changes in crack density and wave velocity in association with crack growth in triaxial tests of inada granite 1 a nondimensional second rank tensor fij called the crack tensor has successfully been introduced to deal with geometrical aspects of microcracks fabric such as anisotropy and crack density unfortunately however its usage for practical purposes is rather limited because its determination involves tedious and time consuming laboratory work we seek the possibility of using the directional change of longitudinal wave velocities to conquer the difficulty associated with the determination of crack tensors a new second rank tensor vij is introduced such that the directional change in the longitudinal wave velocities is represented in terms of the tensor and the crack tensor fij is then given as a function of vij on the basis of the analyses of the crack tensors for one intact and several damaged samples of inada granite we then discuss how microcracks grow through the whole inelastic process terminating at brittle failure the conclusions are summarized as follows the second rank symmetrical tensor vij or its inversion tensor vij 1 can be determined experimentally with sufficient accuracy from the directional change in the squared longitudinal wave velocity it is found that the tensor changes markedly so as to reflect the fabric of the damaged inada granite formed by open microcracks the principal axes of vij 1 are coaxial with the principal axes of fij so that both tensors are correlated in terms of their principal values fi and vi 1 four successive stages can be distinguished in regard to the crack growth as follows in stage 1 the rock behaves like an elastic solid in stage 2 microcracks start to grow so that inelastic volumetric strain is slowly accumulated along with microcracking however crack growth does not occur globally but rather is limited within some local zones probably in each grain in stage 3 microcracking is considerably accelerated suggesting that the micromechanism leading to crack growth changes substantially at the boundary stress between stages 2 and 3 in stage 4 the crack density as well as the dilatancy increases explosively in association with a drop of a few percent in the differential stress after the peak stress is reached interestingly this explosive increase is always associated with the development of a few fault zones experimental evidence seems to support the postulate that inada granite starts to collapse once the crack density f0 f the first invariant of fij attains a threshold value of 7 8 regardless of the applied confining pressure this can be a failure criterion in terms of the crack density and be an extended expression for the so called critical dilatancy for creep failure suggested by kranz and scholz 1977

strain state and kinematic evolution of a fold nappe beneath the samail ophiolite oman abstract the saih hatat domal culmination of the oman mountains arabian peninsula contains a major refolded ne facing recumbent anticlinal fold nappe within pre ordovician sedimentary cover autochthon and mesozoic platform carbonates that underlie the samail and hawasina nappes tracts of overturned stratigraphy covering over a 1000 km 2 are associated with a marked strain gradient towards sheath like a type folds that define the fold nappe lower limb transitional into an elongated sw facing recumbent syncline and the underlying upper plate lower plate shear zone directions of stretching recorded by fibrous pressure shadow fringes on pyrite show a 20 30 counterclockwise rotation in the foliation plane strain and kinematic constraints require the fold nappe to form progressively during top to the ne shearing of the arabian margin with 1 development of a high strain zone and 2 subsequent folding of the strongly deformed to transposed stratigraphy in the hanging wall to the shear zone rolling of the autochthonous stratigraphic layering of the upper limb through the hinge accompanied by differential shear strain produced the regional scale highly attenuated a type folds at the structurally lowest levels this occurred by simple underthrusting of the footwall lower plate as the upper limb of the fold nappe has to be pinned to the autochthon

late palaeozoic to neogene geodynamic evolution of the northeastern oman margin when the highlands of arabia were still covered with an ice shield in the latest carboniferous early permian period separation of gondwana started this led to the creation of the batain basin part of the early indian ocean off the northeastern margin of oman the rifting reactivated an infra cambrian rift shoulder along the northeastern oman margin and detritus from this high was shed into the interior oman basin whereas carbonate platform deposits became widespread along the margin of the neo tethys northern rim of oman drifting and oceanization of the batain basin started only in late jurassic early cretaceous time extensional tectonics was followed in the late cretaceous by contraction caused by the northward drift of greater india and afro arabia this resulted in the collision of afro arabia with an intra oceanic trench and obduction of the semail ophiolite and the hawasina nappes south to southwestward onto the northern oman margin 80 m y ago during the middle cretaceous the oceanic lithosphere including the future eastern ophiolites of oman drifted northwards as part of the indian plate at the cretaceous palaeogene transition 65 ma oblique convergence between greater india and afro arabia caused fragments of the early indian ocean to be thrust onto the batain basin subsequently the lower permian to uppermost maastrichtian sediments and volcanic rocks of the batain basin along with fragments of indian ocean floor eastern ophiolites were obducted northwestward onto the northeastern margin of oman palaeogene neo autochtonous sedimentary rocks subsequently covered the nappe pile tertiary extensional tectonics related to red sea rifting in the late eocene was followed by miocene shortening associated with the collision of arabia and eurasia and the formation of the oman mountains

sheath fold development with viscosity contrast analogue experiments in bulk simple shear it has been shown experimentally that sheath folds can develop passively by kinematic amplification of precursor non cylindrical deflections however sheath folds are most commonly multilayers where rheological contrast can be expected non passive sheath folding therefore we studied a natural occurrence of sheath folds where layers show rheological contrast and used analogue modelling to investigate sheath fold development with viscosity contrast the initial deflection in the experiments was always hemispherical and planar layering parallel to the shear plane under the chosen experimental conditions the results show that 1 the viscosity contrast between layers should be lower than one order of magnitude 10 to generate a sheath fold in both higher and lower viscosity layers otherwise the higher viscosity layer behaves as effectively rigid 2 the lower viscosity layer develops into a tubular fold dragged by the higher viscosity layer that undergoes mixed strain low and shear plane parallel translation high 3 the ratio between ellipticities of external and internal ellipses r re ri significantly departs from 1 as the viscosity contrast increases e g r 0 6 for 7 5 in the case where the higher viscosity layer caps the lower viscosity layer this is in great contrast with passively developed sheath folds for which r 1 when the precursor deflection is hemispherical from the present experimental study and previous work investigating other variables we conclude that r should be cautiously used and that extraction of kinematical information from sheath fold geometry alone can be erroneous

mud volcano eruptions and earthquakes in the northern apennines and sicily italy abstract the relations between earthquakes and the eruption of mud volcanoes have been investigated at the pede apennine margin of the northern apennines and in sicily some of these volcanoes experienced eruptions or increased activity in connection with historical seismic events showing a good correlation with established thresholds of hydrological response liquefaction to earthquakes however the majority of eruptions have been documented to be independent of seismic activity being mud volcanoes often not activated even when the earthquakes were of suitable magnitude and the epicentre at the proper distance for the triggering this behaviour suggests that paroxysmal activity of mud volcanoes depends upon the reaching of a specific critical state dictated by internal fluid pressure and implies that the strain caused by the passage of seismic waves can activate only mud volcanoes in near critical conditions i e close to the eruption seismogenic faults such as the pede apennine thrust often structurally control the fluid reservoirs of mud volcanoes which are frequently located at the core of thrust related folds such an intimate link enables mud volcanoes to represent features potentially suitable for recording perturbations associated with the past and ongoing tectonic activity of the controlling fault system

3d electrical resistivity imaging of the near surface structure of mud volcano vents abstract a near surface study of the 3d electrical resistivity distribution of a cold mud volcano field in new zealand is presented inversion of 16 densely spaced profiles allowed to image the uppermost 25 30 m the mud distribution is characterized by areas of very low resistivity less than 7 m embedded in river terrace sediments with resistivities of above 30 m within the first 4 6 m below the surface a good correlation between mud vents and low electrical resistivities is observed between ca 5 and 15 m depth in contrast the mud distribution does not reflect anymore the distribution of surface vents but is restrained to a few pipe like structures that link a deeper mud reservoir to the vents at the surface the obtained resistivity distribution allows also locating the masterton strike slip fault just north of the mud volcano field confirming the role of this fault as conduit of the mud from deeper layers to the surface

dating the subduction of the arabian continental margin beneath the semail ophiolite oman the presence of high pressure p eclogites along the northeast margin of the arabian continental plate beneath the semail ophiolite demonstrates that subduction of thinned continental crust to pressures of 20 kbar 80 km depth has occurred current debate centers on whether this high p metamorphism occurred prior to during or following ophiolite emplacement which is known to have started ca 95 93 ma five concordant u pb zircon ages from a garnet clinopyroxene phengite crossite eclogite from as sifah northeast oman precisely constrain the age of high p metamorphism at 79 1 0 3 ma this age demonstrates that high p metamorphism occurred during continental subduction 15 m y after formation of the ocean floor that subsequently became the semail ophiolite

classification of mud volcanoes in the south caspian basin offshore azerbaijan abstract a 2d seismic grid in the south caspian basin offshore azerbaijan is used to define the areal distribution of mud volcanoes and to make a classification of the mud volcanoes based on characteristic seismic features a high concentration of mud volcanoes is observed at the southern part of the study area that coincides with the distribution of subsurface structures within the basin mud volcanoes with low relief several tens of meters are concentrated primarily in the northeastern portion of the study area mud volcanoes with large vertical relief greater than 200 m are clustered in the southwest part of the basin mud volcano development in the south caspian basin is generally linked to faults which in some instances are detached at the basement level the seismic database allows us to determine the relative timing of mud flows and gives us valuable information about mechanisms of mud volcanism within the south caspian basin the cycles of mud volcano activity coincides with time of high sedimentation rates regional contraction episode and a major stage for hydrocarbon generation mud volcano formation within the south caspian basin is primarily controlled by compressional tectonic forces and overpressured sediments mud volcano activity may not always be related to the maykop organic rich shale succession late oligocene lower miocene but may also occur at shallower stratigraphic zones

stereology based fabric analysis of microcracks in damaged granite abstract crack related fabric analyses were carried out in terms of crack tensors using inada granite deformed inelastically in a triaxial vessel up to post failure focusing on the fabric changes during brittle failure complementarily numerical simulation tests were conducted to determine the representative volume element rve required for crack surveying numerical simulation tests show that the window size for crack surveying should be at least six times the mean trace length in order to obtain a statistically meaningful crack tensor a larger window is needed to estimate the distribution of crack radii in quartz cracks grow preferentially parallel to the major loading axis crack tensors in quartz can provide a measure of damage reflecting inelastic deformation under differential stress in past geological events during the first stage of inelastic deformation the number density of cracks decreases with a rather sharp increase in crack diameters this happens because pre existing cracks in intact rock join together to make longer cracks however the density remains almost constant during the second stage of loading from 90 to 100 of the peak stress the crack diameter gradually increases due to the stable propagation of cracks when granite is further deformed beyond the peak stress the number density decreases again while sharp increases in crack diameters appear as a result of the forking and coalescence of cracks it is also suggested that load normal grain boundary cracks are generated as a result of the rolling and sliding of disintegrated blocks in the post failure stage

eye to eye with a mega sheath fold a case study from wadi mayh northern oman mountains sheath folds are highly curvilinear folds typically considered to develop by hinge rotation toward the transport direction during intense deformation most sheath folds are recognized on the centi meter to meter scale with very few detailed studies of larger kilometer scale structures we here present evidence for a megascale sheath fold superbly exposed in the northern oman mountains the saih hatat culmination consists of an exhumed highpressure subduction zone with deep level eclogites and garnet blueschists as sifah unit epidote blueschists hulw unit and carpholite bearing metasediments part of the upper plate sheath folds are present at a variety of scales throughout the as sifah hulw and upper plate tectonic packages curvilinear fold hinges along a 15 km long profi le outline the wadi mayh mega sheath fold which closes to the ssw and faces to the nne it consists of at least four secondary sheath folds with cross sectional y z eye folds measur ing 200 m stacked on top of one another within permian and triassic shelf car bonates these eye folds display highly elliptical geometries ryz 5 and cat s eye fold patterns consistent with simple general shear the sheath fold is enveloped by ordovician and older rocks that do not show equal amounts of internal deformation the upper bounding envelope is a detachment that has been subsequently sheath folded the lower boundary of the sheath fold is the upper plate lower plate detachment which forms a major high strain shear zone showing little vertical displacement but signifi cant horizontal displacement the sheath fold displays a ssw elongation x axis of at least 15 km and possibly up to 25 km coupled with signifi cant amounts of vertical fl attening and wnw ese shortening

petrochemistry and origin of sub ophiolitic metamorphic and related rocks in the oman mountains the semail ophiolite complex of the northern oman mountains was obducted during cenomanian to campanian upper cretaceous times onto the arabian continental margin during this time span schistose metamorphic rocks of amphibolite and greenschist facies exhibiting polyphase deformation were formed and accreted below the ophiolite slice whole rock and mineral analyses confirm that the amphibolites were originally tholeiitic basalts comparable to present day occurrences at mid ocean ridges a comparison of trace element geochemistries however suggests that the protoliths were not equivalent to the haybi alkaline and transitional tholeiites found in the underlying structural slice or to the semail ophiolite volcanic rocks which lie structurally higher in the sequence it is therefore suggested that the amphibolites may have been derived from jurassic or lower cretaceous oceanic basalts not recognized elsewhere in the oman mountains structurally beneath the amphibolites within the metamorphic sheet greenschist facies metasedimentary rocks including quartzites and marbles are interbanded with metabasite horizons containing actinolite and less commonly blue crossitic amphiboles it is suggested that the sedimentary and volcanic protoliths were metamorphosed in a subduction zone environment during initial ophiolite displacement and were accreted to the base of the ophiolite during progressive underthrusting

formation and exhumation of ultra high pressure rocks during continental collision role of detachment in the subduction channel 1 uhp rocks commonly form and exhume during the transition from oceanic subduction to continental collision their exhumation in subduction channels depends on the balance between down channel shear traction and up channel buoyancy thermal mechanical upper mantle scale numerical models are used to investigate how variations in material properties of the subducting continental margin affect this balance changes in shear traction leading to crustal decoupling detachment are investigated by varying the onset of strain weakening thermal parameters and convergence velocity variations in buoyancy force are investigated by modifying subducted material density and volume the model results are interpreted in terms of the exhumation number e which expresses the role of the pressure gradient channel thickness effective viscosity and subduction velocity peak metamorphic conditions exhumation velocity and timing of exhumation are temporally and spatially variable and are sensitive to the evolution of e the models reproduce natural ptt constraints and indicate that neither slab breakoff nor surface erosion is required for uhp exhumation

scale invariant sheath folds in salt sediments and shear zones abstract sheath folds are developed in a broad spectrum of geological environments in which material flow occurs including gravity driven surficial deformation in ignimbrites unconsolidated sediments and salt together with deeper level ductile shear zones in metamorphic rocks this study represents the first geometric comparison of sheath folds in these different settings across a wide range of scales elliptical closures defining eye folds represent y z cross sections through highly curvilinear sheath folds our analysis of the published literature coupled with field observations reveals remarkably similar ellipticities r yz for sheath folds in metamorphic shear zones r yz 4 23 salt r yz 4 29 sediment slumps r yz 4 34 glaciotectonites r yz 4 48 and ignimbrites r yz 4 34 nested eye folds across this range of materials n 1800 reveal distinct and consistent differences in ellipticity from the outer r yz to the inner most r y z elliptical rings of individual sheath folds the variation in ratios from outer to inner rings r r yz r y z in gravity driven surficial flows typically displays a relative increase in ellipticity to define cats eye folds r r yz that are remarkably constant r 2 0 99 across 9 orders of magnitude sheath y axes range from 0 1 mm to 75 km our findings lead us to conclude that the geometric properties of sheath folds are scale invariant and primarily controlled by the type and amount of strain with r also reflecting the rheological significance of layering associated with original buckle fold mechanisms the scaling pattern of sheath folds reflects the length scales of the precursor buckle folds and width of deformation zones across a broad range of materials and environments with continued deformation the layering marking the original folds may become increasingly passive to define sheath folds these empirical relationships suggest sheath folding is a fundamental mode of viscous response across a broad spectrum of materials strain rates and scales encompassing a variety of deformation settings

middle permian plume related magmatism of the hawasina nappes and the arabian platform implications on the evolution of the neotethyan margin in oman 1 permian pillow basalts are commonly found in oman either at the base of the hawasina nappes or within the arabian platform successions exposed in the saih hatat tectonic window there is an ongoing debate on whether these lavas include normal mid oceanic ridge basalts nmorb witnessing the permian opening of the neotethys or if they are plume related magmas that are emplaced either on the arabian platform or on its thinned continental margin we sampled these lavas from several paleontologically dated middle permian sites four of them buday ah rustaq al ajal and wadi wasit are located within the hawasina nappes and are exposed as thrust slices overlain by the samail nappe and one wadi aday is within the arabian platform units and is exposed in the saih hatat window these lavas are associated with marine sediments deposited in environments ranging from proximal saih hatat wadi wasit and base of the thrust pile of al ajal to distal buday ah rustaq and top of the al ajal pile with respect to the arabian platform major and trace element features of the basalts allow two groups to be recognized enriched high ti basalts similar to alkali basalts from intracontinental traps rifted continental zones and oceanic islands are exposed in wadi aday wadi wasit and at the structural base of the al ajal pile moderately enriched to slightly depleted low ti tholeiitic basalt magmas resembling the low ti flood basalts and those from seaward dipping reflector sequences are represented in wadi al hulw in saih hatat buday ah rustaq and at the top of the al ajal thrust pile both groups show distinct plume related trace element signatures and they do not include typical nmorb although emplaced in shallow to deep submarine environments these basalts provide no direct evidence for a neotethyan seafloor spreading event in the hawasina basin instead they were likely erupted through the crust of the already rifted and drowned arabian continental margin thus despite their characteristic plume related geochemical signatures the middle permian basalts from oman were not likely emplaced during the evolution of a typical volcanic rifted margin we suggest that they originated from a mantle plume which ascended beneath the arabian passive margin well after the initiation of seafloor spreading of the neotethys

coseimic massive methane release from a submarine mud volcano abstract we report here the discovery of two methane enriched plumes in a water column above the kumano knoll 5 submarine mud volcano kk 5 in nankai trough during 2004 a slight methane enrichment was observed in this region in 2000 and 2010 the deeper of the two plumes spread horizontally at depths near the top of kk 5 whereas a shallow plume spread at a height of 300 m from the top of kk 5 the end member 13 c values of methane in both plumes 46 1 4 8 and 51 4 5 8 in the deep and shallow plumes respectively and methane extracted from sediment in kk 5 52 2 are statistically indistinguishable we conclude that the plumes were created by massive release of methane from kk 5 and that this event probably occurred in response to the large earthquakes m w 7 5 that occurred shortly before our observation in 2004 the discharge rates from submarine mud volcanoes smvs in subduction zones may be highly variable in response to major earthquakes

ground based and uav based photogrammetry a multi scale high resolution mapping tool for structural geology and paleoseismology this contribution reviews the use of modern 3d photo based surface reconstruction techniques for high fidelity surveys of trenches rock exposures and hand specimens to highlight their potential for paleoseismology and structural geology we outline the general approach to data acquisition and processing using ground based photographs acquired from standard dslr cameras and illustrate the use of similar processing approaches on imagery from unmanned aerial vehicles uavs it is shown that digital map and trench data can be acquired at ultra high resolution and in much shorter time intervals than would be normally achievable through conventional grid mapping the resulting point clouds and textured models are inherently multidimensional x y z point orientation colour texture archival and easily transformed into orthorectified photomosaics or digital elevation models dems we provide some examples for the use of such techniques in structural geology and paleoseismology while pointing the interested reader to free and commercial software packages for data processing visualization and 3d interpretation photogrammetric models serve to act as an ideal electronic repository for critical outcrops and observations similar to the electronic lab book approach employed in the biosciences this paper also highlights future possibilities for rapid semi automatic to automatic interpretation of the data and advances in technology

when mud volcanoes sleep insight from seep geochemistry at the dashgil mud volcano azerbaijan the worlds 1500 mud volcanoes are normally in a dormant stage due to the short duration of eruptions their dormant stage activity is often characterized by vigorous seepage of water gas and petroleum however the source of the fluids and the fluid rock interactions within the mud volcano conduit remain poorly understood in order to investigate this type of activity we have combined satellite images with fieldwork and extensive sampling of water and gas at seeping gryphons pools and salsa lakes at the dashgil mud volcano in azerbaijan we find that caldera collapse faults and e w oriented faults determine the location of the seeps the seeping gas is dominated by methane 94 9 99 6 with a 13c v pdb in the 43 9 to 40 4 range consistent throughout the 12 analysed seeps ethane and carbon dioxide occur in minor amounts seventeen samples of seeping water show a wide range in solute content and isotopic composition pools and salsa lakes have the highest salinities up to 101 043 ppm cl and the lowest 18o v smow values 1 4 the mud rich gryphons have low salinities 18 000 ppm cl and are enriched in 18o 18o 4 6 the gas geochemistry suggests that the gases migrate to the surface from continuously leaking deep seated reservoirs underneath the mud volcano with minimal oxidation during migration however variations in gas wetness can be ascribed to molecular fractionation during the gas rise in contrast the water shows seasonal variations in isotopic composition and surface evaporation is proposed as a mechanism to explain high water salinities in salsa lakes by contrast gryphons have geochemical signals suggesting a deep seated water source these results demonstrate that the plumbing system of dormant mud volcanoes is continuously recharged from deeper sedimentary reservoirs and that a branched system of conduits exists in the shallow subsurface while the gas composition is consistently similar throughout the crater the large assortment of water present reflects the type of seep i e gryphons versus pools and salsa lakes and their location within the volcano our data highlight the importance of a carefully planned sampling strategy when the target is water geochemistry whereas the methane content and isotopic composition is relatively independent of the particular seep morphology

nature and origin of sedimentary clasts associated with mud volcanoes in the nile deep sea fan relationships with fluid venting abstract during the last 10 years several marine geological geophysical surveys conducted on the nile deep sea fan have provided much new information about the large fluid seepage phenomenon which characterizes this passive margin segment among the data more than 60 sediment cores have been recovered in this area rock clasts were collected from eight of them as well as during deep sea dives notably in the area of isis osiris and amon mud volcanoes in few areas especially in the western and the north eastern provinces of the nile fan some clasts consist of crust fragments resulting from cementation of muddy sediment by precipitation of high mg calcite these clasts correspond to a simple cementation of the mud by precipitation of high mg calcite as a consequence no obvious textural or faunal difference with the ambient matrix mud can be observed these clasts are made of autochthonous crusts derived from microbial anaerobic oxidation of methane and release of bicarbonate and sulphide in the surrounding pore water these clasts also lack aragonite in most of the other cases menes caldera isis osiris and amon mud volcanoes allochthonous clasts characterized by low mg calcite cement siderite or dolomite mixed with expelled mud outcrop on the seafloor nannofossils have allowed us to date some of these clasts most of the ages range from pliocene to pleistocene one clast is lower cretaceous in age the lithological facies often indicate coastal or deltaic environments some clasts are closely linked to an evaporite rich environment halite gypsum and analcime they all provide useful information on the nature of buried sedimentary series covering the margin their presence on the seafloor is due to the expulsion of a pressurized mixture of sediment water and gas this process is believed to have used pre existing tectonic conduits

cyclic activity of mud volcanoes evidences from trinidad se caribbean fluid and solid transfer in mud volcanoes show different cyclic phases of activity including catastrophic events and periods of relative quiescence characterized by moderate activity this is notably well shown by the compilation of historical data onshore trinidad it appears that each eruptive mud volcano has its own period of catastrophic activity and this period is variable from one volcano to another the frequency of the eruptions seems essentially controlled by local pressure regime within the sedimentary pile the dynamics of expulsion of the mud volcanoes during the quiescent phases has been studied with the help of temperature measurements within the mud conduits the mud temperature in these conduits is notably concurrently controlled by the gas flux endothermic gas depressurizing induces a cooling effect and by the mud flux mud is a vector for convective heat transfer complex temperature distribution was observed in large conduits and pools especially in the bigger pools the temperature distribution characterizes convective cells with an upward displacement of mud above the deep outlet and ring shaped rolls associated with the burial of the mud on the flanks of the pools in tube like shaped narrow conduits the temperature is more regular but we observed different types of profiles with either downward increasing or decreasing temperatures near constant to even negative gradients compared to the general temperature gradient are typical for very dynamic fluid systems the temperature profiles varied from one place to another as well as over time the temperatures measured within the conduits and their base show that the fluid flow is not constant but highly variable through short time periods we observed locally a significant daily change of the temperature of the expelled mud which shows also that the mud flux is changing very rapidly due to the migration dynamics of the mud in fracture systems we also observed very short time period cyclic variations with a frequency of several minutes these high frequencies temperature changes could be related to the dynamics of two phase flows gas and mud through the mud volcano conduits

a method for evaluating the representative elementary volume based on joint survey of rock masses the representative elementary volume of a statistically homogeneous rock mass is defined as the minimum volume beyond which any submass behaves essentially like the whole rock mass a simple but still general method for the determination of the minimum volume is given on the basis of the crack tensor concept it is concluded that the size must be at least three times larger than a typical length of joint traces key words computer simulation rock hydraulics site investigation

3d visualization of sheath folds in ancient roman marble wall coverings from ephesos turkey abstract archaeological excavations and restoration of a palatial roman housing complex in ephesos turkey yielded 40 wall decorating plates of folded mylonitic marble cipollino verde derived from the internal hellenides near karystos greece cipollino verde was commonly used for decoration purposes in roman buildings the plates were serial sectioned from a single quarried block of 1 25 m3 and provided a research opportunity for detailed reconstruction of the 3d geometry of meterscale folds in mylonitized marble a gocad model is used to visualize the internal fold structures of the marble comprising curtain folds and multilayered sheath folds the sheath folds are unusual in that they have their intermediate axis normal to the parent layering this agrees with regional tectonic studies which suggest that cipollino verde structures formed by local constrictional non coaxial flow sheath fold cross section geometry exposed on the surface of a plate or outcrop is found to be independent of the intersection angle of the fold structure with the studied plane consequently a single surface cannot be used as an indicator of the three dimensional geometry of transected sheath folds

crack tensor based evaluation of inada granite behavior due to damage under true triaxial testing condition abstract in the present work wave velocity measurements were implemented to assess the state of damage in specimens of inada granite the specimens were first loaded under true triaxial testing conditions for which different levels of major principal stress with respect to ultimate strength were applied christoffel s stiffness equation was used to derive elastic properties of the domain via p wave velocity measurements the compliance matrix arrays in the strain stress relationship were then calculated in the most heterogeneous case which involved 21 constants furthermore determination of second and fourth rank crack tensors enabled convenient judgment for the degree of anisotropy expected during permeability and dispersivity studies which are very important in environmental studies it was found that while more attempt to model granitic rocks in their real form is useful the orthorhombic symmetry assumption for the rock under study would eventually render best outcome for realistic simulation purposes of mechanical properties finally areas of application for the proposed development are discussed and prospects of future work by the researchers are outlined

tectonics of the arabian margin associated with the formation and exhumation of high pressure rocks sultanate of oman continental crustal rocks now structurally beneath the allochthonous samail ophiolite underwent blueschist to eclogite facies metamorphism prior to the emplacement of the oman ophiolite onto the arabian margin the recognition of a major low angle fault within this polydeformed and polymeta morphosed sequence of metacarbonates metabasites quartzites and quartz mica schists greatly simplifies the interpretation of the structure and metamorphic zonation within the saih hatat window ne oman carpholite bearing upper plate rocks consist of pre permian to jurassic rocks that have been folded into large recumbent nappe structures which exhibit a marked increase in deformation intensity toward the boundary with the lower plate the lower plate rocks have higher peak pressure and temperature assemblages they are exposed in two windows separated by jabal abu daud although more intensely deformed the lower plate rocks are recognizable as metamorphosed continental platform sediments fold axes are parallel to the regional nne ssw lineation sense of shear indicators yield a transport direction of south over north in the lower plate opposite to the sense of motion inferred for the emplacement of the ophiolite lower plate eclogite facies metabasalts are only preserved in kilometer scale megaboudins found in the easternmost window at as sifah these metamorphic assemblages along with their remnant east west fabrics define the existence of a short lived arabian platform directed nascent subduction zone the stretching lineation elsewhere within the upper and lower plates the hatat schist the basement and the metamorphic sole of the ophiolite is consistently nne ssw suggesting that the exhumation of high pressure metamorphic rocks of saih hatat is related to the ophiolite obduction exhumation of the high pressure rocks was accompanied by intense deformation involving regional scale fold nappes in a convergent margin setting the geotherm remained suppressed for a period 30 myr greater than the thermal relaxation time of the crust the geometric and thermal constraints from oman may be applicable to the general problem of the formation and preservation of high pressure low temperature rocks

sm nd and zircon u pb ages from garnet bearing eclogites ne oman constraints on high p metamorphism poly deformed and poly metamorphosed glaucophane eclogite mega boudins beneath the samail ophiolite oman record an early subduction related high p metamorphism as well as subsequent overprinting deformation and metamorphism related to exhumation previously published rb sr ages of 78 ma and 40ar 39ar ages of 82 79 ma record the major ne directed shearing event that partially exhumed the eclogites to a shallower crustal level new sm nd garnet garnet leachate whole rock isochron data from garnet bearing eclogite assemblages in the as sifah subwindow in ne oman are 110 9 ma dg02 87d 5 point isochron and 109 13 ma dg02 86e 3 point isochron on the basis of microfabric and field structural relationships these ages are interpreted to reflect the timing of prograde peak high p metamorphism in the rocks structurally beneath the samail ophiolite this metamorphism clearly predates the age of formation of the obducted samail oceanic lithosphere 97 94 ma as well as the subsequent obduction onto the margin 80 70 ma a u pb shrimp zircon age from small 200 m in length zircons with herring bone textured zoning from dg02 87d indicate that rapid zircon growth associated with high si phengites occurred at 82 1 ma zircon growth is possibly related to liberation of zr on garnet breakdown during decompression metamorphism under high p conditions with exhumation these data require that crustal stacking models attendant with ophiolite obduction are inappropriate to explain the oman high p metamorphism

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

uranium lead isotopic ages of the samail ophiolite oman with applications to tethyan ocean ridge tectonics plagiogranites are a minor but widespread component of the samail ophiolite plutonic member they crystallized from the most fractionated melts generated by magmatic crystallization and differentiation of a steady state magma chamber beneath the tethyan spreading ocean ridge and their ages are thought to mark the time of ocean crust formation isotopic u pb ages of zircons from 13 plagiogranites collected along a 270 km segment of the samail ophiolite subparallel to the regional trend of the sheeted dike complex the former spreading ridge axis direction define a narrow time interval of 93 5 97 9 m y with a pronounced clustering about 95 m y the zircon ages of the plagiogranites agree remarkably well with the early cenomanian to early turonian biostratigraphic ages of sediments that are intercalated within the ophiolite pillow lavas and that lie just above them tippit et al 1981 the agreement of radiometric and biostratigraphic ages provides strong support for the conclusion that the plagiogranite u pb ages closely date the time span of ocean crust formation no step changes in age patterns are observed along the ridge axis sheeted dike direction suggesting that there are no major internal offsets of the ophiolite by transform or other faults along most of the traverse one possible exception occurs at the southeastern end of the sampled interval ibra area where a 3 m y discontinuity might be caused by an unmapped fault assuming that the regional trend of the sheeted dikes n10 25 w marks the direction of the former spreading ridge axis the present array of sample localities spans a distance of 130 to 195 km normal to that axis i e in the spreading direction the data as a whole do not define a clear cut age trend normal to the spreading axis but by eliminating samples that may be aberrant due to faulting the data array suggests a pattern of increasing ages from east to west this would indicate that the samail ophiolite is derived from the western southwestern side of the tethyan spreading system a conclusion reached independently from geological evidence also the gentle age gradient in the spreading direction i e between 130 and 195 km of ocean crust were formed within an age span of no more than 2 m y suggests a very fast spreading rate this conclusion also is supported by independent geologic evidence

a geochemical study on mud volcanoes in the junggar basin china abstract a comprehensive study was performed to characterize for the first time the mud water and gases released from onshore mud volcanoes located in the southern margin of the junggar basin northwestern china chemical compositions of mud along with the geology of the basin suggest that a source of the mud is mesozoic or cenozoic shale oxygen and h isotope compositions of the released water suggest a local meteoric origin combined with the positive eu anomalies of the water a large 18 o shift of the water suggests extensive interaction with rocks gases discharged from the mud volcanoes are predominantly thermogenic hydrocarbons and the high 13 c values 20 vpdb for co 2 gases and dissolved carbonate in muddy water suggest secondary methanogenesis with co 2 reduction after oil biodegradation the enrichments of eu and 18 o in water and the low thermal gradient of the area suggest that the water rock interactions possibly occur deeper than 3670 200 m on the other hand considering the relationship to the petroleum reservoir around the mud volcanoes the depth of the gases can be derived from about 3600 m a depth that is greater than that generally estimated for reservoirs whose gas is characterized by 13 c enriched co 2 oil biodegradation with co 2 reduction likely occurs at a shallower depth along the seepage system of the mud volcano the results contribute to the worldwide data set of gas genesis in mud volcanoes moreover they further support the concept that most terrestrial mud volcanoes release thermogenic gas produced in very deep sediments and may be early indicators of oil biodegradation an important problem in the petroleum industry

structures and timing of permian rifting in the central oman mountains saih hatat abstract we investigated remnants of permian rifting sequences in the saih hatat metamorphic window central oman mountains part of the former arabian continental margin which has been overthrust by the semail ophiolite in the less deformed northwestern part of the saih hatat well preserved or inverted syn sedimentary normal faults indicate ene wsw permian extension we propose new stratigraphic correlations with the more deformed and metamorphosed parts of the saih hatat based on lithostratigraphy and large scale structures unfolding which indicate that breakup of the permian platform resulted in sediment thickening and deepening towards the ene this rift event was coeval with within plate volcanism that was widespread in all compartments of the margin but marked by a single event in the stratigraphic record of the platform in this part of the arabian margin rifting was restricted to a short time interval less than 5 my during the murghabian and volcanism can be correlated with the panjal traps event we propose that this part of the neotethyan margin formed as a volcanic rifted margin in a triple junction setting

active mud volcanoes on and offshore eastern makran pakistan to study the activity source and driving force of the venting of fluidized mud in the coastal makran we carried out reconnaissance surveys of two active onshore mud volcano fields chandragup and jebel u ghurab and of a newly born march 1999 offshore mud volcano malan island all studied on and offshore mud volcanoes line up along one southwest northeast trending structural lineament the axis of the dhak anticline isotopic data point to a bacterial origin of the gas mainly methane mixed benthic foraminiferal faunas and calcareous nannofloras suggest that the source level of the extruded mud is at a sub surface depth of 2 3 km observed mud discharge varied between 0 and 1 4 m3 h 1 and gas discharge rates between negligible amounts to 1 m3 s 1 mud temperatures in the crater lake of chandragup i are near ambient temperatures they rise slightly 1 5 c during episodes of modest mud outflow an area of 160 000 m3 of soft mud was vigorously extruded from the sea floor at a water depth of 10 m within days after 15 march 1999 forming malan island the island was destroyed within a few months after its birth by deep reaching wave action during the sw monsoon this was possibly aided by local subsidence of the mud volcano structure due to the volume loss following rapid degassing and mud extrusion

tectonic development of the samail ophiolite high precision u pb zircon geochronology and sm nd isotopic constraints on crustal growth and emplacement 1 new high precision single grain u pb zircon geochronology and whole rock nd isotopic data provide insight into the magmatic and tectonic development of the samail ophiolite the analyzed rocks can be broadly divided into two groups based on their structural position dates and isotopic composition an older group related to on axis magmatism and a younger group of post ridge dikes sills and stocks on axis gabbros tonalites and trondhjemites yielded th corrected 206pb 238u dates from 96 441 0 062 to 95 478 0 056 ma these dates combined with dates from rioux et al 2012 suggest that most of the ophiolite crust formed at an oceanic spreading center in 1 ma the post ridge intrusions come from all depths in the crust the upper mantle and the metamorphic sole post ridge gabbros tonalites and trondhjemites from the crust and mantle yielded th corrected 206pb 238u dates of 95 405 0 062 to 95 077 0 062 ma a small trondhjemitic pod from the metamorphic sole yielded younger th corrected 206pb 238u dates of 94 90 0 38 to 94 69 0 12 ma isotopic data suggest two distinct sources for the post ridge magmas five of the gabbros and tonalites from the crust have end 96 ma 6 90 0 12 to 7 88 0 16 and two trondhjemites from the upper mantle and metamorphic sole have end 96 ma 7 77 0 08 and 7 01 0 16 the negative end t and u pb dates from the mantle dike require that subduction or thrusting was established below the ophiolite 0 25 0 5 ma after formation of the crust the bimodal isotopic composition of post ridge magmas may reflect coeval decompression and or fluid fluxed melting of the mantle and melting dehydration or assimilation of sediment in the down going plate at this time the new data place temporal constraints on mid ocean ridge and supra subduction zone models for ophiolite formation

plagioclase preferred orientation by tof neutron diffraction and sem ebsd abstract the lattice preferred orientation lpo of an anorthosite composed of andesine sampled from a highly deformed anorthositic mylonite grenville province quebec was measured by tof neutron diffraction and sem ebsd the quantitative texture analysis of neutron data was accomplished by using the rietveld texture analysis with the wimv algorithm implemented in the program package materials analysis using diffraction maud the texture calculations of the ebsd data were performed by using the program beartex analyses from neutron and electron diffraction data gave similar results if ebsd data are smoothed to account for grain statistics the principal pole figures show 010 roughly parallel to the rock foliation 001 poles exhibiting a low angle 25 to the pole to foliation and 100 poles close to the y direction perpendicular to the lineation and foliation pole the 100 crystallographic direction shows a maximum in the lineation direction 010 directions concentrate near the foliation pole the geological deformation conditions and the constructed pole figure patterns indicate that the preferred orientation could be attributed to intracrystalline slip dominantly on 010 with 100 as slip direction elastic properties calculated by averaging document weak anisotropy that has implications for the seismic structure of the lower crust

structural and stratigraphic controls on the origin and tectonic history of a subducted continental margin oman eclogites and blueschists exposed in saih hatat oman record the subduction and exhumation of continental crustal material beneath the cretaceous semail ophiolite during ophiolite obduction the eclogite bearing lower plate originally part of oman s distal continental margin is exposed in two tectonic windows through the less metamorphosed upper plate by a previously mapped low angle high strain decollement structure a major tectonic break currently poorly exposed records the juxtaposition of the highest pressure eclogites and garnet blueschists against lower pressure epidote blueschists the subsequent exhumation of the entire lower plate to mid crustal levels is marked by a pervasive shearing event associated with a regional greenschist facies overprint the decollement truncates structures and the metamorphic field gradient in the lower plate but does not significantly truncate structures or stratigraphy in the upper plate it is not responsible for the exhumation of the high pressure rocks to mid crustal levels most of the displacement across this structure was accommodated during continuing convergence after the subduction system had ceased to be active and post ophiolite emplacement onto the platform carbonate sequences a revised tectonic model is presented which accounts for the structural geochronological and metamorphic observations

when shearing is a cause of folding abstract numerous publications on shearing as a cause of folding do not refute the idea of buckling being the main process responsible for the formation of fold structures deformations of other types may either produce conditions for layer parallel shortening needed for buckling or modify fold shapes but do not generate new fold structures on any scale the origin of similar folds commonly considered to be a result of inhomogeneous shearing across layering may be explained by buckling of a multilayer where layers have uniform favourable rheological properties tightening and amplification of folds near fault surfaces is not necessarily a result of shearing caused by friction at fault surfaces on the contrary in these cases faulting is a result of strain localization during folding recumbent isoclinal folds so common in metamorphic rocks originate mainly by buckling of subvertical planar structures intrafolial folds are usually very flattened relics of former folds the idea of sheath folds being produced mostly by shearing is not confirmed by the available geological data sheath folds that were not produced by shearing are rather common more likely they are formed by constriction or flattening of folds with curved hinges the latter are a result either of fold interference or of the constriction in the layering plane

kilometre scale sheath fold at mattmark and implications for transport direction in the alps folds were the first tectonic features of rocks to be studied and as such are taken as a reference for the interpretation of other structures intuitively fold axes were assumed to be subperpendicular to the direction of transport nevertheless many studies of metamorphic belts showing intense ductile deformation describe folds with axes close to the transport direction in particular sheath folds1 9 are highly curvilinear folds elongated parallel to the direction of transport we discuss here a spectacular large sheath fold situated in a crustal shear zone in the monte rosa nappe swiss alps our analysis implies that both the geometry and significance of folds in the internal alps must be re examined we further demonstrate the existence of crustal ductile shear zones in an area of the alps where previously emphasis was generally placed on fold nappes the movements on these shear zones is often tens of kilometres

structure and sequence of thrusting in deep water sediments during ophiolite emplacement in the south central oman mountains abstract sedimentological and stratigraphical investigations of the deep water passive margin sediments of the oman neo tethys the hawasina ocean when allied with structural relationships between duplexes of these units emplaced on to the oman margin during late cretaceous ophiolite obduction allow the reconstruction of sediment distribution in the hawasina ocean from this starting point and the observed stacking order of duplexes the sequence of thrusting of the oceanic sediments can be deduced imbrication proceeded through foreland propagating thrusts whilst the assembled thrust stack was modified at a late stage of emplacement by out of sequence thrusting related to sequential locking of thrust planes towards the hinterland and gravity sliding off the flanks of a major anticline that developed in the underlying autochthonous shelf and basement two main factors governed duplex and imbricate fan formation and distribution firstly two contrasting sedimentary basins were present along the central oman margin the duru basin distal to the al ayn basin secondly competent sedimentary successions were bulldozed ahead of the semail ophiolite whilst less competent shale and chert units were overridden by the ophiolite or imbricated along its leading edge

late cenozoic central asian drying inferred from a palynological record from the northern tian shan abstract sediments contained in basins adjacent to great mountains provide opportunities to reconstruct the aridification history of central asia here we use a palynological record from the fluviolucustrine jingou river section collected from the northern tian shan nw china to reconstruct aridification in central asia during the late cenozoic biogeomagnetic results show that the section was continuously deposited through the interval 28 4 2 ma the palynological record with the auxiliary of the principal component analysis and the diversity index indicates that a late oligocene wet condition existed in central asia and shifted to dry conditions at 23 8 23 3 ma the dry condition remained until 17 3 ma and subsequently ameliorated to a relatively wet stage to 16 2 ma but then began to increase once again and reached a peak at 13 5 ma that last throughout the late miocene and the early pliocene comparing the aridification process to the global temperature trend and history of tectonics we suggest that the long term drying trend in central asia is dominated by late cenozoic cooling while the dry events that occurred at 23 8 23 3 ma and 16 2 13 5 ma are more likely associated with regional mountain building the land sea redistribution further complicated the drying processes

exhumation of high pressure rocks in northeastern oman the exhumation of high p rocks in the northeast saih hatat window oman mountains formed regional nappes associated with greenschist facies metamorphism exhumation resulted in the juxtaposition of two plates with different structural style stratigraphy and metamorphic history a major crustal discontinuity separates the two plates with lower metamorphic grade rocks in the hanging wall lower plate units were exhumed during strong top to the northeast shearing resulting in the formation of regional closures that evolved by folding and transposition of the high pressure fabrics while the lithostatic pressure was decreasing upper plate units were later exhumed with the juxtaposition of the two plates truncation of lower plate closures and the formation of upper plate nappes that are attenuated and sheathlike toward the upper and lower plate boundary in some high p terranes apparent increases in metamorphic grade down structural section and low grade c type shear bands are often attributed to extensional exhumation in oman however these exhumation features formed during crustal scale contraction at a convergent margin the low geothermal gradient regimes afforded by convergent margins are critical for the generation and preservation of high p low t rocks

obduction related planar and linear fabrics in oman under the oman ophiolites three different types of alpine synmetamorphic fabrics are seen each of them is taken as the signature of a particular stage of the obduction process the complex high grade fabric in the basal metamorphic sheet is linked to the intraoceanic detachment stage pre obduction sensu stricto the l s fabric of the muscat nappes and hatat internal border associated with low temperature high pressure metamorphism is regarded as the effect of an early obduction that is the epicontinental thrusting of the matrah peridotites the much simpler fabric of the anchizonal hawasina and autochthonous cover resulted from the gravity sliding of the semail ophiolites during the final obduction phase

sense of shear in high temperature movement zones from the fabric asymmetry of plagioclase feldspars abstract a new method for determining the sense of shear in plagioclase bearing tectonites from the 010 orientation of plagioclase feldspar is presented the method is based on the asymmetry of the 010 plane with respect to the structural frame foliation and lineation and the dominant activity of the 010 slip plane in the high temperature plasticity of plagioclase feldspar using examples from the zabargad gneisses red sea the method is applied to plagioclases of an25 an45 and compared with other methods of shear sense determination quartz c axis fabrics and microstructural criteria

chemical speciation of redox sensitive elements during hydrocarbon leaching in the junggar basin northwest china abstract bleaching related to seepage of petroleum fluids and subsurface migration of crude oil and natural gas can alter the chemical and mineralogical properties of rocks while concurrently depleting hydrocarbon reservoirs mud volcanoes constitute one type of petroleum seepage present in several areas on the southern margin of the junggar basin in the xinjiang uygur autonomous region nw china the results of xrd xrf xanes and mossbauer spectroscopy on rock samples collected from areas affected by these mud volcanoes revealed an enrichment of certain minerals and elements as well changes in mineralogical molecular or ionic carrier species after bleaching reddish sedimentary rocks showed depletion in silica and enrichment of calcium magnesium manganese and iron other elements including aluminum potassium sodium and titanium were largely unchanged reduced iron and sulfur compounds predominated in the bleached rocks producing changes in color from the original reddish into green deep gray and black iron and calcium were associated with carbonates indicating carbonation of these elements during the bleaching processes manganese also appeared to be associated with carbonate though not with sulfate even though sulfate was present in the bleached rocks alkaline conditions were apparently the dominant because reduced manganese would have been absent under acidic condition the alteration of certain minerals clay minerals in particular was also observed in bleached rocks the alteration of smectite group minerals to chlorite and muscovite for example mineralogical and geochemical changes in rocks bleached by hydrocarbon fluids could provide a better overall understanding of bleaching processes and may have applications in surface geochemical exploitation and remote imaging

evidence of subsurface anaerobic biodegradation of hydrocarbons and potential secondary methanogenesis in terrestrial mud volcanoes abstract the assessment of gas origin in mud volcanoes and related petroleum systems must consider post genetic processes which may alter the original molecular and isotopic composition of reservoir gas beyond eventual molecular and isotopic fractionation due to gas migration and microbial oxidation investigated in previous studies we now demonstrate that mud volcanoes can show signals of anaerobic biodegradation of natural gas and oil in the subsurface a large set of gas geochemical data from more than 150 terrestrial mud volcanoes worldwide has been examined due to the very low amount of c 2 in mud volcanoes isotopic ratios of ethane propane and butane generally the best tracers of anaerobic biodegradation are only available in a few cases however it is observed that 13 c enriched propane is always associated with positive 13 c co2 values which are known indicators of secondary methanogenesis following anaerobic biodegradation of petroleum data from carbon isotopic ratio of co 2 are available for 134 onshore mud volcanoes from 9 countries azerbaijan georgia ukraine russia turkmenistan trinidad italy japan and taiwan exactly 50 of mud volcanoes all releasing thermogenic or mixed methane show at least one sample with 13 c co2 5 pdb thermogenic ch 4 associated with positive carbon isotopic ratio of co 2 generally maintains its 13 c enriched signature which is therefore not perturbed by the lighter secondary microbial gas there is however high variability in the 13 c co2 values within the same mud volcanoes so that positive 13 c co2 values can be found in some vents and not in others or not continuously in the same vent this can be due to high sensitivity of 13 c co2 to gas water rock interactions or to the presence of differently biodegraded seepage systems in the same mud volcano however finding a positive 13 c co2 value should be considered highly indicative of anaerobic biodegradation and further analyses should be made especially if mud volcanoes are to be used as pathfinders of the conditions indicative of subsurface hydrocarbon accumulations in unexplored areas

microstructural based time dependent failure mechanism and its relation to geological background abstract the time dependent hydro mechanical behavior of rocks is important in assessing the long term stability of deep underground excavation sites meant for long term storage of radioactive waste while evaluating the manner in which damage growth progresses at an excavation site it is important to represent the failure criteria and microcrack evolution from the viewpoint of factors pertaining to microcrack geometry such as the crack density we performed creep tests on inada granite samples to examine the effects of water confining pressure and weathering on time dependent failure the crack density of the samples which was damaged at three characteristic stages of creep behavior i e primary secondary and tertiary creep was measured by means of a longitudinal wave velocity test the microcrack evolution and failure criteria are discussed on the basis of the crack tensor determined in the test the following conclusions were reached from the test results 1 the onset of tertiary creep corresponds to the peak stress under static loading conditions and the tertiary creep stage corresponds to the post failure region 2 at the onset of tertiary creep the crack density can be the failure criterion for time dependent failure and crack density can be estimated using the longitudinal wave velocity 3 the time to failure for weathered granitic rock is approximately ten times faster than that for intact granitic rock 4 the ratio of the mica group mineral in the granite may affect the time to failure a fact that offers insight into the time dependent stability of a rock mass on the field scale

vergence and facing patterns in large scale sheath folds the careful geometric analysis of minor structural detail elucidates the relationships and evolution of associated large scale curvilinear hinge geometries developed during wnw directed caledonian thrusting exposed in neoproterozoic moine psammites of the moine nappe reversals in the polarity of structural facing associated with minor folding mark the position of major sheath folds which parallel transport upwardly convex sheaths closing in the direction of thrust transport cored by older gneissose basement inliers are termed culminations whilst those opening in the transport direction and cored by moine psammites are termed depressions sheath folds are bisected by transport parallel and foliation normal culmination depression surfaces which separate not only the reversals in facing but also delineate zones of minor fold hinge obliquity into clockwise and anticlockwise domains relative to the transport direction the sense of obliquity of minor z and s folds is thus dependent on position with respect to the surfaces of culmination and depression and not the fold axial surfaces surfaces of culmination and depression may be superimposed on original overturned antiformal and synformal folds to produce a variety of dome culmination on antiform saddle depression on antiform inverted saddle culmination on synform and basin depression on synform configurations the curvilinear hinges of minor folds may also be asymmetrical about the transport direction and within the plane of the regional foliation to define patterns of fold hinge line vergence classical concepts of fold limb vergence may thus relate to larger antiformal and synformal hinges whilst the fold hinge line vergence defines major curvilinear hinges associated with culminations and depressions major sheath folds may therefore be interpreted in terms of both minor fold hinge line and limb vergence coupled with fold axis obliquity and reversals in the polarity of structural facing the ability to recognise consistent and reliable structural relationships between facing and hinge obliquity at small scales indicates that the regional deformation process forms a linked and coherent system through several orders of magnitude 1999 elsevier science ltd all rights reserved

new high precision p t estimates for oman blueschists implications for obduction nappe stacking and exhumation processes oman blueschists and eclogites lie below the obduction nappe of the semail ophiolite in one of the key areas on earth for the study of plate convergence here new metamorphic and tectonic constraints are provided for the central yet poorly constrained hulw unit sandwiched between the low grade units 10 kbar 300 c and the as sifah eclogites pmax 23 kbar tmax 600 c tweequ multi equilibrium thermobarometry using both compositional mapping and spot analyses and raman spectroscopy of carbonaceous material yield a high precision p t path for the hulw and as sheikh units and reveal that they shared a common p t history in four stages i a pressure decrease from 10 12 kbar 250 300 c to 7 9 kbar 300 350 c ii almost isobaric heating at 8 10 kbar from 300 350 c to 450 500 c iii a pressure decrease at moderate temperatures 450 500 c and iv isobaric cooling at 5 6 kbar from 450 500 to 300 c no significant pressure or temperature gap is observed across the upper plate lower plate discontinuity to the north and west of the hulw unit the combination of tectonic and p t data constrains the stacking chronology of the three main metamorphic units comprising the saih hatat window i e the ruwi quryat the hulw as sheikh and the diqdah as sifah units these results strengthen the view that the tectonic and metamorphic data are conveniently accounted for by a simple n vergent continental subduction of the passive arabian margin below the obduction nappe along a cold p t gradient

the jabal akhdar dome in the oman mountains evolution of a dynamic fracture system the mesozoic succession of the jabal akhdar dome in the oman mountains hosts complex networks of fractures and veins in carbonates which are a clear example of dynamic fracture opening and sealing in a highly overpressured system the area underwent several tectonic events during the late cretaceous and cenozoic including the obduction of the samail ophiolite and hawasina nappes followed by uplift and compression due to the arabia eurasia convergence this study presents the results of an extensive tectonic survey and correlates subseismic scale structures in jabal akhdar faults fractures veins and stylolites with the main tectonic events in the northeastern arabian plate as some of the studied formations host large oil reserves in neighboring areas determining the relative timing of these events in the exhumed rocks is important to understand hydrocarbon distribution and fracture patterns in these reservoirs the formation of early veins and stylolites in the oman mountains is followed by top to the south layer parallel shearing that may be associated with the obduction of the samail and hawasina nappes this compressional tectonic event is followed by normal dip slip to oblique slip faults and veins top to the northeast layer parallel shearing which corresponds to the first stage of exhumation of the autochthonous rocks offsets these structures our new data indicate that this first phase of events is overprinted by complex strike slip networks of veins and fractures as well as by the reactivation and onset of seismic scale faults strike slip structures belong to three distinct events the first one nw se oriented compression is probably associated with the oblique collision of the indian plate against the arabian platform during the late campanian to the mid eocene the second event e w oriented compression is likely to have been formed during the late oligocene middle miocene during uplift the last event ne sw oriented compression probably took place during the miocene pliocene structures of the first two strike slip events have the same orientation as seismic scale faults observed in the subsurface of oman and abu dhabi in addition increasing vein intensity towards the top of the autochthonous formations in the oman mountains as well as the small angle between conjugate vein sets indicate that high fluid pressures that are thought to be present during strike slip deformation

sheath folds as discriminators of bulk strain type abstract nested elliptical closures defining eye folds represent classic y z cross sections through highly curvilinear sheath folds generated during intense ductile deformation in metamorphic rocks systematic analysis of 1425 such eye folds based on our own field observations and examples from the published literature reveals distinct and consistent differences in ellipticites measured from the outer r yz to the inner most r y z elliptical rings of individual sheaths the variation in overall aspect ratios from outer to inner rings is defined as r where r r yz r y z and may display a relative increase or decrease in ellipticity to define cats eye r bulls eye r 1 fold patterns respectively layer thicknesses may also be measured along the y axis parallel to the axial surface t y and at 90 to this along the z axis t z to define the ratio of t yz sheath folds generated during broadly simple shear deformation k 1 display mean r yz 4 61 t yz 3 31 and cats eye folds r 0 69 sheath folds generated during general shear also display cats eye folds with identical mean r 0 69 values but greater thickness variations and elliptical ratios t yz 4 35 r yz 5 76 thus within both simple and general shear dominated deformations the overall variation in layer thickness t yz and ellipticity of eye folds r yz increases with increasing deformation and a greater component of pure shear whilst the r value remains constant and reflects original fold patterns sheath folds formed during constrictional k 1 deformation display markedly lower aspect ratios r yz 2 42 and thickness variations t yz 2 94 together with distinctive bulls eye folds r 1 23 these empirical relationships suggest fundamental and universal constraints on curvilinear fold generation across this broad spectrum of deformation types and allow sheath folds to act as both effective 95 consistent and robust discriminators of bulk strain type

the three dimensional shape and localisation of deformation within multilayer sheath folds abstract sheath folds are widely believed to develop by the passive geometric amplification of folds in which layering has no mechanical influence during non coaxial deformation where layering becomes rheologically significant then active sheath folds may form in which the inner nose of the sheath decouples along detachments and undergoes a translation relative to the outer folded layers that surround and envelope the nose we present a systematic 3 d analysis of multiple folded layer geometries in a serially sectioned natural sheath fold weak layers which are reactivated as detachments define different shaped sheath folds relative to other layers with the sense of cut off along detachments reversing across the axial surface as the inner fold nose has protruded into the surrounding sheath envelope detachment layers are more tightly folded meaning that such active sheath folds are non similar shapes the obliquely oriented bifurcating en echelon nature of the fold hinges developed in adjacent layers suggest that pre cursor folds formed with pronounced 3 d obliquity relative to the subsequent shear plane mineral lineations folded around sheath closures display asymmetric star burst patterns consistent with recrystallisation during active folding and hinge rotation we show that the eye fold shapes exposed in any 2 d y z slice can be used to predict the geometry of marker horizons back along the x axis in the third dimension this self similarity may be of value when tracing stratiform mineralised horizons in large scale sheath folds

tectonic setting origin and obduction of the oman ophiolite the semail ophiolite in the oman mountains is the world9s largest and best preserved thrust sheet of oceanic crust and upper mantle 10 000 km 2 550 km long 150 km wide it was emplaced onto the arabian continental margin during late cretaceous time the ophiolite originated 96 94 ma at a spreading center above a northeast dipping subduction zone associated with initiation of immature island arc tholeiitic lavas lasail arc at the highest levels of the ophiolite simultaneous underthrusting of triassic and jurassic mid oceanic ridge basalt and alkalic volcanic rocks beneath 12 km of upper mantle depleted harzburgites produced garnet clinopyroxene amphibolites formed at temperatures of 850 c dated as 95 93 ma subduction cannot have been initiated at a mid oceanic ridge otherwise the protolith of the amphibolites in the metamorphic sole would be the same age and composition as the ophiolite volcanic rocks above in the northern part of the oman mountains in the bani hamid area united arab emirates 870 m of granulite facies rocks enstatite spinel diopside quartzites garnet diopside wollastonite calc silicate marbles clinopyroxene bearing amphibolites were formed at temperatures similar to those of the garnet diopside amphibolites of the oman sole 800 850 c but at slightly higher pressures as much as 9 kbar they are interpreted as deeper level metamorphosed continental margin sedimentary rocks exhumed by out of sequence thrusting placing granulites over mantle sequence harzburgites during the later stages of obduction subduction of the arabian continental crust beneath the obducting semail ophiolite to 78 90 km depth has been proven by thermobarometry of the as sifah eclogites to 20 23 kbar in the eastern sector in the united arab emirates the subducted continental crust began to partially melt producing unusual biotite muscovite garnet tourmaline cordierite andalusite bearing granites that intrude the uppermost mantle sequence harzburgites and lowermost crustal sequence cumulate gabbros of the ophiolite we suggest that the entire leading northeast edge of the arabian plate was subducted beneath the ophiolite during the final stages of obduction leading to eclogitization of the crustal rocks higher temperatures and pressures in the united arab emirates sector possibly due to a thicker or double thickness ophiolite section led to blueschist amphibolite and granulite facies conditions in the metamorphic sole and crustal melting in the subophiolite basement produced leucocratic granites that intruded up as dikes through the obducted ophiolite a model for ophiolite obduction is presented which accounts for all the structural and metamorphic conditions reported from the oman mountains

active venting at the isis mud volcano offshore egypt origin and migration of hydrocarbons abstract the isis mud volcano is an active camembert like mud expulsion structure in the eastern nile deep sea fan area it has been investigated during the nautinil 2003 and mimes 2004 cruises carried out within the mediflux project active gas rich fluid venting occurs at the isis mud volcano as indicated by enhanced gas content in the sediments having a measured 7 5 mmol of methane per liter of wet sediment in the central area of the mud volcano in addition gas bubble expulsions have resulted in the formation of multiple hydrocarbon plumes in the water column with methane concentrations as high as 1550 nmol l compared to 1 nmol l for background levels in deep water in view of the stable carbon and hydrogen isotopic composition of methane 13 c 55 1 vpdb d 203 vsmow and of higher hydrocarbons 13 c of 30 3 26 1 28 4 and 25 0 vpdb for ethane propane i butane and n butane respectively their origin is mainly thermogenic these isotopic data also show that the wet compounds are co generated with oil and we suggest they predominantly originate from type ii kerogen source rocks of potentially variable maturity levels at the centre of the mud volcano the distinct kink observed in the pore water isotopic and dissolved species composition and its depth level change between subsequent cruises indicates a high frequency of fluid gas expulsion the seawater signature of the pore fluid in the upper part of the sediment column suggests that each expulsion is followed by a downward migration of overlying seawater such downward advection of bottom seawater may not only be related to the replacement of the ejected gas but also to the replacement of lower density pore fluid by bottom seawater this mechanism is thought to be a common feature at mud volcanoes and gas seepage sites in the peripheral zone pore fluid is at seawater concentration and isotopic composition down to a coring depth of 430 cmbsf we suggest that the deeper downward advection of bottom seawater is related to the less frequent fluid gas expulsion occurring at these sites compared to the centre sites in this paper we show that a combination of geochemical tools used for hydrocarbons and pore water geochemistry is a powerful approach to detect sources of ascending fluid and to reveal post eruptional fluidodynamic processes within mud volcanoes

mapping hydrocarbon induced mineralogical alteration in the northern tian shan using aster multispectral data seepage from hydrocarbon reservoirs can cause a number of chemical and or mineralogical changes in overlying rocks and soils these surface changes can be detected by remote sensing imaging systems the advanced spaceborne thermal emission and reflection radiometer aster is an advanced multispectral imaging system in the visible and near infrared vnir to shortwave infrared swir region band ratios of aster vnir and swir data to detect red bed bleaching and secondary carbonate formation induced by hydrocarbon seepage are proposed through analysis of the spectral properties of rock samples results show that aster band ratios of 2 1 and 4 8 can discriminate bleached red beds and secondary carbonate minerals due to hydrocarbon seepage in the northern tian shan they are in good agreement with mineral identification using x ray diffraction the ratio technique derived from aster data may provide a potential approach for hydrocarbon exploration in areas with sparse vegetation cover

gas geochemistry from conventional to unconventional domains abstract gas geochemistry is developing into a powerful tool to understand geological processes and affirm source origins of geo fluids major and trace gases including abundances and isotopes have shown considerable application in natural gas systems for example progress in unconventional gases such as shale gas tight gas and extreme conditions in the deep oceans represent more emerging areas and application of these novel gas related techniques examples where gas geochemistry continues to place key constraints on the origin and migration characteristics of natural gas the p t characteristics of fluids in both subaerial and deep geothermal reservoirs and the dynamics of the accumulation cycles to name but a few this volume will reflect this diversity in scope and application of gas geochemistry focusing on deeper and broader applications in unconventional domains of novel gas geochemical techniques and applications

a case of obduction related high pressure low temperature metamorphism in upper crustal nappes arabian continental margin oman p t paths and kinematic interpretation in the southeastern oman mountains the saih hatat tectonic window reveals arabian continental material beneath the oceanic sensu lato nappes i e the hawasina sedimentary units and the huge sumail ophiolite the northeastern internal half of the window suffered an intense deformation associated with a high pressure low temperature hp lt metamorphism approximately dated at 80 75 ma according to the available stratigraphie data after the deformation due to the absence of collision the obduction inherited structural and metamorphic pattern was virtually unmodified a metamorphic map is established based on mineral assemblages in metapelites and metabasites low grade assemblages occur in the highest units muscat nappes quryat unit characteristic minerals are femg carpholite lawsonite associated with kaolinite or pyrophyllite and locally sudoite in the metapelites while lawsonite and blue amphiboles are found in the metabasites high grade rocks outcrop in the deepest and easternmost units as sifah antiform and are typified by an epidote glaucophane bearing eclogite assemblage intermediate units hulw show assemblages of intermediate grade chloritoid schists and glaucophane bearing metabasites higher grade assemblages such as talc chloritoid were not found inverted gradients are observed locally in the muscat nappes pyrophyllitebearing units above kaolinite quartz bearing units and these are ascribed to late metamorphic thrust displacements which are demonstrated by microstructures a complex p t evolution is fairly well documented by the mineral assemblages prograde evolution in the subophiolitic continental rocks began with a rather hot gradient of about 30 35 c km with chloritoid growth in the higher units thereafter pressure increased with the temperature remaining constant or even decreasing chloritoid replaced by kaolinite oxides and carpholite growth in synkinematic conditions the peak p t conditions are close to 8 kbar 270 c for the muscat nappes and 11 kbar 400 c for the as sifah unit the corresponding surface related gradient is low 10 15 c km during the retrograde evolution pressure and temperature generally decreased concomitantly but in some of the upper units temperature remained constant or increased slightly for some time at which point sudoite growth from carpholite took place the metamorphic pattern and mineral evolution are interpreted in the framework of the late cretaceous obduction the already cold oceanic lithosphere was thrust upon a relatively hot thinned passive margin with coeval basaltic volcanism pressure progressively increased in the passive margin due to the wedge shape of the advancing ophiolite the maximum thickness of which was about 25 km in the as sifah area in this area the overburden was also attributable to the accumulation of continental material up to 5 km thick by means of a complex set of synmetamorphic often conjugated folds and thrusts the basal peridotites of the obducted slab were probably not hotter than 300 c during its thrusting upon the continental margin the temperature of the tectonic pile below the ophiolite remained low because it was thrust above more external and still colder continental areas late thrusting in the same southerly direction controlled the retrograde evolution together with erosional and gravity driven tectonic unloading

damage induced permeability changes in granite a case example at the url in canada abstract this paper concerns both in situ measurements of permeability and numerical modelling of changes in permeability induced by microcrack growth hydraulic experiments including pulse tests with the seppi probe are in progress these tests are a part of the tunnel sealing experiment tsx at the 420 m level of canada s underground research laboratory whose aim is to estimate the in situ hydraulic properties of lac du bonnet granite based on laboratory investigations the anisotropic damage model developed by homand et al comput geotech 22 1998 135 and recently reviewed by shao et al int j rock mech min sci 36 1999 1001 has been extended in order to account for changes in permeability induced by microcrack growth we have implemented this extension in the three dimensional code flac 3 d triaxial compression tests with permeability measurements carried out on two different granites provide a verification of the numerical implementation with a good agreement between experiments and predictions comparison between in situ measurements of permeability and predictions indicates that both the results of numerical modelling and observations are globally in agreement finally numerical modelling as well as the in situ measurements indicate that a depth of 50 70 cm is a good estimation of the extent of excavation disturbed zone in the tsx tunnel

structural evolution metamorphism and restoration of the arabian continental margin saih hatat region oman mountains abstract 170 m y of relatively stable passive margin sedimentation along the northern continental margin of arabia was abruptly terminated during the cenomanian turonian 95 ma when the oman continental margin collapsed and subsided rapidly aruma basin to accommodate obduction of the semail ophiolite complex and underlying thrust sheets haybi and hawasina complexes in the oman mountains the ophiolite was emplaced at least 200 km over the passive margin probably over 450 km in total from ne to sw during the later stages of obduction the leading edge of the continental margin was subducted to depths where carpholite bearing rocks 6 8 kbar blueschist 12 15 kbar and eclogite ca 20 kbar facies metamorphism formed in a ductile deforming ne dipping subduction zone along the northeastern margin of the saih hatat culmination in ne oman the mesozoic shelf carbonates are deformed by recumbent folding on all scales the present day structure is dominated by four sw vergent thrust slices in carpholite grade rocks at higher structural levels overlying lower units of crossite bearing blueschist hulw unit garnet glaucophane chloritoid blueschists and garnet clinopyroxene phengite glaucophane eclogites 15 20 kbar the largest shear zone separates 7 8 kbar hulw unit blueschists above from 12 15 kbar retrogressed eclogites and ca 20 kbar eclogites of the as sifah unit below further inboard sw a major shear zone separates the lower plate hulw blueschist facies rocks from the upper plate sedimentary rocks upper plate lower plate discontinuity which also show carpholite grade hp metamorphism towards the ne restoration of the entire saih hatat continental margin shows that the upper plate lower plate discontinuity cuts down section to the sw as far as the proterozoic hatat schists ne directed extensional crenulation schistosity and nne oriented stretching lineations in the eclogite and blueschist facies rocks are consistent with sw directed exhumation of footwall hp rocks ne facing folds and spectacular sheath folds with greatly attenuated limbs in the upper plate sediments are interpreted as antithetic backfolds with shortening in the upper plate balanced by the subduction of the lower plate consistent with a ne directed subduction of the continental margin rocks beneath the sw obducting ophiolite haybi and hawasina thrust sheets recent suggestions of a nascent sw directed subduction beneath the oman margin are not consistent with the sedimentary evolution of the shelf and slope carbonates or the geological structure of saih hatat two main phases of tectonic uplift of saih hatat and jebel akhdar are firstly the latest cretaceous ramp culmination associated with foreland propagating thrusts in the sw and backfolds in the ne and secondly post late eocene oligocene uplift by ca 2000 m

high resolution surveys along the hot spot affected galapagos spreading center 1 distribution of hydrothermal activity the spatial density of hydrothermal activity along most mid ocean ridges is a robust linear function of spreading rate or magmatic budget but extreme crustal properties may alter this relationship in 2005 2006 we tested the effect of thickened crust on hydrothermal activity using high resolution mapping of plumes overlying the hot spot affected galapagos spreading center from 95 to 89 42 w 560 km of ridge crest plume mapping discovered only two active high temperature vent fields subsequently confirmed by camera tows though strong plume evidence indicated minor venting from at least six other locations total plume incidence ph the fraction of ridge crest overlain by significant plumes was 0 11 0 014 about half that expected for a non hot spot mid ocean ridge with a similar magmatic budget plume distributions on the galapagos spreading center were uncorrelated with abrupt variations in the depth of the along axis melt lens so these variations are apparently not controlled by hydrothermal cooling differences we also found no statistical difference for a significance level of 0 05 in plume incidence between where the seismically imaged melt lens is shallow 2 0 56 km ph 0 108 0 045 and where it is deep 3 4 0 7 km ph 0 121 0 015 the galapagos spreading center thus joins mid ocean ridges near the iceland reykjanes ridge st paul amsterdam south east indian ridge and ascension mid atlantic ridge hot spots as locations of anomalously scarce high temperature venting this scarcity implies that convective cooling along hot spot affected ridge sections occurs primarily by undetected diffuse flow or is permanently or episodically reduced compared to normal mid ocean ridges

tubular folds and sheath folds definitions and conceptual models for their development with examples from the grapesvare area northern sweden abstract two parameters are used in the classification of highly non cylindrical folds the hinge line angle and the ratio of the length of the cone axis to that of the long axis of the cross section of the structure at the position where the hinge angle was measured if in a non cylindrical fold a cross section can be selected so that the hinge angle w measured where the cross section cuts the cone is less than 90 and the length of the cone axis x is more than a quarter of the length of the long axis y of the cross section the fold is a sheath fold a tight sheath fold with w x y 1 can be termed a tubular fold a tubular fold is thus an extreme type of sheath fold while sheath folds with w 20 but x y 0 25 but tubular folds from the grapesvare area comply to the definition given above and they occur in a structural setting that is consistent with the models described

maastrichtian to early tertiary stratigraphy and palaeogeography of the central and northern oman mountains abstract maastrichtian to tertiary sedimentary rocks outcrop extensively around the periphery of the oman mountains they form part of a geologically distinct suite of strata deposited after obduction of the semail ophiolite and thrusting of the hawasina and sumeini imbricates onto the eastern edge of the arabian plate the lithostratigraphy of maastrichtian and early tertiary rocks of the central and northern oman mountains is revised and a number of new formations are erected the proto oman mountains were emergent in the early maastrichtian and were subject to subaerial erosion and weathering nw and w of the mountains gradual subsidence followed during the maastrichtian allowing for formation of a transgressive onlapping sequence represented by the qahlah fluviatile to shallow marine terrigenous clastics and simsima shallow shelf carbonate formations more rapid subsidence ne of the mountains produced fan delta and submarine debris flow turbidite apron sequences comprising the al khawd and thaqab formations respectively a low angle unconformity separates tertiary strata from older units during the palaeogene basinal and slope facies with debris flows and turbidite sequences were deposited directly upon the unconformity surface in rapidly subsiding basins nw muthaymimah formation and nne ruwaydah formation of the oman mountains elsewhere shallow carbonate shelf facies were extensively developed in less rapidly subsiding areas during the palaeogene the palaeocene and early eocene is represented by the jafnayn limestone formation this is succeeded and overlapped by a variety of later eocene units ene and e of the mountains early eocene regression is marked by restricted facies of the rusayl formation overlying the rusayl formation are shallow open shelf limestones of the seeb formation which is rich in alveolinid and nummulitic foraminifera on the arabian side of the mountains the rusayl formation is not developed and the jafnayn formation is succeeded either by the seeb formation or fine grained faunally restricted limestones and marls of the fahud beds which represent intra shelf facies

the early ordovician middle shale member am3 of the amdeh formation and further evidence of conodont faunas from the sultanate of omanap heward et al tremadocian floian shallow marine deposits from oman the middle shale member of the amdeh formation is interpreted to be of early ordovician age based on its trace fossils stratigraphic context and a newly discovered fauna of conodonts the member abruptly overlies the lower quartzite member which may be early cambrian and passes gradationally upward into the upper quartzite member which is probably early middle ordovician the 542 5 m thick middle shale member can be divided into two parts a shaly lower part and a sandy upper part that contains an influx of heavy minerals bioturbation by marine trace fossils is one of the most obvious characteristics of the member the shales and sandstones are interpreted to be of cruziana and skolithos ichnofacies and represent shallow marine shelf shoreface beach and coastal deposits sparse shelly fossils occur in the sandy upper part principally bivalves inarticulate brachiopods ostracods and conodonts the small assemblage of conodonts includes elements interpreted to be tremadocian tetraprioniodus drepanoistodus drepanodus scolopodus tropodus semiacontiodus and teridontus and others which may be floian or ancestral forms of floian taxa balognathidae gen et sp indet a b and aff erraticodon no acritarchs have been recovered probably due to high temperatures experienced during burial to 6 km it is likely that the middle shale member is the seaward equivalent of the mabrouk and barakat formations and an outcrop gamma ray log supports such a correlation the trace fossils sedimentology conodont fauna and the general lack of macrofossils are in keeping with the regional tremadocian floian of the arabian margin of gondwana

synchronous formation of the metamorphic sole and igneous crust of the semail ophiolite new constraints on the tectonic evolution during ophiolite formation from high precision u pb zircon geochronology abstract the semail oman united arab emirates and other tethyan type ophiolites are underlain by a sole consisting of greenschist to granulite facies metamorphic rocks as preserved remnants of the underthrust plate sole exposures can be used to better understand the formation and obduction of ophiolites early models envisioned that the metamorphic sole of the semail ophiolite formed as a result of thrusting of the hot ophiolite lithosphere over adjacent oceanic crust during initial emplacement however calculated pressures from granulite facies mineral assemblages in the sole suggest the metamorphic rocks formed at 35 km depth and are too high to be explained by the currently preserved thickness of ophiolite crust and mantle up to 15 20 km we have used high precision u pb zircon dating to study the formation and evolution of the metamorphic sole at two well studied localities our previous research and new results show that the ophiolite crust formed from 96 12 95 50 ma our new dates from the sumeini and wadi tayin sole localities indicate peak metamorphism at 96 16 and 94 82 ma 0 022 to 0 035 ma respectively the dates from the sumeini sole locality show for the first time that the metamorphic rocks formed either prior to or during formation of the ophiolite crust and were later juxtaposed with the base of the ophiolite these data combined with existing geochemical constraints are best explained by formation of the ophiolite in a supra subduction zone setting with metamorphism of the sole rocks occurring in a subducted slab the 1 3 ma difference between the wadi tayin and sumeini dates indicates that in contrast to current models the highest grade rocks at different sole localities underwent metamorphism and may have returned up the subduction channel at different times

fluid sources and chemical processes inferred from geochemistry of pore fluids and sediments of mud volcanoes in the southern margin of the junggar basin xinjiang northwestern china understanding fluid sources water rock interactions and the biogeochemical processes involved in terrestrial mud volcanoes is necessary in order to predict the chemical processes most responsible for methane emissions to the atmosphere mud sediments ejected from the dushanzi and sikeshu mud volcanoes located along the southern margin of the junggar basin northwestern china were collected by hand core sampling in order to explore whether surface and subsurface geochemical processes occur in their fluids the ionic compositions of the pore fluids minerals and major elements of the ejected sediments and surface sediments were analyzed the pore fluids were mainly derived from ancient deeper sedimentary fluids which had mixed with meteoric surface water but altered by diagenesis processes relative to seawater the mud volcano pore fluids have higher ratios of na cl and li cl and lower ratios of k cl and mg cl the mud sediments are also enriched in illite chlorite and calcite but depleted in smectite in addition they are enriched in ca and mn followed by fe mg and p and depleted in si relative to the wall rocks these chemical and mineralogical changes in the mud sediments and pore fluids are related to diagenesis processes clay mineral dehydration mainly involving the conversion of smectite to illite released large amounts of water ion exchange among clay minerals increased na in the pore fluid water rock interaction increased fe and mn but decreased si in the mud sediments carbonate precipitation decreased ca2 and mg2 concentrations of the pore fluid but increased fe mg and p in the mud sediments these results indicate that the mud volcanoes system is continuously recharged from deeper sedimentary sources the difference in fluid and sediment geochemistry of the mud volcanoes can be ascribed to the different depths of the fluid and mud sources and the different diagenesis processes during the rising of fluid and mud

timing of the tianshan mountains uplift constrained by magnetostratigraphic analysis of molasse deposits abstract the tianshan mountains lie in the actively deforming part of the india asia collision zone the thrust faulting and folding of the neogene and quaternary sediments forming linear roughly east west anticlines at the northern and southern borders of the orogenic belts indicate crustal shortening and thickening in late cenozoic time detailed magnetostratigraphic studies of the molasse deposits of the folded neogene and quaternary strata in the northern edge of the tianshan mountains indicate that the onset of uplift occurred at 7 ma deposition of the thick conglomerates between 7 and 2 58 ma in the studied region was mainly in response to the tectonic uplift while the accumulation of the early pleistocene conglomerates xiyu formation was mostly controlled by both tectonics and climatic cooling our results indicate that the present high relief of the tianshan mountains is the result of two dominant phases of uplift occurring at about 7 2 58 ma and the early pleistocene

permeability tensor for discontinuous rock masses rock masses which commonly contain a large number of discontinuities are treated as homogeneous anisotropic porous media to formulate the corresponding permeability tensor this has been successfully achieved by introducing a symmetric tensor crack tensor which depends only on the geometry of the related cracks aperture size and orientation the principal directions associated with the symmetric crack tensor are coaxial with those of the permeability tensor the first invariant of the crack tensor is proportional to the mean permeability while the deviatoric part is related to the anisotropic permeability these results are well supported by numerical experiments on the permeability of cracked media by long remer wilson and witherspoon an actual rock mass moderately jointed granite was studied to see whether the crack tensor can be determined in situ stereology based on geometrical statistics provides a sound basis for determining the crack tensor in situ the crack tensor is obtained by

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

structure and metamorphism of blueschist eclogite facies rocks from the northeastern oman mountains the northern part of the saih hatat window oman shows high pressure metamorphic rocks derived from shelf sediments and pre premian continental basement and is atypical of sub ophiolite metamorphism elsewhere the high pressure rocks are divided into structural units originally bounded by foreland propagating thrusts formed during ophiolite obduction although now many contacts are backthrusts normal faults or extensional shear zones metamorphic breaks exist across many unit boundaries the deepest unit as sifah has eclogite facies assemblages in metabasites and metapelites which record evolution of p t conditions along a clockwise path culminating al 23 2 5kbar 540 75 c contrasting markedly with overlying units 5 10 kbar 200 500 c although separated by 40 ar 39 ar apparent ages our tectonic model relates all the high p units to a single convergent event in the late cretaceous the as sifah eclogites were exhumed in two stages i tectonic emplacement against other units at c 20 25 km depth and ii exhumation of the entire high p zone by culmination collapse after obduction

3d geometry and kinematic evolution of the wadi mayh sheath fold oman using detailed mapping from high resolution photography abstract the wadi mayh sheath fold in north eastern oman is one of the largest and best exposed sheath folds known and presents a unique opportunity to better understand this somewhat enigmatic style of deformation we undertook high resolution photographic surveying along wadi mayh to document the sheath fold in 61 georeferenced panoramic photomerges here we present ten such images that provide a structural interpretation of the sheath fold and surrounding structure we resolve this structure in a simplified three dimensional model and in two orthogonal cross sections and propose a kinematic evolution to explain the geometry the wadi mayh sheath fold is the most prominent example within what we suggest is a composite sequence of sheath folds which is itself enclosed within a ssw closing recumbent syncline at the base of the major saih hatat nappe sheath folding is accommodated within permian saiq formation limestones showing carpholite assemblages 6 8 kbar 275 375 c a major discontinuity separates this sequence from enveloping older rock units the sequence formed during progressive top to north ductile shearing as the overlying nappe migrated northwards with respect to the underthrusting hulw unit this process occurred during ssw directed exhumation of partially subducted continental crust in ne oman approximately 15 ma after obduction of the oman ophiolite initiated

crustal structure a key constraint on the mechanism of ultra high pressure rock exhumation abstract the distribution of ultra high pressure uhp metamorphic rocks demonstrates that burial to 100 km and rapid exhumation 1 cm a 1 of continental crust is a normal part of early 10 ma continental collision currently there is no comprehensive model for this fundamental tectonic process that also satisfactorily explains the upper crustal structures resulting from early collisional uhp rock exhumation characteristic features requiring explanation include structural domes that are cored by uhp nappes associated medium to high pressure nappes displaying a distinct pressure gap overlying lower grade rocks including suture zone ophiolites and coeval foreland directed thrust faults and syn exhumation normal faults we present a geodynamical model involving crustal burial and exhumation in a subduction channel below an accretionary wedge competition between down channel shear traction and up channel buoyancy forces expressed as the exhumation number e controls burial and exhumation leading to rapid up channel flow when e 1 exhuming uhp material forms a nappe stack and structural dome as it penetrates and destabilises the overlying wedge driving thrusting and extension this solution is compelling because it explains both the geology and the petrology of the tso morari and other uhp complexes and because it demonstrates that pulse like buoyant exhumation from deep in the subduction channel creates observed upper crustal structures this places constraints on the exhumation mechanism and provides a test of alternative models other proposed mechanisms such as continuous circulation in a lithospheric scale wedge or overpressured subduction channel predict different types of upper crustal structures and are therefore unsatisfactory explanations for early collisional exhumation of uhp terranes

sequence of thrusting and origin of culminations in the northern and central oman mountains abstract detailed mapping and structural analysis of three large scale culminations sumeini and asjudi half windows and haybi hawasina window in the oman mountains shows a considerably more complex history of deformation than a simple foreland or downward sequence of thrust development early thrusting processes tended to create a regular stacking order of imbricate slices and major thrust sheets complying with the rules of thrust propagation assembled progressively downwards and forwards in the direction of translation out of sequence thrusts can also be demonstrated in places by truncation of footwall structures folds imbricate slices etc gross strain differences between thrust sheets downward facing structures in footwall units and elimination of thrust sheets beneath late stage thrusts frequently cut up section through the previously assembled stack putting previously younger lower thrust sheets over previously older higher ones many of the culminations in the northern and central oman mountains were formed by ramping associated with this late stage leap frog rethrusting event

tibetan plateau aridification linked to global cooling at the eocene oligocene transition the eocene oligocene transition about 33 5 million years ago was a major global climate event the end of the eocene was unusually warm with no significant ice on antarctica but the oligocene saw the arrival of a permanent antarctic ice sheet two papers this week relate to the continental effects of this global change dupont nivet et al examined sedimentary records from the tibetan plateau and find a drop in atmospheric water which caused cooling and aridification coincident with antarctic cooling previous studies attributed this phenomenon to the rapid uplift of the tibetan plateau but this new work suggests that regional tibetan climate was influenced by global events in an unrelated paper on the same climate transition zanazzi et al explore the cooling in north america at the time using stable isotope measurements from fossil teeth and bones to create a proxy temperature record they find a large drop in mean annual temperature of 8 2 c a greater fall than seen in the oceans this continental transition may explain why many cold blooded reptiles and amphibians became extinct whereas mammals able to regulate their body temperature escaped relatively unscathed precisely dated evidence details that aridification on the tibetan plateau occurred at the time of the eocene oligocene transition in the marine records this suggests a direct link between the palaeontological and palaeoenvironmental changes recorded in continental asia at the time and global climate cooling continental aridification and the intensification of the monsoons in asia are generally attributed to uplift of the tibetan plateau and to the land sea redistributions associated with the continental collision of india and asia1 2 3 whereas some studies suggest that past changes in asian environments are mainly governed by global climate4 5 6 the most dramatic climate event since the onset of the collision of india and asia is the eocene oligocene transition an abrupt cooling step associated with the onset of glaciation in antarctica 34 million years ago7 8 9 however the influence of this global event on asian environments is poorly understood here we use magnetostratigraphy and cyclostratigraphy to show that aridification which is indicated by the disappearance of playa lake deposits in the northeastern tibetan plateau occurred precisely at the time of the eocene oligocene transition our findings suggest that this global transition is linked to significant aridification and cooling in continental asia recorded by palaeontological and palaeoenvironmental changes10 11 12 and thus support the idea that global cooling is associated with the eocene oligocene transition13 14 15 we show that with sufficient age control on the sedimentary records global climate can be distinguished from tectonism and recognized as a major contributor to continental asian environments

geometry and significance of internal windows and regional isoclinal folds in northeast saih hatat sultanate of oman saih hatat contains tiered sets of low angle structural breaks that reflect a complex stacking of sheets which requires multiple upward movement of units within an unstable orogenic wedge in a convergent setting early recumbent folds within the saih hatat window are subparallel to but cut by a major low angle contractional fault decollement that separates lower plate high pressure rocks some eclogites exposed in two windows hulw and as sifah windows from high pressure upper plate rocks containing carpholite and lawsonite parts of this decollement had been mapped or speculated upon to explain the variation in metamorphic grade across saih hatat upper plate fold nappes are controlled by the mapped decollement surface below the decollement sheath like lower plate closures formed independently in an intense zone of top to the northeast shearing eclogites occur within mafic boudins at the structurally lowest level of the retrograde lower plate shear zone this zone was responsible for the partial exhumation of the lower plate very early in the observed structural history and has a normal movement sense the two lower plate windows are essentially foliation domes reflecting fold interference between regional scale sheath like recumbent isoclines and more open upright northwest north and northeast trending fold sets the early upper plate fold nappes reflect a major top to the north or northeast movement of the rocks away from the oman margin at the same time the ophiolite was being emplaced over the top in the opposite direction top to the southwest or south south directed faulting and shearing is superimposed on the early recumbent folds in the mountain range mapped relationships and structural observations agree with bureau de recherches geologiques et minieres mapping that recognised fold nappes in this part of the oman mountains all of the mapped structures are associated with exhumation of the high pressure rocks making reconstruction of the margin during high pressure metamorphism problematic

an equivalent continuum model for coupled stress and fluid flow analysis in jointed rock masses to provide a set of governing equations for solving the coupled stress and fluid flow a rock mass which commonly contains a large number of geological discontinuities is treated as an anisotropic elastic porous medium with the corresponding elastic compliance and permeability tensors hydro mechanical equivalents to the discontinuous mass the hydromechanical equivalents with the special emphasis on the permeability tensor are formulated on the assumption that any crack can be replaced by a set of parallel planar plates connected by two springs two dimensional numerical analyses on seepage flow networks support the validity of the permeability tensor some field evidence is analyzed to examine the applicability of the present model for the practical purpose of rock hydraulics

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

a geochemical approach to earthquake reconnaissance at the baratang mud volcano andaman and nicobar islands abstract variations in the relative composition of constituent gases coming out of the mud volcano near jarwa creek in baratang island middle andaman are discussed on the basis of regional tectonic settings and seismo geochemical features the most abundant gas is ch4 55 7 vol followed by n2 32 2 o2 ar 9 9 co2 2 0 and he 0 2 concentration of the radioactive gas 222rn is relatively high 7500 bq m3 this paper discusses the experimental methods adopted to continuously monitor he ch4 co2 and 222rn with a view to identify pre seismic gas concentration anomalies associated with regional seismic occurrences results related to this gas geochemical monitoring are presented with a purpose to develop ability in ascribing a distinct geochemical anomaly to a particular seismic activity in the region

the geometry and topology of natural sheath folds a new tool for structural analysis abstract curvilinear sheath folds are classically depicted as displaying symmetrical geometries about two orthogonal mirror planes centred along the x y axial surface and the x z medial culmination depression surface which bisects the fold nose however 10 000 geometric analyses of minor folds and fabrics formed during ductile thrusting in the caledonides of northern scotland reveals that major dome and basin sheath folds can display distinct and predictable asymmetries across both axial and medial surfaces the strain is typically heterogeneous so that structural fabrics and younging evidence are preserved within sheath folds at varying stages of development this allows an analysis of the evolution of such structures from tongue folds to more extreme tubular forms geometric relationships between measured orientations of fold hinges axial planes extension lineations and foliations are compared on fabric topology plots ftps which provide an effective tool for monitoring planar and linear fabric rotations with increasing progressive non coaxial deformation they consistently display systematic variation from regions of lower to higher strain on passing from upper to lower fold limbs across major axial surfaces and on crossing medial surfaces from short to long hinge line segments axial and medial surfaces effectively therefore divide major sheath folds into quadrants with different amounts senses and combinations of planar and linear fabric rotation within each domain such heterogeneous deformation implies that models of intense non coaxial deformation uniformly affecting pre existing folds may overestimate bulk displacement and shear strain variable fold hinge line rotation about medial surfaces also provides an effective mechanism for the closure of major sheaths which may otherwise project for unfeasible distances in the x direction bedding cleavage intersections are developed at greater angles to the transport direction than fold hinges which they transect in a consistent and predictable sense thereby confirming the direction of fold rotation even in areas which lack information on fold facing in cross section asymmetric tear drop eyes indicate the sense of fold hinge line vergence whilst fold limb and hinge line asymmetry may be combined on 3 d vergence ranking and rotation grids which allow location and relative strain states of minor structures to be accurately predicted within the overall sheath framework systematic fabric analysis on ftps may be applied to the investigation of ductile deformation across a broad range of scenarios

characteristics of mixed sporopollen assemblage from sediments of dushanzi mud volcano in southern junggar basin and indication to the source of mud and debris ejecta in order to search for the source of muddy eruption debris a series of erupted mud samples were collected from a corn of the dushanzi mud volcanoes in southern junggar basin nw china and analyzed for palynological records two palynomorph groups were revealed in the mixed sporopollen assemblage from the erupted sediments according to their colors the light color group accounting for about 95 of the total was dominated by the chenopodiaceae and artemisia and in a color of faint yellow indicating an immature stage of organic matter evolution the dark color group was composed of cyathidites classopollis schizaeoisporites lygodiumsporites and rugubivesiculites in a color of brown yellow indicating a low maturity to maturity stage of organic matter evolution the palynomorph records suggested that most of the muddy debris ejecta of the dushanzi mud volcano might be sourced from the cenozoic deposits mainly the middle late miocene taxihe and dushanzi formations and a small portion likely from the lower cretaceous tugulu group in addition there is also a possibility that a little part of eruption debris is from the upper jurassic qigu formation the dushanzi anticline occurred strong extrusion and thrust faults in the late himalayan period and the oil and gas reservoirs were destroyed and resulted in eruption of the mud volcano in the dushanzi area