late proterozoic lavas of the central arabian shield evolution of an ancient volcanic arc system a petrological assessment of 11 volcano sedimentary belts in the central arabian shield cas using 118 new analyses is presented the same samples have been used in a rb sr dating programme also reported in this volume the oldest volcano sedimentary belts sequence c 900 ma are chemically immature bimodal suites of low k tholeiites and sodic dacite rhyolite depleted in lithophile elements these lavas have chemical characteristics similar to immature island arcs such as the tonga kermadee and lesser antilles arcs younger lavas of sequence b 900 700 ma are slightly more mature in composition being predominantly calc alkaline and low k arc tholeiite series with higher lithophile element contents they are comparable with pacific island are averages the youngest voluminous lavas sequence a 700 570 ma are generally calc alkaline or high k calc alkaline series lavas with moderately high lithophile element abundances they are comparable to volcanic arcs such as central america and indonesia which are transitional between island arcs and continental margin volcanic arcs the cratonization process in the cas thus involved the superimposition of three volcano sedimentary sequences formed in progressively maturing volcanic arcs early formed immature island arcs were succeeded by chemically more mature island arc deposits and then by deposits formed in volcanic arc s transitional between island arcs and continental margins the evolution ceased at this stage and probably did not advance to the equivalent of an andean continental margin

global crustal stress pattern based on the world stress map database release 2008 the world stress map wsm project is a global compilation of information on the contemporary crustal stress field from a wide range of stress indicators the wsm database release 2008 contains 21 750 stress data records that are quality ranked using an updated and refined quality ranking scheme almost 17 000 of these data records have a c quality and are considered to record the orientation of maximum horizontal compressional stress sh to within 25 as this is almost a triplication of data records compared with the first wsm database release in 1992 we reinvestigate the spatial wave length of the stress patterns with a statistical analysis on a global 0 5 grid the resulting smoothed global stress map displays both the mean sh orientation that follows from the maximum smoothing radius for which the standard deviation is b25 and a countour map that displays the wave length of the stress pattern this smoothed global map confirms that long wave length stress patterns n2000 km exist for example in north america and ne asia these have been used in earlier analyses to conclude that the global stress pattern is primarily controlled by plate boundary forces that are transmitted into the intraplate region however our analysis reveals that rather short wave length of the stress pattern b200 km are quite frequent too particularly in western europe alaska and the aleutians the southern rocky mountains basin and range province scandinavia caucasus most of the himalayas and indonesia this implies that local stress sources such as density contrasts and active fault systems in some areas have high impact in comparison to plate boundary forces and control the regional stress pattern

effects of latent heat release at phase boundaries on flow in the earth s mantle phase boundary topography and dynamic topography at the earth s surface abstract mantle flow models that do not consider the effects of latent heat on phase boundaries typically predict dynamic surface topography too large to be compatible with observations here these effects were implemented in a mantle flow model and resulting changes in dynamic topography and topography of phase boundaries were computed inclusion of these effects was found to reduce the rms amplitude of dynamic topography by about 50 60 m still leaving a substantial misfit from observations in most cases considered generally it also leads to a slight improvement of correlation with dynamic surface and phase boundary topography constrained by observations results thus indicate that the model implemented here is applicable to the earth but that other effects need to be considered as well in order to fully explain phase boundary and dynamic surface topographies

role of crustal stretching on subsidence of the continental crust abstract the principal areas of subsidence of the continental crust are wide intracontinental basins and passive continental margins in many intracontinental basins crustal extension amounts to only a few percent and is unable to explain their subsidence as shown for the timan pechora pre caspian and west texas basins the deep black sea and south caspian basins are underlain by highly attenuated continental crust having velocities in the 7 km s range that shows no evidence for significant extension in passive margins upper crustal extension ranges between 10 and 40 whereas the lower crust is attenuated by 2 3 times e g campos basin north biscay margin large discrepancy between upper crustal stretching and lower crustal attenuation is seen in the crustal configuration of many intracontinental grabens e g baikal and dniepr prypyat basins only in highly extended areas such as the basin and range province and the east china rift system does crustal stretching account for the observed crustal thinning the observed discrepancy between upper extension and crustal thinning across intracontinental rifts and passive margins and particularly in some wide intracontinental basins suggests that crustal stretching alone cannot account for the subsidence of these basins phase transformations in the lower crust probably facilitated by the presence of hydrous fluids can cause rapid 1 ma as well as long term 200 1500 ma upward displacement of the moho discontinuity resulting in high amplitude subsidence of the crust in areas of crustal extension this mechanism can overprint subsidence induced by thermal relaxation of the lithosphere the case of the black sea and south caspian basins shows that density increase of the lithosphere can also occur independently of crustal stretching

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

the case for dynamic subsidence of the u s east coast since the eocene the dynamic subsidence of the united states east coast is addressed using the discrepancy between regional and global estimates of sea level elevation of paleoshorelines and adjoint models of mantle convection that assimilate plate motions and seismic tomography the positions of eocene and miocene paleoshorelines are lower than predicted by global sea levels suggesting at least 50 m and possibly as much as 200 m of subsidence since the end of the eocene dynamic models predict subsidence of the east coast since the end of eocene although the exact magnitude is uncertain this subsidence has been occurring during an overall global sea level fall with the eustatic change being larger than the dynamic subsidence this results in a regional sea level fall in the absence of land subsidence dynamic subsidence is consistent with the difference between eustasy and regional sea level at the new jersey coastal plain

the many surface expressions of mantle dynamics plate tectonic theory suggests that present day topography can be explained by the repeated interactions between the tectonic plates moving along earth s surface however mounting evidence indicates that a significant proportion of earth s topography results from the viscous stresses created by flow within the underlying mantle rather than by the moving plates this dynamic topography is transient varying as mantle flow changes and is characterized by small amplitudes and long wavelengths it is therefore often hidden by or confused with the more obvious topographic anomalies resulting from horizontal tectonic movements however dynamic topography can influence surface processes and thus enter the geological record it has for example played a role in the establishment of amazon drainage patterns in turn surface processes such as the erosion of topographical anomalies could affect mantle flow this emerging view of dynamic topography suggests that the concept of plate tectonics as the driver of surface deformation needs to be extended to include the vertical coupling between the mantle and the surface unravelling this coupling back in time with the help of models and the geological record can potentially provide unprecedented insights into past mantle dynamics

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

why intracontinental basins subside longer 3 d feedback effects of lithospheric cooling and sedimentation on the flexural strength of the lithosphere

the ups and downs of north america evaluating the role of mantle dynamic topography since the mesozoic the driving force for transient vertical motions of earth s surface remains an outstanding question a main difficulty lies in the uncertain role of the underlying mantle especially during the geological past here i review previous studies on both observational constraints and physical mechanisms of north american topographic evolution since the mesozoic i first summarize the north american vertical motion history using proxies from structural geology geochronology sedimentary stratigraphy and geomorphology based on which i then discuss the published physical models overall there is a progressive consensus on the contribution of mantle dynamic topography due to buoyancy structures associated with the past subduction at the continental scale a largely west to east migrating deformation pattern suggests an eastward translation of mantle dynamic effects consistent with models involving an eastward subduction and sinking of former farallon slabs since the cretaceous among the existing models the inverse model based on an adjoint algorithm and time dependent data constraints provides the most extensive explanations for the temporal changes of north american topography since the mesozoic at regional scales debates still exist on the predicted surface subsidence and uplift within both the western and eastern united states where discrepancies are likely due to differences in model setup e g mantle dynamic properties and boundary conditions and the amount of time dependent observational constraints toward the development of the next generation predictive geodynamic models new research directions may include 1 development of enhanced data assimilation capabilities 2 exploration of multiscale and multiphysics processes and 3 cross disciplinary code coupling

cenozoic subsidence and uplift of continents from time varying dynamic topography time varying global dynamic topography has been computed for the entire cenozoic the spherical viscous flow model is driven by a distribution of density heterogeneity based on mesozoic and cenozoic subduction by using the calculated topography the uplift and subsidence histories of five regions fixed to the north american indian australian indonesian and south american continents are computed predicted vertical motions are in qualitative agreement with observed values except for india and south america for australia and north america the predicted periods of uplift and subsidence are out of phase with respect to observations but display the correct overall trend the latest phase of uplift for north america is directly related to the cessation of kula plate subduction after 48 ma dynamic topography depends on the viscosity structure of the mantle a lower mantle that is 50 times more viscous than the upper mantle yields the best agreement between modeled and predicted vertical motions the presence of a low viscosity channel beneath the lithosphere has only a small influence on our results compared to dynamic topography the time varying geoid is insignificant in controlling relative sea level

brittle shear deformation in northern kordofan sudan late carboniferous to triassic reactivation of precambrian fault systems analysis of folding and faulting in the basement of the umm badr and sodiri areas of northern kordofan sudan revealed the existence of four major deformational episodes a late proterozoic deformation d1 produced isoclinal folds in high grade migmatitic gneissic basement and in the metasedimentary belt of umm badr a phase of intense nne ssw ductile shearing d2 in the umm badr belt refolded the earlier structures in the metasediments and is of late pan african age dextral ene wsw brittle shearing d3 of latest pan african age also affected the metasedimentary belt of umm badr a late carboniferous to triassic brittle shearing d4 reactivation event in the umm badr and jebel nehud areas dextral and in the sodiri area sinistral extensively reactivates structures of the previous episodes of deformation exploiting part of the anisotropic zones of weakness age limits for brittle shear deformation in the umm badr and sodiri areas were established from k ar isotopic ages of igneous rocks with varying field relationships to the shearing

strike slip orogens an explanation for the hercynides the nature of oblique plate interactions is not yet well understood the oblique interaction of pacific and n american plates has resulted in large scale migration rotation and accretion of microplates intervening basins are ephemeral individually filled and deformed oblique motion results in zones of both compression and extension the latter may be sufficient to generate new oceanic crust and the former to obduct it both subduction and collision are restricted in time and space the resulting orogen is extraordinarily complex in detail the far more complicated hercynides are the result of dextral interaction between continental plates europe and africa the lateral variability of the orogen the major and long lived strike slip faults the bimodal volcanism and related ore deposits of the european trough the lizard ophiolite and its melanges the nw spanish ophiolites and the iberian pyrite belt are all explained using an oblique collision model in particular the generation deformation and obduction of ophiolites in oblique slip mobile zones is discussed

an integrated approach for identifying aquifers in transcurrent fault systems the najd shear system of the arabian nubian shield groundwater potentials were assessed for major transcurrent fault systems in basement complex terrains using the najd transcurrent shear system of the arabian nubian shield as a test case spatial analysis within a geographical information system environment of relevant data sets field remote sensing geophysical and digital elevation revealed a spatial correlation between existing well locations and distribution of najd transcurrent shear system structural elements i e faults shear zones melange dykes within highly fractured domains suggesting a causal relationship specifically at 1 intersection of najd brittle shear zones and fault systems 2 intersections of two or more fault systems 3 intersections of najd related dykes with the main streams within catchment areas and 4 within tectonic melange for each of the former aquifer types aquifer specific field and satellite based characteristics were identified and used in conjunction with complementary data e g watershed morphology precipitation soil moisture to target aquifers of similar settings postulated well locations were then successfully tested and refined using very low frequency technologies results could potentially highlight the important role of major transcurrent fault systems in providing settings conducive for hosting and transmitting groundwater and could potentially serve as a replicable model for regional assessment of groundwater potentials in similar tectonic and hydrologic settings

total tectonic subsidence a parameter for distinguishing crust type at the u s atlantic continental margin total tectonic subsidence tts is the difference between the prerifting continental crust elevation and the present sediment unloaded basement depth in a sedimentary basin tts is calculated using observations of bathymetry and basement depth and assumptions about sediment density and the loading response of the lithosphere i use the extensional model for sedimentary basin formation to interpret the tts of a passive continental margin that model predicts that the tts on an old margin should define the major crust type boundaries and indicate the lateral distribution of extension within the extended continental crust tts analysis of the u s atlantic continental margin indicates that the boundary between extended continental and oceanic crusts lies along the east coast magnetic anomaly ecma to the north of the blake spur fracture zone bsfz and along the blake escarpment to the south there is no tts anomaly associated with the blake spur magnetic anomaly which seems to be underlain by normal oceanic crust the ecma appears to be associated with a tts minimum but i attribute that to artificially shallow estimates of depth to magnetic basement under the ecma tts estimates of extended continental crust thickness agree well with gravity models except where the problem with magnetic basement depth estimates interferes the amount of crust extension prior to seafloor spreading varies along the strike of the margin the most abrupt change is at the bsfz across the bsfz the amount of extension varies by 160 km but the volume of continental material does not vary the extension variation may be caused by lateral changes in the gross rheology of the continental lithosphere in the case of the bsfz it would be the suture of more ductile pre late paleozoic african craton with more brittle north american craton that could cause the abrupt change

the najd fault system revisited a two way strike slip orogen in the saudi arabian shield abstract the najd strike slip fault system extends over the northeastern arabian shield in a zone 1200 km in length and 300 km wide faults trend nw se with strike lengths 500 km but small sinistral displacements of 240 km najd faults were active in the late proterozoic and post date cratonization of the shield associated secondary structures include grabens thrust faults folds and dike swarms in the southwest of the najd system near zalm initial faulting was dextral and began earlier than formerly thought emplacement of a plutonic complex was controlled by najd fractures of dextral geometry and displacements the same fractures were active before and after deposition of a group of volcanosedimentary rocks in grabens orientated consistently with development in a dextral strike slip regime graben deformation was controlled by sinistral motion along the same fractures responsible for graben development and also by younger fractures of sinistral geometry and displacement dike swarms in the area are also consistent with early dextral and later sinistral shear of najd trend structures in the zalm area occur throughout the najd system and the consistent chronology of older dextral structures dislocated and deformed by younger sinistral faults suggests a reversal in the sense of motion of the najd system as a whole

generation of long wavelength heterogeneity in the mantle by the dynamic interaction between plates and convection lateral variations in seismic velocity through its dependence on temperature can easily be generated at the gravest harmonics including degrees one and two by the dynamic interaction between plates and convection models of thermal convection with a single non subducting plate have been formulated in a cylindrical geometry plates of width one to four times times the thickness of the convecting region strongly modulate the flow by being pushed over cold downwellings and inhibiting cooling of the fluid beneath during rapid motion off of hot regions a large scale pattern of shear is developed causing small uprising limbs to be swept into the largest upwellings both insulation and plume plume collisions pump energy into the lower wavenumber harmonics

a proterozoic rift origin for the structure and the evolution of the cratonic congo basin abstract we interpret the cratonic congo basin a large circular cuvette centrale filled with up to 9 km of proterozoic to neogene sediments as the consequence of a neo proterozoic rift firstly the magnitude and the long term subsidence are consistent with the thermal time constant of a 200 250 km thick lithosphere inferred from several tomographic studies secondly the surface accumulation of sediments is compensated at depth by crustal thinning whose magnitude can be estimated from the analysis of the surface gravity after backstripping the effect of the sediments a residual nw se positive and narrow gravity anomaly is observed across the cuvette centrale and is interpreted as the remaining crustal thinning associated with this rift assuming that isostasy is governed by a necking level and a flexural response to sediment loads we have estimated the combination of the depth of necking and the equivalent elastic thickness of the lithosphere that provide the best fit with the residual gravity i e 10 km and 100 km respectively the corresponding uplift of the upper mantle is in the continuity of the mbuji mayi supergroup to the se and the liki bembian group to the nw these two groups represent older stages of rifting in the congo craton which shows that rifting has periodically affected and weakened the cuvette centrale during a long period of time

development of pull apart basins a comparative study of well mapped active and ancient pull apart basins suggests a qualitative model for their continuous development pull aparts evolve from incipient to extremely developed basins through a sequence of closely related states new and compiled map data from several areas including the northern caribbean and turkey suggests the following stages in pull apart development 1 in rigid intracontinental strike slip plate boundary zones larger pull aparts nucleate at releasing fault bends along segments of the principal displacement strike slip fault zone which are oblique to the theoretical interplate slip lines 2 initial opening across releasing fault bends produces spindle shaped basins defined and often bisected by oblique slip faults connecting the discontinuous ends of the strike slip faults 3 increased strike slip offset produces basin shapes which we colloquially call lazy s shape for basins between sinistral faults and lazy z shape for basins between dextral faults 4

fluid injection and seismic activity in the northern montney play british columbia canada with special reference to the 17 august 2015 mw 4 6 induced earthquake in this article we analyzed the recent seismic activity in the northern montney play of british columbia in 2015 and its connection with fluid injection hydraulic fracturing and long term injection of gas and wastewater disposal in the region the earthquake sequence used in this study includes 676 events from 3 october 2014 to 31 december 2015 from the progress energy earthquake catalog with moment magnitude as small as 1 spatial and temporal correlation of seismic activity with the fluid injection in the region revealed that these events are better correlated with hydraulic fracturing correlation coefficient of 0 17 at confidence level close to 99 7 with a lag time between 0 and 2 days than other types of injection using the double difference relocation technique we obtained depth constraints for some of the events for which supplementary industry provided waveforms were available the depths of these events range from 0 5 to 2 5 km and are mostly constrained above the target zone where hydraulic fracturing was taking place the best fit moment tensor solution for the event on 17 august 2015 gives a moment magnitude of 4 6 and a predominantly thrust mechanism in the northwest southeast direction with a shallow focal depth of 4 km this is consistent with that obtained through double difference relocation for this event 1 3 km given the depth uncertainty of the moment tensor inversion electronic supplement 1 tables of injection volumes and seismicity parameters and figure of monthly distribution of seismic events and location of fluid injection sites in the vicinity of the 17 august 2015 m w 4 6 event 1 http www bssaonline org lookup suppl doi 10 1785 0120160175 dc1

evolution of the west siberian basin the west siberian basin is one of the largest intracratonic basins of the world and an important hydrocarbon province of russia perhaps the most important geologic event in siberia was the emplacement of basalts around 250 ma i e permo triassic boundary covering an area of about 5 10 6 km 2 this volcanism may be responsible for a mass extinction that occurred around permian triassic time the prebasaltic rifting event was limited to the north northeastern sector of the basin initial basin wide subsidence took place in the jurassic as a result of which the western part of siberia became the west siberian basin bounded by uplifts to the east and to the west one of the surprising aspects of the west siberian basin is the abundance of subvertical faults believed to be result of strike slip movement while intraplate inversions and fault reactivation structures have been observed in many cratons subvertical faults observed in the west siberian basin are unique because of their geometries and abundance the differentiation between the effects of tectonics and eustasy in cratonic basins is simple the global eustatic signal is basin wide with regional and local tectonics playing an overprinting role thus the middle jurassic turonian first second and third order cycles in the west siberian basin were primarily driven by eustasy the middle jurassic turonian series can be subdivided into two second order and 16 third order transgressive regressive cycles within dataset extent fourth order cycles appear to be controlled by delta shifting although extensively studied a number of fundamental questions regarding the origin and evolution of the west siberian basin remain unresolved or poorly documented in the literature

the bani ghayy group sedimentation and volcanism in pull apart grabens of the najd strike slip orogen saudi arabian shield abstract the cratonisation of the arabian shield involved the accretion of ensimatic arc terranes in the west and south followed by continental collisions along the nabitah and al amar sutures and the onset of the najd strike slip orogen volcanosedimentary successions which post date these collisions have been proposed as the products of magmatism in transitional volcanic arcs one such succession the bani ghayy group lies unconformably above a series of volcanosedimentary rocks associated with an older active continental margin and was deposited in three separate elongate fault bounded grabens each graben contains coarse fanglomerate and fan delta deposits along the margin and proximal greywackes toward the centre reef limestones occur locally whereas volcanogenic rocks are widespread the latter are geochemically bimodal and with the sediments are typical of continental rifting environments although deformed ultramafic rocks within internal reverse faults suggests that the grabens were floored in part by primitive mantle derived crust deposition of the bani ghayy group post dates incipient motions along fractures of the najd fault system the orientation of the bani ghayy grabens and the geometry of the boundary faults are consistent with development in a regime of northwest trending dextral shear however the bani ghayy grabens are displaced and deformed by later movements of the same faults but in a sinistral sense other successions correlated with the bani ghayy also preserve features consistent with deposition in continental grabens and the possibility that they represent arc volcanism is discounted

