the effects of thermochemical sulfate reduction upon formation water salinity and oxygen isotopes in carbonate gas reservoirs abstract thermochemical sulfate reduction tsr is a well known process that can lead to sour h2s rich petroleum accumulations most studies of tsr have concentrated upon gas chemistry in this study we have investigated palaeoformation water characteristics in a deep anhydrite bearing dolomite sour gas reservoir of permian age in abu dhabi using fluid inclusion stable isotope petrographic and gas chemical data the data show that low salinity isotopically distinct water was generated within the reservoir by reaction between anhydrite and methane the amount of water added to the reservoir from tsr indicated by reduced fluid inclusion salinity and water 18o values varied systematically with the extent of anhydrite reaction with methane water salinity and isotope data show that the original formation water was diluted by between four and five times by water from tsr thus we have shown that large volumes of very low salinity water were generated within the gas reservoirs during diagenesis following gas emplacement the salinity of formation water in evaporite lithologies is therefore not necessarily high modelling based upon a typical khuff gas reservoir rock volume suggests that initial formation water volumes can only be increased by about three times as a result of tsr the extreme local dilution shown by the water salinity and 18o data must therefore reflect transiently imperfect mixing between tsr water and original formation water the creation of large volumes of water has important implications for the mechanism and rate of thermochemical sulphate reduction and the interpretation of gas volumes using petrophysical logging tools

isotope hydrology and geothermometry of the thermal springs damavand volcanic region iran abstract the chemo isotopic characteristics geothermal activity and water origin of the 5 thermal and 7 non thermal springs have been investigated in damavand volcanic region northern iran the damavand thermal waters are characterized by outlet temperature values of 23 to 65 c and the ca cl or ca so4 water types stable isotope values of 49 monthly precipitation samples from 5 stations at 2500 to 3200 m elevations were also measured in the study area and damavand meteoric water line dmwl was drawn as d 7 64 18o 8 93 r2 0 98 n 49 it has a lower slope and intercept than the global meteoric water line gmwl due to isotope kinetic fractionation effects during precipitation the 18o 0 0018 h m a s l 3 12 equation was derived based on precipitation data the reservoir temperature was estimated to be 110 135 c based on different geothermometers damavand volcano can be considered as the main heat source for the thermal springs in the region the conductive process along with the mixing of thermal waters with shallow cold groundwaters is the main cooling mechanisms almost all the thermal waters fall near the lmwl and within prediction interval area indicating meteoric origin and no significant effect of water rock interaction the damavand geothermal reservoir is fed by local meteoric water from altitudes of 2500 to 4100 m and circulates at least 500 m deep near the magma chamber

u th he zircon and archaeological ages for a late prehistoric eruption in the salton trough california usa u th and u th he zircon geochronology redefines the timing of volcanic activity in the salton trough southern california usa the subaerial extension of the incipiently oceanic gulf of california u series disequilibrium corrected u th he zircon analyses for a granophyre ejecta clast from the red island rhyolite dome indicate an eruption age of 2480 470 a calendric dates between 0 and 940 before common era bce error at 95 confidence this eruption age is supported by u th zircon crystallization ages for two obsidian bearing lavas red island the host for the granophyre and obsidian butte a prehistoric quarry for obsidian that is widely distributed in southern california and northern mexico archaeological sites lavas and granophyre display overlapping zircon crystallization age distributions that support field and compositional evidence that they are cogenetic and contemporaneous the u th he eruption age is younger and significantly more precise than previous ages for these volcanoes and is the first indication that the eruption of obsidian flows coincided with human presence in the region a late prehistoric eruption age agrees with the absence of the obsidian butte lithic source among early prehistoric cultural artifacts previously attributed to submergence of the quarry location during hypothesized persistent flooding by ancient lake cahuilla

age of lassen peak california and implications for the ages of late pleistocene glaciations in the southern cascade range lassen peak is a large volcanic dome of late pleistocene age at the southern end of the cascades arc this dacitic dome has a complex phenocryst assemblage of mixed magma origin and has been effectively dated for the first time using the 40 ar 39 ar technique emplacement of the dome occurred after an advance of late pleistocene glaciers from an older volcanic cone to the southwest and from a large volcanic plateau to the east emplacement of the lassen peak dome before the latest major pleistocene glaciation correlated by previous workers with the tioga glaciation of the sierra nevada formed a high peak that intercepted some of the precipitation that previously had fed the plateau ice cap forming a 10 km long glacier from a cirque on the northeast side of the peak the weighted mean 40 ar 39 ar age of the dacite of lassen peak is 28 3 2 7 ka comparison of its remanent magnetic direction to that of sedimentary deposits at mono lake california indicates a correlation to strata of 27 1 ka the dacite of kings creek which erupted from the site of lassen peak before a glacial advance that predated the lassen peak dome overlies peat that has a u th calibrated 14 c age of 37 6 0 2 ka the dacite of kings creek yielded a 40 ar 39 ar age of 32 17 ka the paleomagnetism of this dacite is similar to that of mono lake sediments of 35 1 ka age thus a late pleistocene glacial advance probably began in the lassen region between about 35 and 27 ka

uranium thorium helium dating of apatite experience with samples from different geochemical environments abstract u he dating which during its history has been very problematic might find special application in the field of hydrothermal mineralizations where other methods generally fail the mineral apatite is a potential candidate for this method in order to shed light on various aspects of apatite dating by the u th he method two samples each from different geochemical environments plutonic pneumatolytic and hydrothermal were probed isotope dilution techniques were used for concentration analyses from which 4he model dates also called helium indices after n b keevil were calculated 4he diffusion measurements were carried out for comparison of the 4he retentivities between the samples comparisons of the apatite he indices with plausible reference ages of the sampling locations in combination with results obtained from diffusion experiments show that the u th he dating method applied to apatite yields an age of cooling rather than an emplacement age the calculated closure temperatures are similar to those obtained by the fission track method 100 c our results suggest that the high temperature apatites plutonic and pneumatolytic may be more suitable for he dating than hydrothermal apatite important criteria for the dating of apatite by u th he are the presence of moderate radionuclide concentrations tens of ppm and a minimum abundance of inclusions

the southern caspian a compressional depression floored by a trapped modified oceanic crust the south caspian intracontinental depression floored by oceanic basement is a relatively stable block with minor deformation surrounded by active fold thrust belts of arcuate form talesh alborz and kopeh dagh mountains which have undergone intense late cainozoic crustal shortening the basin is interpreted as a neogene quaternary compressional depression bounded by multi role mountain bordering reverse faults and apparently floored by a late paleozoic triassic or late mesozoic early tertiary modified oceanic crust trapped along an old geosuture it may be a relic of an old paleozoic triassic ocean or else a marginal sea developed behind a mesozoic paleogene ocean and analysis of geological and geophysical data enables a scheme to be suggested the general arcuate shape of the alborz and the talesh bordering mountain belts follows the pattern of the supposed rigid and thickened ocean crust of south caspian depression a tectono sedimentary study of the south caspian region coupled w

modeling of storm surges in the bering sea and norton sound sea level currents and ice distribution are studied in the bering sea during storm events the ice and ice edge are incorporated into storm surge model the interaction of wind ice and water is expressed by the normal and tangential stresses a numerical grid is established for the bering sea and a second refined grid is constructed for norton sound construction of open boundary conditions for the water and ice motion and numerical questions related to the application of a large frictional coefficient for ice are also discussed storm events from february and march 1982 are analyzed and compared with observations of bottom pressure and ice motion made by noaa pacific marine environmental laboratory in the bering sea and sea level observations at stebbins alaska the influence of the ice on the storm surge propagaton is shown particularly that of the fast ice in norton sound the model reproduces several observed features of the ice distribution in the bering sea including the race track region off nome the polynya south of saint lawrence island and the movement of the ice edge

the m2 tide in the beaufort and chukchi seas abstract the amplitude and phase of the m2 tide for the beaufort and chukchi seas were derived from the vertically integrated equations of motion and continuity the boundary conditions at the open boundaries were taken both from previous numerical models and observations the results are shown as co tidal and co range lines and a distribution of current ellipses the results are compared with the few available measurements co tidal and co range lines support the existence of amphidromes at the entrance to the amundsen gulf and in the chukchi sea the former amphidrome has been confirmed by canadian observers it is believed that the latter amphidrome is reported for the first time

gravity driven deformation of damavand volcano iran detected through insar time series the detection and monitoring of gravity driven volcano deformation are vital for understanding volcanic hazards such as landslides lateral blasts and debris avalanches although deformation has been detected at several large active volcanoes e g mount etna vesuvius kilauea these systems also exhibit persistent magmatic activity obscuring the gravity driven signals of ground motion in this study we present a first interferometric synthetic aperture radar insar deformation time series at the dormant damavand volcano in northern iran over the period a d 2003 2008 the high resolution data show a lateral extension of the volcano at the relative rate of as much as 6 mm yr accompanied by subsidence at the rate of as much as 5 mm yr at the volcano summit we find that lateral motion of the east flank is more significant than that of the west flank on the basis of past understanding and modeling of deforming volcanoes elsewhere we interpret this new evidence to reveal long term slow gravity driven deformation possibly in the form of gravitational spreading at damavand this persistent deformation activity is well expressed although no volcanic activity was ever reported in history this finding shows that magmatic activity is not required for spreading and highlights the importance of identifying long lived gravity driven deformation for hazard assessment at dormant or inactive volcanoes

the puguang gas field new giant discovery in the mature sichuan basin southwest china the giant puguang gas field with a proven original in place gas volume of 350 109 m3 12 36 tcfg was discovered in 2003 in the eastern sichuan fold thrust belt of the mature sichuan basin southwest china the field is a combination structural stratigraphic trap closed by lateral depositional change and fault closure the trap evolved from a paleo oil reservoir originating in the triassic jurassic the entrapment of thermal gas which was derived from lower middle silurian and permian source rocks occurred during deep burial in the jurassic cretaceous tertiary quaternary compression transformed the paleotrap into the present gas reservoir gas is contained in the lower triassic feixianguan and the upper permian changxing reservoirs which consist predominantly of dolomitized oolites deposited in shelf and platform margin shoal and backreef environments reservoir quality is characterized by porosity of 1 29 and permeability of 0 01 9664 md with buried depth greater than 5000 m 16 400 ft the discovery of the puguang field exemplifies the successful application of a new play concept and new technology in a mature basin the discovery resulted from a shift in exploration strategy from structures to stratigraphic traps in reef and shoal dolomites and benefited from advanced high resolution seismic techniques the discovery will not only broaden the exploration scope in the sichuan basin but also provide an excellent analog for exploration in other fold thrust belts worldwide

