetrapods from south africa several studies of the marine sedimentary record have documented the evolution of global climate during the permo triassic mass extinction by contrast the continental records have been less exploited due to the scarcity of continuous sections from the latest permian into the early triassic the south african karoo basin exposes one of the most continuous geological successions of this time interval thus offering the possibility to reconstruct climate variations in southern laurasia from the middle permian to middle triassic interval both air temperature and humidity variations were estimated using stable oxygen 18op and carbon 13cc isotope compositions of vertebrate apatite significant fluctuations in both 18op and 13cc values mimic those of marine records and suggest that stable isotope compositions recorded in vertebrate apatite reflect global climate evolution in terms of air temperature oxygen isotopes show an abrupt increase of about 8 c toward the end of the wuchiapingian this occurred during a slight cooling trend from the capitanian to the permo triassic boundary ptb at the end of the permian an intense and fast warming of 16 c occurred and kept increasing during the olenekian these thermal fluctuations may be related to the emeishan south china and siberian volcanic paroxysms that took place at the end of the capitanian and at the end of the permian respectively vertebrate apatite 13cc partly reflects the important fluctuations of the atmospheric 13c values the differences with marine curves being likely due to the evolution of local humidity both the oxygen and carbon isotope compositions indicate that the ptb was followed by a warm and arid phase that lasted 6 ma before temperatures decreased during the late anisian toward that of the end permian environmental fluctuations occurring around the ptb that affected both continental and marine realms with similar magnitude likely originated from volcanism and methane release

a late neogene framework and transpressional system within the yingxiongling range western qaidam basin northeast tibetan plateau insights from seismic reflection profiles and active tectonics abstract the yingxiongling range is a topographically unique and active tectonic belt in the western qaidam basin that has recorded the structural evolution and interactions between itself and surrounding ranges throughout the late cenozoic although a large scale fault fold system within this region accommodates transpressive deformation the overall kinematic pattern remains highly debated regional seismic reflection profiles earthquake distributions focal mechanisms and displacement vector results are used in this study to rebuild a northern verging thrust and wedge tectonic system in a perpendicular direction interpretations of newly acquired three dimensional seismic data the timing of growth strata and the kinematics of active structures strongly support lateral structural deformation propagation and evolution of the southern yingxiongling range in the late neogene a novel analysis of active tectonic and seismic profiles enables us to rebuild the framework kinematics and evolutionary pattern of the yingxiongling range we also provide a new interpretation of lateral differentia along the yingxiongling range based on critical taper theory and suggest that this overall structure is an integrated part of the qimen tagh wedge since the late neogene rapid uplift in this area occurred in response to northward propagation of the qimen tagh wedge

application of apatite u th he thermochronometry to the determination of the sense and amount of vertical fault displacement at the chuquicamata porphyry copper deposit chile chuquicamata is the world s largest porphyry copper deposit notwithstanding the fact that a portion of the orebody has been faulted off by postmineralization movement along the west fault in order to locate the missing portion of the orebody in the vertical dimension a study was designed to estimate the sense and amount of vertical displacement along this major structure by measuring the u th he and fission track ages of vertically distributed apatite samples from each of the crustal blocks fortuna and chuquicamata intrusive complexes bordering the fault apatite u th he ages range from 32 to 16 ma whereas apatite fission track ages range from 33 to 28 ma reflecting the lower closure temperature of the u th he thermochronology method approximately 75 degrees vs approximately 125 degrees c for cooling rates of approximately 10 degrees c m y the u th he ages decrease systematically with depth in both blocks however the age elevation curve for the western fortuna block is shifted vertically with respect to the eastern chuquicamata block indicating that the postmineralization denudation was significantly greater to the west the minimum vertical displacement along the west fault is estimated to be 600 or 100 m implying that the missing portion of the chuquicamata deposit should be located at a present day elevation of at least 3 600 m the new apatite ages combined with previous thermochronometric data rb sr u pb ar ar reveal rapid cooling rates approximately 100 degrees c m y for the chuquicamata deposit following emplacement at about 35 ma thereby indicating that the cu mineralization took place at a depth of less than 4 km

global positioning system measurements from eastern tibet and their implications for india eurasia intercontinental deformation we present and interpret global positioning system gps measurements of crustal motions for the period 1991 1998 for a network encompassing the eastern part of the tibetan plateau and its foreland relative to a eurasian frame defined by minimizing the velocities of 16 gps stations in europe central asia and siberia stations within all parts of the plateau foreland in south china move 6 10 mm yr east southeast indicating that the eastward movement within the plateau is part of a broader eastward movement that involves the plateau and its eastern and northern foreland north of the plateau foreland stations move northeastward at 10 mm yr indicating that the northern boundary of the deformation zone lies north of the plateau with this realization of a eurasian frame the velocity of the gps station at bangalore in southern india implies that the northward motion of india is 5 12 mm yr slower than that predicted from the nuvel 1a plate reconstruction viewed relative to the south china block stations of the northeast plateau bounded on the north by the qilian shan and the altyn tagh fault move nne to ne with velocities ranging from 19 mm yr within the plateau to 5 11 mm yr in its foreland the altyn tagh fault shows left lateral slip of 10 mm yr at 95 e and shortening across the fault of 5 mm yr stations south and west of the xianshuihe xiaojiang fault system define a crustal fragment rotating clockwise at 10 mm yr relative to the south china block around the eastern himalayan syntaxis the gps measurements indicate no significant shortening 3 mm yr within the longmen shan of the central eastern plateau and its adjacent foreland although the longmen shan rise over 6 km in 100 km horizontal distance geological studies indicate that the deformational field was established diachronously in late miocene to pliocene time was characterized by no east west shortening of tibetan crust and has an inhomogeneous style of deformation resulting from a balance of different tectonic processes

timing and formation of porphyry cu mo mineralization in the chuquicamata district northern chile new constraints from the toki cluster the recently discovered toki cluster which includes the toki quetena genoveva miranda and opache porphyry cu mo prospects is located 15 km south southwest of the chuquicamata radomiro tomic mines in northern chile these prospects occur in an area of 5 6 km and are completely covered with neogene alluvial deposits inferred resources for the cluster are estimated at about 20 mt of fine copper with toki and quetena contributing 88 of these resources mineralization in these deposits is associated with tonalite porphyries that intruded andesites and dacites of the collahuasi group and intrusions of the fortuna los picos granodioritic complex hypogene mineralization in the toki cluster consists mainly of chalcopyrite bornite with minor molybdenite with mineralization grading outward to a chalcopyrite pyrite zone and ultimately to a pyrite halo alteration is dominantly of the potassic type with k feldspar and hydrothermal biotite sericitic alteration is relatively restricted to late quartz pyrite veins d type veins previous k ar geochronology for the cluster yielded ages within a range of 34 to 40 ma four new re os ages for toki indicate that molybdenite mineralization occurred in a single pulse at 38 ma re os ages for three different molybdenite samples from quetena are within error of the toki mineralization ages these ages are concordant with a new zircon u pb age of 38 6 0 7 ma from the tonalite porphyry in quetena two re os ages for genoveva 38 1 0 2 and 38 0 0 2 ma are also within error of the toki and quetena molybdenite ages four re os molybdenite ages for opache range between 36 4 and 37 6 ma the miranda prospect is the youngest with an age of 36 ma four new re os ages for the chuquicamata deposit range between 33 and 32 ma whereas nine new 40ar 39ar ages of biotite muscovite and k feldspar range between 32 and 31 ma analyzed molybdenites have re and os concentrations that vary between 21 3 099 ppm and 8 1 231 ppb respectively the highest re and os concentrations are found in the toki prospect three new 40ar 39ar ages for the toki cluster are younger than the re os mineralization ages the age spectra for these three samples show evidence of excess argon and have similar inverse isochron ages of 35 ma that probably reflect a late hydrothermal phyllic event the new geochronological data presented here for the toki cluster indicate that molybdenite mineralization occurred within a very short period probably within 2 ma and synchronously at 38 ma in three mineralization centers toki quetena and genoveva furthermore mineralization at the toki cluster preceded the emplacement of the chuquicamata deposit 35 31 ma and indicates that porphyry cu mo mineralization occurred episodically over a period of several million years in the chuquicamata district

