structurally controlled hydrothermal dolomites in albian carbonates of the ason valley basque cantabrian basin northern spain abstract shallow marine carbonate sedimentation dominated during the albian in the western part of the basque cantabrian basin in northern spain forming the large ramales platform this platform originated on a less subsiding tectonic block facing deeper and more subsiding areas to the south and east which were created by tectonic activity in the basin fracture related hydrothermal dolomites hosted in these albian carbonates are well exposed in the ason valley area mapping in the studied area revealed several dolomite bodies related to main faults that cut the stratification almost at right angles the bodies show a vertical development along fault strike up to 900 m thick from which kilometre scale branches expand following the stratification dolomitization is pervasive and independent of the limestone facies main dolomite facies are fine replacive sucrosic and saddle petrography c o and sr isotopes and fluid inclusion analysis support a polyphase hydrothermal dolomitization at fluid temperatures between 75 c and 240 c and highly variable salinity of up to 22 wt nacl fine dolomite replaced limestone first and then sucrosic and saddle dolomites replaced part of the first dolomite and cemented newly created fracture porosity together with different calcite cements zebra dolomites and hydroclastic breccias are products of this later stage burial analysis of the host rock supports maximum burial temperatures of 80 c and intense tectonic activity from the albian to turonian with a latest albian peak subsidence albian stretching of the crust and subsequent ascent of the isotherms in the area is suggested to have produced sufficient heat to the dolomitizing fluids the structural analysis indicates a strong transtensional tectonic activity in the studied area during albian to turonian time with the creation of an overstep between w e trending and n s trending faults fluids moved from subsiding areas to fractured uplifted parts of the ramales platform enhanced by diapiric activity

geochronology geochemistry and tectonic evolution of the western and central cordilleras of colombia abstract autochthonous rocks of the pre cretaceous continental margin of nw south america the tahami terrane are juxtaposed against a series of para autochthonous rock units that assembled during the early cretaceous allochthonous oceanic crust of the caribbean large igneous province collided with and accreted onto the margin during the late cretaceous we present the first regional scale dataset of zircon u pb la icp ms ages for intrusive and metamorphic rocks of the autochthonous tahami terrane early cretaceous igneous para autochthonous rocks and accreted oceanic crust the u pb zircon data are complemented by multiphase 40ar 39ar crystallization and cooling ages the geochronological data are combined with whole rock major oxide trace element and ree data acquired from the same units to constrain the tectonic origin of the rock units and terranes exposed in the western cordillera cauca patia valley and the central cordillera of colombia the tahami terrane includes lower paleozoic orthogneisses 440 ma that may have erupted during the active margin stage of the rheic ocean basement gneisses were intruded by permian continental arc granites during the final assembly of pangea triassic sedimentary rocks were subsequently deposited in rift basins and partially melted during high t metamorphism associated with rifting of western pangea during 240 220 ma continental arc magmatism during 180 145 ma is preserved along the whole length of the central cordillera and was followed by an early cretaceous out board step of the arc axis and the inception of the quebradagrande arc that fringed the continental margin back stepping of the arc axis may have been caused by the collision of buoyant seamounts which were coeval with plateau rocks exposed in the nicoya peninsular of costa rica rapid westward drift of south america closed the quebradagrande basin in the late aptian and caused medium high p t metamorphic rocks of the arquia complex to exhume and obduct onto the continental margin subduction beneath hot spot derived rocks of the caribbean plateau 100 92 ma formed an intra oceanic arc 92 75 ma which collectively comprise the late cretaceous caribbean large igneous province the remnant ocean basin located between south america and the caribbean large igneous province was partly consumed via continental subduction forming the large antioquia batholith the caribbean large igneous province collided and accreted to south america during 75 70 ma along the cauca almaguer fault resulting in the cessation of both arcs and the paleocene onset of subduction beneath the accreted oceanic crust

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

paleomagnetism of late cretaceous and eocene limestones and chalks from haiti tectonic interpretations we have conducted a paleomagnetic study of limestones and chalks from haiti which suggests that the island of hispaniola is a composite of at least two tectonically independent blocks sampling sites are distributed among three widely separated localities namely les cayes nine sites 18 3 n latitude 73 6 w longitude and beloc five sites 18 4 n latitude 72 6 w longitude which are located on the southern peninsula of haiti and a northern locality ennery six sites 19 5 n latitude 72 5 w longitude stable magnetization components of dual polarity and moderately high blocking temperature were revealed through progressive thermal demagnetization of samples from all of the beloc and ennery sites while seven of the nine les cayes sites possessed unstable magnetizations mean paleolatitudes calculated from beloc and ennery data show 8 of latitudinal separation that is of at least eocene age pole positions beloc 43 2 n latitude 185 8 e longitude 95 25 1 and ennery 66 1 n latitude 31 3 e longitude 95 19 7 show both colatitudinal and angular discordance with the north american apparent polar wander path based on these disparities we demonstrate that the implied tectonic displacements tend to support some aspects of previously published caribbean plate tectonic models

kinematics of the western caribbean collision of the cocos ridge and upper plate deformation subduction of the cocos plate and collision of the cocos ridge have profound effects on the kinematics of the western caribbean including crustal shortening segmentation of the overriding plate and tectonic escape of the central american fore arc cafa tectonic models of the panama region pr have ranged from a rigid block to a deforming plate boundary zone recent expansion of gps networks in panama costa rica and colombia makes it possible to constrain the kinematics of the pr we present an improved kinematic block model for the western caribbean using this improved gps network to test a suite of tectonic models describing the kinematics of this region the best fit model predicts an euler vector for the counterclockwise rotation of the cafa relative to the caribbean plate at 89 10 w 7 74 n 1 193 ma 1 which is expressed as northwest directed relative block rates of 11 3 1 0 16 5 1 1 mm a 1 from northern costa rica to guatemala this model also predicts high coupling along the nicoya and osa segments of the middle american subduction zone our models demonstrate that the pr acts as a single tectonic block the panama block with a predicted euler vector of 107 65 w 26 50 n 0 133 ma 1 this rotation manifests as northeast migration of the panama block at rates of 6 9 4 0 7 8 4 8 mm a 1 from southern costa rica to eastern panama we interpret this motion as tectonic escape from cocos ridge collision redirected by collision with the north andes block which migrates to the northwest at 12 2 1 2 mm a 1

thermal imprint of rift related processes in orogens as recorded in the pyrenees 19 the extent to which heat recorded in orogens reflects thermal conditions inherited from 20 previous rift related processes is still debated and poorly documented as a case study we 21 examine the mauleon basin in the north western pyrenees that experienced both extreme 22 crustal thinning and tectonic inversion within a period of 30 myrs to constrain the time 23 temperature history of the basin in such a scenario we provide new detrital zircon fission 24 track and u th sm he thermochronology data the role of rift related processes in 25 subsequent collision is captured by inverse modeling of our thermochronological data using 26 relationships between zircon u th sm he ages and uranium content combined with 27 thermo kinematic models of a rift orogen cycle we show that the basin recorded significant 28 heating at about 100 ma characterized by high geothermal gradients 80 c km our 29 thermo kinematic modeling and geological constraints support the view that subcontinental 30 lithospheric mantle was exhumed at that time below the mauleon basin such a high 31 geothermal gradient lasted 30 myr after onset of convergence at 83 ma and was relaxed 32 during the collision phase from 50 ma this study suggests that heat needed for ductile 33 shortening during convergence is primarily inherited from extension rather than being only 34 related to tectonic and or sedimentary burial this should have strong implications on tectonic 35 reconstructions in many collision belts that resulted from inversion of hyper extended rift 36 basins

hydrothermal dolomites in sw sardinia italy evidence for a widespread late variscan fluid flow event abstract epigenetic replacive and saddle dolomite frequently forming zebra structures geodic dolomite affected cambrian limestones and early diagenetic dolomites across large areas of the iglesiente sulcis mining district sw sardinia italy the dolomite crops out in an area of more than 500 km 2 and reaches a thickness of up to 600 m or even more this rock represents one of the most extensive dolomites of epigenetic origin yet documented prior to dolomitization the cambrian carbonates underwent ductile deformation and greenschist facies metamorphism the same is true for the overlying tectonic nappes fluid inclusion analysis combined with o and sr isotope data indicate that the dolomitizing fluid can be categorized as a basinal brine the spread in homogenization temperatures shows a gradient with values decreasing from east to west the higher temperatures mean of around 100 c have been measured in eastern parts of the iglesiente area whereas the lowermost temperatures mean of about 85 c have been found along the western coast of iglesiente this fluid certainly can neither have come directly from the low grade metamorphic lithotypes undergoing dolomitization nor from the low temperature metamorphic rocks within the overlying nappes it is assumed that a late variscan hydrothermal event which coincided with extensional tectonics set brine circulation into motion dolomitization may have occurred within circulation cells which were driven by high heat flow fluids originated in the underlying rocks and circulated upward to affect the overlying cambrian carbonates an alternative model is that the dolomitization was caused by hydrothermal brines that originated within basinal areas of the variscan orogenic pile circulating deep within the crust and ascended in the external zone iglesiente sulcis whatever the origin these reducing saline fluids which carried radiogenic sr dolomitized a large volume of early paleozoic rocks the many subhorizontal open cavities within the geodic dolomite only partly filled with cement might indicate fluid overpressure at the time of dolomitization

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

co magmatic sulfides and sulfates in the udachnaya east pipe siberia a record of the redox state and isotopic composition of sulfur in kimberlites and their mantle sources kimberlites of the udachnaya east pipe siberia include a uniquely dry and serpentine free rock type with anomalously high contents of chlorine cl 6 1 wt alkalies na2o k2o 10 wt and sulfur s 0 50 wt referred to as a salty kimberlite the straightforward interpretation is that the na k cl and s rich components originate directly from a carbonate chloride kimberlitic magma that is anhydrous and alkali rich however because brines and evaporites are present on the siberian craton previous studies proposed that the kimberlitic magma was contaminated by the assimilation of salt rich crustal rocks to clarify the origin of high cl alkalies and s in this unusual kimberlite here we determine its sulfur speciation and isotopic composition and compare it to that of non salty kimberlites and kimberlitic breccia from the same pipe as well as potential contamination sources hydrothermal sulfides and sulfates country rock sediment and brine collected in the area the average 34s of sulfides is 1 4 2 2 in the salty kimberlite 2 1 2 7 in the non salty kimberlites and 14 2 5 8 in the breccia the average 34s of sulfates in the salty kimberlites is 11 1 1 8 and 27 3 1 6 in the breccia in contrast the 34s of potential contaminants range from 20 to 42 for hydrothermal sulfides from 16 to 34 for hydrothermal sulfates 34 for a country rock sediment chukuck suite and the regional brine aquifer our isotope analyses show that 1 in the salty kimberlites neither sulfates nor sulfides can be simply explained by brine infiltration hydrothermal alteration or the assimilation of known salt rich country rocks and instead we propose that they are late magmatic phases 2 in the non salty kimberlite and breccia brine infiltration lead to sulfate reduction and the formation of secondary sulfides this explains the removal of salts alkali carbonates and sulfates as well as the minor olivine serpentinization 3 hydrothermal sulfur was added to the kimberlitic breccia but not to the massive kimberlites in situ measurements of sulfides confirm this scenario clearly showing the addition of two sulfide populations in the breccia pyrite pyrrhotites with average 34s of 7 9 3 4 and chalcopyrites with average 34s of 38 0 0 4 whereas the salty and non salty kimberlites preserve a unique population of djerfisherites cl and k rich sulfides with 34s values within the mantle range this study provides the first direct evidence of alkaline igneous rocks in which magmatic sulfate is more abundant than sulfide although sulfates have been rarely reported in mantle materials sulfate rich melts may be more common in the mantle than previously thought and could balance the sulfur isotope budget of earth s mantle

opening of the grenada back arc basin and evolution of the caribbean plate during the mesozoic and early paleogene abstract geological and geophysical data indicate that the grenada basin was presumably created during the paleocene by sundering of a proto eastern caribbean arc into a remnant arc to the west aves swell and an active arc to the east lesser antilles ridge grenada basin spreading is thought to have been penecontemporaneous with the creation of the yucatan basin located at the opposite side of the caribbean sea i suggest that a continuous mesozoic caribbean arc m c a including the greater antilles the aves lesser antilles system and the aruba blanquilla chain netherland venezuelan antilles was initiated in the pacific probably about 130 120 ma ago its arrival in front of and its subsequent motion inside the central atlantic tethyan seaway caused the opening of both yucatan and grenada basins which occurred at the two initial points of contact with the north and south american cratons in contrast to the style of many other island arcs this back arc spreading event occurred only once in the long history of the m c a the lesser antilles appear to be the oldest currently active intra oceanic island arc

mantle plumes and continental tectonics abstract it is now recognised that plumes originate from a thermal boundary layer deep in the mantle a new plume consists of a large head with a diameter of approximately 800 to 1200 km and it is followed by a smaller tail which has a diameter of 100 to 200 km at the top of its ascent the head flattens to form a disk 2000 to 2500 km in diameter that may melt to produce a continental flood basalt or oceanic plateau the tail melts to produce chains of volcanic activity such as the hawaiian emperor chain the ascent of a new plume leads to surface uplift of 500 to 1000 m over a length scale of 2000 km this places the lithosphere under tension but the horizontal forces produced do not result in runaway extension unless the continental lithosphere is already anomalously hot and therefore weak if the lithosphere is cold and strong slow extension leading to a new spreading ridge may postdate plume arrival by 10 to 40 m y the time difference being the time taken to conduct heat from the plume to the overlying lithosphere plume heads may control the timing and position of new ocean ridges but are not the fundamental force that drives plate tectonics the heat from plume tails may weaken the overlying plate and pin the position of spreading the ascent of a mantle plume can also have an important influence on subduction large oceanic plateaus such as the ontong java plateau are more buoyant than normal oceanic crust because they have a thicker basaltic layer and because they are underlain by a 200 km thick layer of hot material from a mantle plume head as a consequence oceanic plateaus are more difficult to subduct than normal oceanic crust this can lead to jamming of plates at subduction zones resulting in a flip in the sense of subduction as appears to have happened in the caribbean region or to obduction of the plateau finally when a plume head is emplaced beneath continental crust heat released from the plume may lead to melting of the overlying crust the granites associated with many greenstone belts and intercontinental magmatic provinces such as the paleozoic lachlan fold belt of eastern australia and the middle proterozoic anorogenic granites of the central and southwestern united states may have formed in this way

tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean example of the western pyrenees 1 in this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western pyrenees the labourd mauleon area situated in the western pyrenees at the termination of the v shaped bay of biscay is an ideal natural laboratory to study how such complex basins evolve in time and space because of a mild inversion of the basin during pyrenean compression the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field the basin shows a complex polyphase evolution that starts with left lateral dominated transtension in latest jurassic early aptian time this event is overprinted by a late aptian early albian extension that is related to the counterclockwise rotation of iberia away from europe leading to the opening of the bay of biscay during this stage the late triassic to jurassic carbonate platform was stretched salt migrated and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor the final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by n40 to n60 transfer faults the sedimentary architecture is characterized by late aptian synrift sediments e g urgonian limestones that were deposited in fault bounded basins and are overlain by thick latest aptian to albo cenomanian sediments e g flysch noir that define a sag sequence the complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic thermal event that postdates mantle exhumation

rift to collision transition recorded by tectono thermal evolution of the northern pyrenees the impact of rift related processes on tectonic and thermal evolution of collisional orogens is poorly documented here we study the northern pyrenees a region that has preserved a geological record of the transition from rifting to collision using modeling of new low temperature thermochronological data including fission track and u th he on apatite and zircon we propose a temporal reconstruction of the inversion of the european rifted margin our data confirm that rifting and related cooling started in the late paleozoic triassic throughout the jurassic and early cretaceous the european margin recorded slow heating during postrift subdsidence modeling of thermochronological data allows distinguishing subsidence and denudation controlled by south dipping normal faults in granitic massifs that reflect a second episode of crustal thinning at 130 110 ma following onset of convergence at 83 ma shortening accumulated into the weak and hot albian cenomanian rift basins floored by both hyperextended continental crust and exhumed subcontinental mantle the lack of cooling during this initial stage of convergence is explained by the persistence of a high geothermal gradient the onset of exhumation related cooling is recognized in the whole pyrenean region at 50 35 ma this timing reveals that the main phase of mountain building started when hyperextended rift basins closed and collision between proximal domains of the rifted margin occurred

interplay between depositional facies diagenesis and early fractures in the early cretaceous habshan formation jebel madar oman abstract diagenesis and fracturing can significantly alter petrophysical properties of subsurface carbonate reservoirs but the impacts of these processes at the inter well scale are hard to predict however the initial distribution of sedimentary facies is easier to predict and could template future diagenetic transformation and potentially influence fracturing as well this paper provides a case study investigating the mutual influence of depositional facies on diagenesis and interpreted early fractures in the berriasian valanginian habshan formation in jebel madar oman the habshan formation mostly comprises ooidal limestones but dolomitized beds a few metres in thickness and laterally correlatable over at least 5 km are present discordant vertical dolomite streaks are present in the limestone but are rare the various sedimentary and diagenetic processes were investigated using fieldwork xrd analysis petrography and geochemistry major and trace elements stable carbon and oxygen isotopes and strontium isotopes the lithologies consist of mud lean ooidal grainstones mud rich ooidal packstones and bioturbated limestones the changes in the amount of fine grained sediment suggest changing energy conditions at a backshoal position of a carbonate platform the mud lean versus mud rich depositional textures impacted on early diagenesis by promoting abundant calcite cementation in the mud lean ooidal grainstones and dolomitization in the mud rich packstones the discordant bodies interpreted as sediment filled early fractures are dolomitized in the same way as the mud rich ooidal packstones dolomitization occurred probably during the valanginian hauterivian in a shallow burial setting and was most likely caused by seepage reflux salt doming post dated dolomitization of the habshan formation the results of this study document the inter relationship between sedimentary facies early diagenesis and early fractures

a preliminary paleomagnetic pole for mid cretaceous rocks from tobago further evidence for large clockwise rotations in the caribbean south american plate boundary zone abstract the island of tobago occupies the eastern end of the central igneous belt of the caribbean south american plate boundary zone volcaniclastic sediment of the albian 100 ma tobago volcanic group and dikes of similar age within it were sampled in two homoclinal sections with different attitudes the mean of virtual geomagnetic poles for 12 sites 25 4 n 24 1 e a95 4 2 is well defined pre tilting and apparently reliable yet is far removed from a similar age reference pole for south america five other paleomagnetic studies of cretaceous rocks from widely separated localities farther west in the plate boundary zone yield pole positions that are remarkably similar to the tobago pole poles obtained from the guajira peninsula of colombia the islands of aruba and bonaire and the caribbean mountains of venezuela are among those that agree with the tobago result the paleolatitudes for study areas within the plate boundary zone are consistent with an origin on or near south america yet the poles throughout the zone are rotated roughly 90 dextral relative motion between the caribbean and south american plates was probably responsible for the rotation

spatial and temporal evolution of hyperextended rift systems implication for the nature kinematics and timing of the iberian european plate boundary we focus on the iberian european plate boundary iepb whose nature age and evolution are strongly debated in contrast to previous interpretations of the iepb as a major lithospheric scale left lateral strike slip fault we propose a more complex deformation history the mapping of rift domains at the transition between iberia and europe emphasizes the existence of spatially disconnected rift systems based on their restoration we suggest that the deformation was partitioned between a set of distinct left lateral transtensional rift systems from the late jurassic to early cretaceous a plate kinematic reorganization at aptian albian time resulted in the onset of sea floor spreading in the western bay of biscay and extreme crustal and lithosphere thinning in intra continental rift basins to the east the formation and reactivation of the iepb is interpreted as the result of the polyphase evolution of a diffuse transient plate boundary that failed to localize the results of this work may provide new insights on 1 processes preceding breakup and the initiation of segmented and strongly oblique shear margins 2 the deformation history of nascent divergent plate boundaries and 3 the kinematics of the southern north atlantic and alpine domain in western europe