40ar 39ar dating of quaternary lavas in northwest iran constraints on the landscape evolution and incision rates of the turkish iranian plateau summary we report five new 40 ar 39 ar ages for basaltic lavas in the maku region of northwest iran between ca 1 87 and 0 40 ma which help constrain the tectonic and landscape evolution of this part of the turkish iranian plateau flows originated from the composite volcanoes ararat agridagi tend urekandyigitdagi ineasternturkey anatolia thesevolcanoesarewithin the turkish iranian plateau which is a consequence of the arabia eurasia collision but has a poorly constrained evolution and surface uplift history current plateau elevations are typically 1 5 2 km and relief between non volcanic summits and basins is typically on the scale of 1 km samples are from flows that passed along pre existing river valleys gorges were cut by re established rivers after the eruptions but the great majority of the local relief 95 per cent lies above the sampled flows and so most likely pre dates the volcanism gorge depths and lava ages allow local quaternary fluvial incision rates to be calculated which are 0 01 to 0 05 mm yr 1 these rates imply slow surface uplift of this part of the turkish iranian plateau during the quaternary we therefore constrain the generation of the great majority of relief in the study area to be pre quaternary and caused by the tectonic construction of the plateau rather than a subcrustal origin related to the quaternary magmatism

deep structure of the alborz mountains by joint inversion of p receiver functions and dispersion curves abstract the alborz mountains represent a tectonically and seismically active convergent boundary in the arabia eurasia collision zone in western asia the orogenic belt has undergone a long lasted tectono magmatic history since the cretaceous the relationship between shallow and deep structures in this complex tectonic domain is not straightforward we present a 2d velocity model constructed by the assemblage of 1d shear wave velocity vs models from 26 seismic stations mainly distributed along the southern flank of the alborz mountains the shear wave velocity structure has been estimated beneath each station using joint inversion of p waves receiver functions and rayleigh wave dispersion curves a substantiation of the vs inversion results sits on the modeling of bouguer gravity anomaly data our velocity and density models show low velocity density anomalies in uppermost mantle of western and central alborz at a depth range of 50 100 km in deeper parts of the uppermost mantle depth range of 100 150 km a high velocity density anomaly is located beneath most of the mountain range the spatial pattern of these low and high velocity density structures in the upper mantle is interpreted as the result of post collisional delamination of lower part of the western and central alborz lithosphere

diagenetic evolution of selected parasequences across a carbonate platform late paleozoic tengiz reservoir kazakhstan abstract predicting the diagenetic modification of reservoir quality in carbonate fields is poorly understood but of paramount importance to reservoir characterization the diagenetic processes and current pore system are reported for two parasequences from the platform center to the margin of the tengiz reservoir 16 km the late visean lvis13 cbs 900 and bashkirian bash2 5 msf 350 parasequences are separated by 8 million years syndepositional fibrous cement 10 rock volume and aragonite skeletal molds developed in both parasequences on subaerial exposure brown soil related calcite and meniscus and pendant cements were emplaced in both parasequences the application of cl petrography to these rocks for the first time has revealed the depositional components and early marine components are altered developing a mottled pattern implying that their original chemistry is not preserved the principal calcite cement shows a complex growth pattern by cl that is unreported from any other calcite cement cl is also used to divide the main cement into stage 1 nonluminescent and stage 2 orange to brown luminescent calcite stage 1 calcite shows vadose meniscus and pendant fabrics followed by uniform phreatic euhedral terminations stage 1 cement is patchily distributed at a millimeter scale 28 to 40 in the visean and 0 5 to 22 in bashkirian grainstones stage 1 cement is more abundant at the center of the platform in the late visean than at its margin abundant stage 1 calcite creates a framework that prevents later compaction preserving a high porosity at the center of the platform this sweet spot is reinforced by the deposition of late stage bitumen cement that occupies 8 rock volume at the margin of the platform but is almost absent at its center stage 1 13c values 2 4 to 1 7 are derived by dissolution of host rock and their 18o values 6 3 to 3 7 are compatible with precipitation from meteoric or mixed marine meteoric water depositional micrite and micritic grains are transformed by dissolution precipitation processes into porous microrhombic calcite not by ostwald ripening microrhombic calcite is ubiquitous in the tengiz icehouse dispelling the myth that this fabric is restricted to greenhouse epochs at 300 million years before significant burial the study grainstones were patchily cemented and dissolved to reach peak porosity their transformed texture set up flow paths that controlled the distribution of later diagenetic products reservoir compartmentalization did not occur through extensive hardground formation at this time as occurs in some greenhouse sequences but ash bands at parasequence boundaries were turned into tonsteins and wackestones were compacted perhaps sufficiently to influence vertical flow cl examination of stage 2 calcite that adds 0 5 to 16 to rock volume reveals that its precipitation was episodic and switched sites as the pore network became blocked through precipitation and compaction and was opened by new fractures a change from acute to equant habit occurred during stage 2 precipitation causing the change from fibrous to equant crystal fabric the 18opdb values of stage 2 calcite 3 to 9 are linked to precipitation from an 18o enriched fluid that evolved to 6 smow at temperatures of 60 c to 120 c using the equation of kim and o neil 1997 many open macropores are lined with small cement crystals that cl shows have all stages of growth present and are terminated by euhedral surfaces these macropores are only partly filled because of cement inhibition not because they were dissolved during burial as was previously claimed late stage dissolution did create some macropores and rounded micrite crystals but its effect on overall platform porosity is small the cl examination of tengiz platform calcite cement has recognized many diagenetic events that cannot be recognized without cl the new tengiz diagenetic textures recognized here are probably present in other carbonate platforms especially those from icehouse epochs

volcanism and erosion during the past 930 k y at the tatara san pedro complex chilean andes geologic mapping together with 73 new k ar and 40ar 39ar age determinations of 45 samples from 17 different volcanic units plus paleomagnetic orientations geochemical compositions and terrestrial photogrammetry are used to define the chronostratigraphy of the tatara san pedro complex an eruptive center at 36 s on the volcanic front of the andean southern volcanic zone the tatara san pedro complex preserves 55 km3 of lavas that erupted from at least three central vent regions remnant unconformity bound sequences of lavas are separated by lacunae that include significant periods of erosion quaternary volcanism commenced ca 930 ka with eruption of voluminous dacitic magma followed 100 k y later by the only major rhyolitic eruption from 780 ka onward more than 80 of the preserved volume is basaltic andesite 52 57 sio2 but petrographically and geochemically diverse dacitic magmas 63 69 sio2 erupted sporadically throughout this younger dominantly mafic phase of activity a few basaltic lavas 49 52 sio2 are present mainly in portions of the complex older than 230 ka the number of vents the petrologic and geochemical diversity and the temporal distribution of mafic and silicic lavas are consistent with emplacement of many separate batches of mafic magma into the shallow crust beneath the tatara san pedro complex over the past million years nearly two thirds of the preserved volume of the tatara san pedro complex comprises the two youngest volcanoes which were active between ca 188 83 ka and 90 19 ka repeated advances of mountain glaciers punctuated growth of the complex with major erosional episodes that removed much of the pre 200 ka volcanic record particularly on the south flank of the complex dating the inception of a glaciation on the basis of preserved material is difficult but the age of the oldest lava above a lacuna may be used to estimate the timing of deglaciation on this basis the argon ages of basal lavas of multiple sequences indicate minimum upper limits of lacunae at ca 830 790 610 400 330 230 110 and 17 ka these are broadly consistent with global ice volume peaks predicted by the oxygen isotope based astronomical time scale and with age brackets on north american glacial advances estimated growth rates for the two young volcanoes are 0 2 to 0 3 km3 k y these are three to five times greater than a growth rate estimated from all preserved lavas in the complex 0 06 km3 k y removal of up to 50 95 of the material erupted between 930 and 200 ka by repeated glacial advances largely explains this discrepancy and it raises the possibility that episodic erosion of mid latitude frontal arc complexes may be extensive and common

u th he dating of apatite a potential thermochronometer abstract we found a gem quality crystal of durango fluorapatite to have a 4he content consistent with complete retention of radiogenic helium since its formation at about 31 ma isothermal heating and step heating analysis reveal 4he loss to occur systematically by volume diffusion at low temperatures the linear low temperature portion of the diffusion data yields an activation energy of 38 5 8 1 kcal mol and a frequency factor of in d 0 a 2 16 4 2 8 sec 1 corresponding to a closure temperature of 105 c 30 c cooling rate 10 c m y it appears that u th he dating of apatite might represent a useful new thermochronometer with a range similar to that of fission track dating of apatite from these results we infer that a number of the too young u th he dates reported in the literature on minerals such as zircon and magnetite may in fact represent valuable records of the low temperature thermal history of their host rocks

insights into the age of the mono lake excursion and magmatic crystal residence time from u th he and 230 th dating of volcanic allanite we present new data for the age of the mono lake excursion at its type locality using the u th he system on allanite we dated wilson creek ash 15 lajoie 1968 to 38 7 1 2 ka 2 se the new age for this ash supports the hypothesis kent et al 2002 zimmerman et al 2006 that the mono lake excursion is coincident with and probably the same event as the laschamp geomagnetic excursion 40 4 2 ka an event that shares similar magnetic characteristics with the excursion identified at mono lake we also estimate an allanite magma residence time of slightly less than 30 ka based on 230 th 238 u disequilibrium and the u th he based eruption age

implications of earthquake focal mechanism data for the active tectonics of the south caspian basin and surrounding regions summary the south caspian basin is a relatively aseismic block within the alpine himalayan belt but is surrounded by zones of high seismicity we used the focal mechanisms of 16 earthquakes whose source parameters we determined from inversion of body waves and the mechanisms of 15 other earthquakes to determine the style of faulting in the seismic belts surrounding the south caspian basin earthquakes beneath the talesh mountains of north west iran and immediately off shore in the south west caspian sea have shallow thrust mechanisms showing that the continental crust of north west iran is overthrusting the oceanic like crust of the south caspian basin earthquakes south of the caspian sea in northern iran show a mixture of focal mechanisms both high angle reverse faulting and left lateral strike slip faulting mechanisms are observed in the high alborz mountains farther south on the edge of the central iran plateau oblique left lateral reverse mechanisms are observed it appears that the ne direction of shortening between central iran and the south caspian basin is partitioned into pure left lateral strike slip and thrusting in the wnw trending high alborz but is accommodated by oblique faulting in lower elevations earthquakes in the kopet dag mountains east of the caspian sea also show a mixture of high angle reverse and strike slip faulting mechanisms and may be another example of the partitioning of oblique slip into strike slip and thrust motion normal faulting mechanisms at centroid depths of 35 50 km dominate in the belt of seismicity that extends across the central caspian sea the significance of the normal faulting earthquakes is enigmatic it is improbable that these events represent the motion between the southern caspian basin and eurasia for they imply a sense of motion that is incompatible with the observed topography and folding in the sediments two shallow earthquakes at about 12 km depth in this belt one a small event and the other a large second subevent of a multiple earthquake have thrusting mechanisms suggesting that shortening occurs as the continental crust of the northern caspian sea is thrust over the oceanic like crust of the southern caspian basin shortening is also suggested by the orientations of folds in the sedimentary cover south of the central caspian sea seismic belt we suggest that this shortening does indeed represent a nne motion of the caspian sea relative to eurasia but that the motion is slow and has not produced many earthquakes the deeper normal faulting events may be related to bending or down dip extension of the incipient subducted slab if the motion of the caspian sea relative to eurasia is indeed slow then the motion in the alborz between central iran and the south caspian basin will be almost the same as that between iran and eurasia as has previously been assumed the combined effect of the overthrusting of the south caspian basin by the talesh alborz mountains in the south and by the continental crust of the northern caspian sea in the north will lead to the eventual destruction of the south caspian basin and the possible formation of an intermediate depth dipping seismic zone within the continental interior similar to that presently observed in the hindu kush