u pb geochronologic constraints on the crustal evolution of the long range inlier newfoundland the long range mountains of newfoundland expose the northeastern most basement inlier of the appalachian orogen u pb results for two samples of basement gneiss reveal crustal formation ages of 1466 10 ma western brook pond charnockite and 1530 8 ma cat arm road gneiss indicating an affinity with pinwarian magmatism 1510 1450 ma in labrador a third sample of basement gneiss from the cat arm road dam site yielded a minimum formation age of 1631 ma these basement gneisses were intruded by granite plutons during two periods of grenvillian magmatism group i at 1032 1022 ma and group ii at 993 985 ma group i intrusions include the 1032 0 1 5 ma lomond river granite and the 1022 0 2 0 ma lake michel igneous suite group ii intrusions include the 999 4 ma potato hill charnockite 993 7 ma horse chops granite 984 9 1 6 ma cloud river granite and may include the apsy granite the metamorphic history of the long range inlier is complex and three discrete proterozoic metamorphic events can

the precordilleran fault system of chuquicamata northern chile evidence for reversals along arc parallel strike slip faults abstract the chilean precordillera situated between the longitudinal valley and the western cordillera of northern chile was the site of the andean magmatic arc from the late cretaceous to the eocene oligocene boundary magmatism came to an end during the incaic tectonic phase 38 ma which caused arc normal shortening and the development of longitudinal dextral strike slip faults precordilleran fault system this magmatic arc tectonism is also related to the formation of the chuqicamata porphyry copper ore deposit as well as of other important deposits of this type in the precordillera structural investigations in and around the chuqicamata open pit mine have shown that wrench tectonics determined the kinematics of the area the n s striking west fissure which separates a 35 ma old non mineralised pluton to the west from a central late paleozoic basement ridge containing the mineralization became a sinistral fault along with other parallel faults in the area the central part is separated from similar paleozoic rocks to the east by the messabi este fault and a narrow faulted and sheared syncline of mesozoic cenozoic sediments this fault bears structures indicating dextral movements which probably are of an age that is similar to the mylonites 34 8 ma in the western pluton the dextral movements preceded the sinistral shear thus the fault system of chuqicamata displays a reversal of arc parallel shear movements according to the orientation of quartz veins in the mineralized body it is presumed that the sense of displacement of these strike slip motions reversed when mineralization started at about 32 ma during this time the stress field must have changed fundamentally the incaic phase dextral transpression is supposed to have been induced by the oblique vector of plate motion the following sinistral transtension corresponds to a time of reduced convergence rate and possibly reduced plate coupling as however the vector of plate motion remained unchanged during that time oblique subduction cannot be used as an argument for arc parallel sinistral shear movements

spatio temporal evolution of aseismic slip along the haiyuan fault china implications for fault frictional properties article history we use 20 years of synthetic aperture radar acquisitions by the ers and envisat satellites to investigate the spatial and temporal variations of strain rates along the 35 km long creeping section of the haiyuan fault at the north eastern boundary of the tibetan plateau we then use the derived displacements to infer the fault s frictional properties and discuss the relationship between creep and the seismic behavior of the fault located in between a millennial seismic gap and the 1920 m8 surface rupture trace this section has an average creep rate of 5 1m m yr about the interseismic loading rate the comparison of average surface velocity profiles derived from sar interferometry across the creeping section reveals a creep rate increase and or a creep migration to shallower depth between the 1990s and the 2000s we apply a smoothed time series analysis scheme on envisat insar data to investigate the creep rate variations during the 2004 2009 time period our analysis reveals that the creep rate accelerated in 2007 although data resolution does not allow to better constrain the onset of creep acceleration and its amplitude both decadal and short term transient behaviors are coeval with the largest earthquakes m 4 5 along the fault segment in recent years from the precise mapping of the surface fault trace we use the fault strike variations and the mohr circle construction to compute the along strike distribution of the friction coefficient along the creeping segment and compare it with the observed distribution of the creep rate we find that the creep rate scales logarithmically with the friction coefficient in agreement with the rate and state friction law in a rate strengthening regime the estimated value of log v 2 10 3 indicates that the earthquakes occurring along the creeping section cannot be the cause for a significant change in the overall segment s creep rate and that the recorded micro seismicity is most likely creep driven finally given the size and frictional properties of the creeping section we estimate based on previous models of dynamic rupture simulations a 0 20 probability for a rupture to break through this section together with the geometrical configuration of the haiyuan fault these results suggest that the creeping segment may act as a persistent barrier to earthquake propagation

asynchronous maximum advances of mountain and continental glaciers the last maximum glacier advance in many mountain ranges appears to have predated the last maximum advance of the wisconsinan continental ice sheets 20 000 years b p published evidence from widely spaced localities in north and south america europe asia and hawai i suggests that some mountain glaciers extended farther during one or more stades early in the last glaciation roughly 115 000 30 000 years b p than at its end when low global temperature and high precipitation presumably were most favorable for the growth of glaciers variations in the timing of glacier advances in different mountain ranges suggest that alpine glaciers are dependent on regional climate as well as global conditions their study might provide sensitive tests for theories of global climate change glacial deposits are often used as time markers in neotectonic and geomorphic studies and their ages sometimes are inferred from distant measurements or from proxy histories of global climate change undated geomorphic features such as moraines sharply incised streams and river terraces which commonly have been associated with the last maximum glacier advance 20 000 years b p or last deglaciation 13 000 years b p may actually be older by a factor of 2 to 4 or more conversely deposits assigned to the maximum advances of the penultimate global glaciation 130 000 years b p may actually date from early in the most recent glacial cycle and be younger by a comparable factor rates of faulting or folding estimated from displacements or deformation and the assumed ages of such geomorphic features might be too great or too small by corresponding factors

settling velocity and mass settling flux of flocculated estuarine sediments new formulations are presented for the settling velocity and mass settling flux the product of settling velocity and sediment concentration of flocculated estuarine mud physics based formulae for these are developed based on assumptions of a two class floc population microflocs and macroflocs in quasi equilibrium with the flow the settling velocities of microflocs and macroflocs are related to floc size and density via the kolmogorov microscale as a function of turbulent shear stress and sediment concentration including height dependence and floc density dependence coefficients in the formulae are calibrated against an existing large data set of in situ observations of floc size and settling velocity from northern european estuaries various measures of performance show that the resulting formulae achieve an improved level of agreement with data compared with other published prediction methods the new formulae with the original calibration coefficients perform well in tests against independent measurements made in two estuaries

