crustal heat production and mantle heat flow in central and eastern europe abstract the conversion of seismic velocity p into radiogenic heat production a enables the distribution of crustal heat sources to be estimated this technique was used to assess the mantle moho heat flow for 49 seismic velocity depth profiles located along five continental traverses in central and eastern europe the effect of pressure and temperature on p was taken into account as was the age dependence of a the uppermost part of the crust is dominated by microcracks that may have allowed a certain redistribution of radioactive elements by deep groundwater migration furthermore owing to the highly variable value of the pressure derivative of v p in the uppermost crust the use of a a p relationship is problematic within this depth range this radioactivity enriched zone the thickness of which can be determined from the parameters of the heat flow heat production relationship was therefore treated separately according to the model adopted for the upper crust the moho heat flow ranges from 14 to 26 mw m 2 in the stable continental areas such as the shields or ancient platforms younger terrains are characterized by elevated moho heat flows of 20 to 40 mw m 2 and the moho heat flow may eventually attain values over 50 mw m 2 in regions characterized by very high surface heat flow such as the pannonian basin for example the present data were compared with crustal models proposed by other authors moho heat flow estimates based on a simple exponential distribution of heat sources valid for the whole crust might be too high if applied to stable continental crust our data confirm a considerable variability in the mantle heat flow corresponding to the large scale tectonothermal evolution with a generally lower moho heat flow typical of consolidated stable continental crust the discrepancy in relation to the above estimates can be accounted for by a heat generation hump beneath an upper zone of exponential decline

crustal and upper mantle structure of stable continental regions in north america and northern europe from an analysis of many seismic profiles across the stable continental regions of north america and northern europe the crustal and upper mantle velocity structure is determined analysis procedures include ray theory calculations and synthetic seismograms computed using reflectivity techniques the p wave velocity structure beneath the canadian shield is virtually identical to that beneath the baltic shield to a depth of at least 800 km two major layers with a total thickness of about 42 km characterize the crust of these shield regions features of the upper mantle of these regions include velocity discontinuities at depths of about 74 km 330 km 430 km and 700 km a 13 km thick p wave low velocity channel beginning at a depth of about 94 km is also present

the variation of heat generation density and seismic velocity with rock type in the continental lithosphere abstract the petrophysical properties radioactive heat generation compressional wave velocity and density are related to rock type in crystalline rocks the cation fraction in the rock forming minerals is applied to determine the relationships quantitatively heat generation exhibits considerable variation with rock type as well as with the geologic age of the rocks therefore the relation between heat generation and rock type has been split into a relation for phanerozoic rocks and another for precambrian rocks which exhibit significantly lower heat generation only 1 3 of that of phanerozoic rocks the interrelations between the petrophysical properties are applied to fennoscandia precambrian terrane and southern bavaria northern alpine foreland phanerozoic rocks to estimate the heat generation by radioactivity in the crust and the heat flow density from the upper mantle

the heat flow heat generation relationship implications for the nature of continental crust abstract the apparent linear relationship between surface heat flow q and heat generation a is usually interpreted in terms of heat flow provinces i e terrains that have a common tectonothermal history and a uniform mantle component of heat flow the slope d of the linear regression of heat flow on heat generation is an indication of the thickness of the upper heat producing layer for many terrains d is numerically similar to the depth of a major mid crustal transition zone these observations are modelled by a two layer crust consisting of an upper layer approximately 10 15 km thick of variable heat generation underlain by a layer about 20 km thick in which heat generation is lower and more uniform than that in the upper layer the model is well able to simulate q a regression parameters for different sets of real data it is also consistent with other geological and geophysical observations the higher and more variable heat generation of the upper layer is consistent with ideas concerning removal of heat producing elements from the lower layer during amphibolite to granulite metamorphism and their redistribution into the upper crust further redistribution of heat producing elements may occur in zones of hydrothermal circulation whose depth is a function of stress pressure and temperature and which may migrate vertically in response to stress changes during uplift and erosion large scale metamorphism to granulite facies has been postulated as one mechanism for stabilisation of continental crust in the late archaean it is shown however that redistribution of heat producing elements in such a process would have only a small effect on crustal geotherms so that partitioning of heat production was not a major factor in the crustal stabilisation

