foreland shortening and crustal balancing in the andes at 30 s latitude excellent surface exposures known benioff zone geometry a dynamic morphology and the availability of industry seismic reflection data all make the andes at 30 s an excellent transect for investigating crustal scale balanced sections 150 170 km of horizontal shortening has occurred in three major belts located between the trench and the foreland the thin skinned east verging precordillera of western argentina accounts for 60 75 of the total shortening and formed mostly since major volcanism ceased at 10 ma industry seismic reflection data show that the decollement of the precordillera belt is located anomalously deep at 15 km the belt is dominated by fault propagation folds and contains several prominent out of sequence thrust faults seismic stratigraphie analysis shows that miocene strata in the iglesia valley located between the precordillera and the crest of the andes accumulated in a piggy back basin onlap relations on the western side indicate that the high cordillera was uplifted as a major fault bend fold over a buried ramp thrusting in the two western belts both in the high cordillera of chile formed during the waning stages of arc volcanism 11 16 ma and account for 25 40 of the shortening the observed shortening is probably greater than can be accounted for with reasonable crustal thicknesses indicating the possibility of continental truncation or erosion along the plate margin or an anomalously thick root held down by the nearly flat subducted nazca plate our preferred crustal geometry puts the ramp between upper and lower crustal deformation west of the high topography requiring crustal scale tectonic wedging to thicken the crust beneath the crest of the andes this non unique model provides a simple explanation of the first order morphology of the andes at this latitude

lithospheric thickness beneath the dabie shan central eastern china from s receiver functions summary p and s receiver functions obtained from a portable array of 34 broad band stations in east central china provide a detailed image of the crust mantle and lithosphere asthenosphere boundaries lab in the dabie shan and its adjacent areas clear s to p converted waves produced at the lab show a thin lithosphere beneath the whole study area based on our results the thickest lithosphere of 72 km is observed beneath the southern part of the area within the yangtze craton whereas beneath the north china platform the lithosphere is only 60 km thick s receiver functions also reveal in good agreement with p receiver functions a maximum depth of the moho beneath the dabie shan orogen at approximately 40 km furthermore we interpret the structural difference at 32 latitude as the probable location of

details of the doublet moho structure beneath lhasa tibet obtained by comparison of p and s receiver functions the collision of the indian and asian plates since about 55 ma has created the largest plateau with the thickest crust on earth there is however no general agreement on the modes of the crustal thickening the crustal thickness of the tibetan plateau still remains poorly determined it is generally accepted that the tibetan crust has roughly double normal thickness and that it thins somewhat toward the north but individual observations of moho depth vary spatially and for different techniques at the same place by greater than 20 km in this work we compare p and s receiver functions at station lsa located in the southern lhasa terrane to determine the crustal thickness beneath the station a doublet moho structure with two significant interfaces at about 60 and 80 km depth in the lower crust is seen clearly in the p receiver functions the deeper phase moho is however absent in the s receiver function data here we model the observed p and s receiver functions by a strong moho topography that dips to the east at an angle of 30 this result may indicate that the moho structure beneath tibet can be very complicated and has strong lateral variations and suggests that a detailed map of moho depth is only possible with 2d dense seismic experiments the moho dips locally perpendicular to the direction of the indian plate motion suggesting that the lower crustal deformation is decoupled from the underlying indian mantle lithosphere the extremely strong moho variation beneath and east of station lsa may also imply a crust mantle interaction specifically delamination or foundering of lower crust down to the upper mantle

an s receiver function analysis of the lithospheric structure in south america 1 we make use of s receiver function to investigate the structure and thickness of the crust and mantle lithosphere in the south american continent and adjacent areas the moho discontinuity has been detected at all stations and goes from 18 km beneath the coast of the continent to 80 km in the andean region the depth of the lithosphere asthenosphere boundary can be clearly detected below those stations that are located on stable areas from 50 km to 160 km the identification of this phase becomes more difficult when the stations are located near subduction zones we also observed the base of the subducted oceanic lithosphere down to depths of 220 km

s local wave seismic anisotropy in the forearc above the subducted nazca plate between 33 s and 34 5 s s wave splitting from local earthquakes within the nazca plate that are deeper than the interplate seismogenic zone enabled the determination of the fast velocity direction and the lag time t in the forearc of the overriding plate data were collected from 20 seismic stations most of which were temporary deployed between 33 5 s and 34 5 s and included part of the normal subduction section to the south and part of the transitional section to flat subduction to the north the fast velocity direction has a complex pattern with three predominant directions northwest southeast north south and northeast southwest and relatively high t a quality evaluation of the highest measurements enabled us to identify possible cycle skipping in some of the measurements which could be responsible for the large observed lag time we consider that most of the anisotropy that was observed in the forearc is probably located in the mantle wedge and a minor part is located in the crust the complex pattern of splitting parameters when the anisotropy is associated at the mantle wedge could be the result of three dimensional variations in the subducting nazca plate at these latitudes also similarities between the splitting parameters and the principal compressional stress direction from pliocene and quaternary rocks suggest that the anisotropy in the crust could originate by tectonic local stress

crustal structure of iceland and greenland from receiver function studies 1 we used data from both permanent and temporary seismic networks on iceland and greenland to investigate the crustal thickness by partly reinterpreting earlier data p receiver functions and adding s receiver functions to better constrain the results we obtained good conversions from the moho and also crustal multiples in both iceland and greenland the central ice covered part of greenland has an average crustal thickness of 40 km typical for a craton at the edges of greenland the crustal thickness decreases to 30 40 km on the east coast of greenland where the track of the iceland plume is thought to have affected the lithosphere the crustal thickness is only 24 26 km in contrast to previous studies we find that the crustal thickness in the east and the northwest coastal regions of iceland is more than 40 km similar to beneath the active volcanic region in the southwest region of iceland and along the mid ocean ridge the crustal thickness is only 25 km or less also in contrast to earlier receiver function interpretations which deduced a broad crust mantle transition zone for iceland we find indications for a normal sharper moho beneath a number of sites

lithospheric density structure of the southern central andes constrained by 3d data integrative gravity modelling the southern central andes sca between 27 s and 40 s is bordered to the west by the convergent margin between the continental south american plate and the oceanic nazca plate the subduction angle along this margin is variable as is the deformation of the upper plate between 33 s and 35 s the subduction angle of the nazca plate increases from sub horizontal 5 in the north to relatively steep 30 in the south the sca contain inherited lithological and structural heterogeneities within the crust that have been reactivated and overprinted since the onset of subduction and associated cenozoic deformation within the andean orogen the distribution of the deformation within the sca has often been attributed to the variations in the subduction angle and the reactivation of these inherited heterogeneities however the possible influence that the thickness and composition of the continental crust have had on both short term and long term deformation of the sca is yet to be thoroughly investigated for our investigations we have derived density distributions and thicknesses for various layers that make up the lithosphere and evaluated their relationships with tectonic events that occurred over the history of the andean orogeny and in particular investigated the short and long term nature of the present day deformation processes we established a 3d model of lithosphere beneath the orogen and its foreland 29 s 39 s that is consistent with currently available geological and geophysical data including the gravity data the modelled crustal configuration and density distribution reveal spatial relationships with different tectonic domains the crystalline crust in the orogen the magmatic arc and the main orogenic wedge is thicker 55 km and less dense 2900 kg m3 than in the forearc 35 km 2975 kg m3 and foreland 30 km 3000 kg m3 crustal thickening in the orogen probably occurred as a result of stacking of low density domains while density and thickness variations beneath the forearc and foreland most likely reflect differences in the tectonic evolution of each area following crustal accretion no clear spatial relationship exists between the density distribution within the lithosphere and previously proposed boundaries of crustal terranes accreted during the early paleozoic areas with ongoing deformation show a spatial correlation with those areas that have the highest topographic gradients and where there are abrupt changes in the average crustal density contrast this suggests that the short term deformation within the interior of the andean orogen and its foreland is fundamentally influenced by the crustal composition and the relative thickness of different crustal layers a thicker denser and potentially stronger lithosphere beneath the northern part of the sca foreland is interpreted to have favoured a strong coupling between the nazca and south american plates facilitating the development of a sub horizontal slab

tectonics of western tibet between the tarim and the indus a tarim to indus traverse provides insight into the tectonics of western tibet the kunlun was the site of a mid paleozoic collision at least three phases of post paleozoic accretion have thickened the blanket of sediments that covers western tibet sizeable parts of western qiangtang have remained stable however since the mid mesozoic since the neogene deformation and volcanism have been localized near the edges of the plateau strike slip motion along the karakorum and altyn tagh faults has been coeval with overthrusting in the himalayas and kunlun such slip partitioning and the volcanism appear to result simply from northward subduction of india and southward subduction of the tarim as tibet is extruded eastwards by india s penetration into asia