two ages of porphyry intrusion resolved for the super giant chuquicamata copper deposit of northern chile by ela icp ms and shrimp zircon u pb ages measured in situ by excimer laser ablation inductively coupled plasma mass spectrometry ela icp ms and verified by sensitive high resolution ion microprobe shrimp on ore bearing felsic porphyries from the chuquicamata porphyry copper molybdenum deposit northern chile identify two discrete igneous events the volumetrically dominant east porphyry has an age of 34 6 0 2 ma whereas the bench and west porphyries yield ages of 33 3 0 3 ma and 33 5 0 2 ma respectively the age of the east porphyry is indistinguishable from a re os age for early molybdenite mineralization 35 ma and the oldest reported 40 ar 39 ar ages for hydrothermal alteration confirming a genetic link with mineralization previous geological studies and 40 ar 39 ar and re os geochronology identify two main hydrothermal events high temperature potassic alteration with chalcopyrite at 33 4 0 3 ma followed by lower temperature quartz sericite alteration with pyrite at 31 1 0 3 ma the ages of the west and bench porphyries match the ages for potassic alteration younger quartz sericite alteration may reflect an additional fourth intrusion concealed at depth the anomalously large size of chuquicamata appears to be due to a protracted igneous history resulting in the superposition of at least two temporally distinct magmatic hydrothermal systems

early permian to late triassic batholiths of the chilean frontal cordillera 28 31 s shrimp u pb zircon ages and lu hf and o isotope systematics abstract one of the major geological units of the main andean range frontal cordillera of north central chile is a group of composite and heterochronous late paleozoic early mesozoic batholiths that extends for 500 km roughly ns along from 26 to 31 s ten new shrimp zircon crystallization ages together with 11 recently published u pb zircon ages by other authors indicate an episodic intrusion history which can be divided in 4 groups mississippian earliest carboniferous 330 326 ma cisuralian earliest permian 301 284 ma latest permian to middle triassic 264 242 ma and late triassic 225 215 ma volcanic rocks in the area span a similar time lu hf and o isotopic systematics in zircon grains from eight of the plutonic rocks indicate the magma source areas have contributed variable amounts of crustal and mantle components zircon 18 o values evolve from crustal values 7 in the earliest permian intrusives to mantle values in the latest permian to upper triassic including evidence for likely hydrothermal alteration of the source 4 zircon ehf values vary in a good linear correlation with the 18 o isotopes from 6 to 0 in rocks older than 270 ma increasing to 2 to 7 from lower to upper triassic 250 to 215 ma the petrogenetic constraints indicated by these values suggest that the influence of magma sources varied with time from predominantly crustal to mantle like in accord with the regional tectonic models the earliest permian rocks were generated in a subduction related magmatic arc which varied towards an extension related environment in the latest permian and triassic

high precision 40ar 39ar dating of two consecutive hydrothermal events in the chuquicamata porphyry copper system chile 40ar 39ar data have been used to resolve the relatively high temperature 350 c potassic alteration event at chuquicamata from the lower temperature 350 c quartz sericite alteration phase four k feldspars from the potassic zone yielded plateau large domain ages in the range 32 9 33 8 ma mean 33 4 0 3 ma the fact that apparent ages of co existing biotites span a similar range suggests that there was very rapid cooling through feldspar and biotite closure temperatures especially if these minerals closed at substantially different temperatures multi domain diffusion modelling of the feldspar data suggests that at this time cooling was rapid ca 60 80 my through closure temperatures of 330 440 c as these closure temperatures are substantially higher than the ones normally assumed for biotite i e about 300 c they and or the calculated cooling rates may be unreliable four sericites from the quartz sericite zone yielded variably discordant age spectra the least discordant of these has a plateau at 31 1 0 3 ma and this is interpreted as the time of this alteration event some k feldspars in the quartz sericite zone were completely overprinted at this later time and most of the other ones studied show partial overprinting overprinting appears to decrease as distance from the central quartz sericite zone increases in the more remote areas effects of the later event appear constrained to narrow fault controlled alteration zones the data are consistent with a conceptual model proposed by zentilli et al zentilli m leiva g rojas j graves m c 1994a the chuquicamata system revisited extended abstract society of economic geologists symposium copper deposits of the andes new developments concepcion chile october 17 18 1994 proceedings 2 1647 1651 wherein potassic alteration by late magmatic fluids occurred at depth prior to rapid exhumation of the system quartz sericite alteration perhaps caused by a new pulse of porphyry intrusion at depth occurred some 2 3 my later principally in the core of the deposit although alteration did propagate outwards through the action of hydrothermal fluids passing through a brittle relatively shallow fracture system

lateral spreading of a near field river plume observations and numerical simulations 1 data collected from the near field region of the merrimack river massachusetts plume were analyzed to examine plume spreading estimates of the plume spreading rate were derived from a direct assessment of the spreading of clustered surface drifters and from density and velocity data along a cross plume arc additionally plume spreading rates were also derived from highly resolved numerical model output roms these three distinct observational and numerical approaches have reasonable agreement and are compared favorably with observations using a control volume approach in a previous study it is demonstrated that these three methods are valid to estimate the plume spreading rate the observations and numerical simulations also allowed estimation of terms in the lateral momentum balance along streamline normals perpendicular to surface layer streamlines one principal finding of this study is that the dominant terms in the lateral momentum balance are the centrifugal force term associated with streamline curvature the buoyancy term the coriolis term and the interfacial stress term furthermore the lateral momentum balance shows that the lateral spreading process is significantly affected by interfacial stress within the first 1 to 2 km but thereafter is locally inviscid however turbulent mixing continues to play an important role in modifying the spreading rate by adjusting the internal wave speed

iron oxide copper gold deposits an andean view iron oxide copper gold iocg deposits defined primarily by their elevated magnetite and or hematite contents constitute a broad ill defined clan related to a variety of tectono magmatic settings the youngest and therefore most readily understandable iocg belt is located in the coastal cordillera of northern chile and southern peru where it is part of a volcano plutonic arc of jurassic through early cretaceous age the arc is characterised by voluminous tholeiitic to calc alkaline plutonic complexes of gabbro through granodiorite composition and primitive mantle derived parentage major arc parallel fault systems developed in response to extension and transtension induced by subduction roll back at the retreating convergent margin the arc crust was attenuated and subjected to high heat flow iocg deposits share the arc with massive magnetite deposits the copper deficient end members of the iocg clan as well as with manto type copper and small porphyry copper deposits to create a distinctive metallogenic signature

a simple universal equation for grain settling velocity abstract a new equation is presented for sediment fall velocity as a function of grain diameter for given values of fluid viscosity and fluid and solid density sediment fall velocity is a fundamental parameter in the modeling and interpretation of fluviatile and coastal deposition the equation applies to the entire range of viscous to turbulent conditions and its simple explicit form makes it easy to use in computer models and other applications in sedimentology geomorphology and engineering the equation is derived from dimensional analysis and converges on stokes law for small grains and a constant drag coefficient for large grains its two physically interpretable parameters are easily adjusted for shape effects or for the use of sieve diameter rather than nominal grain diameter it gives a close fit to published and new experimental data for both quartz sand and low density materials with no more error than previous equations of more complicated form

