burial history of palaeozoic strata in belgium as revealed by conodont colour alteration data and thickness distributions thickness distributions of devono carboniferous formations and their relationship to conodont colour alteration indices cais from over 500 sample locations in belgium and northern france have been studied to reconstruct the thermal alteration and burial history of palaeozoic rocks the depositional centre during eifelian through visean times was located in the subsiding southern part of the dinant basin forming a thick sedimentary pile of probably more than 3 5 km in order to explain conodont cais chiefly resulting from upper carboniferous sedimentation two different depositional centres are considered giving rise to approximately 4 5 km of sediment in the central part of the dinant and namur basins as a consequence of the northward shifting variscan fold belt the upper carboniferous succession in the southern part of the dinant basin and in the rocroi area was reduced or absent conodont cais together with other thermal alteration data from the condroz massif indicate that this area was a structural high for most of the devonian the brabant massif was probably covered with approximately 1 5 2 0 km of upper carboniferous sediments in the south and less than 1 0 km in the central and northern parts in the central campine basin visean strata could have been buried by 3 5 4 5 km of upper carboniferous rocks

reequilibration of fluid inclusions bulk diffusion abstract bulk diffusion of fluid components through quartz which is a nominally anhydrous mineral is one of a series of processes that may alter fluid inclusions in crystals diffusion of water through quartz has been considered an important factor for re equilibration of fluid inclusions however the solubility of water in quartz the nature of the diffusing water related molecules and diffusion coefficients have not been adequately determined to calculate reliable rates of inclusion alteration a new three dimensional mathematical diffusion model is presented to characterize bulk diffusion in quartz with randomly distributed fluid inclusions this model assumes an infinite external fluid source and treats fluid inclusions as instantaneous point sources the computer program reqdif from the software package fluids http fluids unileoben ac at can be used to calculate the effect of diffusion with self defined parameters using a diffusion coefficient of 10 12 m2 s 1 60 the rate of h2o loss or gain of most inclusions is relatively high adapting them within several 10 000 of years to new pore fluid conditions however diffusion according to this model may be restricted and partly inhibited by several important factors such as the low porosity in metamorphic rock and relative low temperatures in sedimentary and diagenetic rocks the imprecision of estimated diffusion coefficients and the undetermined accuracy do not allow reliable diffusion calculations diffusion along micro cracks and dislocations is a more efficient process to transport fluid components through quartz

episodic petroleum fluid migration in fault zones of the northwestern junggar basin northwest china evidence from hydrocarbon bearing zoned calcite cement hydrocarbon bearing zoned calcite cements occur widely in jurassic cretaceous fault zone cores and sandstone outcrops of the northwestern junggar basin northwest china hydrocarbon bearing bands alternate with nearly hydrocarbon free bands at a micron scale analytical results from biomarker organic geochemistry fourier transform infrared microspectroscopy and trace element geochemistry on these zoned cements suggest that at least three different types of fluids have participated in their formation the first fluid type is probably primary unmodified lacustrine formation water from which the hydrocarbon poor bands are formed and are characterized by mg rich calcite the other two types of fluids include basinal fluids e g hot hydrocarbon bearing fluids and meteoric water the hydrocarbon rich bands in which the hydrocarbons have been biodegraded and the mn content is relatively high suggest a mixture of hydrocarbon bearing basinal fluid and meteoric water the alternating growth of hydrocarbon bearing and hydrocarbon free bands of calcite cements implies that the cement formation is episodic it is related to alternating episodes of mixed petroleum bearing fluid and unmodified primary formation waters respectively the fault appears to have been a mixing zone where seismic pumping during the movement of associated regional faults occurred thus in the northwestern junggar basin the micron scale hydrocarbon bearing zoned structure of the calcite cements is likely a reflection of episodic petroleum fluid migration in fault zones

oxidation of methane at the ch4 h2o co2 transition zone in the external part of the central alps switzerland evidence from stable isotope investigations abstract with the aim of understanding the mechanisms that control the metamorphic transition from the ch 4 to the h 2 o co 2 dominated fluid zone in the helvetic domain of the central alps of switzerland fluid inclusions in quartz illite crystallinity index vitrinite reflectance and the stable isotope compositions of vein and whole rock minerals and fluids trapped in quartz were investigated along four cross sections increasing temperature during prograde metamorphism led to the formation of dry gas by hydrocarbon cracking in the ch 4 zone fluid immiscibility in the h 2 o ch 4 co 2 nacl system resulted in cogenetic ch 4 and h 2 o dominated fluid inclusions in the ch 4 zone fluids were trapped at temperatures 270 5 c the end of the ch 4 zone is marked by a sudden increase of co 2 content in the gas phase of fluid inclusions at temperatures 270 5 c in the h 2 o zone the total amount of volatiles within the fluid decreased below 1 mol with no immiscibility this resulted in total homogenization temperatures of h 2 o co 2 ch 4 nacl inclusions below 180 c hydrogen isotope compositions of methane in fluid inclusion have d values of less than 100 in the ch 4 zone typical for an origin through cracking of higher hydrocarbons but where the methane has not equilibrated with the pore water d values of fluid inclusion water are around 40 in isotopic equilibrium with phyllosilicates of the whole rocks within the ch 4 to h 2 o co 2 transition zone d h 2 o values in fluid inclusions decrease to 130 interpreted to reflect the contribution of deuterium depleted water from methane oxidation in the h 2 o zone d h 2 o values increase again towards an average of 30 which is again consistent with isotopic equilibrium with host rock phyllosilicates 13 c values of methane in fluid inclusions from the ch 4 zone are around 27 in isotopic equilibrium with calcite in veins and whole rocks the 13 c ch 4 values decrease to less than 35 at the transition to the h 2 o zone and are no longer in equilibrium with the carbonates in the whole rocks 13 c values of co 2 are variable but too low to be in equilibrium with the wall rock fluids compatible with a contribution of co 2 from closed system oxidation of methane differences in isotopic composition between host rock and alpine fissure carbonate are generally small suggesting that the amount of co 2 produced by oxidation of methane was small compared to the c budget in the rocks and local pore fluids were buffered by the wall rocks during precipitation of calcite within the fissures