seismicity and shape of the subducted nazca plate an updated compilation of earthquake locations and focal mechanism solutions from the international seismological centre and preliminary determination of earthquakes is the basis of a comprehensive study of the geometry of the wadati benioff zone beneath western south america the new data support previous mapping of a sharp flexure rather than a tear in the subducted nazca plate beneath southern peru and provide evidence for a similar flexure in the southward transition from nearly horizontal subduction to a slab with 30 dip at latitude 33 s in contrast the transition from 30 slab dip beneath bolivia to a nearly horizontal dip in the region between 28 s 32 s is more gradual occurring over several hundred kilometers of along strike distance between 20 s and 32 s this southward flattening corresponds to a broadening of a horizontal benchlike part of the subducted plate formed between 100 and 125 km depth the transition in continental tectonic style near 27 s 28 s from a wide volcanically active plateau to a narrow nonvolcanic cordillera appears not to be associated with the main slab flattening which begins to the north of these latitudes but with a more abrupt change in curvature of the subducted slab from convex upward to concave upward immediately below the plate boundary interface the concept of gaussian curvature is applied to slab bending to explain how subduction geometry is affected by the shape of the south american plate we hypothesize that the polarity of vertical curvature in the subducting slab is governed by the orientation of lateral curvature of the plate margin focal mechanism solutions for intermediate and deep earthquakes are grouped by geographic region and inverted for the orientation and relative magnitudes of the principal stresses results of the inversion indicate that downdip extension dominates in the slab above 350 km while downdip compression dominates at greater depths

the lithosphere asthenosphere boundary in the north west atlantic region abstract a detailed knowledge of the thickness of the lithosphere in the north atlantic is an important parameter for understanding plate tectonics in that region we achieve this goal with as yet unprecedented detail using the seismic technique of s receiver functions clear positive signals from the crust mantle boundary and negative signals from a mantle discontinuity beneath greenland iceland and jan mayen are observed according to seismological practice we call the negative phase the lithosphere asthenosphere boundary lab the seismic lithosphere under most of the iceland and large parts of central greenland is about 80 km thick this depth in iceland is in disagreement with estimates of the thickness of the elastic lithosphere 10 20 km found from postglacial rebound data in the region of flood basalts in eastern greenland which overlies the proposed iceland plume track the lithosphere is only 70 km thick about 10 km less than in iceland which is located directly above the proposed plume at the western greenland coast the lithosphere thickens to 100 120 km with no indication of the iceland plume track identified below jan mayen the lithospheric thickness varies between 40 and 60 km

crustal thickness estimation beneath the southern central andes at 30 s and 36 s from s wave receiver function analysis summary we have used the s wave receiver function srf technique to investigate the crustal thickness beneath two seismic profiles from the charge project in the southern central andes a previous study employing the p wave receiver function method has observed the moho interface beneath much of the profiles they found however that the amplitude of the p to s conversion was diminished in the western part of the profiles and have attributed it to a reduction of the impedance contrast at the moho due to lower crustal ecologitization with srf we have successfully detected s to p converted waves from the moho as well as possible conversions from other lithospheric boundaries the continental south american crust reaches its maximum thickness of 70 km along 30 s between 70 w and 68 5 w beneath the principal cordillera and the famatina system and becomes thinner towards the sierras pampeanas with a thickness of 40 km negative phases possibly related to the base of the continental and oceanic lithosphere can be recognized in the summation traces at different depths by comparing our results with data obtained from previous investigations we are able to further constrain the thickness of the crust and lithosphere beneath the central andes

crustal deformation in the south central andes backarc terranes as viewed from regional broad band seismic waveform modelling summary the convergence between the nazca and south america tectonic plates generates a seismically active backarc region near 31 s earthquake locations define the subhorizontal subducted oceanic nazca plate at depths of 90 120 km another seismic region is located within the continental upper plate with events at depths 1 80 th 45 55 km than those of the eastern sierras pampeanas vp 6 0 6 2 km s 1 vp vs 1 70 th 27 35 km in addition we observed an apparent distribution of reverse crustal earthquakes along the suture that connects those terranes finally we estimated average p and t axes over the charge period the entire region showed p and t axis orientations of 275 and 90 plunging 6 and 84 respectively

rates of low ph biological fe ii oxidation in the appalachian bituminous coal basin and the iberian pyrite belt low ph fe ii oxidation can be exploited for the treatment of acid mine drainage amd however natural or engineered terraced iron formations tifs are underutilized for amd treatment because of uncertainties with respect to treatment performance to address this problem we measured the rates of fe ii oxidation multiple times at eight sites in the appalachian bituminous coal basin and at three sites in the iberian pyrite belt ipb longitudinal geochemical transects were measured downstream of emergent anoxic amd sources water velocities were measured at each sampling location and used to transform concentration versus distance profiles into concentration versus travel time for kinetic analysis of field data zero order fe ii oxidation rates ranged from 8 60 to 81 3 10 7 mol l

the lithosphere asthenosphere boundary in the tien shan karakoram region from s receiver functions evidence for continental subduction 1 significant s to p converted wave energy from the crust mantle and lithosphere asthenosphere boundaries the moho and the lab respectively has been observed in the tien shan and karakoram orogenic belts and used for the determination of the thickness of the crust and the mantle lithosphere the moho lies at depths of 45 65 km in the tien shan and adjacent regions and deepens to 70 km depth in pamir and karakoram the thickness of the lithosphere varies between 90 and 120 km underneath the tien shan and increases to a value of 160 km beneath the tarim basin to the south of the tarim basin the lower boundary of the asian lithosphere can be clearly followed to a depth of 270 km beneath central pamir and karakoram while the indian lithosphere is observed beneath the karakoram dipping from 130 km to 170 km towards the north the observations indicate a scenario of continental collision and subduction consistent with seismicity and the surface wave tomography results

revealing the deep structure and rupture plane of the 2010 maule chile earthquake mw 8 8 using wide angle seismic data the 27 february 2010 maule earthquake mw 8 8 ruptured 400 km of the nazca south america plate boundary and caused hundreds of fatalities and billions of dollars in material losses here we present constraints on the fore arc structure and subduction zone of the rupture area derived from seismic refraction and wide angle data the results show a wedge shaped body 40 km wide with typical sedimentary velocities interpreted as a frontal accretionary prism fap landward of the imaged fap the velocity model shows an abrupt velocity contrast suggesting a lithological change which is interpreted as the contact between the fap and the paleo accretionary prism backstop the backstop location is coincident with the seaward limit of the aftershocks defining the updip limit of the co seismic rupture and seismogenic zone furthermore the seaward limit of the aftershocks coincides with the location of the shelf break in the entire earthquake rupture area 33 s 38 5 s which is interpreted as the location of the backstop along the margin published seismic profiles at the northern and southern limit of the rupture area also show the presence of a strong horizontal velocity gradient seismic backstop at a distance of 30 km from the deformation front the seismic wide angle reflections from the top of the subducting oceanic crust constrain the location of the plate boundary offshore dipping at 10 the projection of the epicenter of the maule earthquake onto our derived interplate boundary yielded a hypocenter around 20 km depth this implies that this earthquake nucleated somewhere in the middle of the seismogenic zone neither at its updip nor at its downdip limit

shear wave velocities in the pampean flat slab region from rayleigh wave tomography implications for slab and upper mantle hydration 1 the pampean flat slab region located in central argentina and chile between 29 and 34 s is considered a modern analog for laramide flat slab subduction within western north america regionally flat slab subduction is characterized by the nazca slab descending to 100 km depth flattening out for 300 km laterally before resuming a more normal angle of subduction flat slab subduction correlates spatially with the track of the juan fernandez ridge and is associated with the inboard migration of deformation and the cessation of volcanism within the region to better understand flat slab subduction we combine ambient noise tomography and earthquake generated surface wave measurements to calculate a regional 3d shear velocity model for the region shear wave velocity variations largely relate to changes in lithology within the crust with basins and bedrock exposures clearly defined as low and high velocity regions respectively we argue that subduction related hydration plays a significant role in controlling shear wave velocities within the upper mantle in the southern part of the study area where normal angle subduction is occurring the slab is visible as a high velocity body with a low velocity mantle wedge above it extending eastward from the active arc where flat slab subduction is occurring slab velocities increase to the east while velocities in the overlying lithosphere decrease consistent with the slab dewatering and gradually hydrating the overlying mantle the hydration of the slab may be contributing to the excess buoyancy of the subducting oceanic lithosphere helping to drive flat slab subduction