anomalous subsidence history of the west siberian basin as an indicator for episodes of mantle induced dynamic topography abstract vertical intraplate motions are not easily related to plate tectonics understanding their underlying mechanism is further complicated by poor constraints on the magnitude and timing of these motions western siberia is a prominent intraplate area affected by vertical tectonics shortly after the assemblage of pangaea the region experienced substantial uplift followed by a long period of subsidence that led to formation of the world s largest sedimentary basin the west siberian basin its sedimentary cover has been extensively explored and described in the soviet literature here we digitise compilations of stratigraphic data to calculate the basin s subsidence history by backstripping analysis our results confirm the prolonged and high amplitude regional subsidence that has been noted before and constitutes the basin s first order vertical motion however our backstripping results also reveal a secondary mode of shorter spatial and temporal scales induced by the migration of the maximum subsidence across the basin importantly the generally slow subsidence of the basin was interrupted by uplift events in the early and late cretaceous and in the middle oligocene while the secondary mode of vertical motion is not easily understood in terms of traditional subsidence models restricted to lithospheric cooling after stretching it is consistent with rapid uplift events that have been reported for other locations such as elevated passive continental margins we discuss the geodynamic implications and conclude that the basin may hold important constraints on dynamic topography induced by sublithospheric mantle flow processes

no global scale transgressive regressive cycles in the thanetian paleocene evidence from interregional correlation abstract a detailed examination of transgressions and regressions that occurred during the thanetian 58 7 55 8 ma may provide an important constraint on the global palaeoenvironment seven tectonically stable regions the eastern russian platform northwestern europe northwestern africa northeastern africa the arabian platform the northern gulf of mexico and southern australia represent exceptional records of transgressive regressive t r cyclicity their chronostratigraphic frameworks are sufficiently well constrained to permit accurate correlation surprisingly except for a generally regressive trend occurring in the late thanetian no common t r cycles can be delineated which indicates an absence of global scale t r cyclicity during the thanetian furthermore we find no clear correspondence between documented t r patterns and previously reported eustatic changes we suggest that a warm climate and an absence of major glaciations in the early middle thanetian coupled with only slow eustatic change expected from tectonic processes stabilized thanetian eustatic sea level regional subsidence or uplift possibly generated by mantle flow in the form of dynamic topography governed transgressions and regressions locally and resulted in an inconsistency between t r cycles in different parts of the globe the late thanetian regressive episode which preceded the paleocene eocene thermal maximum may be linked to an advance of glaciation

pre mesozoic geodynamics of the precaspian basin kazakhstan abstract this paper concentrates on the pre mesozoic history of the precaspian basin representing more than half of the 20 km of its sedimentary thickness we present the evolution of sediments deposited in the basin through time by several regional sections of the basin these image from the devonian the creation and evolution of a deep intercontinental basin which existed from carboniferous to permian palinspastic reconstructions show also the evolution of the basin s margins their relations with the southern pre uralian foredeep in the east and carbonate build ups in the southeast we present a reconstruction for the early history of the precaspian basin which became an individual basin only at the end of the permian as a result of the uralian orogeny the basement of the central precaspian depression is characterised by a thin crust where a low velocity layer is absent a layer of abnormally high velocities exists below the crust which on the basis of structural and gravitational field data is interpreted as eclogite we put forward a scenario for the age and emplacement of eclogite lenses at the base of the crust they are possibly implemented in the hangingwall from a westward subduction zone existing during the vendian before the collision giving birth to the proto urals most of the basin subsidence is due to the thinning mainly during devonian and increase of the average density of the crust present crustal density has characteristics of intermediate to lower crust interpreted by some authors as oceanic we propose that the loading effect of the eclogites emplacement may explain also a part of the precaspian basin subsidence

flexural isostasy in the bolivian andes chaco foreland basin development the chaco foreland basin was initiated during the late oligocene as a result of thrusting in the eastern cordillera in response to nazca south america plate convergence foreland basins are the result of the flexural isostatic response of an elastic plate to orogenic and or thrust sheet loading we carried out flexural modelling along a w e profile 21 4 degrees s to investigate chaco foreland basin development using new information on ages of foreland basin strata elastic and sedimentary thicknesses and structural histories it was possible to reproduce present day elevation gravity anomaly moho depth elastic thicknesses foreland sedimentary thicknesses and the basin geometry our model predicted the basin geometry and sedimentary thicknesses for different evolutionary stages measured thicknesses and previously proposed depozones were compared with our predictions our results shed more light on the chaco foreland basin evolution and suggest that an apparent decrease in elastic thickness beneath the eastern cordillera and the interandean zone could have occurred between 14 and 6 ma c 2009 elsevier b v all rights reserved

rb sr isotope study of latest proterozoic volcano sedimentary belts in the central arabian shield five new rb sr whole rock isochrons for volcanic successions assigned to 9sequence9 a in the central arabian shield indicate that very late precambrian c 690 570 ma volcanicity was an important event in the evolution of the shield the following ages are considered to define or approximate to the age of lava extrusion fatimah group 688 30 ma jahhad unit 616 13 ma juqjuq formation 612 22 ma arfan formation 608 9 ma hummah unit 572 23 ma initial 87 sr 86 sr ratios range from 0 7027 to 0 7036 and rb sr ratios are uniformly low 87 srl 86 sr ratio for the jahhad and hummah samples reflects the involvement of less depleted mantle or possibly slight crustal contamination

eroding dynamic topography 1 geological observations of mantle flow driven dynamic topography are numerous especially in the stratigraphy of sedimentary basins on the contrary when it leads to subaerial exposure of rocks dynamic topography must be substantially eroded to leave a noticeable trace in the geological record here we demonstrate that despite its low amplitude and long wavelength and thus very low slopes dynamic topography is efficiently eroded by fluvial erosion providing that drainage is strongly perturbed by the mantle flow driven surface uplift using simple scaling arguments as well as a very efficient surface processes model we show that dynamic topography erodes in direct proportion to its wavelength we demonstrate that the recent deep erosion experienced in the colorado plateau and in central patagonia is likely to be related to the passage of a wave of dynamic topography generated by mantle upwelling

aulacogens and aulacogeosynclines regularities in setting and evolution abstract aulacogens and aulacogeosynclinal zones represent intra continental palaeorifts and inverted palaeorifts they were formed in the process of the break up of continents during the late proterozoic inversion of such basins occurred variably during the baikalian caledonian hercynian and alpine orogenic cycles in response to the build up of intraplate compressional stresses emanating from orogenic belts aulacogens were first recognized on the stable russian platform where they correspond to linear graben type depressions filled with proterozoic sediments often buried beneath a thick cover of palaeozoic and younger sediments some aulacogens have experienced a short period of reactivation during the palaeozoic aulacogeosynclines differ from the genetically related aulacogens by their greater dimensions and the amount of lithospheric extension that can go to the extent of opening of small ocean basins consequently they are characterized by a greater degree of destruction of the continental crust the depth of subsidence and the complexity of their post rift development which commonly terminates with their compressional deformation giving rise to the development of intracontinental linear folded and thrusted structures frequently associated with low grade metamorphism and small intrusions many ancient platforms are characterized by aulacogens metaplatforms are dissected by aulacogens and aulacogeosynclines whereas geosynclinal troughs are the precursors of geosynclinal mobil belts aulacogens aulacogeosynclines and geosynclinal troughs represent a group of negative linear structures which are characterized by an increasing degree of crustal destruction during rifting processes and increasing mobility during lithospheric contraction

neotectonics of the pontides implications for incompatible structures along the north anatolian fault data for the post serravallian neotectonic evolution of the pontides in northern turkey indicate predominant ene wsw shortening with complementary nnw sse extension we present a new fault plane solution for the bartin earthquake 3 september 1968 and compare its mechanism with the movement picture of other neotectonic faults in the pontides and northern greece together with that of the thessaloniki earthquake 20 may 1978 the general strain pattern exhibited by these structures agrees remarkably well with that inferred from early tortonian early pleistocene structures reported from within the north anatolian fault zone which have been interpreted as indicating a possible reversal of the sense of movement along the north anatolian transform fault here we argue that such incompatible structures may be related to the overall e w shortening of anatolia and the southern parts of the black sea resulting from the sideways continental escape from around the african and the arabian promontories rather than to hypothetical reversal of motion along the north anatolian fault for which there is no evidence other than the above mentioned incompatible structures this new model also has important implications for seismicity and earthquake risk in regions contained within the southern part of the black sea plate

phanerozoic marine inundation of continents driven by dynamic topography above subducting slabs a spherical model of mantle flow constrained by the locations of trenches can be used to predict the dynamic topography of the earth s surface and hence the marine inundation of continents for past periods of high sea level the predicted geographical pattern of flooding correlates well with the geological record the high spatial correlation may result from increased plate velocities at these times leading to increased rates of subduction subsidence and inundation at convergent margins

a model for induced seismicity caused by hydrocarbon production in the western canada sedimentary basin over the past three decades a significant number of small magnitude and shallow earthquakes have occurred in the western canada sedimentary basin and are located along its western flank near areas of oil and gas production one of the better documented examples is the swarm of earthquakes associated with the strachan field in the alberta foothills a model based on segall s poroelastic theory is developed to account for the occurrence of earthquakes below the strachan reservoir using this methodology we show that the earthquake of 19 october 1996 underneath the strachan field was most probably triggered by gas extraction the numerical model also implies that gas extraction would cause subsidence and localized changes in in situ stress magnitudes there is a strong correlation between rates of production and the number of seismic events but the onset of major seismic activity postdates the commencement of production by approximately 5 years poroelastic modelling can account neatly for this observe

island arcs and their role in the evolution of the western arabian shield abstract two northeast trending late precambrian ensimatic island arc systems in western saudi arabia are described each displays lithotec tonic provinces that conform to those found in modern examples of plate convergence the younger hijaz arc system 800 700 ma contains a thick fore arc sequence of al ays group turbidites overlying an accretionary prism of metamorphosed and fragmented volcanosedimentary rocks and associated ophiolites of the farri group and the al hinu formation the older asir arc system 900 700 ma is exposed at a much deeper erosional level in which only remnant arc and fore arc deposits are present it is identi fied in part by a frontal arc assemblage of abundant dioritic intrusions and high grade metamorphic rocks that are interpreted as a high t low p belt a mafic volcanic assem blage in th back are c area appears to deline ate an interarc basin situated between the at ta if frontal arc and a lithologically similar remnant arc west of bishah about 700 ma ago the hijaz island arc collided with the asir arc system along a southeast dipping subduction zone now rec ognized as the bi r umq port sudan suture epeirogeny during this period led to the crea tion of an intramassif basin in the hijaz arc system and an accretionary basin in the asir arc system these were filled by volcanic and shallow water to continental molasse depos its of the hadiyah and fatimah groups re spectively continued convergence between 700 and 675 ma ago resulted in development of the northeast trending samran fold belt the collision event marks the cessation of an episode of southeast convergence that is in terpreted as the initial phase in the progres sive eastward evolution of the arabian nubian shield introduction

structural interpretation and tectonic evolution of a part of the najd shear zone saudi arabia using landsat thematic mapper data abstract digital landsat thematic mapper data were used to extrapolate structural features associated with the ajjaj shear zone from well characterized to less well known areas the satellite images were enhanced using a linear mixing model with the spectra of known rock types measured from the images as endmember components the approach uses information for all six spectral bands the effects of desert varnish coating in modulating the spectral response of rock exposures are specifically accounted by using of an empirically derived coat component comparison between the lithologic component images produced from the unmixing procedure and published geologic maps demonstrate that these images can be effectively used to map brittle faults ductile shear zones and certain spectrally distinct lithologies by combining interpretation of the enhanced images with available geologic data it has been shown in this study that the ajjaj shear zone is dominantly a ductile structure characterized by the continuity of rotated layers across the shear zone with a minimum sinistral displacement of 25 to 30 km the northern boundary of this shear zone is dominantly ductile whereas the southern boundary consists of a continuous brittle displacement surface which juxtaposes contrasting lithologies several brittle faults within and crosscutting the ductile shear zone had previously been mapped as najd faults these faults are not strike slip in character and clearly postdate najd deformation in the middle of the area studied the ajjaj shear zone changes orientation from wnw to nnw this change corresponds spatially to the intersection of the shear zone with a n s oriented structure here named the hanabiq shear zone the hanabiq shear zone is one of a set of broadly n s trending dextral shear zones which crosscut the arabian shield proponents of the rigid indentor model for the origin of the najd fault system have suggested that these faults form a conjugate set to the nw trending sinistral najd faults our study presents clear evidence that the ajjaj shear zone postdates the hanabiq shear zone this supports recent criticisms of the rigid indentor model as applied to the najd the tectonic significance of the najd fault system remains as intriguing problem

hydraulic fracturing and the crooked lake sequences insights gleaned from regional seismic networks within central alberta canada a new sequence of earthquakes has been recognized as of 1 december 2013 in a region of previous seismic quiescence near crooked lake 30 km west of the town of fox creek we utilize a cross correlation detection algorithm to detect more than 160 events to the end of 2014 which is temporally distinguished into five subsequences this observation is corroborated by the uniqueness of waveforms clustered by subsequence the crooked lake sequences have come under scrutiny due to its strong temporal correlation 99 99 to the timing of hydraulic fracturing operations in the duvernay formation we assert that individual subsequences are related to fracturing stimulation and despite adverse initial station geometry double difference techniques allow us to spatially relate each cluster back to a unique horizontal well overall we find that seismicity in the crooked lake sequences is consistent with first order observations of hydraulic fracturing induced seismicity

palaeogeological hiatus surface mapping a tool to visualize vertical motion of the continents dynamic topography is a well established consequence of global geodynamic models of mantle convection with horizontal dimensions of 1000 km and amplitudes up to 2 km such physical models guide the interpretation of geological records on equal dimensions continent scale geological maps therefore serve as reference frames of choice to visualize erosion non deposition as a proxy for long wavelength low amplitude vertical surface motion at a resolution of systems or series such maps display conformable and unconformable time boundaries traceable over hundreds to thousands of kilometres unconformable contact surfaces define the shape and size of time gap hiatus in millions of years based on the duration of time represented by the missing systems or series hiatus for a single system or series base datum diminishes laterally to locations anchor points where it is conformable at the mapped resolution it is highly dependent upon scale a comparison of hiatus area between two successive system or series boundaries yields changes in location shape size and duration indicative of the transient nature of vertical surface motion as a single step technique it serves as a quantitative proxy for palaeotopography that can be calibrated using other geological data the tool magnifies the need for geological mapping at the temporal resolution of stages matching process rates the method has no resolving power within conformable regions basins but connects around them when applied to marine seismic sections that relate to rock record not to time biostratigraphic and radiometric data from deep wells are needed before hiatus areas that relate to time can be mapped

u pb zircon geochronology and geological evolution of the halaban al amar region of the eastern arabian shield kingdom of saudi arabia u pb zircon model ages for eleven major units from the halaban al amar region of the eastern arabian shield indicate three stages of evolution 1 plate convergence 2 plate collision and 3 post orogenic intracratonic activity convergence occurred between the western afif and eastern ar rayn plates that were separated by oceanic crust remnants of oceanic crust now comprise the ophiolitic complexes of the urd group the oldest plutonic unit in the study is from one of these complexes and gave an age of 694 8 ma detrital zircons from the sedimentary abt formation of the urd group which is intercalated with the ophiolitic rocks were derived from source rocks with a mean age of 710 ma the abt formation may be an accretionary wedge on the western margin of the ar rayn plate plate convergence was terminated by collision of the afif and ar rayn plates during the al amar orogeny which began about 670 ma during collision the urd group rocks were deformed and in part obducted on to one or both plates synorogenic leucogranitoid rocks were intruded from 670 to 640 ma from about 640 to 630 ma widespread unfoliated dioritic plutons were emplaced in the ar rayn block and represent the end of orogenesis related to collision there is no definitive evidence for a significantly older basement beneath the study region

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

the tectono metallogenic evolution of the arabian shield abstract the arabian shield comprises a group of diverse terranes accreted during the late proterozoic their boundaries are suture zones characterised by tectonised ultramafic bodies aligned within distinct orogenic belts the asir hijaz and midyan terranes consist of a series of late proterozoic immature island arcs and together form the western half of the shield in the east however the afif and ar rayn terranes have a continental affinity with the afif terrane being much older at least early proterozoic and possibly archaean metallogeny within the arabian shield is also diverse and includes cu ni and cr mineralisation associated with proterozoic oceanic crust or ophiolite arc type volcanogenic base and precious metal deposits associated with formerly active plate margins shear zone hosted mesothermal gold mineralisation related to accretionary and strike slip tectonics as well as sn w ta mo ree mineralisation associated with post cratonisation alkali granite magmatism of late proterozic to early phanerozoic age it is possible to trace a systematic evolution in metallogeny both within each terrane and throughout the craton as a whole as a function of crustal development and tectonics although the age range of rocks exposed in the shield is from early proterozoic to tertiary all known styles of primary metallogeny are associated with its cratonisation in the late proterozoic

metacraton nature genesis and behavior article i nfo in this paper we show with examples that cratons involved in intercontinental collisions in a lower plate position are often affected by orogenic events leading to the transformation of their margins in some cases craton interiors can also be shaped by intense collisional processes leading to the generation of intra cratonic orogenic belts we propose to call these events metacratonization and the resulting lithospheric tract metacraton metacratons can appear similar to typical orogenic belts i e active margin transformed by collisional processes but are actually sharply different their main distinctive characteristics not all are present in each metacraton are 1 absence of pre collisional events 2 absence of lithospheric thickening high pressure metamorphism being generated by subduction leading to high gradient in strain and meta morphic intensity 3 preservation of allochthonous pre collisional oceanic terranes 4 abundant post collisional magmatism associated with shear zones but not with lithospheric thickening 5 presence of high temperature low pressure metamorphism associated with post collisional magmatism 6 intraconti nental orogenic belts unrelated to subduction and oceanic basin closures reactivation of the rigid but fractured metacratonic lithosphere will cause doming asthenospheric volcanism emplacement and mineral izations due to repetitive mineral enrichments this paper provides several geological cases exemplifying these different metacratonic features in scandinavia sahara central africa and elsewhere a special focus is given to the saharan metacraton because it is where the term metacraton originated and it is a vastly ex panded tract of continental crust 5 000 000 km 2

density structure of the cratonic mantle in southern africa 1 implications for dynamic topography abstract the origin of high topography in southern africa is enigmatic by comparing topography in different cratons we demonstrate that in southern africa both the archean and proterozoic blocks have surface elevation 500 700 m higher than in any other craton worldwide except for the tanzanian craton an unusually high topography may be caused by a low density high depletion of the cratonic lithospheric mantle and or by the dynamic support of the mantle with origin below the depth of isostatic compensation assumed here to be at the lithosphere base we use free board constraints to examine the relative contributions of the both factors to surface topography in the cratons of southern africa our analysis takes advantage of the sase seismic experiment which provided high resolution regional models of the crustal thickness we calculate the model of density structure of the lithospheric mantle in southern africa and show that it has an overall agreement with xenolith based data for lithospheric terranes of different ages density of lithospheric mantle has significant short wavelength variations in all tectonic blocks of southern africa and has typical spt values of ca 3 37 3 41 g cm 3 in the cape fold and namaqua natal fold belts ca 3 34 3 35 g cm 3 in the proterozoic okwa block and the bushveld intrusion complex ca 3 34 3 37 g cm 3 in the limpopo belt and ca 3 32 3 33 g cm 3 in the kaapvaal and southern zimbabwe cratons the results indicate that 0 5 1 0 km of surface topography with the most likely value of ca 0 5 km cannot be explained by the lithosphere structure within the petrologically permitted range of mantle densities and requires the dynamic or static contribution from the sublithospheric mantle given a low amplitude of regional free air gravity anomalies ca 20 mgal on average we propose that mantle residual dynamic topography may be associated with the low density region below the depth of isostatic compensation a possible candidate is the low velocity layer between the lithospheric base and the mantle transition zone where a temperature anomaly of 100 200 c in a ca 100 150 km thick layer may explain the observed reduction in vs velocity and may produce ca 0 5 1 0 km to the regional topographic uplift

