exhumation of the dora maira ultrahigh pressure unit by buoyant uprise within a low viscosity mantle oblique slip shear zone the brossasco isasca subunit biu of the dora maira massif is currently the only known continental crustal ultrahighpressure uhp unit in the western alps the peak pressure temperature conditions are 3 5 4 5 gpa 730 c exhumation from 3 5 gpa to 1 gpa occurred within 2 2 1 8 ma but the exhumation mechanism is incompletely understood we present a conceptual model for the buoyancy driven exhumation of the biu inside a low viscosity dense mantle shear zone weakened by increased strain rates due to simultaneous strike slip and subduction oblique slip of the european plate two dimensional thermo mechanical models simulate such a buoyant uprise of an ellipse inside an inclined layer simulations i show the feasibility of the conceptual model ii fit the pressure temperature time record and iii constrain effective viscosities the model is compatible with the i small volume of continental crustal uhp rock in the western alps ii minor erosion during exhumation and iii strike slip deformation during the exhumation period

microearthquakes beneath median valley of mid atlantic ridge near 23 n tomography and tectonics data from a microearthquake experiment in the median valley of the mid atlantic ridge near 23 n in 1982 are used to measure earthquake source parameters to determine the laterally heterogeneous seismic velocity structure across the inner floor and to develop a kinematic tectonic model for this portion of the median valley fifty three microearthquakes occurred over a 10 day period beneath the median valley inner floor and eastern rift mountains twenty of 23 well located inner floor epicenters define a line of activity about 17 km long having a strike of n25 e and located near an along axis depression some 300 400 m deeper than surrounding regions earthquakes with well resolved hypocenters generally have focal depths of 4 8 km beneath the seafloor of both the inner floor and the rift mountains the hypocentral locations are robust with respect to plausible lateral variations in seismic velocity structure composite fault plane solutions for inner floor events indicate normal faulting on planes dipping at angles near 45 normal faulting mechanisms although poorly constrained are also indicated for the rift mountain microearthquakes seismic moments approximate fault dimensions and average stress drops for the largest events recorded are 1019 1020 dyn cm 200 400 m and 1 70 bars respectively a twodimensional tomographic inversion of p wave travel time residuals from microearthquakes and local shots indicates a well resolved lateral heterogeneity in crustal velocity structure across the median valley inner floor p wave velocities at 1 5 km depth within a zone less than 10 km wide beneath the central inner floor are lower by several percent than in surrounding regions the most likely explanation for the low velocities is that the region is the site of the most recent local magmatic injection and remains pervasively fractured as a result of rapid hydrothermal quenching of the newly emplaced crustal column by this view the seismic velocity structure at the ridge axis evolves probably by the sealing of cracks and pores within the first few hundred thousand years of crustal accretion consideration of the detailed sea beam bathymetry in this region of the inner floor the characteristics of large earthquakes that the region has experienced during the past 25 years and the results of the microearthquake and tomography analysis suggests that this section of the median valley has been undergoing continued horizontal extension and block faulting without significant crustal injection of magma for at least the past 104 years

fold axis parallel extension in an arcuate fold and thrust belt the case of the helvetic nappes abstract the helvetic nappes of western switzerland are discussed as an example of an arcuate foreland fold and thrust belt in which active fold axis parallel stretching occurred fold axis parallel extension is recorded by 1 1 incremental strain data from pressure shadow fibres the significance of pressure shadow fibres for the determination of the deformation history of a region is discussed pressure shadows are used to quantify the amount of and to describe the distribution of fold axis parallel extension occurring in the helvetic nappes 2 2 the extension directions of conjugate systems of en echelon veins it is shown that an analysis of the geometry of conjugate vein systems can reveal a regional deformation pattern the relative age of the conjugate en echelon vein systems in the helvetic deformation history can be assessed the geometry of the conjugate sets relative to the local anisotropy plane is described and the significance of the preferred orientation of their extension directions is discussed 3 3 fold axis parallel sections a comparison of the regional distribution of the fold axis parallel strain with the shape of the helvetic nappes in fold axis parallel sections shows that the fold axis parallel strain cannot be related to the footwall topography of the nappes it is concluded that the fold axis parallel extension in the helvetic nappes was induced by a change of direction of overthrust shear this change occurred late in the deformation history and was superposed on the already formed nappes the changing direction of overthrust shear is the expression of an overall anticlockwise rotation going on in the overthrusting alpine nappe pile relative to the european plate a rotation which lead to the arcuate shape of the western alps

the first measurements of hydrothermal heat output at 9 50 n east pacific rise abstract despite the importance of the heat output of seafloor hydrothermal systems for the earth s energy budget hydrothermal heat output measurements have been very limited in this paper we report the first measurements of hydrothermal heat output at the ridge 2000 integrated study site on the east pacific rise we focused our work on the bio 9 complex situated at 9 50 n where there has been an extensive measurement and sampling program since 1991 this site is located along the eruptive fissure of the 1991 1992 event and the site of the 1995 earthquake swarm we made direct measurements of advective heat output at several individual vents and at one site of diffuse flow tica although these data do not describe the complete heat flux picture at this vent field the data yield a total hydrothermal heat output of 325 160 mw with 42 21 mw coming from high temperature vents along this 2 km segment of ridge this result assumes a diffuse flux similar to that measured at tica occurs at each high temperature vent site our initial measurements thus suggest that the heat output of the low temperature diffuse venting is approximately 10 times that of the high temperature vents but may also be one or two orders of magnitude greater

crustal magnetization reveals subsurface structure of juan de fuca ridge hydrothermal vent fields a near bottom geophysical survey on the endeavour segment of the northern juan de fuca ridge shows that regions of well defined low crustal magnetization are strongly correlated with both active and extinct submarine hydrothermal vent sites in particular at the main endeavour field we find discrete magnetization lows associated with each cluster of vents magnetization lows are directly centered beneath the vent clusters and have diameters of 100 m which implies a near vertical narrow pipe like source region located directly beneath the surface expression of the vent edifices lows are also separated from each other by only 200 m which further implies highly focused zones magnetization lows are also associated with inactive and extinct vent areas which indicates that alteration of the magnetic minerals in the crust rather than necessarily temporary thermal demagnetization is the primary process responsible for the low magnetization these narrow pipe like bodies are highly characteristic of alteration pipes found in ophiolites and are indicative of hydrothermal fluid up flow zones thus each magnetization low may define an individual upwelling zone with distinct subsurface plumbing and thermal structure the crustal magnetization patterns provide important constraints on the geometry of the subsurface plumbing beneath these hydrothermal vent systems at the main endeavour field magnetization lows are distributed along the trend of the rift valley in a semiregular pattern with a spacing of 200 m arguing that upward flow may be partitioned into regularly spaced intervals along the axis of the rift valley

a kinematic analysis incorporating incremental strain data for the frontal pennine zones of the western french alps abstract an incremental and finite strain study of the zones adjacent to the frontal pennine thrust fpt has been undertaken using syntectonic fibres taken from veins pyrite type pressure shadows and similar fringes from around pebbles in conglomeratic rocks the resultant strain data together with detailed mapping of local deformational geometries and regional trends has shown that the pennine zones show a more complex structural history than previously envisaged the structural analysis divides the pennine zones into two regions north and south of creve tete the southern termination of the valais basin the zones to the south of creve tete mont fut valbuche nielard and aiguille d arves show an essentially piggy back thrust sequence directed towards the foreland in which the elongation of the strain ellipse initially parallels the transport direction wnw but finally rotates to become sub parallel to the tectonic strike nne ssw the structures of the valais zone to the north of creve tete are more complex with both n and wnw verging folds thrusts and strike slip faults here the long axis of the strain ellipse appears initially to parallel the tectonic strike ne sw this is followed by a rotation into the late transport direction wnw this localised alternation between strike and transport parallelism is problematic specific examples of strike parallel extension may be explained in terms of radial transport buttressing against earlier extensional structures strike slip motion and or stretching over lateral culmination walls the major division in fibre pattern north and south of creve tete however is best explained as being a function of compartmentalization of deformation styles between adjacent areas models which invoke a dominant deformation mechanism e g thrust tectonics along the entirety of the alpine chain thus need to be rethought similarly the recognition of widespread strike parallel extension suggests that two dimensional balanced section techniques are simplistic giving only minimum shortening estimates in a single direction and thus failing to reflect the true situation

compression versus extension in the exhumation of the dora maira coesite bearing unit western alps italy abstract several recent papers suggest that uplift and exhumation of high pressure low temperature hp lt metamorphic rocks are due to crustal extension coeval with and or post dating the contraction responsible for the metamorphism a detailed survey of the coesite bearing unit of the southern dora maira massif offers an opportunity to discuss the relative importance of extension and compression in the exhumation tectonics of ultra high pressure uhp rocks this uhp unit consists of pre alpine basement rocks which equilibrated at a depth of 100 km probably 120 100 ma ago it is overlain by two units with a similar lithology and eoalpine metamorphic age and high p t gradients which equilibrated at 60 and 50 km respectively this eoalpine basement complex is intercalated between blueschist facies units the whole pile was affected by a mesoalpine greenschist facies mylonitic deformation during which the early contacts were reactivated as low angle shallow dipping shear zones extension is documented only during the mesoalpine collisional period and is referred to the gravity collapse of a thickened orogenic wedge with an exhumation rate of about 1 mm yr the most important part of the exhumation of the uhp rocks occurred earlier at a higher rate close to 4 mm yr a forced return flow or extrusion tectonics of imbricate slices in an on going subduction setting seems appropriate to account for this early stage the fact that the omission of intermediate pressure rocks between juxtaposed units is an unreliable criterion for demonstrating extension is discussed

evolution of heat flow hydrothermal circulation and permeability on the young southern flank of the costa rica rift we analyze 67 new conductive heat flow measurements on the southern flank of the costa rica rift crr heat flow measurements cover five sites ranging in oceanic crustal age between approximately 1 6 and 5 7 ma and are co located with a high resolution multi channel seismic line that extends from slightly north of the first heat flow site 1 6 ma to beyond odp hole 504b in 6 9 ma crust for the five heat flow sites the mean observed conductive heat flow is 85 mwm 2 this value is approximately 30 per cent of the mean lithospheric heat flux expected from a half space conductive cooling model indicating that hydrothermal processes account for about 70 per cent of the heat loss the advective heat loss fraction varies from site to site and is explained by a combination of outcrop to outcrop circulation through exposed basement outcrops and discharge through faults super critical convection in layer 2a extrusives occurs between 1 6 and 3 5 ma and flow through a thinly sedimented basement high occurs at 4 6 ma advective heat loss diminishes rapidly between 4 5 and 5 7 ma which contrasts with plate cooling reference models that predict a significant deficit in conductive heat flow up to ages 65 10 ma at 5 7 ma the crr topography is buried under sediment with an average thickness 150 m and hydrothermal circulation in the basement becomes sub critical or perhaps marginally critical the absence of significant advective heat loss at 5 7 ma at the crr is thus a function of both burial of basement exposure under the sediment load and a reduction in basement permeability that possibly occurs as result of mineral precipitation and original permeability at the time of formation permeability is a non monotonic function of age along the southern flank of the crr in general agreement with seismic velocity tomography interpretations that reflect variations in the degree of ridge axis magma supply and tectonic extension hydrothermal circulation in the young oceanic crust at southern flank of crr is affected by the interplay and complex interconnectedness of variations in permeability sediment thickness topographical structure and tectonic and magmatic activities with age

unravelling polyphase brittle tectonics through multi software fault slip analysis the case of the voltri unit western alps italy abstract we have analyzed the brittle structures in a key area of the alps apennines transition zone nw italy here two orogens have interfered with each other since oligocene times producing a complex structural evolution and a heterogeneous fault population only relative chronologies can be reconstructed as stratigraphic constraints are lacking we have performed the inversion of fault slip data with two softwares for paleostress calculations combined with field observations at selected structural stations and photo interpretation the resulting incompatible stress tensors can be grouped in this sequence i a strike slip tensor with nnw sse trending 1 event a ii a strike slip tensor with ne sw trending 1 event b and iii an extensional transtensional tensor with nw se or ne sw trending 3 event c we correlated our results with structures of known age from adjacent areas event a is possibly rupelian early chattian linked to far field incipient rifting in the future ligurian provencal basin event b fits oligo miocene shortening the faults may belong to a sinistral strike slip zone that accommodated the oblique component of deformation during the rotation of the corsica sardinia block event c is attributed to a pliocene quaternary neotectonic event therefore combining different inversion procedures with a detailed structural analysis has successfully unravelled the polyphase brittle tectonics

deformation and motion in the western alpine arc we attempt to reconstruct the kinematics deformation and motion of the western alpine arc between the mercantour and aar massifs first we compile a map showing principal extension x direction within three major structural units in the external zone x directions are broadly radial to the alpine arc in the internal zone they are uniform or smoothly varying in some domains whereas in the intermediate zone they often show much scatter next we use geochronological data and p t conditions estimated from metamorphic mineral reactions to time the deformation on each of a series of interval maps we show x directions for strain accumulated during a chosen time interval we argue that these incremental x directions are approximately equivalent to segments of particle paths showing displacements relative to stable europe for 120 100 ma the displacement direction was about n150 and coeval with eclogite facies metamorphism it is interpreted as a direction of overthrusting by the african plate around 40 ma the displacement in the south part of the arc became westerly finally between 25 and 15 ma displacement directions were generally radial to the arc

a mid ocean ridge thermal model constraints on the volume of axial hydrothermal heat flux the depth to the axial magma chamber at three oceanic spreading centers as indicated by seismic reflection surveys is greater than that predicted by conductive cooling thermal models of ridge crests the additional cooling at the ridge axis is owed to the circulation of seawater through the shallow crust a theoretical model for the temperature distribution at spreading centers which includes distributed heat sources and sinks is presented by representing the hydrothermal heat loss as a series of heat sinks the depths to the axial magma chamber at the east pacific rise at latitude 9 n the southern juan de fuca ridge and the lau basin spreading center are modeled heat sinks are added to the input model to increase the solidus depth until the computed magma chamber depth matches the magma chamber depth determined by seismic reflection surveys the thermal modeling indicates that the axial hydrothermal heat flux is between 7 1 106 and 13 8 106 mj m2 or 10 to 20 of the total missing heat at the ridge axis requiring extensive low temperature circulation off axis high temperature vents that are spaced 1 km apart and are active between 4 and 10 of the time would account for the axial hydrothermal heat loss

near axis subsidence rates hydrothermal circulation and thermal structure of mid ocean ridge crests we systematically investigated near axis subsidence on the ridge flanks of intermediate and fast spreading mid ocean ridges using bathymetric data from well surveyed portions of the southeast indian ridge spreading at 72 76 mm yr the northern east pacific rise 91 96 mm yr and the southern east pacific rise 144 mm yr in all three regions the mean subsidence rate of young 1 1 4 ma seafloor is less than 220 m m y 1 2 the distribution of individual estimates shows a distinct peak at 180 220 m m y 1 2 with few profiles having subsidence rates greater than 275 m m y 1 2 the observed subsidence rates are significantly lower than both the worldwide average 350 m m y 1 2 and subsidence rates observed for older lithosphere at the same ridge segments intense hydrothermal circulation at the ridge axis can result in low subsidence rates on the adjacent ridge flanks provided the vigorous flow is confined to the immediate vicinity 5 km of the axis according to our model the extremely vigorous hydrothermal circulation ceases off axis and conductive heat flow becomes a primary mechanism of vertical heat transport on the ridge flanks the very low geothermal gradient within the cooled portion of the uppermost lithosphere retards conductive cooling and the cooled area needs to be heated from below before a geothermal gradient can be established which permits significant heat to be conducted out of the lithosphere as a result subsidence in very young 0 1 1 ma lithosphere is suppressed a simple one dimensional thermal model with a nusselt number parameterization was used to estimate the effect of hydrothermal circulation an upper layer with a high nusselt number and the half space that it overlies are initially at a temperature of 1300 c and the surface is maintained at 0 c after 0 1 m y of cooling about 3 5 to 7 km from the spreading axis the nusselt number of the top layer is set to 1 so that normal conduction is simulated in the cooled layer we used an explicit finite difference method to solve for the temporal changes in temperature with depth this model produces subsidence rates in the range that we observe for nu in the range of 15 30 isotherms resulting from the modeling imply rapid lithospheric thickening very near the axis which is incompatible with most current models for the formation of the bathymetric axial high observed at fast spreading mid ocean ridges

microearthquakes on the endeavour segment of the juan de fuca ridge 1 we report the results of a 55 day microearthquake experiment on the endeavour segment of juan de fuca ridge the network covered a 5 km section of the ridge axis centered on the main vent field and extended 15 km off axis on the west flank the ridge axis and flanks were seismically active and 1750 earthquakes were located with a minimum of five travel time picks including at least one s wave over half the earthquakes occurred in swarms and a waveform cross correlation technique was used to obtain relative locations on the western flank the hypocenters for four swarms at midcrustal depths are compatible with steeply dipping fault planes that strike at 035 050 n and oblique to the abyssal hills focal mechanisms determined from p wave first motions and p s amplitude ratios are predominantly strike slip with north south compression and appear to be affected by the reorganization of the explorer plate earthquakes beneath the ridge axis are concentrated in a band of intense seismicity at 1 5 3 5 km depth to the north of high rise vent field the seismicity defines a plane striking parallel to the ridge axis and dipping east at 70 and the earthquakes appear to extend beneath an axial reflector previously imaged at 2 3 km depth farther south the hypocenters are not compatible with a single fault plane focal mechanisms are characterized by subhorizontal tension axes oriented in all directions except parallel to the ridge and suggest a stress field that is about equally influenced by ridge spreading and hydrothermal cooling

post collisional tectonics in the northern cottian alps italian western alps field mapping and structural analysis have allowed us to characterise the fault geometry and the post metamorphic tectonics of an area located in the northern cottian alps inner western alps two main faulting stages were distinguished here the first oligocene early miocene is related to the development of an e w striking left normal shear zone this shear zone is interpreted as an antithetical of two regional n s right lateral structures the col del lis trana deformation zone ltz and the colle delle finestre deformation zone cfz the second faulting stage post early miocene is related mainly to the development of n s normal faults coeval with the extensional reactivation of the ltz and the cfz we discuss this kinematic evolution in the framework of the geodynamic evolution of the western alps

crack induced seismic anisotropy in the oceanic crust across the east pacific rise 9 30 n the seismic anisotropy of the shallow oceanic crust across the east pacific rise 9 30pn is studied with p wave refraction data collected during a controlled source three dimensional tomography experiment the anisotropy is indicated by a cos 2a pattern of travel time residuals where a is the receiver to shot azimuth the travel time data are best fit by a model containing 4 anisotropy from 500 m to 1 km depth below the sea floor 2 from 1 to 2 km and 0 below 2 km depth the upper 500 m of crust is not independently constrained by the data since ray paths at these depths are oriented near vertically the fast direction of p wave propagation is aligned along a trend oriented 6 10 counterclockwise from the rise axis the results are consistent with the presence of vertically aligned cracks that form on or very near the rise axis are oriented nearly parallel to the rise trend penetrate to less than 2 km depth and provide 6 10 of the total pore space in the shallow crust in comparison with similar studies across slow and intermediatespreading ridges there is no apparent spreading rate dependence of the magnitude of anisotropy fl 2001 published by elsevier science b v

the deep lithosphere in the alps a model inferred from p residuals abstract the tomographic studies of the alps and their surroundings based on the relative p residuals indicated two lithosphere roots attaining depths over 200 km separated by an upwelling of the lithosphere asthenosphere transition beneath the central part of this mountain range the directional dependence of relative p velocities indicates an anisotropic wave propagation in the subcrustal lithosphere beneath the alps and their surroundings the presented model of the deep lithosphere structure suggests several phases of the tectonic development of this region collision of a tip of the adriatic plate with europe in the eastern alps and dextral strike slip movement of the adriatic ending with underthrusting of europe beneath the western alps and counterclockwise rotation the latter contributes to a steep plunge of both plates beneath the eastern alps and to stress accumulation in the friuli region a model with delamination of the rigid upper crust and its rotation resolves some of the inconsistencies between the near surface and deep tectonics and also explains the distribution of seismicity

advanced reservoir characterization to evaluate carbon dioxide flooding spraberry trend midland basin texas the spraberry trend area of west texas once known as the largest uneconomical field in the world contains as much as 10 billion bbl of original oil in place these hydrocarbons are stratigraphically trapped in fine grained low permeability and naturally fractured siltstones and sandstones deposited in submarine fans of permian age despite five decades of production including several large scale waterflood projects recovery from the spraberry rarely exceeds 8 12 lack of scientific attention since the 1960s has resulted in most core samples suffering deterioration and loss hampering any application of new methods for reservoir analysis

geological constraints on the alpine evolution of the mediterranean tethys abstract the geological data on the mediterranean chains and basins are used to point out the constraints that they put on the location through time of oceanic versus continental lithosphere and on the successive relations between them emphasis is put on the rules and conventions which enable us to interpret the geological data in terms of plate tectonics and on the major disputed points for which a solution must be chosen in the first part the location of oceanic versus continental lithosphere is dealt with using the data on the present day basins the ophiolites and the subduction processes a neogene age is retained for the western mediterranean and the surrounding continental blocks are considered to have been previously a part of iberia a cretaceous age is retained for the eastern mediterranean apulia is considered as a part of the african plate except for this period the black sea is considered as a back arc basin formed mostly during the upper cretaceous the ophiolites are used to locate the mesozoic oceans for the double ophiolitic belts of the dinaro hellenides and the taurides the tectonic interpretations which minimise the number of oceanic basins have been retained for the kirsehir block of turkey the chosen solution locates a jurassic ocean to the north and makes it disappear when a cretaceous ocean opens to the south data on the subduction processes added to the information on these basins and led us to consider as oceanic the unknown basements of the carpathian flysch and the maghrebian flysch basins the second part deals with the organisation of basins and platforms emphasising the chronology of their formation and subsequent crushing it furnished step by step constraints on the tectonic history of the system which is related to plate displacement the general pattern derived from these data shows a wedge shaped tethyan ocean which disappeared mostly through repeated subduction below the eastern part of its northern margin the jurassic stage shows westward extension of the ocean between the eurasian and african plates and ends with the dinaro hellenic obduction the cretaceous stage shows a complete reorganisation including individual displacement of the iberian apulian and kirsehir sub plates the tertiary stage shows the general collision between the renewed eurasian and african plates and neogene subduction of the basins which avoided collision

local tomography and focal mechanisms in the south western alps comparison of methods and tectonic implications abstract we investigate how focal solutions and hypocenter locations may depend on the ray tracing algorithm and the strategy of velocity inversion using arrival times from a temporary seismological network in the south western alps a local earthquake tomography has been performed by paul et al paul a cattaneo m thouvenot f spallarossa d bethoux n and frechet j 2001 a three dimensional crustal velocity model of the south western alps from local earthquake tomography j geophys res 106 19367 19390 with the method developed by thurber thurber c h 1993 local earthquake tomography velocity and vp vs theory in seismic tomography theory and practice iyer h m and irahara eds chapman and hall new york 563 583 another inversion of the same data set is performed here using a different tomography code relying on a shooting paraxial method and cubic interpolation of velocities the resulting images display the same main features although thurber s code appears to be more robust in regions with scarce ray coverage and strong velocity contrasts concerning hypocenter location in piemont units one major result is the concentration of hypocenters at the boundary between the mantle wedge of the ivrea body and the european crust forty six focal mechanisms are shown that were computed using both the take off angles in the minimum 1 d model and in the 3 d velocity structures resulting from the two inversions the sets of focal solutions are very similar proving the reliability and the coherency of the focal solutions the widespread extension in the core of the western alps is confirmed whereas a few compressive solutions are found east of the piemont units these results constrain the sharp change of stress tensor and evidence a decoupling of strain beneath the east of dora maira massif up to beneath the north of argentera massif on a geodynamical point of view seismicity and focal mechanism distribution are compatible with the present day models published for the western alps where the major feature is the lithospheric thickening schmid s m and kissling e 2000 the arc of the western alps in the light of geophysical data on deep crustal structure tectonics 19 62 85 implying widespread extension in the core of the western alps sue c thouvenot f frechet j and tricart p 1999 widespread extension in the core of the western alps revealed by earthquake analysis j geophys res 104 25611 25622 however the existence of compressive events dealing at depth with the boundary of ivrea body allows to postulate that this geological structure is still tectonically active even if field work has not shown this so far the insubric line appears to extend toward the south at depth as a blind fault and to play a key role in the dynamics of the south western alps

play analysis and leading edge oil reservoir development methods in the permian basin increased recovery through advanced technologies the permian basin of west texas and southeast new mexico remains an important oil producing province accounting for 17 of united states production 327 million bbl in 2002 with a resource base of such size increased understanding of reservoir geology and improved use of enhanced recovery practices in the basin can have a substantial impact on united states oil production thirty two oil plays covering both the texas and new mexico portions of the permian basin were defined on the basis of reservoir stratigraphy lithology depositional environment and structural and tectonic setting one thousand three hundred and thirty nine significant sized reservoirs cumulative production of 1 million bbl 1 59 105 m3 of oil through 2000 were assigned to a geologic play cumulative production from these reservoirs was 28 9 billion bbl 4 59 109 m3 or 95 of the basin s total examples of successful reservoir development practices are listed by play because methods demonstrated to work well in one reservoir should be applicable to other reservoirs in the play the permian basin is dominantly a carbonate province carbonate reservoirs account for 75 of total oil production clastics 14 mixed clastics and carbonates 8 and chert 3 the plays having the largest cumulative production are the northwest shelf san andres platform carbonate play 4 0 billion bbl 6 31 108 m3 the leonard restricted platform carbonate play 3 3 billion bbl 5 25 108 m3 the pennsylvanian and lower permian horseshoe atoll carbonate play 2 7 billion bbl 4 29 108 m3 and the san andres platform carbonate play 2 2 billion bbl 3 42 108 m3 the permian system dominates production accounting for 73 of cumulative production followed by the pennsylvanian 13 and the ordovician 6 the estimated remaining reserves from that component of the resource base that is already discovered and producing is 3 25 billion bbl 5 17 108 m3

constraints on the accretion of the gabbroic lower oceanic crust from plagioclase lattice preferred orientation in the samail ophiolite abstract oceanic crust represents more than 60 of the earth s surface and despite a large body of knowledge regarding the formation and chemistry of the extrusive upper oceanic crust there still remains significant debate over how the intrusive gabbroic lower oceanic crust is accreted at the ridge axis the two proposed end member models the gabbro glacier and the sheeted sills predict radically different strain accumulation in the lower crust during accretion in order to determine which of these two hypotheses is most applicable to a well studied lower crustal section we present data on plagioclase lattice preferred orientations lpo in the wadi khafifah section of the samail ophiolite we observe no systematic change in the strength of the plagioclase lpo with height above the crust mantle transition no dominant orientation of the plagioclase a axis lineation and no systematic change in the obliquity of the plagioclase lpo with respect to the modal layering and macroscopic foliation evident in outcrop these observations are most consistent with the sheeted sills hypothesis in which gabbros are crystallized in situ and fabrics are dominated by compaction and localized extension rather than by systematically increasing shear strain with increasing depth in a gabbro glacier our data support the hypothesis of macleod and yaouancq 2000 that the rotation of the outcrop scale layering from sub horizontal in the layered gabbros to sub vertical near the sheeted dikes is due to rapid vertical melt migration through upper gabbros close to the axial magma chamber additionally our results support the hypothesis that the majority of extensional strain in fast spreading ridges is accommodated in partially molten regions at the ridge axis whereas in slow and ultra slow ridges large shear strains are accommodated by plastic deformation

tectonostratigraphy of the west alpine foreland correlation of tertiary sedimentary sequences changes in eustatic sea level and stress regimes abstract analysis of the tertiary depositional history of the west alpine foreland shows that its different basins were governed by essentially synchronous tectonostratigraphic scenarios the tectono sedimentary records of the west alpine foredeep and molasse basin and the rhone and massif central grabens demonstrate successions of tectonic deformation events and so called cenozoic rift and foredeep crf sequences which correlate to both changes in eustatic sea level and coeval modification in foreland stress regime since correlative successions developed in the north alpine foreland it seems likely that the western and northern alpine foreland stress fields were repeatedly modified at the same time compressional stresses associated with the intermittent tectonic and sedimentary changes in the foreland originated firstly from the alpine and pyrenean orogens in conjunction with the episodic history of the foreland stress regime the syn orogenic accumulation of widespread tectono sedimentary sequences reflects sequential kinematic events in the adjacent mountain chains the apparent synchroneity of the tectonostratigraphic events in the principal basins of the west alpine foreland testifies for a common geodynamic cause for the occurrence of correlative series of widespread tectonic phases and crf subdivisions

paragenesis of magma chamber internal wall discovered in oman ophiolite gabbros a detailed study in wadi farah reveals a singular point in jebel dihm southern oman ophiolite here we investigated some primitive features of accretion at a fast spreading ridge that has exceptionally been exempt from hydrous alteration while crossing the tbl thermal boundary layer the conjunction of two factors has made this possible in the farah area its location at the point of sharp foliation rotation from the upper to the transitional gabbros and a locally twisted tbl these factors may have favoured the intrusion within the tbl of hydrous wedges transverse to the ridge deeper into the tbl near the active ridge the wedges merge and are covered by veneers of totally fresh gabbros bearing glittering acicular clinopyroxene these gabbros are interpreted as relics of the crystallizing internal wall of the magma chamber that have interacted with hydrous fluids this internal tbl has anisotropic thermal properties and acts as a thermal blanket maintaining high magma chamber temperatures

magmatic accretion and thermal convection at the sheeted dike complex gabbro boundary in superfast spreading crust odp hole 1256d abstract the magmatic processes responsible for accretion of new oceanic plutonic crust at fast spreading centers remain unclear expedition 312 at ocean drilling program hole 1256d on the eastern flank of the east pacific rise barely drilled through the uppermost gabbros but offers unparalleled opportunities to constrain deep magmatic processes and the mode of construction of the gabbroic layer gabbro 1 and gabbro 2 respectively 52 and 24 m thick were intruded in an altered and baked sheeted dike complex both gabbros lack a macroscopic fabric and were until now considered isotropic here we use digital 3 d fabric analysis of plagioclase phenocrysts in 33 non azimuthally oriented samples in contrast with previous observations the two gabbros display a distinct and consistent shape preferred orientation both gabbros exhibit magmatic equilibrated microstructures with minor submagmatic microstructures the calculated rayleigh numbers range between 10 15 and 10 18 proving that the gabbroic magma was initially undergoing turbulent magmatic flow magmatic foliations dip moderately with a mean of 48 in gabbro 1 and 61 in gabbro 2 magmatic lineations plunge in gabbro 1 between 1 and 44 mean 28 while in gabbro 2 plunges range from 6 to 69 mean 41 these inclined magmatic structures combined with the inclined magmatic contacts between the gabbros and their host rock show that these two gabbro bodies instead of being horizontal sills more likely are inclined intrusions that cut obliquely through the sheeted dike complex seismic reflection data around hole 1256d shows inclined reflectors similar to those produced by gabbroic saucer shaped intrusions in passive margins on the basis of the inclined fabrics inclined contacts and the regional seismic data we propose that the uppermost gabbroic intrusions at fast spreading centers form with a saucer shape this new shape of intrusion never reported before in the oceanic environment may constitute a significant component of oceanic accretion

geological setting of the southern termination of western alps a revision of the stratigraphic and tectonic setting of the southern termination of the western alps at the junction of the maritime alps with the westernmost ligurian alps is proposed in response to the alpine kinematic evolution a number of tectonic units formed on the deformed palaeo european continental margin and were arranged in a nw se striking anastomosed pattern along the north eastern boundary of the argentera massif because these tectonic units often cut across the palaeogeographic subdivision of the alpine literature and show only partial affinity with their distinctive stratigraphic features new attributions are proposed the subbrianconnais domain is here intended as a deformation zone and its tectonic units have been attributed to dauphinois and provencal domains furthermore the eocene alpine foreland basin succession has been interpreted based on the affinity of its lithologic characters and age as a single feature resting above all the successions of the different mesozoic domains the cretaceous tectono sedimentary evolution of the studied domains was characterized by intense tectonic controls on sedimentation inducing lateral variations of stratigraphic features and major hydrothermal phenomena since the early oligocene transpressional tectonics induced a ne sw shortening together with significant left lateral movements followed by late oligocene middle miocene right lateral movements along e w to se nw striking shear zones this induced the juxtaposition and or stacking of brianconnais dauphinois and ligurian tectonic units characterized by different metamorphic histories from anchizonal to lower greenschist facies this evolution resulted in the arrangement of the tectonostratigraphic units in a wide transfer zone accommodating the oligocene wnw ward movement of portions of the palaeo european margin placed at the south western termination of western alps and the miocene dextral shearing along se striking faults that bound the argentera massif on its ne side

chemical and thermal constraints on focussed fluid flow in the lower oceanic crust the mechanism of heat extraction from the lower oceanic crust near the ridge axis is poorly constrained despite its importance for understanding both the process of accretion of the plutonic complex and the mass fluxes associated with ridge hydrothermal systems we have investigated the role of zones of focussed fluid flow in the plutonic complex of the oman ophiolite in the near axis cooling of the oceanic crust lineaments identified on aerial photographs that occur at 1 km spacing show evidence for extensive hydrothermal fluid flow through regions 10 to 50 m wide fluid flow is initiated in these regions at 800 c and continues at least into the lower greenschist facies strontium isotope analyses indicate that the fluid flux through these zones is sufficient to transport a metasomatic front from the base of the sheeted dike complex to close to the moho computed minimum fluid fluxes to transport a metasomatic front through the focussed fluid flow zones are 1x108 kgm2 modeling of diffusive exchange of calcium from olivine to clinopyroxene indicates enhanced cooling rates adjacent to the focussed fluid flow zones heat fluxes estimated from the enhanced cooling rates are broadly consistent with the fluid fluxes determined from modeling the sr isotopic composition of samples from the focussed fluid flow zones the combination of independent estimates of the fluid and heat fluxes such as these can provide more rigorous constraints on the thermal history than either approach used in isolation our results show that focussed fluid flow could play a major role in the cooling in the lower oceanic crust significant focussed fluid flow in the lower oceanic crust has important implications for predicting the total mass flux associated with hydrothermal circulation at mid ocean ridges this is because fluids flowing through channels become chemically rock buffered at smaller fluid fluxes than those flowing pervasively through a rock mass thus if focussed fluid flow is an important mechanism of heat loss from the lower oceanic crust the chemical fluxes from ridge hydrothermal systems into the oceans may be smaller than currently thought

facies variability within a mixed carbonate siliciclastic sea floor fan upper wolfcamp formation permian delaware basin new mexico sea floor fans containing both carbonate and siliciclastic detritus are rarely recognized in the rock record but are common within the permian upper wolfcamp formation in the delaware basin in southeast new mexico and west texas one such compositionally mixed fan has been studied in detail as part of an unconventional oil and gas exploration and development program in southeast new mexico three cores were collected through an approximately 100 m 350 ft thick interval that defines the structurally controlled fan cores collected represent the frontal to distal fringe off axis and lateral fringe parts of the fan unlike siliciclastic fans where axial facies are characterized more by turbidites the axis off axis and lateral fringe cores in the wolfcamp are dominated by carbonate debrites coarse carbonate deposition decreases toward the frontal fringe areas where core facies are composed of mixed carbonate siliciclastic mud rich hybrid event beds and background sedimentation the core through the lateral fringe differs from the off axis core in that the debrites in the lateral fringe are thinner and commonly rheologically stratified with finer grained debrites sitting directly on top of coarse grained debrites suggesting a genetic link in their formation the axial facies appear to be dominated by thick amalgamated debrites changes in carbonate content from axis to frontal fringe appear to be gradual but rapid from axis to lateral fringe over a 3 km 2 mi distance the carbonate rich part of the fan trends at least 55 km 34 mi in a northeast southwest direction and extends 18 km 11 mi northwest southeast across

arcuate thrust systems in sandbox experiments a comparison to the external arcs of the western alps in the external western alps two regional structural arcs were generated during tertiary northwest directed collision between the apulian indenter and the european passive margin these arcs distinguished by their geographic position and their age are examined by using a new compilation of structural data and comparing these to the results of sandbox analogue experiments the principal western alpine arc comprises two orthogonal synchronous thrust systems in the late eocene early miocene major shortening 105 km was toward the northwest to west northwest and minor shortening 11 km was toward the southwest shortening in each branch decreased toward the core of the arc during the late miocene and pliocene the jura arc accommodated 35 km of northwest directed shortening while 10 5 km of southwest to south southwest directed shortening was accommodated on the digne thrust system sandbox experiments were used to investigate the role of the motion vector of a rigid rectangular indenter orthogonal diagonal curved or rotational paths and the mechanical stratigraphy of the foreland in the evolution of upper crustal arcuate systems e g presence of a basal easy slip silicone horizon comparison of experimental results with the external alpine arc suggests that the indenter followed a slightly diagonal path with respect to the european margin from the eocene to the early miocene and curved counterclockwise by 10 15 in the middle miocene mechanical stratigraphy experiments support the hypothesis that thick triassic evaporites played a primary role in the evolution of the jura arc the influence of mechanical stratigraphy was most prominent during weak deformation at the external boundaries of the alpine orogen jura fold and thrust belt digne thrust

the effects of spreading rate the magma budget and the geometry of magma emplacement on the axial heat flux at mid ocean ridges we explore two dimensional steady state flow and thermal models of oceanic spreading center structure these models include the effects of hydrothermal heat transport and crustal accretion for two basic accretion geometries 1 a lens model where all crust below the sheeted dike layer passes through a magma lens at the base of the dike layer before subsiding and flowing to deeper levels and 2 a dike model where crust is emplaced in a vertical slot from the surface to moho and subsequently moves horizontally rigidly away from the axis of accretion the axial heat flux resulting from these two end member accretion geometries is compared and an assessment is made of the feasibility of using various observations to differentiate between these two accretion geometries we find that the steady state axial heat flux is predominantly influenced by three factors the spreading rate the magmatic budget crustal thickness and the efficiency of hydrothermal cooling the total steady state heat flux from the neovolcanic zone 2 km wide increases almost linearly with the spreading rate for both the dike and lens accretion geometries the major difference between the dike and the lens models is nonthermal they predict different accumulated strain distributions within off axis crust crustal flow due to crustal accretion within a crustal height dike leads to little accumulated strain while intense crustal strain results from crustal subsidence and flow below a steady state magma lens ophiolite and marine seismic observations of crustal layering appear to be the strongest observational tests to discriminate between these two accretion geometries they currently favor a lens like model of lower crustal accretion

manifestations of hydrothermal discharge from young abyssal hills on the fast spreading east pacific rise flank spectacular black smokers along the mid ocean ridge crest represent a small fraction of total hydrothermal heat loss from ocean lithosphere previous models of measured heat flow suggest that 40 50 of oceanic hydrothermal heat and fluid flux is from young seafloor 0 1 5 ma on mid ocean ridge flanks despite evidence that ridge flank hydrothermal flux affects crustal properties ocean chemistry and the deep sea biosphere few ridge flank vent sites have been discovered we describe the first known seafloor expressions of hydrothermal discharge from tectonically formed abyssal hills flanking a fast spreading ridge seafloor manifestations of fluid venting from two young east pacific rise abyssal hills 0 1 ma at 10 20 n 103 33 2 w 0 5 ma at 9 27 n 104 32 3 w include fault scarp hydrothermal mineralization and macrofauna fault scarp flocculations containing hyperthermophilic microbes and hilltop sediment mounds and craters possibly created by fluid expulsion these visible features can be exploited for hydrothermal exploration of the vast abyssal hill terrain flanking the mid ocean ridge and for access to the subseafloor biosphere petrologic evidence suggests that abyssal hills undergo repeated episodes of transitory fluid discharge possibly linked to seismic events and that fluid exit temperatures can be briefly high enough to transport copper 250 c

active deformation at the southwestern alps ligurian basin junction france italy boundary evidence for recent change from compression to extension in the argentera massif abstract several hundred earthquakes of small and moderate magnitude occur each year at the southwestern alps ligurian basin junction in addition the historical seismicity data attests for earthquakes of magnitude close to 6 5 despite the seismic hazard and the vulnerability of this region the present day driving mechanism of deformation and the major structures accommodating these deformations remain unclear this littoral area presents a strong topographic gradient from 3000 masl on the argentera alpine massif to 2500 m u s l in the ligurian basin and a strong structural inheritage resulting from 50 my geological evolution combining different processes such as continental collision and ocean basin opening we present new results about the kinematics of the corsica sardinia continental block with respect to the western alpine belt from 7 years of continuous gps measurements we show that a small part of the nubia eurasia convergence is certainly transferred northward of the maghrebides deformation belts to the corsica sardinia block in the southwesternmost alps from torino to the mediterranean coast the baselines reveal differential motions of lengthening between the po plain and the argentera and shortening between the argentera and the ligurian domain in a region where few focal solutions are available we determine seven new focal mechanisms located in the argentera massif these new data underline a quaternary change from compression to extension in that part of the western alpine belt the focal mechanisms calculated attest for extensional faulting at shallow level between 1 and 11 km depth we add 7 focal mechanisms from the literature to calculate the stress tensor a homogeneous solution indicates a direction of extension broadly perpendicular to the topographic axis culmination of the argentera in contrast the earthquakes recorded below 15 km at the northwestern margin of the po plain testify reverse faulting and a compressional state of stress in the deep crust thus we point out that the stress field is vertically heterogeneous in the crust of the argentera area the ligurian domain is mainly characterized by reverse and strike slip faulting the major earthquakes are located in the northern margin and at the ocean continent transition these earthquakes are assumed to result from the reactivation in a compressional state of stress of the structures formed during the oligo miocene opening of the ligurian basin finally we propose three hypotheses to explain the current deformation at the alps ligurian basin junction taking into account the far field kinematics between the nubia and the eurasia plates the topographic gradient between the argentera massif and the ligurian oceanic floor and the distribution of the deformations

relationship between spreading rate and the seismic structure of mid ocean ridges different parts of the global mid ocean ridge system create oceanic crust at rates that differ by more than a factor of ten the rates of supply of heat to these different systems must also vary substantially and it is this heat supply in the form of hot mantle material rising beneath the ridge axis that determines the nature of the magmatic tectonic and hydrothermal processes that control the production of new oceanic crust here we present evidence suggesting that a systematic relationship exists between the depth to zones of elevated temperature and partial melt beneath mid ocean ridges and their spreading rate recent seismic measurements provide robust determinations at six different locations of the depth to the top of the axial low seismic velocity zone which suggest that as full spreading rate decreases from 150 to 20 mm yr 1 the depth below the sea floor to the top of the lvz increases from 1 to 4 km although this relationship might arise in a number of ways our preferred explanation is that the major faults that extend to greater depths on slower spreading ridges1 allow a vigorous circulation of cooling sea water to reach greater depths blocking the upward migration of large melt bodies

mid ocean ridge sulfide deposits evidence for heat extraction from magma chambers or cracking fronts numerous seafloor observations show that the sizes of high temperature hydrothermal sulfide edifices vary dramatically with spreading rate on fast spreading ridges venting occurs from spindly chimneys which reach heights of about 10 m while on slow spreading ridges vents are frequently located near the tops of large sulfide mounds whose volumes may reach 105 106 m3 we argue that such variations are the result of a profound difference in the nature of hydrothermal heat extraction between fast spreading ridges where spreading occurs predominantly by magmatism and slow spreading ridges where there is a significant component of tectonic extension along fast spreading ridges a steady state axial magma chamber can be insulated by a relatively thick conductive boundary layer because heat extraction is limited by low permeability in such systems episodes of vigorous venting are linked to diking events not only because these introduce a significant heat source into the upper crust but also because the intrusion of a dike is the primary source of increased permeability near the ridge axis over a time scale of the order of a decade mineral deposition tends to clog the reaction and upflow zones and there is a high probability that young sulfide structures will be buried by subsequent eruptions on slow spreading ridges tectonic extension maintains the fluid pathways necessary to support vigorous convection in the waning stages of magmatism hydrothermal circulation driven by a downward migrating cracking front can cool the entire crust leading to the formation of very large sulfide deposits as the depth of circulation increases overburden pressures reduce the permeability and the hydrothermal heat fluxes decrease progressively once hydrothermal fluids penetrate the moho serpentinization clogs the fluid pathways and high temperature venting ceases until it is reactivated by a fresh magmatic intrusion

regional heat flow variations across the sedimented juan de fuca ridge eastern flank constraints on lithospheric cooling and lateral hydrothermal heat transport seafloor heat flow has been estimated continuously along a transect on the sedimented eastern flank of the juan de fuca ridge to provide constraints on the scale and rate of lateral heat and fluid transport in the upper igneous crust and on the total flux from the young lithosphere beneath the profile extends from 20 km east of the ridge axis where turbidite sediments lap onto the oceanic crust at an age of less than 1 ma and ends 110 km east of the axis over 3 6 ma crust estimated heat flow is derived from the combination of the depth to igneous basement determined from seismic reflection profiles and basement temperatures measured in nine ocean drilling program boreholes along the transect the strategy is based on the knowledge that in this young area upper basement temperatures are locally homogenized by vigorous hydrothermal circulation and hence vary smoothly between drilling sites at the young end of the transect near the region of extensive outcrop heat flow is only 15 of that predicted for lithosphere of this age heat flow increases systematically to the east reaching the full predicted level about 20 km from the point of sediment basement onlap the anomaly can be accounted for by mixing and or eastward flow of cool water in the upper igneous crust beneath the sediment at a darcian rate of the order of 1 m yr a geochemical signature of fresh seawater in basement is observed many tens of kilometers farther to the east although the thermal signature is no longer present along the remainder of the transect the heat flow conforms very well to that predicted by simple boundary layer cooling theory once the thermal effects of rapid sedimentation on this ridge flank are accounted for

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

submarine fan and slope facies of tonkawa missourian virgilian sandstone in deep anadarko basin the tonkawa sandstone missourian virgilian in the anadarko basin consists of upper middle and lower sandstone units separated by intervening shales the lower tonkawa sandstone consists of coarse to pebbly sandstones deposited in thick coarsening upward sequences the unit is up to 400 ft 120 m thick and the sandstones grade to shale from the southeast to the northwest gross sand isopachs outline northwest southeast oriented linear thicks that extend for tens of miles the middle tonkawa sandstone consists of thin and thick bedded fine grained sandstones displaying wavy and flaser bedding a convolute laminae and some small scale cross laminae these sandstones range in thickness from 100 ft 30 m to 400 ft 120 m the thicks in the middle tonkawa extend nly for a few miles and do not show a preferred directional orientation the upper tonkawa sandstone caps the entire sequence and is overlain by oolitic limestones we interpret the lower tonkawa sandstone to represent a submarine fan complex for the following reasons the regional setting indicates that the sandstones were deposited tens of miles from the shelf edge graded beds convolute laminae and load casts indicate transportation by sediment gravity flows the areal geometry of sandstones indicates channelized flows that coalesced to form an overall fanlike geometry the middle tonkawa sandstones are interpreted as a sequence deposited on the basin slope regional setting indicates that the unit is located immediately basinward of the shelf edge and that it progrades over the lower tonkawa sandstone deposition as sheets or aprons is suggested by lateral continuity at least for several miles of individual beds small scale cross laminae wavy and flaser bedding and sharp bed contacts suggest bottom current activity presence of short numerous channels is suggested by the thick beds of middle tonkawa sandstones that extend for only a few miles although the sedimentology and areal geometry of the upper tonkawa are not discussed in this paper the regional setting and lithologic character suggest shallow water nearshore deposition the entire tonkawa clastic sequence is capped by shallow water marine limestone the lower and middle tonkawa sandstones represent offshelf deposition in an interior basin setting the present study shows that the understanding of the geologic setting and the integration of all available data rather than sedimentologic data alone are required for proper identification the following formations in the anadarko basin also appear to contain fan and or slope facies springer morrow springerian morrowan red fork desmoinesian and cleveland marchand and cottage grove all missourian if the deep water sandstones in interior basins are indeed as common as they appear to be in the anadarko basin then it is crucial for stratigraphic exploration that we recognize and document such deposits in other interior basins as well

ductile shear deformation of quartzite in an alpine crustal thrust ambin massif abstract in this paper we show that fabric analysis gives good results when the sampling is done in an homogeneous material in a well known tectonic environment a quartzitic layer situated in the autochtonous basement of the ambin massif below the nappe des schistes lustres french italian alps has been choosen because the first ductile deformation phase is clearly defined by the microstructures and because the metamorphic history is well known the quartz c axis diagrams are characterized by two asymmetric crossed girdles and the one containing the maxima is inclined westwards we propose that these fabrics result from plastic deformation of the quartzite occurring with the basal plane as a dominant gliding plane the fabrics define a shear sense towards the west the angle between the basal planes and the foliation which varies from 15 to 40 is at least qualitatively related to the macroscopic strain our study confirms the existence of a regional large crustal thrust which has occurred during the obduction of oceanic material schistes lustres on the european continent

tectonometamorphic evolution of the chewore inliers partial re equilibration of high grade basement during the pan african orogeny only minor structural reworking during m2 granulite terrane the chewore inliers are isolated outcrops of the zambezi mobile samples within 2 km of the basal thrust margin preserve m1 belt within the mesozoic lower zambezi rift valley in zimbabwe mineral assemblages but these minerals were chemically re equidetailed mapping has recognized four terranes the zambezi librated without recrystallization during m2 at conditions of 5 6 quartzite granulite and ophiolite terranes apart from the 1 5 kbar and 631 100 c granulite terrane samples were ophiolite terrane all are dominated by supracrustal gneisses with totally recrystallized in shear zones at the margin of this terrane concordant granitic orthogneiss units of 1071 8 and 1083 these samples equilibrated at conditions identical to the peak of 8 ma age these terranes experienced low p high t metamorphism m2 at 7 7 1 9 kbar and 590 110 c the re equilibrated m1 terminated by isobaric cooling at 945 34 ma m1 and recrystallized sample sets define two points on the clockwise assemblages of sillimanite spinel garnet garnet orthopyroxene and p t path experienced by the granulite terrane during further two pyroxene mafics are recorded in the granulite terrane and burial and reworking in the pan african orogeny and are consistent conditions of formation were 4 4 1 7 kbar and 800 c m1 with the m2 p t path documented for the other terranes mineral parageneses and associated ductile deformation structures dominate the granulite terrane but m1 mineral parageneses are only preserved as sillimanite spinel inclusions in garnet cores in the other terranes the zambezi quartzite and ophiolite terranes were almost totally recrystallized during reworking in the m2

the influence of intrabasinal faults on the development of a linked thrust system the mesozoic and cenozoic rocks exposed in the arve valley region of the external french alps are used to assess the role of early intrabasinal faults on later thrust fault evolution the early intrabasinal faults produced at some time from latest upper cretaceous to tertiary strike parallel or subparallel to later neo alpine thrusts where early faults dip away from the thrusts they are generally cut through and occasionally are overturned during this process in one example extreme overturning has allowed partial reactivation early faults dipping in the same direction as thrusts may a be reactivated b initiate ramping of the thrust ahead of the preexisting fault c be cut through by the thrust d cause pinning of the thrust at the footwall of the fault and folding against the fault as displacement continues buttressing from this work it is evident that intrabasinal faults exerted a major influence on the distribution of mechanical heterogeneities these heterogeneities include variations of stratigraphic thickness and type across faults fault related unconformities and the presence of the fault itself during the period of contraction such features strongly controlled the development of the stress field produced ahead of an advancing thrust and hence influenced the position of thrust fault propagation within the stratigraphy

cooling of the lower oceanic crust thermal models of mid ocean ridges that balance the influx of heat from magmatic sources with the removal of heat by conduction and hydrothermal circulation allow quantification of cooling of young oceanic crust these models reproduce key observations relating to crustal accretion and hydrothermal cooling at fast spreading ridges the rate of cooling is constrained both by the bathymetry of ridge axes and by olivine compositions from ophiolite gabbros successful models involve extensive hydrothermal cooling of the lower crust within 20 km of the ridge with 50 70 kw of hydrothermal cooling for every 1 m of ridge axis at crustal ages of 0 1 0 4 ma these timates can be used to refine global models of geochemical and thermal fluxes close to spreading ridges

the restoration of thrust systems and displacement continuity around the mont blanc massif nw external alpine thrust belt abstract foreland propagating external thrust belts may be considered as essentially plane strain phenomena so that displacements can be correlated throughout their linked three dimensional fault geometry this approach has been applied to part of the northwest external french swiss alps around the mont blanc basement massif imbricates of basement and cover sequences on the sw margin of this massif restore to a width in excess of 77 km with an implicit shortening of at least 67 km these displacements can be correlated with those in the neighbouring helvetic nappes by transferring movements via lateral branch lines onto the mont blanc thrust by reappraising thrust geometries the helvetic ultrahelvetic nappe complex has been restored to a width of 114 km to the ese of the aiguilles rouges basement massif displacements on the internal se margin of the mont blanc massif estimated by balanced sections and a restoration of the ultrahelvetic klippen in the sub alps exceed 59 km thrust continuity incorporating the restorations of nappes and imbricate geometries around the mont blanc massif is illustrated on a crude restored branch line map which also serves as a preliminary palaeogeographic reconstruction external thrust systems to the east of the external belledonne aiguilles rouges massif restore to a width of at least 140 km in the footwall to the frontal pennine thrust

evaluating the depositional environment lithofacies variation and diagenetic processes of the wolfcamp b and lower spraberry intervals in the midland basin implications for reservoir quality and distribution detailed facies characterization in the wolfcamp b and lower spraberry intervals of two drill cores in the midland basin has yielded five main lithofacies with distinctive physical chemical and biologic attributes the main attributes for facies identification include lithology and or mineralogy texture and or fabric porosity hydrogen index and total organic carbon content the methodologies are focused on detailed core description thin section petrography quantitative x ray diffraction and field emission scanning electron microscopy sem porosity data are primarily based on gas research institute core laboratories measurements and field emission sem assessment moreover the depositional and diagenetic controls on facies development are addressed to assess the dominant geological processes that govern reservoir quality and distribution a model of five end member facies is proposed to characterize source and reservoir elements through delineating facies tracts the five end member facies are as follows facies 1 silty mudstone optimal source and optimal to fair reservoir facies 2 muddy siltstone optimal source and optimal reservoir facies 3 silty calcareous mudstone good source and good reservoir facies 4 bioclastic wackestone floatstone fair source and fair reservoir and facies 5 packstone grainstone poor source and poor to excellent reservoir the proposed facies scheme aims to provide a more comprehensive approach to capture the high vertical and lateral variability in this mixed carbonate and fine grained clastic succession through this detailed textural compositional sedimentologic and diagenetic approach this facies model can be used to better understand reservoir quality and distribution throughout the midland basin

permian bone spring formation sandstone play in the delaware basin part i slope new exploration in the permian leonardian bone spring formation has indicated regional potential in several sandstone sections across portions of the northern delaware basin significant production has been established in the first second and third bone spring sandstones as well as in a new reservoir interval the avalon sandstone above the first bone spring sandstone these sandstones were deposited as submarine fan systems within the northern delaware basin during periods of lowered sea level the bone spring as a whole consists of alternating carbonate and siliciclastic intervals representing the downdip equivalents to thick abo yeso wichita clear fork carbonate buildups along the leonardian shelf margin hydrocarbon exploration in the bone spring has traditionally focused on debris flow carbonate deposits restricted to the paleoslope submarine fan systems in contrast extend a considerable distance basinward of these deposits and have been recently proven productive as much as 40 48 km south of the carbonate trend

centroid depths of mid ocean ridge earthquakes dependence on spreading rate from inversions of teleseismic p and sh waveforms we have determined the source parameters of 50 large earthquakes that occurred during 1962 1983 on slowly spreading mid ocean ridges all events are characterized by predominantly normal faulting on planes that dip at approximately 45 and strike parallel to the local trend of the ridge axis centroid depths range from 1 to 6 km beneath the seafloor the p waves from these earthquakes show strong water column reverberations suggesting that fault rupture extended to the seafloor under the assumption that the centroid depth marks the mean depth of fault slip earthquake faulting extended to a depth of 2 10 km for these earthquakes the water depths inferred from the predominant periods of the water column reverberations constrain the epicenters of these earthquakes to lie within the relatively deep inner floor of the median valley the maximum centroid depths of ridge crest earthquakes decrease with increasing spreading rate and the maximum seismic moment may also decrease with increasing spreading rate these results indicate a general decrease with spreading rate in maximum thickness of the mechanically strong layer beneath the ridge axis region the concentration of large earthquakes within the deepest parts of the median valley and the depth extent of seismic faulting support lithospheric necking models for the origin of the median valley

finite strain patterns in some alpine nappes abstract the patterns of finite strain in some alpine nappes and thrust sheets are reviewed together with their tectonic evolution glarus nappe the finite strain pattern approximately that of heterogeneous simple shear was acquired during upper oligocene times when the helvetic thrust block was deformed together with its infrastructure and basement the glarus thrust was formed during miocene times and modified by pliocene to recent differential uplift morcles nappe this large recumbent fold nappe overrode the aiguilles rouges massif and its cover towards the northwest the finite strain pattern resulted from successive diagenetic compaction multilayer buckling and heterogeneous simple shear high strains occur along the inverted limb of the nappe and fold hinges are oriented subperpendicular to the nw stretching lineation final emplacement of the nappe during the miocene was perhaps a later event chartreuse massif 33 e w shortening was developed across this fold and thrust belt during post helvetian times by decollement along the oxfordian shales in response to thrusting and uplift in the belledonne basement the oxfordian shales had earlier accommodated a pre helvetian probably oligocene deformation in the basement and its trias bajocian cover when n030 trending subhorizontal folds cleavage and a stretching lineation 18 n030 stretching were developed digne nappe detached along the keuper evaporites the cover was displaced westwards in two stages 1 late oligocene with folding cleavage development formation of the frontal slices and an overall e w shortening of 20 and 2 late miocene pliocene after emplacement of the embrunais nappes in the east producing the digne thrust it is concluded that for these alpine nappes geological criteria must be used to establish their evolution if the internal deformation can then be assigned to part of this evolution the pattern of finite strain can be used to quantify and elucidate that part a maximum of information is gained if the incremental deformation history can also be obtained from study of syntectonic fibres

reconciling plate tectonic reconstructions of alpine tethys with the geological geophysical record of spreading and subduction in the alps article a new reconstruction of alpine tethys combines plate kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution from sea floor spreading through subduction to collision in the alps unlike previous models which relate the fate of alpine tethys solely to relative motions of africa iberia and europe during opening of the atlantic our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record the motions of these microplates adria iberia alcapia alkapecia and tiszia relative to both africa and europe during late cretaceous to cenozoic time involved the subduction of remnant tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces 1 131 84 ma intra oceanic subduction of the ligurian part of alpine tethys attached to iberia coincided with eo alpine orogenesis in the alcapia microplate north of africa these events were triggered primarily by foundering of the older 170 131 ma neotethyan subduction slab along the ne margin of the composite african adriatic plate subduction was linked by a sinistral transform system to e w opening of the valais part of alpine tethys 2 84 35 ma subduction of primarily the piemont and valais parts of alpine tethys which were then attached to the european plate beneath the overriding african and later adriatic plates nw translation of adria with respect to africa was accommodated primarily by slow widening of the ionian sea 3 35 ma recent rollback subduction of the ligurian part of alpine tethys coincided with western alpine orogenesis and involved the formation of the gibraltar and calabrian arcs rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable retreating adriatic and african slabs during slow convergence of africa and europe the upper european iberian plate stretched to accommodate this slab retreat in a very mobile fashion while the continental core of the adriatic microplate acted as a rigid indenter within the alpine collisional zone the subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the alps and apennines as well as beneath parts of the pannonian basin the adriatic sea the ligurian sea and the western mediterranean the predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10 30 indicating that parts of slabs may be superposed within the mantle transition zone and or that some of this subducted lithosphere became seismically transparent

cooling rates in the lower crust of the oman ophiolite ca in olivine revisited debate over the mechanism of accretion of the lower oceanic crust has centered around the gabbro glacier and the sheeted sills models the thermal profile of the crust specifically the roles of hydrothermal circulation and cooling rate is a key component in distinguishing between these two models results of this study show no systematic variation of cooling rate with depth in the lower crust of the khafifah section in the wadi tayin massif of the oman ophiolite additionally very high rates recorded near the base of the crust suggest that hydrothermal circulation plays an important role in the removal of heat throughout the crust while the conclusions presented here do not rule out the possibility of accretion by gabbro glacier they do contradict the initial tenet of the gabbro glacier model convective heat loss by hydrothermal circulation can penetrate to moho depths and crystallization is not by necessity constrained to the upper crust on the basis of these results it can be concluded that the sheeted sills model is a thermally viable mechanism for accretion of oceanic lower crust

a numerical model of hydrothermal cooling and crustal accretion at a fast spreading mid ocean ridge 1 there are two competing models for lower crustal accretion at fast spreading ridges in the gabbro glacier model all the lower crust solidifies in a magma lens at the dike gabbro boundary and then flows to its final level in the sheeted sill model the lower crust is formed by sills emplaced at a variety of depths we present a steady state numerical representation of the sill model that explicitly includes hydrothermal circulation the crust is accreted uniformly at the ridge axis at all depths and hydrothermal circulation occurs in crustal rocks that have cooled below a threshold temperature the results show that when the permeability exceeds a threshold value 4 10 14 m2 for a cracking temperature of 800 c and a uniform permeability hydrothermal circulation can cool the entire crust near the ridge axis producing vertical isotherms in the lower crust at lower permeabilities the properties of seawater lead to bimodal cooling with the lowermost crust cooling more slowly than shallower depths these results are reasonably consistent with studies of the seismic structure of the east pacific rise and of plagioclase crystal size distributions in gabbros from oman we infer that the sheeted sill model cannot be discarded on thermal grounds

the arc of the western alps in the light of geophysical data on deep crustal structure recently two international deep seismic campaigns in the western and central alps etude continentale et oceanique par reflexion et refraction sismique progetto strategico crosta profonda ecors crop roure et al 1996b and national research program 20 nrp 20 pfiffner et al 1997 have been completed here we present a synoptic interpretation of the wealth of geophysical data about deep crustal structure of the alps collected during the past 40 years including the two above mentioned geophysical projects the tectonic reinterpretation of the ecors crop high resolution seismic transect is based on an evaluation of the deep crustal structure by integrating new and literature data on surface geology combined with previously published interpretations regarding the central alps schmid et al 1996 this study reveals substantial differences in geometry and kinematics between transects across the western and central alps respectively at depth the transition between the central and western alps is marked by the western limits of an adriatic lower crustal wedge shaped structure and the northeastern limits of a similar structure made of european lower crustal material at the surface it coincides with a corridor of dextral strike slip along the tonale and simplon lines in addition the thickness of the seismogenic zone shows a remarkable variation from over 40 km beneath the penninic realm of the western alps to less than 20 km in the central alps the formation of the western alpine arc was initiated during convergence and collision before 35 myr ago when the adriatic micro plate moving northward with respect to the european foreland caused sinistral transpression in the western alps while the central and eastern alps underwent head on convergence and collision during the post collisional stage i e after 35 myr ago the arcuate shape of the western alps was accentuated by wnw directed movement and anticlockwise rotation of the adriatic microplate decoupled from the central and eastern alps along the tonale simplon dextral shear zone this led to wedging of lower crustal slices both in the western alps and in the central alps the new tectonic interpretation of the ecors crop transect allows a kinematic model to be established for crustal shortening in the western alps during the past 35 myr the ivrea mantle plays the role of a backstop in our tectonic model we distinguish three episodes of post collisional crustal shortening along the ecors crop transect from 35 to 30 ma the brianconnais basement was back thrusted over the gran paradiso units leading to 30 km of crustal shortening first episode in the early miocene movements concentrated mainly along the penninic frontal thrust and resulted in about 60 km shortening second episode post 12 ma shortening within the external massifs is associated with folding in the jura mountains when the crust was shortened by an additional 30 km third episode

estimation of oceanic hydrothermal heat flux from heat flow and depths of midocean ridge seismicity and magma chambers the difference between the heat flow predicted by thermal models of the lithosphere and that measured at the seafloor can be used to estimate the cooling by hydrothermal circulation however this approach may yield an overestimate because measurements in thinly sedimented young crust are typically made at topographic lows where hydrothermal circulation may systematically lower heat flow to circumvent this bias we estimate the cooling using the depths of midocean ridge earthquakes and magma chambers in addition to heat flow data the results indicate deeper hydrothermal circulation at slow spreading ridges and higher near axial hydrothermal heat loss at fast spreading ridges the predicted global hydrothermal heat flux is 80 of that for models constrained only by heat flow

precollisional multistage exhumation of subducted continental crust the sesia zone western alps 1 the sesia zone within the tertiary arc of the western alps is a relic of the subducted part of the adriatic continental margin along the se border of the tethyan ocean the sesia zone comprises three basement nappes which individuated during late cretaceous 65 80 ma subduction to different depths at high pressure hp blueschist eclogite facies conditions peak pressures of 1 0 1 2 1 0 1 5 and 1 5 2 0 gpa the thrusts bounding these nappes developed where the crust was previously thinned during jurassic rifting crustal scale shear zones partly overprinted these early thrusts and exhumed coherent slices of crust containing hp rocks initial exhumation of the internal part of the accreted margin involved thrusting d1 and transpressional shearing d2 along a subvertical e w trending mylonitic shear zone under retrograde blueschist to greenschist facies conditions this exhumation was nearly isothermal to a depth of about 25 km where the basement nappes were juxtaposed subsequent exhumation of these nappes to a common depth of about 15 20 km occurred in the footwall of a greenschist facies top se extensional shear zone d3 preserved in some of the highest mountain peaks of the sesia zone new rb sr mineral ages constrain d2 to have occurred at about 60 65 ma and d3 at about 45 55 ma thus top se extensional exhumation was broadly coeval with eocene se directed subduction of the liguro piemont oceanic lithosphere beneath the adriatic margin slow cooling and erosional denudation of the sesia zone from 45 to 30 ma occurred in the hanging wall of the gressoney extensional shear zone d4 which itself contributed to the exhumation of eocene hp and ultra hp oceanic rocks in its footwall by 30 ma hp rocks of the sesia zone were intruded by shallow granitic plutons which were eroded and redeposited within volcanoclastic sediments oligo miocene insubric backfolding and thrusting d5 only exhumed northeastern parts of the sesia zone where hp metamorphism is absent or was overprinted by tertiary temperature dominated metamorphism most exhumation of continental hp rocks in the sesia zone therefore preceded tertiary alpine collision and coincided with late cretaceous to early tertiary subduction of the adriatic and tethyan lithosphere the transition from d2 to d3 in the sesia zone is interpreted to mark a change from high stress oblique se directed subduction and accretion of the distal adriatic continental margin to nw retreating low stress subduction of the liguro piemont oceanic lithosphere

hydrothermal circulation through mid ocean ridge flanks fluxes of heat and magnesium thermally driven convection of seawater occurs through oceanic crust of all ages at the seafloor spreading axis on mid ocean ridge flanks and in the ocean basins at the ridge axis and on the flanks circulating seawater produces a major chemical exchange between the oceans and the crust based on heat budget constraints and the composition of hot springs between 10 and 40 of the river flux of mg can be taken up during high temperature alteration of the basaltic crust along the ridge axis most of the hydrothermal heat loss however occurs on the mid ocean ridge flanks where the temperatures are lower and the seawater flux correspondingly larger the estimated heat loss on the flanks is so large that upwelling must occur over a large fraction 5 30 of the seafloor less than 65 ma in age if temperatures are 20 c and seepage velocities are on the order of 10 to 100 cm y the circulating seawater needs to lose on average less than 1 2 of its mg content in order to solve the mg mass balance for the oceans chemical fluxes through mid ocean ridge flanks are poorly known because of the wide range of crustal conditions that prevail there and the paucity of study to date the most critical parameter for characterizing crustal conditions is temperature in basement which is a function of crustal age basement topography and sediment thickness and permeability basement temperature which can usually be inferred from heat flow and seismic reflection surveys largely determines the change in the composition of seawater circulating through basement this change can be inferred in turn from profiles of sediment porewater chemistry all sites studied to date with temperatures at the sediment basement interface 25 c have a large component of advective heat loss and show only a small 80 mg loss both types of sites may be important for chemical fluxes whether the cooler sites are important depends on how much the seawater changes in composition as it circulates through the crust only small changes are needed whether the warmer sites are important depends on how much heat is lost by advection in this type of setting the warmer sites could produce significant chemical fluxes even if they are scarce they could account for the entire river input of mg to the oceans even if they represent only 8 20 of the total advective heat loss on ridge flanks

the transition from passive to active margin tectonics a case study from the zone of samedan eastern switzerland the zone of samedan is part of a fossil early mesozoic rift system originally situated in the distal lower austro alpine domain of the adriatic passive continental margin an early mesozoic configuration of asymmetrical rift basins bounded by relative structural highs compartmentalized late cretaceous active margin tectonics jurassic half grabens were folded into arcuate synclines whereas relative structural highs engendered thin imbricated thrust sheets west directed thrusting and folding initiated at the surface and continued to depths favoring mylonitization under lower greenschist facies conditions at this time liguria piemontese ophiolites were accreted to lower austro alpine units directly underlying the zone of samedan late cretaceous orogenic collapse of the adriatic active margin involved the reactivation of west directed thrusts as low angle top to the east normal faults these faults accommodated extensional uplift of liguria piemontese ophiolites and lower austro alpine units beneath and within the zone of samedan during paleogene collision some late cretaceous faults in the zone of samedan were reactivated under lower anchizonal conditions as north directed thrusts the latter stages of this early tertiary thickening were transitional to brittle high angle normal faulting associated with top to the east extension and spreading above the warm uplifting lepontine dome

jura alps and the boundary of the adria subplate abstract the thin skinned jura fold thrust belt is the frontal part of a thick skinned late miocene alpine nappe important late miocene structures in the alps that help define this nappe are the external massifs in the north the orobic thrusts and the piemontese southern alps in the south the giudicarie brenner line in the east and more vaguely the south end of the belledonne massif in the west a bottom boundary compatible with the data is the brittle ductile transition bdt this jura nappe is separated from the latest oligocene early miocene helvetic nappe system most obviously by the late miocene orobic giudicarie brenner fault complex in contrast the distinctive boundary of the early miocene thick skinned helvetic nappe was the iorio tonale line it in the south merging into the piemontese southern alps at what may be termed the locarno singularity the point of minimum width of the thick skinned alps the northern boundary passed through the gotthard and montblanc massifs motion along the southern boundary was dextrally transpressive associated with complex strain partitioning patterns one part of these patterns is the confusing entity comprising the piemontese southern alps and the lepontine dome the slivers composing the piemontese southern alps are dragged dextrally by the iorio tonale strike slip at the locarno singularity and thereby exhibit an important characteristic trait of exotic terranes crustal slivers dragged along strike slip faults the lepontine dome around the locarno singularity on the north side of the iorio tonale line displays the characteristics of a backstop in thrust systems as modeled in sandbox experiments the special boundary functioning as a backstop compatible with the transpressive kinematics was the ivrea body a strong mafic ultramafic granulitic complex which in the early miocene migrated dextrally along the iorio tonale line forcing detachment to descend into the hot middle crust and producing an upsurge of the hot masses in the late miocene jura phase this particular impediment had moved to the west enabling decollement at the brittle ductile transition to propagate across the insubric line into the lombardic domain large scale strain partitioning manifestations resemble those of the equally dextrally transpressive southern boundary of the caribbean plate in spite of a difference in scales the foremost of these manifestations are regional right slip faults slicing through a broad band of contraction accompanied by collapse basins

the tectono metamorphic history of the valaisan domain from the western to the central alps new constraints on the evolution of the alps petrographic and structural studies on metasedimentary rocks of the valaisan domain from the engadine window switzerland to the petit st bernard france show that this entire domain was subjected to high pressure low temperature conditions during the alpine orogeny the pressure and temperature conditions increased from east to west the metasedimentary rocks of the engadine window and the grisons area are characterized by blueschist facies conditions 12 13 kbar 350 400 c defined by mg carpholite and chloritoid occurrences toward the west in the petit st bernard and versoyen units the metamorphic conditions reached the eclogite facies 15 16 kbar 500 c the shortening direction associated with the high pressure metamorphic event was oriented northwest southeast all over the valaisan domain this direction is compatible with the direction of convergence between the european and apulian plates in early tertiary time 65 35 ma in the eastern and central alps blueschist facies rocks occur below the austroalpine nappes over an area of 300 20 km 2 from the tauern window to the grisons area and have a thickness around 10 km this volume of blueschist facies rocks is in contrast with eclogite facies rocks of western alps that form only a small slice with a thickness of 2 to 5 km we interpret the difference in volume and metamorphic conditions from east to west as being due to a change of the subduction style in the east we assume the formation of a large wedge with a thickness of 40 50 km such that rocks underwent blueschist metamorphism and were exhumed before collision between the european and apulian plates in the west the petit st bernard and the versoyen units were metamorphosed and extruded in a subduction channel above the subducting slab the data further allow us to conclude that the valaisan domain was an ocean that was independent of the piemontese ocean and that had an important place in the youngest phase of the evolution of the alps before the collision

high resolution ambient noise tomography of the southwestern alps and the ligurian margin the southwestern alps and the ligurian margin is a region of moderate seismicity with a high rate of small to moderate events identifying the active faults in this very densely populated region is critical to better assess the hazard and mitigate the risk an accurate 3 d velocity model of the shallow to middle crust is a fundamental step to better locate the seismicity and hence the faults from which it originates we performed ambient noise surface wave tomography based on all available continuous seismological data from the french and italian permanent networks resif ingv rsni and current and past temporary experiments alparray cassat sisvar risval in addition to these available data we deployed three more stations to improve the spatial resolution in a region with sparse seismic station coverage overall we used 55 inland seismic stations 5 oceans bottom seismometers and 2 offshore cabled site sensors data span the 2014 2018 time period time series from all available components were cross correlated to reconstruct both rayleigh and love wave green s functions for each station pair rayleigh and love group velocity dispersion curves were semi automatically picked using a frequency time analysis then we regionalize these group velocities to build 2 d rayleigh and love velocity maps between 1 5 and 9 s period using a two step inversion we estimate the best 3 d shear wave velocity model the first step is based on a neighbourhood algorithm to recover the best three layers velocity model at each cell of the model we then use this three layer model as a starting model in a perturbational method based on finite elements at periods up to 5 s the spatial variation of the velocity is well correlated with the effective geology of the area lower velocities are observed in areas where the sedimentary cover is thicker such as the var and paillon valley near nice or in the subalpine domain in the northwestern part of the region higher velocities are retrieved in areas where massifs are present such as the argentera mercantour massifs in the northeastern or the esterel massif in the southwestern part of the region

effects of the legacy of axial cooling on partitioning of hydrothermal heat extraction from oceanic lithosphere the predicted and observed heat flux across the seafloor these methods have assumed a dynamic steady state thermal system we show that this assumption is not warranted and leads to an incorrect partitioning of hydrothermal circulation between ridge axes and flanks to more accurately estimate hydrothermal heat loss on ridge axes and flanks we consider the spatial and temporal extent and vigor of axial hydrothermal circulation in calculating hydrothermal heat extraction axial fluid circulation perturbs the thermal state of oceanic lithosphere for 5 ma after that circulation ceases reducing the hydrothermal heat extraction on ridge flanks we find 30 of hydrothermal heat extracted on axis 10 extractednearaxis fromendofaxialhydrothermalcirculationto1ma and 60 extracted from lithosphere 1 ma

sedimentology and genetic stratigraphy of dean and spraberry formations permian midland basin texas the spraberry trend of west texas once known as the world s largest uneconomic oil field will undoubtedly become an increasingly important objective for the development of enhanced oil recovery techniques in fine grained low permeability low pressure reservoirs as the trend expands facies and stratigraphic data should be integrated into exploration strategies the spraberry and dean formations may be divided into three genetic sequences each consisting of several hundred feet of interbedded shale and carbonate overlain by a roughly equal amount of sandstone and siltstone these sequences record episodes of shelf margin progradation deep water resedimentation of shelf derived carbonate debris followed by influxes of terrigenous clastics into the basin by way of feeder channels or submarine canyons and suspension settling of fine grained sediment from the water column four lithofacies comprise the terrigenous clastics of the spraberry and dean formations 1 cross laminated massive and parallel laminated sandstone 2 laminated siltstone 3 bioturbated siltstone and 4 black organic rich shale carbonate lithofacies occur mostly in the form of thin bedded turbidites slump and debris flow deposits terrigenous clastic rocks display facies sequences isopach patterns and sedimentary structures suggestive of deposition from turbidity currents and long lived saline density underflow and interflow currents clastic isopach patterns reflect an overall southward thinning of clastics in the midland basin channelized flow and suspension settling were responsible for the formation of elongate fan shaped accumulations of clastic sediments