brittle tectonics and pore fluid conditions in the evolution of the great boundary fault around chittaurgarh northwestern india abstract this paper aims at reconstructing paleostress history and deciphering the pore fluid pressure conditions during the reactivation of a regional scale fault paleostress analyses of the mesoscopic structures suggest that three successive events of reactivation on the great boundary fault occurred in thrust type strike slip type and thrust type tectonic settings respectively whereas the pore fluid pressure was supralithostatic during the first and third events of reactivation it was sublithostatic during the second event each event of reactivation induced a fluid pressure gradient which resulted in the focused and enhanced flow of syntectonic fluids within the high permeability locales primarily fractures and faults fluid inclusion study on strike slip veins reveals that the syntectonic fluids were highly dense na ca cl brines of formational water origin stratigraphic evidence in favour of a 2 km thick column of overburden above kaimur sandstone beds implies that the strike slip faulting occurred at 160 202 c temperature and 53 mpa pressure variation in homogenization temperature reflects fluctuation in pore fluid pressure during entrapment of syntectonic fluids and points to seismic pumping as a possible mechanism of fluid flow during faulting high paleogeothermal gradient obtained by fluid inclusion data is ascribed to the high heat flow due to crustal stretching during the proterozoic rifting the basal and intermittent volcanism in the basin and occurrence of berach granite as the basement

tectonics and hydrogeology of accretionary prisms role of the decollement zone abstract at convergent margins the decollement zone comprises the plate boundary and is marked by profound structural disharmony by changes in stress orientation and by a discontinuity in plate velocity the decollement zone initiates in a weak sediment layer typically a low permeability hemipelagic mud lying below a more rapidly deposited stronger more permeable trench turbidite sequence at the deformation front trench turbidites tend to be offscraped whereas the finer grained hemipelagic and pelagic sediments are more likely to be underthrust offscraped materials may undergo only limited burial whereas underthrust deposits can be deeply buried undergo high pressure metamorphism and are more likely to be preserved in the stratigraphic record burial rates associated with underthrusting are high exceeding 20 km my with high rates of underthrusting sediment descending below the decollement zone is probably buried faster than it can dewater resulting in emplacement of relatively high porosity deposits at depth fluids flowing from modern decollement zones have migrated substantial distances laterally and tapped deep sources the episodicity of flow suggests pumping of fluid by cycles of dilation and flow to the decollement zone followed by failure and fluid expansion along the decollement zone possible pressure gradients below the decollement zone allow flow upward into it while maintaining minimum effective stress along it the thickness of sediment underthrust beneath the decollement zone determines whether these deposits are emplaced by diffusive underplating with stratal disruption and efficient dewatering or by coherent underplating with the formation of macroscopic duplexes and transfer of fluid to the base of the accretionary prism deformation mechanisms affecting accreted sediment depend on depth of entrainment into the decollement zone and duration of residence

conodont thermal alteration patterns in palaeozoic rocks from belgium northern france and western germany in this paper thermal patterns based on conodont colour alteration indices cai have been studied in the devonian and carboniferous rocks from belgium northern france and western germany four maps with the exception of the southeastern rheinisches schiefergebirge have been compiled for the investigated area one for the eifelian and givetian a second for the frasnian another for the famennian and one for the tournaisian and visean conodonts have not been found in cambrian rocks from belgium and northern france and as they are scarce in the ordovician to lower devonian formations of this area it was impossible to integrate these cai data into an isograd map in germany in the eastern rheinisches schiefergebirge only a few cai values for the lower devonian strata are available in contrast to the ardennes where in general conodonts show cai values of 3 0 5 0 indices in areas adjacent to the anglo brabant massif e g in the western namur synclinorium and in the eifel hills range between 1 5 and 2 0 slightly higher values occur in the campine basin north of the anglo brabant massif by comparison with cai data from belgium conodont colour alteration indices from the same stratigraphic horizons in some areas of the northern and eastern rheinisches schiefergebirge are up to one index higher in most areas of the rheinisches schiefergebirge the level of metamorphism corresponds to the anchizone regional variations in cai data appear to be related to buried intrusions and associated hydrothermal activity in the southeastern rheinisches schiefergebirge cai data are not completely consistent but it is possible to discern an increase in coalification from the north to the south high index values in the southern rheinisches schiefergebirge are believed to result from regional metamorphism and heating related to numerous intrusive bodies

prograde metamorphic zoning in amphibolite facies pelitic gneisses from kemio southwest finland the metamorphism of the svecofennides in southwestern finland has been studied in pelitic gneisses from the kemio region three metamorphic zones have been distinguished which are characterized in order of increasing grade by the parageneses muscovite quartz biotite sillimanite k feldspar and cordierite k feldspar temperature and load pressure estimates of metamorphism range from 560 25 c 3 0 5 kb for the upper boundary of the muscovite quartz zone to 670 25 c 4 0 5 kb for the cordierite k feldspar zone at a partial water pressure of 0 4 0 1 ptotal

development of fluid conduits in the auriferous shear zones of the hutti gold mine india evidence for spatially and temporally heterogeneous fluid flow abstract the gold mineralization of the hutti mine is hosted by nine parallel n s trending steeply dipping 2 10 m wide shear zones that transect archaean amphibolites the shear zones were formed after peak metamorphism during retrograde ductile d 2 shearing in the lower amphibolite facies they were reactivated in the lower to mid greenschist facies by brittle ductile d 3 shearing and intense quartz veining the development of a s 2 s 3 crenulation cleavage facilitates the discrimination between the two deformation events and contemporaneous alteration and gold mineralization ductile d 2 shearing is associated with a pervasively developed distal chlorite sericite alteration assemblage in the outer parts of the shear zones and the proximal biotite plagioclase alteration in the center of the shear zones d 3 is characterized by development of the inner chlorite k feldspar alteration which forms a centimeter scale alteration halo surrounding the laminated quartz veins and replaces earlier biotite along s 3 the average size of the laminated vein systems is 30 50 m along strike as well as down dip and 2 6 m in width mass balance calculations suggest strong metasomatic changes for the proximal biotite plagioclase alteration yielding mass and volume increase of ca 16 and 12 respectively the calculated mass and volume changes of the distal chlorite sericite alteration ca 11 ca 8 are lower the decrease in 18 o values of the whole rock from around 7 5 for the host rocks to 6 7 for the distal chlorite sericite and the proximal biotite plagioclase alteration and around 5 for the inner chlorite k feldspar alteration suggests hydrothermal alteration during two stage deformation and fluid flow the ductile d 2 deformation in the lower amphibolite facies has provided grain scale porosities by microfracturing the pervasive steady state fluid flow resulted in a disseminated style of gold sulfide mineralization and a penetrative alteration of the host rocks alternating ductile and brittle d 3 deformation during lower to mid greenschist facies conditions followed the fault valve process ductile creep in the shear zones resulted in a low permeability environment leading to fluid pressure build up strongly episodic fluid advection and mass transfer was controlled by repeated seismic fracturing during the formation of laminated quartz gold veins the limitation of quartz veins to the extent of earlier shear zones indicate the importance of pre existing anisotropies for fault valve action and economic gold mineralization

