Mean Heat Flow Research Articles

Terrestrial heat flow in the Sirt Basin, Libya, and the pattern of heat flow across northern Africa

We report 66 new heat flow and 24 new heat production measurements from the Sirt Basin, a late Jurassic‐Miocene sedimentary depression in north central Libya underlain by late Proterozoic basement. Heat flow determinations were made using bottom hole temperatures from oil wells and thermal conductivity measurements from drill core and cuttings; heat production measurements come from core samples of basement rock. Heat flow is fairly uniform throughout the basin, with a mean of 72 ± 9 (s. d.) mW m−2. It is not clear if heat flow from the Sirt Basin is elevated as a consequence of its origin as a late Mesozoic rift. The difference between the mean basin heat flow and the global mean heat flow from tectonically undisturbed late Proterozoic terrains (55 ± 17 mW m−2) is 17 mW m−2, but this difference lies within the uncertainties associated with these mean heat flow estimates. If heat flow from the Sirt Basin is elevated, it could be caused by enhanced crustal heat production and need not be attributed to thermal alteration of the lithosphere related to basin formation. Mean crustal heat production is 3.9 ± 2.1 μW m−3, 1/2 to 3 times greater than surface heat production in other Proterozoic terrains in Africa. From west to east, the pattern of heat flow across northern Africa is characterized by high (80–110 mW m−2) heat flow throughout most of northwestern Africa, normal to perhaps slightly elevated heat flow in the Sirt Basin, low to normal (35–55 mW m−2) heat flow in Egypt inboard of the Red Sea, and high heat (75–100 mW m−2) flow along the Red Sea. High heat flow near the Red Sea and in northwestern Africa along the Mediterranean coast can be readily attributed to Cenozoic tectonic activity, but high heat flow in the Paleozoic Sahara basins of southern Algeria is harder to understand within the tectonic framework of northern Africa. A possible explanation, advanced previously, is that elevated heat flow in the Sahara basins arises from a regional thermal anomaly within the north African lithosphere. If that explanation is correct, then the heat flow distribution in the Sirt Basin and in Egypt away from the Red Sea suggests that the postulated lithospheric thermal anomaly does not extend beyond the Sahara basins to the east.

Heat flow studies in Central Europe with special emphasis on data from former Czechoslovakia

The paper summarizes 208 heat flow values that have been collected in former Czechoslovakia (152 of them in Czech Republic, and 56 in Slovakia). The mean heat flow and its standard deviation for the whole region is 71.0 ± 22.8 mW m -2 . To interpret the regional geothermal activity, the results of similar data from the adjacent part of Central Europe were incorporated into the general picture. The heat flow map was correlated with the crustal thickness pattern, with the radiogenic heat production and the characteristic crustal temperature-depth profiles were constructed. Geothermal data were used to assess the mantle (Moho) heat flow and the thickness of the thermal lithosphere. Special attention was paid to the possible transient component of the heat flow due to the Tertiary-Quaternary volcanism in the northern part of the Bohemian Massif.

Thermochronological and Petroleum Generation Studies next to Dikes in the Upper Jurassic-Lower Cretaceous Strzelecki Group, Onshore Gippsland Basin, Australia: ABSTRACT

