salt transport in the near surface layer in the monsoon influenced indian ocean using hycom 1 salt advection in the top 5 m layer of the monsoon influenced indian ocean has been studied with high resolution hybrid coordinate ocean model hycom simulated sea surface salinity sss during 2003 06 the effect of monsoon reversals and roles of ekman drift and geostrophic currents are emphasized the ekman drift component is found to be more important than the geostrophic component in exchange of salt in the basins an indication of the influence of winds and the associated surface currents the strongest differences in the salt advection terms occurred in the bay of bengal bob an indication of the significant role of advection for the distribution of freshwater and the ekman processes the inter tropical convergence zone itcz is seen to influence advection patterns via ekman drift along the equatorial region this results in the creation of two salt advection bands whose positions vary seasonally this study will help to interpret data from the recently launched soil moisture ocean salinity smos and future aquarius salinity missions for the indian ocean

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

donnees sur la structure de l arc insulaire des petites antilles entre ste lucie et anguilla abstract geological and geophysical data were collected during a marine geological cruise arcante 1 carried out in 1977 1978 between st lucia and anguilla corresponding to about two thirds of the length of the lesser antilles archipelago they allow of a reconsideration of the structural framework of this island arc considered as a whole the lesser antilles ridge is characterized by a pattern contrasting sharply between its northern and southern halves the major discontinuity axis runs to the south of the guadeloupe archipelago the basement of the northern half is supposed to be mainly mesozoic and is connected with the evolution of the greater antilles whilst the southern half was generated only since the eocene the ne flanks of the lesser antilles ridge are steep and dissected by large submarine valleys such as the desirade sea trough their recent sedimentary cover post lower miocene is lacking or very poor enabling the outcropping of older formations volcanic mesozoic basement around la desirade upper cretaceous eocene and oligocene sediments conversely the nw flanks are gently sloping and are draped by a rather thick overburden of plio pleistocene deposits to the south the steep sw flanks are covered with a moderate thickness of recent sediments and display characteristics contrasting with those of the se flanks facing the barbados accretionary prism from the south up to martinique there is only one volcanic ridge of eocene to present age to the north of martinique this ridge splits into two axes the submarine landmarks of these two arcs have been disclosed during the present survey the eastern one or outer arc shows a row of seamounts and islands often marked by strong magnetic dien bien phu bank marie galante agouti bank or heavy gravimetric marie galante grande terre anomalies this outer arc was superimposed on the pre eocene basement and is expressed in the eocene and oligocene volcanic terrains cropping out in the islands of antigua st bartholomew st martin and anguilla which rise from the wide northern insular shelves a major ca 70 km interruption in the continuity of this axis takes place between dien bien phu bank and marie galante la desirade and barbuda islands although pertaining to the limestone caribbees are not included in the outer arc the western or inner arc made up of upper miocene to present volcanics begins with dominica island and terminates at luymes bank but an interruption of about 50 km is to be noted between basse terre and montserrat the outer and inner arcs are separated by the narrow ca 50 km and elongated ca 250 km kallinago depression this intra arc trough is generally filled by less than 1 km of recent sediments and is subdivided into three smaller basins it was not initiated by extensional rifting related to back arc spreading as was previously assumed it is possible that from martinique to guadeloupe an intermediate arc was in activity during the miocene data from exploratory oil surveys provide some new insights into the geology and the structure of the wide saba bank located to the west of the inner arc and near the northern end of the archipelago its volcanic substratum is of upper cretaceous paleocene age and is part of the pre eocene basement of the northern lesser antilles the general characteristics of the ne flanks of the lesser antilles ridge may indicate some tilting toward the west of the northern part of the island arc this may be ascribed to the arrival of atlantic fracture zone ridges barracuda and tiburon in the subduction zone during the miocene this event could explain the jump of the volcanic line from the outer to the inner arc

contrasts in morphology and deformation offshore montserrat new insights from the sea calipso marine cruise data 1 during the december 2007 sea calipso experiment we collected seismic reflection profiles offshore of montserrat off the east coast we imaged deep fans of volcaniclastic debris from three volcanoes progressively active from 2 ma to present near shelf sedimentation rates of 8 9 cm ka are approximated following cessation of local volcanic activity the fans were deposited on sediments with apparent dips towards the ese trending montserrat havers fault system mhfs in southern montserrat the mhfs encloses the soufriere hills volcano has elevated crustal blocks at roche s bluff st georges hill and garibaldi hill and extends off the west coast off the west coast the n dip of two faults supports a n dip interpretation for a major component of mhfs the belham valley fault we propose that local deformation is affected by stress redistributions consistent with a right stepping sinistral en echelon fault system but the interplay of transtension and magmatism has resulted in complex and evolving stress regimes

new insights on the tectonics along the new hebrides subduction zone based on gps results 1 at the new hebrides nh subduction zone ridges born by the subducting australia plate enter the trench and collide with the overriding margin results from gps surveys conducted on both sides of the trench and new bathymetry maps of the nh archipelago bring new light on the complex tectonics of this area convergence vectors present large variations that are not explained by australia pacific a p poles and that define four segments vectors remain mostly perpendicular to the trench and parallel to the earthquake slip vectors slow convergence i e 30 40 mm yr is found at the central segment facing the d entrecasteaux ridge the southern segment moves faster than a p motion predicts 89 to 124 mm yr relatively to a western north fiji basin wnfb reference the northern and southern segments rotate in opposite directions consistently with the extension observed in the troughs east of both segments both rotations combine in central vanuatu into an eastward translation that bulldozes the central segment into the wnfb at 55 mm yr that model suggests that the motion of the central segment forced by the subduction collision of the d entrecasteaux ridge influences the motion of the adjoining segments the new caledonia archipelago is motionless with respect to the rest of the australia plate despite the incipient interaction between the loyalty ridge and the nh margin southeast of the interaction area convergence is partitioned into a 50 mm yr trench normal component accommodated at the trench and a 90 mm yr trench parallel component close to the a p convergence and presumably accommodated by a transform boundary at the rear of the nh arc

recent investigations of the 0 5 ma geomagnetic field recorded by lava flows we present a synthesis of 0 5 ma paleomagnetic directional data collected from 17 different locations under the collaborative time averaged geomagnetic field initiative tafi when combined with regional compilations from the northwest united states the southwest united states japan new zealand hawaii mexico south pacific and the indian ocean a data set of over 2000 sites with high quality stable polarity and declination and inclination measurements is obtained this is a more than sevenfold increase over similar quality data in the existing paleosecular variation of recent lavas psvrl data set and has greatly improved spatial sampling the new data set spans 78 s to 53 n and has sufficient temporal and spatial sampling to allow characterization of latitudinal variations in the time averaged field taf and paleosecular variation psv for the brunhes and matuyama chrons and for the 0 5 ma interval combined the brunhes and matuyama chrons exhibit different taf geometries notably smaller departures from a geocentric axial dipole field during the brunhes consistent with higher dipole strength observed from paleointensity data geographical variations in psv are also different for the brunhes and matuyama given the high quality of our data set polarity asymmetries in psv and the taf cannot be attributed to viscous overprints but suggest different underlying field behavior perhaps related to the influence of long lived core mantle boundary conditions on core flow psv as measured by dispersion of virtual geomagnetic poles shows less latitudinal variation than predicted by current statistical psv models or by previous data sets in particular the brunhes data reported here are compatible with a wide range of models from those that predict constant dispersion as a function of latitude to those that predict an increase in dispersion with latitude discriminating among such models could be helped by increased numbers of low latitude data and new high northern latitude sites tests with other data sets and with simulations indicate that some of the latitudinal signature previously observed in vgp dispersion can be attributed to the inclusion of low quality insufficiently cleaned data with too few samples per site our matuyama data show a stronger dependence of dispersion on latitude than the brunhes data the taf is examined using the variation of inclination anomaly with latitude best fit two parameter models have axial quadrupole contributions of 2 4 of the axial dipole term and axial octupole contributions of 1 5 approximately 2 of the octupole signature is likely the result of bias incurred by averaging unit vectors

