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

the correction for sediment loading on the seafloor available measurements of sediment velocity and density indicate that a factor of 600 m s 1 of two way sediment reflection time will correct seafloor depth to yield basement depth in the absence of sediment loading this simple linear relation is derived from the results of six deep drill holes in abyssal sediments of the north and south atlantic oceans the relation predicts the sediment correction with an accuracy of about 50 m regardless of the lithology sampled down to a depth of 1 5 s of reflection time the cost wells on the u s continental shelf and empirical relations among velocity density porosity and depth provide estimates of the deeper behavior of abyssal sediments and suggest that the 600 m s 1 factor continues to provide a satisfactory sediment correction to a depth of 3 s

time of sinistral slip along the polochic fault of guatemala abstract the polochic fault of guatemala and chiapas mexico was a neogene transform segment of the north american caribbean plate boundary with a total sinistral slip of 130 km principal activity was within the interval from about 10 3 to 6 6 m y b p or less a time bracket based upon k ar ages from volcanic rock clasts in the colotenango beds of northwest guatemala earliest possible movement was established from ages of volcanic rock constituents of the older colotenango conglomerates deposited by streams that flowed north from a terrane now in central guatemala and onto terrane that was subsequently offset along the polochic fault it is believed that the selegua river was connected to the chixoy river of central guatemala this river system deposited the older part of the colotenango conglomerate now in western guatemala about 130 km west of its source area two volcanic clasts from the conglomerate yield ages of 12 3 1 0 and 10 3 1 0 m y the younger age is believed to set the maximum age of sedimentation of this older part of the conglomerate and is probably close in time to initiation of fault activity distinctive brown serpentinite clasts in the conglomerate have been shown to be petrographically mineralogically and geochemically similar to serpentinite from the presumed source area north of salama guatemala a youngest age of major offset is established by the younger part of the colotenango beds a volcaniclastic deposit which fills much of the ancient polochic fault controlled cuilco river valley our studies of volcanic clasts of the younger colotenango conglomerate reveal pristine glass attesting to its relatively young age k ar determination establishes an age of 6 6 0 3 m y b p for these clasts the youngest age of movement has not been established with certainty it lies between the 6 6 m y age and the age of the uppermost volcaniclastic valley fill the synchroneity of spreading in the cayman trough macdonald and holcombe 1978 with transform activity along the polochic suggests strongly that the two were genetically related the earliest data in the bracketed time interval correlates with the age of ongoing spreading for the mid cayman rise the mid miocene to pliocene volcanic arc 9 19 m y b p of mexico and its probable continuation in guatemala 8 19 m y b p sinistrally offset across the polochic fits well with the chronology discussed above for the polochic

paleogene continental margin truncation in southwestern mexico geochronological evidence the reasons for and mechanisms of continental margin truncation in sw mexico where mesozoic cenozoic plutons are situated directly on the pacific coast are not yet well understood large scale dextral and or sinistral displacements of the continental margin terranes now forming parts of baja california or the chortis block have been proposed the well defined along coast nw se decreasing granitoid intrusion age trend 1 2 cm yr in the 100 ma 40 ma time interval between puerto vallarta and zihuatanejo is interpreted by us to be a geometric artifact of oblique continental margin truncation rather than the consequence of a sinistral offset of the chortis block from those latitudes toward the se changes in the dip and velocity of the nnw sse trending cretaceous tertiary subduction zone resulted in a landward migration of the magmatic arc taking into account certain stratigraphic affinities of chortis and the oaxaca and mixteca terranes together with the known displacement rates along the north america caribbean plate boundary the northwesternmost paleoposition of the chortis block with respect to sw mexico was near zihuatanejo in contrast between zihuatanejo and the isthmus of tehuantepec the cessation of the tertiary magmatism decreased more rapidly 7 7 cm yr although the trend is not so obvious starting in the late eocene chortis moved about 1100 km to the se along a transform boundary associated with the opening of the cayman trough based on our geochronological data and structural relationships between mylonite zones and plutons in the acapulco tehuantepec area we propose an approximately 650 km se movement of chortis from about 40 25 ma with a velocity of 6 5 4 3 cm yr since this is considerably slower than the decreasing age trend obtained by us using the geochronological data we consider batholith formation in this segment to predate and postdate the offshore passage of the north america farallon caribbean triple junction geological observations and paleomagnetic data do not give strong support for large scale right lateral displacements of crustal blocks like the baja california given the isotopic data presented the continental margin truncation in sw mexico seems to be the consequence of an interaction of mechanisms of these we regard tectonic erosion associated with the subduction process to be the most important in the northwestern segment on the other hand the lateral removal of material associated with the displacement of chortis is more important in the southeastern segment

deepwater carbonate deposition in response to re flooding of carbonate bank and atoll tops at glacial terminations the late quaternary has experienced large glacial interglacial climatic variations and related 10 s to 100 meters high amplitude sea level fluctuations at milankovich frequencies from 10 s to 100 kyr during which carbonate platform tops have been exposed and re flooded in many occasions this study focuses on the accumulation of calci turbidites the aragonite onset sharp increase in fine sediments and their timing in deep basins adjacent to carbonate platforms a particular emphasis is developed on the occurrence of the first gravity flow event and aragonite onset sharp increase and their linkage to the initial re flooding of the platform tops during deglaciations three basins adjacent to isolated platforms in the bahamas the northern nicaragua rise and the gulf of papua were selected to represent pure carbonate versus mixed systems in quiescent versus tectonically active settings and various carbonate bank top morphologies ranging from atoll to relatively deeply and narrowly flooded flat top banks in spite of these differences each record illustrates a clear relationship between the timing of platform top re flooding and initiation of significant carbonate export by gravity flows and low density plumes into the surrounding basins the concept of re flooding window is introduced to characterize the prolific period of time during which bank and atoll tops are flooded enough to produce large export of bank derived aragonite and of calci turbidites in adjacent basins according to our datasets the main re flooding windows have occurred mainly on the last part of the sea level rise at each glacial termination t those periods being marked by some of the highest rates of sea level rise the analysis of a long piston core from the earthquakes prone walton basin northern nicaragua rise demonstrates that sea level not seismic activities played a major role as trigger mechanism for the initiation of gravity flows since the last four glacial interglacial transitions and supports the existence of an extra glacial termination during the early portion of the transition from mis 7 4 to mis 7 3 tiiia

difference in acoustic properties at seismogenic fault along a subduction interface application to estimation of effective pressure and fluid pressure ratio abstract fluid pressure along subduction plate boundaries plays a role in seismogenesis and tsunami genesis because it is strongly related to the physical properties of faults in this study we conducted p wave velocity vp and s wave velocity vs measurements for the hanging wall and footwall of a fossil subduction interface with pseudotachylyte located at the northern edge of the mugi melange in the cretaceous shimanto belt shikoku southwest japan this area corresponds to the depth of the shallow seismogenic zone in the transition zone between the inner and outer wedges by combining the acoustic properties with parameters obtained from amplitude variation with offset avo analysis on the nankai seismic profile we estimated the fluid pressure at the seismogenic fault the mugi melanges are composed of shale matrices and are juxtaposed with the coherent unit of the hiwasa formation in the north which is composed mainly of sandstone we collected 5 sandstone samples from the hanging wall hiwasa formation and 4 mudstone samples from the footwall mugi melange we conducted velocity measurements while controlling both the fluid pressure and confining pressure by using two pumps the effective pressure in each measurement ranged from 5 to 65 mpa with intervals of 5 mpa the vp and vs of sandstone increase exponentially with effective pressure from 4500 to 5000 m s and 2500 to 3000 m s respectively the vp and vs of the mudstone also increased exponentially from 4100 to 4500 m s and 1900 to 2200 m s respectively we used avo parameters along the decollement based upon a seismic profile of the nankai trough which is off muroto 40 45 km landward from the trench axis corresponding to approximately 66 mpa of effective pressure under a hydrostatic condition by combining the velocities obtained from this study and the avo parameters derived from the muroto seismic data we estimate the mean effective pressures for the hanging wall and the footwall as approximately 10 20 mpa and 8 10 mpa respectively the normalized fluid pressure ratios for the hanging wall and the footwall correspond to approximately 0 82 0 91 and 0 91 0 93 respectively this high fluid pressure indicates a very low effective friction coefficient along the decollement in the transition zone possibly causing a rupture to propagate to the shallower outer wedge and thus generating a large tsunami

depth and age in the cayman trough abstract caribbean plate boundaries are almost everywhere either strike slip or convergent so oceanic crust accreted at the spreading axis within the cayman trough provides information critical to determining the relative motions and tectonic interactions among the caribbean and surrounding plates the tectonic evolution of the trough as inferred from magnetic anomaly identifications is not entirely compatible with either its crustal subsidence or the geological evidence for time of opening and rate of offset movement along the north american caribbean plate boundary a close examination of basement topography and depth within the trough suggests that the total opening of the cayman trough is about 1100 km and that this opening occurred in two stages crust generated by the present ongoing stage of very slow spreading has extensive relief and shows a distinct increase of crustal depth with increasing distance from the spreading center crust generated by an earlier episode of faster spreading is characterized by reduced topographic relief and no appreciable differential subsidence and is separated from the younger crust by distinct topographic breaks the rate of spreading of the current slow spreading episode is15 5mm yr based upon a new crustal subsidence curve which accommodates lateral as well as vertical cooling of the accreting slab the trough has opened at this rate for about 30 ma the rate of opening prior to 30 ma cannot be determined with any reliability from crustal subsidence a reexamination of magnetic anomalies in the central part of the trough shows that these anomalies can be generated at a much slower spreading rate than previously thought this revised interpretation of cayman trough evolution brings magnetic subsidence and geological evidence into much better agreement

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

neogene north american caribbean plate boundary across northern central america offset along the polochic fault abstract the polochic fault was a segment of the north american caribbean plate boundary across central america in the neogene its 130 km of left slip was previously determined by matching structures and stratigraphie outcrop patterns of northwest and central guatemala across the fault additional support for the model and the youthfulness of the recorded offset comes from an essentially perfect match of major geomorphic features across the fault a reconstruction process which eliminates 123 km of left slip brings together rivers and drainage divides that existed before the polochic became active with the reconstruction carried across the isthmus on an east west fault the regional structural geology assumes the coherent pattern of a continuous orogenic belt whose geometry is compatible with the model of collisional tectonics centered on the motagua suture zone confined within this belt narrowed to some 60 km by the reconstruction lie the major laramide thrusts folds and tectonically emplaced serpentinites of guatemala crystalline rocks of guatemala re join the chiapas massif and paleozoic sedimentary rocks exposed in the core of an almost continuous anticlinorium extend from southern chiapas to lake izabal the polochic does not bend in eastern guatemala but continues eastward to the motagua fault where it dies westward drift of the northern block resulted in rifting which extended from eastern guatemala into the caribbean along the cayman trough the honduras depression may represent an element of a triple junction along with the polochic and izabal cayman rift the polochic continues westward into the pacific ocean and offsets the middle america trench the polochic has offset the miocene volcanic belt of northern central america confirming the previous estimate of a neogene time of movement about 300 km of relative east west neogene displacement has been recorded on the mid cayman rise only 130 km of which can be accounted for across the polochic it is suggested that cumulative extension on north south faults south of the motagua fault zone between the trench and the honduras depression might make up that difference

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

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

southeastern caribbean sea level variability and viscoelastic relaxation viscoelastic modeling of earthquakes in the southeast caribbean shows that distant dip slip earthquakes in the lesser antilles and the geometry of the subduction zone play a significant role in vertical deformation observed along the southern caribbean plate margin we find that dip slip earthquakes yield vertical displacements that are 1 2 orders of magnitude greater than those generated by strike slip earthquakes along the caribbean south american plate boundary in addition postseismic vertical displacements are at least as great or greater at distances of several hundred kilometers than the coseismic counterpart depending upon the geometry of the source tide gage data from venezuela suggest that these vertical displacement rates may still be observed several decades after the occurrence of large subduction zone earthquakes ms 7 or greater in addition the uplift rate observed at the tide gages largely follows the anticipated flexure of the caribbean plate due to the subduction process

use of the resistivity method in geological mapping case histories from raniganj coalfield india the effectiveness of the electrical resistivity method has been studied using various configurations with different spacings over the southern boundary fault in the northwestern part and across a dolerite dyke named salma dyke in the central part of the raniganj coalfield india it has been observed that the delineation of the fault and the dyke was made possible under differential tropical weathering conditions geoelectric sections across the fault and the dyke have been prepared on the basis of schlumberger sounding results in profiling wenner two electrode half schlumberger and part of al chalabi s configurations were applied over the southern boundary fault across the dyke alpha beta and gamma wenner schlumberger half schlumberger and two electrode configurations were employed azi muthal two electrode sounding was also studied over the fault the interpretation of the results of apparent resistivity profiles across the southern boundary fault suggests that the wenner and two electrode configurations possess certain diagnostic features which help in mapping a single lithological contact provided sufficient resistivity contrast exists although schlumberger configuration seems to be quite suitable other configurations may also be usefully employed over the dyke

a review of volcanic island evolution and magma production rate an example from a cenozoic island arc in the caribbean different stages of volcanic island evolution are evident in the cenozoic lesser antilles arc developed near the eastern edge of the caribbean plate the early stage of seamount evolution is represented by the kick em jenny submarine volcano near the southern end of the arc the volcanically active islands known as the volcanic caribbees are composed of a series of composite volcanoes and are examples of an emergent volcanic island stage those islands that were formerly active known as the limestone caribbees provide evidence that an erosional to submergent stage occurred in the northern part of the island arc during the oligocene and miocene epochs growth of the islands and underlying crust is dependent upon the magma production rate along the arc which has for the last 100 ka ranged from less than 1 km 3 to 40 km 3 these differences in magma production and volcanic rock composition along the arc are attributed to the obliquity of plate convergence and the plate convergence rates

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

geologic investigations in the cayman trough evidence for thin oceanic crust along the mid cayman rise the mid cayman rise is a 110 km long accreting plate boundary 2cm yr full rate characterized by a deep rift valley eighteen transponder navigated dives were made by the submersible alvin along the rift valley walls in two areas on opposite sides of the rift valley the relief of the walls is produced by a large number of inward facing small throw fault escarpments with vertical displacements ranging from a few tens of meters to perhaps as much as 400 m from these escarpments 142 samples were collected and gabbroic rocks 116 samples characterized by a wide range of compositions and a complex metamorphic history predominate in number over other rock types basalt serpentinized ultramafic we interpret the assemblage of rocks exposed on the escarpments to indicate that a shallow level magma reservoir exists beneath the axis of accretion at the mid cayman rise and creates anomalously thin oceanic crust with a carapace of only several hundreds of meters of diabase and basalt this carapace is und

uplift and subduction erosion in southwestern mexico since the oligocene pluton geobarometry constraints details of the late oligocene to middle miocene uplift and tectonic erosion episodes of the southwestern continental margin of mexico can be inferred using altot geobarometry of igneous hornblendes geochronology and field relations on the basis of such analyses carried out between acapulco and huatulco we find the following 1 calc alkaline batholiths exposed along the coast from acapulco to huatulco mostly in the 35 25 ma age range were emplaced at depths between 13 and 20 km 2 the contact relationships between these plutons and their host rocks and the exposure of volcanic counterparts 70 km from the coastline indicate a landward decrease in the amount of uplift 3 a comparison of the time differences between intrusion and cooling ages of batholiths along the coast suggest that cooling rates were in general higher between acapulco and huatulco than those along the margin between puerto vallarta and manzanillo 700 km northwest of acapulco 4 the uplift of this coastal belt occurred during the late stages of magmatism and after its cessation triggering intensive subaerial erosion of supracrustal rocks and the exposure of midcrustal rocks such as granitic batholiths and amphibolite facies metamorphic assemblages of the xolapa complex these findings in conjunction with the geometry of the present continental margin as well as the offshore tectonic and stratigraphic features support previous interpretations of very active late oligocene to middle miocene subduction erosion after the onset of strike slip tectonics related to the detachment and subsequent eastward displacement of the chortis block subduction erosion involved both trench sediments and crystalline continental framework rocks different rates of continental framework erosion are assessed on the basis of the bathymetric fluctuations of the upper slope trench sediments and the age of the accretionary prism subsidence of the offshore continental basement suggests intense episodes of basal erosion of lower continental crust whereas the construction of the present day accretionary prism and the uplift of the upper slope indicate a decline in the frontal and basal erosion of the continental framework comparing the calculated depths of pluton crystallization with the present depth of the continental crust subducted slab boundary interpreted using previously published seismic refraction and gravity models we conclude that onshore basal erosion played a subordinate role during miocene episodes of subduction erosion major removal of lower crustal sections was probably restricted to offshore regions plate reconstructions of the cocos plate and its predecessors with respect to north america indicate that the uplift and probably the offshore subduction erosion in this region coincided with the initial stages of the subhorizontal trajectory of the guadalupe plate beneath southwestern mexico

post miocene cayman trough evolution a speculative model the cayman trough exhibits cross trough lineations which we interpret as crustal fabric formed parallel to the spreading center at the time of crustal generation alignment and variations of the spreading fabric are roughly symmetrically distributed about the mid cayman spreading center as are variations in the cross trough width of the cayman trough these suggest to us a simple eight stage model of stepwise varying spreading directions and rates for this model it is assumed that 1 tectonic spreading fabric is perpendicular to spreading direction 2 cross trough extension both widens the trough and lengthens the spreading center and 3 cross trough compression narrows the trough but does not shorten the spreading center combining the spreading fabric lineation data with these assumptions we predict a cross trough width variation that is essentially that of the cayman similar variations in spreading direction should be evidenced elsewhere on the plate boundary if the variations we observe do in fact record the history of changes in relative motion between the north american and caribbean plates

sedimentary architecture structural setting and late cenozoic depocentre migration of an asymmetric transtensional basin lake izabal eastern guatemala abstract lake izabal located in eastern guatemala lies in an ew trending basin located along the transform margin between the north american and caribbean plates this plate boundary consists of two main left lateral strike slip faults known as the polochic and motagua fault system pmfs the basin is a 100 20 km lens shaped depression in which the lake occupies its eastern half to the north the basin is confined by a principal deformation zone pdz which is recognized in this area as the most important upper crustal branch of the polochic fault the eastern part of the basin has been uplifted and dissected exposing the basin infill along the slopes of the montana del mico analysis of a set of multichannel seismic reflection profiles most of them acquired within the lake combined with well and outcrop information allowed to outline the structure and evolution of the basin and its stratigraphic architecture the basin is strongly asymmetrical both in cross and along strike directions and is filled up by neogene to quaternary sediments with the deepest side of the basin being to the north close and parallel to the pdz the base of the infill is a mid tertiary unconformity whose differential subsidence through time brought the basin to its present structural setting five main evolutionary stages are recognized based on seismo stratigraphic and structural features which are related to the development and activity of the bordering faults development of the basin began in its easternmost sector a small half graben tilted to the south developed in response to the activity of an oligocene or early middle miocene growth fault in the second stage late miocene the basin tilts to the north causing the sedimentary sequences to thicken towards the northern pdz this stage is dominated by oblique extension and by progressive migration of the basin depocenter towards the west the third stage early pliocene records a strong acceleration of the strike slip activity which causes a rapid westward migration of the depocenter the fourth stage late pliocene although still dominated by regional transtension is related to the development of a transpressional event along the eastern side of the basin as evidenced by the occurrence of folds and reverse faults parallel to the northern bend of the polochic fault during the fifth stage quaternary the eastern part of the basin remains relatively quiescent while the western part undergoes subsidence with localized transtension still related to the activity in this sector of the polochic fault left lateral movement along the polochic fault caused the depocenter to migrate 75 80 km at different velocities with slip rates ranging between 2 1 and 16 3 mm yr this study suggests that the polochic fault developed in the early middle miocene in connection to the deposition of the early sediments of the izabal basin even though an older age oligocene could also be possible to our knowledge this is one of the best examples of sedimentary architecture documenting depocentre migration due to fault movement along a transform system

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

deformation of jamaica and motion of the gonâve microplate from gps and seismic data summary we use velocities from 20 gps sites on the island of jamaica and seismic data from the jamaican seismic network to quantify motion of the proposed gonave microplate and study deformation and earthquake hazard in jamaica all 20 jamaican gps sites move significantly relative to both the caribbean and north american plates thereby confirming the existence of the gonave microplate in a caribbean plate reference frame the fastest site velocities in jamaica are 8 1m m yr 1 representing a minimum estimate for the rate of gonave caribbean plate motion we estimate a firm upper limit of 13 1m m yr 1 for gonave caribbean plate motion assuming that additional elastic or permanent deformation occurs north of jamaica beyond the reach of our gps network the range of estimates for gonave caribbean plate motion exceeds the 3 7m m yr 1 range of geologically derived rates for post 10 ma fault slip in jamaica suggesting that motion has either increased relative to the long term deformation rate or that estimates of the long term deformation rate are too slow minimum and maximum rates for gonave north america plate motion are 6 1m m yr 1 and 11 1m m yr 1 based on the differences between the estimated gonave caribbean rates and a recent gps based estimate of 19 3 1m m yr 1 of caribbean north american plate motion in jamaica these are slower than 15 20 mm yr 1 published estimates of the long term seafloor spreading rate across the cayman spreading centre which records gonave north american plate motion our observations are thus consistent with a model in which gonave caribbean plate motion has increased through time while gonave north america plate motion has decreased possibly reflecting a progressive transfer of slip from plate boundary structures that accommodate gonave north america motion to faults that carry gonave caribbean plate motion in jamaica gps site directions in both the caribbean and north american plate reference frames are parallel to the caribbean north america plate slip direction and are only 10 20 different from the azimuths of the island s major strike slip faults the mean p and t axes for 48 earthquakes since 1941 have near horizontal plunges and are oriented 45 from the predicted plate slip direction the kinematic and seismic data thus indicate that deformation on the island is dominated by left lateral shear along largely e w trending strike slip faults relative to the caribbean plate the jamaican gps velocities exhibit a nearly monotonic increase in site velocities from south to north along a transect orthogonal to the island s major e w faults this velocity gradient likely reflects the accumulation of elastic strain due to frictional locking of the major e w faults velocities however also increase monotonically from the wsw to ene along a transect orthogonal to the island s numerous nnw striking faults consistent with the accumulation of significant elastic shortening along those faults and supportive of an interpretation of those faults as restraining bends seismic hazard assessment based on the gps derived deformation budget likely maximum fault rupture lengths and the historical seismic record suggests approximate repeat times of one to several centuries for earthquakes of maximum magnitudes of m w 7 0 7 3 the strain that has accumulated since the destructive 1692 earthquake near the capital city of kingston is presently sufficient to release a m w 7 2 earthquake in eastern jamaica

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

caribbean tectonics and relative plate motions during the last century three different ways of interpreting the tectonic evolution of the gulf of mexico and the caribbean have been proposed taking into account the bailey willis school of a permanent pre jurassic deep sea basin the edward suess school of a subsided continental terrain and the alfred wegener school of continental separation the present investigation is concerned with an outline of an interpretation which follows that of pindell and dewey 1982 an attempt is made to point out ways in which the advanced hypotheses can be tested the fit of africa north america and south america is considered along with aspects of relative motion between north and south america since the early jurasic attention is given to a framework for reconstructing caribbean plate evolution the evolution of the caribbean the plate boundary zones of the northern and southern caribbean and the active deformation of the caribbean plate

a plate kinematic framework for models of caribbean evolution abstract we define the former relative positions and motions of the plates whose motions have controlled the geological evolution of the caribbean region newly determined poles of rotation defining the approximate spreading histories of the central north and the south atlantic oceans are given for the late jurassic early cretaceous anomaly sequence of the central north atlantic we have used previously published definitions of fracture zone traces and magnetic anomaly picks redetermining the pole positions and angular rotations for various isochrons on an evans and sutherland interactive graphics system for magnetic anomalies younger than the cretaceous quiet period in both oceans we 1 used seasat altimeter data to help define fracture zone traces and 2 identified and used marine magnetic anomalies to determine the positions of spreading isochrons along the flowlines indicated by the fracture zones by the finite difference method the relative paleopositions and the relative motion history between north and south america were computed this analysis defines the size and shape and the rate at which the size and shape changed of the interplate region between north and south america since the middle jurassic thus a plate kinematic framework is provided for the larger plates pertaining to the caribbean region in which can be derived more detailed scenarios for gulf of mexico and caribbean evolution north and south america diverged to approximately their present relative positions from late triassic to early campanian about 84 m y ago time this is the period during which the gulf of mexico and a proto caribbean seaway were formed since the campanian only minor relative motion has occurred from early campanian through to middle eocene times south america diverged only another 200 km and since the middle eocene minor n s convergence has occurred these very minor post early campanian motions have probably been accommodated by imperfect shear and compression along the atlantic fracture zones to the east of the lesser antilles and along the northern and southern borders of the caribbean plate accordingly it is suggested that from campanian time to the present the relative motions between the north and south american plates have had only minor effects on the structural development of the caribbean region primarily using the data of engebretson et al the convergence history of pacific plates with north america was calculated for two points near the western caribbean by completing finite difference solutions the convergence history of the pacific plates with the caribbean and south american plates can be approximated the direction and rate of convergence of the pacific plates with the americas may have controlled the style of subduction and possible microplate migration along the north american south american and western caribbean boundaries that define the eastern pacific plate margin