late metamorphic veins record deep ingression of meteoric water a la icpms fluid inclusion study from the fold and thrust belt of the rhenish massif germany abstract the fluid evolution of late metamorphic quartz vein systems in the fold and thrust belt of the rhenish massif has been studied by microthermometry and la icpms microanalysis the quartz veins are hosted by very low grade organic matter rich metasiltstones and metapelites of the hunsruck nappe complex the veins record two major stages of textural evolution a massive vein filling assemblage with elongate blocky quartz chlorite albite and apatite and a later open space filling assemblage with euhedral crystals of quartz ankerite dolomite and minor calcite and sulfides the euhedral quartz crystals host well preserved fluid inclusion assemblages which made it possible to reconstruct the chemical evolution of the fluid system with time the fluid inclusions are all aqueous two phase with low salinity and three successive fluid generations record a systematic decrease in salinity from 4 7 5 3 to 3 1 3 9 and then to 1 4 1 7 wt eqv nacl the salinity decrease is paralleled by a decrease in homogenization temperatures from 210 225 c to 148 164 c and 124 139 c using la icpms microanalysis of individual fluid inclusions reproducible elemental concentrations of li na k rb cs mg ca ba sr b al as sb s cl and br could be determined the concentrations of the alkali metals and of boron arsenic and antimony are correlated with the fluid salinity element concentrations are highest in the early fluid generation and decrease systematically in the latter two generations the systematic changes in fluid composition salinity homogenization temperature and elemental concentrations are best explained by fluid mixing between a hot metamorphic fluid of moderate salinity that carried elevated concentrations of b as and sb and a cooler dilute fluid that was of meteoric origin the fluid evolution therefore signals deep ingression of meteoric water during late metamorphic exhumation and uplift the molar cl br ratios of the fluid inclusions lie on a linear array that extends from close to seawater to values that are substantially below seawater because evaporitic sources are conspicuously absent in the shallow water marine sequence of the rhenish massif the elevated br concentrations and cl br ratios below seawater are best explained by fluid rock interaction and liberation of br from the organic matter in the metasediments

evolution of metamorphic fluids at the variscan fold and thrust belt in eastern belgium abstract quartz veins in the southern greenschist facies metamorphic border of the stavelot venn massif belgium have been examined a detailed petrographical study of these quartz veins indicates the presence of eleven quartz stages a microthermometric analysis shows the expulsion of three main fluid types during the palaeozoic in the first quartz stage i of caledonian age mixed aqueous gaseous h 2 o co 2 nacl fluid inclusions are present the post caledonian and pre variscan second stage ii is characterised by gaseous co 2 n 2 inclusions occurring along inter crystal grain boundaries and by aqueous h 2 o nacl intra crystal inclusions the quartz stages iii vi which formed during the variscan period contain primary mixed aqueous gaseous h 2 o co 2 nacl inclusions all with an equal bulk chemical composition post variscan quartz stages vii xi could not be investigated microthermometrically the combination of microthermometry chlorite geothermometry and geothermal gradients reveals minimum trapping conditions of 200 mpa and 200 c for stage i quartz and 175 275 mpa and 385 435 c for quartz stages iii vi the trapping conditions of stage ii quartz could not be determined due to the strong recrystallisation of the quartz veins at the lower metamorphic variscan thrust front distinct temperature anomalies are associated with thrust faults as indicated by conodont colour alteration index cai vitrinite reflectance data chlorite geothermometry and fluid inclusion microthermometry the expulsion of metamorphic fluids generated at the southern part of the stavelot venn massif could have caused the distinct temperature anomalies along variscan thrust faults alternatively some of these anomalies could have been induced by deeply circulating meteoric fluids

fluid evolution at the variscan front in the vicinity of the aachen thrust quartz carbonate chlorite veins were studied in borehole samples of the rwth 1 well in aachen veins formed in devonian rocks in the footwall of the aachen thrust during variscan deformation and associated fluid flow primary fluid inclusions indicate subsolvus unmixing of a homogenous h2o co2 ch4 n2 na k cl fluid into a h2o na k cl solution and a vapour rich co2 h2o ch4 n2 fluid the aqueous end member composition resembles that of metamorphic fluids of the variscan front zone with salinities ranging from 4 to 7 nacl equiv and maximum homogenisation temperatures of close to 400 c pressure estimates indicate a burial depth between 4 500 and 8 000 m at geothermal gradients between 50 and 75 c 26 mpa but pressure decrease to sublithostatic conditions is also indicated probably as a consequence of fracture opening during episodic seismic activity a second fluid system mainly preserved in pseudo secondary and secondary fluid inclusions is characterised by fluid temperatures between 200 and 250 c and salinities of 5 nacl equiv bulk stable isotope analyses of fluids released from vein quartz calcite and dolomite by decrepitation yielded dh2o values from 89 to 113 13cch4 from 26 9 to 28 9 vpdb and 13cco2 from 12 8 to 23 3 vpdb the low d and 13c range of the fluids is considered to be due to interaction with cracked hydrocarbons the second fluid influx caused partial isotope exchange and disequilibrium it is envisaged that an initial short lived flux of hot metamorphic fluids expelled from the epizonal metamorphic domains of the stavelot venn massif the metamorphic fluid was focused along major thrust faults of the variscan front zone such as the aachen thrust a second fluid influx was introduced from formation waters in the footwall of the aachen thrust as a consequence of progressive deformation mixing of the cooler and lower salinity formation water with the hot metamorphic fluid during episodic fluid trapping resulted in an evolving range of physicochemical fluid inclusion characteristics