sedimentology palaeoenvironments and biostratigraphy of the pliocene pleistocene carbonate platform of grande terre guadeloupe lesser antilles forearc pliocene and pleistocene deposits from grande terre guadeloupe archipelago french lesser antilles provide a remarkable example of an isolated carbonate system built in an active margin setting with sedimentation both controlled by rapid sea level changes and tectonic movements based on new field sedimentological and palaeontological analyses these deposits have been organized into four sedimentary sequences s1 to s4 separated by three subaerial erosion surfaces sb0 sb1 and sb2 sequences s1 and s2 calcaires inferieurs a rhodolithes deposited during the late zanclean to early gelasian planktonic foraminiferal zones pl2 to pl5 in low subsidence conditions on a distally steepened ramp dipping eastward red algal rich deposits which dominate the western part of grande terre change to planktonic foraminifer rich deposits eastward vertical movements of tens of metres were responsible for the formation of sb0 and sb1 sequence s3 formation volcano sedimentaire calcaires superieurs a rhodolithes and calcaires a agaricia was deposited during the late piacenzian to early calabrian zones pl5 to pt1a on a distally steepened red algal dominated ramp that changes upward into a homoclinal coral dominated ramp deposition of sequence s3 occurred during a eustatic cycle in quiet tectonic conditions its uppermost boundary the major erosion surface sb2 is related to the cala1 eustatic sea level fall finally sequence s4 calcaires a acropora probably formed during the calabrian developing as a coral dominated platform during a eustatic cycle in quiet tectonic conditions the final emergence of the island could then have occurred in late calabrian times

pliocene to pleistocene vertical movements in the forearc of the lesser antilles subduction insights from chronostratigraphy of shallow water carbonate platforms guadeloupe archipelago an integrated stratigraphic study was conducted on the shallow water carbonate platforms of the guadeloupe archipelago to refine the tectonic evolution of the lesser antilles forearc the carbonate platforms are now dated to the zanclean calabrian interval and their demise occurred between 1 5 and 1 07 ma the precise chronostratigraphy allows dating of the main extensional tectonic events since the late miocene an initial episode occurred during the late miocene related to the reactivation of inherited n130 e trending shear zones and led to the emergence of most parts of the forearc subsequently zanclean to early piacenzian carbonate platforms developed in association with a general subsidence of the forearc during the late piacenzan a second extensional episode occurred at this time la desirade underwent major uplift and emergence whereas most of the forearc remained submerged prior to 1 07 ma a third north south extensional episode occurred and led to the final demise of the carbonate platforms thus the forearc was characterized by general subsidence since the early pliocene interrupted by three main extensional episodes and related differential uplifts this suggests that the lesser antilles subduction is probably erosive north of latitude 15 n since c 5 ma related to aseismic ridge subduction supplementary data planktonic foraminiferal assemblages calcareous nannofossil taxa associations 40 ar 39 ar geochronological data and palaeomagnetic data are available at www geolsoc org uk sup18724

current block motions and strain accumulation on active faults in the caribbean the caribbean plate and its boundaries with north and south america marked by subduction and large intra arc strike slip faults are a natural laboratory for the study of strain partitioning and interseismic plate coupling in relation to large earthquakes here we use most of the available campaign and continuous gps measurements in the caribbean to derive a regional velocity field expressed in a consistent reference frame we use this velocity field as input to a kinematic model where surface velocities results from the rotation of rigid blocks bounded by locked faults accumulating interseismic strain while allowing for partial locking along the lesser antilles puerto rico and hispaniola subduction we test various block geometries guided by previous regional kinematic models and geological information on active faults our findings refine a number of previously established results in particular slip rates on the strike slip faults systems bounding the caribbean plate to the north and south and the kinematics of the gonave microplate our much improved gps velocity field in the lesser antilles compared to previous studies does not require the existence of a distinct northern lesser antilles block and excludes more than 3 mm yr of strain accumulation on the lesser antilles puerto rico subduction plate interface which appears essentially uncoupled the transition from a coupled to an uncoupled subduction coincides with a transition in the long term geological behavior of the caribbean plate margin from compressional hispaniola to extensional puerto rico and lesser antilles a characteristics shared with several other subduction systems

continental margin response to multiple arc continent collisions the northern andes caribbean margin abstract an integration of diverse strain markers into a palinspastic reconstruction of the northern andes provides a first order quantitative approximation to the response of a complex margin to two consecutive arc continent collisions a palinspastic reconstruction highlights margin parallel displacements with crustal blocks traveling 400 to 500 km northward while the margin normal shortening component excluding subduction is limited to 100 km the first arc continent collision closed a 500 km wide ocean basin where subduction of atlantic lithosphere took place under an intra oceanic arc 90 to 65 ma old originally 1100 km long and currently stretched 2200 km following collision eastward directed oblique subduction started at 65 ma with 800 km of proto caribbean lithosphere consumed under northwestern south america igniting a short lived magmatic arc along the post collisional margin two molasse deposits track deformation cooling exhumation and erosion of the margin the first heralds the arrival of the first intra oceanic arc to the southernmost northern andes in late campanian times younging northward as the collision propagated north this latest cretaceous molasse deposit records also the first altitudinal gain in the northern andean orogen along the central and real cordilleras the second molasse follows middle to late eocene magmatic arc shut down and regional exhumation and cooling of the margin formation rise and docking of the intra oceanic panama arc closed a 1200 km wide middle eocene seaway and renewed miocene magmatism in the northern andes as the nazca plate started subducting behind the docked arc

paleomagnetic evidence for tertiary anticlockwise rotation in southwest puerto rico late cretaceous and eocene paleomagnetic results from calcareous mudstone limestone and volcaniclastic rocks in southwest puerto rico yield a significant anticlockwise discordance in magnetization direction relative to north american reference data progressive thermal demagnetization has revealed stable characteristic high blocking temperature magnetization components that display an intrasite bipolarity the direction of this stable magnetization in tilt corrected coordinates is consistently either northwest and down or southeast and up the pole position 39 4 n lat 209 6 e long dp 9 3 dm 16 7 n 10 suggests post eocene anticlockwise rotation of the sampling region relative to north america by 45 about a vertical axis a rotating block domain model in which north south compression is superimposed on wnw ese strike slip faults in sw puerto rico can explain the inferred rotation

puzzling features of western mediterranean tectonics explained by slab dragging the recent tectonic evolution of the western mediterranean region is enigmatic the causes for the closure of the moroccan marine gateway prior to the messinian salinity crisis for the ongoing shortening of the moroccan rif and for the origin of the seismogenic trans alboran shear zone and eastern betics extension are unclear these puzzling tectonic features cannot be fully explained by subduction of the east dipping gibraltar slab in the context of the regional relative plate motion frame here we use a combination of geological and geodetic data as well as three dimensional numerical modelling of subduction to show that these unusual tectonic features could be the consequence of slab dragging the north to north eastward dragging of the gibraltar slab by the absolute motion of the african plate comparison of our model results to patterns of deformation in the western mediterranean constrained by geological and geodetic data confirm that slab dragging provides a plausible mechanism for the observed deformation our results imply that the impact of absolute plate motion on subduction is identifiable from crustal observations identifying such signatures elsewhere may improve the mantle reference frame and provide insights on subduction evolution and associated crustal deformation

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

collisional model for rapid fore arc block rotations arc curvature and episodic back arc rifting in subduction settings 1 we review geophysical and geological data from 23 active and ancient plate boundaries to document a compelling spatial and temporal relationship between collision plate boundary curvature rapid tectonic rotations and the occurrence of back arc rifting our observations support a conceptual model where the change from subduction to collision causes rapid fore arc rotation when viewed in a reference frame relative to the bounding tectonic plates leading to marked plate boundary curvature our global compilation reveals that most active back arc rifts are associated with rapidly rotating fore arcs and nearby collisions thus we propose that collision and rapid fore arc rotations play a major role in the evolution and kinematics of back arc basins we conduct numerical modeling to better understand the physical processes behind these observed rapid tectonic rotations at convergent margins our results suggest that the presence of an indentor or choke point in the subduction system e g collision can generate rapid rotation of the fore arc about a nearby pole and lead to back arc rifting the rate of fore arc rotation and back arc rifting depends on the incoming indentor velocity and can be greatly enhanced by slab rollback and the presence of a low viscosity back arc where viscosity of the back arc is low fore arc rotation dominates where back arc viscosity is high the formation of strike slip faults and tectonic escape dominates our observational and model derived results illustrate that shallow crustal forces produced by the entry of buoyant features into subduction zones are a fundamental mechanism for the generation of fore arc block rotations plate boundary curvature back arc rift evolution and tectonic escape in subduction systems rollback of the subducting slab within the mantle will certainly enhance the processes we describe but it is not the only driving force

the tertiary geodynamical evolution of the aegean arc a paleomagnetic reconstruction abstract the paleomagnetic results obtained in the last 5 6 years from tertiary formations in the aegean domain indicate that the lower miocene arc was almost rectilinear with an e w trend and that its curvature has been acquired tectonically in two major phases during the middle miocene a first phase of deformation is characterized by rotations occurring at the two terminations of the arc clockwise in the west epirus anticlockwise in the east southeastern anatolia a second phase of rotation occurring in the last 5 ma about a pole situated in the southern adriatic sea has affected only the northwestern part the data also indicate that the antalya basin has not been involved in the geodynamical evolution of the arc so that the bey daglari represent its easternmost unit a more complex rotational pattern is observed in the internal zones the large rotations measured in evia 48 and skyros 26 probably occurred in the last 5 ma and result from rotation of fault bounded blocks in a shear zone connecting the north aegean trough to the external arc in the izmir region in the karaburun peninsula of western anatolia and in the island of lesbos significant counterclockwise clockwise or null rotations of coherent blocks have taken place during the neotectonic extensional regime furthermore the values of the inclination obtained from both sedimentary and volcanic oligo miocene formations are systematically shallower than expected on the basis of a geocentered dipole field this suggests that the entire studied area has undergone a northward drift of over 1000 km since the middle miocene