the role of magmatically driven lithospheric thickening on arc front migration volcanic activity at convergent plate margins is localized along lineaments of active volcanoes that focus rising magma generated within the mantle below in many arcs worldwide particularly continental arcs the volcanic front migrates away from the interface of subduction the trench over millions of years reflecting coevolving surface forcing tectonics crustal magma transport and mantle flow here we show that extraction of melt from arc mantle and subsequent magmatic thickening of overlying crust and lithosphere can drive volcanic front migration these processes are consistent with geochemical trends such as increasing la yb which show that increasing depths of differentiation correlate with arc front migration in continental arcs such thickening truncates the underlying mantle flow field squeezing hot mantle wedge and the melting focus away from the trench while progressively decreasing the volume of melt generated however if magmatic thickening is balanced by tectonic extension in the upper plate a steady crustal thickness is achieved that results in a more stationary arc front with long lived mantle melting this appears to be the case for some island arcs thus in combination with tectonic modulation of crustal thickness magmatic thickening provides a self consistent model for volcanic arc front migration and the composition of arc magmas

fault slip inversions their importance in terms of strain heterogeneity and kinematics of brittle deformation abstract heterogeneous deformation is intrinsic in natural deformation but often underestimated in the analysis and interpretation of mesoscopic brittle shear faults based on the analysis of 11 222 faults from two distinct tectonic settings the central andes in argentina and the sudbury area in canada interpolation of principal strain directions and scaled analogue modelling we revisit controversial issues of fault slip inversions collectively adhering to heterogeneous deformation these issues include the significance of inversion solutions in terms of 1 strain or paleo stress 2 displacement notably plate convergence 3 local versus far field deformation 4 strain perturbations and 5 spacing between stations of fault slip data acquisition furthermore we highlight the value of inversions for identifying the kinematics of master fault zones in the absence of displaced geological markers a key result of our assessment is that fault slip inversions relate to local strain not paleo stress and thus can aid in inferring the kinematics of master faults moreover strain perturbations caused by mechanical anomalies of the deforming upper crust significantly influence local principal strain directions thus differently oriented principal strain axes inferred from fault slip inversions in a given region may not point to regional deformation caused by successive and distinct deformation regimes this outcome calls into question the common practice of separating heterogeneous fault slip data sets into apparently homogeneous subsets finally the fact that displacement vectors and principal strains are rarely co linear defies the use of brittle fault data as proxy for estimating directions of plate scale motions

receiver function study of the hellenic subduction zone imaging crustal thickness variations and the oceanic moho of the descending african lithosphere summary we use data from recently installed broad band seismographs on the islands of crete gavdos santorini naxos and samos in the hellenic subduction zone to construct receiver function images of the crust and upper mantle from south of crete into the aegean sea the stations are equipped with sts 2 seismometers and they are operated by gfz potsdam university of chania and eth zurich teleseismic earthquakes recorded by these stations at epicentral distances between 35 and 95 have been used to calculate receiver functions the receiver function method is a routinely used tool to detect crustal and upper mantle discontinuities beneath a seismic station by isolating the p s converted waves from the coda of the p wave converted p s energy from the oceanic moho of the subducted african plate is clearly observed beneath gavdos and crete at a depth ranging from 44 to 69 km this boundary continues to the north to nearly 100 km depth beneath santorini island because of a lack of data the correlation of this phase is uncertain north of santorini beneath the aegean sea moho depths were calculated from primary converted waves and multiply reflected waves between the moho and the earth s surface beneath southern and eastern crete the moho lies between 31 and 34 km depth beneath western and northern crete the moho is located at 32 and 39 km depth respectively and behaves as a reversed crust mantle velocity contrast possibly caused by hydration and serpentinization of the forearc mantle peridotite the moho beneath gavdos island located south of crete in the libyan sea is at 26 km depth indicating that the crust south of the crete microcontinent is also thinning towards the mediterranean ridge this makes it unlikely that part of the crust in crete consists of accreted sediments transported there during the present day subduction process which began approximately 15 ma because the backstop i e the boundary between the current accretionary wedge of the mediterranean ridge and the crete microcontinent is located approximately 100 km south of gavdos a seismic boundary at 32 km depth beneath santorini island probably marks the crustal base of the crete microcontinent a shallower seismic interface beneath santorini at 20 25 km depth may mark the depth of the detachment between the crete microcontinent and the overlying aegean subplate the moho in the central and northern aegean at naxos and samos is observed at 25 and 28 km depth respectively assuming a stretching factor of 1 2 1 3 crustal thickness in the aegean was 30 35 km at the inception of the extensional regime in the middle miocene

moho topography and subducting oceanic slab of the chilean continental margin in the maximum slip segment of the 1960 mw 9 5 valdivia chile earthquake from p receiver functions the maximum slip area of the 1960 mw 9 5 valdivia chile earthquake has been investigated down to 100 km depth by a receiver function survey along two trench perpendicular profiles at 39 3 and 39 5 s the data are compared with seismicity and local earthquake tomography we find a slab of ca 35 dip at depths similar to what is observed to the north and south of the study area the slab and the overlying mantle wedge show a local decrease in seismic velocities possibly caused by hydration or underplating of sediments the presence of hydrated or sedimentary rocks would reduce plate coupling in this region in agreement with recent gps measurements the moho is found at depths of 30 to 40 km deepening from the coast to the andes the moho topography is close to isostatic equilibrium under the volcanic centre of villarrica quetrupillan and lanin the moho conversion occurs about 10 km shallower than expected for a standard isostatic model this can be explained by a density reduction in the lower crust due to magmatic processes or by non compensated stress

acid mine drainage in the iberian pyrite belt odiel river watershed huelva sw spain geochemistry mineralogy and environmental implications abstract this work reports the physical properties and water chemistry of 64 amd discharges from 25 different mines in the ipb draining to the odiel river watershed which have been investigated during the hydrologic year 2003 2004 these amd solutions vary largely in flow rate and chemical composition both spatially between the different mine sites suggesting a strong geologic control on amd chemistry and seasonally due to marked hydrologic variations and include cases with very low ph mostly in the range 1 4 4 and extreme sulphate up to 44 g l so 4 2 and metal content e g up to 7 7 g l fe 2 6 g l al or 1 4 g l zn different hydrogeochemical facies of amd namely fe ii anoxic fe iii suboxic and aluminous oxic are recognized in the field as a response to the continuous oxidation and hydrolysis of dissolved fe relevant geochemical aspects of these amd environments are discussed including i the redox chemistry of the fe ii fe iii couple ii the reaction rates for bacterially catalyzed oxidation of fe ii and hydrolysis of fe iii iii the role played by dissolved fe and al in the acidity and chemical buffering of the amd systems and iv the solubility and trace metal retention capacity of the fe oxyhydroxysulphate and hydrated sulphate minerals commonly associated with amd in addition the mineralogy and chemistry of the fe precipitates schwertmannite jarosite goethite ferrihydrite al phases e g basaluminite and mg fe al efflorescent so4 salts e g epsomite hexahydrite copiapite halotrichite rozenite coquimbite present in the amd generating mine sites have also been studied the mineralogy of the fe precipitates is well correlated with the water ph with jarosite at ph 2 schwertmannite at ph 2 4 basaluminite at ph 4 5 and ferrihydrite at ph 6 schwertmannite appears to be the most important mineral phase both in controlling the fe solubility at ph 2 4 and as sorbent of trace elements as cu zn which favours natural attenuation finally a basin scale environmental perspective is given in order to evaluate the impact of amd on the water quality including calculation of metal loadings transported by amd from the most important mine districts in the province

a double seismic zone in the subducting juan fernandez ridge of the nazca plate 32 s central chile 1 the region of central chile offers a unique opportunity to study the links between the subducting juan fernandez ridge the flat slab the double seismic zone dsz and the absence of modern volcanism here we report the presence and characteristics of the first observed dsz within the intermediate depth nazca slab using two temporary seismic catalogs ovalle 1999 and chile argentina seismological measurement experiment the lower plane of seismicity lp is located 20 25 km below the upper plane begins at 50 km depth and merges with the lower plane at 120 km depth where the slab becomes horizontal focal mechanism analysis and stress tensor calculations indicate that the slab s state of stress is dominantly controlled by plate convergence and overriding crust thickness above 60 70 km depth the slab is in horizontal compression and below it is in horizontal extension parallel to plate convergence which can be accounted for by vertical loading of the overriding lithosphere focal mechanisms below 60 70 km depth are strongly correlated with offshore outer rise bend faults suggesting the reactivation of preexisting faults below this depth the large interplane distances for all nazca dszs can be related to the slab s unusually cold thermal structure with respect to its age since lps globally seem to mimic mantle mineral dehydration paths we suggest that fluid migration and dehydration embrittlement provide the mechanism necessary to weaken the rock and that the stress field determines the direction of rupture