cement distribution in a carbonate reservoir recognition of a palaeo oil water contact and its relationship to reservoir quality in the humbly grove field onshore uk abstract the distribution of mineral cements total porosity microporosity and permeability have been determined for the humbly grove oolitic carbonate reservoir middle jurassic great oolite formation weald basin onshore uk using a combination of optical petrography electron microscopy fluid inclusion analysis quantitative xrd wireline data analysis and core analysis data grainstone reservoir facies have porosities ranging between 5 and 24 but are mostly between 11 and 24 permeabilities vary from

diagenetic evolution of the carnian wetterstein platforms of the eastern alps the carbonate platforms of the wetterstein formation of the eastern alps drau range and northern calcareous alps show a distinct facies zonation of reefs and lagoons while some lagoonal areas were episodically emerged and formed lagoonal islands others remained permanently flooded the scale of near surface meteoric or marine diagenesis was related to this lagoonal topography at shallow burial depth cementation was dominated by altered marine solutions which additionally caused recrystallization of metastable constituents of the sediment and earlier marine cements high magnesian calcite aragonite connected with a carbon and oxygen isotopic change to more negative values deeper burial cementation shows a succession with two types of saddle dolomite and three types of blocky calcite carbon and oxygen isotopic values of these cements show a trend towards more negative values from the first to the last generation in the following succession clear saddle dolomite zoned blocky calcite cloudy saddle dolomite post corrosion blocky calcite replacive blocky calcite fluid inclusion studies of the carbonate cements are interpreted to indicate a deeper burial temperature development that first increases from 175 to 317 c followed by a temperature decrease to 163 260 c and subsequent increase up to 316 c whereby the samples of the drau range always show the lowest values calculations of the isotopic composition of the water from which the carbonate cements were precipitated yielded positive 18o values from 6 66 to 17 81 o smow which are characteristic for formation and or metamorphic waters also the isotopic compositions of the palaeofluids probably changed during deeper burial diagenesis following the temperature development

limited thermochemical sulfate reduction in hot anhydritic sour gas carbonate reservoirs the upper jurassic arab formation united arab emirates abstract limited thermochemical sulfate reduction tsr in hot 130 160 c and anhydrite rich sour gas reservoir carbonates of the arab formation upper jurassic is manifested by rare calcitization of anhydrite with slightly lower 13cvpdb values 3 2 to 0 1 than calcite precipitated in equilibrium with late jurassic seawater fluid inclusion microthermometry of calcite that has replaced anhydrite indicates that tsr occurred between 130 c and 160 c the lack of evidence for extensive tsr despite the suitable current temperatures and abundant sulfates in the gas reservoir coupled with the relatively more common tsr related calcite in the flanks water zone than crest gas zone indicate that 1 gas emplacement while the reservoir was buried at shallower depth slowed down or inhibited tsr in the crest even when it subsequently reached depths where extensive tsr would occur and 2 h2s up to 38 vol has migrated from the underlying permo triassic and or jurassic sulfate carbonate deposits this study demonstrates that constraining the timing of hydrocarbon emplacement within the context of burial thermal history is crucial for a better understanding of the origin and distribution of h2s in hot anhydrite rich sour gas reservoirs

prevention of carbonate cementation in petroleum reservoirs by the time a carbonate unit has been buried to the depths of most petroleum reservoirs the significant question is often not how did the pores originate but rather why are they still there preservation of porosity regardless of its origin is a consequence of one or more of the following mechanisms 1 minimal burial 2 reduced burial stress generally due to overpressured pore fluids 3 increased framework rigidity which prevents compaction 4 exclusion of pore waters by petroleum entry 5 stable mineralogy 6 permeability barriers isolating porous intervals from diagenetic fluids and 7 pore resurrection a consequence of the temporary filling of pores with cement that is subsequently removed examples from the stratigraphic record demonstrate that each of these pore preserving mechanisms may control reservoir quality

quaternary syn collision magmatism from the iran turkey borderlands quaternary basaltic and andesitic lavas from the nw iran eastern turkey border area are related to the active arabia eurasia collision the lavas occur within the turkish iranian plateau which ceased crustal thickening before the establishment of a number of volcanic centres within iran and eastern turkey beginning at 10 ma models for generating syn collision magmatism in eastern anatolia have invoked slab break off beneath the thick crust and thin mantle lithosphere of the cenozoic east anatolia accretionary complex and or partial loss of the lower lithosphere here we report geochemical and sm nd rb sr data from a 200 km long n s traverse that samples volcanic flows in nw iran many of which originate from centres in turkey such as ararat and tendurek samples are transitional alkali tholeiitic basalts and andesites ararat samples have lower nb lower large ion lithophile element lile concentrations with 143nd 144nd 0 51290 other volumetrically smaller centres have higher nb higher lile with 143nd 144nd 0 51265 abundances of lile and nb increase from north to south the presumed degree of partial melting increases in the opposite direction away from the arabia eurasia suture melting is inferred to have taken place in the spinel lherzolite field largely from a continental lithosphere source influenced by mesozoic and early cenozoic neo tethyan subduction but a separate source with long term enrichment is needed to explain the high nb lower 143nd 144nd compositions

active transtension inside central alborz a new insight into northern iran southern caspian geodynamics the tectonic activity in the alborz mountain range northern iran is due both to the northward convergence of central iran toward eurasia and to the northwestward motion of the south caspian basin with respect to eurasia inducing a left lateral wrenching along this range these two mechanisms give rise to a nne ssw transpressional regime which is believed to have affected the entire range for the last 5 6 2 m y in this paper we show that the internal domain of central alborz is not affected by a transpressional regime but by an active transtension with a wnw ese extensional axis we show that this transten sion is young middle pleistocene it postdates an earlier n s compression and may have been initiated when the south caspian basin started moving consequently our results suggest that the south caspian basin motion may have taken place more recently than previously proposed

3 d velocity structure of damavand volcano iran from local earthquake tomography damavand volcano is a large intraplate quaternary composite cone overlying the active fold and thrust belt of the central alborz mountains in northern iran in this study we present the first 3 d

burial diagenesis and thermochemical sulfate reduction smackover formation southeastern mississippi salt basin the smackover formation in the southeastern mississippi salt basin has been buried from 3 03 to 6 06 km and subjected to temperatures of 100 to 200c pre hydrocarbon migration burial diagenesis is characterized by precipitation of calcite cement followed by saddle dolomite and late anhydrite these phases formed at temperatures of less than 100c the oxygen isotopic composition of calcite ranges from minus 5 to minus 8 4 pdb and carbon isotopic composition ranges from 3 5 to 6 0 pdb the sulfur isotopic composition of late anhydrites ranges from 18 1 to 19 1 cdt post hydrocarbon migration burial diagenesis is dominated by replacement of previously formed late anhydrite by calcite or calcite plus elemental sulfur and precipitation of post bitumen calcite cement these diagenetic phases formed at temperatures above 150c and are present only in the deep part of the basin the oxygen isotopic compositions of calcites that replace anhydrite range from minus 3 0 to minus 4 0 pdb and carbon isotopic compositions range from minus 2 0 to 4 2 pdb the oxygen isotopic compositions of post bitumen calcites range from minus 3 4 to minus 5 6 pdb and carbon isotopic compositions range from minus 1 6 to minus 16 3 pdb two samples of elemental sulfur have sulfur isotopic compositions of 15 8 and 16 1 cdt the high temperature replacement of anhydrite by calcite more the presence of post bitumen calcite cement the sulfur isotopic composition of sulfates and elemental sulfur and high concentration of hydrogen sulfide indicate that rapid thermochemical reduction of solid sulfates is taking place in the deep part of the mississippi salt basin at temperatures as low as 150c less

middle pleistocene palaeolimnology of a dammed tropical river the zarzal formation cauca valley colombia abstract the plio pleistocene zarzal formation zf offers one of the few examples of alternation between fully lacustrine to fluvial conditions in a major tropical intramontane river in the northern andes i e the cauca river the zf is mainly composed of diatomites mudstones and tuffaceous sandstones deposited in an intramontane depression located between the western and central cordilleras of colombia and associated with the cauca romeral fault system stratigraphic sedimentological micropalaeontological diatoms and geochronological analyses independent u th he dating of apatite and zircon have been performed on two sections of the zf these analyses reveal a fluctuation between volcanic fluvial and lacustrine deposits during the middle pleistocene in addition the presence of soft sediment deformation structures reflects the synergetic effect of tectonism and volcanism on the sedimentation patterns in the cauca river valley our data show that between about 0 48 0 52 ma ionian depositional facies varied from a fluvial dominated environment to a palaeo lake suggesting the impoundment of the river once the lake was formed full lacustrine conditions were frequently interrupted by river pulses bringing terrigenous and previously deposited volcanic material into the lake diatom based palaeolimnological reconstructions and comparisons with the sedimentological records indicate that river episodes played a decisive role on nutrient supply and sediment input controlling important ecological dynamics in the newly formed lake although we cannot unambiguously pinpoint to the influence of volcanic activity on nutrient cycling within the lake our data exhibit a strong relationship between volcanic deposits and changes in flora the latter are possibly linked to the increase in phosphorous availability the combined effects of tectonism and volcanism had major environmental implications in the quaternary evolution of the cauca river causing unprecedented damming of a one of the major torrential tropical rivers in northern south america therefore are of utmost importance when considering risk assessment and management for riverine communities and infrastructure such as dam buildings

