mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

contribution of global potential field data to the tectonic reconstruction of the rio grande rise in the south atlantic abstract the application of advanced enhancement techniques for geophysical anomalies to global gravity wgm2012 and magnetic emag2 models sheds light on the complex tectonic evolution of the rio grande rise rgr in the southern south atlantic long wavelength bouguer gravity lows indicate a thicker crust beneath of the ridge whose nature can be related to a microcontinent or an excess of volcanism within the oceanic realm recently dredged continental rocks reinforce the hypothesis of a microcontinent or at least slivers of continental crust however the reserval magnetic pattern of the processed magnetic anomalies provide no evidence of aborted spreading center similar to the well studied jan mayen microcontinent and the surrounding inactive aegir and active kolbeinsey ridges in the north atlantic ocean the reversal magnetic anomalies show a series n s trending parallel stripes roughly follow the current south american coastline and segmented by e w oriented oceanic fracture zones fzs the magnetic stripes are bended eastwards at the rgr showing a more complex magnetic pattern similar to that in the iceland the aborted cruzeiro do sul rift csr and the jean charcot chain jcc are structures that cross the rgr and contribute to the understanding of the tectonic evolution of the south atlantic ocean nw se oriented extensive gravity lows and bathymetric valleys which mark the csr are segmented by e w trending magnetic lineaments related to fzs this structural configuration suggests that the extensional event which formed the rift and the seamounts chain was replaced by strike slip movements along the fzs in addition we constructed a plate kinematic model for the evolution of the rgr based on bathymetric free air and bouguer gravity and magnetic data our model comprises five main stages of the rgr formation and evolution between late cretaceous and paleocene ca 95 60 ma separated by published seafloor isochrones the proposed model suggests that the rgr was built at the mid atlantic ridge by increased magmatism probably related to the tristan da cunha hotspot

petrology geochemistry and tectonics of the sabzevar ophiolite north central iran abstract the sabzevar ophiolite is a highly dismembered ophiolite complex located along the northern boundary of the central iranian microcontinent cim and is one of the internal iranian group of ophiolites and colored melanges the igneous rocks of this complex consist of peridotites harzburgite dunite and lherzolite serpentinite minor pyroxenite gabbros and a volcanic sequence that exhibits a wide range of composition from basalts and basaltic andesites to rhyodacite dacites rhyolites and basanites sedimentary rocks include a variety of upper triassic to lower cretaceous deep and shallow marine rocks these include pelagic fossiliferous carbonates that are mixed with the pillow basalt and basaltic andesite as interlayers or exotic blocks ranging in size from 10 to 100 m also present are extensive units of radiolarian chert which are interbedded within the basalts and basaltic andesites a combination of petrographic observations and analyses of incompatible trace elements and rare earth elements indicates the presence of at least four different types of extrusive rocks in the sabzevar ophiolite the geochemical data clearly identifies some of the extrusive rocks to have formed from three distinct types of basaltic melts i the group 1 basaltic rocks which formed from an initial melt with n morb like lree depleted chemical signatures and are petrogenetically related to the gabbros ii group 2 basaltic rocks which have e morb chemical signatures and iii group 3 basaltic rocks with lree enriched signatures and incompatible trace element patterns that suggest an island arc affinity the data also suggest that the gabbros and the group 1 basaltic rocks are petrogenetically related and produced by fractionation of plagioclase and to a lesser extent clinopyroxene and hornblende similar to other studied iranian ophiolites e g khoy band e zeyarat dar anar neyriz kermanshah and baft the results from the sabzevar ophiolite demonstrate the presence of relics of mid ocean ridge basalt morb like signatures in the extrusive units of neo tethyan ophiolites and suggests that the fossil oceanic lithosphere preserved in these ophiolites developed at an oceanic spreading center in addition the sabzevar ophiolite contains other volcanic rocks that have non morb like geochemical signatures e g within plate island arc the differences between these geochemical signatures could be a result of a differing upper mantle composition or different degrees of partial melting of the same upper mantle the presence of sizable nb anomalies in the extended rare earth element ree patterns for andesites and the group 3 basalts is characteristic of volcanic arc magmas or possibly are products of the ascending magma that was modified by crustal contamination the presences of the basanites and the silica undersaturated rocks could be attributed to extrusive activity following ophiolite emplacement plate reconstructions suggest that rocks of the sabzevar ophiolite were part of the tethyan oceanic crust that was formed during rifting of a narrow but deep seaway that separated the cim from the eurasian plate the ophiolite was emplaced during northeast dipping subduction i e closure of this segment of the tethyan seaway sabzevar ocean

structures in southwest asia and evolution of the eastern tethys abstract southwest asia comprises the following 1 a two major orogenic belts a northern belt derived from the paleo tethys and a southern belt derived from the neo tethys 2 b minor orogenic belts derived from neo tethyan marginal basins 3 c continental blocks that originated from gondwana by splitting and stripping and subsequently drifted and collided with continental asia in its process of construction and 4 d residual oceanic basins which are assumed as being not yet closed neo tethyan marginal basins the entire region appears as the product of tethyan evolution

critical taper model of fold and thrust belts and accretionary wedges the fold and thrust belts and submarine accretionary wedges that lie along compressive plate boundaries are one of the best understood deformational features of the earth s upper crust although there is considerable natural variation among the many fold and thrust belts and accretionary wedges that have been recognized and explored several features appear to be universal in cross section fold and thrust belts and accretionary wedges occupy a wedge shaped deformed region overlying a basal detachment or decollement fault the rocks or sediments beneath this fault show very little deformation the decollement fault characteristically dips toward the interior of the mountain belt or in the case of a submarine wedge toward the island arc the topography in contrast slopes toward the toe or deformation front of the wedge deformation within the wedge is generally dominated by imbricate thrust faults verging toward the toe and related fault bend folding two north american fold and thrust belts that exhibit these features are shown in figure 1 neither of these two examples is tectonically active today the southern canadian fold and thrust belt was active during the late jurassic and cretaceous 150 100 ma whereas the southern appa lachians were deformed during the late carboniferous to permian alle ghenian orogeny 300 250 ma figure 2 shows two examples that are currently active the taiwan fold and thrust belt produced by the sub duction of the eurasian plate beneath the philippine sea plate suppe 1981 1987 and the barbados accretionary wedge produced by the sub

zircon u pb ages and emplacement history of the nodoushan plutonic complex in the central urumieh dokhtar magmatic belt central iran product of neotethyan subduction during the paleogene abstract the nodoushan plutonic complex is composed of a wide range of felsic and mafic rocks straddling several of the major orogenic zones in iran diorite porphyry diorite granodiorite and granite intrusives belong to the central part of the urumieh dokhtar magmatic belt which is part of the alpine himalayan orogenic belt monzogabbroic members of the complex are instead located within the bordering sanandaj sirjan magmatic metamorphic zone these plutons were emplaced into permian and lower cretaceous sedimentary units and eocene calc alkaline volcanic and subvolcanic rocks new u pb zircon ages reveal that the plutonic complex was assembled incrementally over ca 15 m y during three main episodes at 40 487 0 063 ma near the middle late eocene boundary at 30 52 0 11 ma and 30 06 0 10 ma in the early oligocene middle rupelian and at 24 994 0 037 and 24 13 0 19 ma in the late oligocene latest chattian the activity recorded in the nodoushan plutonic complex represents the final stages of subduction related magmatism prior to the eventual miocene collision between the arabian and eurasian blocks

sedimentary record of late paleozoic to recent tectonism in central asia analysis of subsurface data from the turan and south kazak domains abstract the turan and south kazak domains tsk are in central asia between the caspian sea and the tien shan the area is covered by sediments deposited since the late permian during a series of tectonic events closely related to the history of two oceanic domains paleotethys and neotethys sedimentary basins on the tsk therefore provide constraints on the tectonic development of the southern margin of eurasia since the late permian our study is based on structure contour maps and isopach maps of five key stratigraphic markers of late permian to tertiary age isopach maps help locate major faults and delimit sedimentary basins providing information on vertical motions and in some instances horizontal motions subsidence associated with extension appears to have dominated the tsk from the late permian to the eocene the extension may have been of back arc type in southern eurasia next to the active margin where the paleotethys and neotethys successively subducted toward the north here sedimentary basins are both wide and deep up to 15 km during the mesozoic two compressional events of regional significance occurred in association with accretion of continental blocks at the southern margin of eurasia the first one at the end of the triassic led to strong selective inversion of basins over the turan domain the second one during the late jurassic early cretaceous had weaker effects since the oligocene following collision of both india and arabia with eurasia inversion has become more generalized and compressional basins have formed on the tsk throughout the entire history of development of the tsk from the late permian to the tertiary structures of paleozoic and early mesozoic age have exerted a strong control on sedimentation and especially on the location of depocenters the south kazak domain has registered little subsidence in comparison with the turan domain where some basins have become very deep

the margins of laurussia in central and southeast europe and southwest asia the continuation of the laurussian margin into central and southeast europe and southwest asia is defined by the rheic suture which becomes harder to trace to the southeast because of complex post variscan strike slip displacements and tectonic stacking linked to the cimmerian and alpine cycles the uncertain extent of the neoproterozoic baikalian orogeny fringing baltica ambiguous early paleozoic paleobiogeographic data and strike slip activity complicate the distinction of the tornquist suture from the transeuropean suture zone there is growing evidence for the incorporation of the brunovistulian malopolska and west moesian terranes into the late neoproterozoic cambrian baltican margin the istanbul zonguldak terrane along with the bitesh and east moesia terranes may have been part of the avalonian terrane assemblage although an arabian nubian shield or baltica provenance cannot be excluded the terranes of the armorica terrane assemblage bordering the rheic suture include the outer carpathian tatra getic and balkan terranes in southeast europe and sakarya and the anatolide tauride terrane in turkey further east the rheic suture may be present in the caucasus in all probability between the greater caucasus and the scythian platform or alternatively between the greater caucasus and transcaucasia alborz in northern iran is interpreted as a distal part of transcaucasia the location of the rheic suture in the southeast part of the turan domain of central asia is poorly constrained

biostratigraphic zonation and 40ar 39ar ages for the neotethyan khoy ophiolite of nw iran abstract the khoy ophiolite in northwestern iran represents a piece of oceanic lithosphere formed in the mesozoic neotethys this ophiolite consists from bottom to top of well defined basal metamorphic rocks peridotites gabbros and a variety of upper to lower cretaceous deep marine rocks these include pelagic fossiliferous carbonates and basalts as interlayers or exotic blocks four hornblende separates from gabbros and amphibolites give values from 108 to 111 ma the results from microfossil studies show the presence of late cretaceous e g marginotruncana globotruncana and middle to late eocene e g globorotalia orbulonoides planktonic foraminifera the data suggest that although the initial rifting and crystallization of the oceanic crust of the khoy ophiolite began in the late albian the volcanic activities continued through to the late eocene time another possibility for such variation of lithofacies and biofacies and disturbances in the fossil record may be the result of bioturbation and transportation and rapid changes of depositional conditions during eruption of the basaltic lava flows pelagic sediments alone have been listed and of the foraminiferas the first three are planktonic as would be expected only orbulonoides is a benthic form and aberrant the third possibility is that the khoy ophiolite may represent a classic supra subduction type ophiolite where volcanic members of the different parts of oceanic environment e g morb volcanic arc ocean island are now juxtaposed

space time patterns of magmatism along the tethysides a preliminary study five maps showing spatio temporal evolution of magmatism along the tethysides for the following time intervals late carboniferous and permian 320 248 ma triassic and early jurassic 247 188 ma

southern borderland of triassic laurasia in north east iran results obtained by iranian and european geoscientists in the critical area to the north east of the north iran suture east of mashhad are desribed and discussed a slightly metamorphosed ophiolite belt outcropping as the south easterly continuation of the previously known ophiolites of mashhad along the north eastern perimeter of the fariman torbat e jam depression proved to be either the remnant of a permian ocean floor or more likely the remnant of a narrow ocean trough there is as yet no proof of a triassic age for this ophiolitic belt to the north of this ophiolitic belt an epicontinental triassic sequence is exposed at the southern edge of laurasia in the erosional window of aghdarband this is the result of intermittent sedimentation in a pull apart basin along sinistral strike slip faults the triassic of aghdarband has much in common with other deposits of the triassic tethys however it shows a few unique features e g the early anisiannicomedites fauna of a palaeobiogeographic north tethyan subprovince or volcanogenic sedimentation during the late anisian and the entire ladinian

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

volcanic belts as markers of the mesozoic cenozoic active margin of eurasia abstract from the triassic to the present linear belts of calc alkaline volcanism developed along the southern margin of eurasia in the triassic the calc alkaline belt can be traced in turan fore caucasus crimea and dobrogea its development is related to the closure of the paleo tethys when fragments of gondwana iran afghanistan etc were approaching eurasia since the early jurassic calc alkaline volcanism has been related to subduction of the oceanic crust of the mesozoic tethys five stages of calc alkaline volcanic activity can be distinguished early jurassic middle jurassic early cretaceous late cretaceous paleogene and late miocene quaternary the configuration of the volcanic belts the intensity of the volcanism and the chemistry of the erupted products change considerably from stage to stage mesozoic belts were most pronounced in the pontian transcaucasian segment of the margin starting from the late cretaceous and especially in the cenozoic the volcanic belts can be continuously traced from the balkans to afghanistan most of the belts were actually island arcs formed on the fragments of the hercynian of baikalian basement and in this respect similar to the island arc of japan only the incipient island arcs of senonian age formed close to the passive margin of gondwana are the exceptions they were built on oceanic crust and are geochemically close to the mariana arc at certain times early jurassic eocene parallel chains of island arcs existed in general the situation resembled the present day convergent boundary in the western pacific as closure of the tethys proceeded island arcs gave way to marginal continental volcanic belts with wide spread development of high potassium particularly shoshonitic series peaks of volcanic activity in the bajocian late cretaceous eocene and late miocene present alternated with quiet periods and corresponded to the times when the convergence rate between africa and eurasia increased the opening of the back arc basins is reflected in outbursts of basaltic rift type volcanism these outbursts occurred in the toarcian aalenian bathonian late jurassic aptian turonian and early middle eocene

thrust tectonics of the binalood region ne iran the binalood region in ne iran which is an eastern segment of the alborz mountains is affected by thin skinned tectonics lower paleozoic jurassic cretaceous and cenozoic rock sequences as well as remnants of the paleo tethys oceanic realm are transported in a southwestward direction by several thrust faults which are of two generations 1 cimmerian and 2 alpine structural units in this region form either single thrust sheets or duplexes they have been displaced sequentially in a piggyback style from the hinterland ne to foreland sw under ductile brittle ductile and brittle conditions geometrically they constitute an antiformal stack breached on its southwestern side by major and minor out of sequence thrusts

sequence stratigraphic significance of sedimentary cycles and shell concentrations in the aitamir formation albian cenomanian kopet dagh basin northeastern iran abstract albian cenomanian siliciclastic shallow marine sediments of the aitamir formation kopet dagh basin northeastern iran form strongly asymmetric fining coarsening upward cycles which are interpreted as recording changes in relative sea level deepening shallowing cycles these cycles correspond to depositional sequences in which deposits of the lowstand systems tract are not present the sequence boundary coinciding with the transgressive surface shell concentrations are found in distinct positions within the depositional sequence as transgressive lags at the base of the transgressive systems tract tst in the maximum flooding zone mfz and at or close to the top of the highstand systems tract hst they are dominated by bivalves mainly oysters and or ammonites and differ from each other in a number of stratigraphic sedimentologic palaeoecological and taphonomic features such as species diversity preservation quality orientation percentage of disarticulation and degree of biogenic alteration characteristic features of concentrations at the base of the tsts are moderate time averaging distinct basal erosional surface sorting a chaotic to preferred convex up orientation and nearly total disarticulation of shells they are suggestive of an environment in which reworking and local transport was frequent events similar features are shown by concentrations near the tops of the hsts except that the shells were largely concentrated in lenses rather than in beds as in the transgressive lags associated sedimentary structures indicate deposition above fair weather wave base in a high energy environment concentrations occurring in the mfz in contrast are autochthonous and highly time averaged having accumulated during times of low rates of sedimentation below storm wave base this is supported by their high preservation quality comparatively high percentage of articulated shells shells of infaunal organisms commonly preserved in life position high glauconite content and biogenic alteration being the most important taphonomic features

palaeobiogeographic implications of late bajocian late callovian middle jurassic dinoflagellate cysts from the central alborz mountains northern iran abstract the dalichai formation with an age of late bajocian late callovian was sampled in central alborz mountains of northern iran and studied for palynological palaeobiogeographical and palynocorrelation purposes palynological studies revealed diverse and well preserved dinoflagellate cyst assemblages and lead to identification of three zones i e cribroperidinium crispum late bajocian dichadogonyaulax sellwoodii bathonian to early callovian and ctenidodinium continuum early to middle callovian zones subzone a of the d sellwoodii zone early to middle bathonian was also differentiated this biozonation corresponds to those recognised in northwest europe furthermore the ammonoid families recorded including phylloceratidae oppeliidae reineckeiidae perisphinctidae haploceratidae parkinsoniidae and sphaeroceratidae which confirm the late bajocian to late callovian age are quite similar to those of northwest europe and the northwestern tethys the close similarities of the dinoflagellate cyst assemblages and ammonite fauna of northern iran with those of northwest europe and the northwestern tethys during the middle jurassic indicate direct but episodic marine connection and faunal exchange between the two areas

plate tectonic evolution of the mediterranean middle east region abstract an interpretive model for the mesozoic cenozoic plate tectonic evolution of the mediterranean and adjacent areas is illustrated by a series of paleoposition maps at selected intervals between the late triassic and recent this interval witnessed an important period of tensional development during the triassic and jurassic that fragmented pangea after its late paleozoic consolidation a number of oceanic areas evolved through jurassic time all of which have since been consumed during the alpine orogeny during the cretaceous and tertiary sea floor spreading geometry in the north and south atlantic resulted in convergence between africa and eurasia that controlled the evolution of the mediterranean and adjacent middle east areas from the late mesozoic to recent the interpretation departs from several previous ones in the following respects 1 1 the eastern mediterranean and adjacent middle east area are interpreted to have developed as two seaways with an intervening continental sliver derived from africa that now comprises central turkey and west iran these seaways persisted from the late triassic to late cretaceous by which time they were largely consumed by northward subduction 2 2 spreading that produced the present eastern mediterranean sea developed during the late cretaceous driving the tripolitza eratosthenes iskenderun continental fragments northward from africa to collision with central turkey as the preceding southern arm of the mesozoic tethys sea floor was entirely consumed initial block faulting in this zone occurred during the jurassic and early cretaceous but without subsidence reaching clearly bathyal depths until the cenomanian turonian this differs from the timing of events in the ionian sequence of the pindic nappe of crete which shows a change from shallow carbonate shelf in the triassic to deep basin in the liassic to the north of equivalent platform facies of the tripolitza nappe 3 3 moesia and rhodope are concluded to have been a single plate until a rifting event that started during the late jurassic the balkan mountains are interpreted to represent an alpine inversion of this mesozoic rift system that extended west from the black sea basin 4 4 the eastern carpathian microcontinental sliver is concluded as continuing southward as the serbo macedonian massif that separates rhodope from the vardar zone rather than as rhodope itself 5 5 the scutari pec lineament is considered as representing a major discontinuity between the apulia pannonian plate and adjacent greece and turkey ophiolites to the northwest of this lineament originated in a single oceanic area the vardar zone ophiolites to the southeast of this lineament evolved from two oceanic areas those of interior greece and northern anatolia and the associated ankara melange relating to the vardar zone the former north arm of tethys and the pindos southern anatolia zagros oman ophiolites relating to a former south arm of mesozoic tethys 6 6 based on the history of development of various elements of the alpine system there is a strong suggestion that important dextral movement took place along a major strike slip fault system reaching from the middle east to the central alps between late cretaceous and middle eocene times

the triassic and associated rocks of the nakhlak and aghdarband areas in central and northeastern iran as remnants of the southern turanian active continental margin abstract the triassic succession of the nakhlak area in central iran consists of 1 the lithologicallalam formation which is a sequence of shallowing and coarsening upward marine turbidites deposited equon the forearc side of an accretionary prism 2 the baqoroq formation a resentatsequence of coarse to fine polymictic fluvial conglomerates and 3 the ashin for mation which comprises alternating distal marine shales and sand stones that have turbiditic characteristics these rocks are wnot litholog ically similar to time equivalent lithostratigraphic units of late permian triassic age of the aghdarband area of northeastern iran which are interpreted to be forearc deposits but they may have formed in close association with them in a single tectonic and sedimen tary framework accepting the 135 counterclockwise rotation of the central east iranian microcontinent authorwith respect to the turan plate since triassic time and assuming that the triassic rocks of the nakhlak and the late permian to triassic rocks of the aghdarband formed in a single tectonosedimentary framework on the no rthern side of the paleo tethyan oceanic realm we present here a sequential develop ment in this scheme rocks of the bnakhlak and aghdarband areas are considered deposits of a forearc basin ridge slope centralenvironment the separation of the nakhlak succession from the rest of the turan plate and its transportation to central iran might have occurred as 1 a lithospheric segmen t of the turan plate first detached from turan and then attached to the iranian plate and finally rotated with it in a coun terclockwise direction to successionits present site or 2 as a thin thrust slice first obducted over th e iranian continental shelf and then displaced to cen tral iran by its counterclockwise rotation introduction

stratigraphy and ammonite fauna of the upper shemshak formation toarcian aalenian at tazareh eastern alborz iran abstract with a thickness of 3900 m the tazareh section is one of the thickest developments of the shemshak formation in the alborz range it overlies with sharp and disconformable contact the limestones and dolomites of the lower middle triassic elikah formation and is topped again with a disconformable contact by the marls and limestones of the middle jurassic dalichai formation the nearly exclusively siliciclastic succession represents a range of environments from fluvial channels flood plains swamps and lake systems to storm dominated shelf and a comparatively deep marine and partly dysoxic basin the segment of the section between 2300 and 3500 m is exclusively marine and contains a moderately diverse ammonite fauna ranging from the middle toarcian to the upper aalenian the ammonite fauna comprises 21 taxa among them the new genus shahrudites with two new species shahrudites asseretoi and s stoecklini from the middle aalenian bradfordensis zone the other ammonites from the shemshak formation at tazareh as elsewhere in north and central iran are exclusively tethyan in character and closely related to faunas from western and central europe an ammonite based correlation of toarcian aalenian successions of the eastern alborz with time equivalent strata of the lut block part of the central east iranian microcontinent ca 500 km to the south suggests a strong influence of synsedimentary tectonics during the deposition of the upper shemshak formation