analog modeling of normal faulting above middle east domes during regional extension we study the effects of planform dome shape on fault patterns developing with and without concurrent regional extension oriented oblique to the long axis of the dome the motivation was the need to understand fault and fracture patterns in two adjacent mature hydrocarbon fields in the middle east one an elliptical dome and one an irregularly shaped dome the largest faults have throws of approximately 30 m 98 ft which is close to the resolution limit of older two dimensional seismic reflection data the known fault trends are not parallel to the highest transmissivity direction but could form compartment boundaries fault and fracture patterns developed over the modeled domes provide insight into the populations of faults and fractures that are likely to exist in the reservoirs but have been undetected because they are at or below the resolution limit of reflection seismic data major domal structural elements crestal fault systems end splay systems and radial faults are observed in modeled domes rising both with and without concurrent regional extension experimental results indicate that fault and fracture patterns are influenced by the effects of dome shape regional extension and relative timing of uplift with respect to regional extension the expression of particular sets of faults and fractures associated with concurrent doming and regional extension depends on the interaction among regional extension outer arc extension over the dome and tangential extension around the dome margins our results also indicate that the two adjacent natural domes possibly experienced different kinematic histories from those previously interpreted

burial and exhumation history of the galilee basin australia implications for unconventional hydrocarbon prospectivity this multidisciplinary study describes the burial and exhumation history of the frontier galilee basin in central queensland australia with implications for understanding its geohistory and unconventional gas prospectivity seismic interpretation stratigraphic mapping and an analysis of exhumation through quantifying overcompaction show total subsidence of approximately 2 km 6600 ft from the carboniferous to the late cretaceous punctuated by two major exhumation events triassic exhumation was less than 600 m 1970 ft whereas late cretaceous exhumation was in the order of 1000 m 3300 ft increasing eastward to greater than 1600 m 5250 ft geohistory reconstructions show that permian coal measures generated up to 45 m3 t 1590 ft3 t of gas when modeled temperatures exceeded 100 c 210 f during maximum burial of 1 5 2 km 4920 6560 ft in the late cretaceous in the carboniferous to the mid cretaceous the basin was situated to the west of the eastern australian subduction zone where proto pacific oceanic lithosphere was subducted until circa 100 ma when subduction ceased our study shows that the geohistory of the basin is characterized by rapid subsidence of 50 m m y 165 ft m y followed by rebound at circa 95 ma resulting in an uplift and erosion phase the undersaturation of the coals at present day is explained by this uplift event carbon isotopes indicate that the remaining gas 8 m3 t 280 ft3 t is of mixed biogenic and thermogenic origin therefore dynamic surface topography driven by subduction dynamics and slab breakoff had a profound effect on the subsidence uplift and resource potential of the galilee basin

eurasia africa plate boundary affected by a south atlantic asthenospheric channel in the gulf of cadiz region the gulf of cadiz has been affected by a long and complex geodynamic evolution the lithospheric structure is poorly understood in this region and it also shows a diffuse seismicity spanning over a broad area the canary archipelago has been extensively studied nevertheless there are fundamental topics that are still under debate no studies have addressed or suggested the possibility of a plausible geodynamic connection between both remarkable locations in this study we integrate total tectonic subsidence tts curie point depth cpd bouguer gravity anomaly and seismic information tts shows the existence of a basement bulge in the area of the canary archipelago that extends to the north and in the area of madeira island which extends in a more subtle way to the north too likewise the cpd reaches the shallowest values in the same location at the canary archipelago these two aspects suggest a cause effect relationship between tts and cpd at this specific area gravity data and cpd show a linear feature which links the nw of the canary archipelago and the gulf of cadiz the data we manage in this work show remarkable clues as a the absence of a similar signal in the tts b the fact that cpd it is rather constant along this track c cpd amplitude also almost doubles the values obtained on canary archipelago and d the existence of a clear correlation between seismogenic depths and cpd which points to the existence of a correlation between seismicity and the thermal architecture of the lithosphere all of these evidences support the presence of a lithospheric thinning between canary islands and gulf of cadiz area and in turn the presence of an asthenospheric channel which feeds and alter locally the eurasia africa plate boundary

the geodynamic evolution of the precaspian basin kazakhstan along a north south section abstract several hypotheses exist for the origin and evolution of the precaspian basin there are more than 20 km of sediments deposited yet there is little consensus on the causes of the subsidence except for the presence of a thick salt layer lower permian the main problem is the chronostratigraphic interpretation of the sediments in the centre of the basin where the calibration of seismic data with well data from the basin margins is problematic at deep levels the age of the deepest sediments could be either riphean or devonian a generalised cross section of the precaspian basin roughly perpendicular to the central elongated e w depocentre is used to represent the basin s evolution several evolutionary steps from the end of the riphean until the present are demonstrated tectonic subsidence analysis indicates that there are six main phases of evolution 1 subsidence during an active rifting phase in riphean times 2 rifting during the vendian ordovician poorly dated 3 significant subsidence during the late devonian in an extensional context possibly due to back arc rifting 4 acceleration of subsidence during the late carboniferous permian synchronous with or just following the closure of the uralian ocean a major subsidence phase in the dniepr donets basin and possible subduction to the south of the basin 5 renewed rifting during the triassic coincident with a general phase of extension in eurasia and the opening of the neo tethys and 6 neotectonic subsidence resulting from crustal down bending in a generally compressional setting the nature of the crust underlying the basin is not well known it could be riphean early palaeozoic or devonian oceanic crust or continental crust attenuated during the several episodes of supposed rifting between the riphean and the triassic estimations of crustal thickness in the basin vary and they depend on the interpretation of a high velocity layer situated at the base of the crust the presence and general distribution of this layer is confirmed by gravity data it may be considered as the uppermost mantle as oceanic crust metamorphosed into eclogite at depth during collision and then exhumed and emplaced at the base of the crust or as lower crust transformed in situ into eclogites the crustal thinning factor leading to the observed present crustal thickness assuming an initial thickness of 40 km is 3 3 in the two first cases and 2 in the latter if the crust is considered to be continental the geophysical and subsidence data are discussed in terms of basin forming mechanisms such as 1 intracontinental rifting of early palaeozoic devonian or permo triassic ages 2 oceanisation of continental crust during riphean or devonian time 3 eclogititisation at the base of the crust in the upper mantle or by metamorphism of subducted oceanic crust and 4 down bending due to compressional forces or mantle flow induced by subduction collision processes in carboniferous and recent times

rifting and lower crustal reflectivity a case study of the intracratonic dniepr donets rift zone ukraine 1 intracratonic rifting caused by late devonian extensional stresses in the east european craton created the largest rift zone in europe the pripyat dniepr donets rift southeast ukraine the rift basin is approximately 2000 km long up to 170 km wide and 22 km deep wide angle refraction and reflection seismic data from the donbas basin deep seismic refraction and reflection experiments dobre 99 project together with gravity and magnetic data are analyzed for the structure and evolution of the donbas fold belt which is the uplifted and deformed part of the dniepr donets basin the seismic data are used for identification of large scale crustal structures and modeling of the seismic velocities of the crust and uppermost mantle a ray trace based velocity and density model is derived by joint inversion of gravity and traveltime data the inversion result reveals a zone of high density and velocity beneath the basin at middle to lower crustal levels slightly offset to the ne of the rift axis full waveform synthetic seismograms matching the observed data show high amplitude and low frequency arrivals from this high density body as well as from the moho we interpret the high amplitude low frequency signals as reflections from layered magmatic rocks which intruded into the ductile lower crust during the main rift phase and subsequently were sorted by fractional crystallization the intrusive material thickened the lower crust by approximately 50 this may explain the enigmatic flat moho topography across the rift zone which has been significantly stretched 1 3 the rifting initiated in the late devonian frasnien as a consequence of back arc extension in relation to subduction of the paleo tethys ocean the subducting oceanic slab may have enriched the mantle with volatiles and created convection leading to strong partial melting upwelling and continued rifting in the famennien we interpret the asymmetrical rift geometry as a combination of pure and simple shear tectonic processes

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

seismic tomography surface uplift and the breakup of gondwanaland integrating mantle convection backwards in time mantle density heterogeneities imaged using seismic tomography contain information about time dependent mantle flow and mantle structures that existed in the past we model the history of mantle flow using a tomographic image of the mantle beneath southern africa as an initial condition while reversing the direction of flow and analytically incorporating cooling plates as a boundary condition if the resulting backwards integrated model for structures is used as a starting point for a forwards convection model today s mantle can be adequately reconstructed if we do not integrate backwards more than than about 50 75 ma flow can also be reliably reversed through the mesozoic but only if instability of the lower boundary layer can be suppressed our model predicts that the large seismically slow and presumably hot structure beneath southern africa produced 500 700 m of dynamic topography throughout the cenozoic since 30 ma uplift has moved from eastern to southern africa where uplift rates are 10 m myr consistent with observations during the mesozoic the modeled topographic high is situated near gondwanaland rifting raising the possibility that this buoyant structure may have been involved with this breakup

distribution of oceanic and continental leads in the arabian nubian shield new common lead data for feldspar whole rock and galena samples from the arabian nubian shield together with data from previous work can be divided into two main groups group i leads have oceanic mantle characteristics whereas group ii leads have incorporated a continental crustal component of at least early proterozoic age the group i leads are found in rocks from the red sea hills of egypt and the western and southern parts of the arabian shield group ii leads are found in rocks from the northeastern and eastern parts of the arabian shield as well as from the southeastern shield near najran they are also found in rocks to the south in yemen to the east in oman and to the west at aswan egypt this distribution of data suggests that the arabian nubian shield has an oceanic core flanked by rocks that have developed at least in part from older continental material two mechanisms are suggested by which this older lead component could have been incorporated into the late proterozoic rocks and each may have operated in different parts of the shield the older lead component either was derived directly from an underlying early proterozoic basement or was incorporated from subducted pelagic sediments or sediments derived from an adjacent continent

a correction for sediment load upon the ocean floor uniform versus varying sediment density estimations implications for isostatic correction abstract the isostatic correction for the sediment load on oceanic basement has often been calculated using a uniform sediment density irrespective of either water depth or total sediment thickness an alternative method is proposed here in which the sediment density is calculated using the density depth equations of hamilton 1976 for calcareous clay and terrigenous sediment sequences this alternative method takes into account the water depth and total sediment thickness when estimating the sediment density for example deep water 4000 m sediment sequences are likely to be clay rich thick sediment sequences 2000 m usually have a high terrigenous component and shallow sequences are likely to be calcareous rich sediment thicknesses in excess of 1500 m are generally close to a continental margin these density estimations are compared with measurements from 9 ocean drilling program drill sites 1 deep sea drilling project drill site and from densities derived from seismic interval velocities the most commonly used estimates of uniform sediment density were used to calculate isostatic corrections for a 12 km thick sediment sequence these results were then compared with the results determined using the proposed alternative method of estimating sediment densities the proposed method produces isostatic corrections similar to those derived by published methods for sediment sequences

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

effective petroleum source rocks of the world stratigraphic distribution and controlling depositional factors six stratigraphic intervals representing one third of phanerozoic time contain petroleum source rocks that have provided more than 90 of the world s discovered original reserves of oil and gas in barrels of oil equivalent the six intervals are 1 silurian generated 9 of the world s reserves 2 upper devonian tournaisian 8 of reserves 3 pennsylvanian lower permian 8 of reserves 4 upper jurassic 25 of reserves 5 middle cretaceous 29 of reserves and 6 oligocene miocene 12 5 of reserves this uneven distribution of source rocks in time displays no obvious cyclicity and the factors that controlled the formation of source rocks vary from interval to interval maps that show facies structural forms and petroleum source rocks were prepared for this study analysis of the maps indicates that several primary factors controlled the areal distribution of source rocks their geochemical type and their effectiveness i e the amounts of discovered original conventionally recoverable reserves of oil and gas generated by these rocks these factors are geologic age paleolatitude of the depositional areas structural forms in which the deposition of source rocks occurred and the evolution of biota the maturation time of these source rocks demonstrates that the majority of discovered oil and gas is very young almost 70 of the world s original reserves of oil and gas has been generated since the coniacian and nearly 50 of the world s petrole m has been generated and trapped since the oligocene the term petroleum as used in this study includes oil gas condensate and gas but does not include bitumen and other solid and semisolid oil derivatives

flexural isostasy constraints from gravity and topography power spectra we have used spherical harmonic coefficients that describe earth s gravity anomaly and topography fields to quantify the role of isostasy in contributing to crustal and upper mantle structure power spectra reveal that the gravity effect of topography and its flexural compensation contributes significantly to the observed free air gravity anomaly spectra for spherical harmonic degree 33 400 and lower n 33 degrees but topography appears either uncompensated or fully compensated at these degrees irrespective of the actual te all isostatic models underpredict the spectra at 2 n 12 and so we interpret the low order earth s gravity field as caused at least in part by non isostatic processes due to dynamic motions such as those associated with convective upwellings and downwellings in earth s mantle

fifty years of the wilson cycle concept in plate tectonics an overview it is now more than 50 years since tuzo wilson published his paper asking did the atlantic close and then re open this led to the wilson cycle concept in which the repeated opening and closing of ocean basins along old orogenic belts is a key process in the assembly and breakup of supercontinents this implied that the processes of rifting and mountain building somehow pre conditioned and weakened the lithosphere in these regions making them susceptible to strain localization during future deformation episodes here we provide a retrospective look at the development of the concept how it has evolved over the past five decades current thinking and future focus areas the wilson cycle has proved enormously important to the theory and practice of geology and underlies much of what we know about the geological evolution of the earth and its lithosphere the concept will no doubt continue to be developed as we gain more understanding of the physical processes that control mantle convection and plate tectonics and as more data become available from currently less accessible regions

magnetically inferred basement structure in central saudi arabia abstract a compilation of magnetic data acquired during the past three decades for a region in central saudi arabia where precambrian basement is partly exposed on the arabian shield and partly concealed by overlying phanerozoic strata shows a central sector of conspicuous n s trending anomalies a heterogeneous western sector of short wavelength high intensity anomalies and an eastern sector of low to moderate intensity broad wavelength anomalies anomalies in the western and central sectors correlate with neoproterozoic metavolcanic metasedimentary and intrusive rocks of the arabian shield and are interpreted as delineating extensions of shield type rocks down dip beneath phanerozoic cover these rocks constitute terranes making up part of a neoproterozoic orogenic belt that underlies northeast africa and western arabia and it is proposed that their magnetically indicated easternmost extent marks the concealed eastern edge of the orogenic belt in central arabia the flat magnetic signature of the eastern sector not entirely accounted for as an effect of deep burial may reflect the presence of a crustal block different in character to the terranes of the orogenic belt and speculatively may outline a continental block that according to some tectonic models of the region collided with the neoproterozoic terranes and thereby caused their deformation and tectonic accretion

40ar 39ar geochronology and the paleoposition of christmas island australia northeast indian ocean abstract the christmas island seamount province is an extensive zone of volcanism in the northeast indian ocean consisting of numerous submerged seamounts and flat topped guyots within this region lies two subaerial island groups christmas island and the cocos keeling archipelago christmas island has experienced multiple episodes of volcanism that are exposed sporadically along its coastline here we dated these volcanics using 40ar 39ar geochronology and analysed them for paleomagnetism the oldest exposed volcanism occurred in the eocene between 43 and 37 ma this is followed by a time gap of 33 million years before the eruption of a younger episode of pliocene age 4 32 0 17 ma it has however been suggested by previous workers that there is a much older late cretaceous event beneath the limestone which is unexposed in addition this study conducted the first paleomagnetic analysis of samples from christmas island to determine its paleoposition and the paleomagnetic polarity of the sampled sites two normal and two reversal magnetic events have been recorded that agree with the geomagnetic reversal timescales late eocene 38 39 ma palaeomagnetic data suggest a palaeolatitude of 43 5 11 2 9 0 which is further south than palaeolatitudes around 30 s derived from existing plate reconstruction models for the australian plate however the late eocene palaeomagnetic data are limited only two sites and secular variation may not have been averaged out during the pliocene ca 4 ma we estimate a palaeolatitude of approximately 13 s the presence of the late eocene ages at christmas island correlates well with the cessation of spreading of the wharton ridge 43 ma the initiation of spreading along the south east indian ridge and the transit of christmas island over a broad low velocity zone in the upper mantle this suggests that changes in stress regimes following the tectonic reorganisation of the region prior to 43 ma may have allowed deeper origin mantle melts to rise similarly changes in the plate s stress regime at the flexural bulge of the sunda java subduction zone may be implicated in renewed melting at 4 ma suggesting that tectonic stresses have exerted a first order effect on the timing and emplacement of volcanism at christmas island

stratigraphy and palaeogeography of the siham group direct evidence for a late proterozoic continental microplate and active continental margin in the saudi arabian shield the presence of ancient continental crust in the afif terrane of the arabian shield has been indicated by radiometric data detailed mapping in the central shield reveals a volcano sedimentary succession older than one of the final cratonizing events of the shield and unconformable upon high grade paragneisses providing direct evidence for a western continental margin to the afif terrane in late proterozoic times the basement gneisses were metamorphosed to almandine sillimanite amphibolite facies and preserve evidence of a deformation not seen in any other rocks of the area the siham group unconformable upon this basement was metamorphosed to upper greenschist facies it has been divided into six formations which provide an e w section through the group the lower members are volcanic and are absent in the easternmost formation their clastic content increases eastward a carbonaceous shale with exhalative chert and marble tuffs and associated volcanogenic massive sulphides is associated with the volcanics it is absent in the east where shallow marine marbles and quartzites lie unconformably upon basement rhyolite and conglomerate complete the succession in the west the base of the group is not seen but the shale is associated with numerous sheet like bodies of mafic and ultramafic rock emplaced in an extensional tectonic setting other plutonic rocks are calc alkaline and are emplaced mainly in the west deep water oceanic conditions prevailed in the west and a shallow marine continental shelf environment existed in the east with deposition of the group across this continental margin the stratigraphy of the siham group is particularly akin to the mesozoic of peru magmatic arc and marginal basin were coincident in space and time and the marginal basin was probably extensional there is some limited evldence that it was ensialic the siham group is bounded to the west by a n s suture zone formed in one of the final collisional events in the cratonization of the shield this event caused the deformation of the siham group and marked the termination of the magmatic are

late proterozoic evolution of the northern part of the hamisana zone northeast sudan constraints on pan african accretionary tectonics new structural data from the red sea hills northeast sudan add constraints to accretionary tectonic processes that acted in the arabian nubian shield during the late proterozoic geometric constraints provided by field data are used together with landsat thematic mapper imagery to interpret the regional distribution and structural relations of spectrally and lithologically distinctive rock assemblages in contrast to interpretations reported elsewhere these studies indicate that the hamisana zone a prominent structural feature in the northern red sea hills post dated terrane accretion it is characterized by east west crustal shortening and by steep folds and thrust faults calc alkaline magmatism was contemporaneous with and outlasted main phase deformation thus deformation occurred in an intra arc setting thrust faults were reactivated after east west contraction compromising their usefulness in delineating 9sutures9 or as piercing points across older faults pan african accretionary processes may have been analogous to phanerozoic ophiolite and island arc accretion in the western north american cordillera where penetrative deformation occurred in response to periodic intra plate shortening events rather than an ultimate collision of unrelated crustal fragments such an analogy implies a mechanism for crustal thickening by structural as well as igneous processes during evolution of an accretionary belt in a long lived convergent margin setting consistent with the long standing observation that pan african magmatism became more evolved with time this view emphasizes that an interplay of deformation and magmatism resulted in protracted accretion and crustal thickening in contrast to models where crustal shortening results directly from collision of a volcanic arc microcontinent or other buoyant features

the african plate a history of oceanic crust accretion and subduction since the jurassic we present a model for the jurassic to present evolution of plate boundaries and oceanic crust of the african plate based on updated interpretation of magnetic gravity and other geological and geophysical data sets location of continent ocean boundaries and age and geometry of old oceanic crust jurassic and cretaceous are updated in the light of new data and models of passive margin formation a new set of oceanic palaeo age grid models constitutes the basis for estimating the dynamics of oceanic crust through time and can be used as input for quantifying the plate boundary forces that contributed to the african plate palaeo stresses and may have influenced the evolution of intracontinental sedimentary basins as a case study we compute a simple model of palaeo stress for the late cretaceous time in order to assess how ridge push slab pull and horizontal mantle drag might have influenced the continental african plate we note that the changes in length of various plate boundaries especially trenches do not correlate well with absolute plate motion but variations in the mean oceanic crust age seem to be reflected in acceleration or deceleration of the mean absolute plate velocity

the role of long term rifting history on modes of continental lithosphere extension continental lithosphere extension results in complex basin types with differing structural styles subsidence thermal histories and melt production many studies have examined the role of initial rheological layering geothermal gradients and extension rates during a single rifting event this approach neglects the tectonic history of many basins that are marked by multiple rifting events here we address the role of repeated extension on long term lithospheric strain modes and the resulting basins highlighting cases most affected by previous rifting events we use numerical models of a lithosphere undergoing two rifting events of differing extension rates and separated by cooling to show the effect of early events on subsequent evolution the combination of boundary displacement velocity in both events leads to the formation of various rift basin types ranging from narrow to wide to hyperextended and with variation of subsidence patterns degrees of symmetry and melt yield we show that basin type subsidence and melt production might be strongly affected by previous rifting events illustrating cases in which the previous rifting history cannot be neglected our models reproduce the first order features of earth s sedimentary basins and propose a classification to guide the interpretation of extensional basins and their evolution

large scale lithospheric stress field and topography induced by global mantle circulation stresses in the lithosphere are one indication of processes in the earth interior here we present a calculation of largescale lithospheric stresses caused by global mantle circulation the mantle flow field is calculated based on density structures inferred from global seismic tomography predicted principal stress directions are compared to interpolations based on observed stresses agreement between predictions and observations is often good in regions where lithospheric stresses and mantle tomography are well constrained predicted magnitudes of scalar stress anomalies vary more strongly than predicted stress directions for various tomographic models hotspots preferentially occur in regions where calculated stress anomalies are tensile or slightly compressive results do not strongly depend on radial mantle viscosity structure lithospheric rheology viscous or elastic or plate motion model the model also predicts the directions of motion well for most plates misfits in the predicted magnitudes can be explained qualitatively stress anomalies due to causes within the lithosphere oceanic cooling with age variations in crustal thickness topography isostatically compensated at subcrustal levels are also computed predicted stress directions in the absence of mantle flow can explain observations almost as well as mantle flow nevertheless current models of mantle flow are largely in accord with interpolations of observed principal stress directions and the observed plate motions fl 2001 elsevier science b v all rights reserved

influence of peruvian flat subduction dynamics on the evolution of western amazonia convection in the earth s mantle is mainly driven by cold dense subducting slabs but relatively little is known about how 3d variations in slab morphology and buoyancy affect mantle flow or how the surface above deforms in response i e dynamic topography we investigate this problem by studying the dynamics of an active region of flat slab subduction located in peru in south america here the slab geometry is well known based on the regional seismicity and we have observations from the local geological record to validate our models of particular interest is the widespread subsidence and deposition of the solimoes formation across western amazonia that coincided with the development of the peruvian flat slab during the mid late miocene this formation covers an extensive area from the foredeep to the purus arch located view the mathml source 2000km away from the trench close to the andes the preservation of several kilometers of sedimentary thicknesses can be easily accounted for by flexure based on an estimate of the andean loading we predict 2 8 to 3 6 km of accommodation space that spans 100 km the spatial and temporal history of the solimoes formation however particularly the thick distal foreland accumulations up to 1 2 km deep can only be matched with the addition of a longer wavelength dynamic source of topography following the transition from normal to flat subduction we predict over 1 km of dynamic subsidence view the mathml source 1500km wide that propagates over 1000 km away from the trench tracking the subduction leading edge this is followed by a pulse of dynamic uplift over the flat segment behind it we therefore propose that a combination of uplift flexure and dynamic topography during slab flattening in peru is responsible for the sedimentation history and landscape evolution of western amazonia that eventually led to the configuration of the amazon drainage basin we know today

red sea rifting controls on aquifer distribution constraints from geochemical geophysical and remote sensing data highly productive wells in the central eastern desert of egypt are tapping groundwater in subsided blocks of jurassic to cretaceous sandstone taref formation of the nubian sandstone group and oligocene to miocene sandstone nakheil formation now occurring beneath the red sea coastal plain and within the proximal basement complex aquifer development is related to red sea rifting 1 rifting was accommodated by vertical extensional displacement on preexisting nw se to n s trending faults forming a complex array of half grabens and asymmetric horsts and 2 subsided blocks escaped erosion accompanying the red sea related uplift subsided blocks were identifi ed and verifi ed using satellite data geologic maps and fi eld and geophysical investigations interpretations of very low frequency vlf measurements suggest the faults acted as conduits for ascending groundwater from the subsided aquifers stable isotopic compositions d 19 3 to 53 9 18 o 2 7 to 7 1 of groundwater samples from these aquifers are interpreted as mixtures of fossil up to 70 and modern up to 65 precipitation groundwater volumes in subsided blocks are large within the central eastern desert basement complex alone they are estimated at 3 10 9 m 3 and 10 10 9 m 3 for the

earthquakes near rocky mountain house alberta and their relationship to gas production facilities a 1980 field survey of earthquake activity near rocky mountain house alberta using one digital and six conventional seismographs recorded 146 microearthquakes m 3 4 in 23 days and located 67 of them the located events and probably the unlocated events as well all occurred in a small zone approximately 4 km north south by 4 km east west by 1 km thick centred near 52 12 5 n 115 15 w at a depth of 4 0 km with an uncertainty of 2 km on each of the location coordinates the activity occurred below and or in the strachan d 3a sour gas reservoir which is a devonian aged limestone reef complex in a section of nearly flat lying unfaulted sediments the earthquakes had a composite thrust faulting mechanism with generally north trending intermediate dipping planes in the presence of a regional deviatoric stress field that was horizontally compressive and oriented approximately east west the earthquake activity may be related to the extraction of the natural gas and related fluids from the reservo

the legacy of the ne german basin reactivation by compressional buckling in contrast to previously published models for the area the seismic reflection moho is essentially flat beneath the ne german basin along the dekorp deep seismic profile basin 96 this raises the question whether the present structure of the crust and flat moho reflect the initial formation of the basin or modification by more recent processes a 2d flexural model developed for a thin elastic plate is presented together with lithospheric strength profiles calculated along the basin 9601 reflection seismic line the analysis shows a southward decrease of lithospheric strength below the basin with a lithospheric decoupling between the crust and the mantle the modelling supports the hypothesis that the present moho topography is caused by flexural buckling which caused subsidence of the ne german basin during the upper cretaceous early cenozoic inversion event this suggests that the basin is in isostatic disequilibrium and that compressive stresses are required to keep the present basin geometry

rejuvenation of appalachian topography caused by subsidence induced differential erosion topographic relief continued to develop in the appalachian mountains eastern usa long after the tectonic forces that created the range had become inactive numerical modelling and reconstructions of sediment deposition in the gulf of mexico suggest that the topographic relief was rejuvenated by subsidence induced differential erosion caused by sinking of the subducted farallon slab in the underlying mantle in ancient orogens such as the appalachian mountains in the eastern united states the difference between the high and low points topographic relief can continue to increase long after the tectonic forces that created the range have become inactive climatic forcing1 and mantle induced dynamic uplift2 3 could drive formation of relief but clear evidence is lacking in the appalachian mountains here i use a numerical simulation of dynamic topography in north america combined with reconstructions of the sedimentation history from the gulf of mexico4 to show that rejuvenation of topographic relief in the appalachian mountains since the palaeogene period could have been caused by mantle induced dynamic subsidence associated with sinking of the subducted farallon slab specifically i show that patterns of continental erosion and the eastward migration of sediment deposition centres in the gulf of mexico closely follow the locus of predicted dynamic subsidence furthermore pulses of rapid sediment deposition in the gulf of mexico4 and western atlantic5 correlate with enhanced erosion in the appalachian mountains during the miocene epoch caused by dynamic tilting of the continent the model predicts that such subsidence induced differential erosion caused flexural isostatic adjustments of appalachian topography that led to the development of 400 m of relief and more than 200 m of elevation i propose that dynamically induced continental tilting may provide a mechanism for topographic rejuvenation in ancient orogens

lochkovian earliest devonian transgressions and regressions along the tethyan margin of gondwana a review of lithostratigraphical data abstract global sea level rise and consequent regional transgressions are hypothesized at the beginning of the devonian a brief review of lithostratigraphical data available from three regions of the tethyan margin of gondwana namely northern africa arabia and the tethys himalaya suggests that all of them were characterized by a regressive setting in the lochkovian in contrast data from some terranes of the greater galatian superterrane provide evidence of early lochkovian transgression the regressive setting documented on the tethyan margin of gondwana differs from the transgressive regressive cycles of euramerica and the norm of global sea level rise followed by a highstand only regional tectonic processes including those linked with dynamic topography could explain these differences these processes may have been associated with syn rift uplift preceding the opening of the palaeo tethys ocean mantle uplift at the supercontinent margin or the eo variscan orogenic phase

u pb isotopic evidence for the accretion of a continental microplate in the zalm region of the saudi arabian shield the area covered by this work includes three of the main tectonic units of the arabian shield the afif continental terrain the nabitah suture with its associated mobile belt and the asir ensimatic arc terrain the geology of the zalm area is well understood and this geochronologic and isotopic study confirms that the southern afif terrain was a continental microplate in the late proterozoic the study also provides a time frame for the crustal evolution of this part of the shield the kabid formation is the oldest in the region and comprises pelitic arkosic and felsic high grade paragneisses u pb zircon data from a pelitic garnet sillimanite gneiss show that this part of the continental basement in the southern afif terrain may be as old as 1770 ma isotopic nalyses indicate that lead from the kabid gneiss resided in the upper continental crust for a long period before 1770 ma and consequently archaean source rocks may be present within the southern afif terrain pb and rb sr isotopic data in the zalm region reveal a change in the nature of the underlying crust from continental basement in the northeast to less radiogenic marginal arc rocks in the southwest this change is coincident with both aeromagnetic data and a facies change within a pre collision marginal basin miogeosynclinal continental shelf facies of the siham group lie unconformably over the kabid formation and are in the area of continental lead signatures eugeosynclinal deep water sediments and volcanics in association with ultramafic rocks occur in the area of marginal arc signatures u pb zircon age determinations show that this 9andean9 continental margin developed before about 720 ma and emplacement of calc alkaline plutonic rocks continued until about 690 ma during the period 685 640 ma the continental afif microplate collided with the asir terrain as part of the nabitah orogeny at approximately 640 ma ago the najd strike slip faulting commenced with a dextral phase that controlled the emplacement of granitic plutons as well as the development of a series of large pull apart grabens some of these grabens were floored by new oceanic crust and were filled with volcanosedimentary rocks of the bani ghayy group subsequently the najd fault system changed to sinistral strike slip motion at about 620 ma ago

investigation of regional seismicity before and after hydraulic fracturing in the horn river basin northeast british columbia we systematically re analyzed historical seismograms to verify the existence of background seismicity in the horn river basin of northeast british columbia before the start of regional shale gas development we also carefully relocated local earthquakes that occurred between december 2006 and december 2011 to delineate their spatiotemporal relationship with hydraulic fracturing hf operations in the region scattered seismic events were detected in the horn river basin throughout the study periods the located seismicity within 100 km of the fort nelson seismic station had a clearly increasing trend specifically in the etsho area where most local hf operations were performed the number of events was increased from 24 in 2002 2003 prior to hf operations to 131 in 2011 peak period of hf operations in addition maximum magnitude of the events was shifted from ml 2 9 to ml 3 6 as the scale of hf operation expanded from 2006 2007 to 2011 based on our relocated earthquake catalog the overall b value i

global basin classification system a proposed system classifies sedimentary basins worldwide into specific as well as general categories the geologic history of each basin may be subdivided into cycles using three parameters basin forming tectonics depositional sequences and basin modifying tectonics sedimentary basins may be simple with one or two tectonic sedimentary cycles or they may be complex polyhistory basins with many different cycles and events there are eight simple cycle types in this classification which cover continental continental margin and oceanic areas the eight basic cycle types their depositional fills and tectonic modifiers have been given letter and number symbols so that the specific geologic history of each basin may be written as a formula these formulas may then e compared and similarities or differences between basins noted

soft sediment deformation structures as a tool to recognize synsedimentary tectonic activity in the middle member of the bakken formation williston basin north dakota abstract the bakken formation uppermost devonian lower carboniferous in north dakota consists of black shales with a middle member composed of mixed siliciclastics and carbonates millimeter to decimeter scale soft sediment deformation structures ssds are common in the upper third to quarter of the middle member having been observed in sixty three out of ninety cores studied the nine categories identified herein reflect brittle and ductile deformation and loss of sediment shear in compressional and extensional settings they are interpreted to form due to seismically induced folding liquefaction and fluidization of unconsolidated sediment as well as microfaulting and brecciation of consolidated sediment and reflect synsedimentary tectonic movements e g along faults that were active during deposition the distribution of ssds follows the orientation of the major structural elements rooted in the basement of the williston basin the stratigraphic and spatial distribution of ssds suggests variable tectonic activity cores near the most active fault systems have the highest net thickness of units with ssds whereas those farther from the most active faults exhibit only a few deformed units the predominance of ssds in the upper portion of the middle member suggests there was a change from relative tectonic quiescence to a more active regime which in turn led to modifications of basin geometry and new accommodation patterns synsedimentary deformation might have had a positive effect on reservoir quality in deformed units by increasing porosity and permeability as a result of cohesion loss and rearrangement of grains additionally multiple injection structures and complexes of small scale normal and reverse faults could contribute to better connectivity of reservoir units

extension of the najd shear system from saudi arabia to the central eastern desert of egypt based on integrated field and landsat observations the najd shear system in saudi arabia extends over 1200 km in a nw se direction and has a width of approximately 300 km a digital color mosaic compiled from seven landsat thematic mapper scenes was used to delineate characteristic structural features of the najd system in the midyan region of saudi arabia and to search for similar features in the egyptian eastern desert the digital mosaic was generated using ratios of landsat thematic mapper bands bands 5 4 3 4 5 1 5 7 that are sensitive to the rock content of fe bearing aluminosilicates spectrally opaque phases and hydroxyl bearing or carbonate minerals respectively the mosaic covers approximately 130 000 km of late proterozoic exposures of the arabian nubian shield and has the eastern desert and the midyan region placed in their approximate pre red sea locations the ajjaj shear zone ajz marks the termination of the najd system against the eastern margin of the red sea in the midyan region the ajz aligns with the central eastern desert based on analysis of pre red sea locations analyses of landsat data and field observations show that the ajjaj shear zone and the central eastern desert exhibit the following features in common 1 outcrops that are generally elongate in a nw se direction as a result of folding with fine scale lithologic heterogeneity at the outcrop scale related to deformation associated with faulting 2 nw trending left lateral faults and ductile shear zones 3 subhorizontal nw trending mineral lineations and variably dipping nw trending foliations with local changes in attitude around large competent e g granitic bodies and 4 lithologic contacts that are generally tectonic in nature and related to faulting these features are less common to the north and south of both the ajjaj shear zone and the central eastern desert results are consistent with the najd shear system extending into the eastern desert and dominating the structural patterns within the central part of the eastern desert

investigating the stratigraphy and palaeoenvironments for a suite of newly discovered mid cretaceous vertebrate fossil localities in the winton formation queensland australia the winton formation of central queensland is recognized as a quintessential source of mid cretaceous terrestrial faunas and floras in australia however sedimentological investigations linking fossil assemblages and palaeoenvironments across this unit remain limited the intent of this study was to interpret depositional environments and improve stratigraphic correlations between multiple fossil localities within the preserved winton formation in the eromanga basin including isisford lark quarry and bladensburg national park twenty three facies and six repeated facies associations were documented indicating a mosaic of marginal marine to inland alluvial depositional environments these developed synchronously with the final regression of the eromanga seaway from central australia during the late albian early turonian investigations of regional and local scale structural features and outcrop core and well analysis were combined with detrital zircon provenance signatures to help correlate stratigraphy and vertebrate faunas across the basin significant palaeoenvironmental differences exist between the lower and upper portions of the preserved winton formation warranting informal subdivisions a lower tidally influenced fluvial deltaic member and an upper inland alluvial member this work further demonstrates that the isisford fauna is part of the lower member of the preserved winton formation whereas fossil localities around winton including lark quarry and bladensburg national park are part of the upper member of the winton formation these results permit a more meaningful framework for both regional and global comparisons of the winton flora and fauna

subsidence in intracontinental basins due to dynamic topography the origin of anomalous tectonic subsidence ats of large intracontinental basins long after their most recent phase of extension and last thermal perturbation is the subject of a long standing debate we show that deep earth processes may contribute to the subsidence of these tectonically stable basins by analysing the tertiary mantle convection driven topography history of a global set of more than 220 intracontinental basins integrated into a plate kinematic framework most basins are affected by increasing negative dynamic topography over the last 70 myr due to the motion of many continents away from large mantle upwellings and towards downwellings previously located along the perimeter of the supercontinent pangaea during continental dispersal increasing negative dynamic topography causes dynamic subsidence of the basins creating additional accommodation space we utilise a parameter from a global crustal analysis of intraplate basins termed anomalous tectonic subsidence to quantify sediment accumulation not related to crustal stretching we propose that dynamic subsidence due to plate motions relative to the underlying mantle as well as variations in the large scale convection patterns can significantly contribute to the creation and destruction of accommodation space in intraplate basins

dynamic uplift during slab flattening subduction exerts a strong control on surface topography and is the main cause of large vertical motions in continents including past events of large scale marine flooding and tilting the mechanism is dynamic deflection the sinking of dense subducted lithosphere gives rise to stresses that directly pull down the surface here we show that subduction does not always lead to downward deflections of the earth s surface subduction of young lithosphere at shallow angles flat subduction leaves it neutrally or even positively buoyant with respect to underlying mantle because the lithosphere is relatively warm compared with older lithosphere and because the thickened and hence drier oceanic crust does not undergo the transformation of basalt to denser eclogite accounting for neutrally buoyant flat segments along with large variations in slab morphology in the south american subduction zone explains along strike and temporal changes in dynamic topography observed in the geologic record since the beginning of the cenozoic our results show that the transition from normal subduction to slab flattening generates dynamic uplift preventing back arc marine flooding