hydrogeochemical processes governing the origin transport and fate of major and trace elements from mine wastes and mineralized rock to surface waters abstract the formation of acid mine drainage from metals extraction or natural acid rock drainage and its mixing with surface waters is a complex process that depends on petrology and mineralogy structural geology geomorphology surface water hydrology hydrogeology climatology microbiology chemistry and mining and mineral processing history the concentrations of metals metalloids acidity alkalinity cl f and so 4 2 found in receiving streams rivers and lakes are affected by all of these factors and their interactions remediation of mine sites is an engineering concern but to design a remediation plan without understanding the hydrogeochemical processes of contaminant mobilization can lead to ineffective and excessively costly remediation furthermore remediation needs a goal commensurate with natural background conditions rather than water quality standards that might bear little relation to conditions of a highly mineralized terrain this paper reviews hydrogeochemical generalizations primarily from us geological survey research that enhance our understanding of the origin transport and fate of contaminants released from mined and mineralized areas mobility of potential or actual contaminants from mining and mineral processing activities depends on 1 occurrence is the mineral source of the contaminant actually present 2 abundance is the mineral present in sufficient quantity to make a difference 3 reactivity what are the energetics rates and mechanisms of sorption and mineral dissolution and precipitation relative to the flow rate of the water and 4 hydrology what are the main flow paths for contaminated water estimates of relative proportions of minerals dissolved and precipitated can be made with mass balance calculations if minerals and water compositions along a flow path are known combined with discharge these mass balance estimates quantify the actual weathering rate of pyrite mineralization in the environment and compare reasonably well with laboratory rates of pyrite oxidation except when large quantities of soluble salts and evaporated mine waters have accumulated underground quantitative mineralogy with trace element compositions can substantially improve the identification of source minerals for specific trace elements through mass balances post dissolution sorption and precipitation attenuation reactions depend on the chemical behavior of each element solution composition and ph aqueous speciation temperature and contact time with mineral surfaces for example little metal attenuation occurs in waters of low ph

aftershock seismicity of the 27 february 2010 mw 8 8 maule earthquake rupture zone on 27 february 2010 the mw 8 8 maule earthquake in central chile ruptured a seismic gap where significant strain had accumulated since 1835 shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity here we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines by processing the seismic data between 15 march and 30 september 2010 from stations from iris ipgp gfz and university of liverpool we determined 20 205 hypocentres with magnitudes mw between 1 and 5 5 seismic activity occurs in six groups 1 normal faulting outer rise events 2 a shallow group of plate interface seismicity apparent at 25 35 km depth and 50 120 km distance to the trench with some variations between profiles along strike the aftershocks occur largely within the zone of coseismic slip but extend 50 km further north and with predominantly shallowly dipping thrust mechanisms along dip the events are either within the zone of coseismic slip or downdip from it depending on the coseismic slip model used 3 a third band of seismicity is observed further downdip at 40 50 km depth and further inland at 150 160 km trench perpendicular distance with mostly shallow dipping 28 thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture and presumably above the intersection of the continental moho with the plate interface 4 a deep group of intermediate depth events between 80 and 120 km depth is present north of 36 s within the maule segment a large portion of events during the inter seismic phase originated from this depth range 5 the magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the mw 8 8 maule 2010 earthquake 6 pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of pichilemu 34 5 s these crustal events occur in a 30 km wide region with sharp inclined boundaries and oriented oblique to the trench the best located events describe a plane dipping to the southwest consistent with one of the focal planes of the large normal faulting aftershock mw 6 9 on 11 march 2010

upper mantle structure in the south central chilean subduction zone 30 to 36 s 1 regional p and s wave travel time data were used to obtain three dimensional seismic tomography models for vp vs and vp vs above the subducting slab in central chile and argentina in this region there is an abrupt change from a normal subduction geometry south of 33 s to a flat subduction geometry to the north we find low vp low vs and high vp vs ratios in the southern half of our study area directly beneath the modern active volcanic arc which we interpret as localized pockets of melt in the northern half of our study area above where the subducting nazca plate flattens at 100 km depth we find low vp high vs and low vp vs ratios these unusual results point to a lack of melt or hydrated mineralogies such as serpentine both of which are characterized by high vp vs values the only mantle rocks that have low vp vs and high vs are mg rich compositions such as dehydrated serpentinite or orthopyroxenite we suggest that significant portions of the mantle overlying the flat slab consist of orthopyroxenite formed by a transient fluxing of silica rich fluids such fluids may have come from sediments that were subducted during the initiation of flat subduction at this latitude at 10 ma this would imply that the hydration of mantle material above a flat slab can be a transient phenomenon which leaves little residual free water behind but significantly alters the mantle chemistry

proterozoic early paleozoic evolution in western south america a discussion abstract the hypothesis of exotic terranes in peru bolivia argentina and chile generated discussions on the mode of transfer and extent of accretional events that may have occurred in the southern andes during the late proterozoic early paleozoic initially a tectogenesis based on autochthonous mobile fold belts was discussed following ideas emphasised the fragmentation of the supercontinent rodinia laurentia moving along the west gondwana border and colliding with the gondwana western margin the most important effect of this laurentia gondwana relationship was attributed to the argentine precordillera or cuyania terrane splitting off from laurentia and docking to gondwana in the early paleozoic in this study the most cited arguments for this laurentia precordillera relationship are discussed emphasising paleontological considerations it is shown that these arguments do not exclude a close original vicinity of the precordillera terrane to gondwana the precordillera terrane is suggested to be part of a hypothetical platform which developed between south america africa and antarctica safran platform and which was displaced to its actual position by transcurrent faults the collisional events in the sierras pampeanas ensued from strike slip movements and were responsible for the s and i type transpressional magmatism along the pampean and famatinian terranes the final result of this continent parallel movement of terrane slices is similar to that of a terrane split off from laurentia but the first named way of formation easier explains the general continuity of plate convergence at the western border of gondwana than the laurentia precordillera connection does

geochemistry and stable isotope investigation of acid mine drainage associated with abandoned coal mines in central montana usa the great falls lewistown coal field gflcf in central montana contains over 400 abandoned underground coal mines many of which are discharging acidic water with serious environmental consequences areas of the mines that are completely submerged by groundwater have circum neutral ph and relatively low concentrations of metals whereas areas that are only partially flooded or freely draining have acidic ph 3 and high concentrations of metals the ph of the mine drains either decreases or increases after discharging to the surface depending on the initial ratio of acidity mainly al and fe2 to alkalinity mainly hco3 in acidic fe rich waters oxidation of fe2 after exposure to air is microbially catalyzed and follows zero order kinetics with computed rate constants falling in the range of 0 97 to 1 25 mmol l 1 h 1 in contrast fe2 oxidation in near neutral ph waters appears to be first order with respect to fe2 concentration although insufficient data were collected to constrain the rate law expression rates of fe2 oxidation in the field are dependent on temperature such that lower fe2 concentrations were measured in down gradient waters during the day and higher concentrations at night diel cycles in dissolved concentrations of zn and other trace metals mn ni were also noted for down gradient waters that were net alkaline but not in the acidic drains the coal seams of the gflcf and overlying cretaceous sandstones form a perched aquifer that lies 50 m above the regional water table situated in the underlying madison limestone the d and 18o values of flooded mine waters suggest local derivation from meteoric water that has been partially evaporated in agricultural soils overlying the coal mines the s and o isotopic composition of dissolved sulfate in the low ph mine drains is consistent with oxidation of biogenic pyrite in coal under aerated conditions a clear distinction exists between the isotopic composition of sulfate in the acid mine waters and sulfate in the adjacent sedimentary aquifers making it theoretically possible to determine if acid drainage from the coal mines has leaked into the underlying madison aquifer

reactivation inversion and basement faulting and thrusting in the sierras pampeanas of cordoba argentina during andean flat slab deformation the sierras pampeanas of cordoba are the easternmost uplifted blocks caused by andean foreland deformation over 700 km from the chile trench this deformation started at c 340 ma through basement faults thrusts and reactivation of normal faults of the cretaceous rift during the opening of the atlantic ocean other older faults major oblique lineaments were also reactivated thermochronological and geothermobarometric data indicate that some topographic relief could have been palaeozoic mesozoic relicts and not only produced by the andean orogeny faults are partially controlled by the early cambrian s 2 metamorphic foliation coincident with the curved fault traces at map scale during pliocene time two deformation phases post dating miocene pliocene magmatism are recognized shallow seismicity data c 25 km depth indicate that the sierras de cordoba accommodate quaternary displacement magnetotelluric studies detect the interface between the pampia terrane and the rio de la plata craton the role of the oblique lineaments in the nucleation and development of the tertiary faulting has been little considered they could be correlated with an old pan gondwanan trend during the cretaceous period these lineaments worked in a transtensive way producing the uplift of high grade rocks and segmentation of the mountain chain favouring the diachronous uplift along the ranges recently both the brittle ductile transition at c 23 km depth and the crustal thickness have been determined by seismicity analysis the oblique lineaments displace normally the mohorovicic discontinuity main basement thrusts were probably rooted in the suture between the pampia terrane and the rio de la plata craton

evolution of the tugtutoq central complex south greenland a high level rift axial late gardar centre abstract the tugtutoq central complex tcc comprises at least six intrusions emplaced by ring faulting and or stoping these intrusions are of syenites quartz syenites and granites with peralkaline affinities crystallized at relatively shallow depths probably as a subvolcanic complex the intrusions transect a major dyke swarm marking the axial zone of a narrow mid proterozoic continental rift the tcc appears to have formed from a succession of increasingly fractionated magma batches which are inferred to have arisen from a differentiating parent magma body near the base of the crust a culminating perthosite intrusion bla mane so syenite joined the two separate early intrusive centres to form a composite body elongate along the rift axis a rb sr whole rock isochron indicates an age of 1124 20 ma with a 87sr 86sr i of 0 70345 the magmas were relatively anhydrous although probably halogen rich producing hypersolvus rocks olivines range from fo9fa88tp3 to foofa95tp5 and pyroxenes from di35hd62ac3 to virtually pure aegirine relative to members of the preceding dyke swarm regarded as fast quenched magmas derived from the same deep crustal site of differentiation the tcc units are enriched in alkali feldspar the tcc rocks are interpreted in part as alkali feldspar rich roof facies cumulates and in part as products of salic magmas selectively depleted in fe rich ferromagnesian minerals by gravitative separation as with the salic members of the dyke swarm the tcc rocks exhibit marked negative eu anomalies the tcc is inferred to be underlain by layered meso to melanocratic syenite cumulates comparable to those seen in some of the other south greenland alkaline intrusions

deep structure of the afro arabian hotspot by s receiver functions 1 we investigated deep structure of the afro arabian hotspot by using recordings from geoscope seismograph station atd the records are processed with the s receiver function technique which allows a detection of sp converted phases from the upper mantle discontinuities the seismic data reveal two unusual discontinuities the discontinuity at a depth of 160 km beneath the gulf of aden corresponds to the onset of melting if the water content in olivine is around 800 h 106si melting at this depth requires a temperature close to 1550 c about 120 c higher than the average another remarkable discontinuity is found at a depth of 480 km where s velocity drops with depth by about 0 2 km s this can be the head of another plume which is trapped in the mantle transition zone

contrasting pb isotopic compositions in two intrusive complexes of the gardar magmatic province of south greenland abstract pb isotopic compositions were determined in rocks from two proterozoic alkaline complexes in the gardar province of south greenland both complexes kungn t fjeld and tugtutoq younger giant dyke embrace a comparable range of compositions alkali gabbro ferrosyenogabbro syenite granite but the two lie in contrasting crustal environments kungn t lies within the southern marginal part of the archaean craton tugtutoq lies off the craton in early proterozoic ketilidian granites there are significant initial isotopic pb differences between the two as well as marked pb isotopic variations within each complex these latter are attributed to increasing degrees of crustal contamination accompanying crystal fractionation processes whereas the overall differences between the two complexes reflect the differing isotopic signatures of the country rocks viz the relatively unradiogenic archaean host rocks for kungn t and the more radiogenic proterozoic granitic hosts for tugtutoq

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

three dimensional elastic wave velocity structure of the western and central tien shan arrival times of compressional p and shear s waves generated by earthquakes at local and teleseismic distances and recorded by seismographs located in the western and central tien shan are used to determine one and three dimensional elastic wave velocity structures of the crust and upper mantle beneath the mountain belt the best fit one dimensional structures suggest that the average depth of the mohorovicic discontinuity in this area is 50 km the three dimensional structure of the upper crust reveals thick sediments within each of the major depressions in the region a 7 km thick wedge of sediment beneath the chu depression is outlined at depth by a south dipping plane of seismic activity suggesting the presence of an active decollemont these low velocities extend continuously to the southeast toward issyk kul suggesting a structural relationship between the two however rather than being consumed it appears that issyk kul is overthrusting the surrounding ranges the low velocity sediments in the fergana basin reach depths of 10 km and are bounded on three sides by amorphous bands of seismicity velocities at midcrustal depths generally are lower beneath the central tien shan than beneath the western tien shan this pattern becomes more evident in the uppermost mantle with p velocity contrasts of as much as 10 across a boundary that corresponds roughly to the geographical position of the talasso fergana fault the low velocities beneath the central tien shan exceed 150 km depth but do not appear to be deeper than 300 km depth there is no evidence for a lithospheric root beneath this part of the range rather the low velocities imply the presence of a positive buoyancy force uplifting the mountains evidence that this low velocity region existed before the collision suggests that the tien shan may not owe its rejuvenation simply to its location at the northern edge of a strong tarim basin but rather to an anomalous upper mantle that was easier to deform than the surrounding lithosphere

geochemistry and stable isotope composition of the berkeley pit lake and surrounding mine waters butte montana abstract samples of mine water from butte montana were collected for paired geochemical and stable isotopic analysis the samples included two sets of depth profiles from the acidic berkeley pit lake deep groundwater from several mine shafts in the adjacent flooded underground mine workings and the acidic horseshoe bend spring beginning in july 2000 the spring was a major surface water input into the berkeley pit lake vertical trends in major ions and heavy metals in the pit lake show major changes across a chemocline at 10 20 m depth the chemocline most likely represents the boundary between pre 2000 and post 2000 lake water with lower salinity modified horseshoe bend spring water on top of higher salinity lake water below based on stable isotope results the deep pit lake has lost approximately 12 of its initial water to evaporation while the shallow lake is up to 25 evaporated the stable isotopic composition of so 4 in the pit lake is similar to that of horseshoe bend spring but differs markedly from so 4 in the surrounding flooded mine shafts the latter is heavier in both 34 s and 18 o which may be due to dissolution of hypogene so 4 minerals anhydrite gypsum barite in the ore deposit the isotopic and geochemical evidence suggests that much of the so 4 and dissolved heavy metals in the deep berkeley pit lake were generated in situ either by leaching of soluble salts from the weathered pit walls as the lake waters rose or by subaqueous oxidation of pyrite on the submerged mine walls by dissolved fe iii laboratory experiments were performed to contrast the isotopic composition of so 4 formed by aerobic leaching of weathered wallrock vs so 4 from anaerobic pyrite oxidation the results suggest that both processes were likely important in the evolution of the berkeley pit lake

an intermediate depth tensional earthquake mw 5 7 and its aftershocks within the nazca slab central chile a reactivated outer rise fault abstract an intermediate depth earthquake 7 january 2003 mw 5 7 occurred within the subducting nazca plate at longitude 70 3 w latitude 33 8 s and depth 113 km its focal mechanism shows normal faulting with a slight strike slip component we detected 50 aftershocks within january 2003 using a temporary seismic network installed in the zone their local magnitudes ml range between 1 9 and 3 5 with the strongest events occurring around the mainshock their spatial distribution including the mainshock defines an area of 35 5 10 2 km2 cutting through almost half of the slab s total thickness at an angle of 60 to the slab s surface this area agrees well with one of the mainshock nodal planes however the total seismic area as defined by the aftershock distribution is larger than the rupture area normally expected for an earthquake of moderate magnitude we compare the orientation of the seismic plane with the outer rise fault pattern offshore central chile and find a correlation with the strike of the seafloor spreading fabric the seismic sequence shows similarities with other intermediate depth cases notably the 13 june 2005 tarapaca earthquake in northern chile and similar cases in the pacific slab beneath japan in all these cases the inferred reactivated fault planes probably originate from the outer rise region in agreement with the hypothesis that intermediate depth seismicity is linked to inherited faults consequently even moderate sized earthquakes can reactivate large areas of inherited faults within slabs at depths 100 km furthermore the occurrence of multiple other local events mw 5 with similar focal mechanism and depth to the january 2003 event appear to indicate that the slab becomes mechanically weak 100 km depth the depth extent in the slab of the reactivated pre existing faults is likely governed by the slab s bending unbending stress regime i e the depth to the neutral plane dehydration embrittlement is a possible factor for triggering the seismic sequence

the s receiver functions synthetics and data example summary recently the s receiver function method has been successfully developed to identify upper mantle interfaces s receiver functions have the advantage of being free of s wave multiple reflections and can be more suitable than p receiver functions for studying mantle lithosphere however because of specific ray geometry and interference of diverse phases the s receiver function method has some technical difficulties and limitations we use synthetic seismograms to demonstrate the feasibility and limitations of s receiver functions for studying mantle structures full wavefield seismograms were calculated using the reflectivity method and processed to generate synthetic s receiver functions for s sks and scs waves results show that s receiver functions can be obtained from waveforms of s sks and scs waves the synthetic s receiver functions for these incident waves show s to p converted phases at all discontinuities in the crust and upper mantle useful ranges of epicentral distances for calculation of s receiver functions are 55 85 for s 85 for sks and 50 75 for scs waves we apply both the s and p receiver function methods to data recorded at broadband station ykw3 in northwest canada the study shows that there is significant agreement among different receiver function methods and demonstrates the usefulness of s receiver functions for imaging the mantle lithosphere

lithospheric and upper mantle structure of central chile and argentina summary the tectonics of central chile and argentina have been greatly affected by the shallow dips of the subducting nazca plate which controlled patterns of magmatism and deformation nearly 1000 km away from the plate boundary we calculate receiver functions from data recorded by the charge array which transected the andes and sierras pampeanas in central chile and argentina to better constrain the crustal structure of this region beneath the northern transect of the charge array where the nazca slab flattens near 100 km we find the crust is over 60 km thick beneath the andes and thin to the east the thick crust however extends 200 km to the east of the high elevations estimates of vp vs obtained from receiver functions vary along ancient terrane boundaries exhibiting higher values to the west interestingly we observe that the amplitude of the phase corresponding to the moho on receiver functions diminishes to the west complicating our images of crustal structure we proposed that the observations presented here of thickened crust within a region of low elevations diminished receiver function arrivals and reports of high shear wave speeds atop of the mantle wedge overlying the shallowly subducted nazca slab can be explained by partial eclogitization of the lower crust the moho appears simpler across the southern transect where it can be identified near 50 km depth at its deepest point beneath the andes and shallows eastwards volcanism remains active near the latitudes of our southern transect and we observe multiple crustal lowvelocity zones indicative of regions of partial melt near the centres of volcanism signals related to the nazca slab remain more elusive suggestive of a small impedance contrast between the slab and overlying mantle

the lithosphere asthenosphere boundary beneath the western united states summary s receiver functions from 67 broad band seismic stations in the western united states clearly reveal the existence of a mantle discontinuity with velocity reduction downward which we interpret as the lithosphere asthenosphere boundary lab the average depth of the lab is 70 km the boundary is relatively sharp with an overall sharpness of less than 20 km the boundary is more prominent south of the mendocino triple junction where the farallon plate has completely subducted this may indicate partial melts at the base of the lithosphere caused by the upwelling of the asthenospheric flow through the slab window a double low velocity zone is observed at base of the lithosphere beneath southern sierra nevada implying a second melting zone at a depth of 100 km well correlated with previous studies of lithospheric delamination in the area

age and origin of early proterozoic dolerite dykes in south west greenland samples of three dolerite dykes from south west greenland give a pooled weighted mean rb sr whole rock isochron age of 2 130 65 ma initial 87sr 86sr ratios are 0 70155 0 00018 for one of the dykes naujat and 0 70277 0 00012 for the other two torssut and akinaq a fourth dyke qaqarssuaq did not yield an isochron torssut samples have significantly lower initial 207pb 204pb ratios than samples from the naujat dyke indicating that the torssut dyke has been affected by crustal contamination

lithospheric structure of the aegean obtained from p and s receiver functions combined p and s receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the aegean region are used to map the geometry of the subducted african and the overriding aegean plates we image the moho of the subducting african plate at depths ranging from 40 km beneath southern crete and the western peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern greece however the dip of the moho of the subducting african plate is shallower beneath the peloponnesus than beneath crete and rhodes and flattens out beneath the northern aegean observed p to s conversions at stations located in the forearc indicate a reversed velocity contrast at the moho boundary of the aegean plate whereas this boundary is observed as a normal velocity contrast by the s to p conversions our modeling suggests that the presence of a large amount of serpentinite more than 30 in the forearc mantle wedge which generally occurs in the subduction zones may be the reason for the reverse sign of the p to s conversion coefficient moho depths for the aegean plate show that the southern part of the aegean crustal thickness of 20 22 km has been strongly influenced by extension while the northern aegean sea which at present undergoes the highest crustal deformation shows a relatively thicker crust 25 28 km this may imply a recent initiation of the present kinematics in the aegean western greece crustal thickness of 32 40 km is unaffected by the recent extension but underwent crustal thickening during the hellenides mountains building event the depths of the aegean moho beneath the margin of the peloponnesus and crete 25 28 and 25 33 km respectively show that these areas are also likely to be affected by the aegean extension even though the cyclades crustal thickness of 26 30 km were not significantly involved in this episode the aegean lithosphere asthenosphere boundary lab mapped with s receiver functions is about 150 km deep beneath mainland greece whereas the lab of the subducted african plate dips from 100 km beneath crete and the southern aegean sea to about 225 km under the volcanic arc this implies a thickness of 60 65 km for the subducted african lithosphere suggesting that the aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the cyclades

hydrochemical variations and contaminant load in the rio tinto spain during flood events summary the aim of this work is to study the hydrochemical variations during flood events in the rio tinto sw spain three separate rainfall flood events were monitored in october 2004 following the dry season in general concentrations markedly increased following the first event fe from 99 to 1130 mg l q max 0 78 m 3 s while dissolved loads peaked in the second event fe 7 5 kg s cu 0 83 kg s zn 0 82 kg s q max 77 m 3 s and discharge in the third event q max 127 m 3 s this pattern reflects a progressive depletion of metals and sulphate stored in the dry summer as soluble evaporitic salt minerals and concentrated pore fluids with dilution by freshwater becoming increasingly dominant as the month progressed variations in relative concentrations were attributed to oxyhydroxysulphate fe precipitation to relative changes in the sources of acid mine drainage e g salt minerals mine tunnels spoil heaps etc and to differences in the rainfall distributions along the catchment the contaminant load carried by the river during october 2004 was enormous totalling some 770 t of fe 420 t of al 100 t of cu 100 t of zn and 71 t of mn this represents the largest recorded example of this flush out process in an acid mine drainage setting approximately 1000 times more water and 140 8200 times more dissolved elements were carried by the river during october 2004 than during the dry low flow conditions of september 2004 highlighting the key role of flood events in the annual pollutant transport budget of semi arid and arid systems and the need to monitor these events in detail in order to accurately quantify pollutant transport

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

analysis of geomorphic indices in the southern central andes 23 28 s evidence for pervasive quaternary to recent deformation in the puna plateau abstract satellite data based morphotectonic analyses are popular methods to identify active crustal deformation of large and partly remote regions such as the central andes for the southern central andes between 23 to 28 s the mountain front sinuosity smf index was estimated for 189 first order mountain fronts as well as valley shape vf ratios and basin symmetry t factors for 3366 second order tributary drainage basins the correlation between known fault ages and smf indices shows that the indices can be used as a proxy to infer the ages of faults for which radiometric ages do not exist vf ratios and smf indices point to pronounced quaternary to recent surface deformation on first order reverse faults delimiting mountain fronts by contrast analysis of the transverse topographic symmetry t factor which has been used to assess rotational components of drainage basins points to stochastic variations of erosion possibly due to local lithological heterogeneity rather than to a tectonic influence on basin geometry we also examined 32 mainly nne ssw trending first order basin margins for tilt of alluvial fan deposits and lateral stream migration the symmetry of first order basins in the southern central andes seems to be strongly controlled by quaternary deformation on bivergent first order reverse or thrust faults quaternary deformation of the upper crust in the puna plateau is apparently more pervasive than previously appreciated and has important ramifications for the neogene to recent morphotectonic evolution of the southern central andes

a review of the geodynamic evolution of flat slab subduction in mexico peru and chile abstract subducting plates around the globe display a large variability in terms of slab geometry including regions where smooth and little variation in subduction parameters is observed while the vast majority of subduction slabs plunge into the mantle at different but positive dip angles the end member case of flat slab subduction seems to strongly defy this rule and move horizontally several hundreds of kilometers before diving into the surrounding hotter mantle by employing a comparative assessment for the mexican peruvian and chilean flat slab subduction zones we find a series of parameters that apparently facilitate slab flattening among them trench roll back as well as strong variations and discontinuities in the structure of oceanic and overriding plates seem to be the most important however we were not able to find the necessary and sufficient conditions that provide an explanation for the formation of flat slabs in all three subduction zones in order to unravel the origin of flat slab subduction it is probably necessary a numerical approach that considers also the influence of surrounding plates and their corresponding geometries on 3d subduction dynamics