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

the tectono sedimentary evolution of a hyper extended rift basin the example of the arzacq mauleon rift system western pyrenees sw france in this paper we present a sedimentary and structural analysis that together with maps sections and new ar ar data enable to describe the tectono sedimentary evolution of the mauleon hyper extended rift basin exposed in the w pyrenees hyper extension processes that ultimately resulted in exhuming mantle rocks are the result of the subsequent development of two diachronous detachment systems related to two evolutional stages of rifting an initial late aptian early albian crustal thinning phase is first recorded by the development of a crustal necking zone controlled by the north vergent southern mauleon detachment system during a subsequent exhumation phase active faulting migrates to the north with the emplacement of the northern mauleon detachment system that exhumed north section thinned continental crust and mantle rocks this diachronous crustal thinning and exhumation processes are also recorded by the diachronous deposition of syn tectonic sedimentary tracts above the two supra detachment sub basins syn tectonic sedimentary tracts record the progressive exhumation of footwall rocks along detachment systems tectonic migration from the southern to the northern mauleon detachment system is recorded by the coeval deposition of sag deposits above the necking zone basin and of syn tectonic tracts above exhumed rocks north section located on a hanging wall situation related to the mauleon hyper extension structures the arzacq basin also records a major crustal thinning phase as shown by its subsidence evolution so as by deep seismic images the absence of major top basement structures and its overall sag morphology suggest that crustal thinning processes occurred by decoupled extension of lower crustal levels contrasting with the southern mauleon detachment system reconciling observations from the mauleon and arzacq basins we finally propose in this paper that they were the result of one and the same asymmetric crustal thinning and exhumation processes where extension is accommodated into the upper crust in the mauleon basin lower plate basin and relayed in ductile lower crust below the arzacq basin upper plate basin

the role of the bay of biscay mesozoic extensional structure in the configuration of the pyrenean orogen constraints from the marconi deep seismic reflection survey 1 seismic interpretation of the marconi deep seismic survey enables recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution the new data denotes that two domains with different pyrenean and north foreland structures exist in the bay of biscay in the eastern or basque parentis domain the north pyrenean front is located close to the spanish coast and the northern foreland of the pyrenees is constituted by a continental crust thinned by a north dipping fault that induced the formation of the early cretaceous parentis basin in the western or cantabrian domain the north pyrenean front is shifted to the north and deforms a narrower and deeper foreland basin which lies on the top of a transitional crust formed from the exhumation of lithospheric mantle along a south dipping extensional low angle fault during the early cretaceous the transition between these two domains corresponds to a soft transfer zone linking the shifted north pyrenean fronts and a north to wnw directed thrust that places the continental crust of the landes plateau over the transitional crust of the bay of biscay abyssal plain comparison between this structure and regional data enables characterization of the extensional rift system developed between iberia and eurasia during the late jurassic and cretaceous and recognizes that this rift system controlled not only the location and features of the pyrenean thrust sheets but also the overall structure of this orogen

fore arc motion and cocos ridge collision in central america 1 we present the first regional surface velocity field for central america showing crustal response to interaction of the cocos and caribbean plates elastic half space models for interseismic strain accumulation on the dipping subduction plate boundary fit the gps data well and show strain accumulation offshore and beneath the nicoya and osa peninsulas in costa rica but not in nicaragua since large subduction zone earthquakes occur in nicaragua we suggest that interseismic locking in nicaragua and some other parts of central america occurs but is mainly shallow 20 km depth too far offshore to be detected by our on land gps measurements our data also show significant trench parallel motion for most of the region generally interpreted as due to oblique convergence and strong mechanical coupling between subducting and overriding plates however trench parallel motion is also observed in central costa rica where plate convergence is normal to the trench and in the nicaraguan fore arc where trench parallel motion is fast up to 9 mm a 1 but mechanical coupling is low a finite element model of collision as opposed to subduction involving the aseismic cocos ridge also fits the gps surface velocity field most significantly reproducing the pattern of trench parallel motion we infer that buoyant thickened cns 2 cocos ridge crust resists normal subduction and instead acts as an indenter to the caribbean plate driving crustal shortening in southern costa rica and contributing to trench parallel fore arc motion in costa rica and perhaps nicaragua as a type of tectonic escape

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

interactions between tectonics and fluid circulations in an inverted hyper extended basin example of mesozoic carbonate rocks of the western north pyrenean zone chainons bearnais france abstract interactions between fracturing fluid circulations and fluid chemistry in hyper extended margins are still poorly described as most of them are located offshore buried underneath post rift sediments the southern aquitaine basin and the northern pyrenees constitute an appropriate case study to investigate these interactions since a model of hyper extended margin with mantle exhumation during the lower cretaceous subsequently inverted was recently proposed from a field study we here describe three main sets of fractures set 1 to set 3 they are correlated with main stages of the geodynamic evolution of the basin corresponding to the liassic rifting the aptian cenomanian hyper extension and the pyrenean compression petrographic observations raman and micro thermometry analysis on fluid inclusions icp ms and isotope analysis permitted to determine chemistries temperatures redox conditions gas compositions oxygen and carbon isotopic signatures and ree contents of parent fluids for cements precipitated during each episode in particular saddle dolomite and chlorite precipitated in set 2 fractures during the hyper extension corresponding to the thermal peak at temperatures higher than 300 c the isotopic signature the high co2 content the occurrence of h2s and the high salinity of parent fluids suggest ascending magmatic fluids percolating across triassic evaporites the late and post hyper extensional phase is characterized by hydraulic brecciation in dolomitic formations a decrease in temperature and salinity a decrease in magmatic contribution in parent fluids a closing of the diagenetic system during burial and a switch to reducing conditions during the precipitation of quartz pyrite and calcite the pyrenean compressive phase associated with the third fracturing stage induced a reopening of the diagenetic system and favored a return to oxidizing conditions and infiltrations of meteoric fluids

the toa baja drilling project puerto rico scientific drilling into a non volcanic island arc massif the toa baja drilling project was a broad interdisciplinary experiment to document the in situ geology and geophysics of a non volcanic island arc massif this overview provides a brief summary of oil exploration on puerto rico that lead up to the present investigation and summarizes some of the problems addressed by drilling

plate motions in the north andean region repeated geodetic measurements with the global positioning system gps provide direct measurements of displacements due to plate motions and active crustal deformation in central america and northern south america an area of complex interaction of the nazca cocos caribbean and south american plates the displacement rates for the period 1988 1991 obtained from the results of the first three central and south america casa gps campaigns are in general agreement with the predictions of the nuvel 1 plate motion model but there are differences in detail between the observations and the model the nazca north andes convergence rate vector measured by gps is different from the nuvel 1 vector at 95 confidence the difference implies that the north andes are moving northward relative to south america the measured convergence between the caribbean plate and the north andes suggests that the southern margin of the caribbean plate is located in the south caribbean deformed belt the april 1991 costa rica earthquake and the cocos caribbean convergence rate determined by gps suggest the possibility of significant ongoing deformation between central america and the stable interior of the caribbean plate our gps results are consistent with deformation of the overriding plates at the convergent margins of central and south america and confirm that active convergence is occurring around much of the southern margin of the caribbean plate from colombia west to costa rica costa rica and panama are not part of the stable caribbean plate instead the south caribbean deformed belt and the north panama fold belt probably represent the southern margin of the caribbean plate

episodic folding inferred from syntectonic carbonate sedimentation the santaren anticline bahamas foreland abstract sedimentation coeval with growth of the santaren anticline provides an excellent opportunity to study the relationships between sedimentation and anticline uplift through time the santaren anticline is a kilometre scale nw se trending fold offshore of cuba in the bahamas foreland of the cuban fold and thrust belt the growth strata associated with this anticline consist of a thick package of carbonate sediments that were deposited without major interruptions from neogene and perhaps before to present day the excellent seismic resolution and age control of a number of seismic horizons within the growth strata allowed us to define 25 growth beds each of them representing between 0 1 and 3 2 ma an analysis of the thickness of these beds allowed us to determine accurate quantitative values of cumulative decompacted thickness and crestal structural relief at the time of their deposition in addition for the same periods sedimentation and fold uplift rates were calculated moreover some information on relationships between sedimentation and fold uplift rates was inferred from the growth stratal geometry growth beds that overlap the fold crest and thin over it indicate that sedimentation rates outpaced fold growth rates during their deposition some overlapping beds have constant thickness indicating that no fold uplift occurred during their sedimentation the rest of the growth beds exhibit onlap offlap geometries that do not indicate a unique sedimentation fold uplift rate relationship only in those cases in which the geometry of the underlying bed at the end of its deposition is known is it possible to infer a specific sedimentation fold uplift rate relationship as a result of this analysis we have been able to 1 illustrate that the geometry of the growth strata associated with the santaren anticline results from competition between sedimentation and tectonic fold uplift 2 document the episodic and non steady nature of fold growth and 3 show that short term rates at the scale of hundreds of thousands years provide much insight into the interplay between sedimentation and tectonic fold uplift that control the growth stratal patterns

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

characterization of dolomitizing fluids in the carboniferous of the cantabrian zone nw spain a fluid inclusion study with cryo raman spectroscopy abstract a late diagenetic dolomitization pervasively affected carboniferous carbonates of the variscan cantabrian zone nw spain the process generated replacive and void filling dolomite phases spatially related with various calcite cements the nature of the diagenetic fluids has been investigated by cryo raman spectroscopy i e a combination of raman spectroscopy and low temperature microthermometry which reveals in great accuracy the salinity and the major types of dissolved cations and anions in single fluid inclusions fluid properties obtained only from microthermometry are distinctively different the study demonstrates that this improved analytical method of fluid inclusions is a valuable contribution for the interpretation of fluids in dolomite research in primary fluid inclusions of the cantabrian dolomites hydrohalite and two unknown salt hydrates one of which resembles mgcl2 12h2o were detected by cryo raman spectroscopy whereas only hydrohalite appeared in the calcite primary inclusions the presence of cacl2 hydrates is suspected only from low eutectic temperatures dolomite formed from an evolving fluid as reflected by the highly variable equivalent na ca ratios calculated at high and nearly constant total salinities the approximately constant na ca ratio in the first calcite cement reflects a homogeneous source for the salts cryo raman spectroscopy reveals that different cooling procedures may induce the formation of different phase assemblages within the same fluid inclusion in both dolomite and calcite consequently fluid inclusions display different melting behaviors corresponding to different values of calculated salinities salinity calculation only from microthermometry may lead to an underestimation of true salinities according to an assumed hydrostatic geothermal gradient maximum formation conditions for the dolomites are 150 30 c and 40 10 mpa corresponding to a depth of 3 9 1 0 km the first calcite formed at 130 20 c and 35 5 mpa corresponding to a depth of 3 4 0 6 km the minimum t p of formation is defined by the homogenization conditions

extreme crustal thinning in the bay of biscay and the western pyrenees from observations to modeling recent observations and models of continental rifting in magma poor environments have led to the concept of multiphase stages of lithospheric extension in these concepts it is shown that extreme crustal thinning of the crust predates exhumation of lower crustal and subcontinental mantle rocks during final rifting the bay of biscay is a v shaped ocean basin that opened in aptian albian time in front of this propagating ocean several rift basins formed that show evidence for extreme crustal thinning and locally also mantle exhumation the parentis arzacq mauleon and cantabrian basins in this paper we propose based on geological and geophysical observations and using numerical modeling a model that can explain the extreme crustal thinning observed in the arzacq mauleon and parentis basins our results show that rifting in the bay of biscay was initiated by distributed oblique stretching latest jurassic to early aptian before it underwent an more orthogonal asymmetric thinning and exhumation phase from late aptian to albian time these last two stages of deformation are similar to those observed in orthogonal rift systems we show that thinning is accomplished by the formation of a semibrittle shear zone that allows for the transfer of middle to lower crustal material from the side of the rift collocated with the hanging wall to the side of the rift collocated with the footwall of the detachment system the main difference with an orthogonal rift system appears to be generated by the formation of flower structures during the distributed oblique phase and the capacity of localizing the deformation in the subsequent stages these oblique slip faults form very steep normal faults that induce the development of strongly localized compartmentalized and asymmetric rift basins in the case of the parentis and arzacq mauleon basins these strike slip faults separate upper plate sag basins to the north from lower plate sag basins to the south while the northern sag basins do not show any evidence for exhumation the southern ones are more complex and floored by detachment faults as indicated by the occurrence of syntectonic and posttectonic sediments onlapping directly onto exhumed lower crustal and mantle rocks

