structural evolution of the la trocha fault zone oblique collision and strike slip basins in the cuban orogen 1 the la trocha fault zone acted as a major left lateral transfer zone and is bounded by the la trocha ltf zaza tuinicu ztf cristales ctf and taguasco tgf faults these faults were consistent with the clockwise rotation of convergence and shortening in central cuba from the paleocene to the early eocene 65 48 ma a ssw nne shortening produced transtension in the ltf and transpression in the ztf subsequently during the middle eocene 48 37 ma shortening shifted to a sw ne direction resulting in the normal component of the ltf and transpression in the ztf and ctf since the late eocene 37 ma central cuba has been welded to the north american plate the post welding deformation gave rise to transtension of the ltf and tgf this deformation is consistent with a wsw ene shortening and reflects activity in the transform boundary of the cayman trough both the normal and thrust displacements of these previous faults are corroborated by structural data whereas left lateral displacement is deduced from the concordance between oblique collision and structural features plate kinematics and the structural evolution of the la trocha fault zone indicate that the related central basin is a strike slip polygenetic basin and that the formation of this system i e fault zone strike slip basin was a consequence of the paleogene oblique collision between the caribbean volcanic arc and the bahamas borderland north american plate

the early pliocene re colonisation of the deep mediterranean sea by benthic foraminifera and their pulsed late pliocene middle pleistocene decline abstract article history received 11 november 2008received in revised form 28 january 2009accepted 30 january 2009keywords pliocene pleistoceneextinction of deep sea foraminiferadeep sea circulationre colonisationmediterranean sea ninety ve species and 19 genera of cosmopolitan deep sea benthic foraminifera belonging to the familiespleurostomellidae stilostomellidae and nodosariidae became extinct during the late pliocene middlepleistocene only 50 of these 44 species were present in the pliocene or pleistocene of the deepmediterranean sea odp sites 654 966 967 975 976 being those which had successfully migrated in viathe strait of gibraltar from the deep atlantic following the annihilation of the mediterranean deep sea faunaduring the late miocene messinian crisis most colonisation occurred within the rst 0 8 myrs 5 3 4 5 ma after re establishment of the mediterranean atlantic link with possibly a second lesser period ofimmigration in the late pliocene 3 4 3 0 ma we infer that colonisations may have been fortuitous andfew in number as some common members of the group in the atlantic never succeeded in establishing in themediterranean sea there is no evidence of any new immigration events during the pleistocene implyingthat the present anti estuarine circulation may have been in place throughout this period our studiessuggest that these deep water low oxygen tolerant foraminifera survived the many periods of deep watersapropel formation in the pliocene early pleistocene possibly in somewhat shallower 500 m refuges withdysoxic rather than anoxic conditions the pliocene pleistocene stratigraphic record of this group of elongate cylindrical benthic foraminifera withconstricted and specialised apertures is similar in the west and east mediterranean basins the groupdeclined in abundance ux and diversity in two pulses during the late pliocene 3 1 2 7 ma and the lateearly pleistocene 1 3 1 0 ma in concert with global southern sourced deep water sites aabw cpdw and earlier than the single decline 1 0 0 6 ma in global intermediate water sites unadw aaiw allspecies with one possible exception disappeared earlier in the mediterranean than globally the highestoccurrence of any species of this group in mediterranean sites was 0 8 0 43 ma comparable with 0 7 0 2 maoutside with the youngest survivors being in abyssal deep water thus despite the unusual oceanographic conditions and isolation the deep mediterranean sea was in thiscase neither the centre for the evolution of new species nor a refuge where species survived after they haddisappeared elsewhere 2009 elsevier b v all rights reserved

petrofabrics of high pressure rocks exhumed at the slab mantle interface from the point of no return in a subduction zone sivrihisar turkey the highest pressure recorded by metamorphic rocks exhumed from oceanic subduction zones is 2 5 gpa corresponding to the maximum decoupling depth mdd 80 10 km identified in active subduction zones beyond the mdd the point of no return exhumation is unlikely the sivrihisar massif turkey is a coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record p t fluid deformation conditions during exhumation from 80 to 45 km crystallographic fabrics and other features of high pressure metasedimentary and metabasaltic rocks record transitions during exhumation in quartzite microstructures and crystallographic fabrics record deformation in the dislocation creep regime including dynamic recrystallization during decompression and a transition from prism slip to activation of rhomb and basal slip that may be related to a decrease in water fugacity during decompression 2 5 to 1 5 gpa phengite lawsonite and omphacite or glaucophane in quartzite and metabasalt remained stable during deformation and omphacite developed an l type crystallographic fabric in marble aragonite developed columnar textures with strong crystallographic fabrics that persisted during partial to complete dynamic recrystallization that was likely achieved in the stability field of aragonite p 1 2 gpa results of kinematic vorticity analysis based on lawsonite shape fabrics are consistent with shear criteria in quartzite and metabasalt and indicate a large component of coaxial deformation in the exhuming channel beneath a simple shear dominated interface this large coaxial component may have multiplied the exhuming power of the subduction channel and forced deeply subducted rocks to flow back from the point of no return

counterclockwise p t t paths from amphibolites franciscan complex california relics from the early stages of subduction zone metamorphism overprinting mineral relationships in amphibolites from the franciscan complex california suggest metamorphic evolution from high temperature amphibolite facies to the blueschist facies with increasing p t ratio a counterclockwise p t t path early formed pargasitic amphiboles are both crosscut and rimmed by subcalcic hornblendes that are in turn cut or rimmed by sodic amphiboles some amphibolites are overprinted successively by eclogite and blueschist facies assemblages clinopyroxenes are zoned with increasing jadeite component from core to rim multiple generations of phengites are present in the same sample and are more si rich with each successive generation of growth garnets in eclogite overprinted amphibolites are zoned with an initial mgo increase away from the core to a maximum mgo zone followed by mgo decrease toward the rim garnets in other amphibolites show continually increasing mgo from core to rim several samples representative of the variety of franciscan amphibolites are describ

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

underthrusting and exhumation a comparison between the external hellenides and the hot cycladic and cold south aegean core complexes greece 1 after their emplacement in the course of the late mesozoic and the cenozoic the hellenic nappes became fragmented during late orogenic extension since the late eocene here we focus on the transition of underthrusting during nappe emplacement to exhumation during late orogenic extension to this end we compared previously published data on the structural geological and metamorphic history of the underthrusted parts of the tripolitza and ionian nappes which were exhumed in the cycladic and south aegean windows with newly obtained data on the sedimentary stratigraphic and structural development of the part of these nappes in the foreland in front of the subduction thrust the results allow the identification of two major events event 1 took place around the eocene oligocene transition and marks the onset of underthrusting of the tripolitza nappe below the pindos nappe and the ionian nappe below the tripolitza nappe respectively this led to the uplift and erosion of the pindos unit and the onset of deposition of the tripolitza and ionian flysch in front of the pindos thrust together with the formation of mylonites at the base of the metamorphosed portions of the pindos unit related to the underthrusting of the tripolitza unit event 2 occurred in the latest oligocene to earliest miocene and marks the decoupling of the ionian unit from the underthrusting plate the accretion of the tripolitza and ionian units to the overriding plate and the onset of late orogenic extension and exhumation in the overriding plate this led to the formation of the south aegean and cycladic core complexes and the subsidence of the klematia paramythia half graben throughout the early miocene

timing and evolution of cretaceous island arc magmatism in central cuba implications for the history of arc systems in the northwestern caribbean abstractshrimp and conventional zircon dating place temporal constraints on the evolution of the cretaceous volcanic arc system in central cuba the arc has a consistent stratigraphy across strike with the oldest and deepest rocks in the south in tectonic contact with the 5 10 km wide mabujina amphibolite complex mac and younger rocks in the north the mac is thought to represent the deepest exposed section of the cretaceous volcanic arc and its oceanic basement in cuba we undertook a single zircon geochronological study of five gneisses and two amphibolites from the mac and seven rocks from the manicaragua batholith which intrudes both the mac and the cretaceous volcanic arc a shrimp zircon age of ma for a trondhjemitic orthogneiss mac from the jicaya river dates the oldest phase of granitoid magmatism in this area and the entire caribbean antillean region a tonalitic gneiss collected near the previous sample yielded an age of ma and a further tonalitic gneiss had an age of ma with one in

viscous collision in channel explains double domes in metamorphic core complexes in hot orogens gneiss domes are a response to upper crustal stretching and lower crustal flow two dimensional thermal mechanical modeling shows that localization of extension in the upper crust triggers in the deep crust oppositely verging horizontal flows that converge beneath the extended region upon viscous collision both flowing regions rotate upward to form two upright domes of foliation double domes separated by a steep median high strain zone in such systems horizontal shortening in the infrastructure develops in an overall extensional setting dome material follows a complex depth dependent strain history from shearing in the deep crustal channel to contraction upon viscous collision in the median high strain zone to extension upon advection into the shallow crust this depth dependent strain history is likely a general feature of dome evolution and is arguably well preserved in double domes such as the montagne noire france and naxos greece gneiss domes

structure and tectonic evolution of the southwestern trinidad dome escambray complex central cuba insights into deformation in an accretionary wedge abstract the trinidad dome escambray complex cuba forms part of an accretionary wedge built during intra oceanic subduction in the caribbean from the late cretaceous to cenozoic the structure reflects syn subduction exhumation during thickening of the wedge followed by extension field mapping metamorphic and structural analysis constrain the tectonic evolution into five stages three ductile deformation events d1 d2 and d3 are related to metamorphism in a compressional setting and formation of several nappes d1 subduction fabrics are only preserved as relict s1 foliation and rootless isoclinal folds strongly overprinted by the main s2 foliation the s2 foliation is parallel to sheared serpentinised lenses that define tectonic contacts suggesting thrust stacks and underthrusting at mantle depths thrusting caused an inverted metamorphic structure with higher grade on top of lower grade nappes exhumation started during d2 when the units were incorporated into the growing accretionary wedge along nne directed thrust faults and was accompanied by substantial decompression and cooling folding and thrusting continued during d3 and marks the transition from ductile to brittle ductile conditions at shallower crustal levels the d4 5 events are related to extension and contributed to the final exhumation likely as a core complex d4 is associated with a regional spaced s4 cleavage late open folds and numerous extension veins whereas d5 is recorded by normal and strike slip faults affecting all nappes the p t path shows rapid exhumation during d2 and slower rates during d3 when the units were progressively incorporated into the accretionary prism the domal shape formed in response to tectonic denudation assisted by normal faulting and erosion at the surface during the final stages of structural development these results support tectonic models of sw subduction of the proto caribbean crust under the caribbean plate during the latest cretaceous and provide insights into the tectonic evolution of accretionary wedges in an intra arc setting

structural and tectonic evolution of western cuba fold and thrust belt 1 we present balanced and restored cross sections across the western cuba fold and thrust belt to illustrate its structure and tectonic evolution based on the interpretation of multichannel seismic profiles field data and balancing techniques the nnw sse trending soroa cross section intersects from south to north 1 the los palacios basin 2 the sierra del rosario antiformal stack 3 the bahia honda thrust unit 4 the frontal 3 km thick imbricated thrust sheets and 5 the foredeep basin at depth a duplex that links the sierra del rosario unit and the frontal imbricates is defined using the thickness of the cover thrust sheets of the imbricated north american margin the minimum calculated shortening is of 130 km in a sse or south direction to fit large scale plate tectonic reconstructions however a more allochthonous alternative using thinner cover sequences is also discussed which restores the bahia honda unit 220 km to the south of its present position syntectonic deposits in combination with a forward kinematic model provide a good constraint for the tectonic evolution of the orogen the internally deformed bahia honda unit overthrusted the north america margin cover successions during danian and selandian times 65 5 60 ma before the stacking of these cover rocks during selandian and thanetian times 60 56 ma the growth of a large antiformal stack beneath the sierra del rosario occurred at early middle eocene 56 45 ma generating about 4 km of structural relief between the paleoisland of cuba and the synorogenic seafloor before the final infill of the foredeep

accretion of the franciscan complex attending jurassic cretaceous geotectonic development of northern and central california scattered igneous activity marks the triassic margin of california but an andean volcanic plutonic arc began to form in the sierra nevada white inyo range and klamath mountains at ca 170 ma during underflow of the oceanic lithosphere this calc alkaline belt supplied volcanogenic erosional debris to the mariposa galice proximal overlap sequence by ca 165 160 ma transpression also generated high pressure low temperature basaltic eclogites garnet blueschists and amphibolites along the middle and late jurassic convergent plate junction at ca 170 155 ma most of these returned surfaceward as tectonic blocks only during the mid cretaceous the high grade metamafic metamorphosed mafic blocks that formed during construction of the emergent arc and derived mariposa galice strata predate the onset of franciscan trench deposition near the end of jurassic time the klamath salient evidently migrated 200 km westward an earliest cretaceous westward stepout of the convergent junction apparently formed directly offshore from the klamath imbricate orogen but to the south preexisting oceanic crust capped lithosphere was trapped landward as the coast range ophiolite andean arc detritus began to accumulate on this ophiolitic basement within the great valley forearc and outboard franciscan oceanic trench at ca 145 140 ma because earliest cretaceous relatively continuous great valley strata were deposited on the stable north american plate protected from both surface and subcrustal erosion forearc terrigenous sedimentation also signaled coeval deposition in the outboard trench 10 25 m y after middle and late jurassic initiation of the continental margin calc alkaline arc voluminous sedimentation and the accretion of franciscan and san joaquin sections of great valley rocks took place during mid and late cretaceous time after a flare up in igneous arc activity at 125 120 ma the youngest sierran granites have ca 85 ma ages reflecting extinction of the magmagenic zone beneath northern and central california and presumably reflecting subhorizontal oceanic plate underflow attending the laramide orogeny feebly zeolitized upper cretaceous and lower tertiary franciscan coastal belt rocks derived from the now inactive arc underwent only low pressure burial metamorphism reflecting shallow offloading and or large scale transpression they were not appreciably subducted although coastal belt units are members of the franciscan lithotectonic assemblage their origin contrasts with the rest of the subduction complex

subduction related p t path for eclogites and garnet glaucophanites from the samana peninsula basement complex northern hispaniola eclogite and garnet glaucophanite lenses from the punta balandra unit of the samana basement complex northern hispaniola preserve information of the early metamorphic and tectonic history of subduction in the caribbean island arc and its collision with the north america plate for this reason p t paths were reconstructed from the interpretation of meso and microfabrics mineral assemblages and chemistry with the aid of equilibrium phase diagrams calculated for specific bulk compositions in the cknfmash system and isopleths for selected solution end members the obtained results suggest that the subduction related prograde path evolved from garnet free and garnet bearing lawsonite blueschist facies to phengite eclogite facies conditions at p 22 24 kbar and t 610 625 c with a probable intermediate stage of low p lawsonite eclogite facies the subsequent retrograde p t path entered the epidote blueschist garnet free facies and ended within the greenschist facies field similar to the prograde evolution at low p eclogites and garnet glaucophanites formed in a subduction zone in which oceanic lithosphere was subducted wsw w beneath the caribbean plate

tectonic significance of low temperature blueschist blocks in the franciscan melange at san simeon california abstract the blueschist bearing franciscan melange exposed near san simeon is very similar to the melange terrane forming the central belt north of san francisco epidote bearing low t blueschist blocks at san simeon n 3 are the same age as high t garnet bearing blocks in the northern and diablo range melange terranes 155 150 ma this age approximates the time of initiation of franciscan subduction during the initial stages of franciscan subduction part of the top volcanic sequence from the subducting oceanic plate and small volumes of overlying sediments were imbricated at the bottom of the overriding plate and metamorphosed under high p conditions this underplated material was variably retrograded as subduction refrigerated the forearc blocks actinolitic rinds formed at the contacts between blueschists and intercalated mantle under relatively static conditions as the base of the overriding plate became serpentinized a model is proposed in which exhumation was facilitated by gravity driven seaward oriented extensional thinning of the forearc prism caused by the decrease in subducting plate dip starting around 80 ma that caused the laramide orogeny as this occurred blueschist and graphite schist blocks were plucked from the bottom of the hanging wall incorporated into the shale and water rich shear zone at the plate interface subduction channel shear zone and exhumed during the upward flow of melange driven by the movement of the downgoing plate while subduction was still active

timing of deformational events in the rio san juan complex implications for the tectonic controls on the exhumation of high p rocks in the northern caribbean subduction accretionary prism abstract an integrated structural petrological and geochronological study was undertaken to constrain the tectonic history and controls on the exhumation of the high p rocks of the rio san juan complex in the northern caribbean subduction accretionary wedge in the main structural units of the complex microtextural analyses were performed to identify the fabrics formed at peak of metamorphism in eclogite facies conditions and during the main retrogressive event toward the low p amphibolite or blueschist greenschist facies conditions u pb shrimp dating on zircon rims 71 3 0 7 ma coupled with 40 ar 39 ar analyses on phengite 70 69 ma in felsic sills placed temporal constraints on the exhumation of the jagua clara serpentinite matrix melange during the blueschist facies stage at the early maastrichtian in the cuaba unit u pb tims zircon ages of 89 7 0 1 ma and 90 1 0 2 ma obtained for the crystallization of tonalitic trondhjemitic melts in the lower guaconejo and upper jobito subunits respectively are similar these ages coupled with a u pb shrimp zircon age of 87 1 8 ma obtained in a garnet amphibolite and a group of older 40 ar 39 ar cooling ages on calcic amphibole constrain the exhumation of the guaconejo subunit from the high p stage to the low p stage at the 90 83 ma time interval further the age data collectively supports a genetic relationship between the distributed extensional ductile shearing the related decompression and the local partial anatexis in the subunit at least from the turonian coniacian boundary to the early campanian a group of younger 40 ar 39 ar ages obtained in the mylonitized amphibolites of the basal jobito detachment zone indicates late ductile deformation and exhumation cooling in the late campanian to maastrichtian 75 70 ma therefore structural and age data established deformation partitioning and reworking of retrograde fabrics during 20 ma in the cuaba unit the different exhumation rates obtained for the jagua clara melange can be explained by uplift in two contrasting tectonic settings a first stage of slow exhumation 1 4 mm yr in the subduction channel largely lower than plate velocities and a second stage of relatively fast exhumation 7 6 mm yr up to the surface therefore the exhumation was temporally discontinuous and the velocity increase at 70 ma probably was triggered in response to the entrance of buoyant material in the subduction zone such as a caribeana continental ribbon or the distal part of yucatan bahamas continental margin in contrast the exhumation path of the guaconejo subunit is composed of a first segment from the baric peak to the low p amphibolite stage at 84 83 ma with an exhumation rate of 7 2 mm yr a second segment around the closure temperature of calcic amphibole at 82 70 ma with a rate of 0 4 mm yr and a third segment to the surface exposure at 60 ma with a rate of 1 8 mm yr these velocity differences can be correlated with the p t path proposed for the exhumation of the subunit with an initial isothermal decompression from the peak in the high p amphibolite to the eclogite facies produced by distributed extensional shearing followed by a relatively slow cooling at low p in the newly acquired structural position and the final tectonics mainly partitioned in the late jobito detachment zone the initial fast exhumation can be related to a major modification in the convergence conditions across the intra oceanic subduction zone as a jump of the basal subduction thrust beyond a previously accreted arc terrane

tristan da cunha constraining eruptive behavior using the 40ar 39ar dating technique the historically active volcanic ocean island of tristan da cunha exhibits a complex and dynamic history with numerous often compositionally distinct parasitic centers punctuating the large edifi ce to date the temporal relationship between differing styles of activity has been unclear we have applied high precision 40ar 39ar dating to 15 carefully selected samples from tristan da cunha to ascertain spatio temporal relationships of recent volcanism explore episodicity and establish if the most recent summit activity post dated eruptions from parasitic centers lower on the fl anks this has yielded a new suite of reliable holocene ages with the youngest dated deposit at 3 1 ka 1 a recent fl ow at the summit was constrained to 5 1 ka 1 confi rming that summit and parasitic activity on the volcano s fl anks overlap in time the oldest dated deposits were 118 4 ka 1 from a parasitic cone in the southern sector and 81 10 ka 1 from one of the lowest sub aerial shield forming lava fl ows in the northern sector large scale sector collapse is bracketed between 34 1 ka and 26 5 ka 1 via dating of the youngest headwall lava fl ow and oldest sub aerial scarp fi lling deposits no systematic relationship between the new temporal framework vent location and eruptive compositions was found although magmatic fl ux has been inferred to be relatively low tristan da cunha is capable of relatively frequent eruptions from a wide variety of vent locations across a broad range of compositions

contrasting exhumation p t paths followed by high p rocks in the northern caribbean subduction accretionary complex insights from the structural geology microtextures and equilibrium assemblage diagrams abstract the rio san juan metamorphic complex exposes a segment of a high pressure subduction accretionary complex built during convergence between the caribbean island arc and the north america continental margin it is composed of accreted arc and oceanic derived metaigneous rocks serpentinized peridotites and minor metasediments forming a structural pile combined structural geology microtextural relations multi equilibrium calculations and thermodynamical modelling together with published isotopic ages allow reconstructing the metamorphic p t t paths of each nappe unit and their links to the structural evolution in all units of the complex three major stages m1 to m3 in the tectonothermal evolution have been distinguished the m1 stage corresponds to the prograde evolution towards the pressure peak of metamorphism under blueschist or eclogitic facies conditions the m2 stage is related to the main retrogressive event and is characterized by the s2 l2 fabric development in all lithologies and at all scales the m3 stage represents continuous exhumation from ductile to ductile brittle deformation regimes however the shape of the retrograde p t path the age of the exhumation related d2 structures and the tectonic significance of d2 deformation are different in each structural unit in the upper structural levels of the jagua clara serpentinitic matrix melange the counter clockwise p t path of the eclogite blocks is typical of rocks exhumed in the early stages of intra oceanic subduction zones the clockwise p t path obtained for the lower cuaba unit is characterized by a strong isothermal decompression from the garnet epidote amphibolite and eclogite facies pressure peak this p t evolution can be explained by rapid exhumation caused by extensional tectonics in relation to a major modification of convergence conditions across the subduction zone the p t path also explains local syn m2 partial melting processes because it crosses the wet solidus for iat mafic compositions the p t path obtained for the high p guineal schists with exhumation trajectory following the burial trajectory can be related to exhumation during active subduction this exhumation was most likely driven by a combination of underthrusting of tectonic units and erosion processes available geochronological data and t t p t estimates reveal a late campanian to maastrichtian retrograde m2 metamorphism in the lower structural units of the complex during a consistent d2 top to the ne ene tectonic transport a similar tectonic transport has also been recognized in the metasedimentary nappes of the samana complex during eocene to earliest miocene these relations indicate a northeastward progradation of deformation during the successive tectonic incorporation of arc oceanic and continental derived terrains to the developing caribbean subduction accretionary complex

a reconnaissance paleomagnetic study of cretaceous rocks from central cuba we applied thermal demagnetization to 12 sites of mid and upper cretaceous volcanics and sediments of the zaza terrane central cuba consistent directions of low and or high temperature components were obtained from eight sites the fold test performed on a short wave fold in the upper cretaceous arimao formation is negative as well as the conglomerate test on lava boulders from the same formation whereas site means for the entire data set are better grouped after tilt correction we conclude that the entire cretaceous succession of the zaza terrane was remagnetized in the campanian the measured latitude is lower by 15 6 with respect to the north american apwp indicating ca 1600 600 km northward displacement of the zaza terrane since the campanian also discordant is the measured declination implying 37 11 counterclockwise rotation of the zaza terrane

structural development of a high pressure collisional accretionary wedge the samana complex northern hispaniola abstract the samana metamorphic complex exposes a segment of a high pressure collisional accretionary wedge built during caribbean island arc north america continental margin convergence combined detailed mapping structural and metamorphic analysis and 40ar 39ar geochronology show that the deformation can be divided into five main events early subduction related d1 deformation and high p low t m1 metamorphism under lawsonite blueschist 325 425 c 12 18 kbar rincon marbles and santa barbara schists lower structural nappes and eclogite facies conditions 425 450 c 18 20 kbar punta balandra upper structural nappe was followed by m2 decompression and cooling in the blueschist facies conditions during d2 folding thrusting and nappe stacking 40ar 39ar plateau ages and t t p t estimations revealed late eocene to earliest miocene retrograde m2 metamorphism in the different nappes for a consistent d2 top to the ene tectonic transport which suggests a general northeastward progradation of deformation the d3 event substantially modified the nappe stack and produced open to tight folds with amplitudes up to kilometer scale and the d4 ductile to brittle normal shear zones and faults and related subhorizontal folding record a late extensional deformation which also affects the whole nappe pile non penetrative d3 and d4 fabrics indicate m3 cooling in and under the m3 greenschist facies conditions from the miocene to the present the nappe pile was cut and laterally displaced by a d5 sinistral strike slip and reverse fault system associated with the septentrional fault zone

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

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

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

metamorphic pressure estimates and sediment volumes for the alpine orogeny an independent control on geobarometers theories which regard the deep erosion 20 30 km of orogenic belts as an important factor in the thermal development of the continents rely on pressure estimates from metamorphic geobarometers to give an estimate of the depth scale for this process the imprecision of geobarometers and the apparent lack of sediments that would result from this amount of erosion are frequently made arguments for much smaller erosion depths the alps are a well studied young mountain belt and afford the opportunity to compare overburden masses inferred from geobarometry with sediment masses in the surrounding sedimentary basins this comparison suggests that metamorphic geobarometry has not significantly overestimated burial depths and that the average erosion to date has been over 15 km with a maximum of 25 km or more it is probable that the total erosion in the belt will eventually average 20 25 km with a maximum of around 40 km a significant feature of the sediment distribution is that over 50 of the volume is outside the neighbouring along strike sedimentary basins this fact which accounts for previous low estimates of alpine sediment volumes follows from the response of the lithosphere to loading by continental thickening and may be a common feature of post orogenic sedimentation

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

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