the deep water fold and thrust belt offshore nw borneo gravity driven versus basement driven shortening the deep water region offshore nw borneo is an active fold and thrust belt that hosts a signifi cant number of proven hydrocarbon accumulations in the past two mechanisms have been discussed as primary control for neogene to holocene folding and thrusting in this deep water province 1 basement driven crustal shortening and 2 gravity related delta tectonics in this study new balanced interpretations of regional crustal scale depth migrated twodimensional 2 d multichannel seismicrefl ection profi les are presented that provide for the fi rst time quantitative data on tectonic shortening throughout the entire deep water fold and thrust belt of nw borneo we use our tectonic restorations to compare the amount of deep water shortening on the nw borneo slope to the amount of extension across the nw borneo shelf a key result of this balancing study is the observation that pliocene to holocene gravity driven shortening decreases from south to north while the total amount of shortening increases slightly to the north consequently the amount of purely basement driven compression along nw borneo is strongly inferred to increase toward the north because most of the shortening is late pliocene and younger we interpret the tectonic shortening to be ongoing

rb sr systematics of permian volcanites in the schwarzwald sw germany from the quartz porphyry occurrences of haigerach and geisberg central schwarzwald which were dated by minerals and whole rock samples the whole rock samples generally yielded lower ages than the minerals this result agrees with other studies on apparently rejuvinated whole rock ages of acid volcanic rocks compare mckerrow et al 1980 petrographic and geochemical observations show that two processes disturbed the rb sr relations 1 fast alterations immediately after extrusion such as sericitization during autohydrothermal bleaching in the pipe area of the volcanoes gain of rb addition of common sr 2 loss of radiogenic 87sr due to long lasting exchange processes with groundwaters

3d seismic study of a shale expulsion syncline at the base of the champion delta offshore brunei and its implications for the early structural evolution of large delta systems an example of a late miocene expulsion rollover syncline related to mobile shale is described from 3d seismic data offshore brunei prodelta shales accumulated in the subsiding syncline were altered after deep burial by overpressure increase and hydraulic fracturing consequently seismic facies was modified from a continuous divergent reflection pattern to a low amplitude disrupted to chaotic seismic facies bounded by a high amplitude event that cross cuts original stratification without the resolution provided by 3d data the high amplitude event would be mistaken for early growth faults and the subdued country rock reflections for mobile shale typical features at the base of large deltas this study shows the existence of expulsion rollovers related to mobile shale which have not been described before and demonstrates that not all bright reflections at chaotic coherent facies boundaries are actually fault planes it also suggests that expulsion synclines even during early phases of delta development may be compaction related features rather than ones that drive the shale mass out of the area of progradation

initial observations of lunar impact melts and ejecta flows with the mini rf radar 1 the mini rf radar on the lunar reconnaissance orbiter spacecraft has revealed a great variety of crater ejecta flow and impact melt deposits some of which were not observed in prior radar imaging the craters tycho and glushko have long melt flows that exhibit variations in radar backscatter and circular polarization ratio along the flow comparison with optical imaging reveals that these changes are caused by features commonly seen in terrestrial lava flows such as rafted plates pressure ridges and ponding small 20 km sized craters also show a large variety of deposits including melt flows and ponds two craters have flow features that may be ejecta flows caused by entrained debris flowing across the surface rather than by melted rock the circular polarization ratios cprs of the impact melt flows are typically very high even ponded areas have cpr values between 0 7 and 1 0 this high cpr suggests that deposits that appear smooth in optical imagery may be rough at centimeter and decimeter scales in some places ponds and flows are visible with no easily discernable source crater these melt deposits may have come from oblique impacts that are capable of ejecting melted material farther downrange they may also be associated with older nearby craters that no longer have a radar bright proximal ejecta blanket the observed morphology of the lunar crater flows has implications for similar features observed on venus in particular changes in backscatter along many of the ejecta flows are probably caused by features typical of lava flows

rapid burial and exhumation during orogeny thickening and synconvergent exhumation of thermally weakened and thinned crust variscan orogen in western europe we present a model demonstrating that the presence of a thinned and thermally weakened crustal domain is a prerequisite for the formation of an orogenic root in mountain belts furthermore this mechanism permits burial to 50 to 70 km in time periods of less than 20 myr and exhumation from these depths in less than 10 myr our example from the variscan belt is based on field geology petrology of metamorphic rocks and detailed geochronology it describes an evolution from i sedimentation and magmatism during back arc extension ii compression leading to burial thickening of the lithosphere and granulite facies metamorphism followed by iii exhumation formation of dehydration melts migmatites and late intrusive granites the existing u pb ar ar data constrain this evolution to no more than 20 to 25 myr thermorheological modelling starts from a hot thinned crust forming a narrow 50 km wide orogenic root within 15 myr at a maximum of 50 km depth and subsequent exhumation by extrusion within 7 myr the model explains exhumation rates of 3 to 4 mm year by compressional extrusion and shows that extension cannot do the same job within the same time extrusion transported the internal thermal structure into the upper crust within a short time followed by rapid cooling whereas exhumation through extension would cause mantle upwelling and the formation of a long lived thermal anomaly the latter would contradict the geochronological and petrological database the model explains orogeny as a thermorheological process without needing to involve an external heat source from the mantle and presents a new explanation of the high temperature and low pressure conditions very typical of the variscan orogenic crust

the rotations of the variscides during the carboniferous collision paleomagnetic constraints from the vosges and the massif central france abstract this study aims at completing and refining results from previous paleomagnetic investigations carried out in various outcrops of the european variscan belt sampling was performed in visean effusive and intrusive rocks of the southern vosges basin and the northern massif central all emplaced in the time range 345 340 ma stepwise thermal demagnetization of 254 specimens from 13 sites of the doller valley and nine sites of the massif central has yielded a very similar paleomagnetic record for both areas with the exception of post carboniferous overprints isolated in the southern vosges two groups of directions with both normal and reversed polarity have been evidenced the first group of directions labelled c occurs in both areas and is characterized by scarce pre tectonic magnetizations two sites and by syn tectonic overprints five sites acquired during the late visean convergence i e in the time range 340 328 ma the mean pole co is 28 s 45 e k 139 95 5 the main group labelled b shows a negative fold test and a positive reversal test indicating that the magnetizations are post tectonic overprints acquired after the main tightening phase i e after 328 ma at a few sites in both areas were evidenced syn tectonic b magnetizations that are in favour of an overprinting in the context of post visean extension tectonics the mean post tectonic b direction of the doller valley southern vosges 62 25 k 52 95 6 n 11 vgp 8 n 127 e is consistent with the mean post tectonic b direction 72 23 k 126 95 5 n 6 vgp 3 n 114 e obtained from the tuffs the grey microgranite and the dyke intrusive into the microgranite of the massif central the occurrence of similar paleomagnetic records in the eastern and central variscides implies that from the massif central to the sudetes the belt has probably moved as one block since early carboniferous the change in inclination of the c components suggests a southward drift of the moldanubian and saxothuringien variscides in the late visean 340 328 ma according to geological features in the same time the rhenohercynian crust was underplating the saxothuringian arc and fore arc zone subsequent to 328 ma the drift turned into a rapid clockwise rotation by about 70 around a pole located on southeastern corner of baltica leading to the closure of the rhenohercynian oceanic basin in the namurian large scale overprinting b components likely related to post rotation extension affected the internal belt the convergence continuing the variscides underwent a second clockwise rotation by about 45 in the late namurian westphalian 320 305 ma stacking of the rhenohercynian sedimentary cover and thrusting over the london brabant basement may be related with this motion

geochronology of the mid german crystalline rise west of the river rhine the mid german crystalline rise has its westernmost exposures at the western margin of the rhine graben in the southern pfalz and the northern alsace the outcrops are made up of granitoid rocks and minor volcano sedimentary sequences radiometric ages obtained by u pb pb pb sm nd and rb sr analyses of the igneous rocks from this area range from 433 to 325 ma thus covering a time span from the silurian to the end of the lower carboniferous because the investigated rocks are according to their chemical composition largely related to subduction zone environments the following three geodynamical scenarios are postulated always taking subduction of oceanic crust beneath the mid german crystalline rise into account a subduction of the rheic ocean during the silurian from the north b subduction of the rhenohercynian ocean during the late devonian 369 ma from the north c subduction of the saxothuringian ocean during the lower carboniferous 334 ma from the south

tectonic evolution of the european variscan belt constrained by palaeomagnetic structural and anisotropy of magnetic susceptibility data from the northern vosges magmatic arc eastern france geochronology structural and anisotropy of magnetic susceptibility data from the northern vosges batholith which belongs to the northern vosges mid german crystalline rise arc show contrasting emplacement modes of southern granodiorites and northern granites the ene wsw trending fabrics of granodiorites 346 334 ma are parallel to the metamorphic cleavage affecting the host rocks developed during regional compression the nnw sse trending fabrics of younger granitoids c 330 ma reveal an extensional emplacement mode associated with a normal shear zone separating the two magmatic suites palaeomagnetism shows that the switch from a compressive to an extensional regime coincides with a regional counterclockwise rotation the 330 325 ma extension is further supported by palaeomagnetic and seismic data indicating southeastward tilt of the whole batholith finally the system is rotated clockwise without any structural overprint data from the early carboniferous northern vosges magmatic arc and remote bohemian massif suggest that this evolution is valid for the whole eastern branch of the european variscan belt for which the following model is proposed 1 late devonian early carboniferous east west shortening of the variscides above the rhenohercynian subduction zone 2 axial nnw sse shortening of the assembled variscan orogen associated with 3 internal sinistral rotation of inherited rhenohercynian transform faults and shortening of intervening blocks 4 east west extension and dextral external rotation of blocks between dextrally reactivated transforms supplementary materials analytical procedures for geochronology magnetism anisotropy of magnetic susceptibility and palaeomagnetism are available at www geolsoc org uk sup18635

age of variscan magmatism from the balkan sector of the orogen central bulgaria abstract new high resolution secondary ion mass spectrometry u th pb data obtained from zircon and monazite from representative variscan intrusions in the balkan sector of the variscan orogen central bulgaria constrain the ages of magmatism to the interval 315 285 ma the samples investigated are granitoids from two contrasting intrusive suites calc alkaline granitoids of the first suite include the san nikola granite 311 9 4 1 ma and the petrohan granodiorite 304 6 4 0 ma from the balkan terrane and the smilovene 304 1 5 5 ma and hisara 303 5 3 3 ma granites from the sredna gora terrane zircons from these intrusions predominantly lack inherited cores the second suite consists of two mica leucocratic granites and includes the koprivshtitsa 312 0 5 4 ma and strelcha 289 5 7 8 ma plutons zircons from intrusions of the second suite are 80 90 xenocrystic apparent ages of inherited cores are the magmatic age and slightly older 300 400 ma to ordovician 450 ma ages and to neoproterozoic 600 900 ma ages gabbroic magmas related to the first suite are found only in the more northerly balkan terrane while the leucogranites occur only in the southerly sredna gora terrane although coeval the two suites of intrusions are not genetically related and furthermore were likely derived from different source regions via different melt generating mechanisms we propose a tectonic and petrogenetic model whereby following juxtaposition of the balkan and sredna gora terranes during variscan collision the two suites of magmas were generated by continued subduction under eastern europe due to the influx of mafic magmas into the base of the crust and by influx of water rich fluids into high grade metapsammitic rocks of the sredna gora metamorphic series the new ages are somewhat younger than ages for post collisional intrusions in the central european variscan massifs i e bohemian black forest and vosges where ages of intrusions are predominantly 340 320 ma although some younger intrusions may also occur within the intra alpine massifs both older 340 320 ma and younger 310 290 ma granitoids are present farther west intrusions in the iberian massif appear to be predominantly younger 325 290 ma similar to the intrusions of the balkans this may indicate that collision of adjacent crustal blocks culminated at earlier times in the central and more northerly portions of the orogen and moved both east west and south as the evolution of the orogen progressed

magma pulses in the central variscan belt episodic melt generation and emplacement during lithospheric thinning magmatism in the central part of the variscan orogenic belt in europe has occurred in several distinct episodes each episode spanned a few million years and was characterized by a distinct geochemical signature and geodynamic setting i between 340 and 330 ma visean high k diorites and granitoids within a zone extending parallel the orogen axis possibly tracing a palaeosuture ii at 310 307 ma westphalian calc alkaline granitoids in the intra alpine domain iii at 304 295 ma stephanian subalkaline granitoids in intra alpine and pennine domains and finally iv at 280 270 ma permian granitoids in pennine austroalpine and south alpine domains the generation and emplacement of granitoid melts in the variscan crust are suggested to be short term pulses that are controlled by extensional processes in the lithosphere such as thermal erosion and relaxation of the lithospheric mantle and decompressional melting

the nile deep sea fan an example of interacting sedimentation salt tectonics and inherited subsalt paleotopographic features abstract structural analysis of the nile deep sea fan ndsf indicates that post miocene deformation is largely controlled by down slope movement above a messinian salt layer in contrast to other similar systems the ndsf shows significant lateral asymmetry and three distinct provinces can be recognized regional variations in salt thickness and base salt geometry within the system have led to the presence of structures typical of both gravity gliding and gravity spreading trends of structures within the western and central parts of the ndsf are consistent with forming due to gravity gliding processes this pattern contrasts with that in the eastern ndsf that seem to be much more consistent with deformation due to gravity spreading observed differences in structural style across the ndsf can be related directly to the paleomorphological evolution of the nile cone during messinian time which is perhaps partly related to features that have been inherited from early mesozoic evolution of the north egypt passive margin in the east part of the ndsf the structural evolution has been significantly influenced by the proximity of eratosthenes seamount this large topographic buttress has served to both limit and deflect northeastward allochthonous advance of the messinian evaporites and has thus severely complicated deformation of the overlying plio quaternary sedimentary cover within the broad corridor that runs nnw sse and cuts obliquely across the modern bathymetry of the nile cone

mechanical restoration of gravity instabilities in the brunei margin n w borneo in offshore brunei the baram delta displays pliocene to recent gravitational deformations on top of the overpressured setap shales we use the limit analysis implemented in slamtec to constrain their kinematics and propose first order values of compatible pore pressures using the critical coulomb wedge theory we confirm that extreme overpressure are needed to account for the gravitational deformations currently observed in the delta slamtec simulations quantify the role of the migration of the deltaic system on the deformations and suggest that this overpressure has existed since the initiation of the gravity driven system an inverse analysis is performed to identify the fluid overpressure and sedimentation pattern that best reproduces the forward structural model this inverse approach validates the proposed kinematics since we can reproduce quantities describing the structural style with overpressure coherent with the present day observations it points out the existence of key events explaining the structural interpretations which leads to propose new kinematic models enriched with compatible pore pressure and sedimentation rates this mechanical study highlights how mechanical modelling helps design a cross section with an appropriate kinematics based on mechanical solutions and discuss on the basis of objective mechanical criteria the ranges of pore pressure consistent with a prescribed structural evolution

the rovuma delta deep water fold and thrust belt offshore mozambique abstract we interpret two dimensional seismic reflection data from the rovuma delta basin deep water fold and thrust belts two major arcuate complexes with different architecture and extent are identified while in the northern palma arcuate complex a multitude of steep east dipping thrust related fold anticlines formed above a single main detachment in the southern mocimboa arcuate complex multiple detachments resulted in the formation of thrust duplexes in between the two arcuate domains only few thrust related fold anticlines developed our interpretation of the rovuma basin is a linked system of up dip extension and down dip compression that is mainly driven by gravity tectonics sediment loading and a hinterland uplift due to the development of the east african rift system since the oligocene is proposed as origin of the delta it is shown that the main seaward dipping detachment in early cenozoic strata is likely under compacted and overpressured shale conversely shale diapirism is questionable since the shape and location of such structures in the fold and thrust belts appear simply indicating steeply dipping imbricated folds rooted by a near vertical thrust we suggest that mainly a different rheology and thickness and thus efficiency of the shale detachment across the delta resulted in different morphologies and geometries of the deep water fold and thrust belts

ams record of brittle dilation viscous stretching and gravity driven magma ascent in area of magma rich crustal extension vosges mts ne france orogenic compression related fabrics 340 335 ma were reworked during regional extensional deformation 328 325 ma in a large anatectic crustal domain of the central vosges ne france the extension was first accommodated by brittle dilation affecting vertically anisotropic high grade rocks associated with emplacement of subvertical granitic sheets the ams fabric of granitoids is consistent with highly partitioned transtensional deformation marked by alternations of flat and steep foliations and development of orthogonal lineations this deformation passes to top to the southwest ductile shearing expressed in southerly migmatitic middle crust the ams fabric revealed moderately west dipping foliations bearing subhorizontal nnw sse trending lineations and predominantly plane strain to prolate shapes this fabric pattern is interpreted as a viscous response of stretched partially molten crust during continuous ductile extension vertical ascent of voluminous granites and stoping of the upper crust occurs further south this gravity ascent triggered by extension leads to development of south dipping ams foliations south plunging lineations and oblate fabrics in various crustal granites vertical shortening related to ascent of these 325 ma granitoids and persistent n s stretching is responsible for reworking and remelting of originally vertical compression related fabric in roof supracrustal granites 340 ma and development of highly prolate fabrics in these rocks this work shows that the finite shape of ams fabric ellipsoid is highly sensitive to both strain regime and superpositions of orthogonal deformation events

counter regional normal faults in shale dominated deltas origin mechanism and evolution abstract the niger and brunei deltas are two of the major prolific petroleum deltas of the world as a result large datasets of 2d and 3d seismic are available however some of the structures remain poorly understood because they are poorly imaged and a shale diapir interpretation has often prevailed these two deltas are in places driven by particular landward structures described as counter regional normal faults crnf these faults initiated on the apex of early folds as the shelf break propagated seaward during a first stage of deformation crnf started as diffuse faults rather than localised single faults later as the sediment load increased in the area affected by the crnf a major landward dipping fault developed controlling the delta front emplacement finally the fault was choked by the sedimentary system and another fault landward or seaward developed the description of the pre existing fold structures controlling the development of crnf allows a reassessment of the structural evolution of shale gravity driven tectonics it is agreed that in many cases the existence of mud diapirs and ridges may be discarded

structural styles in the deep water fold and thrust belts of the niger delta the deep water niger delta includes two large fold and thrust belts products of contraction caused by gravity driven extension on the shelf that exhibit complex styles of thrusting these contractional structures formed above multiple detachment levels in the overpressured shales of the akata formation using the patterns of growth sedimentation fold shapes fault plane seismic reflections and combined conventional and shear fault bend folding theories we describe and model the structural styles and kinematics of the fault related folds and imbricate thrust systems that compose these belts individual fault related folds involving both forethrusts and backthrusts are characterized by long planar backlimbs that dip less than the associated fault ramps with upward shallowing of dips in growth strata above the backlimbs suggesting components of progressive limb rotation forelimbs are short compared to backlimbs but growth strata show more consistent dips that suggest a component of folding by kink band migration thus we employ a combination of classic and shear fault bend fold theories to describe these structures including the influence of a weak basal detachment zone in the overpressured shales we expand upon these theories to model the kinematics of imbricate thrust systems which display a complex history of thrusting related to spatial and temporal variations in deposition across the delta regional patterns of folded growth strata are used to define break forward break backward and coeval thrusting involving single and multiple detachment levels we define two main types of imbricate thrust systems type i system with a single basal detachment level and type ii imbricate system with multiple basal detachment levels which cause massive structural thickening of the akata formation and refolding of shallow thrust sheets through the sequential restoration of two regional cross sections across these systems we resolve the structural styles the timing and sequences of thrusting as well as the regional amounts of shortening all of which have important implications for hydrocarbon maturation and charge in the deep water niger delta

surface property variations in venusian fluidized ejecta blanket craters abstract a comprehensive study of magellan cycles 1 and 2 radar data from venus reveals surface roughness and dielectric variations associated with fluidized ejecta blanket feb craters that help illuminate styles of flow ejecta emplacement this study develops new procedures of digital unit mapping and polygon filling algorithms using magellan sar altimetry and radiometry data these techniques allow the extraction of radiophysical information for feb crater materials nearby plains and lava flows such as 1 their specific backscatter o behavior relative to each other and to terrestrial lava surfaces 2 average calculated values of emissivity rms slopes corrected reflectivity and the diffuse component of reflectivity and 3 variations in radar properties along longitudinal traverses that are best explained by surface roughness trends at several spatial scales and or dielectric variations backscatter curve slopes of the febs studied here are consistent with surface textures that are transitional between a a and pahoehoelike average surface property values of ejecta units are relatively similar for a given crater but are discernibly different from other craters individual crater ejecta reflectivity and emissivity values are relatively similar to those for the surrounding plains which may suggest a link between plains material and ejecta dielectric properties increasing feb roughness downflow are interpreted to be associated with more lava like flows while decreasing roughnesses are more similar to trends typical of gravity pyroclastic like or debris like flows most commonly feb crater flow materials exhibit transitions from proximal lava melt like flow styles to distal gravity flow like styles some febs show more complicated behavior however or appear to be more dominated by dielectric differences downflow as inferred from correlations between the data sets such transitions may result from changes in local topography or from overlapping of flow lobes during feb emplacement

sedimentation and shale tectonics of the northwestern niger delta front abstract the modern day slope and outer shelf of the niger delta are characterized by fault bounded sedimentary depocentres and intervening shale structures some of which are diapiric using two dimensional seismic reflection data and stratigraphic information from five wells the neogene history of a 70 30 km portion of the northwestern niger delta shelf and slope has been examined the shale structures were established by late miocene time probably in response to lateral shale withdrawal from beneath the advancing deltaic load combined with compressional uplift and folding of pro delta strata during pliocene and pleistocene time these structures were buried by the prograding delta and extensional growth faulting commenced stacked onlap relationships and stacked erosional channels indicate that the shale structures continued to influence sedimentation patterns throughout this period throughout the pliocene extension and subsidence were concentrated in a graben like depocentre bounded by both regional and counter regional growth faults during the early pleistocene subsidence on the regional growth fault ceased and growth was transferred to the counter regional growth fault set the geometry and history of the depocentre is analogous to salt related depocentres typical of the northern gulf of mexico and atlantic margins of brazil and angola to explain the history of the niger delta study area a model is proposed in which the miocene pleistocene sedimentary package has slid basinward breaking up during extension thereby creating seaward stepping depocentres examples from analogue modelling studies are used to suggest possible origins for the large counter regional growth faults

earth based 12 6 cm wavelength radar mapping of the moon new views of impact melt distribution and mare physical properties abstract we present results of a campaign to map much of the moon s near side using the 12 6 cm radar transmitter at arecibo observatory and receivers at the green bank telescope these data have a single look spatial resolution of about 40 m with final maps averaged to an 80 m four look product to reduce image speckle focused processing is used to obtain this high spatial resolution over the entire region illuminated by the arecibo beam the transmitted signal is circularly polarized and we receive reflections in both senses of circular polarization measurements of receiver thermal noise during periods with no lunar echoes allow well calibrated estimates of the circular polarization ratio cpr and the four element stokes vector radiometric calibration to values of the backscatter coefficient is ongoing radar backscatter data for the moon provide information on regolith dielectric and physical properties with particular sensitivity to ilmenite content and surface or buried rocks with diameter of about one tenth the radar wavelength and larger average 12 6 cm circular polarization ratio cpr values for low to moderate tio 2 mare basalt deposits are similar to those of rough terrestrial lava flows we attribute these high values to abundant few centimeter diameter rocks from small impacts and a significant component of subsurface volume scattering an outflow deposit inferred to be impact melt from glushko crater has cpr values near unity at 12 6 cm and 70 cm wavelengths and thus a very rugged near surface structure at the decimeter to meter scale this deposit does not show radar brightness variations consistent with levees or channels and appears to nearly overtop a massif suggesting very rapid emplacement deposits of similar morphology and or radar brightness are noted for craters such as pythagoras rutherfurd theophilus and aristillus images of the north pole show that despite recording the deposition of orientale material byrd and peary craters do not have dense patterns of radar bright ejecta from small craters on their floors such patterns in amundsen crater near the south pole were interpreted as diagnostic of abundant impact melt so the fraction of orientale derived melt in the north polar smooth plains 1000 km farther from the basin center is inferred to be much lower

palaeozoic evolution of the variscan vosges mountains a geological synthesis of the palaeozoic vosges mountains ne france is presented using existing observations and new data the geodynamic evolution involves 1 early palaeozoic sedimentation and magmatism 2 late devonian subduction triggering back arc spreading 3 early lower carboniferous continental subduction continent continent collision and polyphase deformation and metamorphism of the orogenic root and 4 late lower carboniferous orogenic collapse driven by thermal weakening of the middle crust the evolution is integrated within the framework of the european variscan belt the northern vosges comprise sediments of rhenohercynian affinity separated from tepla barrandian metasediments by a lower carboniferous magmatic arc the latter is correlated with the mid german crystalline rise and is ascribed to the south directed subduction of the rhenohercynian basin the saxothuringian moldanubian suture is thought to be obliterated by the magmatic arc while the lalaye lubine fault is interpreted as the tepla barrandian moldanubian boundary the central vosges are paralleled with the moldanubian domain of the bohemian massif where identical lithologies record the devonian carboniferous se directed subduction of the saxothuringian passive margin below the moldanubian upper plate the southern vosges represent the upper moldanubian crust and are linked to the southern black forest the presence of an oceanic domain to the south of the vosges black forest remains unclear

rifted margins ductile deformation boudinage continentward dipping normal faults and the role of the weak lower crust the stunningly increased resolution of the deep crustal levels in recent industrial seismic profiles acquired along most of the world s rifted margins leads to the unraveling of an unexpected variety of structures it provides unprecedented access to the processes occurring in the middle and lower continental crust we present a series of so far unreleased profiles that allows the identification of various rift related geological processes such as crustal boudinage ductile shear and low angle detachment faulting and a rifting history that differs from the classical models of oceanward dipping normal faults the lower crust in rifted margins appears much more intensely deformed than usually represented at the foot of both magma rich and magma poor margins we observe clear indications of ductile deformation of the deep continental crust along large scale shallow dipping shear zones these shear zones generally show a top to the continent sense of shear consistent with the activity of continentward dipping normal faults cdnf observed in the upper crust this pattern is responsible for a migration of the deformation and associated sedimentation and or volcanic activity toward the ocean we discuss the origin of these cdnf and investigate their implications and the effect of sediment thermal blanketing on crustal rheology in some cases low angle shear zones define an anastomosed pattern that delineates boudin like structures the maximum deformation is localized in the inter boudin areas the upper crust is intensely boudinaged and the highly deformed lower crust fills the inter boudins underneath the boudinage pattern controls the position and dip of upper crustal normal faults we present some of the most striking examples from the margins of uruguay west africa south china sea and barents sea and discuss their implications for the time temperature history of the margins

modeling of fluidized ejecta emplacement over digital topography on venus the flow computer model of mcewen and malin 1989 modified for application to the study of venus fluidized ejecta blankets febs demonstrates that relatively low viscosities yield strengths and initial velocities are required to duplicate the observed flow paths of the outflow materials the model calculates the velocities and simulated flow paths of gravity flows over magellan topography the model is formulated to determine flow movements from initial conditions gravitational acceleration and resistance to motion as described by coulomb viscous and turbulent resistance forces successful duplication of observed feb flow paths has been achieved for the feb craters addams isabella and cochran when used as a simple energy line model the model requires low coefficients of friction to extend febs to near their observed termini in the synthetic aperture radar sar imagery although the resulting straight flow lines do not follow the observed flow paths well for bingham flow the model requires low values of viscosity and yield strength which are more similar to pyroclastic or debris flows than basaltic lavas flows of 100 m depth require 1 to 2 orders of magnitude higher values of both viscosity and yield strength than 10 m deep flows the complicated nature of the flow lines for the low velocity model suggests that febs were probably emplaced under variably laminar and turbulent flow conditions where underlying topography influenced both the direction and energy of flow materials

the age of the kagenfels granite northern vosges and its bearing on the intrusion scheme of late variscan granitoids in the saxothuringian part of the vosges france a first series of variscan plutonic rocks diorites to granites has been intruded by several younger granites rocks of both the older generations have been cross cut by the late orogenic kagenfels granite the averages of the hitherto published mineral ages of the earlier rock generations are 331 and 334 ma respectively whereas rb sr and k ar dates around 290 ma have been reported for the kagenfels granite because of the unlikely large age hiatus a redetermination of the intrusion age of the kagenfels granite formation appeared to be irrevocable the newly obtained mineral ages on the kagenfels granite k ar and 40ar 39ar biotite ages as well as single zircon radiogenic 207pb 206pb data 331 5 ma are about 40 ma older than the previous results they are interpreted as giving the time of emplacement of the kagenfels granite during the latest viscan the mineral ages of the earlier plutonic rocks in this part of the variscan orogeny in all probability are not significantly different from their ages of intrusion therefore the age concordance of all three granitoid generations constrains a rather narrow time interval of orogenic magmatism close to the lower upper carboniferous boundary

devonian permian magmatic pulses in the northern vosges mountains ne france result of continuous subduction of the rhenohercynian ocean and avalonian passive margin

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico ii structure the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope

chronologic modeling of faulted and fractured reservoirs using geomechanically based restoration technique and industry applications we have developed a geomechanically based restoration method to model reservoir deformation the approach founded on the finite element method simulates the physical behavior of the rock mass and considers heterogeneous material properties bedding slip and the mechanical interaction of faults to demonstrate the method s potential we analyze the deformation and fault growth in the hanging wall of a synsedimentary listric normal fault from a sand box model which provides an analog for evaluating complex faulted reservoirs the numerical model results are then analyzed to investigate the chronology of faulting the numerical model corresponds well to the physical model and provides additional insights about reservoir evolution and deformation the approach is also tested on a natural example of folding using outcrop data to study contractional deformation these examples illustrate how undetected faults and fractures reservoir compartmentalization hydrocarbon migration pathways and hydrocarbon traps can be understood in the context of tectonic processes and how this understanding can be exploited in decision making and reducing risk we conclude that the geomechanically based restoration of faulted and fractured reservoirs has significant potential for industry applications compared to common geometric restoration techniques which lack a mechanical basis

re evaluation of mobile shale occurrences on seismic sections of the champion and baram deltas offshore brunei 3d seismic data in the baram and champion delta provinces offshore brunei show that regions thought to be occupied entirely by chaotic seismic data and conventionally interpreted as shale diapirs are regions of dimmed but coherent reflectivity such data indicate shale diapir masses are not present instead dimming can be attributed to sediment intrusive complexes overpressured fluids and gas clouds or processing artefacts in this way significant delta structures are masked on 2d seismic data which are important to interpret delta tectonic evolution the middle miocene recent champion and baram deltaic provinces are characterized by typical gravity tectonics related structures however being situated on an active margin they are also affected by episodic development of contractional structures which are located on older reactive shale bulges and result in inversion of motion on some growth faults the emplacement of shale pipes gas clouds and intrusive complexes is generally relatively late pliocene in comparison with the underlying reactive diapirs late miocene and their emplacement events may be separated in time by several million years late overpressured systems may be related to phases of pore fluid pressure increase during or following periods of inversion tectonics which resulted in phases of enhanced fluid migration in the basin where fluids were either expelled laterally oceanwards or vertically

allochthonous salt structure and stratigraphy of the north eastern gulf of mexico part ii structure abstract the kinematic evolution of allochthonous salt in the north eastern gulf of mexico proceeds in three stages 1 since its middle jurassic deposition the louann salt was loaded by sediments causing episodic basinward movement of salt ultimately leading to large concentrations of salt masses in a slope environment by the end of the lower cretaceous 2 a regime of starved sedimentation during late cretaceous and early oligocene is responsible for the stabilization of these early salt accumulations 3 with renewed rapid accumulation of sediments during the neogene and pliocene extensive allochthonous salt tongues and sheets formed by gravity spreading within the younger sediments of the slope autochthonous salt allochthonous salt and detached allochthonous salt are typical stages of evolution major down to the basin growth faults separate allochthonous salt sheets from their original feeder stocks extension along down to the basin master growth faults is compensated mainly by salt withdrawal and partly by basinward shortening

an experimental investigation of gravity driven shale tectonics in progradational delta abstract many deltas exhibit gravitational deformation of their sedimentary cover in these systems the decollement layers do not always consist of rock salt but sometimes of overpressured shale unlike salt the efficiency of detachment in shale depends on the magnitude of fluid overpressures and it varies through time and space as rapid sedimentary burial progrades into deeper water as a result the gravity deformational domains are progressively translated seaward sandbox models involving high air pore pressures were used to simulate such gravity driven shale tectonics in prograding deltas models were built with sand of various permeabilities and air was injected to simulate the mechanical effects of fluid overpressure our apparatus for the injection of air allowed us to control subsurface pressures in space and time during the experiments and it was used to simulate the advance of the front of the overpressured domain during the sedimentary progradation in our models sand kept obeying a frictional behavior for medium to high pore pressures and the detachment appeared as very thin shear bands compressional belts that formed during the experiment were dominated by asymmetric basinward verging fore thrusts as is often observed in deep water shale detached foldbelts where the value of fluid pressures approached that of the lithostatic stress sand was fluidized resulting in ductile strains analogous to what occurs in highly overpressured mobile shale during progradation ancient buried thrustbelts were reactivated thereby controlling later extension during the experiments sand volcanoes analogous to mud volcanoes formed in relation with tectonic structures some of them developed near normal faults but many of them formed directly above old buried thrusts

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany ii lead isotope evolution of the european hercynides

mechanism of thin skinned detachment in the amazon fan assessing the importance of fluid overpressure and hydrocarbon generation abstract since about 10 ma a wedge of clastic sediment up to 10 km in thickness has accumulated near the mouth of the amazon river forming the amazon fan thin skinned extensional and contractional structures root into a common basal detachment hundreds of kilometers long extensional faults have formed landward of the prograding delta slope and contractional folds and faults have formed seaward of it by plan view restoration we show that extension and contraction balance we therefore infer that slope instability has provided the driving force for thin skinned deformation on seismic data the detachment appears as a sharp surface within late cretaceous strata however there is no evidence at that level for soft layers such as evaporites or muds abnormal fluid pressure provides a more reasonable mechanism for the detachment at depths of several thousand meters deep wells have encountered fluid overpressures amongst the possible causes of abnormal fluid pressures are compaction and hydrocarbon generation although compaction may have contributed to fluid overpressures encountered in wells we argue that hydrocarbon generation provides the best explanation for detachment in cretaceous rocks which were old and lithified when it occurred in particular the broadly triangular area of detachment coincides with an inferred pod of cenomanian turonian source rock which is interpreted to have been in the gas window during detached deformation we have developed new techniques of sandbox modelling to investigate the geometries of fault patterns produced by fluid flow through porous media for the amazon fan we have been able to reproduce the structural pattern on the assumption that fluid overpressures existed over a broadly triangular area beneath the detachment

collision melange and circular basins in north borneo a genetic link abstract attention has been given to the relevance of chaotic rock units including tectonic sedimentary and diapiric melanges in the evolution of subduction related accretionary complexes but they have often been perceived as relicts in suture zones northwest borneo west sabah was evidently a subduction complex which experienced collision caused by the proto south china sea and a consequence of post collision intrusion currently expressed as a 4000 metre high mountain together with gravity tectonics offshore of palawan and borneo the continuous deformation of the accretionary wedge from the collision to the post collision stages is however a matter of contention along with the timing as subduction ceased this study integrates the seismic profiles field observation and topographic interpretation to show that the backstop is composed of ultramafic rocks and a vast amount of severely sheared pillow basalts and radiolarite wide shear bands also exhibit metric phacoid shaped blocks of basalt and radiolarite successor basins cover these collision features to the west and through a system of circular basins overlying a shale matrix engulfing metric blocks of basalts radiolarite and sandstone the chaotic rock unit was occasionally brought to the surface and the overlying strata are deformed as circular synclines and anticlines we therefore suspect that the mechanism of exposing the melange involved a diapiric process that pushed this low viscosity material upward accordingly the entire process illustrates a tectonic evolution involving gravity tectonics from the end of the collision to the post collision setting of northern borneo

the interaction of extensional and contractional deformations in the outer zones of the central apennines italy abstract the relationships among normal faults and thrusts in the apennines of italy are often unclear and the local absence of syn tectonic stratigraphic controls have led to contrasting interpretations on the relative chronology for both classes of structures the activity of normal faults has been variously regarded as due to pre syn or post orogenic extension and the contrasting evidence from different sites has produced an ongoing debate on the normal fault thrust interaction the results of a kinematic analysis on selected composite structures of the outer zones of the central apennines make it possible to unequivocally establish a relative chronology of extensional and contractional deformations detailed mapping outcrop scale observations and structural overprinting relationships support a positive inversion tectonic history where normal faults and fault controlled escarpments formed first and were later deformed by thrusts and related folds all normal faults control the distribution of foredeep deposits thus indicating that the recognised episode of positive inversion is related to the incipient stages of construction of the apennine thrust belt the systematic collection of structural data may help to unravel the evolution of adjacent sectors of the apennine chain as well as of other belt foredeep foreland systems whose extension contraction relationships are poorly constrained

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany lead isotopes of k feldspars from five granites of the se schwarzwald and from metamorphites are positively correlated in 207 204 as well as 208 204 vs 206 204 diagrams

growth faults above shale seismic scale outcrop analogues from the makran foreland sw pakistan abstract the southern makran fold thrust belt pakistan displays unique outcrop examples of well exposed kilometre scale listric growth faults that displace miocene age deltaic growth strata by several hundreds of metres to kilometers the largest growth faults are counter regional landward dipping bounding major clastic depocentres exposed over areas 1000 km 2 stratal offset along these faults can exceed 1 5 km fault zone thicknesses range between ca 100 and 400 m and average fault thickness displacement ratios are around 1 10 high resolution satellite data show in unprecedented detail the faults and the stratigraphic architecture of associated growth sequences which comprise kilometre scale progradational clinoforms thick mudstone units and basinwards wedging sandstone shale deposits the true vertical thickness of the syn kinematic record is in places up to 8 km making the outcrop examples equivalent to major growth faulted successions known from seismic data of large deltas and at least an order of magnitude larger than other outcrop examples a comparison of the makran outcrops with seismic reflection examples offshore nw borneo reveals distinct similarities in the gross depocentre geometries and internal architecture the key control for growth faulting is interpreted to result from sedimentary loading with rapid sedimentary progradation causing the development of rollover synclines by differential compaction and fluid expulsion and counter regional growth faults preferentially forming on the basinward side of these synclines the data and interpretations presented can be used to assess the key parameters that contribute to the development of growth faults and growth successions above shale reinforcing structural and stratigraphic observations from seismic interpretation and modelling studies in demonstrating their occurrence in exposure

excursus on gravity gliding and gravity spreading abstract the terms gravity gliding and gravity spreading have long been used to describe deformation driven by gravity alone however the traditional definitions of these terms cannot be applied unambiguously in many situations the primary difficulties arise because rocks are not ideally rigid detachment surfaces may not be planar substrates may be deformable and rock bodies do not deform in isolation the term gravity spreading is still useful if it is simply defined as gravity driven lateral extension and vertical contraction regardless of basal slope and coherence of the body i suggest that the term gravity gliding should be used rarely and only if the defining characteristics are clearly stated and understood in most cases more detailed descriptions should be used instead of or in addition to either of these terms to capture the behavior of rock masses deforming under gravity

paleomagnetic investigations and k ar dating on the variscan plutonic massif of the champ du feu and its volcanic sedimentary environment northern vosges france abstract paleomagnetic investigations have been carried out on samples from the plutonic series of the champ du feu massif and the devonian ordovician host rocks in order to date the different phases of magnetization a series of samples has been selected for k ar analysis on micas amphiboles and feldspars the diorites granodiorites diabases and hornfelses are characterized by high susceptibilities of up to 10 1 si thermal demagnetization reveals several groups of directions of characteristic magnetization the a direction d 202 i 23 49 n 153 e is consistent with the permian virtual geomagnetic pole for europe the b 1 direction d 59 i 22 11 n 128 5 e was obtained from the effusive parts of the kagenfels granite dated at 284 ma diorites microdiorites and volcanics emplaced a short time after the intrusion of the natzwiller granite dated at 344 and 351 ma display three groups of directions the c 1 direction d 328 i 15 27 n 223 5 e the c 2 d 323 i 38 13 s 222 e and the c 3 d 272 i 41 16 s 260 e the c 1 and c 2 directions agree well with those obtained previously for visean volcanics from the southern vosges in the host rocks we have identified b and c overprintings despite the lack of tectonic control the paleomagnetic data demonstrate at least two important motions of the vosges first a rotation of undetermined direction relative to stable europe which affected the variscan belt between the late visean and 320 ma and second a clockwise rotation which occurred during the stephanian autunian in late variscan time

the moldanubian zone in the french massif central vosges schwarzwald and bohemian massif revisited differences and similarities in order to portray the main differences and similarities between the northeastern variscan segments french massif central fmc vosges black forest and bohemian massif bm we review their crustal scale architectures the specific rock associations and lithotectonic sequences as well as the ages of the main magmatic and metamorphic events this review demonstrates significant differences between the moldanubian domains in thebmand the fmc on this basis we propose distinguishing between the eastern and western moldanubian zones while the vosges black forest mountains are an intermediate section between the bm and the fmc the observed differences are the result of first the presence in the french segment of an early large scale accretionary system prior to the main variscan collision and second the duration of saxothuringian armorican subduction which generated long lived magmatic arc and back arc systems in the bohemian segment while the magmatic activity in the fmc was comparably short lived

precise upb chronometry of 345 340 ma old magmatism related to syn convergence extension in the southern vosges central variscan belt abstract the southern vosges host a large volcano sedimentary basin which contains clastic sediments of famennian late devonian ca 365 ma to late visean ca 340 335 ma age the basin is bordered by an exhumed high grade basement complex and intruded by several granitoid plutons a chronology for basin evolution and magmatism was established dating volcanic rocks of the basin as well as cross cutting granitoid rocks by the u pb technique applied to zircon and titanite the basin evolution started with olistolithic deposits and overlying marine shales that have a famennian fauna ca 365 ma and contain detrital zircons with an age of 386 ma the lowermost rhyolite flows interlayered with the basin sediments and tholeiitic basalts yielded an age of 345 2 ma following a tectonic event at the bottom of the upper visean the rates of sedimentation and volcanism were strongly enhanced leading to basin emersion and were concluded by the extrusion of the uppermost ignimbrite molkenrain rhyolite emplaced at 340 2 ma the whole volcano sedimentary association was subsequently intruded by melts of the ballons and cre tes granites as well as by small monzodioritic and dioritic satellite intrusions along the border of the ballons granite within 3 2 myr 342 1 to 339 5 2 5 ma the zircons of most of the volcanic and plutonic rocks investigated contain inherited lead of 0 6 and 2 1 ga age the differences in initial nd isotopic composition of the ballons and cre tes granites can be explained by differential uptake of crustal material during magma genesis the precise age data prove that magmatism and basin formation in the southern vosges were extremely short lived and coeval to the exhumation of adjacent high grade gneiss terrains revealing an episode of extension at the end of the lower carboniferous between 345 and 340 ma visean the tectonic regime in the internal part of the variscan orogen is that of extension and strike slip while convergent tectonics were still ongoing in the external part of the variscan orogen

microblock rotations and fault coupling in se asia triple junction sulawesi indonesia from gps and earthquake slip vector data the island of sulawesi eastern indonesia is located within the triple junction of the australian philippine and sunda plates and accommodates the convergence of continental fragments with the sunda margin we quantify the kinematics of sulawesi by modeling gps velocities and earthquake slip vectors as a combination of rigid block rotations and elastic deformation around faults we find that the deformation can be reasonably described by a small number of rapidly rotating crustal blocks relative to the sunda plate the southwestern part of sulawesi makassar block rotates anticlockwise at 1 4 myr the northeastern part of sulawesi the bangai sula domain comprises three blocks the central north sula block moves toward the nnw and rotates clockwise at 2 5 myr the northeastern manado block rotates clockwise at 3 myr about a nearby axis and east sulawesi is pinched between the north sula and makassar blocks along the boundary between the makassar block and the sunda plate gps measurements suggest that the trench accommodates 15 mm yr of slip within the makassar strait with current elastic strain accumulation the tectonic boundary between north sula and manado blocks is the gorontalo fault moving right laterally at about 11 mm yr and accumulating elastic strain the 42 mm yr relative motion between north sula and makassar blocks is accommodated on the palu koro left lateral strike slip fault zone the data also indicate a pull apart structure in palu area where the fault shows a transtensive motion and may have a complex geometry involving several active strands sulawesi provides a primary example of how collision can be accommodated by crustal block rotation instead of mountain building