geodynamic evolution of the northern and central andes during early to middle mesozoic times a tethyan model the early to middle mesozoic sedimentary and magmatic history of the northern and central andes i e the nne trending colombian ecuadorian segment and the nw trending peruvian segment exhibits a spatially contrasted evolution involving several successive tectonic and geodynamic settings the late triassic to late liassic period began with a widespread marine transgression from the latest triassic the colombian marine shelf was progressively destroyed by southward propagating extensional tectonic activity but marine sedimentation continued in peru during this time no significant magmatic activity is recorded except in the emerging colombian area this period is interpreted as the result of rifting of a tethyan oceanic arm which separated the colombian and palaeo mexican margins from latest liassic an important calc alkaline magmatic arc developed along the emergent colombian segment further south the north peruvian shelf probably emerged but marine sedimentation continued in southern peru during middle and early late jurassic times the colombian segment was characterized by important magmatic activity and by coarse clastic continental sedimentation along the peruvian segment a turbiditic trough emergent areas and continental basins were created and the scarcity of calc alkaline magmatism suggests that only very local subduction took place this period is regarded as one of the southeastward subduction beneath the colombian segment and of tethyan oceanic crust originating in the newly formed colombian oceanic arm this pattern would have induced a chiefly left lateral transform motion along the peruvian segment by kimmeridgian tithonian times the palaeogeographic framework had drastically changed along the colombian segment magmatic activity ceased and continental accretions occurred along dextral strike slip sutures in peru tectonic activity was recorded by the creation of a new turbiditic trough and by the resumption of detrital sedimentation in the coastal area arc related volcanism indicated that subduction took place beneath this segment this geodynamic change is interpreted as the result of a sharp decrease in the spreading activity of the tethyan ridges and replacement by pacific spreading centres inducing a roughly northeastward convergence direction

holocene paleoearthquakes of the maoergai fault eastern tibet abstract much work about fault activity and seismic hazard assessment has been conducted on major boundary faults of eastern tibet whereas seismic activity on faults between subblocks is poorly understood the maoergai fault 200 km northwest of and parallel to the longmen shan is the eastern branch of the longriba fault zone that divides the bayan har block into the aba and longmen shan subblocks field investigation indicates that the maoergai fault is a purely right lateral strike slip fault active in the late quaternary our trenches combined with radiocarbon dating and bayesian analysis show that three holocene paleoearthquakes ruptured the maoergai fault at 8510 420 7100 70 and 5170 80 cal yr bp respectively this suggests that the fault fits a cluster model with an average recurrence interval of 1700 years and has a high potential of large earthquakes mw 7 2 7 4 in the near future our results also indicate that an apparent fault scarp on a sloping tread provides an alternative site for paleoseismic studies to determine coseismic horizontal displacement on a strike slip fault and using the age of the upper terrace to determine strike slip rate by displaced terrace riser is probably closer to the true value in streams with insufficient capacities of lateral erosion this study provides useful information for the earthquake risk and fault behavior in eastern tibet

relationship between copper tonnage of chilean base metal porphyry deposits and os isotope ratios re os isotopes in pyrite and chalcopyrite from early high temperature hypogene alteration assemblages in chilean porphyry copper deposits identify the source of os and by inference cu in these ore systems typical concentrations for os in both pyrite and chalcopyrite are between 7 and 30 ppt 10 12 g g and for re between 0 200 and 10 ppb 10 9 g g re os isochrons yield ages and initial 187 os 188 os ratios for the sulfides the isotopic data reflect the relative contributions of copper from the mantle and crust in chilean porphyry copper deposits seven ore deposits that reside in different tectonic terranes and represent distinct epochs of mineralization in chile were studied the initial osmium ratios of the first stage of mineralization at each of the deposits range from 0 15 to 5 these values are more radiogenic than the present chondritic mantle 0 13 and indicate significant crustal contributions of os to the magmatic and or hydrothermal systems there is a strong correspondence between the total copper content and initial os isotopic ratios in base metal porphyry deposits the larger deposits have lower initial os ratios than the smaller less significant deposits this relationship implies that larger deposits acquire a greater proportion of os from the mantle the initial os ratio of samples in the central segment of porphyry copper deposits of northern chile also decreases with decreasing age of the deposit a plausible interpretation of the re os data is that the later and larger deposits use regional tectonic and structural features that allow sampling of deeper more primitive magmatic sources

fault zone development and strain partitioning in an extensional strike slip duplex a case study from the mesozoic atacama fault system northern chile abstract upper crustal strike slip duplexes provide an excellent opportunity to address the fundamental question of fault zone development and strain partitioning in an evolving system detailed field mapping of the mesozoic atacama fault system in the coastal cordillera of northern chile documents the progressive development of second and third order faults forming a duplex at a dilational jog between two overstepping master faults the sinistral strike slip nnw striking jorgillo and bolfin faults these are constituted by a meter wide core of foliated s c ultracataclasite and cataclasite flanked by a damage zone of protocataclasite splay faults and veins lateral separation of markers along master faults is on the order of a few kilometers second order nw striking oblique slip subsidiary fault zones do not show foliated ultracataclasite lateral sinistral separations are in the range of 10 to 200 m with a relatively minor normal dip slip component in turn third order east west striking normal faults exhibit centimetric displacement oblique slip sinistral normal fault zones located at the southern termination of the bolfin fault form a well developed imbricate fan structure they exhibit a relatively simple architecture of extensional and extensional shear fractures bound by low displacement shear fractures kinematic analysis of fault slip data from mesoscopic faults within the duplex area document that the nw striking and the ew striking faults accommodate transtension and extension respectively examination of master and subsidiary faults of the duplex indicates a strong correlation between total displacement and internal fault structure faults started from arrays of en echelon extensional extensional shear fractures that then coalesced into throughgoing strike slip faults further displacement leads to the formation of discrete bands of cataclasite and ultracataclasite that take up a significant part of the total displacement we interpret that the duplex formed by progressive linkage of horsetail like structures at the southern tip of the bolfin fault that joined splay faults coming from the jorgillo and coloso faults the geometry and kinematics of faults is compared with that observed in analog models to gain an insight into the kinematic processes leading to complex strike slip fault zones in the upper crust

jurassic to palaeogene tectono magmatic evolution of northern chile and adjacent bolivia from detrital zircon u pb geochronology and heavy mineral provenance heavy mineral provenance data presented in this article reinforce evidence for significant late palaeogene deformation and relief formation along the western margin of the central andean plateau late eocene oligocene onset of molasse type sedimentation records initial range uplift strikingly different basement sources of sediments deposited to the east and west of the late palaeogene range indicate that initial relief development was governed by a bivergent thrust system significantly higher sediment accumulation rates to the east of the range compared to the west suggest that the generated relief acted already as an effective orographic barrier at that time higher precipitation and denudation along the eastern slope facilitated deeper erosion of the trust belt

sediment transport and deposition on a river dominated tidal flat an idealized model study 1 a 3 d hydrodynamic model is used to investigate how different size classes of river derived sediment are transported exported and trapped on an idealized river dominated tidal flat the model is composed of a river channel flanked by sloping tidal flats a configuration motivated by the intertidal region of the skagit river mouth in washington state united states it is forced by mixed tides and a pulse of freshwater and sediment with various settling velocities in this system the river not only influences stratification but also contributes a significant cross shore transport as a result the bottom stress is strongly ebb dominated in the channel because of the seaward advance of strong river flow as the tidal flats drain during ebbs sediment deposition patterns and mass budgets are sensitive to settling velocity the lateral sediment spreading scales with an advective distance settling time multiplied by lateral flow speed thereby confining the fast settling sediment classes in the channel residual sediment transport is landward on the flats because of settling lag but is strongly seaward in the channel the seaward transport mainly occurs during big ebbs and is controlled by a length scale ratio ld xwl where ld is a cross shore advective distance settling time multiplied by river outlet velocity and xwl is the immersed cross shore length of the intertidal zone sediment trapping requires ld xwl 1 leading to more trapping for the faster settling classes sensitivity studies show that including stratification and reducing tidal range both favor sediment trapping whereas varying channel geometries and asymmetry of tides has relatively small impacts implications of the modeling results on the south skagit intertidal region are discussed

asymmetrical river valleys in response to tectonic tilting and strike slip faulting northeast margin of tibetan plateau the northeast margin of the tibetan plateau a particularly important area to understand the mechanism of plateau formation is characterized by large transpressional arcuate faults there is debate on the amount of quaternary sinistral displacement on the major haiyuan fault previously unrecognized systemic asymmetrical valleys have developed between the haiyuan and xiangshan faults southeast tilting and sinistral displacement on the northeast side of the haiyuan fault resulted in southeast migration of large rivers and asymmetrical widening of their valleys leaving a systematic distribution of tilted strath terraces along their northwest sides where asymmetrical widening created by tilting kept pace with sinistral displacement rivers have not been deflected and the increase in valley width downstream from the fault should equate to total lateral displacement since river formation e g yuan river a 7 km asymmetrical valley with a c 2 2 ma paleomagnetic age where river deflection and asymmetrical valley growth are coeval valley width is less than total horizontal displacement e g hebao river a c 2 1 km asymmetrical valley with c 2 km deflection all rivers north of the haiyuan fault converge to cut across the xiangshan mountains as a gorge northeast thrusting of the upthrown side of the xiangshan fault has resulted in degradation and related strath terrace formation as the valleys asymmetrically widened a probable earthquake induced landslide caused by movement on the xiangshan fault in latest pleistocene blocked the gorge causing aggradation along all rivers and their tributaries deposition terraces were formed after the landslide dam was breached together with previous research on the xiangshan fault it is concluded that there has been c 7 km of quaternary sinistral displacement on the haiyuan and xiangshan faults along the northeast margin of the tibetan plateau since the formation of rivers that intersect them copyright 2014 john wiley sons ltd

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

towards accurate numerical calibration of the late triassic high precision u pb geochronology constraints on the duration of the rhaetian numerical calibration of the late triassic stages is arguably the most controversial issue in mesozoic stratigraphy despite its importance for assessing mechanisms of environmental perturbations and associated biologic consequences preceding the end triassic mass extinction here we report new chemical abrasion isotope dilution thermal ionization mass spectrometry zircon u pb dates for volcanic ash beds within the aramachay formation of the pucara group in northern peru that place precise constraints on the age of the norian rhaetian boundary nrb and the duration of the rhaetian the sampled ash bed bearing interval is located just above the last occurrence of the bivalve monotis subcircularis placing this stratigraphic sequence in the uppermost norian perhaps ranging into the earliest rhaetian zircon u pb dates of ash beds constrain the deposition age of this interval to be between 205 70 0 15 ma and 205 30 0 14 ma providing precise constraints on the age of the nrb combined with previously published zircon u pb dates for ash beds bracketing the triassic jurassic boundary we estimate a duration of 4 14 0 39 m y for the rhaetian this ends a prolonged controversy about the duration of this stage and has fundamental implications for the rates of paleoenvironmental deterioration that culminated in the end triassic mass extinction

geomorphic evidence for active faulting in the altyn tagh and northern tibet and qualitative estimates of its contribution to the convergence of india and eurasia a brief traverse across the altyn tagh and kunlun in northern tibet revealed abundant evidence for recent crustal deformation there from ridges offset roughly 10 m and from fresh mole tracks 40 cm or more high along the altyn tagh strike slip fault we conclude that a large earthquake occurred in the past few hundred years accordingly the rate of slip could be relatively high 30 20 mm yr active reverse or thrust faults mark the bases of several mountain ranges in the altyn tagh and kunlun where the neighboring basins lie at elevations less than 4000 m therefore roughly north south crustal shortening appears to be occurring there probably at a rate of several millimetres per year the crustal shortening accommodated by strike slip and reverse or thrust faulting appears to account for a significant part 10 25 of india s convergence with eurasia the broad zone of crustal shortening in northern tibet indicates that the areal extent of the plateau is increasing northward by crustal thickening on its northern margin

estuarine flocs their size settling velocity and density the size and settling velocity of flocs of suspended sediments from the chesapeake bay were measured in laboratory experiments and in the field the curves between floc diameter and settling velocity showed a non stoke s relationship that was best described by the following settling velocity cm s 1 73 floc diameter cm 0 78 furthermore the relationship between floc diameter and settling velocity indicated that the floe density decreased as the floes increased in size in addition to changing density a cylinder shape was found to be the best shape factor

the tectonics of the western ordos plateau ningxia china slip rates on the luoshan and east helanshan faults analysis of the locus style and rate of faulting is fundamental to understanding the kinematics of continental deformation the ordos plateau lies to the northeast of tibet within the india eurasia collision zone previous studies have suggested that it behaves rigidly and rotates anticlockwise within a large scale zone of ene wsw left lateral shearing for this rotation to be accommodated the eastern and western margins of the ordos plateau should be undergoing right lateral shearing and yet the dominant faulting style appears to be extensional we focus specifically on the kinematics of the faults bounding the western margin of the ordos plateau and make new slip rate estimates for two of the major faults in the region the right lateral strike slip luoshan fault and the normal slip east helanshan fault we use a combination of infrared stimulated luminescence dating of offset landforms with high resolution imagery and topography from the pleiades satellites to determine an average right lateral slip rate of 4 3 0 4 mm a 1 uncertainty on the luoshan fault similarly we use 10be exposure dating to determine a vertical throw rate on the east helanshan fault of 0 6 0 1 mm a corresponding to an extension rate of 0 7 0 1 mm a 1 uncertainty both of these results agree well with slip rates determined from the latest campaign gps data we therefore conclude that right lateral shearing is the dominant motion occurring in the western ordos region supporting a kinematic model of large scale anticlockwise rotation of the whole ordos plateau

bounds on the holocene slip rate of the haiyuan fault north central china abstract we measured the offsets of six stream valleys of 30 to 90 m along the northwest southeast trending left lateral haiyuan strike slip fault in north central china minimum ages of these offsets were determined to estimate lower bounds for the holocene slip rate the most reliable bounds are 7 6 1 0 and 6 7 1 0 mm yr with three others that are smaller 3 4 0 7 3 5 0 9 and 4 1 0 4 mm yr and one large value 16 4 5 9 mm yr that we doubt thus the average holocene slip rate of the haiyuan fault is larger than 6 mm yr and probably exceeds 7 mm yr if the average slip rate of 5 to 10 mm yr for the quaternary period is applicable to the holocene epoch the average rate is 8 2 mm yr

tectonics of the jurassic early cretaceous magmatic arc of the north chilean coastal cordillera 22 26 s a story of crustal deformation along a convergent plate boundary the tectonic evolution of a continental magmatic arc that was active in the north chilean coastal cordillera in jurassic early cretaceous times is described in order to show the relationship between arc deformation and plate convergence during stage i circa 195 155 ma a variety of structures formed at deep to shallow crustal levels indicating sinistral arc parallel strike slip movements from deep crustal levels a sequence of structures is described starting with the formation of a broad belt of plutonic rocks which were sheared under granulite to amphibolite facies conditions bolfin complex the high grade deformation was followed by the formation of two sets of conjugate greenschist facies shear zones showing strike slip and thrust kinematics with a nw se directed maximum horizontal shortening i e parallel to the probable late jurassic vector of plate convergence a kinematic pattern compatible to this plate convergence is displayed by nonmetamorphic folds thrusts and high angle normal faults which formed during the same time interval as the discrete shear zones during stage ii 160 150 ma strong arc normal extension is revealed by brittle low angle normal faults at shallow levels and some ductile normal faults and the intrusion of extended plutons at deeper levels during stage iii 155 147 ma two reversals in the stress regime took place indicated by two generations of dikes an older one trending ne sw and a younger one trending nw se sinistral strike slip movements also prevailed during stage iv until 125 ma when the atacama fault zone originated as a sinistral trench linked strike slip fault the tectonic evolution of the magmatic arc is interpreted in terms of coupling and decoupling between the downgoing and overriding plates the structures of stages i and iv suggest that stress transmission due to seismic coupling between the plates was probably responsible for these deformations however decoupling of the plates occurred possibly due to a decrease in convergence rate resulting in extension and the reversals of stages ii and iii