tearing and breaking off of subducted slabs as the result of collision of the panama arc indenter with northwestern south america we present two regional lithospheric cross sections that illustrate eastward and southeastward dipping subducted slabs to depths of 315 km beneath the surface of colombia in northwestern south america these cross sectional interpretations are based on relocated earthquake hypocentral solutions models supported on gravity and magnetic regional data and coda q q c tomography the method of tomographic imaging based on spatial inversion of the coda wave has advantages of providing information on the lateral variations of the anelastic properties and thermal structure of the lithospheric system mapping of earthquake defined benioff zones combined with tomographic imaging reveals the presence of an 240 km long east west striking slab tear named here the caldas tear the proposed caldas tear separates a zone of shallow 20 30 dipping southeastward subduction in the area of colombia adjacent to panama and the caribbean sea which is not associated with subduction related volcanism from an area of steeper 30 40 dipping slab adjacent to the eastern pacific ocean that is associated with an active north south chain of active arc volcanoes we propose that the caldas slab tear separating these two distinct subducted slabs originally formed as the southern boundary of the panama indenter an extinct island arc that began subducting beneath northwestern south america about 12 ma the area south of the panama indenter is miocene oceanic crust of the nazca plate which subducts eastward beneath northwestern south america at normal angles and melts to form a north south trending active volcanic arc in addition to the formation of the caldas tear we propose that impedance of the thicker crustal area of the panama arc indenter over the past 12 ma may have led to down dip break off of previously subducted oceanic crust that is marked by an extremely concentrated and active earthquake swarm of intermediate depth earthquakes beneath east central colombia

impact of basin burial and exhumation on jurassic carbonates diagenesis on both sides of a thick clay barrier paris basin ne france several diagenetic models have been proposed for middle and upper jurassic carbonates of the eastern paris basin the paragenetic sequences are compared in both aquifers to propose a diagenetic model for the middle and late jurassic deposits as a whole petrographic optical and cathodoluminescence microscopy structural fracture orientations and geochemical 18o 13c ree studies were conducted to characterize diagenetic cements with a focus on blocky calcite cements and their connection with fracturation events four generations of blocky calcite cal1 cal4 are identified cal1 and cal2 are widespread in the dominantly grain supported facies of the middle jurassic limestones about 90 of the cementation whereas they are limited in the oxfordian because grain supported facies are restricted to certain stratigraphic levels cal1 and cal2 blocky spars precipitated during burial in a reducing environment from mixed marine meteoric waters and or buffered meteoric waters the meteoric waters probably entered aquifers during the late cimmerian jurassic cretaceous boundary and late aptian early cretaceous unconformities the amount of cal2 cement is thought to be linked to the intensity of burial pressure dissolution which in turn was partly controlled by the clay content of the host rocks cal3 and cal4 are associated with telogenetic fracturing phases the succession of cal3 and cal4 calcite relates to the transition towards oxidizing conditions during an opening of the system to meteoric waters at higher water rock ratios these meteoric fluids circulated along pyrenean oligocene and alpine fractures and generated both dissolution and subsequent cementation in oxfordian vugs in mud supported facies and in poorly stylolitized grainstones however these cements filled only the residual porosity in middle jurassic limestones in addition to fluorine inputs fracturation also permitted inputs of sulphur possibly due to weathering of triassic or purbeckian evaporites or h2s input during paleogene times

oxygen isotopes of marine mollusc shells record eocene elevation change in the pyrenees abstract constraining paleoaltimetry of collisional orogens is critical to understand the dynamics of topographic evolution and climate tectonics retroactions here we use oxygen stable isotope record on oyster shells preserved in marine foreland deposits to examine the past elevation of the pyrenees during the eocene our approach is based on the comparison with the paris basin an intracratonic basin not influenced by orogenic growth the finding of a shift of 1 5 between 49 and 41 ma indicating more negative 18oc in the south pyrenean foreland is interpreted to reflect the inflow of river water sourced from higher elevation in the pyrenees to test this and provide paleoelevation estimate we adopt a morphologic hydrological model accounting for the hypsometry of drainage basin our best fitting model shows that the pyrenees rose up to 2000 m this indicates that the pyrenees reached high elevation in the eocene thus providing new critical constraints on their long term orogenic development 18o of marine mollusc shells are proved potentially attractive for paleoelevation studies especially for mountain belts where elevated continental surfaces have not been preserved

comparative study of the eastern iberides spain and the western pyrenees france mesozoic basins abstract three main periods characterize the geodynamic evolution of the mesozoic basins located in the eastern iberides and the western pyrenees 1 1 from triassic to albian times the breakup of the hercynian basement led to the general formation of different sized half grabens the regional distensional stress which generated such basins was oriented northwest southeast triassic and jurassic then northeast southwest early cretaceous with a high activity in the early triassic the early lias the kimmeridgian the barremian and the late aptian during the early cretaceous period extensional tectonics induced block tilting as well as halokinetic movements of the triassic evaporites 2 2 the albian period put an end to this common evolution the rifting movements lessened considerably in the eastern iberian basin where continental to coastal sandstones were deposited whereas they accelerated in the west pyrenean basin leading to flysch accumulations related to the openning of the bay of biscay 3 3 the late cretaceous was characterized by the same opposed evolution of a shallow carbonate platform in the eastern iberides and a deep terrigenous flysch basin in the western pyrenees during mesozoic times both on the platforms and in the basins the depositional sequence organisation was closely linked to eustatic sealevel changes nevertheless the local extensional process generated important modifications in thickness particularly within the lower triassic the liassic the kimmerdigian and the aptian series as well as within the pyrenean middle and upper cretaceous deposits the structural framework of both eastern iberian and western pyrenean areas was induced by the deformation of the iberian plate related to relative sinistral movements of africa with respect to europe the later structural evolution tertiary tectogenesis was strongly influenced by the inherited mesozoic framework both in the eastern iberides where the extensional structures are preserved and in the western pyrenees where the important compressional stress led to generalized reversal tectonics

thermal control on the modes of crustal thinning leading to mantle exhumation insights from the cretaceous pyrenean hot paleomargins the pre rift mesozoic sequences of the cretaceous passive margins fossilized in the north pyrenean zone npz are characterized by high temperature deformation in relation with thinning of the continental basement our compilation of chronological and geological data confirms a clear correlation between the distribution of the highest paleotemperatures in the pre rift sedimentary cover and the loci of extreme crustal stretching geological evidences such as the occurrence of peridotite bodies directly underlying metamorphic pre rift sediments indicate an early attenuation of the rifted continental crust this leads us to propose a mechanism of rifting involving boudinage of the continental crust the lateral extraction of the paleozoic basement occurred under the pre rift cover that is decoupled on the triassic clays and evaporates the thermal conditions allowing coeval ductile deformation of the crust and of the pre rift sediments leaded to the widening of basins devoid of large faulted blocks we discuss the implications on the origin and significance of the granulites and the relations between flysch deposition and high temperature metamorphism of the pre rift sediments in the npz albian cenomanian flysch sequences were deposited synchronously with the syn metamorphic ductile deformation of the pre rift sequences since the base of the flysch deposits also recorded locally the high temperature tectonic event we propose an original mechanism for the evolution of the basins involving continuous deformation of the pre rift metamorphic sediments at the scale of the pyrenean domain our results suggest a strong lateral variability in the tectonic style of passive margins in direct link with their thermic pattern

isotopic and chemical intra shell variations in low mg calcite of rudist bivalves mollusca hippuritacea disequilibrium fractionations and late cretaceous seasonality isotopic 13c 18o and elemental mg sr mn fe compositions were analysed in sclerochronological profiles of several shells of late cretaceous rudist bivalves from greece turkey somalia and the arabian peninsula the preservation of original compositions of low mg calcite of outer shell layers is indicated by constant and high sr generally low fe and mn and the preservation of fibrous prismatic ultrastructures cyclic variations in 18o and mg are interpreted to reflect seasonal temperature salinity cycles and thus annual growth increments in shells of torreites amplitudes of correlated 13c and 18o cycles cannot be related to reasonable palaeotemperatures or salinity this isotopic pattern reflects vital fractionations of an extent which is unknown from modern bivalves in contrast almost identical ranges and amplitudes of 18o cycles are observed in 13 shells of five species from santonian campanian localities in central greece and northern turkey suggesting that seasonal variations in environmental conditions were recorded without significant vital fractionations the effect of seasonal salinity changes on 18o of the shells is evaluated and mean palaeotemperatures are constrained within the range of 30 32 5 c the annual range of temperature was estimated to be 7 c assuming a constant salinity this agrees with other isotopic proxies of late cretaceous palaeotemperatures and with global circulation models which predict higher low latitude sea surface temperatures than the present ones

the geology of the darien panama and the late miocene pliocene collision of the panama arc with northwestern south america the geology of the darien province of eastern panama is presented through a new geologic map and detailed biostratigraphic and paleobathymetric analysis of its upper cretaceous to upper miocene sediments the sequence of events inferred from the stratigraphic record includes the collision of the panama arc the southwestern margin of the caribbean plate and south american continent three tectonostratigraphic units underlie the darien region 1 precollisional upper cretaceous eocene crystalline basement rocks of the san blas complex form a series of structurally complex topographic massifs along the northeastern and southwestern margins of the darien province these rocks formed part of a 20 m y submarine volcanic arc developed in a pacific setting distant from the continental margin of northwestern south america the northerly basement rocks are quartz diorites granodiorites and basaltic andesites through dacites to rhyolites indicating the presence of a magmatic arc the southerly basement rocks are an accreted suite of diabase pillow basalt and radiolarian chert deposited at abyssal depths precollisional arc related rocks of eocene to lower miocene age consist of 4000 m of pillow basalts and volcaniclastics and biogenic calcareous and siliceous deep water sediments they consist of the eocene oligocene darien formation the oligocene porcona formation and the lower middle miocene clarita formation postcollisional deposits are mostly coarse to fine grained siliciclastic sedimentary rocks and turbiditic sandstone of upper middle to latest miocene age this 3000 m thick sedimentary sequence is deformed as part of a complexly folded and faulted synclinorium that forms the central chucunaque tuira basin of the darien the sedimentary package reveals general shallowing of the basin from bathyal to inner neritic depths during the 12 8 7 1 ma collision of the panama arc with south america the sediments are divided into the upper middle miocene tapaliza formation the lower upper miocene tuira and membrillo formations the middle upper miocene yaviza formation and the middle to upper miocene chucunaque formation the precollisional open marine units of late cretaceous middle miocene age are separated from the overlying postcollisional sequence of middle to late miocene age by a regional unconformity at 14 8 12 8 ma this unconformity marks the disappearance of radiolarians the changeover of predominantly silica deposition from the atlantic to the pacific the initiation of the uplift of the isthmus of panama and the onset of shallowing upward coarser clastic deposition this pattern is also recorded from the southern limon basin of caribbean costa rica to the atrato basin of northwestern colombia by the middle late miocene neritic depths were widespread throughout the darien region and a regional unconformity suggests completion of the central american arc collision with south america by 7 1 ma no pliocene deposits are recorded from either the darien or the panama canal basin and no sediments younger than 4 8 ma have been identified in the atrato basin of colombia suggesting rapid uplift and extensive emergence of the central american isthmus in the latest miocene northward movement of the eastern segment of the panama arc along a now quiescent panama canal zone fault during eocene oligocene time may have dislocated the pre collision arc since collision the portion west of this fault chorotega block has remained stable without rotation to the east in the darien region compression has been accommodated through formation of a panama microplate with convergent boundaries to the north north panama deformed belt and south south panama deformed belt and suturing with south america along the atrato valley deformation within the microplate has been accommodated in the darien province by several major left lateral strike slip faults that were active until the early pliocene since when the plate has behaved rigidly

genesis and controls of hydrothermal dolomitization in sandstones of the appalachian thrust belt quebec canada implications for associated galena barite mineralization abstract the appalachian thrust belt of eastern quebec hosts six epigenetic barite galena sphalerite occurrences in interdigitated carbonate cemented sandstones carbonate clast bearing conglomerates and minor siltstones of the upper cambrian st damase formation two of these the st fabien and cap enrage deposits consist of veins and disseminations enveloped by dolomitized zones and contain ankerite as an essential gangue mineral in contrast the other occurrences consist exclusively of calcite cemented veins and are conspicuously devoid of dolomite the domains of the st fabien and cap enrage deposits are intensely fractured and contain abundant dolomite barite sulfide cemented interconnected fractures and pores whereas those of the other occurrences display relatively minor fractures and pores which are only rarely interconnected this difference in porosity leads to the conclusion that differences in paleo permeability were the most likely reasons for the presence of dolomite and disseminated mineralization in the two deposits and their absence from the vein only occurrences mass balance calculations relating altered and unaltered rock suggest that dolomitization was accompanied by large gains of cao mgo and co 2 and corresponding losses of sio 2 and k 2 o under conditions of constant volume the mass of silica removed from the altered sandstone at st fabien 14 5 g per 100 g of rock when considered in the context of quartz solubility implies a minimum water rock ratio of 2635 a similar value 2500 is indicated by the content of lead of a representative sample of the st fabien deposit and typical concentrations of lead in mississippi valley type fluids the ph of the mineralizing dolomitizing fluid was calculated from the solubility of dolomite and fluid inclusion estimates of m ca 2 m mg 2 and m co 2 to be between 3 9 and 4 6 fluid inclusion data suggest that dolomitization and mineralization at st fabien and cap enrage were the products of interactions between local sedimentary rocks and minor metabasaltic dikes with hydrothermal brines detailed x ray diffraction analysis of the phyllosilicates in the host rocks in and around the st fabien deposit mainly sandstones and minor metabasalt indicates that these brines could have acquired virtually all magnesium and all iron manganese needed for dolomite precipitation as a result of the replacement of chlorite by illite since p t conditions during deposition of the two types of mineralization were similar to each other it is concluded that these conditions did not govern the formation of dolomite

fracture controlled paleohydrogeology in a basement cored fault related fold sheep mountain anticline wyoming united states new geochemical and microstructural data constrain the origins and pathways of paleofluids during the growth of sheep mountain anticline wyoming united states oxygen carbon and strontium isotope studies were performed on prefolding and fold related calcite veins and their sedimentary host rocks and combined to fluid inclusion microthermometry results we show that most of the cements precipitated from paleogene meteoric fluid stable isotopes and fluid inclusion homogenization temperatures further indicate that most veins were mineralized from upward moving fluids after these fluids were heated at depth t 110 c this implies that fluids migrated along the basement thrust underlying the fold and or at the base of the cover above the fault tip the fluids circulated rapidly in the diffuse synfolding and early folding fracture network the zone of preferential migration of the warm fluids is currently located in the backlimb of the fold which supports some of the previously published structural interpretation of the subsurface this study also highlights the potential of combined fracture analysis and geochemical analyses of paleofluid flows in fractures to constrain both the deformation history and the fluid flow during basement involved shortening in laramide style forelands

the role of cementation in the diagenetic history of devonian reefs western canada devonian givetian and frasnian reef reservoirs in alberta and british columbia contain 60 of the conventional recoverable oil and 20 of the recoverable gas in the western canada sedimentary basin although the depositional history of these reefs is well understood it is the diagenetic overprint that is often responsible for their reservoir quality regardless of differences in size depositional history and age most reefs have been subjected to diagenesis in essentially three environments 1 submarine marine to hypersaline pore waters 2 subaerial fresh to brackish pore waters and 3 subsurface below phreatic aquifers saline to brackish pore waters primary porosity and permeability are altered by the overlapping processes of cementation and solution vadose and or phreatic that occur early in the diagenetic history in reef interiors these subaerial processes produce stratified reservoirs with impermeable barriers cemented beds to vertical flow e g golden spike swan hills judy creek submarine cementation is rare in most reefs but can be locally pervasive resulting in occlusion of bank margin and fore reef porosity absence of significant subsurface cementation in many reefs e g redwater golden spike aids in preservation of the reservoirs formed during earlier diagenesis

intra oceanic subduction shaped the assembly of cordilleran north america the western quarter of north america consists of accreted terranes crustal blocks added over the past 200 million years but the reason for this is unclear the widely accepted explanation posits that the oceanic farallon plate acted as a conveyor belt sweeping terranes into the continental margin while subducting under it here we show that this hypothesis which fails to explain many terrane complexities is also inconsistent with new tomographic images of lower mantle slabs and with their locations relative to plate reconstructions we offer a reinterpretation of north american palaeogeography and test it quantitatively collision events are clearly recorded by slab geometry and can be time calibrated and reconciled with plate reconstructions and surface geology the seas west of cretaceous north america must have resembled today s western pacific strung with island arcs all proto pacific plates initially subducted into almost stationary intra oceanic trenches and accumulated below as massive vertical slab walls above the slabs long lived volcanic archipelagos and subduction complexes grew crustal accretion occurred when north america overrode the archipelagos causing major episodes of cordilleran mountain building a new explanation for the origin of the accreted terranes that form the mountainous cordillera of western north america is proposed and tested stationary intra oceanic subduction deposited massive slab walls in the mantle and grew volcanic archipelagos at the surface which were overridden by and accreted to north america during cretaceous times the generally accepted account of how the geology of western north america developed involves the oceanic farallon plate acting as a conveyor belt sweeping crustal terranes onto the continental margin as it moves beneath the north american plate this model fails to explain many aspects of this accreted terrane and here karin sigloch and mitchell mihalynuk present an alternative model based on new tomographic images of lower mantle slabs and modelling of deep mantle structure in the region they propose that during the cretaceous period there were a series of island arcs west of north america beneath which proto pacific plates subducted into almost stationary trenches long lived volcanic archipelagos and subduction complexes grew above the slabs and then accreted onto north america as it overrode the archipelagos causing episodes of cordilleran mountain building

intra panthalassa ocean subduction zones revealed by fossil arcs and mantle structure the vast panthalassa ocean once surrounded the supercontinent pangaea subduction has since consumed most of the oceanic plates that formed the ocean floor so classic plate reconstructions based on magnetic anomalies can be used only to constrain the ocean s history since the cretaceous period 1 2 and the triassic jurassic plate tectonic evolution of the panthalassa ocean remains largely unresolved 3 4 geological clues come from extinct intra oceanic volcanic arcs that formed above ancient subduction zones but have since been accreted to the north american and asian continental margins 4 here we compile data on the composition the timing of formation and accretion and the present day locations of these volcanic arcs and show that intra oceanic subduction zones must have once been situated in a central panthalassa location in our plate tectonic reconstructions 5 7 to constrain the palaeoposition of the extinct arcs we correlate them with remnants of subducted slabs that have been identified in the mantle using seismic wave tomographic models 8 9 we suggest that a series of subduction zones together called telkhinia may have defined two separate palaeo oceanic plate systems the pontus and thalassa oceans our reconstruction provides constraints on the palaeolongitude and tectonic evolution of the telkhinia subduction zones and panthalassa ocean that are crucial for global plate tectonic reconstructions and models of mantle dynamics the spatial uncertainty in reconstructions of oceanic basins increases the further we go back in time because oceanic plates subduct plate reconstructions for the triassicjurassic history of the panthalassa ocean once surrounding the pangaea supercontinent are based on the premise that the pacific plate formedinthemiddlejurassicasatriangle 2 originatingfromatriple junction between the farallon phoenix and izanagi plates fig 1 the preserved area of jurassic palaeoplates represents only a small portion 10 of the oceanic crust of the jurassic panthalassa ocean the remaining part along with pre jurassic oceanic plate configurations is entirely unconstrained however the geology of the circum panthalassa continental margins provides evidence that early mesozoic subduction related volcanism occurred in the panthalassa ocean 4 10 on subduction continental fragments volcanic arcs ophiolites and ocean floor sediments collided with or accreted to the continental margins of in particular western north america far east asia and japan marine microfossils in these sediments and palaeomagnetic data constrain their age and palaeolatitude but their palaeolongitudes remain undetermined palaeogeographic reconstructions therefore show uncorrelated intra panthalassa exotic terranes essentially

impact of geodynamics on fluid circulation and diagenesis of carbonate reservoirs in a foreland basin example of the upper lacq reservoir aquitaine basin sw france abstract orogeny driven fluids that circulate in foreland basins can have strong impacts on petroleum systems and reservoir properties this applies to the upper cretaceous lacq reservoir of the aquitaine basin in southwestern france located north of the pyrenean mountains we study a drillcore from a 650 m deep oil reservoir to document how the evolution of a foreland basin which formed after a hyperextension phase affected fluid circulation and eventually reservoir diagenesis using drillcore samples petrographic observations fluid inclusion studies coupled with thermodynamic modeling isotopic and rare earth element geochemistry as well as basin modeling were performed to investigate and describe the fluid types and sources the pressure temperature evolution and the timing of diagenetic fluid flow early diagenesis involves some bacterial activity represented by micrite rims and framboidal pyrites as well as early dolomitization involving a mixture of meteoric and formation fluids during burial dolomite overgrowth saddle dolomites coarse blocky calcites and anhydrites precipitate the last products consist of iron oxide precipitation and meteoric recharge of the reservoir with groundwater our results indicate that after the deposition of the paleocene flysch formation mg rich low salinity hot and relatively deep clay released fluids migrated along thrust faults from deeper parts of the basin during the climax of the compressional pyrenean phase eocene they acted as dolomitizing hydrothermal fluids with a thermal disequilibrium in the order of 30 40 c hotter than the ambient host rocks another orogeny driven hydrothermal and mg poor fluid mixed with oil generated by jurassic barremian source rocks and precipitated calcites and anhydrites finally during uplift oxidizing fluids were laterally introduced as the present day groundwater hence by combining different petrographic geochemical and modeling proxies we document how the eocene orogenic phase played a crucial role in basin scale fluid flow and carbonate diagenesis

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

rare earth elements in pore waters of marine sediments abstract the rare earth elements rees were measured in pore waters of the upper 25 cm of sediment from one site off peru and three sites on the california margin the pore water ree concentrations are higher than sea water and show systematic down core variations in both concentration and normalized pattern from these analyses and from comparison to other chemical species measured dissolved fe mn ba oxygen nitrate phosphate it is suggested that pore water rees can be grouped into three categories those that are from an fe source those that are from a poc source and cerium oxide rees from the fe source appear where anoxia is reached they have a distinctive middle ree mree enriched pattern the concentrations in this source are so elevated that they dominate ree trends in the fe oxide reduction zone the net result of flux from the poc source is relative enrichment of heavy rees hrees over light rees lrees reflecting remineralizing poc and complexation with doc a common linear ree pattern seen in both oxic and anoxic sediments is associated with this poc source as well as a hree enriched pattern that is seen in surficial sediments at the peru site overall the pore water results indicate that mn oxides are not an important carrier of rees in the oceans a ree biogeochemical model is presented which attempts to reconcile ree behavior in the water and sediment columns of the oceans the model proposes that poc fe oxide and ce oxide sources can explain the ree concentration profiles and relative abundance patterns in environments ranging from oxic sea water to anoxic pore water the model is also consistent with our observation that the ce anomaly of pore water does not exceed unity under any redox condition

the caribbean north america cocos triple junction and the dynamics of the polochic motagua fault systems pull up and zipper models the polochic motagua fault systems pmfs are part of the sinistral transform boundary between the north american and caribbean plates to the west these systems interact with the subduction zone of the cocos plate forming a subduction subduction transform triple junction the north american plate moves westward relative to the caribbean plate this movement does not affect the geometry of the subducted cocos plate which implies that deformation is accommodated entirely in the two overriding plates structural data fault kinematic analysis and geomorphic observations provide new elements that help to understand the late cenozoic evolution of this triple junction in the miocene extension and shortening occurred south and north of the motagua fault respectively this strain regime migrated northward to the polochic fault after the late miocene this shift is interpreted as a pull up of north american blocks into the caribbean realm to the west the pmfs interact with a trench parallel fault zone that links the tonala fault to the jalpatagua fault these faults bound a fore arc sliver that is shared by the two overriding plates we propose that the dextral jalpatagua fault merges with the sinistral pmfs leaving behind a suturing structure the tonala fault this tectonic zipper allows the migration of the triple junction as a result the fore arc sliver comes into contact with the north american plate and helps to maintain a linear subduction zone along the trailing edge of the caribbean plate all these processes currently make the triple junction increasingly diffuse as it propagates eastward and inland within both overriding plates

multiple scale facies and reservoir quality variations within a dolomite body outcrop analog study from the middle triassic sw german basin abstract this study focuses on a porous dolomite body in the proximal part of an epeiric carbonate ramp triassic muschelkalk south german basin analogous to hydrocarbon bearing dolomite reservoirs in the middle east e g khuff and arab formations the dolomite body is made up of shoal lagoonal and peritidal facies types and is built by a three fold hierarchy of cycles 3rd order to 5th order the best reservoir quality occurs in finely crystalline lagoonal dolo mudstones mean k 37 8 md 20 2 with micro intercrystalline and vuggy porosity coarsely crystalline shoal related dolo grainstones show variable reservoir potential mean k 30 1 md 4 4 due to late diagenetic modification reservoir quality significantly decreases in the non dolomitized foreshoal section mean k 4 5 md 3 6 stratigraphically the most porous dolomite occurs in the upper regressive portion of the 3rd order cycle reservoir quality progressively decreases towards the limy bottom of the section outcrop mapping showed high lateral continuity for the distribution of facies types and poroperm values on the scale of several 10s of meters within correlated 5th order cycles considerable facies and poroperm heterogeneity is already observed on the 100s of meters scale on a 1000s of meters scale the facies and lithology distribution is controlled by the geometry of a gently inclined carbonate ramp during regression a progradational pattern is recognized marked by a basinward migration of backshoal facies and a down dip decrease of dolomite body thickness lithology facies and poroperm data from outcrops and cores were used for 3d modeling with the software petrel the modeled variations in the poroperm distribution are consistent with the degree of heterogeneity expected for a combination of laterally persistent lithology and highly variable facies results of this study may help to better understand the reservoir heterogeneity of inner ramp dolomite bodies and can be applied to improve characterization and modeling of similar dolomite reservoirs

the mesozoic tertiary evolution of the aquitaine basin the aquitaine basin situated in southwest france with an area of about 60 000 km 2 has the form of a triangle which opens towards the atlantic bay of biscay and is limited to the north by the hercynian basement of brittany and the massif central and to the south by the pyrenean tertiary orogenic belt beneath the tertiary sequence 2 km thick and which outcrops over much of the basin a mesozoic series up to 10 km thick rests generally on a tectonized hercynian basement but locally it covers narrow nw se trending post orogenic trenches of stephano permian age the mesozoic history can be subdivided into four major structural sedimentary episodes 1 during a triassic taphrogenic phase a continental evaporitic complex developed with associated basic magmatism 2 throughout the jurassic a vast lagoonal platform developed initially lower lias as a thick evaporitic sequence followed by a uniform shale carbonate unit indicating a relative structural stability 3 the end of the jurassic and the lower cretaceous saw a fragmentation of this platform due to an interplay between the iberian and european tectonic plates resulting in an ensemble of strongly subsident sub basins 4 during the upper cretaceous and until the end of the neogene the evolution of the aquitaine basin was influenced by the pyrenean orogenic phase with the development towards the south of a trench infilled by flysch which from the upper eocene is succeeded by a thick post orogenic molasse complex the main hydrocarbon objectives in the basin are situated in the jurassic platform e g the lacq giant gas field and the cretaceous sub basins e g the cazaux and parentis oil fields to date production has been about 4 times 10 7 m 3 of oil and about 15 times 10 10 m 3 of gas since the first gas discovery st marcet in 1939

late cretaceous to late eocene palaeogeographic evolution of southwest europe abstract a synthesis of personal research concerning the peri pyrenean region and previously published data is presented as a series of palaeogeographic reconstructions subsequent to the progressive regression at the end of the cretaceous the sea invaded three times parts of the earlier senonian marine domain on both sides of the eastern palaeo pyrenees pre cuisian climatic rewarming combined with cuisian continental epeirogenic deformations resulted in major biogeographic modifications during the cuisian local tectonics forced the sea from the northern pyrenean basin whereas in the southern pyrenean basin the sea retreated much later as a consequence of the pyrenean tectonic phase however the pyrenean tectogenesis seems to have affected a much larger region including the alps shoreline migrations are compared and related to the geodynamic behaviour of the meridional and septentrional european provinces in order to distinguish between tectonic and eustatic causes

basin scale thermal and fluid flow histories revealed by carbonate clumped isotopes δ47 middle jurassic carbonates of the paris basin depocentre the reconstruction of past diagenetic conditions in sedimentary basins is often under constrained this results from both the analytical challenge of performing the required analyses on the minute sample amounts available from diagenetic mineral phases and the lack of tracers for some of the diagenetic parameters the carbonate clumped isotopes thermometry 47 opens new perspectives for unravelling the temperatures of diagenetic phases together with the source of their parent fluids two parameters that are otherwise impossible to constrain in the absence of exploitable fluid inclusions here is reported the study of a large number of sedimentary and diagenetic carbonate phases from middle jurassic reservoirs of the paris basin depocentre by combining detailed petrographic observations with a large number of 47 data n 45 on a well documented paragenetic sequence including calcite and dolomite burial cements the data reveal carbonate crystallization at temperatures between 29 c and 98 c from fluids with 18owater values between 7 and 2 in response to the progressive burial and uplift of the paris basin throughout 165 myr of basin evolution coupled to the time temperature evolution previously estimated from thermal maturity modelling these temperatures allow determining the timing of four successive cementation episodes the overall dataset indicates a history of complex water mixing with a significant contribution of hypersaline waters from the triassic aquifers migrated upward along faults during the cretaceous subsidence of the basin subsequent large scale infiltrations of meteoric waters induced a dilution of these pre existing brines in response to the paris basin uplift in the tertiary overall the data presented here allow proposing an integrated approach to characterize the cementation events affecting the studied carbonate reservoir units based on temperature oxygen isotope composition and salinity of the parent fluids as well as on petrographic grounds this article is protected by copyright all rights reserved

an emerging thermochronometer for carbonate bearing rocks 47 u pb assessing the thermal evolution of sedimentary basins is critical for understanding the origin of natural resources including ores geothermal fluids or hydrocarbons and for deciphering larger scale tectonic and geodynamic evolutions modern reconstructions of past subsurface temperatures mostly rely on thermochronometers that are not applicable to carbonate rocks e g fission track and u th he analyses here by coupling carbonate clumped isotope 47 thermometry and laser ablation u pb geochronology on a complete paragenetic sequence we demonstrate the applicability of an emerging thermochronometer for carbonate bearing rocks paired 47 and u pb data were obtained for calcite and dolomite phases precipitated in a middle jurassic carbonate hydrocarbon reservoir of the paris basin depocenter france the absolute thermochronological data allow the precise reconstruction of the thermal history of these rocks from shallow burial temperatures 40 c occurring in the late jurassic toward a progressive burial and heating stage up to 87 c during the cretaceous followed by a cooling stage down to 69 c during the tertiary uplift of the basin the inferred time temperature path based on 47 u pb data is mostly consistent with the thermal scenario independently deduced from organic maturity indicators from the underlying lower jurassic shales the 47 u pb thermochronological data also highlight a thermal anomaly during aptian albian time that requires revisiting the accepted timing for hydrocarbon migration in the middle jurassic reservoir carbonates

