neogene caribbean plate rotation and associated central american tectonic evolution during the neogene the caribbean plate moved eastward with respect to the north and south american plates reconstructing this motion by closing the cayman trough along its bounding transform faults creates a gore of ocean between northern central america and southern mexico we present instead a reconstruction which juxtaposes these two continental areas by strike slip motion using geological evidence from around the cayman trough the strike slip fault zones of northern central america and the continental margin of southern mexico as our constraints we propose that seafloor spreading began in the cayman trough at 30 5 ma and that subsequently there was 1100 km of relative plate displacement at an average rate of 3 7 0 6 cm yr this neogene plate motion cannot be achieved by rigid plate rotation about a single pole which implies that central america must have rotated anticlockwise relative to the rest of the plate there is evidence for internal plate deformation in central america consistent with such a sense of rotation our suggestion of an originally easterly trending arc in southern central america is more consistent with the timing and geometry of the collision of panama with northern colombia and the resultant deformation than were earlier models that depicted collision of a northerly trending arc

the north anatolian fault and complexities of continental escape abstract before the plio pleistocene the proto north anatolian fault zone was occupied by two separate faults a wnw striking right lateral eastern segment which extended to the black sea and a wsw striking left lateral western segment during the plio pleistocene most of the right lateral displacement on the eastern fault was transferred from the black sea extension to the western fault converting the latter to a right lateral structure and giving rise to the modern north anatolian fault zone this model explains the evidence first reported by hancock barka for an apparent plio pleistocene reversal of displacement along the western part of the fault the model may also account for the plio pleistocene change in regional stress in southwestern anatolia

clastic domains of sandstones in central eastern venezuela trinidad and barbados heavy mineral and tectonic constraints on provenance and palaeogeography current models for the tectonic evolution of northeastern south america invoke a palaeogene phase of inter american convergence followed by diachronous dextral oblique collision with the caribbean plate becoming strongly transcurrent in the late miocene heavy mineral analysis of cretaceous to pleistocene rocks from eastern venezuela barbados and trinidad allow us to define six primary clastic domains refine our palaeogeographic maps and relate them to distinct stages of tectonic development 1 cretaceous passive margin of northern south america 2 palaeogene clastics related to the dynamics of the proto caribbean inversion zone before collision with the caribbean plate 3 late eocene oligocene southward transgressive clastic sediments fringing the caribbean foredeep during initial collision 4 oligocene middle miocene axial fill of the caribbean foredeep 5 late eocene middle miocene northern proximal sedimentary fringe of the caribbean thrustfront and 6 late miocene recent deltaic sediments flowing parallel to the orogen during its post collisional mainly transcurrent stage domain 1 3 sediments are highly mature comprising primary guayana shield derived sediment or recycled sediment of shield origin eroded from regional palaeogene unconformities in trinidad palinspastic restoration of neogene deformation indicates that facies changes once interpreted as north to south are in fact west to east reflecting progradation from the maturin basin into central trinidad across the nw se trending bohordal marginal offset distorted by about 70 km of dextral shear through trinidad there is no mineralogical indication of a northern or northwestern erosional sediment source until oligocene onset of domain 4 sedimentation paleocene middle eocene rocks of the scotland formation sandstones in barbados do show an immature orogenic signature in contrast to venezuela trinidad domain 2 sediments this requires 1 at least a bathymetric difference if not a tectonic barrier between them and 2 that the barbados deep water depocentre was within turbidite transport distance of the early palaeogene orogenic source areas of western venezuela and or colombia domains 4 6 from late oligocene show a strong direct or recycled influence of caribbean orogen igneous and metamorphic terranes in addition to substantial input from the shield areas to the south the delay in the appearance of common caribbean detritus in the east relative to the paleocene and eocene appearance of caribbean influenced sands in the west reflects the diachronous eastward migration of caribbean foredeep subsidence and sedimentation as a response to eastward younging collision of the caribbean plate and the south american margin

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

interaction between active tectonics erosion and diapirism a case study from habble rud in southern central alborz northern iran abstract the alborz mountain chain is a region of active deformation within the arabia eurasia continental collision zone the southern part of central alborz mountains in the north of iran represents complex tectonics because it is located at the border of two developing continental sedimentary basins between southern central alborz and central iran an arid and semi arid climate a large extent of quaternary sediments rugged topography salt domes and faults with historical seismicity influence the habble rud river catchment in the present research a number of tectonic geomorphologic indices were extracted from satellite imagery and 10 m dem digital elevation model data in order to identify relative tectonic activity within the basin the indices include stream length gradient index sl drainage basin asymmetry af index of mountain front sinuosity smf hypsometric integral hi index of drainage basin shape bs ratio of valley floor width to valley height vf and fault density fd due to the presence of heterogeneous indices for all sections of the catchment causing large extension of habble rud 3260 km2 all of the variables such as extremely erodible formations faults and folds and salt tectonics on the southern part were put into a matrix table as a new approach the variables were put into the saw simple additive model model as one of madm multi attribute decision making models techniques the study area was divided into four regions according to the values of saw these classes include very high 11 high 48 3 moderate 34 7 and low activity 3 4 the result of the model suggests that the study area is located on a changing tectonic trend in central alborz from nw se to ne sw the regions with high relative tectonic activity in hr catchment correspond to the active garmsar and sorkhe kalout faults and diapirs

origin of cariaco basin southern caribbean sea abstract the cariaco basin an anoxic basin in the central eastern venezuelan continental borderland is located in the area of overlap of two en echelon right lateral strike slip fault zones the moron and el pilar fault zones on the basis of 28 acoustic reflection profiles across it the basin is interpreted as a pull apart basin due to east west tension in the area of the right step between the two fault zones 125 km of overlap and 35 km separation the offset along the fault zones is less than 100 km and at least 25 km its age is most probably quaternary as suggested by the thickness of the sedimentary fill and the estimated rate of deposition and because strike slip displacement along the master faults probably began no earlier than the late tertiary the cariaco basin is the largest pull apart basin along the bocono moron el pilar fault system which is a part of the caribbean south america plate boundary

subduction of the caribbean plate and basement uplifts in the overriding south american plate the new tectonic interpretations presented in this paper are based on geologic field mapping and gravity data supplemented by well logs seismic profiles and radiometric and earthquake data the present caribbean south american plate boundary is the south caribbean marginal fault where subduction is indicated by folding and thrusting in the deformed belt and a seismic zone that dips 30 to the southeast and terminates 200 km below the maracaibo basin the caribbean south american convergence rate is estimated as 1 9 0 3 cm yr on the basis of the 390 km length of the seismic zone and a thermal equilibration time of 10 m y the caribbean south american convergence has produced a northwest southeast maximum principal stress direction 1 in the overriding south american plate the mean 1 direction for the maracaibo santa marta block is 310 10 based on earthquake focal mechanism determinations and structural and gravity data on the overriding south american plate basement blocks have been uplifted 7 12 km in the last 10 m y to form the venezuelan andes sierra de perija and the colombian santa marta massif crystalline basement of the venezuelan andes has been thrust to the northwest over tertiary sediments on a fault dipping about 25 and extending to the mantle in the sierra de perija mesozoic sediments have been thrust 16 26 km to the northwest over tertiary sandstones along the cerrejon fault a thrust fault dipping 15 10 to the southeast is consistent with field mapping and gravity and density data the santa marta massif has been uplifted 12 km in the last 10 m y by northwest thrusting over sediments the basement block overthrusts of the perijas venezuelan andes and the santa marta massif are pliocene pleistocene analogs for laramide orogenic structures in the middle and southern rocky mountains of the united states the nonmagmatic basement block uplifts along low angle thrust faults reveal horizontal compression in the overriding plate over 500 km from the convergent margin present day east northeast west southwest 080 compression is indicated by earthquake focal mechanisms and strike slip motion on the bocono fault these earthquakes are intraplate deformation associated with east west 080 nazca south american convergence

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

paleogeographic and tectonic implications of quartzose sandstones of barbados the provenance of paleogene sandstones on the island of barbados is relevant to various models of the tectonic evolution of the southern caribbean area modal point counts of 26 sandstones from barbados show that the constituent grains most likely were derived from a composite craton interior and orogenic margin abundant detrital polycrystalline quartz grains have affinities to a spectrum of low to high rank metamorphic plutonic crystalline source rocks microprobe data suggest that feldspars were derived from metamorphic or plutonic source terrances the complex heavy mineral suite of the terrigenous sandstones including glaucophane chloritoid titanite zircon and aluminosilicates supports derivation from orogenic and cratonal terranes due to the complex history of the south american caribbean plate boundary and poor age constraints on timing of deposition widely contrasting models have been proposed concerning the provenance of the sandstones convergence between the aruba orchila arc and continental south america during the paleogene resulted in the formation of an e w trending foreland fold thrust belt and foredeep dominant sediment dispersal was to the east northeast along tectonic strike the present study shows that the terrigenous sandstones on barbados probably were deposited in deep sea fans to the north of present day araya peninsula during and shortly after the late middle eocene probable source terranes include the guayana shield the caribbean mountain system interior foreland fold thrust belt and possibly to a lesser extent the lesser antilles magmatic arc or predecessor arc

neogene block tectonics of eastern turkey and northern south america continental applications of the finite difference method continental plate boundary zones are generally wide diffuse zones of deformation within which in the upper 5 to 15 km may be recognized blocks which are bounded by fault zones within which strain is highly concentrated and along which slip rates are fairly high 2 30 m ma 1 these blocks may be irregular flakes defined by older crustal inhomogeneities of an upper brittle crust below which strain occurs in a ductile and more homogeneous lower crust with examples from the convergent plate boundary zone of eastern turkey and the southern caribbean plate boundary zone of northern south america we use plate slip rates and trends and slip rates of faults to construct block vector diagrams to deduce the sums of relative motion among block mosaics slip rates and trends of ill defined block boundaries and the extent to which blocks are internally strained

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

palaeoecology palaeogeography and depositional environments of upper cretaceous rocks of western venezuela abstract the end of the early cretaceous in northern south america was marked by regional palaeoceanographic change in western venezuela this change was highlighted near the end of the albian by drowning of the maraca formation shallow water carbonate platform regional marine transgression continued during the cenomanian and turonian in western venezuela with drowning of the more southerly guayacan member capacho and escandalosa formations carbonate platform deposition of organic carbon rich intervals of the la luna and navay formations occurred unconformably on maraca formation and guayacan member shallow water carbonates and continued through the early santonian during this interval the maracaibo and barinas apure basins were characterized by low oxygen or anoxic bottom water conditions away from the basin margins deposition of organic carbon lean upper la luna and navay formation strata show that bottom water oxygen content increased from the late santonian through the end of the cretaceous the siliceous and phosphatic late santonian to early maastrichtian tres esquinas member and the glauconitic late campanian to early maastrichtian socuy member both of the la luna formation represent the final phase of la luna deposition in the maracaibo basin tectonic uplift in eastern colombia during the campanian and maastrichtian caused progradation of the colon mito juan and burguita formation deltas and eventual infilling of the maracaibo and barinas apure basins

opposed shear senses inferred from neotectonic mesofracture systems in the north anatolian fault zone abstract the 1200 km long north anatolian fault zone is a right lateral intracontinental transform boundary which was initiated in the late neogene sediments of pliocene to holocene age in basins between cerkes and erbaa within the convex northwards arc of the fault zone are deformed by syn sedimentary and post depositional mesoscopic faults and joints the mesofractures which strike obliquely to the fault zone include reverse faults normal faults normal shear joints conjugate vertical joints and strike slip faults each type of structure occurs in two geometrical groups one comprises four systems of fractures the other is made up of five systems the directions of secondary compression and or extension inferred from the first group of mesofractures which are restricted to sediments of pliocene to early pleistocene age are interpreted as being related to left lateral shear along the north anatolian fault zone the directions of compression and or extension inferred from the second group of mesofractures which cut sediments of pliocene to late holocene age were generated during right lateral shear the presence of the second group of mesofractures is understandable because they are related to the shear sense which operates at the present day but those interpreted as being related to left lateral shear are more puzzling their development implies one or more reversals of the dominant sense of displacement several tentative models to explain such reversals are proposed including regional and local influences the latter related to mechanical constraints and or the effects of other fault systems

the andean ophiolitic megastructures on the buga buenaventura transverse western cordillera valle colombia abstract a structural study of the buga buenaventura transverse in the central part of the western cordillera of colombia has shown the presence of three structural units which from bottom to top and from west to east are the rio dagua unit the rio calima unit and the loboguerrero window unit all three units comprise strata between 120 and 80 m y old overlying a basement of green rocks showing the characteristics of submarine flows the bolivar ultrabasic and basic massif is geographically linked to the rio calima unit in which green rocks predominate and is separated from it by a tectonic contact the upper part of the massif on the other hand shows high temperature metamorphic rocks formed during its emplacement the rio dagua unit shows two tectonic phases with isoclinal folding and development of schistosity the first phase is contemporaneous with low grade metamorphism equivalent to lower greenschist facies conditions the loboguerrero window unit shows a large recumbent fold oriented towards the southeast deformation in the rio calima unit is weaker and appears to correspond to a higher structural level than in the two other units as the attitudes of the s1 schistosity in the rio dagua unit and of the shear zones located at the green rocks sediments contact in this same unit are similar to that of the overthrust at the base of the rio calima unit we are led to postulate that the overthrust belongs to the first phase of deformation as also does the recumbent fold in the loboguerrero window unit we are thus led to propose a southeastward direction of emplacement for the nappes in the western cordillera of colombia in conclusion the authors extend their observations and propose a new structural interpretation of the occidente colombiano

musings in tectonics i outline and discuss my career in the context of the history of structural geology and tectonics the progressive developments that led to plate tectonics the people who have encouraged and influ

four phase tectonostratigraphic development of the southern caribbean abstract although the stratigraphy of northern south america and the southern caribbean has been studied in detail in many areas a clear understanding of the sequence of tectonic events and their relation to regional stratigraphy has not been forthcoming since northern south america collided with southern north america in the late palaeozoic we identify four discrete tectonic phases from the stratigraphy of the area that is now the southern caribbean these phases derived from a synthesis of regional stratigraphy were 1 panama arc collistion with colombia in the late miocene early pliocene which drove a complex triangular wedge bounded by strike slip faults northward into the caribbean 2 right lateral strike slip faulting associated with post eocene eastern motion of the caribbean ocean floor into the gap between the separating americas 3 island arc development and collision associated with the entry of the present caribbean ocean floor an area of buoyant ocean crust into the gap between the separating americas and 4 continental rifting and passive margin development in the late jurassic early cretaceous associated with the separation of north and south america approximately along the palaeozoic suture zone overprinting of younger structures on inherited structures from previous phases is responsible for the overall complexity of the region

fine structure of a postfailure wadati benioff zone the hypocentral distribution of locally recorded aftershocks of the great ms 8 1 michoacan mexico earthquake of september 19 1985 defines a narrow wadati benioff zone structure roughly 10 km thick dipping 14 at n23 e this is in good agreement with the source geometry obtained by waveform modeling of the 1985 michoacan mainshock and the large 1979 petatlan earthquake in the adjoining region we inverted for the crustal velocity structure in the epicentral region by applying the levenberg marquardt non linear least squares algorithm to our local aftershock data the velocity model consists of a layer with linearly increasing velocity in depth overlying a dipping constant velocity halfspace our hypocentral location program uses a velocity model of the same form together with ray tracing the earthquake hypocentral resolution obtained with this program is significantly better than that from conventional approaches hypo and looks very promising for use in velocity structures with an important dipping interface like subduction zones

late cretaceous miocene diachronous onset of back thrusting along the south caribbean deformed belt and its importance for understanding processes of arc collision and crustal growth 1 the venezuelan basin is obliquely subducted to the east southeast beneath the continental south american plate at the east west trending south caribbean deformed belt scdb a 50 100 km wide wedge of accreted sedimentary rocks derived both from offscraping of the 0 5 to 1 km thick sedimentary cover of the subducting venezuelan basin and from incorporation of clastic sediments derived from the continental margin of south america in this paper we describe the structure and sequence stratigraphy of five late cretaceous to recent sedimentary sequences overlying a 230 000 km2 area of the southern venezuelan basin and beata ridge the data set includes 5900 km of 2d seismic reflection data that are tied to lithologic and age data taken from dsdp sites 146 149 and 150 in the central part of the venezuelan basin we use observed patterns of wedging in mapped and dated sedimentary sequences adjacent to the scdb to determine the age of the diachronous west to east initiation of thrusting and subduction at the scdb the onset of subduction in the scdb corresponds with the cessation of thrusting from west to east along the zone of collision between the intraoceanic caribbean arc and the south american continent this correlation in the age of deformation indicates that collision between the caribbean arc and the south american continent led to subduction polarity reversal a process that is commonly observed at various stages of tectonic evolution in other areas of active arc continent collision including japan and sunda

new insights into the history and origin of the southern maya block se mexico u pb shrimp zircon geochronology from metamorphic rocks of the chiapas massif the histories of the pre mesozoic landmasses in southern mexico and their connections with laurentia gondwana and among themselves are crucial for the understanding of the late paleozoic assembly of pangea the permian igneous and metamorphic rocks from the chiapas massif as part of the southern maya block mexico were dated by u pb zircon geochronology employing the shrimp sensitive high resolution ion microprobe facility at stanford university the chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks shrimp data from an anatectic orthogneiss demonstrate that the chiapas massif was part of a permian 272 ma active continental margin established on the pacific margin of gondwana after the ouachita orogeny latest permian 252 254 ma medium to high grade metamorphism and deformation affected the entire chiapas massif resulting in anatexis and intrusion of syntectonic granitoids this unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics shrimp data of zircon cores from a metapelite from the ne chiapas massif yielded a single grenvillian source for sediments the majority of the zircon cores from a para amphibolite from the se part of the massif yielded either 1 0 1 2 or 1 4 1 5 ga sources indicating provenance from south american sunsas and rondonian san ignacio provinces

subduction of the eastern panama basin and seismotectonics of northwestern south america spreading along the cocos nazca plate boundary since the breakup of the farallon plate in the miocene has resulted in the formation of the panama basin and a complex interaction of plates in and near northwestern south america current plate boundaries have been defined and segments of subducted lithosphere identified through selection of hypocentral locations of earthquakes considering only well located events and through focal mechanism determinations the existence of relict plate boundaries bathymetric features and the panamanian isthmus has affected the subduction process of the nazca plate beneath south america and determined the present day configuration of the subducting lithospheric plate there is no single triple junction separating the caribbean south american and nazca plates instead the panamanian isthmus and surrounding areas are accommodating east west compression and a lesser degree of north south compression along a series of thrust faults striking nw to ne and the andean ranges of ecuador colombia and venezeula are moving as a block nne relative to the rest of the south american plates along a system of faults following the front of the eastern cordillera the subducted portions of the panama basin and old farallon plate have become segmented into three pieces recognized in this study from north to south they are 1 a bucaramanga segment continuous with the caribbean seafloor northwest of colombia 2 a cauca segment continuous with oceanic crust nazca plate currently being subducted beneath south america at the colombia ecuador trench and 3 an ecuador segment at the northern end of the subducted lithospheric plate which is dipping at a small angle to the east beneath northern peru the segmentation of the subducted plate can be explained by the buoyancy of bathymetric features which have been partially subducted

patterns and mechanisms of coseismic and postseismic slips of the 2011 mw 7 1 van turkey earthquake revealed by multi platform synthetic aperture radar interferometry on 23rd october 2011 a mw 7 1 reverse slip earthquake occurred in the bardakci saray thrust fault zone in the van region eastern turkey earlier geodetic studies have found different slip distributions in terms of both magnitude and pattern in this paper we present several cosmo skymed csk envisat asar and radarsat 2 interferograms spanning different time intervals showing that significant postseismic signals can be observed in the first three days after the mainshock using observations that combine coseismic and postseismic signals is shown to significantly underestimate coseismic slip we hence employed the csk pair with the minimum postseismic signals to generate one conventional interferogram and one along track interferogram for further coseismic modelling our best fit coseismic slip model suggests that 1 this event is associated with a buried nnw dipping fault with a preferable dip angle of 49 and a maximum slip of 6 5 m at a depth of 12 km and 2 two unequal asperities can be observed consistent with previous seismic solutions significant oblique aseismic slip with predominant left lateral slip components above the coseismic rupture zone within the first 3 days after the mainshock is also revealed by a postseismic csk interferogram indicating that the greatest principal stress axis might have rotated due to a significant stress drop during the coseismic rupture