reported supergene sphalerite rims at the chuquicamata porphyry deposit northern chile revisited evidence for a hypogene origin previous studies attributed a supergene origin to sphalerite rimming copper minerals occurring in chuquicamata in a mineral assemblage including typically chalcocite digenite cu1 85s1 12 and u1 99s1 01 covellite cus and cu1 08s0 92 and sphalerite up to 1 2 wt fe microscopic observations on samples from a central and a southern section completed by scanning electronic microscope sem backscattering electron imaging and electron microprobe analyses suggest that all sphalerite in chuquicamata is hypogene a scenario backed by observations in each step that explains the formation of the peculiar sphalerite rims is the following 1 precipitation of chalcopyrite typical of the early and main hydrothermal stages 2 precipitation of sphalerite rimming chalcopyrite and in voids and in weakness sites during the late hydrothermal stage 3 partial or total replacement of chalcopyrite by chalcocite digenite during the late hydrothermal stage and 4 formation of lamellar covellite principally at the expense of chalcopyrite suggesting increasingly oxidizing and or acidic conditions this covellite may be linked to supergene processes and or to the late hydrothermal stage the findings of the present work have implications for the position of the lower limit of the supergene enrichment in the eastern southern part of the deposit as the sphalerite rims now interpreted as hypogene were the only potential supergene sulfide in the eastern vertical section of the southern section

a geochemical traverse across the north chilean andes evidence for crust generation from the mantle wedge major and trace element and sr and nd isotope analyses are presented on 186 0 ma magmatic rocks along an east west traverse across north chile at 22 s esr ranges from 25 to 100 and end from 6 to 9 but the low end and high esr values are in rocks generated in the last 15 ma it is argued that previous discussions of petrogenesis in north chile have been hampered because the changes in magma chemistry in this area of unusually thick crust reflect not one but two processes one results in a progressive shift of esr from 25 to 20 and end from 6 to 6 in jurassic to recent rocks which is accompanied by increasing ta sm and sr and decreasing th ta the second is largely confined to the younger rocks and it is characterised by esr increasing up to 100 with increasing sio2 and decreasing sr and it results in relatively shallow trends on an end esr diagram the preferred interpretation is that trend 1 is due to the mobilisation of old late proterozoic mantle lithosphere as magmatism migrated eastwards and that trend 2 is due to crustal melting and contamination with differentiation in this area of thickened continental crust it follows that the mantle wedge is the principal site of crust generation and it is argued that 20 of the sr in the recent northern chile rocks is derived from the subducted ocean crust

flood dispersal and deposition by near bed gravitational sediment flows and oceanographic transport a numerical modeling study of the eel river shelf northern california 1 a large flood of the eel river northern california created a thick sediment deposit between water depths of 50 and 70 m in january 1997 the freshwater plume however confined sediment delivery to water depths shallower than 30 m mechanisms proposed to explain the apparent cross shelf transport include dispersal by oceanographic currents resuspension by energetic waves and gravitationally forced transport of a thin layer of fluidized mud field observations indicate that these processes were all active but cannot determine their relative significance or whether these mechanisms alone explain the location size and timing of deposition approximately 30 of the sediment delivered by the eel river is accounted for in the midshelf mud bed and inner shelf but the fate of the remaining 70 is uncertain a three dimensional hydrodynamic model was used to examine potential mechanisms of sediment transport on the eel river shelf the model includes suspended sediment transport and was modified to account for a thin near bed layer of fluidized mud it was used to simulate flood dispersal on the eel river shelf to compare the relative importance of transport within the near bed fluid mud layer to suspended sediment transport and to evaluate sediment budgets for floods settling properties of fine grained sediment both within the flood plume and the fluid mud layer critically impact depositional patterns to a lesser degree wind driven ocean currents influence the volume of sediment that escapes the shelf and wave magnitude affects the cross shelf location of flood deposits though dilute suspension accounts for a large fraction of total flux cross shelf transport by gravitational forcing appears necessary to produce a midshelf mud deposit similar in volume location and timing to those seen offshore of the eel river

late paleozoic early triassic magmatism on the western margin of gondwana collahuasi area northern chile abstract the basement in the altiplano high plateau of the andes of northern chile mostly consists of late paleozoic to early triassic felsic igneous rocks collahuasi group that were emplaced and extruded along the western margin of the gondwana supercontinent this igneous suite crops out in the collahuasi area and forms the backbone of most of the high andes from latitude 20 to 22 s rocks of the collahuasi group and correlative formations form an extensive belt of volcanic and subvolcanic rocks throughout the main andes of chile the frontal cordillera of argentina choiyoi group or choiyoi granite rhyolite province and the eastern cordillera of peru thirteen new shrimp u pb zircon ages from the collahuasi area document a bimodal timing for magmatism with a dominant peak at about 300 ma and a less significant one at 244 ma copper mo porphyry mineralization is related to the younger igneous event initial hf isotopic ratios for the 300 ma zircons range from about 2 to 6 indicating that the magmas incorporated components with a significant crustal residence time the 244 ma magmas were derived from a less enriched source with the initial hf values ranging from 2 to 6 suggestive of a mixture with a more depleted component limited whole rock 144nd 143nd and 87sr 86sr isotopic ratios further support the likelihood that the collahuasi group magmatism incorporated significant older crustal components or at least a mixture of crustal sources with more and less evolved isotopic signatures

paleoseismology and slip rate of the western tianjingshan fault of ne tibet china abstract we present results from a detailed investigation of the horizontal displacement distribution timing of paleoearthquakes and left lateral slip rate on the western tianjingshan fault measurements of 240 offset streams and ridges confirm that the fault is left lateral and record evidence of repeated 3 4 m coseismic offsets along the 60 km long fault this suggests that 6 earthquakes may have occurred along the entire western tianjingshan fault with repeated occurrence of earthquakes of mw 7 2 7 5 structural and stratigraphic relationships exposed in our five trenches in combination with previously reported studies further indicate that the fault has ruptured in as many as six paleoearthquakes since the late quaternary paleoseismic data show that the average recurrence interval for holocene earthquakes is approximately 5 000 yr the most recent earthquake along the western tianjingshan fault occurred 1 2 0 1 kyr bp indicating that this fault segment did not rupture in the m 7 5 historical earthquake of 1709 that ruptured the central tianjingshan fault we estimate that the holocene slip rate of the western tianjingshan fault is 1 1 1 2 mm yr based on measurements of the age and offset of stream channels compared with the relatively fast slip rate of the haiyuan fault 4 6 mm yr we suggest that the tianjingshan fault acts as an essential active fault accommodating the sinistral displacement and crustal shortening deformation in ne tibet

the field of crustal velocity in asia calculated from quaternary rates of slip on faults rates of quaternary faulting when treated as measures of strain rates within regions several times larger than the depths of brittle faulting yield a velocity field for asia that matches the average relative velocity between the indian and eurasian plates over the past 2 myr nuvel 1a and the velocity of shanghai with respect to eurasia measured with very long baseline interferometry vlbi by using rates of slip on discrete surfaces faults to define average strain rates we explicitly assume that the large scale deformation can be treated as that of a continuum depending on the jcales over which strain rates are averaged 87 to 93 per cent of the assumed strain ites are fit within assigned 1 sigma uncertainties and 97 to 99 per cent are fit within 2 sigma the internal consistency of these data and the agreement with independent rates nuvel 1a and vlbi test the validity of treating large scale deformation of continents as that of a continuum in the calculated velocity field a large fraction 85 per cent of india s convergence with eurasia is absorbed by crustal or lithospheric thickening among consistently misfit assumed strain rates are those dominated by high rates of strike slip faulting strain associated with 20 30 mm a 1 of slip on the altyn tagh karakax and karakorum faults is inconsistent with the distributions of strain in surrounding regions we conclude that these rates all of which are based on correlations of ages of offset landforms with changes in global climate and not on radiometric dating have been systematically overestimated lateral transport out of india s northward path is relatively minor south china is calculated to move east southeast at less than 10 mm a 1

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

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

characterisation of triassic rifting in peru and implications for the early disassembly of western pangaea abstract triassic igneous and sedimentary rocks exposed within the basement of the andes were deposited in a series of rifts and may record the early disassembly of western pangaea these rocks are sporadically exposed along almost the entire length of western south america although reliable geochronological and isotopic data are sparse we combine new geochronological zircon u pb isotopic hf nd and geochemical data with stratigraphic observations to constrain the age and tectonic setting of the mitu rift of southern peru the peruvian mitu rift is compared with other triassic rifts in colombia and ecuador palanda rift 240 225 ma bolivia mitu rift triassic bolivia chile and argentina e g cuyo basin 246 230 ma and conclusions are reached regarding the relationship between triassic extension along the western margin of pangaea and the eventual formation of the proto caribbean and central atlantic oceans the mitu rift peru was active during 245 240 to 220 ma and was synchronous with rifting along the pacific margin of colombia and ecuador along the chilean margin and western argentina and probably rifting within bolivia rifting north of the huancabamba deflection was accompanied by subduction and led to seafloor spreading whereas rifting along the peruvian and chilean margins mainly occurred in the absence of subduction and terminated prior to the formation of extensive transitional crust extension within peru and chile probably occurred via a combination of transtension steepening and detachment of an arrested slab we propose that plate tectonic forces initiated the early break up of pangaea by attenuating its margins and enhancing mantle upwelling prolonged extension may have propagated along pre existing weak zones that extended into the continental interior captured melts derived from the upwelled mantle forming a lip e g central atlantic magmatic province became hot and weak and eventually lead to the formation of a juvenile ocean e g central atlantic

late pleistocene slip rate of the central haiyuan fault constrained from optically stimulated luminescence 14c and cosmogenic isotope dating and high resolution topography the haiyuan fault is a major left lateral active fault of the india asia collision zone while the 1000 km long fault between hala lake in the west to liupan shan in the east accommodates eastward displacement of northeast tibet relative to the gobi alashan to the north the amount of slip accumulated and its slip rate remain debated we revisit the site of daqing or sangedun at 102 7 e in gaudemer et al 1995 to better constrain the long term slip rate of the haiyuan fault in its central part we used terrestrial lidar to build a high resolution dem and unmanned aerial vehicle to build an aerial photomosaic with 0 1 m resolution to survey the offset terraces their geomorphology and the fault trace we refine the geomorphological interpretation of the site measure riser offsets and determine their relation to terrace formation the well constrained age of the highest terrace t3 at 13 7 1 5 ka determined from the combination of surface and sub surface osl 14 c and terrestrial in situ 10 be cosmogenic nuclide dating associated with the maximum lower terrace riser offset of 88 m yield a minimum slip rate of 6 4 1 2 mm yr over the late pleistocene the age of the intermediate terrace t2 is bracketed between 8 0 ka 14 c and 12 ka 10 be the ages and vertical offsets of the 2 highest terraces is used to infer the age of t2 offset vertically 5 7 m at 5 4 1 ka its 29 2 m offset is consistent with a rate of 6 5 mm yr given the vertical offset youngest terrace t1 of 1 3 0 2 m its age is estimated at 1 2 0 2 ka in agreement with the youngest surface exposure age overall a slip rate of 5 8 mm yr fits all offset and age data at the daqing site the smallest offset of a gully incised into t1 of 6 0 0 5 m is potentially associated with the most recent slip event that occurred in the last millennia

late pleistocene holocene activity of the zemuhe fault on the southeastern margin of the tibetan plateau abstract a n s trending active fault zone which includes the anninghe zemuhe and xiaojiang faults forms the tectonic boundary of the tibetan plateau on its southeastern margin marking the limit of the eastward extrusion of the tibetan plateau in this paper we document the late pleistocene holocene activity of the zemuhe fault which is the central segment of the fault zone we have been able to determine slip rate and the average recurrence interval of large earthquakes upon the fault based on aerial photograph interpretations field investigations trench excavations and radiocarbon age data the zemuhe fault is mainly characterized by left lateral offsets with a horizontal slip rate of 10 12 mm yr and a vertical slip component of 2 0 2 4 mm yr trench investigations and 14 c ages reveal that at least four large earthquakes occurred during the last 1100 1500 years indicating an average recurrence interval of 300 400 years for m 7 0 7 5 earthquakes consistent with the documented history of the region our results confirm that the zehume fault plays an important role as a tectonic boundary in releasing the strain energy caused by the southeastwards motion of the tibetan plateau the energy is released in the form of repeated large earthquakes

displacement along the haiyuan fault associated with the great 1920 haiyuan china earthquake abstract we used a plane table and an alidade to construct detailed topographic maps of offset features stream channels dry gullies and old terrace walls along the fault zone that ruptured during the 1920 haiyuan earthquake m 8 7 in ningxia and gansu china the maximum displacement appears to have reached 10 m at shikaguangou between the salt lake and xianzhou basins in southern ningxia the average displacement along the 100 km of the fault that we studied was about 8 m assuming that the average slip rate to be between 5 and 10 mm yr the recurrence interval for events similar to that in 1920 would be about 800 to 1600 yr

right lateral shear and rotation as the explanation for strike slip faulting in eastern tibet the convergence of two continents can be accommodated by crustal thickening and by lateral transport of crust out of the path of the converging continents1 3 the principal features suggesting that lateral transport is important are major strike slip faults striking roughly orthogonally to the orientation of convergence between the continents displacement on such faults is imagined to allow lateral transport of material with respect to the converging continents possibly accounting for a large fraction of the convergence between the two continents the most spectacular example of such strike slip faulting is in the eastern part of the tibetan plateau where three major left lateral faults with slip rates of 10 mm yr 1 and several smaller roughly parallel faults dominate the regional strain field2 3 cobbold and davy4 suggested that these faults may be rotating in a clockwise fashion here we put bounds on that rate of rotation and conclude that the image of lateral transport on such faults2 known also as continental escape extrusion or expulsion is an illusion and that instead the left lateral slip on east striking planes in eastern tibet is a manifestation of north striking right lateral simple shear if this conclusion is correct the east striking left lateral faults and the crustal blocks between them are rotating clockwise at 1 2 myr 1 the east west dimension of eastern tibet is shortening at 10 20 mm yr 1 and little material is moving eastward out of india s path into eurasia by left lateral simple shear

late pleistocene holocene slip rate along the hasi shan restraining bend of the haiyuan fault implication for faulting dynamics of a complex fault system we thank the associate editor and an anonymous reviewer for their insightful comments that greatly improve this manuscript we are grateful to rene boutin at laboratoire d hydrologie et geochimie de la surface and aster team g aumaitre d bourles and k keddadouche at aster cerege for icp aes and ams measurements respectively part of this work was supported by insu cnrs france and the university of strasbourg j van der woerd for the al and be concentration analyses at lhyges and ipgs and for 10be 9be and 26al 27al ratios measurements on the aster ams facility gerege aix en provence france supported by insu cnrs and ird we thank yang ye for his help with the chi square modeling of the depth profile data and a s meriaux for her help with error propagation and mean age calculations part of this work has been supported by the cnrs pics program france chine all slip rate data discussed in the paper but the ones derived in this study are extracted from the published literature listed in the reference list pleiades imagery is available for purchase from airbus industry https www intelligence airbusds com en 8692 pleiades this is ipgp contribution 4090

three dimensional mechanical modeling of the gps velocity field around the northeastern tibetan plateau and surrounding regions article i nfo the northeastern corner of the tibetan plateau is a complex tectonic region with different fault mechanisms from left lateral thrusting of the qilian shan left lateral strike slipping of the haiyuan fault along the plateau edge and right lateral extension across the alashan and the ordos out of the northeastern tibetan plateau here we use 3d finite element models incorporating fault as coulomb type friction zone to investigate mechanical relation between crustal rheology and long term deformation of the main active fault systems models are constrained with gps velocity field and available geological slip rates crustal rheology is simplified as an elastobrittle upper part underlying with viscoelastic crust we test models with fault frictions from 0 4 to 0 02 on different fault systems and mean viscosities of the lower crust from

paleoearthquakes and rupture behavior of the lenglongling fault implications for seismic hazards of the northeastern margin of the tibetan plateau

variability in cohesive sediment settling fluxes observations under different estuarine tidal conditions the mass settling flux which is defined as the product of the concentration and the settling velocity is of prime importance with respect to both stratified and well mixed estuarine conditions the determination of these fluxes for applied modelling purposes in high energy tidal estuarine environments is very problematic this is because the muddy sediments which dominate in estuaries flocculate producing a variety of sizes and settling velocities and this flocculation process is not understood well enough to be fully described theoretically by drawing on examples of floc spectra acquired in situ using the inssev system this study explains how mass settling fluxes in the near bed region can vary by three or four orders of magnitude in meso and macro tidal estuaries throughout a single tidal cycle a floc population representative of dilute suspension conditions on a neap tide indicated only 35 of the floc mass was macroflocs 160 m however the macrofloc settling velocity 2 4 mm s 1 three times faster than the microflocs which meant the former fraction contributed 57 of the 205 mg m 2s 1 settling flux both highly concentrated 4 6 g l 1 and very turbulent spring tide conditions 1 6 n m 2 produced a bi modal distribution in terms of the floc size and dry mass with the former 54 of the mass was contained within the 240 480 m size fraction with a further 25 of the dry floc mass in the flocs over 480 m in diameter these large flocs had settling velocities between 4 8 mm s 1 which meant 99 5 of the settling flux 33 5 g m 2s 1 was accredited to the macroflocs the high turbulence environment saw the dry floc mass distribution shift 60 40 in favour of the microflocs the microfloc settling velocity was 1 45 mm s 1 0 35 mm s 1 faster than the larger macrofloc fraction in terms of the total mass settling flux 0 9 g m 2 s 1 this translates into the microflocs contributing 70 during high turbulence at slack water the flux only reached 12 mg m 2 s 1 and macrofloc growth was mainly attributed to differential settling continuous floc observations made over a complete tidal cycle revealed that the asymmetrical distribution of the tidal energy generated throughout the spring conditions in the tamar estuary demonstrated a distinct control on the flocculation process the less turbulent ebb produced 86 of the total tidal cycle mass settling flux of which only 8 of the settling flux was outside the turbidity maximum an attempt to simulate these large settling fluxes by using a constant settling rate of 0 5 mm s 1 under estimated the tidal cycle settling flux by 78 with less than 15 of the total flux being estimated during the advection of the turbidity maximum on the ebb in contrast using a faster constant settling velocity parameter of 5 mm s 1 representative of the macrofloc fraction resulted in a mass flux over estimate of 116 for the tidal cycle duration

topographic divides formed by active flexural folding in the ne marginal zone of the tibetan plateau abstract topographic divides along the northeastern marginal zone of the tibetan plateau separate tributary drainage systems that flow into the yellow river field investigations and topographic analysis indicate that i late quaternary holocene sedimentary sequences are deformed into a series of left stepping wnw ese trending en echelon flexural folds ii the folds form topographic divides that separate drainage systems that flow into the yellow river and iii the regional axis of maximum compressive stress as inferred from flexural folds and active fault related structures trends ene wsw consistent with geophysical and seismic data these results demonstrate that the topographic divides formed through active flexural folding and faulting in the northeastern marginal zone of the tibetan plateau corresponding to the ongoing northeastward shortening of the plateau accommodating the eurasia india continental collision

transformation of displacement between strike slip and crustal shortening in the northern margin of the tibetan plateau evidence from decadal gps measurements and late quaternary slip rates on faults abstract studies of late quaternary geological slip rates and the gps decadal slip rates along the major strike slip faults in the northern margin of the tibetan plateau show that slip rates remain relatively constant along the middle sections of each fault and decrease rapidly toward the ends our recent studies suggest that the slip rates are low

a laboratory examination of floc characteristics with regard to turbulent shearing abstract turbulent shear generated within the water column is recognised as having a controlling influence over both the flocculation of fine grained cohesive sediments within estuarine waters and their respective aggregate break up this study examines the inter relationships between floc characteristics over increasing turbidity 80 200 mg l 1 and turbulent shear 0 0 6 n m 2 environments by the use of a laboratory flume within which a suspension can be sheared at a controlled rate and with an unintrusive macro lens miniature video camera mounted in a viewing port on the flume channel wall the camera enables the direct simultaneous measurement of both floc size and settling velocity from which accurate estimates of floc effective density and porosity can be made measurements were made 120 s after the induced turbulence has ceased the instrument has an upper viewing turbidity limit of 210 mg l 1 and a lower resolution of 20 m the sediment was collected from the inter tidal mudflats at weir quay on the tamar estuary in devon southwest england the results indicated that increasing turbidity at low shear levels encouraged floc growth but the effect of the increasing turbulent shear 0 35 n m 2 together with increasing concentration in suspension causes disruption rather than enhancing the flocculation process at shears up to 0 35 n m 2 the largest size and settling velocity flocs were produced at high concentrations whereas above 0 35 n m 2 disruption caused smaller flocs at higher concentrations the use of algorithms which were based either on a single floc characteristic i e size or settling velocity or a mean fractal dimension were seen not to accurately approximate the experimental data a multiple regression analysis of the experimental data produced the following formula based on mean values of the 20 largest flocs sampled under each of the imposed environmental conditions referred to as max20size mean values settling velocity 0 301 0 00337 rms of the gradient in turbulent velocity fluctuations 0 000606 spm 0 00335 floc size which proved to be the most accurate representation with an r 2 value of 0 95 a similar formula was determined for the average value of the four fastest settling flocs within each sample group max4w s this highlights the importance of modelling algorithms that are developed from data that take into account effective density variations i e simultaneous size and settling velocity measurement