obliquity along plate boundaries most of the plate boundaries are activated obliquely with respect to the direction of far field stresses as roughly only 8 of the plate boundaries total length shows a very low obliquity ranging from 0 to 10 sub orthogonal to the plate displacement the obliquity along plate boundaries is controlled by i lateral rheological variations within the lithosphere and ii consistency with the global plate circuit indeed plate tectonics and magmatism drive rheological changes within the lithosphere and consequently influence strain localization geodynamical evolution controls large scale mantle convection and plate formation consumption and re organization thus triggering plate kinematics variations and the adjustment and re orientation of far field stresses these geological processes may thus result in plate boundaries that are not perpendicular but oblique to the direction of far field stresses this paper reviews the global patterns of obliquity along plate boundaries using gplate we provide a statistical analysis of present day obliquity along plate boundaries within this framework by comparing natural examples and geological models we discuss deformation patterns and kinematics recorded along oblique plate boundaries

caribbean intra plate deformation paleomagnetic evidence from st barthelemy island for post oligocene rotation in the lesser antilles forearc abstract as subduction zones and their related processes are often studied in 2d or cylindrical 3d sections the dynamic effects of trench curvature and its evolution through time remain under explored whereas temporal variations in trench trend may be estimated through restoring upper plate deformation we investigate the forearc deformation history of the strongly curved northern lesser antilles trench connecting the near orthogonal lesser antilles subduction zone with the motagua cayman transform plate boundary our new paleomagnetic dataset consists of 310 cores from eo oligocene magmatic rocks and limestones from st barthelemy island the limestones yielded a post folding magnetization containing a similar magnetic direction to those stored in magmatic rocks that intrude the folded carbonates both indicating a post oligocene 15 and perhaps up to 25 counterclockwise rotation of the island our results highlight that the present day trench curvature formed progressively during the cenozoic allowing us to discuss different tectonic scenarios explaining ne caribbean plate deformation and to identify key targets for future research on tectonic architecture and the potential present day activity of intra plate deformation that may pose seismic hazards

vertical variation of oxygen isotope in bay of bengal and its relationships with water masses 1 we present here for the first time comprehensive depth specific near surface to 1800 m oxygen isotope 18o data set of 175 water samples collected from 22 different locations in the bay of bengal bob during july august 2009 and december january 2012 2013 the study is aimed to constrain the water mass parameters using oxygen isotope and salinity four water masses are identified on the basis of temperature salinity relationship a bay of bengal water bobw 0 50 m b mixed zone mz 60 120 m c indonesian throughflow itf 200 500 m and d indian ocean deep water idw 600 1800 m our study shows 1 18o salinity correlation slope 0 15 0 01 intercept 4 58 0 24 r2 0 89 n 54 for the bobw is found to be consistent with surface bob water reported earlier 2 relatively lower correlation r2 0 24 n 47 in underlying mixed zone suggesting mixing of various water masses 3 significant linear correlation between 18o and salinity in idw r2 0 70 indicating depleted less saline water from southern hemisphere spread up to 18 n and 4 vertical profiles at various sampling locations showing a continuous enrichment of 18o 0 6 0 8 within top 60 100 m irrespective of their proximity to coastline in conjunction with a sharp decrease in 14c data below the same depth zone 60 100 m as reported earlier we suggest the 18o value reaches to its acme at a zone of mixing between younger bobw and relatively older itf this preliminary study indicates oxygen isotope and salinity together can be used to identify different water masses in the bob

a test of alternative caribbean plate relative motion models two contrasting models have been proposed to describe the present day motions between the caribbean plate and neighboring plates one model based on both north america caribbean and cocos caribbean data assumes that north america caribbean motion is reflected by the spreading rate approximately 2 cm yr inferred from magnetic anomalies at the cayman spreading center and the azimuths of nearby transforms jordan 1975 this geometry was used by minster and jordan 1978 in deriving global plate motion model rm2 the other model based only on north america caribbean data uses rates and azimuths inferred from the geometry of the lesser antilles wadati benioff zone sykes et al 1982 the cayman spreading center data were discounted assuming that they underestimate the full north america caribbean motion owing to the complex tectonics of the greater antilles the latter model assumes plate convergence at the lesser antilles at a rate about twice as fast as and an azimuth differing by 25 from the jordan model the two models also differ in their predictions of south america caribbean motion the jordan model predicts oblique convergence whereas sykes et al predict oblique divergence we use the nuvel 1 global relative motion data set which incorporates recent data not used in earlier studies to discriminate between the alternative models we find that the jordan geometry provides a better fit to the direction of north america caribbean motion moreover we find that models based on this geometry better fit the direction of cocos caribbean motion observed in earthquake slip vectors along the middle america trench since the prediction of this direction depends strongly on the rate of north america caribbean motion we conclude that the jordan model better describes caribbean plate motions the discrepancy between the two models results from the different methods of estimating plate motions sykes et al 1982 report that they determined a caribbean north america convergence rate of approximately 4 cm yr from the length of the lesser antilles wadati benioff zone we employ a similar procedure and obtain a rate closer to 2 cm yr we also find that the method they report using to determine the convergence direction is unable to distinguish between the alternative azimuths we thus conclude that estimates of the rate and direction of plate motion from wadati benioff zone configurations are insufficiently robust and that such estimates are better derived using rates from magnetic anomalies and azimuths from transform faults and slip vectors we further conclude that successful estimates of relative motion require internal consistency between the euler vectors of all relevant plates as demonstrated by the powerful cocos caribbean constraint not incorporated in the sykes et al model

the polyphased tectonic evolution of the anegada passage in the northern lesser antilles subduction zone the influence of the highly oblique plate convergence at the northern lesser antilles onto the margin strain partitioning and deformation pattern although frequently invoked has never been clearly imaged the anegada passage is a set of basins and deep valleys regularly related to the southern boundary of the puerto rico virgin islands prvi microplate despite the publications of various tectonic models mostly based on bathymetric data the tectonic origin and deformation of this passage remains unconstrained in the absence of deep structure imaging during cruises antithesis 1 and 3 2013 2016 we recorded the first deep multichannel seismic images and new multibeam data in the northern lesser antilles margin segment in order to shed a new light on the structure and tectonic pattern of the anegada passage we image the northeastern extent of the anegada passage from the sombrero basin to the lesser antilles margin front our results reveal that this northeastern segment is an ew trending left stepping en echelon strike slip system that consists of the sombrero and malliwana pull apart basins the malliwana and anguilla left lateral faults and the ne sw compressional restraining bend at the malliwana hill reviewing the structure of the anegada passage from the south of puerto rico to the lesser antilles margin front reveals a polyphased tectonic history the anegada passage is formed by a nw se extension possibly related to the rotation or escape of prvi block due to collision of the bahamas bank currently it is deformed by an active wnw ese strike slip deformation associated to the shear component of the strain partitioning resulting from the subduction obliquity

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

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

tectonic evolution and mantle structure of the caribbean we investigate whether predictions of mantle structure from tectonic reconstructions are in agreement with a detailed tomographic image of seismic p wave velocity structure under the caribbean region in the upper mantle positive seismic anomalies are imaged under the lesser antilles and puerto rico these anomalies are interpreted as remnants of atlantic lithosphere subduction and confirm tectonic reconstructions that suggest at least 1100 km of convergence at the lesser antilles island arc during the past 45 myr the imaged lesser antilles slab consists of a northern and southern anomaly separated by a low velocity anomaly across most of the upper mantle which we interpret as the subducted north america south america plate boundary the southern edge of the imaged lesser antilles slab agrees with vertical tearing of south america lithosphere the northern lesser antilles slab is continuous with the puerto rico slab along the northeastern plate boundary this results in an amphitheater shaped slab and it is interpreted as westward subducting north america lithosphere that remained attached to the surface along the northeastern boundary of the caribbean plate at the muertos trough however material is imaged until a depth of only 100 km suggesting a small amount of subduction the location and length of the imaged south caribbean slab agrees with proposed subduction of caribbean lithosphere under the northern south america plate an anomaly related to proposed oligocene subduction at the nicaragua rise is absent in the tomographic model beneath panama a subduction window exists across the upper mantle which is related to the cessation of subduction of the nazca plate under panama since 9 5 ma and possibly the preceding subduction of the extinct cocos nazca spreading center in the lower mantle two large anomaly patterns are imaged the westernmost anomaly agrees with the subduction of farallon lithosphere the second lower mantle anomaly is found east of the farallon anomaly and is interpreted as a remnant of the late mesozoic subduction of north and south america oceanic lithosphere at the greater antilles aves ridge and leeward antilles the imaged mantle structure does not allow us to discriminate between an intra americas origin and a pacific origin of the caribbean plate key points tectonic reconstructions for the caribbean validated by seismic tomography cenozoic lesser antilles and mesozoic greater antilles subduction confirmed tomography gives insight into geodynamics of lesser antilles

tectonics of the virgin islands basin north eastern caribbean the tectonics of the virgin islands basin are controlled by the plate boundary between the puerto rico virgin islands microplate and the stable part of the caribbean plate several contradicting theories about the formation and development of this basin have previously been proposed as part of the danish galathea 3 expedition extensive marine geological investigations of the basin were carried out in march 2007 including sediment coring and acquisition of multi beam and two dimensional seismic data this paper represents a summary of the key observations from the multi beam and the seismic data set the interpretation of these observations leads to the proposition of a tectonic model for the virgin islands basin the model consists of n s to nw se directed extension combined with e w trending sinistral strike slip and the new structural evidence from the virgin islands basin is entirely consistent with the most recently published gps data

tectonic and sedimentary architecture of the karukera spur a record of the lesser antilles fore arc deformations since the neogene the karukera spur is an easternmost submerged rise of the lesser antilles fore arc in the guadeloupe archipelago culminating about 4000 m above the fore arc basin 150 km west of the deformation front the analysis of 3500 km 2d high resolution multichannel seismic reflection and multibeam bathymetric data and the study of 14 core samples allow for the first time to reconstruct its sedimentary anatomy and tectonic evolution seven seismic units us1 to us7 are evidenced organised into four major depositional sequences separated by erosional surfaces units us1 to us4 thicken to the south southeast on the spur the sedimentary deposits rest upon a deeply eroded metamorphic basement of the caribbean plate as in la desirade island sequence 1 units us1 and us2 remains unknown in its lower part because it does not outcrop its upper part comprises early miocene shallow water carbonates sequence s2 unit us3 only comprises an upper miocene transgressive systems tract deposited into basinal environment it is bounded by major erosional surfaces sb2 and sb3 sequence 3 us4 to us6 is zanclean to pleistocene it is dominantly composed of shallow water reefal deposits sequence 4 corresponds to recent deposits the karukera spur experienced three main extensional episodes with alternations between uplift and subsidence periods uplifts are responsible for emersions and erosions subsidence severely drowned shallow water deposits the first extensional episode led to the formation of horsts and grabens in the basement prior to early miocene deposits the second extensional episode occurred during upper miocene in accordance with data in surrounding islands the third tectonic episode developed since calabrian noticeable is the constant reactivation of n130 n150 n150 n180 and n40 trending faults since early miocene and the neoformation of e w trending faults since calabrian our results suggest that at the latitude of guadeloupean archipelago the lesser antilles subduction zone is an erosional margin because of the successive sweepings of the santa lucia then tiburon ridges

palaeomagnetism of the central cuban cretaceous arc sequences and geodynamic implications abstract a detailed palaeomagnetic study of cretaceous age volcanic and sedimentary arc rocks from central cuba has been carried out samples from 32 sites 12 localities were subjected to detailed demagnetisation experiments nineteen sites from the los paso matagua provincial and cabaiguan formations yielded high unblocking temperature dual polarity directions of magnetisation which pass the fold tests with confidence levels of 95 or more and are considered to be primary in origin the palaeomagnetic inclinations are equivalent to palaeolatitudes of 9 n for the aptian 18 n for the albian a synfolding remanence identified in 5 sites from the younger hilario formation indicates a late cretaceous remagnetisation at a palaeolatitude of 16 n our results are in good agreement with previous palaeogeographic models and provide the first high quality palaeomagnetic data demonstrating the gradual northward movement of the cretaceous volcanic arc throughout the cretaceous the declination values obtained all indicate significant and similar amounts of anticlockwise rotation from the oldest sequences studied through to the late cretaceous remagnetisation this rotation is most likely related to collision of the arc with the north american plate and transpressional strike slip movement along the northern margin of the caribbean plate as it progressed eastwards into the large proto caribbean basin

rapid microplate rotations and backarc rifting at the transition between collision and subduction using global positioning system velocities from convergent plate boundaries in papua new guinea new zealand tonga vanuatu and the marianas we note a spatial correlation between rapid tectonic block rotations and the transition from subduction to collision we present a mechanism for the block rotations in which the change from collision of a buoyant indentor to normal subduction exerts a torque on the upper plate microplate this work improves our understanding of the causes of rapid vertical axis rotations often observed in paleomagnetic studies we also show how collision induced rotations may lead to backarc rifting

seismicity and seismic gap in the lesser antilles arc and earthquake hazard in guadeloupe summary a seismic study of the lesser antilles arc has been carried out first for the period 1950 1978 for which we can use local seismic networks to draw maps of instrumental seismicity then for the period 1530 1950 for which we have catalogues of felt earthquakes the striking feature of the spatial distribution of foci is the cluster of epicentres in the northern half of the arc all large earthquakes m 7 5 are located north of 14 latitude seismicity cross sections through the arc show a variable dipping subduction zone along the arc the deep seismic zone is steeper in the centre of the arc than on the extremity the time space diagram for historical seismicity and the evidence of a seismic gap at the east of guadeloupe lead us to consider the northern half arc as a likely site for a large earthquake in the near future the seismic slip rate calculated from all major earthquakes since 1530 is of much greater value than that obtained from recent plate tectonic models suggesting that the recurrence rate of earthquakes is more than many hundreds of years with a possible aseismic creep

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

indian ocean response to anomalous conditions in 2006 1 the equatorial indian ocean eio exhibited anomalous conditions characteristic of an indian ocean dipole iod during 2006 the eastern eio had cold sea surface temperature anomalies ssta lower sea level shallow thermocline and higher chlorophyll than normal the anomalies in the east restricted to the south of the equator were highest off sumatra the western pole of the iod was marked by warm ssta and deeper thermocline with maxima on either side of the equator an ocean general circulation model of the indian ocean forced by quikscat winds reproduces the iod of 2006 remarkably well the switch over to cooling in the east and warming in the west happened during may and july respectively in the east airsea heat flux initiated cold ssta in the model which were sustained later by oceanic processes in the west surface heat fluxes and horizontal advection caused warm ssta and contribution by the latter decreased after august citation vinayachandran p n j kurian and c p neema 2007 indian ocean response to anomalous conditions in 2006 geophys res lett 34 l15602 doi 10 1029 2007gl030194

incipient continental collision and plate boundary curvature late pliocene holocene transtensional hellenic forearc crete greece u ring t c brachert write in their recent paper ten veen kleinspehn 2003 proposed that the western messara graben of central crete underwent transtensional deformation since about 3 4 ma transtension is supposed to be dominantly resolved along 070 striking sinistral faults and that the 070 striking faults have strike slip normal slip ratios of 10 100 1 ten veen kleinspehn 2003 then use their results from the western messara graben to propose that sinistral transtension should represent tectonic escape of central and eastern crete during incipient collision of the libyan passive margin the interpretation of the kinematic data on which ten veen kleinspehn 2003 base their tectonic model is in contrast to earlier studies which have attributed the young i e pliocene to recent kinematics of crete largely to radial extension angelier et al 1982 fassoulas 2001 ring et al 2001 ten veen kleinspehn 2003 p 167 argued that onshore structural assemblages is critical to deciphering forearc kinematics and therefore we present our kinematic data from onshore faults in the western and central messara graben and compare our data together with the fault slip data of fassoulas 2001 from the heraklion graben and microseismicity data hatzfeld et al 1993 delibasis et al 1999 with the fault slip data of ten veen kleinspehn 2003 fig 9 for discussing the kinematics of the young faults we believe that fault slip data directly reflect the kinematics of the faults from which they were collected and therefore allow testing the proposition often veen kleinspehn that sinistral transtension is supposed to be mainly resolved at the 070 striking faults the latter of which are known to be an integral part of the youngest set of faults on crete fassoulas 2001 and are in part seismically active delibasis et al 1999 in general

trench bending initiation upper plate strain pattern and volcanism insights from the lesser antilles arc st barthelemy island french west indies the upper plate deformation pattern reflects the mechanical behavior of subduction zones here we focus on the consequences of the entrance of a buoyant bank into the caribbean subduction zone during the eocene by studying the oldest exposed rocks belonging to the lesser antilles volcanic arc using a novel geochronological data set we show that the volcanic arc activity on the island of st barthelemy spanned over the mid eocene to early miocene with a westward migration of the tectono volcanic activity which is comparable to what has already been observed on other volcanic islands in the lesser antilles the kinematics analysis allows us to identify a switch in the stress field from pure to radial extension at the oligo miocene hinge with a subhorizontal 3 that has a mean trend of n20 a three step restoration of the regional deformation indicates that this switch from pure parallel to the trench extension to radial extension may reflect a strain partitioning initiation affecting the upper caribbean plate in response to trench bending that followed the entrance of the bahamas bank into the subduction zone we show that the northern end of the lesser antilles arc shows a tectono volcanic evolution which is similar to the southern one the north south dichotomy in the perpendicular to the trench extension 15 in the north versus 30 in the south may reflect different slab ends that are highly curved to the north restraining the extension in the upper plate versus a tear to the south allowing a larger amount of extension within the upper plate

mass spectra of sn 2 hydroxyarchaeol a polar lipid biomarker for anaerobic methanotrophy 1 extremely 13c depleted sn 2 hydroxyarchaeol is widely observed at marine methane seep sites it is the first biosynthetic product that provides information about a previously unknown microorganism involved in anaerobic methanotrophy a process that occurs widely in marine sediments the mono and di tms derivatives of this compound yield sharply differing and distinctive mass spectra depending on reaction conditions either of these products can be formed in the course of conventional analyses

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

salinity variability in the arabian sea argo floats deployed in the arabian sea provided an opportunity to look at the temporal variability of the core depth of arabian sea high salinity water mass ashsw at three locations in the north central and southern arabian sea these three locations show distinctly different variability patterns at the northern location we see a prominent semi annual cycle whereas at the central location an annual cycle dominates comparison with topex jason sea level data shows that this difference can be attributed to the influence of rossby waves at the central location in the southern arabian sea the variability in core depth is also dominated by an annual mode but there are 2 high frequency components near the madden julian oscillation frequencies thus the salinity distribution in the arabian sea apparently is influenced by both remote forcing and ocean atmospheric coupling

neotectonics of the caribbean a compilation of earthquake focal mechanism solutions together with the interpretation of inclined intermediate depth seismic zones neogene strike slip faults fault controlled basins and volcanism is used to test three existing models for the neotectonic i e neogene or post oligocene development of the caribbean the current models although based on different hypotheses using different data sets are similar and suggest varying degrees of convergence between the caribbean and either north or south american plates or convergence between the caribbean plate and continental fragments of the northwestern corner of south america using model 1 previous workers have interpreted the disposition of fracture zones and magnetic anomalies in the central and south atlantic as indicating that the caribbean plate is being compressed by north south convergence between the americas with the result that it is being driven eastward relative to the americas along strike slip faults while producing east west trending subductionlike convergent zones along northern and southern plate margins using model 2 previous workers have interpreted the azimuths of active strike slip faults and focal mechanism solutions and closure of three plate velocity circuits as indicating that the south american plate converges in a west northwesterly direction on the southern margin of the caribbean plate and has produced compressional features while strike slip motion dominates along the northern boundary using model 3 previous workers have interpreted focal mechanism solutions and the pattern of strike faulting and basin development in northwestern south america to suggest right lateral displacement of the northwestern corner of south america relative to the craton with convergence and compression in the south central caribbean our integration of geologic information on faults basins and volcanism considerably extends the limited record of plate interactions known from historical reports of the past few hundred years and recorded earthquakes and suggests that 1 relative motion between the north american and caribbean plates is dominantly east west strike slip motion although areas of complex internal deformation associated with restraining bend or compressional strike slip fault segments have been identified in jamaica hispaniola and central america 2 relative motion between the south american and caribbean plates is dominantly east west strike slip motion although an area of restraining bend deformation has been identified in the araya peninsula of venezuela 3 relative motion between a triangular continental fragment of northwestern south america the maracaibo block ranges from northwest to northeast along the south central margin of the caribbean and appears to be driven mostly by the late miocene pliocene collision of the panama arc although additional driving forces may include the collision of the carnegie ridge and or oblique subduction to the northeast in ecuador and 4 relative motion internal deformation may be occurring at a very slow rate between fault bounded blocks within the caribbean plate as a result of the convergence of the maracaibo block and or eastward motion of the caribbean plate relative to a continental promontory of north america in northern central america because the caribbean margins are composed mainly of anisotropic easily deformed continental and arc lithosphere plate boundaries are zones of diffuse deformation and it is difficult to assess the degree of convergence between the americas although data from the caribbean itself suggest that it may be smaller than the amount inferred by some workers using model 1 fracture zone and magnetic anomalies in the atlantic some of the compressional features cited as evidence for the relative convergence of the americas may be instead related to the convergence between the maracaibo block relative to the southern margin of the caribbean many aspects of caribbean neotectonics remain less than completely understood but more integration of seismic and geologic studies particularly exploratory fault trenching of onshore faults and seismic profiling of offshore faults should lead to rapid advances

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

implications of the diffuse deformation of the indian ocean lithosphere for slip partitioning of oblique plate convergence in sumatra oblique plate convergence between indian ocean lithosphere and continental crust of the sunda plate is distributed between subduction on the sunda megathrust and upper plate strike slip faulting on the sumatran fault zone in a classic example of slip partitioning over the last decade a destructive series of great earthquakes has brought renewed attention to the mechanical properties of these faults and the intervening forearc crustal block while observations of forearc deformation over the earthquake cycle indicate that the forearc crust is fundamentally elastic the spatial pattern of slip vector azimuths for earthquakes sourced by rupture of the sunda megathrust is strongly inconsistent with relative motion of two rigid plates permanent and distributed deformation therefore occurs in either the downgoing lithospheric slab or the overriding forearc crust previous studies have inferred from geodetic velocities and geological slip rates of the sumatran fault that the forearc crust is undergoing rapid trench parallel stretching using new geological slip rates for the sumatran fault and an updated decadal gps velocity field of sumatra and the forearc islands we instead show that permanent deformation within the forearc sliver is minor and that the sumatran fault is a plate boundary strike slip fault the kinematic data are best explained by diffuse deformation within the oceanic lithosphere of the wharton basin which accommodates convergence between the indian and australian plates and has recently produced several large earthquakes well offshore of sumatra the slip partitioning system in sumatra is fundamentally linked with the mechanical properties of the subducting oceanic lithosphere

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

tectonics and history of the andaman sea region abstract the andaman sea is an active backarc basin lying above and behind the sunda subduction zone where convergence between the overriding southeast asian plate and the subducting australian plate is highly oblique the effect of the oblique convergence has been formation of a sliver plate between the subduction zone and a complex right lateral fault system the late paleocene collision of greater india and asia with approximately normal convergence started clockwise rotation and bending of the northern and western sunda arc the initial sliver fault which probably started in the eocene extended through the outer arc ridge offshore from sumatra through the present region of the andaman sea into the sagaing fault with more oblique convergence due to the rotation the rate of strike slip motion increased and a series of extensional basins opened obliquely by the combination of backarc extension and the strike slip motion these basins in sequence are the mergui basin starting at 32 ma the conjoined alcock and sewell rises starting at 23 ma east basin separating the rises from the foot of the continental slope starting at 15 ma and finally at 4 ma the present plate edge was formed alcock and sewell rises were separated by formation of the central andaman basin and the faulting moved onshore from the mentawai fault to the sumatra fault system bisecting sumatra

arabian sea and bay of bengal exchange of salt and tracers in an ocean model exchanges of mass and salt between the mixed layers in the arabian sea and the bay of bengal are examined in a model of the indian ocean using passive tracers as a tool to map the pathways inflow of high salinity water from the arabian sea into the bay of bengal is significant and occurs after the mature phase of the southwest monsoon freshwater transport out of the bay of bengal is southward throughout the year along the eastern boundary of the indian ocean low salinity water transport into the arabian sea occurs in the somali current during the southwest monsoon closing a clockwise path of water mass transport only a small fraction of low salinity water is advected into the eastern arabian sea from the bay of bengal