compaction behavior of argillaceous sediments as function of diagenesis the paper presents the results of laboratory compaction tests on samples of kimmeridge clay taken from two different locations in the uk the main objective of the laboratory tests is to determine how diagenesis affects the hydro mechanical properties and compaction behavior of argillaceous sediments the two kimmeridge clays used in the tests are essentially from the same parent material but have undergone different degrees of mechanical and chemical diagenesis the laboratory tests are designed to determine the effects of mechanical loading and chemical processes on changes in porosity permeability compressibility strength and effective horizontal stress in argillaceous materials another objective of the study is to investigate the adequacy of soil mechanical constitutive models in predicting the response of argillaceous materials to conditions corresponding to burial depths in sedimentary basins the tests on kimmeridge clay are carried out to as high as 150 mpa effective vertical stress corresponding to about 9 km in burial the results indicate that mechanical compaction and burial depth cannot explain the differences in the hydro mechanical behavior of the tested materials the differences in hydro mechanical response are attributed to chemical diagenesis by precipitation of minerals in the pores of the sediment other observed effects of chemical diagenesis on hydro mechanical behavior of lithified sediments are 1 increase in apparent pre consolidation stress 2 decrease in compressibility 3 decrease in permeability and 4 decrease in effective horizontal stress implications of the results to fluid flow and overpressure development in sedimentary basins are discussed

relationships between the petrophysical properties density seismic velocity heat generation and mineralogical constitution the petrophysical properties density p compressional wave velocity v p and heat generation a exhibit considerable variation with rock type to characterize a given rock quantitatively a single parameter the cation fraction expressed by the k value has been found to be suited best 100 crystalline rocks have been sampled to cover the widest possible range in k value from silicic types like granophyres and granites through granodiorites tonalites diorites gabbros amphibolites hornblendites pyroxenites to ultrabasic rocks p k a and v p were determined experimentally the latter at 0 5 kbar 50 mpa the interrelations between these properties were established by regression analysis the relation k and v p k show a linear dependence whereas a k a and a v p follow exponential laws in a w m 3 12 20 230 5 k mole cm 3 in a 22 5 8 15 g cm 3 and in a 16 5 2 74 v p km s all correlation coefficients are better than 0 9

seismic crustal structure of the proterozoic north australian craton between tennant creek and mount isa seismic recording along a 600 km traverse across the southern part of the north australian craton indicates that lateral velocity variations exist in the middle lower crust taken together with other data from the craton there is evidence for midcrustal velocities increasing from east to west and from south to north these trends could result from a greater proportion of high velocity granulites being emplaced at higher levels in the crust between tennant creek and mount isa the velocity structures near the surface are compatible with an assemblage of younger and older metamorphic rocks intruded by granites near surface 0 5 km p wave velocities on the tennant creek inlier increase from 5 47 km s at the surface to about 6 2 km s at 6 km depth and correspond with low grade metamorphics of the warramunga group interspersed with weathered granites overlying amphibolite facies rocks of older metamorphic domains in the mount isa geosyncline velocities of 6 03 6 15 km s correspond to the leichhart metamorphics interspersed with granites in the middle crust p wave velocities of 6 85 km s occur at a depth of 26 km near tennant creek whereas such velocities are not evident until depths of about 37 km near mount isa there is therefore a trend for midcrust velocities to increase from east to west the lower crust is characterized by velocities of 7 3 7 5 km s and the upper mantle velocities of 8 16 8 20 km s are reached at depths of 51 54 km exposed granulite facies rocks in central australia are low in heat producing elements and are compatible with the low surface heat flow generally measured in precambrian australia these data taken together with laboratory velocity measurements on worldwide samples reported elsewhere indicate that middle to lower crustal rocks could be an assemblage of granulite facies rocks varying from pyroxene granulite in the middle crust through hornblende granulite to garnet granulite in the lower crust

radioelement concentrations in the deep profile through precambrian basement of the vredefort structure the vredefort basement granite in south africa forms the core of an undomed and overturned sequence of precambrian strata slawson 1976 proposed that the granite core has also been overturned exposing to view a thick section through the archean crust incrasing in depth toward the center of the dome profiles across the vredefort basement provide an opportunity for studying the distribution of u th and k with depth in the upper and middle crust detailed radioelement concentration profiles across the granitic basement showed that 1 the central part of the basement core is depleted in th and u relative to the perimeter and the concentration of th and u falls off regularly from the basement margin inward 2 the distribution of the radioelements and the distribution of heat production with depth over the outer 8 km are consistent with an exponential depth function 3 the felsic rocks of the central basement are characterized by high k u and th u ratios and the ratios k u k th and th u increase from the margin inward and 4 mafic granulites which occur in the central regions of the dome have normal k u k th and th u ratios high grade metamorphic environment resulted in the depletion of bothmore u and th relative to k in the greater proportion of the felsic rocks from the central regions of the vredefort basement depletion of u was far greater than that of th the normal th u k u and k th ratios in mafic rocks in close proximity to the felsic rocks suggest that mineral assemblages have a strong control on the behavior of the radioelements during regional metamorphism in the vredefort basement less

vertical distribution of heat production in the continental crust abstract using an experimentally established formula seismic velocity vp was converted to heat production a to investigate the vertical distribution of heat sources the conversion performed for a number of characteristic 1 d seismic crustal sections from various tectonic units in central europe yields a general decrease of a with depth z the pattern of decrease depends on geological age young tectonic units with high heat flow exhibit a more rapid decrease the depth dependence of a does not exactly follow the simple exponential law a z a 0 exp z d in general the logarithmic decrement d decreases with depth from 20 30 km at a depth of 10 km to about 10 km at the base of the crust in the uppermost 10 km layer of the crust a certain redistribution of u and th can occur by deep groundwater migration through microcrack networks at depths greater than 10 km geochemical constraints fairly constant th u and k u ratios suggest that the rate of decrease of the heat producing radioelements u th and k is similar

thermal and rheological structures of the xisha trough south china sea the xisha trough located in the northwest of the south china sea scs mainly rifted 30 ma ago has been a failed rift since the cessation of the seafloor spreading of the nw subbasin based on the velocity depth model along profile obh 4 across the xisha trough a seven layer density depth model is used to estimate density structure for the profile the relationship between seismic velocity and radiogenic heat production is used to estimate the vertical distribution of heat sources in the lower crust the 2 d temperature field is calculated by applying a 2 d numerical solution of the heat conduction equation and the thermal lithosphere thickness is obtained from the basalt dry solidus bds the rheology of the profile is estimated on the basis of frictional failure in the brittle regime and power law steady state creep in the ductile regime rheological model is constructed for a three layer model involving a granitic upper crust a quartz diorite lower crust and an olivine upper mantle gravity modeling supports basically the velocity depth model the moho along profile obh 4 is of relatively high heat flow ranging from 46 to 60 mw m 2 and the moho beat flow is higher in the trough than on the flanks the depth of the thermal lithospheric lower boundary is about 54 km in the center deepens toward two sides and is about 75 km at the northern slope area and about 70 kin at the southern xisha zhongsha block rheological calculation indicates that the two thinnest ductile layers in the crust and the thickest brittle layer in the uppermost mantle lie in the central region showing that the xisha trough has been rheologically strengthened which are mainly due to later thermal relaxation in addition the strengthening in rheology during rifting was not the main factor in hampering the breakup of the xisha trough c 2002 elsevier science b v all rights reserved

relationship between seismic velocity and heat production comparison of two sets of data and test of validity abstract an empirical relationship between compressional wave velocity v p and radiogenic heat generation a is frequently used to estimate heat production distributions in the continental crust two data sets from rybach and buntebarth 1 and kern and siegesmund 2 have been re evaluated and made comparable bulk density was included as a further parameter to investigate the relationships v p a v p and a statistical analysis shows reasonably high and comparable regression coefficients for the first two relationships but much less agreement for the a relationship

the vertical structure of limb hazes in the martian atmosphere abstract profiles of scattered light above the planetary limb from over 100 viking orbiter images are used to constrain the temporal and spatial behavior of earosols suspended in the martian atmosphere the data cover a wide range of seasons locations and viewing geometry providing information about the aerosol optical properties and vertical distribution the vertical resolution of the data is about 1 5 km with an absolute elevation accuracy of 1 to 4 km viking orbiter camera colibration algorithms provided reflectance accuracies to 7 absolute allowing meaningful radiometric analysis the typical atmospheric column contains one or more discrete optically thin ice like haze layers between 30 and 90 km elevation depending on season whose composition is inferred to be water ice below the detached hazes there is a continuous haze extending to the surface the continuous haze is rarely observed above 50 km and is much redder in color than the detached hazes above implying a composition that has a strong dust component the aerosol distribution exhibits a strong seasonal control inferred to be driven by the variable solar flux around the orbit of mars

determination of earthquake focal mechanisms and crustal structure in eastern australia using surface waves abstract the surface waves from two medium sized m 5 5 earthquakes in southeast australia 1966 mt hotham and 1982 wonnangatta were examined to determine average s wave crustal structure for the region and the focal mechanisms of the two earthquakes the s wave models were determined from an analysis of the group velocities of the rayleigh waves for all paths a two layer crust overlying a moho at about 40 km is required to fit the observations in the upper layer down to about 25 km the velocity gradients are very small and the s wave velocities are in the range 3 4 3 6 km s in the lower crust the s wave velocities increase gradually to about 4 6 km s at the moho where the velocity gradients are again very small the region where the s wave velocities increase significantly with depth corresponds to the region of the lower crust which generates strong seismic reflections mathur 1983 the thin crust postulated beneath bass strait and tasmania johnson 1973 is not substantiated by these data and a crustal thickness of about 40 km is also required for this region for the longer profiles 1800 km to the north and northwest of the earthquakes the velocity step at the moho is smaller than for the shorter profiles 700 km however because the surface waves are less dispersed for the shorter profiles the resolution is poorer and the models less reliable for the 1982 wonnangatta earthquake the surface wave synthetics from a focal mechanism similar to that obtained by denham et al 1985 fit the observations at five regional stations very well and confirm the nw se compressive stress regime found by other workers however for the 1966 mt hotham earthquake the surface wave synthetics generated from the normal faulting solution which was obtained from an analysis of p wave first motions denham et al 1985 do not agree with the rayleigh wave trains observed at australian stations rather the surface wave observations support a thrust fault type mechanism with the pressure axis having a similar direction to that obtained from the 1982 wonnangatta earthquake and other earthquakes in the region

heat flow and geodynamics in the tyrrhenian sea the present heat flow in the southern tyrrhenian sea appears as a transient thermal wave that has migrated eastward in time the higher heat flow in the south eastern side of the basin confirms the suggestion of an eastward migrating rift punctuation of the tyrrhenian backarc extension in lithospheric boudins is accompanied by a concentrated increase in heat flow generated by asthenospheric intrusions and related magmatism progressively moving eastward the migration of the asthenosphere in the same direction could explain these phenomena

a test of the relationship between seismic velocity and heat production for crustal rocks new heat production data of 40 rock samples comprising a wide variety of crustal rocks are compared with respective p wave velocities and densities in order to test the empirical velocity density heat production systematics proposed by rybach and buntebarth 1 2 which have been used by several investigators to determine heat production with depth in the crust our laboratory data do not convincingly fit any of the proposed relationships the lack of confirmation is attributed to the fact that the physical rock properties are mainly related to the single crystal properties of the respective major minerals whereas heat production in the rocks results from radiogenic components which are largely concentrated in accessory minerals

a heat production model of the crust and upper mantle abstract experimental evidence on the relationship between seismic velocity and radiogenic heat production has been used to estimate the vertical distribution of heat sources in the continental lithosphere the derived differentiation rate of the radioelements with depth has been investigated to depths 100 km in various world wide tectonic provinces the results show that more pronounced upward differentiation steeper heat production distribution corresponds to regions of higher heat flow and usually higher crustal temperatures thus crustal distributions of radiogenic heat may be related to tectonic age and crustal evolution the vertical distribution of heat production can be traced even in the subcrustal lithosphere and confirms the upward concentration of a substantial part of the radioelements into the crust at the expense of the upper mantle reflecting the early stages of crustal separation while in the uppermost crust the distribution of the heat sources seems to be controlled by uranium and thorium in the upper mantle it is potassium which controls it data obtained may be important in the geothermal modelling deep temperature calculation and in determinations of moho heat flow

the role of pre existing faults in basin evolution constraints from 2d finite element and 3d flexure models the lithospheric driving forces which cause intraplate basin deformation are relatively constant over large areas consequently lateral variations in deformation and stress and strain concentrations seem to be primarily caused by pre existing heterogenities in the rheological signature of the continental lithosphere underlying the sedimentary basins in this paper we explore the weak character of upper crustal faults and their control on basin shape for a number of case studies on intraplate phanerozoic basin settings using a 2d finite element and a 3d flexure model of key importance is the integration of seismic data and field observations with the tectonic modelling allowing the investigation of deformation processes and their expressions on different scales operating on different levels of the lithosphere finite element models for sub basin scales incorporating weak upper crustal faults predict strong control of these weak zones on local stress distributions and subsequent deformation in agreement with observed deformation patterns slip along upper crustal faults control stress distribution and subsequent faulting in overlying sedimentary rocks the effect of weak upper crustal fault movements on basin wide regional upper crustal flexure is looked at in two case studies on 1 extensional tectonics in the lake tanganyika rift zone east africa and 2 compressional tectonics in the central system and tajo basin central spain both settings indicate that basement warpings are controlled by large amounts of slip along so called weak crustal scale border faults which are mostly planar adopting border fault displacements in the 3d flexure model the results indicate low effective elastic thickness eet values in a range of 3 7 km for induced basement deflection patterns in accordance with observations the low eet values most likely reflect a partly decoupling of upper crustal and subcrustal deformation facilitated by the weak lower crust and in agreement with standard rheological assumptions for phanerozoic lithosphere in contrast the inferred weakness of upper crustal faults relative to surrounding rock is not evident from uniform rheological assumptions however observations of reactivations of faults which are not preferably aligned with the stress field and reactivations of basin deformation on long time scales are in support of this feature

subsurface granites in the franconian basin as the source of enhanced geothermal gradients a key study from gravity and thermal modeling of the bayreuth granite the franconian basin in ne bavaria is a region of gravity low between the bohemian massif in the east and the kraichgau terrane in the west borehole measurements have identified the northern part of the franconian basin as a regional geothermal anomaly and new heat flow calculations give values of 100 mw m2 distinct negative bouguer anomalies observed in this basin are modeled as granitic intrusions in the saxothuringian basement that underlies the permo mesozoic units the interpretation of gravity gradients in combination with the filtering of gravity data gives the possible depth constraints of the intrusive bodies the resulting depths were cross checked using microstructural studies of quartz veins in the basement rocks at 1341 m depth the quartz shows structures typical for low temperature plasticity and we infer a deformation temperature of ca 300 c this indicates a considerable pre permian uplift of at least 7 km for parts of the saxothuringian basement and supports depth estimates from gravity data the heat supply of granitic intrusions by radiogenic decay is modeled considering several scenarios for the geological conditions recovered by the obernsees borehole model for conductive heat transfer the 1390 m deep drillhole is in a marginal position to the most pronounced negative bouguer anomaly it could be shown that the saxothuringian basement including heat producing granites heat production rates 4 6 w m3 covered by the insulating sedimentary rocks 1 35 km of permian to lower jurassic units can account for the enhanced geothermal gradient 38 c km that were measured in the borehole

time dependent thermal state of the lithosphere in the foreland of the eastern carpathians bend insights from new geothermal measurements and modelling results summary the time dependent heat budget thermal evolution and rheology of the lithosphere in the last 13myr along a 120 km long profile in the foreland of the eastern carpathians bend is presented the study area a complex tectonic environment in the vicinity of the wellknown intermediate depth seismogenic vrancea zone includes the deepest sedimentary basin in romania 18 km with a recent rapid evolution in the last 13myr 8 km of sediments detailed high resolution temperature logs in the depth ranges from 0 700 m to 0 2400 m in eight thermally stabilized boreholes together with logging and geological information on structure lithology and time evolution of the sedimentary pile have been used to model the thermal evolution by means of a 2 d finite element model which includes sedimentation history sediment compaction lateral and vertical variation of thermal properties of sediments and consolidated crust modelling results have been compared to measured temperatures corrected for palaeoclimate effects in a trial and error iterative approach sedimentation palaeoclimate undercompaction and heat refraction effects on one hand and the heat generated in the upper crust on the other combine to explain the observed subsurface temperature field and in particular the pronounced curvature of the vertical temperature profiles the neogene quaternary sedimentation resulted in a rather uniform deficit of the surface heat flux of about 12 mw m 2 in the study area in spite of the marked lateral variation of the sedimentary pile thickness the palaeoclimate effect is responsible for a surface heat flux depression of 7 8 mw m 2 uniform along the study profile unlike older sedimentary basins in the study area transient sedimentation thermal effects add to palaeoclimate effects in establishing the temperature field in the depth range of geothermal measurements the lateral variation of the palaeoclimatically corrected surface heat flux from the centre of the focsani depression 40 mw m 2 to its margin and the foreland platform 70 mw m 2 is mainly the result of the lateral variation of the heat produced in the upper crust where thickness varies from 7 to 21 km respectively a heat production of 2 3 wm 3 for the southeastern end of the profile and of 2 15 wm 3 for the rest of it has been modelled as a result of the sedimentation process temperature variations as large as 70 100 c occurred in the pre neogene sediments and the crystalline crust immediately under the sedimentary pile with consequences on the metamorphic state and rheological behaviour of the foreland

heat production in the continental crust part i data converted from seismic velocities and their attempted interpretation abstract when using the simple exponential distribution of radiogenic heat production a with depth z a z a o exp z d the statistical analysis of a large number of heat production profiles converted from the observed seismic velocity vs depth profiles and the experimental knowledge of the relationship between seismic velocity and heat production disclosed certain relations between the logarithmic decrement d value and heat flow tectonic age and crustal thickness the d valuein this respect characterizes the depth rate of the differentiation of the heat production in all tectonic units the d parameter decreases with depth as the next step the more complicated distribution law a z a o exp z d a was applied where a characterizes the quantity of removed heat sources by the processes accompanying the crustal evolution such as remelting metamorphosis leaching by underground waters etc all parameters a o a and d are constant within each particular tectonic province and parameter d does not depend on depth contrary to the former law the amount of removed heat sources a reflects the initial concentration of heat sources and is higher in young tectonic terranes in areas of high heat flow and in regions of thin crust