the nevados de payachata volcanic region 18 s 69 w n chile subduction related volcanism in the nevados de payachata region of the central andes at 18 s comprises two temporally and geochemically distinct phases an older period of magmatism is represented by glaciated stratocones and ignimbrite sheets of late miocene age the pleistocene to recent phase 0 3 ma includes the twin stratovolcanoes volcan pomerape and volcan parinacota the nevados de payachata volcanic group and two small centers to the west i e caquena and vilacollo both stratovolcanoes consist of an older dome and flow series capped by an andesitic cone the younger cone i e v parinacota suffered a postglacial cone collapse producing a widespread debris avalanche deposit subsequently the cone reformed during a brief second volcanic episode a number of small relatively mafic satellitic cinder cones and associated flows were produced during the most recent activity at v parinacota at the older cone i e v pomerape an early dome sequence with an overlying isolated mafic spatter cone and the cone forming andesitic dacitic phase mostly flows have been recognized the two nevados de payachata stratovolcanoes display continuous major and trace element trends from high k2o basaltic andesites through rhyolites 53 76 sio2 that are well defined and distinct from those of the older volcanic centers petrography chemical composition and eruptive styles at v parinacota differ between pre and post debris avalanche lavas precollapse flows have abundant amphibole at sio2 59 wt and lower mg numbers than postcollapse lavas which are generally less silicic and more restricted in composition compositional variations indicate that the magmas of the nevados de payachata volcanic group evolved through a combination of fractional crystallization crustal assimilation and intratrend magma mixing isotope compositions exhibit only minor variations pb isotope ratios are relatively low 206pb 204pb 17 95 18 20 and208pb 204pb 38 2 38 5 87sr 86sr ratios range 0 70612 0 70707 143nd 144nd ratios range 0 51238 0 51230 and 18osmow values range from 6 8 o to 7 6 o smow a comparison with other central volcanic zone centers shows that the nevados de payachata magmas are unusually rich in ba up to 1800 ppm and sr up to 1700 ppm and thus represent an unusual chemical signature in the andean arc these chemical and isotope variations suggest a complex petrogenetic evolution involving at least three distinct components primary mantle derived melts which are similar to those generated by subduction processes throughout the andean arc are modified by deep crustal interactions to produce magmas that are parental to those erupted at the surface these magmas subsequently evolve at shallower levels through assimilation crystallization processes involving upper crust and intratrend magma mixing which in both cases were restricted to end members of low isotopic contrast

magmatic evolution and porphyry epithermal mineralization in the taftan volcanic complex southeastern iran abstract the taftan volcanic complex is located above the makran subduction zone in sistan and baluchestan province southeastern iran the earliest volcanic activity at taftan started in the late miocene 8 ma with eruption of andesitic to dacitic lava onto a cretaceous to eocene volcanic and sedimentary paleosurface 20 km to the northwest of the current volcanic edifice later plio pleistocene volcanism consisted of voluminous andesitic and dacitic lavas and pyroclastic flows 3 1 to 0 4 ma taftan and the neighbouring bazman volcano are the southeasternmost and youngest manifestations of arc related volcanism in iran which began with the eocene miocene urumieh dokhtar magmatic arc udma in northwest and central iran and extends into western pakistan chagai arc major porphyry cu mo au deposits are associated with miocene to pliocene intrusive rocks in the kerman section of the eocene neogene urumieh dokhtar magmatic arc in southeastern iran e g sar cheshmeh meiduk and at reko diq and saindak in the late cretaceous quaternary chagai arc in western pakistan in a gap of 300 km between these two belts several porphyry and epithermal prospects are exposed in the miocene pliocene sections of the taftan volcanic complex including the kharestan 6 10 0 80 ma and bidester porphyry epithermal cu au deposits 4 3 ma and the siah jangal epithermal au deposit late miocene in addition several argillic to advanced argillic and fumarolic alteration zones occur in plio pleistocene volcanic rocks around the current volcanic edifice these deposits have received limited exploration electron microprobe analyses of amphibole magnesio hastingsite phenocrysts and magnetite ilmenite mineral pairs from the taftan and bazman volcanic rocks indicate a change of crystallization temperature and magmatic oxidation state from 1000 c and fmq 1 in andesitic rocks to 900 c and fmq 2 in dacitic rocks magmatic water content was 4 wt as indicated by the ubiquitous presence of amphibole phenocrysts major and trace element compositions of the taftan and bazman volcanic rocks show calc alkaline to high k calc alkaline affinity with relative depletions of nb ta and ti and enrichments of large ion c elements lile th and u on normalized diagrams these trace element patterns including listric shaped normalized rare earth element profiles and relatively high sr y and la yb ratios are similar to those of fertile miocene igneous rocks from the kerman belt and chagai arc and suggest that the taftan suite in particular should be prospective for porphyry cu ore formation regionally there is no clear geochemical difference between the neogene kerman belt rocks which are thought to post date the onset of collision between the afro arabian and eurasian plates late oligocene to earliest miocene and the subduction related bazman taftan and chagai belt magmas the porphyry deposits formed in these distinct settings are also virtually indistinguishable this suggests that most of the processes affecting the geochemistry and metallogeny of the magmas in both settings take place in the lithosphere albeit that the ultimate source of the magmas is in the supra subduction zone asthenospheric mantle wedge in collisional environments subduction related material previously crystallized in the deep lithosphere is simply being remobilized

remote sensing of damavand volcano iran using landsat imagery implications for the volcano dynamics abstract remote sensing techniques are applied to retrieve land surface temperature lst radiative heat flux rhf geothermal heat flux ghf and to map hydrothermal alteration zones around the damavand stratovolcano iran landsat enhanced thematic mapper plus etm day and nighttime images are used and merged to available geological data to identify thermal anomaly areas rhf is determined using the stefan boltzmann equation after preprocessing geometric radiometric and atmospheric correction and processing emissivity calculation and lst retrieval of thermal infrared bands in order to estimate ghf from daytime image solar radiation and albedo maps are generated to minimize these effects the ghf values are derived from nighttime image using the background subtraction technique using boolean operation only those pixels with the ghf values greater than 30 w m 2 obtained from daytime image and the ghf values greater than 10 w m 2 estimated from nighttime image are identified as thermal anomalies the geothermal areas are identified by combining the thermal anomaly map and other geological information thermal anomalies have close spatial correlation to faults thermal springs and high heat flow measurements from subsurface data and lithology some of the thermal anomalies and hydrothermal alteration areas also overlap active deformation areas this suggests role of heat and hydrothermal alteration on flank instability processes the thermal anomaly areas show an arc shaped pattern this pattern and the concentration of higher ghf areas in the eastern sector of the volcano are consistent with a release of fluids in a transition zone between a transpressional and a transtensional tectonic regime the combination of thermal infrared data with other geological information layers can be used to detect geothermal areas as well as to analyze the complex relationships among geothermal activity active tectonics and gravity instability processes on volcanoes

rheomorphism of welded tuffs abstract peralkaline welded tuffs from the islands of gran canaria canary islands and pantelleria italy show abundant evidence for post depositional flow it is demonstrated that rheomorphism or secondary mass flowage can occur in welded tuffs of ignimbrite and air fall origin the presence of a linear fabric is taken as the diagnostic criterion for the recognition of the process deposition on a slope is an essential condition for the development of rheomorphism after compaction and welding internal structures produced during rheomorphic flow can be studied by the methods of structural geology and show similar dispositions to comparable features in sedimentary slump sheets it is shown that secondary flowage can occur in welded tuffs emplaced on gentle slopes provided that the apparent viscosity of the magma is sufficiently low compositional factors favor the development of rheomorphism in densely welded tuffs of peralkaline type

cenozoic exhumation history of the alborz mountains iran new constraints from low temperature chronometry the alborz mountains in the north of the turkish iranian plateau mainly developed in the cenozoic as a consequence of the closure of neo tethys and continental collision between arabia and eurasia cenozoic growth of the fold and thrust belt exploited an older palaezoic mesozoic crustal fabric but the extent to which this governed the overall form of the mountain belt is unclear to determine when and how the alborz mountain belt has grown apatite fission track aft and u th he ahe thermochronometry were performed on 46 bedrock samples collected along 8 transects across the range aft central ages range from 157 24 ma to 10 1 ma with most ages falling between 40 ma and 10 ma ahe ages range from 17 2 ma to 6 1 ma the data revealed enhanced exhumation ca 35 5 ma minor exhumation between ca 30 20 ma and an increase in exhumation thereafter this pattern matches the tripartite mid cenozoic stratigraphy of central iran where upper oligocene lower miocene carbonates are sandwiched between terrestrial clastic formations the most intriguing thermochronometric signal found is a major acceleration of exhumation that initiated in the late miocene to early pliocene recorded by the ahe data there does not appear to be a direct tectonic cause for pliocene intensified erosion as convergence rates between arabia and eurasia have remained relatively constant enhanced exhumation at this time may reflect a climatically induced intensification of erosion during caspian isolation and base level fall or a regional tectonic re organization of the arabia eurasia collision or both

block rotation induced by the change from the collision to subduction implications for active deformations within the areas surrounding south caspian basin abstract northern of iran is experiencing a complex deformation due to the northward convergence of arabian plate since late cenozoic the majority of this complexity is due to the presence of a rigid old thickened oceanic crust of the south caspian basin scb this rigid block trapping between eurasia and central iran makes an inhomogeneous body in the context of deforming zone composed by alborz talesh apsheron balkhan caucasus and kopeh dagh located in south west northwest north and east of the scb respectively among them the formation and evolution of the alborz orocline are under debates the presence of sinistral strike slip faults with normal separation initially understood by nw motion of northern alborz inferred by gps measurements raised long debates in the latest proposition it is assumed that the scb is rotating clockwise this study however shows that the model of scb s rotation and or nw ward motion of scb is not kinematically consistent therefore it aims at constraining the alborz northern central iran and nw iran as a sliver block are rotating around the scb the block rotation is facilitated by geo sutures inherited since paleozoic therefore this article specifically pays attention to the active extensional tectonic regime as a signal for the area that is under rotational movement the block rotation induced by the change from the collision in kopeh dagh to subduction scb and kura basin beneath alborz talesh apsheron balkhan and great caucasus respectively and consequently the reactivation of ancient geo sutures in northern iran led to a rapid rotation of microcontinents this assumption may account for the ongoing deformational pattern in alborz and nw iran the disharmonic arabian plate convergence and scb s retreating induce forces by the block rotation and cause episodic tectonic activities that are responsible for current tectonic complexity in the north of iran if the climax of the collision was 5 ma then the block rotation and related deformation are younger events with respect to the collision and subduction

cenozoic thermal evolution of the central sierra nevada california from uth he thermochronometry apatite u th he cooling ages are reported for igneous apatite samples from the central sierra nevada and compared to published apatite fission track ages and track length data from the same mineral separates helium ages are youngest at low elevations and increase systematically toward higher elevations ranging from 43 to 84 ma at yosemite valley 32 to 74 ma at kings river canyon and 23 to 75 ma at mt whitney helium ages from high elevation samples are generally concordant with corresponding fission track ages while lower elevation helium ages are substantially younger cooling histories inferred from present laboratory derived fission track annealing and helium diffusion models do not match well suggesting that either helium diffusion rates or fission track annealing rates are miscalibrated at temperatures below about 60 c for geologic exposure periods unlike the fission track results the helium data do not indicate a very low geothermal gradient in the sierra nevada during early to middle tertiary time

zircon u pb age constraints from iran on the magmatic evolution related to neotethyan subduction and zagros orogeny abstract this study reports zircon la icpms u pb ages of 50 igneous rock samples from the urumieh dokhtar magmatic arc udma and sanandaj sirjan structural zone ssz in iran these results together with literatures and our unpublished age data better delineate the magmatic evolution related to the neotethyan subduction and subsequent zagros orogeny that resulted from the arabia eurasia collision subduction related magmatism was active during jurassic time as evidenced by the presence of widespread i type granitoids from the middle to late jurassic 176 144 ma in the ssz after a protracted magmatic quiescence in the early cretaceous igneous activity renewed inland in the udma from which we identify late cretaceous granitoids 81 72 ma in jiroft and bazman areas the southeastern segment of the udma the udma volcanism was most active and widespread during the eocene and oligocene 55 25 ma much longer lasting than previously thought as just an eocene pulse such a prolonged igneous flare up event in the udma can be correlated to armenia where coeval calc alkaline rocks are common the udma magmatism ceased progressively from northwest to southeast with magmatic activities ending the early miocene ca 22 ma in meghri the middle miocene ca 16 ma in kashan and the late miocene ca 10 6 ma in anar respectively the southeastward magmatic cessation is consistent with the notion of oblique and diachronous collision between arabia and eurasia post collisional volcanism started ca 11 ma in saray east off the urumieh lake which along with later eruptions in sahand 6 5 4 2 ma and sabalan 0 4 ma volcanoes forms a compositionally unique component of the vast volcanic field covering much of the lesser caucasus nw iran and eastern anatolia regions

volcanic gas emissions from taftan and damavand the iranian volcanoes abstract volcanic gas sampling and so2 flux measurements were performed on taftan volcano 3920 m height se iran makran volcanic arc and damavand volcano 5610 m height northern iran alborz mountains both volcanoes possess near summit fumarolic fields with moderately intensive gas jets and temperatures up to 160 c taftan and 175 c damavand gases of both volcanoes contain mmol mol h2o 910 930 co2 50 80 so2 3 7 h2s 2 5 5 hcl 5 8 2 and hf 0 1 0 13 both volcanoes are also similar in terms of minor gas species mmol mol he 0 0005 0 0011 h2 0 00077 0 0046 n2 ex 0 15 0 30 and ar ex 0 0006 0 0012 where subscript ex denotes non atmospheric fraction d 18o systematics has shown that damavand fumarolic gases contain 60 65 of magmatic fraction whereas the taftan emissions correspond to almost pure magmatic andesitic vapor low amount of nitrogen in taftan gases and its isotopic composition may be explained by low input of nitrogen containing organic matter with the subducting slab due to specific geometry of the makran subduction zone namely by the presence of an accretionary prism of a considerable size the origin of high ch4 content in damavand gases and very low concentrations of c2h6 and higher hydrocarbons 0 65 mmol mol co2 ch4 80 ch4 c2h6 104 is unclear fumaroles of taftan volcano are poor in ch4 similar to many other arc volcanoes co2 ch4 105 3he 4he isotopic composition expressed as r ra was measured at 7 0 7 5 for taftan and 6 65 for damavand corresponding to the co2 3he ratio of 1 0e 10 the 34s of the total sulfur is 7 6 2 2 for taftan fumaroles and 8 1 2 2 for damavand fumaroles 13c co2 is 5 9 2 0 damavand and 4 3 0 15 taftan concentrations of major gas species h2o co2 s hcl ratios and isotopic data r ra co2 3he 34s show that the volcanic gas composition on both volcanoes have a distinct arc signature this conclusion is especially important for the intraplate damavand volcano which has an uncertain tectonic affinity but according to the latest geochemical studies was considered having hotspot rift origin mini doas measurements of the so2 fluxes showed 20 12 t d so2 at taftan and 43 20 t d so2 at damavand which places both volcanoes as small so2 emitters

compositional variations and magma mixing in the 1991 eruptions of hudson volcano chile the august 1991 eruptions of hudson volcano produced 2 7 km3 dense rock equivalent dre of basaltic to trachyandesitic pyroclastic deposits making it one of the largest historical eruptions in south america phase 1 of the eruption p1 april 8 involved both lava flows and a phreatomagmatic eruption from a fissure located in the nw corner of the caldera the paroxysmal phase p2 began several days later april 12 with a plinian style eruption from a different vent 4 km to the south southeast tephra from the 1991 eruption ranges in composition from basalt phase 1 to trachyandesite phase 2 with a distinct gap between the two erupted phases from 54 60 wt sio2 a trend of decreasing sio2 is evident from the earliest part of the phase 2 eruption unit a 63 65 wt sio2 to the end unit d 60 63 wt sio2 melt inclusion data and textures suggest that mixing occurred in magmas from both eruptive phases the basaltic and trachyandesitic magmas can be genetically related through both magma mixing and fractional crystallization processes a combination of observed phase assemblages inferred water content crystallinity and geothermometry estimates suggest pre eruptive storage of the phase 2 trachyandesite at pressures between 50 100 megapascal mpa at 972 26 c under water saturated conditions log fo2 10 33 0 2 it is proposed that rising p1 basaltic magma intersected the lower part of the p2 magma storage region between 2 and 3 km depth subsequent mixing between the two magmas preferentially hybridized the lower part of the chamber basaltic magma continued advancing towards the surface as a dyke to eventually be erupted in the northwestern part of the hudson caldera the presence of tachylite in the p1 products suggests that some of the magma was stalled close to the surface 0 5 km prior to eruption seismicity related to magma movement and the p1 eruption combined with chamber overpressure associated with basalt injection may have created a pathway to the surface for the trachyandesite magma and subsequent p2 eruption at a different vent 4 km to the south southeast

gas souring by thermochemical sulfate reduction at 140 c reply natural gas in the permian triassic khuff formation of abu dhabi contains variable amounts of h2s gas souring occurred through thermochemical sulfate reduction of anhydrite by hydrocarbon gases sour gas is observed only in reservoirs hotter than a critical reaction temperature 140 c petrographic examination of core from a wide depth range showed that the anhydrite reactant has been replaced by calcite reaction product only in samples deeper than 4300 m gas composition data show that only reservoirs deeper than 4300 m contain large quantities of h2s i e 10 at present day geothermal gradients 4300 m is equivalent to 140 c fluid inclusion analysis of calcite reaction product has shown that calcite growth only became significan at temperatures greater than 140 c thus three independent indicators all show that 140 c is the critical temperature above which gas souring by thermochemical sulfate reduction begins the previously suggested lower temperature thresholds for other sour gas provinces 80 130 c derive from gas composition data that may not allow adequately either for the reservoir temperature history or for the migration of gas generated at higher temperatures into present traps conversely published proposals for higher threshold temperature 180 200 c derive from short duration experimental data that are not easily extrapolated to geologically realistic temperatures and time scales therefore the temperature of 140 c derived from our study of the khuff formation may be th best estimate of temperature required for in situ thermochemical sulfate reduction to produce the high h2s concentrations encountered in deep carbonate gas reservoirs

a tibetan model for the early tertiary western united states a comparative study of the geology of the early tertiary western united states and the modern tibetan and turkish iranian plateaux indicates that these three regions situated in the hinterland of major orogenic belts share a common taphrogenic evolutionary path both the tibetan and turkish iranian plateaux have high mean elevations above sea level 5 km and 2 0 2 5 km respectively have experienced fast uplift and widespread unroofing during the last 10 8 ma and are undergoing extension nearly perpendicular to the plate convergence direction successive accretionary and collisional events accompanied by significant shortening and underplating during the formation of these plateaux resulted in the generation of overthickened continental crust 50 km that is currently in the process of extending a two stage magmatism characterized by widespread calc alkaline volcanism followed and or overlapped by bimodal basaltic to rhyolitic volcanism occurs synchronously with crustal extension and thinning the plateaux in general have an internal closed drainage system and are drained by antecedent rivers near their edges the early tertiary western us cordillera displayed similar geological and geomorphic features to those observed in the tibetan and turkish iranian plateaux in the aftermath of a prolonged mesozoic orogeny and underwent an orogenic collapse starting around mid tertiary time a n trending crustal welt with a maximum thickness of 60 km and an elevation around 3 km formed a highland with alpine flora in the hinterland of the cordilleran orogenic belt and separated internal drainage basins and saline lakes on the east from major flood plains of antecedent river systems on the west this highland subsequently became the locus of crustal extension metamorphic core complex formation and wide spread calcalkaline volcanism 9ignimbrite flare up9 this early stage of orogenic collapse was followed by the basin and range extension characterized by block faulting and bimodal volcanism starting around 18 16 ma the basin and range extension and associated subsidence resulted in development of the great basin with a mean elevation of 1 5 km above sea level and a crustal thickness of 30 km similarities in the post orogenic evolutionary paths of these three regions indicate that continental lithosphere reacts to overthickening in a consistent way through large scale crustal remobilization and extensional collapse regardless of the mode and nature of its orogenic build up

exhumation of the west central alborz mountains iran caspian subsidence and collision related tectonics crystallization and thermal histories of two plutons in the west central alborz also elburz elburs mountains northern iran are combined with crosscutting relations and kinematic data from nearby faults to determine the cenozoic tectonic evolution of this segment of the youthful euro arabian collision zone u pb 40 ar 39 ar and u th he data were obtained from zircon biotite k feldspar and apatite the akapol pluton intruded at 56 2 ma cooled to 150 c by ca 40 ma and stayed near that temperature until at least 25 ma the nearby alam kuh granite intruded at 6 8 0 1 ma and cooled rapidly to 70 c by ca 6 ma these results imply tectonic stability of the west central alborz from late eocene to late miocene time consistent with miocene sedimentation patterns in central iran elevation correlated u th he ages from the akapol suite indicate 0 7 km m y exhumation between 6 and 4 ma and imply 10 km of alborz uplift that was nearly synchronous with rapid south caspian subsidence suggesting a causal relation uplift south caspian subsidence and subsequent folding reversal of alborz strike slip from dextral to sinistral and eastward extrusion of central iran coarse zagros molasse deposition dead sea transform reorganization red sea oceanic spreading and north and east anatolian fault slip all apparently began ca 5 2 ma suggesting a widespread tectonic event that we infer was a response to buoyant arabian lithosphere choking the neo tethyan subduction zone

storm surges in the beaufort and chukchi seas specific problems of storm surge modeling in the polar seas are analyzed the vertically integrated equations of motion and continuity are applied to the prediction of the storm surge wave in both the ice free and ice covered seas the interactions of atmosphere ice and water are expressed by the normal and tangential stresses a numerical grid is set over the chukchi and beaufort seas and three storm surges are simulated and briefly described patterns of motion and sea surface geometry are related to low and high atmospheric pressure systems comparison of the measured and computed sea level and observed and computed ice edge proves that the model is suitable to reproduce both water and ice motion

the influence of rock fabric and mineralogy on thermochemical sulfate reduction khuff formation abu dhabi abstract thermochemical sulfate reduction tsr is the reaction between anhydrite and petroleum fluids at elevated temperatures to produce h2s and calcite in this study of the dolomite hosted hydrocarbon gas reservoirs in the permo triassic khuff formation abu dhabi a geochemically well constrained rock gas system we demonstrate for the first time a clear influence of rock texture and mineralogy on the rate and extent of tsr reactions and thus on h2s concentration in the gas phase the controls on the rate on h2s accumulation were tsr reaction kinetics tsr became significant as temperature exceeded 140 c a critical threshold temperature for chemical reaction between aqueous sulfate and aqueous methane anhydrite dissolution rate once initiated the subsequent reaction rate was controlled by the rate of supply of aqueous sulfate to the reaction site sulfate limitation is indicated by the lack of fractionation of sulfur isotopes between sulfate and sulfide i e suggesting total reaction for each unit of sulfate that dissolves also finely crystalline anhydrite began reacting at a lower temperature than coarse crystalline anhydrite likely a result of relative surface area suggesting that anhydrite dissolution was the rate limiting step transport rates are unlikely to have been rate limiting at the earliest stage of reaction because anhydrite was replaced in situ by calcite on the very edges of anhydrite nodules and crystals transport rate later as tsr proceeded it became transport controlled as calcite growing on the surface of anhydrite crystals began to isolate them from dissolved methane tsr ceased once calcite had effectively armor plated totally isolated the remaining anhydrite finely crystalline anhydrite underwent more extensive and more rapid tsr than coarser anhydrite crystals because these had a greater ratio of surface area to volume allowing more and faster dissolution and requiring more calcite to isolate them from methane localized loss of h2s occurred in the reservoir by reaction with indigenous fe bearing clays consequently reservoirs with a relatively high siliciclastic content have less h2s than would be expected from the advanced state of anhydrite replacement by calcite in order to predict tsr related h2s concentration in hydrocarbon gases it is thus important to understand the diagenetic and textural characteristics of the reservoir as well as the thermal and petroleum emplacement history

dynamics of cementation in response to oil charge evidence from a cretaceous carbonate field u a e abstract oil charge is thought to inhibit the growth of cements within subsurface pore systems we explore this phenomenon in a giant cretaceous carbonate field from u a e where the oil filled crest porosity ranges from 10 to 50 and permeability from 0 08 to 830 md but coeval water leg porosity is reduced to 10 to 23 and permeability to 0 1 to 4 md only 5 of primary interparticle pores 30 m diameter in the crest are fully cemented compared to 99 of pores in the water leg syntaxial calcite burial cements 10 m diameter in the oil leg show 12 cathodoluminescence zones with oil inclusions n 27 occurring in four of the five final zones mean in situ ion microprobe 18ovpdb data from the oil leg cements range from 1 2 in the oldest zone decreasing to 10 3 in zone 11 returning to 7 7 in the final zone the oldest distinguishable cement zone in the water leg shows highly variable 18o from 3 6 to 9 3 with a mean of 7 3 and with subsequent zones decreasing to a mean value of 9 4 for the youngest cement zone decreasing 18o values are interpreted as indicating increasing temperature reflecting burial and the evolution of pore water composition broadly similar trends in the oil and water legs suggest precipitation under the same general conditions unlike the oil leg cements the final zone in the water leg occludes nearly all remaining pore space the 18ovpdb of bulk micrite from the water leg shows an average of 7 4 n 9 compared to 6 2 n 10 from the oil leg suggesting the precipitation of further micrite cement at greater burial depths we infer that burial cementation slowed in the presence of oil due to a reduction of potential nucleation sites as well as porewater and solute movement within weakly oil wet pores whereas continued flow and solute movement through all pores including the micropores

generation of isotopically and compositionally distinct water during thermochemical sulfate reduction tsr in carbonate reservoirs triassic feixianguan formation sichuan basin china abstract thermochemical sulfate reduction tsr the reaction of petroleum with anhydrite in reservoirs resulting in the growth of calcite and the accumulation of h2s has been documented in the feixianguan formation dolomite reservoir in the sichuan basin china fluid inclusion salinity and homogenization temperature data have shown that tsr results in a decrease in salinity from a pre tsr value of 25 wt down to 5 wt as a result of water created as a byproduct of progressive tsr we have studied the isotopic character of the water that resulted from tsr in the feixianguan formation by analyzing the oxygen isotopes of tsr calcite and determining the oxygen isotopes of the water in equilibrium with the tsr calcite at the temperatures determined by aqueous fluid inclusion analysis we have compared these tsr waters to water that would have been in equilibrium with the bulk rock also at the temperatures determined by aqueous fluid inclusion analysis we have found that the tsr waters are relatively depleted in oxygen isotopes by up to 8 compared to what would be expected at equilibrium between the bulk rock and water since this type of water was specifically derived from anhydrite the generation of relatively large volumes of low salinity low 18o water associated with advanced tsr in the feixianguan formation has also been reported in the permian khuff formation in abu dhabi and from sour devonian fields in the western canada basin this suggests that tsr derived water may be a common phenomenon the effects of which on mesogenetic secondary porosity and reservoir quality have previously been underappreciated

the nevados de payachata volcanic region 18 s 69 w n chile ii evidence for widespread crustal involvement in andean magmatism volcanism extending over 11 ma is represented in the rocks of the nevados de payachata region culminating in the formation of two large composite stratocones within the last 500 000 years chemically distinct mafic magmas are erupted at a number of parasitic centers these cannot be related to each other by crystal fractionation and do not appear to be direct parents for the differentiated suites of the composite cones two distinct trends are defined by the intermediate and evolved rocks a high lile large ion lithophile element tio2 and ce yb lineage among the youngest rocks including the two major stratocones and a more typical calc alkaline trend among the older 1 ma rock types within individual volcanic centers differentiation involves fractionation of plagioclase pyroxene and hornblende with biotite and k feldspar in the more evolved rock types isotopic compositions sr pb nd o vary little with differentiation from basaltic andesite to rhyolite or with age contamination during differentiation from basalt to rhyolite may occur but the most mafic rocks erupted in the region are already enriched in incompatible trace elements and therefore may be insensitive to the effects of interaction with the crust the majority of data are similar to baseline compositions cenozoic parental magmas from other parts of the central andes and may reflect a relatively homogeneous magma source or source mixture throughout this central volcanic zone cvz which is distinct from the southern and northern andes and from island arc volcanic rocks

tectonic magmatic and metallogenic evolution of the tethyan orogen from subduction to collision abstract this paper reviews the tectonic magmatic and metallogenic history of the tethyan orogen from the carpathians to indochina focus is placed on the formation of porphyry cu mo au deposits as being the most characteristic mineral deposit type formed during both subduction and collisional processes in this region relatively little is known about the history of the paleotethys ocean which opened and closed between gondwana and eurasia in the paleozoic and few ore deposits are preserved from this period the neotethyan ocean opened in the permian early triassic as the cimmerian continental fragments the cores of turkey iran tibet and indochina rifted from the northern gondwana margin and drifted northwards these microcontinents docked with the eurasian margin at various points in the mesozoic and cenozoic and formed a complex archipelago involving several small back arc basins and remnants of the paleotethyan ocean the main neotethyan ocean and these smaller basins were largely eliminated by collision with india and africa arabia in the early eocene and early mid miocene respectively although neotethyan subduction continues beneath the hellenic arc and the makran the majority of porphyry type deposits are found in association with neotethyan subduction mainly in the mesozoic and paleogene and syn to post collisional events in the mid paleogene to neogene they are found throughout the orogen but some sections are particularly well endowed including the carpathians balkans rhodopes eastern turkey lesser caucasus nw iran se iran sw pakistan southern tibet and se tibet indochina other sections that appear barren may reflect deeper levels of erosion young sedimentary cover or lack of exploration although there may also be real reasons for low prospectivity in some areas such as minimal subduction e g the western mediterranean region or lithospheric underthrusting as proposed in western tibet over the last decade improved geochronological constraints on the timing of ore formation and key tectonic events have revealed that many porphyry deposits that were previously assumed to be subduction related are in fact broadly collision related some forming in back arc settings in advance of collision some during collision and others during post collisional processes such as orogenic collapse and or delamination of subcontinental mantle lithosphere while the formation of subduction related porphyries is quite well understood collisional metallogeny is more complex and may involve a number of different processes or sources these include melting of orogenically thickened crust previously subduction modified lithosphere including metasomatized mantle underplated mafic rocks or lower crustal arc plutons and cumulates or upwelling asthenosphere e g in response to delamination slab breakoff back arc extension or orogenic collapse the most fertile sources for syn and post collisional porphyry deposits appear to be subduction modified lithosphere because these hydrated lithologies melt at relatively low temperatures during later tectonomagmatic events and retain the oxidized and relatively metalliferous character of the original arc magmatism unusually metallically enriched lithospheric sources do not seem to be required but the amount of residual sulfide phases in these rocks may control metal ratios e g cu au in subsequent magmatic hydrothermal ore deposits relatively au rich deposits potentially form in these settings as observed in the carpathians e g rosia montan turkey kisladag copler and iran sari gunay dalli although the majority of syn and post collisional porphyries are cu mo rich and resemble normal subduction related deposits e g in the gangdese belt of southern tibet this similarity extends to the associated igneous rocks which being derived from subduction modified sources largely retain the geochemical and isotopic character of those original arc magmas while still retaining a broadly calc alkaline character these rocks may extend to mildly alkaline shoshonitic compositions and may display adakite like trace element signatures high sr y and la yb ratios reflecting melting of deep crustal garnet amphibolitic sources but they are otherwise hard to distinguish from normal subduction related magmas small post collisional mafic alkaline volcanic centers are common throughout the orogen but for the most part appear to be barren however similar rocks in other post subduction settings around the world are associated with important alkalic type porphyry and epithermal au cu deposits and the potential for discovery of such deposits in the tethyan orogen should not be overlooked

water drag coefficient of first year sea ice in may 1977 eddy flux measurements of momentum were made with a three component ultrasonic current meter in the oceanic boundary layer under a first year floe of fast sea ice in barrow strait n w t by using eddy correlation methods values of horizontal reynolds stress were computed from each of 20 data runs of about 1 hour duration during which the mean current was reasonably steady a least squares analysis in which water stress was assumed proportional to the square of the mean current yielded a value for the 1 m water drag coefficient of 1 32 10 3 with a standard deviation of 0 06 10 3 the diameter of the floe was greater than 1 km and its mean thickness was 128 cm with a standard deviation of 4 cm and a maximum deviation of 7 cm

the geology of damavand volcano alborz mountains northern iran damavand volcano located in northern iran is a large 400 km 3 composite cone that is currently dormant it shows fumarolic activity near the summit but no evidence of eruption in the past 1000 yr the volcano represents an isolated focus of magmatism of uncertain tectonic affinity although geophysical and geochemical constraints point toward a local hotspot plume origin possibly associated with lithospheric delamination rather than any association with subduction new u th he and 40 ar 39 ar geochronological constraints indicate that the present cone young damavand has been constructed over 600 k y on an older eroded edifice of indistinguishable composition younger than 1 8 ma damavand activity has been characterized by the eruption of radially directed trachyandesite lava flows almost exclusively from summit vents limited pyroclastic activity has yielded thin fallout pumice lapilli layers and a few pyroclastic flows only one significant pyroclastic event is recognized in the remnants of a welded ignimbrite ponded and preserved along the haraz river drainage relatively short periods of volcanic eruptive activity were interspersed with longer periods of erosion in which volcanic products were transported particularly as hyperconcentrated flows into the surrounding drainage systems to be further reworked into epiclastic deposits occasional catastrophic events punctuated this interplay between volcanism and erosion at least one sector collapse is signified by the presence of a large debris avalanche deposit and the regional drainage systems appear to have been frequently dammed by incursions of volcanic material

heightened north pacific storminess during synchronous late holocene erosion of northwest alaska beach ridges a progradational regime of falling sea level and or high sediment input has produced extensive beach ridge plains in northwest alaska during the last 4000 yr eleven chukchi sea beach ridge complexes oriented at various angles to wind fetch provide a cumulative history of longshore transport and erosion archaeological and geological upper limiting radiocarbon ages n 59 allow correlations between depositional units on seven beach ridge complexes progradation started 4000 yr b p at nearly all complexes as eustatic sea level stabilized two disconformities or truncations are found on most of the complexes providing time parallel storm horizons dated at 3300 1700 and 1200 900 14c yr b p between 1700 and 1200 14c yr b p most of the complexes prograded indicating the predominance of less stormy conditions modern synoptic patterns that produce chukchi beach ridge erosion are linked to northerly shifts in north pacific storm tracks the regionwide beach ridge erosional truncations correlate with records of glacier expansion heightened precipitation evident in tree rings stream flooding and shelf deposits reworked by storm surges

diagenesis of the devonian southesk cairn carbonate complex alberta canada marine cementation burial dolomitization thermochemical sulfate reduction anhydritization and squeegee fluid flow abstract one of the largest geological features in the deep part of the alberta basin in western canada is the middle to upper devonian southesk cairn carbonate complex sccc the sccc is located at depths of about 5000 m adjacent to the disturbed belt of the rocky mountains rising to depths of 3000 m in a northeastward direction over a distance of 150 km the sccc produces oil and gas with up to about 30 h2s from several stratigraphic levels the diagenesis of the sccc was investigated by means of petrography and geochemistry stable isotope compositions were determined for fibrous calcite cements matrix dolomite saddle dolomite and sparry calcite fibrous calcites have stable isotope values of 18o 7 5 to 4 5 pdb and 13c 2 0 1 0 pdb matrix dolomite samples have stable isotope values of 18o 8 1 to 4 9 pdb and 13c 0 to 1 0 pdb saddle dolomite samples range from 18o 9 8 to 7 1 pdb and 13c 1 0 to 0 pdb sparry calcite samples have 18o 13 7 to 7 2 pdb and 13c 24 0 to 0 pdb the sr isotope values of all analyzed samples span a broad range from 0 7080 to 0 7320 showing considerable scatter but also one distinctive pattern i e values higher than 0 7220 occur only at depths in excess of about 4000 m whereas lower values scatter throughout the entire depth range furthermore the sr isotope values of sparry calcites decrease northeastward similarly the fluid inclusion homogenization temperatures of these calcites display a general decrease updip whereas the salinities show no general spatial trends the uncorrected homogenization temperatures range from about 85 to 180 c and the nacl equivalent salinities range from about 17 to 24 weight the d values of brines obtained from seven wells range from 79 to 20 smow and their 18o values range from 1 5 to 8 7 smow the sulfur isotope values of the dissolved sulfate ranges from 34s 10 1 to 24 5 cdt the sr isotope values of the brine samples range from 0 7109 to 0 7255 elemental sulfur isotope values cluster tightly around 34s 18 0 to 18 4 cdt the values of secondary anhydrites range from 34s 18 4 to 26 7 cdt values for solid bitumen vary from 34s 19 5 to 20 2 cdt integration of all data reveals a complex diagenetic evolution from the middle devonian to the recent the paragenetic sequence consists of 24 distinct diagenetic phases which have been grouped into 5 diagenetic stages stage i density driven convection in near surface settings likely superimposed on and or aided by tidal pumping facilitating marine cementation stage ii cellular convection facilitating pervasive matrix dolomitization aided by compaction stage iii hydrocarbon migration stage iv thermochemical sulfate reduction forming sour gas and regional squeegee flow forming sparry calcite cements and localized flow through faults stage v fluid flow driven by erosional rebound in the overlying mesozoic strata and remnant squeegee flow this study yielded several important results 1 the prolific repertoire of diagenetic textures found in the southesk cairn carbonate complex serves as a means of comparison for petroliferous carbonate complexes elsewhere especially in sour gas provinces close to orogenic fronts 2 the diagenetic evolution contains long periods of relative tranquility that were punctuated by several episodes of intense diagenetic activity 3 both thermochemical sulfate reduction and squeegee type fluid flow are recorded in late diagenetic sparry calcite cements 4 the effect of the various burial diagenetic episodes on the hydrocarbon reservoir properties throughout the entire reef complex was highly variable specifically matrix dolomitization thermochemical sulfate reduction and the emplacement of secondary and tertiary anhydrites affected the hydrocarbon reservoir properties throughout the entire reef complex on the other hand squeegee fluid flow was insignificant in terms of affecting the reservoir properties

thermochemical sulfate reduction and fluid evolution of the lower triassic feixianguan formation sour gas reservoirs northeast sichuan basin china the dolomite hosted lower triassic feixianguan formation from the northeast sichuan basin china is an economically important reservoir that contains sour natural gas these reservoirs were initially filled with oil later replaced by gas during burial to 7000 m 22 965 ft followed by uplift to about 4000 m 13 123 ft we have studied the souring process thermochemical sulfate reduction tsr and diagenetic evolution of the feixianguan formation using detailed petrology fluid inclusion studies and stable isotope data from carbonate minerals pre tsr diagenesis included in time order the eodiagenetic main stage of dolomitization by a reflux mechanism fracture related calcite cementation barite quartz celestite and fluorite mineralization and a dolomite recrystallization stage thermochemical sulfate reduction resulted in anhydrite replacement by calcite petroleum destruction formation of sulfur rich pyrobitumen and elemental sulfur and generation of large volumes of and diagenesis during tsr can be subdivided into oil stage tsr and gas stage tsr with oil stage tsr defined by the presence of primary oil and bitumen inclusions in the tsr calcite based on aqueous inclusion homogenization temperatures oil stage tsr commenced at a temperature of 116 c with a mode between 130 c and 140 c gas stage tsr started at a temperature of 135 c and continued to maximum burial temperatures of about 220 c trace amounts of pyrite barite quartz and celestite grew during tsr post tsr diagenesis was dominated by fracture related calcite precipitation as well as celestite and anhydrite crystallization formation water salinity increased from depositional values 3 5 wt up to 24 wt during pre tsr dolomite recrystallization probably because of an influx of evaporite associated water from the overlying jialingjiang formation although pre tsr barite quartz celestite and fluorite mineralization was associated with a transient decrease in water salinity during tsr formation water salinity decreased from 26 wt to as low as 4 wt as a result of water being produced during tsr reactions

estimation of coda wave attenuation in the central and eastern alborz iran the quality factor of coda q c waves has been estimated by using single backscattering and single isotropic scattering models the earthquakes used were recorded by three permanent and one temporary network located in the central and eastern alborz iran the database was composed of 746 local earthquakes with local magnitude from 1 1 to 5 7 the estimated q c has been found to be similar for lapse times greater than twice the s wave travel time 2 t s for both methods the estimated q c for central frequencies 1 0 hz shows less frequency dependency compared with the higher frequencies by using a q f n relation the average frequency dependence of q c for the whole area has been estimated as 59 f 1 03 69 f 0 97 78 f 0 97 105 f 0 93 123 f 0 89 159 f 0 79 and 203 f 0 68 for central lapse times 30 40 50 65 85 110 and 155 s respectively we found the value of q decreases at an average depth of 78 km which may be the result of high dissipating media at this depth the average q c values estimated for central and eastern alborz and their frequency dependent relationships are similar to those of tectonically active regions

zircon hf isotopic constraints on magmatic and tectonic evolution in iran implications for crustal growth in the tethyan orogenic belt abstract this study presents coupled zircon u pb and hf isotopic analyses of 82 igneous rocks that are mainly from the urumieh dokhtar magmatic arc udma and sanandaj sirjan zone ssz iran together with additional 11 samples from armenia along the central part of the neotethyan orogenic belt the results provide an overview of the isotopic variations for several important magmatic stages which can improve our understanding of magmatic and crustal evolution regarding the life cycles of tethys oceans during the past 600 myr in iran and adjacent regions late neoproterozoic cambrian 595 511 ma basement rocks in the ssz and central iran which were part of the cadomian magmatic arc yield zircon ehf t values from 11 to 3 and are attributed to have partially evolved with juvenile magmas in the arabian nubian shield along the northern margin of gondwana carboniferous 349 311 ma a type granitoids in the northwestern ssz show mostly positive zircon ehf t values from 5 to 1 and they are interpreted as the product involving a moderate mantle contribution in an extensional environment affiliated with the initial rifting of the neotethys late triassic 219 203 ma granitoids in the eastern alborz give slightly lower zircon ehf t values between 3 and 3 as a result of the progress of closing the paleotethys middle jurassic 165 ma granitoids in the ssz and central udma representing an early phase of neotethyan subduction related magmatism exhibit similar zircon ehf t values from 5 to 3 implying an origin of mixed juvenile and reworked sources to form the magmas late cretaceous 81 72 ma intrusive rocks in the southeast udma yield bimodal zircon ehf t values from 15 to 11 in the jiroft and from 5 to 9 in the bazman areas suggesting that the latter involves a reworked crustal component at the latest cenozoic magmatic rocks with ages

the fate of co2 derived from thermochemical sulfate reduction tsr and effect of tsr on carbonate porosity and permeability sichuan basin china abstract this article discusses the role of methane in thermochemical sulfate reduction tsr the fate of tsr derived co2 and the effect of tsr on reservoir porosity and permeability and the causes of the anomalously high porosity and permeability in the lower triassic soured carbonate gas reservoirs in the northeast sichuan basin southwest china the lower triassic carbonate reservoirs were buried to a depth of about 7000 m and experienced maximum temperatures up to 220 c before having been uplifted to the present day depths of 4800 to 5500 m but they still possess porosities up to 28 9 and permeabilities up to 3360 md the present day dry gas reservoirs evolved from a paleo oil accumulation and experienced varying degrees of tsr alteration as evidenced from the abundant sulfur rich solid bitumens and varying h2s and co2 concentrations tsr occurred mainly within the oil and condensate wet gas windows with liquid hydrocarbons and wet hydrocarbon gases acting as the dominant reducing agents responsible for sulfate reduction sulfur rich solid bitumen and h2s generation and calcite precipitation methane dominated tsr was a rather late event and had played a less significant role in altering the reservoirs intensive h2s and co2 generation during tsr resulted in calcite cementation rather than carbonate dissolution which implies that the amount of water generated during tsr was volumetrically insignificant 13c depleted co2 derived from hydrocarbon oxidation preferentially reacted with ca2 to form isotopically light calcite cements and the remaining co2 re equilibrated with the 13c enriched water rock systems with its 13c rapidly approaching the values for the host rocks which accounted for the observed heavy and relatively constant co2 13c values the carbonate reservoirs suffered from differential porosity loss by tsr involved solid bitumen generation and tsr induced calcite and pyrite precipitation intensive tsr significantly reduced the porosity and permeability of the intervals expected to have relatively high sulfate contents the evaporative platform dolostones and the platform margin shoal dolostones immediately underlying the evaporative facies early oil charge and limited intensity of tsr alteration together with very low phyllosilicate content and early dolomitization accounted for the preservation of anomalously high porosities in the reservoirs above the paleo oil water contact a closed system seems to have played a special role in preserving the high porosity in the gas zone reservoirs below the paleo oil water contact the closed system which is unfavorable for deep burial carbonate dissolution and secondary porosity generation was favorable for the preservation of early formed porosity in deeply buried carbonates especially sucrosic and vuggy dolostones have a high potential to preserve such porosity

diurnal tides in the arctic ocean a two dimensional numerical model with a space grid of about 14 km is applied to calculate diurnal tidal constituents k1 and o1 in the arctic ocean calculated corange and cotidal charts show that along the continental slope local regions of increased sea level amplitude highly variable phase and enhanced currents occur it is shown that in these local regions shelf waves topographic waves of tidal origin are generated in the arctic ocean and northern atlantic ocean more than 30 regions of enhanced currents are identified to prove the near resonant interaction of the diurnal tides with the local bottom topography the natural periods of oscillations for all regions have been calculated the flux of energy averaged over the tidal period depicts the gyres of semitrapped energy suggesting that the shelf waves are partially trapped over the irregularities of the bottom topography it is shown that the occurrence of near resonance phenomenon changes the energy flow in the tidal waves first the flux of energy from the astronomical sources is amplified in the shelf wave regions and afterwards the tidal energy is strongly dissipated in the same regions

origin of the absarokite banakite association of the damavand volcano iran trace elements and sr nd pb isotope constraints the activity of the damavand volcano central alborz northern iran began 1 8 ma ago and continued up to 7 ka bp although the volcanic suite is clearly of shoshonitic affinity only two petrographic types can be distinguished in the studied lavas 1 weakly differentiated absarokites 49 sio2 51 scattered around the volcano but with a regional extension 2 highly differentiated banakites 59 sio2 63 which form the bulk of the 4 000 m thick volcanic pile all lavas are alkalic 3 7 k2o 5 ree and lile rich e g 85 la 148 ppm 9 th 32 ppm and show highly fractionated ree patterns 69 la yb 115 and pronounced nb ta negative anomalies the absarokites are characterised by sr 0 7045 0 7046 and nd 0 51266 0 51269 isotope compositions close to the bulk earth values and distinct from those of the banakites 0 7047 87sr 86sr 0 7049 0 51258 143nd 144nd 0 51262 the pb isotope ratios are also slightly lower in the absarokites than in the banakites 18 71 206pb 204pb 18 77 15 62 207pb 204pb 15 63 38 85 208pb 204pb 38 91 and 18 77 206pb 204pb 18 84 15 62 207pb 204pb 15 64 38 94 208pb 204pb 39 06 respectively overall there is a clear tendency towards higher sr pb and lower nd isotope ratios with increasing degree of differentiation this study suggests that the absarokites result from a low degree of partial melting 5 of a highly metasomatized mantle source which inherited its characteristics from an old subduction setting the initiation of volcanic activity 1 8 ma ago results from variations in the lithospheric thermal regime probably related to lithospheric delamination as proposed for anatolia pearce et al 1990 the banakites are mainly generated by extensive fractional crystallisation 70 of the absarokitic magma with a limited amount a few percents of assimilation of an old crustal component in the form of bulk assimilation or afc processes which both can explain the sr nd and pb isotope data

separation of intrinsic and scattering attenuation in the crust of central and eastern alborz region iran abstract in this study more than 380 local earthquakes 2 m l q d coda q c intrinsic q i and scattering quality factor q sc in the crust of central and eastern alborz region the events were recorded by one temporary and two permanent networks the quality factors of shear and coda waves have been individually estimated at different frequency bands by using coda normalization cnm method and single backscattering sbs method respectively average frequency dependent relationships have been estimated for q d and q c as 111 4 f 0 85 0 04 and 112 8 f 1 02 0 06 respectively the intrinsic quality factor q i has been separated from the scattering quality factor q sc by using individually estimated q c and q d values the average frequency dependent relationships of q i and q sc have been calculated in the form of 108 f 1 00 and 784 f 0 56 respectively the results of this study suggest that s wave s attenuation q d 1 is dominated by the intrinsic attenuation the attenuation of coda waves has been observed similar to the intrinsic attenuation which indicates the coda decay is mostly caused by the intrinsic attenuation it has been observed that the scattering mean free path is frequency independent at frequencies greater than 6 hz the results of this study are similar to the tectonically active regions

lateral variations of high frequency seismic wave propagation at regional distances across the turkish and iranian plateaus in this study we investigate crustal and uppermost mantle physical properties that characterize some of the continental plateaus of the middle east this is done as part of a larger effort to map and compare high frequency wave propagation at regional distances across the earth s continental plateaus thousands of short period wwssn seismograms recorded at stations located in the middle east and produced by earthquakes with epicentral distances less than about 20 were examined visually in an effort to study lateral variations of high frequency 0 5 2 hz seismic wave propagation across this area particularly to the north of the zone of continental collision between the africa arabian and eurasian plates variations of frequencies and amplitudes of sn and lg relative to p are examined and mapped throughout the region and this work is supplemented by a study of velocities of pn sn and lg sn amplitude variations are very striking in this area an important observation of this study is that sn propagates efficiently beneath a major part of the turkish and iranian plateaus sn is strongly attenuated however in the northernmost portion of the plateaus south of the black and caspian seas and in an area between the two seas these regions are characterized in general by active tectonism including volcanism faulting and folding however this active tectonism is not restricted to the areas of high sn attenuation but appears to extend beneath other parts of the iranian and turkish plateaus patterns of lateral variations in the propagation of lg are not as consistent as those for sn lg propagates efficiently across turkey iran and adjacent regions but the lg waves that cross the turkish and iranian plateaus are weak and have relatively long predominant periods of about 2 5 s the lg phase is not observed when the path of propagation crosses the southern caspian and the black seas consistent with the evidence of oceanic type crustal structure beneath these seas lg is also not observed from subcrustal events located in the hindu kush region the velocity of pn beneath most of the plateau areas and particularly in the regions of sn attenuation ranges between 8 0 and 8 2 km s velocities for sn and lg throughout the middle east are about 4 5 and 3 4 km s respectively it is possible to interpret the efficient sn propagation and the relatively normal uppermost mantle p and s velocities beneath a major part of the turkish iranian plateau as indicating a partial underthrusting of the arabian continental plate beneath the iranian and turkish continental blocks alternatively the mapped regions of efficient sn propagation and high sn attenuation may result from a differential cooling of a past thermal anomaly in this case the isostatic compensation of the plateaus could be due to an anomalously hot uppermost mantle that developed behind the mid to upper tertiary subduction zone s in this region and to a subsequent crustal shortening after the collision of the arabian and eurasian plates our results cannot uniquely confirm the validity of the above proposed models

the growth of a mountain belt forced by base level fall tectonics and surface processes during the evolution of the alborz mountains n iran abstract the idea that climatically modulated erosion may impact orogenic processes has challenged geoscientists for decades although modeling studies and physical calculations have provided a solid theoretical basis supporting this interaction to date field based work has produced inconclusive results the central western alborz mountains in the northern sectors of the arabia eurasia collision zone constitute a promising area to explore these potential feedbacks this region is characterized by asymmetric precipitation superimposed on an orogen with a history of spatiotemporal changes in exhumation rates deformation patterns and prolonged km scale base level changes our analysis suggests that despite the existence of a strong climatic gradient at least since 17 5 ma the early orogenic evolution from 36 to 9 6 ma was characterized by decoupled orographic precipitation and tectonics in particular faster exhumation and sedimentation along the more arid southern orogenic flank point to a north directed accretionary flux and underthrusting of central iran conversely from 6 to 3 ma erosion rates along the northern orogenic flank became higher than those in the south where they dropped to minimum values this change occurred during a 3 myr long km scale base level lowering event in the caspian sea we speculate that mass redistribution processes along the northern flank of the alborz and presumably across all mountain belts adjacent to the south caspian basin and more stable areas of the eurasian plate increased the sediment load in the basin and ultimately led to the underthrusting of the caspian basin beneath the alborz mountains this underthrusting in turn triggered a new phase of northward orogenic expansion transformed the wetter northern flank into a new pro wedge and led to the establishment of apparent steady state conditions along the northern orogenic flank i e rock uplift equal to erosion rates conversely the southern mountain front became the retro wedge and experienced limited tectonic activity these observations overall raise the possibility that mass distribution processes during a pronounced erosion phase driven by base level changes may have contributed to the inferred regional plate tectonic reorganization of the northern arabia eurasia collision during the last 5 ma

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk