geometric and kinematic models for detachment folds with fixed and variable detachment depths abstract detachment folds are defined by competent rock units and are cored by incompetent units deformed internally above a detachment horizon we have developed two geometric models to constrain possible geometries and kinematic paths for ideal detachment folds the models each independently relate fold geometry to shortening and to detachment depth model assumptions include plane strain constant competent bedlength constant cross sectional area chevron fold geometry and no bed parallel shear outside the fold detachment depth is constant in one model but may vary in the other thus allowing evaluation of the implications for fold geometry and kinematics of fixed vs variable detachment depth detachment folds formed above a detachment unit of constant thickness constant detachment depth must be initially symmetrical and cannot grow with fixed hinges fixed arc length or a self similar geometry detachment folds formed above a detachment unit of variable thickness variable detachment depth must also be initially symmetrical but any one fold geometry can have a range of possible initial and final detachment depths kinematic paths for folds with fixed hinges fixed arc lengths migrating hinges variable arc lengths and selfsimilar geometries are all possible if detachment depth varies the change in detachment depth during deformation can be determined using the variable detachment depth model if either initial or final detachment depth is known the models demonstrate a wider range of variability in the geometry and kinematics of ideal detachment folds particularly for the variable depth model than is the case for ideal fault bend and fault propagation folds this variability limits the usefulness of simple geometric models for reconstructing the geometry of natural detachment folds balancing cross sections over a sufficient area and evaluating strain may compensate for these limitations

structure and evolution of the northern potwar deformed zone pakistan the northern potwar deformed zone npdz is part of the active foreland fold and thrust belt of the salt range and potwar plateau in northern pakistan about 500 km of seismic reflection profiles are integrated with surface geologic and drilling data to examine the deformation style and structure of the npdz with particular emphasis on history of deformation of the dhurnal oil field the seismic lines suggest that the overall structure of the eastern npdz is a duplex structure developed beneath a passive roof thrust the roof thrust is generated from a tipline in the miocene murree formation and the sole thrust is initiated from the same eocambrian evaporite zone that extends 80 km southward beneath the soan syncline and salt range the dhurnal oil field structure is a pop up at the southern margin of the npdz and developed beneath the passive roof thrust the passive roof thrust crops out just north of dhurnal on the steep northern limb of the soan syncline an overstep passive roof thrust sakhwal fault is interpreted west of dhurnal this fault developed due to

new insights into salt tectonics in the northern dutch offshore a framework for hydrocarbon exploration the northern dutch offshore is an area that has seen less hydrocarbon exploration activity than other areas of the netherlands acquisition of a new regional 3d seismic dataset allowed further testing and re evaluation of established geological concepts in this area it is recognized that the presence and movement of upper permian zechstein evaporites had a major impact on depositional patterns in mesozoic sediments structural development and hydrocarbon migration as such this study looks specifically at the role of salt tectonics in tectonosedimentary development to assess this salt tectonic evolution within its structural context a restoration of the step graben and dutch central graben was performed it follows that depositional patterns are closely linked to the nature of salt structure movement and the timing of regional tectonism for example during late triassic rifting salt pillows developed and sedimentation focused away from salt structures into depocentres along regional fault trends restoration results show that this interplay between salt movement and tectonism is needed to accommodate the sedimentation patterns associated with the formation of the step graben and central graben during the triassic and jurassic and later during late cretaceous and cenozoic inversion tectonics 2018 the author s

a new approach to backstripping and sequential restoration in subsalt sediments in this paper a new approach to calculating and restoring the effects of physical compaction in subsalt units is presented the loading of subsalt units and associated physical compaction is controlled by a combination of suprasalt sedimentation and salt movements here it is proposed that the change in load affecting the subsalt units is equivalent to the thickness between paleosurfaces of the basin regional levels reconstructed for successive stratigraphic horizons this is in contrast to suprasalt units where the changes in load are equivalent to the thickness of the stratigraphic unit the new approach is integrated into a complete workflow for sequential restoration in a salt basin which involves 1 removing the effects of physical compaction in suprasalt units 2 reconstructing the paleosurfaces of the basin regional level 3 restoring faults 4 unfolding to the reconstructed regional level to restore the effects of salt movement in the suprasalt units 5 reconstructing the change in load affecting subsalt units and restoring the associated physical compaction and 6 restoring any isostasy and postrift thermal subsidence results obtained using this workflow are compared with other methodologies to assess the differences in subsalt sediment thickness and structural configurations these results suggest that the workflow proposed in this paper will improve the accuracy of sequential restoration of subsalt hydrocarbon plays allowing their structural configurations through time to be more accurately quantified and will ultimately reduce the risks in developing subsalt resources

evolution of salt structures during burial of salt sheets on the slope northern gulf of mexico abstract shallow buried allochthonous salt sheets are the dominant type of salt structure along the lower slope of the northern gulf of mexico trailing landward margins of the sheets are buried during continental margin progradation while their leading edges advance basinward under thin cover during burial a series of daughter structures including stocks massifs and remnant structures evolved as the sheet was segmented by extension and differential loading during extension fault bound basins on the upper surface of the sheet initiated the growth of salt rollers some rollers matured into stocks and massifs as sediment accumulated rapidly in circular salt withdrawal basins that were localized over the initial fault bound basins lateral extension is a key mechanism in initiating salt structural evolution however simple vertical subsidence of sediments is the primary displacement mechanism where the salt is completely displaced a salt weld discontinuity identifies its former stratigraphic position a variety of structures in the eastern green canyon area have been identified overlying a neogene salt weld including remnant salt structures mature stocks massifs and sedimentary structures such as turtle structure anticlines

gravity driven thin skinned extension above zechstein group evaporites in the western central north sea an application of computer aided section restoration techniques normal faulting and halokinesis have been important controls on the deposition and subsequent deformation of mesozoic and tertiary strata in the north sea in addition to the previously documented mechanisms of salt withdrawal dissolution and differential sedimentary loading it is recognized that gravity driven thin skinned extension above inclined salt layers has played an important part in north sea basin development commercial section restoration software has been used to facilitate depth conversion restoration and decompaction of seismic sections selected from an interpreted regional database in the western central north sea allowing validation of the interpretations and a graphical and highly quantitative description of salt assisted extension results of this work show that zechstein group evaporites were deposited in shallow sag basins during the permian triassic sedimentary pods were generated by localized deposition in synclinal basins and grabens above the evaporites bedded salt became folded while mobile salt flowed to fill anticline cores since the early jurassic regional tectonic tilting related to post rift subsidence and increasing sedimentary overburden have caused allochthonous mesozoic and tertiary strata to extend by gravity spreading above the mobile salt layer which detaches the allochthon from the underlying autochthonous late palaeozoic rocks concave up listric normal faults sole out in the salt layer propagate into the overlying cover sewuence and have been active at different geological times causing stratal thickening and folding within the allochthon antithetic and synthetic normal faults have developed producing complex upward branching fault systems in map view the listric faults form curvilinear en echelon arrays the faults linked by relay ramps fault blocks are typically 3 7 km wide 2 3 km thick and 7 10 km long salt movement during the jurassic tertiary has been driven by active extension of the cover causing salt to fill potential voids created by fault block rotation thus salt highs occur beneath sites of extension the listric faults generally dip in the same direction as the sub salt surface although there are also some major counter regional faults during extension regional dips have increased up to about 5 which is sufficient for gravity driven extension above a salt layer a total extension of about 6 has occurred the gravity driven thin skinned extension documented in the western central north sea is a phenomenon which can be recognized elsewhere in the north sea basin and can be readily compared with similar phenomena already documented in offshore angola brazil nova scotia and the gulf of mexico

the enigma of the albian gap spatial variability and the competition between salt expulsion and extension the albian gap is a uniquely large up to 65 km wide and 450 km long enigmatic salt related structure in the santos basin offshore brazil it is located near the basin margin and trends ne i e subparallel to the brazilian coastline the gap is characterized by a near complete absence of albian strata above depleted aptian salt its most remarkable feature is an equivalently large equally enigmatic basinward dipping supra salt rollover that contains a post albian sedimentary succession that is up to 9 km thick owing to its unique geometry size and counter regional aspect the origin and evolution of the albian gap has been the centre of debate for 25 years this debate revolves around two competing models that is did it form as a result of thin skinned i e supra salt extension or progradational loading and salt expulsion the extension driven model states that the albian gap and overlying rollover formed as a result of post albian gravity driven extension accommodated by slip on a large counter regional listric normal fault the cabo frio fault conversely the expulsion driven hypothesis states that the albian gap was established earlier during the albian and that post albian deformation was controlled by differential loading vertical subsidence and basinward salt expulsion in the absence of significant lateral extension this study utilizes a large c 76 000 km2 dense 4 8 km line spacing depth migrated 2d seismic dataset that fully covers and thus permits for the first time a detailed quasi 3d structural analysis of the entire albian gap in this study we focus on 1 the evolution of base salt relief and the original salt thickness variations and 2 the geometry of the post albian rollover and its related faults and salt structures to constrain the kinematics of the albian gap and how this relates to the evolution of the base salt relief we also apply novel structural restoration workflows that incorporate flexural isostasy in addition to a detailed sequential reconstruction of the intra gap rollover sequences our results show that the geometry and kinematics of the albian gap vary along strike and that both post albian extension and expulsion play a significant role in its evolution basinward dipping growth wedges salt rollers and listric normal faults record extension whereas sigmoidal wedges halokinetic sequences and upturned near diapir flaps the latter two associated with large diapirs bounding the downdip edge of the gap record basinward salt expulsion and inflation where the albian gap is relatively wide 50 km these processes alternate and operate at approximately equal proportions our results are consistent with the amount of basinward translation inferred from the analysis of ramp syncline basins located downdip on the sao paulo plateau our results seemingly reconcile one of the longest running debates in salt tectonics as well as having more general implications for understanding the regional kinematics and dynamics of salt related structures in other salt basins in particular the controls on the development of large counter regional faults supplementary material uninterpreted versions of the seismic sections are available at https doi org 10 6084 m9 figshare c 5023088

extraction and carbon isotope analysis of co2 from scapolite in deep crustal granulites and xenoliths abstract carbon isotope compositions of scapolite from granulite facies gneisses and lower crustal xenoliths document the composition and constrain the source of carbon in scapolite from the lower crust co 2 is extracted from scapolite without fractionating carbon isotopes by reaction with phosphoric acid at 25 or 75 c thus partial yields of co 2 from scapolite are sufficient for accurate carbon isotopic analysis isotopic compositions of coexisting scapolite and calcite in high grade calc silicate gneisses and marbles and consideration of the crystal chemical environment of co 3 in the scapolite structure indicate little fractionation of 13 c 12 c between scapolite and calcite 0 1 1 2 at equilibrium conditions of 650 800 c the carbon isotope composition of co 2 extracted from scapolite in twenty nine samples of regional granulite facies gneisses amphibolites calc silicate gneisses and crustal xenoliths yield values of 13 c that range from 10 to 1 pdb high grade marbles and graphitic paragneisses are precluded as major sources of carbon for scapolite in the high grade rocks analyzed in this study as the former are isotopically enriched and the latter isotopically depleted in 13 c 12 c relative to the range of isotopic compositions determined here the 13 c values for mafic granulites and amphibolites in granulite terranes composed of supracrustal sequences 10 1 to 4 0 may reflect the isotopic composition of diagenetic carbonate present in their basaltic protoliths the values of 13 c for scapolite in mafic xenoliths and some granulite facies orthogneisses 8 2 to 1 2 are consistent with crystallization of the scapolite from a mafic melt or derivation of co 2 from mafic melts emplaced in the lower crust or upper mantle the values of 13 c for scapolites from calc silicate gneisses and calc silicate xenoliths 10 0 to 2 9 may result from depletion of 13 c 12 c as a result of decarbonation of calcite bearing protoliths during prograde metamorphism

testing thin skinned inversion of a prerift salt bearing passive margin eastern prebetic zone se iberia abstract detailed geologic mapping combined with well and seismic data from the eastern prebetic zone se iberia reveal extensional and contractional structures that permit characterization of passive margin development and its incorporation into a thin skinned fold and thrust belt the study area is represented by nw directed ene trending folds and thrusts faults locally disrupted by the nw trending matamoros basin and the active jumilla and la rosa diapirs these structures resulted from the thin skinned inversion of the proximal part of the eastern south iberian passive margin containing prerift salt here upper jurassic to santonian thick skinned extension controlled the accumulation of sediment over mobile prerift salt this in turn defined the style of salt tectonics characterized by monoclinal drape folds suprasalt extensional faults and diapirs the structural and sedimentological analysis suggests that during extension salt localizes strain thus decoupling sub and suprasalt deformation thick skinned extension controls suprasalt deformation as well as its location and distribution which changes over time salt also localizes strain during inversion the preexisting salt structures weaker than adjacent areas preferentially absorb the contractional deformation in addition the stepped subsalt geometry that results from thick skinned extension also controls the shortening propagation therefore the degree of strain localization depends on the thickness of the suprasalt cover and on the dip of subsalt faults relative to the thin skinned transport direction

analysis of folding and deformation within layered evaporites in blocks bm s 8 9 santos basin brazil the sao paulo plateau in the deepwater santos basin is the site of numerous recent pre salt petroleum discoveries the area is characterized by a thick sequence of layered evaporites comprising primarily halite with subordinate anhydrite and carnalite and trace amounts of other minerals the sequence is divided into six stratigraphic packages three relatively competent beams containing the bulk of the stronger anhydrite and three relatively weak detachment layers observed structural styles range from the simple to the complex including upright open folds inclined thrusted folds recumbent isoclinal folds sheath folds and superposed folds mul tiple detachments lead to polyharmonic folding disharmonic folding and overtightened folds major anticlinal structures contain acoustically transparent material surrounding disrupted highly deformed pieces of the lower two beams the deformation is non coaxial with anticlines forming a polygonal pattern and fold hinges that are highly curvilinear the sao paulo plateau is a contractional province that formed in response to proximal extension at the albian gap during convergent gravity gliding spreading of the margin shortening possibly began during the waning stages of evaporite deposition but the bulk of the movement occurred during the santonian mid eocene the evaporite sequence shortened much more than the cover because of extreme updip attenuation and consequent basinwards flow beneath the cover deeper levels of evaporite exhibit more shortening due to strain partitioning across internal detachments

stratigraphic record of translation down ramps in a passive margin salt detachment abstract ramp syncline basins filled with synkinematic sediments record the incremental translation history and translation rates of strata transported over basement ramps on passive margins movement of strata over a stratabound salt detachment is stratigraphically recorded as an isopach thick on the seaward side of a monoclinal ramp this growth syncline gradually moves seaward down and then off the monocline as if on a conveyor belt this shift creates accommodation space for a new isopach thick to form just landward of the older one repetition of this cycle creates a shingled series of isopach thicks within the ramp syncline basin kinematic forward models and restored cross sections from the kwanza basin angola show that the stratigraphic pattern of ramp syncline basins is most influenced by three factors 1 the relative rates of translation and aggradation control the curvature of the axial trace of the growth synclines 2 bathymetric scarps above basement ramps can create spectacular seaward dipping onlap surfaces 30 km long downdip adjoining ramps generate stacked interfering onlap surfaces 3 salt diapirs or anticlines are commonly shortened at the top of the ramp especially where this coincides with the base of the continental slope diapir shortening provides a buffer to absorb sliding from its landward side and impede sliding on its seaward side this buffering can have a major control on the entire gravity spreading system containing the diapirs

porphyry cu mo au deposits related to melting of thickened mafic lower crust examples from the eastern tethyan metallogenic domain abstract most porphyry cu deposits in the world occur in magmatic arc settings and are formed in association with calc alkaline arc magmas related to subduction of oceanic lithosphere this contribution reviews a number of significant porphyry cu deposits in the eastern tethyan metallogenic domain they widely occur in a variety of non arc settings varying from post late collisional transpressional and extensional environments to intracontinental extensional environments related to orogenic and anorogenic processes their spatial temporal localization is controlled by strike slip faults orogen transverse normal faults lineaments and their intersections in these non arc settings these deposits are dominated by porphyry cu mo deposits with minor porphyry cu au and epithermal au deposits and exhibit a broad similarity with those in magmatic arcs the associated magmas are generally hydrous relatively high fo2 high k calc alkaline and shoshonitic and show geochemical affinity with adakites they are distinguished from arc magmas and or oceanic slab derived adakites by their occurrence as isolated complexes high k2o contents 1 2 8 5 and much wider range of end t values 10 to 3 and positive ehf t values 4 6 to 6 9 these potassic magmas are most likely formed by partial melting of thickened juvenile mafic lower crust or delaminated lower crust but also involving various amounts of asthenospheric mantle components key factors that generate hydrous fertile magmas are most likely crust mantle interaction processes at the base of thickened lower crust in non arc settings rather than oceanic slab dehydration as in arc settings breakdown of amphibole in thickened lower crust e g amphibole eclogite and garnet amphibolite during melting is considered to release fluids into the fertile magmas leading to an elevated oxidation state and higher h2o content necessary for development of porphyry cu mo au systems copper and au in hydrous magmas are likely derived from mantle derived components and or melts which either previously underplated and infiltrated at the base of the thickened lower crust or were input into the primitive magmas by melt mantle interaction in contrast mo and part of the s in the fertile magmas are probably supplied by old crust during melting and subsequent ascent

restorations of faulted domes we illustrate recently developed techniques of three dimensional 3 d geomechanical structural restoration applied to resolve the kinematics of deformation in the sedimentary cover above mobile salt our study area is one of the hydrocarbon bearing domes in eastern arabia we used 3 d seismic reflection and well data to build a 3 d structural geomodel for the well imaged part of the sedimentary cover the geomodel includes faults and a 3 2 km 2 mi thick section of permian to cenozoic sediments and is restored from the jurassic to the present day the development of the structures is characterized by stages of normal faulting in the jurassic and cretaceous and a subsequent stage of low amplitude folding in the late cretaceous we interpret that the development of the structures in the sediment cover is caused by the movement of a deep nonpiercing salt pillow the structures grew under the control of gradually changing deforming mechanisms from dominantly faulting to folding the transition from normal faulting to domal folding is indicative of a reactive salt diapir these restoration results improve our understanding about the kinematic history of the structures developed within the jurassic and cretaceous sedimentary section which contains most of the hydrocarbon resources in arabia moreover they illustrate the potential of geomechanical restoration methods to investigate structures above mobile salt systems

salt structural styles and kinematic evolution of the jequitinhonha deepwater fold belt central brazil passive margin abstract salt structures in linked extensional contractional systems of passive margin sedimentary basins and deepwater fold belts play an important role in the evolution of rifted continental margins the 100 km wide jequitinhonha basin with its salt detached deepwater fold belt provides insight in the post rift salt deformation processes in deepwater fold belts of the central brazilian continental margin seismic interpretation and kinematic analysis of basin scale 2d sections provide insights into the salt tectonic processes related depositional systems salt basin geometry and kinematic evolution of the deepwater fold belt several salt kinematic domains have been identified the most evident is the long term contractional domain in the distal basin which formed impressive salt cored anticlines salt walls and salt massifs reaching 4 km in thickness the post rift basin evolution was dominated by thin skinned deformation and was initiated by differential loading of early post rift shallow marine carbonates subsequently the system was mainly driven by gravity gliding of the overburden on the aptian salt detachment the depocenters were controlled by early post rift salt mobilization and ranged from asymmetric grabens and rollovers to minibasins with vertically stacked or shifting depocenters and formed the basis of the deepwater fold belt architecture in the jequitinhonha basin the structural styles and kinematic evolution of the deepwater fold belt were strongly controlled by the original salt thickness the distribution of albian campanian depocenters and thickness variations in the overburden sediments early cretaceous short wavelength folds have been overprinted by long wavelength folding owing to increased strength and thickness of the overburden since paleogene times large amplitude salt cored folds developed in the deepwater basin due to contraction of pre existing salt walls and formed margin parallel nnw sse trending narrow structural highs separated by wide depocenters ongoing uplift with reduced sediment accumulation over contractional diapirs or crestal erosion of the deepwater anticlines supported long term strain localization and positive feedback in the active deepwater contractional deformation

cross section restoration of salt related deformation best practices and potential pitfalls abstract cross section restoration typically assumes plane strain deformation and area conservation constraints that are usually invalid for salt because of its characteristic three dimensional flow and possible dissolution thus restoration of salt related deformation provides added challenges and uncertainty in this review paper we summarize the historical development of ideas methods and applications of restoration in salt basins while most published restorations do not maintain salt area constraints on its variation range from arbitrary assumptions to quantitatively incorporating isostatic calculations we illustrate several scenarios in which the presence of salt adds ambiguity to restoration primarily because it can hide deformation diapirs can widen during extension and narrow during shortening translating overburden can move into salt and drive allochthonous advance secondary minibasin subsidence can be accommodated at both shallow and deep salt levels and allochthonous salt can record evacuation of deeper salt although we caution against using restoration to test and validate small scale details of interpretations we emphasize that sequential restoration remains an essential tool in structural and basin analyses however because of the uncertainties a regional three dimensional approach and sound geological reasoning are critical for deriving meaningful and useful results from cross section restoration of salt structures

mayum an orogenic gold deposit in tibet china abstract located in western tibet china the mayum orogenic gold deposit was discovered in 2002 with estimated resources of 80 tonnes gold the gold mineralization is hosted by neoproterozoic cambrian schists and is controlled by nearly parallel e w trending bedding concordant fracture zones the au orebodies are composed of auriferous quartz veins and altered rocks with the au grades ranging from 2 23 g t to 69 56 g t and containing the 34s values of 18 separates of sulfides from auriferous quartz veins show a large variation from 0 2 to 16 8 the lead isotope compositions of sulfides from the gold ore are characterized by highly radiogenic values and very wide ranges of ratios 18 324 to 20 819 for 206pb 204pb 15 679 to 15 856 for 207pb 204pb and 38 401 to 41 204 for 208pb 204pb these data indicate that lead and sulfur in the quartz veins have multiple sources and were derived from the different wall rocks as the fluid flowed through them fluid inclusions indicate that the ore fluid was co2 rich with salinities mainly between 1 and 6 wt nacl equiv and homogenization temperatures predominantly ranging from 260 to 280 c the 18o values for quartz from auriferous veins range from 13 7 to 16 3 and the calculated 18oh2o values in equilibrium with quartz vary from 5 54 to 9 48 it suggests that the ore fluid may be derived from deep metamorphic deep crustal gold transporting fluids although a contribution from magmatic source cannot be ruled out 40ar 39ar age dating on the sericite from the alteration associated with the auriferous quartz veins in the mayum gold deposit gives a plateau like age of 59 34 0 62 ma later than the onset of the indo asian collision it is believed the gold mineralization was related to the indo asian collision and was formed during the early stage of orogenesis

a systematic technique for the sequential restoration of salt structures abstract a method is described for the sequential restoration of cross sections in areas of salt tectonics where deformation is confined to the salt and higher layers the subsurface geometry evolves with time through the interaction of various processes sedimentation compaction isostatic adjustment thermal subsidence if present faulting and salt withdrawal diapirism the technique systematically calculates and removes the effects of each of these processes during specified time intervals defined by the interpreted horizons it makes no assumptions about salt kinematics and generally results in the area of the salt layer changing through time the method is described for restoration of extensional terranes but it is also suitable for areas of contractional salt tectonics with only minor modifications after converting an interpreted seismic profile to depth the top layer is stripped off and the underlying section is decompacted according to standard porosity depth functions a deep baseline unaffected by compaction or deformation is used to restore any isostatic compensation or thermal subsidence isostasy is calculated according to the airy model and differential sedimentary loading across a section is shown to be approximately balanced by changes in salt thickness so that the load is evenly distributed after these processes have been reversed the resulting geometry and the seismic data are used to create the sea floor template for structural restoration fault offsets are removed and the layers down to the top salt are restored to this template while the base salt remains fixed the resulting space between the restored top salt and the fixed base salt defines the restored salt geometry in addition the difference between the sea floor template and a fixed sea level provides a measure of the change in water depth ignoring eustatic changes in sea level the technique is applied to an interpreted seismic profile from the eastern green canyon ewing bank area of offshore louisiana the section is characterized by a variety of salt structures including salt rollers a diapiric massif a remnant salt sheet and a salt weld which are shown to have derived from an originally continuous salt sheet which has been modified by sedimentary loading early loading created vertical basin growth that was accommodated primarily by salt withdrawal and associated diapiric rise through the process of downbuilding once the salt weld formed continued sedimentation was accommodated by a lateral increase in basin size caused by down dip extension on listric growth faults

syn tectonic magmatism and the development of compositional layering ungava orogen northern quebec canada abstract layer and foliation parallel emplacement of granitic veins was an important process in the regional development of compositional layering in now exhumed middle crustal sections of both archean and paleoproterozoic age in the northern ungava peninsula quebec canada in the archean superior province diorite and tonalite plutons were penetratively deformed and metamorphosed at granulite facies conditions coeval with voluminous granitic magmatism the paleoproterozoic narsajuaq arc contains evidence for contemporaneous magmatism transpressional deformation and granulite facies metamorphism prior to its collision with the superior province basement in both plutonic domains regional compositional layering is defined by 1 metre to kilometre scale alternation of generally well foliated tonalite and quartz diorite bodies and 2 centimetre to kilometre scale variably deformed granitic veins and sheets that lie parallel to layering tectonic foliation in the host rocks syn tectonic intrusion of a substantial portion of the veins along extension fractures sub parallel to layering foliation i e at high angle to the regional shortening direction is interpreted to have occurred due to the combination of a strong anisotropy and high magma pressures compositional layering generated and or enhanced by this process may contribute to the overall seismic reflectivity of the middle and lower crust

calculating detachment depth and dip angle in sedimentary wedges using the area depth graph abstract we apply the area depth strain method ads to predict the depth and the dip angle for an underlying bedding parallel detachment in sedimentary wedge structures with stratigraphic wedge strata using an area depth graph an area depth relationship is proposed and simplified to a linear relationship with depth as a function of excess area this proposed ads method gives the depth and dip angle of the detachment at any location in sedimentary wedges the method does not yield the shortening magnitude from the area depth graph because the area depth relationship is different for this structural example from the established methods we test the method by predicting the detachment depth and dip angle of two natural wedge structures that are well constrained the niger delta fold and thrust belt which has a single detachment and the cascadia detachment fold which has multiple detachments the predicted geometric values are generally consistent with the geometric characteristics of the two systems the ads method is a powerful method for constructing subsurface structural geometries using well constrained near surface geometry for decollement sedimentary wedges and is independent of bed length bed thickness and regional horizon throws

upper crustal shortening and forward modeling of the himalayan thrust belt along the budhi gandaki river central nepal a balanced cross section along the budhi gandaki river in central nepal between the main central thrust including displacement on that fault and the main frontal thrust reveals a minimum total shortening of 400 km minimum displacement on major orogen scale structures include 116 km on the main central thrust 110 km on the ramgarh thrust 95 km on the trishuli thrust and 56 km in the lesser himalayan duplex the balanced cross section was also incrementally forward modeled assuming a generally forward breaking sequence of thrusting where early faults and hanging wall structures are passively carried from the hinterland toward the foreland the approximate correspondence of the forward modeled result to observe present day geometries suggest that the section interpretation is viable and admissible in the balanced cross section the trishuli thrust is the roof thrust for the lesser himalayan duplex the forward model and reconstruction emphasize that the lesser himalayan duplex grew by incorporating rock from the footwall and transferring it to the hanging wall along the main himalayan thrust as the duplex developed the lesser himalayan ramp migrated southward the movement of lesser himalayan thrust sheets over the ramp pushed the lesser himalayan rock and the overburdens of the greater and tibetan himalayan rock toward the erosional surface this vertical structural movement caused by footwall collapse and duplexing in combination with erosion exhumed the lesser himalaya

flash vaporization during earthquakes evidenced by gold deposits fluids flowing through cavities in earth s crust can deposit gold thermo mechanical modelling of a fluid filled cavity that expands suddenly during an earthquake shows that the drop in pressure would cause the fluid to vaporize and deposit the gold almost instantaneously

the effect of allochthonous salt on the petroleum systems of northern green canyon and ewing bank offshore louisiana northern gulf of mexico the northern green canyon ewing bank region northern gulf of mexico basin contains the oxfordian neogene tithonian neogene albian neogene turonian neogene and eocene neogene petroleum systems the systems encompass 42 fields or discoveries in the study area and include four subsalt discoveries essential elements of the systems include source shales of oxfordian tithonian albian turonian and eocene age neogene siliciclastic turbidite reservoirs allochthonous salt and overburden strata ranging in age from jurassic to quaternary the petroleum systems of the area are significantly affected by the evolution of allochthonous salt the high thermal conductivity of salt retards the thermal maturation of subsalt petroleum source rocks and causes late generation and migration from them most traps were formed during the pliocene pleistocene and the generation migration accumulation of petroleum ranges from early miocene to the holocene the critical moment of peak oil generation for each source varies spatially and temporally as a function of the overlying sediments and allochthonous salt evolution the impermeability of salt prevents vertical petroleum migration and causes migration pathways to be deflected laterally up the dip of base salt where salt welds form petroleum migration is unimpeded and continues vertically by integrating predictions of potential source rocks structural restorations thermal maturation modeling regional salt maps and petroleum systems logic we can determine petroleum migration pathways and zones of concentration all 42 fields or discoveries within the study area are associated with predicted zones of paleosubsalt petroleum concentration present day salt geometries do not delineate many of these zones because of salt weld formation during the pleistocene this generation migration and accumulation technique enables geoscientists to focus their exploration efforts toward areas with a greater probability of success

radial gravitational gliding on passive margins abstract gravitational gliding of uppermost sediments down a passive margin is possible if there is a basal layer of evaporite or other soft material to allow detachment in examples from the gulf of mexico and the brazilian margin gliding has produced three main structural domains an uppermost domain of downdip extension an intermediate domain of rigid gliding and a lowermost domain of downdip contraction domain boundaries are established by changes in slope in this paper we examine three kinds of gravitational gliding depending on the paths followed by material particles in ideal parallel gliding particle paths are parallel straight lines trending downslope this should occur where the margin is perfectly straight in ideal radial gliding particle paths are radii of a circle and the margin is shaped like a circular cone natural margins will not have ideal shapes but divergent gliding will tend to occur off coastal salients convergent gliding off coastal re entrants a simple kinematic model based on ductile behaviour illustrates some essential features of radial gliding changes in radius during divergent gliding produce strike parallel extension during convergent gliding they produce strike parallel contraction vertical strains also differ divergent gliding produces an uppermost domain of strong vertical thinning balanced by extensions in all horizontal directions similarly convergent gliding produces a lowermost domain of strong vertical thickening balanced by contractions in all horizontal directions these deformed states cannot be restored by simple techniques based on section balancing we have done three experiments using analogue materials sand to model the brittle behaviour of sediments silicone putty to model the ductile behaviour of basal layers of evaporite the experiments were properly scaled to account for gravitational forces experiment i reproduced convergent gliding above a basement with a conical upper surface strike parallel contraction was responsible for radial folds on the lower slopes the lowermost domain had a complex fold pattern indicating contraction in all horizontal directions experiment 2 reproduced divergent gliding above a basement with a pyramidal upper surface strike parallel extension produced radial rifts on the upper slopes the uppermost domain had a complex polygonal pattern of normal faults indicating extension in all horizontal directions experiment 3 also reproduced divergent gliding but due to non uniform sediment thickness we have examined the many seismic profiles both downdip and alongstrike available for the brazilian margin alongstrike profiles show structures which we attribute to strike parallel strains around the santos re entrant syn sedimentary growthfolds indicate strike parallel contraction increasing downslope this argues for a mechanism of convergent gliding in contrast around the campos salient normal growth faults and associated salt rollers indicate strike parallel extension decreasing downslope this argues for a mechanism of divergent gliding the pattern of oil fields in the campos area including the giant marlim field seems to be closely controlled by divergent gravitational gliding and associated processes radial gliding should occur on other passive margins as well especially where the coastline is sinuous structures around the western gulf of of mexico seem to indicate convergent gliding at the scale of the entire gulf structures at a smaller scale around the mississippi delta seem to indicate divergent gliding

primary basins and their boundaries in the deep water northern gulf of mexico origin trap types and petroleum system implications primary basins form stratigraphically continuous successions on autochthonous salt and therefore in the northern gulf of mexico contain all the components of a petroleum system source reservoir trap and seal most primary basins are encased entirely in salt or in some combination of salt and welds petroleum exploration in the deep water gulf of mexico is currently focused on primary basin targets and increasingly those at their lateral boundaries however as these boundaries are commonly poorly imaged robust structural models are critical to interpretation of their structural evolution and relative petroleum system risk using three dimensional seismic data we define three tectonostratigraphic provinces that characterize primary basin depocenters 1 a disconnected salt stock canopy province in mississippi canyon 2 an amalgamated salt stock canopy province in northern atwater valley southeastern green canyon walker ridge and southern keathley canyon and 3 a bucket weld province in western green canyon garden banks and northern keathley canyon we recognize six trap types in the primary basins 1 autochthonous salt cored folds 2 turtle structures 3 base of salt truncations 4 salt feeders 5 salt ridges and 6 bucket welds most primary basin explorations to date have targeted traps in one of the first four styles future primary basin exploration will increasingly focus on the traps formed by bucket welds and salt cored ridges the contrasting evolution of these features has implications for reservoir continuity charge access and trap configuration of primary basin boundary trap types salt feeders have the lowest petroleum system risk followed by bucket welds with salt cored ridges having the highest risk

mesozoic diapirism in the pyrenean orogen salt tectonics on a transform plate boundary the mesozoic history of the pyrenean region was dominated by the opening of the north atlantic ocean and the left lateral movement of iberia relative to europe most deformation was tensional or transtensional but this style was interrupted by several short compressional events perhaps related to bends in the transform plate boundary or minor changes in plate movement directions these compressional events were recorded by deformation adjacent to and above salt structures which were the weakest parts of the system and so served as especially sensitive strain barometers the alternation of extension and shortening controlled the location and style of salt structures evaporites were initially deformed during the latest jurassic early cretaceous neocimmerian transpression which formed salt cored anticlines above west northwest east southeast trending basement faults transtension in the aptian albian caused salt domes to pierce to the surface at the intersections of these anticlines with reactivated northwest southeast and northeast southwest trending basement structures transtension was at least locally interrupted by brief periods of transpression at the aptian albian and albian cenomanian boundaries transpression shortened the diapirs causing rotation uplift and erosion of beds near the salt most diapirs were buried during the late cretaceous in some cases postburial hydrothermal circulation dissolved much of the halite causing the diapirs to sag and the basins to form in roof strata finally the entire region was shortened during the late cretaceous tertiary pyrenean orogeny which greatly distorted many of the preexisting geometries

modelling the coupling between salt kinematics and subsidence evolution inferences for the miocene evolution of the transylvanian basin large scale diapiric salt movements affect the architecture of sedimentary basins and often prevent the understanding of their mechanics by hiding or distorting subsidence patterns one good example is the evolution of the transylvanian basin which formed during miocene times in an area located in between the rapid slab rollback and continental collision recorded at the exterior of the carpathians and the extension of the neighbouring pannonian basin in the absence of major genetic fault systems quantifying these external tectonic forcing factors requires an accurate reconstruction of subsidence evolution having the advent of a detailed 3d geometrical model of the transylvanian basin we apply a 3d numerical modelling technique that couples salt re distribution and subsidence evolution to quantify and understand the basin kinematics and vertical motions two techniques backward and forward modelling are coupled in order to discriminate between salt migration driven by overburden and the influence of external tectonic forcing factors the results show that salt kinematics was more complex than simple unidirectional migration suggesting the existence of areas with significant subsidence hidden by the inward salt migration and areas with apparent large subsidence that are in reality artefacts of outwards salt migration additionally the results suggest that parts of the basin have been successively affected by in and out ward salt migration events an effect of localising subsidence and overburden furthermore accelerated moments of salt migration took place during the main miocene contraction events recorded at the exterior of the carpathians demonstrating that salt migration is enhanced by intraplate stresses our study also infers that the subsidence of the transylvanian basin is the result of the superposition of the contraction at the exterior of the orogenic chain and the back arc extension

area balancing as a test of models for the deep structure of mountain belts with specific reference to the alps abstract basic concepts of structural restoration are applied to crustal cross sections through mountain belts to explore large scale tectonic models and deep structure however restored sections should account for variations in pre orogenic crustal thicknesses crustal balancing approaches are reviewed and applied to two alpine sections coinciding with deep seismic experiments nrp 20 east central alps and ecors crop western alps existing studies assume large 300 km orogenic contraction and only moderately thinned pre orogenic crust the resulting restored sections contain more crust than is imaged beneath the present day alps the missing crust generally assumed to be subducted two kinematic modifications reduce the requirement for subduction thinning and buoyancy driven return flow of ultra high pressure metamorphic rocks during orogenesis and pre orogenic hyperextension using large stretching factors for the pre orogenic crust negates crustal subduction on both alpine transects if the lower crust was approximately rigid restorations of the central alps require strongly depth heterogeneous stretching of upper and lower crust during mesozoic rifting relaxing this requirement allows uniform lithospheric stretching a corollary consistent with published subsidence estimates restorations make implicit statements on the form of pre orogenic basins and the structure of continental margins incorporated into mountain belts that can in turn provide tests of tectonic models

evolution of tectono sedimentary systems in the kumano basin nankai trough forearc abstract sedimentary deposits in the distal kumano forearc basin of the nankai accretionary margin off kii peninsula japan have been imaged using three dimensional 3d seismic data the seismic data along with logging and core data from the integrated ocean drilling program iodp show that the unconformity between the accretionary prism and overlying forearc sediments is time transgressive the unconformity at site c0002 separates 5 ma prism rocks from 3 65 ma basin deposits at site c0009 it separates 5 6 ma prism from 3 8 ma basin sediments acoustic reflections in the basal deposits are sub parallel to the underlying accretionary prism the acoustic facies varies in thickness from 50 to 750 m the mudstone deposits and laterally equivalent turbidites are interpreted as lower trench slope deposits the condensed slope sediment ss section decreases in age from 3 5 to 1 5 ma at site c0002 to 1 5 0 9 ma at c0009 acoustic sequences within the lower forearc basin lfb contain higher proportions of silt and sand turbidites and progressively onlap the ss unit along a low angle discontinuity kl in a landward direction because of the landward onlap of the lfb unit the oldest lfb strata at c0002 are older than 1 67 ma whereas those at c0009 are younger than 0 9 ma thus the amount of time missing or characterized by condensed sedimentation across the kl unconformity decreases in duration in the landward direction the landward onlapping sequences tilt progressively landward in response to regional uplift along an out of sequence thrust oost mega splay fault regional tilting shifted the basin s depocenter progressively landward expanding that part of the basin from 10 km in width to 30 km the onset of sand silt turbidite deposition in the distal basin began after more accommodation space was created by the uplift of the outer ridge along the splay fault at 1 9 ma conversely turbidites of the upper forearc basin ufb progressively onlap lfb in a seaward direction furthermore the respective thicknesses of the lfb and ufb units switch from the seaward side of the basin c0002 farther landward c0009 the lfb unit is 800 m thick in the seaward region whereas it is only 200 300 m thick in the landward region the ufb unit is

restoration of cross sections to constrain deformation processes of extensional terranes abstract restoring balanced cross sections constrains the possible deformation processes affecting extensional terranes with a ductile substratum such as salt and syndeformational sedimentation cross sections are divided into fault blocks and shear domains each of which can be undeformed with a different set of parameters the success of restorations is judged by compatibility between the blocks and the reasonableness of the restored structures fault blocks in physical models restore with simple shear at about 60 dipping in the direction which removes extension corresponding to an antithetic orientation in the hangingwalls of normal growth faults and subparallel to the fault in the footwall other components of the deformation are rigid rotation translation and decompaction shear angles inferred from natural examples are more varied ranging from vertical to moderately inclined nearly always dipping in a direction that removes extension

growth folds above propagating normal faults abstract growth folds above the upper tips of normal faults are ubiquitous in extensional settings especially during the early phases of extension and in salt rich basins as slip accumulates on the underlying normal fault the geometry and size of the fold changes these changes reflect the dip throw displacement and propagation rate of the underlying normal fault as well as the thickness and rheology of the overlying cover these changes also have a marked impact on the architecture and distribution of synkinematic sediments as well as the styles of secondary deformation accommodating strain within the growing fold here we analyse a large dataset of natural and physically and numerically modelled growth folds to i characterise their diagnostic features ii investigate the controls on their geometry size and differences and iii describe how they grow with increasing extensional strain we demonstrate that larger fault throws and a thicker and weaker cover are associated with larger growth folds in contrast small fault throws as well as thin and strong brittle cover are associated with smaller growth folds we show that the geometry and size of growth folds vary through time the width and thus the wavelength of the fold is established relatively early during fold growth whereas fold amplitude increases gradually with increasing fault throw fold width and amplitude become increasingly similar during fold evolution until the fold is breached by the underlying normal fault we also derive a number of preliminary empirical relationships between readily observable structural and stratigraphic parameters in our dataset that may help estimate the geometry and size of poorly exposed i e in the field or imaged i e in the subsurface growth folds in addition we discuss how fault growth models i e constant length vs propagating may impact the three dimensional evolution of growth folds finally our work shows that growth folds are likely more common than previously thought for example although they are well documented in areas characterised by weak ductile cover strata and low strain rates our dataset illustrates that growth folds may also occur in brittle relatively strong rocks and in regions with high strain rates however the underlying controls on fold occurrence remain elusive

structural style and evolution of the nordkapp basin norwegian barents sea after three decades of research and hydrocarbon exploration in the nordkapp basin norwegian barents sea the dynamics of mesozoic salt mobilization is still poorly understood both progradationa

geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding this paper presents geometric arguments for modifying the conventional concept for the evolution of concentric fold trains above nonductile detachment zones the common geometric model for concentric folding above a detachment invokes a wave train with fixed fold axes regularly spaced along the fold panel limb lengths from crest to trough remain constant as the limb dips increase to uplift the anticlinal crests while the synclinal troughs slide parallel to the detachment plane the basic depth to detachment calculation which derives from the law of conservation of volume requires that the area of uplift above regional for a concentric anticline be equal to the arithmetic product of the shortening and the depth to detachment this imposes a geometric constraint with which a constant limb length anticline growing by increasing limb dip above a fixed detachment plane cannot comply unless in the early stages mobile material in the detachment zone flows from the synclinal troughs to the anticlinal crests and then in the later stages the flow direction reverses relatively few detachment zones contain a significant amount of mobile salt or shale therefore in most concentric detachment fold trains a basic geometric incompatibility exists between the conventional geometric model and themore law of conservation of volume the conflict can be resolved by an evolutionary fold model wherein the anticlinal fold limbs are short at the inception of folding and grow longer as dips increase and the fold grows in this model the anticlinal axes generally are fixed and the synclinal axes active which has structural and economic implications for the distribution of permeability and syntectonic sediments as well as for the migration and entrapment of hydrocarbons 18 figs less

structural restoration of seismic and geologic sections in extensional regimes seismic sections from extensional basins can be structurally transformed to produce restored seismic sections showing subsurface geology of the past restoration is achieved using a simple and effective algorithm which is suited for use in an interactive seismic interpretation environment seismic data are resampled along paleovertical trajectories which are the deformed equivalents of what were originally closely spaced vertical lines paleoverticals are generated within the present day section as follows 1 origin points are equally spaced along a reference horizon that corresponds to an original depositional surface 2 paleovertical segments are vertical within fault blocks 3 paleoverticals are offset across faults by the reference horizon slip and 4 restor d depth is equated to distance down a paleovertical these rules can be modified to conform with such styles of extensional deformation as vertical simple shear inclined shear or rigid rotation and to account for compaction structures with complex fault patterns readily are restored several examples from the gulf of mexico and offshore west africa show that seismic restoration is useful for 1 unravelling structural and stratigraphic history 2 revealing tectonically masked features and 3 checking interpretations across faults for seismic correlation and structural balance geologic sections can be restored in similar fashion

structural models of faulted detachment folds faulted detachment folds represent a common structural style in several hydrocarbon producing fold and thrust belts including the zagros idaho wyoming utah carpathian and albanide belts and several deep water fold belts including the mississippi fan and per dido belts these structures form in units with high competency contrasts and display a transition in deformational behavior from detachment folding to progressive fault propagation with increasing shortening the structures first form by symmetric or asymmetric detachment folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require the movement of material from the synclines to the anticlines contin ued shortening results in tighter folds with limb rotation by hinge migration limb segment rotation and internal shear rotation of limb segments between locked hinges results in thrust faults which propagate through deformation zones on the frontlimb and possibly the backlimb the faults may terminate both up and down section within brittle or ductile deformation zones eventually a through going fault connects one of the major faults with the basal detach ment variations in the structural geometry are related to the rela tive thickness and competency of the units and the mechanisms of deformation because faulted detachment folds superficially resem ble fault propagation folds their geometry can be misinterpreted in areas of poor data quality characteristic features for distinguish ing these structures include 1 smaller variations in anticlinal length during fold evolution 2 a more open and rounded fold geometry 3 complex and nonuniform variations in fault slip 4 a significant variation in deformational behavior among different units and 5 fold fault relationships indicating transition from folding to faulting such as footwall synclines and decapitated fold geometries

fluid inclusion geochemistry and ar ar geochronology of the cenozoic bangbu orogenic gold deposit southern tibet china abstract located along the southern part of the yarlung zangbo suture zone in southern tibet bangbu is one of the largest gold deposits in tibet auriferous sulfide bearing quartz veins are controlled by second or third order brittle fractures associated with the regional qusong cuogu zhemulang brittle ductile shear zone fluid inclusion studies show that the auriferous quartz contains aqueous inclusions two phase and three phase co2 bearing inclusions and pure gaseous hydrocarbon inclusions the co2 bearing inclusions have salinities of 2 2 9 5 nacleq and homogenization temperatures th of 167 336 c the d 18o and 13c compositions of the bangbu ore forming fluids are 105 5 to 44 4 4 7 to 9 0 and 5 1 to 2 2 respectively indicating that the ore forming fluid is mainly of metamorphic origin with also a mantle derived contribution the 3he 4he ratio of the ore forming fluids is 0 174 to 1 010 ra and 40ar 36ar ranges from 311 9 to 1724 9 calculations indicate that the percentage of mantle derived he in fluid inclusions from bangbu is 2 7 16 7 these geochemical features are similar to those of most orogenic gold deposits dating by 40ar 39ar of hydrothermal sericite collected from auriferous quartz veins at bangbu yielded a plateau age of 44 8 1 0 ma with normal and inverse isochronal ages of 43 6 3 2 ma and 44 3 ma respectively this indicates that the gold mineralization was contemporaneous with the main collisional stage between india and eurasia along the yarlung zangbo suture which resulted in the development of near vertical lithospheric shear zones a deep metamorphic fluid was channeled upward along the shear zone mixing with a mantle fluid the mixed fluids migrated into the brittle structures along the shear zone and precipitated gold sulfides and quartz because of declining temperature and pressure or fluid immiscibility the bangbu is a large scale cenozoic syn collisional orogenic gold deposit

structural geometry and evolution of the ku zaap and maloob structures campeche bay mexico the ku zaap and maloob structures consist of an arcuate series of fold thrust structures which change orientation from approximately east west to north northwest south southeast along a structural salient in the offshore campeche bay mexico the structures are related to a series of thrust faults which merge into the maloob thrust the ku zaap and maloob fields located on these structures together constitute an important complex of fields with proven remaining reserves of approximately 1850 mmboe the structures formed during three main periods of deformation 1 a jurassic cretaceous extensional episode 2 a miocene compressive phase during which the main trap forming structures were formed and 3 a pliocene to holocene extensional episode resulting in several listric growth faults three dimensional 3 d models of the main reservoir unit upper cretaceous breccia and other prospective reservoir units eocene and kimmeridgian constructed by integrating 3 d seismic interpretation well data and a series of balanced structural cross sections provide an understanding of the geometry and evolution of the structures the zaap maloob and sub maloob structures are interpreted as a series of faulted detachment folds detaching within salt and other jurassic ductile units the front limbs of these structures are typically cut by thrust faults with small displacements terminating in the lower tertiary section the ku and pakal structures also originated as a detachment fold but was faulted relatively early in its deformational history the frontal zone of this structure is marked by a closely spaced thrust system consisting of the ku pakal 1 and maloob thrusts the 3 d models provide an accurate picture of the structural geometry of the principal reservoir units which will be useful for future production from the fields and for exploration in adjacent areas in the basin

restoration of basins driven by extension and salt tectonics example from the cotiella basin in the central pyrenees the structure of the cotiella basin consists of four well differentiated salt floored sub basins which contain more than 6 km of halokinetic growth strata and have been interpreted to be formed by gravity driven extensional faults and diapirism during the middle coniacian early santonian the subsequent pyrenean orogeny late santonian to miocene inverted the extensional basins and squeezed the diapirs leaving little trace of the original salt volume although both the extensional and the salt related features of the cotiella basin were preserved this paper provides new insights into the evolution of the cotiella basin by establishing a correlation between sub basins by means of structural restorations the workflow followed and the assumptions made during the restoration of the inversion and especially of the extensional structures are outlined in detail

comparison of evolutionary and static modeling of stresses around a salt diapir abstract we compare an evolutionary with a static approach for modeling stress and deformation around a salt diapir we show that the two approaches predict different stress histories and very different strains within adjacent wall rocks near the base of a rising salt diapir significantly higher shear stresses develop when the evolutionary analysis is used in addition the static approach is not able to capture the decrease in the hoop stress caused by the circumferential diapir expansion nor the increase in the horizontal stress caused by the rise of the diapir hence only the evolutionary approach is able to predict a sudden decrease in the fracture gradient and identify areas of borehole instability near salt furthermore the evolutionary model predicts strains an order of magnitude higher than the strains within the static model more importantly the evolutionary model shows significant shearing in the horizontal plane as a result of radial shortening accompanied by an almost equivalent hoop extension the evolutionary analysis is performed with elfen and the static analysis with abaqus we model the sediments using a poro elastoplastic model overall our results highlight the ability of forward evolutionary modeling to capture the stress history of mudrocks close to salt diapirs which is essential for estimating the present strength and anisotropic characteristics of these sediments

geomechanical modeling of an extensional fault propagation fold big brushy canyon monocline sierra del carmen texas field structural data from the big brushy canyon monocline developed in cretaceous strata of west texas are combined with nonlinear finite element modeling to help bridge the gap between geometric kinematic and mechanical analysis techniques for understanding the deformation history of reservoir scale geologic structures the massive santa elena limestone is offset along a steep normal fault and fault displacement is accommodated upward by the folding of the buda limestone and boquillas formation and the thinning in the intervening del rio clay mesostructures within competent buda limestone beds are concentrated in the monocline limb instead of the hinge and include bed perpendicular veins that accommodate bed parallel extension and bedding plane slip surfaces that offset the veins and accommodate flexural slip finite element models were constructed to reproduce the monocline geometry and deformation distribution as well as to assess the effect of material properties and boundary conditions on structural evolution the initial model configuration replicated the assumed predeformational geometry included frictional sliding surfaces to allow for bedding parallel slip and used a displacement boundary condition at the base of the santa elena footwall to simulate fault motion geometry and strain evolution were tracked so that 1 fold shape 2 cumulative extension and 3 layer parallel shear strain could be compared to field observations iterative model runs successfully matched field data and revealed the importance of benchmarking the model results against monocline geometry layer parallel extensional strain and bedding slip in the natural example our results illustrate the potential use of this modeling approach whereby calibration is performed using available data and is followed by strain measurement throughout the model domain to aid in prediction of subseismic faults and fractures this geomechanical modeling approach provides a powerful tool for site specific subsurface deformation prediction in hydrocarbon reservoirs that incorporates details of the local mechanical stratigraphy and structural setting

structural analysis of a salt cored transfer zone in the south timbalier block 54 offshore gulf of mexico implications for restoration of salt related extensional structures the style of faulting in offshore louisiana gulf of mexico is characterized by short arcuate regional and counterregional growth faults which commonly form complex transfer zones above shallow miocene level salt bodies south timbalier block 54 st54 constitutes one such area where a basinward dipping regional and a landward dipping counterregional growth fault form a convergent transfer zone structural interpretation using three dimensional 3 d seismic and well data reveals that the eastern and western flanks of the structure contain salt in the footwalls of the main regional and counterregional faults the salt rises to a much shallower stratigraphic level in the central part of the transfer zone forming a symmetric salt diapir secondary antithetic and synthetic faults adjacent to the two main faults and extending into the transfer zone accommodate slip between the main faults kinematic restoration of a series of north south trending cross sections across the structure show that upslope evacuation of salt is the result of sediment loading and growth fault movement and the location of the transfer zone is possibly controlled by the allochthonous salt the entire area is characterized by down to basin movement with the major regional and counterregional faults displaying footwall and hanging wall fixed deformation respectively the presence of the crestal graben above the salt high and the timing of maximum salt evacuation from the flanks suggest that active or reactive diapirism occurred during part of the deformation history a 3 d structural model using depth converted horizons balanced cross sections and well tops accurately portrays the subsurface structure understanding the evolution of the structure in st54 provides insight on similar structures in other areas in offshore louisiana and the relationship between salt evacuation and transfer zone development

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

analysis of normal fault populations in the kumano forearc basin nankai trough japan 1 multiple orientations and generations of faults from 3 d coherency mapping 1 analyses of normal faults in the kumano forearc basin of the nankai trough reveal multiple normal fault populations in a region generally thought to be under compression most faults have offsets of less than 20 m and dips of 60 70 and show no growth structures indicating that the faults were active for short periods of time the oldest generation of faults is older than 0 9 ma and strikes 50 60 the next oldest faults strike 160 170 are older than 0 44 ma and are related to local uplift along the western edge of the region the youngest faults cut the seafloor shallow faults near the se margin of the basin curve from 100 in the middle of the survey area to 145 at the se corner of the area the pattern of the two youngest fault populations is consistent with the regional stress pattern maximum horizontal stress subparallel to the trench orientations of older fault populations are caused by uplift of the underlying accretionary prism implying that the forearc basin region is not as stable as previously thought reconstruction of displacements on the youngest faults shows that the overall horizontal extension is less than 2 concentrated near the seaward edge of the basin the active normal faults distributed throughout the basin support the idea that the horizontal stress parallel to the plate convergence direction does not reach the critical stress to activate or form thrust faults and produce horizontal shortening within the shallow portion of the inner wedge

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

analysis and application of coal seam seismic waves for detecting abandoned mines two in seam reflection surveys and one transmission survey were acquired at an abandoned underground mine near hurley virginia to demonstrate the feasibility of detecting abandoned mine voids utilizing coal seam seismic waves standard commonly available tools for seismic reflection processing were used the mine was detected and located by using trapped coal seam seismic waves observed in both the transmission and reflection data detecting the void however was not good enough to replace drilling entirely we conclude that in seam seismic methods can be used for detection but if a potential void is detected focused drilling should be applied for accurate mapping and to circumvent potentially hazardous areas

paleostress pattern and salt tectonics within a developing foreland basin north western subhercynian basin northern germany analysing the paleostress field in sedimentary basins is important for understanding tectonic processes and the planning of drilling campaigns the subhercynian basin of northern germany is a perfect natural laboratory to study the paleostress field in a developing foreland basin the simple layer cake geometry of the basin fill is dominated by several piercing and non piercing salt structures we derived the paleostress field from the orientation of fracture sets faults slickensides and stylolites on a regional scale the basin fill is characterized by a horizontal compressional paleostress vector that is mainly nne ssw oriented which reflects the late cretaceous inversion phase in central europe we show that the local paleostress field is distinctly perturbated due to the salt structures along the edge of the salt pillows the maximum horizontal paleostress vector is deflected by up to 90 from the regional trend in the case of the elm salt pillow it forms a radial pattern restoration of balanced cross sections demonstrates at least 9 of the shortening of the north western part of the subhercynian basin was achieved by folding the salt structures in the north western subhercynian basin are the result of varying stress conditions initial extension in the triassic caused first salt movements that prevailed during the jurassic and early cretaceous most important is the late cretaceous contractional phase that shortened the diapirs and led to the formation of the salt pillows between diapirs due to detachment folding we derive four main controlling factors for such salt dominated contractional basins 1 the wedge shape basin fill is the product of the dynamic load at the southern margin of the basin 2 a basal salt layer fed the diapirs and acted as a detachment horizon during the later shortening 3 detachment folding was the dominating deformation mechanism during contraction and 4 the pre existing diapirs controlled the position of the detachment folds

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

geometry and kinematics of single layer detachment folds detachment folds form above below or above and below bed parallel thrusts where thrust displacement is transferred into folding geometric and kinematic models are developed for individual single layer detachment folds formed above the tip line of a thrust we analyze three different detachment fold shapes kink bands chevron and box detachment folds and consider three principal detachment fold models 1 constant limb dip where the detachment fold grows by limb lengthening 2 constant limb length where the detachment fold grows by limb rotation and 3 variable limb length and variable limb dip where the detachment fold grows by both limb rotation and limb lengthening the allowance for variable forelimb thickness and excess layer parallel shear enables us to de elop a wide range of possible detachment fold geometry the geometric validity fields for folds with excess parallel shear are reduced when forelimb thinning takes place folds formed with constant limb length are likely to lock up in the initial amplification stages whereas larger amounts of shortening can be taken up by folds formed with variable limb length the manner in which a fold evolves affects the fracture and porosity features of the folded strata therefore determining which mechanism operated to form a specific detachment fold is of particular importance in hydrocarbon exploration the models we present are aimed at permitting more accurate geometric and kinematic interpretations of individual detachment folds examples of detachment folds are analyzed to illustrate the po ential benefits and limitations of the geometric model presented

structure and kinematics of the central sivas basin turkey salt deposition and tectonics in an evolving fold and thrust belt this work has been made possible by funding from total s a in the framework of the structural geology chair at e2s university of pau pays adour held by jean paul callot

a comparison of orogenic gold mineralisation in central victoria aus western south island nz and nova scotia can implications for variations in the endowment of palaeozoic metamorphic terrains abstract the palaeozoic western lachlan orogen in victoria se australia the buller terrane western south island new zealand and the meguma terrane nova scotia canada are remarkably similar in regard to their geological age and history structural make up and the setting and formation of orogenic lode and disseminated style gold deposits within these fold belts a comprehensive review of the principal characteristics of orogenic gold deposits in each of the three historically important gold provinces illustrates the many similarities but it also reveals several major geological structural tectonic geochemical and geochronological differences that may account for the disparity in contained gold and overall endowment between the three fold belts aspects that stand out as potentially playing a critical role in the generation of a phanerozoic world class orogenic gold province include 1 the presence of a hydrated oceanic character substrate that can provide a fertile source rock for both fluids and metals 2 asthenospheric thermal input to trigger and sustain crustal devolatilisation and melting 3 the existence of a number of near vertical deep seated faults 4 substantial transcurrent movement and 5 evolution of an accretionary subduction system that promotes development of an extensive fore arc system with prolonged fluid generation and circulation quantification of these controlling factors provide a significantly improved understanding of the processes that control the genesis of orogenic gold deposits and also have the potential to enable discrimination between more and less gold favourable orogens and parts of orogens

numerical study of seismic scattering and waveguide excitation in faulted coal seams finite difference p sv simulations of seismic scattering characteristics of faulted coal seam models have been undertaken for near surface p and s wave sources in an attempt to understand the efficiency of body wave to channel wave mode conversion and how it depends on the elastic parameters of the structure the synthetic seismograms clearly show the groups of channel waves generated at the fault one by the downgoing p wave and the other by the downgoing s wave these modes travel horizontally in the seam at velocities less than the s wavespeed of the rock a strong airy phase is generated for the fundamental mode the velocity contrast between the coal and the host rock is a more important parameter than the density contrast in controlling the amplitude of the channel waves the optimal coupling from body wave energy to channel wave energy occurs at a velocity contrast of 1 5 strong guided waves are produced by the incident s sources for source angles of 75 to 90 close to the near side face of the fault as the fault throw increases the amplitude of the channel wave also increases the presence of a lower velocity clay layer within the coal seam sequence affects the waveguiding characteristics the displacement amplitude distribution is shifted more towards the lower wavespeed layer the presence of a washout zone or a brecciated zone surrounding the fault also results in greater forward scattering and channel wave capture by the coal seam

influence of overlapping decollements syntectonic sedimentation and structural inheritance in the evolution of a contractional system the central kuqa fold and thrust belt tian shan mountains nw china

modeling stress evolution around a rising salt diapir abstract we model the evolution of a salt diapir during sedimentation and study how deposition and salt movement affect stresses close to the diapir we model the salt as a solid visco plastic material and the sediments as a poro elastoplastic material using a generalized modified cam clay model the salt flows because ongoing sedimentation increases the average density within the overburden sediments pressurizing the salt stresses rotate near a salt diapir such that the maximum principal stress is perpendicular to the contact with the salt the minimum principal stress is in the circumferential direction and drops near the salt the mean stress increases near the upper parts of the diapir leading to a porosity that is lower than predicted for uniaxial burial at the same depth we built this axisymmetric model within the large strain finite element program elfen our results highlight the fact that forward modeling can provide a detailed understanding of the stress history of mudrocks close to salt diapirs such an understanding is critical for predicting stress porosity and pore pressure in salt systems

fluid inclusion and noble gas studies of the dongping gold deposit hebei province china a mantle connection for mineralization the dongping gold deposit 100 t au occurs about 200 km inboard of the northern margin of the north china craton the deposit is mainly hosted by syenite of a middle paleozoic alkalic intrusive complex that was emplaced into late archean basement rocks both groups of rocks are intruded by late jurassic to early cretaceous crustal melt granite dikes and stocks some within a few kilometers of the deposit the gold ores were deposited during this latter magmatic period at about 150 ma a time that was characterized by widespread regional north south compression that formed the east west trending yanshan deformational belt the ores include both the telluride mineral bearing low sulfide quartz veins and the highly k feldspar altered syenite with most of the resource concentrated in two orebodies 1 and 70 fluid inclusion microthermometry indicates heterogeneous trapping of low salinity e g 5 7 wt nacl equiv fluids that varied from a few to 60 mole percent nonaqueous volatile species laser raman spectroscopy confirms that the vapor phase in these inclusions is dominated by co2 but may be comprised of as much as 9 mole percent h2s and 20 mole percent n2 methane concentrations in the vapor phase are consistently 1 mole percent the variable phase ratios are consistent with fluid immiscibility during ore formation fluid inclusion trapping conditions are estimated to be 250 to 375 c and 0 6 to 1 0 kbar helium isotope studies of fluid inclusions in ore stage pyrites indicate 3he 4he ratios of 2 1 to 5 2 ra ra 1 4 10 6 for air for orebody 1 and 0 3 to 0 8 ra for orebody 70 the former data suggest that at least 26 to 65 percent mantle helium occurs in the fluids that deposited the veins in orebody 1 the lower values for orebody 70 which is characterized by a more disseminated style of gold mineralization are interpreted to reflect an increased interaction of ore fluids with surrounding crustal rocks which may have contributed additional 4he to the fluids a mantle source for at least some of the components of the gold forming fluid is consistent with upwelling of hot asthenosphere and erosion of as much as 100 to 150 km of cool archean lithosphere beneath the craton during this time the dongping deposit is located along the 100 km wide north south gravity lineament which marks the western border of the thinned crust as both regional metamorphism of mesoproterozoic and younger cover rocks and widespread granite magmatism also occurred at ca 150 ma it is unclear as to whether one or both of these also contributed fluid and or metals to the hydrothermal system importantly these new data suggest that economically significant gold deposits of similar mineral style and fluid composition which are scattered along the margins of the craton may all be products of a fluid originally partly sourced within the mantle

salt tectonics in the sw alps italy france from rifting to the inversion of the european continental margin in a context of oblique convergence abstract the sw alps result from the inversion of the european continental margin during the oblique convergence between europe and adria since the cretaceous the orogenic deformation is controlled by two factors the inherited sedimentary and structural record and the geodynamic interaction between the two plates in this paper we present a stratigraphic and structural analysis of the external sw alps ventimiglia menton area in order to define the sedimentary and deformational geometries of the chain and to reconstruct the evolutionary history the field data highlight the preeminent role played by inherited salt structures which derive from the depositional history experienced by the european margin since the mesozoic onwards from late triassic to jurassic evaporites and carbonates deposited as a response to the thetyan rifting the following emplacement of the cretaceous flysch and of the eocene foreland basin succession was strongly influenced by the extensionally triggered salt diapirism and by the interactions with deformations connected to the pyrenees dynamics the resulting geologic discontinuities i e diapir induced highs and basins inherited normal and trasform faults strongly influenced the successive oligo miocene evolution of the belt in the study area observed changes in the thrusts and folds kinematics are considered as the results of rotation during their approaching to inherited highs furthermore the overturning of thrusts and folds in the front of the diapiric flanks are associated with the progressively salt squeezing into the anticlines cores promoted by ongoing alpine compression finally the kinematic data from the study area show radical differences in the tectonic transport direction with respect to the rest of the sw alps nw to w ward in the ventimiglia menton area s to sw ward in provence and ligurian alps this difference is interpreted to be caused by the relative motions of crustal blocks dominated by transpressive tectonics in the frame of the oligo miocene western mediterranean geodynamics

balancing sub and supra salt strain in salt influenced rifts implications for extension estimates the structural style of salt influenced rifts may differ from those formed in predominantly brittle crust salt can decouple sub and supra salt strain causing sub salt faults to be geometrically decoupled from but kinematically coupled to and responsible for supra salt forced folding salt influenced rifts thus contain more folds than their brittle counterparts an observation often ignored in extension estimates fundamental to determining whether sub and supra salt structures are kinematically coherent and the relative contributions of thin i e gravity driven and thick skinned i e whole plate stretching deformation to accommodating rift related strain is our ability to measure extension at both structural levels we here use published physical models of salt influenced extension to show that line length estimates yield more accurate values of sub and supra salt extension compared to fault heave before applying these methods to seismic data from the halten terrace offshore norway we show that given the abundance of ductile deformation in salt influenced rifts significant amounts of extension may be ignored leading to the erroneous interpretations of thin skinned gravity gliding if a system is kinematically coherent supra salt structures can help predict the occurrence and kinematics of sub salt faults that may be poorly imaged and otherwise poorly constrained

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

seam waves what are they part 1 when a shot is fired inside a coal seam much of the seismic energy produced may be trapped inside the seam f f evison first observed this phenomenon in 1955 while working in a coal mine in new zealand developments in the subsequent 35 years have produced a powerful technique for predicting before mining commences the characteristics of a particular coal seam

evolution of the cretaceous astrid thrust belt in the ultradeep water lower congo basin gabon the lower congo basin contains the greatest salt based fold and thrust belt off africa s atlantic margin our study area in the anton marin and astrid marin exploration blocks is in the northern part of the basin gravity driven tectonic shortening began soon after the aptian salt deposition forming gentle west trending salt cored anticlines which together with salt diapirs created a template for later thrusting in the late cretaceous a thrust front propagated landward into the study area and thrusts formed above salt anticlines and diapirs formation of a hanging wall wedge of growth strata was recorded when each thrust fault ruptured the seabed thrusting began after widespread salt thinning as autochthonous salt was expelled into older passive diapirs thinning stiffened the detachment so that thrusts verge strongly seaward structural restorations dip corrected isochron maps and fault activity graphs all show that the landward edge of the thrust belt propagated landward three main pulses of shortening episodically reactivated thrust faults as the thrust front broke landward as thrusting culminated precursor passive diapirs were squeezed and extruded small allochthonous sheets translation culminated in major erosional scouring from which we infer epeirogenic slope steepening in the late cretaceous as shortening spread updip into the previously extensional domain during the late cretaceous to paleogene older extensional faults were inverted and new extensional faults formed orthogonally parallel to the regional paleoslope the structural pattern created in the late cretaceous when the paleoslope dipped southward remains recognizable in the little deformed neogene strata although the present continental slope dips westward

contractional salt tectonic system in the south dezful embayment zagros abstract the dezful embayment in zagros has traditionally been interpreted as a typical fold belt with multiple detachment levels including a lower detachment at the basement cover interface and an upper detachment along the miocene gachsaran halite bearing evaporites this paper constrains diapiric processes in the gachsaran detachment coeval with regional shortening that resulted in complex and hitherto unstudied salt structures and flanking synclinal minibasins in this paper well tied seismic interpretation is integrated with field and remote sensing mapping cross section construction and stepwise tectono sedimentary restoration the results indicate that after the deposition of mishan lower aghajari pre kinematic overburden sediments detachment folding initiated above the gachsaran evaporites during late tortonian times as a result of regional shortening the salt cored anticlines later actively pierced their roof to subsequently rise as passive diapirs and evolve into salt walls synclinal minibasins developed due to salt evacuation into flanking walls during the deposition of the lahbari mb in messinian pliocene remarkable sedimentary thickening and lateral shifts in minibasin depocenter towards the salt walls accompanied by overturned collars and hook halokinetic sequences are diagnostics of near surface syndepositional passive growth of diapirs during this stage from pliocene to recent the major episode of regional shortening has squeezed these precursor salt walls to form thrust welds in conclusion the well exposed structures of south dezful show an early shortening stage then a transition to a combination of shortening and passive diapirism and final thrusting along diapirs this evolution model may be more common in other salt influenced fold thrust belts than is currently recognized

the shanggong gold deposit eastern qinling orogen china isotope geochemistry and implications for ore genesis abstract the shanggong au deposit in the xiong er terrane east qinling china has resources of about 30 ton au making it one of the largest orogenic mesothermal au deposits hosted in volcanic rocks of the mesoproterozoic xiong er group three stages of hydrothermal activity are recognized early middle and late of which two early and middle were ore producing and characterized by quartz pyrite and polymetallic sulfides respectively the third and late stage is represented by a carbonate quartz assemblage hydrogen oxygen and carbon isotope systematics of the shanggong deposit from a previous work suggest that the early stage fluids were derived from magmatic and or metamorphic devolatilization of sedimentary rocks at depth this is supported by new c s and published sr and pb isotopic data presented in this paper these new data 13c values ranging from 1 5 for early stage ankerite to 2 2 for late stage ankerite negative 34s values for sulfides from the middle stage 19 2 to 6 3 suggest a contribution from organic matter and that the ore fluid evolved from deeply sourced to shallowly sourced with those of the middle stage representing a mixture of these two fluid systems the comparison of the hydrogen oxygen carbon sulfur lead strontium isotope systematics between the shanggong deposit and the main lithologies in the xiong er terrane shows that neither these nor the underlying lower crust and mantle or combinations thereof could be considered as the source of ore fluids for the shanggong au deposit a likely source was a carbonaceous carbonate sandstone shale chert sequence in the underthrusted guandaokou and luanchuan groups exposed south of the xiong er terrane ar ar and rb sr isochron ages for mineral phases of the early middle and late stages together with geological field data constrain the timing of the hydrothermal activity and au metallogenesis at 242 10 167 7 and 112 7 ma respectively this metallogenesis and associated granitic magmatism can be related to the continental collision between the yangtze and north china cratons that resulted in the formation of the qinling orogen led to the different hydrothermal systems that were responsible for the three stages that formed the shanggong au deposit over a period of about 130 myrs

interpretation validation on vertically exaggerated reflection seismic sections abstract reflection seismic data is usually displayed with a vertical exaggeration factor in the range 2 6 irrespective of whether it is time or depth domain data this vertical exaggeration gives certain advantages to stratigraphic and structural interpretation and is sometimes a prerequisite to view long wavelength structures however vertical exaggeration distorts geological structures affecting dip curvature line length cross sectional area volume and angular relationships reflection seismic can be assigned a vertical exaggeration heterogeneity factor based on the extremes of seismic velocities in the absence of appreciable poorly compacted units and bathymetry and generally on depth domain data vertical exaggeration is relatively homogeneous analytical solutions are derived to quantify the distortion of angular relationships curvature and bed thickness under homogeneous vertical exaggeration modelled extensional and compressional geometries give acceptable area balance restorations using vertical shear under homogeneous vertical exaggeration these vertically exaggerated restorations are neither admissible nor viable because the deformed and restored state sections are unrealistic given low heterogeneity of vertical exaggeration and relatively simple structure that typifies many extensional geometries and some thrust geometries aspect ratios of 1 1 are not definitively required for section validation by restoration

dynamics of prolonged salt movement in the gluckstadt graben nw germany driven by tectonic and sedimentary processes the formation of salt structures exerted a major influence on the evolution of subsidence and sedimentation patterns in the gluckstadt graben which is part of the central european basin system and comprises a post permian sediment thickness of up to 11 km driven by regional tectonics and differential loading large salt diapirs salt walls and salt pillows developed the resulting salt flow significantly influenced sediment distribution in the peripheral sinks adjacent to the salt structures and overprinted the regional subsidence patterns in this study we investigate the geometric and temporal evolution of salt structures and subsidence patterns in the central gluckstadt graben along a key geological cross section the post permian strata were sequentially decompacted and restored in order to reconstruct the subsidence history of minibasins between the salt structures the structural restoration reveals that subsidence of peripheral sinks and salt structure growth were initiated in early to middle triassic time from the late triassic to the middle jurassic salt movement and salt structure growth never ceased but were faster during periods of crustal extension following a phase from late jurassic to the end of the early late cretaceous in which minor salt flow occurred salt movement was renewed particularly in the marginal parts of the gluckstadt graben subsidence rates and tectonic subsidence derived from backstripping of 1d profiles reveal that especially the early triassic and middle keuper times were periods of regional extension three specific types of salt structures and adjacent peripheral sinks could be identified 1 graben centre salt walls possessing deep secondary peripheral sinks on the sides facing away from the basin centre 2 platform salt walls whose main peripheral sinks switched multiple times from one side of the salt wall to the other and 3 graben edge pillows which show only one peripheral sink facing the basin centre

megaflaps adjacent to salt diapirs megaflaps are steep stratal panels that extend far up the sides of diapirs or their equivalent welds they have multiple kilometer fold widths and structural relief and are thus distinct from smaller scale composite halokinetic sequences maximum dips range from near vertical to completely overturned although overturned megaflaps are associated with flaring salt there is no direct link between megaflap formation and the initiation of salt sheets strata within a megaflap are usually convergent and the lower boundary is typically concordant with the top salt the upper boundary ranges between a prominent onlap surface and a more diffuse zone of gradual rotation and thinning and growth strata likewise display both onlap and stacked wedge geometries we use quantitative cross section restoration to elucidate the origin and development of megaflaps megaflaps typically represent the relatively thin roofs of early salt structures that include single flap active diapirs passive diapirs salt pillows and salt sheets they develop during halokinetic drape folding as the minibasin sinks during contractional squeezing of the diapir and its roof or during some combination of the two the kinematics are dominated by either limb rotation or kink band migration in which roof strata move through a fold hinge into a lengthening steep megaflap both restoration results and direct field evidence suggest that internal strain is minor with little bed lengthening and thinning recognition and understanding of megaflaps are critical to successful petroleum exploration of three way truncation traps against salt megaflaps also have implications for the lateral seal of stratigraphic traps and fluid pressures in minibasins

the evolution of allochthonous salt along a megaregional profile across the northern gulf of mexico basin sequential restorations of a north south megaregional cross section across the north central gulf of mexico basin from east central louisiana to the abyssal plain define a dynamic complex history of sedimentation salt flowage and salt evacuation proprietary composite seismic profiles 590 km 33 wells and published depth to basement maps were used to constrain the section in depth thirteen sequential structural restorations incorporating both decompaction and isostatic subsidence thermal and tectonic were then constructed from the late cretaceous to the holocene the restorations highlight and constrain a protracted history of deformation that is primarily controlled by gravity and the progradation of cenozoic sediments over salt early stages of the tectonic history of the northern gulf of mexico basin were related to differential thermal subsidence resulting from early middle jurassic rifting during the cenozoic the evolution of the basin was dominated by the influx of large clastic depocenters which caused the basinward evacuation of autochthonous jurassic salt salt extrusion from the autochthonous layer was accomplished by inclined salt bodies which flowed into salt glaciers or sheets near the sea floor evacuation of allochthonous salt layers provided significant sediment accommodation and unusually thick sedimentary sections were deposited such as the terrebonne trough of southern louisiana 3 7 km of miocene strata salt sheet formation and evacuation occurred progressively basinward through time in response to basinward shifts of major cenozoic sedimentary depocenters as a salt sheet neared complete evacuation the underlying autochthonous salt layer would begin to evacuate providing additional sediment accommodation that caused autochthonous salt flowage basinward and the formation of the next allochthonous salt sheet basinward of the depocenter the area of autochthonous salt progressively decreased through time and currently represents at most 45 of its maximum along this transect the total area of salt through time was more stable with variations of only 30 from its maximum this relationship is a function of lateral salt flow into and out of the plane of section and possible salt dissolution the restorations indicate that very little translation or extension 1 46 occurred at the autochthonous salt level during the evolution of the basin the majority of translation or extension occurred above allochthonous salt sheets 25 and was compensated laterally by salt flow displacements above allochthonous salt sheets were driven by gravitational instabilities caused by the slope gradient

evolution of ore forming fluids in the sawayaerdun gold deposit in the southwestern chinese tianshan metallogenic belt northwest china the sawayaerdun gold deposit was discovered in the early 1990s and is the largest orogenic gold deposit in the chinese tianshan gold mineralization occurs in quartz veins which are hosted in carbonaceous metasediments and controlled by faults and fractures three major hydrothermal events can be identified at sawayaerdun an early barren quartz vein stage middle stage quartz veins with pyrite and gold mineralization and late carbonate quartz veins fluid inclusion studies of quartz pyrite and carbonate formed during the major hydrothermal stagesshow distinct changes in fluid temperature composition and redox conditions occurred during fluid evolution three types of fluid inclusions have been identified at sawayaerdun h2o nacl l v h2o nacl co2 l v and co2 l v fluids trapped in early barren quartz have high temperatures 280 420 c low salinities 3 wt nacl equiv high cl and are co2 rich middle stage quartz contains fluids with lower temperatures 210 310 c and variable salinities 0 8 17 5 wt nacl equiv they are commonly s rich co2 containing and relatively reduced compared with early stage fluids in contrast hydrothermal pyrite hosted in middle stage quartz veins trapped fluids formed over a narrower temperature range 220 270 c more oxidized high co2 ch4 ratio and have higher ca k and mg than fluids in quartz late stage carbonate is dominated by fluids with low temperatures 200 c and low contents of cl s and k fluid immiscibility probably commenced at the onset of mineralization along with middle stage quartz formation resulting in the generation of coexisting fluid inclusions with distinguishable vapor liquid ratios and salinities the compositional difference between fluids trapped in pyrite and quartz indicate fluid mixing may have occurred during the mineralization stage the oxidized fluids probably a mixture of meteoric water and fluids generated during water host rock interaction emerged into the ore forming system to generate extensive metals precipitation the fluid immiscibility and fluid mixing are most likely caused by pressure decrease during late paleozoic uplift and erosion in the chinese southern tianshan area comparison of fluids between four major mineralization zones at sawayaerdun indicate that zone ii is similar to the most important zone iv and the order of similarity is probably zone ii xi i which could be applied to the future mineral exploration in this area

structural segmentation inversion and salt tectonics on a passive margin evolution of the inner kwanza basin angola the kwanza basin angola is divided into the inner and outer kwanza salt basins separated by a chain of synrift basement highs on which aptian 112 122 ma salt is thin or absent north to northwest trending basement structures in the inner kwanza basin have repeatedly been reactivated since neocomian 144 127 ma rifting reactivation formed three northwest striking fold and thrust belts near basement uplifts the thrust belts are bounded by northeast striking rift related transfer fault zones that were apparently reactivated during subsequent shortening three episodes of postrift basement involved shortening are documented in the inner kwanza basin 1 albian early cenomanian 112 96 ma 2 senonian 89 65 ma and 3 oligocene holocene 34 0 ma we relate the albian early cenomanian event to ridge push the senonian event to global plate reorganization and oligocene holocene shortening to uplift of the african superswell structural segmentation of the inner kwanza basin controlled the evolution of salt structures adjacent to basement uplifts diapirs were initiated as buckle folds some anticlines were unroofed by erosion and evolved into passive salt walls elsewhere broad salt walls were triggered by either detached extension or basement block uplift these walls grew until they exhausted their supply of salt thereafter dissolution rates exceeded rates of salt inflow so the walls began to subside withdrawal of salt from the walls produced the elongate sedimentary troughs for which the basin is famous trough fill ranges in age from cenomanian to pliocene and this age varies greatly from trough to trough and along strike within troughs

use of cross section restoration to determine paleobathymetry and sea floor paleotopography in the gulf of mexico basin a systematic technique for sequential restoration of salt related extensional structures incorporates airy isostasy to quantify both the loading subsidence and the change in water depth during any time interval the results are used to generate paleo sea floor templates for restoration and to reconstruct evolving salt and sediment geometries paleobathymetries calculated by the restoration technique are compatible with paleobathymetric environments derived from biofacies analysis of benthic foraminifers sampled in five wells along a reflection seismic profile from western eugene island offshore louisiana northern gulf of mexico furthermore both aggradation and progradation rates measured from the restorations are consistent with regional depositional patterns the results demonstrate that the restoration method adequately determines paleobathymetry and sea floor paleotopography restoration of multiple sections can provide a framework for the estimation of sediment transport and deposition geometries and facies development 26 refs 3 figs

resolving mantle and crustal contributions to ancient hydrothermal fluids hear isotopes in fluid inclusions from dae hwa wmo mineralisation south korea abstract helium and argon isotopes from fluid inclusions in individual colour zones b c d and e of a large scheelite crystal from the 88 ma dae hwa w mo deposit south korea trace the source and history of the ore fluids a gradual decrease of the fluid 3 he 4 he 3 he 36 ar and 40 ar 36 ar from the core to the edge of the scheelite reflects the progressive dilution of a magmatic fluid by meteoric water and is consistent with the previously observed decrease of 18oh2o and fluid inclusion homogenisation temperatures th shelton et al 1987 the covariation of fluid inclusion he ar isotope systematics with 18o and th defines a magmatic component with 3 he 4 he 1 2 10 6 3 he 36 ar 0 01 and 40 ar 36 ar 1000 anomalously high helium and argon isotope ratios in zone d fluids represents undiluted magmatic noble gases this may reflect local variation in the magmatic gas flux or gas loss due to boiling of the hydrothermal fluids prior to mixing with magmatic gas helium and argon isotope systematics constrain mantle and crustal components in the hydrothermal fluids 40 ar 3 he 4 5 104 are close to the mid ocean ridge basalt value implying that 40ar is mantle in origin radiogenic isotope ratios of the mantle endmember 40 ar 4 he 0 69 0 06 are similar to contemporary geothermal fluids the coincidence of mantle derived he and ar in the fluids is strong evidence that mantle melting during late cretaceous subduction triggered the crystal melting responsible for granite formation 40 ar 4 he of the meteoric fluid 0 007 0 001 is far lower than the crystal production ratio 0 2 implying an origin in crust below 200 c

seismic response to collapse structures in the southern north sea abstract the presence of probable salt dissolution associated collapse structures in the north sea based on the evidence of contemporary seismic data was discussed by lohmann 1972 since then little attention has been paid to them in north sea literature although many oil companies will have studies on file this paper describes and illustrates a selection of such features in the area from recent seismic data and suggest a broad classification for them as they are seen on the seismic section based on mode of origin reference will also be made to certain types of carbonate dissolution and collapse effects

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

paleogeographic evolution of a segmented oblique passive margin the case of the sw iberian margin the sw iberian margin is an oblique passive margin developed during the mesozoic as part of the opening of the westernmost ligurian tethys the algarve basin developed on the sw iberian margin and its sedimentary record was strongly controlled by tectonics the algarve basin was dominated during the mesozoic by wsw ene trending extensional faults and their associated depocenters segmented by oblique nw se transfer zones two major nw se trending transfer zones connected the algarve basin to the gorringe bank in the west and to the betic basin in the east the sw iberian margin was later inverted during late cretaceous to cenozoic times due to convergence between africa and iberia inversion of the algarve basin and the sw iberian margin was controlled by both the wsw ene and nw se trending structures formed during the passive margin phase the evolution of the algarve basin during the mesozoic and up to the paleogene is documented in this paper through paleogeographic reconstructions based on field geology and reinterpretation of offshore seismic and well data

computerized balanced cross section locace to reconstruct an allochthonous salt sheet offshore louisiana abstract the evolution of an allochthonous salt sheet underlying the mississippi fan is quantified using the two dimensional locace balanced section program a first set of tests shows that the shape of the principal normal fault associated with the salt sheet is inconsistent with a roll over geometry when using flexural slip or simple 120 linear shear criteria with a fixed footwall geometry the next test with corrected fault geometry allows coherent restoration at the early lower miocene using the flexural slip criterion in two dimensional reconstructions the area of salt cannot be balanced i e the area available for salt is considerably wider than the actual salt area shown on the initial section thus either salt was dissolved or perhaps more likely salt moved outside the plane of section calling for a three dimensional volumetric reconstruction procedure the final interpretation is geometrically consistent and suggests that since early lower miocene time a large amount of salt moved out of the plane of section forming the allochthonous salt masses an attempt to approximately balance salt volumes in three dimensions suggests that the amount of salt escaping the system is at least 18

paleomagnetic and inner diapiric structural constraints on the kinematic evolution of a salt wall the bicorb quesa and northern navarres salt wall segments case prebetic zone se iberia abstract paleomagnetism together with an analysis of the internal structure of the bicorb quesa and northern navarres salt wall segments prebetic zone in se iberia were used to constrain their kinematics and driving mechanisms paleomagnetic data from upper triassic red beds of the selected salt related structures and from the miocene rocks belonging to adjacent syn diapiric half grabens reveal 15 30 counter clockwise vertical axis rotations of the salt wall rocks and a 20 clockwise rotation of the jurassic miocene cover block located south of the salt wall this together with the salt wall structure indicates that the origin of the salt wall was linked to the motion of a late miocene thin skinned extensional fault system which detached on the upper triassic evaporites specifically the salt wall formed by the south southwest displacement with a 20 clockwise rotation component of a cover block bounded northwards by the detachment disruptions generated by the motion of pre existent basement faults the upper triassic detachment level was first affected by a counter clockwise vertical axis rotation and during the paleogene earliest miocene building of the iberian chain by tight wnw trending folds and sse directed minor thrusts this study also shows that paleomagnetism together with the analysis of the internal structure can successfully depict the geometry and kinematic evolution of complex salt wall structures

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

geometry of thin skinned tectonic systems in relation to detachment layer thickness in sedimentary basins characterizing features of both extensional and compressional thin skinned systems may be controlled by the thickness of the underlying mobile material within extensional fault arrays detachment layer thickness in conjunction with detachment dip controls variations in fault spacing and polarity because rigid fault blocks are only free to rotate as long as there is enough underlying mobile material to redistribute between the fault block keels different styles of extensional fault array range from single polarity arrays with closely spaced faults thin detachment to arrays where the fault blocks rotate until the fault blocks separate from one another thick detachment departure from this relationship depends on the amount of internal deformation that can be sustained by the domino fault blocks within contractional zones detachment folds occur where the amount of mobile material can fill the evolving fold core via redistribution thrusts occur where there is insufficient mobile material to sustain detachment fold growth the variations in extensional and contractional style that are described here in relation to mobile layer thickness can be combined to give an idealized model of regional variation in structural style in relation to regional variation in stratigraphy applying this model to a salt basin an allochthon in the area of thickest salt may be characterized by updip raft tectonics and downdip detachment fold belts this style would be laterally transitional toward areas of thinner or lower net salt to updip domino fault arrays and downdip thrust systems

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex