erosional control on the geometry and kinematics of thrust belt development in the central andes long term erosion rates in the central andes may have influenced not only mean elevation and relief but also the regional geometry and kinematic history of the orogenic belt a drastic along strike erosional gradient exists in the modern central andes from a high erosion region directly north of the 17 5 s bend in the andes to a low erosion region south of the bend this gradient has existed since 10 15 ma based on fission track analyses of middle miocene to holocene denudation and qualitative evaluations of the preservation potential of middle late tertiary volcanic edifices and synorogenic sediment global positioning system velocity data indicate conflicting patterns of active surface shortening north and south of the 17 5 s bend whereas present day shortening in the thrust belt north of the bend is distributed over much of the width of the belt south of the bend it is concentrated near the eastern frontal margin structural data suggest a similar kinematic situation during late miocene to holocene shortening an out of sequence chronology of thrusting in the narrow 200 km wide thrust belt to the north versus a forward breaking sequence of thrusting in the relatively wide 350 km wide thrust belt to the south the long term internal deformation and limited width of the thrust belt north of the bend are attributed to prolonged subcritical thrust wedge conditions induced by rapid erosion rates since 10 15 ma such conditions inhibit thrust front advance and favor distributed deformation within the thrust belt interior in the thrust belt south of the bend a progressive eastward migration of thrusting is interpreted to be the result of long term critical thrust wedge conditions promoted by extremely low rates of denudation since middle miocene time

uplift history of the central and northern andes a review the elevation of the andean cordillera is a crucial boundary condition for both climatic and tectonic studies the andes affect climate because they form the only barrier to atmospheric circulation in the southern hemisphere and they intrigue geologists because they have the highest plateau on earth formed at a noncollisional plate margin the altiplano puna yet until recently few quantitative studies of their uplift history existed this study presents both 1 a review of the quantitative paleoelevation estimates that have been made for the central and colombian andes and 2 an examination of the source and magnitude of error for each estimate in the central andes paleobotanical evidence suggests that the altiplano puna had attained no more than a third of its modern elevation of 3700 m by 20 ma and no more than half its modern elevation by 10 7 ma these data imply surface uplift on the order of 2300 3400 m since the late miocene at uplift rates of 0 2 0 3 mm yr paleobotanical and geomorphological data suggest a similar uplift history for the eastern cordillera namely no more than half the modern elevation present by 10 ma no evidence exists for an exponential increase in uplift rate as has been interpreted from fissiontrack data these uplift rates mostly reflect mean surface uplift rather than rock uplift that is uplift of material points because little dissection of the western eastern cordillera has occurred south of lat 19 s and of the altiplano puna thus the central andean plateau appears to be young in the colombian andes paleobotanical data imply rapid uplift of the eastern cordillera between 2 and 5 ma at rates on the order of 0 6 3 mm yr however some of this uplift is likely rock uplift due to erosion driven isostatic rebound rather than mean surface uplift

controls on the strength of coupling among climate erosion and deformation in two sided frictional orogenic wedges at steady state 1 many important insights regarding the coupling among climate erosion and tectonics have come from numerical simulations using coupled tectonic and surface process models however analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered we present an approximate analytical solution for two sided orogenic wedges obeying a frictional rheology and in a condition of flux steady state that makes explicit the nature and sensitivity of the coupling between climate and deformation we make the simplifying assumption that the wedge grows in a self similar fashion consistent with airy isostasy such that topographic taper is invariant with orogen width tectonic influx rate and climate we illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen scale erosion rule we show that steady state orogen width crest elevation and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process remarkably we show that for most combinations of parameters in the erosion law rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux further assuming frontal accretion with no underplating the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro wedge and retro wedge and the time averaged trajectories of rocks through the orogen the restriction to invariant frictional properties is conservative in these respects systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate erosion and deformation than shown here

epicenter distribution and magnitude of earthquakes in fold thrust belts insights from sandbox models scaled analogue models are used to illustratethe eect of basal friction and erosion on fault activity andhence on epicentre distribution and magnitude of earth quakes in the sedimentary cover of active fold thrust belts model results suggest that in fold thrust belts shortenedabove low friction ductile decollements rock salt or over pressured mudstone low to moderate magnitude earth quakes mw 5 3 5 6 distributed over a wide area occuralong several long lived thrust faults conversely in areasshortened above high friction decollements large magnitudeearthquakes mw 6 6 6 8 distributed over a narrowzone are likely to occur along few short lived thrust ramps calculated magnitude of earthquakes from models and theirdistribution are in agreement with recorded earthquake pat tern from the zagros mountain belt which is partially short ened above a ductile decollement of hormuz salt formation model results also showed that erosion reactivates older in active thrusts and promotes formation of out of sequencethrusts

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

formation of internally drained contractional basins by aridity limited bedrock incision 1 low internal relief aridity and internal drainage characterize the puna altiplano plateau and the tibetan plateau and the tarim basin structurally these areas are reverse fault bounded terrains with intervening wedge top basins that store thick accumulations of sediment for millions of years orographic barriers along the margins of these basins are oriented normal to moisture bearing winds resulting in regional aridity the combination of this aridity rapid shortening and uplift rates and resistant exposed lithologies coincides with the location of these internally drained basins we hypothesize that these large internally drained areas persist indefinitely when uplift overwhelms the fluvial systems and defeats the channel network to test this hypothesis we developed models of channel defeat to examine the threshold conditions required to fragment the channel network the results of these models suggest that low erodibility rocks moderate to high uplift rates and low precipitation favor defeat of orogen traversing channels most coupled tectonic landscape development models prevent the development of internal drainage and so may overestimate the voracity of erosion in regimes that favor internal drainage profoundly influencing predicted orogenic growth patterns

the permian to cretaceous structural evolution of the western approaches basin melville sub basin uk summary the tectonic sedimentary evolution of the western part of the western approaches basin melville sub basin was initiated during early permian times when synrift clastic sedimentation and volcanism commenced within an ene trending half graben this sequence thickened to the south and onlapped a high to the north during the permian an early nnw sse basin extension was accommodated on an array of ene wsw trending normal faults linked by nnw sse orientated transfer faults this was followed by a period of ene wsw extension along the basin axis when the normal and transfer faults of the previous faulting episode swapped roles this was possibly related to early rifting in the bay of biscay both sets of faults appear to be controlled to some extent by variscan thrusts and strike slip faults within the basement during the upper triassic the ridge in the north subsided allowing a thick sequence of salt to be deposited where there had previously been a topographic high during jurassic times sedimentation extended across the permian triassic half graben into the french sector this was followed by an episode of rifting and wrench deformation and inversion during which the permian to jurassic basin was domed and uplifted the cretaceous to tertiary sedimentation which followed probably resulted from postrift thermal subsidence related to cooling of the continental platform adjacent to the opening atlantic ocean steep normal and or strike slip faults data from the earliest part of this postrifting stage

a fold and thrust belt along the western flank of the eastern cordillera of colombia style kinematics and timing constraints derived from seismic data and detailed surface mapping the eastern cordillera of colombia is considered to be the result of compression and uplift during the late miocene pliocene andean orogeny nevertheless detailed mapping carried out on a portion of the fold belt exposed along the western flank of the eastern cordillera suggests that deformation began in late paleocene early eocene time in the form of a west vergent forward propagating fold and thrust belt several structures related to this event remain concealed beneath the late paleocene late eocene unconformity and synkinematic sediments are preserved locally within some of these thrust sheets the relief generated during this deformational episode constrained the depositional axis of late eocene fluvial sediments to run along the present day crestal zone of the eastern cordillera onlapping basal miocene molassic sediments on tilted middle miocene fluvial deposits suggest that a series of seismically delineated intercutaneous wedges located at the thrust front formed in late miocene time these structures mark the onset of the andean deformational episode thrusting polarity reversed during the latter event that is toward the hinterland and paleogene structures were reactivated additionally the late paleocene early eocene unconformity surface was folded and incorporated into north plunging folds and cretaceous extensional faults were inverted as a result the eastern cordillera developed its present pop up doubly vergent fold belt geometry flanked by thick molassic sequences that document the miocene pliocene andean orogeny regionally the latest campanian maastrichtian uplift of the central cordillera paleocene early eocene thrusting in the middle magdalena valley and along the western flank of the eastern cordillera and ultimately inversion and major uplift of the entire eastern cordillera in late miocene pliocene time attests to the eastward propagation of deformation from the central toward the eastern cordillera kinematically the driving element of deformation would have been the obliquely accreting western terranes of the central and western cordilleras and the panama arc these transferred their easterly component of convergence to the eastern cordillera through a basal intracrustal detachment

the pliocene and quaternary of the high plain of bogota colombia a history of tectonic uplift basin development and climatic change abstract the high plain of bogota in the eastern cordillera of colombia represents a large tectonic basin that is filled with hundreds of metres of lacustrine and fluvial sediments in the centre of the basin the sediment sequence attains a thickness of nearly 600 m and covers a time span of the last 3 ma late pliocene quaternary still older sediments of mainly fluvial origin cover the adjacent mountain slopes the age of these sediments reaches back into the late miocene to 6 ma and older the sediment sequence of the bogota area has been the subject of extensive stratigraphical and palynological studies for decades the results of these studies have provided a unique picture of the pliocene quaternary geological history of a tropical montane region three main factors have influenced the evolution of the landscape sedimentation and vegetation development these are the tectonic uplift of the andes between ca 5 and 3 ma the development of the large tectonic sedimentary basin of bogota after ca 3 5 ma and the quaternary climatic fluctuations and glaciations starting shortly after ca 2 7 ma

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

apatite fission track analysis apatite fission track aft analysis has been widely used during the past 30 years to constrain the low temperature thermal histories of many igneous metamorphic and sedimentary rocks in a wide range of geological settings applicable geological settings include orogenic belts rifted margins faults sedimentary basins cratons and mineral deposits the types of geologic problems that can be addressed include the timing and rates of tectonic events sedimentary basin evolution the timing of hydrocarbon generation and ore mineralization the absolute age of volcanic deposits the effects of major climatic changes on the near surface geothermal gradient and long term landscape evolution early work by naeser 1967 and wagner 1968 1969 first established the basic procedures that enabled the fission track dating method to be applied routinely to these geologic problems fleischer et al 1975 summarized the early studies of the broader discipline of nuclear track detection in different solid state materials more recent comprehensive overviews of fission track applications have been provided by naeser and mcculloh 1989 wagner and van den haute 1992 gallagher et al 1998 van den haute and de corte 1998 dumitru 2000 and gleadow et al 2002 etched natural fission tracks in several apatite grains are shown in figure 1 successful aft analysis is limited by the following 1 the availability of apatite from which useful aft data can be obtained often due to a lack of apatite of sufficient grain size and quality within available rock types or alternatively the lack of available rock samples due to minimal outcrop exposure or other reasons 2 economic considerations in terms of the time and money required to obtain sufficient aft data 3 the inherent limitations of aft data to resolve geological thermal history information often related to limited numbers of accumulated spontaneous fission tracks due to

tectonic inversion in the santa barbara system of the central andean foreland thrust belt northwestern argentina 1 the santa barbara system sbs of northern argentina is a 400 km long segment of the subandean foreland thrust belt it is characterized by predominantly west verging relatively high angle thrust faults many of these faults are reactivated normal faults from one branch of a complex cretaceous to paleogene rift system heteroaxial folding in parts of the sbs is probably due to a slight component of range parallel dextral strike slip motion acting on preexisting faults striking north and ne during inversion regional balanced cross sections along two transects across the northern sbs indicate that the major faults flatten into a detachment in the basement at about 10 km depth neogene e w contraction in the sbs is of the order of 21 26 km rift extension is not very well constrained but was probably less than 10 km the structural style of the sbs differs from the thin skinned subandean thrust belt to the north and from the large wavelength sierras pampeanas basement uplifts to the south the changes between the different styles are sharp and coincide with the northern and southern boundaries of the rift in the foreland suggesting that crustal or lithospheric heterogeneities exert an overriding control on foreland structural style

climatic and ecologic changes during miocene surface uplift in the southern patagonian andes abstract the up to 4 km high southern patagonian andes form a pronounced topographic barrier to atmospheric circulation in the southern hemisphere westerlies and cause one of the most drastic orographic rain shadows on earth geologic data imply that this climatic pattern has been established or significantly enhanced during miocene surface uplift of this andean segment we report evidence for important climatic and ecologic changes in the eastern foreland of the patagonian andes that appear to be the result of this uplift to provide constraints on miocene plant ecosystems and precipitation in the eastern leeward foreland of the patagonian andes we determined carbon and oxygen isotope values of pedogenic carbonate nodules from a 500 m thick section of the continental santa cruz formation the age of these deposits was constrained by ar ar dating of intercalated tuffs which range from 22 to 14 ma at 16 5 ma the 13 c values increase by 3 the 18 o values decrease by 2 and the scatter in the oxygen isotope data increases significantly we interpret these changes as the consequence of 1 km surface uplift in this andean segment from the 18 o values and increased aridity to its east from the 13 c values and the increased scatter in the 18 o values sediments overlying the santa cruz formation are very limited in extent and volume and dominated by coarse conglomerates related to pleistocene and older glaciations it thus seems that by 14 ma deposition in the eastern foreland of the southern patagonian andes had essentially ceased as the result of rain shadow formation

archean granite greenstone tectonics at kolar south india interplay of diapirism and bulk inhomogeneous contraction during juvenile magmatic accretion 1 the structural study of the kolar greenstone belt and surrounding granite gneiss terrains combined with u pb dating reveals that the middle and lower crustal tectonoplutonic pattern of the eastern dharwar craton developed during a major magmatic accretion event between 2550 and 2530 ma the granite greenstone pattern resulted from the interference of gravity driven sagging of the greenstones i e diapirism e w bulk inhomogeneous shortening combined with horizontal n s stretching and syntectonic juvenile pluton emplacement bulk inhomogeneous contraction is accommodated by the synchronous development of a pervasive n s trending vertical foliation shallow stretching lineation and conjugate strike slip shear zone pattern within and outside the greenstone belt resulting in regional horizontal pure shear deformation the plutons around the greenstone belt record regional contraction by developing one set of strike slip c s fabrics of the shear zone pattern the development of the granite greenstone pattern was coeval and compatible with deformation during juvenile magmatic accretion melting and granulite metamorphism in the lower crust the kolar example points to a specific crustal rheology that allowed sagduction of the greenstones and regional distributed bulk inhomogeneous strain due to mechanical homogeneity and low viscosity provided by large scale melting during the accretion event this example further suggests specific boundary conditions to the craton that allowed e w inhomogeneous shortening to be accommodated by n s stretching and spreading of the crust without significant tectonic thickening such tectonoplutonic pattern is specific to the archean and may develop as a consequence of mantle plume activity in intracontinental settings

el nino s tropical climate and teleconnections as a blueprint for pre ice age climates 1 at 2 7 million years ago the warm equable climates of early and middle pliocene time used here to mean from 5 to 2 7 ma were replaced by recurring ice ages most attempts to explain the change appeal either to changes in co2 in the atmosphere or reduced heat transport by the atlantic ocean the sources of the strongest teleconnections in the current climate however lie in the tropics and such connections occur by transport of heat and moisture by the atmosphere the most prominent of these teleconnections link aberrations in sea surface temperatures in the equatorial pacific el nino southern oscillation enso variations with warm and dry or cool and wet anomalies in extratropical climates we show that in most cases early and middle pliocene climate both in equatorial regions and in the extratropics differ from present day climates with the same spatial pattern as that associated with enso for instance not only was canada warmer during early pliocene time than at present as it is during el nino but the region surrounding the gulf of mexico appears to have been cooler and a bit wetter as it commonly is during el nino a virtually permanent el nino like state appears to have characterized pre ice age climates suggesting that transport of heat by the atmosphere was the principal mechanism that maintained extratropical warmth accordingly cooling and the growth of recurring ice sheets in the northern hemisphere resulted from the development of a strong walker circulation and a weakening of the hadley circulation

climatic forcing of asymmetric orogenic evolution in the eastern cordillera of colombia new apatite fission track data paleoelevation estimates from paleobotany and recently acquired geological data from the eastern cordillera of colombia document the onset of increased exhumation rates in the northeastern andes at ca 3 ma the eastern cordillera forms an efficient orographic barrier that intercepts moisture laden winds sourced in the amazon lowlands leading to high rainfall and erosion gradients across the eastern flank of the range in contrast the drier leeward western flank is characterized by lower rates of deformation and exhumation in light of the geological evolution of the eastern cordillera the combination of these data sets suggests that the orographic barrier reached a critical elevation between ca 6 and ca 3 ma which ultimately led to protracted yet more focused erosion along the eastern flank sequentially restored structural cross sections across the eastern flank of the eastern cordillera indicate that shortening rates also have increased during the past 3 ma from fission track and structural cross section balancing we infer that accelerated exhumation led to increasing tectonic rates on the eastern flank creating a pronounced topographic and structural asymmetry in the eastern cordillera the tectonic and climatic evolution of this orogen thus makes it a prime example of the importance of climatic forcing on tectonic processes

latitudinal variation of denudation in the evolution of the bolivian andes latitudinal gradients in topography relief climate and deformation have been used to suggest that climate driven erosion has exerted a first order control on the development of the central andes we synthesize the spatial and temporal variations in denudation across the eastern bolivian andes 14 22 s from new and existing estimates to test whether physical evidence exists to support the hypothesis that erosion influences thrust belt evolution basin morphometry channel network indices climate and longitudinal river profiles indicate a northward increase in relative relief fluvial incision and denudation short term denudation rate averages from landslide mapping and sediment flux data range from 1 to 9 mm yr in the north compared to 0 3 to 0 4 mm yr in the south long term denudation rate estimates from thermochronology cosmogenic radionuclides foreland basin sediment volumes stra tigraphy paleoerosion surface degradation and balanced cross sections range from 0 04 to 1 6 mm yr with rates up to more than twice as fast in the north when comparing estimates from the same method the shorter term denudation rates exhibit the greatest variance our denudation synthesis shows that an along strike disparity in denudation greater in the north has existed throughout the holocene and perhaps existed since as early as the late miocene our denudation synthesis also suggests that the disparity and denudation rates have increased to the present correlations between the thrust belt geology geometry geomorphology climate and kinematics of the orogenic wedge provides a case study in observing the regional scale interactions between uplift climate and erosion we conclude that the denudation history uplift history and tectonic geomorphic correlations suggest that models of the evolution of the bolivian andes should incorporate a latitudinal erosion gradient for the last 10 kyrs to perhaps 10 myrs

erosion and tectonics at the margins of continental plateaus the topography across the eastern margin of the central andean plateau north of 18 s beni region bears a strong resemblance to the topography of the southern margin of the tibetan plateau nepal himalaya with both regions featuring a steep frontal slope and high peaks at the plateau edge in contrast the topography of the eastern margin of the central andean plateau south of 18 s pilcomayo region tapers toward the foreland more gently and has no line of high peaks at the margin both the himalayan and the beni regions have been the sites for large amounts of denudation and in both regions geologic evidence suggests that erosion has been sufficiently vigorous for the physiographic plateau margin to have retreated toward the plateau interior during the neogene we hypothesize that the steep frontal slope and high peaks of the beni region and himalayan front largely reflect the high orographic precipitation and high erosion rates occurring in these regions and that the more gentle topography of the semiarid pilcomayo region reflects a tectonic landform only slightly modified by erosion we propose that orographic precipitation impinging on a plateau margin will generally tend to drop moisture low on the slope eroding back the plateau while enhancing or maintaining the steep long wavelength slope a numerical model coupling orographic precipitation erosion and tectonic uplift demonstrates the plausibility of this hypothesis the erosional efflux in both the beni and nepal himalaya have been considerable and simple mass balance calculations for the himalaya suggest that during the neogene the erosional mass efflux has generally outpaced the tectonic mass influx this contrasts with the apparent prior domination of tectonic influx and may reflect a decrease in the rate of tectonic addition during the same period and or increased late cenozoic erosion rates

mechanics and erosion of basement cored uplift provinces 1 basement cored uplift provinces are often characterized by high angle reverse faulting along preexisting crustal heterogeneities which may greatly affect the mechanics of deformation and the coupling between erosion and orogenic structure herein we construct a coupled deformation erosion model to understand the mechanics and erosion of mountain belts in which the spatial distribution of deformation is largely influenced by the presence of preexisting high angle faults in this case deformation is accommodated along and topography is built above these structures this topographic loading leads to increasing lithostatic stresses beneath these regions as a result active deformation may migrate to frictionally stronger structures in adjacent regions where lithostatic loading is lower the migration of deformation to such nearby structures depends on the hubbert rubey pore fluid pressure ratio of the crust the orientations of the frictionally weaker and stronger preexisting faults 1 and 2 respectively the friction coefficients b1 and b2 and hubbert rubey fluid pressure ratios b1 and b2 of these faults and the surface slope of the topography above the frictionally weaker structure assuming zero surface slope above the frictionally stronger structure in general we found that for a given and 1 as b1 increases b1 b2 increases and 2 decreases the value of b2 required to force deformation to migrate increases however as erosional processes lead to decreasing surface slopes deformation will be inhibited from migrating to frictionally stronger structures in adjacent regions our model results may help to explain some aspects of the deformation observed and the possible correlation between precipitation and the migration of deformation within these tectonic provinces

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

multiscale variability in north american summer maximum temperatures and modulations from the north atlantic simulated by an agcm abstractsix recurrent thermal regimes are identified over continental north america from june to september through a k means clustering applied to daily maximum temperature simulated by echam5 forced by historical ssts for 1930 2013 and validated using ncep doe amip ii reanalysis over the 1980 2009 period four regimes are related to a synoptic wave pattern propagating eastward in the midlatitudes with embedded ridging anomalies that translate into maximum warming transiting along two other regimes associated with broad continental warming and above average temperatures in the northeastern united states respectively are characterized by ridging anomalies over north america europe and asia that suggest correlated heat wave occurrences in these regions their frequencies are mainly related to both la nina and warm conditions in the north atlantic removing all variability beyond the seasonal cycle in the north atlantic in echam5 leads to a significant drop in the occurrences of the regime associated w

impact of submesoscale processes on dynamics of phytoplankton filaments in monterey bay ca during northwesterly upwelling favorable winds the development of a southward flowing cold jet along the entrance to the bay is often observed this dense cold jet separates warm waters of the anticyclonic circulation offshore from the water masses inside the bay interactions between the cold jet and the offshore anticyclonic circulation generate ageostrophic secondary circulation asc cells due to submesoscale processes as for example flow interaction with the development of surface frontogenesis and nonlinear ekman pumping based on observations and modeling studies we evaluate the impact of these submesoscale processes on the formation of chlorophyll a filaments during late spring earlier summer and late summer time frames we show that during the late summer time frame asc leads to the development of filaments with high values of chlorophyll a concentration along the edge of the cold jet in contrast to the earlier summer time when the asc mixes phytoplankton much deeper to the area below of the euphotic depth and chlorophyll a filaments are 3 4 times weaker

cenozoic contractional reactivation of mesozoic extensional structures in the eastern cordillera of colombia 1 the eastern cordillera of colombia is key to understanding the role of inherited basement anisotropies in the evolution of active noncollisional mountain belts in particular the rio blanco guatiquia region of the eastern cordillera is exemplary in displaying a variety of phenomena that document the importance of the orientation geometry and segmentation of preorogenic anisotropies we document the first unambiguous evidence that extensional basement structures played an important role in determining the locus of deformation during contractional reactivation in the eastern cordillera detailed structural field mapping and analysis of industry seismic reflection profiles have helped to identify the inherited san juanito naranjal and servita normal faults and associated transfer faults as important structures that were inverted during the cenozoic andean orogeny apparently the more internal faults in the former rift basin were not properly oriented for an efficient reactivation in contraction however these faults have a fundamental role as strain risers as folding is concentrated west of them in contrast reactivated normal faults such as the more external servita fault are responsible for uplifting the eastern flank of the eastern cordillera in addition these structures are adjacent and intimately linked to the development of thin skinned faults farther east in part the superimposed compression in this prestrained extensional region is compensated by lateral escape the dominant presence of basement involved buckling and thrusting and the restricted development of thin skinned thrusting in this inversion orogen makes the eastern cordillera a close analog to the intraplate atlas mountains of morocco and other inverted sectors of the andean orogen farther south

paleostress evolution of the northern andes eastern cordillera of colombia implications on plate kinematics of the south caribbean region 1 new tectonic field data and paleostress determinations in the eastern cordillera of colombia enable us to identify stress regimes that prevailed in the northern andes since late cretaceous times until present day these regimes were characterized by an e w to wsw ene active contraction from late cretaceous to late paleocene this direction subsequently changed to nw se and finally became wnw ese during the andean tectonic phase the characteristics and relative chronology of these regimes were deduced from field structures and stratigraphic criteria using stress inversion of fault slip data sets to evaluate our model we used the rotation poles of the south america caribbean and nazca plates relative to north america and paleogeographic reconstructions of the caribbean region to derive a kinematic model of the northern andes assuming a general correspondence between the regional convergence directions and the regional compression we built a theoretical model of the regional stress regimes based on kinematics of the northwestern south america since late cretaceous times this model reveals a major variation at the end of the paleocene when relative divergence shifted to convergence between the americas this is in agreement with our tectonic model based on independent tectonic field data inversion in the eastern cordillera this regional kinematic and tectonic change which affected the caribbean at the end of the paleocene was responsible for and consistent with the major change in stress patterns and structural style in the eastern cordillera it is also coeval with the development of a major regional unconformity in colombia

stable isotope paleoaltimetry a critical review stable isotope paleoaltimetry makes use of systematic trends in the distribution and isotopic composition of modern precipitation with climate and topography and of the potential to estimate the isotopic composition of paleoprecipitation from authigenic in situ formed minerals to illustrate the usefulness as well as potential limitations of this method we review 1 processes controlling the isotopic composition of modern precipitation 2 stable isotope data from modern precipitation across regions of high topography and 3 stable isotope data from authigenic minerals that have been used to infer paleotopography from this we conclude that stable isotope studies of authigenic minerals can permit useful inferences on paleotopography with uncertainties that critically depend on a detailed understanding of local to global scale paleoclimate during the time interval of interest

basement balancing of rocky mountain foreland uplifts restorable cross sections of foreland basement uplifts must contain faults whose curvatures are consistent with the relative slip and tilt between adjacent basement blocks cylindrical fault surfaces can explain the uniform dip of strata on the back side of foreland uplifts local zones of shortening and extension occur in hinge zones above transitions in fault curvature high curvature fault splays form fault wedges of basement which ease the transition from thrust and reverse faulting of basement blocks to folding in the sedimentary cover 20 references 4 figures

thrust geometry controlled by erosion and sedimentation a view from analogue models analogue sandbox models have been set up to study thrust systems formed above two decollements and affected by erosion and sedimentation the deformation was imaged by x ray scanner three erosion sedimentation conditions were tested for all the experiments a duplex develops between the two decollement levels for the experiment without erosion and without sedimentation ramp anticlines form in the upper series for the model with syntectonic sedimentation and without erosion the shortening in the upper series is first characterized by fault related folds and then by a forward propagation of the decollement that induces the development of a piggy back basin for the experiment with erosion and sedimentation a passive roof duplex is formed relationships between structural style and syntectonic superficial conditions in classical thin skinned thrust belts are similar to those found in the analogue models the ramp anticlines of the jura developed with low erosion and low sedimentation and the large sub andean thrust belt is controlled by syntectonic sedimentation whereas the passive roof duplex of pakistan is synchronized with intense erosion this study outlines the crucial effect of the superficial mass transport phenomena in the tectonic style of thrust belts

steady state erosion of critical coulomb wedges with applications to taiwan and the himalaya 1 orogenic structure appears to be partially controlled by the addition to and removal of material from the mountain belt by tectonic accretion and geomorphic erosion respectively we developed a coupled erosion deformation model for orogenic wedges that are in erosional steady state and deform at their coulomb failure limit erosional steady state is reached when all material introduced into the wedge is removed by erosion that is limited by the rate at which rivers erode through bedrock we found that the ultimate form of a wedge is controlled by the wedge mechanical properties sole out depth of the basal decollement erosional exponents basin geometry and the ratio of the added material flux to the erosional constant as this latter ratio is increased wedge width and surface slopes increase we applied these models to the taiwan and himalayan orogenic wedges and found that despite a higher flux of material entering the former the inferred ratio was larger for the latter calculated values for the erodibility of each wedge showed at least an order of magnitude lower value for the himalaya relative to taiwan these values are consistent with the lower precipitation regime in the himalaya relative to taiwan and the exposure of crystalline rocks within the himalayan orogenic wedge independently determined rock erodibility estimates are consistent with the accretionary wedge sediments and metasediments and the crystalline and high grade metamorphic rocks exposed within taiwan and the himalaya respectively therefore differences in rock type and climate apparently lead to key differences in the erosion and hence orogenic structure of these two mountain belts

development of the colombian foreland basin system as a consequence of diachronous exhumation of the northern andes this study addresses multiple controls on foreland basin accommodation and contributes to enhanced understanding of the evolution of the northern andes the middle magdalena valley basin mmvb eastern cordillera and llanos basin are part of a late cretaceous cenozoic foreland basin system east of the colombian central cordillera mechanical modeling indicates that the primary control on complex distributions of sedimentary thicknesses facies and unconformities was lithospheric flexure in response to crustal loads from the central and eastern cordilleras shorter wavelength folding and paleoaltitude determined the local character of strata our mechanical modeling consists of the application of orogenic and sedimentary loads extracted from geologic data on a continuous elastic lithosphere the results validate two major basin configurations the first configuration was a maastrichtian early eocene foreland basin coupled with central cordillera uplift growth strata record continuous sedimentation in the eastern cordillera whereas regional unconformities in the llanos basin distal foreland basin reflect isostatic adjustments of the basin s amplitude and wavelength to central cordillera episodic uplift and tectonic quiescence the second major basin configuration was characterized by central cordillera erosion since middle eocene times recorded by a regional pediment surface in the absence of central cordillera effective loading loads from onlapping sediments and eastern cordillera piggyback sub basins provoked post middle eocene accommodation in the mmvb and llanos basin intensified eastern cordillera uplift during the neogene produced basinal tilting recorded by unconformities in the mmvb this study highlights the importance of assessing the causes of tectonic accommodation as a foundation for interpretation of the evolution of large foreland and intermontane basins