k ar dating of magmatic sericite crystallites for determination of cooling paths of metamorphic overprints a combined optical and x ray characterisation of fine grained micas in granodioritic to tonalitic dikes and intrusions of the eastardennes eifel nappe linksrheinisches schiefergebirge germany belgium was completed with k ar dating of separated size fractions from these rocks in each sample the k ar ages decrease with decreasing size fraction but the same size fractions of the different samples yield different ages application of the closure temperature concept to the k ar ages of the various size fractions indicates that the crystallite size expressed as cis fwhmser001ad and coherent scattering domain csd thickness acts as the effective radius of ar diffusion a linear model may describe the correlation between k ar ages and crystallite thickness the ages younger than the model prediction are caused by the occurrence of microcline as an accessory k bearing mineral phase the obtained k ar ages were interpreted as representative of the cooling path of the magmatic components in the eastardennes eifel nappe below 330 c the k ar age of the largest size fraction of the tonalitic dike v11 313 6 7 2 ma is the closest value for the age of the variscan cleavage development the oldest age of the hydrothermally altered tonalitic dike 300 2 8 4 ma might represent an episode of hydrothermal fluid migration after cleavage development it represents at least a minimum age the microcline age 242 8 6 0 ma of the hill intrusion may represent the closure temperature of this mineral at about 140 c

accretion of a rifted passive margin the late paleozoic rhenohercynian fold and thrust belt middle european variscides in the western rhenish massif the rhenohercynian fold and thrust belt of the middle european varsicides exposes a telescoped complete devonian to early carboniferous passive margin this permits the analysis of geometry and kinematic processes of passive margin accretion to an erogenic wedge during variscan collision 330 300 ma the sedimentary cover of the passive margin was shortened by some 50 or 180 km crustal scale balancing and restoration reveals a wide symmetric rift with a central graben a marginal plateau separated this failed lower devonian rift from an emsian middle devonian oceanic basin in the south remnants of which are preserved in the southernmost imbricates and the giessen harz nappes the seismically well imaged aachen midi detachment faille du midi acted as the basal decollement of this thin to thick skinned orogenic wedge it shows a ramp and flat geometry from the blind tip down to middle crustal levels owing to its position below the base of the basin fill the thick synrift sequence and structure controlled structural evolution during contraction by localizing thrust branch lines and by inversion of rift structures synthetic to the subduction direction with formation of basement footwall shortcuts moreover the three dimensional detachment geometry shows large scale oblique ramp flat features which control the architecture of the belt and the distribution of metamorphic grade rocks and fabrics from the detachment show that the latter was located at the transition into the ductile field at the fossil 300 400 c isotherm in the restored section the detachment trajectory displays a saucershaped geometry rising to the surface at the rear and at the front this suggests that the basal detachment propagated into the passive margin by ductile failure during lithospheric flexure under the load of an advancing upper plate the regional pattern of synkinematic metamorphic grade shows varying modes of margin accretion basal underplating into the orogenic wedge by the shelf slope and marginal plateau with formation of duplex stacks and elongate thrust sheets and frontal accretion of the remaining thicker failed rift in the north into the propagating wedge with formation of several imbricate fans cyclical changes in accretion history and or critical taper are suggested by spaced domains of out of sequence thickening these are also related to internal domainal kinematic partitioning of the wedge controlled by oblique collision

crack seal microstructure evolution in bi mineralic quartz chlorite veins in shales and siltstones from the rwth 1 well aachen germany abstract in core samples from the deep geothermal well rwth 1 we studied variscan quartz chlorite veins formed by crack seal processes in siliciclastics at the brittle to ductile transition these sheared veins are common in sections of the well which are interpreted as variscan thrust zones based on image logs and seismic data microstructures interpreted to reflect different stages in the evolution of such crack seal veins suggest the veins started in microcracks sealed by quartz and chlorite to veinlets crossing multiple grains and bundles of veinlets evolving by progressive localization into low angle extensional shear veins and high angle dilational jog veins in the sheared veins chlorite and quartz ribbons show evidence for crack seal and simultaneous ductile shearing during vein evolution forming peculiar fin shaped microstructures in quartz ribbons in high angle dilational jogs fibrous crystals of quartz and chlorite point to multiple crack seal events with simultaneous growth of two different mineral phases this is interpreted to be the basic microstructural process in the veins we extend earlier models of polycrystal growth in fractures and present a series of 2d simulations of the kinematics of crystal growth in these bi mineralic veins for both localized and non localized cracking results are compared with the observed microstructures we show that when the relative growth rates of the two mineral phases are different serrated grain boundaries evolve the similarities between observation and model suggest that the assumption of our model is valid although many second order processes require a more detailed study we propose that the principles observed here can be applied to other bi mineralic crack seal veins

evolution of palaeofluids at the variscan thrust front in eastern belgium the geochemical evolution of the fluids migra ting at the variscan thrust front in eastern belgium has been investigated by a petrographic mineralogical and geoche mical study of ankerite quartz and ferroan calcite veins hosted by lower devonian rocks three vein generations have been recognized the first generation consists of quartz chlorite and ankerite filling pre to early variscan extensional fractures the second generation is present as shear veins of variscan age and contains quartz chlorite and ferroan calcite the third generation consists of ankerite filling post variscan fractures the oxygen and carbon isotopic composition of the two ankerite phases and of the ferroan calcites are respectively between 16 4 and 11 4 pdb between 17 8 and 1 7 pdb this range is greater than that of calcite nodules in the lower devonian siliciclastic sediments 18o 15 6 to 11 1 pdb and 13c 13 4 to 10 2 pdb this suggests precipitation of the carbonate veins from a fluid which was at most only partly isotopically buffered by the calcite nodules in the host rock the calculated oxygen isotopic composition of the ambient fluid from which the calcite veins formed is between 7 8 and 10 0 smow two main fluid types have been recognized in fluid inclusions in the quartz and carbonates the first fluid type is present as secondary fluid inclusions in the first and second vein generations the fluid has a salinity of 0 5 7 2 eq wt nacl and a high but variable homogenization temperature th 124 188 c two origins can be proposed for this fluid it could have been expelled from the lower devonian or could have been derived from the metamorphic zone to the south of the area studied taking into account the microthermometric and stable isotope data and the regional geological setting the fluid most likely originated from metamorphic rocks and interacted with the lower devonian along its migration path this is in agreement with numerical simulations of the palaeofluid and especially the palaeotempera ture field which is based on chlorite geothermometry and vitrinite reflectance data the second fluid type occurs as secondary inclusions in the shear veins and as fluid inclusions of unknown origin in post variscan ankerite veins therefore it has a post variscan age the inclusions are characterized by a high salinity 18 6 22 9 eq wt cacl2 the composition of the fluid is similar to that which caused the development of mississippi valley type pb zn deposits in belgium

empirical calibration of the oxygen isotope fractionation between quartz and fe mg chlorite abstract an empirical calibration has been made of the oxygen isotope fractionation between chlorite and quartz using samples from localities in metamorphic terrains where the formation temperature has been constrained by independent methods e g fluid inclusion homogenization temperatures mineral assemblages and petrology of the host rocks to the veins thermodynamic modeling and raman spectrometry textural equilibrium of chlorite and quartz was a pre requisite and the chemical composition of chlorite was determined the chlorite analyzed had a range in fe mg varying between 0 35 and 0 7 except for pure mg chlorite fe mg substitution within the range measured does not change the oxygen isotope fractionation between quartz and chlorite measurably the results support a linear correlation for chlorite quartz fractionation over the temperature range given by this study 240 550 c 1000 ln 0 01323 0 002 t c 10 97 0 92 the presently established geothermometer can be applied to quartz chlorite fractionations in low grade metamorphic rocks and may be extrapolated to diagenetic systems

mineralogy and mineral chemistry of detrital heavy minerals from the rhine river in germany as evidence to their provenance sedimentary and depositional history focus on platinum group minerals and remarks on cassiterite columbite group minerals and uraninite in the course of studying the gold bearing heavy mineral spectrum of sediments from the upper rhine river a distinct suite of detrital grains comprising platinum group minerals pgm cassiterite columbite group minerals and uraninite was identified and investigated using conventional and modern analytical methods this study aimed to characterize the selected mineral groups mineralogically and geochemically in order to identify possible source areas and to reconstruct different aspects of the complex sedimentary history of the rhine river sediments the pgm assemblage is dominated by grains of ru os ir alloys 70 followed by pt fe alloys sperrylite and rare other pgm accordingly this pgm assemblage represents highly mature physically and chemically extremely resistant compounds which may have experienced and survived repeated reworking during their sedimentary history pt fe alloys and sperrylite may originate from various sources however the predominant ru os ir alloy grains point to an origin from ophiolite sequences of unknown age but likely pre alpine variscan or older the exact locations of the primary sources and the complex prolonged sedimentary history of the detrital pgm with possibly multiple intermittent storages remain unknown detrital cassiterite grains were dated by the u pb method using la icp ms the age dates of cassiterite largely overlap with zircon age distributions by peaking distinctly at ca 325 ma majority of ages thereby implying a predominantly variscan age of the cassiterite grains and possible derivation from mineralization in the black forest area columbite group minerals are dominantly tapiolite originating from pegmatites rare uraninite grains attest that this mineral experienced rapid erosion transport and deposition in a reducing environment

colloidal gold and silica in mesothermal vein systems some of the textural features of mesothermal gold quartz veins may be best explained by the initial precipitation of amorphous silica gel colloid which subsequently crystallizes to quartz this can occur in brittle ductile shear zones where a significant fluid pressure drop occurs during stick slip failure such a process rapidly supersaturates the hydrothermal fluid with respect to amorphous silica which precipitates instead of quartz owing to favorable kinetics depressurization also commonly leads to fluid unmixing and destabilization of soluble gold complexes however the presence of colloidal silica can stabilize gold colloid allowing further transport of particulate gold in suspension in the hydrothermal fluid silica gel would be highly unstable under mesothermal conditions and would undergo rapid syneresis and crystallization to form quartz solid impurities would tend to be expelled toward grain boundaries this model can account for the primary anhedral aggregate textures typical of mesothermal quartz veins the concentration of gold along grain boundaries and the formation of discrete gold nuggets and the rare occurrence of low order silica polymorphs and relict spheroidal structures the transport of gold in colloidal form may be one reason for the frequently consistent bulk grade distribution in gold quartz vein systems over many hundreds of metres in some cases kilometres of depth in addition the formation of charged colloidal particles may help to explain the attraction of gold grains to specific mineral surfaces

fluid evolution during burial and variscan deformation in the lower devonian rocks of the high ardenne slate belt belgium sources and causes of high salinity and c o h n fluids fluid inclusions in quartz veins of the high ardenne slate belt have preserved remnants of prograde and retrograde metamorphic fluids these fluids were examined by petrography microthermometry and raman analysis to define the chemical and spatial evolution of the fluids that circulated through the metamorphic area of the high ardenne slate belt the earliest fluid type was a mixed aqueous gaseous fluid h2o nacl co2 ch4 n2 occurring in growth zones and as isolated fluid inclusions in both the epizonal and anchizonal part of the metamorphic area in the central part of the metamorphic area epizone in addition to this mixed aqueous gaseous fluid primary and isolated fluid inclusions are also filled with a purely gaseous fluid co2 n2 ch4 during the variscan orogeny the chemical composition of gaseous fluids circulating through the lower devonian rocks in the epizonal part of the slate belt evolved from an earlier co2 ch4 n2 composition to a later composition enriched in n2 finally a late variscan aqueous fluid system with a h2o nacl composition migrated through the lower devonian rocks this latest type of fluid can be observed in and outside the epizonal metamorphic part of the high ardenne slate belt the chemical composition of the fluids throughout the metamorphic area shows a direct correlation with the metamorphic grade of the host rock in general the proportion of non polar species i e co2 ch4 n2 with respect to water and the proportion of non polar species other than co2 increase with increasing metamorphic grade within the slate belt in addition to this spatial evolution of the fluids the temporal evolution of the gaseous fluids is indicative for a gradual maturation due to metamorphism in the central part of the basin in addition to the maturity of the metamorphic fluids the salinity of the aqueous fluids also shows a link with the metamorphic grade of the host rock for the earliest and latest fluid inclusions in the anchizonal part of the high ardenne slate belt the salinity varies respectively between 0 and 3 5 eq wt nacl and between 0 and 2 7 eq wt nacl while in the epizonal part the salinity varies between 0 6 and 17 eq wt nacl and between 3 and 10 6 eq wt for the earliest and latest aqueous fluid inclusions respectively although high salinity fluids are often attributed to the original sedimentary setting the increasing salinity of the fluids that circulated through the lower devonian rocks in the high ardenne slate belt can be directly attributed to regional metamorphism more specifically the salinity of the primary fluid inclusions is related to hydrolysis reactions of cl bearing minerals during prograde metamorphism while the salinity of the secondary fluid inclusions is rather related to hydration reactions during retrograde metamorphism the temporal and spatial distribution of the fluids in the high ardenne slate belt are indicative for a closed fluid flow system present in the lower devonian rocks during burial and variscan deformation where fluids were in thermal and chemical equilibrium with the host rock such a closed fluid flow system is confirmed by stable isotope study of the veins and their adjacent host rock for which uniform 180 values of both the veins and their host rock demonstrate a rock buffered fluid flow system

fluid regimes during late stages of a continental collision physical chemical and stable isotope measurements of fluid inclusions in fissure quartz from a geotraverse through the central alps switzerland fluid evolution during neo alpine metamorphism during late stages of the continental collision between europe and africa was studied by analyzing fluid inclusions in alpine fissure quartz collected in forty nine localities along a geotraverse through the central alps switzerland the methods employed include microthermometry micro raman spectroscopy k na thermometry and stable isotope analysis early fluid inclusions provide evidence of close to peak metamorphic temperatures of the late tertiary or neo alpine metamorphic event fluid composition evolved along the geotraverse from north to south as follows higher hydrocarbons were dominant in the low and medium grade diagenetic zones methane was the main volatile in the high grade diagenetic and low grade anchizone water dominated in the highgrade anchizone and low grade epizone with co2 10 mol in the high grade epizone and in the mesozone higher hydrocarbons and ch4 were the products of kerogen maturation and cracking of preexisting petroleum large water supplies originated from the dehydration of cooler metasedimentary rocks that were overthrust by crystalline basements of the lepontines aar and gotthard massifs carbon isotope analyses suggest that the co2 component was derived from oxidation of graphitic matter especially in the vicinity of sulfate bearing metasediments and from decarbonation reactions in the aar and gotthard massifs as well as in the helvetic axen nappe and its underlying north helvetic flysch high fluid pressures prevailed and favored nappe transport by contrast in the southern lepontine area very low early fluid pressures were probably related to dry rocks and scarce metasediments and to high geothermal gradients that resulted from intense uplift and erosion between 26 and 18 ma retrograde fluid evolution was recorded by a succession of fluid inclusion populations in each alpine fissure it was controlled by uplift and cooling and characterized by decreasing contents of volatiles and an increase in 18o of host quartz tectonic activity led to episodic pressure drops of at least 0 5 to 2 kbar and promoted fluid unmixing channelized flow and rapid growth of skeletal quartz channelized rather than pervasive fluid migration at temperatures 450 c and under conditions of brittle deformation is documented by episodic increases in salinity and by fluid flushing through the massifs there is stable isotope evidence for involvement of meteoric water only in late crystallizing quartz formation of alpine fissures and fissure minerals was the result of a unique coincidence of late continental collision 450 c fluid expulsion from overthrust metasediments uplift and erosion

origin and evolution of high salinity zn pb mineralising fluids in the variscides of belgium high salinity na ca cl rich fluids 20 wt salts in inclusions in gangue and ore minerals from mesozoic mississippi valley type mvt deposits in the verviers synclinorium eastern belgium and in cretaceous vein calcites at the variscan front were investigated by microthermometric and crush leach analysis the mvt deposits formed at temperatures of 110 c while the cretaceous vein calcites were precipitated at temperatures 50 c their cl br content cl br ratio between 246 and 458 suggests that the fluids probably originated by the evaporation of seawater during basin development at the southern margin of the caledonian brabant massif in the late palaeozoic the na ca k content na 29 700 49 600 ppm ca 25 700 46 200 ppm k 1 000 5 620 ppm is similar to that of the mineralising fluids in other pb zn districts interpreted to be of evaporative origin e g newfoundland east tennessee polaris furthermore comparison of the na ca k content of the fluids with that of an evolved evaporitic brine enables the recognition of major water rock interactions that modified the fluid composition it indicates that the ambient fluids participated in the early diagenetic dolomitisation of upper palaeozoic carbonates and also in the albitisation of plagioclase in lower palaeozoic siliciclastics of the caledonian basement illitisation of smectites or dissolution of k feldspar probably controlled the k content of the fluids a model is proposed where the bittern brines migrated down into the deep subsurface because of their density during extension after the variscan orogeny these fluids were finally expelled along extensional faults resulting in the formation of zn pb deposits

syn to late orogenic quartz veins marking a retrograde deformation path in a slate belt examples from the high ardenne slate belt belgium abstract an integrated structural petrographic and microthermometric methodology has been applied on syn to late orogenic quartz veins from the high ardenne slate belt belgium to define their relative timing the quartz precipitates which do not show any mutual cross cutting relationships represent the meso scale brittle accommodation during fold initiation amplification and locking crystal plastic deformation structures and p t trapping conditions indicate that the different processes accommodating folding occurred in a progressive manner along a retrograde deformation path associated with the gradual exhumation of the slate belt from ca 7 5 to 6 km depth successive veining occurred from peak metamorphic conditions ca 300 c and 190 mpa measured in extrados veins to subsequent lower p t conditions in the periphery of a lenticular vein ca 275 c and 180 mpa late orogenic saddle reef filling ca 245 c and 160 mpa and the core of a lenticular vein ca 220 c and 150 mpa open cavity growth and fluid assisted brecciation indicate that veining occurred under overpressured fluid conditions it is therefore fair to assume that the high ardenne slate belt acted at least episodically as a mid crustal overpressured fluid reservoir not only in the earliest and latest stages but also during the main stage of orogeny

generation and maintenance of abnormal fluid pressures beneath a ramping thrust sheet isotropic permeability experiments abstract we have investigated the mechanisms responsible for the evolution of excess pore pressures within and beneath a ramping thrust sheet i e fluid flow porosity compression and thermal expansion of water and the sensitivity of pore pressure to a variety of physical parameters e g permeability thrust sheet velocity heat flux coupled pore pressure and temperature equations were solved numerically in two dimensions using a generalized hydrostratigraphy of north american thrust belts because of the lack of either symmetry or a steady state in this problem both deposition and thrust loading stages were simulated the dominant mechanisms controlling pore pressure evolution were fluid flow and compression of pore space by vertical loading thermal expansion of the fluids was found to be insignificant in generating excess pore pressures at common thrust loading rates the results indicate that it is possible to generate high pore pressure to lithostatic pressure ratios within thrust sheets by depositional loading prior to thrusting high values of are generated and maintained during thrust loading for reasonable assumptions about the conditions thought to have existed in thrust belts values of were not constant throughout the model the highest values tended to concentrate near the surface of the model and within and below the toe of the thrust sheet the magnitude and distribution of excess pore pressures and values were found to be especially sensitive to variations in permeability excess pore pressure generation by compression exceeded pore pressure dissipation by fluid flow for permeabilities less than approximately 10 16 m 2 permeabilities greater than approximately 10 16 m 2 produced hydrostatic pore pressure gradients the models demonstrate that permeability inhomogeneity due to lithologic variations may exert a strong control on the magnitude and spatial distribution of excess pore pressures within thrust sheets in addition these models indicate that it is unlikely that fluid pressure is high everywhere in a moving thrust sheet