paleomagnetic evidence for late miocene counterclockwise rotation of north coast carbonate sequence puerto rico a paleomagnetic study of the essentially undeformed middle tertiary carbonate sequence along the north coast of puerto rico reveals statistically significant pre pliocene discordance of characteristic component directions against those expected from cratonic north america for much of the section despite generally weak to moderately weak magnetic intensities confirmation of the magnetization as primary in origin comes from the presence of two distinct components of magnetization intrasite bipolarity and or the reproducibility of measurements the mean geographic direction for the upper oligocene to middle miocene strata is 335 2 degree 32 9 degree and the corrected mean paleomagnetic pole is 207 6 degree 66 5 degree n 3 alpha 95 4 3 degree this suggests a counter clockwise ccw block rotation of puerto rico and its microplate of 24 5 degrees plus minus 5 8 degrees during the late miocene using a width of 250 km for the northern caribbean plate boundary zone ncpbz between the north american plate and caribbean plate the mean left lateral displacement implied is 1 8 to 2 4 cm yr which agrees fairly well with published relative motion rates for the two plates average rotation rate for 50 ma to 20 ma was 0 7 degree my but perhaps as great as 4 degree my in the miocene resolution of mean paleolatitude indicates northward motion of a degree or lessmore during the period of rotation causes of this short lived rotation may include 1 tectonic escape from the inhibiting presence of the bahama banks and beata ridge during eastward motion of puerto rico along the sinistral transpressive puerto rico trench and muertos trough fault systems or 2 changes in relative plate motions of the caribbean and north american plate during the late miocene less

extension and transtension in the plate boundary zone of the northeastern caribbean the authors propose that the caribbean ca north american na plate boundary zone pbz from the puerto rico trench to the venezuelan basin from mona canyon east has been in left transtension over the last 15 20 ma a boundary normal component of extension occurs throughout the pbz and is a principal cause of the puerto rico trench such extension is due to wnw velocity of na ca and the northward pullaway of na from its s dipping slab which is below puerto rico strike slip motion may be taken up among terranes in the pbz by rigid ccw rotation and by oblique slip at their boundaries rotation of the largest terrane puerto rico virgin islands prvi has caused such major structures as the muertos thrust and anegada passage the model implies na ca velocity estimated from cayman transforms is more accurate than that from slip vectors from seisms in the na slab

archaeal and bacterial lipids in authigenic carbonate crusts from eastern mediterranean mud volcanoes abstract we investigated the distributions and 13 c values of lipid biomarkers in authigenic methane related carbonate crusts formed on eastern mediterranean mud volcanoes a highly diverse suite of microbial membrane lipids was detected strongly 13 c depleted lipids diagnostic for archaea include isoprenoid glycerol diethers isoprenoid glycerol dialkyl glycerol tetraethers and several c 20 c 35 isoprenoid hydrocarbons bacterial lipids mainly consist of dialkyl glycerol diethers branched fatty acids and hopanoids showing important 13 c depletions albeit less than archaeal lipids the data provide further evidence for the involvement of archaea and bacteria in the anaerobic oxidation of methane aom and in the sequestration of methane derived carbon in authigenic carbonate crusts varying distributions and isotopic compositions of 13 c depleted lipids argue for heterogeneous aom related microbial consortia expanding on existing work at cold seeps distinctive biomarker features and inferred microbial assemblages are observed in these crusts in agreement with available phylogenetic data for the samples our results support the potential of lipids for distinguishing methanotrophic communities despite the observed variances conservative features in the abundances and isotopic offsets of microbial biomarkers occur likely reflecting the overall relationships between archaea and bacteria and the nature of carbon flow between them

carbonate formation by anaerobic oxidation of methane evidence from lipid biomarker and fossil 16s rdna carbonate chimneys and other carbonate structures occur widespread in the gulf of cadiz and probably reflect the presence of cold seeps and associated release of methane in the geological past possibly in the early pleistocene but it is unclear under what conditions and by which processes these carbonates were formed we studied a fossil methane related carbonate crust collected from the kidd mud volcano in the gulf concentrations of microbial lipids their stable carbon isotope composition sequences of fossil 16s rrna genes of anaerobic methanotrophic archaea in combination with mineralogical and carbon and oxygen isotopic composition of carbonate were obtained for seven different horizons of the crust this combination of organic and inorganic geochemical techniques with molecular ecological methods gave a consistent view on processes resulting in the formation of the crust and indicated that it took place in two phases and in a downward direction archaeal lipid biomarkers and fossil 16s rrna gene sequence data revealed the dominance of archaeal anme 2 group and elevated methane partial pressures during the formation of the top part of the crust the lower part of the carbonate was likely formed in an environment with reduced methane fluxes as revealed by the dominance of fossil remains of anme 1 archaea the combination of these methods can be used as an effective tool to reconstruct in unprecedented detail the palaeo biogeochemical processes resulting in the formation of carbonate fabrics this interdisciplinary strategy may also be applied for other fossil methane derived carbonates generating new concepts and knowledge about past methane related carbonate systems

spatial and temporal variability of central indian ocean salinity fronts observed by smos soil moisture and ocean salinity smos sea surface salinity sss measurements in addition to other data are used to study the occurrence of salinity fronts in the poorly sampled indian ocean which exhibits unique seasonal wind and current reversals the strength and extent of salinity fronts are analyzed to understand their variabilities salinity fronts computed from smos compare favorably with those computed from argo floats data with smos showing higher magnitudes and more detailed structure of the fronts than argo strong salinity fronts are observed along the equatorial region with meridional migration of the fronts following the migration of the intertropical convergence zone itcz and meridional ocean currents linked with these fronts are less saline subsurface waters that are sustained by the itcz influenced precipitation and warm near surface layer during the 2010 negative indian ocean dipole event the equatorial front was influenced more by the increased sss along the equator rather than precipitation additional factors such as advective processes aid the dynamics of fronts in the tropical indian ocean zonal currents advect less saline waters from the eastern indian ocean into the central indian ocean additionally the indonesian throughflow transports less saline waters to the region south of the equator which eventually influence sss front dynamics

transtensional deformation of montserrat revealed by shear wave splitting here we investigate seismic anisotropy of the upper crust in the vicinity of soufriere hills volcano using shear wave splitting sws analysis from volcano tectonic vt events soufriere hills which is located on the island of montserrat in the lesser antilles became active in 1995 and has been erupting ever since with five major phases of extrusive activity we use data recorded on a network of seismometers between 1996 and 2007 partially spanning three extrusive phases shear wave splitting in the crust is often assumed to be controlled either by structural features or by stress aligned cracks in such a case the polarization of the fast shear wave would align parallel to the strike of the structure or to the maximum compressive stress direction previous studies analyzing sws in the region using regional earthquakes observed temporal variations in which were interpreted as being caused by stress perturbations associated with pressurization of a dyke our analysis which uses much shallower sources and thus only samples the anisotropy of the upper few kilometres of the crust shows no clear temporal variation however temporal effects cannot be ruled out as large fluctuations in the rate of vt events over the course of the study period as well as changes in the seismic network configuration make it difficult to assess average delay times of approximately 0 2 s similar in magnitude to those reported for much deeper slab events suggest that the bulk of the anisotropy is in the shallow crust we observe clear spatial variations in anisotropy which we believe are consistent with structurally controlled anisotropy resulting from a left lateral transtensional array of faults which crosses the volcanic complex

implications of paleomagnetic data on the collision related bending of island arcs paleomagnetic studies from the marianas central philippines ryukyus sulawesi fiji new hebrides all show major differences in the declination values observed from individual islands within the same arc comparable differences are not observed in the inclination values a simple plate tectonic model would predict that each island arc should experience the same rotation along its entire length as the plate moves around its rotation axis bathymetry from each of these arcs show that the differentially rotated segments of the upper plate occur in areas where the downgoing plate carries a feature such as a seamount chain rifted continental fragment or an island arc the coincidence of the bathymetric feature and the discordant paleomagnetic declination data support an earlier hypothesis of vogt 1973 that these features are buoyant zones on the downgoing plate which interact with the margin of the upper plate as a result of this interaction the upper plate boundary is locally deformed in addition to the paleomagnetic evidence other geologic and geophysical data from these areas suggest such interactions for example there appears to be a good correlation between the deflections in major structures around the collision zone and the paleomagnetic directions that are reported as this deformation proceeds eventually the stresses resulting from the collision may result in any of the following tectonic processes 1 slip line style strike slip faults allowing for the sideward extrusion of portions of the upper plate tapponnier et al 1983 2 changes in the polarity of the subduction zone 3 development of strike slip faults around the margin of the indenter or 4 reorganization of the entire plate margin in addition data from the marianas southern end of the ryukyu arc and the lau basin suggest that back arc basin development may result from the collision related deformation

reconnaissance de structures tectoniques et volcaniques sous marines de l arc recent des petites antilles kick em jenny qualibou montagne pelee nordouest de la guadeloupe abstract a multibeam bathymetric survey seacarib 1 was carried out in april 1985 on board the r v conrad lamont doherty geological observatory off the western coasts of several islands of the lesser antilles complementing a previous survey of the same type arcante 2 thermosite 1980 devoted to adjoining areas in guadeloupe martinique and st lucia it allowed us to precisely map submarine volcanoes in a marginal setting behind the recent arc the main volcanic axis of the archipelago emplaced during the neogene the kick em jenny volcano south of the grenadines is the only active submarine volcano of the lesser antilles it is a small and very young cone probably only tens or hundreds of years old which was hydrothermally active during the survey the directeur volcano guadeloupe is the largest submerged volcanic centre thus far detected in the lesser antilles having been formed between 3 3 and 2 9 ma during the 1980 survey two other large volcanoes were discovered off southern basse terre guadeloupe vieux fort volcano 2 5 2 0 ma and in front of fort de france bay martinique schoelcher volcano older than 4 2 ma several other much smaller volcanoes have been mapped off the same coasts particularly the bouillante seapeaks guadeloupe moreover large tectonic structures cut the recent arc transversally and obliquely the well known qualibou depression on the island of st lucia was interpreted in various ways neither the hypothesis of a large caldera the western side of which collapsed offshore nor the suggestion of a huge rotational gravity slide are confirmed the depression seems more likely to have been controlled by tectonic factors shaping a complex graben structure the seaward extension appears to be restricted to a northern channel the soufriere channel the st pierre fault in martinique is a large transverse feature extending seaward down to some 2000 m depth to the south it bounds the mount pelee active volcanic system and the escarpment of the fault forms a dam against subaqueous pyroclastic flows running down from the volcano these flows are responsible for the unusually smooth morphology of the submarine flanks the zombi fault of northwest guadeloupe is part of a first order feature extending along at least 130 km from montserrat in the north to marie galante in the east this curved fracture cuts across the northern central part of the lesser antilles passing progressively from a subparallel to a transverse orientation with respect to the axis of the island arc these types of surveys are important because they provide better understanding of the structure and recent geological evolution of the recent volcanic arc they are also a useful complementary tool for geothermal and seismological studies

the role of salinity on the dynamics of the arabian sea mini warm pool warmer 28 c sea surface temperature sst occurs in the south eastern arabian sea seas 5 13 n 65 76 e during march april and is known as the arabian sea mini warm pool asmwp in this study we address the role of salinity and the upper layer heat and salt budgets in the formation and collapse of this asmwp an assessment of level 3 sea surface salinity sss data from the soil moisture and ocean salinity smos satellite mission for the year 2010 shows that smos is able to capture the sss variability in the seas analysis of temperature salinity and currents from the hybrid coordinate ocean model hycom during 2003 06 and in situ temperature and salinity data from argo floats during 2003 06 for the seas revealed that low salinity waters cap the top 60 m of the seas in january february this minimum salinity was concurrent with the formation of a barrier layer and with the time when the seas gained little net heat flux and the equatorward flowing east india coastal current eicc fed low saline waters into the seas subsequently the net heat flux increased to a peak value under the increased salinity stratification leading to the formation of the asmwp in march april the asmwp collapsed by may due to increase in sss and the associated weakening of the salinity stratification the monsoon onset vortex in may 2004 could be related to the minimum sss that occurred in february 2004 followed by higher sst and heat content of the asmwp in april 2004

analysis of nrm directions from the rossello composite implications for tectonic rotations of the caltanissetta basin sicily abstract the paleomagnetic results of the pliocene marine marls from the rossello composite section 30 in the caltanissetta basin of sicily have been analysed to determine the amount and timing of tectonic rotations the analysis shows that there is a consistent inclination error for the nrm component which is removed between 500 and 600 c which may be caused by compaction of the sediment differences in inclination error throughout the composite section are related to differing carbonate content a higher carbonate content implying less compaction and smaller inclination error furthermore consistent differences are found between directions of normal and reversed polarities as well as between directions of the lower and upper part of the composite section these differences are to a large extent related to differences in carbonate content porosity and influence of weathering the caltanissetta basin shows a total clockwise rotation of 34 occurring since the early pliocene the magnetostratigraphy of the rossello composite section shows that from the miocene pliocene boundary 5 2 ma up to the gilbert gauss boundary 3 6 ma there were no tectonic rotations of the caltanissetta basin further we speculate that 10 of this total clockwise rotation occurred during approximately kaena times ca 3 05 ma and that at least 24 of this clockwise rotation is younger than the gauss matuyama boundary 2 6 ma

kinematic reconstruction of the caribbean region since the early jurassic abstract the caribbean oceanic crust was formed west of the north and south american continents probably from late jurassic through early cretaceous time its subsequent evolution has resulted from a complex tectonic history governed by the interplay of the north american south american and paleo pacific plates during its entire tectonic evolution the caribbean plate was largely surrounded by subduction and transform boundaries and the oceanic crust has been overlain by the caribbean large igneous province clip since 90 ma the consequent absence of passive margins and measurable marine magnetic anomalies hampers a quantitative integration into the global circuit of plate motions here we present an updated quantitatively described kinematic reconstruction of the caribbean region back to 200 ma integrated into the global plate circuit and implemented with gplates free software our reconstruction includes description of the tectonic units in terms of euler poles and finite rotation angles our analysis of caribbean tectonic evolution incorporates an extensive literature review to constrain the caribbean plate motion between the american continents we use a novel approach that takes structural geological observations rather than marine magnetic anomalies as prime input and uses regionally extensive metamorphic and magmatic phenomena such as the great arc of the caribbean the clip and the caribbean high pressure belt as correlation markers the resulting model restores the caribbean plate back along the cayman trough and major strike slip faults in guatemala offshore nicaragua offshore belize and along the northern andes towards its position of origin west of the north and south american continents in early cretaceous time we provide the paleomagnetic reference frame for the caribbean region by rotating the global apparent polar wander path into coordinates of the caribbean plate interior cuba and the chortis block we conclude that formation of the caribbean plate west of the north and south americas as a result of panthalassa pacific spreading leads to a much simpler plate kinematic scenario than proto caribbean atlantic spreading placing our reconstruction in the most recent mantle reference frames shows that the clip originated 2000 3000 km east of the modern galapagos hotspot and may not have been derived from the corresponding mantle plume finally our reconstruction suggests that most if not all modern subduction zones surrounding the caribbean plate initiated at transform faults two of these along the southern mexican and nw south american margins evolved diachronously as a result of migrating trench trench transform triple junctions

the caribbean and farallon plates connected constraints from stratigraphy and paleomagnetism of the nicoya peninsula costa rica plate kinematic reconstructions play an essential role in our understanding of global geodynamics but become increasingly difficult to constrain back in geological time due to the subduction of oceanic lithosphere here we attempt to kinematically reconstruct the cretaceous and older plate tectonic history of the caribbean plate within the mesozoic panthalassa paleo pacific ocean to this end we present new paleomagnetic data from jurassic and cretaceous oceanic sedimentary and volcanic large igneous province related rocks of the nicoya peninsula and murcielago islands of northwestern costa rica we use these data in combination with constraints from marine magnetic anomalies to infer the age of the lithospheric basement seismic tomography to locate deep mantle plume generation zones and general kinematic feasibility to test different reconstruction scenarios connecting the caribbean plate to the farallon plate as restored from pacific spreading records our resulting reconstruction implies that the western caribbean subduction zone initiated around 100 ma in an intraoceanic setting breaking up oceanic lithosphere of at least 70 myr old

stress interaction between subduction earthquakes and forearc strike slip faults modeling and application to the northern caribbean plate boundary 1 strike slip faults in the forearc region of a subduction zone often present significant seismic hazard because of their proximity to population centers we explore the interaction between thrust events on the subduction interface and strike slip faults within the forearc region using three dimensional models of static coulomb stress change model results reveal that subduction earthquakes with slip vectors subparallel to the trench axis enhance the coulomb stress on strike slip faults adjacent to the trench but reduce the stress on faults farther back in the forearc region in contrast subduction events with slip vectors perpendicular to the trench axis enhance the coulomb stress on strike slip faults farther back in the forearc while reducing the stress adjacent to the trench a significant contribution to coulomb stress increase on strike slip faults in the back region of the forearc comes from unclamping of the fault i e reduction in normal stress due to thrust motion on the subduction interface we argue that although coulomb stress changes from individual subduction earthquakes are ephemeral their cumulative effects on the pattern of lithosphere deformation in the forearc region are significant we use the coulomb stress models to explain the contrasting deformation pattern between two adjacent segments of the caribbean subduction zone subduction earthquakes with slip vectors nearly perpendicular to the caribbean trench axis is dominant in the hispaniola segment where the strike slip faults are more than 60 km inland from the trench in contrast subduction slip motion is nearly parallel to the caribbean trench axis along the puerto rico segment where the strike slip fault is less than 15 km from the trench this observed jump from a strike slip fault close to the trench axis in the puerto rico segment to the inland faults in hispaniola is explained by different distributions of coulomb stress in the forearc region of the two segments as a result of the change from the nearly trench parallel slip on the puerto rico subduction interface to the more perpendicular subduction slip beneath hispaniola the observations and modeling suggest that subduction induced strike slip seismic hazard to puerto rico may be smaller than previously assumed but the hazard to hispaniola remains high

geomagnetic secular variation and the statistics of palaeomagnetic directions in this study we examine the role of palaeosecular variation psv in the use of statistics for palaeomagnetic studies and we provide new reliability criteria for palaeomagnetic poles or directions we first conclude that fisher statistics should not be applied to average palaeomagnetic directions but to virtual geomagnetic pole vgp distributions instead secondly we strongly advocate that typical properties of geomagnetic field behaviour are taken into account in the assessment of palaeomagnetic data sets the latitude dependent properties e s k provide useful guidelines for the reliability of a palaeomagnetic data set a reliable assessment of these properties depends on the sufficient number of palaeomagnetic samples being taken therefore as an additional instrument of assessing data sets we provide a n dependent a95 envelope bounded by an upper limit a95max and a lower limit a95min that helps to ascertain whether or not a distribution has sufficiently well sampled psv and therefore geomagnetic field behaviour applying these criteria is indispensable for studies of geomagnetic behaviour or for studies aiming at using tk03 gad for inclination error correction through the elongation inclination e i method for palaeomagnetic studies aimed at geological reconstructions they form helpful guidelines and increase the confidence in the rocks having faithfully recorded the field an analysis of published eastern mediterranean data shows that the vast majority of studies do not conform to the van der voo criteria in particular with respect to n and a95 we have provided criteria that are on the one hand more lenient lower n may still provide relevant information and on the other hand more strict for high n the criterion of a95 16 should be adapted to a requirement of lower a95 e g a95 80

molecular and isotopic analysis of anaerobic methane oxidizing communities in marine sediments convergent lines of molecular carbon isotopic and phylogenetic evidence have previously indicated hinrichs k u hayes j m sylva s p brewer p g delong e f 1999 methane consuming archaebacteria in marine sediments nature 398 802 805 that archaea are involved in the anaerobic oxidation of methane in sediments from the eel river basin offshore northern california now further studies of those same sediments and of sediments from a methane seep in the santa barbara basin have confirmed and extended those results mass spectrometric and chromatographic analyses of an authentic standard of sn 2 hydroxyarchaeol hydroxylated at c 3 in the sn 2 phytanyl moiety have confirmed our previous tentative identification of this compound but shown that the previously examined product was the mono tms rather than di tms derivative further analyses of 13 c depleted lipids appreciably more abundant in samples from the santa barbara basin have shown that the archaeal lipids are accompanied by two sets of products that are only slightly less depleted in 13 c these are additional glycerol ethers and fatty acids the alkyl substituents in the ethers mostly monoethers with some diethers are non isoprenoidal the carbon number distributions and isotopic compositions of the alkyl substituents and of the fatty acids are similar suggesting strongly that they are produced by the same organisms their structures n alkyl and methyl branched n alkyl require a bacterial rather than archaeal source the non isoprenoidal glycerol ethers are novel constituents in marine sediments but have been previously reported in thermophilic sulfate and nitrate reducing organisms which lie near the base of the rrna based phylogenetic tree based on previous observations that the anaerobic oxidation of methane involves a net transfer of electrons from methane to sulfate it appears likely that the non archaeal 13 c depleted lipids are products of one or more previously unknown sulfate reducing bacteria which grow syntrophically with the methane utilizing archaea their products account for 50 of the fatty acids in the sample from the santa barbara basin at all methane seep sites examined the preservation of aquatic products is apparently enhanced because the methane oxidizing consortium utilizes much of the sulfate that would otherwise be available for remineralization of materials from the water column

what drives microplate motion and deformation in the northeastern caribbean plate boundary region the north caribbean plate boundary zone is a broad deformation zone with several fault systems and tectonic blocks that move with different velocities the indentation by the bahamas platform the bahamas collision is generally invoked as a cause of this fragmentation we propose that a second driver of deformation is the western edge of the south dipping puerto rico slab moving sideways with the north america plate the westward motion of the slab edge results in a push on the caribbean plate farther west we refer to this second mechanism for deformation as slab edge push the motion of the north america plate relative to the caribbean plate causes both drivers to migrate from east to west the bahamas collision and slab edge push have been operating simultaneously since the miocene the question is the relative importance of the two mechanisms we use mechanical finite element models that represent the two mechanisms from the late oligocene 30 ma to the present for the present both models successfully reproduce observed deformation implying that both models are viable back in time the slab edge push mechanism better reproduces observations neither mechanism successfully reproduces the observed miocene counterclockwise rotation of puerto rico we use this rotation to tune a final model that includes fractional contributions of both mechanisms we find that the slab edge push was the dominant driver of deformation in the north caribbean plate boundary zone since 30 ma

paleomagnetic constraints on the mesozoic cenozoic paleolatitudinal and rotational history of indochina and south china review and updated kinematic reconstruction abstract paleomagnetic data have long been used to hypothesize that the cenozoic extrusion of the indochina block along the left lateral ailao shan red river fault as a result of the india asia collision may have been associated with a major southward paleolatitude shift of as much as 10 15 and a vertical axis rotation of as much as 25 40 however although numerous paleomagnetic studies have been conducted in the southeast margin of the tibetan plateau and in the indochina region during the last few decades the detailed rotation as well as the latitudinal displacement of the indochina block remain controversial because of apparently contradicting paleomagnetic results geological constraints also yield contrasting estimates on the amount of displacement along different segment of the ailao shan red river fault 700 200 km in the northwest but only 250 km in the southeast in this paper the available paleomagnetic data from the southeast margin of the tibetan plateau and indochina as well as the south china block from jurassic and younger rocks are compiled and critically reviewed using the new paleomagnetic toolkit on paleomagnetism org our results show that 1 the south china block has declinations that reveal no significant rotations relative to eurasia since latest jurassic inclinations are consistently shallower than expected which is likely the result of inclination shallowing in sedimentary rocks 2 there is no paleomagnetically resolvable southward motion of the indochina block with respect to eurasia based on the paleomagnetic data paleomagnetic inclinations are in fact lower than expected probably due to inclination shallowing in sediments 3 paleomagnetic declinations reveal large more or less coherently rotating blocks in the northern indochina domain and the se tibetan margin that rotated up to 70 clockwise much more than the 10 15 rotation of the stable se part of the indochina block these blocks are bounded by fold thrust belts and strike slip faults which we interpret to have accommodated these block rotations during the cenozoic we designed a new tool on the online open access portal paleomagnetism org that allows testing whether euler rotations in a kinematic reconstruction fulfill paleomagnetic data using this tool we built a first order kinematic reconstruction of rotational deformation of northwest indochina in cenozoic we show that the northwestern part of indochina extruded 350 km more along the ailao shan red river fault than the southeastern part accommodated by internal northwest indochina rotation and deformation estimates of 250 km of extrusion of the southeastern part of the indochina then predicts 600 km of left lateral motion along the northwestern part of the ailao shan red river fault which reconciles the small and large estimates that prevail in the literature of extrusion of indochina from the tibetan realm during the cenozoic india asia collision

arc parallel extension and localization of volcanic complexes in guadeloupe lesser antilles 1 subduction of atlantic seafloor under the caribbean plate causes shallow earthquakes within the lesser antilles volcanic arc such earthquakes above the subduction interface show strike slip or normal fault plane solutions the latter with e w striking nodal planes to better assess seismic hazard and the coupling between volcanism and tectonics we investigated faulting related to overriding plate deformation in the guadeloupe archipelago using aerial photographs satellite spot images and topographic maps 1 25000 scale we mapped active and middle to late pleistocene fissures and normal fault systems that cut the uplifted coral platforms grande terre and marie galante and the volcanic rocks of basse terre the available marine geophysical data show that the faults extend offshore to bound submarine rifts the e w striking 1500 m deep v shaped marie galante rift separates the two islands of marie galante and grande terre normal faults in the north of grande terre appear to mark the similarly v shaped western termination of the 5000 m deep n 50e to n130 e striking desirade graben three shallow m 5 5 earthquakes 6 may 1851 29 april 1897 3 august 1992 appear to have ruptured segments of the marie galante rift boundary faults the young la grande decouverte volcanic complex of basse terre including the 1440 a d soufriere dome lies within the western termination of the marie galante rift the ancient volcanic shoulders of the rift buttress the active dome to the north and south which may explain why major prehistoric sector collapses and pyroclastic avalanches have been directed southwestward into the caribbean sea or southeastward into the atlantic ocean the marie galante rift is typical of other troughs transverse to the northeastern edge of the caribbean plate we interpret such troughs which are roughly orthogonal to the arc to result from slip partitioning and extension perpendicular to plate convergence that they disappear southward implies that they result from interaction between the caribbean and north american plates

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