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

tertiary and quaternary geodynamics of southern lut iran as deduced from palaeomagnetic isotopic and structural data abstract palaeomagnetic measurements and k ar age determinations carried out on lavas from dash e lut in southeast iran reveal an anticlockwise rotation of about 90 of the depression south of lut between paleocene and miocene time it is probably associated with the collision between india and asia

geohistory analysis and petroleum reservoir characteristics of lower cretaceous neocomian sandstones eastern kopet dagh basin northeastern iran the eastern part of the kopet dagh basin of northeastern iran contains over 4000 m of upper jurassic through tertiary strata deposited in a variety of shallow marine and terrestrial environments geohistory diagrams from well and outcrop data provide a useful mechanism with which to relate the stratigraphic framework of this part of the basin to the tectonic history of the region during some episodes of regional tectonic uplift e g episodes occurring 99 95 ma 74 70 ma and 63 54 ma sediment accommodation space continued to be created in the basin due to sediment loading and compaction of increased amounts of fine grained sediments in some cases concomitant with eustatic sea level rises much of the post jurassic subsidence in this part of the kopet dagh basin was aused by sediment loading rather than tectonism the effects of basin geohistory on petroleum reservoir properties were studied using the lower cretaceous neocomian shurijeh formation as an example detailed petrologic sedimentologic and geohistory analyses done on this formation show that the petroleum reservoir properties of shurijeh sandstones were affected by their depositional settings and the subsequent subsidence of these units through meteoric and compactional hydrogeologic regimes in this part of the kopet dagh basin these rocks consist mostly of sublitharenitic red beds deposited during a regressive phase of sedimentation dominated by rapid siliciclastic sediment supply the lower and middle parts of the interval studied were deposited in low sinuosity braided fluvial systems and the upper part was deposited in high inuosity meandering systems by relating the paragenetic sequence of the shurijeh sandstones to the geohistory of this formation we determined the timing of both porosity destroying and porosity enhancing diagenetic processes and related these processes to the timing of petroleum generation

patterns of sand transport on vegetated foredunes the aeolian development of coastal foredunes is studied at two sites along the dutch coast amounts of sand transport are measured in cross sections over the foredunes and changes in surface height are monitored sand transport decreases rapidly landward of the vegetation boundary near the dunefoot changes in surface roughness and topography generate turbulence and upward flow causing a small part of the sand to be transported in suspension patterns of transport are found to be closely related to air flow which in turn is related to topography and vegetation density with steeper topography the amounts of sand transported landward from the dunefoot increase if vegetation density is low during oblique onshore winds most of the sand accumulates at the dune front during perpendicular onshore winds a large proportion of the sand is deposited landward of the slope when deflection of flow occurs landward transport of sand is interrupted

platform carbonates of the upper jurassic mozduran formation in the kopet dagh basin ne iran facies palaeoenvironments and sequences abstract the mozduran formation a thick carbonate succession over 1200 m of the upper jurassic callovian kimmeridgian in northeast iran has been studied to determine its palaeoenvironments and sequences detailed petrographic investigations have led to the recognition of several microfacies and microfacies groups which constitute four palaeoenvironmental associations tidal flat beach lagoonal platform margin and open marine most of the mozduran formation sediments were deposited on a rimmed carbonate platform adjacent to a deeper marine environment the mozduran carbonate succession consists of five thick shallowing upward sequences 3rd order cycles no major hiatus has been recognized between these cycles therefore the contacts are considered subtidal conformities drowning unconformities these 3rd order cycles can be correlated with those recognized in upper jurassic strata in other parts of the world thus they are considered largely eustatic mainly tectono eustatic in origin numerous small scale shallowing upward cycles parasequences are contained within the major shallowing upward cycles both subtidal and peritidal parasequences showing an abrupt deepening of microfacies have been recognized a combination of episodic subsidence and autocyclic processes could have been responsible for the formation of these small scale cycles rapid carbonate accumulation reflected in rare first generation marine cements including meteoric cements resulted in grain to grain pressure solution and sutured contacts during burial with late cements filling the remaining pores many of the platform margin grainstones packstones have been replaced by coarsely crystalline dolomite possibly through seawater pumping and kohout convection during the transgressive and highstand phases of sea level