an alternative interpretation of the cayman trough evolution from a reidentification of magnetic anomalies magnetic data were collected during the wilkes 1973 and seacarib ii 1987 cruises to the cayman trough a new interpretation of magnetic data is carried out an isochron pattern is drawn up from our anomaly identifications an early eocene age 49 ma ypresian for cayman trough opening is proposed instead of the late oligocene or middle eocene ages suggested by previous studies our plate tectonic reconstruction is simpler and fits the on land geology jamaica and cuba and the tectonics our reconstruction shows a southward propagation of the spreading centre between magnetic anomalies 8 and 6 26 and 20 ma the trough width increases by 30 km in this period the southward propagation of the cayman spreading centre from the middle oligocene to the early miocene induced the development of the restraining bend of the swan islands the formation of a 1 km high scarp on the eastern trace of the cayman trough transform fault walton fault and the formation of a pull apart basin hendrix pull apart magnetic anomalies and magnetization maps give information about the deformation and the rocks the proposed evolutionary model of the cayman trough from the inception of seafloor spreading to the present configuration is presented in relation to the tectonic escape of the northern boundary of the caribbean plate from the maastrichtian to the present

along strike segmentation in the northern caribbean plate boundary zone hispaniola sector tectonic implications abstract the north american noam plate converges with the caribbean carib plate at a rate of 20 0 0 4 mm yr towards 254 1 plate convergence is highly oblique 20 10 resulting in a complex crustal boundary with along strike segmentation strain partitioning and microplate tectonics we study the oblique convergence of the noam and carib plates between southeastern cuba to northern puerto rico using new swath multibeam bathymetry data and 2d multi channel seismic profiles the combined interpretation of marine geophysical data with the seismicity and geodetic data from public databases allow us to perform a regional scale analysis of the shallower structure the seismotectonics and the slab geometry along the plate boundary due to differential rollback between the noam oceanic crust north of puerto rico and the relative thicker bahamas carbonate province crust north of hispaniola a slab tear is created at 68 5 w the northern margin of puerto rico records the oblique high dip subduction and rollback of the noam plate below the island arc those processes have resulted in a forearc transpressive tectonics without strain partitioning controlled by the septentrional oriente fault zone sofz and the bunce fault zone bfz meanwhile in the northern margin of hispaniola the collision of the bahamas carbonate province results in high plate coupling with strain partitioning sofz and northern hispaniola deformed belt nhdb in the northern haitian margin compression is still relevant since seismicity is mostly associated with the deformation front whereas strike slip earthquakes are hardly anecdotal although in hispaniola intermediate depth seismicity should disappear diffuse intermediate depth hypocenter remains evidencing the presence of remnant noam subducted slab below central and western hispaniola results of this study improve our understanding of the active tectonics in the ne caribbean that it is the base for future assessment studies on seismic and tsunamigenic hazard

formation of patterned ground and fine scale soil development within two late holocene glacial chronosequences jotunheimen norway abstract chronosequences of 250 to 130 years were established on two late holocene glacier forelands in the jotunheimen region of southern norway patterned features occurring within chronologically established time units were studied young patterned features forming 10 20 years after deglaciation are frost active vegetation cover is minimal within the young patterned features consisting of bryophytes organic crusts soil development within patterned ground is also minimal absent because frost action retards horizonization with time and distance from the glaciated ice margin frost activity declines within the patterned features suggesting that a thin active periglacial zone exists near the ice margin initially frost activity decreases at the borders of the features with the centers stabilizing later in time this results in fine scale soil heterogeneity and variations of soil development fine scale pedogenic development is first encountered at the borders of patterned ground that has developed on terrain exposed since the 1930s yet soil development is predominantly absent at the centers of patterned ground with time and distance from the ice margin frost activity declines and allows patterned features to homogenize from border to center positions in regard to soil characteristics across the chronosequences soils within patterned features pedogenically follow previous soil chronosequence studies evolving from usda classifications of entisols into inceptisols frost disturbance within patterned ground however produces a lag effect that results in longer periods of time for pedogenesis to occur and thinner soils than that of the surrounding terrain

statistical tests of additional plate boundaries from plate motion inversions we have investigated the application of the f ratio test a standard statistical technique to the results of relative plate motion inversions the method tests whether the improvement in fit of the model to the data resulting from the addition of another plate to the model is greater than that expected purely by chance this approach appears to be useful in determining whether additional plate boundaries are justified we confirm previous results favoring separate north american and south american plates with a boundary located between 30 n and the equator using chase s global relative motion data we show that in addition to separate west african and somalian plates separate west indian and australian plates with a best fitting boundary between 70 e and 90 e can be resolved these results are generally consistent with the observation that the indian plate s internal deformation extends somewhat westward of the ninetyeast ridge the relative motion pole is similar to minster and jordan s and predicts the nw se compression observed in earthquake mechanisms near the ninetyeast ridge

geochemical effects of decoupled fractional crystallization and crustal assimilation most models of crustal assimilation assume that the amount of assimilant added to the magma is proportional to each infinitesimally small amount of solid removed during crystallization afc in some magmatic systems however assimilation and crystallization are not strictly related and the mass assimilated is decoupled from and therefore varies independently of the mass crystallized fca the geochemical consequences of fca are examined and compared to those of afc the behavior of incompatible elements is identical during afc and fca and ratios of these elements do not allow discrimination between the two processes major oxide least squares mass balance models do not discriminate between afc and fca at f 0 7 f fraction of melt remaining however fca yields magmas richer in compatible elements and with higher sr isotopic ratios than afc at a given value of f repeated cycles of fca and afc combined with magma mixing fam may result in unusual geochemical trends such as the evolution of a calc alkaline basaltic parent to a tholeiitic daughter magma or the evolution of low and medium k calc alkaline basalts to high k andesites dacites trachyandesites or trachydacites lavas erupted by the volcano micro profitis ilias on santorini hellenic arc greece provide an example of magmas which evolved by combined fractionation assimilation by fca and mixing

a model for tectonic rotations about a vertical axis abstract the rotation of a rigid ellipsoidal inclusion within a highly viscous fluid orientated so that two of the principal axes remain horizontal is used as a model for the rotation of crustal inclusions in wide zones of continental deformation this model is also applicable to other geological problems involving the rotation of inclusions in a matrix the pattern of behaviour in such a model is shown to be complex in general the rotation rate of the inclusion is a function of all components of the velocity field of the deforming medium and the horizontal aspect ratio of the inclusion however for a given velocity field this aspect ratio must exceed a critical value before the inclusion can rotate continuously inclusions with lower aspect ratios will rotate for a certain range of orientations in an opposite direction to the sense of shear in the deforming zone the possibility of the inclusion changing shape during rotation adds to the complexity of behaviour

gps estimates of microplate motions northern caribbean evidence for a hispaniola microplate and implications for earthquake hazard summary we use elastic block modelling of 126 gps site velocities from jamaica hispaniola puerto rico and other islands in the northern caribbean to test for the existence of a hispaniola microplate and estimate angular velocities for the gonave hispaniola puerto rico virgin islands and two smaller microplates relative to each other and the caribbean and north america plates a model in which the gonave microplate spans the whole plate boundary between the cayman spreading centre and mona passage west of puerto rico is rejected at a high confidence level the data instead require an independently moving hispaniola microplate between the mona passage and a likely diffuse boundary within or offshore from western hispaniola our updated angular velocities predict 6 8 1 0 mm yr 1 of left lateral slip along the seismically hazardous enriquillo plantain garden fault zone of southwest hispaniola 9 8 2 0 mm yr 1 of slip along the septentrional fault of northern hispaniola and 14 15 mm yr 1 of left lateral slip along the oriente fault south of cuba they also predict 5 7 1 mm yr 1 of fault normal motion in the vicinity of the enriquillo plantain garden fault zone faster than previously estimated and possibly accommodated by folds and faults in the enriquillo plantain garden fault zone borderlands our new and a previous estimate of gonave caribbean plate motion suggest that enough elastic strain accumulates to generate one to two mw 7 earthquakes per century along the enriquillo plantain garden and nearby faults of southwest hispaniola that the 2010 m 7 0 haiti earthquake ended a 240 yr long period of seismic quiescence in this region raises concerns that it could mark the onset of a new earthquake sequence that will relieve elastic strain that has accumulated since the late 18th century

micromorphology of atlantic rankers on the coast of northern portugal summary the micromorphological examination of atlantic rankers on the coast of northern portugal shows the importance of alternating phases of landscape stability and instability during the genesis of the profiles archaeological artifacts and marine deposits allow the dating of these events recent pedogenesis is characterized by the formation of a microgranular structure and the illuviation of amorphous organic matter remnants of an older leached phase in the gelfa section reflect an initial weakly base desaturation stage during historical times the soil was buried under eolian sands

modeling the crust and upper mantle in northern beata ridge caribe norte project the complex tectonic region of ne caribbean where hispaniola and puerto rico are located is bordered by subduction zone with oblique convergence in the north and by incipient subduction zone associated to muertos trough in the south central caribbean basin is characterized by the presence of a prominent topographic structure known as beata ridge whose oceanic crustal thickness is unusual the northern part of beata ridge is colliding with the central part of hispaniola along a transverse ne alignment which constitutes a morphostructural limit thus producing the interruption of the cibao valley and the divergence of the rivers and basins in opposite directions the direction of this alignment coincides with the discontinuity that could explain the extreme difference between west and east seismicity of the island different studies have provided information about beata ridge mainly about the shallow structure from mcs data in this work caribe norte 2009 wide angle seismic data are analyzed along a wnw ese trending line in the northern flank of beata ridge providing a complete tectonic view about shallow middle and deep structures the results show clear tectonic differences between west and east separated by beata island in the haiti basin area sedimentary cover is strongly influenced by the bathymetry and its thickness decreases toward to the island in this area the upper mantle reaches 20 km deep increasing up to 24 km below the island where the sedimentary cover disappears to the east the three seamounts of beata ridge provoke the appearance of a structure completely different where sedimentary cover reaches thicknesses of 4 km between seamounts and moho rises up to 13 km deep this study has allowed to determine the moho topography and to characterize seismically the first upper mantle layers along the northern beata ridge which had not been possible with previous mcs data

actively evolving microplate formation by oblique collision and sideways motion along strike slip faults an example from the northeastern caribbean plate margin abstract the pattern of folding faulting and late quaternary coral reef uplift rates in western and central hispaniola haiti and dominican republic suggest that the elongate gonave microplate a 190 000 km2 area of the northeastern caribbean plate is in the process of shearing off the caribbean plate and accreting to the north american plate late cenozoic transpression between the southeastern bahama platform and the caribbean plate in hispaniola has inhibited the eastward motion of the northeastern corner of the plate transpression is manifested in western and central hispaniola by the formation of regional scale folds that correspond to present day anticlinal topographic mountain chains continuous with offshore anticlinal ridges areas of most rapid quaternary uplift determined from onland coral reefs 125 ka and younger coincide with the axial traces of these folds offshore data suggest recent folding and faulting of the seafloor onshore reef data do not conclusively require late quaternary folding but demonstrate that tectonic uplift rates of the axial areas of the anticlines decrease from the northwest peninsula of haiti 0 37 mm yr to to the central part of the coast of western haiti 0 19 mm yr to the south central part of western haiti 0 mm yr formation of the 1200 km long enriquillo plantain garden walton fault zone as a bypass strike slip fault has isolated the southern edge of the gonave microplate and is allowing continued unimpeded eastward motion of a smaller caribbean plate past the zone of late neogene convergence and quaternary uplift of coral reefs in hispaniola offshore seismic reflection data from the jamaica passage the marine strait separating jamaica and haiti show that the enriquillo plantain garden fault zone forms a narrow but deep active fault bounded trough beneath the passage the active fault is continuous with active faults mapped onshore in western haiti and eastern jamaica the bathymetric deep is present because the jamaica passage fault segment represents a 50 km wide transtensional left step of the fault trace between haiti and jamaica onshore satellite imagery and field observations suggest that the enriquillo plantain garden fault forms a continuous trace extending from central hispaniola east of lake enriquillo dominican republic to the westernmost end of the southern peninsula of haiti the regional lineament corresponds to a recent fault scarp in quaternary alluvium of the clonard pull apart basin in the central part of the southern peninsula of haiti and suggests that at least this part of the lineament has undergone recent slip calmus 1983 has suggested a total offset of 30 50 km of the enriquillo plantain garden fault zone in the southern peninsula of haiti using the apparent offset of lithologic units seismic reflection data from lake enriquillo document recent deformation of quaternary lake sediments where the lineament crosses the lake leveling of the crest of a late holocene coral reef and associated algal tufa around lake enriquillo demonstrate late holocene vertical movement and tilting in a 1500 m wide zone parallel to the fault trend lateral offset is difficult to show in the enriquillo valley area because of rapid recent sedimentation into the valley the pattern of inactive strike slip faults and fold belts of cenozoic age in cuba and the yucatan basin suggest that two elongate microplates were sheared off the proto caribbean plate and accreted to the north american plate by a similar process in paleocene and eocene times age of terminal deformation in western central and eastern cuba is consistent with southeastward younging and migration of arc collision the similarity of the size and sequence of events in cuba suggests that the process of oblique collision and sideways motion of the plate along a new strike slip fault towards a free face may be an important process of microplate formation and interplate transfer in other areas

a combined o sr nd and pb isotopic and trace element study of crustal contamination in central andean lavas i local geochemical variations systematic variations in o sr nd and pb isotopic ratios and in sr nd pb and rb trace element abundances in central andean andesitic lavas are analyzed in terms of combined crustal assimilation and fractional crystallization the results of integrated isotopic model calculations show that observed local isotopic and trace element variations within the arequipa and barroso volcanic groups of southern peru are best fit by a simple model involving shallow or intermediate depth crustal assimilation of charcani gneiss or an equivalent rock accompanied by dominantly plagioclase fractional crystallization a consequence of this result is that the rbsr pseudoisochrons reported for the arequipa and barroso volcanics are wholly artifacts of the combined processes of assimilation and plagioclase fractionation as are all of the pb isotopic variations measured in the same lavas already interpreted by tilton and barreiro 14 to be the result of crustal contamination isotopic and trace element compositions of the primary magmas for the arequipa and barroso volcanic series are obtained by correcting for assimilation and fractional crystallization the starting magmas are characterized over the entire range of permissible primary compositions by high87sr 86sr ratios low143nd 144nd ratios and high sr concentrations relative to normal island arc andesites these results appear to require prior contamination of the magmas but not involving plagioclase fractionation the uncertainty in pb and o isotope ratios computed for possible primary magmatic compositions is sufficiently large however that it is not possible to preclude a subcrustal origin for at least some regional variation in sr and nd isotopic ratios

seismic hazard of the enriquillo plantain garden fault in haiti inferred from palaeoseismology the enriquillo plantain garden fault zone is the primary plate bounding fault system in haiti and was initially thought to be responsible for the 2010 earthquake palaeoseismic analyses of the fault system indicate that it ruptured during a large earthquake in either 1750 or 1770 but did not rupture during the 2010 earthquake the enriquillo plantain garden fault zone is recognized as one of the primary plate bounding fault systems in haiti1 2 the strike slip fault runs adjacent to the city of port au prince and was initially thought to be the source of the 12 january 2010 mw 7 0 earthquake haiti experienced significant earthquakes in 1751 and 1770 refs 3 4 5 but the role of the enriquillo plantain garden fault zone in these earthquakes is poorly known we use satellite imagery aerial photography light detection and ranging lidar and field investigations to document quaternary activity on the enriquillo plantain garden fault we report late quaternary left lateral offsets of up to 160 m and a set of small offsets ranging from 1 3 to 3 3 m that we associate with one of the eighteenth century earthquakes the size of the small offsets implies that the historical earthquake was larger than mw 7 0 but probably smaller than mw 7 6 we found no significant surface rupture associated with the 2010 earthquake the lack of surface rupture coupled with other seismologic geologic and geodetic observations6 7 suggests that little if any accumulated strain was released on the enriquillo plantain garden fault in the 2010 earthquake these results confirm that the enriquillo plantain garden fault remains a significant seismic hazard

a soil chronosequence in the semi arid environment of patagonia argentina abstract soil development with time was investigated on beach ridges with ages ranging from about 1380 to 6240 14c years bp at the eastern coast of central patagonia the main pedogenic processes are accumulation of organic matter and carbonate leaching and accumulation within the upper part of the soils soil formation is strongly influenced by incorporation of eolian sediments into the interstitial spaces between the gravel of which the beach ridges are composed different amounts of eolian material in the soils lead to differentiation into leptosols containing 10 fine earth in the upper 75 cm and regosols containing 10 fine earth soil depth functions and chronofunctions of organic carbon calcium carbonate ph ca zr mg zr k zr na zr fe zr mn zr and si al obtained from x ray fluorescence analysis were evaluated to establish soil chronofunctions mean values of the horizon data of 0 10 cm below the desert pavement were used which were weighted according to the horizon thicknesses the depth function of ph shows a decrease towards the surface indicating leaching of bases from the upper centimeters chronofunctions of ph show that within 6000 radiocarbon years of soil development ph drops from 7 0 to 6 6 in the leptosols and from 8 1 to 7 5 in the regosols the higher ph of the regosols is due to input of additional bases from the eolian sediments chronofunctions of ca zr and k zr indicate progressive leaching of ca and k in the regosols showing close relationships to time r2 0 972 and 0 995 na leaching as indicated by decreasing na zr ratios shows a strong correlation to time only in the leptosols r2 0 999 both leptosols and regosols show close relationships to time for fe zr r2 0 817 and 0 824 mn zr r2 0 940 and 0 803 and si al 0 971 and 0 977 indicating enrichment of fe and mn and leaching of si leaching of mobile elements takes place on a higher level in the regosols than in the leptosols from the beginning of soil formation hence a significant part of the eolian sediments must have been incorporated into the beach ridges very soon after their formation

crustal thickness and bulk poisson ratios in the dominican republic from receiver function analysis abstract the dominican republic dr comprises the eastern two thirds of the island of hispaniola which is located on the caribbean north american plate boundary previous studies have described the shallow structure and stratigraphy of the island but due to a dearth of broadband seismic data little is known about the lower crust and mantle since august 2014 thirteen broadband three component seismic stations have been deployed temporarily in the dr they are combined with four permanent broadband stations in the dr and three in neighboring haiti to enhance studies of hispaniola s lower crust and upper mantle we report results of a receiver function study using teleseismic data recorded by these stations specifically we compute receiver functions and determine crustal properties via h stacking we propose additional intracrustal and upper mantle layers based on identifications of prominent and coherent p to s converted phases observed in receiver function gathers our results show that crustal thickness varies beneath the island of hispaniola over the range 13 47 km with a median of 24 km and bulk vp vs ratios vary over 1 58 1 99 with median 1 79 receiver function modeling reveals intracrustal discontinuities at station paph port au prince haiti at a depth of 8 0 km station jidr jimani dr 8 8 km depth and sddr sabaneta dr 15 8 km depth additional discontinuities appear in the upper mantle beneath paph 60 1 km depth pcdr punta cana 60 km sdd santo domingo 70 km and sc01 santiago 81 km two north south cross sections show variations in bulk vp vs ratios that are consistent with expectations based upon surface geology but variations in crustal thickness are more scattered and do not conform to expectations from simple tectonic models of hispaniola s formation our stacking results reveal consistency between vp vs ratios in four distinct regions which are consistent with the compositional domains identified by previous studies

a mathematical model of trace element and isotopic behavior during simultaneous assimilation and imperfect fractional crystallization the process of coupled assimilation and fractional crystallization afc is one of the most popular petrogenetic concepts that explains magmatic differentiation conventional geochemical models for this process assume that crystals are removed instantaneously from the magma body as they are produced however recent advances in isotopic microanalysis have clarified that the crystals are suspended within the magma body for a certain period affecting the whole rock composition in response to the intra grain isotopic zoning this study develops a mass balance model for simultaneous assimilation and imperfect fractional crystallization aifc to describe the effects of suspended crystals on the path of magma evolution the mass balance differential equations for the liquid and suspended crystals are solved simultaneously the analytical solution of the aifc equations gives a quantitative account of the evolution paths of trace elements and isotopes within bulk crystals liquid and magma crystals plus liquid the chemical path of the magma differs markedly from that predicted by the conventional afc model

neotectonics of hispaniola plate motion sedimentation and seismicity at a restraining bend abstract the pattern of neogene faulting volcanism and sedimentation in hispaniola helps to resolve a problem that arises in attempting to determine the direction of caribbean plate motion from earthquakes alone namely how well do earthquake mechanisms define plate motion hispaniola occupies a compressional north step or restraining bend in the generally east west trending motagua cayman trough puerto rico trench fault system which marks an active plate boundary zone pbz of left lateral strike slip motion between the north america and caribbean plates four areas are distinguishable in hispaniola from field mapping and from the interpretation of satellite imagery and conventional aerial photographs two of these areas consist of active left lateral strike slip fault systems that roughly define the northern and southern coasts of the island the structure of both fault systems suggest a roughly east west trending direction of relative plate motion consistent with previous findings the intervening area consists of en echelon mountain ranges thrust up at the restraining bend from the early miocene a pleistocene volcanic province within this area is interpreted as defining a diffuse extensional fault termination of the southern strike slip fault zone the fourth area in eastern hispaniola is interpreted as being underthrust by discontinuous fragments of lithosphere in response to convergence at the restraining bend it appears possible that thinner young island arc lithosphere may be more prone to subduction than to escape or flaking processes that are more important in older more buoyant lithosphere

some thermal constraints on crustal assimilation during fractionation of hydrous mantle derived magmas with examples from central alpine batholiths following assimilation at different levels in the crust we test by heat and mass balance the extent of assimilation of crustal country rocks in different local plutonic

chronosequence development and soil variability from a variety of sub alpine post glacial landforms and deposits in the southeastern san juan mountains of colorado abstract surficial processes acting on post glacial alpine and sub alpine landscapes vary at small temporal and spatial scales and are thus often difficult to conceptualize in the context of large scale landscape evolution models soils developing in this setting can thus provide valuable information about landform genesis sedimentology and age relatively few post glacial chronosequences have been examined in these settings however particularly for the variety of landforms and parent materials that exist within alpine and sub alpine environments here we examine a chronosequence of relatively young post glacial landforms with varying parent materials and climate histories we dug and described 39 soil pits in the upper conejos river valley of colorado on a variety of deposits and landforms including alluvial fans terraces colluvium glacial till and terminal moraines and compared soil properties with radiocarbon ages from the area our results suggest that some typical chronosequence soil properties e g ph structure color do not correlate with time over short time scales however extractable iron ratios feo fed show a relatively strong correlation with age across late pleistocene and holocene time scales and maximum profile clay content shows a weak but statistically significant relationship with age both of these trends are stronger when examined across a single parent material differences in initial parent material texture and dust inputs seem to be the most significant complicating factors over post glacial time scales soil property development through time is most inconsistent in cumulic alluvial fan soils this observation may indicate that alluvial fans are more responsive to sub basin scale processes as opposed to fluvial terraces that are more likely respond to processes active across the entire basin these differences would explain why stratigraphically similar alluvial fans are mantled by soils with varying development nonetheless horizonation clay content and extractable iron ratios provide a useful tool for correlating young deposits assigning ages and interpreting the geomorphic history of complex post glacial environments

the 2010 haiti earthquake a complex fault pattern constrained by seismologic and tectonic observations after the january 12 2010 haiti earthquake we deployed a mainly offshore temporary network of seismologic stations around the damaged area the distribution of the recorded aftershocks together with morphotectonic observations and mainshock analysis allow us to constrain a complex fault pattern in the area almost all of the aftershocks have a n s compressive mechanism and not the expected left lateral strike slip mechanism a first order slip model of the mainshock shows a n264 e north dipping plane with a major left lateral component and a strong reverse component as the aftershock distribution is sub parallel and close to the enriquillo fault we assume that although the cause of the catastrophe was not a rupture along the enriquillo fault this fault had an important role as a mechanical boundary the azimuth of the focal planes of the aftershocks are parallel to the north dipping faults of the transhaitian belt which suggests a triggering of failure on these discontinuities in the western part the aftershock distribution reflects the triggering of slip on similar faults and or alternatively of the south dipping faults such the trois baies submarine fault these observations are in agreement with a model of an oblique collision of an indenter of the oceanic crust of the southern peninsula and the sedimentary wedge of the transhaitian belt the rupture occurred on a wrench fault at the rheologic boundary on top of the under thrusting rigid oceanic block whereas the aftershocks were the result of the relaxation on the hanging wall along pre existing discontinuities in the frontal part of the transhaitian belt

the northern caribbean plate boundary in the jamaica passage structure and seismic stratigraphy multibeam bathymetry data and multichannel seismic reflection profiles have been collected at the end of 2012 along the enriquillo plantain garden fault zone epgfz in the jamaica passage between jamaica and hispaniola analysis of the data set reveals the tectonic evolution and the stratigraphic complexity of the northern caribbean boundary stratigraphic correlations with previous marine and on land studies are proposed to place the identified seismic sequences in their regional tectonic history two distinct crustal domains are interpreted typical stratigraphic sequences for the rifted blocks of the eastern cayman trough margin are identified in five basins of the jamaica passage highlighting the eastward limit of the cayman trough margin these inherited basins are deformed and folded during a first phase of compression that could correspond to the regional tectonic rearrangement recorded in the early miocene about 20 ma a distinct crustal domain that we propose to relate to the carib beds caribbean typical reflectors a b and v is identified in the southern part of the jamaica passage indicating that the caribbean large igneous province could extend up to the extreme northeast part of the lower nicaragua rise the left lateral epgfz currently cuts across two pre existing basins the morant and matley basins during the activity of the epgfz these basins are deformed and folded indicating a second phase of compression in contrast the navassa basin located in the middle of the jamaica passage results from the strike slip motion of the epgfz and is interpreted as an asymmetrical basin bordered by the epgfz only on its northern side

carbonate platforms along the southeast bahamas hispaniola collision zone the southeast bahama banks have been colliding with the island of hispaniola along a restraining bend within the northern caribbean plate boundary zone since the late miocene a seamarc ii seismic reflection investigation was conducted along the deep water flanks of mouchoir bank and navidad bank to evaluate the response of these carbonate platforms to active plate tectonic collision overall our data provide evidence of large scale platform margin retreat which contrasts sharply with the prograding platform margins in the tectonically passive northwest bahamas north of silver bank there is a large 5 000 km2 deep water 3 000 4 000 m plateau that records the drowning and step back 50 km of an early cretaceous carbonate platform margin intact uneroded segments of this cretaceou platform margin may occur along the seaward edge of the deep water plateau bahama escarpment separated by large 20 km across erosional reentrants a coalescing system of broad up to 10 km shallow 200 m relief canyons akin to mountainous avalanche chutes funnel debris into the reentrants from the flank of silver bank the reentrants are interpreted as zones of structural weakness produced by passage of the atlantic spreading center along a transform plate boundary during the late jurassic early cretaceous drowning and step back appear to be part of a global response of carbonate platforms to a mid cretaceous tectonic pulse of ocean crust formation and relative sea level rise the southern margin of mouchoir bank has also been drowned and has stepped back by about 30 km this event occurred during the late tertiary prior to the mid pliocene and is attributed to tectonic tilting and subsidence resulting from oblique underthrusting of the southeast bahamas beneath hispaniola the southern margin of mouchoir bank is also characterized by large 20 km across amphitheater shaped scallops that expose tertiary shallow water limestones along their deep water flanks seaward of one scallop is a large 25 km wide 50 km long mass movement with flow lines preserved on the seafloor we interpret these scallops as catastrophic collapse structures triggered by large earthquakes generated along the collision zone since the late tertiary south of navidad and silver banks is a very complex seafloor morphology resulting in part from the accretion of a portion of the bahamas onto hispaniola there is also a series of e w oriented down to basin normal faults that have caused the platform margin to retreat extensional stress along this predominantly transpressive plate boundary may be a consequence of rotation of the nearby puerto rico block or lithospheric bending during oblique subduction this study provides an initial framework within which to view the actualistic response of carbonate platforms to plate tectonic collision

from transcurrent faulting to frontal subduction a seismotectonic study of the northern caribbean plate boundary from cuba to puerto rico recent marine and onland geophysical and geological investigations along the northern caribbean plate boundary call for a review of its tectonic interpretation in the light of a new compilation of the seismological data avalaible from cuba to puerto rico we show that the shallow seismicity in the northeastern caribbean is concentrated along an east west trending lineament corresponding to the trace of the major strike slip fault system the most intense seismicity is located around restraining bends such as southern cuba and northern hispaniola the stress and strain distribution deduced from focal mechanisms and microtectonic analysis lead us to infer a small n s convergence component associated with the major eastward strike slip motion of the caribbean plate versus north america earthquake distribution and focal mechanisms suggest the existence of a lithospheric slab inherited from the frontal subduction under the lesser antilles diping down under puerto rico and eastern hispaniola we propose a model in which this slab is disconnected from the atlantic oceanic lithosphere by transcurrent faulting along the plate boundary

pliocene lower pleistocene shallow water mixed siliciclastics and carbonates yanigua and los haitises formations in eastern hispaniola dominican republic the virtually unfolded sedimentary cover of the cordilleras central and oriental in the eastern dominican republic eastern hispaniola tropical north atlantic largely consists of pliocene to early pleistocene mixed siliciclastics and carbonates these deposits have been grouped into two laterally interfingering mapping units the yanigua and los haitises formations the former mainly siliciclastics comprises marl marly limestone and minor conglomerate sandstone lignite and carbonaceous clay and crops out closest to the basement the los haitises formation mainly consists of limestone and intercalating beds of marly limestone and marl lithological mapping at the 1 50 000 scale and facies analysis of twelve measured sections and of additional fourteen outcrops suggest that these deposits mainly formed on a shallow water marine platform fringing the precursor reliefs of the cordillera oriental and the southeastern end of the cordillera central only a limited proportion of sediment formed in floodplains and marshes marl and marly limestone dominated the inner platform sediments terrigenous mud decreased away from the emergent basement and carbonate sedimentation dominated the more external platform corals molluscs echinoids foraminifers bryozoans coralline algae and halimeda are the main components with varying amounts of carbonate mud the platform was generally a low energy environment with seagrass patches in the inner platform corals grew as isolated colonies or as small patch reefs dominated by porites in marly and bioclastic substrates branching corals stylophora and acropora grew in extensive carpets in more distal areas at least in the last stage of its development early pleistocene the platform was rimmed by a reef barrier similar to the holocene caribbean barrier reefs with acropora gr palmata a cervicornis porites montastrea siderastrea and diploria as the main reef builders

segmentation and kinematics of the north america caribbean plate boundary offshore hispaniola we explored the submarine portions of the enriquillo plantain garden fault zone epgfz and the septentrional oriente fault zone sofz along the northern caribbean plate boundary using high resolution multi beam echo sounding and shallow seismic reflection the bathymetric data shed light on poorly documented or previously unknown submarine fault zones running over 200 km between haiti and jamaica epgfz and 300 km between the dominican republic and cuba sofz the primary plate boundary structures are a series of strike slip fault segments associated with pressure ridges restraining bends step overs and dogleg offsets indicating very active tectonics several distinct segments 50 to 100 km long cut across pre existing structures inherited from former tectonic regimes or bypass recent morphologies formed under the current strike slip regime along the most recent trace of the sofz we measured a strike slip offset of 16 5 km which indicates steady activity for the past 1 8 ma if its current gps derived motion of 9 8 2 mm yr has remained stable during the entire quaternary

seamarc ii mapping of transform faults in the cayman trough caribbean sea seamarc ii maps of the southern wall of the cayman trough between honduras and jamaica show zones of continuous well defined fault lineaments adjacent and parallel to the wall both to the east and west of the cayman spreading axis these lineaments mark the present active traces of transform faults which intersect the southern end of the spreading axis at a triple junction the swan islands transform fault to the west is dominated by two major lineaments that overlap with right stepping sense across a large push up ridge beneath the swan islands the fault zone to the east of the axis named the walton fault is more complex containing multiple fault strands and a large pull apart structure the walton fault links the spreading axis to jamaican and hispaniolan strike slip faults and it defines the southern boundary of a microplate composed of the eastern cayman trough and western hispaniola the presence of this microplate raises questions about the veracity of caribbean plate velocities based primarily on cayman trough opening rates

a micromorphological examination of two alpine soil chronosequences southern norway the micromorphological characteristics of young alpine soils 230 years old from two chronosequences in norway are examined lenticular and alveolar microstructures together with matrix granules suggest that cryic processes are operative in subsurface ae b c horizons organic matter accumulation decomposition and incorporation are evident in surface l f ah horizons whereas hydration of biotite and translocation of silt and fine sand sized mineral particles organic material and sesquioxides seem major processes in subsurface ae b horizons consideration of depth related differences of quantitative micromorphological data has allowed assessment of the intensity of these pedogenic processes chronofunctions are constructed for each soil horizon from the quantitative data this approach allows soil development at the two sites to be assessed in a temporal context steady state conditions do not appear to be attained within the 230 years available for soil development at these sites

complex rupture during the 12 january 2010 haiti earthquake initially the devastating mw 7 0 12 january 2010 haiti earthquake seemed to involve straightforward accommodation of oblique relative motion between the caribbean and north american plates along the enriquillo plantain garden fault zone here we combine seismological observations geologic field data and space geodetic measurements to show that instead the rupture process involved slip on multiple faults primary surface deformation was driven by rupture on blind thrust faults with only minor deep lateral slip along or near the main enriquillo plantain garden fault zone thus the event only partially relieved centuries of accumulated left lateral strain on a small part of the plate boundary system together with the predominance of shallow off fault thrusting the lack of surface deformation implies that remaining shallow shear strain will be released in future surface rupturing earthquakes on the enriquillo plantain garden fault zone as occurred in inferred holocene and probable historic events we suggest that the geological signature of this earthquake broad warping and coastal deformation rather than surface rupture along the main fault zone will not be easily recognized by standard palaeoseismic studies we conclude that similarly complex earthquakes in tectonic environments that accommodate both translation and convergence such as the san andreas fault through the transverse ranges of california may be missing from the prehistoric earthquake record

muertos trough subduction microplate tectonics in the northern caribbean the relative plate motion between the north american and caribbean plates has been commonly assumed to take place in the form of oblique subduction along the puerto rico trench1 west of hispaniola this plate boundary becomes pure strike slip nevertheless it has been suggested that this boundary is more diffuse with part of the plate motion taken up by subduction along the muertos trough mt south of hispaniola2 5 fig 1 but there has been no direct seismological evidence of subduction to confirm this here we present the results of a study of the 24 june 1984 earthquake beneath mt the focal mechanism shows thrusting at a depth of 32 km which together with reports of a great earthquake in 1751 confirms that mt is an active plate boundary this implies that plate motion is accommodated by several tectonic boundaries delineating microplates caught between the caribbean and north american plates fig 4

crustal structure of western hispaniola haiti from a teleseismic receiver function study haiti located at the northern caribbean plate boundary records a geological history of terrane accretion from cretaceous island arc formations to the eocene to recent oblique collision with the bahamas platform little is presently known about the underlying crustal structure of the island we analyze p waveforms arriving at 27 temporary broadband seismic stations deployed over a distance of 200 km across the major terrane boundaries in haiti to determine the crustal structure of western hispaniola we compute teleseismic receiver functions using the extended time multi taper method and determine crustal thickness and bulk composition vp vs using the h stacking method three distinctive and fault bounded crustal domains defined by their characteristic moho depth distributions and bulk crustal vp vs are imaged across haiti we relate these domains to three crustal terranes that have been accreted along the plate boundary during the northeastwards displacement of the caribbean plate and are presently being deformed in a localized fold and thrust belt in the northern domain made up of volcanic arc facies the crust has a thickness of 23 km and vp vs of 1 75 0 1 typical of average continental crust the crust in the southern domain is part of the caribbean large igneous province caribbean lip and is 22 km thick with vp vs of 1 80 0 03 consistent with plume related rocks of late cretaceous age significantly thicker the crust in central haiti has values of moho depths averaging 41 km and with vp vs of 1 80 0 05 we propose that the central domain is likely constructed of an island arc upper crust with fragments of dense material originating from mafic lavas or lip material we produce a crustal profile along a n s transect across haiti accounting for the surface geology shallow structural history and new seismological constraints provided by variations of crustal thickness and bulk composition

shifts in the source of the parana basalts through time magmatism occurred intermittently in the parana region of south america between 240 50 ma with the peak of magmatic activity between 138 126 ma comprising the parana continental flood basalts cfb detailed chemical subdivision of the parana basalts into six units allowed stratigraphic correlations to be made implying a northward migration of magmatism following the rifting of the south atlantic however 40ar 39ar ages do not uphold the chronostratigraphic nature of such magmatic units instead they indicate a southeastwards migration major elements extrapolated to 8 wt mgo are used to investigate changes in magma type with time and are interpreted in terms of parameters such as pressure depth of melting and the nature of the source region fertile refractory and water content the oldest parana unit originated by melting at the greatest depths 90 120 km shifting to shallow levels 30 60 km for the younger units accompanying this decrease in pressure the source material undergoing partial melting became progressively more refractory in major elements and also more hydrous this hydrous metasomatism occurred after major element depletion of the lithosphere at shallow levels the data is consistent with conductive heating of a stratified source region inferred to lie within the lithospheric mantle which is relatively fertile but anhydrous at depth and also appears to be younger in age than the relatively major element refractory hydrous lithosphere at shallower depths thus the interaction of asthenosphere and lithosphere can be determined within an integrated age tectonic and thermal framework

significant earthquakes on the enriquillo fault system hispaniola 1500 2010 implications for seismic hazard abstract historical records indicate frequent seismic activity along the north east caribbean plate boundary over the past 500 years particularly on the island of hispaniola we use accounts of historical earthquakes to assign intensities and the intensity assignments for the 2010 haiti earthquakes to derive an intensity attenuation relation for hispaniola the intensity assignments and the attenuation relation are used in a grid search to find source locations and magnitudes that best fit the intensity assignments here we describe a sequence of devastating earthquakes on the enriquillo fault system in the eighteenth century an intensity magnitude m i 6 6 earthquake in 1701 occurred near the location of the 2010 haiti earthquake and the accounts of the shaking in the 1701 earthquake are similar to those of the 2010 earthquake a series of large earthquakes migrating from east to west started with the 18 october 1751 m i 7 4 7 5 earthquake probably located near the eastern end of the fault in the dominican republic followed by the 21 november 1751 m i 6 6 earthquake near port au prince haiti and the 3 june 1770 m i 7 5 earthquake west of the 2010 earthquake rupture the 2010 haiti earthquake may mark the beginning of a new cycle of large earthquakes on the enriquillo fault system after 240 years of seismic quiescence the entire enriquillo fault system appears to be seismically active haiti and the dominican republic should prepare for future devastating earthquakes online material table listing small earthquakes and figures of intensity assignments and intensity magnitude estimates

relative motion between the caribbean and north american plates and related boundary zone deformation from a decade of gps observations global positioning system gps measurements in 1986 1994 and 1995 at sites in dominican republic puerto rico cuba and grand turk define the velocity of the caribbean plate relative to north america the data show eastward motion of the caribbean plate at a rate of 21 1 mm yr 1 standard error in the vicinity of southern dominican republic a factor of 2 higher than the nuvel 1a plate motion model prediction of 11 3 mm yr independent measurements on san andres island and an euler vector derived from these data also suggest a rate that is much higher than the nuvel 1a model available data combined with simple elastic strain models give the following slip rate estimates for major left lateral faults in hispaniola 1 the north hispaniola fault offshore the north coast of hispaniola 4 3 mm yr 2 the septentrional fault in northern dominican republic 8 3 mm yr and 3 the enriquillo fault in southern dominican republic and haiti 8 4 mm yr the relatively high plate motion rate and fault slip rates suggested by our study combined with evidence for strain accumulation and historical seismicity imply that seismic risk in the region may be higher than previous estimates based on low plate rate low fault slip rate models and the relatively low rate of seismicity over the last century

enriquillo plantain garden fault zone in jamaica paleoseismology and seismic hazard the countries of jamaica haiti and the dominican republic all straddle the enriquillo plantain garden fault zone epgfz a major left lateral strike slip fault system bounding the caribbean and north american plates past large earthquakes that destroyed the capital cities of kingston jamaica 1692 1907 and port au prince haiti 1751 1770 as well as the 2010 haiti earthquake that killed more than 50 000 people have heightened awareness of seismic hazards in the northern caribbean we present here new geomorphic and paleoseismic information bearing on the location and relative activity of the epgfz which marks the plate boundary in jamaica documentation of a river bank exposure and several trenches indicate that this fault is active and has the potential to cause major destructive earthquakes in jamaica the results suggest that the fault has not ruptured the surface in at least 500 yr and possibly as long as 28 ka the long period of quiescence and subdued geomorphic expression of the epgfz indicates that it may only accommodate part of the 7 9 mm yr plate deformation rate measured geodetically and that slip may be partitioned on other undocumented faults large uncertainties related to the neotectonic framework of jamaica remain and more detailed fault characterization studies are necessary to accurately assess seismic hazards

age and spreading history of the cayman trough as determined from depth heat flow and magnetic anomalies the opening of the cayman trough records aspects of relative motion between the north american and caribbean plates essential to accurate reconstruction of caribbean evolution assessment of opening rates based upon basement subsidence analysis as well as magnetic anomaly interpretation shows that the trough may have opened at one third to one half previously proposed rates depths to basement show that the crust has subsided away from the present axis in two stages a younger stage characterized by substantial and asymmetric greater to the east subsidence preceded by an older stage of slight increases of depth with distance depth to age relations calculated from subsidence curves which accommodate lateral as well as vertical cooling of the accreting slab indicate that the trough has opened at an overall rate of less than 15 mm yr since 25 30 ma and at 20 30 mm yr prior to 30 ma marine magnetic anomalies show lineations perpendicular to the trough including a distinct central anomaly but the pattern is neither well defined nor symmetrical about the present axis however partial anomaly sequences can be identified on both sides of the axis and the distribution of these sequences indicates that spreading may have involved frequent short ridge jumps mostly eastward the overall rate of opening as indicated by this interpretation of the magnetics is about 15 and 30 mm yr since and prior to 26 ma both subsidence and magnetics indicate that the trough opened by at least 45 50 ma

transpressional rupture of an unmapped fault during the 2010 haiti earthquake the enriquillo plantain garden strike slip fault accommodates the relative motion between the north american and caribbean plates and was thought to have ruptured during the 2010 haiti earthquake satellite data instead indicate that a blind thrust fault possibly related to the haitian fold thrust belt was responsible and caused some contractional deformation on 12 january 2010 a mw 7 0 earthquake struck the port au prince region of haiti the disaster killed more than 200 000 people and caused an estimated 8 billion in damages about 100 of the country s gross domestic product1 the earthquake was initially thought to have ruptured the enriquillo plantain garden fault of the southern peninsula of haiti which is one of two main strike slip faults inferred to accommodate the 2 cm yr 1 relative motion between the caribbean and north american plates2 3 here we use global positioning system and radar interferometry measurements of ground motion to show that the earthquake involved a combination of horizontal and contractional slip causing transpressional motion this result is consistent with the long term pattern of strain accumulation in hispaniola the unexpected contractional deformation caused by the earthquake and by the pattern of strain accumulation indicates present activity on faults other than the enriquillo plantain garden fault we show that the earthquake instead ruptured an unmapped north dipping fault called the leog ne fault the leog ne fault lies subparallel to but is different from the enriquillo plantain garden fault we suggest that the 2010 earthquake may have activated the southernmost front of the haitian fold and thrust belt4 as it abuts against the enriquillo plantain garden fault as the enriquillo plantain garden fault did not release any significant accumulated elastic strain it remains a significant seismic threat for haiti and for port au prince in particular

crustal contamination identified in keweenawan osler group tholeiites ontario a trace element perspective in the lake superior area voluminous middle proterozoic tholeiitic basalt with minor rhyolite and interflow sediments occupy the midcontinent rift and overlie archean and older proterozoic basement the 3000 m thick section of gently dipping 10 sse basalts on the black bay peninsula is divided into three suites based on the relationship between stratigraphy petrography and geochemical variations e g mg number a1 2 o 3 la sm and gd yb the lower suite consists of augite olivine porphyritic lavas with high mg number sio 2 tio 2 and gd yb but low la sm the overlying central suite flows are either aphyric or plagioclase porphyritic and have lower mg number sio 2 la sm and gd yb decline upward through the central suite the upper suite lavas are either aphyric or plagioclase porphyritic and element ratios plot on slightly different trends compared to the central suite the lower suite has a narrow compositional range the average of the four most primitive lavas is used

seismic exploration of continental strike slip zones abstract seismic exploration of both palaeozoic and active strike slip zones shows strike slip faults that penetrate all or most of the crust offsets on the moho are evident particularly at young and active zones with a component of compression such as the alpine fault of new zealand where a change in crustal thickness of about 20 km is observed moho offsets for the old palaeozoic strike slip zones are usually much less prominent careful migration of crustal seismic reflection data from some of these zones shows that instead of sharp offsets the moho structure consists of a localized keel type crustal thickening of a few kilometres in amplitude and occurs over a zone approximately 10 km wide the large moho offsets of young strike slip zones may in some cases partially decay with time active strike slip zones are becoming an important focus of study but seismic exploration is hampered by complex near surface geology 3d structure and the difficulty of imaging steeply dipping structure in the subsurface in order to meet this challenge a wide range of seismic techniques is now being deployed these include wide angle seismic reflection refraction p wave delays and the study of guided s waves results from california give geophysical images of vertical strike slip faults that penetrate to the moho in contrast the alpine fault of new zealand appears to be a surface manifestation of an inclined 40 ramp extending down to the lower crust and along which uplift and exhumation of the continental crust and possibly strike slip motion is taking place

how transpressive is the northern caribbean plate boundary transpressive deformation at the northern caribbean plate boundary is accommodated mostly by two major strikeslip faults but the amount and location of accommodation of the compressional component of deformation is still debated we collected marine geophysical data including multi beam bathymetry and multichannel seismic reflection profiles along this plate boundary around hispaniola in the jamaica passage and in the gulf of gon ve the data set allows us to image the offshore active strike slip faults as well as the compressional structures we confirm that the enriquillo plantain garden fault zone epgfz in the jamaica passage has a primary strike slip motion as indicated by active left lateral strike sliprelated structures i e restraining bend asymmetrical basin en echelon pressures ridges and horsetail splay based on topographic cross sections across the epgfz we image a very limited compressional component if any for at least the western part of the jamaica passage toward the east of the jamaica passage the fault trace becomes more complex and we identify adjacent compressional structures in the gulf of gon ve distributed folding and thrust faulting of the most recent sediments indicate active pervasive compressional tectonics estimates of shortening in the jamaica passage and in the gulf of gon ve indicate an increase of the compressional component of deformation towards the east which nonetheless remains very small compared to that inferred from block modelling based on gps measurements

slip rate and earthquake recurrence along the central septentrional fault north american caribbean plate boundary dominican republic 1 the septentrional fault zone sfz is the major north american caribbean strike slip plate boundary fault at the longitude of eastern hispaniola the sfz traverses the densely populated cibao valley of the dominican republic forming a prominent scarp in alluvium our studies at four sites along the central sfz are aimed at quantifying the late quaternary behavior of this structure to better understand the seismic hazard it represents for the northeastern caribbean our investigations of excavations at sites near rio cenovi show that the most recent ground rupturing earthquake along this fault in the north central dominican republic occurred between a d 1040 and a d 1230 and involved a minimum of 4 m of left lateral slip and 2 3 m of normal dip slip at that site our studies of offset stream terraces at two locations rio juan lopez and rio licey provide late holocene slip rate estimates of 6 9 mm yr and a maximum of 11 12 mm yr respectively across the septentrional fault combining these results gives a best estimate of 6 12 mm yr for the slip rate across the sfz three excavations two near tenares and one at the rio licey site yielded evidence for the occurrence of earlier prehistoric earthquakes dates of strata associated with the penultimate event suggest that it occurred post a d 30 giving a recurrence interval of 800 1200 years these studies indicate that the sfz has likely accumulated elastic strain sufficient to generate a major earthquake during the more than 800 years since it last slipped and should be considered likely to produce a destructive future earthquake

relationships between crustal contamination and crystallisation in continental flood basalt magmas with special reference to the deccan traps of the western ghats india the upper part of the deccan traps sequence bushe to mahabaleshwar formations shows a statistically significant tendency for the most mafic lavas to be the most contaminated by crustal materials this is the reverse of the relationship shown by suites evolving by contamination accompanied by fractional crystallisation afc the observed correlations e g between mg number and sr isotope initial ratios are partly an accidental consequence of the fact that the most mafic lavas are more abundant in the lower part of the sequence while contaminant availability declines in the upper part it is probable however that the correlations are augmented by increased contamination of hotter magma batches during ascent through dykes a process during which fractional crystallisation is suppressed by magmatic turbulence the absence of afc relationships suggests that most of the contamination took place during the ascent stage rather than in a magma chamber other continental flood basalt provinces such as the parana and etendeka do show afc relationships and it is speculated that this may be a result of magma chamber contamination coupled with flow rates which prevent contamination during ascent

micromorphological aspects of arctic alpine pedogenesis in the okstindan mountains norway summary the micromorphology of five arctic alpine soil types has been examined in relation to the processes of organic matter decomposition development of microstructure translocation and weathering in surface horizons the activity of microorganisms and mesofauna is apparent and organic matter is involved in the formation of spongy granular and crumb structures the structures in the subsurface horizons are predominantly single grain and lenticular showing coatings of illuvial fines on the upper surfaces of individual grains and peds illuviation of organo metallic complexes is also recognized in the form of coatings and structural development of granular and crumb elements the only evidence for weathering is the occasional fracture of biotite grains these features and processes are discussed in the context of arctic alpine pedogenesis

the caribbean plate pulled pushed or dragged 1 mechanical coupling between the lithosphere and the asthenosphere remains a controversial topic in the geosciences beneath the caribbean plate shear wave splitting measurements indicate ew strain in the asthenosphere which can be interpreted as mantle flow driving or resisting motion of the overlying lithosphere here we constrain the average shear traction on the base of the caribbean plate by balancing all torques these torques result from body forces that act on the caribbean slab pull ridge push lateral density variations from plate boundary friction and from basal shear tractions we obtain a range of physically realistic torque solutions which we examine further by computing the corresponding stresses and rotations within the caribbean plate for comparison with observations the deformation field for the caribbean is particularly sensitive to the amount of friction on intraplate faults representative models have a good fit with observations and are characterized by 1 a near zero basal shear traction 0 3 mpa 2 lithosphere averaged plate boundary friction 10 mpa 3 local forces due to indenters and trench pull 4 a net pull by the caribbean slab and 5 intraplate fault shear stresses on the order of tens of megapascals we conclude that the mechanical coupling of the caribbean plate to the underlying asthenosphere is small

melanges and olistostromes in the puerto plata area northern dominican republic as a record of subduction and collisional processes between the caribbean and north american plates abstract the cordillera septentrional records the oblique subduction and collisional processes between the caribbean and north american plates during late cretaceous to early palaeogene times the puerto plata basement complex of this range is considered to represent a fragment of the frontal part of the great arc of the caribbean in hispaniola that originated during thrusting of the caribbean plate onto the north american shelf this paper describes and interprets melange type formations spatially related to this basement complex and its associated sedimentary cover the imbert fm such formations include the san marcos olistostromic fm and a unit of serpentinic breccias located at the base and interbedded in the lower section of the former both units are eocene in age have been mainly deposited by syntectonic subaqueous mass transport processes and typically host a varied mixture of blocks of known and unknown origin including high p metamorphic rocks knockers cartoon models of palaeotectonic reconstructions depicting the final stages of subduction and the onset of collisional process in early and middle eocene times respectively are proposed in order to show the original relationships among all geological units involved in the study area the serpentinic breccias are interpreted as being the result of extensive sedimentary recycling of peridotite and serpentinite massive bodies or subduction related melanges when exposed at the surface by return flow during early exhumation stages of the accretionary complex coevally with the end of island arc volcanism this process is inferred to be the triggering mechanism for the feeding of originally deep sited knockers probably in combination with strike slip tectonics and associated mud diapirism the slightly younger san marcos fm records the collision event and main exhumation stage while displaying the typical features present in olistostromes and other mass wasting gravitationally driven deposits recognized in extensive areas of forearc and accretionary complexes involved in arc continent collisional processes

is there a northern lesser antilles forearc block 1 a systematic discrepancy exists between slip vectors of thrust fault earthquakes at the lesser antilles trench lat and the predicted direction of north american caribbean convergence a possibility has been that the discrepancy resulted because neither was well constrained estimating caribbean motion has been challenging owing to the limited data along the plate s complex boundaries similarly earlier studies had few slip vectors because interplate thrust events are infrequent to address these difficulties we estimate a new caribbean north america euler vector using recently available gps data from sites in the presumably stable interior of the caribbean and compare the predicted velocities to a larger set of slip vectors the discrepancy persists suggesting the northern lesser antilles forearc nlaf moves as a distinct entity from both the caribbean and north america for simplicity we treat its motion as a coherent block but because gps sites are not within the nlaf distributed deformation is also possible although there is no geologic evidence for the boundaries of the presumed nlaf block gps data show that the motions of martinique barbados and trinidad are similar to that of the caribbean suggesting that none are on the nlaf block and the southern lat is weakly coupled

morphotectonics of the central muertos thrust belt and muertos trough northeastern caribbean multibeam bathymetry data acquired during the 2005 spanish r v hesperides cruise and reprocessed multichannel seismic profiles provide the basis for the analysis of the morphology and deformation in the central muertos trough and muertos thrust belt the muertos trough is an elongated basin developed where the venezuelan basin crust is thrusted under the muertos fold and thrust belt structural variations along the muertos trough are suggested to be a consequence of the overburden of the asymmetrical thrust belt and by the variable nature of the venezuelan basin crust along the margin the insular slope can be divided into three east west trending slope provinces with high lateral variability which correspond to different accretion stages 1 the lower slope is composed of an active sequence of imbricate thrust slices and closed fold axes which form short and narrow accretionary ridges and elongated slope basins 2 the middle slope shows a less active imbricate structure resulting in lower superficial deformation and bigger slope basins 3 the upper slope comprises the talus region and extended terraces burying an island arc basement and an inactive imbricate structure the talus region is characterized by a dense drainage network that transports turbidite flows from the islands and their surrounding carbonate platform areas to the slope basins and sometimes to the trough in the survey area the accommodation of the ongoing east west differential motion between the hispaniola and the puerto rico virgin islands blocks takes place by means of diffuse deformation the asymmetrical development of the thrust belt is not related to the geological conditions in the foreland but rather may be caused by variations in the geometry and movement of the backstop the map view curves of the thrust belt and the symmetry of the recesses suggest a main north south convergence along the muertos margin the western end of the investigator fault zone comprises a broad band of active normal faults which result in high instability of the upper insular slope

morphostructure at the junction between the beata ridge and the greater antilles island arc offshore hispaniola southern slope abstract oblique convergence between the caribbean plate s interior and the inactive greater antilles island arc has resulted in the collision and impingement of the thickened crust of the beata ridge into southern hispaniola island deformation resulting from this convergence changes from a low angle southward verging thrust south of eastern hispaniola to collision and uplift in south central hispaniola and to left lateral transpression along the southern peninsula of haiti in western hispaniola using new swath bathymetry and a dense seismic reflection grid we mapped the morphological structural and sedimentological elements of offshore southern hispaniola we have identified four morphotectonic provinces the dominican sub basin the muertos margin the beata ridge and the haiti sub basin the lower slope of the muertos margin is occupied by the active muertos thrust belt which includes several active out of sequence thrust faults that were they to rupture along their entire length could generate large magnitude earthquakes the interaction of the thrust belt with the beata ridge yields a huge recess and the imbricate system disappears the upper slope of the muertos margin shows thick slope deposits where the extensional tectonics and slumping processes predominate the northern beata ridge consists of an asymmetrically uplifted and faulted block of oceanic crust our results suggest that the shallower structure and morphology of the northern beata ridge can be mainly explained by a mechanism of extensional unloading from the upper cretaceous onward that is still active residually along the summit of the ridge the tectonic models for the northern beata ridge involving active reverse strike slip faults and transpression caused by the oblique convergence between the beata ridge and the island arc are not supported by the structural interpretation the eastern bahoruco slope an old normal fault that acts as a passive tear fault accommodating the sharp along strike transition from low angle thrusting to collision and uplifting

diachronous uplift and recycling of sedimentary basins during cenozoic tectonic transpression northeastern caribbean plate margin abstract four marine sedimentary sequences of late cretaceous to pleistocene age crop out in the 320 km long 1 to 30 km wide peralta rio ocoa belt of hispaniola haiti and dominican republic the four sedimentary sequences are dominated by marine turbiditic rocks ranging up to 11 5 km in apparent thickness and exhibit mainly northwest to southeast belt parallel paleocurrents the three younger sequences are generally in fault or unconformable contact with the underlying sequence from northwest to southeast the four belts become progressively wider younger less metamorphosed less folded and faulted and lower in topographic elevation we interpret the three younger sequences as a syn tectonic stratigraphic record of diachronous northwest to southeast transpressional closure of a coniacian danian back arc basin represented by the oldest exposed sedimentary sequence at the northwest end of the belt and inferred at depth beneath the three younger sequences using the stratigraphic record we infer the following three stages in the closure of the back arc basin and the overlying younger basins stage one latest cretaceous to early late eocene closure a minimum of 11 km of paleocene turbidites and limestone in the padre las casas area and a minimum of 11 5 km of early eocene to early late eocene pelagic limestone mudstone sandstone and siltstone in the peralta and sierra el numero areas was deposited in an elongate basin derived from the first stage of latest cretaceous early late eocene closure and erosion of the coniacian danian back arc basin to the northwest paleocene eocene turbidites in both areas contain large amounts of reworked campanian paleocene microfauna and exhibit northwest to southeast belt parallel paleocurrents syn deformational features in eocene sedimentary rocks in the peralta and sierra el numero area indicate that convergent deformation accompanied sedimentation witschard and dolan 1990 stage two middle eocene to early miocene closure up to 8 6 km of middle eocene to early miocene turbidites debris flows and olistostromes of the rio ocoa group of the dominican republic were deposited in an elongate basin derived from middle eocene to early miocene closure uplift and erosion of the peralta group to the west and northwest turbidites contain reworked eocene faunas and lithologies similar to those in the underlying peralta group and exhibit northwest to southeast belt parallel paleocurrents erosion of late cretaceous island arc and overlying paleogene carbonate rocks of the cordillera central provided additional belt perpendicular sources of coarser grained conglomerate and olistostromes following deposition of the rio ocoa group both the peralta and the rio ocoa group were deformed in a southwest verging fold and thrust belt during the early miocene stage three middle miocene to recent closure up to 1 5 km of middle miocene to pleistocene sandstone conglomerate and reefal limestone of the ingenio caei group of the dominican republic were deposited in an elongate basin above a pronounced angular unconformity developed on the older deformed rocks of the rio ocoa group sediments of the ingenio caei group were derived from middle miocene to recent closure uplift and erosion of the rio ocoa and peralta groups to the northwest onshore exposures of the ingenio caei group can be correlated with submerged strata seen on seismic reflection profiles across the offshore san pedro basin recent submarine clastic sedimentation in the san pedro basin is dominated by northwest to southeast influx of clastic turbidites derived from active erosion of onshore exposures of the rio ocoa and ingenio caei groups middle miocene to recent sediments of the san pedro basin are being actively shortened by northward to northeastward directed underthrusting along the muertos trench underthrusting at the muertos trench is suggested to represent ongoing closure of the back arc basin thought to be deeply buried beneath the san pedro basin tectonic transpression along the closing back arc basin marks one edge of an actively deforming microplate within the north america caribbean strike slip plate boundary zone

3 d velocity structure in southern haiti from local earthquake tomography we investigate 3 d local earthquake tomography for high quality travel time arrivals from aftershocks following the 2010 m7 0 haiti earthquake on the leog ne fault the data were recorded by 35 stations including 19 ocean bottom seismometers from which we selected 595 events to simultaneously invert for hypocenter location and 3 d vp and vs velocity structures in southern haiti we performed several resolution tests and concluded that clear features can be recovered to a depth of 15 km at 5 km depth we distinguish a broad low velocity zone in the vp and vs structure offshore near gonave island which correlate with layers of marine sediments results show a pronounced low velocity zone in the upper 5 km across the city of leog ne which is consistent with the sedimentary basin location from geologic map at 10 km depth we detect a low velocity anomaly offshore near the trois baies fault and a nw se directed low velocity zone onshore across petit go ve and jacmel which is consistent with a suspected fault from a previous study and that we refer to it in our study as the petit go ve jacmel fault these observations suggest that low velocity structures delineate fault structures and the sedimentary basins across the southern peninsula which is extremely useful for seismic hazard assessment in haiti

tectonic controls on magmatism associated with continental break up an example from the parana etendeka province the high and low ti basalts of the parana etendeka province were primarily derived from old trace element enriched source regions in the lithospheric mantle and they are associated with dyke swarms of different orientations these swarms appear to reflect different amounts of extension and it is inferred that the high and low ti magma types were characterised by different melt generation rates of 0 15 km3 yr 1 and 0 4 km3 yr 1 respectively stewart et al earth planet sci lett 143 1996 95 109 there is probably a gap of 2 myr between the end of the main phase of cfb magmatism and the oldest rocks on the adjacent ocean floor a simple numerical model has been used to constrain the amounts and rates of melt generated from the continental lithosphere and asthenosphere under finite duration extension melting in the mantle is assumed to be controlled by the dry peridotite solidus in the asthenosphere and the hydrous 0 2 h2o peridotite solidus in the lithosphere for a maximum of 4 and a duration of extension of 10 myr the derivation of melt from the asthenosphere by dry peridotite melting depends primarily on potential temperature tp and is relatively insensitive to the thickness of the mbl while the converse is the case for melt derived from the lithosphere by hydrous peridotite melting for a tp of 1450 50 c inferred from the crustal thickness estimates along the rio grande rise and walvis ridge the model successfully generates 2 4 km of lithosphere derived melt before producing significant volumes of asthenosphere derived melt it is concluded that increases of melt volume with time can be generated by decompression melting of the mantle lithosphere critically in areas of significant melt generation within the mantle lithosphere during extension and break up there is likely to be a gap in the volcanic record between the end of melt generation in the lithosphere and the onset of melting in the underlying asthenosphere no such gap is present if all melts are generated within the mantle plume and thus these models may in principle be tested in the geologic record

oblique collision in the northeastern caribbean from gps measurements and geological observations 1 previous caribbean gps studies have shown that the rigid interior of the caribbean plate is moving east northeastward 070 at a rate of 18 20 3 mm yr relative to north america this direction implies maximum oblique convergence between the island of hispaniola on the caribbean plate and the 22 27 km thick crust of the bahama carbonate platform on the adjacent north america plate we present a tectonic interpretation of a 15 site gps network which spans the hispaniola bahama oblique collision zone and includes stable plate interior sites on both the north america and caribbean plates measurements span the time period of 1994 1999 in a north america reference frame gps velocities in puerto rico st croix and the lesser antilles indicate that these areas move as a single block in an east northeast direction 070 at a rate of 19 20 mm yr consistent with the movement of the rigid interior of the caribbean plate gps velocities at six sites in central and eastern hispaniola dominican republic show drastically different behavior with more eastwardly strikes 080 and much slower rates 4 17 mm yr than areas of the stable caribbean plate the boundary between the relatively slower moving hispaniola collisional zone and the relatively faster moving uncollided puerto rico virgin islands area is the mona passage where late neogene rifting occurs in a broad zone elastic modeling favors strain partitioning with oblique slip on the outer low angle submarine thrust faults north hispaniola muertos and strike slip on the inner subvertical subaerial strike slip faults septentrional enriquillo

earthquake source parameters for the 2010 january haiti main shock and aftershock sequence summary previous analyses of geological and geodetic data suggest that the obliquely compressive relative motion across the caribbean north america plate boundary in hispaniola is accommodated through strain partitioning between near vertical transcurrent faults on land and low angle thrust faults offshore in the dominican republic earthquake focal mechanism geometries generally support this interpretation little information has been available about patterns of seismic strain release in haiti however due to the small numbers of moderate to large earthquakes occurring in western hispaniola during the modern instrumental era here we analyse the damaging mw 7 0 earthquake that occurred near port au prince on 2010 january 12 and aftershocks occurring in the four months following this event to obtain centroid moment tensor cmt solutions for 50 earthquakes with magnitudes as small as mw 4 0 while the 2010 january main shock exhibited primarily strike slip motion on a steeply dipping nodal plane strike 250 dip 71 and rake 22 we find that nearly all of the aftershocks show reverse faulting motion typically on high angle 30 45 nodal planes two small aftershocks mw 4 5 and 4 6 located very close to the main shock epicentre show strike slip faulting with geometries similar to the main shock one aftershock located off the south coast of haiti shows low angle thrust faulting we also examine earthquakes occurring in this region from 1977 2009 successful analysis of four such events provides evidence for both strike slip and reverse faulting the pattern of seismic strain release in southern haiti thus indicates that partitioning of plate motion between transcurrent and reverse structures extends far west within hispaniola while we see limited evidence for low angle underthrusting offshore most reverse motion appears to occur on high angle fault structures adjacent to the enriquillo fault our results highlight the need to incorporate seismogenic slip on compressional structures into hazard assessments for southern haiti

an inversion approach to assimilation and fractional crystallisation processes a numerical inversion program has been developed to investigate isotope and trace element variations in suites of related rocks in terms of assimilation and fractional crystallisation processes major element compositions constrain the degree of fractionation and the program may be used to calculate the isotope and trace element composition of either the crustal contaminant or of the parental magmas once the contaminant is known the ratio of the rate of assimilation to the rate of fractional crystallisation and the bulk partition coefficients can be varied with changes in magma composition the approach is illustrated with a suite of calc alkaline rocks from the cerro galan centre in nw argentina and a suite of continental flood basalts from the southern parana in brazil both exhibit striking increases in 87sr 86sr with increasing sio2 consistent with progressive contamination during differentiation within the continental crust in detail both suites contain a subset of samples which have undergone relatively little contamination and a subset characterised by relatively high sio2 and 87sr 86sr reflecting larger crustal contributions individual samples within the more contaminated subset can be modelled in terms of assimilation with fractional crystallisation afc processes although no clear progressively contaminated liquid lines of descent are preserved at both cerro galan and the southern parana the associated dacites and rhyodacites appear to have similar compositions to the crustal contaminants thus the inversion program has been used to investigate the amount of contamination the relationship between the amount of contamination and the amount of crystals removed by fractional crystallisation and the isotope and trace element contents of the parental magmas prior to afc the latter are estimated to have had 87sr 86sr 0 7055 and 143nd 144nd 0 51256 at cerro galan and 0 7090 and 0 51226 respectively in the southern parana

strain partitioning and fault slip rates in the northeastern caribbean from gps measurements 1 gps data collected in the dominican republic from 1994 to 2001 show that oblique convergence between the north american and caribbean plates is partitioned between 5 2 2 mm yr 1 of dip slip reverse motion on the north hispaniola thrust approximately n s and 12 8 2 5 mm yr 1 and 9 0 9 0 mm yr 1 of approximately e w left lateral strike slip motion on the septentrional and enriquillo faults 95 confidence the agreement between gps and paleoseimological slip rates on the septentrional fault together with the 770 960 years since the last major earthquake and the 800 1200 years maximum repeat time of major earthquakes may indicate that the septentrional fault is currently in the late phase of its rupture cycle

seismic structure of the crust in the western dominican republic abstract the contact between the caribbean and north american plates is a tectonically complicated boundary where the deformation is accommodated in north and south of hispaniola by the enriquillo plantain garden and septentrional oriente fault zones epgfz and sofz we present a crustal and tectonic study of the northeastern caribbean plate boundary from wide angle seismic data was acquired during the geoprico do 2005 and caribe norte 2009 surveys showing two transects crossing from north to south north american plate noam bahamas platform central hispaniola and caribbean plate cp the results presented include two 2 d p wave velocity models of 425 km and 200 km long oriented nne ssw and ene ssw respectively obtained by the travel time forward and inverse modeling of the was data our study defines that the contact between bahamas platform north american plate and hispaniola corresponds to oblique subduction with the moho dipping 11 in the nne ssw direction furthermore in the south our results reveal the existence of an anomalous deep reaching zone of lateral velocity variation in the mantle that could be associated with epgfz and a possible detached oceanic slab from noam that could explain the deep seismicity in the region

new challenges for tafoni research a new approach to understand processes and weathering rates cavernous tafoni type weathering is a common and conspicuous global feature creating artistic sculptures which may be relevant for geochemical budgets weathering processes and rates are still a matter of discussion field evidence in the type locality corsica revealed no trend of size variability from the coast to subalpine elevations and the aspect of tafoni seems to be governed primarily by the directions of local fault systems and cleavage and only subordinately by wind directions or the aspect of insulation rem analysis of fresh tafone chips confirmed mechanical weathering by the crystallization of salts as conchoidal fracturing of quartz is observed the salts are only subordinately provided by sea spray as calcium and sodium sulfates rather than halite dominate even close to the coast characteristic element ratios compare well with aerosols from mixed african and european air masses sulfates are largely derived from sahara dust indicated by their sulfur isotopic composition salt crystals form by capillary rise within the rock and subsequent crystallization in micro cracks and at grain boundaries inside rain protected overhangs siderophile bacteria identified by raster electron microscopy rem analysis of tafone debris contribute to accelerated weathering of biotite and tiny sulfide ore minerals by applying 10be exposure dating weathering rates of large mature tafone structures were found to be about an order of magnitude higher than those on the exposed top of the affected granite blocks copyright 2010 john wiley sons ltd

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

geodynamical evolution of central andes at 24 s as inferred by magma composition along the calama olacapato el toro transversal volcanic belt abstract miocene to recent volcanism on the puna plateau central andes developed in three geological settings a volcanic arc in the western cordillera miocene recent b trans arc along the main nw se transverse fault systems miocene and c back arc mainly monogenic volcanic centres pliocene quaternary we have studied the evolution of the arc trans arc volcanism along one of the most extensive transverse structures of central andes the calama olacapato el toro at 24 s compositional variations from arc to trans arc volcanism provide insights into petrogenesis and magma source regions puntas negras and rincon volcanic centres are arc type and have typical calc alkaline geochemical and sr nd pb isotopic characteristics east of the arc lavas of the tul tul del medio and pocitos complexes tumepo are heavy rare earth element depleted and could be derived from 20 30 of partial melting of a lower crustal garnet bearing metabasite these liquids could be variably mixed with arc magmas at the base of the crust mash this suggests important contributions from lower crustal sources to tumepo centres products at the quevar and aguas calientes volcanic complexes to the east of tumepo show a prominent upper crustal signature high 86sr 87sr low 143nd 144nd and could represent mixtures of 20 30 tumepo type liquids with up to 70 80 of upper crustal melts we propose a geodynamic model to explain geochemical variations for the arc trans arc transverse volcanism from the upper miocene to recent in our model arc volcanism is linked to dehydration of the subducting nazca plate which produces typical calc alkaline compositions during the upper miocene 10 5 ma lithospheric evolution in the puna plateau was dominated by thickening of ductile lower crust and thinning of the lithosphere lower crustal melting was promoted by concomitant asthenospheric upwelling and water release from the amphibolite eclogite transformation yielding tumepo magmas with lower crustal signatures at the same time the eastern sector of the puna plateau experienced westward underthrusting of the brazilian shield and upper crustal brittle deformation partial melts from underthrust upper crustal wedges mixed with lower crustal magmas to produce lavas at aguas calientes and quevar during pliocene to quaternary delamination of the lithosphere and lowermost crust promoted a widespread monogenetic ocean island basalt type and shoshonitic volcanism

mantle hotspots plumes and regional tectonics as causes of intraplate magmatism in continental areas it is often difficult to determine the cause of intraplate magmatism large volumes of magma high eruption rates and the presence of a hotspot trace on the adjacent ocean floor are all evidence for the presence of an anomalously hot mantle however in many continental magmas there are chemical variations with time which are inferred to reflect changes from asthenospheric to predominantly lithospheric source regions or vice versa it is argued that these chemical characteristics constrain whether magmatism was triggered by the emplacement of a mantle plume or by lithospheric extension

petrogenesis of rhyolites and trachytes from the deccan trap sr nd and pb isotope and trace element evidence trachytes and rhyolites from salsette island north of bombay have distinctive trace element and isotope features which mark them out from typical crustal melts their highly incompatible trace element and sr nd and pb isotope ratios are similar to those of the associated deccan flood basalts thus the rhyolites and trachytes are closely related to the basalts and a striking compositional gap between 50 and 65 sio2 suggests that the high sio2 rocks evolved by 10 15 partial melting followed by variable amounts of fractional crystallisation the source material could have been basalt within the deccan trap or related gabbroic rocks in deep crustal sill complexes the rhyolites yield an rb sr whole rock age of 61 5 1 9 ma with a slightly high initial 87sr 86sr 0 7085 18 it is argued that crustal extension provides a suitable regime for the generation of acid magmas by partial melting of associated basic rocks

tafoni in the el chorro area andalucia southern spain using a combination of field laboratory and micromorphological evidence this study examines tafoni singular tafone in the el chorro area of andalucia southern spain and makes inferences concerning the processes responsible for their formation twenty five tafoni were randomly selected for field examination the morphology of these cavernous rock domes is characterized by a helmet shaped outer roof and an arched shaped cavern often with a partially overhanging visor measurements of height width and depth of the caverns revealed marked variations in size the presence or absence of lichen cover surface varnish overhanging visor cavern backwall stripes rock flaking weathering pits and cavern floor sediments was also noted surface hardness values obtained using a schmidt hammer are relatively low but significantly higher on the outer roof of the tafoni than on the inner cavern walls analysis of sediment samples collected from the cavern backwalls and floors indicates predominantly sandy textures alkaline ph values and some base cation enrichment micromorphological analysis of thin sections prepared from undisturbed blocks reveals large quantities of pore filling cement consisting mainly of calcite mineral grains affected by weathering and pseudomorphic replacement and dark rounded nodules with a metallic appearance in terms of their formation different processes appear to act on different parts of the landform on the outer roof surfaces case hardening resulting from near surface cementation and surface varnish development is dominant on the inner cavern surfaces however core softening resulting from granular disintegration and flaking dominates exfoliation weathering running water and wind deflation also appear to play an important role in tafone formation a phased model of tafone evolution is proposed whereby the features pass through four phases of development initiation enlargement amalgamation and degradation in the study area there are examples of tafoni in each of these phases much of the evidence suggests that the tafoni are actively developing under current environmental conditions

plate boundary readjustment in oblique convergence example of the neogene of hispaniola greater antilles the haitian fold and thrust belt is the major mountain belt of haiti western part of hispaniola greater antilles and resembles a compressive restraining bend between the two major faults which have driven the opening of the cayman basin since the eocene during the rifting stage from the middle to the late eocene this area underwent an extensional evolution with fissural volcanic activity along ne sw tilted blocks the haitian fold and thrust belt was constructed from the early miocene until the present by stacking sedimentary units into a collisional wedge perpendicular to the tilted blocks which was propagating to the southwest during the construction of the wedge piggyback basins were formed and progressively uplifted during the late neogene convergence is localized in the cul de sac enriquillo trough where the active front proceeds southward onto the beata ridge in this area miocene to quaternary wrench structures of the lower plate like the southern peninsula and the enriquillo plantain garden faults are reactivated as normal faults owing to the loading of the fold and thrust belt

from intra oceanic subduction to arc accretion and arc continent collision insights from the structural evolution of the rio san juan metamorphic complex northern hispaniola the rio san juan metamorphic complex exposes a segment of a high pressure subduction accretionary complex built during caribbean island arc north america continental margin convergence it is composed of accreted arc and oceanic derived metaigneous rocks serpentinized peridotites and minor metasediments forming a structural pile combined detailed mapping structural and metamorphic analysis and geochronology show that the deformation can be divided into five main events d1 d5 an early subduction related d1 deformation and m1 metamorphism produced greenschist mafic rocks of the gaspar hernandez peridotite tectonite blueschist and eclogite metamafic blocks in the jagua clara melange high p epidote amphibolite and eclogite cuaba unit and lower blueschist and greenschist facies conditions morrito unit this was followed by m2 decompression and cooling in the blueschist greenschist and low p amphibolite facies conditions the shape of the retrograde p t path the age of the exhumation related d2 structures and the tectonic significance of d2 deformation are different in each structural unit published u pb and 40ar 39ar plateau ages and t t p t estimations reveal diachronic turonian coniacian to maastrichtian retrograde m2 metamorphism in the different structural units of the complex during a consistent d2 top to the ne ene tectonic transport regionally a similar top to the ene tectonic transport also took place in the metasedimentary nappes of the samana complex during the eocene to earliest miocene this kinematic compatibility indicates a general northeastward progradation of deformation in the northern caribbean convergent margin as the successive tectonic incorporation of arc oceanic and continental derived terrains to the developing caribbean subduction accretionary complex took place d3 d5 deformations are discontinuous and much less penetrative recording the evolution from ductile to brittle conditions of deformation in the complex the d3 event substantially modified the nappe stack and produced open folds with amplitudes up to kilometer scale the late paleocene eocene d4 structures are ductile to ductile brittle thrusts and inverse shear bands d5 is a tertiary entirely brittle deformation that had considerable influence in the geometry of the whole complex from the miocene to the present it has been cut and laterally displaced by a d5 sinistral strike slip fault system associated with the septentrional fault zone

modeling wide angle seismic data for crustal structure southeastern grenville province a modeling methodology for obtaining two dimensional 2 d crustal structure from wide angle seismic data is applied to data from the southeastern grenville province pre modeling steps include 1 assignment of arrival pick uncertainties for appropriate data fitting and weighting using an empirical relationship based on signal to noise ratio 2 using a modified form of travel time reciprocity to avoid unreasonable levels of model heterogeneity and 3 identifying data unsuitable for 2 d modeling the goal of the travel time inversion amplitude modeling approach is to obtain a minimum structure and minimum parameter model that takes into account both horizontal and vertical variations in the resolution of typical wide angle data each step of a layer stripping procedure involves a series of inversions in which a one dimensional or simple starting model is improved with additional velocity and or interface nodes until a satisfactory trade off between travel time fit parameter resolution and complete ray coverage of all source receiver pairs is achieved using zero vertical velocity gradient layers and head waves during preliminary first arrival inversion can 1 decrease the number of intermediate models 2 allow greater lateral heterogeneity to be imaged and 3 simplify incorporation of amplitude modeling constraints into the final model using amplitude distance curves allows quantitative modeling of the relative amplitude and offset variations of phases discrepancies between observed and calculated reflection amplitudes are used to infer fundamental non step like velocity changes at layer boundaries later arrivals due to unresolved velocity anomalies are modeled using reflecting segments that float within the model without an associated velocity structure these reflectors provide a spatial image like that obtained from vertical incidence reflection data as opposed to a velocity image the model of grenville crustal structure is more detailed than a model obtained from a previous interpretation of the data and includes elements analogous to those imaged in nearby deep reflection data a crustal scale zone of wide angle reflectors with an average easterly apparent dip of 13 defines a major grenvillian terrane boundary

deformation of the caribbean region one plate or two new deep penetrating high resolution multichannel seismic reflection data collected in the eastern caribbean during r v ewing cruise ew9501 imaged both the crustal structure and overlying stratigraphic successions on the basis of this new multichannel seismic data we define the geologic development of the beata ridge and venezuelan basin the caribbean crust was formed by seafloor spreading in late jurassic early cretaceous time prior to the senonian widespread and rapid eruption of basaltic flows began in concert with extensional deformation of the caribbean crust thick volcanic wedges characterized by divergent reflectors are observed along the boundary that separates rough from smooth oceanic crust are coincident with an abrupt shallowing of the moho and appear to be bounded by a large northwest dipping fault system the locus of major extensional deformation migrated through time from the venezuelan basin to the western flank of the beata ridge extensional unloading of the beata ridge footwall caused uplift and rotation of the ridge sediment thicknesses and stratal geometry observed across the venezuelan basin and beata ridge suggest that the majority of the deformation in this region occurred during and soon after the emplacement of the volcanics minor fault reactivation in the neogene along the eastern flank of the beata ridge is associated with an accommodation zone i e tear fault that records a change in the deformation style from bending and subduction of the caribbean plate along the muertos trough south of puerto rico to compressional deformation and obduction of the caribbean plate south of hispaniola we propose that this difference in deformational style is in part a consequence of the thicker crust on the beata ridge which is more resistant to subduction

neotectonics of puerto rico and the virgin islands northeastern caribbean from gps geodesy the boundary between the north american and caribbean plates is characterized primarily by left lateral motion along predominantly east west striking faults seismicity and marine geophysical survey data are consistent with at least two and possibly three microplates in the diffuse boundary zone in the northeastern caribbean 1 the gonave 2 the hispaniola and 3 the puerto rico northern virgin islands prvi we discuss results from gps geodetic measurements acquired since 1994 to test the microplate hypothesis define prvi translation and rotation within the boundary zone and constrain prvi neotectonics gps derived velocities are analyzed with respect to both north american and caribbean plate reference frames integrated displacements across prvi are limited to a few millimeters per year consistent with a rigid prvi and permitting calculation of an average velocity for prvi the motions of prvi relative to north america and the caribbean are 16 9 1 1 mm yr toward n68 e 3 1 and 2 4 1 4 mm yr toward s79 w 26 1 respectively in contrast with some recent models ongoing rotation of prvi about a nearby 25 distant vertical axis is not supported by the geodetic data in addition we argue against eastward tectonic escape of prvi and favor a simple progressive increase in velocity across the plate boundary zone requiring that the summed magnitude of strike slip fault slip rates will equal the total plate motion rate between the caribbean and north america gps data are consistent with components of left lateral strike slip faulting along the muertos trough south of puerto rico and shortening across the puerto rico trench comparison of gps velocities for prvi with respect to north america with total north america caribbean relative motion suggests up to 85 of north american caribbean plate motion is accommodated by the puerto rico trench and offshore faults north of puerto rico differences in gps derived velocities from hispaniola and prvi yield east west extension across the n s trending mona rift of a few millimeters per year when estimated elastic strain accumulation effects along the north hispaniola deformed belt and the septentrional fault zone are considered the opening rate implies an age of the mona rift of 2 3 million years agreeing with marine geophysical data that support a young age for the structure

seismic stratigraphy and structure of the caribbean igneous province multichannel seismic reflection profiles reveal the tectonic and stratigraphic complexity of the caribbean province a smooth reflector b forms the top of widespread cretaceous volcanic flows drilled during dsdp leg 15 and odp leg 165 in addition we also show other seismic evidence of volcanism sills and dipping horizons the southern parts of the venezuela and colombia basins are underlain by rough basement that shows many characteristics of oceanic crust several thick volcanic plateaus separated by deep basins with thin crust comprise the caribbean volcanic province in the venezuela basin only normal oceanic crust is present but in other basins this crust is underlain by underplated volcanic material the crust of the venezuela basin is less than 5 km thick and was probably formed in the pacific during the jurassic refraction data indicate that a thin layer 2v is formed by original oceanic crust overlain by a thin volcanic layer an intra basement reflection sub b marks the top of original oceanic crust that is sandwiched between an upper volcanic layer and lower underplated material this underplated layer forms a very thick layer 3v beneath the beata and nicaragua volcanic plateaus the upper part of layer 3v is gabbroic and outcrops on the beata ridge the thickening occurs mainly in the high velocity lower part of layer 3v and is attributed to the presence of magnesian rocks picrites or ultramafic cumulates a highly reflective horizon r is located at the top of this layer we present a model where the galapagos plume is 2500 km wide but has narrow heads that formed the caribbean volcanic plateaus separated by deep basins the caribbean igneous province is compared to similar volcanic features in the indian ocean kerguelen plateau and in the western pacific ocean ontong java plateau nauru and pigafetta basins the thick plateaus of the caribbean province resemble the kerguelen and ontong java plateaus whereas the deep basins present some similarities with the nauru and pigafetta basins the caribbean igneous province is younger 90 75 ma than the indian and pacific plateaus 110 130 ma however several geological evidences from land and geophysical offshore observations indicate that the onset of volcanic activity in the caribbean province could be as old as 115 ma

the neotectonic setting of puerto rico the island of puerto rico in the northeast caribbean lies within a broad deformation zone between the caribbean and north american plates the simplest model for the tectonic setting of puerto rico has major strike slip movement on nearly east west lines in the vicinity of the puerto rico trench coupled to a small counterclockwise rotation of a puerto rico block within the broader plate boundary zone this simple model is attractive because it predicts the tectonic regime south of puerto rico and provides an explanation for a possible component of extension across the puerto rico trench west of 65 5 w gloria long range sidescan sonar data and seismic reflection profiles have been used to test this model by mapping the major tectonic features across the plate boundary north and south of puerto rico to the north the new data help to resolve between conflicting models of underthrusting or strike slip motion at the puerto rico trench no direct evidence of compression is seen although evidence for normal and strike slip movement is abundant this combined with regional considerations leads us to conclude that the main east west trending part of the puerto rico trench between 65 5 w and 68 w lies within a strike slip regime although oblique convergence occurs both to the east and west where the plate boundary trends east southeast to the south of puerto rico underthrusting of the caribbean plate beneath the island decreases from west to east and it is ultimately replaced by extension in the virgin islands basin east of 65 w