geochemistry of highly saline fluids in siliciclastic sequences genetic implications for post variscan fluid flow in the moravosilesian palaeozoic of the czech republic ubiquitous post variscan dolomites occur in zn pb cu veins at the nizk jesenik mountains and the upper silesian basin lower and upper carboniferous siliciclastics at the eastern part of the bohemian massif crush leach stable isotope oxygen and carbon and microthermometry analysis of the fluid inclusions in dolomites enable understanding the geochemistry origin and possible migration pathways of the fluids homogenisation temperatures of fluid inclusions range between 66 and 148 c with generally higher temperatures in the nizk jesenik mountains area than in the upper silesian basin the highest homogenisation temperatures up to 148 c have been found near major regional faults and the lowest in a distant position or at higher stratigraphic levels highly saline 16 6 28 4 eq wt nacl h2o nacl cacl2 mgcl2 fluids occur in inclusions na cl br systematics of trapped fluids and a calculated oxygen isotopic fluid composition between 0 9 and 3 0 v smow indicate that the fluid was derived from evaporated seawater stable isotopic modelling has been used to explain stable isotopic trends isotopic values 13c 6 0 2 0 v pdb 18o 15 5 22 5 v smow of dolomites resulted from fractionation and crystallisation within an open system at temperatures between 80 and 160 c rock buffering explains the isotopic composition at low w r ratios organic matter maturation caused the presence of isotopically light carbon in the fluids and fluid rock interactions largely controlled the fluid chemistry k li br and na contents k cl i cl and li cl molar ratios the fluid chemistry reflects well the interaction between the fluid and underlying limestones as well as with clay and organic rich siliciclastics no regional trends in temperature or fluid geochemistry favour a fluid migration model characterised by an important vertical upward migration along major faults a permeable basement and fractured sedimentary sequence enhanced the general nature of the fluid system fluid characteristics are comparable with the main post variscan fluid flow systems in the polish cracow silesian ore district and german sedimentary basins

mississippi valley type pb zn mineralization in eastern belgium indications for gravity driven flow mississippi valley type deposits are widespread in carboniferous strata in eastern belgium five successive fe rich fracture filling calcite generations have been recognized in the veins containing the pb zn mineralization of bleiberg fluid inclusion evidence indicates that all the calcites formed from fluids with salinities between 16 0 and 23 1 equivalent wt nacl the trapping temperature of the fluid inclusions decreases from 125 c in the first two calcite generations to 50 c in the last two vein cements the 13 c values of the calcites vary between 0 1 and 8 3 relative to pdb peedee belemnite the oxygen isotopic composition of the ambient fluids calculated from the trapping temperature and the isotopic composition of the calcites varies between 5 2 and 7 6 relative to smow standard mean ocean water the low 13 c values of the calcites are explained by the contribution of 12 c from co 2 released during the oxidation of organic matter in the upper carboniferous shales and the coupled reduction of sulfate in the mineralizing brine the highly variable oxygen isotopic composition of the ambient fluids the low 18 c value of the water from which one calcite cement precipitated and the intense water rock interaction necessary to leach metals indicate that the original fluids had a low 18 c and that those fluids became enriched in 18 o by water rock interaction waters with such low 18 c values must have had a meteoric origin flow of these waters into the deeper subsurface was likely gravity driven and took place from the uplifted parts of the variscan orogen toward the foreland basin

biotite breakdown and the formation of gahnite in metapelitic rocks from kemio southwest finland the formation of ferroan gahnite by breakdown of zinc bearing biotite has been studied in metapelitic gneisses from the kemio region in southwestern finland spinel compositions range from herc50 gahn40spin10 to herc15gahn82spin3 biotite contains up to 0 24 wt zno individual spinel grains show a gradual compositional zoning owing to increasing zinc contents towards the grain margins

the compositional limits of fluid immiscibility in the system h2onaclco2 as determined with the use of synthetic fluid inclusions in conjunction with mass spectrometry abstract the compositional limits of fluid immiscibility in the system nacl h2o co2 were investigated from 500 to 700 c at pressures of 1 2 and 3 kbar synthetic fluid inclusions formed in quartz prisms were equilibrated with high temperature high pressure fluids in hydrothermal pressure vessels the inclusions were analyzed optically by mass spectrometry and by microthermometry the fields of immiscibility were defined as a function of temperature and pressure mass spectrometry was used to validate the existence of the immiscible fluids and to determine the co 2 h 2 o ratios of the two coexisting phases microthermometry i e the measurement of the melting temperature of solid sodium chloride was used in conjunction with the results of the mass spectrometry measurements to define the tie lines within the two phase fields isochores and the location of a portion of the isopleth were determined for composition nacl8 9 h2o76 1 co215 0

contrasting origin of palaeofluids in a strike slip fault system calcite cements in a dextral strike slip fault system in the variscan front complex belgium have been investigated to determine the origin of the fluids migrating along the fault system generation of non ferroan and ferroan calcites occurs along the fault plane a right stepover between two faults is occupied by a breccia it formed due to repeated hydraulic implosions within a dilational jog ferroan calcites cement the breccia the general geological setting and the microthermometric data tt 50 c indicate that calcite precipitation along the faults took place at shallow depth however the geochemistry and origin of the fluids from which the calcites along the fault plane and in the breccia precipitated were different the non ferroan calcites along the fault plane precipitated from a highly saline fluid 18 1 to 25 3 eq wt cacl2 at a temperature around 50 c secondary inclusions in trails in these calcites demonstrate that similar highly saline fluids reached temperatures of at least 130 c the latter migrated from a depth of over 4 km implying the fluid was tapped from the lower palaeozic siliciclastic basement the ferroan calcites along the strike slip fault plane also formed from highly saline fluids but which interacted with upper palaeozoic strata before migration to shallow depth in contrast primary fluid inclusions in the ferroan calcites in the breccia indicate cementation occurred from a low salinity fluid 1 7 to 8 6 eq wt nacl at a temperature of 50 c or less this fluid likely originated from shallow depth the contrasting origin of the fluids indicate different flow regimes have been intersected by the faults during their strike slip reactivation

evolution of ptygmatic folds in migmatites from the type area s finland abstract it is proposed that ptygmatic folds in migmatites form during leucosome melanosome differentiation volume loss by depletion of quartz and feldspar takes place in the interlimb domains of folds leaving a residual melanosome buckling leucosomes increase in volume due to this process and are protected from substantial thinning concurrent with tectonic segregation albeit at a lower rate the leucosome expands by replacing the melanosome this process is induced by fluid activity at the leucosome boundary as suggested by the occurrence of secondary offshoot veinlets segregation and growth causes the most typical aspect of ptygmatic folds preservation of an overall buckle shape during the stage when the folds become isoclinal and devoid of interlimb matrix

pleistocene suvero slide paola basin southern italy abstract the suvero slide covers an area of about 225 km 2 in the paola slope basin on the eastern tyrrhenian margin the shape and lateral extent of the deposit reflect topographic confinement of the slide between the continental slope and a morphologic barrier formed by a margin parallel slope ridge no headwall or slide plane comparable in scale with the slide deposit were found suggesting that quasi in situ deformation of semi consolidated sediments took place when the failed materials reached the floor of the slope basin the failure occurred downslope from a basement high originating from local uplift continued uplift after the suvero slide occurred is documented by the presence of steep upper slope gradients within the study area and by the presence of small scale creep and failure events that postdate the suvero slide

the use of a combined structural stable isotope and fluid inclusion study to constrain the kinematic history at the northern variscan front zone bettrechies northern france abstract a detailed structural stable isotope and fluid inclusion study of distinct vein generations has been performed in a kilometre scale syncline to correlate the temperature pressure conditions of vein formation with specific deformation episodes the structural relationship of the veins with cleavage folds faults and with one another allows the identification of pre syn and post variscan carbonate vein generations the stable isotope composition of the vein calcites and dolomites is very similar to that of the surrounding limestones and dolostones respectively this indicates that the cements were precipitated from fluids buffered by the host rock and implies that the temperature pressure characteristics of the fluids reflect the thermal history of the deformation history within the syncline microthermometric data of primary fluid inclusions were used to estimate the temperature pressure conditions at precipitation time and thus of the deformation pressure corrected trapping temperatures for the veins show a temperature evolution from pre variscan 310 c to variscan 260 200 c and post variscan 75 c this evolution indicates that the syncline developed not at a specific depth but rather as an active progressive deformation process during transport along the northern variscan thrust front

macflincor and its application to fluids in archean lode gold deposits abstract macflincor was developed to process laboratory data gathered on fluid inclusions and to calculate isochores for geologically important fluids composed of h2o c02 ch4 nacl and n2 within the program interactive diagrams are available to describe those chemical systems which cannot be adequately constrained numerically the user can choose from various published equations of state describing fluid behavior and can easily compare the results obtained by using different equations the program once the basic fluid parameters have been established allows the data to be used to determine the p t trapping conditions to evaluate possible pressure corrections and to compare different depths of formation based on the pressure calculations and given geothermal gradients for illustrative purposes macflincor has been utilized here to constrain different physical chemical parameters of fluid inclusions trapped in ore related quartz veins and breccias of archean lode gold deposits in western australia inferred pressures from individual deposits show a wide range of values which may be due to post entrapment modifications and or observational uncertainties including estimation of liquid vapor ratios

late variscan fluid migration at the variscan thrust front of eastern belgium numerical modelling of the palaeothermal and fluid flow field modelling of the palaeothermal field at the variscan thrust front in eastern belgium indicates significant temperature modifications by late variscan palaeofluids migrating from internal to peripheral parts of the orogen a detailed set of calibration data chlorite geothermometry microthermometry organic rank gives evidence of temporary palaeotemperature variations at the variscan thrust front obviously connected to the migration of hot low saline palaeofluids these thermal events likely enhanced organic maturation vitrinite reflectance conodont alteration of devonian and carboniferous sediments which accumulated long before the variscan orogeny occurred numerical simulation 2d finite element method of the palaeothermal field includes coupled heat transport by thermal conduction and fluid flow palaeothermal scenarios yield successive palaeotemperatures 200 300 c which are indicated by the control data due to relatively short term fluid ascent along the detachment and the imbricate thrust front the simulated flow velocities are up to tens of metre per year lasting several thousand years non steady state solution in the scenarios modelled these thermal events occur in a realm of enhanced bulk temperatures due to elevated basal heat flow densities 90 mw m 2 and an additional burial depth of some kilometres the simulated temperature enhancement due to fluids ascending at the variscan thrust front is several tens degrees the scenarios demonstrate long distance fluid migration during or after deformation of the palaeozoic basin and its effect on the palaeothermal field

characterization of pyrolysates from maceral components of tarim coals in closed system experiments and implications to natural gas generation abstract the macerals vitrinite exinite fusinite and semi fusinite from low maturity coal vrr 0 40 of the manjiaer sag tarim basin were isolated and subjected to isothermal pyrolysis in a sealed stainless steel reactor at temperatures ranging from 250 to 550 c in 50 c intervals for a duration of 72 h gas yields chemical and isotopic compositions vary significantly for the different coal macerals total gas yields predominantly ch4 and co2 from exinite and vitrinite are much higher than those from fusinite and semi fusinite carbon dioxide generated from exinite is slightly enriched in 13c 13 c co 2 range 19 7 to 12 2 as compared to co2 produced from vitrinite 13 c co 2 range 22 4 to 19 1 methane produced from exinite 13 c ch 4 range 35 0 to 30 3 tends to be isotopically lighter than methane generated from inertinite fusinite and semi fusinite 13 c ch 4 range 33 7 to 25 2 interestingly the 13 c ch 4 values of all macerals show a similar evolution pattern with temperature the initial gas is isotopically heavy then becomes lighter at moderate temperatures and finally becomes heavier again this may be an indication of isotopic heterogeneity within the coal precursors hydrocarbon potential of coal closely depends on the maceral composition exinite shows the highest hydrocarbon generation potential followed by vitrinite while inertinite has only a poor hydrocarbon potential with increasing thermal stress n alkane parameters such as oep and cpi decrease while the c 21 c 22 ratio increases and the bimodal pattern of the n alkane distribution changes to a unimodal pattern the pr ph ratio varies irregularly through catagenesis