Fluid inclusion, apatite fission track analysis (AFTA[reg sign]) annealing, mean random vitrinite reflectance (Rv-r) data and heat flow modeling studies of nine basalt dikes ranging from 0.06 m to 40 in thick in the Strzelecki Group were used to constrain the conditions of contact metamorphism of coaly sedimentary organic matter (SOM) to investigate it as an extended-duration natural analog to hydrous pyrolysis experiments. Thermal history reconstruction suggests that at the time of dike intrusion the host rock was at a paleotemperature of 100 to 120[degrees]C. Reequilibrated fluid inclusions in the host rocks next to thin dikes (< 3.4 m thick) suggest maximum temperature (T[sub peak]) systematically increases towards the dike margin to around 550[degrees]C. These T[sub peak] data are in fair agreement with those predicted by a conductive heat flow model and measured Rv-r. AFTA indicates the time of uplift and cooling as mid to Late Cretaceous and that paleotemperatures were too high for heating duration information to be recorded by annealing of tracks in apatite near the dikes. The estimated T[sub peak] next to some larger dikes (20 to 40 m thick) as indicated by an extended zone of elevated Rv-r did not fit the pattern seen next tomore » the thin dikes. Heat flow modeling along with whole rock elemental and isotopic data suggest that the extended zone of increased Rv-r is caused by convection of heated fluids. This is in contrast to the apparent advection effects found adjacent to thin dikes. Laboratory hydrous pyrolysis compares well with contact metamorphism next to thin dikes with respect to the composition of the free hydrocarbons except in samples very close to the dike. Close to the dike, fluid inclusion evidence indicates a water vapor or super-critical phase in the rock making the organic geochemistry results diverge from.« less

Heat flow variations in the Grenville Province, Canada

Heat flow and heat production data provide strong constraints on the composition and evolution of the continental crust. Four new heat flow and heat production data from the Grenville Province in Canada are presented and included in local and regional analyses of heat flow variations. Thirty heat flow data are now available in the Late Proterozoic Grenville Province, where the mean heat flow (41 ± 11 mW · m −2) does not differ from that in the Archean Superior Province (41 ± 9 mW · m −2). It is shown that varying crustal heat production or heat refraction effects account for most local heat flow variations. The average crustal heat production is lower than in the other Late Proterozoic provinces because the tectonic evolution of the Grenville promoted the emplacement of large mafic bodies. Statistical analyses of heat flow and heat production data in the Grenville Province, in the surrounding provinces (Canadian Appalachians and Superior Province) and in the Norwegian Shield indicate that, within each province, the range of heat flow and heat production variations attains 40 mW · m −2 and 2 μW · m −3 respectively. However, the patterns on the histograms are distinctive and are shown to be regulated by the vertical distribution of heat production. Crustal structure and composition of the Grenville Province and the Norwegian Shield account for similarities and differences in the heat flow and heat production patterns of the two areas. Mantle heat flow in the Grenville Province lies between 9 and 16 mW · m −2, as in the Superior Province and in the Norwegian Shield.

A Study of Natural Convection in a Rotating Enclosure

The local and mean natural convection heat transfer characteristics and flow fields were studied experimentally and numerically in an air-filled, differentially heated enclosure with a cross-sectional aspect ratio of one. The enclosure is rotated above its longitudinal horizontal axis. A Mach-Zehnder interferometer was employed to reveal the entire temperature field, which enable the measurement of the local and mean Nusselt numbers at the hot and cold surfaces. Laser sheet flow visualization was employed to observe the flow field. The result showed that the Coriolis and centrifugal buoyancy forces arising from rotation have a remarkable influence on the local heat transfer when compared with the nonrotating results. Local heat fluxes were obtained as a function of Taylor (Ta≤4×105) and Rayleigh numbers (104&lt;Ra≤3×105), at different angular positions of the enclosure. In addition, a series of interferograms, stream function and isotherm plots demonstrated the strong effect of rotation on the flow field and heat transfer. A correlation of Nusselt number as a function of Taylor and Rayleigh numbers is presented.

Heat flow from the Earth's interior: Analysis of the global data set

We present a new estimate of the Earth's heat loss based on a new global compilation of heat flow measurements comprising 24,774 observations at 20,201 sites. On a 5° × 5° grid, the observations cover 62% of the Earth's surface. Empirical estimators, referenced to geological map units and derived from the observations, enable heat flow to be estimated in areas without measurements. Corrections for the effects of hydrothermal circulation in the oceanic crust compensate for the advected heat undetected in measurements of the conductive heat flux. The mean heat flows of continents and oceans are 65 and 101 mW m−2, respectively, which when areally weighted yield a global mean of 87 mW m−2 and a global heat loss of 44.2 × 1012 W, an increase of some 4–8% over earlier estimates. More than half of the Earth's heat loss comes from Cenozoic oceanic lithosphere. A spherical harmonic analysis of the global heat flow field reveals strong sectoral components and lesser zonal strength. The spectrum principally reflects the geographic distribution of the ocean ridge system. The rate at which the heat flow spectrum loses strength with increasing harmonic degree is similar to the decline in spectral strength exhibited by the Earth's topography. The spectra of the gravitational and magnetic fields fall off much more steeply, consistent with field sources in the lower mantle and core, respectively. Families of continental and oceanic conductive geotherms indicate the range of temperatures existing in the lithosphere under various surface heat flow conditions. The heat flow field is very well correlated with the seismic shear wave velocity distribution near the top of the upper mantle.

Considerations on the global seismic sequences: the second and the third largest aftershocks

Statistical considerations on the occurrence of the second largest aftershock of an earthquake sequence have been developed using global data. The time distribution of the second, M2, and the third, M3, largest aftershocks are studied here as well. The probability that these two aftershocks would occur in the first 24 hr after the main shock is more than 50 per cent. It was found that the second and the third largest aftershocks are distributed like the first largest aftershock. The difference, D2, is determined between the magnitudes of the main shock, M, and the second largest aftershock, M2, of an earthquake sequence. Using a complete data set, it was found that the difference, D2, has a mean of about 2.0. Two distinct cases of the M2 occurrence are observed. The first case (case 1) corresponds to normal aftershock sequence evolution, where M2 follows M1 (which is the largest aftershock of a sequence), while in the second one (case 2) M2 precedes M1. The values of the time distribution are totally different between case 1 and case 2. An attempt is made to interpret the temporal occurrence of the aftershocks, with respect to the surface (terrestrial) heat flow. The mean heat flow value for case 1 is qA= 1.61 ± 0.86, while for case 2 this is qB= 1.38 ± 0.82. It is shown that when the heat flow is high, the three largest aftershocks (M1, M2 and M3) temporally occur closer to the main shock.

Evidence of intrapermafrost groundwater flow beneath an active rock glacier in the Swiss Alps

AbstractTemperature measurements in borehole 2/1987 through rock glacier Murtèl Corvatsch revealed a very high mean heat flow of 150 mW/m2. Between 52 m and 56 m depth, seasonal variations are observed; above and underneath this zone temperatures have remained negative during the last 4 years. In addition, a zero curtain effect at the same depth hints at the existence of a water aquifer which is active mainly in summer. This phenomenon is interpreted as a talik at about 55 m depth. The permafrost may have a total thickness of approximately 100 m. The high heat flow is a result of the boundary conditions at the surface (mean annual temperature: −3 °C) and at the aquifer (at a depth of about 50 m), where the temperature is close to 0 °C.

Heat flow on the southern Colorado Plateau

Heat-flow data from the study area in the southern Colorado Plateau indicate a pattern of local anomalies having relatively high heat flow superimposed on a regional, intermediate heat-flow setting. While many of the conventional heat-flow data are relatively shallow and may be perturbed by groundwater circulation, bottom-hole temperature data from two relatively deep petroleum exploration drill holes near the southern plateau periphery yield intermediate heat-flow estimates. The mean heat flow within the volcanically active Jemez zone does not appear to be significantly greater than the mean heat flow for the remainder of the study area. This is due to the presence of high heat-flow values outside the Jemez zone. Sites with relatively high heat flow located towards the plateau interior and away from recent volcanic activity of the Jemez zone may reflect magma intrusion and/or groundwater movement along crustal zones of weakness associated with Laramide deformation (monoclines). The heat-flow data are consistent with coal maturation data, which suggest that any regional post-Cretaceous thermal events that may be associated with the southern Plateau boundary have been initiated relatively recently, or are occurring at relatively great depths, or are occurring south of the Jemez lineament.

Heat flow and heat generation in the Archaean Dharwar cratons and implications for the Southern Indian Shield geotherm and lithospheric thickness

We report terrestrial heat flow density measurements from 11 new sites in the Archaean Eastern and Western Dharwar cratons of the Southern Indian Shield. The new values, together with already published data, have yielded a mean heat flow of 40 ± 3.4 (s.d.) mW m −2 ( n = 11) for the Eastern Dharwar craton, which is a predominantly gneiss-granite terrain. The mean heat flow in the Archaean supracrustal belts of Western Dharwar craton, which is a granite-greenstone terrain, is 31 ± 4.1 (s.d.) mW m −2 ( n = 4). The observed difference in surface heat flow between the two cratons is ascribed to differences in radiogenic heat production in upper crustal layers, inferred to be related to different crust-forming processes. It has been argued that low heat production appears to be an inherent characteristic of the crust similar to that of the Western Dharwar craton, which evolved during the early Archaean and suffered depletion of the lithophile elements of its lower crust prior to the late Archaean. Radiogenic heat production measurements were carried out on borehole core samples for one heat flow site (Sortur), and data have been compiled from the literature on three other sites and on a variety of rocks of the Southern Indian Shield. Heat flow and radiogenic heat production for Sortur, when combined with the published data, define a linear relation ( r = 0.97) with a slope of 11.5 km and an intercept of 23 mw m −2. The thickness of the thermal lithosphere beneath the Dharwar cratons is over 200 km, thereby indicating, beneath the cratons, the existence of deep continental roots-a concept which is also supported by teleseismic P-wave travel time data. The geothermal data has clearly demonstrated that the Archaean Dharwar cratons of the Indian landmass are associated with low mean surface heat flow (37.7 mW m −2), reduced heat flow, Moho heat flux (12–17 mW m −2), and a cool and thick lithosphere—all characteristics of many Archaean-early Proterozoic terrains of other shields. It is inferred that the thermal structure of the South Indian lithosphere is identical with that of other cratons.

Heat flow, hydrothermal circulation and basalt intrusions in the Guaymas Basin, Gulf of California

The Guaymas Basin is part of an en echelon series of short, seafloor-spreading segments in the Gulf of California. The basin is separated from adjacent deeps by long, northwest-southeast-striking transform faults, and divided into subparallel, northern and southern troughs which trend northeast to southwest. Rapid sedimentation (1 to 5 m ka −1) results in a striking morphological contrast between seafloor spreading in the Guaymas Basin and that in more mature, mid-ocean settings. Basalt does not extrude onto the seafloor in the basin as flows and pillows, but instead intrudes into a thick sediment layer. The presence of relatively unconsolidated sediments lining the floor of the basin make this setting ideal for the study of axial heat flow and the thermal budget of oceanic crustal formation. Thermal data delineate several modes of heat transfer in both troughs of the basin, with negligible heat flow in some areas and values greater than 3 W m −2 in others. Broad heat flow highs, several square kilometers in area, result from a combination of deep, conductive heat flow, slow, intergranular fluid circulation and vigorous hydrothermal venting. Areas of low heat flow between heat-flow highs and near normal faults which bound the basin may be indicative of hydrothermal recharge. The geometry of faults, shallow sills and broad northeast-southwest structural trends in the basin largely seems to govern the distribution of heat flow. The highest values are clustered within a few isolated zones in each trough, with a total area of about 30 km 2. Variations in heat flow of two orders of magnitude occur over distances as small as a few hundred meters. Fourteen hydrothermal vents in the southern trough of the Guaymas Basin have been sampled directly, and found to have temperatures in excess of 250°C. Locally, conductive heat flow at the seafloor is significantly raised in the vicinity of these vents, but the general pattern appears to require more deeply seated, conductive heat sources. The mean heat flow in the southern trough is 453 ± 342 (s.d.) mW m −2. A simple analysis of the heat budget in the southern trough suggests that the total intruded section between the top of the magma chamber and the seafloor may be unusually thin, perhaps only several hundred meters in thickness.

Calculation of the Mean Thermal Conductivity of Heterogenious Solid Mixture with the Voronoi-Polyhedron Element Method.

A method of discretizing a three-dimensional closed space into the Voronoi-polyhedron elements was applied to the numerical analysis of heat-conduction problems in heterogeneous solid mixtures. The computation was done for various mixtures of two randomly distributed components. Thermal conductivity of the two-component mixture is more strongly affected by the arrangement of components with respect to the mean heat flow direction than by the shape of components. The statistical mean of thermal conductivity can be roughly approximated by the geometrical average. Empirical formulae were obtained from the results. In order to accurately predict the thermal conductivity of a mixture of three or more components, the numerical calculating method divised in this study can be employed successfully.

Terrestrial heat flow in east and southern Africa

We report 26 new heat flow and 13 radiogenic heat production measurements from Zimbabwe, Zambia and Tanzania, together with details and some revisions of 18 previous heat flow measurements by other investigators from Kenya and Tanzania. These measurements come from Archean cratons, Proterozoic mobile belts, and Mesozoic and Cenozoic rifts. Heat flow data from eight new sites in the Archean Zimbabwe Craton are consistent with previous measurements in the Archean Kaapvaal‐Zimbabwe Craton and Limpopo Belt (Kalahari Craton) and do not change the mean heat flow of 47±2 mW m−2 (standard error of the mean) in the Kalahari Craton based on 53 previous measurements. Eight new sites in the Archean Tanzania Craton give a mean heat flow of 34±4 mW m−2. The mean heat flow from nine sites in the Proterozoic Mozambique Belt to the east of the Tanzania Craton in Kenya and Tanzania is 47±4 mW m−2. Twelve measurements in the Mesozoic rifted continental margin in east Africa give a mean heat flow of 68±4 mW m−2; four measurements in the Mesozoic Luangwa and Zambezi Rifts range from 44 to 110 mW m−2 with a mean of 76±14 mW m−2. In comparing heat flow in east and southern Africa, we observe a common heat flow pattern of increasing heat flow away from the centers of the Archean cratons. This pattern suggests a fundamental difference in lithospheric thermal structure between the Archean cratons and the Proterozoic and early Paleozoic mobile belts which surround them. Superimposed on this common pattern are two regional variations in heat flow. Heat flow in the Tanzania Craton is lower by about 13 mW m−2 than in the Kalahari Craton, and in the Mozambique Belt in east Africa heat flow is somewhat lower than in the southern African mobile belts at similar distances from the Archean cratonic margin. The two regional variations can be explained in several ways, none of which can as yet be elevated to a preferred status: (1) by variations in crustal heat production, (2) by thin‐skinned thrusting of the Mozambique Belt over the Tanzania Cratonic margin, (3) by lateral heat transfer from beneath the rift flanks into the rifts, or (4) by lower mantle heat flow beneath all of eastern Africa prior to the Cenozoic development of the East African rift system.

Computer acquisition and analysis of skin temperature and heat flow data from heat flux transducers

A computer-controlled system for the collection and analysis of skin temperature and heat flow data originating from an array of heat flux transducers is describe. The systems is based on a program (‘THERMAL’) that reads, stores, prints and displays skin temperatures and heat flow data every 2 min for up to 4 h. It also simultaneously calculates important environmental physiology parameters such as mean skin and mean body temperatures as well as mean heat flow according to four different combinations of transducers such as the established 3-, 4-, 7- and 12-point (site) formulae. Core temperature, heart rate and environmental condition indices such as dry bulb, wet bulb and globe temperatures are also continuously monitored.

Heat flow and the thermal origin of hot spot swells: The Hawaiian Swell revisited

We present 150 new heat flow measurements obtained at eight sites along a 1230‐km‐long profile across the Hawaiian Swell about 700 km ESE of Midway Island. Most of the measurements include in situ thermal conductivity determinations, which helped to reduce the statistical uncertainties (95% confidence) at all sites to &lt;±2.l mW m−2. Surprisingly, there is no systematic variation in heat flow across the axis of the swell. With one exception, the mean heat flow (corrected for sedimentation) at each site is within ±10% of the mean value of 57.7±4.3 (S.D.) mW m−2 for all sites. At the two sites at either end of the profile, clearly located off the swell, the observed heat flow is &gt;59 mW m−2, about 20% higher than the predicted heat flow for 100 Ma seafloor based on simple lithospheric cooling models. Thus even though there is a small increase in heat flow with age along the swell, when compared with the off‐swell heat flux, the anomalous heat flow associated with the Hawaiian Swell is probably of the order of 5–10 mW m−2 and arguably may not exist at all. A previous investigation [Von Herzen et al., 1982] may have overestimated the magnitude of the heat flow anomaly associated with the Hawaiian Swell by comparing heat flux measurements on the swell with values expected for simple lithospheric cooling models. The heat flow anomalies associated with the Bermuda Rise and the Cape Verde Rise may also be smaller than previously estimated, given the uncertainties in the heat flux on the normal seafloor surrounding these swells. The lack of a significant heat flow anomaly associated with the bathymetric expression of the Hawaiian Swell is inconsistent with simple models of lithospheric reheating. Dynamic support, accompanied by modest temperature increases (&lt;100°–200°C) confined to the lower lithosphere, and underlying asthenosphere appear to be required to explain both the height of the swell and its small heat flow anomaly. However, detailed modeling of the origin of midplate swells, and their associated heat flow anomalies, is hampered by our lack of understanding of the thermal evolution of old (&gt;80 Ma) oceanic lithosphere.

Three-dimensional thermal convection in a spherical shell

Independent pseudo-spectral and Galerkin numerical codes are used to investigate three-dimensional infinite Prandtl number thermal convection of a Boussinesq fluid in a spherical shell with constant gravity and an inner to outer radius ratio equal to 0.55. The shell is heated entirely from below and has isothermal, stress-free boundaries. Nonlinear solutions are validated by comparing results from the two codes for an axisymmetric solution at Rayleigh number Ra = 14250 and three fully three-dimensional solutions at Ra = 2000, 3500 and 7000 (the onset of convection occurs at Ra = 712). In addition, the solutions are compared with the predictions of a slightly nonlinear analytic theory. The axisymmetric solution is equatorially symmetric and has two convection cells with upwelling at the poles. Two dominant planforms of convection exist for the three-dimensional solutions: a cubic pattern with six upwelling cylindrical plumes, and a tetrahedral pattern with four upwelling plumes. The cubic and tetrahedral patterns persist for Ra at least up to 70000. Time dependence does not occur for these solutions for Ra [les ] 70000, although for Ra &gt; 35000 the solutions have a slow asymptotic approach to steady state. The horizontal and vertical structure of the velocity and temperature fields, and the global and three-dimensional heat flow characteristics of the various solutions are investigated for the two patterns up to Ra = 70000. For both patterns at all Ra, the maximum velocity and temperature anomalies are greater in the upwelling regions than in the downwelling ones and heat flow through the upwelling regions is almost an order of magnitude greater than the mean heat flow. The preferred mode of upwelling is cylindrical plumes which change their basic shape with depth. Downwelling occurs in the form of connected two-dimensional sheets that break up into a network of broad plumes in the lower part of the spherical shell. Finally, the stability of the two patterns to reversal of flow direction is tested and it is found that reversed solutions exist only for the tetrahedral pattern at low Ra.

Thermal field near the axial zone of mid-oceanic ridges and heat balance of oceanic lithosphere

Data on heat flow and hydrothermal circulation near the axis of mid-oceanic ridges are considered. A statistically significant difference in mean heat flow values for a young crust of the Pacific and Atlantic oceans has been suggested. Combination of data on heat flow and hydrothermal activity of the young crust in these oceans suggests a difference in heat flow at the base of the permeable layer. A qualitative comparison of the heat flow and the character of seismicity in these regions is carried out.

Flow and heat transfer characteristics of stirling engine regenerator in oscillating flow.

For the design of stirling engine, the basic data on various regenerator materials are required to be offered which have to be incorporated to the design by computerized simulation. The, pressure loss and gas temperature were instantaneously measured for various regenerator materials installed in oscillating fluid flow. Hydraulic diameter is used as the representative length defined by friction factor and Reynold's number, and flow characteristics of different materials were able to be unifomly adjusted. It was found that heat regeneration loss was able to be evaluated by utilizing the hydraulic diameter, length of regenerator, mean temperature on both side of regenerator, mean heat flow. Such simple eavaluation method is effective when it is applyed to actual engine. By using the frictional loss factors and heat regenerating loss obtained by this study, the effect of wire diameter and length of regenerator on indicated thermal efficiency was clarified. 14 refs., 12 figs., 1 tab.

Terrestrial heat flow above the Andean Subduction Zone in Bolivia and Peru

We report 35 new and 9 revised terrestrial heat flow measurements overlying the Andean subduction zone in Bolivia and Peru. The measurement sites are distributed in the Andean Cordillera, the Altiplano, the sub‐Andean ranges, and the sedimentary platform and basins to the east of the Andes. They fall in the distance range 75–900 km from the Peru‐Chile trench. Sites in the Peruvian Cordillera have a mean heat flow of 41 mW m−2, whereas those in the Bolivian Cordillera and Altiplano average 84 mW m−2. The sub‐Andean ranges and the adjacent sedimentary platform have a mean heat flow of 50 mW m−2. The higher heat flow of the Bolivian Cordillera and Altiplano lies to the east of Quaternary volcanoes along the Bolivia‐Chile border and in southernmost Peru and thus can be recognized as a “back arc” heat flow high. Neither Quaternary volcanism nor high heat flow are present in central and northern Peru. This contrasting along‐strike pattern correlates with the variable angle of subduction of the Nazca plate beneath the region. Beneath Bolivia the subduction is at about 30°–35°, whereas beneath Peru it is subhorizontal and may be providing a cold underplate to the overlying Peruvian lithosphere. Extensive Miocene volcanism in Peru suggests, however, that heat flow in Peru 10 Ma ago was likely similar to that in Bolivia in the present day and implies a change in subduction and a rapid diminution of heat flow in Peru over the past 10 Ma. Imbrication of cold oceanic lithosphere beneath Peru, analogous to that beneath western British Columbia, may provide a mechanism for rapid reduction of the heat flow.

Inversion of bottom‐hole temperature data: The Pineview field, Utah‐Wyoming thrust belt

The present day temperature field in a sedimentary basin is a constraint on the maturation of hydro‐carbons; this temperature field may be estimated by inverting corrected bottom‐hole temperature (BHT) data. Thirty‐two BHTs from the Pineview oil field are corrected for drilling disturbances by a Horner plot and inverted for the geothermal gradient in nine formations. Both least‐squares [Formula: see text] norm and uniform [Formula: see text] norm inversions are used; the [Formula: see text] norm is found to be more robust for the Pineview data. The inversion removes random error from the corrected BHT data by partitioning scatter between noise associated with the BHT measurement and correction processes and local variations in the geothermal gradient. Three‐hundred thermal‐conductivity and density measurements on drill cuttings are used, together with formation density logs, to estimate the in situ thermal conductivity of six of the nine formations. The thermal‐conductivity estimates are used in a finite‐element model to evaluate 2-D conductive heat refraction and, for a series of inversions of synthetic data, to assess the influence of systematic and random noise on the inversion results. A temperature‐anomaly map illustrates that a temperature field calculated by a forward application of the inversion results has less error than any single corrected BHT. Mean background heat flow at Pineview is found to be [Formula: see text] (±13 percent), but is locally higher [Formula: see text] due to heat refraction. The BHT inversion (1) is limited by systematic noise or model error, (2) achieves excellent resolution of a temperature field although resolution of individual formation gradients may be poor, and (3) generally cannot detect lateral variations in heat flow unless thermal‐conductivity structure is constrained.