crustal deformation of the andean foreland at 31 30 s argentina constrained by magnetotelluric survey abstract twenty five new long period magnetotelluric sites near 31 5 s were collected in a west east profile this profile and the previous one aligned with and adjacent to the eastern end have been merged to form a single profile of more than 700 km long extending from the precordillera to the chaco pampean plain the geotectonic scenario is characterized by a modern flat subduction zone of the nazca plate located at a depth of around 120 km and clearly defined by the distribution of earthquake hypocenters recorded by local and regional networks a bulge shape at 68 5 w with an anomalous dip to the west is observed within this segment the smooth slab deformation might result from the restriction on eastward motion due to the presence of an electrically resistive zone the magnetotelluric model shows that this thick zone of increased resistivity is found from shallow crustal levels to upper mantle depths the bulge geometry allows hot fluids and volatiles to rise from the deeper asthenospheric wedge and reach the lower crust reducing its viscosity and letting it flow the zones of low resistivity in the lower crust show spatial correlation with the areas of foreland deformation from precordillera to the sierras pampeanas and may also suggest a ductile regime shear zones reactivated by cenozoic faulting must necessarily have their roots in the levels of the ductile lower crust associated to conductive channels the zone where the lower crust is closer to the surface coincides with the areas of greatest structural relief and erosion the interface between the folded ductile lower crust and the brittle upper crust might act as the main level of decollement of the bordering structures between the precordillera sierra de pie de palo and the sierras pampeanas in addition the geometry of the interface might be conditioning the vergence of those structures

a lithospheric velocity model for the flat slab region of argentina from joint inversion of rayleigh wave phase velocity dispersion and teleseismic receiver functions fil ammirati jean baptiste ministerio de ciencia tecnologia e innovacion productiva agencia nacional de promocion cientifica y tecnologica argentina universidad nacional de san juan facultad de ciencias exactas fisicas y naturales departamento de geofisica y astronomia argentina

generalised receiver functions and seismic interferometry abstract classical seismological receiver functions are correlational or deconvolutional combinations of vertical and horizontal component seismometer recordings of earthquake waves that focus information on near receiver subsurface earth structure and properties we show that seismic interferometry can be thought of as a generalisation of receiver functions analysis to cases where recordings at pairs of receivers are considered simultaneously and where either the same or different component recordings are combined further seismic interferometry uses any of deconvolution convolution and cross correlation and energy from either impulsive or random noise sources we show both how receiver functions can logically be extended to a new convolutional form and that the now little used correlational form of receiver functions contains more intuitive information than previously realised seismic interferometry has provided other extraordinary extensions to seismologists arsenal passive noise recordings can be converted into seismograms from virtual imagined earthquakes that in turn can be used to image the real earth active sources e g earthquakes or man made sources can be redatumed into new virtual sources elsewhere or can be converted into virtual sensors seismometers that record seismograms from other real earthquakes man made sources or noise sources that occur either in the future or in the past and the ability to construct virtual sources and sensors at desired times and locations rather than having to wait for earthquake sources that occur at uncontrollable locations promises more repeatable monitoring of changes in earth subsurface properties over time indeed so called coda wave interferometry offers unprecedented accuracy in detecting such changes finally existing theoretical extensions to other regimes such as electromagnetic electrokinetic and diffusive energy propagation may lead to future revolutions in other domains of science

evidence for a missing crustal root and a thin lithosphere beneath the central alborz by receiver function studies summary the alborz mountains build the northern part of the alpine himalayan orogen in western asia they are located south of the caspian sea and form an east west range across the north of iran this region is one of the most active tectonic areas as it undergoes extensive crustal deformation and shortening in the present work we used data from 11 permanent stations of the tehran telemetry seismic network to estimate the thickness of the crust and mantle lithosphere beneath the central alborz region by p and s receiver function methods results of both p and s receiver functions revealed a relatively large crustal thickness beneath this region 51 54 km which can be associated with the shortening process related to the orogenic belt no remarkable crustal thickening has been detected below the high topography of central alborz a thick crust 67 5 km is observed locally in the region beneath the damavand volcano which is possibly related to the magmatic addition at the base of the crust beneath the volcanic region the s receiver functions exhibit the existence of a seismic discontinuity in the upper mantle at a depth of 90 km which we interpreted as the base of the lithosphere the missing crustal root and the relatively thin lithosphere beneath the alborz may imply that sublithospheric mantle could be responsible for and support the elevation of the alborz

proto iceland plume caused thinning of irish lithosphere abstract the lithosphere asthenosphere boundary lab separates the rigid lithospheric plates from the hot convective mantle in the region of the north atlantic this boundary is widely influenced by the spreading head of the proto iceland plume p kumar et al the lithosphere asthenosphere boundary in the north west atlantic region earth planet sci lett 236 2005 249 257 that also caused the evolution of the british tertiary volcanic province btvp with the giant s causeway basalts as famous landmark using teleseismic shear wave receiver functions we map the lab underneath ireland and find a distinctive lithospheric thinning of about 30 km towards the northern part of the island as this region is part of the btvp we explain the lithospheric thinning in agreement with geochemical results by thermal erosion originating from the head of the proto iceland plume

kinematics of neogene to recent upper crustal deformation in the southern central andes 23 28 s inferred from fault slip analysis evidence for gravitational spreading of the puna plateau abstract elucidating the tectono morphologic evolution of the central andes is important for understanding the mechanical behaviour of non collisional orogens at convergent plate boundaries fault kinematic data from the southern central andes are generally interpreted in terms of changes in plate boundary kinematics or vertical axis rotation associated with the formation of the andean orocline however none of these hypotheses accounts adequately for neogene to recent horizontal extension and vertical shortening of upper crust documented from the puna plateau and the adjacent eastern cordillera based on new and compiled fault kinematic data in total 4746 brittle faults at 317 stations we propose that strain axis configurations in the southern central andes are controlled by 1 local deformation kinematics 2 the far field deformation caused either by the orogen normal shortening component of plate convergence or by removal of lithospheric mantle and 3 differences in lithospheric thickness and respective surface elevation i e gravitational potential energy specifically the puna plateau and eastern cordillera have been undergoing horizontal shortening and gravitational spreading of the upper crust whereas the topographically lower pampean ranges continue to undergo horizontal shortening only although less apparent in the fault kinematic data than the e w and nw se extension orogen parallel extension is inherent to the puna plateau and eastern cordillera and compensates likely for overall wnw ese shortening and enhanced surface elevation the importance of orogen parallel extension in the deformation kinematics of topographically elevated parts of the southern central andes is underscored by the strike slip components on prominent reverse and thrust faults the data supports geodynamic interpretations in which the evolution of topography and lithospheric thickness influence significantly changes in upper crustal kinematics of the southern central andes

crustal thickness beneath the andes and sierras pampeanas at 30 s inferred from pn apparent phase velocities 1 we obtained a 2d crustal model beneath central chile and western argentina using apparent pn phase velocities recorded along an ew trending transect at 30 s this model is characterized by a thick 65 km crustal root beneath the high cordillera a 60 km thick crust beneath the precordillera and a gradual shallowing of moho depths beneath the sierras pampeanas from 55 km in the west to 40 km in the east beneath the sierras pampeanas where very little crustal shortening is observed the thick crust must be explained by means other than simple tectonic shortening isostatically balanced crustal thickness is consistently shallower than our model shows suggesting the existence of dynamic forces possibly linked to the flat slab

abnormal seismological and magmatic processes controlled by the tearing south american flat slabs abstract the influence of flat slab subduction on the formation of intra slab earthquakes volcanic activities and mantle seismic velocity anomalies remains unclear we attempt to better understand these processes by simulating the two flat slabs in peru and chile using data orientated geodynamic models our results successfully reproduce the observed flat slabs as mainly due to two subducting aseismic ridges in contrast to the traditional view of flat slab subduction we find that these slabs are internally torn as is due to the 3d nature of the subducting buoyancy features this broken slab configuration confirmed by regional tomography naturally explains the abnormal distribution of and stress regimes associated with the intermediate depth earthquakes we further show that the slab tearing process could also better explain the formation of adakitic and ore forming magmatism the evolution of the magmatic arc and the enigmatic mantle seismic structures beneath these regions we propose that slab tearing may represent a common result of buoyancy feature subduction and that the resulting mantle processes could affect the long term geodynamic evolution of continents

an inverted continental moho and serpentinization of the forearc mantle volatiles that are transported by subducting lithospheric plates to depths greater than 100 km are thought to induce partial melting in the overlying mantle wedge resulting in arc magmatism and the addition of significant quantities of material to the overlying lithosphere asthenospheric flow and upwelling within the wedge produce increased lithospheric temperatures in this back arc region but the forearc mantle in the corner of the wedge is thought to be significantly cooler here we explore the structure of the mantle wedge in the southern cascadia subduction zone using scattered teleseismic waves recorded on a dense portable array of broadband seismometers we find very low shear wave velocities in the cold forearc mantle indicated by the exceptional occurrence of an inverted continental moho which reverts to normal polarity seaward of the cascade arc this observation provides compelling evidence for a highly hydrated and serpentinized forearc region consistent with thermal and petrological models of the forearc mantle wedge this serpentinized material is thought to have low strength and may therefore control the down dip rupture limit of great thrust earthquakes as well as the nature of large scale flow in the mantle wedge

segmentation in continental forearcs links between large scale overriding plate structure and seismogenic behavior associated with the 2010 mw 8 8 maule chile earthquake abstract subduction along the active margin of a continental plate occurs in a context where the overriding plate s crust and lithospheric mantle may contain inherited structures significantly predating the present tectonic conditions of the margin these structures are persistent over very long term time scales 105 to 106 years and are thought to play an important role in both seismogenic processes on the megathrust and development of topography along coastlines we use receiver functions calculated from broadband seismic data collected along the chilean forearc between 33 s and 38 5 s in the vicinity of the 2010 mw 8 8 maule earthquake to determine the structure of the overriding south american continental plate and subducting nazca oceanic plate along and inboard of the seismogenic portion of the megathrust we show that the chilean forearc is divided into three structurally distinct zones a northern zone where the continental crust intersects the subducting plate well inboard of the coast at 35 40 km depth a central zone where the continental crust tapers to

crustal thickness and mantle wedge structure from receiver functions in the chilean maule region at 35 s a temporary passive seismic network of 21 broad band stations was deployed in central chile between 35 s to 36 s the network recorded data prior to the magnitude mw 8 8 2010 maule earthquake at a latitude of the major slip and surface deformation the experiment was conducted to survey crustal and mantle structures and to assess the state of hydration of the mantle wedge we present results of a teleseismic p receiver function study supporting a continental moho at approx 38 km depth phase conversion at this boundary could be observed continuously from the intersection of the subducting slab with the continental moho towards the andes the character of receiver functions indicated little evidence for infiltration of water from the subducting plate into the overlying mantle wedge suggesting that only a small amount of water is released from the subducting plate aftershocks of the maule earthquake and post seismic slip reached depths of 50 km and hence slip spread down dip of the continental moho in the post seismic phase co seismic rupture however occurred updip of the continental moho spare aftershock seismicity is observed at the intersection of the continental moho with the subducting slab

cenozoic tectonics of the high andes of west central argentina 30 36 s latitude abstract the structure of the central andes shows three distinctive segments characterized by different geometries these geometries are superimposed on the present large scale plate tectonic setting characterized by distinct subduction segments the northern la ramada segment is a thick skinned fold and thrust belt formed by tectonic inversion of a late triassic rift the central aconcagua segment consists of a thin skinned fold and thrust belt while the southern malargue segment like the first one is a thick skinned fold and thrust belt developed by tectonic inversion of a late triassic early jurassic rift system during late cenozoic times the amount of shortening gradually decreases from north to south as indicated by the crustal roots of the central andes the different geometries along the principal cordillera controlled the abrupt changes in the shortening among segments the structure of precordillera and sierras pampeanas has also been considered in order to account for the total shortening in the la ramada segment the main shortening occurred in the precordillera in the aconcagua segment in the principal cordillera while in the malargue segment the shortening is widely distributed in a broader principal cordillera because south of the flat slab subduction segment the precordillera and sierras pampeanas are missing

upper mantle stratification by p and s receiver functions summary seismic stratification of the upper mantle is investigated by applying two complementary techniques to the records of the graefenberg array in southern germany the anisotropic p receiver function technique kosarev et al 1984 vinnik montagner 1996 is modified by using summary seismic events instead of individual events and different weighting functions instead of the same function for the harmonic angular analysis of the sv and t components of the pds phases the summary events provide better separation of the second azimuthal harmonic than the individual events the parameters of the second harmonics of sv and t thus evaluated should be similar if they reflect the effects of azimuthal anisotropy this can be used as a criterion to identify the anisotropy to detect the sdp phases and their azimuthal variations caused by azimuthal anisotropy we have developed a stacking technique which can be termed the s receiver function technique it includes axis rotation to separate interfering p and s arrivals determination of the principal m component of the s wave motion deconvolution of the p components of many recordings by their respective m components and stacking of the deconvolved p components with weights depending on the level of noise and the angle between the m direction and the backazimuth of the event both techniques yield consistent results for the graefenberg array as indicated by the p receiver functions the upper layer of the mantle between the moho and 80 km depth is anisotropic with dvs vs around 0 03 and the fast direction close to 20 clockwise from north the fast direction of anisotropy below this layer is around 110 the boundary between the upper and the lower anisotropic layers is manifested by the detectable pds and sdp converted phases shear wave splitting in sks is strongly dominated by azimuthal anisotropy in the lower layer asthenosphere

crust mantle interaction in the evolution of the ilimaussaq complex south greenland nd isotopic studies sm nd isotopic compositions were determined for the peralkaline ilimaussaq complex of the gardar province of southern greenland the majority of the samples in the agpaitic and augite syenitic units have near chondritic initial nd 0 whereas a few samples trend towards nd values as low as 6 at the time of intrusion 1143 ma this latter value from a sample taken from the margin of the complex lying on the evolutionary trend for ketilidian country rock granitoids suggests that large scale contamination took place only at the margins of the complex the similarity of the nd isotopic compositions of the augite syenite and agpaitic units suggests that their parental magmas were derived from the same reservoir a comparison of the nd with existing sr and hf isotopic data for the complex suggests an origin by combined assimilation fractionation processes assimilation fractional crystallization modeling of the isotopic compositions indicates that the ilimaussaq magmas could have formed through fractional crystallization of a basaltic melt while assimilating granitic crust the model requires initially higher assimilation rates from basalt to augite syenite composition with subsequent decreasing assimilation rates from augite syenite to agpaitic compositions alkali granites which formed after the intrusion of the augite syenites have isotopic compositions intermediate between those of the augite syenites and the surrounding ketilidian basement this implies even greater amounts of assimilation and is interpreted as evidence for an origin through fractionation of a basaltic or augite syenite magma with concurrent assimilation of ketilidian crust

continental and oceanic crustal structure of the pampean flat slab region western argentina using receiver function analysis new high resolution results summary the pampean flat slab of central chile and argentina 30 32 s has strongly influenced cenozoic tectonics in western argentina which contains both the thick skinned basement cored uplifts of the sierras pampeanas and the thin skinned andean precordillera fold and thrust belt in this region of south america the nazca plate is subducting nearly horizontally beneath the south american plate at 100 km depth to gain a better understanding of the deeper structure of this region including the transition from flat to normal subduction to the south three iris passcal arrays of broad band seismic stations have been deployed in central argentina using the dense siembra array combined with the broader charge and esp arrays the flat slab is imaged for the first time in 3 d detail using receiver function rf analysis a distinct pair of rf arrivals consisting of a negative pulse that marks the top of the oceanic crust followed by a positive pulse which indicates the base of the oceanic crust can be used to map the slab s structure depths to moho and oceanic crustal thicknesses estimated from rf results provide new more detailed regional maps an improved depth to continental moho map shows depths of more than 70 km in the main cordillera and 50 km in the western sierras pampeanas that shallow to 35 km in the eastern sierras pampeanas depth to moho contours roughly follow terrane boundaries offshore the hotspot seamount chain of the juan fernandez ridge jfr is thought to create overthickened oceanic crust providing a mechanism for flat slab subduction by comparing synthetic rfs based on various structures to the observed rf signal we determine that the thickness of the oceanic crust at the top of the slab averages at least 13 19 km supporting the idea of a moderately overthickened crust to provide the additional buoyancy for the slab to remain flat the overthickened region is broader than the area directly aligned with the path of the jfr however and indicates along with the slab earthquake locations that the flat slab area is wider than the jfr volcanic chain observed in the offshore bathymetry further rfs indicate that the subducted oceanic crust in the region directly along the path of the subducted ridge is broken by trench parallel faults one explanation for these faults is that they are older structures within the oceanic crust that were created when the slab subducted alternatively it is possible that faults formed recently from tectonic underplating caused by increased interplate coupling in the flat slab region