geological context of water altered minerals in valles marineris mars 1 greater than 15 000 km2 of the layered deposits within valles marineris are associated with water altered minerals yet their origin and history of alteration remain a mystery there are numerous competing hypotheses for the formation of the interior layered deposits including aeolian lacustrine and volcanic recent orbiter spectroscopic data have indicated that water has played a role in their geological history thermal emission spectrometer tes measurements have revealed significant crystalline hematite bearing deposits within valles marineris typically related to interior layered deposits these hematite deposits found with a wide range of albedo values are associated with relatively steep bedrock exposures but can also be seen downslope on flat surfaces where they may be a lag deposit more recently observatoire la mineralogie l eau les glaces et l activite omega data have shown hydrated sulfates covering more than 13 000 km2 area of valles marineris sulfates are found in numerous topographic settings and geological units but are typically located along the flanks of interior layered deposits and nearby low lying floor units here we study the detailed morphologies of hematite and sulfate bearing units such as mantled wall units mass wasting blocky deposits massive floor deposits and tectonically altered floor units all of these terrains have diverse erosional styles and varied crater populations in both hematite and sulfate bearing units occasionally found in conjunction with one another formation processes require contributions from water the results indicate a wide range of diversity within an individual mineral class between mineral classes and also among morphological types the diversity of geological settings and properties suggest that any single unified formation mechanism is improbable

mantle exhumation crustal denudation and gravity tectonics during cretaceous rifting in the pyrenean realm sw europe insights from the geological setting of the lherzolite bodies 1 the pyrenean peridotites lherzolites form numerous small bodies of subcontinental mantle a few meters to 3 km across exposed within the narrow north pyrenean zone npz of mesozoic sediments paralleling the north pyrenean fault recent studies have shown that mantle exhumation occurred along the future npz during the formation of the albian cenomanian pyrenean basins in relation with detachment tectonics this paper reviews the geological setting of the pyrenean lherzolite bodies and reports new detailed field data from key outcrops in the bearn region only two types of geological settings have to be distinguished among the pyrenean ultramafic bodies in the first type sedimented type or s type the lherzolites occur as clasts of various sizes ranging from millimetric grains to hectometric olistoliths within monogenic or polymictic debris flow deposits of cretaceous age reworking mesozoic sediments in dominant proportions as observed around the lherz body in the second type tectonic type or t type the mantle rocks form hectometric to kilometric slices associated with crustal tectonic lenses both crustal and mantle tectonic lenses are in turn systematically associated with large volumes of strongly deformed triassic rocks and have fault contacts with units of deformed jurassic and lower cretaceous sediments belonging to the cover of the npz these deformed mesozoic formations are not older that the aptian early albian they are unconformably overlain by the albian cenomanian flysch formations and have experienced high temperature low pressure mid cretaceous metamorphism at variable grades such a tectonic setting characterizes most of the lherzolite bodies exposed in the western pyrenees these geological data first provide evidence of detachment tectonics leading to manle exhumation and second emphasize the role of gravity sliding of the mesozoic cover in the preorogenic evolution of the pyrenean realm in the light of such evidence a simple model of basin development can be inferred involving extreme thinning of the crust and mantle uprising along a major detachment fault we demonstrate coeval development of a crust mantle detachment fault and generalized gravitational sliding of the mesozoic cover along low angle faults involving triassic salt deposits as a tectonic sole this model accounts for the basic characteristics of the precollisional rift evolution in the pyrenean realm

late cretaceous early tertiary paleomagnetism of aruba and bonaire netherlands leeward antilles for a paleomagnetic study of the upper cretaceous of the netherlands leeward antilles we have analyzed 187 oriented samples from the complex norite tonalite batholith and the diabase schist tuff formation on aruba and 44 oriented samples from various igneous units of the washikemba formation on bonaire both alternating field and thermal demagnetization procedures were used to demagnetize the samples most of the cores yielded univectorial zijderveld diagrams above 10 20 mt or 400 c virtual geomagnetic poles calculated from site means were then compared with equivalently aged poles for cratonic south america and other caribbean sites the washikemba formation of bonaire and the diabase schist tuff formation of aruba yield poles that are similar to those of guajira colombia and the caribbean mountains of northern venezuela whereas they are rotated approximately 90 with respect to the pole for stable south america the batholith on aruba yields a pole which is rotated clockwise over approximately 20 with respect to the south american pole thus our data strongly support the hypothesis that aruba and bonaire have been rotated clockwise by as much as 90 since the late cretaceous in addition paleolatitudes calculated from the inclinations of the paleomagnetic vectors suggest that there was a northward drift with respect to south america of perhaps as much as 10 of the islands during the rotation although this can hardly be called a statistically significant amount

reactivity of dolomitizing fluids and mg source evaluation of fault controlled dolomitization at the benicassim outcrop analogue maestrat basin e spain abstract the mechanisms responsible for the formation of huge volumes of dolomitized rocks associated with faults are not well understood we present a case study for high temperature dolomitization of an early cretaceous aptian albian ramp in benicassim maestrat basin e spain in this area seismic scale fault controlled stratabound dolostone bodies extend over several kilometres away from large scale faults this work aims at evaluating different mg sources for dolomitization estimating the reactivity of dolomitizing fluids at variable temperature and quantifying the required versus available fluid volumes to account for the benicassim dolostones field relationships stable 13 c and 18 o isotopes as well as radiogenic 87 sr 86 sr isotopes indicate that dolomitization at benicassim was produced by a high temperature fluid 80 c 13 c and 18 o isotopic compositions for dolomite vary from 0 5 to 2 9 v pdb and from 21 1 to 24 3 v smow respectively a mg source analysis reveals that the most likely dolomitizing fluid was seawater derived brine that interacted with underlying triassic red beds and the paleozoic basement geochemical models suggest that evolved seawater can be considerably more reactive than high salinity brines and the maximum reactivity occurs at about 100 c mass balance calculations indicate that interstitial fluids with high pressure and or high temperature relative to the normal geothermal gradient cannot account for the volume of dolomite at benicassim instead a pervasive fluid circulation mechanism like thermal convection is required to provide a sufficient volume of dolomitizing fluid which most likely occurred during the late cretaceous post rift stage of the maestrat basin this study illustrates the importance of fluid budget quantification to critically evaluate genetic models for dolomitization and other diagenetic processes

pervasive subsurface dolomitization of the nisku formation in central alberta abstract the nisku formation in the subsurface of central alberta canada contains pervasive dolomites that occur mainly as a replacement of reefal limestones the degree of pervasive dolomitization increases downdip along a structural homocline from about 25 to 100 vol and associated replacive anhydrites increase from about 5 to 20 vol pervasive dolomites occur as two types one type consists of almost non porous and impermeable mosaics of cloudy crystals that have diameters of 5 300 microns the other type has significant intercrystalline porosity and permeability and consists of cloudy and clear crystals ranging in size from 100 500 microns cathodoluminescence zonation is rare but modulated structures observed with tem are common both types of dolomite have strong xrd ordering refl ctions and are nearly stoichiometric sr concentrations 25 125 ppm increase and mn concentrations 20 400 ppm decrease upwards in several cores the boron contents of both dolomite types 20 50 ppm are enriched relative to other diagenetic phases 18 ppm the sr isotope ratios vary from 0 7089 0 7107 and are enriched relative to devonian and younger seawater oxygen and carbon isotope ratios cluster around 5 8 permil pdb and 2 0 permil pdb respectively and are similar to those of remnant calcites from the combination of stratigraphic petrographic petrophysical and geochemical data it is inferred that both types of matrix dolomite formed contemporaneously from the same fluids in a flow regime with predominantly upward fluid movement at temperatures between about 40 50 c and at burial depths of about 300 1 000 m most anhydrites formed originally as gypsum during the advanced stages and after matrix dolomitization and later recrystallized to the anhydrites now present based on all accumulated data and on mass balance calculations at least two types of subsurface flow could have caused pervasive dolomitization and gypsification anhydritization 1 expulsion of burial compaction water i e chemically modified seawater with or without additional contributions of m bearing formation waters from deeper parts of the basin e g middle devonian brines and 2 thermal convection of formation fluids originally underlying and or overlying the nisku

modification of an oceanic plateau aruba dutch caribbean implications for the generation of continental crust the generation of the continental crust may be connected to mantle plume activity however the nature of this link and the processes involved are not well constrained an obstacle to understanding relationships between plume related mafic material and associated silicic rocks is that later tectonic movements are liable to obscure the original relationships particularly in ancient greenstone belts studies of younger analogous regions may help to clarify these relationships on the island of aruba in the southern caribbean a sequence of partly deformed mafic volcanic rocks intruded by a predominantly tonalitic batholith is exposed the mafic lavas show geochemical and isotopic affinities with other basaltic picritic and komatiitic rocks that crop out elsewhere in the caribbean these are well documented as belonging to an 88 91 ma plume related oceanic plateau which is allochthonous with respect to the americas and is thought to have been formed in the pacific region the 85 to 82 ma tonalitic rocks share some geochemical characteristics high sr and ba low nb and y with archaean tonalite trondhjemite granodiorite ttg suites field relationships suggest that deformation of the plateau sequence possibly related to collision with a subduction zone was synchronous with intrusion of the aruba batholith new incremental heating 40ar 39ar dates combined with existing palaeontological evidence show that cooling of the batholith occurred shortly after eruption of the plateau basalt sequence sr nd isotopic data for both rock suites are uniform 87sr 86sri 0 7035 endi 7 whereas pb isotopes are more variable plateau sequence 206pb 204pb 18 6 19 1 207pb 204pb 15 54 15 60 208pb 204pb 38 3 38 75 aruba batholith 206pb 204pb 18 4 18 9 207pb 204pb 15 51 15 56 208pb 204pb 38 0 38 5 this suggests that there has been a minor sedimentary input into the source region of the batholith however the limited time interval between basaltic and tonalitic magmatism makes a normal subduction related origin for the tonalites improbable instead models involving derivation of tonalite from partial melting of the plateau sequence or alternatively genesis in an unusual subduction zone environment are investigated

early subduction related orogeny in the northern andes turonian to eocene magmatic and provenance record in the santa marta massif and rancheria basin northern colombia terra nova 23 26 34 2011 abstract the timing of orogeny in the northern andes and the mechanism driving it are still debated we have studied the age composition and provenance of granitoids and sandstones of the santa marta massif and rancheria basin northern colombia to relate deep seated and surface tectonic processes attending the late cretaceous palaeogene history of the northern andes our results indicate the development of five tectonic episodes 1 collision of northwestern south america with a 92 80 ma caribbean arc 70 ma 2 late collisional to early subduction metamorphism and magmatism 65 ma 3 distal accumulation of a thick siliciclastic sequence 60 58 ma 4 renewed arc magmatism 58 50 ma and 5 magmatic quiescence and block uplift post 50 ma the first episodes are related to the onset of subduction and the last episode is related to shallow subduction and oblique convergence similar events in colombia and ecuador reveal that the late cretaceous eocene orogeny of the northern andes was influenced by the collision and subduction of the caribbean oceanic plate

