on the trace of the iapetus suture in ireland and britain the iapetus suture in ireland and britain is that line which separates caledonian rocks of the laurentian and avalonian continents the suture is cryptic nowhere is there an exposed fault zone containing ophiolite remnants blue schist melanges or trench deposits instead a suture line may be traced with varying degrees of confidence through a series of faults that traverse the iapetus suture zone which contains two or more tectonostratigraphic terranes several data sets are utilized to constrain this trace the distribution of faunal provinces caused by oceanic separation can be used most reliably to define early ordovician terranes fauna1 intermingling in the mid ordovician reduces provinciality and the confidence of terrane identification using faunal data the late ordovician and particularly silurian tectonostratigraphic histories of terranes either side of the suture suggest that amalgamation of the terranes elimination of the iapetus ocean and development of the suture zone had begun by the ashgill therefore the resolution of the suture trace becomes unreliable where ordovician rocks do not crop out because silurian turbidite fans of laurentian provenance may have dispersed across a significant width of avalonian crust similarly the precision of structural identification of the suture zone by correlating the suture with a major fold facing confrontation may be weakened by late overthrusting tectonic interleaving of crustal flakes in the zone is supported by geophysical evidence which suggests that some major boundaries in the lower crust do not always coincide with their inferred projections in outcrop tectonic and sedimentary mixing of crustal blocks and sediments in the zone is further reflected by nd and pb isotopic patterns the rb sr patterns of granites record a stronger distinction between north and south of the suture despite these difficulties we depict a possible suture trace in ireland that departs significantly from the traditionally placed line by following a ne sw aligned trace through the slane fault and the navan tipperary lineament and thence through a dog leg to pass north of the dingle peninsula

a geochemical study of solid bitumen in an eocene epithermal deposit owen lake british columbia canada abstract the owen lake deposit british columbia canada is an epithermal polymetallic deposit related to eocene volcanic activity and igneous intrusions the deposit contains both solid and liquid hydrocarbons generated during early and late stages of ore deposition gc ms py gc rock eval electron microprobe as well as carbon isotope fluid inclusion and optical techniques have been applied and the results integrated into a deposit model incorporating fluid flow fluid source and thermal structure of the volcanic terrane most solid bitumen examined is of the albertite variety and is related to the latest stage of mineral deposition gas chromatography of saturated hydrocarbons yielded n alkanes from c15 to c33 with a maximum at n c23 steranes and diasteranes are of low abundance relative to n alkanes terpanes and hopanes regular steranes dominate over rearranged steranes hopanes dominate over tricyclic terpanes and gammacerane is a significant component aromatic compounds are very low in abundance and are represented mainly by triaromatic steroids these results together with carbon isotope values suggest a mixed marine terrestrial organic source of the bitumen with saline or hyper saline conditions prevailing during deposition or very early diagenesis of the source rock based on the geological framework of the deposit two possible sources of the solid bitumen together with the fluid path are suggested

fluid inclusion and vitrinite reflectance geothermometry compared to heat flow models of maximum paleotemperature next to dikes western onshore gippsland basin australia abstract nine basalt dikes ranging from 6 cm to 40 m thick intruding the upper jurassic lower cretaceous strzelecki group western onshore gippsland basin were used to study maximum temperatures t max reached next to dikes t max was estimated from fluid inclusion and vitrinite reflectance geothermometry and compared to temperatures calculated using heat flow models of contact metamorphism thermal history reconstruction suggests that at the time of dike intrusion the host rock was at a temperature of 100 135 c fracture bound fluid inclusions in the host rocks next to thin dikes t max systematically increases towards the dike margin to at least 500 c the estimated t max next to the thickest dike thickness d 40 m suggests an extended zone of elevated r v r to at least a distance from the dike contact x of 60 m or at x d 1 5 using a normalized distance ratio used for comparing measurements between dikes regardless of their thickness in contrast the pattern seen next to the thin dikes is a relatively narrow zone of elevated r v r heat flow modeling along with whole rock elemental and isotopic data suggests that the extended zone of elevated r v r is caused by a convection cell with local recharge of the hydrothermal fluids the narrow zone of elevated r v r found next to thin dikes is attributed to the rise of the less dense heated fluids at the dike contact causing a flow of cooler groundwater towards the dike and thereby limiting its heating effects the lack of extended heating effects suggests that next to thin dikes an incipient convection system may form in which the heated fluid starts to travel upward along the dike but cooling occurs before a complete convection cell can form close to the dike contact at x d r v r often decreases even though fluid inclusion evidence indicates that t max is still increasing further fluid inclusion evidence indicates that the evolution of water vapor or supercritical fluids in the rock pores corresponds to the zone where r v r begins to decrease the generation of the water vapor or supercritical fluids near the dike contact seems to change vitrinite evolution reactions these metamorphic conditions closer to the dike than x d 0 3 make vitrinite reflectance unreliable as a geothermometer the form of the r v r profile as it indicates t max can be interpreted using temperature profiles estimated from various heat flow models to infer whether the dike cooled by conduction incipient convection or a convection cell a contact aureole that consists of decreasing r v r or t max extending out to x d 2 and that has a t contact t magma t host 2 appears to be a signature of simple conductive cooling incipient convection is indicated by a r v r profile that decreases to background levels at x d r v r profile and consistently high r v r that may not decrease to background levels until beyond distances of x d 1 5

the thermal history of the bowen basin queensland australia vitrinite reflectance and clay mineralogy of late permian coal measures abstract the thermal history of the bowen basin queensland australia has been investigated using vitrinite reflectance data and clay mineralogy vitrinite reflectance data combined with a study of clay mineral reactions indicates that the maximum temperatures which induced organic maturation of the bowen basin coals and extensive clay mineralisation are not related to deep burial metamorphism during the latest middle triassic earliest late triassic as previously believed the results of the present study indicate that the development of a zone of high heat flow in the latest late triassic had a major control on the thermal history of the bowen basin high palaeogeothermal gradients estimated in the northern bowen basin are interpreted to result from convective heat transfer during a hydrothermal event variable heat distributions due to localised fracture enhanced permeable zones acting as hot reservoirs in the deeper part of the basin may have been responsible for some significant local thermal anomalies in the lower coal measures the estimated palaeogeothermal gradients in the southern bowen basin also indicate high heat flow in the lower sections of the stratigraphy sections in the southern bowen basin however are believed to reflect a rock dominated semi closed system with low water rock ratio where rocks are impervious to circulating fluids and thus heat transfer may have occurred by conduction the correlation between vitrinite reflectance and clay mineralogy shows a delay in illitisation reaction relative to organic maturity for many illite smectite i s mixed layer clays in the northern bowen basin this phenomenon can be explained as a result of insufficient time for the completion of mineral reactions and a variable potassium supply in relatively impermeable rocks the relationship between i s expandability and vitrinite reflectance for the bowen basin data compared to basins with known tectonic regimes suggests a thermal history in a rift setting for the bowen basin the effect of thin igneous intrusions on clay mineral reactions is very limited intensive illitisation due to heating of intrusions can only be observed in narrow zones immediately adjacent to intrusive bodies this further demonstrates that mineral reactions are too slow to record the effect of extremely short heating duration in contrast to organic maturity indicators these differences between mineral and organic parameters aid in the identification of local contact metamorphic effects

thermal and tectonic history of the ordos basin china evidence from apatite fission track analysis vitrinite reflectance and k ar dating apatite fission track analysis vitrinite reflectance data and k ar dating of permian carboniferous and mesozoic core samples have been successfully integrated to reconstruct the thermal and tectonic history of the ordos basin china apatite fission track ages of carboniferous jurassic sedimentary rocks range between 3 and 137 ma and are significantly younger than the stratigraphic ages confined fission track lengths demonstrate exclusively mixed length distribution indicating complex thermal history the data suggest that the samples must have all experienced higher paleotemperatures in the past mean vitrinite reflectance values r0 of the triassic rocks range from 0 61 to 1 06 giving a high coalification gradient of 0 36 km and suggesting a high paleothermal gradient of 57 c km permian carboniferous rocks have ro values on the order of 1 0 3 0 and locally up to 4 0 6 0 some high r0 values coincide with positive gravity and magnetic anomalies k ar dating on permian triassi samples reveals distinct illitization at 170 160 ma during which a thermal event occurred due to subsurface magmatic intrusion related to the early yanshanian movement the petroleum source rocks of the upper triassic experienced peak temperatures ranging from 90 to 160 c corresponding to the oil window and permian carboniferous source rocks were heated to more than 150 c passing through and out of the gas window due to rapid uplift and erosion in response to the rise of the qinghai tibet plateau associated with the asia india collision and the himalayan orogeny cooling has taken place at least since approximately 23 ma the difference in the rate and amount of uplift between the eastern and western parts of the basin resulted in differential uplift and the present day s ructural pattern of the basin

evolution of the northern belt southern uplands implications for the southern uplands controversy conodont and graptolite dating provide a high resolution biostratigraphical framework for correlation across the southern upland fault the establishment of an early caradoc age for the red chert and volcanic sequences within the northern belt of the southern uplands confounds the accretionary prism model and our data support the view that following the obduction of the ballantrae ophiolite fan complexes prograded southeastwards across a narrow fault bounded shelf into the deep basin of the northern belt the fan complexes were initiated by uplift in the hinterland caused by the intrusion of plutons into the midland valley terrane sedimentation was controlled by regional extension subsidence and eustasy through the llanvirn and caradoc basic lavas with attenuated within plate geochemical signatures were erupted during the early caradoc peak of extension and may have just post dated the initiation of southwards subduction beneath the lake district

geologic controls on thermal maturity patterns in pennsylvanian coal bearing rocks in the appalachian basin thermal maturation patterns of pennsylvanian strata in the appalachian basin were determined by compiling and contouring published and unpublished vitrinite reflectance vr measurements vr isograd values range from 0 6 in eastern ohio and eastern kentucky western side of the east kentucky coal field to greater than 5 5 in eastern pennsylvania southern anthracite field schuylkill county corresponding to astm coal rank classes of high volatile c bituminous to meta anthracite vr isograds show that thermal maturity of pennsylvanian coals generally increases from west to east across the basin the isograds patterns which are indicative of maximum temperatures during burial can be explained by variations in paleodepth of burial paleogeothermal gradient or a combination of both however there are at least four areas of unusually high rank coal in the appalachian basin that depart from the regional trends and are difficult to explain by depth of burial alone 1 a west northwestward salient centered in southwestern pennsylvania 2 an elliptically shaped northeast trending area centered in southern west virginia and western virginia 3 the eastern part of black warrior coal field alabama and 4 the pennsylvania anthracite region in eastern pennsylvania high rank excursions in southwest pennsylvania the black warrior coal field and the pennsylvania anthracite region are interpreted here to represent areas of higher paleo heat flow related to syntectonic movement of hot fluids towards the foreland associated with alleghanian deformation in addition to higher heat flow from fluids the pennsylvania anthracite region also experienced greater depth of burial the high rank excursion in southwest virginia was probably primarily controlled by overburden thickness but may also have been influenced by higher geothermal gradients

short paper arc reversal in the scottish southern uplands geological data permit interpretation of the northern belt of the southern uplands as an ordovician forearc basin in a northwest facing arc this collided with laurentia in the latest ordovician reversed and collided with cadomia in the early devonian since the earliest plate tectonic model for the british caledonides dewey 1969 and the interpretation of the southern uplands as ocean floor and trench sediments imbricated at a southwest facing arc mitchell 1974 the concept of northwestward subduction beneath the northern belt has been more or less undisputed mitchell mckerrow 1975 leggett et al 1979 leggett 1987 mckerrow 1988 mckerrow soper 1989 however the more recent geological as opposed to palaeontological data mckerrow 1987 and references therein are more compatible with interpretation of the northern belt as a forearc basin formed above southeastward subducting lithosphere in the proposed model fig l by the llanvirn or llandeilo subduction of an oceanic basin iapetus 1 had begun beneath an are system to the southeast fig 1a there was no major accretionary wedge and southeast of the forearc ridge in the northern belt forearc basin diachronous deposition of moffat shale was followed by greywacke sedimentation and local eruption of basaltic lavas until the caradoc the associated cockburnland volcanic arc lay immediately to the south of the northern belt morris 1987 stone et al 1987 hutton murphy 1987 and possibly included the lake district on the northern margin of cadomia the northwest flank of the volcanic arc supplied andesitic detritus to the forearc basin morris

the application of electron microscopy and microanalysis in conjunction with organic petrology to further the understanding of organic mineral association examples from mount isa and mcarthur basins australia organic petrology supported by electron microscopical and micro analytical techniques was applied to organic matter in proterozoic sediments to better understand hydrothermal processes responsible for ore grade mineralisation it was shown that organic maturation was not only closely linked to the geological history of the sediments but also highlighted heat transfer by convection as differentiated from conduction solely through sediment burial and step wise subsidence water rock ratios effect organic maturation in hydrothermal systems and erratic reflectance profiles are indicators of convective heat transfer identification and characterisation of organic materials in terms of source rock and migrated hydrocarbons was shown to be a powerful tool in reconstructing the thermal history of sediments identifying hydrothermal episodes fluid pathways and heat source in the northern australian proterozoic basins higher reflectance of organic matter towards the central parts of the mount isa basin and some of the most northerly parts point to proximity to higher heat flow at times in contrast to relatively low temperatures prevailing in the western parts of the basin next to the murphy inlier a close correlation shown between peak organic reflectance values and super sequence boundaries farther highlighted the valuable information to be gained from organic petrology by allowing the separation of processes responsible for metal dissolution and transportation from those inducing precipitation c 2001 elsevier science b v all rights reserved

stratigraphic control of hot fluids on anthracitization lackawanna synclinorium pennsylvania abstract the lackawanna synclinorium of pennsylvania contains abundant coal that was altered to anthracite rank during the late paleozoic alleghanian orogeny why did the coal in the synclinorium undergo anthracitization two alternatives have been suggested 1 the region was buried deeply during and or after the alleghanian orogeny and thus became hot in response to earth s geothermal gradient and 2 hot fluids migrating from the orogen toward the foreland carried heat into the coal and caused anthracitization if the second hypothesis is correct the region should contain evidence that hot fluids passed through the coal field observations illite crystallinity studies and fluid inclusion analyses indicate that the coal bearing pottsville and llewellyn formations and an underlying detachment fault called the pottchunk fault at or slightly below the base of the pottsville formation acted as a regional aquifer for the migration of hot fluids during the alleghanian orogeny the presence of quartz veins and the hydrothermal minerals tosudite and pyrophyllite in strata above the pottchunk fault and the apparent absence of an illite crystallinity burial gradient in the underlying strata suggest that fluids migrated through large pores in coarse grained sandstones through abundant fractures that developed in response to alleghanian deformation and along the pottchunk fault the quartz veins tosudite and pyrophyllite mineralization do not occur below the pottchunk fault except at one locality suggesting that fluid flow was greater above the fault perhaps because fracturing accompanying deformation increased permeability of the fault s hanging wall fluid inclusions in the pottsville and llewellyn formations indicate fluids achieved a minimum temperature of 270 c at a depth of 3 1 8 5 km heat flow calculations constrained by fluid inclusion data show the heat carried by the migrating fluids through the coal bearing strata was sufficient to elevate the rock temperature to anthracite grade conditions 250 c assuming that the fluid event lasted about 1 year thus deep burial 6 9 km of the coal bearing strata in the lackawanna synclinorium was not required for anthracitization anthracitization was likely the result of stratigraphically controlled hot fluid migration through the coal bearing strata at shallow depths 5 km

fluid inclusion technique for determining maximum temperature in calcite and its comparison to the vitrinite reflectance geothermometer theory laboratory experiments and empirical observation suggest that many aqueous fluid inclusions in calcite reequilibrate during overheating and therefore some homogenization temperatures t h record a temperature close to the maximum reached by the rock this characteristic suggests that aqueous fluid inclusions in calcite can be used to establish maximum temperature t peak to test this hypothesis we have compiled fluid inclusion t peak mean random vitrinite reflectance r m and present day t peak from 46 diverse geologic systems that have been at t peak from 10 4 to 10 6 yr present t peak ranged from 65 to 345 c t h modes and means ranged from 59 to 350 c and r m data ranged from 0 4 to 4 6 spanning the temperature and thermal maturity range associated with burial diagenesis hydrothermal alteration and low grade metamorphism plots of t h and t peak data for systems thought to be currently at maximum temperature demonstrate close agreement between t h and present t peak in sedimentary basins although caution should be applied the relation suggests that t h of aqueous fluid inclusions in calcite may be a useful measure of maximum temperature this study also compares t h to mean random vitrinite reflectance r m to offer further support for the use of t h as a measure of t peak and to provide a better understanding of r m t h correlates well with r m and results in a curve similar to r m vs t peak calibrations determined by other workers the strong correlation correlation coefficient r 0 93 between t peak and r m in these systems suggests that maximum temperature is the major control on thermal maturation

ordovician faunas in mass flow deposits southern scotland in the ordovician northern belt of the southern uplands basal volcanics arenig are followed by cherts llanvirn llandeilo then by graptolite shales llandelio lower caradoc and finally by caradoc greywackes within the greywackes kirkcolm formation are a number of occurrences of fossiliferous conglomerate and overlying mudstone these can be traced along strike for some 30 km the conglomerates and especially the mudstones yield rich mid caradoc shelly assemblages brachiopods 20 spp trilobites 14 spp gastropods bivalves bryozoans and the first known palaeozoic scleractiniamorph coral these occurrences are interpreted as mass flow deposits derived by downslope movement from a now vanished shelf to the north and may belong either to a single gigantic debris flow event or to a series of smaller but roughly contemporaneous flows strong faunal similarities to faunas at girvan western scotland and tyrone northern ireland lying north of the southern upland fault may suggest sinistral strike slip movement of no more than a few hundred kilometres

a vitrinite reflectance kinetic model incorporating overpressure retardation abstract the models currently used to predict maturation and hydrocarbon generation in petroleum basins use time and temperature as controlling parameters a small number of studies have indicated that overpressure can retard maturation although some of the published information from experimental investigations appears to be conflicting careful examination of the experimental conditions shows that both vitrinite reflectance and hydrocarbon generation are retarded by overpressures overpressure appears to result in the retention of volatiles within the molecular structure which prevents the molecular reorganisation necessary to produce higher reflectance values using a database containing vitrinite reflectance from both overpressured and normally pressured wells a kinetic model presro has been developed in which overpressure modifies the arrhenius a factor the model has been tested on two different basins south china sea and sable exhibiting a range of time temperature overpressure characteristics the results suggest that the maturity and timing of the onset of hydrocarbon generation differ significantly from those predicted by current models

subsurface fractures and their relationship to stress history in east texas basin sandstone abstract subsurface fractures were sampled with more than 400 m of core from the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 600 m thick that was deposited in the gradually subsiding gulf coast basin depth to the top of the formation in east texas now ranges between 1800 and 2900 m fractures in sandstone exhibit features that are due to intermittent fracturing and sealing crack seal which suggest that the fractures are the result of episodes of fluid pressure in excess of hydrostatic correlation of the vein mineral precipitation sequence with the diagenetic history and the results of previous 18 o studies of quartz cement indicates that fractures propagated at depths of between 900 and 1500 m during the migration of quartz precipitating fluids fracture permeability provides a mechanism for the passage of large fluid volumes recorded by the precipitation of extensive quartz cement in the formation fractures stopped propagating before maximum burial depth was achieved during approximately 1500 m of subsequent burial fractures either remained partly open or were sealed by postkinematic ankerite and clay minerals

deep crustal structure and carboniferous basin development within the iapetus convergence zone northern england seismic reflection data from northern england are interpreted to show a northward dipping caledonian thrust zone lying beneath the faulted southern margin of the northumberland trough the thrust zone lies upon the updip projection of a northward dipping high conductivity layer in the middle and lower crust identified by magnetotelluric sounding together these features indicate the presence of a crustal scale caledonian shear zone dipping north at an average angle of 20 25 extensional reactivation of the middle and upper crustal parts of the shear zone in carboniferous times led to development of the northumberland trough reappraisal of the birps nec seismic profile suggests the presence of the same or similar crustal shear zone reactivated to form the offshore extension of the northumberland trough the shear zone probably formed as a major compressive or transpressive feature during late caledonian acadian continental collision in the lower crust the shear zone lies close to or may actually represent the iapetus suture at middle to upper crustal levels the shear zone lies wholly within avalonian english crust well to the south of the faunally determined iapetus suture westward extrapolation of the shear zone indicates that it may crop out within the northern lake district perhaps as the causey pike and associated thrusts the faunal suture is likely to subcrop north of the lake district and alston block beneath the central part of the northumberland trough

organic maturation levels thermal history and hydrocarbon source rock potential of the namurian rocks of the clare basin ireland abstract vitrinite reflectance data from two inland cored boreholes confirm high maturation levels throughout the onshore part of the irish clare basin and suggest erosion of 2 to 4 km of late carboniferous cover and elevated palaeogeothermal gradients in the carboniferous section the observed maturation gradients are fully consistent with the published hypothesis of a late carboniferous permian superplume beneath pangaea but local vertical reversals in gradients also suggest a complex thermal regime probably involving advective heating the uppermost visean lower namurian clare shale is laterally extensive and up to 300 m thick although this unit is post mature toc values of up to 15 suggest that it could have considerable hydrocarbon source rock potential in any less mature offshore parts of the basin

on the fundamental difference between coal rank and coal type abstract this article addresses the fundamental difference between coal rank and coal type while theoretically settled long ago as being different aspects of coal systems science the two concepts are still often confounded in recent years this has resulted in the publication of several works stating that coal type changes with coal rank coal type refers solely to coals depositional origin and the maceral mineral admixture resulting from that origin coal types typically fall in to two categories humic coals developed from peat and sapropelic coals developed from organic mud either type may be allocthonous or autochthonous and within types further refinement of depositional environment can be made coal rank refers to the changes in geochemistry and resultant changes in reflectance caused by increasing thermal maturity of the coal thus it provides an overprint of maturity on existing coal types with proper techniques such as use of crossed polars and etching maceral forms can be differentiated even at high ranks and the original coal type determined

does the golden spike still glitter a modus operandi for precambrian stratigraphy is suggested which combines the geochronometrical scale and late proterozoic chronostratigraphy the development of phanerozoic stratigraphical classification is followed from the pioneering days of murchison through the growing understanding of fossils in relation to time and the later distinction of rock and time rock to the advent of the golden spike criticisms of chronostratigraphy global standard stratigraphy are assessed and its value upheld stratigraphical procedures such as those of event stratigraphy are useful in particular situations but correlative methods in the phanerozoic are dominated by biostratigraphy examples are taken of its use and potential in north american cordilleran palaeozoic stratigraphy in the triassic system as a whole and in the caledonides of britain and ireland

cleavage development within a foreland fold and thrust belt southern pyrenees spain abstract in the southern pyrenees lithologically distinct cleavage fronts are each parallel to bedding and dip 20 towards the foreland pressure solution was the dominant mechanism of cleavage development the mudstone cleavage front is coincident with the 195 c paleoisotherm and is associated with a pressure solution strain of 5 a mechanical twin strain of 4 and a deviatoric stress magnitude of 65 mpa illite crystallinity measurements define a geothermal gradient of 15 c km 1 and indicate that the paleoisotherms are bedding parallel deviatoric stress magnitudes from calcite twins were regionally constant at 65 mpa and principal stress axes were perpendicular to cleavage temperature was the primary control on deformation micromechanisms and the position and orientation of the cleavage front within the foreland thrust wedge deformation below the cleavage front occurs predominantly by pressure solution which in conjunction with mechanical twinning and microfracturing produces a quasi plastic rheology stress magnitudes determined from mechanical twinning of carbonate grains and long term 10 6 10 76 y strain rates determined for regional folds and faults suggest an apparent macroscopic viscosity of 9 8 10 18 to 7 2 10 19 pa s for the lower thrust wedge above the cleavage front temperature pressure solution strain total strain and mesoscale deformation diminish the region of the thrust wedge above the 100 c paleoisotherm is characterized by large brittle faults with cataclastic fault zones and negligible grain scale deformation indicating an elastico frictional rheology

thermal and burial history of the cracow silesia region southern poland assessed by conodont cai analysis abstract conodont colour alteration cai data have been applied in the reconstruction of palaeothermal conditions in the cracow silesia region southern poland the analysis of conodont cai values supplemented by electron spin resonance esr data provided a complex maturity pattern which coincides well with the tectonostratigraphical divisions of this region during the variscan and alpine diastrophic cycles the palaeozoic rocks in the upper silesian coal basin attained the observed thermal maturity during late carboniferous or permian time just after the tectonic inversion of the basin vertical maturity trends suggest that palaeo geothermal gradients were significantly higher than the present values the irregular maturity pattern recognized in the cracow myszkow zone is related to the thermal overprint of intrusive igneous rocks on the maturity field resulting from the relatively shallow burial this pattern has not been modified by mesozoic hydrothermal events the low maturity level of devonian and early carboniferous rocks in the substrate of the carpathian foredeep is a product of the subsidence during miocene time the implications for hydrocarbon generation and further exploration are discussed the cai data are consistent with other indicators of organic metamorphism previously used in this region the study highlights also features about the conodont colour alteration such as the influence of silica mobilization on conodont colour which limit the application of the cai method

the southern uplands controversy report of a discussion meeting held at burlington house on 12 february 1986 the idea for a discussion meeting followed from remarks made by professor c h holland 1986 in his presidential address to this society in 1985 when he expressed concern about the uncritical application of the accretionary prism model to the southern uplands of scotland it has since become apparent that divergent views are held both among those against the model and those in favour of it this meeting served to air some of these different opinions even if it has not immediately resolved many of the arguments most of the contributors to the meeting see the society newsletter for january 1985 have produced written papers for this volume and so far only one or two have modified their views between writing their abstract and submitting their paper the concept of an accretionary prism model developed gradually a comparison of scotland with burma suggested that the southern uplands were like western burma where trench and oceanic sediments are being underthrust by subduction processes mitchell mckerrow 1975 with the development of modern analogues from the pacific seeley et al 1974 karig sharman 1975 the model was applied to the southern uplands with more emphasis mckerrow et al 1977 leggett et al 1979 a b 1982 moseley 1977 1978 was one of the first to express doubts about this model he believed that the iapetus ocean had closed by the end of the ordovician and thus like many others

petroleum generation simulation over six years of hydrocarbon formation from torbanite and brown coal in a subsiding basin abstract dry samples of torbanite and soft brown coal from which mineral matter and material soluble in chloroform have been removed have been artificially matured in an attempt to simulate conditions in a subsiding sedimentary basin with a constant geothermal gradient sealed tubes were increased in temperature by 1 c per week beginning at 100 c a tube containing each source material was opened and analysed at yearly intervals for six years olefins and carbon monoxide were not significant products at any stage at less than 300 c torbanite generated a paraffinic crude oil in 35 yield while the brown coal gave a wet co2 rich natural gas in most respects these experiments which are possibly as slow as can be realistically planned within a human time scale appear to have duplicated geochemical hydrocarbon generation

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

paleomagnetic results from volcanic rocks of the shelve inlier wales evidence for a wide late ordovician iapetus ocean in britain abstract in order to shed light on the early paleozoic paleogeography of iapetus bordering continents samples for paleomagnetic study were collected from middle ordovician llanvirn volcanic rocks of the shelve inlier welsh borderland the folding within the inlier is constrained to late ordovician ashgill time thus offering a fold test with tight age brackets after stepwise thermal demagnetization a pre folding characteristic magnetization component was isolated from 95 specimens the mean of 11 site mean directions for the characteristic magnetization gives d i 116 4 67 9 k 89 4 95 4 9 and the paleomagnetic pole lies at 26 6 n 36 1 e p 6 9 m 8 2 the fold test is positive at the 99 confidence level indicating that the magnetization was acquired during the middle or late ordovician we infer from geological considerations that this magnetization is not a primary thermoremanence but was acquired during late ordovician time as a result of a thermochemical disturbance of that age our results indicate that southern britain was near 51 south latitude during the later ordovician since middle to late ordovician paleolatitudes for gondwana and laurentia are well determined our result can be used to test various scenarios for the closure of iapetus we conclude that 1 the iapetus ocean in britain still had a latitudinal width of some 30 at this time thus rendering a postulated ordovician closure unlikely 2 southern britain avalon and hercynian europe all occupied high latitudes during the later ordovician consistent with a paleoposition near the northern margin of gondwana and 3 the acadian orogeny in britain and north america could have been the result of the collision of gondwana and laurentia during early devonian time

metabentonites in the moffat shale group southern uplands of scotland geochemical evidence of ensialic marginal basin volcanism metabentonites occur extensively in the moffat shale group of the southern uplands of scotland at dob s linn 135 metabentonite beds 1 50 cm thick occur in ashgill to llandovery strata representing an aggregate thickness of 6 m of compacted ash accumulated over approximately 25 ma the metabentonites are characterized by relatively high concentrations of trace elements including ba cs hf nb rb ta th u y zr and rees which were inherited from evolved vitric ash immobile trace element data indicate that a spectrum of silicic ash compositions accumulated ranging from subalkaline to mildly peralkaline in the late ordovician n gracilis to g persculptus biozones subalkaline ash falls predominated whereas peralkaline ash falls predominated in the llandovery silurian p acuminatus to m convolutes biozones giving way to predominantly subalkaline ash falls during accumulation of the m sedgwickii to r maximus biozones changeovers in the dominant ash types are marked by increased proportions of ash the magmas from which the ash types evolved were generated in an ensialic arc transitional to a back arc setting and involved attenuated sialic crust and mantle characterized by variable depletion in hfs elements lithological petrological and ree characteristics suggest that the moffat shale group is not exclusively pelagic in origin and probably accumulated in a back arc basin bordering an ensialic arc terrane

implications for timing of andean uplift from thermal resetting of radiation damaged zircon in the cordillera huayhuash northern peru abstract the cordillera huayhuash is a north south oriented range along the drainage divide of the northern peruvian andes the range has high topography with peaks in excess of 5500 m and the second highest peak in peru nevados yerupaja 6617 m bedrock is dominated by folded mesozoic miogeoclinal rocks unconformably overlain by mid tertiary volcanics intruded by late tertiary granitic rocks and silicic dikes zircon fission track zft and u th he zhe dating of zircons along a west east transect elucidates the thermal evolution of exhumed and uplifted rocks the stability of fission tracks in zircons is a function of single grain radiation damage in samples with grain to grain variability in radiation damage resetting results in variable resetting and multiple age populations low retentive zircons lrzs which have a partly disordered crystalline structure have significant radiation damage and a low temperature of annealing ca 180 200 c high retentive zircons hrzs which are nearly cry

chemostratigraphy k ar ages and illitization of silurian k bentonites from the central belt of the southern uplands down longford terrane british isles the central belt of the southern uplands terrane in both scotland and ireland is a faulted and imbricated sequence of caradoc to llandovery shales and llandovery turbidites with numerous interbedded k bentonites the bentonites are composed dominantly of r3 ordered mixedlayer illite smectite i s containing 90 95 illite and represent the product of illitization during low grade metamorphism k ar age determination on the m size fraction gave a range from 379 10 to 406 10 ma the fixed k is thought to have originated in the precursor ash and was remobilized during the transformation of smectite to i s k ar ages record a retrograde thermal event that post dates wenlock prehnite pumpellyite facies metamorphism and is contemporaneous with cooling and uplift during the end silurian early devonian collision of laurentia with the east avalonian terrane differences in rb and other trace elements between the k bentonite beds are due in part to differences in original ash composition and can be used to group the beds within biostratigraphically defined boundaries the chemical identification of groups of k bentonite beds offers additional criteria for their stratigraphical correlation on a regional scale

experimental study on the pressure dependence of vitrinite maturation we conducted the first systematic experiments over a pressure range of 0 5 to 20 0 kbar at temperatures of 200 to 350 c and run durations of 2 4 and 7 days to investigate the influence of pressure on vitrinite reflectance the data indicate that applied pressure lowers vitrinite reflectance the suppression appears to be stronger under wet than under dry conditions in addition high pressure favors liptinite preservation at temperatures 300 c whereas at the same temperature range yet at low pressure liptinite is decomposed our data fit an empirical rate equation which expresses rr as a function of pressure temperature and time the derived equation satisfactorily describes our experiments and enables extrapolations to geological timescales values of rr calculated for a pressure of 0 5 kbar are remarkably consistant with previous numerical pressure independent models a literature review shows that previous experimental data and field observations are inconsistent regarding the effect of pressure on vitrinite maturation this and some previous studies suggest that vitrinite maturation is suppressed by increased pressure whereas other workers regarded pressure as having little influence on the rate of coalification we suggest that original virinite composition experimental design and natural environment tectonic regime play important roles regarding the effects of pressure on vitrinite maturation interpretation of geothermal histories of sedimentary rocks based on vitrinite reflectance data must therefore include evaluation of the pressure otherwise vitrinite reflectance data from high pressure terranes should be interpreted with caution if used as a quantitative paleogeothermometer

tectono magmatic controls of post subduction gold mineralisation during late caledonian soft continental collision in the southern uplands down longford terrane britain and ireland a review abstract the southern uplands down longford terrane sudlt within the british caledonides hosts several economically significant gold occurrences including a 45 km long gold trend in central ireland that includes the proven deposit at clontibret however the region is relatively underexplored for gold and the well constrained geology and tectonic history of the terrane provide a firm geological framework for investigating the roles of tectonic magmatic and metamorphic processes in gold mineralisation during the transition from subduction of oceanic lithosphere to soft thin skinned continental collision the sudlt is an ordovician silurian fore arc accretionary complex that evolved into a foreland basin fold and thrust belt during continental collision in earliest devonian times comparable terranes in phanerozoic orogenic belts globally host significant orogenic gold deposits however the sudlt exhibits a very low metamorphic grade and mineralisation exhibits similarities with orogenic intrusion related and post subduction porphyry gold systems gold in the sudlt predominantly occurs as a lattice constituent of arsenopyrite and pyrite within quartz carbonate veins and disseminated within phyllic and propylitic potassic alteration haloes around quartz carbonate veins and some minor intrusions fluid inclusion data indicate that the gold was deposited from a low salinity mesothermal 330 c carbonic fluid of mixed magmatic metamorphic origin consistent with caledonian orogenic conditions gold mineralisation occurred at shallow crustal depths of less than 10 km and exhibits a broad spatial association with major ne sw trending caledonoid shear zones d1 economically significant gold mineralisation in the sudlt is most commonly hosted by transverse nw se and n s trending fractures d3 constrained to between 418 and 410 ma that cut anchizone epizone facies volcaniclastic turbiditic metasedimentary host rocks the mineralised d3 structures cut and are cut by broadly coeval polyphase diorite and granodiorite intrusions gold mineralisation is associated with the early dioritic i type metaluminous oxidised phase of trans suture suite magmatism that straddles the iapetus suture but predates the later emplacement of s type granitic magma the host structures were subsequently reactivated during late palaeozoic mesozoic and cenozoic times and host younger base metal deposits pb zn cu sn sb mineralisation occurred in early devonian times 418 and 410 ma following arrival of the avalonian continental margin at the subduction trench at 420 ma coeval with the onset of regional transtension post subduction lithospheric mantle delamination and k lamprophyric and mafic to intermediate calc alkaline magmatism gold in the sudlt therefore provides a case study for relationships between post subduction porphyry and orogenic gold mineralisation in soft continental collision zones the transient geodynamic setting between subduction and transtension common during soft continental collision provided the critical elements of the mineralising system a metasomatically fertilised mantle source transient geodynamics favourable lithospheric architecture for the rapid transfer of mass and energy from subcrustal to upper crustal levels thin skinned deformation and relatively low exhumation favours the preservation of mineral deposits in the upper crust

paleocurrent evidence for lateral displacement of the pliocene colorado river delta by the san andreas fault system southeastern california more than 600 paleocurrent measurements from fluvial paleochannels of the early colorado river delta plain preserved in the palm spring formation in the fish creek vallecito fcv section of southern california indicate that the fcv section was on the gulf of california southeastern flank of the delta plain as recently as 2 8 ma these measurements imply 130 km of tectonic translation to the northwest since 2 8 ma which can be accounted for by the displacement histories of baja california and component faults of the san andreas system stratigraphic data from the fcv section and other neogene localities when plotted on a palinspastic base indicate 1 marine transgression of a narrow gulf of california rift basin and bouse embayment site of modern lower colorado river by 5 5 ma and 2 uplift of the bouse embayment initiation of the lower colorado river and southward progradation of the delta to essentially its present position by 4 ma

implications for organic maturation studies of evidence for a geologically rapid increase and stabilization of vitrinite reflectance at peak temperature cerro prieto geothermal system mexico discussion a short term rapid heating and cooling of the rock in well m 94 below 1300 m was caused by a pulse of hot water passing through the edge of the cerro prieto mexico geothermal system below 1300 m the peak paleotemperatures were about 225 250 degrees c but equilibrium well log temperatures indicate a decrease to 150 210 degrees c at present this hot water pulse sharply increased vitrinite reflectance to levels comparable to those measured in the central part of the system even though studies of apatite fission track annealing indicate that the duration of heating was only 10 0 10 1 yr in m 94 in contrast to 10 3 10 4 yr in the central part of the system these data indicate that sedimentary organic matter chemically reacts quickly to temperature increases of about 125 degrees c above ambient even when the higher temperature existed for only 10 0 10 1 yr the quick change of the vitrinite reflectance geothermometer indicates that thermal maturation reactions can stabilize after a geologically short period of heating to a level consistent with peak temperature under moderate to high temperature diagenesis in open fluid rich geothermal systems cerro prieto is one of the most intensively studied and well known geothermal systems in the world thus data from cerro prieto are a benchmark to compare with the predictions of published thermal maturation models such as those formulated by j karweil n v lopatin and a k burnham and j j sweeney these thermal maturation models inaccurately predict duration of heating at cerro prieto the kinetic equations used in these models explicitly allow thermal maturation to continue indefinitely at peak temperature which does not seem to be the case at cerro prieto

relationships between thermal maturity indices calculated using arrhenius equation and lopatin method implications for petroleum exploration thermal maturity can be calculated with time temperature indices tti based on the arrhenius equation using kinetics applicable to a range of types ii and iii kerogens these ttis are compared with tti calculations based on the lopatin method and are related theoretically and empirically via vitrinite reflectance to the petroleum generation window the ttis for both methods are expressed mathematically as integrals of temperature combined with variable linear heating rates for selected temperature intervals heating rates control the thermal maturation trends of buried sediments relative to arrhenius ttis lopatin ttis tend to underestimate thermal maturity at high heating rates and overestimate it as low heating rates complex burial histories applicable to a range of tectonic environments illustrate the different exploration decisions that might be made on the basis of independent results of these two thermal maturation models

late caledonian dyke swarms in southern scotland a regional zone of primitive k rich lamprophyres and associated vents siluro devonian magmatism in the southern uplands scotland and northern ireland includes a hitherto neglected regional sw ne zone c 10 km wide and 300 km long of calc alkaline lamprophyre dykes lamprophyres were locally emplaced contemporaneously with small 100 km depths b a contribution from subducted sedimentary material and c volatile components added metasomatically in the crust or mantle during ascent rb sr isochron and new k ar biotite hornble

thermal history of alberta deep basin comparative study of fluid inclusion and vitrinite reflectance data the thermal history of the alberta deep basin the gas saturated westernmost part of the western canadian sedimentary basin has been studied by analyzing aqueous and hydrocarbon fluid inclusions in diagenetic cements and comparing the results with coal maturity data results indicate that most of the diagenetic quartz druse precipitated from low salinity fluids 2 3 wt at a temperature of 170 195 c calcite cement precipitated after quartz druse during uplift and cooling at temperatures of 108 169 c inclusions rich in larger hydrocarbon molecules occur in cements that precipitated at 150 c whereas methane rich inclusions occur in cements that precipitated at 165 c or at lower temperatures after significant uplift and cooling of the b sin maximum burial temperatures tmb calculated from vitrinite reflectance data using the lopatin waples tti ro calibration are significantly lower 150 c than the temperature at which quartz druse precipitated in the same area 190 c an equation directly relating tmb and ro proposed by barker and pawlewicz in 1986 yields maximum burial temperatures 200 210 c only slightly higher than the fluid temperatures the results from this study suggest that hot fluids migrated updip along permeable conglomerates and bedding plane fractures to produce unexpectedly high geothermal gradients 38 c km in the western part of the study area the apparent restriction of hot fluids to the western part of the study area sugge ts that convective heat transfer by fluids may have operated on a scale of only tens of kilometers in lower cretaceous rocks of the alberta deep basin

is the southern uplands of scotland really an accretionary prism we argue that there is little which demands the accretionary prism model for the widespread silurian rocks of the southern uplands of scotland and ireland with new data from ireland we reinterpret these rocks as the turbidite fill of a successor basin that formed after the subduction of iapetus oceanic crust finally stopped at the end of the ordovician the structure of the basin is a sinistral transcurrent imbricate stack the result of oblique terminal collision of cadomia with laurasia at the end of the silurian

stochastic thermal history modelling 1 constraining heat flow histories and their uncertainty we introduce a novel application of the markov chain monte carlo mcmc method to address the problem of characterising uncertainties in modelled thermal histories as real data are never perfect uncertainties in measurement will be propagated through to final estimates of hydrocarbon volumes types and locations and therefore it is important to characterise the nature of the uncertainty at each stage of the modelling process here we specifically consider heat flow parameters used to generate thermal history models and illustrate the use of the mcmc method on both synthetic and real well data we show that this technique is able to both recover a good data fitting model and perhaps more importantly to characterise the uncertainties on every heat flow model parameter the approach described here is generally applicable for characterising the parameter uncertainties in various other aspects of basin modelling

a model of hydrocarbon generation from type i kerogen application to uinta basin utah we have developed a computer model that can predict when and how much oil and gas are generated from a source rock during its burial and later uplift kinetic parameters for the oil and gas generation reactions are obtained from high pressure pyrolysis experiments carried out over a wide range of heating rates and temperatures in our kinetic model which applies only to green river shale we use a single activation energy of 52 4 kcal mole and different pre exponential factors for different products of primary pyrolysis which allows us to extrapolate laboratory derived kinetics to geologic heating rates this model is in contrast to the wide distributions of activation energies or artificially low apparent activation energies used in some models of petroleum formation hen extrapolated to geologic heating rates on the order of 10 c m y our kinetics show that the temperature of the maximum rate of oil generation tp changes by about 15 c when the heating rate is changed by an order of magnitude changes in pressure have relatively minor effects on the kinetics of oil generation but are important for gas generation reactions we used geophysical data from oil fields in the uinta basin of utah to develop a thermal history model of green river formation source rocks this time temperature history was used to predict the maturation level of the kerogen at a given depth and to predict changes in the compositional characteristics of the oil the shape of calculated oil generation rate curves as a function of depth in the basin mimics the shape of the overpressure curves this similarity suggests that oil gas generation may be an important cause of overpressuring maturation levels and compositional characteristics of the oil predicted by our model agree very well with characteristics of the oil recovered from the basin

mechanisms of coal metamorphism case studies from paleozoic coalfields controls on coal metamorphism can be complex in this paper we examine four paleozoic coalfields the western kentucky portion of the illinois basin the pennsylvania anthracite fields the south wales coalfield and the bowen basin an increase in temperature with depth of burial is certainly a factor in coal metamorphism in many coalfields however including the coalfields reviewed here it has become apparent that such a simple mechanism does not explain the coal rank patterns observed the flow of hydrothermal fluids through the coals has been proposed as a cause of coal metamorphism evidence includes inverted rank gradients elevated cfl as an indicator of brine fluids isotopic evidence for hydrothermal fluids and vein and cleat mineral assemblages in any case multiple hypotheses must often be evaluated in the examination of any coalfield since the simple paradigm of coal rank increases with a simple increase in temperature with increasing depth does not fit the evidence observed in many cases

the iapetus model a plate tectonic concept for the variscan belt of europe abstract a plate tectonic model is presented explaining the evolution of the variscan belt of europe it regards the iapetus ocean and its branch the tornquist sea as the only ocean involved in the caledonian variscan and alleghenian mega orogen the iapetus and its marginal basins disappeared through oblique subduction and collision in the following sequence 1 1 northeastern iapetus including the tornquist sea caledonian orogeny 2 2 central iapetus acadian orogeny 3 3 adjacent marginal basins variscan orogeny and 4 4 southwestern iapetus alleghenian orogeny the area of the variscides was part of the continental margin of gondwana made up of ridges and ensialic basins no ocean lay within the variscan area during the palaeozoic although patches of oceanic crust probably existed in rift basins e g the lizard ophiolite after the silurian early devonian closure of northwestern and central iapetus the variscan area was surrounded by cratons on three sides in a manner similar to that around the modern mediterranean sea the subsequent variscan orogeny was essentially an ensialic thrusting and folding induced by a further approach of gondwana toward laurentia after the variscan collision gondwana rotated clockwise to the west by moving along a strike slip zone this rotation during the carboniferous opened the palaeo tethys in the east and caused the alleghenian collision in the west the middle ordovician to permian palaeogeography is presented on a series of maps modelling tectonic displacement and plate motions avalonia is interpreted as the ordovician volcanic island arc of gondwana separated from mainland gondwana by an oceanic gulf or a back arc basin the iberian arc may have originated by a continental escape of iberia from the center of collision into the oceanic gulf the variscan austro alpine and southern alpine units are today located near their earliest early carboniferous position

strain related differences in the crystal growth of white mica and chlorite a tem and xrd study of the development of metapelitic microfabrics in the southern uplands thrust terrane scotland tem and xrd techniques were used to study crystal growth characteristics of the fabric forming phyllosilicates which developed in response to low grade metamorphism and tectonic imbrication in part of the southern uplands thrust terrane prograde regional metamorphism ranging from late diagenesis through the anchizone to the epizone was accompanied by the development of a slaty cleavage which is commonly bedding parallel tem measured mean thicknesses of white mica and chlorite crystallite populations increase with advancing grade and correlate with xrd measured crystallinity indices analytical tem data show that prograde changes in composition lead to a net loss of si ca and minor fe from the fabric forming phyllosilicates white micas are paragonite poor phengites with a mean b lattice parameter of 9 037 a and indicate an intermediate pressure series of metamorphism with a field gradient of 25 c km chlorite compositions evolved from diabantite with intergrown corrensite to ripidolite over an estimated temperature range of 150 320 c field gradient and temperature estimates suggest that crystal growth and fabric development occurred at burial depths ranging from 6 km to at least 13 km in the thrust terrane during late diagenesis crystal growth of white mica and chlorite was predominantly a consequence of polytypic and phase transitions and resulted in similar size distributions which resemble typical ostwald ripening curves under anchizonal and epizonal conditions white mica grew more rapidly than chlorite because of its greater ability to store strain energy and recover from subgrain development as a result crystal thickness distributions are not typical of ostwald ripening in contrast chlorite crystals which grew under these conditions developed subgrain boundaries at high strain rates which were only partially recovered at low strain rates these retained dislocations reduce the crystallite thicknesses detected by tem and xrd compared with those of white mica these differences in strain induced crystal growth indicate that white mica illite and chlorite crystallinity indices are likely to show significant differences where low grade metamorphism is closely associated with tectonic fabric development

xenoliths of iapetus suture mylonites in county down lamprophyres northern ireland two caledonian lamprophyre dykes intruding upper llandovery greywackes in the central belt of the southern uplands down longford terrane on the coast of down carry numerous cognate and incognate xenoliths the incognate xenolith population is dominated by schistose or mylonitic basic and intermediate metavolcanics some of which are macroscopically banded and rodded the geochemistry of one large xenolith is that of a calc alkaline ensialic magmatic arc basalt remarkably similar to the basalts of the borrowdale volcanics the xenolith has undergone pumpellyite actinolite facies metamorphism in a deep seated shear zone at depths between 7 and 30 km these incognate xenoliths apparently provide the first direct geological evidence of the lithological nature of the unexposed basement of the southern uplands down longford terrane they offer strong support for the hypothesis that the southern uplands was underthrust along the iapetus suture by a basement of lake district type the surface interpreted as the suture on the winch 2 seismic reflection profile inclines to the north to a depth of 21 km below the county down lamprophyre outcrops the lamprophyres have sampled both basement and iapetus mylonites one of the host lamprophyres has been dated by k ar hornblende at 415 12 ma this implies a minimum of 30 km of underthrusting on the suture before the end of the silurian

pressure temperature time paths the past decade has been a time of unprecedented improvement in our ability to reconstruct the thermal evolution of orogenic belts like many instances of rapid advancement in science this achievement can be traced to the convergence of disparate research directions the new field of thermochronology the study of the time temperature evolution of rocks derived from the realization by geochronologists that many mineral iso topic systems could be used to determine the time of cooling of a terrain through a series of predictable temperatures e g armstrong 1966 wagner et ai 1977 harrison mcdougali 1980 berger york 1981 petrologists have made great progress in their ability to discern the pressure tem perature history of metamorphic rocks through the improvement of con ventional thermobarometric techniques see bohlen lindsley 1987 and essene 1989 for reviews and the development of important new approaches to relating changes in mineral chemistry to changes in environ mental parameters spear selvcrstonc 1983 st onge 1987 from a theoretical standpoint several geophysical papers in the midto late 1970s and early 1980s explored heat transfer processes in orogenic belts and the role of these in the development and preservation of metamorphic mineral assemblages oxburgh england 1974 bickle et a1 1975 bird et a1 1975 england richardson 1977 toksoz bird 1977 england thompson 1984 among others the integration of geochronologic and petrologic techniques aliows us

the age and provenance of metasedimentary rocks in the quetico subprovince ontario from single zircon analyses implications for archean sedimentation and tectonics in the superior province abstract u pb isotopic analyses have been performed on single detrital zircon grains from greywacke samples collected along the northern boundary of the quetico subprovince in northwest ontario secondary lead loss was virtually eliminated by choosing crack free grains and removing the outer surface using air abrasion thus the 207 pb 206 pb age can be considered a good approximation to the age of crystallization of each grain zircons in the quetico metasediments show a range of ages from 2698 3 ma to 3009 4 ma deposition and metamorphism of the metasediments is bracketed within a 10 5 ma time span between crystallization of the youngest detrital zircon grain and a late tectonic intrusion the blalock pluton which cuts the sediments and has a zircon age of 2688 4 ma the most easterly metasediment sample contains zircons with ages which cluster around 3007 6 ma which is within error of the age of a batholith dated in the adjacent marmion lake area of the wabigoon subprovince this along with the fact that most detrital zircons were only slightly abraded by sedimentary transport suggests that the source of many zircons may have been proximal from the north there is also a significant cluster of young zircon ages in the range 2698 2709 ma surprisingly only a few ages correspond to the time of most intense arc type felsic volcanism 2710 2745 ma in the main greenstone belt of the western wabigoon subprovince sedimentary deposition occurred at a time of extensive deformation in the adjacent wabigoon subprovince the pattern of detrital grain ages indicates that this involved uplift of a complex older sialic landmass petrographic evidence for the presence of substantial felsic volcanic detritus as well as the fact that many of the zircons only slightly pre date deposition indicates that much of the sediment was probably derived from erosion of active felsic volcanic centers these data combined with regional geochronological and field studies favour deposition in a basin formed by late orogenic collisional events

a comparative study between present and palaeo heat flow in the qiangtang basin northern tibet china the qiangtang basin is a significant prospective area for hydrocarbon and gas hydrate resources in the tibetan plateau china however relatively little work has been performed to characterise heat flow in this basin which has restricted petroleum and gas hydrate exploration in this study we compare present and palaeo heat flow in the qiangtang basin to provide information on geothermal regime hydrocarbon generation and permafrost that is necessary for further petroleum and gas hydrate exploration we base our study on temperature data from a thermometer well thermal conductivity tests vitrinite reflectance data homogenisation temperature data from fluid inclusions stratigraphic information and a time independent modelling approach our results indicate that in the central qiangtang basin the present thermal gradient is approximately 15 5 c km and heat flow is approximately 46 69 mw m 2 heat flow in the qiangtang basin is not relatively stable since the early jurassic as previous research has suggested and it is generally decreasing with time additionally there is a clear difference between the hottest thermal regime of the southern and northern qiangtang depressions during cretaceous to pleistocene time in the southern qiangtang depression the palaeogeothermal gradient is approximately 32 0 c km and palaeo heat flow is approximately 70 mw m 2 however in

volcanic clasts in silurian conglomerates of the midland valley hagshaw hills inlier scotland and their meaning for caledonian plate tectonics 34 igneous clasts of predominantly rhyolitic composition of the parishholm and hareshaw conglomerate silurian hagshaw hills inlier midland valley scotland have been analysed for major and trace element contents the geochemical composition of the clasts indicates different source areas firstly some clasts are derived from rhyolites of a within plate setting peralkaline rhyolites of oceanic islands or continental rifts and secondly other clasts are derived from calc alkaline to high k rhyolites such rhyolites erupt mainly above convergent plate boundaries but occur also in continental areas of crustal extension both conglomerates were shed from the direction of the southern uplands into the midland valley since no calc alkaline rhyolites are known in the southern uplands a volcanic terrane should have been situated during the silurian in the area where the southern uplands lie now the geotectonic character of this terrane cannot unequivocally be identified with the help of the trace element data of the clasts therefore several models are discussed

a caradoc failed rift within the ordovician marginal basin of wales the dolerite and basalt intrusions within the lower palaeozoic sequence of northwest wales are largely restricted to the outcrop of ordovician strata their distribution and close association with known volcano tectonic structures were controlled by a tectonic framework of deep seated fractures in central and northern snowdonia volcanism during caradoc times was related to the evolution of a fracture controlled trough an increase in the extensional stress across the trough with time is reflected in the progressive increase in basaltic magma movement during the volcanic cycle the trough represents an attempted rift in the lithospheric plate which failed to create an ocean basin and was subsequently aborted

continental margin tectonics forearc processes recent studies of convergent plate margins and the structural development of forearc terranes are summarized in a critical review of u s research from the period 1987 1990 topics addressed include the geometry of accretionary prisms coulomb wedge taper and vertical motion in response to tectonic processes offscraping vs underplating or subduction the response to oblique convergence fluids in forearc settings the thermal framework and the effects of fluid advection and serpentinite seamounts also included is a comprehensive bibliography for the period

precursor and ambient rock paleothermometry to assess the thermicity of burial dolomitization in the southern cantabrian zone northern spain paleozoic rocks in the cantabrian zone and the variscan foreland fold and thrust belt on the iberian peninsula have been affected by a sequence of diagenetic to epizonal thermal events late to post variscan hot fluid circulation caused a large scale burial dolomitization and ore mineralization mostly in cambrian and a lower to middle carboniferous carbonate sucessions the goal of this study is to analyze and compare the temperatures experienced by the carbonate precursor rocks as well as the under and over lying siliciclastic ambient rocks to gain a better understanding of the thermicity of dolomitization these temperatures are evaluated based on published paleothermal datasets combined with new data obtained from rock eval pyrolysis and vitrinite reflectance analysis of carboniferous rocks rich in organic matter the overall results indicate that reworking of detrital sediments in synorogenic ambient siliciclastics results in an anomalously high thermal maturity recorded by bulk rock techniques such as illite crystallinity and rock eval pyrolysis in situ vr derived paleotemperatures recorded by ambient siliciclastic rocks appear to be higher compared to cai derived temperatures for carbonate precursor rocks this variation in thermal maturity is likely related to the analytical techniques used to obtain cai and vr data and the empirical equations applied to calculate corresponding paleotemperatures conodont fragments were not as sensitive compared to vitrinite and the color alteration process could have suffered from hydrothermal alteration a secondary cause might be a different response to mechanical deformation between siliciclastic and carbonate units during the variscan and post variscan geodynamic evolution of the study area rigid precursor carbonate units experienced fluid circulation mainly along distinct and spaced fracture zones creating fracture related dolomite geobodies and ore mineralization soft ambient siliciclastic rocks experienced more diffuse fluid circulation and heat dissipation the different paleothermometry datasets compiled for the study area indicate that the fluids circulating during late to post variscan times with associated fracture related dolomitization and ore mineralization in carbonate precursors are hydrothermal the highest paleotemperatures were recorded in ambient and precursor rocks in the highly tectonized northern part of the study area where several thrusts and faults allowed intense fluid circulation positive temperature anomalies within the precursor carbonates correlate well with the occurrence of dolomite geobodies and ore mineral deposits such anomalies could thus be used as an exploration tool for hydrothermal dolomite bodies in analog sub surface settings

preliminary sulphur isotope data of diagenetic and vein sulphides in the lower palaeozoic strata of ireland and southern scotland implications for zn pb ba mineralization genetic models for many irish lower carboniferous zn pb ore deposits invoke a dual supply of sulphide the dominant source is from the bacteriogenic reduction of lower carboniferous seawater sulphate but a significant minor supply is derived from deep seated sources the 34 s range of the latter component varies among the deposits from the lightest range of 15 to 0 at keel to the heaviest of 4 to 14 4 in the navan tatestown area we hypothesize that such sulphur is leached mainly from diagenetic sulphide minerals in the underlying lower palaeozoic sediments 6 s of pyrite in the silurian ordovician moffat shales 17 1 to 0 6 and of sphalerite and galena in lower palaeozoic hosted veins at salterstown 8 7 to 4 5 and wanlockhead 10 3 to 5 1 are consistent with the hypothesis below the navan ore deposit lower palaeozoic shales containing minor diagenetic pyrite with a very wide range in 34 s have been found 34 s is typically heavy 16 but extreme values up to 62 are encountered the general enrichment in 34 s is in accord with the noticeably heavy isotopic composition of deep seated sulphur in the navan orebody and its tatestown satellite our preliminary results therefore suggest that geographical variations in the 34 s range of lower palaeozoic diagenetic write may have contributed to the isotopic variation in the deep seated sulphur among the irish deposits

paleostress directions from the preferred orientation of closed microfractures fluid inclusion planes in sandstone east texas basin u s a abstract closed extensional microfractures are useful indicators of paleostress directions in shallowly buried quartz cemented quartz arenites of the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 670 m thick that was deposited in the gradually subsiding northern gulf of mexico basin the closed microfractures are syndiagenetic fluid inclusion rich planes that have an ene strike that is subparallel to contemporary quartz filled extension veins and regional normal faults indicating that closed microfractures contain the maximum paleostress direction these microstructures are potentially useful for mapping paleostress trajectories in passive margin and platform settings particularly where samples are obtained from core previous experimental studies of microfracture closure suggest that microfractures evolved into fluid inclusion planes by dendritic quartz precipitation in east texas microfracture closure may have occurred at temperatures as low as 85 c and depths as shallow as 1500 m

the iapetus suture in the british isles the position of the iapetus ocean suture can be traced between ordovician fossil localities in the southern uplands and the lake district which contain respectively distinct north american and european faunas the southern uplands contains north american caradoc faunas in the northern belt and is considered to have been accreted onto the laurentian north american margin between the llandeilo and the end of the wenlock deep seismic reflection profiling shows that a surface probably parallel to the suture zone dips down to the northwest from the solway line in eastern ireland the surface trace of the suture coincides with the navan fault which separates the longford down massif from ordovician sediments containing european faunas the navan silvermines fault may represent the surface expression of the suture but it is masked by wenlock turbidites which appear to have crossed over the plate boundary northward subduction of continental crust below the margin of laurentia during the late silurian may explain the influx of turbidite fans from the north or north west onto depressed crust to the south of the suture termination of subduction coincides with the widespread acadian orogeny in the emsian at 395 5 ma

thermal maturity patterns in alaska implications for tectonic evolution and hydrocarbon potential nearly 10 000 vitrinite reflectance and conodont color alteration index determinations from sedimentary rocks in alaska were used to produce a thermal maturity map of rocks exposed at the surface and to evaluate subsurface thermal maturity relations in the colville and cook inlet basins rocks exposed at the surface of the tertiary interior basins and in the aleutian forearc and backarc basins uniformly are of very low thermal maturity indicating that these basins are at or near maximum burial have seen little uplift and exhumation and are probably thermally immature with respect to hydrocarbon generation in contrast many sedimentary basins show elevated levels of thermal maturity at the surface with the highest values at basin margins this geometry suggests a patt rn of greater uplift along basin margins possibly reflecting isostatic readjustments as crustal loads are removed by erosion we investigated thermal maturity relations in three sedimentary basins colville cook inlet and kandik in more detail thermal maturity patterns in the colville basin are broadly asymmetric indicating systematic differential uplift ranging from a minimum of no uplift in the north point thomson area to 9 13 km of uplift and exhumation in the central brooks range even greater uplift further to the south is indicated by the presence of greenschist facies and higher grade metamorphic rocks this pattern may reflect the deflexing of the lithosphere subsequent to the principal episode s of crustal convergence and thickening these patterns further suggest a similar thermal history for the proximal colville basin and the northern foothills belt suggesting the possibility of hydrocar on accumulations in the foothills thermal maturity isograds within the brooks range cut major thrust faults indicating that maximum burial postdated the principal phases of thrusting in contrast isograds in the foothills belt to the north are warped broadly by local structure indicating continued north south shortening subsequent to maximum burial such deformation could have remobilized hydrocarbons in early traps a broad southward extension of thermally immature rocks in the central portions of the foothills belt suggests relatively young east west shortening parallel to the strike of the orogene a feature that to date has not been included in regional tectonic syntheses alternatively the thermal maturity pattern could be explained by tectonically unrelated episodes of uplif in the eastern and western parts of the brooks range in the cook inlet basin vitrinite reflectance isograds also are indicative of relatively greater uplift at the basin margins than at the basin center which appears to be presently at its maximum burial depth uplift in the cook inlet basin may reflect compression along the faults bounding the basin relatively high thermal maturity along the western margin of the basin also may reflect magmatic heat sources from the alaska peninsula aleutian volcanic arc the seldovia arch a major structural feature of the end page 1874 basin does not appear to deform vitrinite reflectance isograds implying that deformation on that structure ceased prior to maximum burial in the kandik basin a thermal maturity anomaly thermally mature younger rocks in fault contact with thermally immature older rocks provides clues to the nature and timing of east west thrusting mesozoic foreland basin deposits associated with thrusting buried paleozoic rocks of the easternmost part of this fold and thrust belt to relatively shallow depths driving potential hydrocarbon source rocks into the oil generation window the western foreland basin deposits were overridden by advancing thrusts and tectonically buried to as deep as 10 km these disparate thermal domains are juxtaposed along the glenn creek fault which may represent a terrane boundary in east central alaska

regional fractures i a mechanism for the formation of regional fractures at depth in flat lying reservoirs 1 regional fractures may form slowly at depth in extension and parallel to regional horizontal tectonic compression such fracture sets can be common in reservoirs despite the absence of flexure of the strata and are commonly important contributors to reservoir permeability such fractures make good targets for deviated wells high formation pore pressure is crucial to creating low effective confining stresses and brittle rock properties in the reservoirs conditions conducive to fracturing despite deep burial but pore pressure does not exceed the least principal stress and does not cause tensile fracturing the mechanism of natural hydraulic fracturing is incompatible with the characteristics of most regional fracture sets rather many regional fractures form duri g far field compression initiate at locally induced tensile stresses caused by flaws in the rock and propagate in the plane of the maximum and intermediate compressive stresses the differential stress required for initiation and propagation of regional fractures is well below that necessary for shear failure in the presence of high pore pressure fractures can be held open at depth by a tectonic basinwide dilatancy of the strata and the open void space commonly becomes mineralized

vein cements and the geochemical evolution of subsurface fluids in the visean of the campine basin poederlee borehole belgium upper visean reef mound carbonates from the campine basin northern belgium have a complex diagenetic history which reflects the evolution of subsurface fluids in the basin primary pores became cemented by marine fibrous stage a and shallow burial stage b c and d scalenohedral and blocky calcites tectonic deformation then created successive networks of fractures which acted as conduits for aggressive fluids and which were subsequently cemented by six stages of carbonate cement fluid inclusion evidence suggests that the first cloudy columnar calcite cements in fractures stage e formed at or below 50 c these calcites have a 18 o of 13 3 pdb and they are interpreted to have grown in meteoric waters 18 o 6 7 to 7 4 smow after a further period of fracturing and dissolution white blocky calcites stage f 18 o 9 1 pdb precipitated around 60 c from fluids with a 18 o 0 9 smow later fractures contain brown columnar and blocky calcites stage g with a 18 o of 12 1 pdb and a minimum homogenization temperature t h of c 90 c giving a pressure corrected precipitation temperature of 95 c an oxygen isotopic composi tion of 0 6 smow is indicated for the fluid granular to bladed ferroan calcites stage h blocky ferroan calcites stage i 18 o 9 8 pdb and t h 128 c and saddle dolomites stage j 18 o 10 0 pdb and t h 147 c are the last diagenetic carbonate phases methane has been detected in the vapour phase of the fluid inclusions in the blocky ferroan calcites the ferroan calcites and the saddle dolomites are interpreted to have formed respectively at 150 c and 200 c in 18 o rich fluids 7 9 smow and 10 9 smow the stable isotope values of the fluids indicate an abrupt change from a meteoric composition towards marine derived compactional fluids and basinal brines enrichment in 18 o is mainly attributed to the dewatering dehydration of clay minerals in the adjacent upper carboniferous strata the paragenetic sequence of cements described here is comparable to that encountered in other lower carboniferous limestones where there is not such an extensive data base of fluid inclusion and stable isotopic data it is suggested that the large change in the pore fluid composition documented here might be a common subsurface process and that the interpretation of diagenetic temperatures from isotopic data alone can be very misleading

organic geochemical indicators of dynamic fluid flow processes in petroleum basins a variety of preliminary geophysical geochemical and geological observations anderson et al geophysics 12 17 april 1991a b anderson oil gas j 85 91 26 april 1993 along with well production data schumacher aapg ann conv abstr april 1993 have led to the hypothesis that fluid injection into eugene island block 330 ei 330 in the u s louisiana gulf coast may be a continuing episodic process with the most recent injections having occurred on short geologic time scales 10 000 yr or less organic geochemical evidence presented here suggests these processes may occur on very short time scales years a process called dynamic fluid injection was proposed to explain these observations and is envisioned as episodic pressure build up followed by rapid escape of gas and oil through geopressure and injection into overlying reservoirs

a deep seismic reflection transect across the irish caledonides new reflection profiles recorded to 18s c 60km along a 600 km north south transect west of ireland wire lines provide a cross section of the irish caledonides from lewisian basement in the north to the variscan fold and thrust belt in the south and constrain the offshore extrapolations of major caledonide structures we interpret the profiles as showing the great glen fault and associated ne trending strike slip faults as near vertical structures which cut the whole crust and the uppermost mantle beneath the surface trace of the fair head clew bay line we image a north dipping zone which soles into horizontal layers just above the reflection moho the north dipping zone separates south dipping reflections above and to the north from north dipping reflections below and to the south from the fair head clew bay line as far south as the iapetus suture the lower crust contains north dipping packages of reflectors possibly related to acadian accretionary underplating the iapetus suture zone can be identified as a zone more than 50 km wide dipping north at 30 from 5 km depth offshore dingle peninsula to sole into the moho at c 30 km depth west of the shannon estuary in the upper crust the shallow part of the iapetus suture zone appears to be transported to the north by late caledonian retrocharriage or by variscan thrusting the iapetus suture does not penetrate through the present day reflection moho but there are scattered reflectors in the mantle not continuous with crustal reflectors perhaps relics of a subducted slab we recognize lower crustal reflectivity and the reflection moho along almost all the wire profiles regionally the travel time to the reflection moho varies from 9 s c 28 km offshore donegal northwest of ireland to 12 s c 35 km offshore kerry and cork southwest of ireland apparent moho offsets rapid lateral changes in the travel time to the reflection moho north of donegal and north of mayo are probably due to the great glen fault and associated faults the lower crustal reflectivity varies considerably in thickness and prevalent dip direction along the wire profiles in donegal bay this reflectivity is observed at depths less than 5 km c 1 5s whereas west of kerry prominent reflectivity is only observed beneath 6s c 17 km though the age of crustal reflectors cannot in general be determined beneath central ireland from donegal to dingle the lower crustal reflectors mimic in dip direction the structural vergence of the exposed dalradian and early palaeozoic rocks so that the lower crustal reflectivity patterns and probably much of the crust must be caledonian in age

tectonostratigraphy of the glen app area southern uplands scotland anatomy of an ordovician accretionary complex the stratigraphy and structure of the glen app coastal area northwestern southern uplands are characterized by structural repetition of both chaotic and coherent units of the middle ordovician caradocian tappins group the chaotic unit the currarie formation comprises blocks including basalt chert and terrigenous sedimentary rocks set in folded and in places sheared red to grey siliceous mudstone the coherent unit is turbiditic and is divided into the dalreoch formation in the north and the corsewall formation in the south the former is characterized by inclined isoclinal folds and thrusts whereas the latter shows a homoclinal dip although both are largely overturned northwards small scale duplexes are observed within the coherent turbidites of the dalreoch formation and chaotic units larger duplexes identified on the basis of mapping are oriented at an oblique angle to the general trend of regional structures the chemistry of basalt blocks within the currarie formation shows a within plate type suggesting an origin as seamounts the tectono stratigraphy of the area is interpreted as the result of accretion of a substantial seamount at a subduction zone during mid ordovician time thrust interleaving of chaotic and coherent units is inferred to have taken place in and above the decollement zone while thick turbidite beds without strong folding were probably preserved below the decollement and emplaced below a large scale nappe interpretation of the glen app area as part of an accretionary complex confirms that an ocean basin remained open in part of the iapetus system at least until caradocian times

fractures in the northern plains stream patterns and the midcontinent stress field fractures in late cretaceous to late pleistocene sediments in saskatchewan eastern montana and western north dakota form two vertical orthogonal sets trending northeast southwest and northwest southeast the pattern is consistent regardless of rock type or age except for concretionary sandstone both sets appear to be extensional in origin and are similar in character to joints in alberta modem stream valleys also trend in the same two dominant directions and may be controlled by the underlying fractures elevation variations on the sub mannville early cretaceous unconformity form a rectilinear pattern also parallel to the fracture sets suggesting that fracturing was initiated at least as early as late jurassic it may have begun earlier but there are insufficient data at present to extend the time of initiation we interpret the fractures as the result of vertical uplift together with plate motion the westward drift of north america the northeast southwest directed maximum principal horizontal