gondwana accretion tectonics and implications for the geodynamic evolution of eastern arabia first structural evidence of the existence of the cadomian orogen in oman jabal akhdar dome central oman mountains abstract this work describes two early cambrian folding events within cryogenian to earliest cambrian rocks of the western jabal akhdar dome ne oman this sequence is truncated at an angular unconformity and overlain by a permo mesozoic succession that is folded into a wide gentle anticline that differs in style and intensity of deformation from that below the unconformity an older paleozoic deformation d1 have been identified within limestone of the hajir formation in which f1 metric folds reflect ductile deformation affecting neoproterozoic cambrian rocks with low dip angle axial planes a younger event d2 has refolded the f1 folds with open to close f2 folds with sub vertical to steep axial planes dipping towards nnw and fold axes plunging either ene wards with 50 or sw wards with 30 at the northern and southern flanks of the jabal akhdar dome respectively the f2 folds have been discussed by previous authors as possibly hercynian in age while the f1 folds are here firstly presented revealing a uniform ne vergence of f1 folds after restoration at pre d2 geodynamic conditions first structural evidence of a tectonic event in eastern arabia dates between 542 and 525 5 ma d1 due to the convergence between arabia and microcontinents and or oceanic subduction of the proto tethys ocean d1 and d2 are related to ne sw and nw se main compressional directions respectively based on geometric and time considerations d1 correlates with the cadomian and d2 with the angudan orogenies our evidences directly question former discussions of the presence of the hercynian orogen in eastern arabia

reflectance of dispersed vitrinite in palaeozoic rocks with and without cleavage implications for burial and thermal history modeling in the devonian of rursee area northern rhenish massif germany abstract vitrinite reflectance is used as coalification parameter in coals and as maturity and palaeotemperature indicator in sedimentary rocks in high grade diagenetic rocks i e rocks at the boundary between diagenesis and metamorphism vitrinites become increasingly anisotropic therefore it has been suggested to study maximum minimum reflectance instead of mean reflectance for rocks which reached this stage in the present study vitrinite reflectance data from a folded sequence of the northern rhenish massif germany are combined with microtectonic study of thin sections in samples in which both bedding and cleavage are present we show that vitrinites in different microtectonic domains cleavage domains and microlithons show significant differences in both maximum vitrinite reflectance and vitrinite reflectance anisotropy this behaviour is due to a strong partitioning of deformation in cleavage domains as compared to microlithons so that vitrinite reflectance is controlled by the thermal and deformation history accordingly estimation of maximum palaeotemperatures during burial should be based on vitrinite reflectance measurements in microlithons unaffected by deformation after maximum burial based on this finding burial and temperature history of the rursee area in the eastern rhenish massif is reconstructed numerical simulations indicate a maximum burial at the siegen ems boundary of about 5000 m and a maximum burial temperature of about 220 c

maturation and bulk chemical properties of a suite of solid hydrocarbons abstract in this paper we present strong correlations of solid hydrocarbon reflectance shro to vitrinite reflectance vro and bulk chemical properties aromaticity tmax h c etc these correlations suggest that like kerogen in coals and sedimentary rocks solid hydrocarbons vary systematically during maturation as a consequence shro is especially useful as a maturity indicator in rocks lacking vitrinite such as pre devonian rocks and many organic rich marine rocks unlike other organic maturationv indicators the utility of solid hydrocarbons is not limited by botanical evolution but rather the generative potential of the petroleum system solid hydrocarbons also known as solid bitumen asphalt dead oil migrabitumen and pyrobitumen are genetically defined as solid phase accumulations of predominantly hydrocarbons produced by petroleum generation in source rocks they may occur over a range of concentrations in outcrop and well samples in all components of petroleum systems although accumulations of solid hydrocarbons from exhumed reservoirs are well reported the extent and utility of disseminated solid hydrocarbons in shales is less understood solid hydrocarbons are found in organic rich to very lean mature rocks as a residual product of generation disseminated solid hydrocarbons exhibit three optical forms anisotropic coked granular and relatively uniform homogenous only the homogenous solid hydrocarbons are recommended for correlation purposes with other thermal indicators

first indication of storegga tsunami deposits from east greenland a 2 73 m long sediment sequence from loon lake located at 18m a s l on outer geographical society o east greenland was investigated for its chronology and changes in physical and biogeochemical properties macrofossils and grain size distribution the predominance of marine fossils throughout the sequence dated by 14c ams to between 8630 and 7535 cal yr bp shows that the loon lake at that time was a marine basin which according to existing sea level curves was about 15 35 m deep the sequence mainly consists of fine grained homogeneous sediments which are interrupted by a 0 72 m thick sandy horizon with erosive basis and distinct fluctuations in the grain size distribution and in the physical and biogeochemical properties according to the radiocarbon dates this sandy horizon was deposited after 8500 8300 cal yr bp and is interpreted as originating from the storegga tsunami the record from loon lake provides the first indication of storegga tsunami deposits from east greenland copyright 2006 john wiley sons ltd

a geomorphological reconnaissance of the submarine part of the east rift zone of kilauea volcano hawaii more than half of the intensely active east rift zone of kilauea volcano crops out underwater along the crest of the submarine puna ridge i present multibeam bathmetry of the entire ridge near bottom photographic and sonar observations of the plunging crest of its deeper distal half and seismic profiles across the ridge tip and the adjacent structural moat analysis of large scale relief small scale topography and superficial rock types indicates that the rift zone is actively propagating across the moat but is probably a superficial structure that does not penetrate the underlying oceanic crust that its tip is covered with large lava flows erupted at high rates and is surrounded with extensive debris flow deposits and that the axial topography at depths of 2 4 km is dominated by gaping fissures and collapse pits showing a preponderance of intrusive rather than extrusive events some aspects of this central volcano rift zone such as its geometry at small lateral offsets resemble those at interplate rift zones along fast spreading mid ocean rises but the great contrast in lithosphere thickness results in fundamental structural differences

geochemical comparison of reservoir solid bitumens with diverse origins abstract geochemical and petrologic comparison of solid bitumens with various origins from reservoirs in zaire canada and kazakhstan were studied to provide insight into their formation processes and their physical and chemical properties results of this study can help develop methods for treatment and removal of solid bitumen and evaluating producibility of associated hydrocarbon fluids characterization of these solid bitumens reveals a wide range in quantity and composition of extractables soluble material and in solid bitumen reflectance which indicate significant differences in formation processes hydrocarbon source and thermal maturity the zaire and kazakhstan samples represent end members of the spectrum of solid bitumens studied solid bitumens from the motoba field zaire are highly extractable and low in thermal maturity 0 2 0 3 bitumen reflectance reservoir mixing of a cretaceous lacustrine sourced oil and a tertiary marine sourced oil of different thermal maturities appears to be responsible for their formation in contrast solid bitumens from the tengiz field kazakhstan are characterized by their extremely low extractables high bitumen reflectance 1 and low atomic h c ratios

guyot and seamount morphology and tectonics of the hawaiian emperor elbow by multi beam sonar abstract five guyots and five seamounts are shown from the southernmost end of the emperor chain an area called the hawaiian emperor bend or the milwaukee seamount group in the north central pacific ocean the data are from the u s naval oceanographic office navoceano multi beam survey files the bend is shown to occur over an area encompassing 260 km questions are raised as to the relative proximity of different flat top depths and formational possibilities in the light of the differing geomorphology on the features in addition there are two new features taish and go shirakawa seamounts and four additional new names of features are introduced antoku guyot toba guyot and genji and go sanj seamounts

the storegga slide tsunami comparing field observations with numerical simulations abstract deposits from the storegga tsunami have been found in coastal areas around the norwegian sea and north sea from the northeast coast of england to beyond the arctic circle in northern norway the tsunami deposits reach onshore elevations of 10 12 m above sea level of their time in western norway 3 6 m in northeast scotland and above 20 m on the shetland islands these elevations are compared with surface wave elevations derived from a numerical simulation of the storegga slide a good agreement is obtained for a retrogressive slide that descends at 25 30 m s and that has short time lags of 15 20 s between each individual slide block

green mosses date the storegga tsunami to the chilliest decades of the 8 2 ka cold event abstract chlorophyll in dead plants ordinarily decomposes completely before permanent burial through exposure to light water and oxygen here we describe 8000 year old terrestrial mosses that retain several percent of its original chlorophyll the mosses were ripped of the land surface carried 50 100 m off the norwegian coast of the time and deposited in depressions on the sea floor by the storegga tsunami a little of the chlorophyll survived because within hours after entraining it the tsunami buried the mosses in shell rich sediments these sediments preserved the chlorophyll by keeping out light and oxygen and by keeping the ph above 7 three factors known to favour chlorophyll s stability because the green mosses were buried alive their radiocarbon clock started ticking within hours after the storegga slide had set off the tsunami radiocarbon measurement of the mosses therefore give slide ages of uncommon geological precision and these together with a sequence of ages above and below the boundary date the storegga slide to the chilliest decades of the 8 2 ka cold event at 8120 8175 years before ad 1950 north atlantic coastal and fjord climatic records claimed to show evidence of the 8 2 cold event should be carefully examined for possible contamination and disturbance from the storegga tsunami

two new microscopic ductile kinematic indicators from the oman mountains abstract two novel shear sense indicators were observed in different tectonic settings the first one pdt occurs in a calcmylonite associated with extension the second one dragged intergrowths was discovered in mylonitized plagiogranite trondhjemite dikes with vertical to sub vertical foliation and strike slip deformation within harzburgite the calcite mylonite displays shear planes characterized by parallel laminae which differ in composition they contain light colored calcite while darker impurities consist of hematite goethite and rutile pdts are associated with microthrusts the thrusts form an acute angle with the mylonitic foliation thrusting between two microthrusts created pull aparts filled with drusy calcite the shear sense of the pdts is revealed by 1 shortening and related imbrication of the thrust laminae 2 pull apart structures and 3 drag folds at either end of the microthrusts the indicated shear is confirmed by independent evidences one pdt is up to 0 5 mm wide and 1 mm long the mylonitized plagiogranite contains a k feldspar porphyroclast 2 mm long featuring dragged k feldspar quartz intergrowth due to rotation during high temperature conditions bending occurs on either end of the object the original orientation of the intergrowth was subparallel to the foliation as a result an s shaped object formed the deduced shear sense is independently confirmed

maturity and petrography of bitumens in the carboniferous of ireland abstract a set of bitumen samples from the carboniferous of ireland shows a general trend of increasing maturity southwards across the island this trend is consistent with a similar southwards increase in maturity exhibited by the host rocks vitrinite reflectance reflecting proximity to the hercynian orogen to the south of ireland increasing maturity is reflected by decreasing h c ratio and increasing reflectance bireflectance and anisotropy and is accompanied by heavier carbon isotope composition for the most mature samples bitumen reflectance is the most sensitive parameter and ranges up to 3 6 most of the bitumens occur in hydrothermal mineral veins and were generated locally by the passage of hot fluids through carboniferous shales and limestones some bitumens contain inclusions of metalliferous and other inorganic minerals high sedimentation rates during the carboniferous caused hydrocarbon generation before the late carboniferous hercynian orogeny so that the bitumens experienced thermal overprinting by the orogeny and show the same maturity trend as the country rocks anisotropy is exhibited by all bitumen samples with reflectances of 2 0 or over mesophase textures occur in bitumens with reflectances over 3 0 including one case where fluid inclusion homogenization temperatures in coeval minerals calcite and fluorite are less than 200 c

hydrocarbon generation and migration under a large overthrust the carbonate platform under the semail ophiolite jebel akhdar oman abstract the natih b source rock of the jebel akhdar dome in the oman mountains hosts at least three different generations of solid bitumen this study presents detailed analyses of thermal maturity based on solid bitumen reflectance rock eval pyrolysis fourier transform infrared spectroscopy and raman spectroscopy of matrix and solid bitumen the natih b source rock was sampled in different valleys wadis around the jebel akhdar dome detailed petrography of organic material was conducted by optical and scanning electron microscopy sem the petrographic data was used to calibrate an integrated thermal basin model of the wadi nakhr area due to ophiolite obduction the natih b source rock was buried to 7 4 to 8 km and a maximum temperature of c 240 c hydrocarbon generation and associated primary migration was burial induced and took place from 78 to 66 ma with solid bitumen precipitation in the source rock a resulting high reflective solid bitumen generation reflects temperatures of deepest burial in the order of 225 c to 240 c based on an elaborated paragenetic sequence two other solid bitumen generations were linked to two oil migration events taking place during uplift 55 50 ma and 48 45 ma after deepest burial around 65 ma

lateglacial and holocene relative sea level changes and first evidence for the storegga tsunami in sutherland scotland we reconstruct one of the longest relative sea level rsl records in northwest europe from the north coast of mainland scotland using data collected from three sites in loch eriboll sutherland that we combine with other studies from the region following deglaciation rsl fell from a late glacial highstand of 6 8 m od ordnance datum c mean sea level at c 15 k cal a bp to below present then rose to an early holocene highstand and remained at c 1 m od between c 7 and 3 k cal a bp before falling to present we find no evidence for significant differential holocene glacio isostatic adjustment between sites on the northwest lochinver loch laxford north loch eriboll and northeast wick coast of mainland scotland this suggests that the region was rapidly deglaciated and there was little difference in ice loads across the region from one site at the head of loch eriboll we report the most westerly sedimentary evidence for the early holocene storegga tsunami on the scottish mainland the presence of the storegga tsunami in loch eriboll is predicted by a tsunami wave model which suggests that the tsunami impacted the entire north coast of scotland and likely also the atlantic coastline of northwest scotland

lithological dependency and anisotropy of vitrinite reflectance in high rank sedimentary rocks of the ibbenburen area nw germany implications for the tectonic and thermal evolution of the lower saxony basin abstract covering a depth interval of 1200 m thirty one rock samples were collected from a well drilled in the beust field of the ibbenburen anthracite mine lower saxony basin nw germany these rock samples consist of high rank coals anthracites claystones siltstones and sandstones of pennsylvanian age analytical methods include the measurement of random vitrinite reflectance vr r rotational reflectance vr rot as well as maximum and minimum reflectances vr max and vr min enabling the evaluation of the lithological influence on vitrinite reflectance as well as the indication of tectonic stresses in the lower saxony basin by applying the ris reflectance indicating surface analysis method this study shows that not only due to the high rank of the studied samples and associated anisotropic character but also due to lithological dependency a partially significant scatter of measured vr r can be observed the scatter in coals is significantly less than in other sedimentary rocks e g standard deviation in coals can be up to 7 less than in siltstones the expected increase of standard deviation with increasing rank and accordant anisotropy was not observed for vr r but rather for vr max with the exception of coals displaying a relatively constant and low deviation throughout the depth maturity interval mean vr r values of coals differ from those of other sedimentary rocks at equal depths vr r measured in claystones is consistently higher compared to associated coal seams and can be elevated by up to 10 silt and sandstones always display lower vr r with differences of up to 16 at very high levels of thermal maturity vitrinite reflectance depends not only on maximum paleotemperature but also on lithology leading to differences in pressure propagation and thus deformation additionally radioactive trace elements in coals and organic matter rich claystones provide a local secondary heat source 40 k and 232 th are preferentially bound to clay particles which are enriched in the studied claystones and depleted in the silt and sandstones possibly leading to higher vitrinite reflectance observed in the claystones ris analysis shows a predominantly negative biaxial distribution indicating the absence of thermal overprinting by a possible intrusion bramsche massif during the late cretaceous which would have induced a uniaxial distribution instead this implies in addition to vertical stresses due to depositional loading the presence of a secondary stress field not perpendicular to bedding which is related to the inversion of the lower saxony basin this information presents in combination with previous basin modeling results additional evidence for deep subsidence with subsequent uplift being the cause for the present day maturity patterns observed in the lower saxony basin

the anatomy of a pull apart basin seismic reflection observations of the dead sea basin the dead sea basin dsb located along the african arabian plate boundary constitutes a good example of a pull apart basin because of its large dimensions its structural simplicity and its active subsidence a coherent three dimensional picture of the dsb has been constructed on the basis of analysis of seismic stratigraphy together with the interpretation of previously published geological and geophysical data despite the large known vertical offsets across the basin deformation takes place mainly along the transverse and longitudinal faults and the intervening sediments are relatively undeformed and are hardly tilted comparison between e w seismic lines indicate that the basin has widened by the collapse and tilting of arcuate blocks from the western margin but that its original shape is a full graben the southern and central parts of the basin are divided into equidistant segments 20 30 km long by transverse faults activity along these faults commenced only during the pleistocene long after the dead sea strike slip fault system was formed and migrated northward with time a likely scenario for the development of the dsb is one in which the basin grows northward with time by a simultaneous propagation of the southern strand of the dead sea fault and a retardation of the northern strand

polyphase thermal evolution in the infra cambrian ara group south oman salt basin as deduced by maturity of solid reservoir bitumen petrographic and organic geochemical analyses on solid reservoir bitumen from the late precambrian to early cambrian ara group indicate polyphase thermal evolution in the south oman salt basin sosb the ara group constitutes a complex petroleum system in the deep subsurface 3 5 km of interior oman salt diapirs encase isolated partly highly overpressured carbonate bodies intra salt stringers which represent a predominantly self charging hydrocarbon system a large number of stringer cores show that reservoir quality is decreased by the presence of solid reservoir bitumen by using different microscopy techniques this solid reservoir bitumen has been identified within pores pore throats and microfractures of the carbonates solid bitumen reflectance measurements brr were converted to vitrinite reflectance vrr using a new improved calibration vitrinite reflectance geothermometry shows that maximum paleo temperatures have a highly heterogeneous distribution paleo temperatures of 380 c were obtained from coke like solid reservoir bitumen which most likely formed from thermal cracking of oil in our model this process is related to hydrothermal fluids deriving from deeper pre salt strata of the sosb which entered the intra salt carbonate stringers during times of basement tectonic activity via hydrofractures this caused the formation of high maturities pyrobitumens in close vicinity to the fractures and precipitation of migrabitumens with increasing distance to the ht source which is supported by the geochemical composition of the solid reservoir bitumens the influx of these fluids into the carbonate stringers is considered to represent a major contribution to their strong overpressures 2007 elsevier ltd all rights reserved

microfractures within the fault damage zone record the history of fault activity 1 for faults without sedimentary covers there is no robust method to obtain paleoseismic data that is crucial for the prediction of future damaging earthquake events sudden failure along faults during earthquakes induces off fault damage surrounding such basement faults we showed that the quaternary active fault has the damage zone characterized by a fracture density that decays exponentially with distance from the fault for both healed and open microfractures in contrast quaternary inactive faults contain only healed microfracture damage zone cross cutting relationships between microfractures and a minimum healing temperature of 100 c suggest that healed microfractures formed before and at deeper levels than did unhealed microfractures the damage zone defined by open microfractures reflects the recent fault movement during exhumation associated with erosion and regional uplift from the maximum depth at which microfractures may remain unhealed microfracture analysis can therefore be used to examine the history of basement fault activity

thermal metamorphism of bitumen in archean rocks by ultramafic volcanic flows abstract thermally metamorphosed bitumen samples associated with an archean ultramafic volcanic sequence near timmins ontario canada were examined using reflected and transmitted light microscopy and x ray diffraction the bitumen occurs in aphanitic to fine grained chemical and clastic meta sediments intercalated with the volcanic flows and in derived metasedimentary xenoliths engulfed in the flows this thermally altered bitumen was apparently derived from biogenic organic carbon in the original archean sediments the organic components of the samples consist of epi impsonite to cata impsonite and pyrolytic carbons the latter occur in conical layered radial and spherulitic forms the maximum temperature of formation of the pyrolytic carbon has been estimated at 700 c which is consistent with its occurrence in xenoliths in these high temperature 1300 1500 c volcanic flows

constrictional extensional tectonics in the northern oman mountains its role in culmination development and the exhumation of the subducted arabian continental margin

evidence for a tsunami from a mesolithic site in inverness scotland temporary excavations at castle street inverness described by wordsworth 1985 proceedings of the society of antiquaries of scotland 115 89 103 disclosed a mesolithic horizon covered by a layer of marine sand the sand layer is similar in appearance and age to a sand layer frequently found in coastal sediments in eastern scotland and recently attributed to a tsunami generated by submarine sliding on the continental slope off storegga south west norway which took place c 8000 5000 radiocarbon years bp there is some evidence that the tsunami may have affected other mesolithic sites and it may ultimately prove a useful chrono stratigraphic marker

the minimal response to contact metamorphism by the devonian buchan caves limestone buchan rift victoria australia abstract a 2 2 m thick late eocene dike that intruded the devonian buchan caves limestone near murrindal victoria has produced a narrow contact aureole only centimeters wide in the adjacent host rock mean solid bitumen reflectance ranges from about 2 4 to 2 7 and shows little change up to 6 m away from the dike contact carbon and oxygen isotope values also show little change except at the dike contact the most detectable response of the rock to contact metamorphism is the proportion of solid bitumen grains with finely granular mosaic structure increase towards the dike also under cathodoluminescence cl excitation the host rock is initially observed to be recrystallized to a uniform bright orange color by 1 cm away from the contact however cl shows preservation of sharp boundaries in finely zoned burial cements a regional study of thermal maturation and a geothermometer based on solid bitumen reflectance indicate paleotemperatures near 200 c were widespread in the buchan rift during peak burial near the time of the devonian tabberabberan deformation the lack of response of the buchan caves limestone to contact metamorphism is attributed to 1 prior heating to near 200 c and 2 the fact that the dike intruded into cool near surface low porosity rocks which may have been in the vadose zone

evidence for three north sea tsunamis at the shetland islands between 8000 and 1500 years ago abstract coastal fen and lake deposits enclose sand layers that record at least three holocene tsunamis at the shetland islands the oldest is the well known storegga tsunami ca 8100 cal yr bp which at the shetlands invaded coastal lakes and ran up peaty hillsides where it deposited sand layers up to 9 2 m above present high tide level because sea level at ca 8100 cal yr bp was at least 10 15 m below present day sea level the runup exceeded 20 m in two lakes we also found deposits from a younger tsunami dated to ca 5500 cal yr bp the sediment facies are similar to those of the storegga tsunami rip up clasts sand layers re deposited material and marine diatoms runup was probably more than 10 m yet another sand layer in peat outcrops dates to ca 1500 cal yr bp this sand layer thins and fines inland and was found at two sites 40 km apart and traced to ca 5 6 m above present high tide the oldest tsunami was generated by the storegga slide on the norwegian continental slope we do not know what triggered the two younger events

absolute ages of multiple generations of brittle structures by u pb dating of calcite direct dating of brittle structures is challenging especially absolute dating of diagenesis followed by a series of superimposed brittle deformation events we report 22 calcite u pb ages from tec

geochemical study of calcite veins in the silurian and devonian of the barrandian basin czech republic evidence for widespread post variscan fluid flow in the central part of the bohemian massif abstract carbonate fracture cements in limestones have been investigated by fluid inclusion and stable isotope analysis to provide insight into fluid evolution and deformation conditions of the barrandian basin silurian devonian of the czech republic the fractures strike generally north south and appear to postdate major variscan deformation the most common fracture cement is calcite that is locally accompanied by quartz natural bitumen dolomite mn oxides and fluorite three successive generations of fracture filling calcite cements are distinguished based on their petrographical and geochemical characteristics the oldest calcite cements stage 1 are moderate to dull brown cathodoluminescent fe rich and exhibit intense cleavage subgrain development and other features characteristic of tectonic deformation less tectonically deformed variable luminescent fe poor calcite corresponds to a paragenetically younger stage 2 cement first melting temperatures t e of two phase aqueous inclusions in stages 1 and 2 calcites are often around 20 c suggesting that precipitation of the cements occurred from h 2 o nacl fluids the melting temperature t m has values between 0 and 5 8 c corresponding to a low salinity between 0 and 8 9 eq wt nacl homogenization temperatures t h from calcite cements are interpreted to indicate precipitation at about 70 c or less no distinction could be made between the calcite of stages 1 and 2 based on their fluid inclusion characteristics in some stage 2 cements inclusions of highly saline up to 23 eq wt nacl brines appear to coexist with low salinity inclusions the low salinity fluid possibly contains na k mg and ca chlorides the high salinity fluid has a h 2 o nacl cacl 2 composition blue to yellow green fluorescing hydrocarbon inclusions composed of medium to higher api gravity oils are also identified in some stages 1 and 2 calcite cements stage 1 and 2 calcites have 18 o values between 13 2 and 7 2 pdb the lower range of the calculated 18 o values of the ambient fluids 3 5 to 2 7 smow indicate precipitation of these cements from deeply circulating meteoric waters the presence of petroleum hydrocarbon inclusions in some samples is interpreted to reflect partial mixing with deeper basinal fluids the paragenetically youngest stage 3 calcite cement has only been encountered in a few veins these calcites are characterised by an intensely zoned luminescence pattern with bright yellow and non luminescent zones inclusions of mn oxides and siliceous sinters are commonly associated with stage 3 calcite which is interpreted to have precipitated from shallower meteoric waters regional structural analysis revealed that the calcite veins of the barrandian basin belong to a large scale system of north south trending lineaments that run through the territory of the czech republic the veins probably reflect episodes of fluid migration that occurred along these lineaments during late stages of the variscan orogeny

petrology and k ar ages of dredged samples from laysan island and northampton bank volcanoes hawaiian ridge and evolution of the hawaiian emperor chain summary the hawaiian emperor volcanic chain is made up of at least 107 indentifiable shield volcanoes chase and others 1970 bargar and jackson 1974 clague and others 1980 and is the longest linear island and seamount chain in the pacific fig 1 beginning at the active volcanoes kilauea and mauna loa on the island of hawaii this chain of volcanoes extends west northwestward along the hawaiian ridge for a distance of 3 500 km where it turns northward and continues another 2 300 km as the emperor seamounts ending near the intersection of the aleutian and kurile trenches it is now thought that the hawaiian emperor chain was formed as the pacific lithospheric plate moved first northward and then northwestward relative to the hawaiian hot spot a more or less stable melting anomaly in the asthenosphere and that the bend in the chain reflects a major change in pacific plate motion several mechanisms have been proposed to explain the hawaiian and other hot spots including a propagating fracture betz and hess 1942 jackson and wright 1970 diapiric upwelling along a line of structural weakness green 1971 mcdougall 1971 thermal morgan 1972a 1972b or chemical anderson 1975 plumes of gravitationally unstable material rising from the deep mantle shear melting coupled with thermal feedback shaw 1973 and geographically stabilized by gravitational sinking of refractory residua shaw and jackson 1973 and extrusion induced by lateral motion along plate boundaries handschumacher 1973 despite the variety of dynamic models proposed there has yet to be devised a definitive experiment to test any of them all these mechanisms are however encompassed by the general or kinematic hot spot hypothesis which when used in the broadest sense implies neither mechanism nor excess heat

properties of thermally metamorphosed coal from tanjung enim area south sumatra basin indonesia with special reference to the coalification path of macerals abstract thermally metamorphosed tertiary age coals from tanjung enim in south sumatra basin have been investigated by means of petrographic mineralogical and chemical analyses these coals were influenced by heat from an andesitic igneous intrusion the original coal outside the metamorphosed zone is characterized by high moisture content 4 13 11 25 wt and volatile matter content 40 wt daf as well as less than 80 wt daf carbon and low vitrinite reflectance vr max 0 52 0 76 those coals are of subbituminous and high volatile bituminous rank in contrast the thermally metamorphosed coals are of medium volatile bituminous to meta anthracite rank and characterized by low moisture content only 80 wt daf and vitrinite reflectance vr max 1 87 6 20 all the studied coals have a low mineral matter content except for those which are highly metamorphosed due to the formation of new minerals the coalification path of each maceral shows that vitrinite liptinite and inertinite reflectance converge in a transition zone at vr max of around 1 5 significant decrease of volatile matter occurs in the zone between 0 5 and 2 0 vr max a sharp bend occurs at vr max between 2 0 and 2 5 above 2 5 the volatile matter decreases only very slightly between vr r 0 5 and 2 0 the carbon content of the coals is ascending drastically above 2 5 vr r the carbon content becomes relatively stable around 95 wt daf vitrinite is the most abundant maceral in low rank coal 69 6 86 2 vol liptinite and inertinite are minor constituents in the high rank coal the thermally altered vitrinite composes 82 4 93 8 vol mosaic structures can be recognized as groundmasss and crack fillings the most common minerals found are carbonates pyrite or marcasite and clay minerals the latter consist of kaolinite in low rank coal and illite and rectorite in high rank coal change of functional groups with rank increase is reflected most of all by the increase of the ratio of aromatic c h to aliphatic c h absorbances based on ftir analysis the oxygen index values of all studied coals are low oi 2 g toc and the high rank coals have a lower hydrogen index t max increases with maturity 420 440 c for low rank coals and 475 551 c for high rank coals based on the above data it was calculated that the temperature of contact metamorphism reached 700 750 c in the most metamorphosed coal

dating tsunami deposits present knowledge and challenges abstract dating approaches for fine sediment tsunami deposits can be divided into two categories 1 dating directly using materials from within a tsunami deposit and 2 dating indirectly using materials from above and below it for the former optically stimulated luminescence osl dating has a possible advantage in that is can directly date the burial age of sediments laid down by a tsunami however because of methodological limitations osl dating cannot always provide a reliable age although 14c and u th dating of reworked material from within a tsunami deposit are possible means of determining the age of the event the results merely represent a maximum age of deposition for these reasons dating is commonly achieved indirectly from 14c dates taken from samples in sections immediately above and below a tsunami deposit however indirectly dated results do not provide a precise timing of the event therefore there are distinct limitations in the ability to obtain high precision dating of past tsunamis recent methodological developments including the application of bayesian statistical analysis to radiocarbon dating results and the selection of appropriate dating materials has significantly improved the accuracy of age determination by reducing errors this review presents several methodological improvements that have enhanced tsunami deposit age estimation the most important points for a more precise tsunami age estimation are the numbers of 14c samples dated coupled with the use of bayesian statistical analysis these points are applicable not only to tsunami deposits but also to many other past geohazard events

cumulative right lateral fault slip rate across the zagros makran transfer zone role of the minab zendan fault system in accommodating arabia eurasia convergence in southeast iran the zendan minab zone is the transition zone between the zagros collision to the west and makran subduction to the east it is also linked to the north with the nayband gowk fault system that bounds the lut block to the east the total convergence rate between arabia and eurasia is estimated to range between 23 and 35 mm yr 1 in a nne trending direction the deformation through the minab zendan system is accommodated within two fault systems the western n160 e trending minab zendan fault system and the eastern north south sabzevaran jiroft fault system the study area is characterized by a well defined succession of quaternary deposit levels the age of these deposits was estimated by archaeological data regional palaeoclimate correlations and constrained by additional in situ10be dating in another paper in this study these deposits exhibit offsets both lateral and vertical that are evaluated by satellite image analysis and gps profiles thanks to offsets and ages the strike slip rates associated with the minab zendan and the sabzevaran jiroft fault systems are calculated to be 5 1 1 3 or 6 6 1 5 and 6 2 0 7 mm yr 1 respectively these results allow an evaluation of the velocity vector of the musandam peninsula oman with respect to the lut block of 11 4 2 0 or 12 9 2 2 mm yr 1 in a n10 15 e direction close to the gps estimates this study also constrains the in plane slip rates for each fault previous works indicate that the zagros accommodates only 10 mm yr 1 of shortening while 10 mm yr 1 should be accommodated by the alborz mountains in northern iran this last 10 mm yr 1 may be accommodated through the nayband gowk system and the east iranian ranges implying that the two fault systems constituting the zagros makran transfer zone have different geodynamic roles the western minab zendan fault system links the makran and zagros deforming zones whereas the northwestern jiroft sabzevaran fault system is transmitting the deformation to the nayband gowk system and then to the alborz ranges the presence of another such strike slip zone within the makran seems to indicate that the accommodation zone between the zagros and makran is wide of the order of 400 km we interpret this deformation pattern that accompanies the genesis of the immature transform zone by a flexure of the slab under the zagros makran transfer zone instead of a tear in the slab that may be expected to induce a sharper transition zone

moss growth patterns and timing of human exposure to a mesolithic tsunami in the north atlantic the storegga tsunami triggered 8150 yr ago by one of the largest submarine slides on earth flooded margins of the north sea and the norwegian sea that were occupied by mesolithic peoples sand deposits of storegga age overlie the remains of coastal settlements in norway and scotland the resulting casualties however depend on the season when the tsunami struck human exposure would have been least in summer and early autumn when mesolithic peoples went to the mountains to hunt reindeer the hunters returned to the coast in late autumn to settle into their winter quarters here we use moss stems to show that the storegga tsunami happened in late autumn the storegga tsunami deposits contain samples of the moss hylocomium splendens some of these stems retain green color and chlorophyll that imply burial alive h splendens has a characteristic growth cycle where new segments branch off from previous year s growth the storegga mosses have segments more mature than those of modern july and august samples but as mature as those from october through december the enormous storegga tsunami thus occurred late enough in the year to have reached a large fraction of the people then inhabiting western norway and northeast scotland for those who survived the tsunami the loss and destruction of dwellings boats equipment and supplies must have made the following winter very difficult

quantification of loss of calcite pyrite and organic matter due to weathering of toarcian black shales and effects on kerogen and bitumen characteristics abstract comparison of geochemical data on posidonia shale early toarcian from a shallow unweathered core and from adjacent weathered exposures of the same fades was performed results revealed that quantitatively the most affected petrographic constituent is pyrite and that organic matter and carbonate were also altered by weathering due to this process of weathering the bulk composition of organic matter especially the molecular composition of soluble organic matter and the fluorescence colour of organic particles are changed estimates of weathering rates reveal that the annual release of sulphur and organic carbon from black shales may significantly add to anthropogenic pollution

geography and history of the louisville hotspot chain in the southwest pacific the louisville ridge is a 4300 km long late cretaceous and cenozoic hotspot chain the south pacific equivalent of the hawaiian emperor chain its northwestern end is being consumed by the tonga kermadec subduction zone but seabeam and magnetic mapping shows that the chain still includes more than 60 major volcanoes of both normal and reversed polarity distributed along a 75 km wide band that can be fitted to small circles about three successive poles of pacific plate hotspot rotation this band obliquely crosses fracture zones of the eltanin system but there is little interaction and no evidence of any genetic connection between the two structures forty of the louisville volcanoes grew above sea level and are preserved as high latitude i e coral free guyots they are spaced less than 100 km apart along most of the chain but there are none within 750 km of the inferred present location of the hotspot beneath a swell at the southeast end of the chain the rate of volcano building by the louisville hotspot declined sharply about 20 m y ago after being remarkably constant at 3 4 103 km3 m y for the previous 50 m y and none of the louisville volcanoes built during the past 10 12 m y the time of most profuse hawaiian volcanism has reached sea level however a seamount from which pleistocene lavas were dredged rises to within 540 m of the sea surface from the crest of the hotspot swell at 50 5 s 139 2 w guyot heights demonstrate that a hotspot swell several hundred meters high has persisted throughout the known life of the chain and sometimes had an isostatic depression on its loaded crest the depths of guyot shelf breaks increase systematically to the northwest from 530 to 2100 m proportional to the square root of volcano age with some scatter and tilting caused by plate boundary tectonism and local isostatic subsidence and uplift

the holocene storegga slide tsunami in the united kingdom all currently known sites in the united kingdom with evidence for the holocene storegga slide tsunami are described information on the altitude distribution stratigraphical context age particle size profile and microfossil characteristics of the deposits is presented the tsunami involved a greater area than previously described reaching a coastline over 600 km long the ubiquitous sand layer which forms the main deposit associated with the event is shown to exhibit a consistent morphology and a particle size profile marked by fining upwards sequences an analysis of new and previously published radiocarbon dates indicates that from evidence in the united kingdom the event took place sometime around 7100 radiocarbon years bp 7900 calibrated years bp a new isobase model for mainland scotland and adjacent areas providing a preliminary estimate of land uplift since the tsunami is presented the model estimates contemporary sea surface level offshore at 14 m below the present day mean high water spring tides tsunami sediment run up is greatest in inlets where it reaches at least 25 m on shetland and at least 5 m along the mainland coastline to the south and run up of the tsunami would have exceeded these values the tsunami sediments identified here are considered particularly valuable as a synchronous marker horizon

the sedimentology of middle holocene tsunami facies in northern sutherland scotland uk abstract lagoonal sediments attributed to the main holocene marine transgression in strath halladale northern sutherland contain a complex coarser layer believed to have been deposited during the tsunami associated with the second storegga slide off south west norway the coarser sequence is dated at between 7590 50 and 7290 50 radiocarbon years bp 6507 6260 cal bc and 6228 6029 cal bc detailed stratigraphical analysis has determined a distinctive suite of sedimentary sub units within the coarser layer in marked contrast to the sediments which occur above and below a pronounced erosional unconformity with the underlying sediments is recorded with the base of the tsunami layer characterised by eroded material from the underlying peat the presence of a mixed diatom assemblage although fragmentary indicates a chaotic accumulation of the deposit with all habitats represented variations in particle size within the sequence disclose striking similarities with those from contemporary tsunami deposits the run up of the tsunami sediments is calculated at a minimum of 4 6 m this is the first occasion on which a deposit of the second storegga slide tsunami has been found outside the north sea basin and indicates that the area affected by the tsunami may have been larger than has been previously described

the influence of solid reservoir bitumen on reservoir quality 1 reservoir bitumen precipitates in pore systems from the alteration of trapped or migrating oil in carbonate and siliciclastic reservoirs reservoir bitumen is not readily identified on typical log suites where it is read as open porosity which has hampered its broad recognition as a reservoir altering cement when present as a solid it can be as influential on reservoir quality as carbonate silica or authigenic clay cements and should therefore be evaluated as part of the diagenetic evolution of any pore system whenever encountered five morphotypes of reservoir bitumen have been identified and named droplets carpets peanut brittle vesicular and digitate data from east texas gulf coast and west african examples indicate that reservoir bitumen can significantly reduce total effective porosity permeability can be significantly reduced by restricted or closed pore throats and by fines migration even when bitumen occurs in only moderate amounts the occurrence and distribution of bitumen on well field and regional scales can range from uniform and predictable to irregular and unpredictable but mappable through examination of core and cuttings within a trap bitumen can cause heterogeneity and form permeability barriers not related to depositional facies or pre bitumen diagenesis and reservoir quality it economic importance must be recognized when reservoir parameters are adversely affected impacting reserves calculations recovery factors and secondary recovery programs on a regional scale predictive models can be developed to determine the areas of a trend or portions of a stratigraphic section that are most likely to be affected and these models can be incorporated with other data for evaluating expected reservoir quality in regional play assessments

low temperature recrystallization in calcite mechanisms and consequences vein calcite dominated fault rocks collected from several locations show evidence for intense intracrystalline plasticity and interface twin and grain boundary mobility leading to dynamic recrystallization of calcite at temperatures 150 250 c significantly below those at which these features are commonly anticipated these observations require a reappraisal of calcite deformation at low temperature particularly the capability for dynamic recrystallization in the apparent absence of significant thermally activated recovery processes the cyclic introduction of coarse grained calcite veins is observed to be essential for the initiation of intracrystalline deformation and associated dynamic recrystallization the introduction of veins generates an essentially monomineralic rock of a grain size larger than the protolith as a result the mylonitization does not occur within a given protolith but rather in the introduced secondary calcite through hall petch type grain size dependent dislocation interactions stress is locally increased and the resulting increase in dislocation densities promotes grain boundary migration the recognition that nominal high temperature creep processes and associated microstructures can occur outside their expected temperature range has implications for fault rheology strength and fault permeability and porosity

postobductional extension along and within the frontal range of the eastern oman mountains abstract the oman mountains formed by late cretaceous obduction of the tethys derived semail ophiolite this study concerns the postobductional extension on the northern flank of the mountain belt nine sites at the northern margins of the jabal akhdar nakhl and saih hatat domes of the eastern oman hajar mountains were investigated the northern margins are marked by a system of major interconnected extensional faults the frontal range fault while the vertical displacements along the saih hatat and westerly located jabal nakhl domes measure 2 25 6 25 km 0 5 4 5 km and 4 7 km respectively it amounts to 1 5 km along the jabal akhdar dome extension had started during the late cretaceous towards the end of ophiolite emplacement two stages of extension can be ascertained late cretaceous to early eocene and probably oligocene at the eastern part of the frontal range fault system wadi kabir and fanja graben faults of similar strike along the intervening and differently striking fault segments at sad and sunub the same two stages of deformation are deduced the first stage is characterized again by extension the second stage is marked by dextral motion including local transtension probable oligocene extension affected the batinah coast fault while it also affected the wadi kabir fault and the fanja graben it is unclear whether the western portion of the frontal range fault also went through two stages of deformation bedding parallel ductile and brittle deformation is a common phenomenon hot springs and listwaenite are associated with dextral releasing bends within the fault system as well as a basalt intrusion of probable oligocene age a structural transect through the frontal range along the superbly exposed wadi bani kharous jabal akhdar dome revealed that extension affected the frontal range at least 2 5 km south of the frontal range fault also here bedding parallel shearing is important but not exclusive a late cretaceous thrust was extensionally reactivated by a branch fault of the frontal range fault extension may be ductile limestone mylonites ductile and brittle ooid deformation boudinaged belemnite rostra shear bands or brittle extension is heterogeneously distributed within the frontal range extension is mainly related to orogenic gravitational collapse of the oman mountains collapse may have been associated with isostatic rebound and rise of the two domes in the western part of the study area the frontal range fault has a listric morphology it is probably horizontal at a depth of 15 km below the batinah coastal area the fault seems to use the clay and tuff bearing aruma group as shear horizon the depth of 15 km may coincide with the brittle ductile transition of quartz and feldspar rich rocks close to this depth the listric batinah coast fault curves into the frontal range fault extension along the frontal range and batinah coast faults probably reactivated preexisting late cretaceous thrust faults during post late eocene time the latter fault is likely mechanically related to the wadi kabir fault via the fanja graben fault and the sunub fault segment listwaenite and serpentinite cluster preferably around the extensional faults the semail gap probably functioned as a sinistral transform fault or fault zone during the permian

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

estimating original thickness and extent of the semail ophiolite in the eastern oman mountains by paleothermal indicators abstract the oman mountains preserve permo mesozoic sedimentary rocks of the arabian passive margin that were overridden during late cretaceous time by deep water sediments of the hawasina units and by the semail ophiolite a portion of the neo tethyan oceanic crust and upper mantle passive margin sequences are exposed in the jabal akhdar culmination jac and in the jabal salakh range at the oman mountains thrust front samples of these sequences were investigated by x ray diffraction of the clay size fraction to evaluate the thermal evolution of the subophiolite rocks and estimate the thickness and extent of the obducted ophiolites the sedimentary succession from the northern flank of the jac shows a clay mineral assemblage characterized by long range ordered mixed layer i s with an illite content between 85 and 92 and the occurrence of pyrophyllite and or paragonite suggesting maximum paleotemperatures between 150 and 200 c in deep diagenetic conditions on the southern flank of the jac temperature dependent clay minerals indicate maximum paleotemperatures ranging between 120 and 150 c indicating a reduced ophiolite thickness towards the south ooid strain analyses of the subophiolite rocks from the northern flank of jac show a component of flattening and stretching in the z x plane as a result of plastic deformation and pressure solution on the southern flank such ductile deformation is absent suggesting a brittle rheology for the subophiolite carbonates and a reduced overburden 1d thermal modeling reveals that the sub ophiolite units of the jac were overthrust by 4 5 km thick semail ophiolite and hawasina units during the coniacian and exhumed since the campanian the subophiolite rocks of the jabal salakh range were buried under 1 35 km of synobduction clastics and overthrust by 2 km thick hawasina units suggesting a decrease of the thickness of allochthonous units from ne to sw consistent with strain analysis and their direction of emplacement

late cretaceous late turonian coniacian and santonian petroleum source rocks as part of an oae tarfaya basin morocco abstract late turonian coniacian and santonian source rock samples from a recently drilled well tafaya sondage no 2 2010 in the tarfaya basin were analyzed for quantity quality maturity and depositional environment of the organic matter om to our knowledge such a thick sequence of organic matter rich turonian to santonian source rocks was investigated in that great detail for the first time organic geochemical and organic petrological investigations were carried out on a large sample set from the 200 m thick sequence in total 195 core samples were analyzed for total organic carbon corg total inorganic carbon contents and total sulfur ts contents rock eval pyrolysis and vitrinite reflectance measurements were performed on 28 samples chosen on the basis of their corg content non aromatic hydrocarbons were analyzed on selected samples by way of gas chromatography flame ionization detection gc fid and gc mass spectrometry gc ms the organic matter rich carbonates revealed a high source rock potential representing type i kerogen and a good preservation of the organic matter which is mainly of marine phytoplankton origin hi values are high 400 900 mg g corg and in a similar range as those described for more recent upwelling sediments along the continental slope of north africa ts corg ratios as well as pristane over phytane ratios indicate variable oxygen content during sediment deposition all samples are clearly immature with respect to petroleum generation which is supported by maturity parameters such as vitrinite reflectance 0 3 0 4 tmax values 401 423 c production indices s1 s1 s2 0 1 as well as maturity parameters based on ratios of specific steranes and hopanes

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

multiphase structural evolution of a continental margin during obduction orogeny insights from the jebel akhdar dome oman mountains the structural evolution of the carbonate platform in the footwall of the semail ophiolite emplaced onto the passive continental margin of arabia helps to better understand the early stages of obduction related orogens these early stages are rarely observable in other orogens as they are mostly overprinted by later mountain building phases we present an extensive structural analysis of the jebel akhdar anticline the largest tectonic window of the oman mountains and integrate it on different scales outcrop observations can be linked to plate motion data providing an absolute timeframe for structural generations consistent with radiometric dating of veins top to s overthrusting of the semail ophiolite and hawasina nappes onto the carbonate platform during high plate convergence rates between arabia and eurasia caused rapid burial and overpressure generation and migration of hydrocarbons and bedding confined veins but no major deformation in the carbonate platform at reduced convergence rates subsequent tectonic thinning of the ophiolite took place above a top to nne crustal scale ductile shear zone deforming existing veins and forming a cleavage in clay rich layers in early campanian times ongoing extension occurred along normal to oblique slip faults forming horst graben structures and a precursor of the jebel akhdar dome campanian to maastrichtian this was followed by ne sw oriented ductile shortening and the formation of the jebel akhdar dome deforming the earlier structures thereafter exhumation was associated with low angle normal faults on the northern flank of the anticline we correlate the top to nne crustal scale shear zone with a similar structure in the saih hatat window to develop a unified model of the tectonic evolution of the oman mountains

solid bitumen in calcite veins from the natih formation in the oman mountains multiple phases of petroleum migration in a changing stress field abstract solid bitumen in calcite veins in natih limestone on the southern flank of the jebel akhdar anticline provide evidence for at least two previously unrecognized petroleum migration events in the oman mountains we present field observation of bituminous calcite veins combined with microscopy using highly polished thin sections this allows imaging of solid bitumen in reflected light and study of its microstructural context in transmitted light straight and en echelon black impregnated bedding normal natih a calcite veins strike 110 they formed as one of the earliest structures in an extensional stress regime at the end of cretaceous turonian santonian either by flexure of the arabian plate wasia aruma break or by subsidence during subduction the veins always contain planar arrays of small during the first migration event microfracturing during obduction of the semail ophiolite and emplacement of the hawasina thrust sheets in santonian campanian times formed pathways for oil into the veins mosaic type solid bitumen formed during further vein growth it has a higher solid bitumen reflectance br r 3 40 3 76 combined with a high optical anisotropy compared to the underlaying thermally overmature natih b source rock br r 3 10 3 14 the higher reflectance of mosaic type solid bitumen is interpreted to result from deformation and does not reflect maximum burial temperatures which are inferred to have been about 225 c the second migration event is indicated by low reflective homogeneous type solid bitumen with palaeotemperatures br r 0 86 0 92 about 145 c lower than maximum burial it occurs along pressure solution seams which cross cut the veins showing that this is the latest event in the paragenetic sequence interpreted to have formed after lateral intraformational oil migration from the active natih oil kitchen located approximately 40 km sw of the study area during doming and uplift of the oman mountains in oligocene to pliocene times

gravity profiles across the samail ophiolite oman four hundred and sixty gravity stations have been established over the samail ophiolite and adjacent units exposed in the oman mountains the bouguer anomaly pattern follows more or less parallel to ophiolite exposures along the coastal areas the bouguer anomaly values range from 20 to 140 mgal and increase northward four gravity profiles across the ophiolite are correlated with known geology and structure the main gravity profile extending 325 km northward from ibra to muscat and into the gulf of oman shows two positive bouguer anomalies 85 over the southern folded ophiolite nappe and 110 mgal near the shoreline at muscat that are associated with two nappes of tabular form the nappes are nearly continuous and there is no evidence that they are rooted in the mantle the gravity high across the southern nappe is centered over the axis of the synform maximum nappe thickness its position over the gabbro peridotite contact rather than over the peridotite suggests extensive serpentinization of the peridotite at the southern end of the profile in the ibra dome area the negative bouguer anomaly 10 to 15 mgal is interpreted as an infracambrian salt piercement similar to those in the zagros fold belt geologic modeling of the main gravity profile provides a good correlation in terms of known thicknesses of the mappable ophiolite units the nature of the gravity anomaly across the continental margin indicates a transition from 42 km thick continental crust to a thinner 16 18 km oceanic crust the two gravity profiles in the north oman region show a doublet of positive residual bouguer anomalies 50 to 90 mgal the anomalies correlate well with imbricated ophiolite exposures a result of low angle thrusting caused by strong compressive forces in the absence of imbricate thrusting the gravity profile in the central region has only one large positive residual bouguer anomaly 130 mgal the anomalies of all the four profiles are further analyzed to elucidate the nappe transport distances

guyots of the mid emperor chain mapped with multibeam sonar abstract bathymetry of seven of the middle emperor chain guyots from u s naval oceanographic office multibeam narrow beam swath mapping surveys is presented these data are contoured at a 100 fm interval using different theories on formation juxtaposed with the accurate bathymetry of this chain tectonic possibilities are shown for changes in plate direction and conduit activity fluctuations the range for one complete pulse of this activity is shown to be 280 nm 518 km for the emperor chain

west northwest directed obduction of the batain group on the eastern oman continental margin at the cretaceous tertiary boundary the batain coast area in eastern oman is dominated by allochthonous permian to late maastrichtian sedimentary and volcanic rocks batain group unconformably overlain by neoautochthonous tertiary sediments the allochthonous rocks of the batain coast were previously attributed to the hawasina complex the permian to coniacian santonian sedimentary infill of the neo tethyan hawasina basin off northern oman previous structural interpretations suggested that the batain group along with the hawasina complex and the semail ophiolite was obducted in the coniacian to campanian from ne to sw onto the northern oman continental margin results of our work in the batain area differ from previous interpretations with most significant differences concerning timing and direction of obduction our results show that wnw directed tectonic movements formed a fold and thrust belt and led to the obduction of allochthonous rocks onto the east oman continental margin during latest maastrichtian earliest paleocene times this is coeval with emplacement of ophiolitic fragments along the eastern coast of oman eastern ophiolite belt but is about 15 20 myr later than emplacement of hawasina complex and semail ophiolite in northern oman postemplacement structural evolution during the tertiary involved intraplate extension possibly reflecting the red sea gulf of aden opening and late tertiary shortening related to convergence between arabia and eurasia late tertiary contractional deformation resulted in refolding of the batain nappes and in folding of the overlying tertiary sediments a palinspastic reconstruction of the batain area indicates that the permian to upper cretaceous sediments were formerly deposited in the batain basin a part of the proto indian ocean along the present day eastern oman margin this leads us to propose that permian breakup of gondwanaland created both continental margins of oman and led to the opening of two major basins the neo tethyan hawasina basin in the north and the proto indian ocean batain basin in the east the latter separating arabia from greater india

distribution of seamounts in the north atlantic the paucity of multi narrow beam bathymetric data in the ocean basins has meant that previous studies of seamount distribution and size have relied on wide beam echo sounder data and small1 8 amounts of seabeam multi narrow beam data since 1967 however the us naval oceanographic office has been collecting multi narrow beam bathymetric data9 14 here we use an extensive collection of such data to locate over 800 seamounts in the north atlantic we find that ridge crest generated seamounts are formed only between iceland and the hayes fracture zone where there are contributions of plume material to the mid ocean ridge plumbing system it appears that in the slow spreading north atlantic an injection of plume material into the ridge plumbing system is necessary for the formation of seamounts at the ridge crest

oily old ores evidence for hydrothermal petroleum generation in an archean volcanogenic massive sulfide deposit oil is formed in some modern seafloor vent systems after rapid thermal maturation of sedimentary organic matter by hydrothermal fluids although most of this petroleum escapes into the ocean some hydrocarbons may be trapped as fluid inclusions in hydrothermal precipitates or as bituminous residues in cavities however the geological record lacks evidence of this phenomenon which is unfortunate because it could be significant for understanding the history of petroleum genesis the processes of hydrothermal mineralization and perhaps the origin and early evolution of life from the pilbara craton of australia we report the discovery of pyrobitumen and oil in an early archean ca 3235 ma deep sea volcanogenic massive sulfide deposit the oil occurs in fluid inclusions within hydrothermal barite and pyrobitumen is intergrown with polymetallic sulfides petrographic textures show that the oil was emplaced and thermally altered coked before late stage sulfide mineralization the results demonstrate that subseafloor hydrothermal petroleum generation was active during the early archean possibly providing an energy and carbon source for a subsurface microbiota metabolizing hydrothermal sulfur species

tectonic evolution of the intra uplift vigodi gugriana khirasra netra fault system in the seismically active kachchh rift basin india implications for the western continental margin of the indian plate abstract the e w striking kachchh rift basin krb at the western continental margin of indian plate is located in the northern part of gujarat state india krb has undergone polyphase deformation owing to changing stress field since late triassic we establish the kinematic framework along the nw striking intra uplift vigodi gugriana khirasra netra fault system vgknfs located at the western part of the krb the vgknfs consists of 0 25 50 km long sub parallel striated reactivated dip slip faults a total of 1150 fault slip data consisting of fault planes and striations attitude were recorded from 66 sites including a single site with systematic joints slip sense of faults was determined by documenting kinematic indicators paleostress analysis was carried out using win tensor t tecto faultkin and sg2ps to compare and validate the results the chi square statistical analysis was undertaken to evaluate how relevant are paleostress analysis results to the present day compressional stress field geophysical investigations were conducted at selected sites using ground penetrating radar gpr to understand the shallow subsurface geometry and trace the continuity of faults buried below patchy alluvial cover 15 17 m long 2d gpr cross sections were recorded across faults using monostatic antenna of 200 mhz frequency two major deformation events d1 and d2 are determined in the present study the extension event d1 shows w and nw nnw extension during late triassic to late cretaceous it occurred during the rift phase of krb in response of the break up of gondwanaland the latest event d2 shows nne ne compression from late cretaceous up to the present it is interpreted to have developed during post rift inversion phase induced by collision of the indian plate with the eurasian plate at 55 ma

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

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

origin of intraplate volcanoes from guyot heights and oceanic paleodepth the height of a guyot as measured from the surrounding regional sea floor to the vol cano s slope break records the water depth at the time the guyot submerged thus guyot heights may be used as indicators of the paleodepth of the surrounding ocean floor we compile data on the heights of 68 intraplate guyots and atolls in the pacific ocean as well as 46 volcanic islands in the pacific atlantic and indian oceans we find that guyot heights generally increase with the age of the lithosphere upon which they werc cmplaced although therc is a large amount of scattcr in nearly all cases seamount height and thus seafloor paleodepth is less than expzcted of normal seafloor these results suggest that most of the volcanoes in this study formed on anomalously shallow seafloor consistent with formation at hotspots to characterize thermal anomalies associ ated with these hotspot swells we model guyot heights by calculating the isostatic uplift predicted for normal lithosphere that has been partly reheated and is underlain by anomalously hot mantle this model is able to explain the anomalous water depth at most of the seamounts with hotspot thermal anomalies of 100 30o0c the heights of a few volcanic chains however are not anomalously low suggesting that these volcanoes are not associated with hotspots in addition the observed trend of hawaiian emperor guyot heights as well as the subdued morphology and gravity signature of the oldest emperor seamounts supports our hypothesis that cretaceous age meiji seamount may have formed on or near a spreading center

morphostructural study and type of volcanism of submarine volcanoes over the pitcairn hot spot in the south pacific undersea volcanoes found at about 80 km southeast of the island of pitcairn are believed to be the manifestation of a hot spot activity located near 129 30 w 25 10 s along the strike of the mururoa gambier pitcairn volcanic alignment hydrothermal activities and recent volcanic flows were observed on the two largest 20 km in basal diameter and shallowest 60 m and 450 m depth volcanoes more than twenty other smaller volcanic edifices 0 25 made up of ancient morb type tholeiitic rocks are inferred to be inherited from the epr axial regions the shallow volcanic activity which occurred on the two largest edifices are classified as 1 reactive eruptions with hydromagmatic activities giving rise to volcanic ejecta bombs xenoliths and ash and 2 quiet eruptions which formed pillows and or lobated lavas and large massive flows intrusives dyke and sill were observed cutting through the volcanic ejecta near the summit 500 m depth of the seamounts the general structural orientations of the rift zones recognized from the bathymetry of individual volcanoes n160 180 n80 n30 and n120 are comparable to those observed in the society and austral hot spot regions these orientations were inferred as corresponding to the structural discontinuities of the ancient oceanic crust and to the regional stress field of the pacific plate rock samples from the pitcairn region consist of alkali basalts basanites trachyandesites and trachytes which are closer in chemical composition to some of the volcanics from the society rather than to those from the austral hot spot regions

posterosional volcanism in the cretaceous part of the hawaiian hotspot trail multibeam bathymetry and seismic reflection profiling shows the cretaceous products of the hawaiian hotspot to be a ridge of coalesced guyots that prolong the n nw trend of the more isolated paleocene emperor seamounts a 10 000 km2 plateau detroit plateau where the trail changes strike to nw and the obruchev rise hotspot ridge which extends to the kamchatka trench the northernmost guyots were submerged and tilted southeast by the load of new shield volcanoes added to the end of the chain then secondary volcanism built small cones on their summit platforms and in a gap between two guyots dredged rock samples and the distribution of the cones indicates that on one guyot these submarine eruptions were in the alkalic postshield stage of hawaiian volcanism and at another were probably in the alkalic rejuvenated stage seamount building eruptions at detroit plateau produced lavas nepheline melilitites that belong geochemically to the alkalic rejuvenated stage and are very similar to pleistocene lavas in the hawaiian islands however these eruptions postdated passage off the hotspot plume by a much longer time than the 0 5 2 5 m y observed in the hawaiian islands and were probably initiated by different tectonic processes

the storegga slides evidence from eastern scotland for a possible tsunami abstract the second storegga slide on the continental slope off western norway has been dated at between 8000 and 5000 yrs b p a prominent sand layer in flandrian holocene deposits along the coast of eastern scotland and dated at approximately 7000 yrs b p may have been deposited by a tsunami generated by the slide the altitude and stratigraphy of the layer allow estimates to be made of the magnitude of the earthquake which initiated the slide

propagation of the storegga tsunami into ice free lakes along the southern shores of the barents sea this paper is part of anders romundset s doctoral thesis which is available in munin at http hdl handle net 10037 2703

observations on gulf of alaska seamount chains by multi beam sonar abstract geomorphic and age data are presented for the dellwood denson dickins giacomini and ely seamounts the tsimshian seachannel and the southern juan de fuca ridge with brown bear bear cub grizzly bear and cobb seamounts formational speculations extrapolated to a regional scale allow the strikes and outer limits of the seamount chains to be interpreted six of these chains are shown in the gulf of alaska none of which conform to the pratt welker or kodiak bowie in the literature different strikes show the chains plate to have rotated 23 about 17 m y ago morphology also shows that there are four less guyots in the gulf than previously thought and that at least in the gulf of alaska guyot heights do not necessarily reflect sealevel during erosion

metamorphic evolution of a very low to low grade metamorphic core complex danubian window in the south carpathians the danubian window characterized by diagenetic to low greenschist facies conditions at a high thermal gradient is evidently of great interest for methodological studies because high metamorphic thermal gradient conditions during low grade metamorphism have received little attention so far the general increase in metamorphic grade from sw to ne in the danubian window is indicated by mineral parageneses studies as well as by illite kubler index ki measurements and organic matter reflectance omr for the first time this study distinguishes between metamorphic conditions related to jurassic ocean floor cretaceous nappe stacking post collisional accommodation and syn kinematic getic detachment metamorphism and cooling after oligocene exhumation the occurrence of the prehnite pumpellyite facies in the severin cosustea units in the southeastern area is the result of cretaceous metamorphism remnants of ocean floor metamorphism prevailed the highest pressure is constrained by the upper stability limit of prehnite to be at around 4 0 kbar the danubian units situated within the diagenetic zone were not below 200 8c due to epidote formation the ki omr and mineral data indicate diagenetic conditions assuming temperatures between 200 and 250 8c pressures between 1 8 and 2 6 kbar were calculated using kinetic and numerical maturity models orogenic collisional cretaceous peak pressure conditions of 4 0 1 0 kbar are found in the danubian nappes not altered by a subsequent syn detachment metamorphic overprint highest temperatures in chloritoid schists and epidote hornblende bearing mylonites have been inferred for samples from the northern border of the danubian window between 300 and 400 8c along a synto post detachment retrograde pressure path post dating the chloritoid formation the occurrence of clinozoisite chlorite quartz suggests temperatures 300 8c in the northwest while the association andalusite quartz and biotite muscovite indicates temperatures between 370 and 400 8c at 3 5 kbar in the northeast it is demonstrated that the slope of the regression lines between ki and omr data gives valuable qualitative information about the relative magnitudes of p and t the slope of the regression line for the danubian window samples indicates normal heat flow conditions during nappe stacking and hyperthermal conditions during the formation of the getic detachment high thermal gradient conditions can easily be explained by partly isothermal decompression during the getic detachment event the elevation of the geotherm being caused by crustal thinning and rapid exhumation of the danubian units probably also a higher heat flux prevailed at the end of the getic detachment at a time when the retrograde chloritoid decomposition reactions took place documenting late stage ht greenschist facies metamorphism from siegesmund s fugenschuh b froitzheim n eds tectonic aspects of the alpine dinaridecarpathian system geological society london special publications 298 281 315 doi 10 1144 sp298 14 0305 8719 08 15 00 the geological society of london 2008 location of the study area and

ninigi and godaigo seamounts twins of the emperor chain by multi beam sonar abstract bathymetry is shown for two heretofore unknown seamounts in the emperor chain ninigi and godaigo seamounts they were discovered by the u s naval oceanographic office and named by the author very accurate bathymetry and positioning allows a clarification of previous mid chain bathymetric charts and an explanation of hot spot multiple conduit flow

prodigious submarine landslides on the hawaiian ridge the extensive area covered by major submarine mass wasting deposits on or near the hawaiian ridge has been delimited by systematic mapping of the hawaiian exclusive economic zone using the side looking sonar system gloria these surveys show that slumps and debris avalanche deposits are exposed over about 100 000 km2 of the ridge and adjacent seafloor from kauai to hawaii covering an area more than 5 times the land area of the islands some of the individual debris avalanches are more than 200 km long and about 5000 km3 in volume ranking them among the largest on earth the slope failures that produce these deposits begin early in the history of individual volcanoes when they are small submarine seamounts culminate near the end of subaerial shield building and apparently continue long after dormancy consequently landslide debris is an important element in the internal structure of the volcanoes the dynamic behavior of the volcanoes can be modulated by slope failure and the structural features of the landslides are related to elements of the volcanoes including rift zones and fault systems the landslides are of two general types slumps and debris avalanches the slumps are slow moving wide up to 110 km and thick about 10 km with transverse blocky ridges and steep toes the debris avalanches are fast moving long up to 230 km compared to width and thinner 0 05 2 km they commonly have a well defined amphitheater at their head and hummocky terrain in the lower part oceanic disturbance caused by rapid emplacement of debris avalanches may have produced high level wave deposits such as the 365 m elevation hulopoe gravel on lanai that are found on several islands most present day submarine canyons were originally carved subaerially in the upper parts of debris avalanches subaerial canyon cutting was apparently promoted by the recently steepened and stripped slopes of the landslide amphitheaters

structure and evolution of the northern oman margin gravity and seismic constraints over the zagros makran oman collision zone abstract the obduction process in oman during late cretaceous time and continental to oceanic subduction along the zagros makran region during the tertiary are consequences of the arabian eurasian collision resulting in construction of complex structures composed of the oman ophiolite belt the zagros continental mountain belt and the makran subduction zone with its associated accretionary wedge in this paper we jointly interpret bouguer anomaly and available petroleum seismic profiles in terms of crustal structures we show that the gravity anomaly in northern oman is characterized by a high amplitude negative positive couple the negative anomaly is coincident with late cretaceous fiqa and tertiary pabdeh foreland basins and with the zagros oman mountain belts whereas the positive anomaly is correlated to the ophiolite massifs the bouguer anomaly map indicates the presence of a post late cretaceous sedimentary basin the sohar basin centred north of the batinah plain we interpret the negative positive couple in terms of loading of the elastic arabian lithosphere we estimate the different cretaceous to recent loads including topography ophiolite nappes sedimentary fill and the accretionary prism of the makran trench a new method using mindlin s elastic plate theory is proposed to model the 2d deflection of the heterogeneous elastic arabian plate taking into account boundary conditions at the ends of the subducted plate we show that remnant ophiolites are isolated from tethyan oceanic lithosphere in the gulf of oman by a continental basement ridge a nw prolongation of the saih hatat window loading the northward limited ophiolite blocks explains the deflection of the fiqa foredeep basin west of the musandam peninsula the tertiary pabdeh foredeep is probably related to the emplacement of a 8 km thick tectonic prism located on the musandam peninsula and in the strait of hormuz final 2d density models along profiles through the oman mountain belt and the gulf of oman are discussed in the framework of late cretaceous obduction of the tethys and synchronous subduction and exhumation of the oman margin

rapid emplacement of the oman ophiolite thermal and geochronologic constraints in understanding of ophiolite emplacement requires knowledge of the elapsed time between igneous crystallization and intraoceanic thrusting and the rate and duration of that thrusting hornblende 4oar 39ar ages demonstrate that the igneous oceanic crust in oman crystallized and cooled to 825 k in 1 2 m y hornblende ages from metamorphic rocks and from cross cutting dikes require that the basal metamorphic thrust fault beneath the ophiolite also cooled below 825 k in 1 2 m y motion along the sole thrust accounted for 200 km of displacement at a rate of 100 200 mm yr on the basis of age relationships and thermal considerations we favor a two stage model for the initial stages of samall ophiolite emplacement intraoceanic thrusting over 2 m y old lithosphere at 150 km m y parallel to a spreading ridge for 1 2 m y followed by equally rapid and brief thrusting over cold and old lithosphere preservation of the samail ophiolite is a direct result of its young age and positive buoyancy at the time of ocean closure and we propose that all ophiolites that originated near spreading centers and were emplaced onto continents were young at the time of intraoceanic thrusting

monsoon triggered formation of quaternary alluvial megafans in the interior of oman a vast bajada consisting of coalescing low gradient 0 3 alluvial fans exceeding 100 km in length formed along the southwestern margin of the oman mountains it comprises an old fan sequence of inferred miocene to pliocene age termed barzaman formation diagenetically highly altered to dolomitic clays and a thin veneer of weakly cemented quaternary gravels a combination of remote sensing lithological analyses and luminescence dating is used to interpret the complex aggradation history of the quaternary alluvial fans from the interior of oman in the context of independent regional climate records from satellite imagery and clast analysis four fans can be discerned in the study area while two early periods of fan formation are tentatively correlated to the miocene pliocene and the early pleistocene luminescence dating allows the distinction of five phases of fan aggradation during the middle late pleistocene these phases are correlated with pluvial periods from marine isotope stage mis 11 through 3 when southern arabia was affected by monsoonal precipitation it is concluded that the aggradation of the alluvial fans was triggered by the interplay of increased sediment production during arid periods and high rainfall with enhanced erosion of hillslopes and transport rates during strong monsoon phases however the lack of fine grained sediments bioturbation and organic material implies that although the quaternary fans are sourced by monsoonal rains they formed in a semi arid environment thus it appears that in contrast to the oman mountains the interior was not directly affected by monsoonal precipitation

seismic velocity structure at the southeastern margin of the arabian peninsula summary the lithospheric structure in oman has been determined by analyzing teleseismic p receiver functions recorded at broad band and short period seismic stations of the oman seismological network lithospheric structure is obtained by jointly inverting receiver functions and rayleigh wave group velocities derived from continental scale surface wave tomography of pasyanos we observe relatively thick crust 40 48 km within the ophiolite formed mountains in northern oman the crustal thickness is about 35 km within the passive continental margin of the southern oman region uppermost 5 km crustal shear wave velocities are faster in the northern ophiolite regions compared to the southern oman region while shear velocities in the middle crust are faster in the southern oman region compared to the ophiolite region this observation coincides well with cretaceous to eocene marine platform sequences overlying precambrian to cambrian basement of the southern part joint inversion analysis shows that the moho depth of oman varies from 34 km in the southern region to 48 km in the northern part

vitrinite anisotropy resulting from simple shear experiments at high temperature and high confining pressure abstract orientations of r 0 max and r 0 min of vitrinite have been determined in coal samples that have been deformed in simple shear experiments at t 650 900 c confining pressures of 0 8 and 1 0 gpa and constant displacement rates of 10 5 10 6 s 1 samples chosen are a high volatile bituminous coal and two anthracites shear strains up to 3 0 were attained in experiments that lasted up to 100 h high temperature and large strains have facilitated an increase in r 0 max an increase in anisotropy bireflectance and reorientation of r 0 max and r 0 min results of these experiments indicate that tectonic strain at and above semi anthracite rank enhances the degree of molecular ordering leading to preferential growth of graphite and that vitrinite anisotropy may track with tectonic strain