geodynamics of the northern andes subductions and intracontinental deformation colombia new regional seismological data acquired in colombia during 1993 to 1996 and tectonic field data from the eastern cordillera ec permit a reexamination of the complex geodynamics of northwestern south america the effect of the accretion of the baudo panama oceanic arc which began 12 myr ago is highlighted in connection with mountain building in the ec the istmina and ibague faults in the south and the santa marta bucaramanga fault to the northeast limit an e se moving continental wedge progressive indentation of the wedge is absorbed along reverse faults located in the foothills of the cordilleras northward of 5 n and transpressive deformation in the santander massif crustal seismicity in colombia is accurately correlated with active faults showing neotectonic morphological evidences intermediate seismicity allows to identify a n ne trending subduction segment beneath the ec which plunges toward the e se this subduction is interpreted as a remnant of the paleo caribbean plateau pcp as suggested by geological and tomographic profiles the pcp shows a low angle subduction northward of 5 2 n and is limited southward by a major e w transpressive shear zone normal oceanic subduction of the nazca plate np ends abruptly at the southern limit of the baudo range northward the np subducts beneath the choco block overlapping the southern part of the pcp cenozoic shortening in the ec estimated from a balanced section is 120 km stress analysis of fault slip data in the ec northward of 4 n indicates an e se orientation of 1 in agreement with the pcp subduction direction northward near bucaramanga two stress solutions were observed 1 a late andean n80 e compression and 2 an early andean nw se compression

diagenesis in mesozoic carbonate rocks in the north pyrenees france from mineralogy and fluid inclusion analysis example of rousse reservoir and caprock abstract fluid rock interaction is of key interest for deciphering the geodynamic history of complex geological environments in this paper we describe the mineralogy and petrography of the rousse reservoir the upper jurassic dolomie de mano formation as well as the reconstruction of its thermal and pressure history we also investigate the base of the reservoir caprock the campanian breccia a satellite of the giant gas field of lacq in the south west of france rousse was a gas producer until it moves to a co2 storage site in 2010 rousse is located within a deep isolated faulted carbonate jurassic horst overlain by a 4500 m thick overburden that is composed of a series of turbiditic flysch deposits of upper cretaceous cenomanian to tertiary eocene age cores were sampled from two wells rousse 1 and 2 and were analyzed by icp ms xrd sem epma tem cathodoluminescence and fluid inclusion techniques pressure temperature p t conditions were derived by modeling data from fluid inclusions trapped in the fracture minerals of the dolomie de mano formation and the campanian breccia in the dolomie de mano diagenesis was dominated by three dolomite episodes followed by a calcite stage in fractures the second and third dolomitizations were associated with fracturing episodes these dolomites precipitated from low saline

origin of dolomite in the arab d reservoir from the ghawar field saudi arabia evidence from petrographic and geochemical constraints a significant proportion of oil production from the kim meridgian arab d strata in the ghawar field saudi arabia originates from dolomitized rocks stratigraphic petrographic and geochemical data suggest that at least four episodes of dolomitization affected these sediments the lower portion of the arab d zone 3 is only partially dolomitized with the dolomite frequently being associated with firm grounds we propose that these dolomites were formed on an outer ramp setting with a maximum water depth of 50 m during a period of nondeposition with the dolomitization process being promoted by the oxidation of organic material and the diffusion of mg 21 from the overlying seawater the dolomites in zone 2b are geochemically dis tinct compared to those in zone 3 in that they have relatively positive oxygen isotope compositions 2 1t o22 compared to 26 5 the relatively positive oxygen isotope composition and the geochemical sim ilarity of zone 2b to the dolomites in zone 1 which are intimately associated with the overlying evaporites has led us to conclude that the zone 2 dolomites probably formed by the reflux of hypersaline fluids through the sediments these hypersaline fluids bypassed zone 2a by moving through the grain dominated sediments early cemen tation and dolomite formation made these units more susceptible to later fracturing that affected the entire arab d formation this frac turing allowed higher temperature fluids to leach the dolostones there by removing any remaining calcite and partially resetting the oxygen isotope composition of some of the dolomites as a result of this later dolomitization event rocks that were only partially dolomitized were leached creating units with extremely high permeability and porosity super k intervals dolomites in the lower zone 3 were recrystallized during burial by the normal geothermal gradient leading to the pre sent negative oxygen isotope values zone 1 dolomites are petrograph ically distinct from zone 2 dolomite in that they are mimetic and fabric preserving although they are geochemically similar this mimetic style of dolomitization occurs immediately adjacent to the overlying anhy drite and is interpreted to have formed very shortly after deposition from hypersaline brines recovery and their presence is inferred from a combination of production data and the diameter of the bore hole as measured using the caliper log as a result of the importance of dolomite in the formation of the super k intervals within the arab d an understanding of the paragenesis of these zones is important not only in predicting super k formation within the arab d but also as an analogue for understanding other dolomitized res ervoirs with high permeability and porosity previous characterization work of dolostones from the arab d in the ghawar field cantrell et al 2004 has identified three types of dolomite with distinctive petrographic stratigraphic and geochemical characteristics fabric preserving non fabric preserving and baroque dolomite fabric pre serving dolomite is very finely crystalline in which petrographic details of the original limestone fabric are usually well preserved fabric preserving dolomite contains low concentrations of fe average 247 ppm fe and relatively positive oxygen isotope values average

global plate motion frames toward a unified model 1 plate tectonics constitutes our primary framework for understanding how the earth works over geological timescales high resolution mapping of relative plate motions based on marine geophysical data has followed the discovery of geomagnetic reversals mid ocean ridges transform faults and seafloor spreading cementing the plate tectonic paradigm however so called absolute plate motions describing how the fragments of the outer shell of the earth have moved relative to a reference system such as the earth s mantle are still poorly understood accurate absolute plate motion models are essential surface boundary conditions for mantle convection models as well as for understanding past ocean circulation and climate as continent ocean distributions change with time a fundamental problem with deciphering absolute plate motions is that the earth s rotation axis and the averaged magnetic dipole axis are not necessarily fixed to the mantle reference system absolute plate motion models based on volcanic hot spot tracks are largely confined to the last 130 ma and ideally would require knowledge about the motions within the convecting mantle in contrast models based on paleomagnetic data reflect plate motion relative to the magnetic dipole axis for most of earth s history but cannot provide paleolongitudes because of the axial symmetry of the earth s magnetic dipole field we analyze four different reference frames paleomagnetic african fixed hot spot african moving hot spot and global moving hot spot discuss their uncertainties and develop a unifying approach for connecting a hot spot track system and a paleomagnetic absolute plate reference system into a hybrid model for the time period from the assembly of pangea 320 ma to the present for the last 100 ma we use a moving hot spot reference frame that takes mantle convection into account and we connect this to a pre 100 ma global paleomagnetic frame adjusted 5 in longitude to smooth the reference frame transition using plate driving force arguments and the mapping of reconstructed large igneous provinces to core mantle boundary topography we argue that continental paleolongitudes can be constrained with reasonable confidence

coupling δ47 and fluid inclusion thermometry on carbonate cements to precisely reconstruct the temperature salinity and δ18o of paleo groundwater in sedimentary basins abstract diagenetic minerals may provide information about the burial history of geological units and can have practical applications for instance for reconstructing the geochemical and thermal histories of sedimentary basins clumped isotope or 47 thermometry on carbonates opens a new avenue for interpreting carbonate formation temperature and thermal history of rocks yet most of current knowledge on 47 systematics has been acquired via theoretical or experimental studies with only limited validation by the rock record at geological conditions timescales here we investigate calcitic and dolomitic cements representative of three genetically different cementation phases from a well documented mineral paragenesis of a carbonate unit middle jurassic paris basin france we compare 47 with fluid inclusions microthermometry fim data that were independently obtained from the same calcite and dolomite crystal specimens the range of homogenization temperatures th found for cal1 cal2 and dol1 fluid inclusions fit remarkably well i e within 47 measurements t 47 for a temperature range between 60 and 100 c and salinities between 0 and 15 wt nacl eq this provides a consistent rock based validation of the experimentally determined 47 calibration with formation temperature for both calcite and dolomite mineralogy such findings also confirm the applicability of 47 thermometry in low temperature diagenetic environments i e below circa 100 c which provides higher precision than fim measurements i e typical uncertainties of 6 c with three 47 measurements though significantly less time consuming importantly this study underlines how the coupling of both techniques can help to evaluate the degree of preservation of the original temperature information captured by either fluid inclusions or 47 compositions and interpret each proxy as confidently accurately as possible moreover because both fim and 47 measurements can provide independent constraints on the geochemistry of diagenetic paleofluids via their salinity and 18 o composition this study also highlights the benefits of coupling both techniques to further unravel the nature of paleofuids finally we propose a practical guideline as a basis for future applications of combined fim and 47 thermometry

effects of smectite dehydration and illitisation on overpressures in sedimentary basins a coupled chemical and thermo hydro mechanical modelling approach abstract diagenetic smectite dehydration and smectite to illite transition in clay rich sediments can contribute to the generation of overpressure in sedimentary basins because of the release of water associated with these mineralogical reactions however the challenge of deciphering the contribution of smectite dehydration and illitisation to fluid pressure amongst other mechanisms generating overpressure requires the different mechanisms at play to be jointly considered here we developed a coupled chemical and thermo hydro mechanical code named surp to calculate the overpressure generation in a sedimentary pile because of sediment compaction during its burial temperature increase water flow and because of the release of water by clay dehydration and illitisation for this purpose a revised thermodynamic model describing smectite dehydration by a solid solution approach was considered together with the different thermo hydro mechanical processes occurring in sedimentary basins the surp code was applied to the case study of an overpressured passive margin in the niger delta composed of thick shale layers in a sedimentary pile in this geological scenario smectite dehydration was simulated and could explain 10 30 20 50 bar of the present day overpressure in the main reservoirs in addition to compaction disequilibrium

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

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

lead isotope composition of central american volcanoes influence of the galapagos plume 1 lead isotopic analyses of lavas from central america both along and behind the volcanic arc help to clarify source components in the mantle wedge analysis of previous pb isotopic data had implied that little or no marine sediment lead was added to the central american source region as all samples fell within the morb field in contrast to other information e g ba la 10be 87sr 86sr that indicated a high subduction component the data presented here include several analyses of local marine sediment showing it to be exceptionally unradiogenic in pb and thus permitting high sediment contributions to the mantle source region without significant changes in pb isotopes combined pb nd and pb sr isotopic diagrams clearly illustrate the influence of crustal contamination for samples from guatemala and honduras and of subducted sediment for all lavas of the volcanic front samples collected behind the volcanic front are derived from mixing between enriched and depleted mantle sources and in central costa rica extending to the back arc overlap pb sr and nd isotope values for both cocos island and some components of the galapagos hot spot the restricted geographical occurrence of the enriched mantle signature in central america coupled with the persistence of the signal well into the back arc region imply that these lavas are sampling galapagos plume influenced mantle the presence of this plume component beneath southern central america and extending to the northeast beneath the caribbean confirms a galapagos hot spot origin for this part of caribbean plate

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

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

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

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk