shallow fault zone dilatancy recovery after the 2003 bam earthquake in iran earthquakes radiate from slip on discrete faults but also commonly involve distributed deformation within a broader fault zone especially near the surface variations in rock strain during an earthquake are caused by heterogeneity in the elastic stress before the earthquake by variable material properties and geometry of the fault zones and by dynamic processes during the rupture stress changes due to the earthquake slip both dynamic and static have long been thought to cause dilatancy in the fault zone that recovers after the earthquake decreases in the velocity of seismic waves passing through the fault zone due to coseismic dilatancy have been observed followed by postseismic seismic velocity increases during healing dilatancy and its recovery have not previously been observed geodetically here we use interferometric analysis of synthetic aperture radar images to measure postseismic surface deformation after the 2003 bam iran earthquake and show reversal of coseismic dilatancy in the shallow fault zone that causes subsidence of the surface this compaction of the fault zone is directly above the patch of greatest coseismic slip at depth the dilatancy and compaction probably reflects distributed shear and damage to the material during the earthquake that heals afterwards coseismic and postseismic deformation spread through a fault zone volume may resolve the paradox of shallow slip deficits for some strike slip fault ruptures

forces controlling the present day state of stress in the andes the present day state of stress in the andes is expected to be controlled primarily by two different types of forces 1 the resistive force exerted on the western overriding margin of the south american plate and 2 forces that arise from the thickened crust of the andes i e the effect of topography and its compensating crustal root we have studied these forces on the basis of a model for the dynamics of the entire south american plate in which the andes are embedded in this model a given set of forces is constrained by the criterion that the net torque on the plate should vanish a thin elastic shell representation is used to calculate the intra plate stress field associated with the various force distributions we define a reference model for the present study that incorporates a uniform magnitude for the resistance associated with convergence along the western plate margin fpcr plate contact resistance and does not include the effects of topography subsequently we investigate the effect of lateral variation in the magnitude of fpcr and add the topography related forces the main results are 1 a uniform magnitude of fpcr leads to a better match with the observations than a magnitude that is a function of the dip of the lithosphere subducting below the western plate margin 2 the amount of horizontal compression across the andes found in the case that ridge push is considered to be the only force driving the south american plate is small compared to the value required to sustain the andes

effect of the altiplano puna plateau south america on the regional intraplate stresses abstract a previous compilation of stress data for the sub andean region of northwest argentina is complemented with eight additional earthquake focal mechanisms seven events 5 3 5 5 mb had their mechanisms determined by inversion of teleseismic body waves short period p waves and long period sh waves all events had predominantly reverse faulting mechanisms five had almost pure dip slip motion and two had a component of oblique motion the other mechanism was a composite fault plane solution of the hualfin catamarca series of july 1986 maximum 4 mb determined with data from a local temporary network and the permanent inpres regional network the local data shows that the hualfin events occurred on a single fault plane oriented nw se with predominantly strike slip motion the stress data in the sub andean region suggests a radial pattern around the altiplano puna plateau with compressional stresses tending to be perpendicular to the eastern front of the plateau this indicates that local spreading stresses due to lateral density variations crustal thickening or lithospheric thinning of the plateau may be comparable or even exceed the plate wide regional stresses at the southeastern border of the puna plateau where a stress rotation of about 30 may be detected preliminary order of magnitude calculations indicate that the local plateau induced compression can be about 1 2 times greater than the regional horizontal deviatoric stress the present predominance of the local stress over the regional stress is consistent with the decrease of the nazca south america convergence rate observed since about 10 20 ma

gravity anomalies and flexure of the brazilian shield beneath the bolivian andes abstract seismological and geological data suggest that the brazilian shield is now underthrusting beneath the sub andes in order to constrain the minimum amount of shortening that results from this underthrusting we analyzed bouguer gravity anomalies over the shield and the bolivian andes assuming that they are due primarily to variations in crustal thickness that in turn are due to the flexure of an effectively elastic plate brazilian shield loaded by the weight of the andean mountain range gravity anomalies show that airy type isostatic equilibrium does not exist the sub andes are overcompensated and the chaco plain to the east is undercompensated the flexure of the plate can help explain both the overcompensation and the undercompensation if the brazilian shield behaves as an essentially elastic plate that extends at least 150 km and probably 200 km beneath the sub andes and the cordillera oriental and if the flexural rigidity of the plate is between 0 1 and 2 10 24 n m the fit of observed and calculated anomalies however is far from perfect and additional sources of short wavelength anomalies appear to be present assuming that the sediments and sedimentary rocks in the sub andes and cordillera oriental were deposited on the brazilian shield and that later they were overthrust eastward onto one another causing the present topography and the deflection of the plate we computed a family of estimates for the minimum amount of crustal shortening these estimates depend strongly on the amount of sedimentary rock deposited before deformation which does not seem to be well constrained by published geologic mapping nevertheless the calculations suggest that at least 100 km of crustal shortening have occurred and probably more implying that the andes may have been built mostly by crustal shortening

high concentrations of manganese and sulfur in deposits on murray ridge endeavour crater mars mars reconnaissance orbiter hirise images and opportunity rover observations of the 22 km wide noachian age endeavour crater on mars show that the rim and surrounding terrains were densely fractured during the impact crater forming event fractures have also propagated upward into the overlying burns formation sandstones opportunity s observations show that the western crater rim segment called murray ridge is composed of impact breccias with basaltic compositions as well as occasional fracture filling calcium sulfate veins cook haven a gentle depression on murray ridge and the site where opportunity spent its sixth winter exposes highly fractured recessive outcrops that have relatively high concentrations of s and cl consistent with modest aqueous alteration opportunity s rover wheels serendipitously excavated and overturned several small rocks from a cook haven fracture zone extensive measurement campaigns were conducted on two of them pinnacle island and stuart island these rocks have the highest concentrations of mn and s measured to date by opportunity and occur as a relatively bright sulfate rich coating on basaltic rock capped by a thin deposit of one or more dark mn oxide phases intermixed with sulfate minerals we infer from these unique pinnacle island and stuart island rock measurements that subsurface precipitation of sulfate dominated coatings was followed by an interval of partial dissolution and reaction with one or more strong oxidants e g o 2 to produce the mn oxide mineral s intermixed with sulfate rich salt coatings in contrast to arid regions on earth where mn oxides are widely incorporated into coatings on surface rocks our results demonstrate that on mars the most likely place to deposit and preserve mn oxides was in fracture zones where migrating fluids intersected surface oxidants forming precipitates shielded from subsequent physical erosion

source model of the 2007 mw 8 0 pisco peru earthquake implications for seismogenic behavior of subduction megathrusts we use interferometric synthetic aperture radar teleseismic body waves tsunami waveforms recorded by tsunameters field observations of coastal uplift subsidence and runup to develop and test a refined model of the spatiotemporal history of slip during the mw 8 0 pisco earthquake of 15 august 2007 our preferred solution shows two distinct patches of high slip one patch is located near the epicenter while another larger patch ruptured 60 km further south at the latitude of the paracas peninsula slip on the second patch started 60 s after slip initiated on the first patch we observed a remarkable anticorrelation between the coseismic slip distribution and the aftershock distribution determined from the peruvian seismic network the proposed source model is compatible with regional runup measurements and open ocean tsunami records from the latter data set we identified the 12 min timing error of the tsunami forecast system as being due to a mislocation of the source caused by the use of only one tsunameter located in a nonoptimal azimuth the comparison of our source model with the tsunami observations validate that the rupture did not extend to the trench and confirms that the pisco event is not a tsunami earthquake despite its low apparent rupture velocity 1 5 km s we favor the interpretation that the earthquake consists of two subevents each with a conventional rupture velocity 2 4 km s the delay between the two subevents might reflect the time for the second shock to nucleate or alternatively the time it took for afterslip to increase the stress level on the second asperity to a level necessary for static triggering the source model predicts uplift offshore and subsidence on land with the pivot line following closely the coastline this pattern is consistent with our observation of very small vertical displacement along the shoreline when we visited the epicentral area in the days following the event this earthquake represents to our knowledge one of the best examples of a link between the geomorphology of the coastline and the pattern of surface deformation induced by large interplate ruptures

miocene quaternary structural evolution of the uyuni atacama region andes of chile and bolivia abstract we describe the miocene quaternary geological structural evolution of the region between the salar de uyuni and de atacama andes of chile and bolivia we recognized four main tectonic events based on fold geometry fault kinematics and stratigraphic data the oldest event of miocene age is characterized by folding and reverse faulting of the sedimentary successions with an e w direction of shortening in the northern part of the studied area and a wnw ese shortening in the southern part the following two events of pliocene age are characterized by lower shortening amounts they occurred first by reverse faulting with a nw se trending greatest principal stress 1 computed with striated fault planes and a vertical least principal stress 3 followed by pervasive strike slip faulting with the same nw se trending 1 and a horizontal ne sw 3 the fourth event dating to the late pliocene quaternary is characterized by normal faulting the 3 still trends ne sw whereas the intermediate principal stress 2 exchanged with 1 volcanism accompanied both the contractional transcurrent and extensional tectonic phases the mio pliocene compression appears directly linked to a rapid convergence and an apparently important coupling between the continental and oceanic plates the e w to wnw ese direction of shortening of the miocene structures and the nw se 1 of the pliocene structures seem to be more linked to an intra andean re orientation of structures following the wnw directed absolute motion of the south american plate the extensional deformations can be interpreted as related to gravity forces affecting the highest parts of the volcanic belt in a sort of asymmetrical sw ward collapse of the belt

interseismic coupling and seismic potential along the central andes subduction zone we use about two decades of geodetic measurements to characterize interseismic strain build up along the central andes subduction zone from lima peru to antofagasta chile these measurements are modeled assuming a 3 plate model nazca andean sliver and south america craton and spatially varying interseismic coupling isc on the nazca megathrust interface we also determine slip models of the 1996 m w 7 7 nazca the 2001 m w 8 4 arequipa the 2007 m w 8 0 pisco and the m w 7 7 tocopilla earthquakes we find that the data require a highly heterogeneous isc pattern and that overall areas with large seismic slip coincide with areas which remain locked in the interseismic period with high isc offshore lima where the isc is high a m w 8 6 8 8 earthquake occurred in 1746 this area ruptured again in a sequence of four m w 8 0 earthquakes in 1940 1966 1974 and 2007 but these events released only a small fraction of the elastic strain which has built up since 1746 so that enough elastic strain might be available there to generate a m w 8 5 earthquake the region where the nazca ridge subducts appears to be mostly creeping aseismically in the interseismic period low isc and seems to act as a permanent barrier as no large earthquake ruptured through it in the last 500 years in southern peru isc is relatively high and the deficit of moment accumulated since the m w 8 8 earthquake of 1868 is equivalent to a magnitude m w 8 4 earthquake two asperities separated by a subtle aseismic creeping patch are revealed there this aseismic patch may arrest some rupture as happened during the 2001 arequipa earthquake but the larger earthquakes of 1604 and 1868 were able to rupture through it in northern chile isc is very high and the rupture of the 2007 tocopilla earthquake has released only 4 of the elastic strain that has accumulated since 1877 the deficit of moment which has accumulated there is equivalent to a magnitude m w 8 7 earthquake this study thus provides elements to assess the location size and magnitude of future large megathurst earthquakes in the central andes subduction zone caveats of this study are that interseismic strain of the forearc is assumed time invariant and entirely elastic also a major source of uncertainty is due to fact that the available data place very little constraints on interseismic coupling at shallow depth near the trench except offshore lima where sea bottom geodetic measurements have been collected suggesting strong coupling

shear stresses on megathrusts implications for mountain building behind subduction zones 1 shear stresses on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone in this study the temperatures and shear stresses on megathrusts in 11 subduction zones around the pacific rim hikurangi tonga izu ogasawara western nankai northeastern japan aleutians western alaska cascadia northern chile southern chile and se asia northern sumatra have been determined the main constraint is that vertical normal stresses beneath the highlands behind the subduction zone are nearly equal to horizontal normal stresses in the plane of a trench or arc normal section for a typical brittle and ductile megathrust rheology frictional shear stress gz for depth z and ductile shear stress a exp b rt at temperature t where a b are rheological parameters treated as constants rheological constants common to all the megathrusts crust mantle b are determined by simultaneously solving for the force balance in the overlying wedge and megathrust thermal structure using a simplex minimization algorithm taking account of the induced mantle corner flow at depth 65 15 km 2 and constant radiogenic heating 0 65 0 3 w m 3 2 throughout the crust the a constants are solved individually for each subduction zone assuming that the maximum depth of interplate slip earthquakes marks the brittle ductile transition the best fit solution shows two groupings of megathrusts with most subduction zones having a low mean shear stress in the range 7 15 mpa crust 0 032 0 006 mantle 0 019 0 004 and unable to support elevations 2 5 km for a typical frictional sliding coefficient 0 5 the low effective coefficients of friction suggest high pore fluid pressures at 95 lithostatic pressure tonga and northern chile require higher shear stresses with crust 0 095 0 024 mantle 0 026 0 007 suggesting slightly lower pore fluid pressures at 81 lithostatic ductile shear in the crust is poorly resolved but in the mantle appears to show a strong power law dependency with b 36 18 kj mol 1 amantle values are sensitive to the precise value of b but are in the range 1 20 kpa the power law exponent n for mantle flow is poorly constrained but is likely to be large n 4 the brittle ductile transition in the crust occurs at temperatures in the range 370 c 512 c usually close to the base of the crust and in the mantle at much lower temperatures 180 c 300 c possibly reflecting a marked change in pore fluid pressure or quasi ductile and subfrictional properties in subduction zones where the subducted slab is older than 50 ma a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are 300 c in much younger subduction zones the stress transmission is confined mainly to the crust the shear stresses particularly in the crust may be kept low by some sort of lubricant such as abundant water rich trench fill which lowers the frictional sliding coefficient or effective viscosity and or raises pore fluid pressure the unusual high stress subduction zone in northern chile lacks significant trench fill and may be poorly lubricated with a mean shear stress 37 mpa required to support elevations 4 km in the high andes however where the crust is thin in sediment starved and poorly lubricated subduction zones such as tonga the mean shear stress will still be low sediment may lubricate megathrusts accommodating underthrusting of continental crust such as in the himalayas or eastern central andes which have a low mean shear stress 15 mpa

surface deformation associated with the november 23 1977 caucete argentina earthquake sequence leveling data are combined with seismic observations from the november 23 1977 ms 7 4 caucete earthquake in western argentina in order to constrain models of crustal deformation in the sierras pampeanas tectonic province the spatial pattern and amount of uplift 1 m that accompanied this earthquake suggest 4 m of slip on a north south trending west dipping fault with a dip of 35 a downdip width of 24 km and a length of 80 km the top of the fault is 17 km below the surface these fault parameters are generally consistent with the seismic focal mechanism and moment of the main shock which occurred near the top of the fault the fault length is derived from the distribution of local and relocated teleseismic aftershocks and from analysis of the main shock a double event in which the two shocks occurred 21s apart and were separated by 65 km along the proposed fault plane strike the fault width is determined from the locations of the larger hypocenters along the preferred fault plane this fault is buried beneath the north south striking sierra pie de palo a laramide style crystalline basement uplift in the western part of the sierras pampeanas province the buried fault model is consistent with the lack of observed coseismic surface faulting and the broad east west symmetric character of the overlying sierra pie de palo by combining the 1977 earthquake observations with topographic relief and with estimates of the age of deformation for the sierras pampeanas basement uplifts we calculate a shortening rate of the order of 10 mm yr for the past 5 m y for this andean back arc province and estimate an average recurrence time of the order of 1000 years for earthquakes of this magnitude beneath the sierra pie de palo

late quaternary slip rates across the central tien shan kyrgyzstan central asia 1 slip rates across active faults and folds show that late quaternary faulting is distributed across the central tien shan not concentrated at its margins nearly every intermontane basin contains neogene and quaternary syntectonic strata deformed by holocene north south shortening on thrust or reverse faults in a region that spans two thirds of the north south width of the central tien shan slip rates on eight faults in five basins range from 0 1 to 3 mm yr fault slip rates are derived from faulted and folded river terraces and from trenches radiocarbon optically stimulated luminescence and thermoluminescence ages limit ages of terraces and aid in their regional correlation monte carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95 confidence limits faults in basins appear to merge at relatively shallow depths with crustal scale ramps that underlie mountain ranges composed of pre cenozoic rocks the sum and overall pattern of late quaternary rates of shortening are similar to current rates of north south shortening measured using global positioning system geodesy this similarity suggests that deformation is concentrated along major fault zones near range basin margins such faults separated by rigid blocks accommodate most of the shortening in the upper crust index terms 8107 tectonophysics continental neotectonics 9320 information related to geographic region asia 8010 structural geology fractures and faults

quaternary normal and reverse faulting and the state of stress in the central andes of south peru field studies in the andes of southern peru show that in the high andes and pacific lowlands quaternary and recent faults are normal this extensional tectonics postdates compressional deformations of pliocene early quaternary age in the sub andes the observed deformations are compressional they affect early quaternary deposits some of the faults separate quaternary deposits from the bedrock and thus are clearly of tectonic origin and not landslide effects striations on the fault planes indicate n s trending extension in the high andes and pacific lowlands the total amount of crustal stretching is small probably of the order of 1 during the last 1 2 m y in the sub andes folds and faults affecting neogene and early quaternary deposits result from n s shortening nevertheless it is supposed that this n s shortening is of early quaternary age the present day compression probably strikes e w judging from focal mechanisms in the sub andes of central peru southern bolivia and northwest argentina data from structural analysis of faults and from earthquake focal mechanisms allow us to surmise the state of stress in the andes of southern peru the high andes and pacific lowlands subjected to n s trending extension are bounded by two zones of e w trending compression the sub andes to the east and the contact between the convergent nazca and south america plates to the west in our model the maximum horizontal compressive stress trajectory hmax is roughly parallel with the e w convergence between the two plates hmax corresponds to 1 in the sub andes and to 2 in the high andes the latter situation is caused by the elevated mass of the high andes where zz the vertical stress is inferred to be 1 thus the third principal stress axis being orthogonal to the other two axes it is oriented n s allowing extension to occur in that direction on the other hand in the sub andes zz is 3 and horizontal e w shortening occurs the state of stress in the andean continental crust above the 30 dipping slab appears to be different from that in the andes of central peru situated above the flat subducting segment in this region compressional deformantion affect a wider part of the cordillera

the state of stress in an overriding plate situated above a flat slab the andes of central peru in the andes of central peru that are situated above a flat dipping slab analysis of both structural data collected in the field and available focal mechanisms show that the quaternary and recent state of stress is characterized by n s trending extension in the western cordillera and along the pacific coast whereas e w trending compression prevails in the sub andean lowlands and at the contact between the nazca and south american plates the eastern cordillera deformations suggest an intermediate state of stress i e strike slip faulting characterized by e w trending compression and n s trending extension thus major fault zones striking nw se i e parallel to the central peruvian andes are normal with a sinistral component in the western cordillera e g cordillera bianca and reverse sinistral in the eastern cordillera e g cordillera de huaytapallana this state of stress displays similarities with that of southern peru and may be also interpreted as an effect of compensated high topography in this model the vertical stress zz increases with the topography and hmax is considered as fairly constant trending e w roughly parallel to the convergence on both edges of the andes tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then hmax is 2 allowing hmin striking n s to be 3 along the pacific coast tectonics is not compressional as expected and a nearly neutral state of stress may be due to a topographical effect related to the nearby deep peru chile trench however a conspicuous difference occurs in the andes of central peru in respect to the southern peru andes compressional strike slip tectonics is observed in the eastern cordillera indeed the mean elevation of the eastern cordillera is 3 7 km whereas that of the western cordillera is 4 2 km allowing an intermediate state of stress to occur therefore in central peru a lower mean andean topography and a stronger coupling consequence of the flat subduction seems to explain that compressional tectonics is distributed in a more widespread area than in southern peru superficial deformations related to the subduction of the aseismic nazca ridge are restricted to the coastal domain opposite to this ridge they support the fact that submarine topography of large extension may subduct without producing compressional deformation in the overriding plate which can be reminiscent of a collisional setting

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

effective elastic thickness of south america and its implications for intracontinental deformation 1 the flexural rigidity or effective elastic thickness of the lithosphere te primarily depends on its thermal gradient and composition consequently maps of the lateral variability of te in continents reflect their lithospheric structure we present here a new te map of south america generated using a compilation of satellite derived grace and champ missions and terrestrial gravity data including egm96 and sagp and a multitaper bouguer coherence technique our te maps correlate remarkably well with other proxies for lithospheric structure areas with high te have in general high lithospheric mantle shear wave velocity and low heat flow and vice versa in this paper we focus on the te of the stable platform we find that old cratonic nuclei mainly archean and early middle proterozoic have in general high te 70 km while the younger patagonian phanerozoic terrane has much lower te 20 30 km suggesting that te is related to terrane age as has already been noted in europe within cratonic south america te variations are observed at regional scale relatively lower te occurs at sites that have been repeatedly reactivated throughout geological history as major sutures rift zones and sites of hot spot magmatism today these low te areas are surrounded by large cratonic nuclei they concentrate most of the intracontinental seismicity and exhibit relatively high surface heat flow and low seismic velocity at 100 km depth this implies that intracontinental deformation focuses within relatively thin hot and hence weak lithosphere that cratonic interiors are strong enough to inhibit tectonism and that the differences in lithospheric rigidity structure and composition between stable cratons and sites of intracontinental deformation are not transient and may have been maintained in some cases for at least 500 m y

extension and dynamics of the andes inferred from the 2016 parina huarichancara earthquake the mw 6 1 2016 parina earthquake led to extension of the south peruvian andes along a normal fault with evidence of holocene slip we use interferometric synthetic aperture radar seismology and field mapping to determine a source model for this event and show that extension at parina is oriented ne sw which is parallel to the shortening direction in the adjacent sub andean lowlands in addition we use earthquake source models and gps data to demonstrate that shortening within the sub andes is parallel to topographic gradients both observations imply that forces resulting from spatial variations in gravitational potential energy are important in controlling the geometry of the deformation in the andes we calculate the horizontal forces per unit length acting between the andes and south america due to these potential energy contrasts to be 4 8 1012 n m along strike of the mountain range normal faulting at parina implies that the andes in south peru have reached the maximum elevation that can be supported by the forces transmitted across the adjacent foreland which requires that the foreland faults have an effective coefficient of friction urn x wiley jgrb media jgrb53009 jgrb53009 math 00010 2 additionally the onset of extension in parts of the central andes following orogen wide compression in the late miocene suggests that there has been a change in the force balance within the mountains we propose that shortening on weak detachment faults within the andean foreland since 5 9 ma reduced the shear tractions acting along the base of the upper crust in the eastern andes leading to extension in the highest parts of the range

on the strength of interplate coupling and the rate of back arc convergence in the central andes an analysis of the interseismic velocity field 1 we interpret the interseismic crustal velocity field of the central andes using a simple three plate model in which the andean mountain belt is treated as a rigid microplate located between the nazca and south american soam plates we assume that the euler vectors associated with these plates are strictly coaxial and that the surface velocity field can be decomposed into an elastic loading field driven by locking of the main plate boundary and a smaller contribution associated with back arc convergence we obtain our best fit to the geodetic velocities if the main plate boundary is fully 100 locked between depths of 10 50 km and 8 5 of nazca soam plate convergence is achieved in the back arc by underthrusting of the brazilian shield beneath the subandean zone

nonuniform surface uplift of the andean plateau revealed by deuterium isotopes in miocene volcanic glass from southern peru abstract proposals for rapid late miocene surface uplift driven by large scale lithospheric removal beneath the central andean plateau have been based largely on temperature sensitive paleoaltimeters both the magnitude and mechanism of this proposed pulse of uplift have been challenged first climatic general circulation models support protracted uplift with predicted temperature and isotopic shifts enhanced by attainment of threshold elevations second tectonic models in which surface elevations are compensated by regional contraction and crustal thickening question the need for lithospheric removal and predict broadly coeval uplift of the entire plateau we present hydrogen isotope data using a novel temperature insensitive volcanic glass proxy from continuous well dated lower to middle miocene basin fill in the western cordillera of the northern plateau that show a rapid decrease in d values 62 8 at 19 16 ma with extremely negative values continuing into the pliocene we propose that the basin reached its current elevation by 16 ma 6 myr earlier than proposed for the central plateau the rapid decrease in d values is consistent with punctuated surface uplift of 2 2 3 7 km between 19 and 16 ma whereas the 3 7 km upper estimate assumes a static climate similar to modern the 2 2 km lower estimate conservatively incorporates modeled changes in the isotopic composition of precipitation associated with elevation change comparison of these results to existing paleoelevation estimates from the andean plateau facilitates a tentative reconstruction of earliest middle miocene paleotopography showing a central depression with flanking hinterland and thrust belt highlands this apparent pattern of nonuniform plateau uplift contradicts shortening proportional topographic growth over tens of myr we propose that temporally and spatially irregular surface uplift may be linked to pronounced local variability in crustal shortening and or piecemeal removal of dense mantle lithosphere insofar as these irregularities reflect the scale of heterogeneity for surface uplift processes available paleoelevation estimates point to a principal uplift mechanism that varies over relatively short

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

alpha particle x ray spectrometer apxs results from gusev crater and calibration report 1 the chemical composition of rocks and soils on mars analyzed during the mars exploration rover spirit mission was determined by x ray analyses with the alpha particle x ray spectrometer apxs details of the data analysis method and the instrument calibration are presented measurements performed on mars to address geometry effects and background contributions are shown cross calibration measurements among several instrument sensors and sources are discussed an unintentional swap of the two flight instruments is evaluated new concentration data acquired during the first 470 sols of rover spirit in gusev crater are presented there are two geological regions the gusev plains and the columbia hills the plains contain soils that are very similar to previous landing sites on mars a meteoritic component in the soil is identified rocks in the plains revealed thin weathering rinds the underlying abraded rock was classified as primitive basalt one of these rocks contained significant br that is probably associated with vein filling material of different composition one of the trenches showed large subsurface enrichments of mg s and br disturbed soils and rocks in the columbia hills revealed different elemental compositions these rocks are significantly weathered and enriched in mobile elements such as p s cl or br even abraded rock surfaces have high br concentrations thus in contrast to the rocks and soils in the gusev plains the columbia hills material shows more significant evidence of ancient aqueous alteration

athena microscopic imager investigation 1 the athena science payload on the mars exploration rovers mer includes the microscopic imager mi the mi is a fixed focus camera mounted on the end of an extendable instrument arm the instrument deployment device idd the mi was designed to acquire images at a spatial resolution of 30 microns pixel over a broad spectral range 400 700 nm the mi uses the same electronics design as the other mer cameras but has optics that yield a field of view of 31 31 mm across a 1024 1024 pixel ccd image the mi acquires images using only solar or skylight illumination of the target surface a contact sensor is used to place the mi slightly closer to the target surface than its best focus distance about 66 mm allowing concave surfaces to be imaged in good focus coarse focusing 2 mm precision is achieved by moving the idd away from a rock target after the contact sensor has been activated the mi optics are protected from the martian environment by a retractable dust cover the dust cover includes a kapton window that is tinted orange to restrict the spectral bandpass to 500 700 nm allowing color information to be obtained by taking images with the dust cover open and closed mi data will be used to place other mer instrument data in context and to aid in petrologic and geologic interpretations of rocks and soils on mars

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

correspondence and least squares analyses of soil and rock compositions for the viking lander 1 and pathfinder landing sites correspondence analysis is a dual q and r mode factor analysis that allows simultaneous visualization of relationships between normalized variables and samples the usefulness of the technique is first illustrated with an analysis of a simulated feldspar compositional data set and then applied to analysis of patterns among variables and samples for compositions obtained for viking lander 1 soils and pathfinder rocks and soils for the martian data the first two factors capture 90 of the variance data projected onto the plane defined by these two factors fall within a mixing triangle defined by three geologically plausible end members basaltic shergottite andesite and a halide kieserite evaporite however examination of data projected onto the second and third factors shows that the compositions are systematically displaced from the mixing triangle plane in the same general direction as the fe vector inclusion of a fe oxide e g hematite or maghemite as a reasonable fourth end member forms a mixing tetrahedron that encapsulates the data least squares mixing analysis of the data with these four end members and the elemental suite measured at both landing sites si al ti fe mg ca s cl implies that aeolian dust on rocks is a physical mixture of basalt and andesite derived materials in approximately equal proportions soil components at the two landing sites are similar to each other and less basalt like than the aeolian dust and viking 1 soils are more andesite rich than the pathfinder soils

extensional basin evolution in the cordillera blanca peru stratigraphic and isotopic records of detachment faulting and orogenic collapse in the andean hinterland 1 sedimentologic provenance oxygen isotope and 40ar 39ar results provide insights into late cenozoic evolution of an extensional hinterland basin in the peruvian andes the 5 6 5 km cordillera blanca composes the glaciated footwall of a low angle normal fault parallel to active contractional structures in the andean fold thrust belt the 200 km long wsw dipping 19 36 cordillera blanca detachment fault accommodated 12 15 km of dip slip displacement inducing subsidence of the hanging wall supradetachment basin which is filled by 1300 m of conglomerate sandstone siltstone and limited carbonate of the upper miocene pliocene lloclla formation lithofacies associations are attributed to lacustrine fan delta to proximal stream dominated alluvial fan sedimentation provenance data record footwall unroofing of jurassic through miocene volcanic and sedimentary rocks during nw directed axial dispersal of sediment provenance data record the appearance of footwall derived granite clasts from the upper miocene cordillera blanca batholith and a change to transverse wsw directed transport variations in the character and preservation of basin fill suggest along strike propagation of the fault through time initial extension and subsidence is constrained to the latest miocene by an 40ar 39ar biotite age of 5 4 0 1 ma for a basal tuff in the lloclla formation estimation of paleolake water composition shows very negative 18o vsmow values 13 6 to 18 2 indicating that high elevations comparable to modern were already attained in the cordillera blanca during earliest normal faulting and basin evolution these results lend support to models suggesting that substantial shortening crustal thickening and surface uplift were necessary precursor conditions for the generation of the cordillera blanca detachment fault

postseismic relaxation and transient creep 1 postseismic deformation has been observed in the epicentral area following the 1992 landers m 7 3 1999 chi chi m 7 6 1999 hector mine m 7 1 2002 denali m 7 9 2003 san simeon m 6 5 and 2004 parkfield m 6 0 earthquakes the observations consist of repeated gps measurements of the position of one monument relative to another separation 100 km the early observations t 0 1 year are well fit by the function a c log t where t is the time after the earthquake and a and c are constants chosen to fit the data because a log t time dependence is characteristic of transient primary creep the early postseismic response may be governed by transient creep as benioff proposed in 1951 that inference is provisional as the stress conditions prevailing in postseismic relaxation are not identical to the constant stress condition in creep experiments the observed logarithmic time dependence includes no characteristic time that might aid in identifying the micromechanical cause

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

ancient impact and aqueous processes at endeavour crater mars the rover opportunity has investigated the rim of endeavour crater a large ancient impact crater on mars basaltic breccias produced by the impact form the rim deposits with stratigraphy similar to that observed at similar sized craters on earth highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits gypsum rich veins cut sedimentary rocks adjacent to the crater rim the gypsum was precipitated from low temperature aqueous fluids flowing upward from the ancient materials of the rim leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate rich sandstones of the meridiani region

in flight calibration and performance of the mars exploration rover panoramic camera pancam instruments 1 the mars exploration rover panoramic camera mer pancam instruments have acquired more than 60 000 high resolution multispectral stereoscopic images of soil rocks and sky at the gusev crater and meridiani planum landing sites since january 2004 these images combined with other mer data sets have enabled new discoveries about the composition mineralogy and geologic geochemical evolution of both sites one key to the success of pancam in contributing to the overall success of mer has been the development of a calibration pipeline that can quickly remove instrumental artifacts and generate both absolute radiance and relative reflectance images with high accuracy and precision in order to influence tactical rover driving and in situ sampling decisions this paper describes in detail the methods assumptions and models algorithms in the calibration pipeline developed for pancam images based on new measurements and refinements performed primarily from flight data acquired on mars major calibration steps include modeling and removal of detector bias signal active and readout region dark current electronic shutter smear and pixel to pixel responsivity flatfield variations pancam images are calibrated to radiance w m2 nm sr using refined preflight derived calibration coefficients or radiance factor i f using near in time measurements of the pancam calibration target and a model of aeolian dust deposition on the target as a function of time we are able to verify that the absolute radiance calibration of most pancam images is accurate to within about 10 or less and that the filter to filter and pixel to pixel precision of the calibrated relative reflectance data both based on measurements of the pancam calibration target are typically about 3 and 1 or less respectively examples are also presented of scientific applications made possible by the high fidelity of the calibrated pancam data these include 11 color visible to near ir spectral analysis calculation of true color and chromaticity values and generation of super resolution image data products this work represents a follow on and enhancement to the pancam preflight calibration process described by bell et al 2003

parallel thrust and normal faulting in peru and constraints on the state of stress abstract we present evidence for recent normal faulting in the cordillera blanca of peru along planes trending approximately n40 w parallel to the chain this type of faulting suggests that there is an important component of extension perpendicular to the chain and contrasts markedly with the underthrusting of the nazca plate on the west side of peru and with the folding and thrusting observed in the sub andes on the eastern flank of the chain these contrasting styles of deformation and associated stress fields can be explained by buoyancy forces due to the high mountains and crustal roots in so far as this explanation is correct the difference in elevation between zones of normal and thrust faulting can be used to place an upper bound of 500 bars on the average stress difference in the crust

retrieval of compositional end members from mars exploration rover opportunity observations in a soil filled fracture in marathon valley endeavour crater rim the opportunity rover investigated a gentle swale on the rim of endeavour crater called marathon valley where a series of bright planar outcrops are cut into polygons by fractures a wheel scuff performed on one of the soil filled fracture zones revealed the presence of three end members identified on the basis of pancam multispectral imaging observations covering 0 4 to 1 m red and dark pebbles and a bright soil clod multiple overlapping alpha particle x ray spectrometer apxs measurements were collected on three targets within the scuff zone the field of view of each apxs measurement contained various proportions of the pancam based end members application of a log maximum likelihood method for retrieving the composition of the end members using the 10 apxs measurements shows that the dark pebble end member is compositionally similar to average mars soil with slightly elevated s and fe in contrast the red pebble end member exhibits enrichments in al and si and is depleted in fe and mg relative to average mars soil the soil clod end member is enriched in mg s and ni thermodynamic modeling of the soil clod end member composition indicates a dominance of sulfate minerals we hypothesize that acidic fluids in fractures leached and oxidized the basaltic host rock forming the red pebbles and then evaporated to leave behind sulfate cemented soil

rapid late miocene rise of the bolivian altiplano evidence for removal of mantle lithosphere abstract the oxygen isotopic compositions of carbonates deposited in the northern altiplano demonstrate a rapid change in late miocene time which we attribute to an increase in elevation rainfall samples over an elevation transect adjacent to the altiplano of northern bolivia display a systematic decrease in mean annual 18 o values and define a local 18 o vs altitude gradient r gonfiantini m a roche j c olivry j c fontes g m zuppi the altitude effect on the isotopic composition of tropical rains chem geol 181 2001 147 167 which we apply to paleo meteoric water values determined from carbonates age constraints from magnetostragraphy and paleoelevation estimates suggest surface uplift of 2 5 to 3 5 km occurred between 10 3 ma and 6 8 0 4 ma when the altiplano rose to its current elevation only the removal of dense eclogitic lower crust and mantle lithosphere can generate a change of this magnitude and rapidity this change coincides with an 30 decrease in the rate of convergence between the south america and nazca plates and the propagation of deformation into the eastern subandean zone which we infer to have resulted from the increase in the force per unit length applied by the elevated andean plateau to the surrounding lowlands

plateau style accumulation of deformation southern altiplano 1 employing surface mapping of syntectonic sediments interpretation of industry reflection seismic profiles gravity data and isotopic age dating we reconstruct the tectonic evolution of the southern altiplano 20 22 s between the cordilleras defining its margins the southern altiplano crust was deformed between the late oligocene and the late miocene with two main shortening stages in the oligocene 33 27 ma and middle late miocene 19 8 ma that succeeded eocene onset of shortening at the protoplateau margins shortening rates in the southern altiplano ranged between 1 and 4 7 mm yr with maximum rates in the late miocene summing rates for the southern altiplano and the eastern cordillera we observe an increase from eocene times to the late oligocene to some 8 mm yr followed by fluctuation around this value during the miocene prior to shutoff of deformation at 7 8 ma and transfer of active shortening to the sub andean fold and thrust belt shortening inverted early tertiary graben and half graben systems and was partitioned in three fault systems in the western central and eastern altiplano respectively the east vergent fault systems of the western and central altiplano were synchronously active with the west vergent altiplano west flank fault system from these data and from section balancing we infer a kinematically linked western altiplano thrust belt that accumulated a minimum of 65 km shortening evolution of this belt contrasts with the eastern cordillera which reached peak shortening rates 8 mm yr in between the above two stages hence local shortening rates fluctuated across the plateau superimposed on a general trend of increasing bulk rate with no trend of lateral propagation this observation is repeated at the shorter length and time scales of individual growth structures that show evidence for periods of enhanced local rates at a timescale of 1 3 myr we interpret this irregular pattern of deformation to reflect a plateau style of shortening related to a self organized state of a weak crust in the central south american back arc with a fault network that fluctuated around the critical state of mechanical failure tuning of this state may have occurred by changes in plate kinematics during the paleogene initially reactivating crustal weak zones and by thermal weakening of the crust with active magmatism mainly in the neogene stage

focal mechanisms of intraplate earthquakes in bolivia south america intraplate seismic activity in bolivia is mainly located in the central region 16 19 s 63 67 w which includes the east andean cordillera and the sub andean sierras at this region there is a bend in the trend of the main geological structures from nw se in the north to n s in the south focal mechanisms have been calculated for 10 earthquakes of magnitudes 4 9 5 6 using first motion p waves from long period instruments their solutions correspond to reverse faulting some with a large component of strike slip motion their solutions can be grouped into two types one with pure reverse faulting on planes with azimuth nw se and the other with a large strike slip component on planes with azimuths nearly n s or wnw ese the maximum stress axis p axis is practically horizontal dipping less than 5 oriented in a mean n56 e direction this orientation may be related with the direction of compression resulting from the collision of the nazca plate against the western margin of the south american continent wave form analysis of long period p waves for one event restricts the focal depth to 8 km in the sub andean region seismic moments and source dimensions determined from spectra of rayleigh waves are in the range of 1016 1017nm and 17 24 km respectively the central bolivia region can be considered as a zone of intraplate deformation situated between the bolivian altiplano and the brazil shield

smectite deposits in marathon valley endeavour crater mars identified using crism hyperspectral reflectance data the 100 m wide marathon valley crosscuts the cape tribulation rim segment of the 22 km diameter noachian age endeavour impact crater on mars single scattering albedo spectra retrieved from three compact reconnaissance imaging spectrometer for mars crism full resolution targeted frt regularized to 18 m pixel and two along track oversampled ato regularized to 12 m pixel observations indicate the presence of fe3 mg2 smectite exposures located in marathon valley with combination vibration metal oh absorption strength comparable to smectite spectral signatures in mawrth vallis the opportunity rover was directed to the exposures and documented the presence of shoemaker formation impact breccias that have been isochemically altered likely by fracture controlled aqueous fluids

velocity structure of the andes of central peru from locally recorded earthquakes arrival times of local events recorded during two short term seismic fied investigations in central peru are used to determine the p and s velocity structures above the slab in a segment of the andes where the subduction is horizontal the velocities in the upper crust can be related to the sedimentary cover the moho depth is estimated to be about 50 km below the western part of the sub andean zone and deepens gently to the west reaching 60 km under the western cordillera an uplift of high velocity material is observed under the coastal zone associated with a cluster of earthquakes in and above the slab the asymmetrical structure of the crust below the eastern cordillera reflects the convergence process in this part of the andes the shortening occurs along active reverse steeply west dipping faults involving the crust in its entirety on the eastern border of the cordillera the compression then decreases toward the east

normal faulting along the southern margin of the puna plateau northwest argentina 1 though orogen parallel shortening and vertical extension have dominated the tectonic evolution of the central andes a significant kinematic shift from horizontal contraction to extension appears to have occurred within the high puna altiplano plateau with the establishment of extension oblique to the orogen since late miocene time we present data from the southern margin of the puna plateau nw argentina where new normal faults have been documented in the fiambala punta negra and la quebrada areas the unifying characteristics of these areas are that young normal faults reactivate or crosscut older thrust and reverse faults the relationship between the faults and the late miocene pliocene punaschotter conglomerate suggests that the extensional faulting must be younger than 3 5 to 7 ma existing data are incomplete but indicate that similar horizontal extension has occurred in many regions throughout the puna altiplano plateau while shortening continues along the plateau margins given the spatial and temporal distribution of this late miocene to pliocene kinematic shift both lithospheric loss in the puna plateau and plateau wide gravitational extensional spreading enhanced by slowing of plate convergence rate could be responsible the young disorganized horizontal extension in the andes today may be the precursor to more pronounced extension such as observed on the tibetan plateau since mid miocene time

active detachment faulting above the peruvian flat slab the cordillera blanca detachment fault in the peruvian andes is to our knowledge the first active detachment to be documented above a modern flat slab crustal detachment has unroofed the ca 8 ma cordillera blanca batholith now the backbone of the highest mountain range in peru large magnitude slip along the fault was thermally enhanced by emplacement of the batholith the penultimate magmatic event prior to flattening of the nazca slab however extensional models based on arc magmatism and crustal thickening alone do not adequately explain the scale or structural asymmetry of a series of young deep seated west dipping normal faults across peru here we show that the onset of detachment faulting coincided with subduction of the aseismic nazca ridge and consequent flattening of the nazca slab we propose that slab buoyancy from ridge subduction triggered extensional collapse of the prethickened continental crust and that this buoyancy drove footwall uplift that exceeds basin subsidence the west dipping asymmetry of late cenozoic extensional faults in peru may be controlled by a preexisting crustal anisotropy older thrusts and or formation of riedel like shears kinematically linked to the flat nazca slab

space time distribution of afterslip following the 2009 l aquila earthquake 1 the inversion of multitemporal dinsar and gps measurements unravels the coseismic and postseismic afterslip slip distributions associated with the 2009 mw 6 3 l aquila earthquake and provides insights into the rheological properties and long term behavior of the responsible structure the paganica fault well resolved patches of high postseismic slip 10 20 cm appear to surround the main coseismic patch maximum slip 1 m through the entire seismogenic layer above the hypocenter without any obvious depth dependent control time series of postseismic displacement are well reproduced by an exponential function with best fit decay constants in the range of 20 40 days a sudden discontinuity in the evolution of released postseismic moment at 130 days after the main shock does not correlate with independent seismological and geodetic data and is attributed to residual noise in the insar time series the data are unable to resolve migration of afterslip along the fault probably because of the time interval six days between the main shock and the first radar acquisition surface fractures observed along the paganica fault follow the steepest gradients of postseismic line of sight satellite displacements and are consistent with a sudden and delayed failure of the shallow layer in response to upward tapering of slip the occurrence of afterslip at various levels through the entire seismogenic layer argues against exclusive depth dependent variations of frictional properties on the fault supporting the hypothesis of significant horizontal frictional heterogeneities and or geometrical complexities we support the hypothesis that such heterogeneities and complexities may be at the origin of the long term variable behavior suggested by the paleoseismological studies rupture of fault patches with dimensions similar to that activated in 2009 appears to have a 500 year recurrence time interval documented by paleoseismic and historical studies in addition to that paleoseismological evidence of large 0 5 m coseismic offsets seems to require seismic events recurring every 1000 2000 years characterized by 1 multisegment linkage 2 surface ruptures larger than in 2009 and 3 complete failure of the 2009 coseismic and postseismic patches

rock abrasion tool mars exploration rover mission 1 the rock abrasion tool rat is an integral part of the athena science payload serving primarily as the geologist s rock hammer the rat will expose fresh surfaces of martian rocks to other instruments on the payload the rat also brushes dust and debris from an excavated hole or unaltered rocks to accomplish these tasks autonomously the rat a sophisticated 3 axis precision controlled device was designed data products derived from rat telemetry enable the rat to also act as an important rock physical properties science instrument the returned rat grinding and penetration rate data will be inverted and compared to a rock library on the earth the design is also very compact and lightweight the rat is contained within a cylinder 128 mm long and 85 mm in diameter and has a mass of 687 g

strain accumulation controls failure of a plate boundary zone linking deformation of the central andes and lithosphere mechanics 1 we make use of observations on orogenic strain accumulation and deformation partitioning in the central andes to explore the backarc strength evolution at the lithospheric scale in plan view the altiplano puna plateaux experienced rapid initial increase of surface area undergoing active deformation during the cenozoic beyond the maximum lateral extent reached around 10 15 ma 40 50 of entire proto andes undergoing deformation at 10 20 total strain rapid localization initiated at the eastern flank of the altiplano inter and subandean thrust belt but not at the puna latitude localization was associated with a significant increase in bulk shortening rate average fault slip rates equally increased by an order of magnitude following a protracted period of stable average rates estimates of strength evolution based on force balance calculations and critical wedge analysis suggest significant backarc weakening driving this change after the middle miocene strain accumulation led to localization and weakening with development of a detachment propagating through crust and upper mantle we find that lithosphere scale failure resulting from strain weakening beyond a critical strain threshold c 20 and fault coalescence with formation of a weak detachment in shales effective coefficient of friction 0 1 plays a key role in the evolution of the andes strain related lithosphere weakening appears to dominate over the impact of external forcing mechanisms such as variations of plate convergence mantle assisted processes or erosion comparison of these orogen scale observations with experimental rock rheology indicates substantial similarity of deformation behavior with similar weakening thresholds across a wide range of scales

ancient aqueous environments at endeavour crater mars opportunity has investigated in detail rocks on the rim of the noachian age endeavour crater where orbital spectral reflectance signatures indicate the presence of fe 3 rich smectites the signatures are associated with fine grained layered rocks containing spherules of diagenetic or impact origin the layered rocks are overlain by breccias and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the endeavour impact compositional data for fractures in the layered rocks suggest formation of al rich smectites by aqueous leaching evidence is thus preserved for water rock interactions before and after the impact with aqueous environments of slightly acidic to circum neutral ph that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate rich rocks at meridiani planum

depths and focal mechanisms of crustal earthquakes in the central andes determined from teleseismic waveform analysis and insar 1 we investigate the depths of crustal earthquakes mw 5 5 earthquakes from the global cmt catalog and previous work spanning 1944 2007 for 38 well recorded events we use teleseismic p and sh waveforms to model the strike dip rake focal depth and source time function we use insar observations of surface deformation from 9 earthquakes to compare inferred fault parameters with the waveform inversions and global catalogs to assess their accuracies while the depths from the insar and waveform analyses generally agree within error horizontal and depth errors in global catalogs are 10 to 50 km as found elsewhere as noted in previous work the majority of crustal earthquakes occur in the eastern cordillera and foreland regions of the central andes although a few normal and strike slip earthquakes occur beneath the altiplano plateau and in the forearc in southern peru and northernmost chile we propose a new interpretation of one of the basement thrusts shira mountain peru as a pop up block on the basis of our new earthquake depths we confirm that earthquakes in the flat slab areas of peru and argentina are within the sometimes aseismic lower crust lower crustal earthquakes are globally found in all types of tectonic settings only when the thermal lithosphere is more than 80 km thick and the amount of recent shortening extension is 30

recent slow normal and strike slip faulting in the pasto ventura region of the southern puna plateau nw argentina 1 recent normal and strike slip faulting on the puna plateau of nw argentina has been linked to lithospheric foundering gravitational spreading plate boundary forces and a decrease in crustal shortening from north to south however the timing kinematics and rate of extension remain poorly constrained we focus on the pasto ventura region nw argentina located on the southern puna plateau and recent deformation 1 ma field mapping and kinematic analysis across offset volcanic cinder cones show that the overall extension direction is subhorizontal is oriented ne sw to nne ssw and occurs at a slow time integrated rate of 0 02 to 0 08 mm yr since at least 0 8 0 5 ma a regional compilation from this study and existing data shows that recent extension across the puna plateau is subhorizontal but varies in azimuthal orientation dramatically data from the pasto ventura region are consistent with a number of models to explain normal and strike slip faulting on the puna plateau all of which likely influence the region some role for lower lithospheric foundering through dripping appears to be seen based on the regional extension directions and ages of mafic volcanism in the southern puna plateau

a continuum model of continental deformation above subduction zones application to the andes and the aegean large scale continental tectonics of back arc extensional and andean type compressional environments are investigated by using the thin viscous sheet model to calculate the deformation within continental lithosphere that is subjected to horizontal forces on its plate boundaries and to basal drag from the asthenospheric flow beneath the shear tractions acting on the base of a deformable lithosphere are derived from a corner flow model that assumes a rigid subducting plate and a deformable overlying plate because the calculated shear tractions and the deformation within the overlying plate are interdependent the corner flow and the thin viscous sheet models are solved simultaneously we use a perturbation method to obtain analytical solutions for the velocity and strain rate fields within the overlying continental lithosphere the solutions depend on the angle of subduction the dimensionless thickness of the lithosphere and the ratio of asthenospheric to lithospheric viscosities which governs the viscous coupling between the asthenosphere and the lithosphere calculations are compared with observations from the andes and the aegean our results explain some of the features of the deformation in these regions that have heretofore not been explained by other models our model predicts that in a compressional environment a broad region of uplifted topography will tend to develop above a more steeply dipping slab 30o rather than above a shallower slab 10o 15o this is in accord with observations in the various segments of the central andes for an extensional environment the model predicts that a zone of compression can develop near the trench and that extensional strain rate can increase with distance from the trench as is observed in the aegean we also estimate the effective viscosities of 102o pa s for the asthenosphere 2x 1021 pa s for the aegean lithosphere and 1022 pa s for the andean lithosphere

characteristics and consequences of flow in the lower crust in some places there is strong evidence that the lower continental crust has flowed so as to smooth out variations in crustal thickness caused by differential crustal extension or shortening in order to better understand the processes involved we investigate the behavior of a fluid layer over a fluid half space to see how such a system responds to the deformation of its upper and lower boundaries this simple system can be used to study both the decay of crustal thickness contrasts and the behavior of a thin lithospheric sheet the changing response of the system to variations in density and viscosity contrasts and to different boundary conditions imposed on the fluid interface can easily be studied analytically the most important results are that variations in crustal thickness on a wavelength of a few times the thickness of the flowing channel will decay quickest and that large lateral variations in crustal thickness cause the fluid to develop a steep front which may cause a topographic step above it at the earth s surface deformation within the channel will be principally by simple shear the clear association of lower crustal flow with regions of thickened crust and magmatic activity suggests that both can reduce the viscosity of the lower crust to levels at which flow can occur the smoothing of crustal thickness contrasts leads to differential vertical motions and is thus a method by which substantial tilting can occur without faulting this differential uplift may be responsible for rotating and exhuming some of the detachment faults in metamorphic core complexes in the basin and range province of the western united states it is also a method of causing structural inversion in basins that does not require the reactivation of normal faults as thrusts or reverse faults

source mechanisms of moderate size earthquakes and stress orientation in mid plate south america summary fault plane solutions of six mid plate earthquakes with magnitudes ranging from 4 8 to 5 5 mb were determined using p wave first motion data and the relative amplitudes of short period teleseismic depth phases pp and sp these results together with previous studies show a predominance of reverse and strike slip faulting indicating horizontal compressional stresses in mid plate south america the orientation of the p axes however is not uniform in western and southwestern brazil the p axes are oriented approximately e w probably due to the nazca south america plate convergence in eastern brazil the direction of the p axes show more scatter but an average e w direction is consistent with the available data on the contrary in northern brazil the p axes of two events in the amazon basin trend approximately n s a direction perpendicular to the direction of absolute plate motion as well as to the relative plate motions nazca south america and south america africa

decelerating nazca south america and nazca pacific plate motions space geodetic estimates of the rate of nazca south america convergence and nazca pacific spreading averaging over several years show that present day rates are significantly slower than the 3 million year average nuvel 1a model the implied rates of deceleration are consistent with longer term trends extending back to at least 20 ma about the time of initiation of andes growth and may reflect consequences of ongoing subduction and construction of the andes e g increased friction and viscous drag on the subducted slab as the leading edge of south america thickens

changes in the tectonic regime above a subduction zone of andean type the andes of peru and bolivia during the pliocene pleistocene this paper adresses the changes in the tectonic regime in the peruvian and bolivian andes that have occurred since the upper miocene when the present day elevation of the cordillera above sea level has been almost reached the stress patterns are deduced essentially from a field study of fault kinematics and a numerical inversion of the slip vector data measured on the fault planes the cuzco fault system in southern peru is chosen as an example to illustrate the methodology used in this region striations on both active and holocene faults are in agreement with a n s extension but faults affecting early pleistocene deposits exhibit two families of striations the younger results from the previous n s extension the older involving reverse motions results from either an e w or a n s compression faults affecting pliocene formations often show an oldest family of striations resulting from a ne sw or an e w trending extension thus three tectonic regimes are demonstrated which are also supported by regional unconformities and sedimentological data 1 a pliocene extensional regime 2 a lower pleistocene compressional regime and 3 a mid pleistocene present day extensional regime similar analyses conducted in the pacific and sub andean lowlands allow sketching of the successive pliocene pleistocene stress patterns in the central andes the quaternary and present day stress pattern is characterized by a n s extension in the high andes and in the pacific lowlands and by an e w compression in the sub andean lowlands and at the contact between the nazca and south american plates this stress pattern is interpreted at a large wavelength 100 km as an effect of compensated topography this model supposes that the vertical lithospheric stress zz increases with the topography the crustal thickness and the low density mantle beneath and that the lithospheric maximum compressional horizontal stress hmax trending e w roughly parallel to the convergence is fairly constant on both edges of the andes the tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then the e w trending hmax is 2 and hmin trending n s is 3 allowing extension to occur in this direction the pliocene stress pattern was characterized by a ne sw or an e w trending extension in the high andes in the pacific lowlands and possibly in the sub andean lowlands this stress pattern was clearly different from the present day one because the e w trending stress was hmin this required a weak push or eventually tractional boundary forces acting on the south american lithosphere it is suggested that this might result from a strong slab pull due to a long steeply dipping slab which decreased the value of the xx stress transmitted to the overriding plate the early pleistocene state of stress was compressional since the elevation of the andes had not markedly decreased during this period this required an increase of the e w trending stress value this resulted from a strong coupling between the two lithospheric plates possibly due to a rupture of a long slab under its own weight other spatial changes in the stress pattern are related to the particular situation of the forearc to the subduction of the buoyant nazca ridge and to the different dips of the slab extension in the high andes is of small magnitude of the order of 1 during the last 1 2 m y in a few basins it may have attained 40 during the pliocene 5 3 m y

seismicity and average velocities beneath the argentine puna plateau a network of 60 seismographs was deployed across the andes at 23 5 s the array was centered in the backarc atop the puna high plateau in nw argentina p and s arrival times of 426 intermediate depth earthquakes were inverted for 1 d velocity structure and hypocentral coordinates average velocities and v p v s in the crust are low average mantle velocities are high but difficult to interpret because of the presence of a fast velocity slab at depth although the hypocenters sharply define a 35 dipping benioff zone seismicity in the slab is not continuous the spatial clustering of earthquakes is thought to reflect inherited heterogeneties of the subducted oceanic lithosphere additionally 57 crustal earthquakes were located seismicity concentrates in the fold and thrust belt of the foreland and eastern cordillera and along and south of the el toro olacapato calama lineament tocl focal mechanisms of two earthquakes at this structure exhibit left lateral strike slip mechanisms similar to the suggested kinematics of the tocl we believe that the puna north of the tocl behaves like a rigid block with little internal deformation whereas the area south of the tocl is weaker and currently deforming

late miocene early pliocene onset of n s extension along the southern margin of the central andean puna plateau evidence from magmatic geochronological and structural observations abstract extensional faulting typifies many of the earth s cenozoic orogenic plateaus the altiplano puna plateau in the southern central andes is the world s second largest orogenic plateau it contains a rich array of extensional fractures and normal faults with closely associated mafic volcanic flows dykes and cones this is in stark contrast to the foreland areas which record protracted shortening and continuous eastward growth of the mountain belt within the puna area a kinematic change over from shortening to extension has previously been inferred to have occurred during the quaternary however our research in the southern puna together with earlier petrologic investigations in the south central part of the plateau indicates an earlier onset for the extensional tectonism our analysis has focused on the eastern portion of the cordillera de san buenaventura in the southernmost part of the plateau where we mapped two upper miocene pliocene volcanic units associated with extensional faulting the aguada alumbrera ignimbrite and the la hoyada volcanic complex the structural inventory of these units records n s extensional deformation in the puna associated with the development of e w oriented fractures dykes normal and strike slip faults and folds new 40ar 39ar dating of magmatic rocks together with their relationships with the mapped structures reveal that widespread extension in the southern puna had already commenced by 5 ma and possibly as early as 7 ma although the extensional structures on the puna are typically associated with mafic volcanism the upper miocene pliocene la hoyada volcanic complex hosts dykes of intermediate compositions mafic to intermediate magmatism and extensional tectonism in this region is thus contemporaneous with and structurally akin to that in the central and northern parts of the plateau the ubiquitous cogenetic relationship between mafic volcanism and extensional tectonism both within the puna plateau and along its eastern flanks clearly indicates that the normal faulting is a regional phenomenon that is broadly coeval with an inferred rapid and large scale uplift of the altiplano puna plateau and a decrease in plate convergence rates these observations are compatible with a mantle delamination scenario in which the delamination of lithospheric mantle may have produced an ensuing weakening of the crust and regional uplift which may in turn have generated the conditions necessary to trigger gravitational extensional collapse beginning in the late miocene to early pliocene

vnir multispectral observations of aqueous alteration materials by the pancams on the spirit and opportunity mars exploration rovers multispectral visible and near infrared vnir observations from the mars exploration rover pancam multispectral stereo camera systems are consistent with materials having been subjected to various aqueous processes ferric oxides in the form of hematite in the burns and grasberg formations of meridiani planum have been well characterized by opportunity on the basis of strong 535 and 864 nm absorptions and positive 754 1009 nm and 934 1009 nm slopes on the rim of noachian aged endeavour crater opportunity has observed light toned veins with high ca and s as determined by the rover s alpha particle x ray spectrometer apxs and a negative 934 1009 nm slope in vnir spectra extracted from pancam data indicative of a 1000 nm h2o overtone absorption together these observations indicate that the veins are composed of gypsum rocks overturned by opportunity on the murray ridge portion of the endeavour crater rim display dark and light toned coatings the dark toned coatings have a red featureless slope that is consistent with the slope observed in laboratory spectra of high valence manganese oxide minerals potential mn oxide coatings may also be associated with some exposures of the grasberg formation apxs results for high mg and s in the light toned coatings of the murray ridge overturned rocks and a negative 934 1009 nm slope are consistent with hydrated mg sulfates opportunity has also observed spectral features in rocks that are consistent with orbital observations of fe smectites as well as al smectites and possible hydrated silica in light toned fracture fill materials the spirit rover observed sulfate rich light toned soils exposed by the rover s wheels several of these soil observations contained spectral features such as a broad absorption centered near 800 nm consistent with ferric sulfate minerals a finding confirmed by the rover s mossbauer spectrometer spirit also excavated light toned si rich soils these soils have a flat near infrared spectrum with a drop in reflectance from 934 1009 nm that is consistent with free water contained in voids or adsorbed onto the surface of the silica

plio quaternary geodynamic evolution of a segment of the peruvian andean cordillera located above the change in the subduction geometry the cuzco region abstract the cuzco region which is located above a change in subduction geometry appears to be characterized by a variable plio quaternary tectono sedimentary evolution essentially located along the major fault system that separates the high plateaux from the eastern cordillera after the higher surface formation of the high plateaux a set of neogene basins were filled by miocene fluvio torrential series and by plio pleistocene fluvio lacustrine deposits the neogene series have been affected by compressional tectonic forces attributed to the late miocene this compression is followed by roughly e w trending syn sedimentary extensional tectonics attributed to the pliocene it is related to reactivation of the pre existing major faults basin evolution and volcanic activity concentrated along the faults in the early pleistocene fluvio lacustrine deposits are affected by syn and post sedimentary compressional tectonism it is characterized by shortening that trends both n s and e w and produces folding and faulting of the sedimentary cover extensional tectonism trending roughly n s has been taking place from the middle pleistocene to the present it is coeval with shoshonitic volcanic activity and with sedimentation of fluvio lacustrine terraces torrential fans and moraines quaternary and active normal faults due to this tectonism are located in a narrow zone more than 100 km long between the high plateaux and the eastern cordillera and two 15 km long fault sectors in the eastern cordillera characteristic pleistocene scarps 400 m or more high are due to the cumulative normal offset and there are also little scarps with heights ranging between 2 and 20 m which are related to holocene fault reactivations recent fault reactivation on the cuzco fault system during the april 5 1986 earthquake m b 5 3 is due to the n s trending extension this state of stress located at a mean elevation of roughly 3730 m is generally homogeneous to different scales the active cuzco normal faults may be a consequence of adjustment between the compensated western cordillera and the undercompensated eastern cordillera this latter being uplifted higher than its isostatic equilibrium due to compression acting on its eastern edge the variation of the state of stress during the plio quaternary is in agreement with the variations of the compressional boundary forces it may be explained by variation of the convergence rate or by the variation of pull slab forces

transition from basement involved to thin skinned thrusting in the cordillera oriental of southern bolivia the eastern flank of the central andes in southern bolivia and northern argentina is underlain by a fold and thrust belt of neogene age it comprises an external thin skinned segment with basal detachment in silurian shales subandean ranges and an internal segment where units as deep as precambrian metasedimentary and igneous rocks are involved in thrusting eastern cordillera oriental between the cordillera oriental and the subandean ranges an intermediate segment interandean zone intervenes north of the argentinian bolivian border 22 s the structure of the interandean zone is characterized by folded and thrust faulted cambrian to triassic strata balanced cross sections across the western subandean ranges the interandean zone and the eastern cordillera oriental are based on previously available data and recent field work they suggest that the geological structure can be interpreted in terms of two major basement involved thrusts here referred to as interandean and subandean thrusts the more internal interandean thrust caused the development of broad basement anticlines in the eastern cordillera oriental however at shallower levels its displacement was accommodated by thin skinned folding and thrusting in the interandean zone in sequence activation of the subandean thrust uplifted the interandean zone on top of an imbricate basement sheet and caused the development of the thinskinned subandean ranges farther east published radiometric data and subsidence history of the subandean foreland basin suggest that the interandean thrust was active between about 10 ma and 5 ma the subandean thrust is still active southward displacement transfer from the subandean thrust onto the interandean thrust and a southward dipping lateral ramp of the interandean thrust result in the gradual transition from the interandean zone north of 22 s to the cordillera oriental of northern argentina a similar but larger scale transfer may be involved in the southern termination of the thin skinned subandean ranges of argentina at 23 s shortening in the western part of the thrust belt is of the order of 80 90 km total shortening in the eastern andean thrust belt from the undeformed foreland to the eastern margin of the cordillera oriental is 140 150 km

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

the nature of orogenic crust in the central andes 1 the central andes 16 22 s are part of an active continental margin mountain belt and the result of shortening of the weak western edge of south america between the strong lithospheres of the subducting nazca plate and the underthrusting brazilian shield we have combined receiver function and surface wave dispersion results from the banjo seda project with other geophysical studies to characterize the nature of the continental crust and mantle lithospheric structure the major results are as follows 1 the crust supporting the high elevations is thick and has a felsic to intermediate bulk composition 2 the relatively strong brazilian lithosphere is underthrusting as far west 65 5 w as the high elevations of the western part of the eastern cordillera ec but does not underthrust the entire altiplano 3 the subcrustal lithosphere is delaminating piecemeal under the altiplano ec boundary but is not completely removed beneath the central altiplano the altiplano crust is characterized by a brittle upper crust decoupled from a very weak lower crust that is dominated by ductile deformation leading to lower crustal flow and flat topography in contrast in the high relief inland sloping regions of the ec and sub andean zone the upper crust is still strongly coupled across the basal thrust of the fold thrust belt to the underthrusting brazilian shield lithosphere subcrustal shortening between the altiplano and brazilian lithosphere appears to be accommodated by delamination near the altiplano ec boundary our study suggests that orogenic reworking may be an important part of the felsification of continental crust

experimental constraints on the strength of the lithospheric mantle 1 to provide a better understanding of rheological properties of mantle rocks under lithospheric conditions we carried out a series of experiments on the creep behavior of polycrystalline olivine at high pressures 4 9 gpa relatively low temperatures 673 t 1273 k and anhydrous conditions using a deformation dia differential stress and sample displacement were monitored in situ using synchrotron x ray diffraction and radiography respectively experimental results were fit to the low temperature plasticity flow law on the basis of this analysis the low temperature plasticity of olivine deformed under anhydrous conditions is well constrained by our data with a peierls stress of p 5 9 0 2 gpa a zero stress activation energy of ek 0 320 50 kj mol 1 and ap 1 4 10 7 s 1 mpa 2 compared with published results for high temperature creep of olivine a transition from low temperature plasticity to high temperature creep occurs at 1300 k for a strain rate of 10 5 s 1 for a geological strain rate of 10 14 s 1 extrapolation of our low temperature flow law to 873 k the cutoff temperature for earthquakes in the mantle yields a strength of 600 mpa the low temperature high stress flow law for olivine in this study provides a solid basis for modeling tectonic processes occurring within earth s lithosphere

multiple pulses of neogene compressive deformation in the ayacucho intermontane basin andes of central peru strata of the neogene ayacucho intermontane basin central peru can be subdivided into three tectonostratigraphic units the larampuquio volcanics consisting largely of intermediate lavas and coarse conglomerates of similar lithology the unconformably overlying huanta formation consisting of a lower part formed predominantly of lacustrine and volcaniclastic sedimentary rocks and an upper part composed largely of intermediate lavas tuffs and conglomerates and the unconformably overlying ayacucho formation consisting of complexly interfingering volcaniclastic sedimentary rocks silicic tuffs and lavas of intermediate to silicic composition radiometric ages of 17 3 0 2 m y and 18 3 0 6 m y have been obtained on tuffs from the upper and lower parts of the larampuquio volcanics determinations on 2 rocks from the lower member of the huanta formation indicate an age of 11 4 0 5 m y and a rock from the upper member is dated at 9 3 0 3 m y b p units of the ayacucho formation yield ages showing that it was deposited between 7 7 and 6 m y ago the intervening molinoyocc and puchcas volcanics were erupted between 9 9 and 7 4 m y ago these units may postdate the huanta formation or may be associated in part with the huanta and in part with the ayacucho formation coarse conglomerates of the larampuquio volcanics represent debris eroded from highlands uplifted during the first and most intense pulse of the late cenozoic quechuan phase of andean compressive tectonism that began in the early miocene folding of the larampuquio volcanics may have taken place during this or a subsequent pulse of compression a marked unconformity between the huanta and ayacucho formations demonstrates a period of deformation between 8 5 and 9 5 m y ago compression also was active during at least part of the deposition of the ayacucho formation as shown by inter fingering wedges of coarse clastic debris along the northeastern margin of the basin and by angular unconformities within the formation folded rocks of the ayacucho formation and its equivalents to the west are overlain by undeformed volcanic units dated at 3 8 0 4 m y b p and 5 5 m y b p bracketing a well defined pulse of deformation slightly younger than 6 m y these subsequent episodes of compressive deformation represent recurrent pulses of the quechuan phase folding related to these late quechuan pulses is restricted in the andes to northwest trending belts corresponding to reactivated fault zones in the pre neogene substratum a system of north trending dikes in the huachocolpa district 70 km west of ayacucho suggests relaxation of compression in the pliocene and compression of quaternary age has been recognized in the huancayo area 170 km northwest of ayacucho taken together with the first pulse of quechuan deformation in the early and middle miocene these data indicate at least four pulses of crustal compression during the late cenozoic separated by periods during which compressional stresses were at least partly relaxed and at times possibly replaced by extension

lithospheric flexure and bending of the central andes gravity anomaly and topography data are used to define the effective elastic thickness of the lithosphere t in the bend region of the central andes values of z increase from nearly zero north and south of the bend to values greater than 50 km at the bend in bolivia there is a close correlation between t and the style and magnitude of the shortening in the central andes since the late miocene in the bend region where the lithosphere is flexurally strong with large t foreland deformation is concentrated into a thin skinned fold and thrust belt above a basal decollement which has absorbed more than 100 km of shortening further north and south where the lithosphere is flexurally weak with low t foreland deformation is more complex involves basement and has absorbed less shortening the along strike gradients in foreland shortening have accommodated both clockwise and anticlockwise rotations about a vertical axis of almost the entire width of the bolivian andes we speculate that the observed variation in t is related to the proximity of the brazilian shield and has been an important factor in controlling the nature and amount of foreland deformation and hence bending of the central andes the flexural properties of the lithosphere may play an important role in determining the large scale evolution of mountain belts

estimates of te from goce data abstract the cold upper part of the lithosphere can support the elastic stresses that govern rigid plate movements and support the earth s topography in many regions the thickness t e of the layer involved can be estimated from the relationship between surface gravity measurements and topography however there are extensive regions of the continents where the topography is well determined but the gravity field is not the obvious solution to this problem is to use the satellite rather than the surface gravity field the wavelength range of interest 200 500 km requires a satellite with a low orbit the first satellite to satisfy this requirement is the gravity field and steady state ocean explorer goce measurements of the elements of the gravity gradient tensor and determinations of the spherical harmonic coefficients of the gravity field based on goce observations are used to estimate t e for hawaii these estimates are 18 4 km and 21 4 km respectively and agree well with a value of 18 2 km obtained from the surface gravity field determined from altimetry an attempt to estimate the value of t e of the central north atlantic using goce data was not successful whereas surface data gives a value of about 4 km estimates for tibet and surrounding regions where the gravity field from surface measurements is poorly determined are 25 32 km the nw part of s america gives 17 24 km the difference in the values of t e from the two regions probably results from the difference in lithospheric thicknesses estimates of t e from central and southern africa of 31 34 km are less well constrained than are those from tibet and s america these results show that the data from goce can be used to estimate the value of t e where it is poorly determined from surface measurements is greater than 15 km and where large topographic loads produce large gravity anomalies

did shortening in thick crust cause rapid late cenozoic uplift in the northern bolivian andes abstract this study explores the role of crustal shortening as a mechanism for late cenozoic surface uplift in the northern bolivian andes between c 16 s and c 19 s based on new geological cross sections across the corque corocoro basin in the altiplano c 60 km thick crust today and published radiometric ages of volcanic rocks in the context of a simple 2d crustal balancing model deformation since c 10 ma mainly between 10 and 6 ma involved 28 7 km of shortening across the corque corocoro basin with a wider zone of lower crustal strain and a total of c 70 km of underthrusting in the subandes the uplift model is supported by dynamical analyses and is identical within 2 error to published palaeo elevation proxies with 2 5 0 5 km of surface uplift in the corque corocoro basin since c 10 ma 1 8 0 5 km between 10 and 6 ma and 1 6 0 5 km outside the basin in this way the late cenozoic palaeo elevation record in the northern bolivian andes can be explained within error entirely in terms of the late cenozoic crustal thickening expected for the observed history of crustal shortening